Department of Pediatrics, University of Hawaii John A. Burns School of Medicine




НазваниеDepartment of Pediatrics, University of Hawaii John A. Burns School of Medicine
страница14/176
Дата08.10.2012
Размер5.08 Mb.
ТипДокументы
1   ...   10   11   12   13   14   15   16   17   ...   176

Chapter II.3. Infant Formulas

Nadine Tenn Salle, MD


A 24 year old first time mother brings her two week old son to your office for a well child examination. She is a single mother with strong family support. She will be returning to work in one week and has elected not to breastfeed. Today she is seeking your advice concerning her infant's nutrition.


In a 1986 policy statement, the American Academy of Pediatrics (AAP) reaffirmed its position on four issues pertinent to infant nutrition (1):

1. The AAP will continue to promote breastfeeding as the first form of infant nutrition.

2. The AAP will continue to work to maintain and improve the high quality of infant formulas in the United States because in some cases, breastfeeding is not practical or desired.

3. The AAP will continue to recommend against direct to consumer advertising of infant formula.

4. The AAP will continue to encourage the special supplement nutrition program for women, infants and children (WIC) and hospital nurseries, and programs to make available a diversity of formulas.

The AAP adheres to the belief that pediatricians have a responsibility for infant nutrition, have an obligation to be knowledgeable about the nutritional needs of both healthy normally developing infants as well as infants with unique nutritional needs such as those with metabolic, gastrointestinal, infectious and oncologic disease conditions (1).

Breast milk is considered to be the optimal nutrient for the term or near term infant as an exclusive source of nutrition during the first six months of life. Breast milk combined with the introduction of solids is recommended for the second six months of an infant's life (2).


There are indications for the use of infant formula:

1. As a supplement or substitute for breast milk when a mother cannot or chooses not to breast-feed.

2. Infants whose mothers are infected with organisms known to be transmittable by human milk (e.g., HIV)

3. Infants whose mothers are undergoing chemotherapy.

4. Infants whose mothers are receiving medication or drugs that are excreted into human milk.

5. Infants who are unable to tolerate human milk because of metabolic disorders (e.g., galactosemia).


In the event breast feeding is neither practical nor desired, there are a number of commercially available infant formulas that have been formulated to simulate human breast milk and provide an infant's nutritional requirements. On average, a neonate will drink about 165 cc of formula/kg/day (2.5 ounces/pound/day) and about 30-90 cc (1-3 ounces) per feeding. The caloric content of most infant formulas closely approximates that of human milk at 2/3 kcal/cc (20 kcal/oz). Infants are often their own best regulators, thus variation with each feeding should be expected. During the first 6 months of life, infants require 95-115 kcal/kg/day; 8-12% of these calories should be derived from protein, 30-50% from fat and 40-60% from carbohydrates. If these nutritional requirements are met, an infant will typically gain 25-40 grams per day (30 grams = 1 ounce) in the first 3 months and 15-20 grams in the second 3 months. Infant formulas are designed to mimic the nutritional composition of human milk, but in reality they contain a number of differences in the protein, fat and carbohydrate content.

Human milk contains approximately 1.1 g/dL of protein as compared to 1.5g/dL in most standard formulas. This represents 6-8% of an infant's total caloric intake. Milk protein can be divided into two classes based on relative solubility in acid: whey (acid soluble) and casein (acid insoluble). The whey:casein ratio of human milk is 70:30 as compared to a ratio of 18:82 for cow milk. The clinical significance of the difference in whey:casein ratio between human and bovine milk is illustrated when unmodified casein-predominant cow milk enters the acidic environment of the human stomach and forms a relatively hard curd of casein and minerals. This curd can be difficult for an infant to digest. Thus, the AAP recommends that cow's milk not be used until after the first birthday. Special toddler's milk is now being marketed as a transitional formula to whole cow's milk; however there are no proven special benefits compared to a toddler eating a balanced diet that includes milk and juice.

Lipid constitutes approximately 50% of the calories in human milk (5.7g/100 kcal) and standard infant formula (4.4-6.0g/100 kcal). The predominant portion of lipid in human and cow milk is triacyl glycerol. Triacyl glycerol is composed of a glycerol backbone with 3-hydroxyl group esterified to fatty acids.

Essential fatty acids lineoleic and alpha lineolinic acid play a crucial role in neurodevelopment. Approximately 5-7% of total calories in human milk and 1% of total calories in cow milk is lineoleic acid. The amount of lineoleic acid considered adequate is controversial but it in generally agreed it should not be more than 20%. For this reason all cow milk based formulas add vegetables oil (containing relatively large amounts of lineoleic and lineolinic) to their preparations. Most commercial infant formulas contain at least 10% of total fatty acids as lineoleic acid.

The primary carbohydrate source found in both human milk and formulas is lactose (except in lactose free formula). Lactose is a disaccharide that is converted to simple sugars, galactose and glucose by a lactase enzyme. Disaccharides require conversion to simple sugars to enable absorption through the gut via a monosaccharide transport system. The carbohydrate source in soy based formula is glucose polymers (also referred to as corn syrup solids) and/or sucrose. Sucrose is converted to simple sugars, fructose and galactose for absorption (3).

The iron content of human milk is much less than that of iron fortified cow milk based formula, but the bioavailability of human milk iron is much higher. Guidelines from the committee on nutrition of the AAP recommends 2-3 mg/kg/day of elemental iron. In a term infant, iron deficiency is uncommon before 4-6 months of age because of the abundance of iron stores at birth. Iron deficiency is most common among children 6 months to 3 years of age. To compensate for the depletion of iron stores by growth, dietary iron must be provided. Exclusively breastfed infants may require diet supplementation with iron (1 mg/kg/day) and vitamin D (400 IU/day) at 4-6 months of age. Standard formulas (about 32 ounces per day) will meet 100% of RDA for vitamins and minerals for term infants. Low iron formulas defined by the FDA as containing less than 6.7 mg/L of iron, once contained less than 1.5mg/L of iron, resulting in an unacceptably high rate of iron deficiency and anemia. Over the past five years, formula manufacturers have increased the amount of iron in low iron formulas to 4-5mg/L. A public perception that iron causes constipation and other feeding problems has allowed for the continued market of low iron containing formulas. There is no data to support this belief and the AAP recommends iron-fortified formulas.

Symptoms of cow milk protein allergy typically begin between week 4 to 6, but the sensitivity may occur as early as 48 hours or may present in adulthood. The presence of gastrointestinal symptoms such as bloody stools, diarrhea and vomiting can indicate pathophysiological intolerance related to a specific component of cow milk formula. Symptoms such as flatus, fussiness and colic are less likely and difficult to directly relate to components of cow milk. True cow milk protein allergenicity as documented by a double-blinded study is present in less than 6% of the population (5,6). Some surveys show as high 30% of formula fed infants are switched to hypoallergenic formulas because of a perceived or suspected protein allergy (7). Hypoallergenic formulas are created by extensively hydrolyzing the cow milk protein (usually casein), thereby reducing its molecular weight to less than 1250 kDa. Proteins less than 1250 kDa are far less likely to produce a IgE-mediated allergic response (6). Hypoallergenic hydrolyzed casein formulas are effective in preventing protein allergy. It is however prudent to truly diagnose cow milk allergic infant before starting these formulas whose most significant disadvantage is a greater cost when compared to regular formula. Breastfeeding is even more strongly advocated in infants with milk hypersensitivity.

