A 67-year-old woman presented to a regional Emergency Department with rapidly increasing confusion, unsteady gait, and vomiting (x2) after commencing bowel preparation (Prepkit C® polyethylene glycol (PEG) x 1, sodium picosulfate (NaP) x 2) for colonoscopy.
Presentation: GCS 8 (Eye 4, Verbal 2, Motor 2), BP 120/80, PR 78; assessed as mildly hypovolemic. Investigations: Na 118 mmol/L; K 3.6 mmol/L; BIC 21 mol/L; Cl 89 mmol/L; glu 7.9 mmol/L; Cr 76 umol/L; Se Osm (calc) 248 mosm/kg; urine SG 1.010 [Corrected Ca 2.35 mmol/L, cortisol 416 nmol/L, TSH 0.61mIU/L]. Perfusion CT brain: possible seizure activity. Management: 250 mls of 0.9% saline over 2 hours before transfer to a tertiary hospital ED when assessed as euvolaemic. At that time GCS 10 (E4, V1, M5) Na 119 mmol/L; Se Osm 248 mosm/kg; U Osm 373 mmosm/kg, uNa38 mmol/L. MRI: normal; EEG: moderate encephalopathy. 500 mls/day fluid restriction was initiated. Na increased to 125 mmol/L after 24 hours with UO 4890 mls and CGS 14 (E5, V4, M5). After 48 and 72 hours, Na levels 133 and 135 mmol/L with return to baseline clinical function.
Na was 139 mmol/L 8 weeks prior. Medications were pantoprazole and propranolol. As per colonoscopy protocol instructions, water intake was estimated to be 4.5L over the preceding 8 hours. Only 1 sachet of NaP was consumed.
A diagnosis of acute water intoxication with hyponatraemic encephalopathy was made.
Our patient was prescribed standard combination hyperosmotic (NaP) and isosmotic (PEG) bowel preparation. Severe hyponatraemia is a rare adverse effect, reported more commonly with NaP (0.09%) than PEG (0.04%) (1), usually with co-morbidities and/or medications known to precipitate hyponatraemia (2).
Besides age, our patient had no risk factors for hyponatraemia and consumed the recommended volume of water. Patients preparing for colonoscopy should be counselled about this rare but potentially life-threatening complication.