Simplified treatment strategies to fluid therapy in diarrhea

Transcription

1 Pediatr Nephrol (2003) 18: DOI /s ORIGINAL ARTICLE Farahnak Assadi Lawrence Copelovitch Simplified treatment strategies to fluid therapy in diarrhea Received: 14 April 2003 / Revised: 25 July 2003 / Accepted: 29 July 2003 / Published online: 2 October 2003 IPNA 2003 Abstract Dehydration resulting from diarrhea remains an important cause of morbidity and mortality among infants and children worldwide. Although it is well established that rapid and generous intravenous restoration of extracellular fluid, followed by oral rehydration therapy (ORT) should be used in children with severe dehydration, physicians continue to be reluctant to use such therapy. Applying the principle of body fluid physiology to the current treatment of dehydration, we developed a simple and yet effective treatment strategy to fluid therapy for children with diarrheal dehydration using commercially manufactured solutions. Children with mild-to-moderate dehydration are best treated with ORT using commercially available oral solutions containing meq/l of Na +. Children who have clinical evidence of severe dehydration should receive intravenous fluids, ml/ kg of 0.9% saline in the first 2 4 h to restore circulation. Oliguric patients with severe acidosis should receive a physiological dose of bicarbonate to correct blood ph level to Once circulation is restored, the ORT should be given in small quantities to replace losses of water and Na + over 6 8 h. Age-appropriate diet should be started as soon as tolerated. Those who cannot tolerate ORT should receive intravenous rehydration for the remainder of the deficit and maintenance. Addition of 20 meq/l K + to rehydration solutions permits repair of cellular K + deficits without risk of hyperkalemia. The amount of Na + given to replace maintenance and deficit fluids varies with the forms of dehydration. Isonatremic dehydration is best treated with 5% dextrose in 0.45% saline containing 20 meq/l KCl over 24 h. Hyponatremic dehydration is F. Assadi L. Copelovitch Section of Nephrology, Department of Pediatrics, Rush University Medical College, Chicago, Illinois, USA F. Assadi () ) Section of Nephrology, Rush Children s Hospital, 1725 W. Harrison Street, Suite 710, Chicago, IL 60612, USA fassadi@rush.edu Tel.: Fax: best treated with 0.9% saline and 0.45% saline alternately in a 1:1 ratio in 5% dextrose containing 20 meq/l KCl over 24 h. Hypernatremic dehydration is best treated with 5% dextrose in 0.2% saline containing 20 meq/l KCl over 2 3 days to avoid cerebral edema. Maintenance hydration is best treated with 5% dextrose in 0.2% saline containing 20 meq/l KCl. Ideal commercial intravenous maintenance and deficit solutions have yet to appear. Keywords Diarrheal dehydration Oral rehydration therapy Rapid rehydration therapy Introduction Rapid and generous restoration of extracellular fluid (ECF) volume with 0.9% saline followed by oral rehydration therapy (ORT) has become the gold standard of therapy in infants with moderate-to-severe dehydration [1, 2, 3]. Rapid restoration of ECF volume will allow early feedings, shortens the length of hospital stay, and significantly reduces the mortality rate to less than 3 per 1,000 [2]. Despite the efficacy of rapid rehydration, few physicians are actually using this therapeutic regimen [2, 3]. This likely stems from the lack of adequate training in the use of rapid hydration therapy, practice variations with regard to expansion of ECF in dehydration, or confusion about the risks versus benefits of rapid rehydration therapy. For example, in a recent report [4], Moritz and Ayus proposed giving 0.9% saline rather than the standard 0.25% saline for meeting current maintenance fluids requirements [5]. The American Academy of Pediatrics (AAP) Provisional Committee on gastroenterology recommends rapid restoration of ECF volume by infusing ml/kg 0.9% saline or Ringer s solution over a 1-h period, followed by an additional ml/kg if the circulation is not fully restored [2]. However, larger quantities and much shorter periods of administration may be required to restore perfusion of the gastrointestinal tract and kidneys [6].

