Hyponatraemia: encephalopathy in post-operative patients is rare but often fatal.

Clinical bottom line (level 4)

  1. Hyponatraemia is uncommon post-operatively.
  2. Around a tenth of patients with hyponatraemia develop encephalopathy.
  3. Menstruating women appear to have an increased susceptibility to hyponatraemic encephalopathy (NNH = 2 at unknown) .
  4. Nearly half of patients with hyponatraemic encephalopathy develop permanent brain damage or die.
Ayus et al: Annals of Internal Medicine 1992; 117 (11): 891-897
Expires July 2005

The study

Case-control study with unblinded, unobjective outcomes, not adjusted for confounding factors, not validated in an independent set of patients.

Setting: two university hospitals, USA

739 patients (aged ?, 58% female) post-operative patients with hyponatraemia (Na <128 mmol/l)
Cases: 65 patients (% female, mean age ): developed encephalopathy
Controls: 674 patients (% female, mean age ): did not develop encephalopathy

Factors studied:
  • death or brain damage


    • Factors summarised:
  • female gender
  • menstruating vs menopausal


    • Outcomes studied:
  • death or brain damage
  • mortality
  • permanent brain damage

    • The evidence

    Patient expected event rate for death or brain damage: 8.0%
    risk factor for
    death or brain damage     		unadjusted OR
    (95% CI)    		 NNH
    (95% CI)
    female gender 28
    (5 to 141)     		2
    (1 to 4)
    menstruating vs menopausal 26
    (11 to 62)     		2
    (1 to 2)

    Patient expected event rate for mortality: 43%
    Patient expected event rate for permanent brain damage: 9.2%
    • Control rate assumed to be 65/645 (total population available for controls).

    Comments

    1. Details of therapy to correct hyponatraemia are not given. Medical and nursing management may have differed substantially between groups.
    2. Failure to adjust for confounding factors makes results far less certain.

    Citation

    1. Ayus JC, Wheeler JM, Arieff AI: Post-operative hyponatraemic encephalopathy in menstruant women. Annals of Internal Medicine 1992; 117 (11): 891-897
    Search Terms: encephalopathy and hyponatremia in Medline
    Contributor: Tim Ringrose and Chris Ball, July 2000
    Reviewer:

    Clinical Question.
    Patient
    Intervention or Exposure
    Outcome