estudio de caso electrolitos

7/29/2019 Estudio de Caso Electrolitos

1/8Copyright 2013 Infusion Nurses Society. Unauthorized reproduction of this article is prohibited.

270 Copyright 2013 Infusion Nurses Society Journal of Infusion Nursing

The Art and Science of Infusion NursingThe Art and Science of Infusion Nursing

Electrolyte disorders are frequently encoun-

tered in both inpatient and outpatient set-tings. The most common electrolyte disor-ders are those involving disorders in serumsodium, hypo-, and hypernatremia.1

Disorders in serum sodium are frequently iatrogenic,from improper fluid management; therefore, fluid man-agement requires great care. The management of disor-ders in serum sodium can be quite complicated becausetherapy can vary significantly according to the etiologyof the disorders. Nurses are on the front line of care forpatients at risk for, or who have developed, a disorder

in serum sodium. They therefore must be able to recog-nize and treat a disorder in serum sodium when it isoccurring. This article will discuss 9 case studies relatedto fluid therapy and disorders in serum sodium. Threecases will discuss each of the following: (1) the adjust-ment of maintenance intravenous fluids (mIVFs) in theacutely ill patient, (2) the treatment of hyponatremia,and (3) the treatment of hypernatremic dehydration.The objective of these cases is to illustrate key conceptsin the prevention and management of disorders insodium and water homeostasis.

ADJUSTMENT OF mIVFs IN THEACUTELY ILL PATIENT

Intravenous fluid (IVF) therapy is an integral compo-nent of the care of the acutely ill patient. The objectiveof mIVFs in the acutely ill patient is to maintain vascu-lar perfusion while avoiding fluid overload and volumedepletion, and to maintain normal serum biochemistrieswhile avoiding hypo- or hypernatremia.2 A one-size-fits-all approach to mIVFs cannot be used for all acute-ly ill patients because there will be unique physiologicissues that could require adjustments in both the com-position and quantity of fluids administered. In general,

Author Affiliations: Department of Pediatrics, Childrens Hospitalof Pittsburgh of UPMC, University of Pittsburgh School ofMedicine, Pittsburgh, Pennsylvania.

Michael L. Moritz, MD, is an associate professor of pediatrics atthe University of Pittsburgh School of Medicine and the clinicaldirector of pediatric nephrology and medical director of pediatricdialysis at the Childrens Hospital of Pittsburgh of UPMC.Dr Moritz is a leading expert in the epidemiology and treatment ofdisorders of sodium and water homeostasis in children.

The author of this article has no conflicts of interest to disclose.

Corresponding Author: Michael L. Moritz, MD, Division ofNephrology, Childrens Hospital of Pittsburgh of UPMC, OneChildrens Hospital Drive, 4401 Penn Ave, Pittsburgh, PA 15224([email protected]).

ABSTRACTDisorders in serum sodium, hyponatremia and hyper-

natremia, are frequently encountered in both inpa-

tient and outpatient settings. Many sodium disorders

are iatrogenic, caused by inappropriate intravenous

fluid management. The methods of prevention and

treatment of serum disorders differ based on the

underlying disease states. Nine cases are presented

to illustrate different aspects of fluid management,

with an emphasis on the prevention and treatment of

disorders in serum sodium. Key concepts that are

discussed are (1) when to use an isotonic fluid ver-

sus a hypotonic fluid, (2) when to restrict or liberalize

maintenance intravenous fluids, (3) how to use 3%

sodium chloride for the treatment of hyponatremic

encephalopathy, (4) when to use desmospressin to

prevent the overcorrection of chronic hyponatremia,

and (5) strategies to treat different causes of hyperna-

tremic dehydration in children.

