Hemanshu Prabhakar

The trigemino-cardiac reflex: An update of the current knowledge

The trigemino-cardiac reflex (TCR) is clinically defined as the sudden onset of parasympathetic activity, sympathetic hypotension, apnea, or gastric hypermotility during central or peripheral stimulation of any of the sensory branches of the trigeminal nerve. Clinically, the TCR has been reported to occur during craniofacial surgery, manipulation of the trigeminal nerve/ganglion and during surgery for lesion in the cerebellopontine angle, cavernous sinus, and the pituitary fossa. Apart from the few clinical reports, the physiologic function of this brainstem reflex has not yet been fully explored. The manifestation of the TCR can vary from bradycardia and hypotension to asystole. From the experimental findings, the TCR represents an expression of a central reflex leading to rapid cerebrovascular vasodilatation generated from excitation of oxygen-sensitive neurons in the rostral ventro-lateral medulla oblongata. By this physiologic response, the systemic and cerebral circulations may be adjusted in a way that augments cerebral perfusion. This review summarizes the current state of knowledge about TCR.

Management of the trigeminocardiac reflex: facts and own experience.

The trigeminocardiac reflex (TCR) is defined as the sudden onset of parasympathetic dysrhythmia, sympathetic hypotension, apnea, or gastric hyper-motility during stimulation of any of the sensory branches of the trigeminal nerve. The proposed mechanism for the development of TCR is--the sensory nerve endings of the trigeminal nerve send neuronal signals via the Gasserian ganglion to the sensory nucleus of the trigeminal nerve, forming the afferent pathway of the reflex arc. It has been demonstrated that the TCR may occur with mechanical stimulation of all the branches of the trigeminal nerve anywhere along its course (central or peripheral). The reaction subsides with cessation of the stimulus. But, some patients may develop severe bradycardia, asystole, and arterial hypotension which require intervention. The risk factors already known to increase the incidence of TCR include: Hypercapnia; hypoxemia; light general anesthesia; age (more pronounced in children); the nature of the provoking stimulus (stimulus strength and duration); and drugs: Potent narcotic agents (sufentanil and alfentanil); beta-blockers; and calcium channel blockers. Because of the lack of full understanding of the TCR physiology, the current treatment options for patients with TCR include: (i) risk factor identification and modification; (ii) prophylactic measures; and (iii) administration of vagolytic agents or sympathomimetics.

Sudden asystole during surgery in the cerebellopontine angle

SummaryWe report a case of a 40-year-old lady undergoing surgery for a tumor in the cerebellopontine angle. Intraoperatively, patient had a sudden asystole without prior warning sign of bradycardia. It could have been the severe form of trigeminocardiac reflex. The cardiac rhythm returned spontaneously once the surgical manipulation stopped. The remainder of the operation was uneventful and no complication occurred afterwards. The possible mechanism of the event is discussed.

Rupture of aorta and inferior vena cava during lumbar disc surgery

SummaryMajor vascular injury during lumbar disc surgery has been recognized as an unusual but well described complication. A potentially fatal outcome can be avoided by a high index of suspicion and an early diagnosis.We present a rare case of aortic and inferior vena caval injury in a 50-year-old female patient undergoing intervertebral disc surgery at lumbar one and two levels. A quick diagnosis and prompt management resulted in a favourable outcome for the patient.

Current concepts of optimal cerebral perfusion pressure in traumatic brain injury.

Traumatic brain injury (TBI) consists of varied pathophysiological consequences and alteration of intracranial dynamics, reduction of the cerebral blood flow and oxygenation. In the past decade more emphasis has been directed towards optimizing cerebral perfusion pressure (CPP) in patients who have suffered TBI. Injured brain may show signs of ischemia if CPP remains below 50 mmHg and raising the CPP above 60 mmHg may avoid cerebral oxygen desaturation. Though CPP above 70 mmHg is influential in achieving an improved patient outcome, maintenance of CPP higher than 70 mmHg was associated with greater risk of acute respiratory distress syndrome (ARDS). The target CPP has been laid within 50-70 mmHg. Cerebral blood flow and metabolism are heterogeneous after TBI and with regional temporal differences in the requirement for CPP. Brain monitoring techniques such as jugular venous oximetry, monitoring of brain tissue oxygen tension (PbrO2), and cerebral microdialysis provide complementary and specific information that permits the selection of the optimal CPP. This review highlights the rationale for use CPP directed therapies and neuromonitoring to identify optimal CPP of head injured patients. The article also reviews the evidence provided by various clinical trials regarding optimal CPP and their application in the management of head injured patients.

Effect of intraoperative dexmedetomidine on postoperative recovery profile of children undergoing surgery for spinal dysraphism.

