J Thorac Cardiovasc Surg 2006;131:251
© 2006 The American Association for Thoracic Surgery
Assumed oxygen consumption in the determination of cardiac output in children after cardiac surgery
Jia Li, MD, PhD,
Igor E. Konstantinov, MD, PhD,
Glen S. Van Arsdell, MD,
Andrew N. Redington, MD, FRCP
Cardiac Program, Hospital for Sick Children, Toronto, Ontario, Canada
To the Editor:
We read with interest the article by Fakler and associates
1
titled "Assumed oxygen consumption frequently results in large errors in the determination of cardiac output." However, we were surprised that our previous article was not cited. We used respiratory mass spectrometry to continuously measure oxygen consumption (VO
2) and compared these direct measurements with estimated VO
2 values using 4 equations, including that of Lafarge and Miettinen. We studied ventilated children with congenital heart disease both during cardiac catheterization and in the intensive care unit early after cardiopulmonary bypass surgery.
2
We showed an overestimation of VO
2 in children during cardiac catheterization and an underestimation in the postoperative children, with all 4 equations being particularly unreliable in the postoperative group.
As rightly pointed out by Fakler and colleagues,
1
use of assumed VO
2 will result in large errors in the calculation of hemodynamic variables, such as cardiac output and systemic and pulmonary vascular resistance. This issue becomes particularly important in patients during the early postoperative period, when VO
2 is not only increased as a result of systemic inflammatory response syndrome but is also highly dependent on temperature,
3
the use of inotropes and vasoactive drugs,
4
and ventilatory manipulation.
5
Thus although the conclusions of Fakler and colleagues
1
support our previous observations regarding the use of estimated VO
2 during cardiac catheterization, we believe our data suggest the need for even greater caution in the more highly dynamic hemodynamic milieu of the postoperative cardiac intensive care unit.
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References
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- Fakler U, Pauli C, Hennig M, Sebening W, Hess J. Assumed oxygen consumption frequently results in large errors in the determination of cardiac output. J Thorac Cardiovasc Surg 2005;130:272-276.[Abstract/Free Full Text]
- Li J, Bush A, Schulze-Neick I, Penny DJ, Redington AN, Shekerdemian LS. Measured versus estimated oxygen consumption in ventilated patients with congenital heart disease. the validity of predictive equations. Crit Care Med 2003;31:1235-1240.[Medline]
- Li J, Schulze-Neick I, Lincoln C, Shore D, Scallan M, Bush A, et al. Oxygen consumption after cardiopulmonary bypass surgery in children. determinants and implications. J Thorac Cardiovasc Surg 2000;119:525-533.[Abstract/Free Full Text]
- Penny DJ, Sano T, Smolich JJ. Increased systemic oxygen consumption offsets improved oxygen delivery during dobutamine infusion in newborn lambs. Intensive Care Med 2001;27:1518-1525.[Medline]
- Li J, Hoskote A, Hickey C, Van Arsdell G, Redington A, Adatia I. Hypercapnia improves systemic oxygenation and decreases oxygen consumption and blood lactate levels in children after bidirectional cavopulmonary shunt operation. Crit Care Med 2005;33:984-989.[Medline]
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References