Primary lactose intolerance such as lactase deficiency and galactosemia, occurs approximately in 1:1000 infants. Secondary lactose intolerance by contrast is far more common and often presents with protracted diarrhea. The lactase enzyme is located at the villous tip of the intestine and appears to be more vulnerable than sucrase that is found deeper in the crypt. An infectious diarrhea may cause denuding and the lactase enzyme may take up to a week to fully recover. A low lactose or lactose free formula may reduce carbohydrate malabsorption (and subsequent exacerbation of diarrhea by an osmotic mechanism) during the illness. The lactose free cow-milk based formulas are designed to treat primarily secondary lactase deficiency. The contrast to lactose containing formulas is the substitution of its carbohydrate source. Instead of lactose, a corn syrup solid and/or sucrose is used.

Soy formulas support the growth of normal term infants through the first year of life. Soy formulas may be used in lieu of cow milk formula and in formula fed infants whose parents want their children to adhere to a vegetarian diet. Phytate in soy formula in addition to the absence of lactose diminish the absorption of divalent cations such as iron, calcium and zinc in the intestinal lumen. Supplementation of soy formula with iron, calcium and zinc has largely overcome these issues (8,9). Phytogens in soy formulas have the potential for hormonal action at critical points in development. The AAP has noted that limited human data does not support these concerns (10).

Summary of formulas:


Cow's milk based formulas:

Indications: Term or near term infant.

Protein: whey-predominant; carnitine and taurine usually added.

Carbohydrate: lactose.

Fat: vegetable oils.

Brands: Enfamil with iron, Similac with iron, Good Start (100% whey protein, thus may be used for constipation), Lacto-free (uses corn syrup and/or sucrose), Similac PM 60/40 (60:40 ratio of whey to casein, less Ca, P, K for cardiac and renal patients).


Soymilk based formulas:

Indications: Lactose deficiency or galactosemia, strict vegetarians, IgE mediated reaction to cow milk protein.

Protein: 2.2g/dl of protein from a plant source, cysteine and taurine as well as an additional methionine added.

Carbohydrate: corn syrup (glucose polymer), sucrose.

Fat: vegetable oils.

Brands: Isomil, ProSobee.


Casein Hydrosylate formulas:

Indications: Milk or soy protein intolerance, colic.

Protein: casein hydrolysate (hypoallergenic).

Carbohydrate: glucose oligosaccharides modified cornstarch.

Fat: MCT, corn oil.

Brands: Pregestimil, Nutramigen, Alimentum (increased MCT fat concentration; for cystic fibrosis patients).


Questions

1. The American Academy of Pediatrics recommends what form of nutrition for infants?

2. What is an appropriate quantity of formula for an infant?

3. When is iron supplementation required for an infant?

4. When comparing breast milk vs. cow's milk based formulas, which has a higher: a) kcal/cc? b) Concentration of casein protein? c) Carbohydrate content? d) Fat content?

5. What is the clinical significance of the whey:casein ratio in cow milk?

6. What is the main form of carbohydrate in breast milk? Cow's milk based formula? Soy based formula?


References

1. Breastfeeding and the use of human milk. American Academy of Pediatrics. Work Group on Breastfeeding. Pediatrics 1997;100(6):1035-1039.

2. Hall RT, Caroll RE. Infant feeding. Pediatr Rev 2000;21(6):191-200.

3. Greer FR. Formulas for the healthy term infant. Pediatr Rev 1995;16(3):107-113.

4. Blecker U, Sothern MS, Suskind RM. Iron-fortified infant formulas. Pediatr Rev 1999;20(10):359.

5. Oldaeus G, et al. Allergenicity screening of "hypoallergenic" milk-based formulas. J Allergy Clin Immunol 1992;90(1):133-135.

6. Oldaeus G, et al. Cow's milk IgE and IgG antibody responses to cow's milk formulas. Allergy 1999;54(4):352-357.

7. Schrander JJ, et al. Cow's milk protein intolerance in infants under 1 year of age: a prospective epidemiological study. Eur J Pediatr 1993;152(8):640-644.

8. Mimouni F, et al. Bone mineralization in the first year of life in infants fed human milk, cow-milk formula, or soy-based formula. J Pediatr 1993;122(3):348-354.

9. Hertrampf E, et al. Bioavailability of iron in soy-based formula and its effect on iron nutriture in infancy. Pediatrics, 1986;78(4):640-645.

10. American Academy of Pediatrics. Committee on Nutrition. Soy protein-based formulas: recommendations for use in infant feeding. Pediatrics 1998;101(1 Pt 1):148-153.


Answers to questions

1. Breastfeeding is regarded first and foremost except when it is not practical, desired or medically contraindicated.

2. From a practical standpoint, whether it is breast milk or infant formula, a healthy term infant is the best regulator of the frequency and quantity of their nutritional intake. However, since we are scientists at heart; during the first 6 months of life approximately 95-115 kcal/kg/day is recommended.

3. In a term infant, iron deficiency is uncommon before 4-6 months of age because of the abundance of iron stores at birth. To compensate for the depletion of iron stores by growth, dietary iron must be provided to exclusively breastfed infants. Iron fortified formulas can prevent iron deficiency in formula fed infants. Guidelines from the Committee on Nutrition of the AAP recommend 2-3 mg/kg/day of elemental iron.

4a. They are about the same. Human milk contains approximately 2/3 kcal/cc (20 kcal/oz). The standard infant formula usually remains close to this range.

4b. Whey:Casein of human milk is 70:30 as compared to a ratio of 18: 82 for cow milk. Please refer to the text to review the clinical significance of this profile difference.

4c. The carbohydrate content is about the same.

4d. Lipids constitute approximately 50% of the calories in human milk (5.7 g/100kcal) and standard infant formula (4.4-6.0 g/100kcal).

5. The clinical significance of the difference in whey:casein ratio between human and bovine milk is illustrated when unmodified casein-predominant cow milk enters the acidic environment of the human stomach and forms a relatively hard curd of casein and minerals. This curd can be difficult for an infant to digest. Thus, the AAP recommends that cow's milk not be used until after the first birthday.

6. Lactose is the main carbohydrate in mammalian milk. The lactose concentration of human milk is 7g/dL, cow milk contains 5 g/dL. Lactose is added to most standard infant formula to achieve the concentration of human milk. Soy formulas do not contain lactose; they contain sucrose, glucose polymers, or a mixture of the two.


