Residual neuromuscular block using rocuronium attenuates the acute hypoxic ventilatory response in patients with untreated obstructive sleep apnea (OSA), according to preliminary data from a study presented at Euroanaesthesia 2015, the European Society of Anaesthesiology’s (ESA) annual meeting (abstract 1AP16-4).
Historically, of course, OSA has been associated with significant respiratory complications during the postoperative recovery period. For the ESA study, a team of researchers from Sweden sought to explore how neuromuscular blocking agents interact with the hypoxic control of breathing in patients with OSA.
“It is of importance to investigate how our commonly used anesthetic drugs interact with control of breathing in OSA patients [because they] have a disturbed regulation of breathing due to repetitive intermittent hypoxia during sleep,” explained study co-author Malin Jonsson Fagerlund, MD, PhD, associate professor, Department of Physiology and Pharmacology at Karolinska Institutet, in Stockholm. “Also, there is a distinction between untreated and treated OSA patients. It has been demonstrated that the regulation of breathing is normalized after one month of treatment.”
Dr. Fagerlund and her colleagues studied 11 newly diagnosed and untreated OSA patients in the supine position with a 30-degree head-up tilt, using a face mask, with standard circulatory and respiratory monitoring as well as thoracic and abdominal impedance bands. They assessed neuromuscular function using mechanical adductor pollicis train-of-four response after supramaximal ulnar nerve stimulation. They then measured participants’ individual baseline isocapnic hypoxic ventilatory response and normoxic hypercapnic ventilatory response. The study patients were then treated via continuous positive airway pressure (CPAP) devices, set at 6 to 7 cm H2O, followed by three series of ventilatory response tests (control, during rocuronium-induced residual neuromuscular block and after recovery).
With results for eight of the 11 patients studied (mean age, 49 years; mean body mass index, 30.3 kg/m2), the researchers found no difference in individual baseline hypoxic ventilatory response and normoxic hypercapnic ventilatory response with or without CPAP. In these patients, residual neuromuscular block (33.2 mg rocuronium infused for 49 minutes) caused a reduction in hypoxic ventilatory response, while hypercapnic ventilatory response was unaffected. The authors attributed this to “a depression of the peripheral chemosensitivity.”
“Patients with untreated, mostly newly diagnosed, obstructive sleep apnea have a reduced ventilatory response to acute hypoxia during partial neuromuscular blockade by rocuronium,” Dr. Fagerlund noted. “In contrast, that the hypercarbic ventilatory response was unaffected demonstrated that this is not due to impairment of mechanical components of breathing, but rather an impaired regulation of breathing in response to acute hypoxia.”
Toby N. Weingarten, MD, associate professor of anesthesiology at Mayo Clinic, in Rochester, Minn., noted that OSA is a significant clinical challenge during the administration of anesthesia, given that the vast majority of adults with the condition are undiagnosed. In a recent study, he and his team at Mayo Clinic found that patients with diagnosed or undiagnosed OSA who experience respiratory depression in the postanesthesia care unit “have a substantially higher risk of postoperative respiratory complications compared to other patients,” and separate studies, he added, have demonstrated that the use of neuromuscular blocking agents is associated with increased rates of postoperative complications, such as unplanned reintubation.
“Anesthesia providers need to be aware of residual neuromuscular blockade even after reversal of these medications as a potential source of respiratory depression during anesthesia recovery,” said Dr. Weingarten, who was not involved in the Karolinska Institutet study. “The authors of this abstract study a potential mechanistic cause of reduced ventilatory response in patients receiving rocuronium beyond the obvious cause of residual muscle weakness—reduced hypoxic ventilatory response. The authors were able to isolate the effects of residual muscle weakness by demonstrating that normoxic hypercarbic ventilatory response was preserved. While interesting, how clinically relevant this finding is compared to the role of residual muscle weakness needs to be further studied.”
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