Key result
Halving the ventilator rate and doubling tidal volume produced an immediate change in end-tidal PCO2 that positively correlated with the original arterial-end-tidal difference (r=0.64).
Why the study?
Does halving the ventilator rate and doubling tidal volume improve the estimate of arterial PCO2 from end-tidal PCO2 in ventilated patients?
Does halving the ventilator rate and doubling tidal volume improve the estimate of arterial PCO2 from end-tidal PCO2 in ventilated patients?
Effect estimate: r=0.64
Halving the ventilator rate and doubling tidal volume provides a theoretical method to improve the non-invasive estimate of arterial PCO2 from end-tidal PCO2, though clinical utility requires further verification due to value spread.
To use end-tidal PCO2 as a non-invasive estimate of arterial PCO2, one adds a nominal value, representing the arterial-end-tidal PCO2 difference. How much does one add? We hypothesized that, halving the ventilator rate and simultaneously doubling tidal volume, the immediate change in end-tidal PCO2 would be proportional to the original arterial-end-tidal PCO2 difference. We ventilated 31 patients at 20 breaths per minute (bpm), sampled arterial blood, and changed the rate to 10 bpm. The change in end-tidal PCO2 was, as hypothesized, positively correlated to the original arterial-end-tidal difference at 20 bpm (r=0.64). End-tidal PCO2 increased in 23 patients. Thus, in theory, this method could offer some improvement in the estimate of arterial PCO2 from end-tidal. However, because of the considerable spread of values, a separate study is needed for verification.
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Fletcher et al. (2000) studied Ventilated patients (n=31). Halving ventilator rate and doubling tidal volume vs. Baseline (20 bpm) was evaluated on Correlation between change in end-tidal PCO2 and original arterial-end-tidal difference (r=0.64). Halving the ventilator rate and doubling tidal volume produced an immediate change in end-tidal PCO2 that positively correlated with the original arterial-end-tidal difference (r=0.64).
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