Key words: dehydration, demyelination, diabetes

insipidus, encephalopathy, fluid therapy, hypona-

tremia, hypernatremia, saline

Case Studies in Fluid andElectrolyte Therapy

Michael L. Moritz, MD

DOI: 10.1097/NAN.0b013e318297bd7f


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VO LU ME 36 | NU MBER 4 | JU LY/AUGUST 20 13 Copyright 2013 Infusion Nurses Society 271

Copyright 2013 Infusion Nurses Society. Unauthorized reproduction of this article is prohibited.

the maintenance need for fluids in an acutely ill hospi-talized patient is approximately 1500 mL/m2/d, whichcorrelates to 2.4 L/d in the average-sized adult.3 Thisquantity of fluids should be sufficient both to maintainvascular perfusion and to correct subclinical volumedepletion if it is present. The following 3 cases will dis-cuss how to adjust the rate and composition of mIVFsfor patients with pneumonia but with different underly-ing disease states. The discussion will be restricted tothe choice of sodium chloride (NaCl) composition inthe IVF and will not discuss the potassium or dextroseconcentration.

Case #1. Pneumonia

A 65-kg, 42-year-old female is traveling on business.She presents to the local emergency department (ED)with a 3-day history of fever, chills, and a productivecough with decreased oral intake. On physical examina-

tion, she appears ill, is tachypneic, and is mildly dehy-drated. A chest X-ray reveals bilateral lower-lobe pneu-monia. Her blood work is unremarkable. She is given a0.9% NaCl (154 mEq/L) fluid bolus, feels improved,and urinates. She is not deemed well enough to returnalone to her hotel room and is admitted for IVF therapyand intravenous (IV) antibiotics.Question: What would be the most appropriate rateand sodium composition of the mIVFs and why?Answer: An appropriate rate would be 100 mL/h witha sodium composition of 0.9% NaCl (154 mEq/L).

Discussion

This patient presented to the ED mildly dehydrated andwas volume expanded with 0.9% NaCl. Much of theextracellular volume deficit has already been corrected,so a standard maintenance rate of IVF at 100 mL/hshould be sufficient both to maintain good vascularperfusion and to correct any remaining subclinical vol-ume depletion. If the patient is deemed to be volumedepleted, it would be preferable to administer an addi-tional fluid bolus of 0.9% NaCl rather than to increase

the rate of mIVF. For a variety of reasons, the mostappropriate composition of IVF would be 0.9% NaCl,which is an isotonic fluid. This patient likely has somesubclinical extracellular volume depletion with someremaining extracellular volume deficit that will requirereplacement. An isotonic fluid, such as 0.9% NaCl, is amore effective extracellular volume expander than amore hypotonic fluid, such as 0.45% NaCl (77 mEq/L)or 0.2% NaCl (34 mEq/L), because sodium is restrictedto the extracellular space. Administering 0.9% NaClwould maintain vascular perfusion better than a hypo-tonic fluid with a lower sodium concentration because

0.9% NaCl primarily remains in the extracellular space,whereas a more hypotonic fluid would distribute into

both intracellular and extracellular space. This patienthas both hemodynamic and nonhemodynamic stimulifor antidiuretic hormone (ADH) production.4 ADHplays a critical role in renal concentration and dilution.ADH increases water permeability in the cortical col-lecting ducts, thus increasing urine concentration andimpairing free water excretion. Pneumonia is a non-hemodynamic stimulus for ADH production. Patientswith pneumonia frequently develop hyponatremia dueto the syndrome of inappropriate antidiuretic hormone(SIADH) production. Therefore, hypotonic fluidsshould be avoided, and 0.9% NaCl should be adminis-tered when indicated.5,6

Key concept: The most appropriate mIVF for mostacutely ill patients is 0.9% NaCl because it is an excel-lent volume expander and will help prevent the develop-ment of hyponatremia in the presence of ADH excess.

Case #2. Congestive Heart Failure and

Pneumonia

An 80-kg, 72-year-old male with congestive heart fail-ure (CHF) that is well controlled with a low-sodiumdiet presents to the local ED with a 3-day history offever, chills, and a productive cough with decreased oralintake. On physical examination, he appears ill, istachypneic, and is mildly dehydrated. A chest X-rayreveals bilateral lower lobe pneumonia. His blood workis unremarkable. He is given a 0.9% NaCl (154 mEq/L)fluid bolus, feels improved, and urinates. He is notdeemed well enough for discharge and is admitted for

IVF therapy and IV antibiotics.Question: What would be the most appropriate rateand sodium composition of the IVFs and why?Answer: An appropriate rate would be 60 mL/h with asodium composition of 0.9% NaCl.

