Abnormal Sodium

National Pediatric Nighttime Curriculum Written by Julia Aquino, MD Floating Hospital for Children at Tufts Medical Center

Learning objectives

After this module learners will be able to:  Describe principles of acute fluid management in the correction of hypernatremia and hyponatremia  Recognize the signs and symptoms that require immediate attention in patients with disordered sodium  Consider the level of care appropriate for patients requiring correction of hypernatremia and hyponatremia

Case #1 (intern)

 You have just finished sign out and you are reviewing your patient list to prioritize the most ill patients when your pager goes off:  “Lab called with critical value for patient in 735: sodium 160. Please advise. –Kevin”

You review your sign out…

 7 month old otherwise healthy male admitted directly from clinic in the late afternoon with gastroenteritis and dehydration. He has had minimal PO intake and decreased urine output.

 Tachycardic and febrile when the admitting team saw him but otherwise stable.

 Overnight plan: floor staff is placing an IV, giving a 20cc/kg NS bolus and will call night team to reassess when complete.

You head to room 735

As you go to the bedside to assess the patient, you review some questions:  What are possible etiologies of hypernatremia?

 What about in this patient specifically?

 What do I need to worry about immediately?

 Should I call my senior?

 Can I take care of this patient on the floor or does he need a higher level of care?

At the bedside

 VS: T 38.5, HR 120, RR 30, BP 90/60, O2 sat 99% RA  His nurse, Kevin, tells you that the NS bolus is almost complete and that the patient has been irritable since arriving to the floor  Physical exam: General: irritable infant; HEENT: mucous membranes dry, anterior fontanelle slightly sunken; Chest: clear; CV: tachycardic, regular rhythm, II/VI systolic ejection murmur; Abdomen: soft, hyperactive bowel sounds; Extremities: normal skin turgor, cap refill 3 seconds  What is your overall assessment of this patient?

 What is your next step?

A) Stop the bolus —this patient is hypernatremic and NS is an inappropriate fluid choice B) Give another 20cc/kg bolus of NS C) Call a renal consult

Next steps

You give another normal saline bolus and the patient’s perfusion, heart rate and mental status start to normalize Kevin asks you what fluids you want to hang now….

  What do you need to consider when correcting the sodium in hypernatremic dehydration?

What do you need to worry about if correcting too fast?

Calculating free water deficit

 Free water deficit is the minimum amount of fluid necessary to correct serum sodium  Estimate of free water deficit:

4mL x body weight x desired change in sodium

 Goal is to correct sodium at a rate no faster than 0.5 mEq/L/hour  Add maintenance fluid needs and account for any ongoing losses

Ongoing management

 What fluid should you choose?

 When should you recheck a sodium?

Hypernatremia

 Defined as serum sodium >/= 145mEq/L  Causes: Excess sodium intake Increased free water losses Decreased free water intake Concentrated formula, salt ingestion (seawater, accidental, Munchausen-by-proxy), hypertonic IV fluids, sodium bicarbonate, blood products 1) Renal: diabetes insipidus, diuretics, tubular disorder 2) GI: diarrhea, vomiting, colostomy/ileostomy output, malabsorption 3) Insensible: fever, tachypnea, burns Ineffective breastfeeding, poor access to water, blunted thirst mechanisms, fluid restriction

Clinical Manifestations and Evaluation of Hypernatremia

 Early neurologic signs include agitation and irritability  can progress to seizure and coma  Neurologic exam can reveal increased tone, brisk reflexes and nuchal rigidity  Lab evaluation can include:  Serum osmolarity  Serum glucose  Urine osmolarity and specific gravity

Neurologic Sequelae

 In acute phase:  Intracellular fluid moves to extracellular space volume loss in brain separation from meninges  If hypernatremia has existed for >2-3 days:  Neurons protect themselves by making osmolytes to maintain gradient  With rapid correction, neurons can swell leading to cerebral edema  Mortality estimated at 10-16% despite correct rate of rehydration

Case #2 (senior)

You are doing your late evening rounds on the ward when one of the nurses pulls you aside:  “One of the post-op orthopedic patients has a sodium of 115 and I can’t reach the primary team. Can you help me?”

