Abstract 79: Minimal Hemodynamic Effects of Varying Respiratory Rate and Tidal Volume During CPR but Large Impact on End Tidal PCO2
Background: Ventilation with excessive respiratory rate is considered detrimental during CPR, because it increases intrathoracic pressure limiting venous return and thus the generation of forward blood flow. We hypothesized that ventilation with excessive tidal volume is also detrimental, and examined in a swine model of VF the hemodynamic effects of various respiratory rates and tidal volumes during CPR while concomitantly examining the effect on end-tidal pCO2 (PETCO2), a useful surrogate measurement of blood flow during low-flow states.
Methods: VF was induced in male pigs and left untreated for 8 minutes before providing 8 minutes of uninterrupted chest compressions (100/min) with a LUCASTM device. Four groups of 4 pigs each were randomized to one of four combinations of respiratory rate (bpm) and tidal volume (ml/kg); i.e., 10/6, 10/18, 33/6, or 33/18. The breaths were delivered using an 840 Nellcor Puritan Bennett ventilator.
Results: Data (mmHg, mean ± SD) are shown in the order listed above. Ventilation with 33 bpm and 18 ml/kg increased the mean airway pressure (1±2, 2±2, 4±2, 15±3; p = < 0.001) and the airway pressure prior to breath delivery indicative of air trapping (−1±0, −1±1, −1±0, 8±6; p = 0.002). The decompression right atrial pressure increased proportional to minute-volume (7±3, 10±2, 12±1, 13±2; p = 0.026) but — contrary to our hypothesis — the coronary perfusion pressure (23±1, 17±6, 18±6, 21±2; NS) and the cerebral perfusion pressure (31±3, 23±8, 30±12, 31±3; NS) remained unaffected. The minimal hemodynamic effects contrasted with a large effect on PETCO2 (Figure), with a high dependency on tidal volumes delivered at currently recommended respiratory rates.
Conclusions: Large variation in respiratory rate and tidal volume had minimal hemodynamic effects during CPR but markedly impacted PETCO2 suggesting that controlled ventilation could be useful to enhance the precision with which PETCO2 can be used to monitor the blood flow being generated.
- © 2010 by American Heart Association, Inc.