Discussion

CHF is an edematous state in which there is an impairedability to excrete both salt and water. In general, IVFsare best avoided, and the patient should be managed

with an oral sodium restriction. In this case, the patientis acutely ill and likely has some remaining subclinicalvolume depletion; therefore, he would benefit from IVF.The volume of fluids should be restricted in order toprevent fluid overload. An appropriate rate of mIVFwould be 60% of standard mIVF, or 60 mL/h or1.5 L/d.2 The patient should be monitored for the devel-opment of fluid overload, and mIVF should be discon-tinued as soon as possible. If signs of fluid overloaddevelop, the mIVF should be either discontinued orrestricted to a rate of 40 mL/h. The best choice of fluidfor this patient would be 0.9% NaCl because there may

still be some subclinical volume depletion. A morehypotonic fluid, such as 0.45% NaCl, could result in


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hyponatremia. Hyponatremia is a common finding inpatients with CHF and is an independent risk factor formortality. Therefore, the serum sodium should bemonitored, and prophylactic measures should be takento prevent hyponatremia from occurring.7

Key concept: Patients with edematous states such asCHF should have their mIVF restricted to 40% to 60%of the standard rate in order to prevent fluid overload.

Case #3. Sickle Cell Disease and Pneumonia

A 21-year-old, 70-kg African American male collegestudent presents to the local ED with a 3-day history offever, chills, and a productive cough with decreased oralintake, and he is experiencing acute pain. On physicalexamination, he appears ill, is tachypneic, and is mildlydehydrated. A chest X-ray reveals bilateral lower lobepneumonia. His blood chemistries are unremarkable.He is given a 0.9% NaCl (154 mEq/L) fluid bolus and

feels improved. He is admitted for IVF therapy, IV anti-biotics, and pain control.Question: What would be the most appropriate rateand sodium composition of the IVFs and why?Answer: An appropriate rate would be 150 mL/h witha sodium composition of 0.45% NaCl.

Discussion

A variety of physiological issues must be taken intoconsideration in the fluid management of a patient withsickle cell disease. Acutely ill patients with sickle cell

disease must be particularly well hydrated because vol-ume depletion can promote red cell sickling. In addi-tion, a renal concentrating defect is a universal findingin patients with sickle cell disease; therefore, patientswith sickle cell disease will have higher fluid require-ments due to increased obligatory urinary losses.8 Thispatient may also have subclinical volume depletion, soadditional fluids may be required to correct the remain-ing volume deficit. For all of these reasons, the safestapproach would be to increase the quantity of mIVF toapproximately 50% above the standard maintenance

rate, which in this case would be about 150 mL/h. Thebest choice of IVF would be 0.45% NaCl. Patients withsickle cell disease are isosthenuric, meaning that theycan neither concentrate nor dilute their urine. The urineosmolality of patients with sickle cell disease is approx-imately the same as plasma osmolality, which is about300 mOsm/kg. The urinary sodium composition ofpatients with sickle cell disease is approximately that of0.45% NaCl; the remainder of the solute loss is primar-ily urea. The administration of 0.9% NaCl to a patientwith a renal concentrating defect could result in hyper-natremia. Hypernatremia could be particularly harmful

for a patient with sickle cell disease because hypertonic-ity can promote red cell sickling. On the other hand,

research has shown that hypotonicity can actually pre-vent red cell sickling; therefore, patients with sickle celldisease should have their serum osmolality kept at thelower limits of normal.9 Patients with sickle cell diseaseare not immune to the development of hyponatremia, sosignificantly hypotonic fluids, such as 0.2% NaCl,should be avoided because they could result in hypona-

tremia with hyponatremic encephalopathy.Key concept: Patients with significant renal concentrat-ing defects will require hypotonic mIVF at an increasedrate.

