Continuous monitoring of oxygen consumption in patients undergoing weaning from mechanical ventilation.
BACKGROUND
The extubation or discontinuation of mechanical ventilatory support (MVS) is only the final step in the weaning process, and an improvement in the efficiency of the weaning process is required for more successful extubation or discontinuation of MVS.


OBJECTIVE
To evaluate whether continuous monitoring of oxygen consumption (VO2) using the metabolic gas monitor is a useful predictor of failure to tolerate a weaning trial of reduced MVS.


METHODS
Twenty adult patients meeting the criteria for weaning, who required MVS > or = 7 days and who were previously deemed to have failed weaning by their attending physicians. A weaning trial was defined as a 30-min period during the strengthening training of our standardized weaning protocol. The average VO2, respiratory rate (RR), tidal volume (TV), minute ventilation (VE) and energy expenditure (EE) were recorded in respiratory muscles for a stable period of 20 min at rest and for the last 5 min of the trial. Subsequently, the oxygen cost of breathing (OCOB), the ratio of respiratory frequency to tidal volume (f/VT), DeltaRR, DeltaTV, DeltaVE, and DeltaEE were calculated.


RESULTS
Two hundred and eight weaning trials, including 145 successful trials and 63 failed trials from 20 patients were evaluated. In nonparametric analysis, a statistical difference in OCOB, DeltaRR, and DeltaEE was found between successful and failed weaning trials, while no statistical differences were found for the other parameters. An OCOB < 30% was the most accurate predictor of outcome of a weaning trial, and an f/VT < 105 was the least accurate. In a multiple logistic analysis, the OCOB revealed the highest odds ratio among all parameters.


CONCLUSIONS
Measuring the OCOB was clinically beneficial in avoiding the induction of an excessive movement load on the respiratory muscles. In patients treated with MVS, continuous monitoring of VO2 is a useful to predict success or failure of trials attempting to reduce MVS.
Miwa
Keisuke
K
Department of Surgery, Kurume University School of Medicine, 67 Asahi-machi, Fukuoka 830-0011, Japan. keisuke@med.kurume-u.ac.jp
Mitsuoka
Masahiro
M
Takamori
Shinzo
S
Hayashi
Akihiro
A
Shirouzu
Kazuo
K
D000368:Aged; D002153:Calorimetry, Indirect; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008991:Monitoring, Physiologic; D010101:Oxygen Consumption / Q000502:physiology*; D011237:Predictive Value of Tests; D012119:Respiration; D012121:Respiration, Artificial; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D015300:Ventilator Weaning