Propofol Hypnosis Research Articles

Effect-site concentrations of remifentanil causing bradycardia in hypnotic and non-hypnotic patients

Although the induction of anaesthesia with remifentanil often causes bradycardia, the relationship between the effect-site concentration (Ce) of remifentanil and instantaneous heart rate (HR) has remained unclear. The present study examined the relationship between instantaneous HR and remifentanil Ce at the induction of anaesthesia with and without propofol hypnosis, to facilitate safe management of anaesthesia induction with remifentanil. Instantaneous HR was calculated every 5s using an electrocardiographic real-time analysis system (MemCalc/Makin2; GMS, Tokyo, Japan). At the beginning of anaesthesia induction, continuous infusion of remifentanil (1μgmin-1kg-1) preceded hypnosis with propofol in 13 patients [non-hypnosis group; mean age, 67.8 (17.5) years], while propofol bolus (30-50mg) was injected together with continuous remifentanil medication in 18 patients [hypnosis group; mean age, 62.9 (16.5)years]. Remifentanil Ce was estimated every 5s using the three-compartment model proposed by Minto et al. and the relationship between estimated remifentanil Ce and instantaneous HR was examined. In the hypnosis group, HR was significantly lower than basal HR when remifentanil Ce was increased to 3.5ngml-1 (p<0.05), whereas no significant HR reduction was found in the non-hypnosis group until remifentanil Ce reached >5ngml-1 (p<0.05). The induction of anaesthesia using remifentanil with propofol hypnotics significantly reduces HR even in a low remifentanil Ce insufficient to suppress the cardiovascular response at tracheal intubation. Preparations to treat bradycardia are recommended for the safe management of anaesthesia induction when remifentanil is combined with hypnotics.

Bispectral Index Dynamics During Propofol Hypnosis Is Similar in Red-Haired and Dark-Haired Subjects

Bispectral Index Dynamics During Propofol Hypnosis Is Similar in Red-Haired and Dark-Haired Subjects

Disinhibition of Histaminergic Neurons: Lack of Effect on Arousal Switch Following Propofol Hypnosis

Transitions between wake and sleep are a routine and essential part of our lives. The bistable “switch” model of consciousness considers these two mutually exclusive states to be governed by interconnected subcortical nuclei ([Saper et al., 2010][1]). Wake- or sleep-promoting nuclei enforce

Bispectral Index Dynamics During Propofol Hypnosis Is Similar in Red-Haired and Dark-Haired Subjects

We have previously shown that red hair is associated with increased desflurane requirement for immobility, compared with dark hair. The effect of red hair on IV anesthetic requirement remains unknown. We tested the hypothesis that the propofol concentration in the effect site associated with half maximal electroencephalogram response, Ce50, is at least 50% higher in subjects with red hair. We modeled the propofol concentration versus electroencephalogram response relationship using a 2-step approach in 29 healthy dark- and red-haired volunteers receiving a propofol infusion to produce loss of consciousness. Bispectral Index (BIS) was the measure of drug effect. The parameters of a 3-compartment pharmacokinetic model were fit to measured arterial propofol concentrations. The relationship between effect-site propofol concentration (Ce) and BIS was characterized using a sigmoid Emax model. Model performance and accuracy of the estimated parameters were evaluated using accepted metrics and bootstrap resampling. The effect of hair color on the Ce50 for BIS response in the final model was assessed using a threshold of 6.63 (P<0.01) in reduction of -2 log likelihood. The influence of body weight on the model was also assessed. The inclusion of hair color as a model covariate did not improve either the pharmacokinetic or the pharmacodynamic model. A separate analysis for the dark- and red-haired subjects estimated a median (95% confidence interval) Ce50 BIS of 2.71 μg/mL (2.28-3.36 μg/mL) and 2.57 μg/mL (1.68-3.60 μg/mL), respectively. Body weight was a significant covariate for the CL1 and V1. Red hair phenotype does not affect the pharmacokinetics or pharmacodynamics of propofol.

From the Edge of Oblivion

From the Edge of Oblivion

Entropy during propofol hypnosis, including an episode of wakefulness.

Depth of anaesthesia has proved to be a complex process to quantify. Monitors based on bispectral analysis of the electroencephalogram and auditory evoked potential have been available, but only recently has a monitor based on entropy become available. This study determined state entropy and response entropy in nine healthy volunteers during propofol hypnosis with a brief intervening period of wakefulness. Both the calculated entropy indices decreased with increasing levels of sedation (r2 = 0.58 and 0.61, respectively) and they showed a high correlation with each other (r2 = 0.94). However, an overlap was observed in real time indices between different stages of the Observer's Assessment of Alertness/Sedation Scale. Only three of the nine volunteers had explicit memories from the episode of wakefulness. Electroencephalographic entropy monitors seem to have potential for staging clinical hypnotic effects.

The effect of a dissociative dose of ketamine on the bispectral index (BIS) during propofol hypnosis

Study Objective: To compare the effect of a standardized stimulus during propofol-only hypnosis on the bispectral index (BIS) value with the effect of the injection of local anesthesia for surgery during ketamine plus propofol hypnosis (dissociative monitored anesthesia care). To determine whether ketamine increases the level of propofol hypnosis when used in dissociative doses. Design: Descriptive case study. Setting: Private practice office plastic surgery suites. Patients: 30 nonpremedicated ASA physical status I and II adult female (23) and male (7) patients scheduled for elective cosmetic surgery. Interventions: Hypnosis was induced via slow (60 to 80 drops [gtts]/min), dilute (5 mg/ml) propofol solution. Hypnosis was induced using the BIS monitor as an adjunct to traditional vital signs and verbal contact. Patients were engaged in conversation and note was taken of the BIS value when verbal contact was lost and when BIS appeared to stabilize (BIS 1). A standardized stimulus (0.3 ml 1% lidocaine plain via 30-gauge needle) was applied to the area of the supraorbital nerve. Note was taken of the highest BIS value (BIS 2) in the patient response. The BIS returned to baseline hypnosis (BIS 1) and a 50-mg dissociative dose (independent of body weight) of ketamine was administered. Two minutes were allowed to elapse and then the surgeon was allowed to inject the local anesthesia for the proposed surgery. Note was taken of the BIS value (BIS 3) in response to the surgeon’s injection. Measurements and Main Results: The average delta (BIS 2 − BIS 1) was 9.5 ± 6.9. Patients did not move in response to the surgeon’s injection: BIS 3 = BIS 1. When movement occurred, the injection was terminated and additional ketamine was given before resuming the injection. Sixteen patients received ketamine 50 mg, 12 received ketamine 100 mg, one received ketamine 150 mg, and one received ketamine 200 mg. Men required an average 19% less propofol than women in this group. Conclusion: This study demonstrated a positive BIS response to a standardized local anesthetic stimulus during propofol-only hypnosis and a zero response during ketamine plus propofol hypnosis (dissociative anesthesia). Ketamine administered in dissociative doses does not deepen the level of propofol hypnosis. Hypnosis alone does not imply general anesthesia. Patients move in response to inadequate local anesthesia. Because the ketamine analgesia is only transitory and the primary analgesia is not given intravenously, propofol-ketamine technique is not a total intravenous anesthetic technique (TIVA). Instead, propofol-ketamine technique may be classified as a form of monitored anesthesia care (MAC).