Failure in measuring gas exchange in the ICU.
OBJECTIVE
This study was performed on patients after coronary artery bypass surgery, and in healthy volunteers to assess discrepant oxygen consumption (VO2) measurement between indirect calorimetry and Fick methods. Further evaluations were performed to point out the technical failure.


METHODS
In this prospective study, the VO2 was assessed in the patients using a commercial indirect calorimeter and the reverse Fick method. This calorimeter does not directly measure gas flow, but it assumes a constant preset flow. Bench testing of the calorimeter was performed in spontaneous and respirator mode using a reference calorimeter in healthy volunteers.


RESULTS
An important overestimation of VO2 and carbon dioxide production (VCO2) of approximately 30% was found in both groups. The actual flow was lower than the preprogrammed value. This lead to spuriously high fractions of carbon dioxide and low fraction of oxygen. VCO2 and VO2, calculated with the overestimated gas flow value were overestimated, while respiratory quotient remained unchanged. Technical check-up revealed leaks in the mixing chamber and in the sampling lines.


CONCLUSIONS
Indirect calorimetry is a useful clinical tool, but the investigator has to be very attentive to all potentially interfering factors and hazards.
Bracco
D
D
Institute of Physiology, University of Lausanne, Switzerland.
Chioléro
R
R
Pasche
O
O
Revelly
J P
JP
D001783:Blood Flow Velocity; D002153:Calorimetry, Indirect / Q000295:instrumentation*; D002245:Carbon Dioxide / Q000097:blood; D001026:Coronary Artery Bypass; D004868:Equipment Failure; D006801:Humans; D007362:Intensive Care Units; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D011446:Prospective Studies; D011652:Pulmonary Circulation; D011659:Pulmonary Gas Exchange
D002245:Carbon Dioxide; D010100:Oxygen