[Trigemino-cardiac reflex during skull-base neurosurgeries: a case report]

The Trigemino-cardiac reflex [TCR] has been studied as a phenomenon including; bradycardia, arterial hypotension, apnea and gastric hypermotility during manipulation of the peripheral or central parts of the trigeminal nerve. We report a case of a 26-year-old man undergoing surgery for a skull base extra axial tumor in right petrous bone suspected to metastasis of a previous renal cell carcinoma which had been treated four years ago. The patient presented with continuous and unilateral headache and difficulty in swallowing, sensory neural hearing loss, nasal speech and tongue deviation to left side. He underwent general anesthesia with standard monitoring and total intravenous anesthetic technique. The first episode of sudden onset bradycardia and hypotension related to surgical manipulation was detected intraoperatively in which the heart rate spontaneously returned to normal level once the surgical manipulation stopped. However, it repeated several times by beginning of tumor resection and manipulation in the region of trigeminal nerve. The intensity of bradycardia in subsequent episodes of TCR was relatively crescendo and had no fatigability. Finally, it was treated by administration of a single dose of atropine [0.5mg/IV] and did not happen again. The risk of TCR should be considered in any neurosurgical intervention involving trigeminal nerve and its branches, especially at the skull base surgeries. The vigilance of the medical team and continuous intraoperative hemodynamic monitoring alerts the surgeons to interrupt surgical maneuvers upon the TCR occurrence, immediately.

Experimental study of oculocardiac reflex (OCR) with graded stimuli.

The present study was conducted to observe the effect of graded mechanical stimuli on occurrence of oculocardiac reflex (OCR). The experiments were carried out in twenty albino rabbits of either sex weighing between 1-2 kg. Changes in heart rate and/or cardiac rhythm (oculocardiac reflex) were studied by applying traction with progressively increasing weights to medial rectus muscle. Mean threshold value of square wave mechanical stimulus just sufficient to produce oculocardiac reflex was found to be 19 +/- 8.52 g. As the traction weights were progressively increased, more and more decrease in heart rate was observed. It was concluded that once the threshold value of stimulus was reached, the oculocardiac reflex showed a graded response with progressively increasing traction weights.

Prediction of oculocardiac reflex in strabismus surgery using neural networks

Successfully predicting an oculocardiac reflex (OCR) is difficult to achieve despite various proposed maneuvers. The aim of this study was to test the models built up by neural networks to predict the occurrence of OCR during strabismus surgery in children. Premedication was not given. Atropine 0.01 mg/kg was medicated just before induction. Induction was performed with fentanyl or ketorolac, followed by propofol. Atracurium or vecuronium was given for intubation. Anesthesia was maintained with O2-N2O with continuous propofol infusion. Chi-square test was performed for induction agents, gender, weight, muscle blockade, repaired muscle, number of repaired muscles, duration of operation to detect any association between the occurrence of OCR and to develop the model of neural networks. The multi-layer perceptron, radial basis function and Bayesian backpropagation network were tested. The occurrence of OCR was significantly associated with gender and repaired muscle (p < 0.05). Gender, repaired muscle and age were considered as input for the multi-layer perceptron, radial basis function and Bayesian backpropagation network. Three neural networks had predicted the same correction rate in the occurrence of OCR as being 87.5% overall among 16 patients' records tested. These models are conceptually different in predicting compared to conventional maneuvers, and have the advantage of testing individually and foretelling the propensity. By comparison neural networks use grouped experiential data and predict OCR by the learning rule. Neural networks require a relatively abundant number of experienced and homogenous patients' records to establish an accurate model. The multi-layer perceptron, radial basis function and Bayesian backpropagation modeling network may be an alternative way, and preferable to vagal tone maneuvers if the associated relationships to the occurrence of OCR are more clearly defined.