Cerebral hypoxia after etomidate administration and temporary cerebral artery occlusion

Effects of anesthesia on cerebral blood flow, metabolism, and neuroprotection

Administration of anesthetic agents fundamentally shifts the responsibility for maintenance of homeostasis from the patient and their intrinsic physiological regulatory mechanisms to the anesthesiologist. Continuous delivery of oxygen and nutrients to the brain is necessary to prevent irreversible injury and arises from a complex series of regulatory mechanisms that ensure uninterrupted cerebral blood flow. Our understanding of these regulatory mechanisms and the effects of anesthetics on them has been driven by the tireless work of pioneers in the field. It is of paramount importance that the anesthesiologist shares this understanding. Herein, we will review the physiological determinants of cerebral blood flow and how delivery of anesthesia impacts these processes.

Comparative study between the effects of dexmedetomidine and propofol on cerebral oxygenation during sedation at pediatric cardiac catheterization

Introduction:

Nowadays, assessment of brain oxygen saturation, which is simply appliable and noninvasive method, can provide the anesthesia plans to be optimized according to the needs of the brain, which is the main target organ. Brain may be exposed to hypoxia due to supply-demand imbalance of oxygen not only in general anesthesia procedures but also in sedation practices. The aim of the study is to compare the effects of dexmedetomidine and propofol which are widely used agents for pediatric catheterization procedures on brain oxygen saturation using Fore-Sight.

Material and Methods:

A total of 44 patients undergoing diagnostic cardiac catheterization between 1 and 18 years old were included in the study. All patients, who were randomly divided into two groups, had ASA physical status I-II. In Group Propofol (Group P, n = 22), induction of sedation was made by midazolam (0.5 mg,iv) + propofol (1m/kg,iv), and in Group Dexmedetomidine (Group D, n = 22), induction of sedation was made by midazolam (0.5 mg,iv) +dexmedetomidine (1mcg/kg, iv). Throughout the sedation, cerebral tissue oxygen saturation (SctO₂) was recorded by Fore-Sight in addition to routine monitoring.

Results:

There were no statistically significant differences between the groups in terms of demographic data, hemodynamic data and sedation scores. On other hand, statistically significant decreases in cerebral tissue oxygen saturation were detected especially at 5th and 10th minutes, in Group D, while cerebral oxygenation level did not decrease in Group P. Though, statistically significant difference was determined between two groups in terms of cerebral oxygen saturation, the obtained data was not interpreted as cerebral desaturation.

Conclusion:

As a conclusion, there was a statistically significant but clinically insignificant decrease in cerebral tissue oxygen saturation in dexmedetomidine group compared to propofol group. Although it does not seem to be important in hemodynamic stabilization, we assume that may cause problems for clinically unstable patients.

Monitoring of brain and systemic oxygenation in neurocritical care patients

Maintenance of adequate oxygenation is a mainstay of intensive care, however, recommendations on the safety, accuracy, and the potential clinical utility of invasive and non-invasive tools to monitor brain and systemic oxygenation in neurocritical care are lacking. A literature search was conducted for English language articles describing bedside brain and systemic oxygen monitoring in neurocritical care patients from 1980 to August 2013. Imaging techniques e.g., PET are not considered. A total of 281 studies were included, the majority described patients with traumatic brain injury (TBI). All tools for oxygen monitoring are safe. Parenchymal brain oxygen (PbtO2) monitoring is accurate to detect brain hypoxia, and it is recommended to titrate individual targets of cerebral perfusion pressure (CPP), ventilator parameters (PaCO2, PaO2), and transfusion, and to manage intracranial hypertension, in combination with ICP monitoring. SjvO2 is less accurate than PbtO2. Given limited data, NIRS is not recommended at present for adult patients who require neurocritical care. Systemic monitoring of oxygen (PaO2, SaO2, SpO2) and CO2 (PaCO2, end-tidal CO2) is recommended in patients who require neurocritical care.

Comparative Study of Brain Protection Effect between Thiopental and Etomidate Using Bispectral Index during Temporary Arterial Occlusion

OBJECTIVE

This study was conducted to compare the effect of etomidate with that of thiopental on brain protection during temporary vessel occlusion, which was measured by burst suppression rate (BSR) with the Bispectral Index (BIS) monitor.

