Canadian journal of anaesthesia = Journal canadien d'anesthésie
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Eighty patients undergoing elective thoracotomy were studied to assess the possibility of predicting arterial oxygenation (PaO2) during one-lung anaesthesia (OLA). The first 50 patients were studied retrospectively. The method of multiple linear regression was used to construct a predictive equation for PaO2 during OLA. ⋯ Four of 30 patients had a predicted PaO2 at ten minutes of OLA < 150 mmHg. Of these, 2/4 subsequently required abandonment of OLA for pulse oximetric saturation < 85%. We conclude that although it is not possible to predict an individual patient's PaO2 during OLA with a high degree of accuracy, it is possible, before the initiation of OLA, to identify those patients whose arterial oxygenation is likely to decrease to low levels during OLA.
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Although pressure controlled-inverse ratio ventilation (PC-IRV) has been used successfully in the treatment of respiratory failure, it has not been applied to the treatment of respiratory dysfunction during anaesthesia. With PC-IRV the inspiratory wave form is fundamentally altered so that inspiratory time is prolonged (inverse I:E), inspiratory flow rate is low, and the peak inspiratory pressure is limited. Positive end-expiratory pressure (PEEP) can be applied and the mean airway pressure is higher than with conventional ventilation. ⋯ There were significant increases of (A-a) DO2 at 30 and 60 min (41 and 43%). These changes were less than those reported in a previous study using conventional tidal volume ventilation (7.5 ml.kg-1) and were similar to those in patients whose lungs were ventilated with high tidal volumes (12.7 ml.kg-1). Thus, in this clinical model of compromised gas exchange, arterial oxygenation was better with PC-IRV than with conventional ventilation, but not better than with large tidal volume ventilation.
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Inadequate tissue oxygen uptake autoregulation has been reported during the first hours after extracorporeal circulation for cardiac surgery. In the present study, we examined whether a dependence of oxygen consumption (VO2) on oxygen delivery (DO2) can be detected 24 hr after cardiac surgery using two different vasodilating agents. Cardiac output in triplicate was measured by thermodilution. ⋯ Phentolamine did not alter skin microvascular blood flow, whereas prostacyclin increased skin microvascular blood flow by 33 +/- 3%. The results of the present study demonstrate a supply-dependency of VO2 in clinically stable patients 24 hr after cardiac surgery, suggesting the presence of an inadequate tissue O2 uptake autoregulation. The type of the vasodilator used to increase DO2 seems to play an important role in detecting such a supply-dependency of VO2, as well as changes of skin blood flow.