Normal saline washout bolus may reverse effects of phrenic nerve paralysis during interscalene nerve block

Patients undergoing shoulder surgeries are often given an interscalene nerve block prior to the surgery. This block is a type of regional anesthesia that has been shown to improve postoperative pain outcomes. However, it is associated with a rare but serious complication, especially in patients with a history of lung impairment or comorbidities, called phrenic nerve paralysis. In phrenic nerve paralysis, the one or both sides of the diaphragm stop working, leading to significant difficulty breathing and possibly death.

Researchers at Stanford University have looked at whether using a large volume normal saline washout bolus through a pre-existing interscalene catheter would help to reverse the effects of phrenic nerve paralysis. Led by Mariam Sarwary, MD, the investigators also tried to determine the timeframe needed for this technique to take effect before attempting other rescue efforts.

Twenty adult patients undergoing elective primary total shoulder arthroplasty were enrolled in the study and received standard ultrasound-guided interscalene nerve block catheters and analgesia. Digital spirometer was used to determine baseline and postoperative lung function. Patients were then randomly selected to either receive a saline washout or not. Lung assessments were conducted again at specified intervals. The researchers observed a statistically significant improved outcome in forced vital capacity (FVC), a measure of exhaled air, in the study group at 30 minutes after the intervention.

Past studies have looked at how to reverse phrenic nerve palsy, but Dr. Sarwary noted that this is the first double-blinded, randomized control study to show a clinical improvement in FVC at 30 minutes and the study supports evidence that changes in FVC are most sensitive to phrenic nerve function.