gms | German Medical Science

The trigeminocardiac reflex (TCR), a phenomenon consisting of bradycardia or even asystolia along with arterial hypotension, can be elicited by surgical manipulation of the trigeminal nerve on its intra- or extracranial course.

In neurosurgery the TCR is described to occur during stimulation of the trigeminal ganglion, and during procedures like trigeminal sensory root rhizotomy or dorsal root entry zone radiofrequency thermocoagulation of the trigeminal nucleus caudalis as well as during posterior fossa surgery.

To our knowledge, there is no study available yet, analyzing the influence of hypotension due to the TCR on postoperative hearing outcome in vestibular schwannoma surgery.

Therefore, we designed a study to evaluate the impact of the TCR on the postoperative auditory function in the treatment of such lesions.

One hundred subsequent vestibular schwannomas operations were evaluated prospectively to determine parameters influencing postoperative auditory function.

In the neurosurgical literature, the TCR has been defined as the onset of bradycardia with a heart rate lower than 60 beats/minute accompanied by a drop of the MABP of 20% or more caused by intraoperative manipulation or traction of the trigeminal nerve. The heart rate and the MABP are expected to return spontaneously to normal levels with cessation of manipulation or traction.

Upon the occurrence of the TCR, the anesthesiologist informed the surgeon immediately, who stopped preparation of the tumor and interrupted the eliciting mechanism. The cessation of surgical stimulation was followed by a normalization of the hemodynamic parameters in all cases. Intravenous administration of vagolytics like atropine was not necessary to control the TCR in any of these cases. Surgery could be continued without any further occurrence of the TCR. Postoperatively, for at least 24 hours, continuous monitoring of the hemodynamic and respiratory parameters and repeated neurological examinations were performed on the intensive care unit.

Of 100 vestibular schwannoma patients studied in this series, 11 (11%) presented evidence of the TCR during tumor resection.

There were no significant differences between the TCR and the non-TCR groups concerning gender, age, tumor side, MABP and preoperative medical diseases or medication. The TCR influenced the postoperative hearing function in the patients with large vestibular schwannomas (T3 and T4).

With an overall hearing preservation of 47%, 11.1% of the TCR group and 51.4% of the non-TCR group showed preserved hearing function, postoperatively. In larger tumors (T3 and T4), patients with an intraoperative TCR had a significantly worse postoperative hearing function than those without a TCR during vestibular schwannoma surgery (p=0.005).

Interrupting the eliciting mechanism is the principal treatment modality for the TCR. The cessation of trigeminal nerve manipulations is followed by a normalization of the hemodynamic parameters.

Some authors recommend the use of atropine to treat the TCR and to prevent new episodes. In our series however, the symptoms disappeared within 20 seconds after ceasing of the manipulation, without the necessity for any medication. In all cases the surgery could be continued without further problems while modifying the surgical maneuvers in terms of traction intensity and/or area of manipulation.

An already compromised vascular supply in the internal auditory canal due to tumor compression can be further decreased in cases of sudden intraoperative hypotension occurring along with the TCR. This mechanism may lead to decreased auditory function or even deafness, despite morphological preservation of the cochlear nerve during surgery.

Gentle and smooth manipulations in the region of the trigeminal nerve while avoiding traction have proven to be the most important surgical maneuvers to decrease the occurrence of the TCR. As soon as this phenomenon has occurred immediate feedback to the surgeon is essential to give him the opportunity to stop the eliciting surgical maneuver quickly and effectively.

The trigeminocardiac reflex is a common intraoperative phenomenon and is of major importance as a negative prognostic factor for hearing preservation in vestibular schwannoma surgery. Bearing this in mind informing patients’ pre- and postoperatively can be improved. For normalization of hemodynamic parameters a modification of surgical maneuvers is sufficient without the necessity of additional medication. Further study of this phenomenon will advance the knowledge of risk factors and the understanding of the underlying physiological mechanisms. Such studies may help to improve hearing preservation in vestibular schwannoma surgery by controlling the occurrence of the TCR.