Why are infants more vulnerable to fluid and electrolyte imbalances than adults?
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Overview Show
Practice EssentialsDehydration is a common complication of illness observed in pediatric patients presenting to the emergency department (ED). Early recognition and early intervention are important to reduce risk of progression to hypovolemic shock and end-organ failure. In most cases, volume depletion in children is caused by fluid losses from vomiting or diarrhea. On physical examination, combinations of findings can be used to determine the degree of dehydration. Laboratory studies are of limited utility in cases of mild dehydration, but they may be considered under certain conditions and are recommended in patients with more severe dehydration. Mild or moderate volume depletion should be treated with oral rehydration when possible. Intravenous fluid therapy is necessary when oral therapy fails or volume depletion is severe. For patient education information, see the Children's Health Center, as well as Dehydration in Children.  PathophysiologyDehydration versus volume depletionThe terms dehydration and volume depletion are commonly used interchangeably but they refer to different physiologic conditions resulting from different types of fluid loss. [1] Volume depletion denotes reduction of effective circulating volume in the intravascular space, whereas dehydration denotes loss of free water in greater proportion than the loss of sodium. The distinction is important because volume depletion and dehydration can exist independently or concurrently and the treatment for each is different. However, much of clinical literature does not differentiate between the 2 conditions; this article will therefore follow this convention and use the terms dehydration, hypovolemia, and volume depletion interchangeably to refer to intravascular fluid deficits here. Body fluid distributionThe body contains 2 major fluid compartments: the intracellular fluid (ICF) and the extracellular fluid (ECF). The ICF comprises of two thirds of the total body water (TBW), while the ECF accounts for the remaining third. The ECF is further divided into the interstitial fluid (75%) and plasma (25%). The TBW comprises approximately 70% of body weight in infants, 65% in children, and 60% in adults. Infants' and children’s higher body water content, along with their higher metabolic rates and increased body surface area to mass index, contribute to their higher turnover of fluids and solute. Therefore, infants and children require proportionally greater volumes of water than adults to maintain their fluid equilibrium and are more susceptible to volume depletion. Significant fluid losses may occur rapidly, leading to depletion of the intravascular volume. SodiumVolume depletion can be concurrent with hyponatremia. This is characterized by plasma volume contraction with free water excess. An example is a child with diarrhea who has been given water to replace diarrheal losses. Free water is replenished relative to the lack of sodium and other solutes. In hyponatremic volume depletion, the patient may appear more ill clinically than actual fluid losses would otherwise indicate. The degree of volume depletion may be clinically overestimated. Serum sodium levels less than 120 mEq/L may result in seizures—the risk of seizure is much higher in the setting of acute onset of hyponatremia, as opposed to gradual onset. If intravascular free water excess is not corrected during volume replenishment, the shift of free water to the intracellular fluid compartment may cause cerebral edema, especially in children. In hypernatremic volume depletion, plasma volume contracts with a disproportionately larger loss of free water. An example is the child with diarrhea whose fluid losses have been replenished with hypertonic soup, boiled milk, water and baking soda, or improperly diluted infant formula. Volume has been restored, but free water has not. The degree of volume depletion may be underestimated and the patient may appear less ill clinically than fluid losses indicate. Usually, at least a 10% volume deficit exists with hypernatremic volume depletion. As in hyponatremia, hypernatremic volume depletion may result in serious central nervous system (CNS) effects