- Significant hypophosphatemia (SH) is common after major surgery and may be associated with considerable morbidity, including respiratory and cardiac failure. The contribution of SH to these complications after cardiac surgery is not well defined. In this prospective study, levels of serum phosphorus and other electrolytes (potassium, magnesium and calcium) were measured in 566 consecutive patients (395 men, 182 women; mean age 65.5+/-11.1 years) undergoing elective cardiac surgery at three time points: prior to surgery, immediately on admission to the ICU, and on the first postoperative day. Preoperative (type of surgery, Bernstein-Parsonnet risk estimate), intraoperative (duration of bypass and cross-clamp, intraoperative fluid and blood product use) and postoperative data (duration of ventilation, duration of ICU and hospital stay, requirement for cardioactive drug support, development of atrial fibrillation, and mortality) were collected. Patients were divided into two groups according to the immediate postoperative phosphate level: SH, phosphate <0.48 mmol/l (mean phosphate 0.28+/-0.13 mmol/l, n = 194), and a control group (mean phosphate value 0.84+/-0.08 mmol/l, n = 372). Patients with SH received treatment with sodium or potassium phosphate (0.8 mmol/kg body weight over 6-12 h). SH was present in 34.3% of patients. There were no differences in the baseline characteristics between the two groups. Patients with SH received more intraoperative blood product transfusions. The postoperative course of patients with SH was characterized by prolonged ventilation (2.1+/-1.7 versus 1.1+/-0.9 days, P = 0.05), more patients requiring cardioactive drugs (12-24 h 16 versus 10.9%, P = 0.05 and >24 h 23.5 versus 13.8%, P = 0.05); and a prolonged hospital stay (7.8+/-3.4 versus 5.6+/-2.5 days, P = 0.05). SH was common after open-heart surgery and was associated with an increased incidence of important complications. We suggest that phosphate levels be routinely measured immediately after surgery and appropriate therapy instituted.