Body mass index as a risk factor for increased serum lactate during craniotomy

An increase in serum lactate can occur in patients undergoing craniotomy. We hypothesized that prolonged craniotomy for brain tumor resection leads to inadequate tissue perfusion as demonstrated by increased level of lactate. This study attempts to determine the mechanism and identify any modifiable risk factors. METHODS. Prospective, observational study of 18 patients undergoing craniotomy for brain tumor resection. The primary outcome was that peak serum lactate would correlate with length of surgery. Secondary outcomes included lactate at 3, 6 and 9 hours, creatine kinase (CK) and myoglobinuria overtime. These values were correlated with expected risk factors for lactatemia including length of surgery, Body Mass Index (BMI), hypotension, hemoglobin and mannitol therapy. RESULTS. Serum lactate consistently increased in the first 3 hours in all patients (2.21±1.22 mmol/L) with a peak increase at 9 hours (3.73±1.62 mmol/L) (P<0.05 for both). The peak serum lactate did not correlate with length of surgery (P=0.799). However, the change in lactate over 3 hours (Δ3hrLactate) did correlate with BMI (P=0.010). Serum CK was increased at 12 hours (P<0.05) and reached a peak level greater than 1000 U/L in 8 of 18 patients. Six of these patients experienced myoglobinuria. No other parameters correlated with increased lactate.

We observed a consistent and early increase in serum lactate in patients undergoing craniotomy, which correlated with BMI, but not length of surgery. Associated increases in CK and myoglobinuria support the hypothesis that elevated BMI contributed to muscle ischemia and tissue breakdown during craniotomy. Future studies are required to establish the overall clinical significance and mechanism of hyperlactatemia during neurosurgery.