Sympathetic nervous system does not mediate reflex pupillary dilation during desflurane anesthesia

Area of Science:

• Anesthesiology
• Autonomic Nervous System Physiology
• Ophthalmology

Background:

• Pupil size is regulated by the sympathetic and parasympathetic nervous systems.
• Noxious stimuli cause pupillary dilation in both anesthetized and unanesthetized individuals.
• Sympathetic pathways mediate dilation in unanesthetized humans, while parasympathetic inhibition causes dilation in cats under certain anesthetics.

Purpose of the Study:

• To test the hypothesis that pupillary dilation during desflurane anesthesia results from a parasympathetic reflex.
• To elucidate the mechanism of pupillary dilation in response to noxious stimuli under desflurane anesthesia.

Main Methods:

• Six volunteers received topical dapiprazole to block alpha-I adrenergic receptors, while six others received tropicamide to block muscarinic receptors.
• Desflurane anesthesia was induced, followed by noxious electrical stimulation and a desflurane concentration increase to elicit sympathetic activation.
• Infrared pupillometry was used to measure pupil diameter and light reflex amplitude.

Main Results:

• Dapiprazole induced miosis, but pupillary dilation to noxious stimuli and desflurane changes was similar in blocked and unblocked pupils.
• Tropicamide administration resulted in a dilated pupil with inhibited light reflex; noxious stimulation caused only slight additional dilation.
• These findings indicate that sympathetic pathways do not mediate pupillary dilation under desflurane anesthesia.

Conclusions:

• Pupillary dilation during desflurane anesthesia in response to noxious stimuli or increased anesthetic concentration is not mediated by the sympathetic nervous system.
• The exact mechanism causing this dilation remains undetermined, though inhibition of the pupillo-constrictor nucleus is a possibility.