Ann Thorac Surg 2005;80:1483-1484
© 2005 The Society of Thoracic Surgeons
New technology
Invited commentary
Robert Savage, MD
a
,
Lars G. Svensson, MD, PhD
b
a Department of Cardiovascular Anesthesia,Center for Aortic Surgery, The Cleveland Clinic Foundation, 9500 Euclid Ave, F25, Cleveland, OH 44195
b Marfan and Connective Tissue Disorder Clinic, The Cleveland Clinic Foundation, 9500 Euclid Ave, F25, Cleveland, OH44195
(Email: svenssl{at}ccf.org).
The article by Knobloch and colleagues [1] characterizes the innovative application of Doppler ultrasound to noninvasively measure the beat-to-beat cardiac output in post-cardiac surgery patients. In this study of 36 consecutive patients they compared "mean" noninvasive (USCOM Doppler device) with invasive values of cardiac output as determined by a Baxter continuous thermodilution cardiac output pulmonary artery catheter. Correlation indices demonstrated a statistically significant (p < 0.05) correlation index of 0.794. In addition the noninvasive Doppler derived cardiac output correlated with the stroke volume (0.946; p < 0.01) and the central venous O2 saturation (0.474). Direct measurements of right-sided cardiac output by epivascular Doppler interrogation of the pulmonary artery revealed identical Doppler and thermodilution cardiac output results (4.95 vs 4.97 L/min) [2].
The authors correctly identify a number of limitations in their study. These limitations included the use of a thermodilution cardiac output as a "gold standard" without confirmation by other validated methods (Fick cardiac output, electrical impedance), the inherent error involved in correlating beat-to-beat Doppler derived cardiac output data with a method that measures a thermodilution cardiac output from a non-simultaneous hemodynamic time interval. The Doppler data derived from this study was conducted by a single expert operator without mention of independent blinding of the results and the method (modal vs envelope margin) for determining the velocity–time integral, thereby inducing the potential for operational bias. Finally the authors site the dependency on the imaging window quality for providing reliable spectral envelope data derived from pulse-wave Doppler interrogation of left-sided and right-sided stroke volumes.
Previous studies have demonstrated inconsistencies between the various gold standards of determining cardiac output [2, 3]. These variances are more frequently encountered in the setting of higher cardiac output states (CO > 5.0 L/min). In addition, utilization of right sided thermodilution or electrical impedance technologies are inherently less reliable estimates of hemodynamic indices of left ventricular performance in the setting of significant tricuspid regurgitation, which was not an exclusionary criteria in the current study [4, 5].
Not addressed in this study and in need of further investigation is the physiologic variation in cardiac output and the parameters that influence it, such as respiration, patient position, changes in stroke volume, and heart rate (cardiac output = stroke volume x heart rate). Ideally, volume loop curves and dP/dt curves should also be available at the bedside to assess myocardial function and outcomes of pharmacologic or heart rate manipulations.
Despite the presence of these limitations, this study does suggest the potential value of this innovative technology to assist in the perioperative management of the cardiac surgery patient. In non-hyperdynamic cardiac surgery patients, pulsed-wave Doppler may provide a reliable and practical technique of accurately determining hemodynamic indices of cardiac performance. Many cardiovascular centers have established perioperative management protocols based on thermodilution derived indices. The ability to rapidly obtain similar indices by noninvasive Doppler ultrasound encourages the utilization of less invasive strategies in lower risk patients. However, such a perioperative monitoring strategy is intuitively coupled with the implication that expertise for 24 hours, 7 days a week is available to obtain quality Doppler derived data in the critical care setting. Such expertise would require the training of perioperative health care providers in the cognitive and technical aspects for providing quality Doppler derived data as well as its accurate interpretation.
 |
References
|
|---|
- Knobloch K, Lichtenberg A, Winterhalter M, Rossner D, Pichlmaier M, Phillips R. Non-invasive cardiac output determination by two-dimensional independent Doppler during and after cardiac surgery Ann Thorac Surg 2005;80:1479-1484.[Abstract/Free Full Text]
- Gonzalez J, Delafosse C, Fartoukh M, et al. Comparison of bedside measurement of cardiac output with the thermodilution method and the Fick method in mechanically ventilated patients Crit Care 2003:7171-7178.
- Dhingra VK, Fenwick JC, Walley KR, Chittock DR, Ronco JJ. Lack of agreement between thermodilution and Fick cardiac output in critically ill patients Chest 2002;122:990-997.[Abstract/Free Full Text]
- Yung GL, Fedullo PF, Kinninger K, Johnson W, Channick RN. Comparison of impedance cardiography to direct Fick and thermodilution cardiac output determination in pulmonary arterial hypertension Congest Heart Fail 2004:107-110.
- Heerdt PM, Blessios GA, Beach ML, Hogue CW. Flow dependency of error in thermodilution measurement of cardiac output during acute tricuspid regurgitation J Cardiothorac Vasc Anesth 2001;15:183-187.[Medline]
Top
References