Dhanesh K. Gupta

Intraoperative acceleromyography monitoring reduces symptoms of muscle weakness and improves quality of recovery in the early postoperative period

Background: The subjective experience of residual neuromuscular blockade after emergence from anesthesia has not been examined systematically during postanesthesia care unit (PACU) stays. The authors hypothesized that acceleromyography monitoring would diminish unpleasant symptoms of residual paresis during recovery from anesthesia by reducing the percentage of patients with train-of-four ratios less than 0.9. Methods: One hundred fifty-five patients were randomized to receive intraoperative acceleromyography monitoring (acceleromyography group) or conventional qualitative train-of-four monitoring (control group). Neuromuscular management was standardized, and extubation was performed when defined criteria were achieved. Immediately upon a patients arrival to the PACU, the patients train-of-four ratios were measured using acceleromyography, and a standardized examination was used to assess 16 symptoms and 11 signs of residual paresis. This examination was repeated 20, 40, and 60 min after PACU admission. Results: The incidence of residual blockade (train-of-four ratios less than 0.9) was reduced in the acceleromyography group (14.5% vs. 50.0% control group, with the 99% confidence interval for this 35.5% difference being 16.4–52.6%, P < 0.0001). Generalized linear models revealed the acceleromyography group had less overall weakness (graded on a 0–10 scale) and fewer symptoms of muscle weakness across all time points (P < 0.0001 for both analyses), but the number of signs of muscle weakness was small from the time of arrival in the PACU and did not differ between the groups at any time. Conclusion: Acceleromyography monitoring reduces the incidence of residual blockade and associated unpleasant symptoms of muscle weakness in the PACU and improves the overall quality of recovery.

Opioid-volatile anesthetic synergy : A response surface model with remifentanil and sevoflurane as prototypes

Background:Combining a hypnotic and an analgesic to produce sedation, analgesia, and surgical immobility required for clinical anesthesia is more common than administration of a volatile anesthetic alone. The aim of this study was to apply response surface methods to characterize the interactions between remifentanil and sevoflurane. Methods:Sixteen adult volunteers received a target-controlled infusion of remifentanil (0–15 ng/ml) and inhaled sevoflurane (0–6 vol%) at various target concentration pairs. After reaching pseudo–steady state drug levels, the Observers Assessment of Alertness/Sedation score and response to a series of randomly applied experimental pain stimuli (pressure algometry, electrical tetany, and thermal stimulation) were observed for each target concentration pair. Response surface pharmacodynamic interaction models were built using the pooled data for sedation and analgesic endpoints. Using computer simulation, the pharmacodynamic interaction models were combined with previously reported pharmacokinetic models to identify the combination of remifentanil and sevoflurane that yielded the fastest recovery (Observers Assessment of Alertness/Sedation score ≥ 4) for anesthetics lasting 30–900 min. Results:Remifentanil synergistically decreased the amount of sevoflurane necessary to produce sedation and analgesia. Simulations revealed that as the duration of the procedure increased, faster recovery was produced by concentration target pairs containing higher amounts of remifentanil. This trend plateaued at a combination of 0.75 vol% sevoflurane and 6.2 ng/ml remifentanil. Conclusion:Response surface analyses demonstrate a synergistic interaction between remifentanil and sevoflurane for sedation and all analgesic endpoints.

When is a bispectral index of 60 too low?: Rational processed electroencephalographic targets are dependent on the sedative-opioid ratio.