2 Despite these recommendations, many pediatric texts recommend giving 20 ml/kg saline for acute ECF expansion, followed by the remainder of the deficit therapy over 1 2 days [7, 8, 9]. Moreover, amounts of Na + recommended for treating various forms of dehydration vary from one regimen to another [6, 10]. Variability in the use of fluid therapy in dehydration has become problematic and often confusing to both pediatricians and pediatric residents. When too many fluid regimens are prescribed more confusion and miscalculation will occur. Miscalculation may lead to errors in management, causing potentially fatal complications [11, 12]. There is growing evidence that practitioners need more information in these areas. Efforts to simplify fluid therapy in dehydration by targeting the electrolyte abnormalities that underlie the various forms of dehydration can help most physicians to effectively and accurately initiate therapy and hopefully reduce the high mortality rate associated with dehydration [11, 13]. In this article, we apply the principles of body fluid physiology to the treatment of diarrheal dehydration in an effort to develop a very simple and yet effective rehydration regimen. Simplified explanations help practitioners readily understand the concepts. Review of body fluids compartments and compositions Understanding fluid therapy in dehydration requires knowledge of body fluid compartments and compositions. The infant and child differ from adults with respect to the size of the ECF compartment. The full-term infant, with about 12% body fat, has about 75% of body weight as water, while in the premature baby, 80% or more of body weight is water [14]. In the newborn infant, approximately 45% of body weight presents as ECF. This decreases rapidly to about 30% of body weight by 1 year of age and then slowly until 12 yeas of age, when the ECF compartment accounts for 20% of lean body mass [14, 15]. In contrast to ECF, the relative volume of ICF remains constant during growth. Because of the agerelated reduction in relative ECF volume, ICF becomes proportionately larger than ECF during late infancy. Sodium (Na + ) is the major cation in the ECF, while potassium (K + ) and magnesium are the major cations in the ICF. Major anions of the ECF are chloride (Cl Ÿ ) and bicarbonate (HCO3 Ÿ ), and those in the intracellular space are proteins and organic phosphate [16]. In the ECF, Na + and Cl Ÿ constitute 90% or more of the effective solutes. The serum Na + concentration defines the relative amount of Na + and water in plasma [16]. The main difference between plasma and interstitial fluid is the higher protein content in the former. The relative impermeability of the capillary endothelium to protein sets up a Gibbs-Donnan effect, which accounts for the slight differences in distribution of diffusible ions between plasma and interstitial fluid [16]. The balance of Starling forces determines the steady size of the plasma and interstitial compartments [16]. Active pumping of Na + out of cells offsets the oncotic pressure of non-diffusible organic phosphates and proteins, and thereby ordinarily prevents swelling and bursting of the cell [16]. Maintenance requirements 1153 At rest, an individual expends a defined amount of energy to maintain body homeostasis. The heat generated from this energy is lost, in part by evaporation of water from skin and from the lungs, which is termed insensible water loss [17] (Table 1). Infants and young children expend more daily energy per unit mass than do older children and adults, due to a greater ratio of surface area to total body weight in small children, as well as a greater related energy expenditure [18, 19]. Holiday and Segar [20] recommended giving 100 ml of water for each 100 kcal of energy (Table 2). They also recommended 3 meq