FRCA Notes

The Oculo-Cardiac Reflex

Resources

  • The oculocardiac (a.k.a Aschner reflex) is a bradycardic response to traction on the extra-ocular muscles
  • Although traction of any of the extra-ocular muscles can trigger the reflex, it occurs most commonly during manipulation of the medial rectus muscle
  • It is more common in paediatric patients and those undergoing strabismus surgery (incidence ~60%)

  • Naturally, the remedy for this is to politely ask the surgeon to release whatever stimulus has just been applied
  • It is a trigemino-vagal reflex

  • The afferent arc is via the long and short ciliary nerves to the ciliary ganglion
  • From there it is carried by the ophthalmic branch of the trigeminal nerve to the trigeminal ganglion, and on to the trigeminal nuclei

  • The efferent impulses conveyed by vagus nerve (CNX) fibres
    • To the sino-atrial node: oculocardiac reflex
    • To the respiratory centres in the pons and medulla: oculo-respiratory reflex
    • To the vomiting centre: oculo-emetic reflex

  • It typically causes a sinus bradycardia that resolves once surgical stimulus is removed
    • It can also cause non-sinus dysrhythmias or even sinus arrest
    • Hyperventilation or respiratory arrest may be seen with the oculo-respiratory reflex

  • Prevention of the oculo-cardiac reflex is important, as triggering it will significantly increase the risk of PONV

Pre-operative

  • One can block the afferent limb of the reflex prior to surgery with regional anaesthesia
  • Premedication with glycopyrrolate or atropine may also be effective, as long as one is willing to tolerate the ensuing tachycardia
  • One should ensure other risk factors for PONV are addressed

Intra-operative

  • Hypercapnoea sensitises the reflex
    • It is associated with a doubling of the incidence of bradycardia, and appropriate ventilation should be provided to negate this

  • A suitable depth of anaesthesia should be maintained
    • Both the incidence and severity of the bradycardic reflex are greater at a BIS of 60 compared to 40 (BJA, 2008)
    • There is no reported difference in the incidence between sevoflurane and desflurane (BJA, 2007), although sevoflurane is associated with less bradycardia than halothane

  • Both suxamethonium and rocuronium appear to attenuate the reflex, although the former will increase IOP
  • Atracurium is associated with a higher incidence of bradycardia than pancuronium