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The purpose of this prospective study is to describe the hemodynamic and cardiac variation during a trial of non-invasive ventilation (NIV) in the process of weaning from ventilatory support. A continuous hemodynamic monitoring was performed with a pulse contour method, the MostCare (Vytech Health, Laboratoires Pharmaceutiques Vygon, Ecouen, France). This device could be used to identify the early warnings of cardiovascular dysfunction, which may contribute to unsuccessful weaning.
Fourteen patients, admitted to our ICU between January and July 2009, were included in the study: six intubated on respiratory failure due to cardiogenic pulmonary edema (CPE; 52 ± 18 years, four male (M), two female (F)), eight intubated on chronic obstructive pulmonary disease (COPD; 71 ± 16 years, four M, four F). The NIV trial was performed with a face mask: pressure support (PS) = 5 to 10 cmH2O, positive end-expiratory pressure (PEEP) = 5 to 7 cmH2O. Cardiovascular variables and gas exchange data were measured at three defined points in time: 1 hour before the extubation (T1), continuously during the NIV trial (a mean value was calculated and expressed as T2), and at the end of the NIV trial with the patient in spontaneous breathing (T3).
The variation of cardiac index (CI) was: T1 2.53 ± 0.43 ml/minute/m2 CPE vs 3.2 ± 0.64 ml/minute/m2 COPD; T2 2.93 ± 0.93 ml/minute/m2 CPE vs 2.9 ± 1.33 ml/minute/m2 COPD; T3 1.96 ± 0.61 ml/minute/m2 CPE vs 3.3 ± 1.37 ml/minute/m2 COPD. The variation of CI depended on the variation of stroke volume (SV), while the heart rate (HR) did not change during the trial. We calculated the oxygen delivery (DO2) by the correlation of CI and gas exchange: T1 767 ± 218 ml/minute CPE vs 839 ± 134.3 ml/minute COPD, T2 917 ± 417 ml/minute CPE vs 701 ± 349 ml/minute COPD, T3 760 ± 404 ml/minute CPE vs 753 ± 340 ml/minute COPD. The variation of CI and DO2, observed within and among the two groups was never significant.
Both groups of patients were successful in achieving spontaneous ventilation. In our opinion, continuous hemodynamic monitoring may provide helpful beat-to-beat information and it might be used, combined with the gas exchange and oxygen saturation monitoring, during the weaning process as a predictor of cardiovascular instability or respiratory failure. Moreover, continuous hemodynamic monitoring enables one to be aware of the variation of systemic oxygen delivery, and these data could be used to value critically ill patients during the weaning process.