Influence of Inter-scalene Blockade on Postoperative Episodic Desaturation in Patients at High Risk of Obstructive Sleep Apnea (OSA)

History & Significance:

Obstructive sleep apnea (OSA) is a syndrome of sleep related airway obstruction (snoring) and reduction in blood oxygen levels affecting between 2% and 24% of the general population1. In other words, a person stops breathing repeatedly during sleep when they have OSA. Breathing stops because the airway collapses and prevents air from getting into the lungs. The impact of OSA on systemic heart and lung disease is slow and progressive over a course of years. Exposure to anesthesia increases the tendency for postoperative airway obstruction and reduction in oxygen levels2, both of which could have significant impact on patient well-being.

Recent advances in general anesthetics, opioid analgesic drugs and surgical techniques have made outpatient surgery common for a significant proportion of patients. It is estimated that approximately 50% of procedures currently performed in the University of Michigan Health System are day-case procedures, the vast majority of which require deep sedation or general anesthesia. The reduction in postoperative hospital based care has placed considerable emphasis on the efficient delivery of pain relief and has resulted in an increased usage of peripheral nerve blocks to reduce the need for intravenous sedative opioid analgesics and deep levels of anesthesia.

Shoulder surgery is a particularly good example where a nerve block in the neck region (typically an inter-scalene brachial plexus block) placed before anesthesia provides good pain relief with early recovery and less side effects directly related to opioid analgesics. Nevertheless, one of the side effects of the interscalene nerve block is temporary (12-18 hours) weakness of the diaphragm muscle on the same side as the block, due to phrenic nerve blockade. As a result, there is a change in the patient's breathing pattern which is typically compensated by increased work by other muscles in the respiratory system3. However, it is important to note that shoulder joint disease is more common in middle-aged patients who are typically at greater risk of OSA. The baseline abnormalities in respiration in OSA patients put them at increased risk of breathing abnormalities after the inter-scalene nerve block. As a result, this surgery presents unique challenges to the anesthesiologist looking to balance the benefit and risks of inter-scalene nerve blocks. Unfortunately, there are no studies that look at the effect of anesthesia and inter-scalene blocks on breathing patterns and oxygen saturation levels after discharge from outpatient surgery, as measured by spirometry, sleep studies and pulse oximetry. We therefore propose to study the changes in lung function tests and blood oxygen levels after an inter-scalene block and general anesthesia for outpatient shoulder surgery.

It is possible that future screening for out-patient shoulder surgery includes preoperative overnight oxygen saturation measurement to identify patients at high-risk of changes in oxygen levels. These patients may benefit from hospital admission after surgery for close observation. Thus, this study could have significant implications for patient safety and resource utilization.