Postoperative Respiratory Depression: Knowledge that Anesthesiologists Should Have
The Mayo Clinic’s Dr. Toby N. Weingarten discusses postoperative respiratory depression. He asks who, when, and how we can prevent it from occurring. The “wake up effect” occurs when a nurse arrives at the bedside to take vital signs in a hypoxic patient. The patient wakes up, starts breathing better, and oxygen saturations temporarily improves. This is one of the reasons the APSF states that “intermittent nursing vital sign checks have low to moderate sensitivity, specificity, and reliability and a slow response time”.
It is important to consider the timing of when postoperative respiratory events occur. ASA closed claims analysis of opioid induced respiratory depression (OIRD) stated that 88% of respiratory events happen in the first postoperative day. The most dangerous period seems to be the first few hours after PACU discharge. During their PACU stay, patients are highly monitored. Nurses are coaching their patients to breathe. When the patient finally arrives to his room and is able to rest, this is when the patient dies.
Dr. Weingarten cautions that while OSA is an important risk factor for opioid induced respiratory depression, some other important high-risk groups are often overlooked. These include patients with cardiovascular disease, CNS disease (Parkinson’s and dementia), and the elderly. Patients with a disability and those with high tolerance (home opioids, benzodiazepines, and gabapentin use) are also at higher risk. Medications associated with the highest risk of respiratory depression in the PACU include long acting volatile anesthetics (isoflurane), higher doses of midazolam, and gabapentin use. Gabapentin has shown to have a synergistic effect in combination with opioids, and may be dangerous in patients who already have a high risk of postoperative respiratory depression.
PACU stay can help shed light onto who will eventually experience a critical respiratory event. Standard PACU discharge criteria evaluates for respiratory obstruction and oxygen saturation but not respiratory drive. Dr. Bhargavi Gali at the Mayo Clinic developed more sensitive discharge criteria for PACU which includes four specific events: hypoventilation, apnea, desaturations, and ‘pain sedation mismatch’. Pain sedation mismatch is when the patient complains of severe pain while sedated. PACU discharge is delayed if any of these events occur. The use of advanced monitoring or CPAP after PACU should be considered. Warning signs in the PACU tell us that troubling respiratory events may occur after discharge onto the floor.
Dr. Frances F.T. Chung, University of Toronto, discusses her literature review that discovered 60 cases of death or near-death reports due to respiratory depression. The 60 cases had a mean age 49 years, male (62%), mean BMI 42, undiagnosed OSA (17%), and only one-third received postoperative CPAP. People dying from opioid induced respiratory depression (OIRD) are not one typical phenotype. OSA patients may be young, skinny, or elderly. They may not report daytime sleepiness. For this reason many OSA cases go undetected.
Dr. Chung challenges us to consider, is postoperative oxygen therapy is a friend or foe? The reality is that most OSA patients do not use their CPAP machines. The benefit of postoperative oxygen use in the OSA patient (not using CPAP) is that they experience fewer apnea/hypopnea episodes per hour. What happens to the CO2? Patients who are retaining CO2 are like time bombs. Postoperative OSA patients with oxygen supplementation do not desaturate until very late, but when they do they are already suffering from carbon dioxide narcosis.
APSF recommends continuous monitoring of oxygenation and ventilation for ALL postoperative patients. No patient should be harmed by OIRD. Current guidelines by Medicare/Medicaid call for monitoring every 2.5 hours postoperatively. These goals are not being met for most of our patients. Additionally, spot checks are not helpful as Dr. Weingarten described the “wake up” effect that often occurs. CO2 is a better detector of respiratory depression. The future monitoring system will be continuous for both oxygenation and ventilation. The patient will wear it home.
It is estimated that 1,200 surgical cases will have respiratory complications. Dr. Chung reminds us to be on high alert for opioid induced respiratory depression. Surgery and anesthesia often lose sight of this problem after the PACU-the patient is in no man’s land. We need to own this problem.
*Coverage from the Review Course Lecture, Postoperative Respiratory Depression: Who? When? How? Knowledge that Anesthesiologists Should Have