Acid-sensing ion channels blockade attenuates pressor and sympathetic responses to skeletal muscle metaboreflex activation in humans

In animals, the blockade of acid-sensing ion channels (ASICs), cation pore-forming membrane proteins located in the free nerve endings of group IV afferent fibers, attenuates increases in arterial pressure (AP) and sympathetic nerve activity (SNA) during muscle contraction. Therefore, ASICs play a role in mediating the metabolic component (skeletal muscle metaboreflex) of the exercise pressor reflex in animal models. Here we tested the hypothesis that ASICs also play a role in evoking the skeletal muscle metaboreflex in humans, quantifying beat-by-beat mean AP (MAP; finger photoplethysmography) and muscle SNA (MSNA; microneurography) in 11 men at rest and during static handgrip exercise (SHG; 35% of the maximal voluntary contraction) and postexercise muscle ischemia (PEMI) before (B) and after (A) local venous infusion of either saline or amiloride (AM), an ASIC antagonist, via the Bier block technique. MAP (BAM +30 ± 6 vs. AAM +25 ± 7 mmHg, P = 0.001) and MSNA (BAM +14 ± 9 vs. AAM +10 ± 6 bursts/min, P = 0.004) responses to SHG were attenuated under ASIC blockade. Amiloride also attenuated the PEMI-induced increases in MAP (BAM +25 ± 6 vs. AAM +16 ± 6 mmHg, P = 0.0001) and MSNA (BAM +16 ± 9 vs. AAM +8 ± 8 bursts/min, P = 0.0001). MAP and MSNA responses to SHG and PEMI were similar before and after saline infusion. We conclude that ASICs play a role in evoking pressor and sympathetic responses to SHG and the isolated activation of the skeletal muscle metaboreflex in humans. NEW & NOTEWORTHY We showed that regional blockade of the acid-sensing ion channels (ASICs), induced by venous infusion of the antagonist amiloride via the Bier block anesthetic technique, attenuated increases in arterial pressure and muscle sympathetic nerve activity during both static handgrip exercise and postexercise muscle ischemia. These findings indicate that ASICs contribute to both pressor and sympathetic responses to the activation of the skeletal muscle metaboreflex in humans.

Intravenous Regional Anesthesia Using a Forearm Tourniquet: A Safe and Effective Technique for Outpatient Hand Procedures

Background: Bier block provides anesthesia of an entire extremity distal to the tourniquet without necessitating direct injection at the surgical site. This avoids obscuring anatomy with local anesthetic and anesthetizes a wide area, allowing for multiple procedures and incisions. We hypothesize that a low-volume Bier block with forearm tourniquet, rather than a traditional brachial tourniquet, is a safe, well-tolerated, and effective anesthesia technique. Methods: All cases in which adult patients underwent hand procedures using Bier block anesthesia by a single surgeon over a 4-year period were reviewed. Data collected included patient demographics, procedure(s) performed, complications, tourniquet time and settings, procedure and in-room time, and supplemental medications administered. Results: In all, 319 patients were included, 103 from a university hospital and 216 from an ambulatory surgery center. The most commonly performed procedures were carpal tunnel release (205 cases) and trigger digit release (83 cases). Most patients received a 125-mg dose of lidocaine for the Bier block; many also received additional sedatives. Twenty-three patients received no additional medications. No patients required conversion to general anesthesia. One complication (0.3%) occurred, with paresthesias and tinnitus that resolved without intervention. The average tourniquet time was 24 minutes (SD = 4.3 minutes). Patients were discharged at a median of 49 minutes postoperatively, and 9.1% of patients received supplemental analgesics prior to discharge. Conclusions: Regional anesthesia achieved with a forearm tourniquet and intravenous local anesthetic provides adequate pain control, permits timely discharge home, and has a low complication rate. It should be considered for use in outpatient hand procedures.