THE MANAGEMENT OFHYPONATREMIA

Hyponatremia, defined as serum sodium < 135 mEq/L,is the most common electrolyte abnormality and occursin as many as 30% of hospitalized patients. The most

serious complication of hyponatremia is hyponatremicencephalopathy, which can result in death or permanentneurologic impairment if not recognized and treatedpromptly.10 A less common yet potentially serious com-plication of hyponatremia is cerebral demyelination,which results from the overcorrection of severe andchronic hyponatremia.11 When cerebral demyelinationoccurs, it can be either symptomatic or asymptomatic.

The classic neurologic features are mutism, dysar-thria, spastic quadriplegia, ataxia, and pseudobulbarpalsy with a locked-in stare. Not all patients are atequal risk for the development of hyponatremic enceph-alopathy or cerebral demyelination, so one must be ableto identify high-risk patients for either complication. Itis now recognized that even mild hyponatremia canhave neurologic manifestations12 and increases the riskof all-cause mortality in hospitalized patients.13 Thenext 3 cases will illustrate groups at high risk for thedevelopment of hyponatremic encephalopathy and ofcerebral demyelination.

Case #4: Acute Symptomatic Hyponatremia

A 28-year-old female undergoes an appendectomy.Postoperatively she is placed on 0.45% NaCl at120 mL/h. Twelve hours later she develops a headache,nausea, and vomiting and is treated with narcotics.Twenty-four hours later she is confused and combativeand is taken for an emergent head computed tomogra-phy (CT). En route to the CT, she suffers generalizedtonic-clonic seizures. Rapid bedside testing reveals aserum sodium level of 122 mEq/L.Question: How should this be managed?Answer: The patient should receive two to three100-mL boluses of 3% NaCl (513 mEq/L) in rapid

sequence until the patient stops seizing in order toacutely increase the serum sodium by 4 to 6 mEq/L.


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Discussion

This case illustrates many important points about thepathogenesis of hyponatremic encephalopathy.Postoperative patients are at particularly high risk for thedevelopment of hyponatremia because they have numerousstimuli for ADH production, including pain, stress, nausea,vomiting, narcotics, and third spacing.14 Elevated ADH

production alone, though, is not sufficient to develophyponatremia. For hyponatremia to develop, there must bea source of free water. In this case, the patient received asignificant amount of free water from excessive administra-tion of hypotonic fluids, 0.45% NaCl. The most importantstep that can be taken to prevent postoperative hypona-tremia is avoidance of hypotonic IVF and administration ofisotonic fluids, 0.9% NaCl, when IVF is indicated.5,15,16

This patient developed classic symptoms of hyponatremicencephalopathy. The universal early symptoms of hypona-tremic encephalopathy are headache, nausea, and vomit-

ing. These early symptoms were overlooked in this patient.More advanced symptoms, such as confusion, combative-ness, and finally seizures, then progressed. This patientssodium was not particularly low at 122 mEq/L. There are2 reasons for this: (1) this is an acute hyponatremia with arapid fall in serum sodium, so the brain has less time toadapt to the hyponatremia, and (2) menstruant females areat increased risk for developing hyponatremic encephalop-athy because estrogen impairs brain adaptation to hypona-tremia.14,17 Females are approximately 30 times morelikely to die or suffer permanent neurologic impairmentfrom hyponatremic encephalopathy than males, and men-

struant females are approximately 25 times more likelythan postmenopausal females.14 The definitive treatmentfor hyponatremic encephalopathy is the rapid administra-tion of 3% NaCl (513 mEq/L) in order to quickly increasethe serum sodium and decrease brain edema.18 The medicalpractitioner should administer 3% NaCl in 2 to 3 sequen-tial boluses of 100 mL (2 mL/kg in children) in order toraise the serum sodium quickly by approximately 4 to 6mEq/L. A small yet rapid rise in serum sodium is effectivein reducing brain swelling yet will not result in neurologicinjury from overcorrection.Key Concepts:

1. Postoperative patients and menstruant females areat particularly high risk for developing hypona-tremic encephalopathy.

