Cardiac output measurements during cross-clamping of the descending thoracic aorta in pigs - A comparison between transit-time ultrasound, thermodilution and pulsed Doppler ultrasound

Background: Cross-clamping of the descending thoracic aorta (XC) induces an increase in cardiac output (CO). The intention of this study was to evalua te the high CO during XC by the use of clinically available methods (thermo dilution and pulsed Doppler ultrasound) compared to transit-time ultrasound flowmetry of the ascending aorta as the gold standard. Method: Ten pigs were anaesthetised with ketamine and fentanyl. The descend ing thoracic aorta was cross-clamped for 30 min, and cardiac output was mea sured with pulmonary artery thermodilution technique, pulsed Doppler ultras ound on the aortic annulus and transit-time ultrasound flowmetry of the asc ending aorta. Results: At 15 min following XC, CO increased from 1.7 l/min to 4.6 l/min m easured with transit-time ultrasound (P<0.05). With thermodilution techniqu e, CO increased from 2.6 l/min to 5.7 l/min (P<0.05), and from 2.4 l/min to 6.0 l/min measured with Doppler ultrasound (P<0.05). There was an increase in mean arterial pressure of 81% and heart rate increased 76% (P<0.05). Conclusion: XC of the descending thoracic aorta induces an increase in CO o f 171%. Thermodilution and pulsed Doppler ultrasound are reliable methods f or detecting high cardiac output during thoracic aortic surgery.