Modification of ketamine-induced intracranial hypertension in neurosurgical patients by pretreatment with midazolam

Molecular Mechanisms and Therapeutics for Spinocerebellar Ataxia Type 2

The effective therapeutic treatment and the disease-modifying therapy for spinocerebellar ataxia type 2 (SCA2) (a progressive hereditary disease caused by an expansion of polyglutamine in the ataxin-2 protein) is not available yet. At present, only symptomatic treatment and methods of palliative care are prescribed to the patients. Many attempts were made to study the physiological, molecular, and biochemical changes in SCA2 patients and in a variety of the model systems to find new therapeutic targets for SCA2 treatment. A better understanding of the uncovered molecular mechanisms of the disease allowed the scientific community to develop strategies of potential therapy and helped to create some promising therapeutic approaches for SCA2 treatment. Recent progress in this field will be discussed in this review article.

Advancing emergency airway management practice and research

Emergency airway management is one of the vital resuscitative procedures undertaken in the emergency department (ED). Despite its clinical and research importance in the care of critically ill and injured patients, earlier studies have documented suboptimal intubation performance and high adverse event rates with a wide variation across the EDs. The optimal emergency airway management strategies remain to be established and their dissemination to the entire nation is a challenging task. This article reviews the current published works on emergency airway management with a focus on the use of airway management algorithms as well as the importance of first‐pass success and systematic use of rescue intubation strategies. Additionally, the review summarizes the current evidence for each of the important airway management processes, such as assessment of the difficult airway, preparation (e.g., positioning and oxygenation), intubation methods (e.g., rapid sequence intubation), medications (e.g., premedications, sedatives, and neuromuscular blockades), devices (e.g., direct and video laryngoscopy and supraglottic devises), and rescue intubation strategies (e.g., airway adjuncts and rescue intubators), as well as the airway management in distinct patient populations (i.e., trauma, cardiac arrest, and pediatric patients). Well‐designed, rigorously conducted, multicenter studies that prospectively and comprehensively characterize emergency airway management should provide clinicians with important opportunities for improving the quality and safety of airway management practice. Such data will not only advance research into the determination of optimal airway management strategies but also facilitate the development of clinical guidelines, which will, in turn, improve the outcomes of critically ill and injured patients in the ED.

Interpretation of lumbar puncture opening pressure measurements in children

BACKGROUND

Understanding the reference range of cerebrospinal fluid opening pressure (CSFOP) in children is essential to the diagnosis of elevated intracranial pressure. Recent studies have highlighted several clinical elements that need to be considered when interpreting CSFOP measures.

EVIDENCE ACQUISITION

This review and recommendations are based on peer-reviewed literature, primarily from the past decade, as well as the author's clinical and research experience.

RESULTS

CSFOP measures ≤28 cm H2O can be considered "normal" for most children. The patient's depth of sedation, body mass index, and sedation medication can sometimes result in small increases in CSFOP. Patient age and leg position (flexed vs extended) in the lateral decubitus position do not seem to significantly impact CSFOP measures.

CONCLUSIONS

The threshold of a normal CSFOP should not be interpreted in isolation, but instead, in concert with other clinical and examination findings to help the physician make a well-informed assessment of whether a child has elevated intracranial pressure.

The effect of ketamine on intracranial and cerebral perfusion pressure and health outcomes: a systematic review

STUDY OBJECTIVE

We synthesize the available evidence on the effect of ketamine on intracranial and cerebral perfusion pressures, neurologic outcomes, ICU length of stay, and mortality.

METHODS

We developed a systematic search strategy and applied it to 6 electronic reference databases. We completed a gray literature search and searched medical journals as well as the bibliographies of relevant articles. We included randomized and nonrandomized prospective studies that compared the effect of ketamine with another intravenous sedative in intubated patients and reported at least 1 outcome of interest. Two authors independently performed title, abstract, and full-text reviews, and abstracted data from all studies, using standardized forms. Data from randomized controlled trials and prospective studies were synthesized in a qualitative manner because the study designs, patient populations, reported outcomes, and follow-up periods were heterogeneous. We used the Jadad score and Cochrane Risk of Bias tool to assess study quality.