2. The treatment of hyponatremic encephalopathy isthe administration of 3% NaCl (513 mEq/L) toacutely increase the serum sodium by approxi-mately 5 mEq/L.

Case #5. Thiazide-Induced Hyponatremia

An 80-year-old, 42-kg widowed female presents to theED after falling in her home. She appears lethargic anda bit confused but otherwise looks well. She is found to

have a hip fracture. Biochemistries reveal a serumsodium of 105 mEq/L and potassium level of 3.2mEq/L. Her past medical history reveals that she wasstarted on a thiazide diuretic a few months ago for thetreatment of hypertension. She is also on a selectiveserotonin reuptake inhibitor (SSRI) for depression fol-lowing the loss of her husband and regularly takesnonsteroidal anti-inflammatory drugs (NSAIDs) forosteoarthritis. She has a poor appetite and eats little.Nephrology is consulted, and they recommend giving a100-mL 3% NaCl fluid bolus, placing her on a fluidrestriction, and stopping the thiazide diuretic. Bloodwork is repeated 4 hours later, and the serum sodium isnow 115 mEq/L. The urine output is 500 mL/h, with aurine osmolality of 60 mOsm/kg.Question: What is the appropriate treatment now?Answer: Desmopressin should be administered to pre-vent overcorrection of hyponatremia.

Discussion

Severe hyponatremia is a well-described, yet poorly under-stood, complication from thiazide diuretics.19 Thiazidediuretics work by inhibiting the thiazide-sensitive NaClcotransporter in the distal convoluted tubule, and as suchthey do not antagonize the action of ADH and do notimpair water reabsorption. Some patients have an idiosyn-cratic reaction to thiazides and develop severe hypona-tremia. This patient was also on SSRIs and NSAIDs, bothof which have an SIADH-like effect and can producehyponatremia. Another risk factor for the patient was her

poor appetite. Elderly females frequently consume a low-solute diet, referred to as the tea and toast diet, whichincreases the risk of developing hyponatremia due todecreased renal solute load.20 Despite the development ofprofound hyponatremia, this patient was minimally symp-tomatic. The reasons for this are twofold: (1) this a chronichyponatremia that likely occurred over weeks, and there-fore the brain had time to adapt, and (2) the elderly are atless risk for hyponatremic encephalopathy as the brainatrophies with age, leaving more room in the cranium forbrain expansion.10 This patients fall and subsequent frac-

ture were likely a consequence of her hyponatremia. It isnow known that mild chronic hyponatremia can producesubtle neurologic impairment and an unsteady gait, leadingto falls and fractures in the elderly.12,21,22 In addition,chronic hyponatremia appears to stimulate bone deminer-alization and contribute to osteoporosis.23,24

A 100-mL bolus of 3% NaCl was given to acutelyraise the serum sodium by a few milliequivalents in thispatient because she was mildly symptomatic. This vol-ume expansion was sufficient to suppress ADH, result-ing in a free water diuresis and overcorrection ofhyponatremia. This patient is at high risk for develop-

ing cerebral demyelination from overcorrection ofhyponatremia for many reasons. She has many of therisk factors for developing cerebral demyelination


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NaCl may not always be effective in preventing hypona-tremia, especially in patients with CNS disease. Thispatient could have either a severe case of SIADH orcerebral salt wasting (CSW).27 SIADH and CSW aresimilar conditions that can be nearly indistinguishable.In SIADH, fluid retention and subclinical volumeexpansion from excess ADH release is the primary eventthat leads to natriuresis as a compensatory mechanism.In CSW, an inappropriate natriuresis with volumedepletion is the prime event, with ADH release and fluidretention being the compensatory mechanism. In eithercondition, a 3% NaCl infusion will have to be startedin addition to the 0.9% NaCl in order to raise the serumsodium and preserve intravascular volume. The serumsodium should be raised to the high normal range (142-145 mEq/L) to prevent cerebral edema. In all likelihood,a combination of 50 mL/h of 3% NaCl and 50 mL/h of0.9% NaCl would have to be given to both raise andmaintain the serum sodium. The 3% NaCl and 0.9%

NaCl infusions must be titrated to maintain serumsodium. This patient should not be treated with fluidrestriction because this could lead to volume depletionif the patient has CSW.Key concept: Patients with CNS disease are at particu-larly high risk for developing neurologic deteriorationfrom hyponatremia, and the addition of a 3% NaClinfusion may be needed to maintain a normal serumsodium level.

