Capnography ‘useful adjunct’ to colonoscopy care

Jun 6 2012

By Lynda Williams

Monitoring carbon dioxide levels improves detection of altered respiration and apnea in sedated patients undergoing colonoscopy, show ColCap Study results.

The research conducted in 760 patients demonstrated that the risk for arterial oxygen desaturation was significantly reduced by the addition of capnography to standard monitoring, consisting of clinical observation, pulse oximetry, blood pressure, and electrocardiogram.

Oxygen saturation (SaO₂) fell by 5% or more or below 90% in 38.9% of patients in the open capnography arm compared with 53.2% of patients given standard care with blinded capnography, report Stefan von Delius (Technical University Munich, Germany) and co-workers.

The incidence of hypoxemia (SaO₂ <90%; 12.5 vs 19.8%), and severe hypoxemia (SaO₂ ≤85%; 3.7 vs 7.8%) also fell significantly with capnography.

In multivariate analysis, age, body mass index, propofol dose, and use of capnography were significant and independent risk factors for the incidence of oxygen desaturation.

However, capnography did not significantly alter the risk for bradycardia or hypotension, nor influence propofol dose, nor the time taken to leave the procedure room. Patient satisfaction and cooperation did not significantly differ between the treatment groups.

"Early interventions induced by capnography were not considered as unpleasant by the patient and did not impair the procedure," the team comments.

Writing in the American Journal of Gastroenterology, the team reports that apnea and altered ventilation were detected in 56.7% of patients undergoing open capnography versus 2.1% of controls. Capnography had 18 false-positive episodes of apnea or altered ventilation in 15 patients; technical problems were identified in five patients but no cause was found for the remaining cases.

Noting the discrepancy between the rates of apnea and altered ventilation, and the rate of oxygen desaturation, von Delius et al suggest that hypoxemia may have been due to subclinical hypoventilation or other factors such as coughing or aspiration.

"Capnography is able to considerably contribute to the prevention of respiratory complications; however, it has to be kept in mind that the presence of a normal capnogram does not guarantee sufficient oxygenation," they emphasize.

"Therefore, capnography cannot replace standard monitoring and clinical observation of the patient but can be considered a useful adjunct."

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