His nurse gives you more info…

 Patient is a 16yo with cerebral palsy and global developmental delay who is post operative day #2 from posterior spinal fusion.  He has been wretching and not tolerating g tube feeds so has been on maintenance IV fluids of D5 ½NS + 20mEq/L KCl all day.  His mother is at the bedside and feels he is not himself.

At the bedside

 VS: T 38.0, HR 90, BP 100/75, RR 20, O2 98%RA  General: neurologically impaired child moaning in bed, less responsive to voice/touch per mother; HEENT: lips dry, mucous membranes slightly dry; Chest: CTAB; CV: RRR, nl S1, S2; Abdomen: g-tube intact, hypoactive bowel sounds; Extremities: well perfused; Neuro: increased tone and spasticity in extremities, responds to voice with a moan, responsive to painful stimuli

Next steps

 You initiate a rapid response and transfer to the PICU should happen shortly. Your immediate next step should be: A) Prompt administration of hypertonic saline (3%) B) Emergent head CT C) Fluid restriction due concern for SIADH

Your patient stabilizes…

Your patient is returning to baseline mental status and you stop the hypertonic saline.

 What general guidelines do you use to think about ongoing fluid management?

 Why are you worried about the rate of correction?

Hyponatremia

 Defined as serum sodium

Causes of hyponatremia

Decreased total body water Increased total body water Normal total body water Pseudohyponatremia GI losses (diarrhea, emesis), diuretics, RTA, 3 rd spacing CHF, acute renal failure, SIADH, water intoxication (dilute formula feeding) Hypoglycemia Severe hyperlipidemia or hypoproteinemia • Hyperglycemia leads to hyperosmolarity with translocation of fluids from intracellular to extracellular space • Pseudohyponatremia: displacement of plasma water resulting in falsely low serum by laboratory measurement

Clinical manifestations of hyponatremia

 Neurologic symptoms related to edema caused by hypo-osmolarity  Children at higher risk due to higher brain-to-skull ratio  Symptoms include headache, nausea, emesis, weakness  Severity worsens as edema increases leading to signs of cerebral herniation  Respiratory changes, posturing, pupillary changes, seizure

Lab evaluation of hyponatremia

 Serum osmolarity if concerned for pseudohyponatremia  Urine osmolarity to evaluate for impaired ability to excrete free water  Urine sodium    <25 mEq/L consistent with volume depletion >25Meq/L consistent with renal tubular dysfunction, SIADH, diuretic use Must be interpreted with caution since affected by IV fluids, fluid restriction, diuretic use

Fluid management goals

 Hyponatremia with neurologic symptoms is a

medical emergency Clinical picture

Seizure No seizure activity but not at neurologic baseline Asymptomatic

Fluid

3% hypertonic saline 3% hypertonic saline 0.9% normal saline

Rate

raise serum sodium by 4-8 mEq/L/hour until seizure activity stops raise serum sodium by 1mEq/L/hour until: -patient at baseline -plasma sodium increases by 20-25mEq/L OR -serum sodium increases to 125-130mEq/L raise sodium no faster than 0.5 mEq/L/hour

Why are we concerned about the rate of correction?

 Excessive changes in serum sodium can lead to cerebral demyelination (central pontine myelinolysis)   Usually occurs several days after correction Presents with confusion, quadriplegia, confusion or pseudocoma  Recent data shows rate of correction may have little affect on development of demyelination  Magnitude of correction and underlying illness more important contributing factors  Risk of untreated hyponatremia far exceeds that of rapid correction so

do not hesitate to use hypertonic saline for symptomatic patients

Key learning points

 Always prioritize hemodynamic stability over sodium correction  Correction calculations for both hypernatremia and hyponatremia are general guidelines —sodium should be monitored frequently to ensure safe rate of correction  Symptomatic hyponatremia is a medical emergency and should be managed in a closely monitored setting with 3% hypertonic saline

References

 Chung C, Zimmerman D. Hypernatremia and hyponatremia: current understanding and management.

