Phosphate salt bowel preparation regimens alter perioperative acid-base and electrolyte balance

Hyperphosphatemic acidosis and severe electrolyte disturbances caused by phosphate salts (PO) used for mechanical bowel preparation have been described in occasional case reports prior to bowel resection surgery. We hypothesized that PO used preoperatively for bowel preparation may cause more pronounced acid base and electrolyte changes than polyethylene glycol (PG).

Forty American Society of Anesthesiologists physical status II-III patients were randomly allocated to receive either PO or PG for bowel preparation before intra-abdominal surgery (bowel resection or other major elective intra-abdominal surgeries). Measurements of pH, base deficit, blood gases, lactate, hemoglobin, calcium, magnesium, potassium and phosphorus were undertaken before the laxative administration, intraoperatively, and postoperatively.

Preoperative demographic, hemodynamic and laboratory data were similar in the two groups. Intraoperative calcium (8.4 [0.6] vs 9 [0.5] mg x dL(-1)) and pH (7.35 [0.04] vs 7.41 [0.03]) were lower, while lactate (1.3 [0.4] vs 0.9 [0.3] mmol x L(-1)) was higher with PO. Postoperative calcium, magnesium and potassium were lower (8 [0.5] vs 8.9 [0.2] mg x dL(-1), 1.68 [0.3] vs 1.8 [0.4] and 3.5 [0.36] vs 3.7 [0.33] mEq x L(-1) respectively) while phosphorus (4.1 [0.3] vs 3.3 [0.2] mEq x L(-1)) was higher with PO. A higher percentage of abnormal values for calcium, potassium, phosphorus and base deficit (66% vs 33%, 25% vs 10%, 19% vs 2% and 28.3% vs 5% respectively) were observed with PO.

Calcium and magnesium changes were more pronounced in patients who received PO for bowel preparation.