Question 7.3

College Answer

a) Water intoxication secondary to bowel prep.

b)

• Airway control and treat seizures as indicated.
• Correct hypovolaemia.
• Check serum osmolality (expected to be low).

• Hypertonic saline to increase [Na+] by approx. 0.5 mmol/L/hour to achieve safe level to limit seizures (> 118 mmol/L) – balance between gradual increase in sodium and achieving safe level to limit seizures.

• Correct hypokalaemia.
• Fluid restriction.

• Cease any medications that predispose to hyponatraemia (anti-depressants, thiazide diuretics, PPIs, ACEIs).
• CT brain to assess for cerebral oedema.

Discussion

Hyponatremia is discussed in greater detail elsewhere.

In this electrolyte panel, the hyponatremia is the single most deranged electrolyte, and can account for seizures, which can in turn account for the increased tone. This sort of bowel-prep-associated hyponatremia is apparently a well-known complication of outpatient colonoscopy.

There are no fancy equations to apply in order to answer this question. Judging by the college answer, the examiners were interested in the candidate's understanding of sodium replacement for symptomatic hyponatremia.

If one were to approach the answer systematically, one might write something like this:

• Attention to the ABCS, with management of life-threatening problems simultanous with a rapid focused examination and a brief history
• Airway
  • Control the airway in view of uncosciousness; assess the need for urgent intubation
• Breathing/ventilation
  • Maintain normoxia and normocapnea
  • Ensure a mandatory mode while the patient is obtunded
• Circulatory support
  • Protect the myocardium by replacing potassium aggressively
• Monitoring
  • careful monitoring of sodium during replacement
• Specific investigations
  • Serum osmolality
  • Urinary sodium (should be low in water intoxication)
• Specific management
  • Fluid restriction
  • Hypertonic saline administration to increase serum sodium

The college answer recommends to raise the sodium by no more than 0.5mmol/hr,to avoid pontine myelinolysis. However, in their answer to the very similar Question 24 from the first paper of 2016, the college recommend to raise the sodium level by 2-4% over 30 minutes if the patient is symptomatic, i.e. confused or having seizures. This  change in approach reflects a change in the multinational society recommendations: in the recent European guidelines (Spasovski et al, 2014) the guideline development group felt that the risk of brain oedema outweighs the risk of osmotic demyelination syndrome.

Frizelle, F. A., and B. M. Colls. "Hyponatremia and seizures after bowel preparation: report of three cases." Diseases of the colon & rectum 48.2 (2005): 393-396.

Salik, James M., and Paui Kurtin. "Severe hyponatremia after colonoscopy preparation in a patient with the acquired immune deficiency syndrome." The American journal of gastroenterology 80.3 (1985): 177-179.

Nagler, Jerry, David Poppers, and Meredith Turetz. "Severe hyponatremia and seizure following a polyethylene glycol-based bowel preparation for colonoscopy." Journal of clinical gastroenterology 40.6 (2006): 558-559.

Lien, Y. H., J. I. Shapiro, and L. Chan. "Study of brain electrolytes and organic osmolytes during correction of chronic hyponatremia. Implications for the pathogenesis of central pontine myelinolysis." Journal of Clinical Investigation88.1 (1991): 303.

Mohmand, Hashim K., et al. "Hypertonic saline for hyponatremia: risk of inadvertent overcorrection." Clinical Journal of the American Society of Nephrology 2.6 (2007): 1110-1117.

Laureno, Robert, and Barbara Illowsky Karp. "Myelinolysis after correction of hyponatremia." Annals of Internal Medicine 126.1 (1997): 57-62.