Comparison of propofol pharmacokinetic and pharmacodynamic models for awake craniotomy: A prospective observational study

Comparing two airway management strategies for moderately sedated patients undergoing awake craniotomy: A single-blinded randomized controlled trial

BACKGROUND

In the monitored anesthesia care (MAC) setting for awake craniotomy (AC), maintaining airway patency in sedated patients remains challenging. This randomized controlled trial aimed to compare the validity of the below-epiglottis transnasal tube insertion (the tip of the tube placed between the epiglottis and vocal cords) and the nasopharyngeal airway (simulated by the above-epiglottis transnasal tube with the tip of the tube placed between the epiglottis and the free edge of the soft palate) with respect to maintaining upper airway patency for moderately sedated patients undergoing AC.

METHODS

Sixty patients scheduled for elective AC were randomized to receive below-epiglottis (n = 30) or above-epiglottis (n = 30) transnasal tube insertion before surgery. Moderate sedation was maintained in the pre- and post-awake phases. The primary outcome was the upper airway obstruction (UAO) remission rate (relieved obstructions after tube insertion/the total number of obstructions before tube insertion).

RESULTS

The UAO remission rate was higher in the below-epiglottis group [100% (12/12) vs 45% (5/11); P = .005]. The tidal volume values monitored through the tube were greater in the below-epiglottis group during the pre-awake phase (P < .001). End-tidal carbon dioxide (EtCO₂ ) monitored through the tube was higher in the below-epiglottis group at bone flap removal (P < .001). During the awake phase, patients' ability to speak was not impeded. No patient had serious complications related to the tube.

CONCLUSION

The below-epiglottis tube insertion is a more effective method to maintain upper airway patency than the nasopharyngeal airway for moderately sedated patients undergoing AC.

Supraglottic devices for airway management in awake craniotomy

Awake craniotomy is a unique technique utilized for mapping neuro and motor function during neurosurgical procedures close to eloquent brain tissue. Since active communication is required only during surgical manipulation of eloquent brain tissue and the patient is "sedated" during other parts of the procedure, different methods for anesthesia management have been explored. Furthermore, airway management ranges from spontaneous breathing to oro or nasotracheal intubation. Case reports have described the use of laryngeal masks (LMs) previously; however, its safety compared to tracheal intubation has not been assessed.We conducted a retrospective analysis of 30 patients that underwent awake craniotomy for tumor surgery to compare the feasibility and safety of different airway management strategies. Nasal fiberoptic intubation (FOI) was performed in 21 patients while 9 patients received LM for airway management. Ventilation, critical events, and perioperative complications were evaluated.Cannot intubate situation occurred in 4 cases reinserting the tube after awake phase, while no difficulties were described reinserting the LM (P < .0001). Furthermore, duration of mechanical ventilation after tumor removal was significantly lower in the LM group compared to FOI group (62 ± 24 vs. 339 ± 82 [min] mean ± sem, P < .0001). Postoperatively, 2 patients in each group were diagnosed with and treated for respiratory complications including pneumonia, without statistical significance between groups.In summary, LM is a feasible airway management method for patients undergoing awake craniotomy, resulting in reduced ventilation duration compared to FOI procedure.

The number and kind of antiepileptics affect propofol dose requirement for anesthesia: observational study

The propofol dose requirement and the emergence time are affected by antiepileptic use. The effects on anesthesia of the number and kind of antiepileptic agents have not been reported. We investigated the relationship between the kind and number of antiepileptic agents and the propofol dose requirement for anesthesia and emergence time in intravenous general anesthesia for dental treatment for patients with neurological disorders. We studied 247 patients with neurological disorders who underwent dental treatment under intravenous general anesthesia. Patients were categorized according to the number of antiepileptics (none, single agent, two kinds, and three or more kinds of antiepileptics) and the kind of antiepileptic (carbamazepine, valproate, phenobarbital, phenytoin, zonisamide, clobazam, or topiramate) being received. The propofol dose requirement for anesthesia, emergence time, and predicted blood propofol concentration at emergence were evaluated. Patients on three or more kinds of antiepileptics had significantly lower propofol dose requirement (reduction in 25%, compare with no use) and predicted blood propofol concentration at emergence (reduction in 41%) and significantly longer emergence time (extension in 50%) (P < 0.05). Valproate and clobazam reduced the propofol dose (valproate 9% and clobazam 19%) and predicted blood propofol concentration at emergence (valproate 18% and clobazam 33%), while phenobarbital increased these parameters (30% and 125%) (P < 0.05). The number and kind of antiepileptics effects propofol dose requirement. In particular, valproate and clobazam reduce the propofol dose requirement, while phenobarbital increases this.Clinical trial registration UMIN No. UMIN000014179.

Possible neurotoxicity of the anesthetic propofol: evidence for the inhibition of complex II of the respiratory chain in area CA3 of rat hippocampal slices

Propofol is the most frequently used intravenous anesthetic for induction and maintenance of anesthesia. Propofol acts first and formost as a GABA_A-agonist, but effects on other neuronal receptors and voltage-gated ion channels have been described. Besides its direct effect on neurotransmission, propofol-dependent impairment of mitochondrial function in neurons has been suggested to be responsible for neurotoxicity and postoperative brain dysfunction. To clarify the potential neurotoxic effect in more detail, we investigated the effects of propofol on neuronal energy metabolism of hippocampal slices of the stratum pyramidale of area CA3 at different activity states. We combined oxygen-measurements, electrophysiology and flavin adenine dinucleotide (FAD)-imaging with computational modeling to uncover molecular targets in mitochondrial energy metabolism that are directly inhibited by propofol. We found that high concentrations of propofol (100 µM) significantly decrease population spikes, paired pulse ratio, the cerebral metabolic rate of oxygen consumption (CMRO₂), frequency and power of gamma oscillations and increase FAD-oxidation. Model-based simulation of mitochondrial FAD redox state at inhibition of different respiratory chain (RC) complexes and the pyruvate-dehydrogenase show that the alterations in FAD-autofluorescence during propofol administration can be explained with a strong direct inhibition of the complex II (cxII) of the RC. While this inhibition may not affect ATP availability under normal conditions, it may have an impact at high energy demand. Our data support the notion that propofol may lead to neurotoxicity and neuronal dysfunction by directly affecting the energy metabolism in neurons.

