Incidence of Hemidiaphragmatic Paralysis After Ultrasound Guided Low Dose Interscalene Brachial Plexus Block

Background and Aims: Hemidiaphragmatic paralysis is a complication of single shot and continuous interscalene brachial plexus block that can be minimised by ultrasound guided extra fascial catheter placements and by limiting the amount of local anaesthetic administered. In this study, we report incidence of hemidiaphragmatic paralysis with patient-controlled infusion of low volume of ropivacaine after ultrasound guided low dose interscalene brachial plexus block (LD-ISB). Methods: Patients aged 18-65 years undergoing surgery for shoulder dislocation or proximal humerus fracture were recruited and administered general anaesthesia. Before extubation ultrasound guided LD-ISB (10 ml of 0.5% ropivacaine) was administered and a catheter tunneled so that patient controlled interscalene analgesia (PCIA) could be given with low volume ropivacaine. PCIA was initiated after four hours in the post operative recovery to deliver background infusion of 2 ml/h, bolus of 5ml (0.2% of ropivacaine) with lockout interval of 30 minutes for a total duration of 24 hours. Incidence of hemidiaphragmatic paralysis was recorded at extubation using M-mode ultrasonography. Before start of PCIA i.e. at 4 hours and after start of PCIA i.e. 6,12 and 24 h after extubation. Results: PCIA after LD-ISB was administered to 29 patients. Subsequently, two patients were excluded due to catheter dislodgement. The incidence of complete and partial paresis of diaphragm after extubation was 85% and 3.7% with LD-ISB respectively but was resolved before start of PCIA i.e., at 4 hours. Thus, at time of commencement of PCIA all patients had normal diaphragmatic excursions and subsequently at 6,12 and 24 h no paresis/paralysis was reported in patients administered only the background infusion or an additional single bolus dose of ropivacaine with the background infusion. Partial paresis was noted in all patients in which two bolus doses/h were administered. All patients with paresis had diaphragmatic excursion normalised in the next recording made at 4 hours and no complication was reported in any patient. VAS (Visual Analog Scale) was below 3 at all time points. Conclusion: Partial/complete paresis after a single shot injection of 10 ml of 0.5% ropivacaine resolves in 4 hours. PCIA initiated after it for subsequent 20 hours with a single bolus dose of 5ml of 0.2% ropivacaine and background infusion at 2 ml/h does not cause phrenic paresis. Partial paresis is reported with two bolus doses/h, but it is clinically asymptomatic. Thus, the above dose regimes are safe and effective in managing post-operative pain. Keywords: Interscalene block, Diaphragmatic paresis, Ropivacaine, continuous infusion, Analgesic efficacy