Chapter II.4. Fluids and Electrolytes

Loren G. Yamamoto, MD, MPH, MBA


Case 1: A 4 year old male presents to the emergency department with a history of vomiting and diarrhea. He has had 10 episodes of vomiting (clear then yellow tinged) and 8 episodes of diarrhea with some mucusy material in the first few episodes. The diarrhea is now watery and the last few episodes have been red in color. The diarrhea odor is very foul. He has had a fever with a maximum temperature measured at 101 degrees at home. His parents gave him a sports drink (red color), and then they tried clear Pedialyte. Despite this, he continues to have vomiting and diarrhea. He feels weak and tired and he looks slightly pale at times. He has only urinated twice in the last 15 hours.

Exam: VS T 38.2 degrees (oral), P 110, R45, BP 90/65, oxygen saturation 100% in room air. Weight 18 kg. He is alert and cooperative, but not very active. He is not toxic or irritable. His eyes are not sunken. TMs are normal. His oral mucosa is moist but he just vomited. His neck is supple. Hear and lung exams are normal except for tachycardia. His abdomen is soft and non-tender. Bowel sounds are normoactive. He has no inguinal hernias and his testes are normal. His overall color is slightly pale, his capillary refill time is 2 seconds over his chest, and his skin turgor feels somewhat diminished.

He is clinically assessed to be 5% dehydrated by clinical criteria. Oral versus IV rehydration is discussed with his parents who indicate that they have tried oral hydration and are not happy with the results. They now have emesis on their furniture and carpet and he has splattered some diarrhea over the bathroom floor, so they would like the IV for him. An IV is started and a chemistry panel is drawn at the same time. A rectal swab for culture is also obtained. Normal saline is infused at 360 cc/hour for two hours (total of 720 cc). The resident on the case questions the high IV rate. It is pointed out that 360 cc is only 20 cc/kg which replaces only 2% of the body's weight (i.e., it corrects 2% dehydration), it doesn't include maintenance fluids, and 360 cc is the same volume as a soft drink can. He is also given ondansetron (Zofran) for nausea relief. His chemistry panel shows Na 135, K3.4, Cl 99, bicarb 15. During the first hour of the IV fluid infusion, he says that he feels much better. He more awake and his color improves. During the second hour of IV fluid infusion, he falls asleep. At the end of the two hours, he is awakened and since he feels better, he is discharged from the ER with instructions to rest and continue oral hydration efforts.

Three days later, his rectal swab is growing Salmonella. His parents are called. They indicate that he still has some diarrhea, but only about two episodes per day and his vomiting has stopped. He is on a regular diet and continues to improve. Because he has improved, no antibiotic treatment is started. However, vigorous hand washing and hygiene regarding dishes/utensils for all family members is recommended.


Case 2: An 18 month old female is directly admitted to the hospital from her primary care physician's office. She has had 15 episodes of diarrhea and 5 episodes of vomiting. She has a fever with a maximum temperature of 102.4 degree measured on a tympanic thermometer. She is weak, pale and her eyes are sunken. Her weight in the office is 11.0 kg which is decreased from her weight in the office of 11.6 kg just three days ago during a well child check. Urine output is difficult to assess because of the diarrhea.

Exam: VS T 37.8, P 110, RR 40, BP 100/60, oxygen saturation 100% in room air. Weight 11.0 kg. She is alert, but subdued and quite. She is not toxic and not irritable. Her eyes might be slightly sunken. Her oral mucosa is sticky (tacky). Her neck is supple. Heart regular, no murmurs. Lungs are clear. Abdomen is scaphoid, soft and non-tender with hyperactive bowel sounds. No inguinal hernias are present. Her skin turgor is diminished, but no tenting is present. Capillary refill time is 3 seconds over her thighs. Her extremities are cool in her feet, but warm elsewhere.

An IV is started and a chemistry panel is drawn. A stool rotavirus rapid assay is done which is positive. She is given 220 cc of normal saline IV over one hour and she feels much better. The appearance of her eyes have normalized and she is more active. Her chemistry panel shows Na 134, K 3.4, Cl 97, bicarb 12. The resident then writes the following IV orders: IV D5-1/3NS+20 mEq KCl per liter run at 88 cc/hour for 8 hours, then 66 cc/hour for 16 hours. She is also permitted to eat and drink small amounts, so a low fat diet without fruit juice is ordered for her. The medical student following the case asks how these IV orders are determined.


Since children are small, critical attention must be paid to fluid and electrolyte balance. An fluid administration could result in clinically significant overhydration, underhydration, or electrolyte imbalance. Normal humans will consume fluids and nutrients in response to their body's needs and regulation occurs automatically without any thought to this process. However, in pathologic conditions such as gastroenteritis, burns, neurologic dysfunction, etc., fluid losses may be excessive and the body's ability to respond to these deficits may not be intact. The purpose of this chapter is to familiarize the reader with normal fluid and electrolyte requirements. Much of this chapter consists of numbers, some of which should be memorized for personnel who provide medical care to children frequently. These will be called everyday basic numbers and are summarized in a table at the end of this chapter. Other numbers can be looked up in references when the need arises.

Body composition is 60% to 75% water. The 60% applies to adults and the 75% applies to newborns. Younger children have more water than adults. These numbers are estimates because body fat variations will modify these percentages as well (obese individuals have lower body water percentages). Out of this, about 60% is intracellular and 40% is extracellular. Of the extracellular fluid, 3/4 is interstitial and 1/4 is circulating as plasma (1). There is also a small percentage known as transcellular water (about 2%) which consists of synovial fluid, pericardial fluid, pleural fluid, bowel secretions, cerebral spinal fluid, etc. (1). This can be summarized below as:

Total body water: 60%-75% of body weight

Intracellular: 30%-40% of body weight

Extracellular: 20%-25% of body weight

Interstitial: 15% of body weight

Plasma: 5% of body weight


However, total blood volume is actually 8% to 9% of body weight for children and 7% of body weight for adults (2). This is because the red blood cell elements of blood are not considered to be "body water". Thus, if plasma consists of 5% of the body weight, a few more percentage points would account for the circulating blood volume (which is larger than the circulating plasma volume).

Fluid losses occur routinely through urine, stools, respiratory vapor and insensible skin losses. Perspiration can exaggerate skin losses. Illness and exercise can exaggerate respiratory fluid loss through vapor. Other conditions such as burns, vomiting, diarrhea, hemorrhage, diuretics, etc., can also exaggerate fluid losses.

Maintenance fluid volume for 24 hours can be calculated as follows: 100 cc/kg for the first 10 kg of body weight, 50 cc/kg for the next 10 kg of body, then 20 cc/kg thereafter. Thus, the maintenance fluid volume 40 kg patient would be calculated as: 10kg X 100 cc/kg + 10kg X 50 cc/kg + 20kg X 20 cc/kg = 1000cc + 500cc + 400cc = 1900cc per day. A shortcut for patients over 20 kg is to take 1500 cc and then add 20 cc/kg for additional weight above 20 kg. Maintenance electrolytes are calculated using maintenance fluid volumes as 3 mEq Na (sodium) and 2 mEq K (potassium) per 100cc of maintenance fluid. Thus, the 40 kg patient above would require 57 mEq Na (3 X 19) and 38 mEq K (2 X 19) per day.