Clin Ped Emerg Med

. 2009; 10: 272-278.

 Moritz M and Ayus JC. Disorders of water metabolism in children: hyponatremia and hypernatremia.

Pediatr Rev

. 2002; 23: 371-380.

 Schwaderer AL, Schwartz GJ. Treating hypernatremic dehydration.

Pediatr Rev

. 2005; 26: 148-150.

 Waseem M, Hussain A. Index of suspicion.

Pediatr Rev

. 2004; 25: 397-399.

Questions:

1) A 1 month old patient with RSV bronchiolitis and dehydration develops vomiting and altered mental status leading to generalized a tonic-clonic seizure. Her serum sodium is 118 mEq/L. The most likely mechanism for her clinical deterioration is: A) Demyelination B) Cerebral edema C) Brainstem herniation D) Intracranial hemorrhage

Questions:

A) Incorrect. Demyelination can occur as result of hyponatremia, but it usually presents several days following the change in sodium with confusion, pseudocoma or a suggests that it is not the rate of correction that leads to demyelination, rather the magnitude of correction necessary and the underlying illness.

“locked-in” state. Recent data

B) Correct. Hyponatremia leads to an influx of fluid from the extracellular space to the intracellular space cause cerebral edema. Early neurologic manifestations including headache, vomiting, seizure and altered mental status are a direct result.

C) Incorrect. Cerebral edema from hyponatremia can lead to brainstem herniation, but this would present with respiratory arrest, asymmetric pupillary changes or decorticate posturing.

D) Incorrect. Hyponatremia rarely leads to intracranial hemorrhage. Hypernatremia can cause this due to acute loss of brain volume from loss of fluid from the intracellular space leading to rupture of cerebral veins.

Questions:

2) The goal rate of correction for a patient with a serum sodium of 165 mEq/L who is hemodynamically stable is: A) As quickly as possible B) 0.01 mEq/hour C) 0.5 mEq/hour D) 2 mEq/hour

Questions:

The correct answer is C. This is a straight forward knowledge question, requiring the learner to recall the goal rate of sodium correction in a patient with hypernatremia who is hemodynamically stable.

Questions:

3) A 3 year old is admitted with gastroenteritis and dehydration. His serum sodium is 167 mEq/L. Once he is hemodynamically stable, fluid management should be focused on providing: A) Glucose B) Free water C) Sodium D) Potassium E) Chloride

Questions:

B is the correct answer. Hypernatremia is a total body free water deficit rather than an excess of sodium.

Questions:

4) All of the following are possible etiologies for hyponatremia EXCEPT: A) Dilute formula feeding B) SIADH C) Diabetes insipidus D) Non-osmotic release of ADH secondary to acute illness

Questions:

C is the correct answer. Diabetes insipidus leads to hypernatremia.

Questions:

5) A 2 year old patient with central diabetes insipidus is admitted with a sodium of 170 mEq/L. The labs findings most consistent with his diagnosis are: A) Elevated serum osmolarity and concentrated urine B) Decreased serum osmolarity and dilute urine C) Decreased serum osmolarity and concentrated urine D) Elevated serum osmolarity and dilute urine

Questions:

D is the correct answer. Central diabetes insipidus leads to decreased ADH production. This leads to an inability to concentrate urine and an increase in serum osmolarity, hypernatremia and dilute urine.

Questions:

6) A 4 month old has been receiving improperly mixed formula with 1 scoop per 4 oz of water. She presents with generalized tonic-clonic seizure and a serum sodium of 118 mEq/L. The appropriate fluid to use for immediate management of her hyponatremia is: A) Normal saline B) 1/2 Normal saline C) 3% Hypertonic saline D) None-fluid restrict due to concern for SIADH

Questions:

C is the correct answer. This is a straightforward knowledge question requiring learners to recall that symptomatic hyponatremia is an emergency requiring prompt treatment with hypertonic saline.