Background: Smooth recovery from anesthesia is desirable in children undergoing surgery for spinal dysraphism who are nursed in prone position during the postoperative period. Dexmedetomidine may be beneficial in these children owing to its sedative, anxiolytic, and opioid-sparing properties with minimal respiratory depression. Methods: Thirty-six children with spinal dysraphism at lumbosacral area, aged 8 to 12 years, undergoing corrective surgery were randomized to receive either dexmedetomidine or volume-matched saline (placebo) after positioned prone until beginning of skin closure. Inspired concentration of sevoflurane was changed to keep the bispectral index score between 45 and 55. Perioperative hemodynamics, intraoperative fentanyl and sevoflurane consumption, and postoperative recovery profile and fentanyl consumption was observed by blinded observers. Postoperative pain, emergence agitation (EA), and discharge readiness from postanesthesia care unit was evaluated using the modified objective pain score, agitation Cole score, and modified Aldrete score, respectively. Fentanyl 0.5-1 µg/kg was administered for pain (objective pain score ≥4) or severe EA (agitation Cole score ≥4) lasting for >5 minutes. Results: The 2 groups did not differ significantly with respect to demographics, duration of anesthesia, emergence, and extubation times. The intraoperative consumption of sevoflurane and fentanyl was significantly less in dexmedetomidine group (0.2±0.1 vs. 0.3±0.1 mL/min, P<0.0001 and 2.3±0.5 vs. 3.1±0.6 &mgr;g/kg, P=0.0001, respectively), along with a lower mean heart rate (P<0.001). The mean systolic blood pressure (P=0.98) and incidence of bradycardia and hypotension was comparable in between the 2 groups. Postoperatively, the children in dexmedetomidine group had significantly lower pain scores (P<0.0001), agitation scores (P<0.0001), and time to achieve full modified Aldrete score [0 (0 to 10) vs. 10 (0 to 20) min, P=0.001]. The postoperative consumption of fentanyl was significantly less in dexmedetomidine group [0 (0 to 1.04) vs. 0.88 (0 to 3) µg/kg, P=0.003], along with a longer time of first analgesic requirement [600 (5 to 2100) vs. 5 (5 to 185) min, P=0.0001]. The mean heart rate and systolic blood pressure were higher in placebo group (P<0.001), whereas no difference was observed in respiratory rate (P=0.73) and arterial oxygen saturation (P=0.36). The number of patients with postoperative nausea and vomiting was significantly lower in dexmedetomidine group [2 (11.1%) vs. 9 (50%), P=0.03]. Conclusions: Intraoperative use of dexmedetomidine in children undergoing spinal surgery results in a favorable recovery profile with reduced postoperative pain and EA, without adverse perioperative hemodynamic effects.

Trigemino-cardiac reflex and antecedent transient ischemic attacks

Objectives: The trigemino-cardiac reflex (TCR) is a brainstem reflex that has gained enormous interest in recent years and was initially described by Schaller and coworkers as a centrally inducible reflex during skull-base surgery. In the meantime, parts of its functional consequences have been described. Here, we present a study that gives special reference to preventive factors of the TCR and investigates the hypothesis linking preceding transient ischemic attacks (TIAs) to the occurrence of TCR. Methods: We retrospectively reviewed 338 consecutive patients with the histological diagnosis of a pituitary adenoma, who were operated on from 2000 to 2006 in the Neurosurgery department of the University of Gottingen in Germany. Depending on the occurrence of intraoperative TCR, patients were divided into TCR and non-TCR groups. In 19 of these patients (6%), we found the intraoperative occurrence of the TCR. The patient characteristics between the two subgroups were comparable. Results: There was a statistically significant difference between the subgroups of precedent TIA (TCR: 11% vs non-TCR: 4%) versus nonprecedent TIA (TCR: 89% vs non-TCR: 96%) regarding the intraoperative occurrence of the TCR (χ2: p < 0.01). Conclusion: A precedent TIA less than 6 weeks before operation represents a significant risk factor for subsequent intraoperative occurrence of the TCR. Our data may indicate, for the first time, the existence of an oxygen-conserving reflex not only in animals but also in humans. Its neuroprotective effect in the context of the TCR is discussed.

Predicting difficult laryngoscopy in acromegaly: a comparison of upper lip bite test with modified Mallampati classification.