This is translated into an IV rate in cc/hour by dividing the total volume of fluids by 24 hours. To deliver 1900 cc of fluid over 24 hours, the IV rate would have to be 80 cc/hr (roughly 1900 divided by 24).

The type of IV fluid is dependent on the electrolyte requirements. IV fluid basically comes as percentage of normal saline. Normal saline contains 0.9 grams of NaCl per 100 cc of fluid (0.9%). This is roughly 150 mEq of Na per liter. I remember this because I know that the body's normal osmolarity is 290 (or about 300). If "normal" saline has a "normal" osmolarity, then it's osmolarity must be about 290 mosm/liter. Therefore, half of its osmolar particles must be Na (sodium) and the other half must be Cl (chloride) to give a total osmolarity of about 300. Therefore, the concentration of Na (sodium) in normal saline (NS) is about 150 mEq/liter and the concentration of chloride in NS is about 15 mEq/liter. Half normal saline contains 75 mEq/liter. 1/3NS contains 50 mEq/liter and 1/4NS contains about 38 mEq/liter. It turns out that this is not exact. I could provide you with a table with the exact numbers, but no one can remember these. Fortunately, when selecting IV fluids, we just need to know approximate numbers. Therefore, following the rule of using "normal saline" permits one to know the approximate sodium concentrations of all IV fluids. Lactated Ringer's solution (LR) is similar to NS, but it also contains some potassium, lactate and calcium. Since LR also has a "normal" osmolarity, it will have less Na than NS in order to maintain its normal osmolarity. LR resembles the blood more physiologically. LR's electrolyte concentrations are Na 130 mEq/liter, K 4 mEq/liter, Cl 110 mEq/liter, lactate (similar to bicarbonate) 28 mEq/liter.

Since maintenance electrolytes are based 3 mEq Na and 2 mEq K per 100 cc of maintenance IV fluid, this will require a solution with 30 mEq Na per liter. The closest to this is 1/4 NS with about 38 mEq/liter. Potassium is always added as a separate electrolyte to the bag (with the exception of LR which already contains small amounts of potassium). The IV order that would be written for maintenance fluids on a 40 kg patient would be: IV D5-1/4NS + 20 mEq KCl per liter run at 80 cc/hr.

What exactly does maintenance mean? If the IV order above was accidentally written for 40cc/hr, would the patient become dehydrated? Alternatively, if the IV order was accidentally written for 200 cc/hr, would the patient develop pulmonary edema? If the IV order was instead written for D5NS (instead of D5-1/4NS), would the patient become hypernatremic? The answer to all of these questions is no (most of the time). By calculating the maintenance fluid volume for a 75 kg average adult, the maintenance volume would be 1500 cc + 55 kg X 20 cc/kg = 3000 cc. 30 cc is roughly one ounce. That's roughly 100 ounces, i.e., about 3 quarts or 8 soft drink cans per day. As an average busy adult, I normally do not drink this much, yet I do not become dehydrated. Also on some days, I consume a lot of salt (potato chips, etc.) and on some days I don't consume much salt. Yet my serum Na level stays in the normal range. If I drink an excess of fluid, my kidneys urinate more free water and if I don't drink much, my kidneys retain water and I don't put out much urine. Normal kidneys are able to compensate for wide ranges of fluid and electrolyte intake. Excess fluid and electrolyte intake is urinated out as excess, while inadequate intake results in renal retention of fluid and/or electrolytes to maintain normal fluid volumes and electrolyte balance. The kidney has to do some work to remove excess substances or to retain substances which are in short supply. Renal consumption of ATP can be used as a marker of the amount of work performed by the kidney. Renal ATP consumption is high when excess fluid is consumed because it must work to excrete free water. Renal ATP consumption is high when insufficient fluid is consumed because it must work to retain water. In contrast, renal ATP consumption is low between these extremes because the kidneys do not have to work as hard. ATP consumption is lowest when the maintenance volume is consumed. Thus, maintenance volumes and electrolytes are beneficial because this results in minimizing the stress and workload on the kidneys. This is not very important in healthy individuals going about their everyday lives, but it becomes more important in very ill patients whose bodily functions are under great stress. Maintenance calculations using the formula provided are only valid under the assumption of the "average hospital patient". Some well people (e.g., while playing in a soccer game) will require more fluids than the maintenance calculation to minimize renal ATP consumption, while some well people (e.g., while reading a book) will require less fluids than the maintenance calculation to minimize renal ATP consumption. Special patients (e.g., severe burns) will require larger volumes of fluids to maintain fluid balance. Thus, the "maintenance" calculations provide a basic guide to determine the fluid and electrolyte intake that minimizes work stress on the kidneys of average hospital patients.

Although oral electrolyte solutions are commonly utilized for rehydration, they are actually maintenance electrolyte solutions. The most commonly recommended oral electrolyte solution known as Pedialyte contains 45 mEq Na per liter and 20 mEq K per liter. Sports drinks such as Gatorade have less sodium than this.

When a fluid deficit state is encountered, assessment of the severity is usually categorized as percent dehydration, which is really the volume of fluid loss as a percentage of body weight. Mild dehydration is 5% or less, moderate is about 10%, and severe dehydration is about 15% or greater. This classification is relative and not well standardized. Ideally, one could use their baseline body weight to determine the percentage of fluid loss, but this is almost never useful because growing children almost never have a known baseline body weight just prior to becoming ill. Additionally, factors such as anorexia and the duration of illness may lead to loss of lean body mass as well which adversely affects the weight calculation. Clinical and laboratory criteria have been developed to estimate dehydration percentage categories, but these are similarly flawed. Unfortunately, there is no certain way to accurately determine the degree of dehydration, therefore all clinical information (including weight loss if known) should be used to ESTIMATE the dehydration severity.

Criteria for 5% dehydration include: no tears when crying, oliguria, sticky (tacky) oral mucosa, less active than usual. Criteria for 10% dehydration include: sunken eyes, diminished skin turgor. Criteria for 15% dehydration include obvious shock (tachycardia, hypotension, cool extremities) and skin tenting. It should be noted that early signs of shock may appear as early as the 5% dehydration level. All of these clinical criteria have some flaws and they are not universally agreed upon. It is often not possible to estimate the urine output because of frequent diarrhea. The oral mucosa may appear to be moist if the patient has just vomited. Sunken eyes may be hard to determine if you don't know what the patient normally looks like. This is best assessed by asking the parent if the eyes look different. Parents will often use the word "hollow" to describe sunken eyes. A ketotic odor to the breath may signify ketosis due to poor oral intake which somewhat correlates with dehydration.

