A bioimpedance respiratory monitor seems to be carving out a niche for itself in perioperative monitoring. A group of Texas researchers has found that this novel technology (ExSpiron, Respiratory Motion Inc.) allows clinicians to adjust total IV anesthesia (TIVA) to minute ventilation in outpatient GI procedures, thereby preventing potential episodes of inadequate ventilation.
“Death or serious adverse events, such as brain injury, are rare but devastating complications under general anesthesia,” said Johnny Nguyen, DO, a resident at the University of Texas Medical Branch at Galveston (UTMB). “About 45% of those claimed events are due to hypoxia and respiratory arrest. So we wanted to test this novel, noninvasive device to see if it can help decrease hypoventilation during TIVA.”
Advances in other forms of monitoring have done little to prevent hypoventilation secondary to anesthesia, which continues to be a significant cause of respiratory arrest, especially in remote locations where both personnel and monitoring are limited.
“The ExSpiron is a noninvasive device that uses bioimpedance to measure minute ventilation and respiratory rate,” said co-investigator Thuan M. Ho, MD, also a resident at UTMB. “You apply the sensors from the sternal notch to the cricoid process and at the midaxillary line. It takes about 30 seconds for the device to determine a baseline value, and then it shows a percentage of what the patient’s predicted minute ventilation is.”
The investigators included 65 American Society of Anesthesiologists (ASA) physical status classification I to III patients (age range, 30-84 years) in the study, all of whom were undergoing upper and lower GI endoscopies under TIVA using propofol with or without remifentanil. In each patient, baseline minute ventilation was obtained prior to TIVA and then was monitored and recorded (every 5 seconds or 0.2 Hz) for the duration of the case.
The sensor and device were placed in all patients, but in controls (n=38) the monitor was covered and data blinded to the anesthesia provider during the case. In the ExSpiron group (n=27), the anesthesia provider titrated TIVA to achieve minute ventilation between 40% and 80% of baseline values. All data were collected retrospectively between July and December 2015.
Apneic Episodes Reduced
Drs. Ho and Nguyen reported that low minute ventilation levels (40% of baseline) occurred in the control group 32±4% of the time. In contrast, patients whose minute ventilation was monitored by the device fell to such levels only 12±3% of the time (P=0.0003).
Interestingly, patients who were monitored by the noninvasive device had significantly higher minute ventilation over time than controls (P<0.05). Furthermore, monitored patients experienced a 25% to 30% reduction in apneic episodes.
Session moderator Meg Rosenblatt, MD, professor and chair of anesthesiology and professor of orthopaedics at Mount Sinai St. Luke’s Hospital and Mount Sinai West Hospital, in New York City, wondered whether the study had changed the investigators’ practice. “Is this a piece of equipment that you will now add to the way you practice?”
“Not yet,” Dr. Ho responded. “We are currently evaluating the technology. Our results are promising but our department has not made a final decision.” Dr. Nguyen added, “Going forward, I think it’s a monitor we can definitely use.” Their findings were originally reported during the 2016 annual meeting of the International Anesthesia Research Society (abstract S-23).
Dr. Rosenblatt said, “I think one of the potential uses of this machine may be in monitoring in morbidly obese patients with PCAs [patient-controlled anesthesia] on the floor.”
Girish Joshi, MD, said, “In my opinion, the end point of therapy should not be minute ventilation, but an adequate level of sedation for the procedure—and then you look at the effects of respiratory depression using this device.” Dr. Joshi is professor of anesthesiology and pain medicine at the University of Texas Southwestern Medical Center, in Dallas.