Na +, 2 meq K +, and 2 meq Cl Ÿ for each 100 kcal of energy consumed (Table 3). Fever increases daily energy requirements by about 10 kcal/kg per day for each degree of temperature elevation [18, 19]. The addition of 5% glucose to the maintenance fluid provides sufficient calories to prevent severe protein catabolism. Thus, 5% dextrose in 1/4 saline with 20 meq/l KCl is a suitable solution for maintenance therapy. Table 1 The relationship between metabolism and maintenance fluids Route ml/100 kcal metabolized energy Insensible Skin Ÿ30 Lungs Ÿ15 Renal Ÿ55 Gastrointestinal Ÿ10 Water of oxidation +15 Total for maintenance Ÿ100 Table 2 Relationship between body weight and caloric expenditure Body weight Daily caloric expenditure Daily water requirements 3 10 kg 100 kcal/kg 100 ml/kg kg 1,000 kcal+50 kcal/kg for each kg in excess of 10 kg 1,000 ml+50 ml/kg for each kg in excess of 10 kg >20 kg 1,500 kcal+20 kcal/kg for each kcal in excess of 20 kg 1,500 ml+20 ml for each kcal in excess of 20 kg

3 1154 Table 3 The estimated daily needs for electrolyte maintenance Electrolyte Sodium Chloride Potassium meq/100 ml water requirements 3 meq 3 meq 2 meq Table 4 Estimation of the severity of dehydration Degree of dehydration Mild Moderate Severe Weight loss Infants 5% 10% 15% Children 3% 6% >9% Volume of deficit Infants 50 ml/kg 60 ml/kg 150 ml/kg Children 30 ml/kg 100 ml/kg >90 ml/kg Pulse Normal Tachycardia Tachycardia Capillary refill <2 s 2 4 s >4 s Anterior fontanel Normal Normal Sunken Tears Present Decreased Absent Mucous membrane Normal Dry Parched Urine specific gravity >1.020 >1.020, oliguria Oliguria or anuria Blood pressure Normal Normal Orthostatic to shock Estimation of the volume of deficit Acute weight loss and clinical findings signify the severity of dehydration. In infants, mild-to-moderate dehydration implies that the child has lost ml/kg of body weight as water. In severe dehydration the estimated water loss is about 150 ml/kg body weight [7]. With older children and adults, it is recommended to use 3%, 6%, and 9% for the mild, moderate, and severe degrees of dehydration, respectively [7, 8]. Clinical signs of tachycardia, decreased skin turgor, sunken eyes and fontanel, lethargic or impaired mental status, and oliguria predict a more than 10% weight loss [7, 8, 9]. A capillary refill time of 2 3 s corresponds to ml/kg loss, s corresponds to ml/kg, and more than 4 s corresponds to 150 ml/kg [21] (Table 4). Initial rapid hydration is necessary for children with clinical signs and symptoms of severe dehydration. Initial therapy requires administration of ml/kg 0.9% saline in the first 1 h to expand the ECF volume [2]. Rapid administration of larger quantities, ml/kg, may be necessary to restore circulation [6]. Once ECF volume is expended and renal perfusion restored, one can change to hypotonic fluids at a slower rate to replace maintenance requirements, remaining deficit fluids, and any ongoing abnormal losses. Acidosis is readily corrected when circulation is restored. It is important to closely monitor fluid electrolytes and acid-base status after the initial rehydration therapy. Oliguric children with plasma ph lower than 7.25, after the initial volume expansion, should be given HCO3 Ÿ intravenously in the amount to correct plasma ph to 7.25, equivalent to a H + concentration of 55 nmol/l, using the modified Henderson-Hasselbalch equation [22]: HCO3 deficit ¼ TBW ½ðdesired HCO3 levelþ ðcurrent HCO3 levelþš Desired plasma HCO3 level ¼ ðh þ ¼ 24 PCO2=HCO3 Þ This equation allows rapid calculation of any component if two of the other terms are known. For instance, for a 20-kg child with a ph of 7.10, HCO3 Ÿ of 6 meq/l, and PCO 2 of 20 meq/l, this equation will give a desired HCO3 Ÿ level of 8.7 meq/l. The amount of HCO3 Ÿ deficit should be given over 1 2 