RESULTS

We retrieved 4,896 titles, of which 10 studies met our inclusion criteria, reporting data on 953 patients. One study was deemed at low risk of bias in all quality assessment domains. All others were at high risk in at least 1 domain. Two of 8 studies reported small reductions in intracranial pressure within 10 minutes of ketamine administration, and 2 studies reported an increase. None of the studies reported significant differences in cerebral perfusion pressure, neurologic outcomes, ICU length of stay, or mortality.

CONCLUSION

According to the available literature, the use of ketamine in critically ill patients does not appear to adversely affect patient outcomes.

Ketamine does not increase intracranial pressure compared with opioids: meta-analysis of randomized controlled trials

BACKGROUND

Ketamine is traditionally avoided in sedation management of patients with risk of intracranial hypertension. However, results from many clinical trials contradict this concern. We critically analyzed the published data of the effects of ketamine on intracranial pressure (ICP) and other cerebral hemodynamics to determine whether ketamine was safe for patients with hemodynamic instability and brain injuries.

METHODS

We systematically searched the online databases of PubMed, Medline, Embase, Current Controlled Trials, and Cochrane Central (last search performed on January 15, 2014). Trial characteristics and outcomes were independently extracted by two assessors (Xin Wang, Xibing Ding). For continuous data, mean differences (MD) were formulated. If the P value of the chi-square test was >0.10 or I(2) <50%, a fixed-effects model was used; otherwise, the random effects model was adopted.

RESULTS

Five trials (n = 198) met the inclusion criteria. Using ICP levels within the first 24 h of ketamine administration as the main outcome, the use of ketamine leads to the same ICP levels as opioids [MD = 1.94; 95% confidence interval (95% CI), -2.35, 6.23; P = 0.38]. There were no significant differences in mean arterial pressure values between the two groups (MD = 0.99; 95% CI, -2.24, 4.22; P = 0.55). Ketamine administration was also comparable with opioids in the maintenance of cerebral perfusion pressure (MD = -1.07; 95% CI, -7.95, 5.8; P = 0.76).

CONCLUSIONS

The results of this study suggest that ketamine does not increase ICP compared with opioids. Ketamine provides good maintenance of hemodynamic status. Clinical application of ketamine should not be discouraged on the basis of ICP-related concerns.

Hemodynamic consequences of ketamine vs etomidate for endotracheal intubation in the air medical setting

OBJECTIVE

Recent drug shortages have required the occasional replacement of etomidate for endotracheal intubation (ETI) by helicopter emergency medical services (HEMS), with ketamine. The purpose of this study was to assess whether there was an association between ketamine vs etomidate use as the main ETI drug, with hemodynamic or clinical (airway) end points.

METHODS

This retrospective study used data entered into medical records at the time of HEMS transport. Subjects, 50 ketamine and 50 etomidate, were accrued from 3 US HEMS programs. The study period was from August 2011 through May 2012. Data collection included demographics, diagnostic category, ETI drugs use, ETI success, and complications. Hemodynamic parameters were assessed for up to 2 sets of vital signs before airway management and up to 5 sets of post-ETI vital signs. Significance was defined at the P < .05 level.

RESULTS

Patients on ketamine and etomidate were similar (P > .05) with respect to age, sex, scene/interfacility mission type, trauma vs nontrauma, neuromuscular blocking agent use, and rates of coadministration of fentanyl or midazolam. All patients had successful airway placement. Peri-ETI hypoxemia was seen in 10% of etomidate and 16% of ketamine cases (P = .55). The pre-ETI and post-ETI were similar between the ketamine and etomidate groups with respect to systolic blood pressure and heart rate at every vital signs assessment after ETI.

