A systematic review of the respiratory effects of ultrasound-guided phrenic nerve block.

Ultrasound-guided phrenic nerve blocks (UPNBs) have emerged as a promising intervention for clinical conditions involving the diaphragm and adjacent structures. However, UPNB is often understood as an unintended but potentially critical complication of interscalene brachial plexus block (ISB) rather than a planned procedure. Therefore, we review the existing data on the effectiveness of UPNBs in enhancing respiratory functioning. We searched Medline, EMBASE, Web of Science, and Google Scholar for clinical data related to UPNBs up until May 2025. The primary outcome of this review was to determine the impact of UPNB in minimizing dyspnea or desaturation among patients. Secondary outcomes included UPNB's effectiveness in reducing the intensity and frequency of hiccups and enhancing pulmonary function testing (PFT) and arterial blood gas (ABG) values. Twenty-six studies met the inclusion criteria. The findings show that UPNB does not induce or worsen dyspnea among patients. The injection produced better saturation, with some studies reporting 99% and 96% - 100% oxygen saturation. Besides, phrenic nerve block injection is vital in reducing diaphragmatic pain. Patients who exhibited intractable or persistent hiccups had their frequency and severity reduced or vanished after the nerve block injection. Our findings show that UPNB positively affected ABG samples (fair PaO2, PaCO2, and arterial pH) and spirometry/PFT values (fair FEV1, FVC, and PEF). UPNB enhanced oxygen saturation, reduced intractable hiccups, and preserved PFT and ABG values. Additionally, UPNB did not induce or worsen dyspnea and desaturation. Nevertheless, more clinical trials are needed to confirm these findings.