Territorial and Extraterritorial Trigeminocardiac Reflex: A Review for the Neurosurgeon and a Type IV Reflex Vignette

Abstract

The trigeminocardiac reflex (TCR) is a complex and, sometimes, fatal event triggered by overstimulation of the trigeminal nerve (TN) and its territorial and spinal cord branches. We reviewed and compiled for the neurosurgeon key aspects of the TCR that include a novel and straightforward classification, as well as morphophysiology, pathophysiology, neuromonitoring and neuromodulation features. Further, we present intraoperative data from a patient who developed extraterritorial, or type IV, TCR while undergoing a cervical surgery. TCR complexity, severity and unwanted outcomes indicate that this event should not be underestimated or overlooked in the surgical room. Timely TCR recognition in surgical settings is valuable for applying effective intraoperative management to prevent catastrophic outcomes.

Keywords: neuromodulation; neuromonitoring; neurophysiology; spinal cord; trigeminocardiac reflex trigeminal nerve.

Figure 1. Blink reflexes and valsalva maneuver

Four traces recorded from left (l) and Right (r) orbiculari oculi muscles after applying electrical stimulation of 0.2 ms duration at six times sensory threshold at the supraorbital nerve (asterisk).  Nociceptive A beta (R1), nociceptive A delta (R2), and ultra-nociceptive C fibers (R3) related responses were induced in a 36-year-old healthy male. Shaded area shows R3 response modulation during normal NB and while doing VM. Horizontal: 200 ms, vertical: 20 uV. NB: normal breathing, VM: Valsalva maneuver.

Figure 2. Schematic diagram depicting of hemodynamic neuromodulation of TCR elicited by territorial and extraterritorial TN stimulation

BP: blood pressure; CN: cranial nerve; eTTN: extraterritorial trigeminal nerve, HR: heart rate; TCR: trigemino cardiac reflex; TN: trigeminal nerve. V1: ophthalmic branch, V2: maxillary branch, V3: mandibular branch. For types I, II, III and IV, and classes A and B definitions see text.

Figure 3. Extraterritorial TCR and somatosensory evoked potentials

SSEPs were obtained by stimulating A beta fibers of the left ulnar nerve 200 times at 50 mA. Representative N20 recordings (A) were within normal limits at pre-incision time (8:57). There was a 50% reduction of N20 amplitude decrement and more than 10% of N20 latency prolongation in both cortical and subcortical recordings (B) during laminoplasty (11:08). Surgical neurophysiologist noticed the neurosurgeon, who continued with the surgical procedure despite the advice. Three minutes after SSEP became undetectable (11:38) cardiac arrest happened. Cardiopulmonary resuscitation procedures were applied (11:50) (thick arrow). Patient successfully recovered and transferred to the ICU. X-axis: military time not at actual scale. Y-axis: numeric values represent DBP, SBP, and MABP in mm Hg, and HR in beats/min. Red dot: incision, pink line: exposure, orange line: laminoplasty. DBP: diastolic blood pressure, HR: heart rate, ICU: intensive care unit, MABP: mean arterial blood pressure, SBP: systolic blood pressure, *: patient develops cardiac arrest, §: Lowering anesthesia medications (remifentanil and propofol) was unsuccessful. Vertical: one microvolt; horizontal: five milliseconds.