CONCLUSION

Initial assessment of ETI success and complication rates, as well as peri-ETI hemodynamic changes, suggests no concerning complications associated with large-scale replacement of etomidate with ketamine as the major airway management drug for HEMS.

The emerging use of ketamine for anesthesia and sedation in traumatic brain injuries

Traditionally, the use of ketamine for patients with traumatic brain injuries is contraindicated due to the concern of increasing intracranial pressure (ICP). These concerns, however, originated from early studies and case reports that were inadequately controlled and designed. Recently, the concern of using ketamine in these patients has been challenged by a number of published studies demonstrating that the use of ketamine was safe in these patients. This article reviews the current literature in regards to using ketamine in patients with traumatic brain injuries in different clinical settings associated with anesthesia, as well as reviews the potential mechanisms underlying the neuroprotective effects of ketamine. Studies examining the use of ketamine for induction, maintenance, and sedation in patients with TBI have had promising results. The use of ketamine in a controlled ventilation setting and in combination with other sedative agents has demonstrated no increase in ICP. The role of ketamine as a neuroprotective agent in humans remains inconclusive and adequately powered; randomized controlled trials performed in patients undergoing surgery for traumatic brain injury are necessary.

Pretreatment with midazolam blunts the rise in intracranial pressure associated with ketamine sedation for lumbar puncture in children

OBJECTIVE

Ketamine has a long history of use during pediatric procedural sedation. Concerns about raising intracranial pressure may limit use in certain situations. Whereas some data suggest that benzodiazepine coadministration may blunt this response, pediatric data during procedural sedation do not exist. We evaluated the effects of midazolam pretreatment on intracranial pressure during ketamine sedation in children.

DESIGN

Prospective, randomized clinical study.

SETTING

Outpatient Medical Observation unit at Kosair Children's Hospital.

PATIENTS

A total of 25 oncology patients in whom sedated lumbar puncture was scheduled.

INTERVENTIONS

Patients alternated between sedation in Group A (midazolam/ketamine prior to lumbar puncture) or Group B (ketamine only prior to lumbar puncture). Opening pressure, medication doses, sedation depth, and complications were recorded. A control group of non-ketamine-sedated patients (Group C) was added to differentiate drug vs. disease-specific opening pressure changes. Between-group differences were compared by linear mixed effects model or contingency table with p < 0.05 considered significant.

MEASUREMENTS AND MAIN RESULTS

Twenty-five patients aged 82 ± 49 months were sedated 84 times. Thirty-five sedations were in Group A, 39 in Group B, and 10 in Group C. Mean (95% confidence interval) adjusted opening pressure in Group A (22.0 [12.3, 22.2] cm H2O) was lower than Group B (26.5 [24.0, 29.2] cm H2O, p = 0.013). Opening pressure in Group C (17.3 [12.3, 22.2] cm H2O) was lower than in Group B (p = 0.002) but not in Group A (p = 0.096). Ketamine doses were similar between Groups A and B (1.4 ± 0.6 mg/kg vs. 1.4 ± 0.4 mg/kg, p = NS). Mean midazolam pretreatment dose was 0.09 ± 0.02 mg/kg and did not correlate with measured opening pressure. Four patients, all in Group B, experienced significant emergence reactions.

CONCLUSION

While pretreatment with midazolam is associated with a reduction in intracranial pressure compared with sedation with ketamine alone, ketamine-containing regimens are associated with higher opening pressures than non-ketamine-containing regimens.

Ketamine prevents seizures and reverses changes in muscarinic receptor induced by bicuculline in rats