h, depending on the severity of signs and symptoms of acidosis. Reassessment of acidbase status and adjustments in HCO3 Ÿ dosage are required within 2 h. ORT should be started as soon as tolerated, usually 6 12 h after parenteral therapy has begun, and continued for the remaining 24 h to replace deficit fluids [1, 2, 23]. The ORT should be given in a small volume, 5 ml every minute, to minimize gastric distention and reflux vomiting. Children should be fed an age-appropriate diet as soon as rehydration is complete [1, 2, 23]. There is no role for the clear liquid diet in diarrhea-induced dehydration. The osmolality of the oral solutions should be kept below or about 325 mosmol/l to prevent osmotic diarrhea. This can be achieved by using a commercially available oral rehydration solution containing meq/l Na +, 20 meq/l K + 20 g/l glucose, and 30 mmol/l acetate [1, 2, 23]. Children who cannot retain ORT should continue receiving parenteral rehydration therapy for 24 h or longer until the oral intake can be resumed. Depending on the type of dehydration, varying amounts of Na + are given to replace maintenance and deficit fluids. Isonatremic dehydration Isonatremic dehydration (serum Na + concentration meq/l) is the most common form of diarrheal dehydration in children. In isonatremic dehydration, water and Na + are lost in physiological proportion (isotonic loss), thus maintaining the serum Na + concentration within the normal range [24]. For a 10-kg infant whose estimated deficit is 1,000 ml and maintenance is another 1,000 ml, 2,000 ml should be given in 24 h. Because 50% of this solution is for deficit (0.9% saline) and 50% for maintenance (0.2% saline), the Na + concentration in delivered fluid is equivalent to 0.45% saline. When urine output is established, K + may be added. Diarrhea stools, on average, contain 20 meq/l K + [25]. Prolonged vomiting of small intestinal fluid in association with diarrhea may result in more than 20 meq/l K + in lost fluids. The fluid deficit plus maintenance should be administered over 24 h. Thus, 5% dextrose in 1/2 saline with 20 meq/l KCl is an appropriate solution for children with isonatremic dehydration (Table 5).

4 Table 5 Recommended intravenous fluid therapy in dehydration Type of fluid therapy Maintenance Isotonic dehydration Hypotonic dehydration Hypertonic dehydration 1155 Solution 5% dextrose in 1/4 saline with 20 meq/l KCl over 24 h 5% glucose in 0.45% saline with 20 meq/l KCl given over 24 h 5% glucose in 0.9% saline with 20 meq/l KCl given over 12 h followed by 5% dextrose water in 0.45% saline with 20 meq/l KCl given over the next 24 h 5% dextrose water in 0.2% saline containing 20 meq/l KCl to be given over the number of days necessary to lower the Na + concentration by 10 meq/day Hyponatremic dehydration Hyponatremic dehydration (serum Na + concentration <130 meq/l) occurs when sodium loss is disproportionately greater than the water loss or if a considerable amount of free water is given for replacement [24]. Because serum osmolality is low, water shifts from ECF into the ICF, making the symptoms of ECF volume contraction more severe than in the other forms of dehydration. Treatment of hypotonic dehydration is similar to that of isotonic dehydration, except that extra Na + loss should be provided using the following equation: Extra Na þ deficit ¼ TBW ½ð135 meq=lþ ðmeasured serum Na þ ÞŠ With the addition of this Na +, the dehydration will change from hyponatremic to isonatremic; thus, the patient still will require isotonic fluid replacement. For a 10-kg infant with hyponatremic (serum Na meq/l) dehydration whose estimated deficit is 1,000 ml and maintenance requirement is another 1,000 ml, 2,000 ml should be administered over 24 h. Because half of this is for deficit (containing 135 meq Na + plus an extra 60 