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 analgesia unilateral phrenic paresis detected M-mode ultrasonography. Primary outcome incidence of hemidiaphragmatic paresis after 24 hours and secondary outcomes included pain scores, cumulative fentanyl and tramadol requirements and incidence of adverse events in first hours.

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;) Background Hemidiaphragmatic paresis after performance of interscalene block (ISB) is secondary to the rostral spread of local anaesthetic towards the phrenic nerve (predominantly the ventral root of C4). 1 This is due to anatomical continuity of the fibrous sheath enveloping the brachial and the cervical plexus. Phrenic nerve block is associated with significant reductions in ventilatory function; 21-34% decrease in forced vital capacity (FVC), 17-37% decrease in forced expiratory volume in first second (FEV 1 ), and 15.4% decrease in peak expiratory flow rate (PEFR). 2 A reduction in both volume and concentration of local anaesthetic (10 ml of 0.25% bupivacaine) has demonstrated a reduced incidence (20%) of phrenic nerve block. 3 Use of ultrasound (US) facilitates the use of lower volumes of local anaesthetic and ensures more precise deposition of the local anaesthetic around the brachial plexus. US guided ISB performed by Renes et al. with 10 ml of 0.75% ropivacaine reported a substantially lower incidence of hemidiaphragmatic paresis (13.33%). 4 Continuous interscalene analgesia with patient-controlled infusion of local anesthetic is the gold standard for management of pain after surgery of shoulder joint and proximal humerus. It obviates the need of supplemental opioid administration, improves sleep quality and ensures maximum patient satisfaction. 5 The incidence of diaphragmatic paresis with continuous interscalene analgesia is 85% with catheter placements using anatomical landmark technique and is decreased to 20% in patients with catheters placed using a nerve stimulator. 6 US guided catheter placements and reduced volume of local anaesthetics further decrease the incidence of hemidiaphragmatic paralysis. 7,8,9 We hypothesized that patient controlled infusion of low volume of ropivacaine for a period of 24 hours would provide effective analgesia and would not cause unilateral phrenic paresis detected using M-mode ultrasonography. Primary outcome was incidence of hemidiaphragmatic paresis after 24 hours and secondary outcomes included pain scores, cumulative fentanyl and tramadol requirements and incidence of adverse events in first 24 hours. Patients with polytrauma, head injury (GCS<15) and chronic opioid abuse were excluded from enrolment in the study. Patients with coagulopathy, severe respiratory disease (FEV 1 /FVC <0.7 and FEV 1 < 80% of predicted), infection at the block site, prior history of neck surgery or radiation to the neck, associated neurological deficit in the arm or with suspicion of nerve injury, allergy to amide local anaesthetics and inability to operate PCA were included in MA group. Intravascular needle placement was ruled out by aspiration and 3-4 ml of saline was injected to hydro dissect the potential space. A non-stimulating multi-orifice catheter was advanced past the needle tip and tunneled subcutaneously in a posterior and medial trajectory below the hairline. 10 ml of 0.5% ropivacaine was administered through the catheter and spread of local anaesthetic confirmed using US.

Methodology
MA (Group II)Acetaminophen (1 gm) and diclofenac 75 gm was administered before extubation in patients and subsequently continued in the post-operated period on a thrice and twice a day dosing respectively.
Patients were extubated and shifted to the PACU. Descriptive statistics (means, standard deviation (SD), frequencies, and percentages) were used to characterize the sample. Continuous data e.g. age, weight, duration of anesthesia, heart rate (HR), mean arterial pressure (MAP), etc was expressed as mean ±SD. Categorical data e.g. gender, incidence of paralysis are expressed as frequency and percentage. P value of <0.05 was considered as statistically significant and <0.001 was considered as highly significant.
Sample size calculation: Incidence of hemidiaphragmatic paralysis with continuous interscalene brachial plexus block (CISB) has been reported to be 41%. We presumed that with the low dose regime used in our study the incidence would be 30%. In order to detect this difference with an a error of 0.05 and power of 80%. Allowing for a 10% drop-out rate, we planned to recruit a total of 54 subjects.Thus a sample size of 27 for each group was selected. This is in contrast to previous study in which the incidence of hemidiaphragmatic paresis on POD 1 was 15% (95% CI 5-32%) when interscalene catheters were bolus dosed with 20 ml of 0.5% ropivacaine before surgery, followed by an infusion of ropivacaine 0.2% at 4 ml h -1 with patient-controlled boluses of 4 ml available every 30 min for the first 2 days. 10 Our study is the first to propose a drug dosing regimen of the local anaesthetic in CISB which minimises the chances of hemidiaphragmatic paresis and provides adequate pain relief.