MANAGEMENT OF

HYPERNATREMIC DEHYDRATION

Hypernatremia, defined as serum sodium> 145 mEq/L,usually occurs in patients who have an impaired abilityto consume fluids. Patients at high risk for developinghypernatremia are infants and small children, the elder-ly, and patients with profound neurological impair-ment.28 Patients who develop hypernatremia will usu-ally have a source of excessive free water losses, eitherfrom diarrhea, a renal concentrating defect, or increasedinsensible losses. Free water losses alone are not a suf-

ficient reason to develop hypernatremia, though,because hypernatremia should not develop in someonewho has unrestricted access to fluids. Hypernatremia isa powerful stimulus for thirst. In any patient who devel-ops hypernatremia, the causes for both decreased fluidintake and free water losses should be investigated.1,29

The treatment of hypernatremia is twofold: (1) toexpand the extracellular volume to restore perfusionand (2) to provide sufficient free water to correct serumsodium. Extracellular volume expansion is the first pri-ority, and correction of hypernatremia should only beundertaken once good perfusion has been established.

The amount of volume expansion and free waterrequirements largely depend on the etiology of the

including chronic (> 48 hours) and severe hyponatremia(115 mEq/L), thiazide diuretic use, hypokalemia, mal-nutrition, and the potential for overcorrection in theserum sodium by > 25 mEq/L in 48 hours.

Preventing overcorrection of severe hyponatremiawhen a free water diuresis is occurring can be difficult.4

In this situation, the safest and most effective approachis to administer desmopressin.4 Desmopressin is a syn-thetic replacement for human arginine vasopressin,which increases renal water reabsorption. The adminis-tration of desmopressin will stop the free water diuresis,and the remainder of the serum sodium can be correctedslowly with fluid restriction. If desmopressin is used,care must be taken that the serum sodium is not inad-vertently lowered. Desmopressin is available for IV,subcutaneous, oral, and intranasal administration.Key Concepts:

1. Patients with severe (< 115 mEq/L) and chronic

(>

48 hours) hyponatremia are at risk for develop-ing cerebral demyelination from overcorrection(> 25 mEq/L/48 h) of hyponatremia.

2. Desmopressin can be used to prevent an overcor-rection of severe hyponatremia when a free waterdiuresis is occurring.

Case #6. Hyponatremia in Central Nervous

System Disease

A 21-year-old male is admitted to the medical intensivecare unit for what appears to be viral encephalitis. Hisserum sodium level upon admission is 142 mEq/L. Heis placed on 0.9% NaCl at 100 mL/h. Eighteen hourslater, his serum sodium is 134 mEq/L, urine sodiumis 255 mEq/L, and urine osmolality is 900 mOsm/kg.Question: How should the IVFs be managed now?Answer: Health care personnel should start a 3% NaClinfusion and decrease the rate of the 0.9% NaCl infu-sion.

Discussion

Patients with central nervous system (CNS) disease areat particularly high risk for neurologic deteriorationfrom hyponatremia.4 One feature of encephalitisis vasogenic cerebral edema, meaning that there isincreased interstitial fluid in the brain. Hyponatremiawould induce a component of cytotoxic cerebral edema,meaning that there would be an increase in brain cellwater content from water moving into the brain. Apatient with encephalitis may not be able to regulatebrain cell volume as an otherwise healthy person can,and even a minor fall in serum sodium can contribute toneurologic deterioration.25,26

This patient experienced an acute fall in serum sodi-um even with 0.9% NaCl. Administration of 0.9%


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500 mL of free water, an amount sufficient to correct theserum sodium. The actual rate of correction in serumsodium will likely differ significantly for these calculations,which are all based on crude estimates, and the renalresponse to fluid therapy as well as ongoing gastrointesti-nal fluid losses are not accounted for. These calculationsprovide a basis for initiating therapy, but further adjust-ments to the rate and composition of fluids will be neces-sary. Once this child is doing better, IVF should be taperedoff and feeds should be resumed.Key concept: Volume expansion with 0.9% NaClshould precede correction of the free water deficit.

