The effects of epidural anesthesia on ventilatory response to hypoxia.

STUDY OBJECTIVE

To evaluate the effects of epidural morphine on the ventilatory response to hypoxia in patients having abdominal surgery and to compare the effects of epidural lidocaine.

DESIGN

Open-label, randomized study.

SETTING

Shimane Medical University Hospital, Shimane, Japan.

PATIENTS

Sixteen consenting, unpremedicated ASA physical status I and II patients undergoing abdominal surgery.

INTERVENTIONS

Patients were administered 2 mg of morphine diluted in 10 ml of saline or 10 ml of 2% lidocaine from an epidural catheter that was inserted the day before surgery.

MEASUREMENTS AND MAIN RESULTS

On the day before surgery, ventilatory parameters consisting of minute expiratory volume (VE), tidal volume (VT), respiratory frequency (f), and oxygen saturation by pulse oximeter (SpO2) were measured during resting state and hypoxic challenge. The same measurements were repeated 30 minutes after the epidural injection before surgery. The slope of VE/SpO2 decreased significantly from 1.6 +/- 0.3 to 1.2 +/- 0.2 after epidural morphine, although ventilatory values such as f, VT, VE, and PaCO2 were unchanged. Epidural lidocaine produced no significant changes in ventilatory response.

CONCLUSION

Epidural anesthesia with morphine, but not lidocaine, reduced the ventilatory response to hypoxia indicated by VE/SpO2.