Background: Opioids are commonly used in conjunction with sedative drugs to provide anesthesia. Previous studies have shown that opioids reduce the clinical requirements of sedatives needed to provide adequate anesthesia. Processed electroencephalographic parameters, such as the Bispectral Index (BIS; Aspect Medical Systems, Newton, MA) and Auditory Evoked Potential Index (AAI; Alaris Medical Systems, San Diego, CA), can be used intraoperatively to assess the depth of sedation. The aim of this study was to characterize how the addition of opioids sufficient to change the clinical level of sedation influenced the BIS and AAI. Methods: Twenty-four adult volunteers received a target-controlled infusion of remifentanil (0–15 ng/ml) and inhaled sevoflurane (0–6 vol%) at various target concentration pairs. After reaching pseudo–steady state drug levels, the modified Observer’s Assessment of Alertness/Sedation score, BIS, and AAI were measured at each target concentration pair. Response surface pharmacodynamic interaction models were built using the pooled data for each pharmacodynamic endpoint. Results: Response surface models adequately characterized all pharmacodynamic endpoints. Despite the fact that sevoflurane–remifentanil interactions were strongly synergistic for clinical sedation, BIS and AAI were minimally affected by the addition of remifentanil to sevoflurane anesthetics. Conclusion: Although clinical sedation increases significantly even with the addition of a small to moderate dose of remifentanil to a sevoflurane anesthetic, the BIS and AAI are insensitive to this change in clinical state. Therefore, during “opioid-heavy” sevoflurane–remifentanil anesthetics, targeting a BIS less than 60 or an AAI less than 30 may result in an unnecessarily deep anesthetic state.

Adenosine-Induced Flow Arrest to Facilitate Intracranial Aneurysm Clip Ligation: Dose-Response Data and Safety Profile

BACKGROUND: Adenosine-induced transient flow arrest has been used to facilitate clip ligation of intracranial aneurysms. However, the starting dose that is most likely to produce an adequate duration of profound hypotension remains unclear. We reviewed our experience to determine the dose-response relationship and apparent perioperative safety profile of adenosine in intracranial aneurysm patients. METHODS: This case series describes 24 aneurysm clip ligation procedures performed under an anesthetic consisting of remifentanil, low-dose volatile anesthetic, and propofol in which adenosine was used. The report focuses on the doses administered; duration of systolic blood pressure <60 mm Hg (SBP<60 mm Hg); and any cardiovascular, neurologic, or pulmonary complications observed in the perioperative period. RESULTS: A median dose of 0.34 mg/kg ideal body weight (range: 0.29–0.44 mg/kg) resulted in a SBP<60 mm Hg for a median of 57 seconds (range: 26–105 seconds). There was a linear relationship between the log-transformed dose of adenosine and the duration of a SBP<60 mm Hg (R2 = 0.38). Two patients developed transient, hemodynamically stable atrial fibrillation, 2 had postoperative troponin levels >0.03 ng/mL without any evidence of cardiac dysfunction, and 3 had postoperative neurologic changes. CONCLUSIONS: For intracranial aneurysms in which temporary occlusion is impractical or difficult, adenosine is capable of providing brief periods of profound systemic hypotension with low perioperative morbidity. On the basis of these data, a dose of 0.3 to 0.4 mg/kg ideal body weight may be the recommended starting dose to achieve approximately 45 seconds of profound systemic hypotension during a remifentanil/low-dose volatile anesthetic with propofol induced burst suppression.

Revascularization for complex intracranial aneurysms.

The modern management of intracranial aneurysms includes both constructive and deconstructive strategies to eliminate the aneurysm from the circulation. Both microsurgical and endovascular techniques are used to achieve this goal. Although most aneurysms can be eliminated from the circulation with simple clip reconstruction and/or coil insertion, some require revascularization techniques to enhance tolerance of temporary arterial occlusion during clipping of the aneurysm neck or to enable proximal occlusion or trapping. In fact, the importance of revascularization techniques has grown because of the need for complex reconstructions when endovascular therapies fail. Moreover, the safety and feasibility of bypass have progressed due to advances in neuroanesthesia, technological innovations, and ~ 5 decades of accumulating wisdom by bypass practitioners. Cerebral revascularization strategies become necessary in select patients who possess challenging vascular aneurysms due to size, shape, location, intramural thrombus, atherosclerotic plaques, aneurysm type (for example, dissecting aneurysms), vessels arising from the dome, or poor collateral vascularization when parent artery or branch occlusion is required. These techniques are used to prevent cerebral ischemia and subsequent clinical sequelae. Bypass techniques should be considered in cases in which balloon test occlusion demonstrates inadequate cerebral blood flow and in which there is a need for Hunterian ligation, trapping, or prolonged temporary occlusion. This review article will focus on decision making in bypass surgery for complex aneurysms. Specifically, the authors will review graft options, the utility of balloon test occlusion in decision making, and bypass strategies for various aneurysm types.