The serum bicarbonate is a measure of metabolic acidosis, but this can be misleading as well since sodium bicarbonate can be lost directly from diarrhea. However, an increased anion gap (calculated as Na minus Cl minus bicarb, which should be less than 12) is almost always present in clinically significant dehydration since lactic acid is produced in a dehydrated state (due to cellular hypoperfusion and a relative increase in anaerobic metabolism). This requires some thinking. For example, in vomiting patients, their bicarbonate initially increases (because of gastric acid loss resulting in a metabolic alkalosis); however, as fluid loss continues, they become dehydrated and a metabolic acidosis would indicate the presence of dehydration. In a patient with diarrhea, the bicarbonate value may be low from diarrheal losses of bicarbonate. So if the serum bicarbonate is relatively low and an increased anion gap is not present, this may not signify dehydration. However, the presence of an increased anion gap would indicate the presence of lactic acid production and dehydration. Similarly in diabetic ketoacidosis, the production of ketoacids and lactic acid results in an increased anion gap. Other clinical situations could affect the bicarbonate value and the anion gap in unusual ways, but this discussion is beyond the scope of this chapter. The above examples pertain to gastroenteritis only.

Replacing the fluid deficit (i.e., rehydration) can be done via oral rehydration or IV rehydration. Rehydration via a nasogastric tube is theoretically possible, but this option is not very popular since it possesses some of the negative characteristics of both oral and IV options. Oral hydration is generally preferable since this can be done at home, it is less invasive and it requires less costly resources. The AAP has published a practice guidelines on the management of acute gastroenteritis (3). Oral rehydration has been demonstrated to be successful in most (or perhaps nearly all) cases of gastroenteritis. The oral rehydration solution (ORS) developed by the World Health Organization takes advantage of the principle that glucose and sodium are co-transported in equimolar quantities across the GI mucosa. ORS contains this balance to optimize fluid absorption during gastroenteritis. Glucose in excess of sodium may remain in the bowel lumen as an unabsorbed osmotic particle which retains fluid in the bowel and inhibits fluid absorption.

ORS has been demonstrated to be efficacious even in children who are vomiting. The standard strategy is to give a small amount of fluid at a time. Giving 5 cc every 1 to 2 minutes reduces the volume remaining in the stomach at any given time. Since the stomach is similar to a bag, it is difficult for the stomach to vomit if only a small fluid volume is present. Giving 5 cc every minute results in a maximum fluid administration rate of 300 cc per hour, but this is very labor intensive for parents who must do this continuously for it to work. More commonly, 30 cc (1 ounce) is given every 15 minutes which results in a maximum fluid administration rate of only 120 cc per hour. This is more within the realm of what most parents are willing to do at home. If the child is not vomiting, then ORS can be given ad lib. It should be noted that a major difference between the clinical utilization of oral rehydration in the U.S. and other countries, is that American parents are very different from parents in much poorer countries. While parents in other countries may be willing to administer 5 cc every 1 to minutes, while the child continues to have a few emesis episodes, American parents are not likely to be this persistent. Often, if their child is not tolerating 30 cc every 15 minutes, American parents will frequently utilize the option of going to an emergency department for IV rehydration. Children in poorer countries do not have this option and despite sustaining greater degrees of dehydration, they are satisfactorily rehydrated via the oral route. It can be said that oral rehydration usually works for parents who are willing to persevere. In poor countries where an IV is rare, rehydration with ORS is life-saving to a very large number of children. In the U.S. severe dehydration is less common (better hygiene and nutrition), yet IV rehydration is used frequently for mild dehydration.

ORS is somewhat distasteful because it is rather salty and not very sweet. Even Pedialyte with much less sodium than ORS, is not very good tasting despite flavoring it. Significantly dehydrated children will usually drink ORS. Children who are not very dehydrated are not thirsty enough to be willing to drink ORS. However, some children who are significantly dehydrated do seem to refuse ORS or Pedialyte since they are either anorexic, too weak to drink, or are refusing because of behavioral reasons (i.e., "spoiled"). Children with mild dehydration can be placed on near normal diets (avoiding fat and excessive sugar), with good results in most instances.

Many textbooks will indicate that children with severe dehydration should be given immediate IV fluid boluses. While this is the standard practice in the U.S., it should be noted that in poor countries, many children with severe dehydration are successfully rehydrated using ORS. However, because severe dehydration is likely associated with a greater mortality risk than mild dehydration, it is reasonable to aggressively treat severe dehydration using IV fluids to reduce this risk. Even moderate dehydration could be treated using IV fluids since this reduces the risk of progression toward severe dehydration with its associated higher mortality risk. In the U.S. where IV fluid infusion resources are plentiful, there should be no hesitation to utilize IV fluids for severe dehydration.

For rapid IV rehydration, a fluid infusion utilizing normal saline (NS) or lactated Ringer's (LR) of 20 cc/kg is a common starting point. For severe dehydration, this should be given as a rapid bolus (over less than 10 minutes), but for mild dehydration this can be given over one hour. The term "isotonic" fluid is often used, but this is actually a misnomer. NS and LR are isotonic, but so is D5-1/4NS. All of these solutions have measured osmolarities of approximately 290. NS and LR behave very similarly since both have sodium concentrations similar to that of the serum. The major difference between NS/LR and D5-1/4NS is that NS/LR stays within the vasculature, while D5-1/4NS does not. Since fluid follows osmotic particles, the fluid volume will go, where the osmotic particles go. When NS/LR are used, the osmotic particles are largely sodium and chloride in concentrations very close to that of the circulating plasma. These ions stay within the circulating plasma and thus, the fluid volume expands the intravascular space preferentially. D5-1/4NS has a glucose concentration of 5000 mg/dL (D5W = 5% glucose = 5 grams/100cc). The serum concentration of glucose is only about 100 mg/dL. Thus, when D5-1/4NS is infused, the excess glucose is taken up by cells and converted to glycogen and the fluid volume leaves the intravascular space to enter the intracellular space. This might promote cellular edema under some circumstances, but at the very least, the fluid does not effectively expand the intravascular space. Thus, rather than use the term "isotonic IV fluids" to describe NS and LR, it would be more accurate to use the term "intravascular volume expanding IV fluids".

It should be noted that 20 cc/kg is actually a small volume. Take for example a 4 year child who weighs about 20 kg. 20 cc/kg results in a 400 cc fluid infusion. For mild dehydration this can be given over 1 hour so the IV rate would be 400 cc/hr for one hour. While this sounds like a very fast IV rate for a small child, this is actually a small volume. 20 cc/kg only replaces 2% of the body's weight, and thus it correctly for only 2% dehydration, which would be considered very mild and not generally in need of IV fluid rehydration. The 2% is determined by 400 cc divided by 20 kg (20,000 gms), or by 20 cc/kg (20 cc per 1000 cc = 2%). Another way to appreciate the truly small size of this fluid volume infusion is to equate this to soft drink cans, which are 12 ounce cans. Since 1 ounce equals 30 cc, a typical 12 ounce soft drink can contains 360 cc, which is similar to the 400 cc fluid infusion. One could say that we are giving a single can of IV fluid over an hour. Looking at it this way, most of us can see that this is not very much. Most 4 year olds can drink 3 or 4 soft drink cans on a hot day after a soccer game. Thus, 20 cc/kg fluid infusion volumes should almost always be repeated.

For severe dehydration in the range of 15%, the patient would actually need 150 cc/kg to fully replace the fluid deficit. For a patient with 5% dehydration, the patient would actually need 50 cc/kg to fully replace the fluid deficit. In addition to the deficit replacement, maintenance fluid needs must be added in.

