RESUMO
Background: The use of noninvasive ventilation (NIV) during and after extubation is common. We designed this study to determine the optimal strategy to compensate for mask leaks and achieve effective ventilation during NIV by comparing commonly used operating room ventilator systems and a regular facemask. Methods: We tested four operating room ventilator systems (Dägger Zeus, Dägger Apollo, Dägger Fabius Tiro, and General Electric Healthcare Carestation 650) on a lung model with normal compliance and airway resistance and evaluated pressure control ventilation (PCV), volume control ventilation (VCV), and AutoFlow mode (VAF). We set the O2 flow at 10 L/min and the maximal flow at 13, 16, or 26 L/min. We simulated five leak levels, from no leak to over 40 L/min (I to V levels), using customized T-pieces placed between the lung model and the breathing circuit. We recorded the expired tidal volume (Vte) from the lung model and peak inspiratory pressure via two flow/pressure sensors that were placed distally and proximally to the T-pieces. Results: 1. Comparison of four ventilators: with any given ventilation mode, an increase in leak level caused a decrease in Vte. With PCV, only Zeus produced Vte larger than 150 ml at leak level V. 2. Effect of ventilation mode on Vte: across all four ventilators, PCV resulted in a higher Vte than VCV and VAF (P < 0.01). PCV mode with all ventilators at leak level II provided Vte values that were equal to or greater than those obtained with no leak. 3. Effect of O2 flow on Vte Using PCV mode: only Carestation 650 Vte at leak level II during PCV were significantly greater with 16 L/min O2 flow compared with 10 L/min O2 flow (P < 0.01). 4. Actual leak: increasing the O2 flow from 10 L/min to the maximum O2 flow dramatically increased the real leak with all 4 ventilators at any fixed leak level (P < 0.01). 5. Preset PIP vs. actual PIP with PCV: at low preset PIP and leak levels such as leak II and III, the discrepancy between preset PIP and actual PIP was small. The disparity between the preset and actual PIP grew when the target PIP and the leak level were raised. Conclusion: For NIV using a mask, the ventilator is preferred whose Pressure generator is Turbine, the PCV mode is preferred in the ventilation mode and the oxygen flow is set to 10 L/min or maximum oxygen flow.
RESUMO
To evaluate the hypothesis that adding dexmedetomidine to ropivacaine prolongs axillary brachial plexus block. Forty-five patients of ASA I~II and aged 25-60 yr who were scheduled for elective forearm and hand surgery were randomly divided into 3 equal groups and received 40 ml of 0.33% ropivacaine + 1 ml dexmedetomidine (50 µg) (Group DR1), 40 ml of 0.33% ropivacaine + 1 ml dexmedetomidine (100 µg) (group DR2) or 40 ml of 0.33% ropivacaine + 1 ml saline (group R) in a double-blind fashion. The onset and duration of sensory and motor blocks and side effects were recorded. The demographic data and surgical characteristics were similar in each group. Sensory and motor block onset times were the same in the three groups. Sensory and motor blockade durations were longer in group DR2 than in group R (P < 0.05). There was no significant difference in the sensory blockade duration between group DR1 and group R. Bradycardia, hypertension and hypotension were not observed in group R and occurred more often in group DR2 than in group DR1. Dexmedetomidine added to ropivacaine for an axillary brachial plexus block prolongs the duration of the block. However, dexmedetomidine may also lead to side effects such as bradycardia, hypertension, and hypotension.