An evaluation of remifentanil propofol response surfaces for loss of responsiveness, loss of response to surrogates of painful stimuli and laryngoscopy in patients undergoing elective surgery.

INTRODUCTION:In this study, we explored how a set of remifentanil-propofol response surface interaction models developed from data collected in volunteers would predict responses to events in patients undergoing elective surgery. Our hypotheses were that these models would predict a patient population’s loss and return of responsiveness and the presence or absence of a response to laryngoscopy and the response to pain after surgery. METHODS:Twenty-one patients were enrolled. Anesthesia consisted of remifentanil and propofol infusions and fentanyl boluses. Loss and return of responsiveness, responses to laryngoscopy, and responses to postoperative pain were assessed in each patient. Model predictions were compared with observed responses. RESULTS:The loss of responsiveness model predicted that patients would become unresponsive 2.4 ± 2.6 min earlier than observed. At the time of laryngoscopy, the laryngoscopy model predicted an 89% probability of no response to laryngoscopy and 81% did not respond. During emergence, the loss of responsiveness model predicted return of responsiveness 0.6 ± 5.1 min before responsiveness was observed. The mean probability of no response to pressure algometry was 23% ± 35% when patients required fentanyl for pain control. DISCUSSION:This preliminary assessment of a series of remifentanil-propofol interaction models demonstrated that these models predicted responses to selected pertinent events during elective surgery. However, significant model error was evident during rapid changes in predicted effect-site propofol-remifentanil concentration pairs.

Adenosine for temporary flow arrest during intracranial aneurysm surgery: a single-center retrospective review.

BACKGROUND:Clip application for temporary occlusion is not always practical or feasible. Adenosine is an alternative that provides brief periods of flow arrest that can be used to advantage in aneurysm surgery, but little has been published on its utility for this indication. OBJECTIVE:To report our 2-year consecutive experience with 40 aneurysms in 40 patients for whom we used adenosine to achieve temporary arterial occlusion during aneurysm surgery. METHODS:We retrospectively reviewed our clinical database between May 2007 and December 2009. All patients who underwent microsurgical clipping of intracranial aneurysms under adenosine-induced asystole were included. Aneurysm characteristics, reasons for adenosine use, postoperative angiographic and clinical outcome, cardiac complications, and long-term neurological follow-up with the modified Rankin Scale were noted. RESULTS:Adenosine was used for 40 aneurysms (10 ruptured, 30 unruptured). The most common indications for adenosine were aneurysm softening in 17 cases and paraclinoid location in 14 cases, followed by broad neck in 12 cases and intraoperative rupture in 6 cases. Troponins were elevated postoperatively in 2 patients. Echocardiography did not show acute changes in either. Clinically insignificant cardiac arrhythmias were noted in 5 patients. Thirty-six patients were available for follow-up. Mean follow-up was 12.8 months. The modified Rankin Scale score was 0 for 29 patients at the time of the last follow-up. Four patients had an modified Rankin Scale score of 1, and scores of 2 and 3 were found in 2 and 1 patients, respectively. CONCLUSION:Adenosine appears to allow safe flow arrest during intracranial aneurysm surgery. This can enhance the feasibility and safety of clipping in select circumstances.

