Obese Have Less Respiratory Insufficiency Than Nonobese During Endoscopy

Obese patients showed less respiratory insufficiency (RI) than their nonobese counterparts during endoscopic surgery, according to a new study. The result was counterintuitive.

Because of their higher rates of obstructive sleep apnea, pulmonary hypertension and other cardiopulmonary disorders, obese patients generally are thought to be at increased risk for sedation-related complications, such as RI. Consequently, these patients often are sedated more conservatively and monitored more closely than nonobese patients. However, the new study, conducted by Michael Oberding, MD, and his colleagues at the University of Vermont College of Medicine, in Burlington, have found this not to be true, raising questions about the need for closer monitoring of all patients undergoing procedural sedation.

Dr. Oberding and his team used an ExSpiron (Respiratory Motion) respiratory volume monitor (RVM) to measure respiratory parameters during complex upper endoscopy surgery. Specifically, they noted the incidence of RI—measured as low minute ventilation (LMV)—in 18 obese and 43 nonobese patients. LMV was defined as minute ventilation less than 40% of baseline minute ventilation, and time with LMV during and after the procedure was calculated for each patient.

Patient age, height, procedure length and post-procedure length did not differ significantly between the obese and nonobese groups. Additionally, when normalized by body weight, both sets of patients received a similar amount of propofol during the procedure (P=0.64).

In contrast, obese patients spent significantly less time with LMV during (5.3%±2.5% vs. 17.6%±3.5%; P=0.03) and after (7.4%±3.4% vs. 1.2%±0.6%; P=0.05) the procedure than nonobese patients. “We were surprised that the results were different than where our intuition would lead us,” Dr. Oberding said. “Also, our prior assumption that obese patients would receive a lower propofol dose was found to be incorrect.”

Since the RVM system—unlike secondary indicators such as SpO₂ or EtCO₂—provides continuous monitoring for detection of RI, it can allow for real-time sedative dosing. According to Dr. Oberding, this provides a safer and more controlled approach to sedation than uniformly reducing sedative use in potentially at-risk populations. “I could use the reduction in the tidal volume to guide how much therapy to use,” he said, “and I could reduce my propofol infusion long before [the patient has] a collapse.”

By enabling clinicians to focus their efforts on preventing instead of resolving RI, he said, widespread use of an RVM could improve patient safety, reduce staffing and help lower health care costs.