Tonsillectomy and postoperative respiratory monitoring
Myron Yaster MD and Lynne G. Maxwell MD
It’s another day and another tonsillectomy article! Admittedly, today’s PAAD by Efune et al.1 is something I’ve been very interested in for a very, very long time. Many of the children who undergo tonsillectomy have a diagnosis of sleep disordered breathing…this despite the fact that few have had a formal sleep study. Obviously, you can’t ignore and pretend that the underlying diagnosis isn’t real, although many of us do. What is their risk of postoperative obstsructive respiratory events? So, what do you with these patients after surgery? Admit them overnight, and if so, where? The regular wards? The ICU? A hybrid high surveillance unit? And, if admitted for monitoring, how are they monitored, by whom, and for how long? Further, for those deemed safe for discharge home immediately after surgery (or having been admitted to the hospital and then discharged home), is it safe to use opioids for analgesia? Finally, many of these questions are not unique to tonsillectomy patients. Many patients carry a sleep disordered breathing diagnosis, like virtually all newborns or patients on PCA, or have other risk factors for postoperative airway obstruction, such as obesity. Indeed, many patients are at risk for opioid-induced respiratory depression whether they are in- or out-patients. What to do?
How to monitor these myriad patients for respiratory depression is a fundamental question. Pulse oximetry? Capnography? Impedance pneumography? Respiratory volume monitor (RVM) (ExSpiron®1Xi, Respiratory Motion Inc, Watertown, MA)? Transcutaneous CO2? Today’s PAAD offers some guidance. Many of you may be unfamiliar with the RVM. The RVM is a noninvasive, impedance-based monitor that is approved by the Food and Drug Administration for monitoring breathing and lung volumes in children 1–18 years of age.2,3 The RVM continuously measures tidal volume, respiratory rate, and minute ventilation (MV), the latter as both an absolute number (L/min) and a percentage of predicted MV based on the child’s body surface area (MVpred, %). The RVM chest padset is placed during anesthesia induction and control measurements are made in intubated patients to sync the RVM measured tidal volume with that of the anesthesia machine spirometer. The validity of this correlation in children was discussed in a previous PAAD (PAAD 02/08/2022 A non-invasive respiratory volume monitor https://ronlitman.substack.com/p/a-non-invasive-respiratory-volume) which included reference to an earlier intraoperative study.3 Myron Yaster MD
Original article
Efune PN, Pinales P, Park J, Poppino KF, Mitchell RB, Szmuk P. Pediatric obstructive sleep apnea: a prospective observational study of respiratory events in the immediate recovery period after adenotonsillectomy. Anaesth Crit Care Pain Med. 2024 Aug;43(4):101385. doi: 10.1016/j.accpm.2024.101385. Epub 2024 May 4. PMID: 38705239.
“This prospective, observational cohort study, performed in a single center (UT Southwestern Medical Center, Children’s Health Medical Center, Dallas TX) aimed to collect preliminary data in the immediate postoperative period of high-risk children having adenotonsillectomy, to help inform a future study intended to seek risk factors for overnight respiratory complications. Our primary outcome was respiratory depression and airway obstruction in the post-anesthesia care unit (PACU), which we measured using a non-invasive respiratory volume monitor (RVM). Our secondary outcomes included clinically apparent respiratory events and hypoxemia in the PACU.”1
The authors enrolled 60 children <18 yo (median age 4yo) having adenotonsillectomy. “All children received general anesthesia with volatile anesthetic and endotracheal intubation. Induction type ( i.e. , volatile versus intravenous), medication administration, and emergence conditions were at the discretion of the anesthesiologist. No elements of the anesthetic were controlled for study purposes. Nasopharyngeal or oral airway placement prior to extubation and deep versus awake extubation was observed and recorded by study staff. Participants were monitored continuously using the RVM during the entire PACU stay. A priori , we defined the primary outcome of airway obstruction and respiratory depression as episodes of MVpred less than 40% for at least two minutes.”1,4 They also measured pulse oximetry with and without blow by oxygen and defined hypoxemia “as episodes of oxyhemoglobin saturation less than 90% for at least 10 seconds”. Finally, 41 (68%) patients had a preoperative polysomnogram and 28 of these (68%) had severe OSA.”1 Patients were scheduled for admission “because of at least one of the following: age less than three years; obesity, defined as BMI greater than 98th percentile for age and sex, or severe (AHI > 10 events per hour during polysomnogram).”1