The cholinergic system has been implicated in several experimental epilepsy models. In a previous study bicuculline (BIC), known to antagonize GABA-A postsynaptic receptor subtype, was administered to rats at subconvulsant (1mg/kg) and convulsant (7.5mg/kg) doses and quinuclidinyl benzilate ([(3)H]-QNB) binding to CNS membranes was determined. It was observed that ligand binding to cerebellum increases while it decreases in the case of hippocampus. Saturation binding curves showed that changes were due to the modification of receptor affinity for the ligand without alteration of binding site number. The purpose of this study was to assay muscarinic receptors employing other BIC dose (5mg/kg), which induces seizures and allows the analysis of a postseizure stage as well. To study further muscarinic receptor involvement in BIC induced seizures, KET was also employed since it is a well known anticonvulsant in some experimental models. The administration of BIC at 5mg/kg to rats produced a similar pattern of changes in [(3)H]-QNB binding to those recorded with 1.0 and 7.5mg/kg doses. Here again, changes were observed in receptor binding affinity without alteration in binding site number for cerebellum or hippocampus membranes. Pretreatment with KET (40 mg/kg) prevented BIC seizures and reverted [(3)H]-QNB binding changes induced by BIC administration. The single administration of KET invariably resulted in [(3)H]-QNB binding decrease to either cerebellar or hippocampal membranes. KET added in vitro decreased ligand binding likewise. Results of combined treatment with KET plus BIC are hardly attributable to the single reversion of BIC effect since KET alone invariably decreased ligand binding. It is suggested that besides alteration of cholinergic muscarinic receptor other(s) neurotransmitter system(s) may well also be involved.

Sedation for critically ill or injured adults in the intensive care unit: a shifting paradigm

As most critically ill or injured patients will require some degree of sedation, the goal of this paper was to comprehensively review the literature associated with use of sedative agents in the intensive care unit (ICU). The first and selected latter portions of this article present a narrative overview of the shifting paradigm in ICU sedation practices, indications for uninterrupted or prolonged ICU sedation, and the pharmacology of sedative agents. In the second portion, we conducted a structured, although not entirely systematic, review of the available evidence associated with use of alternative sedative agents in critically ill or injured adults. Data sources for this review were derived by searching OVID MEDLINE and PubMed from their first available date until May 2012 for relevant randomized controlled trials (RCTs), systematic reviews and/or meta-analyses and economic evaluations. Advances in the technology of mechanical ventilation have permitted clinicians to limit the use of sedation among the critically ill through daily sedative interruptions or other means. These practices have been reported to result in improved mortality, a decreased length of ICU and hospital stay and a lower risk of drug-associated delirium. However, in some cases, prolonged or uninterrupted sedation may still be indicated, such as when patients develop intracranial hypertension following traumatic brain injury. The pharmacokinetics of sedative agents have clinical importance and may be altered by critical illness or injury, co-morbid conditions and/or drug-drug interactions. Although use of validated sedation scales to monitor depth of sedation is likely to reduce adverse events, they have no utility for patients receiving neuromuscular receptor blocking agents. Depth of sedation monitoring devices such as the Bispectral Index (BIS©) also have limitations. Among existing RCTs, no sedative agent has been reported to improve the risk of mortality among the critically ill or injured. Moreover, although propofol may be associated with a shorter time to tracheal extubation and recovery from sedation than midazolam, the risk of hypertriglyceridaemia and hypotension is higher with propofol. Despite dexmedetomidine being linked with a lower risk of drug-associated delirium than alternative sedative agents, this drug increases risk of bradycardia and hypotension. Among adults with severe traumatic brain injury, there are insufficient data to suggest that any single sedative agent decreases the risk of subsequent poor neurological outcomes or mortality. The lack of examination of confounders, including the type of healthcare system in which the investigation was conducted, is a major limitation of existing pharmacoeconomic analyses, which likely limits generalizability of their results.

Sedation for critically ill adults with severe traumatic brain injury: a systematic review of randomized controlled trials

OBJECTIVES

To summarize randomized controlled trials on the effects of sedative agents on neurologic outcome, mortality, intracranial pressure, cerebral perfusion pressure, and adverse drug events in critically ill adults with severe traumatic brain injury.

DATA SOURCES

PubMed, MEDLINE, EMBASE, the Cochrane Database, Google Scholar, two clinical trials registries, personal files, and reference lists of included articles.