Case #8: Hypernatremia in the

Neurologically Impaired Patient

A 7-year-old, 25-kg female with mental retardation andcerebral palsy who is fed via a gastrostomy tube pre-sents to the ED with a 5-day history of fever, cough, and

irritability. She is diagnosed with pneumonia but hasotherwise been tolerating feeds and is not experiencingvomiting or diarrhea. Lab work reveals a serum sodiumlevel of 184 mEq/L, blood urea nitrogen of60 mg/dL, and creatinine of 1.4 mg/dL. A urine osmo-lality is 1200 mOsm/kg. On further investigation, she isfound to have previous outpatient serum sodium levelsin the range of 145 to 150 mEq/L.Question: How should this patient be managed?Answer: The patient should receive a fluid bolus of20 to 40 mL/kg of 0.9% NaCl in order to establishgood perfusion. The patient could then resume tube

feeding and could be administered additional waterthrough the gastrostomy tube at 50 mL/h.

Discussion

Patients with severe neurologic impairment are at highrisk for developing hypernatremia because they do nothave access to water. These patients are frequently chron-ically dehydrated because their nutrition is restricted inorder to keep them from becoming obese. As a conse-quence of this, they may not get enough water to main-

tain good hydration. The patient has a history of mildhypernatremia, signifying that she has been chronicallyhypernatremic and underhydrated. With this acute ill-ness, her insensible losses have increased, and she hasbecome progressively more hypernatremic. The dehydra-tion can be subclinical because fluid loss is primarily freewater and has occurred over an extended period of time.As in the previous case, the primary objective is to restorevascular perfusion, so the patient should be given a fluidbolus of 0.9% NaCl. Because the fluid loss is primarilyfree water, fewer fluid boluses will be needed to volumeexpand the patient. IVFs may not be necessary because

the child is tolerating the gastrostomy feeds. Oral feedsare the preferred method of correcting hypernatremia

hypernatremia and whether there are ongoing freewater losses.

The following 3 cases will illustrate how the manage-ment of hypernatremia can vary significantly on thebasis of the underlying etiology.

Case #7. Diarrheal Dehydration

A 6-month-old, 7-kg male presents to the ED with a3-day history of fever, vomiting, and diarrhea. The childis assessed to be 10% dehydrated on exam. Biochemistriesreveal a serum sodium level of 156 mEq/L, total carbondioxide of 12 mEq/L, blood urea nitrogen of 40 mg/dL,and creatinine of 0.8 mg/dL.Question: How should the fluids be managed?Answer: This child should receive 0.9% NaCl fluidboluses totaling 50 mL/kg in order to restore extracel-lular volume, followed by 0.45% NaCl at a rate ofapproximately 150% of standard maintenance volume

to correct the remaining deficit and serum sodium.

Discussion

This case is a fairly typical presentation of a child withhypernatremic diarrheal dehydration. The hypernatremiadeveloped primarily because the child was unable to takeoral fluids. On exam the child appears 10% dehydrated,which means that the extracellular volume is reduced by10% of the body weight. Therefore, this childs volumedeficit is approximately 100 mL/kg of body weight. Theprimary objective is to restore the extracellular volume.