as a result of structural changes in central neurons. However, cerebral shrinkage occurs instead of cerebral edema. This may result in intracerebral hemorrhage, seizures, coma, and death. Overly rapid correction of hypernatremia, however, may result in cerebral edema. For this reason, volume restoration should be performed gradually over 48 hours, not to exceed a rate of 8 mEq/L per 24 hours. [2] Gradual restoration prevents a rapid shift of fluid across the blood-brain barrier and into the intracellular fluid compartment. PotassiumPotassium shifts between intracellular and extracellular fluid compartments occur more slowly than free water shifts. Serum potassium levels may not reflect intracellular potassium levels. Although a potassium deficit is present in all patients with volume depletion, it is not usually clinically significant. However, failure to correct for a potassium deficit during volume replacement may result in clinically significant hypokalemia. Potassium should not be added to replacement fluids until adequate urine output is obtained. Acid and base problemsThe most common acid-base derangement that occurs with volume depletion, especially in infants, is metabolic acidosis. Mechanisms include bicarbonate loss in stool, ketone production from starvation, and lactic acid production from decreased tissue perfusion. Decreased renal perfusion also causes decreased glomerular filtration rate, which, in turn, leads to decreased hydrogen (H+) ion excretion. These factors can combine to produce a metabolic acidosis. In most patients, acidosis is mild and easily corrected with volume restoration; increased renal perfusion permits excretion of excess H+ ions in the urine. Administration of glucose-containing fluids after initial resuscitation further decreases ketone production. EtiologyThe mechanisms of dehydration may be broadly divided into 3 categories: (1) decreased intake e.g. due to diseases such as stomatitis, (2) increased fluid output e.g. from diarrhea or osmotic diuresis from uncontrolled diabetes mellitus, and (3) increased insensible losses e.g. such as with fever. Pediatric dehydration is frequently the result of increased output from gastroenteritis, characterized by vomiting and diarrhea. [3] However, vomiting and diarrhea may be caused by other processes as summarized below. CNS causes of vomiting include the following:
GI causes of vomiting include the following:
Endocrine causes of vomiting include the following:
Renal causes of vomiting include the following:
GI causes of diarrhea include the following:
Endocrine causes of diarrhea include the following:
Volume depletion from increased output not caused by vomiting or diarrhea may be divided into renal or extrarenal causes. Renal causes of volume depletion include the following examples:
Hormonal pathology impacting renal physiology
Extrarenal causes of volume depletion include the following examples:
Other causes of volume depletion as mentioned above include poor oral intake and insensible losses from fever, sweating, burns, or pulmonary processes. EpidemiologyDehydration, particularly from gastroenteritis, is a common pediatric complaint in the ED. Approximately 30 million children are affected annually, with 1.5 million presenting to outpatient care, 200,000 requiring hospitalizations, and 300 dying in the United States. [5] Worldwide, according to the Centers for Disease Control and Prevention (CDC), for children younger than 5 years, the annual incidence of diarrheal illness is approximately 1.5 billion, while deaths are estimated between 1.5 and 2.5 million per year. Though these numbers are staggering, they actually represent an improvement from the early 1980s, when the death rate was approximately 5 million per year. [5] Infants and younger children are more susceptible to volume depletion than older children. In general, however, pediatric patients with volume depletion have an excellent prognosis if they are appropriately treated. Morbidity varies with the degree of volume depletion and the underlying cause. The severely volume-depleted infant or child is at risk for death from cardiovascular collapse. Hyponatremia resulting from replacement of free water alone may cause seizures. Improper management of volume repletion may cause iatrogenic morbidity or mortality.