STUDY SELECTION

Randomized controlled trials of propofol, ketamine, etomidate, and agents from the opioid, benzodiazepine, α-2 agonist, and antipsychotic drug classes for management of adult intensive care unit patients with severe traumatic brain injury.

DATA EXTRACTION

In duplicate and independently, two investigators extracted data and evaluated methodologic quality and results.

DATA SYNTHESIS

Among 1,892 citations, 13 randomized controlled trials enrolling 380 patients met inclusion criteria. Long-term sedation (≥24 hrs) was addressed in six studies, whereas a bolus dose, short infusion, or doubling of plasma drug concentration was investigated in remaining trials. Most trials did not describe baseline traumatic brain injury prognostic factors or important cointerventions. Eight trials possibly or definitely concealed allocation and six were blinded. Insufficient data exist regarding the effects of sedative agents on neurologic outcome or mortality. Although their effects are likely transient, bolus doses of opioids may increase intracranial pressure and decrease cerebral perfusion pressure. In one study, a long-term infusion of propofol vs. morphine was associated with a reduced requirement for intracranial pressure-lowering cointerventions and a lower intracranial pressure on the third day. Trials of propofol vs. midazolam and ketamine vs. sufentanil found no difference between agents in intracranial pressure and cerebral perfusion pressure.

CONCLUSIONS

This systematic review found no convincing evidence that one sedative agent is more efficacious than another for improvement of patient-centered outcomes, intracranial pressure, or cerebral perfusion pressure in critically ill adults with severe traumatic brain injury. High bolus doses of opioids, however, have potentially deleterious effects on intracranial pressure and cerebral perfusion pressure. Adequately powered, high-quality, randomized controlled trials are urgently warranted.

Spinal anaesthesia and monitored conscious sedation for repair of infantile meningomyelocele

OBJECTIVES

Monitored conscious sedation combined with spinal anaesthesia (MCSS) to repair myelomeningocoele (MM) has received little attention in the literature. It has the potential of rapid postoperative recovery, minimal perioperative morbidity and probable reduced cost of management. The objective of this study was to prospectively analyze the safety and effectiveness of MCSS during repair of MM in infants.

MATERIALS AND METHODS

This series consists of a prospective study of the clinical features, anaesthetic technique and perioperative outcome of 30 infants who underwent repair of MM under MCSS. The procedure was considered safe and effective if no event occurred during anaesthesia resulting in the procedure being aborted or postoperative complication related to the anaesthetic technique.

RESULTS

There were 19 males and 11 females. The median age of the patients was 3 months ranging from 2 days to 12 months. The study included patients with lumbar (four patients), lumbosacral (23 patients) and sacral (three patients) MM. None of the cases needed to be converted to general anaesthesia. The mean duration of surgery was 56.4 min (median = 55 min; range of 40-85 min). There was no significant perioperative morbidity or mortality.

CONCLUSIONS

The prevailing adverse socioeconomic status, health undermining religious belief, paucity of neurosurgeons/neuroanaesthetists and inadequate facilities in sub-Saharan Africa delay the presentation and surgical intervention of patients with MM. This technique is useful if the exclusion criteria are adhered to and should be considered as one of the armamentarium in economically challenged environments as it is probably cheaper than general anaesthesia.

Effectiveness of ketamine in decreasing intracranial pressure in children with intracranial hypertension

OBJECT

Deepening sedation is often needed in patients with intracranial hypertension. All widely used sedative and anesthetic agents (opioids, benzodiazepines, propofol, and barbiturates) decrease blood pressure and may therefore decrease cerebral perfusion pressure (CPP). Ketamine is a potent, safe, rapid-onset anesthetic agent that does not decrease blood pressure. However, ketamine's use in patients with traumatic brain injury and intracranial hypertension is precluded because it is widely stated that it increases intracranial pressure (ICP). Based on anecdotal clinical experience, the authors hypothesized that ketamine does not increase-but may rather decrease-ICP.

