Immunomodulation of innate immunity by brachial plexus blockade: a crossover study

The autonomic nervous system regulates innate immune function in response to afferent pain signals from injured tissue.1 During acute inflammation, vagal release of acetylcholine suppresses the expression of CD11b, a surface integrin regulating neutrophil transmigration to injured tissue. Whether regional anaesthesia modulates innate neuroimmune control has not been tested. We tested the hypothesis that brachial plexus block modulates the innate immune response to ischaemic tissue injury. With written informed consent, under Holter heart rate monitoring, 17 subjects (mean age, 50 yr [standard deviation 19]; 53% female) underwent ultrasound-guided supraclavicular block (20 ml bupivicaine 0.5%). Once motor block developed, subjects underwent 3× 5-min cycles of arm ischaemia induced by supra-systolic occlusion of the brachial artery using a sphygmomanometer. Brachial artery occlusion was repeated 6 weeks later, without supraclavicular block. We quantified (using flow cytometry) surface expression of CD11b+ in neutrophils after whole blood incubation with Escherichia coli lipopolysaccharide (endotoxin 10 ng ml–1) or saline (control) in the same subjects with or without supraclavicular block. Lipopolysaccharide-induced neutrophil CD11b+ was reduced by 3615 units (95% confidence interval [CI], 475–6754; P=0.03; repeated-measures analysis of variance) after arm ischaemia alone, but remained unchanged with arm ischaemia under supraclavicular block (mean difference, 2331 units; 95% CI, –3921 to 8582; P=0.73). RR interval increased (reduced heart rate) after arm ischaemia by 40 ms (95% CI, 13 to 66; P=0.003) indicating increased vagal activity. RR interval remained unaltered after arm ischaemia under supraclavicular block (mean difference, 20 ms; 95% CI, –11 to 50; P=0.19). Arm ischaemia reduces neutrophil activation, an anti-inflammatory effect that is associated with increased vagal activity but prevented by supraclavicular block. Despite definitive pain relief, regional analgesia may adversely affect neuroimmune regulation after tissue injury (Fig. 1). 1.Pavlov VA, Tracey KJ. Nat Neurosci 2017; 20: 156–66