Upper lip bite test (ULBT) is a simple test for predicting difficult intubation. However, it has not been evaluated in acromegalic patients. The primary aim of this study was to compare ULBT with modified Mallampati classification (MMPC) to predict difficult laryngoscopy in acromegalic patients. Over a 5-year period, 64 acromegalic and 63 nonacromegalic patients presenting for excision of pituitary tumor were enrolled. Preoperative airway assessment was done using MMPC and the ULBT. Under anesthesia, laryngoscopic view was assessed using Cormack-Lehane (CL) grading. MMPC III/IV and ULBT grade III were considered predictive of difficult laryngoscopy that was defined as Cormack-Lehane grades III or IV. Difficult intubation was defined as more than 2 direct laryngoscopy attempts involving change of blade or use of bougie/fiberoptic bronchoscope/intubating laryngeal mask airway. Sensitivity, specificity, positive and negative predictive values, and accuracy of both tests in predicting difficult laryngoscopy were calculated. Incidence of difficult laryngoscopy and intubation in acromegalics were 24% and 11%, respectively. MMPC and ULBT predicted difficulty in 61% and 14% acromegalics, respectively. However, only 26% and 44% of the laryngoscopies predicted to be difficult by MMMC and ULBT, respectively, were actually difficult. MMPC failed to predict 33% of difficult laryngoscopies whereas ULBT failed to predict 73%. Neither test predicted difficulty in 33% laryngoscopies that turned out to be difficult. Twenty-seven percent of the difficult laryngoscopies were correctly predicted by both tests. In acromegalic group, MMPC was more sensitive, whereas ULBT was more specific. Sensitivity and accuracy of both tests were less in acromegalic patients compared with nonacromegalic controls.

A randomized, double-blinded comparison of ondansetron, granisetron, and placebo for prevention of postoperative nausea and vomiting after supratentorial craniotomy.

Postoperative nausea and vomiting (PONV) are frequent and distressing complications after neurosurgical procedures. We evaluated the efficacy of ondansetron and granisetron to prevent PONV after supratentorial craniotomy. In a randomized double-blind, placebo controlled trial, 90 adult American Society of Anesthesiologists I, II patients were included in the study. A standard anesthesia technique was followed. Patients were divided into 3 groups to receive either placebo (saline), ondansetron 4 mg, or granisetron 1 mg intravenously at the time of dural closure. After extubation, episodes of nausea and vomiting were noted for 24 hours postoperatively. Statistical analysis was performed using χ2 test and 1-way analysis of variance. Demographic data, duration of surgery, intraoperative fluids and analgesic requirement, and postoperative pain (visual analog scale) scores were comparable in all 3 groups. It was observed that the incidence of vomiting in 24 hours, severe emetic episodes, and requirement of rescue antiemetics were less in ondansetron and granisetron groups as compared with placebo (P<0.001). Both the study drugs had comparable effect on vomiting. However, the incidence of nausea was comparable in all 3 groups (P=0.46). A favorable influence on the patient satisfaction scores, and number needed to prevent emesis was seen in the 2 drug groups. No significant correlation was found between neurosurgical factors (presence of midline shift, mass effect, pathologic diagnosis of tumor, site of tumor) and the occurrence of PONV. We conclude that ondansetron 4 mg and granisetron 1 mg are comparably effective at preventing emesis after supratentorial craniotomy. However, neither drugs prevented nausea effectively.

Comparative evaluation of percutaneous retrogasserian glycerol rhizolysis and radiofrequency thermocoagulation techniques in the management of trigeminal neuralgia.

BACKGROUND: Among the percutaneous procedures for the treatment of trigeminal neuralgia, percutaneous anhydrous glycerol rhizolysis (PRGR) and radiofrequency (RF) ablation of trigeminal neuralgia have stood the test of time. OBJECTIVE: A prospective study was conducted to compare PRGR and RF ablation techniques in patients with trigeminal neuralgia in terms of (1) efficacy of pain relief, (2) duration of pain relief and (3) side effects. METHODS: All patients presenting to our pain clinic for the first time for the treatment of trigeminal neuralgia were enrolled to receive either PRGR or RF ablation; the treatment was chosen by the patient. Demographic data, magnetic resonance imaging scan, relevant medical disease, amount of anhydrous glycerol, lesion temperature, and total duration of RF were noted. The presence or absence of cerebrospinal fluid egress, immediate pain relief, duration of pain-free period, need for repeat injection or additional peripheral nerve block, and recurrence of pain were also noted. The degree of pain relief was recorded every 3 months. Any complications during the procedure and side effects were also recorded. RESULTS: Seventy-nine patients underwent either PRGR (n = 40) or RF thermocoagulation (n = 39). A total of 23 patients (58.9%) in the PRGR group and 33 patients (84.6%) in the RF group experienced excellent pain relief. The mean duration of excellent pain relief in the PRGR and RF groups was comparable. By the end of the study period, 39.1% patients in the PRGR group and 51.5% patients in the RF group experienced recurrence of pain. CONCLUSION: Both PRGR and RF techniques can achieve acceptable pain relief with minimal side effects.