Readmission After Cardiac Surgery: The Role Of Intraoperative Myocardial Acidosis

Introduction: To determine the role of regional myocardial acidosis (RMA) present at the end of cardiopulmonary bypass on unplanned hospital readmission within 30-days or 6-months after cardiac surgery. Methods: Myocardial tissue pH (corrected to 37degreesC: pH37C) was monitored intraoperatively in 221 patients during cardiac surgery. pH37C < 6.85 in either the anterior or posterior LV wall at the end of cardiopulmonary bypass was used to define RMA. Readmission data was retrospectively abstracted from a centralized VA computerized database. Logistic regression models were constructed to identify predictors of any unplanned readmission and readmissions for cardiac causes only. Results: 13.8% (28 of 203) of patients were readmitted within 30-days and 27.1% (59 of 218) of patients were readmitted within 6-months postoperatively. Cardiac causes accounted for 42.9% (30-days) and 54.2% (6-months) of all readmissions. The mean number of readmissions was 1.67 ± 1.24. Median time to readmission was 15 days (30-days) and 32 days (6-months). RMA was independently associated with a 6 times increased risk of readmission within 30-days and a 4 times increased risk within 6-months (Table). RMA was also independently associated with readmission for cardiac causes (p < 0.05). Risk factor Readmission within 30 days postoperatively (c-index = 0.79) Readmission within 6 months postoperatively (c-index = 0.72) Odds ratio (95% CI) p Value Odds ratio (95% CI) p Value Preoperative ASA class IV/V 3.10 (1.11, 8.69) 0.031 — — pH 37C <6.85 at end of cardiopulmonary bypass 6.09 (1.94, 19.11) 0.0019 3.79 (1.62, 8.84) 0.0021 Postoperative in-hospital atrial fibrillation 2.79 (1.01, 7.74) 0.049 — — Postoperative in-hospital myocardial infarction — — 16.23 (1.13, 32.57) 0.040 Postoperative in-hospital stay <6 days 4.78 (1.35, 16.97) 0.016 — — Conclusions: Regional myocardial acidosis (pH37C < 6.85) at end of cardiopulmonary bypass, which is reflective of intraoperative myocardial ischemia and is also known to induce myocyte apoptosis, independently determines unplanned readmission rates within 30 days and 6 months postoperatively. This is the first study to demonstrate this association and underscores the importance of avoiding myocardial tissue acidosis during cardiac surgery.