Title: Incidence, Severity, and Risk Factors for Hypotension and Bradycardia in
Patients Undergoing Shoulder Surgery in the Sitting Position Under Interscalene Block Plus Sedation.
Tamin Wafa M.D., Mark C. Kendall M.D., Edward Yaghmour M.D., Radha Sukhani, M.D.
Northwestern University Feinberg School of Medicine, Chicago, Illinois

Introduction: An alarming high incidence (13-39%) of clinically dangerous vaso-vagal episodes, sudden severe hypotension and bradycardia (HBE), have been described in association with interscalene block (ISB) using epinephrine containing local anesthetics in sedated patients undergoing surgery in the sitting position (1,2). The present prospective study evaluated clinically important hypotension following ISB preformed in patients operated on in the sitting position to determine the incidence of hypotension and HBE, and to examine the relationship of patient and surgical factors in this group that may predispose them to hypotensive episodes.
Methods: After IRB approval and written informed consent, 243 consecutive ASA PS I-III adults that received an ISB plus sedation for shoulder surgery were recruited over a 1 year period. ISB’s were performed using a peripheral nerve stimulator guided approach (Winnie’s) and 0.6% levobupivacaine 0.5ml/kg (total volume 30-40ml) with epinephrine 1:200,000. Intraoperative sedation consisted of propofol or midazolam/fentanyl. Supplemental oxygen and 500ml of a 0.9% saline solution were administered prior to surgery. Episodes of hypertension (SBP > 160 mmHg) were treated with labetatol (HR > 60bpm) or hydralazine (HR < 50 bpm) in 5mg increments. Clinically relevant hypotension was defined as a fall in SB
> 20% of the post induction SBP necessitating treatment with a vasopressor. An HBE episode was defined an acute (< 5min duration) decrease in HR of > 30 bpm or HR < 50 bpm and/or SBP decrease of > 30 mmHg or SBP < 90 mmHg (2). SBP and HR after induction, 5 to 10 mins prior to the hypotensive episode and prior to therapeutic intervention (relevant hypotensive episode), and the time in mins from ISB placement to the occurrence of the episode were recorded. Patient characteristics including preoperative antihypertensive medications, anesthetic, surgical and clinical characteristics were compared in patients with and without relevant hypotension using the Mann Whitney U test and the 2 tests. HR and SBP as well as the time from ISB placement and assumption of the sitting position were compared in patients with relevant hypotension compared to those with HBE using repeated measures ANOVA and grouped t-tests. A P<0.05 was required to reject the null hypothesis.
Results: Clinically relevant hypotension occurred in 28 patients (11.5%), and HBE criteria were met by 16 (6.6%). Patients that had hypotensive episodes were older, more frequently ASA PS > 1 and receiving beta-blockers (risk ratio 95% CI, 4.5 (1.7 to 11.8)) and/or calcium channel blockers (4.5 (1.7 to 17.8)) preoperatively. SBP and HR following induction and before the hypotensive episode as well as the time from ISB were not different in the HBE subset compared to those with hypotensive episodes but not HBE.
Hypotension (SBP<90 mmHg) with concurrent bradycardia (HR<50 bpm) characteristic of vaso-vagal syncope occurred in 5 (2%) patients.
Conclusion: The important finding of this study is that clinically relevant hypotension and HBE following ISB with patients in the sitting position is much lower than that previously reported. In addition, acute hypotension with concurrent bradycardia, which may indicate vagal response to severe central hypovolemia, occurred in only 2% patients. Patients undergoing these procedures who are receiving preoperative beta or calcium channel blockers may be at greatest risk of hypotension.

References:
1. A’lessio et al. Anesth & Anal 1995; 80:1158-62
2. Ligouri et al. Anesth & Anal 1998; 87:1320-5

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