The association between colonic cleansing and hypokalaemia was studied
prospectively by monitoring the serum potassium levels in four groups
of patients: groups 1 (55 patients), 2 (72 patients), and 3 (97 patie
nts) received the same 2-day preparation of 15 g magnesium sulphate an
d 10 mg bisacodyl twice daily; group 4 (96 patients) received a 1-day
preparation of 2.4 mg sennoside per kg of bodyweight. Groups 1 and 2 w
ere on diuretics, but only group 2 received potassium supplementation.
Serum potassium levels were measured before and after bowel preparati
on. Hypokalaemia was present prior to cleansing in six (11%), and afte
r cleansing in 20 (36%) of the 55 patients in the group 1 patients on
diuretics but without potassium supplements. There was, after cleansin
g, no significant fall in serum potassium in the group 2 patients on d
iuretics who received potassium supplements. No hyperkalaemia resulted
from supplementation. A significant fall of the mean level of serum p
otassium occurred in patients in both group 3 (2-day-preparation) and
group 4 (1-day-preparation). We conclude that both 1 day and 2 days of
cleansing with cathartics may result in a significant fall in serum p
otassium, which can be prevented by oral potassium supplements. Potass
ium supplements (three times a day 15 ml of potassium chloride with 0.
9 mmol K per ml during the preparation) in patients on diuretics may b
e prudent to avoid the risk of cardiac arrhythmia.