Interventional neuroradiology—anesthetic considerations

Interventional neuroradiologic procedure represents treatment of central nervous system disease by endovascular access for the purpose of delivering therapeutic agents, including both drugs and devices. For optimal anesthetic management, anesthesiologists should be familiar with specific radiological procedures and their potential complications. This article provides a brief overview of special considerations in conducting general anesthesia, sedation, and cerebral hemodynamic monitoring for patients undergoing interventional neuroradiologic procedures.

Anesthetic Management of Deep Hypothermic Circulatory Arrest for Cerebral Aneurysm Clipping

This article will briefly review the rationale for DHCA in the setting of cerebral aneurysm treatment. We will then use the main aspects of the protocol practiced by the senior author (WLY), as a point of departure to review the issues regarding anesthetic and perioperative management. Rationale The ability to temporarily eliminate or reduce blood flow into an aneurysm gives the surgeon an important advantage—without flow, an aneurysm is converted from a hard, pulsating mass into a soft, collapsed sac, allowing more aggressive manipulation of the aneurysm to complete its dissection. With most aneurysms, temporary occlusion of the proximal parent artery or arteries will effectively control blood flow into the lesion. With large or complex aneurysms, the aneurysm mass may prevent optimal visualization and clip application to the neck. Collapse of the aneurysm mass creates more working space for dissection and precise clip application. Deep hypothermic circulatory arrest is used for aneurysms that cannot be adequately controlled by conventional surgical or endovascular techniques. Aneurysms in the anterior circulation are, in general, accessible enough to be managed with temporary clipping. Aneurysms that defy conventional treatment are typically in the posterior circulation and large (10 –25 mm in diameter) or giant (25 mm in diameter) in size. 11 Often these aneurysms cannot be collapsed easily because of the breadth of the neck, the complexity of the arterial branches at the base, the presence of thrombus or endovascular coils in the lumen, artheroma or calcium in the walls, and fusiform configuration. These anatomic features make direct clipping more difficult and lower the efficacy of conventional techniques. The surgeon’s ability to manage these anatomic factors is directly related to operative exposure. When proximal and distal arteries are inaccessible with these complex aneurysms, DHCA may provide the only safe and effective means of vascular control. Deep hypothermic circulatory arrest should be considered an option of last resort for these unusual aneurysms, when all conventional techniques have failed or have been carefully considered. Rarely, DHCA has also been proposed or described for other central nervous system lesions, such as tumors 8 or arteriovenous malformations, 12 but this discussion is not

TOTAL INTRAVENOUS ANESTHESIA: ADVANTAGES FOR INTRACRANIAL SURGERY

OBJECTIVE Although volatile anesthetics have been widely accepted in anesthetic management for neurosurgery, they reduce vascular resistance, resulting in increased cerebral blood flow and increased intracranial pressure (ICP). In patients with elevated ICP who undergo craniotomy, the increase in ICP during surgery from inhaled anesthetics can make the surgery more difficult, thereby increasing the risk of ischemic cerebral insults. Total intravenous anesthesia (TIVA) using propofol and analgesic drugs (remifentanil or fentanyl) and excluding simultaneous administration of any inhaled drugs is being used in patients undergoing craniotomy because of its potential to reduce ICP and ease access to the operative site. METHODS We reviewed the literature and describe our experience with TIVA, with emphasis on hemodynamic stability, effects on ICP, emergence from anesthesia, extubation times, and return of cognitive function in patients undergoing craniotomy for space-occupying lesions. RESULTS TIVA with propofol is similar to inhaled anesthetics with regard to hemodynamic stability, emergence times, extubation times, early cognitive function, and adverse events. In several prospective, randomized clinical trials, evidence suggests that ICP is decreased and cerebral perfusion pressure is increased in patients receiving TIVA when compared with those receiving volatile anesthetics during elective craniotomy procedures. CONCLUSION The impact of TIVA on ICP, brain swelling, and access to the operative site in patients with severely elevated ICP has yet to be evaluated and is the subject of a future study at our institution.