Author Coauthor(s) Specialty Editor Board Kirsten A Bechtel, MD Associate Professor of Pediatrics, Section of Pediatric Emergency Medicine, Yale University School of Medicine; Co-Director, Injury Free Coalition for Kids, Yale-New Haven Children's Hospital Kirsten A Bechtel, MD is a member of the following medical societies: American Academy of Pediatrics Disclosure: Nothing to disclose. Chief Editor Muhammad Waseem, MBBS, MS, FAAP, FACEP, FAHA Professor of Emergency Medicine and Clinical Pediatrics, Weill Cornell Medical College; Attending Physician, Departments of Emergency Medicine and Pediatrics, Lincoln Medical and Mental Health Center; Adjunct Professor of Emergency Medicine, Adjunct Professor of Pediatrics, St George's University School of Medicine, Grenada Muhammad Waseem, MBBS, MS, FAAP, FACEP, FAHA is a member of the following medical societies: American Academy of Pediatrics, American Academy of Urgent Care Medicine, American College of Emergency Physicians, American Heart Association, American Medical Association, Association of Clinical Research Professionals, Public Responsibility in Medicine and Research, Society for Academic Emergency Medicine, Society for Simulation in Healthcare Disclosure: Nothing to disclose. Additional Contributors Timothy E Corden, MD Associate Professor of Pediatrics, Co-Director, Policy Core, Injury Research Center, Medical College of Wisconsin; Associate Director, PICU, Children's Hospital of Wisconsin Timothy E Corden, MD is a member of the following medical societies: American Academy of Pediatrics, Phi Beta Kappa, Society of Critical Care Medicine, Wisconsin Medical Society Disclosure: Nothing to disclose. Acknowledgements Richard G Bachur, MD Associate Professor of Pediatrics, Harvard Medical School; Associate Chief and Fellowship Director, Attending Physician, Division of Emergency Medicine, Children's Hospital of Boston Richard G Bachur, MD is a member of the following medical societies: American Academy of Pediatrics, Society for Academic Emergency Medicine, and Society for Pediatric Research Disclosure: Nothing to disclose. Ann G Egland, MD Consulting Staff, Department of Operational and Emergency Medicine, Walter Reed Army Medical Center Ann G Egland, MD is a member of the following medical societies: American College of Emergency Physicians, American Medical Association, Association of Military Surgeons of the US, Medical Society of Virginia, and Society for Academic Emergency Medicine Disclosure: Nothing to disclose. Terrance K Egland, MD Director, Business Planning and Development, Bureau of Medicine and Surgery Terrance K Egland, MD is a member of the following medical societies: American Academy of Pediatrics Disclosure: Nothing to disclose. James Li, MD Former Assistant Professor, Division of Emergency Medicine, Harvard Medical School; Board of Directors, Remote Medicine Disclosure: Nothing to disclose. Alison Wiley Lozner, MD Resident Physician, Harvard Affiliated Emergency Medicine Residency, Brigham and Women's Hospital; Clinical Fellow in Emergency Medicine, Harvard Medical School Alison Wiley Lozner, MD is a member of the following medical societies: American Academy of Emergency Medicine and American College of Emergency Physicians Disclosure: Nothing to disclose. James Kimo Takayesu, MD, MSc Assistant Professor in Surgery, Director of Undergraduate Medical Education, Consulting Staff, Massachusetts General Hospital; Associate Residency Director, Harvard Affiliated Emergency Medicine Residency Partners James Kimo Takayesu, MD, MSc is a member of the following medical societies: Alpha Omega Alpha, American College of Emergency Physicians, Sigma Xi, and Society for Academic Emergency Medicine Disclosure: Nothing to disclose. Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference Disclosure: Nothing to disclose. Wayne Wolfram, MD, MPH Associate Professor, Department of Emergency Medicine, Mercy St Vincent Medical Center Wayne Wolfram, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American Academy of Pediatrics, and Society for Academic Emergency Medicine Disclosure: Nothing to disclose. Why are infants more vulnerable to fluid and electrolytes than adults?Infants are more vulnerable to fluid and electrolyte imbalance than adults due to the following factors: high surface-to-body-weight ratio. limited ability to excrete solutes and to concentrate urine. low ability to express thirst.
Why infants are more vulnerable at risk to dehydration than adults?Infants are particularly susceptible to the ill effects of dehydration because of their greater baseline fluid requirements (due to a higher metabolic rate), higher evaporative losses (due to a higher ratio of surface area to volume), and inability to communicate thirst or seek fluid.
Why are children more susceptible to dehydration than adults?Children are more prone to dehydration and heat illness than adults because they have more body surface area per pound of weight. Young athletes, practicing hard in the summer heat, are at particular risk.
Why is the fluid balance more critical in children than adults?Children have a higher cardiac reserve, allowing them to compensate for significant volume loss much longer than adults. Initially, near age-appropriate vital signs may be present despite ongoing fluid losses.
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