Plasma magnesium concentrations were monitored during orthotopic liver
transplantation. Magnesium supplementation was not given, although in
traoperative calcium, potassium, and sodium bicarbonate were given as
required. We found that there were significant falls in magnesium conc
entration to below our laboratory lower limit of normal, occurring chi
efly during the anhepatic phase of surgery. Two patients with hypomagn
esemia but normal potassium and calcium ion concentrations developed v
entricular extrasystoles. Magnesium is a smooth muscle relaxant, dilat
ing coronary arteries and peripheral vessels. It also exerts an antiar
rhythmic effect and may have a permissive effect on the actions of cat
echolamines. Magnesium supplementation may be indicated during orthoto
pic liver transplantation because of the potentially beneficial effect
s and to avoid possible deleterious effects of hypomagnesemia. However
, magnesium levels need to be monitored to avoid the unwanted side eff
ects of hypermagnesemia.