Fentanyl co-administration decreases the induction dose requirement of propofol in patients with supratentorial tumors and not in patients with spinal lesions

Intracranial Space-occupying Lesion Inducing Intracranial Hypertension Increases the Encephalographic Effects of Isoflurane in a Swine Model

BACKGROUND

Patients with a brain tumor are susceptible to the hypnotic effect of anesthetics depending on the tumor's size. We investigated whether intracranial space-occupying lesions (ICSOLs) inducing intracranial hypertension increase isoflurane's effect on electroencephalographic (EEG) results.

MATERIALS AND METHODS

After anesthetic induction with isoflurane, 11 swine were studied with regard to isoflurane's effect on EEGs at 0.5% to 2.0% inhalational concentration at sequential stages: baseline 1, ICSOL 1, baseline 2, ICSOL 2, baseline 3. At each ICSOL stage, an intracranial epidural balloon catheter was inflated and the intracranial pressure maintained at twice the baseline pressure. The balloon was deflated after each ICSOL stage (baselines 2 and 3). A 95% spectral edge frequency (SEF), which correlates with anesthetic hypnosis, was used to measure isoflurane's effect. Pharmacodynamics was characterized using a sigmoidal inhibitory maximum effect model for the SEF versus end-tidal concentration.

RESULTS

ICSOL shifted the relations between SEF and the effect-site concentration (Ce) downward. Baseline and 50% of the maximum spectral edge effect levels significantly decreased during balloon inflation. The Ce that produced SEF=15 was 1.12 (1.04-1.20) (mean [95% confidence interval])% for baseline 1; 0.92 (0.81-1.03) for ICSOL 1; 1.02 (0.94-1.11) for baseline 2; 0.88 (0.82-0.94) for ICSOL 2; 1.05 (0.93-1.17) for baseline 3. Isoflurane's effect on EEGs increased during balloon inflation, with the alteration tending to recover after balloon deflation.

CONCLUSIONS

ICSOLs inducing intracranial hypertension increase the EEG effect of isoflurane, and external compression from the brain surface enhances the anesthetic hypnosis despite minimum brain injury.

Pharmacokinetics and pharmacodynamics of propofol: changes in patients with frontal brain tumours

Background

Models of propofol pharmacokinetics and pharmacodynamics developed in patients without brain pathology are widely used for target-controlled infusion (TCI) during brain tumour excision operations. The goal of this study was to determine if the presence of a frontal brain tumour influences propofol pharmacokinetics and pharmacodynamics and existing PK-PD model performance.

Methods

Twenty patients with a frontal brain tumour and 20 control patients received a propofol infusion to achieve an induction-emergence-induction anaesthetic sequence. Propofol plasma concentration was measured every 4 min and at each transition of the conscious state. Bispectral index (BIS) values were continuously recorded. We used non-linear mixed-effects modelling to analyse the effects of the presence of a brain tumour on the pharmacokinetics and pharmacodynamics of propofol. Subsequently we calculated the predictive performance of Marsh, Schnider, and Eleveld models in terms of median prediction error (MdPE) and median absolute prediction error (MdAPE).

Results

Patients with brain tumours showed 40% higher propofol clearance than control patients. Performance of the Schnider model (MdPEpk -20.0%, MdAPEpk 23.4%) and Eleveld volunteer model (MdPEpk -8.58%, MdAPEpk 21.6%) were good. The Marsh model performed less well (MdPEpk -14.3%, MdAPEpk 41.4%), as did the Eleveld patient model (MdPEpk -30.8%, MdAPEpk 32.1%).

Conclusions

Brain tumours might alter the pharmacokinetics of propofol. Caution should be exerted when using propofol TCI in patients with frontal brain tumours due to higher clearance.

Trial registry number

NCT01060631.

Determination of the minimum infusion rate of alfaxalone during its co-administration with fentanyl at three different doses by constant rate infusion intravenously in goats

OBJECTIVE

To determine the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement of the extremities in response to standardized noxious stimulation during its co-administration with fentanyl at three different doses by constant rate infusion (CRI) intravenously (IV) in goats.

STUDY DESIGN

Prospective, blinded, randomized crossover, experimental.

ANIMALS

Eight healthy goats; four does and four wethers.

METHODS

For induction of anaesthesia, a bolus of fentanyl was administered at 0.005 mg kg(-1) (LFent), 0.015 mg kg(-1) (MFent) or 0.03 mg kg(-1) (HFent) followed by alfaxalone at 2.0 mg kg(-1) . For maintenance, the goats received alfaxalone at an initial infusion rate of 9.6 mg kg(-1)  hour(-1) and one of three fentanyl treatments: 0.005 mg kg(-1)  hour(-1) (LFent), 0.015 mg kg(-1)  hour(-1) (MFent) or 0.03 mg kg(-1) hour(-1) (HFent). The MIR of alfaxalone was determined during fentanyl CRI by testing for responses to stimulation (clamping on a digit with Vulsellum forceps) every 30 minutes. Some cardiopulmonary parameters were measured.

RESULTS

The alfaxalone MIR median (range) was 6.7 (6.7-8.6), 2.9 (1.0-6.7) and 1.0 (1.0-4.8) mg kg(-1)  hour(-1) during LFent, MFent and HFent, respectively. Alfaxalone MIR was significantly lower during MFENT and HFENT compared to LFENT. Significantly low oxygen haemoglobin saturation (SaO2 ) and arterial oxygen partial pressure (PaO2 ), observed 2 minutes into anaesthesia after all fentanyl treatments, were the most remarkable adverse cardiopulmonary effects observed. Recovery from anaesthesia was severely affected by high doses of fentanyl with excitatory behavioural signs predominant for up to 2 hours post-administration after MFent and HFent.

CONCLUSIONS AND CLINICAL RELEVANCE

Fentanyl reduces alfaxalone MIR in goats in a dose-dependent manner. Immediate oxygen supplementation after induction of general anaesthesia is recommended to prevent hypoxaemia. Doses of fentanyl equal to or greater than 0.015 mg kg(-1)  hour(-1) tend to be associated with severe excitatory behaviour and should be avoided when fentanyl is administered to goats.

Neuroanesthesiology update

We review topics pertinent to the perioperative care of patients with neurological disorders. Our review addresses topics not only in the anesthesiology literature, but also in basic neurosciences, critical care medicine, neurology, neurosurgery, radiology, and internal medicine literature. We include literature published or available online up through December 8, 2013. As our review is not able to include all manuscripts, we focus on recurring themes and unique and pivotal investigations. We address the broad topics of general neuroanesthesia, stroke, traumatic brain injury, anesthetic neurotoxicity, neuroprotection, pharmacology, physiology, and nervous system monitoring.