Xenon anesthesia for awake craniotomy: safety and efficacy

BACKGROUND

The asleep-awake-asleep (AAA) craniotomy is a technique that offers the opportunity of having a patient fully cooperative during the awake phase, and minimizes the possible discomfort, due to the asleep phase. The aim of this prospective observational study was to test the use of xenon in the first asleep phase of an AAA craniotomy, in patients undergoing craniotomy for brain tumor resection.

METHODS

The data have been collected from 40 awake craniotomy procedures, performed in patients with cerebral tumor, treated with the AAA technique. Patients were treated with xenon during the asleep phase, and quality of mapping, complications and qualitative judgment of the experience given by the patients were recorded.

RESULTS

The mapping was carried out as planned in 37 out of 40 cases. The doses of xenon administered during the first asleep phase of the anesthesia was 13±2 L. Time for awakening after xenon was switched off was 5±1 minute. A combination of xenon and regional anesthesia (with no need for additional systemic anesthetics) was adequate to accomplish craniotomy in 27/40 patients (67.5%). On the day after the operation, 37 patients recalled the testing procedure for mapping during the awake period, none had recollection of local anesthetic injections for regional anesthesia or sound associated with the neurosurgical drill. Five patients (12.5%) reported mild pain during tumor removal (VAS Score less than three).

CONCLUSIONS

In this case series, xenon anesthesia was successfully used for the sedative phase of an awake craniotomy accomplished with an AAA approach.

Comparison of the Effects of Dexmedetomidine on the Induction of Anaesthesia Using Marsh and Schnider Pharmacokinetic Models of Propofol Target-Controlled Infusion

Background

The study aimed to determine the effects of dexmedetomidine on the induction of anaesthesia using different models (Marsh and Schnider) of propofol target-controlled infusion (TCI).

Methods

Sixty-four patients aged 18-60 years, American Society of Anaesthesiologists (ASA) class I-II who underwent elective surgery were randomised to a Marsh group (n = 32) or Schnider group (n = 32). All the patients received a 1 μg/kg loading dose of dexmedetomidine, followed by TCI anaesthesia with remifentanil at 2 ng/mL. After the effect-site concentration (Ce) of remifentanil reached 2 ng/mL, propofol TCI induction was started. Anaesthesia induction commenced in the Marsh group at a target plasma concentration (Cpt) of 2 μg/mL, whereas it started in the Schnider group at a target effect-site concentration (Cet) of 2 μg/mL. If induction was delayed after 3 min, the target concentration (Ct) was gradually increased to 0.5 μg/mL every 30 sec until successful induction. The Ct at successful induction, induction time, Ce at successful induction and haemodynamic parameters were recorded.

Results

The Ct for successful induction in the Schnider group was significantly lower than in the Marsh group (3.48 [0.90] versus 4.02 [0.67] μg/mL; P = 0.01). The induction time was also shorter in the Schnider group as compared with the Marsh group (134.96 [50.91] versus 161.59 [39.64]) sec; P = 0.02). There were no significant differences in haemodynamic parameters and Ce at successful induction.

Conclusion

In the between-group comparison, dexmedetomidine reduced the Ct requirement for induction and shortened the induction time in the Schnider group. The inclusion of baseline groups without dexmedetomidine in a four-arm comparison of the two models would enhance the validity of the findings.

Propofol-induced mitochondrial and contractile dysfunction of the rat ventricular myocardium

Propofol is a short-acting hypnotic agent used in human medicine for sedation and general anesthesia. Its administration can be associated with serious cardiovascular side-effects that include decrease in arterial blood pressure and cardiac output. The aim of the present study was to evaluate propofol effects on mitochondrial respiration, myocardial contractility and electrophysiology in the same samples isolated from the heart ventricles of adult rats. Mitochondrial oxygen consumption was measured in permeabilized samples dissected from free walls of both ventricles using high-resolution respirometry. State LEAK was determined with malate and glutamate. Active respiration was induced by ADP (state PI) and further by succinate, a Complex II substrate (PI+II). Rotenone was injected to measure state PII. Antimycin A, a Complex III inhibitor was used to determine residual oxygen consumption (ROX). N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride and ascorbate were injected simultaneously for respirometric assay of cytochrome c oxidase activity (CIV). Isometric contractions and membrane potentials were determined on multicellular preparations isolated from right and left ventricles. Propofol concentrations used ranged from 0.005 to 0.5 mmol/l. All respiratory parameters were significantly higher in the left control ventricles compared to the right ones. Propofol significantly decreased Complex I activity at concentration 0.025 mmol/l and papillary muscle contraction force at 0.1 mmol/l. Propofol did not affect action potential duration at any concentration studied. Our study suggests that mechanisms contributing to the impaired myocardial contraction during propofol anesthesia might include also mitochondrial dysfunction manifested by compromised activity of the respiratory Complex I.