Significant hypomagnesemia after celiotomy: Implications of preoperative bowel cleansing with sodium phosphate purgative

Abstract

Serum magnesium levels are rarely measured in routine chemistry panels. A decrease in total serum magnesium levels, however, has been shown to correspond with an increase in the risk for postoperative dysrhythmias, general morbidity, and mortality after various operative procedures. 1 Chernow B Bamberger S Stoiko M Vadnais M Mills S Hoellerich V et al. Hypomagnesemia in patients in postoperative intensive care [published correction appears in Chest 1989;95:1362]. Chest. 1989; 95: 391-397 Crossref PubMed Scopus (204) Google Scholar , 2 Shakerinia T Ali IM Sullivan JA. Magnesium in cardioplegia: is it necessary?. Can J Surg. 1996; 39: 397-400 PubMed Google Scholar , 3 Siddiqui MN Zafar H Alvi R Ahmed M. Hypomagnesaemia in postoperative patients: an important contributing factor in postoperative mortality. Int J Clin Pract. 1998; 52: 265-267 PubMed Google Scholar , 4 Maslow AD Regan MM Heindle S Panzica P Cohn WE Johnson RG. Postoperative atrial tachyarrhythmias in patients undergoing coronary artery bypass graft surgery without cardiopulmonary bypass: a role for intraoperative magnesium supplementation. J Cardiothorac Vasc Anesth. 2000; 14: 524-530 Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar Between January 1998 and March 2001, 171 patients underwent a celiotomy, 157 (92%) of whom had undergone preoperative bowel cleansing with sodium phosphate, usually in combination with oral neomycin and metronidazole. There were 151 major procedures and 20 minor operations. Preoperative serum magnesium levels (normal range: 1.7-2.5 mg/dL [0.7-1.03 mmol/L]) before bowel cleansing differed from postoperative levels (means: 2.0 vs 1.53 mg/dL; two-tailed paired t test, P <.0001). The proportion of patients with a less than normal magnesium level (preoperative: 10%) varied postoperatively from 42% without bowel preparation to 70% after bowel cleansing (chi-square analysis: P =.04). Other postoperative laboratory parameters that correlated with the postoperative magnesium level included serum phosphate (multiple regression analysis; r = −0.151, P =.002), potassium (r = 0.25, P =.009), and total calcium (r = 0.123, P =.04) but not albumin. Postoperative serum magnesium levels were lower after a prior bowel preparation (1.5 vs 1.8 mg/dL; two-tailed t test, P =.02). In a multiple regression analysis, preoperative bowel cleansing was the only parameter that affected the occurrence of a postoperative, below normal serum magnesium level significantly (odds ratio: 3.2; 95% CI: 1.04-9.8; P =.04).