Comparison between capnodynamic and thermodilution method for cardiac output monitoring during major abdominal surgery: An observational study

BACKGROUND: Cardiac output (CO) monitoring is the basis of goal-directed treatment for major abdominal surgery. A capnodynamic method estimating cardiac output (CO(EPBF)) by continuously calculating nonshunted pulmonary blood flow has previously shown good agreement and trending ability when evaluated in mechanically ventilated pigs. OBJECTIVES: To compare the performance of the capnodynamic method of CO monitoring with transpulmonary thermodilution (CO(TPTD)) in patients undergoing major abdominal surgery. DESIGN: Prospective, observational, method comparison study. Simultaneous measurements of CO(EPBF) and CO(TPTD) were performed before incision at baseline and before and after increased (+10 cmH(2)O) positive end-expiratory pressure (PEEP), activation of epidural anaesthesia and intra-operative events of hypovolemia and low CO. The first 25 patients were ventilated with PEEP 5 cmH(2)O (PEEP(5)), while in the last 10 patients, lung recruitment followed by individual PEEP adjustment (PEEP(adj)) was performed before protocol start. SETTING: Karolinska University Hospital, Stockholm, Sweden. PATIENTS: In total, 35 patients (>18 years) scheduled for major abdominal surgery with advanced hemodynamic monitoring were included in the study. MAIN OUTCOME MEASURES AND ANALYSIS: Agreement and trending ability between CO(EPBF) and CO(TPTD) at different clinical moments were analysed with Bland--Altman and four quadrant plots. RESULTS: In total, 322 paired values, 227 in PEEP(5) and 95 in PEEP(adj) were analysed. Respectively, the mean CO(EPBF) and CO(TPTD) were 4.5 ± 1.0 and 4.8 ± 1.1 in the PEEP(5) group and 4.9 ± 1.2 and 5.0 ± 1.0 l min(−1) in the PEEP(adj) group. Mean bias (levels of agreement) and percentage error (PE) were −0.2 (−2.2 to 1.7) l min(−1) and 41% for the PEEP(5) group and −0.1 (−1.7 to 1.5) l min(−1) and 31% in the PEEP(adj) group. Concordance rates during changes in CO(EPBF) and CO(TPTD) were 92% in the PEEP(5) group and 90% in the PEEP(adj) group. CONCLUSION: CO(EPBF) provides continuous noninvasive CO estimation with acceptable performance, which improved after lung recruitment and PEEP adjustment, although not interchangeable with CO(TPTD). This method may become a tool for continuous intra-operative CO monitoring during general anaesthesia in the future. TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT03444545.