Therefore, this child should receive 0.9% NaCl fluidboluses totaling approximately 50 mL/kg, which wouldreplace about half of the volume deficit acutely and restorevascular volume. Continuous fluids could then be startedto correct both the remaining volume deficit and freewater deficit. Standard maintenance fluids of a child of thissize would be 100 mL/kg/d. The childs remaining volumedeficit is 50 mL/kg; therefore, an IVF rate equaling 150%of standard maintenance, or 44 mL/h or 1000 mL/d,should be sufficient to restore the volume deficit and main-tain good hydration. The composition of fluids should be

0.45% NaCl. This would have sufficient sodium toreplace the volume deficit and free water to correct thehypernatremia. This child does not have a very high serumsodium level, so a large amount of free water is not neededto correct the serum sodium, and an excessively hypotonicfluid should not be used. As a general rule of thumb, thefree water deficit can be estimated by assuming that 4 mL/kg of free water is required to decrease the serum sodiumby 1 mEq/L. A reasonable rate of correction for this childsserum sodium would be 10 mEq/L in the first 24 hours.The amount of free water needed to decrease serum sodi-um by 10 mEq/L in 24 hours would therefore be 280 mL

(4 mL/kg 7 kg 10 mEq/L). This child would be getting1000 mL/d of 0.45% NaCl, which would contain


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could then be corrected via the oral route once desmo-pressin is started. This patients serum sodium wouldhave been higher and she would have appeared more illif she had complete central diabetes insipidus with aurine osmolality 100 mOsm/kg.Key concept: A less than maximally concentrated urinein the context of hypernatremia is suggestive of diabetesinsipidus.

SUMMARY

An understanding of fluid and electrolyte therapy is essen-tial in caring for the acutely ill patient. Disorders in serumsodium, hypo- and hypernatremia, are common in bothinpatient and outpatient settings, and the managementdiffers significantly depending on the etiology. Hospitalizedpatients are at high risk for developing hyponatremia dueto numerous stimuli for ADH production, and generally

speaking, the administration of an isotonic fluid, such as0.9% NaCl, is the most appropriate IVF to prevent thedevelopment of hyponatremia. A more hypotonic fluid,such as 0.45% NaCl, should be reserved for patients witheither hypernatremia or ongoing free water losses. Patientswho develop hospital-acquired hyponatremia are at riskfor developing hyponatremic encephalopathy. Patients athighest risk for developing hyponatremic encephalopathyare postoperative patients, menstruant females, andpatients with underlying CNS disease. Symptomatichyponatremia should be treated with 3% NaCl with agoal of increasing the serum sodium by 5 mEq/L acutely.

Hypernatremic dehydration is most often seen in childrenor the elderly and is usually associated with significantvolume depletion. The goal of therapy is to initiallyrestore extracellular volume by administering 0.9%NaCl. Hypotonic fluids can then be administered eitherintravenously or orally to lower the serum sodium oncecirculatory volume has been restored.

REFERENCES

1. Moritz ML, Ayus JC. Disorders of water metabolism in children:

hyponatremia and hypernatremia. Pediatr Rev. 2002;23(11):371-380.

2. Moritz ML, Ayus JC. Intravenous fluid management for the

acutely ill child. Curr Opin Pediatr. 2011;23(2):186-193.

3. Holliday MA, Segar WE. The maintenance need for water in

parenteral fluid therapy. Pediatrics. 1957;19:823-832.

4. Moritz ML, Ayus JC. New aspects in the pathogenesis, preven-

tion, and treatment of hyponatremic encephalopathy in children.

Pediatr Nephrol. 2010;25(7):1225-1238.

5. Moritz ML, Ayus JC. Prevention of hospital-acquired hyponatremia:

a case for using isotonic saline. Pediatrics. 2003;111(2):227-230.

6. Moritz ML, Ayus JC. Hospital-acquired hyponatremia: why are

there still deaths? Pediatrics. 2004;113(5):1395-1396.

7. Gheorghiade M, Abraham WT, Albert NM, et al. Relationship

between admission serum sodium concentration and clinical

and are associated with the fewest complications. Thischild primarily needs increased fluid via the gastrostomytube. The childs feeding schedule should be reviewed andoptimized, and additional free water should be adminis-tered via the gastrostomy tube at a rate of50 mL/h, with the goal of lowering the serum sodiumlevel by about 0.5 mEq/h. This child is at risk for devel-oping seizures during the correction of hypernatremiabecause the serum sodium is extremely elevated and hasbeen chronic in duration. The rate of serum sodium cor-rection should be reduced once the serum sodium is

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