The trigeminocardiac reflex (TCR) is defined as the sudden onset of parasympathetic dysrhythmia, sympathetic hypotension, apnea, or gastric hypermotility during stimulation of any of the sensory branches of the trigeminal nerve. Clinically, the TCR has been reported in all the surgical procedures in which a structure innervated by the trigeminal nerve is involved. Although, there is an abundant literature with reports of incidences and risk factors of the TCR; the physiological significance and function of this brainstem reflex has not yet been fully elucidated. In addition, there are complexities within the TCR that requires examination and clarification. There is also a growing need to discuss its cellular mechanism and functional consequences. Therefore, the current review provides an updated examination of the TCR with a particular focus on the mechanisms and diverse nature of the TCR.

ABSTRACT; The trigeminocardiac reflex (TCR) is a brainstem reflex describing the acute hemodynamic perturbations in neurosurgical patients. The roles of different anatomic locations of this reflex arc on end responses have been found to be variable. In this article, we have highlighted the role and importance of different TCR pathway (peripheral vs central) mechanisms, their manifestations and the various risk factors associated with these. In addition, new insights into various other non-neurosurgical conditions, in special relation to neurointerventional procedures, are also presented in this article. This study is a narrative review based on a PubMed/Google search (from 1 January 1970 to 31 March 2013) on this topic. The common manifestations, such as hypotension and bradycardia, are vagal-dominated responses; however, unusual manifestations, such as hypertension and tachycardia, signify the involvement of the sympathetic nervous system. In addition, there is a complex interaction of the various sensory receptors at the Gasserian ganglion, and this is responsible for the different presentations. There are many surgical as well as nonsurgical risk factors associated with TCR. Interestingly, TCR may affect functional outcome and has been found to be involved in some normal physiological mechanisms, including bruxism. TCR is a complex neurophysiological reflex and there are variable presentations depending upon the peripheral or central stimulation surrounding the Gasserian ganglion. We suggest, for the first time, that if the TCR is initiated at the Gasserian ganglion, it reacts in a different manner from the better-known central or peripheral TCR.

Trigeminocardiac reflex (TCR) is defined as sudden onset of parasympathetic dysrhythmia including hypotension, apnea, and gastric hypermotility during stimulation of any branches of the trigeminal nerve. Previous publications imply a relation between TCR and depth of anesthesia. To gain more detailed insights into this hypothesis, we performed a systematic literature review.Literature about occurrence of TCR was systematically identified through searching in Cochrane Central Register of Controlled Trials (CENTRAL), PubMed (MEDLINE), EMBASE (Ovid SP), and the Institute for Scientific Information (ISI Web of Sciences) databases until June 2013, as well as reference lists of articles for risk calculation. In this study, TCR was defined as drop in mean arterial blood pressure and heart rate, both >20% to baseline. We calculated intraoperative cerebral state index (CSI) of each TCR-case using a newly developed method. These data were further divided into 3 subgroups: CSI <40 (deep anesthesia), CSI 40–60 (regular anesthesia), and CSI >60 (slight anesthesia).Including 45 studies with 910 patients, 140 (15%) presented with TCR, and 770 (85%) without TCR during operation. TCR occurrence showed a 1.2-fold higher pooled risk slighter anesthesia (CSI <40: 13%, at CSI 40–60: 21%, and at CSI >60: 27%) compared with deeper anesthesia. In addition, we could discover a 1.3-fold higher pooled risk of higher MABP drop with a strong negative correlation (r = −0.935; r2 = 0.89) and a 4.5-fold higher pooled risk of asystole during TCR under slight anesthesia compared with deeper anesthesia.Our work is the first systematic review about TCR and demonstrates clear evidence for TCR occurrence and a more severe course of the TCR in slight anesthesia underlying the importance of skills in anesthesia management during skull base surgery. Furthermore, we have introduced a new standard method to calculate the depth of anesthesia.