Incidence of Hemidiaphragmatic Paralysis with Patient Controlled Infusion of Low Volume of Ropivacaine after Ultrasound Guided Low Dose Interscalene Brachial Plexus Block, A Prospective Observational Study

BACKGROUND Hemidiaphragmatic paralysis is a complication of single shot and continuous interscalene brachial plexus block that can be minimised by ultrasound guided extrafascial catheter placements and by limiting the amount of local anaesthetic administered. We hypothesized that patient controlled infusion of low volume of ropivacaine for a period of 24 hours would not cause hemidiaphragmatic paralysis and would provide adequate analgesia.METHODS 54 patients aged 18-65 years undergoing surgery for shoulder dislocation or proximal humerus fracture were recruited and allocated into two groups of 27 each, patient controlled interscalene analgesia (PCIA) and multimodal analgesia (MA). Interscalene catheter was inserted at end of surgery and 10 ml of 0.5% ropivacaine was administered as single bolus dose. PCIA was initiated after four hours to deliver background infusion of 2 ml/hr, bolus of 5ml (0.2% of ropivacaine) with lockout interval of 30 minutes for a total duration of 24 hours. Incidence of hemidiaphragmatic paralysis using M-mode ultrasonography was recorded at extubation,4,6,12 and 24hrs. Numerical rating scale (NRS) for pain, patient satisfaction score and complications were also recorded. Acetaminophen (1 gm) and diclofenac 75 gm were used in MA group.RESULT No diaphragmatic paresis was reported in patients administered the background infusion or single bolus doses of ropivacaine and scanned at 4, 6,12 and 24 hrs. Partial paresis was noted in all patients in which two bolus doses/hour were administered 30 minutes after the second bolus. All patients with paresis had diaphragmatic excursion normalized in the next recording made at 4 hours and no complication was reported in any patient. NRS was below 3 at all time points in PCIA and the cumulative fentanyl and tramadol consumption was significantly higher in MA group. The incidence of complete and partial paresis of diaphragm was 85%and 3.7% after single shot bolus dose respectively and had resolved before start of infusion after 4 hours.CONCLUSION Patient controlled low volume continous infusion of ropivacaine (2 ml/hr of 0.2% of ropivacaine) with administration of a single bolus dose of 5ml in an hour does not cause unilateral phrenic paresis. Partial paresis is reported with two bolus doses/hour.Clinical trial number NCT03081728 (clinicaltrials.gov;)