OK, what did they find? “Respiratory volume monitoring in the immediate postoperative period after pediatric high-risk adenotonsillectomy identifies impaired ventilation more frequently than is clinically apparent. Thirty-nine (65%) had at least one episode of PACU respiratory depression or airway obstruction measured using the RVM, while only 21 (35%) had clinically apparent respiratory events.”1
So just think about these results for a moment. Respiratory depression and airway obstruction were identified in 65% of patients even though clinical PACU monitoring picked up only 35%! This was even more remarkable since the clinical observations were done by trained study personnel and not by bedside nurses, who may have variable standards of observation. Thus, monitoring these patients is not only important, but HOW they are monitored makes a difference. Further, an key component of standard monitoring, pulse oximetry (desaturation) was not a good monitor of respiratory depression and airway obstruction probably because of the use of blow by oxygen in the PACU, which was routinely used in the PACU from the time of arrival until the patient awakened, “making pulse oximetry an unreliable indicator of inadequate ventilation in this patient population”1
Who was most at risk? For RVM identified respiratory depression and airway obstruction, BMI, ASA PS, and comorbidities were associated. For episodes of hypoxemia, perhaps not surprisingly, younger age, admission for observation due to age alone, ASA PS score, presence of multiple comorbidities, premedication with opioids, and nasopharyngeal or oropharyngeal airway placement before extubation. The etiology of the relationship of postoperative hypoxemia to airway placement prior to extubation was unclear, “ since the decision to place these airway adjuncts was at the discretion of the anesthesiologist, [and] it may be reflective of an unmeasured confounder. Having 2 or more comorbidities was associated with both RVM detected respiratory depression/airway obstruction and hypoxemia in the PACU. A hint at predictive value of the RVM was that 20/21 (95%) of patients who had no RVM detected respiratory depression/airway obstructive events in the PACU had no clinical respiratory events of any severity on the postoperative ward. The authors plan a future study in which RVM is continued on the postoperative ward in order to evaluate the relationship between the absence of events in the PACU to events during overnight admission, in an effort to establish criteria for possible safe discharge.
We agree with the authors that “the primary limitation of this study is the small sample size.”1 There is a lot more work that needs to be done in this area and today’s PAAD by Efune et al. points us in the right direction. Do you have a respiratory volume monitor in your practice? Do you use it? Send your thoughts, experiences, and comments to Myron who will post in a Friday reader response.
References
1. Efune PN, Pinales P, Park J, Poppino KF, Mitchell RB, Szmuk P. Pediatric obstructive sleep apnea: a prospective observational study of respiratory events in the immediate recovery period after adenotonsillectomy. Anaesth Crit Care Pain Med 2024;43(4):101385. (In eng). DOI: 10.1016/j.accpm.2024.101385.
2. Atkinson DB, Sens BA, Bernier RS, Gomez-Morad AD, Imsirovic J, Nasr VG. The Evaluation of a Noninvasive Respiratory Volume Monitor in Mechanically Ventilated Neonates and Infants. Anesthesia and analgesia 2022;134(1):141-148. (In eng). DOI: 10.1213/ane.0000000000005562.
3. Gomez-Morad AD, Cravero JP, Harvey BC, et al. The Evaluation of a Noninvasive Respiratory Volume Monitor in Pediatric Patients Undergoing General Anesthesia. Anesthesia and analgesia 2017;125(6):1913-1919. (In eng). DOI: 10.1213/ane.0000000000002029.
4. Voscopoulos CJ, MacNabb CM, Freeman J, Galvagno SM, Jr., Ladd D, George E. Continuous noninvasive respiratory volume monitoring for the identification of patients at risk for opioid-induced respiratory depression and obstructive breathing patterns. The journal of trauma and acute care surgery 2014;77(3 Suppl 2):S208-15. (In eng). DOI: 10.1097/ta.0000000000000400.