The accuracy of non-invasive nasal capnography in morbidly obese patients after bariatric surgery.

STUDY OBJECTIVE to assess the accuracy of nasal capnography for the monitoring of ventilation in extubated morbidly obese patients, following bariatric surgery. DESIGN prospective descriptive study. SETTING Post-anesthesia care unit. PATIENTS 25 consecutive morbidly obese patients admitted to the PACU after open bariatric surgery. INTERVENTION Patients had a nasal cannula designed to administer oxygen (3 L/min) and to sample expired CO2 by a coaxial catheter. MEASUREMENTS Capnographic waveform, end-tidal CO2 (ETCO2) and respiratory rate (RRd) were displayed by a capnometer (Datex-Ohmeda). Arterial CO2 pressure (PaCO2) was measured by blood gas analysis. Respiratory rate was measured by visual inspection of chest breathing motions (RRm). Differences between PaCO2 and ETCO2 and between RRd and RRm were calculated for every simultaneous set of measurements. RESULTS Bias, precision, limits of agreement (bias +/- 2 precisions) between PetCO2 and PaCO2 were respectively as follows: 3.1, 1.4, 0.3 to 5.9 mmHg with a Pearson correlation coefficient of 0.6 and a P value of 0.001. As for RRd v/s RRm the values were: 2, 0.5, 1 to 3 breaths per minute and 0.8 with the same P value for the Pearson coefficient. CONCLUSION Limits of agreement between PaCO2 and ETCO2 pressure and between RRd and RRm are clinically acceptable. Nasal capnography is accurate for the monitoring of ventilation in extubated morbidly obese patients, following bariatric surgery.