Oxygen sensing in the carotid body: inhibited hypoxic respiratory drive with muscle relaxant

Abstract

role. Acetylcholine (ACh) is known as a neurotransmitter at the neuromuscular junction, at preganglionic synapses, and at all postganglionic parasympathetic fibers. The role of ACh in respiratory control has been extensively studied, and it is thought to play a role in carotid body chemotransduction. Eriksson and colleagues [6] recently observed that vecuronium-induced partial neuromuscular block [corresponding to a train of four (TOF) ratio of 0.70] inhibits the respiratory response to hypoxia but not to hypercarbia, although resting ventilation is sustained during air breathing. This inhibitory effect on the hypoxic respiratory response has also been observed with other nondepolarizing muscle relaxants, such as atracurium and pancuronium [7]. A possible pathway has been suggested by blocking the nicotinic ACh receptors on type I glomus cells in the rat [8]. In addition, Wyon and colleagues [9] demonstrated that hypoxia-induced phrenic nerve activities were partially blocked by arterial injection of vecuronium near the carotid body in the anesthetized rabbit. However, the importance of cholinergic signal transmission during hypoxia in the carotid body is still controversial. It is well known that ACh is released during moderate hypoxemia [10], but ACh is not the sole neurotransmitter in the carotid body [11]. Furthermore, hypoxic respiratory control is not known to interact with muscle relaxants, and clinical adverse effects have been never reported. These considerations have stimulated further investigations of the interaction of neuromuscular blocking and the inhibition of neurochemical sensitivity with hypoxia in the carotid body.If this inhibitory effect is confirmed in clinical situations and reversed by anticholinesterase (anti-ChE), anesthesiologists might be recommended to administer more anti-ChE (neostigmine, physostigmine, edrophonium etc) than necessary to restore the clinical findings of reversed muscle relaxant, such as head lift and hand grip, to reverse inhibition of the hypoxic respiratory drive. Furthermore, we might add another risk