meq) and half for maintenance (containing 30 meq/l Na + ), the Na + concentration in delivered fluid is about 112 meq/l. However, there is no such commercially available solution. A simplified approach is to use isotonic saline (154 meq/l Na + ) and 1/2 saline (77 meq/l Na + ) alternately in a 1:1 ratio (Table 5). K + replacement is the same as in the other forms of dehydration. Patients with a serum Na + concentration less than 125 meq/l are often symptomatic, especially if the hyponatremic dehydration has developed rapidly over a few hours. Symptomatic patients require infusion of hypertonic 3% saline (0.5 meq/ml) in an amount to increase the serum Na + level to 125 meq/l. The rise in serum Na + of 2 meq/l per hour is considered safe and unlikely to cause central pontine myelinolysis [13, 26]. Hypernatremic dehydration Hypernatremic dehydration (serum Na + concentration >150 meq/l) occurs when the lost fluid contains less Na + than water (hypotonic fluid) [24]. Because of the ECF hyperosmolality, water is osmotically moved from ICF into the extracellular space [24]. To compensate, cells generate osmotically active particles (idiogenic osmoles) that pull water back into the cell to restore ICF volume [27, 28]. With aggressive rehydration, the ECF osmolality may fall more rapidly than the cell can dissipate the idiogenic osmoles. The correction of symptomatic hyponatremia should be of a sufficient pace and magnitude to reverse the symptoms, but not so rapid and large as to cause osmotic demyelination. The initial rate of correction is 1 2 meq/l per hour for several hours. Patients with a serum Na + concentration less than 125 meq/l are often symptomatic, especially if the hyponatremic dehydration has developed rapidly over a few hours. Symptomatic patients require infusion of hypertonic saline (3%) in an amount to increase the serum sodium level to 125 meq/l. Rapid correction of hypernatremic dehydration can cause disastrous neurological consequences, including cerebral edema, seizures, and death [29]. The elevated serum Na + concentration should be corrected by no more than 10 meq/l per day to avoid cerebral edema. A faster pace of correction is prudent in patients with hypernatremia that has developed quickly over a period of hours [30]. Hypernatremic dehydration occurs with severe prolonged diarrhea associated with a decreased free water intake and increased insensible water loss. The total body water (TBW) loss exceeds the total body Na + losses. Under these circumstances, the free water deficit can be estimated using the following equation [7]: Free water deficit ¼ ðnormal TBWÞ ðcurrent TBWÞ Current TBW ¼ TBW target Na þ ð150 meq=lþ=current Na þ or ðtbw ð1 ½150=current Na þ ŠÞÞ With the addition of this free water, the dehydration will change from hypotonic to isotonic; thus, the patient still requires isotonic fluid replacement. Estimated deficit plus maintenance requirements should be spread out over the number of days necessary to lower the Na + concentration to 150 meq/l. For a 10-kg infant with a serum Na + concentration of 170 meq/l, whose estimated deficit is 1,000 ml and 2 days maintenance is 2,000 ml, 3,000 ml should be given over 48 h. The estimated free water deficit of 800 ml should contain no Na + (free water). The remaining 200 ml of deficit fluid would be isotonic containing 31 meq Na +. Because one-third of the total volume is for deficit (31 meq/l Na + ) and two-third for

