Noninvasive ventilation during spontaneous breathing anesthesia: an observational study using electrical impedance tomography.

STUDY OBJECTIVE: To assess the effects of noninvasive ventilation (NIV) during spontaneous breathing anesthesia on functional residual capacity and ventilation distribution.

DESIGN: Prospective and observational study.

SETTING: Operating room, military teaching hospital.

PATIENTS: Eighteen adult patients submitted to digestive endoscopic procedures under spontaneous breathing anesthesia.

INTERVENTIONS: Anesthetic management was standardized. Patients were submitted to combined digestive endoscopic procedures (gastric fibroscopy and colonoscopy) under spontaneous breathing anesthesia in lateral decubitus position. Anesthesia was induced with propofol intravenous 1 mg/kg. Repeated boluses of propofol were administered according to the patients' clinical needs during endoscopic procedures. Ventilation distribution and functional residual capacity were assessed by electrical impedance tomography.

MEASUREMENTS: Ventilation distribution was assessed by electrical impedance changes in left and right lung, and functional residual capacity changes were evaluated by measurement of end-expiratory lung impedance changes. Measures were performed before anesthesia induction, 5 minutes after anesthesia induction during gastric fibroscopy, at the end of gastric fibroscopy, 5 minutes after NIV application during colonoscopy, and at the end of colonoscopy.

MAIN RESULTS: In awake patients, tidal volume was primarily distributed to the dependent lung (57.5% vs 43.1%; P=.009). After anesthesia induction, we observed a shift of ventilation to the nondependent lung (43.1% before anesthesia, 58.9% after anesthesia; P=.002) and marked decrease in end-expiratory lung impedancemetry of -1.68UI (4.47). Noninvasive ventilation application resulted in a significant increase of end-expiratory lung impedancemetry of 1.33 (6.49) (P=.005) but did not impact ventilation distribution.

CONCLUSIONS: This study showed that NIV application in pressure support mode during spontaneous breathing anesthesia increased functional residual capacity. Other studies are needed to evaluate the clinical impact of this technique during anesthesia, especially in patients with poor respiratory conditions.