METHODS

The authors conducted a prospective, controlled, clinical trial of data obtained in a pediatric intensive care unit of a regional trauma center. All patients were sedated and mechanically ventilated prior to inclusion in the study. Children with sustained, elevated ICP (> 18 mm Hg) resistant to first-tier therapies received a single ketamine dose (1-1.5 mg/kg) either to prevent further ICP increase during a potentially distressing intervention (Group 1) or as an additional measure to lower ICP (Group 2). Hemodynamic, ICP, and CPP values were recorded before ketamine administration, and repeated-measures analysis of variance was used to compare these values with those recorded every minute for 10 minutes following ketamine administration.

RESULTS

The results of 82 ketamine administrations in 30 patients were analyzed. Overall, following ketamine administration, ICP decreased by 30% (from 25.8 +/- 8.4 to 18.0 +/- 8.5 mm Hg) (p < 0.001) and CPP increased from 54.4 +/- 11.7 to 58.3 +/- 13.4 mm Hg (p < 0.005). In Group 1, ICP decreased significantly following ketamine administration and increased by > 2 mm Hg during the distressing intervention in only 1 of 17 events. In Group 2, when ketamine was administered to lower persistent intracranial hypertension, ICP decreased by 33% (from 26.0 +/- 9.1 to 17.5 +/- 9.1 mm Hg) (p < 0.0001) following ketamine administration.

CONCLUSIONS

In ventilation-treated patients with intracranial hypertension, ketamine effectively decreased ICP and prevented untoward ICP elevations during potentially distressing interventions, without lowering blood pressure and CPP. These results refute the notion that ketamine increases ICP. Ketamine is a safe and effective drug for patients with traumatic brain injury and intracranial hypertension, and it can possibly be used safely in trauma emergency situations.

Effects of sufentanil or ketamine administered in target-controlled infusion on the cerebral hemodynamics of severely brain-injured patients*

OBJECTIVE

The manual injection of a bolus of opioid in patients with brain injury induces an increase in intracranial pressure related to a decrease in mean arterial pressure. Such an effect has not been observed with the use of ketamine. The use of target-controlled infusion would minimize or suppress this adverse effect of opioid. This study evaluated the effects of an increase in plasma concentrations of sufentanil or ketamine administered by target-controlled infusion on cerebral hemodynamics.

DESIGN

Prospective, randomized study.

SETTING

Intensive care unit in a trauma center.

PATIENTS

Thirty patients with severe traumatic brain injury.

INTERVENTIONS

Patients were assigned to receive sedation consisting of sufentanil-midazolam or ketamine-midazolam using target-controlled infusion. Twenty-four hours after the onset of sedation, the target concentrations of sufentanil or ketamine were doubled for 15 mins. Blood samples were collected to determine the actual plasma concentration of sufentanil and ketamine, before and 15 mins after concentration change.

MEASUREMENTS AND MAIN RESULTS

The baseline values of intracranial pressure and cerebral perfusion pressure were similar in both groups. The two-fold increase in drug concentrations did not involve a significant change for intracranial pressure, cerebral perfusion pressure, and mean velocity of middle cerebral artery in both the ketamine and the sufentanil groups. The measured plasma concentrations of sufentanil and ketamine were 0.4 +/- 0.2 ng/mL and 2.6 +/- 2.2 mug/mL, respectively, before the increase in concentrations and 0.7 +/- 0.4 ng/mL and 5.5 +/- 3.8 mug/mL after.

CONCLUSIONS

The present study shows that the increase in sufentanil or ketamine plasma concentrations using a target-controlled infusion is not associated with adverse effects on cerebral hemodynamics in patients with severe brain injury. The use of target-controlled infusion could be of interest in the management of severely brain-injured patients. However, there is a need for specific pharmacokinetic models designed for intensive care unit patients.

Safety of sedation with ketamine in severe head injury patients: comparison with sufentanil

OBJECTIVE

The aim of the study was to compare the safety concerning cerebral hemodynamics of ketamine and sufentanil used for sedation of severe head injury patients, both drugs being used in combination with midazolam.

