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  • Hypernatremia

Hypernatremia

Table of Contents
  • Overview
  • Triage
  • Causes
  • Clinical Features
  • Investigations
  • Classification
  • Management
  • References

Overview #

Hypernatremia: serum sodium >145mmol/L, severe >160mmol/L (1)

  • Indicates hypertonicity and decreased cell volume, all patients have high serum osmolality (1)
  • Inadequate water intake is an important cause in the very young and very old (2)

Key Points

  • Major causes: dehydration, thiazide diuretics
  • Maximum reduction 0.5mmol/L per hour
  • Maximum reduction 10mmol/L in 24 hours

Triage #

Attend within hours

  • Unless impaired mental status

Causes #

Major cause of hypernatremia = water depletion = dehydration

Unreplaced water loss (which requires an impairment in either thirst or access to water) (3)

  • Inadequate water intake
  • Insensible and sweat losses
    • increased by fever, exercise, exposure to high temperatures
  • Gastrointestinal losses
    • Osmotic diarrhoea NOT secretory diarrhoea
  • Burns
  • Central or nephrogenic diabetes insipidus
    • Reduced anti-diuretic hormone (ADH) release or renal resistance to ADH
  • Drugs
    • Thiazide and related diuretics (indapamide, hydrochlorothiazide, chlortalidone)
  • Osmotic diuresis

Increased urine output with low Na/K concentration (< plasma concentration)

  • Glucose in uncontrolled diabetes mellitus
  • Urea in high-protein tube feedings or recovery from azotaemia
  • Mannitol
  • Hypothalamic lesions impairing thirst or osmoreceptor function
    • Primary hypodipsia
    • Reset osmostat in mineralocorticoid excess

Water loss into cells (transient) (3)

  • Severe exercise
  • Rhabdomyolysis (1)
  • Seizures

Sodium overload (3)

  • Intake or administration of hypertonic sodium solutions
  • Enemas
  • ICU-acquired positive solute balance

Clinical Features #

Signs and symptoms (1, 3)

  • Orthostatic hypotension
  • Oliguria
  • Excess thirst
  • Lethargy
  • Weakness 
  • Confusion, irritability
  • Seizures
  • Coma

Neurological symptoms due to depletion of intracerebral fluid (2)

History

  • Fluid intake (low)
    • Altered mental status
    • Access to water
    • Physical restraints
    • Unable to communicate need for water
  • Fluid losses
    • Diuretics
    • Diarrhoea, vomiting
  • Diabetes insipidus

Examination

  • Fluid assessment

Investigations #

Initial InvestigationsSignificance
VBGQuick assessment of electrolytes
UECAccurate serum sodium level
FBEHaematocritRaised in hypovolaemia
Urine osmolality (if unclear cause)<300mosmol/kgLikely diabetes insipidus300-600mosmol/kgLikely osmotic diuresis or diabetes insipidus>600mosmol/kgLikely extra renal water losses
Further InvestigationsSignificance
Urine NaDistinguish between GIT/renal/insensible loss/Na overload<25mEq/LWater loss and volume depletion>100mEq/LNa ingestion, hypertonic saline
Plasma osmolalityPaired with urine osmolality to determine response and distinguish water loss vs partial diabetes insipidus
CT/MRI BrainDiscussion with senior staff necessary

Classification #

  1. Acute (uncommon)
    • Hypernatremia for <48 hours
    • Diabetes insipidus or salt poisoning
  2. Chronic (majority of patients)
  • Hypernatremia for >48 hours
  • This will impact how quickly you can reduce serum Na levels ???? risk of cerebral oedema

Management #

Escalate to senior team member: registrar

Acute Hypernatremia 

Aim: replace water deficit in 24 hours (2, 4)

  • Correct cause and replace fluid deficit
  1. Oral fluid replacement^ (if able) OR
  2. IV glucose 5%
    • Rate: 3-6mL/kg/hr 
  • Replace ongoing free water losses
  • Monitor serum Na 1-2 hourly until <145mmol/L

If over/undercorrection noted escalate to senior team members

  • Osmotic demyelination is rare in acute hypernatremia (as no time for cerebral adaptation) (4)

Monitor for hyperglycaemia

Chronic Hypernatremia

Aim: lower serum Na by 10mEq/L in 24 hours (2, 4)

  • Correct cause and replace fluid deficit
  1. Oral fluid replacement^ (if able) OR
  2. IV glucose 5% (see below for rate calculation)
  • Replace ongoing free water losses
  • Monitor serum Na 4-6 hourly
    • Once target correction rate reached, monitor 12-24 hourly

If over/undercorrection noted escalate to senior team members

  • Undercorrection
    • Increase rate of glucose infusion
  • Overcorrection
    • May require hypotonic 0.45% normal saline as even slow rates of glucose may be too much (4, 6)
    • CALL OUT BOX:
      • 0.45% normal saline sodium content is 154 mmol/L
      • If serum sodium is >154 mmol/L, administering normal saline will still lower the level, slower than dextrose

Monitor for hyperglycaemia and any change in neurological signs or symptoms (escalate if noticed)

Diabetes Insipidus: TO BE ESCALATED TO ENDOCRINOLOGY FOR EXPERT ADVICE

  • Desmopressin* (1, 3, 4, 5)
  • Regulation of water intake (If impaired thirst sensation)

References #

  1. Papadakis, MA, McPhee SJ, Rabow MW. Current Medical Diagnosis & Treatment 2021. 60th ed. New York: McGraw-Hill Education; 2021.
  2. eTG Complete [Internet]. Melbourne (Vic): Therapeutic Guidelines Ltd; 2014. Hypernatremia [updated 2021 Mar; cited 2021 Aug 25]. Available from: https://tgldcdp.tg.org.au.acs.hcn.com.au/viewTopic?topicfile=electrolyte-abnormalities&guidelineName=Other#toc_d1e632
  3. Sterns RH. Etiology and evaluation of hypernatremia in adults. In: Emmett M, Forman JP, editors. UpToDate. [Internet]. UpToDate; 2019 [updated 2019 Sep 23; cited 2021 Aug 25]. Available from: https://www.uptodate.com/contents/etiology-and-evaluation-of-hypernatremia-in-adults?search=hypernatremia&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2
  4. Sterns RH, Hoorn EJ. Treatment of hypernatremia in adults. In: Emmett M, Forman JP, editors. UpToDate. [Internet]. UpToDate; 2020 [updated 2020 Jul 23; cited 2021 Aug 25]. Available from: https://www.uptodate.com/contents/treatment-of-hypernatremia-in-adults?search=hypernatremia&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
  5. eTG Complete [Internet]. Melbourne (Vic): Therapeutic Guidelines Ltd; 2019. Arginine vasopressin replacement and diabetes insipidus in hypopituitarism [updated 2020 Dec; cited 2021 Aug 25]. Available from: https://tgldcdp.tg.org.au.acs.hcn.com.au/viewTopic?topicfile=hypopituitarism&sectionId=bmg2-c13-s7#bmg2-c13-s7
  6. Kim SW. Hypernatemia: successful treatment. Electrolyte Blood Press. 2006 Nov;4(2):66-71. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3894528/#:~:text=Patients%20should%20be%20given%20intravenous,unable%20to%20tolerate%20oral%20water 
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Updated on May 1, 2023
Table of Contents
  • Overview
  • Triage
  • Causes
  • Clinical Features
  • Investigations
  • Classification
  • Management
  • References

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