Resuscitation of shock requires 20 cc/kg NS/LR as a rapid infusion and repeated until perfusion is restored. In most instances, fully rehydrating the patient very rapidly is not necessary and this may be harmful if excessive fluid shifts occur. Once satisfactory fluid resuscitation has stabilized the patient, continued rehydration and maintenance fluids can be administered more gradually.

Some patients with mild dehydration will prefer IV rehydration instead of oral rehydration. Although IV rehydration requires more resources and is more invasive, it has some definite advantages. Once the IV is in, fluid infusion is comfortable, rapid, and is not dependent on GI cooperation for absorption. Studies comparing IV and oral rehydration need to compare an "endpoint" to determine if the endpoint is better in one group or the other. Mortality is the most objective endpoint to measure. For mild dehydration, mortality risk is very low regardless of whether rehydration occurs orally or IV. IV rehydration results in rehydration certainty with minimal work by parents. Oral rehydration requires more work on the part of parents and some uncertainty exists as to whether it will be successful. Most parents bringing their child to an emergency department for IV hydration, have already attempted oral rehydration and they are not fully satisfied with the results. Even though IV rehydration may not be required, it is reasonable to offer it. Put yourself in the body of the child who is experiencing the vomiting and diarrhea. Imagine that you/he/she has vomited 8 times and has had 7 episodes of diarrhea beginning 8 hours ago. You have tried oral rehydration with ORS, but the vomiting and diarrhea have continued. Would you prefer to continue drinking ORS or would you prefer an IV fluid infusion, during which you would have to lie down and get some rest? At some point, many of us would prefer the IV route even though it is not required to avoid mortality. A rule of thumb is that an IV fluid infusion can be considered if V+D (vomiting and diarrhea episodes) is greater than or equal to 10. At this level, sufficient discomfort has been sustained by the patient and mild dehydration is likely. Most mildly dehydrated patients who are given 20 cc/kg per hour for 2 hours (total 40 cc/kg), feel much better with less nausea and fatigue. For such mild patients, they can usually be discharged from the emergency department to catch up on some rest. After a nap or overnight rest, oral rehydration attempts can resume, which are likely to be successful. Compare this to a similar oral rehydration patient, who is not permitted a nap and a period of bowel rest, and who must continue oral rehydration.

For inpatients who are hospitalized for IV rehydration, more time is available to gradually rehydrate the patient. Assuming that rapid IV fluid resuscitation has already taken place (or determined to be unnecessary), inpatient rehydration is a more complex calculation than emergency department rehydration. However, this knowledge is generally required for medical students and pediatric residents.

Fluid administration over a 24 hour period consists of deficit replacement plus maintenance administration. This is best described with the example presented in the case at the beginning of the chapter. A 12 month old male with vomiting and diarrhea is assessed to be 5% dehydrated by clinical criteria. His weight is 10 kg at presentation, but his pre-illness weight is not known. The patient's fluid deficit volume is 5% of 10 kg = 500 cc. The patient's maintenance fluid volume is 1000 cc. Fluid administration is generally broken up into 8 hour blocks for the next 24 hours. The maintenance fluid volume is administered evenly over the three 8 hour blocks. Half of the deficit volume is given in the first 8 hours, with one-fourth of the deficit volume given in the next two 8 hour blocks. This is diagrammed below:


First Second Third

8 hours 8 hours 8 hours


Maintenance volume 1/3 1/3 1/3

Deficit volume 1/2 1/4 1/4


Fitting the clinical data for the patient's case results in the following volume calculations:

First Second Third

24 hours 8 hours 8 hours 8 hours


Maintenance volume 1000 cc 333 cc 333 cc 333 cc

Deficit volume 500 cc 250 cc 125 cc 125 cc

Maintenance+Deficit 1500 cc 583 cc 458 cc 458 cc

IV rate 73 cc/hr 57 cc/hr 57 cc/hr


The IV rate is determined by the sum of the maintenance and deficit fluid volumes for the 8 hour block, divided by 8 hours as noted above. The next step is to determine the type of IV fluid to use (i.e., the optimal electrolyte content of the IV fluid). For maintenance IV fluids, Na is given as 3 mEq/100 cc of IV fluid, K is given as 2 mEq/100 cc of IV fluid. These electrolytes are replaced evenly over the three 8 hour blocks, as noted below (maintenance Na and K).


First Second Third

24 hours 8 hours 8 hours 8 hours


Maintenance volume 1000 cc 333 cc 333 cc 333 cc

Maintenance Na 30 mEq 10 mEq 10 mEq 10 mEq

Maintenance K 20 mEq 7 mEq 7 mEq 7 mEq


Deficit volume 500 cc 250 cc 125 cc 125 cc

Deficit Na ?? ?? ?? ??

Deficit K ?? ?? ?? ??


Maintenance+Deficit 1500 cc 583 cc 458 cc 458 cc

IV rate 73 cc/hr 57 cc/hr 57 cc/hr


The deficit sodium and potassium are more difficult to determine. First of all it should be noted that if the onset of dehydration is rapid (e.g., over 12 hours), most of the fluid is lost from the extracellular space (intravascular and interstitial fluid). If the onset of dehydration is very gradual and prolonged (e.g., over 7 days), relatively more fluid is lost from the intracellular space as well, since the longer time interval permits fluids to shift from the ICF to the ECF space. The ECF (similar to plasma) has a high Na concentration (137 mEq/L) and a low K concentration (3.5 mEq/L). The ICF is the opposite of this to maintain a transmembrane gradient, such that the intracellular K concentration is about 140 mEq/L, while the intracellular Na concentration is close to zero. Deficit Na and K are calculated by the split of ECF and ICF. The ECF volume lost concomitantly loses 140 mEq/L of Na, while the ICF volume lost concomitantly loses 140 mEq/L of K. Short term dehydration results in mostly ECF loss (i.e., more Na and less K), while dehydration occurring over a prolonged period, results in more ICF loss (i.e., more K and less Na). The table below estimates the degree of ICF and ECF loss based on the duration of gastroenteritis symptoms.