DESIGN

Prospective, randomized, double-blind study.

SETTING

Intensive care unit in a trauma center.

PATIENTS

Twenty-five patients with severe head injury.

INTERVENTIONS

Twelve patients received sedation with a continuous infusion of ketamine-midazolam and 13 with a continuous infusion of sufentanil-midazolam. All patients were mechanically ventilated with moderate hyperventilation.

MEASUREMENTS AND MAIN RESULTS

Prognostic indicators (age, Glasgow Coma Scale scores, computed tomography diagnosis, and Injury Severity Scale score) were similar in the two groups at study entry. Measurements were carried out during the first 4 days of sedation. The average infusion rates during this time were 82 +/- 25 micro x kg x min ketamine and 1.64 +/- 0.5 microg x kg x min midazolam in the ketamine group and 0.008 +/- 0.002 microg x kg x min sufentanil and 1.63 +/- 0.37 microg x kg x min midazolam in the sufentanil group. No significant differences were observed between the two groups in the mean daily values of intracranial pressure and cerebral perfusion pressure. The numbers of intracranial pressure elevations were similar in both groups. The requirements of neuromuscular blocking agents, propofol, and thiopental were similar. Heart rate values were significantly higher in the ketamine group on therapy days 3 and 4 ( <.05). With regard to arterial pressure control, more fluids were given on the first therapy day and there was a trend toward greater use of vasopressors in the sufentanil group. Sedative costs were similar in the two groups.

CONCLUSION

The results of this study suggest that ketamine in combination with midazolam is comparable with a combination of midazolam-sufentanil in maintaining intracranial pressure and cerebral perfusion pressure of severe head injury patients placed under controlled mechanical ventilation.

Use of sedative and analgesic agents in neurotrauma patients: effects on cerebral physiology

Sedation and analgesia is used primarily in the intensive care unit (ICU) to limit the stress response to critical illness, provide anxiolysis, improve ventilatory support, and facilitate adequate ICU care. However, in the neurotrauma ICU there are many other reasons for the use of these agents. The primary aim is to prevent secondary cerebral damage by maintaining adequate cerebral perfusion pressures. This is accomplished in several different ways. Controlling intracranial pressure (ICP) and maintaining an adequate mean arterial pressure (MAP) is at the cornerstone of this management. Lowering the metabolic demands of the brain is also an important consideration as a treatment strategy. Analgesic and sedative agents are utilized to prevent undesirable increases in ICP and to lower cerebral metabolic demands. Concerns surrounding the use of these agents include time to awakening after discontinuation, effect on the cerebrovasculature, and the effect on patient outcome. There are many different pharmacological agents available, each with their distinct advantages and disadvantages. The purpose of this review is to evaluate the pharmacokinetic and pharmacological effects of each of these agents when used in neurotrauma patients.

Primate anesthesia

This article provides an update on some of the recent advances in primate anesthesia. It focuses in particular on some of the newest information available regarding the effects of opioids and alpha-2 agonists in primates, and how these effects are different from what we might expect in other companion animals. It reviews the important properties of the latest induction and inhalation agents, and stresses the need for continuous monitoring of the anesthetized patient.

Intravenous agents and intraoperative neuroprotection. Beyond barbiturates

The authors discuss the role of intravenous anesthetic agents in brain protection. The newer intravenous anesthetics, etomidate and propofol, have been proposed as neuroprotective agents. Thiopental remains the drug of choice, however, for use prior to intraoperative ischemic events. The anesthetic ketamine presents surprising similarities to other N-methyl-D-aspartate receptor inhibitors, but remains controversial in its use in neurologically compromised patients.