METHODS

Temporary parent artery occlusion was performed in forty one patients during cerebral aneurysm surgery. They were randomly assigned to one of two groups. General anesthesia was induced and maintained with 1.5-2.5 vol% sevoflurane and 50% N(2)O. The pharmacological burst suppression (BS) was induced by a bolus injection of thiopental (5 mg/kg, group T) or etomidate (0.3 mg/kg, group E) according to randomization prior to surgery. After administration of drugs, the hemodynamic variables, the onset time of BS, the numerical values of BIS and BSR were recorded at every minutes.

RESULTS

There were no significant differences of the demographics, the BIS numbers and the hemodynamic variables prior to injection of drugs. The durations of burst suppression in group E (11.1±6.8 min) were not statistically different from that of group T (11.1±5.6 min) and nearly same pattern of burst suppression were shown in both groups. More phenylephrine was required to maintain normal blood pressure in the group T.

CONCLUSION

Thiopental and etomidate have same duration and a similar magnitude of burst suppression with conventional doses during temporary arterial occlusion. These findings suggest that additional administration of either drug is needed to ensure the BS when the temporary occlusion time exceed more than 11 minutes. Etomidate can be a safer substitute for thiopental in aneurysm surgery.

Sedation and analgesia in children with developmental disabilities and neurologic disorders

Sedation and analgesia performed by the pediatrician and pediatric subspecialists are becoming increasingly common for diagnostic and therapeutic purposes in children with developmental disabilities and neurologic disorders (autism, epilepsy, stroke, obstructive hydrocephalus, traumatic brain injury, intracranial hemorrhage, and hypoxic-ischemic encephalopathy). The overall objectives of this paper are (1) to provide an overview on recent studies that highlight the increased risk for respiratory complications following sedation and analgesia in children with developmental disabilities and neurologic disorders, (2) to provide a better understanding of sedatives and analgesic medications which are commonly used in children with developmental disabilities and neurologic disorders on the central nervous system.

Etomidate revisited

The major advantage of etomidate is its lack of cardiovascular side effects. In addition, etomidate is supposed to be neuroprotective. The side effects of etomidate include adrenal suppression and myocloni. A review of the recent literature on etomidate, its clinical use, its side effects and its mechanism of action was performed. Among others, major recent advances include a new drug preparation devoid of propylene glycol and its side effects, a new pretreatment technique that may reduce the incidence of myocloni, and the identification of its site of action in the central nervous system.

Perioperative management of complex skull base surgery: the anesthesiologist's point of view

The anesthetic management of complex skull base surgical procedures provides unique problems and concerns for the neuroanesthesiologist. Positioning to access the skull base could put the patient at risk for peripheral nerve injury and some of the positions may increase the risk for air emboli. In addition, tumor pathology and involvement with vital structures could increase the chances for substantive blood loss, destruction of associated nerves or vessels, and may require temporary occlusion of the carotid artery necessitating intraoperative neuroprotection. Neurophysiological monitors may also be used to safeguard nerve function and anesthetic techniques must be adjusted to accommodate their use. Finally, postoperative morbidity may be affected by surgical approach to the skull base and the anesthesiologist should be aware of which approach may produce a greater incidence of pain, nausea, and vomiting in the postoperative period.

The authors discuss the anesthetic concerns and management for complex cranial base surgery. Different approaches will be discussed and comparisons of perioperative parameters between these approaches will be made with data provided by retrospective chart review of more than 600 skull base procedures performed at the authors' institution over the last 10 years. This information should help guide decision making concerning anesthetic management for these skull base procedures.

