Hypomagnesemia after major abdominal operations in cancer patients: clinical implications

Serum magnesium levels are rarely measured in routine chemistry panels. The extent and impact of postoperative serum magnesium changes remain unclear.

One hundred seventy-one cancer patients who had undergone celiotomy procedures during a 38-month period were evaluated retrospectively for postoperative electrolyte alterations, with special emphasis on serum magnesium. Clinicopathologic predictors and early postoperative outcome correlations were examined.

There were 151 major procedures and 20 minor operations. All postoperative electrolyte and hematocrit values were significantly different from preoperative values, except for serum phosphate. Preoperative total serum magnesium (normal range: 1.7-2.5 mg/dL {0.7-1.03 mmol/L}), obtained prior to any bowel cleansing, differed from postoperative levels (means +/- standard deviation: 2.0 +/- 0.46 vs. 1.53 +/- 0.33 mg/dL; p < 0.0001). A lowered postoperative serum magnesium was observed in those patients who had either undergone an operation with curative intent (p = 0.0035), a major resection (vs. no resection, p = 0.0259), or preoperative bowel cleansing with sodium phosphate (p = 0.024). Other laboratory serum parameters that correlated with the postoperative magnesium level included postoperative levels of phosphate (p = 0.009), potassium (p = 0.01), and total calcium (p = 0.012), as well as preoperative calcium (p = 0.017). The complication rate was 20%, with five postoperative deaths (2.9%). Postoperative morbidity was predicted by preoperative potassium (p = 0.004) and albumin levels (p = 0.016); deaths were predicted by postoperative infections (p = 0.0007) and correlated to postoperative hypokalemia (p = 0.03).

Major abdominal cancer operations lead to significant electrolyte alterations. The severity of these changes correlates with the resection extent, especially in procedures with curative intent. In addition, bowel cleansing with sodium phosphate may participate in lowering serum magnesium as well as other electrolytes. In light of our postoperative magnesium replacement policy, no untoward events could be linked to postoperative hypomagnesemia in this series. To evaluate the impact of postoperative hypomagnesemia or magnesium replacement on postoperative outcomes requires a prospective randomized trial.