Results
There has been no doubt that continous interscalene block (CISB) provides superior analgesia, compared with single-injection interscalene block, for up to 48 h after major shoulder surgery but the importance of CISB-related changes in respiratory indices has always been questionable. 11 This study highlights the fact that the limitations faced by the clinicians due to phrenic nerve block can be avoided by choosing lower doses.
Results of our study are comparable to those of Cuvillon et al 12  Sinha et al 13 reported diaphragmatic paresis in 93% of patients administered 10ml of 0.5% ropivacaine using USG-guided interscalene block. In this study we report a lower incidence (85%) which can be partly explained by the difference in the technique used i.e. extrafascial injections at C6-C7.
Hartrick et al 14 administered various volumes (5, 10, 20ml) of 0.75% ropivacaine as a bolus in patients receiving continuous infusion(0.2% ropivacaine @ 4ml/hr) following arthroscopic shoulder surgery. Clinically significant dyspnea (33%) was reported in patients receiving 20ml volume with significant diaphragmatic impairment. Higher pain scores were seen in patients receiving 5ml volume. Thus, we have used 10 ml of 0.5% ropivacaine in our study as the initial bolus dose. Authors have described the minimum effective volume of local anaesthetic (0.75% ropivacaine) for shoulder analgesia in 95% patients for US-guided administrations at the C7 root level as 3.6 ml. 15 This dose does not lead to hemidiaphragmatic paralysis but its analgesic efficacy needs further evaluation.
Continuous interscalene nerve blocks are not popular among the anaesthesiologists due to high catheter failure placement rate. 6,16 The incidence in our study was 6.8%. Sakae et al 17 has reported extended duration of blockade(1408 vs 1111 mins) and significant reduction in VAS scores at 24hrs post surgery with 4 mg dexamethasone as an adjuvant to ropivacaine for ultrasound-guided ISB. However we do not recommend the same as corticosteriod mediated neuro-toxicity is known and long term follow up is thus necessary for detecting complication rate and assessing safety.
Limitations of this study are that it was an observational trial in which blinding and random allocation was not done. Comparision of diaghragmatic excursion in controls was not done. Potential for inter observer variability in distance measurements using onscreen caliper tool was not excluded as evaluation of the reproducibility of these measurements was not done. Results of this study relate only to interscalene block performed for analgesic purposes and may not apply for surgical anaesthesia.

Conclusion
We conclude that patient controlled interscalene analgesia with a background infusion of 0.2% ropivacaine at a rate of 2ml/hr and a single bolus dosing of 5ml of 0.2% ropivacaine in an hour for a period of 24 hours does not cause diaphragmatic paresis. Ultrasound guided interscalene brachial plexus block at C6-C7 root using 10ml of 0.5% ropivacaine causes diaphragmatic paresis in 85% patients which is resolved by 4 hours. Thus, hemidiaphragmatic paresis should not be considered as a complication of interscalene block as it has been considered in contemporary literature in regional anaesthesia rather it should be thought of an expected sequelae which can be decreased and then eliminated by the use of lower volumes of local anaesthetics placed outside brachial plexus sheath using ultrasound guidance.

Funding-none
Authors' contributions-all authors have read and approved the manuscript.

1.
PK-This author helped perform the literature search, data extraction, and statistical analysis, design the study, draft and critically revise the manuscript, interpret the results, and perform a critical review of the manuscript for intellectual content.

2.
TS-This author helped perform the literature search and data extraction, design the study, draft the manuscript, critically revise the manuscript, interpret the results, and perform a critical review of the manuscript for intellectual content.

3.
VS-This author helped draft the manuscript, critically revise the manuscript, interpret the results, and perform a critical review of the manuscript for intellectual content.

4.
SS-This author helped, critically revise the manuscript, interpret the results, and perform a critical review of the manuscript for intellectual content.

5.
DKC-This author helped, critically revise the manuscript, interpret the results, and perform a critical review of the manuscript for intellectual content.

6.
RK-This author helped, critically revise the manuscript, interpret the results, and perform a critical review of the manuscript for intellectual content.

Figure 2
Post-operative pain management Study Flow Diagram