Respiratory depression occurs more often and is more severe in patients undergoing gastroenterologist-led colonoscopy than in those attended by an anesthesiologist during gastrointestinal endoscopy, according to a new study. Routine monitoring of tidal volumes and minute ventilation may help prevent respiratory depression in future cases, the researchers found.
Monitoring respiratory function during sedation for GI procedures can be challenging, but delayed detection of respiratory compromise may lead to increased patient morbidity and mortality. At many institutions, dedicated anesthesia staff are used in higher-risk cases, whereas lower-risk cases are managed by GI personnel. Choice of sedative can also differ between specialties: Although propofol is commonly used by anesthesiologists, GI staff often select other agents.
“We conducted two studies on our GI floor using a noninvasive respiratory monitor to compare the degree of respiratory depression between upper endoscopy and colonoscopy,” said Donald M. Mathews, MD, professor of anesthesiology at the University of Vermont College of Medicine, in Burlington. Dr. Mathews reported the findings at the 2016 annual meetings of both the International Anesthesia Research Society (IARS; abstract S-26) and the Society for Ambulatory Anesthesia (SAMBA; abstract 11).
The first of the two studies was an observational trial of colonoscopy patients managed by GI staff. Patients were sedated with a combination of meperidine and midazolam. In the second, controlled trial, upper endoscopy patients were managed by anesthesia personnel and sedated using propofol with or without other agents, such as fentanyl, ketamine and midazolam.
All patients received routine monitoring, including capnography and an impedance-based respiratory volume monitor (ExSpiron, Respiratory Motion Inc.). Baseline minute volume was determined before sedation for each patient; care providers were blinded to the respiratory volume monitor’s measurements. The researchers classified minute ventilation less than 40% of baseline values as potentially unsafe, which matches extubation criteria from the National Heart, Lung, and Blood Institute’s acute respiratory distress syndrome (NHLBI ARDS) network.
The trial included 22 patients (13 women, 54±15 years of age; body mass index [BMI], 27.3±6.6 kg/m2) undergoing upper endoscopy procedures and 25 patients (14 women, 60±8 years of age; BMI, 28.9±4.3 kg/m2) undergoing colonoscopy.
Respiratory Depression Rates
Upper endoscopy procedure times were found to range from 14 to 64 minutes (average, 31.2±2.7 minutes) and colonoscopy procedure times ranged from seven to 39 minutes (average, 17.3±1.6 minutes; Figure 1). Whereas endoscopy patients spent an average of 13.2%±3.0% of the procedure at unsafe minute ventilation levels, per the NHLBI ARDS guidelines, the colonoscopy patients spent a significantly higher percentage of the procedure time at these unsafe levels (21.7%±5.2%; Figure 2).
“The colonoscopy patients had a remarkable amount of respiratory depression,” Dr. Mathews said.
The study also revealed that while only 9.1% of upper endoscopy patients had an unsafe minute ventilation for more than 33% of the procedure time, 20% of the colonoscopy group patients also did. In addition, while no endoscopy patient spent more than half of the procedure at an unsafe minute ventilation level, 16% of colonoscopy patients did. “There were five colonoscopy patients who were really quite depressed,” Dr. Mathews noted at the IARS meeting.
“We also unblinded the anesthesiologists to the respiratory volume monitor and found there was significantly less time spent below the 40% minute ventilation threshold” with use of the monitor, he said at the IARS meeting. “So there’s evidence of efficacy for the monitor in terms of caregivers altering their care.”
The investigators also asked anesthesiology staff t o rate the utility of the monitor. “Some people thought it was useful, some moderately useful and some not useful at all,” Dr. Mathews said. “And the percentage of time spent below 40% minute ventilation was directly correlated to what people thought about the monitor. So people who liked the monitor had very little time spent below 40% of baseline.”
The research team attributed the reduction in unsafe minute ventilation to use of the monitor. Similar improvements may be possible if the monitor is used during colonoscopy procedures, Dr. Mathews noted at the SAMBA meeting. “Is the benefit of seeing real-time tidal volume, respiratory rate and minute ventilations so appealing that practitioners intuitively think it will lead to better care, such as occurred with the introduction of pulse oximetry?” Dr. Mathews asked.
Furthermore, Dr. Mathews wondered whether there is a need for more specific ventilatory monitoring during sedation procedures or whether traditional practices, such as capnography, are good enough. During the presentation at SAMBA, others asked about the position of the patients and the depth of sedation. Dr. Mathews said he would like to study these factors more in the future.
Despite these positive results, some questioned the financial effect of using the monitor. “I guess the question is what does this all mean,” said Tong Joo (T.J.) Gan, MD, professor and chairman of anesthesiology at Stony Brook University School of Medicine, in New York, during the IARS presentation. “Yes, you saw a lower incidence of time spent below 40% of baseline minute ventilation, but what is the real outcome?”
“The 40% benchmark comes from extubation criteria,” Dr. Mathews replied. “So if you’re below 40% when you’re extubated, that’s considered dangerous territory. Now these are different populations, so it may not be as relevant. And in fact, in the colonoscopy group there was just one jaw lift. On the other hand, we know from other databases that there are occasional disasters in these spaces, and those disasters are typically respiratory mediated.”
“I’m going to put on my administrator hat and ask if you want to use this in all GI patients,” Girish Joshi, MD, said at the IARS meeting. “Look at the number of colonoscopies performed every year. Is it cost-effective to use this monitor in all of them? So I believe our role is to show which patients this device can be useful in, rather than just showing that it works.” Dr. Joshi is professor of anesthesiology and pain medicine at the University of Texas Southwestern Medical Center, in Dallas.
Dr. Mathews acknowledged the question of cost at the SAMBA meeting. “Someone asked me, ‘So what?’ Despite the revealed respiratory depression, everyone did OK. Is it possible that this type of monitoring would reveal the rare patient who does not ‘do OK’ and allow caregivers to intervene before a disaster?”
This question is hard to answer, Dr. Mathews said, because a study would need to be large and these events are rare. However, monitoring could be the next step in figuring out when and how certain procedures turn into negative outcomes. In addition, the University of Vermont team is interested in using the monitor to understand why patients can respond so differently to postoperative opioids in terms of ventilatory depression.
“We think that using the monitor, in combination with genomic testing, might reveal who is at increased risk following surgery,” Dr. Mathews said.
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