Duration of symptoms (4):

Less than 3 days: 80% ECF, 20% ICF

3 days or longer: 60% ECF, 40% ICF


Since our patient's dehydration occurred over one day, the ECF/ICF loss ratio is 80%/20%. Of the 500 cc fluid deficit, 400 cc is ECF loss, while 100 cc is ICF loss. ECF fluid loss contains 140 mEq Na per liter, while ICF fluid loss contains 140 mEq K per liter. Thus, the deficit Na lost is 140 X 0.4L = 56 mEq. The deficit K lost is 140 X 0.1L = 14. Deficit sodium is replaced in the same proportion as deficit fluid (i.e., 1/2, 1/4, 1/4) over the three 8 hour blocks. In contrast, only half of the deficit potassium is replaced and this is split evenly over the three 8 hour blocks (i.e., 1/6, 1/6, 1/6). This is a conservative approach since hyperkalemia due to a miscalculation could result in a life-threatening dysrhythmia. Another approach is to withhold all potassium until urine output is established and to begin potassium replacement at that time. The deficit and maintenance electrolytes can now be determined as in the table below:


First Second Third

24 hours 8 hours 8 hours 8 hours


Maintenance volume 1000 cc 333 cc 333 cc 333 cc

Maintenance Na 30 mEq 10 mEq 10 mEq 10 mEq

Maintenance K 20 mEq 7 mEq 7 mEq 7 mEq


Deficit volume 500 cc 250 cc 125 cc 125 cc

Deficit Na (ECF 80%) 56 mEq 28 mEq 14 mEq 14 mEq

Deficit K (ICF 20%) 14 mEq 2.5 mEq 2.5 mEq 2.5 mEq


Maintenance+Deficit volume 1500 cc 583 cc 458 cc 458 cc

Maint+Def Na 86 mEq 38 mEq 24 mEq 24 mEq

Maint+Def K 34 mEq 9.5 mEq 9.5 mEq 9.5 mEq


IV rate 73 cc/hr 57 cc/hr 57 cc/hr

Na concentration 65 mEq/L 52 mEq/L 52 mEq/L

K concentration 16 mEq/L 21 mEq/L 21 mEq/L


For the first 8 hour period, the Na concentration must approximate 65 mEq/L, which somewhere between 1/2NS and 1/3NS. The IV order for the first 8 hour block could be "IV D5-1/2NS + 16 mEq KCl per liter run at 73 cc/hour for 8 hours." For the next 16 hours, the Na concentration must approximate 52 mEq/L which is approximately 1/3NS. The IV order for the next 16 hours should be "IV D5-1/3NS + 21 mEq KCl per liter run at 57 cc/hour for 16 hours".

Although this process is rather complex, a short cut exists. For 5% dehydration, which is the most common type of hospitalization, the fluid calculations can be approximated by D5-1/2NS + 20 mEq KCl per liter run at twice the maintenance rate for the first 8 hours, followed by D5-1/3NS + 20mEq KCl per liter run at 1.5 times the maintenance rate for the next 16 hours. For percentages other than 5%, this short cut will not work. For dehydration which occurs over more than 3 days, there is a greater loss of ICF (hence, more potassium loss) and relatively less ECF loss (hence, relatively less sodium loss), so the order can be modified to: D5-1/3+25 mEq KCl per liter run at 2 times maintenance for 8 hours, then 1.5 times maintenance for the next 16 hours.

Other factors can make these calculations even more complex. If the patient was given several rapid bolus infusions of NS in the preliminary resuscitation in the ED stabilizing the patient from 10% to 4% dehydration, a large amount of sodium was given initially. If the patient has hyponatremic or hypernatremic dehydration, then the sodium deficit will need to be recalculated. However in the acute resuscitation phase, it doesn't matter whether the patient is hyponatremic, normonatremic or hypernatremic, because the initial IV fluid indicated for resuscitation bolus infusions is NS or LR. The correction of hyponatremia, hypernatremia, hypokalemia and hyperkalemia is beyond the scope of this chapter. However, most cases of mild sodium and potassium imbalance, will eventually correct with most methods of calculating fluid replacement, as long as the kidneys remain functional to ultimately correct the imbalance. Correcting extreme deviations of sodium and potassium should be done with caution. Rapid electrolyte correction can result in cellular damage due to excessive fluid shifts. The use of 3% sodium chloride solution (more than 3 times the osmolarity of NS) should be used with extreme caution since this can cause severe hypernatremia in a short period of time. Administering potassium IV to correct hypokalemia is also dangerous, especially for infants since a small dose of IV potassium can easily make the patient critically hyperkalemic. A general recommendation is that, if the patient is stable, it is best to correct the electrolyte imbalance slowly.


Every day basic numbers to know (and memorize):

Maintenance fluid volume calculation: 100, 50, 20

Maintenance electrolytes: 3meq Na/100cc, 2meq K/100 cc

Volume expanding bolus (NS or LR): 20 cc/kg NS

Normal osmolarity 290 mosm/liter

30 cc = 1 ounce.


Questions:


1. Which of the following sets of signs and symptoms are most consistent with 5% dehydration?

a. oliguria, tears with crying, less active than usual, normal skin turgor, moist oral mucosa.

b. oliguria, no tears with crying, less active than usual, sticky oral mucosa, normal or slightly diminished skin turgor.

c. oliguria, no tears with crying, sunken eyes, soft doughy skin (diminished skin turgor) without tenting.

d. oliguria, sunken eyes, tenting, tachycardia, hypotension.


2. Which of the following sets of signs and symptoms are most consistent with 10% dehydration?

a. oliguria, tears with crying, less active than usual, normal skin turgor, moist oral mucosa.

b. oliguria, no tears with crying, less active than usual, sticky oral mucosa, normal or slightly diminished skin turgor.

c. oliguria, no tears with crying, sunken eyes, soft doughy skin (diminished skin turgor) without tenting.

d. oliguria, sunken eyes, tenting, tachycardia, hypotension.


3. Calculate the maintenance IV fluid and rate for a 4 kg infant and for a 25 kg 6 year old.


4. Estimate the concentration of sodium in NS, 1/2NS, 1/3NS and 1/4NS.


5. The resident writes an order for "isotonic" IV fluid to be bolused immediately for a patient with shock and severe dehydration. You look at all the IV fluid bags and notice that NS has an osmolarity of 310, LR has an osmolarity of 275, and D5-1/4NS has an osmolarity of 320. You grab a bag of D5-1/4NS. The resident tells you to get normal saline instead. Why is D5-1/4NS inappropriate even though it is "isotonic"?


6. You calculate the 24 hour maintenance volume for a 3 kg child with severe neurologic dysfunction. His maintenance volume is 300 cc/day. He is currently being fed infant formula via a nasogastric tube at 3 ounces every 3 hours. You do a calculation and notice that he is getting 720 cc/day which is more than twice his maintenance volume. Why isn't this child in congestive heart failure from fluid overload? Explain what maintenance means.


7. You are working as a volunteer physician in a refugee camp of a poor country. The clinic staff has a total of 5 IV sets and there are over 100 children presenting to your clinic with diarrhea and dehydration today. You are seeing a 10 month old infant who is thin and appears to be about 10% dehydrated. Should you use one of the IV sets, or should you implement oral rehydration? A company has donated 1000 liters of Pedialyte which are available for use. What is your rehydration plan for this patient?