Neuroprotection with anaesthetic agents

The term 'neuroprotection' is used to refer to any prophylactic measure that is initiated during the peri-ischaemic period in order to improve neuronal survival. Cell death after ischaemia has an immediate, necrotic and a delayed, apoptotic origin. The major biochemical mechanisms that are involved in this process include transmembrane ionic fluxes and intracellular calcium increase, excitotoxicity, free radical formation, peroxynitrite production, release of inflammatory mediators, mitochondrial dysfunction, cytochrome c release, and activation of caspases and transcription factors. Strategies of neuroprotection essentially impact on those biochemical pathways. The label 'neuroprotectant' requires that the therapy has basic properties that are consistent with potential mechanisms of neuroprotection, and that conclusive results are available from animal studies that can be converted into clinical benefit. The present review focuses on neuroprotective effects of anaesthetics and is based on the most recently published reports.

Continuous monitoring of regional cerebral blood flow during temporary arterial occlusion in aneurysm surgery

OBJECT

Temporary arterial occlusion (TAO) during aneurysm surgery carries the risk of ischemic sequelae. Because monitoring of regional cerebral blood flow (rCBF) may limit neurological damage, the authors evaluated a novel thermal diffusion (TD) microprobe for use in the continuous and quantitative assessment of rCBF during TAO.

METHODS

Following subcortical implantation of the device at a depth of 20 mm in the middle cerebral artery or anterior cerebral artery territory, rCBF was continuously monitored by TD microprobe (TD-rCBF) throughout surgery in 20 patients harboring anterior circulation aneurysms; 46 occlusive episodes were recorded. Postoperative radiographic evidence of new infarction was used as the threshold for failure of occlusion tolerance. The mean subcortical TD-rCBF decreased from 27.8+/-8.4 ml/100 g/min at baseline to 13.7+/-11.1 ml/100 g/min (p < 0.0001) during TAO. The TD microprobe showed an immediate exponential decline of TD-rCBF on clip placement. On average, 50% of the total decrease was reached after 12 seconds, thus rapidly indicating the severity of hypoperfusion. Following clip removal, TD-rCBF returned to baseline levels after an average interval of 32 seconds, and subsequently demonstrated a transient hyperperfusion to 41.4+/-18.3 ml/l 00 g/min (p < 0.001). The occurrence of postoperative infarction (15%) and the extent of postischemic hyperperfusion correlated with the depth of occlusion-induced ischemia.

CONCLUSIONS

The new TD microprobe provides a sensitive, continuous, and real-time assessment of intraoperative rCBF during TAO. Occlusion-induced ischemia is reliably detected within the 1st minute after clip application. In the future, this may enable the surgeon to alter the surgical strategy early after TAO to prevent ischemic brain injury.

Measurement of intracerebral oxygen pressure: practicalities and pitfalls

Two probes, using different technologies, are currently available to measure tissue oxygen pressure. One of these also measures oxygen pressure, carbon dioxide pressure, pH and temperature. Research has delineated normal brain tissue oxygen pressure as 25-45 mmHg and ischemic thresholds of less than 10 mmHg that are related to ischemic injury. Oxygen pressure measures are correlated with other indicators of brain oxygenation such as jugular bulb oxygen saturation and near infrared spectroscopy, but are more reliable for detecting regional ischemic events. Oxygen pressure is correlated with local blood flow in the brain, and treatments that enhance tissue perfusion improve oxygenation.

Monitoring of the central nervous system

Clinical studies have shown a close relationship between variables such as hypoxia, increased intracranial pressure, arterial hypotension, or seizures and neurological outcome. This indicates the need for monitoring techniques of the central nervous system including measurements of cerebral blood flow, cerebral oxygenation and neuronal function. Semiquantitative changes in cerebral blood flow can be measured continuously using transcranial Doppler sonography. Measurements of jugular venous oxygen saturation or tissue oxygenation reflect the balance between cerebral oxygen delivery and cerebral oxygen demand. Near-infrared spectroscopy appears to be a technology with potential for non-invasive measurements of cerebral oxygen saturation and mitochondrial oxygen availability. The current technology is, however, of limited clinical utility. Brain electrical monitoring techniques such as electroencephalogram and evoked potentials are sensitive and specific to detect changes in neuronal function caused by cerebral ischaemia. Electroencephalogram and evoked potential measurements of depth of anaesthesia and specific electroencephalogram patterns for pharmacodynamic quantification of drug effects may gear the dosage of anaesthetics according to the anaesthetic effect.