To the Editor:
We read with great interest the review by Scharoun et al.1 in which the authors discuss anesthesia management for ophthalmic artery chemosurgery focusing on unexpected respiratory and cardiovascular complications. We address some issues.
The authors advocate systematic and early intravenous administration of epinephrine to treat any decrease in lung compliance, which is the main complication of this procedure. This therapeutic option is questionable. Admittedly, epinephrine dilates bronchial airways.2 However, the main action of this mixed α- and β-adrenergic receptor agonist is on the cardiovascular system, with vasoconstricting, chronotropic, and inotropic effects, also causing several side effects including arrhythmia and systemic hypertension. A decrease in lung compliance can often occur on its own, with neither bradycardia nor hypotension, so cardiovascular therapy is not required and should be used with caution.
Propofol is a therapeutic alternative for the following reasons. First, it provides bronchodilatory effects, acting directly on the smooth muscle of the airway, as well as centrally on γ-aminobutyric acid receptors located in the airway-related vagal neurons in the nucleus of the solitary tract.3,4 Second, because the decrease in lung compliance is caused here by an autonomic reflex, propofol administration, by inducing deeper anesthesia, should inhibit vagal response and thus prevent a steep rise in intrathoracic pressure. This is supported by a systematic review suggesting a relationship between trigeminal reflex and depth of anesthesia during skull base surgery.5 Moreover, a previous study reports that an adequate Bispectral Index target inhibits the oculocardiac reflex during sevoflurane anesthesia for pediatric strabismus surgery.6 Lastly, these respiratory complications do not affect adults but only toddlers and children, whose sympathetic immaturity and increase in vagal tone are more susceptible to autonomic reactions.7,8 This supports the use of hypnotic agents, such as propofol, to prevent and treat the respiratory events. We acknowledge, however, that to date no prospective study has assessed the effect of anesthetic depth on complications during ophthalmic artery chemosurgery.
We agree with the theory that catheter manipulation of the ophthalmic artery may stimulate trigeminal afferents and cause a trigeminal reflex, resulting in respiratory and cardiovascular complications. However, a few questions remain. Although all intracranial arteries are innervated by trigeminal afferents, there are few reports of trigeminal reflex during endovascular procedures involving other intracranial arteries.9 Why does the trigeminal reflex occur particularly in the internal carotid artery and ophthalmic artery? What kind of trigger (e.g., pain stimulus or stretching stimulus) causes these complications and at what threshold? Research focusing on the mechanism of these specific complications could help to prevent or reduce them.
The authors declare no competing interests.