8. Calculate an IV rehydration to be administered over 24 hours for a 16 kg child who is 7% dehydration from vomiting and diarrhea which has taken place over 4 days. Start by filling in the table below:


First Second Third

24 hours 8 hours 8 hours 8 hours


Maintenance volume ______cc ______cc ______cc ______cc

Maintenance Na _____mEq _____mEq _____mEq _____mEq

Maintenance K _____mEq _____mEq _____mEq _____mEq


Deficit volume ______cc ______cc ______cc ______cc

Deficit Na _____mEq _____mEq _____mEq _____mEq

Deficit K _____mEq _____mEq _____mEq _____mEq


Maintenance+Deficit volume ______cc ______cc ______cc ______cc

Maint+Def Na _____mEq _____mEq _____mEq _____mEq

Maint+Def K _____mEq _____mEq _____mEq _____mEq


IV rate _____cc/hr _____cc/hr _____cc/hr

Na concentration ____mEq/L ____mEq/L ____mEq/L

K concentration ____mEq/L ____mEq/L ____mEq/L

Type of IV fluid ________ ________ ________


References

1. Adelman RD, Solhaug MJ. Part VII - Pathophysiology of Body Fluids and Fluid Therapy. In: Behrman RE, Kleigman RM, Jenson HB (eds). Nelson Textbook of Pediatrics, 16th edition. 2000, Philadelphia: W.B. Saunders.

2. Chapter 3-Shock. In: American College of Surgeons Subcommittee on Advanced Trauma Life Support. Advanced Trauma Life Support for Doctors Student Course Manual, 6th edition. 1997, Chicago: American College of Surgeons, p. 93.

3. American Academy of Pediatrics, Provisional Committee on Quality Improvement, Subcommittee on Acute Gastroenteritis. Practice parameter: the management of acute gastroenteritis in young children. Pediatrics 1996;97(3):424-435.

4. Cronan K, Norman ME. Chapter 86-Renal and Electrolyte Emergencies. In: Fleisher GR, Ludwig S, Henretig FM (eds). Textbook of Pediatric Emergency Medicine, 4th edition. 2000, Philadelphia, Lippincott Williams & Wilkins, pp. 811-858.


Answers to questions

1. b

2. c

3. 4kg: 4 X 100 = 400 cc over 24 hours. 3 mEq Na per 100 cc, 2 mEq K per 100 cc. D5-1/4NS + 20 mEq KCl per liter run at 17 cc/hour. 25 kg: 1500 + 5 X 20 = 1600 cc over 24 hours. Maintenance electrolytes are the same. D5-1/4NS + 20 mEq KCl per liter run at 67 cc/hour.

4. Since normal osmolarity is about 300, the Na concentration in NS must be about half that (since Na and Cl ions make up the total osmolarity), which is 150 mEq/L. 1/2NS is half that (75 mEq/L), 1/3NS is 50 mEq/L and 1/4NS is 38 mEq/L.

5. An intravascular volume expanding fluid is required to resuscitate severe dehydration and hypovolemic shock. D5-1/4NS is not an intravascular volume expanded (see text). NS and LR are intravascular volume expanders. The resident should not have used the term "isotonic" since what he/she really meant, was to administer an intravascular volume expanding IV solution.

6. The patient has normal kidneys, which will regulate his overall fluid status. Even normal infants drink about 250 cc/kg (about 2.5 times maintenance), which is why they use a lot of diapers. Since formula is only 2/3 of a calorie per cc, he needs more than maintenance to reach maintenance caloric intake. His excess fluid volume will be urinated out. Maintenance fluid volume is the volume which results in minimum work for the kidney. If less than maintenance fluid is taken in, the kidney must work (consume energy) to retain fluid. If more than maintenance fluid is taken in, the kidney must work to excrete excess fluid. Kidney energy consumption (work) is minimized at some point between these two extremes and this is the "maintenance volume". Patients receiving fluid volumes less than or greater than maintenance will not likely develop fluid balance problems as long as their kidneys are functioning normally. However, if they are very ill, it would be best to minimize renal stress by optimizing their fluid balance.

7. Oral rehydration with WHO ORS should be implemented immediately. Pedialyte is for maintenance fluid, is suboptimal for rehydration and is only useful for children with mild dehydration. This child is not ill enough to utilize one of the 5 IV sets available. According to studies, the mortality rate for oral rehydration and IV rehydration are the same for this type of dehydration.

8. 24 hour maintenance volume is 1300 cc. This is split up into three even 8 hour blocks. Maintenance electrolytes are 3 mEq Na and 2 mEq K per 100 cc. Deficit volume is 1120 cc (7% of 16 kg), half of which is given in the first 8 hour block with the other half distributed over the next two 8 hour blocks (1/4 for each 8 hour block). Since dehydration has occurred over a 4 day period, 60% of the deficit comes from the ECF (672 cc) and 40% comes from the ICF (448 cc). Thus, the sodium replacement for ECF fluid is 140 mEq per liter and the potassium replacement for ICF is 140 mEq per liter. The Na deficit is replaced as the deficit fluid is replaced over the next three 8 hour blocks (1/2 + 1/4 + 1/4). Half of the K deficit is replaced distributed evenly over the three 8 hours blocks (1/6 + 1/6 + 1/6). The results of these calculations are shown below:


Weight 16 kg First Second Third

7% dehydration 24 hours 8 hours 8 hours 8 hours


Maintenance volume 1300 cc 433 cc 433 cc 433 cc

Maintenance Na 39 mEq 13 mEq 13 mEq 13 mEq

Maintenance K 26 mEq 9 mEq 9 mEq 9 mEq


Deficit volume 1120 cc 560 cc 280 cc 280 cc

Deficit Na (60%) 94 mEq 47 mEq 24 mEq 24 mEq

Deficit K (40%) 63 mEq 10 mEq 10 mEq 10 mEq


Maintenance+Deficit volume 2420 cc 993 cc 713 cc 713 cc

Maint+Def Na 133 mEq 60 mEq 37 mEq 37 mEq

Maint+Def K 89 mEq 19 mEq 19 mEq 19 mEq


IV rate 124 cc/hr 89 cc/hr 89 cc/hr

Na concentration 60 mEq/L 52 mEq/L 52 mEq/L

K concentration 19 mEq/L 27 mEq/L 27 mEq/L


D5-1/3NS+19 mEq KCl per liter run at 124 cc/hour for 8 hours, then D5-1/3NS+27 mEq KCl per liter run at 89 cc/hour for 16 hours. The KCl should actually be approximated to 20 mEq/L for the first 8 hours, then 25 mEq/L for the next 16 hours. This would make it easier for the nursing staff to carry out the order.


1   ...   10   11   12   13   14   15   16   17   ...   176

Похожие:

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconProfessor, Department of Neuroscience, Johns Hopkins University School of Medicine

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconUniversity of Pennsylvania School of Medicine

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconUniversity of Virginia School of Medicine

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconPrepared by Susan S. Grover, Eric Chason & J. R. Zepkin of William & Mary Law School, Emmeline P. Reeves of University of Richmond Law School, Robert W. Wooldridge, Jr of George Mason University Law School & C. Scott Pryor of Regent University Law School

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconCardiff University, School of Medicine [2011]

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconThe Johns Hopkins University School of Medicine

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconUniversity at buffalo school of medicine and biomedical sciences

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconHistology and embryology university of split school of medicine

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconDuke University School of Medicine, Durham, North Carolina

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine iconJohns Hopkins bloomberg school of public health johns hopkins university school of medicine

Разместите кнопку на своём сайте:
Библиотека


База данных защищена авторским правом ©lib.znate.ru 2014
обратиться к администрации
Библиотека
Главная страница