5 1156 maintenance (30 meq/l Na + ), the Na + concentration in delivered fluid is about 30 meq/l, equivalent to 0.2% saline. Hypocalcemia is occasionally seen during treatment. This can be avoided by adding a 20-ml ampoule of 10% calcium gluconate in a liter of rehydration fluid [10]. Thus, the use of 5% dextrose in 1/4 saline with 20 meq/l KCl given over 48 h is recommended for children with hypertonic dehydration (Table 5). References 1. Hirschhorn N, Greenough WB (1991) Progress in oral rehydration therapy. Sci Am 264: AAP Provisional Committee on Quality Improvement, Subcommittee on Acute Gastroenteritis (1996) Practice parameter: the management of acute gastroenteritis in young children. Pediatrics 97: Holliday M (1996) The evolution of therapy for dehydration: should deficit therapy still be taught? Pediatrics 98: Mortiz ML, Ayus JC (2003) Prevention of hospital acquired hyponatremia: a case for using isotonic saline in maintenance therapy. Pediatrics 111: Chesney RW (1998) The maintenance need for water in parenteral fluid therapy. Pediatrics 102: Holliday MA, Friedman AL, Wassner SJ (1999) Extracellular fluid restoration in dehydration: a critique of rapid versus slow. Pediatr Nephrol 13: Awazu M, Devarajan P, Stewart CL, Kaskel F, Ichikawa I (1990) Maintenance therapy and treatment of dehydration and overhydration. In: Ichikawa I (ed) Pediatric textbook of fluids and electrolytes. Williams and Wilkins, pp Seigal NJ, Carpenter T, Gaudio KM (1994) The pathophysiology of body fluids. In: Osaki FA (ed) Principles and practice of pediatrics, 2nd edn. Lippincott, Philadelphia, pp Finberg L, Kraveth RE, Hellerstein S (1993) Water and electrolytes in pediatrics: physiology, pathophysiology and treatment, 2nd edn. Saunders, Philadelphia 10. Finberg L (2002) Dehydration in infancy and childhood. Pediatr Rev 23: Arieff AI, Ayus JC, Fraser CL (1992) Hyponatremia and death or permanent brain damage in healthy children. BMJ 304: Finberg L (1973) Hypernatremic (hypertonic) dehydration. N Engl J Med 286: Laureno R, Karp BI (1997) Myelinolysis after correction of hyponatremia. Ann Intern Med 126: Holliday MA (1987) Body composition, metabolism, and growth. In: Holliday MA, Barratt TM, Vernier RL (eds) Pediatric nephrology, 2nd edn. Williams and Wilkins, Baltimore, pp Yoshioka T, Litaka K, Ichikawa I (1990) Body fluid compartments. In: Ichikawa I (ed) Pediatric textbook of fluids and electrolytes. Williams and Wilkins, Baltimore, pp Valtin H (1983) The body fluid compartments In: Valtin H (ed) Renal function mechanisms preserving fluid and solute balance in health, 2nd edn. Little Brown, Boston, pp Bligh J, Anderson KG (1973) Glossary of terms for thermal physiology. J Appl Physiol 35: Simmons CF Jr, Ichikawa I (1990) External balance of water and electrolytes. In: Ichikawa I, Awazu M, Kon V, Barakat A (eds) Volume disorders. Pediatric textbook of fluids and electrolytes. Williams and Wilkins, Baltimore, pp Winters RW (1973) The body fluids in pediatrics. Little Brown, Boston, pp Holiday MA, Segar WE (1957) The maintenance need for water in parenteral fluid therapy. Pediatrics 19: Saavedra JM, Harris GD, Li S, Finberg L (1991) Capillary refilling (skin turgor) in the assessment of dehydration. Am J Dis Child 145: Kassirer JP, Bleich HL (1965) Rapid estimation of plasma carbon dioxide tension from ph and total carbon dioxide content. N Engl J Med 272: Santosham M, Greenough WB 3rd (1991) Oral rehydration therapy: a global perspective. J Pediatr 118:S44 S Fanestil DD, Moore FD (1994) Compartmentation of body water. In Narins RG (ed) Clinical disorders of fluid and electrolytes metabolism. McGraw-Hill, New York, pp Darrow DC, Pratt EL, Flett J, Gamble AH, Weiss HA (1949) Disturbances of water and electrolytes in infantile diarrhea. Pediatrics 1: Adrouge HJ, Madias NE (2000) Hyponatremia. N Engl J Med 342: Gullans SR, Verbalis JG (1993) Control of brain volume during hyperosmolar and hypoosmolar conditions. Annu Rev Med 44: Lein YH, Shapiro JI, Chan L (1990) Effects of hypernatremia on organic brain osmoles. J Clin Invest 85: Finberg L (1981) Dehydration and osmolality. Am J Dis Child 135: Adrouge HJ, Madias NE (2000) Hypernatremia. N Engl J Med 342: