Effects of two levels of partial neuromuscular block with atracurium on the ventilatory response to hypercapnia in anesthetized Beagles.

Abstract

OBJECTIVE To evaluate effects of 2 levels of partial neuromuscular block on the ventilatory response to a hypercapnic challenge in anesthetized dogs and to evaluate effects of edrophonium for reversing partial neuromuscular block. ANIMALS 6 healthy adult Beagles. PROCEDURES Each dog was anesthetized twice with propofol and dexmedetomidine. End-tidal partial pressure of CO2 (Petco2), tidal volume (Vt), and peak inspiratory flow (PIF) were measured during breathing at rest. Maximal Vt and PIF (VtMAX and PIFMAX, respectively) in response to a hypercapnic challenge consisting of 10% CO2 inhaled for 1 minute were measured. Variables were measured before administration of atracurium (baseline), during moderate (train-of-four [TOF] ratio, 0.3 to 0.5) and mild (TOF ratio, 0.6 to 0.8) atracurium-induced neuromuscular block, and after neuromuscular block recovery (TOF ratio, ≥ 0.9) following administration of edrophonium or saline (0.9% NaCl) solution. Dogs for which any variable returned to < 80% of the baseline value were identified. RESULTS Partial neuromuscular block increased Petco2; it impaired Vt at rest and VtMAX but not PIF at rest and PIFMAX. All variables except Petco2 returned to baseline values when the TOF returned to ≥ 0.9. After recovery from neuromuscular block, significantly more dogs had a VtMAX < 80% of the baseline value when edrophonium was not administered. CONCLUSIONS AND CLINICAL RELEVANCE Partial neuromuscular block in anesthetized Beagles decreased spontaneous ventilation at rest and impaired the response to a hypercapnic challenge. Response to hypercapnic challenge might remain partially impaired after recovery of the TOF ratio to ≥ 0.9.