[Effects of changes in ion concentrations, osmolarity, and pH on recovery from atracurium- or vecuronium-induced neuromuscular blockade].

OBJECTIVES

To determine changes in sodium, potassium, calcium, magnesium and chloride ion concentrations in blood, osmolarity, and pH during surgery, and to assess the influence of such changes on atracurium- or vecuronium-induced neuromuscular blockade under inhaled or intravenous anesthesia.

MATERIAL AND METHODS

Prospective study randomizing 119 ASA 1-2 patients; 52.1% of the patients received atracurium (26.8%, with isoflurane; 25.2%, with propofol) and 47.9% received vecuronium (23.5%, with isoflurane; 24.3%, with propofol). The neuromuscular blockade was confirmed by electromyography of the adductor pollicis muscle (stimuli delivered to the cubital nerve). Two venous blood samples were extracted to measure ureic nitrogen, creatinine, glucose, ion concentrations (sodium, chloride, potassium, calcium, and magnesium), and osmolarity. Arterial blood gases and pH were also assessed. The first blood sample was extracted on inserting the venous catheter and the second on recovery of 25% of the first train-of-four twitch.

RESULTS

The onset and duration of action for equipotent doses of atracurium and vecuronium were similar. Likewise, recovery was also similar. Plasma chloride ion and glucose levels tended to rise during surgery, while sodium, potassium and magnesium ion concentrations fell. Both total and effective plasma osmolarities also decreased. Fluid replacement therapy during surgery was at least partly responsible for these changes. Low calcium and magnesium concentrations and alkalosis prolonged some phases of atracurium recovery, while low sodium levels shortened the duration of some atracurium-induced blockade recovery phases. The effect of changes in chloride ion concentrations on recovery was variable. High chloride, low calcium, and especially low sodium ion concentrations shortened some phases of the vecuronium-induced blockade, while alkalosis prolonged its duration.

CONCLUSIONS

Changes in electrolyte concentrations and pH as a result of standard fluid replacement therapy are moderate, well tolerated, and do not exercise a strong effect on the behavior of the neuromuscular blockade.