Ketamine does not increase cerebral blood flow velocity or intracranial pressure during isoflurane/nitrous oxide anesthesia in patients undergoing craniotomy

Ketamine's effect on cerebral hemodynamics is controversial. We hypothesized that ketamine would not increase intracranial pressure (ICP) and cerebral blood flow (CBF) velocity in anesthetized, ventilated patients. Twenty patients requiring craniotomy for brain tumor or cerebral aneurysm were studied. After induction with thiopental, anesthesia was maintained with isoflurane and nitrous oxide in oxygen. During controlled ventilation (PaCO2 34 +/- 1 mm Hg); middle cerebral artery blood flow velocity (VMCA), mean arterial blood pressure (MAP), bilateral frontooccipital processed electroencephalogram (EEG), and ICP were measured before and for 10 min after intravenous ketamine 1.0 mg/kg. Cerebral arteriovenous oxygen content difference (AVDO2) and cerebral perfusion pressure (CPP) were calculated. After ketamine, MAP, CPP, PaCO2, and AVDO2 were unchanged. ICP decreased from 16 +/- 1 mm Hg to 14 +/- 1 mm Hg (mean +/- SE; P < 0.001) and VMCA decreased from 44 +/- 4 cm/s to 39 +/- 4 cm/s (P < 0.001). Total EEG power decreased (P < 0.02). These results suggest that ketamine can be used in anesthetized, mechanically ventilated patients with mildly increased ICP without adversely altering cerebral hemodynamics.

Protecting the ischemic spinal cord during aortic clamping. The influence of anesthetics and hypothermia

Infrarenal circumaortic occlusion devices were operatively placed in 74 New Zealand white rabbits. Two days after operation the animals were randomly assigned to one of seven treatment groups: I, control, n = 23; II, halothane, n = 8; III, thiopental, n = 12; IV, ketamine (30 mg/kg intravenously), n = 6; V, halothane+hypothermia, n = 8; VI, thiopental+hypothermia, n = 12; VII, ketamine+hypothermia, n = 5. In each group, the infrarenal aorta was occluded for 21 minutes. Final neurologic recovery after restitution of blood flow was graded as acute paraplegia, delayed paraplegia (neurologic deficit developing after initial recovery), or normal. Halothane alone was of no benefit. Hypothermia with any anesthetic was completely protective and reduced neurologic deficits to 0% compared with 91% in controls (p less than 0.05). Thiopental and ketamine treatment each reduced acute paraplegia to 17% (as compared with 61% in controls) and increased delayed paraplegia from 30% in controls to 75% and 50%, respectively (p less than 0.05 for thiopental, p = 0.10 for ketamine). The authors interpret the increase in delayed deficits and decrease in acute deficits as being the result of partial spinal cord protection. These findings document that this model of spinal cord ischemia is sufficiently sensitive to identify interventional treatments that protect the ischemic spinal cord.

[Comparative hemodynamic effects of midazolam and flunitrazepam in head injury patients under controlled ventilation]

The haemodynamic effects of midazolam were compared with those of flunitrazepam in 10 patients with severe head injury under controlled ventilation. Right atrial pressure, pulmonary pressure, pulmonary capillary wedge pressure and cardiac output were measured using a Swan-Ganz thermodilution catheter. Arterial pressure (Pa) was recorded by radial arterial canulation. All patients in this cross-over study received midazolam (0.15 mg X kg-1) and flunitrazepam (0.02 mg X kg-1) intravenously randomly, with 24 h between the two injections. The measurements were first carried out before and then 5, 10, 20, 30 and 60 min after injection. The only significant variations after midazolam and flunitrazepam were a fall in Pa (from 93 +/- 12 to 81 +/- 11 mmHg for midazolam and from 89 +/- 14 to 78 +/- 20 mmHg for flunitrazepam) and in cardiac index (from 4.80 +/- 1.03 to 4.17 +/- 1.14 l X min-1 X m-2 for midazolam and from 5.18 +/- 1.32 to 4.54 +/- 1.03 l X min-1 X m-2 for flunitrazepam). The small decrease in heart rate was not significant. The cardiovascular changes after midazolam and flunitrazepam were small and similar for both drugs. It seemed that midazolam and flunitrazepam were safe for sedating head injured patients under controlled ventilation.