Society for Technology in Anesthesia Section Editor: Dwayne Westenskow An Uncalibrated Pulse Contour Method to Measure Cardiac Output During Aortic Counterpulsation Sabino Scolletta, MD,* Federico Franchi, MD,* Fabio Silvio Taccone, MD,† Katia Donadello, MD,† Bonizella Biagioli, MD,* and Jean-Louis Vincent, MD, PhD† BACKGROUND: Less-invasive monitoring systems, such as pulse contour methods, are increasingly being used to estimate cardiac output (CO). However, alterations in the arterial waveform caused by intraaortic balloon pump counterpulsation may affect the ability of pulse contour algorithms to determine CO. We investigated the reliability of an uncalibrated pulse contour method, the MostCare system, in patients with cardiac failure receiving intraaortic balloon pump counterpulsation by comparing its measurements of CO with those determined by an intermittent thermodilution method. METHODS: The study included 15 patients requiring hemodynamic support with an intraaortic balloon pump after coronary artery bypass graft surgery. A pulmonary artery catheter was inserted and CO was determined by bolus thermodilution (ThD-CO). The MostCare device was directly connected to the standard monitoring system for analysis of the radial artery pressure wave and computation of CO (MostCare-CO). Data were collected at 3 different intraaortic balloon pump rates (1:1, 1:2, 1:4) and after intraaortic balloon pump removal. RESULTS: One hundred six pairs of ThD-CO and MostCare-CO measurements were analyzed. There was a good correlation between ThD-CO and MostCare-CO (r = 0.90, 95% confidence interval [CI] = 0.86 – 0.93; P  0.001). The mean bias of all CO measurements corrected for repeated measures was -0.2 L/min with limits of agreements of -1.31 to 0.91 L/min (lower 95% CI, -1.72 to -0.90; upper 95% CI, 0.50 –1.32) and a relative percentage error of 24. There were close agreements between ThD-CO and MostCare-CO at the different intraaortic balloon pump rate settings. Changes in CO were calculated separately for the 2 methods and data comparison showed a correlation of 0.82 (95% CI = 0.76 – 0.87; P  0.001) and a mean bias of 0.14 L/min with limits of agreement of -1.31 to 1.59 L/min (lower 95% CI, -1.62 to -1.00; upper 95% CI, 1.28 –1.90). CONCLUSION: The MostCare system provided measurements of CO that were comparable to ThD-CO in patients assisted with an intraaortic balloon pump. The reliability of the MostCare system is not significantly affected by changes in arterial waveform morphology caused by inflation and deflation of the intraaortic balloon pump. (Anesth Analg 2011;113:1389 –95) T he intraaortic balloon pump is an important tool to support the heart in critically ill patients with severe heart failure. Monitoring of cardiac output (CO) is essential to guide treatment during intraaortic balloon pump therapy and weaning. 1 The thermodilution method is re- garded as the “gold standard” technique for CO (ThD-CO) measurement, but insertion of a pulmonary artery catheter is invasive and is associated with various risks and complica- tions. 2 As an alternative, several pulse contour methods have been developed that use specific algorithms to compute CO from analysis of the arterial pressure waveform. 3 During intraaortic balloon pump assistance, the shape of the arterial pressure curve is distorted. First, the intraaortic balloon pump inflates with the appearance of the dicrotic notch and peak-augmented diastolic pressure is inscribed. The balloon then deflates just before opening of the aortic valve and creates a potential vacuum, which decreases the aortic end-diastolic pressure below the patient’s baseline value. Deflation is maintained until the onset of a new diastole. 4 These changes in pressure waveform morphology can affect the reliability of pulse contour methods when used in conjunction with an intraaortic balloon pump. The MostCare system (Vytech Health, Padua, Italy) is a new, uncalibrated pulse contour method that has been validated in various clinical conditions. 5–10 The aim of this study was to investigate the reliability of the MostCare system in patients with cardiac failure who were supported with an intraaortic balloon pump, by comparing its CO measurements with ThD-CO. METHODS Patients The study was approved by the IRB, and written informed consent was obtained from each patient before coronary artery bypass grafting. We studied consecutive patients who required hemodynamic support with an intraaortic balloon pump in the intensive care unit after elective bypass grafting. Exclusion criteria were the presence of arrhythmias with severe hemodynamic instability, aortic regurgitation or stenosis, tricuspid valve insufficiency, or ascending aorta pathologies, because all these situations From the *Department of Anaesthesia and Intensive Care, University of Siena, Siena, Italy; and †Department of Intensive Care, Erasme Hospital, Universite ´ Libre de Bruxelles, Bruxelles, Belgium. Accepted for publication July 20, 2011. Conflicts of Interest: See Disclosures at the end of the article. Reprints will not be available from the authors. Address correspondence to Jean-Louis Vincent, MD, PhD, Department of Intensive Care, Erasme University Hospital, Route de Lennik, 808-1070 Brussels, Belgium. Address e-mail to jlvincen@ulb.ac.be. Copyright © 2011 International Anesthesia Research Society DOI: 10.1213/ANE.0b013e318230b2de December 2011 • Volume 113 • Number 6 www.anesthesia-analgesia.org 1389