The relationship between pulmonary artery acceleration time and mean pulmonary artery pressure in patients undergoing cardiac surgery: An observational study.

BACKGROUND: A noninvasive method of estimating pulmonary arterial pressures is required, as the use of the pulmonary artery catheter (PAC) is decreasing in cardiac anaesthesia. Pulmonary hypertension is defined as a mean pulmonary artery pressure (MPAP) at least 25 mmHg and this can be estimated echocardiographically by measuring the pulmonary acceleration time (PAT). This relationship has not been validated when measured using transoesophageal echocardiography (TOE) in anaesthetised patients having cardiac surgery. OBJECTIVE: We hypothesised that there was a quantifiable relationship between PAT and MPAP. We aimed to assess this relationship in cardiac surgical patients undergoing general anaesthesia with TOE. DESIGN: An observational study. SETTING: Catholic University Hospital, Leuven, Belgium, between August and December 2013. PATIENTS: Ninety-eight patients having cardiac surgery, where intraoperative TOE was used and a PAC was inserted as part of routine care. INTERVENTIONS: Nil. MAIN OUTCOME MEASURES: PAT and MPAP were measured simultaneously with TOE and the PAC and this relationship was assessed. RESULTS: PAT and MPAP measurements were possible in all patients. There was a curvilinear relationship between PAT and MPAP with a PAT of less than 107 ms detecting pulmonary hypertension with a sensitivity of 75% and a specificity of 94.8%. The area under the receiver operating characteristic (ROC) curve was 0.87 [95% confidence interval (95% CI) 0.80 to 0.95]. Below a PAT of 107 ms, the relationship was relatively linear and could be described by the equation MPAP (mmHg) = 77 -  (0.49 x PAT). Ninety-five percent of the pressures estimated by this equation are within ±13.8 mmHg of the measured pressure. CONCLUSION: Estimation of PAT with TOE in anaesthetised cardiac surgical patients is possible. PAT is good at discriminating between patients with and without pulmonary hypertension, with a cut-off of less than 107 ms detecting pulmonary hypertension with a sensitivity of 75% and specificity of 94.8%.