A randomized controlled trial of the effect of preoperative dexmedetomidine on the half maximal effective concentration of propofol for successful i-gel insertion without muscle relaxants

The EC50 of propofol with different doses of dexmedetomidine during gastrointestinal endoscopy: A double-blind, placebo-controlled trial

PURPOSE

The goal of this study was to evaluate the dose-response relationship between dexmedetomidine and propofol in sedating patients and to determine the optimal dosage of dexmedetomidine during gastrointestinal endoscopy.

METHODS

One hundred fifty patients were divided into 5 groups, each receiving a loading dose of dexmedetomidine (0.4, 0.6, 0.8, 1.0 µg/kg) or saline, with propofol for sedation. The median effective concentration (EC50) of propofol was calculated using the modified Dixon up-and-down approach. Adverse effects, vital signs, procedure, and recovery times were recorded.

RESULTS

The EC50 of propofol in groups NS, D0.4, D0.6, D0.8, and D1.0 were 3.02, 2.44, 1.97, 1.85, and 1.83 µg/mL, respectively. Heart rate in the dexmedetomidine groups decreased more than the NS group (P < .001). The mean arterial pressure (MAP) in the NS group experienced a decline compared to groups D0.8 and D1.0 when the plasma concentration and effect-site concentration reached equilibrium. Additionally, the respiratory rate was found to be lower in groups NS, D0.4, D0.6, and D0.8 (P < .05). Recovery time in groups D0.8 and D1.0 was longer than the NS group (P < .05). Bruggemann comfort scales score was higher in group D1.0 (P < .05). No significant difference was found in the incidences of hypotension and bradycardia, and the dose of ephedrine and atropine. Respiratory depression was significantly reduced in groups D0.8 and D1.0 compared to the NS group.

CONCLUSION

A single dose of 0.6 to 0.8 µg/kg of dexmedetomidine should be recommended in combination with propofol for gastrointestinal endoscopy. And the EC50 of propofol is 1.97 to 1.85 µg/mL.

Dexmedetomidine decreases the 50% effective dose (ED50) of intravenous propofol required to prevent tracheal intubation response in Beagles

OBJECTIVE

To determine the 50% effective dose (ED50) of intravenous propofol required for successfully preventing tracheal intubation response in Beagles co-induced with dexmedetomidine.

ANIMALS

36 adult male Beagles.

PROCEDURES

The dogs were randomly assigned to either group D1, group D2, or group C (received 1 µg/kg, 2 µg/kg dexmedetomidine intravenously, or the same amount of normal saline as dexmedetomidine, 10 mL). The first dog in each group received 6 mg/kg of propofol for induction. The pump speed of propofol was 600 mL/h. The dosage varied with increments or decrements of 0.5 mg/kg based on the Dixon up-and-down method. The duration of eye-opening after propofol administration was recorded. Changes in heart rate (HR) and respiratory rate (RR) were recorded at 5 timepoints: after entering the operation room and prior to propofol administration (T1), 1 and 3 min after propofol administration (T2 and T3), 3 and 5 min after intubation (T4 and T5).

RESULTS

The required ED50 of propofol that prevented tracheal intubation response in D1, D2, and C groups were 6.4 mg/kg (95% CI, 6.1 to 6.7 mg/kg), 5.8 mg/kg (95% CI, 5.67 to 6 mg/kg), and 8.3 mg/kg (95% CI, 8 to 8.5 mg/kg), respectively. The recovery time of group D2 was significantly longer than that of groups D1 and C (P < .05). The differences in HR among the 3 groups were significant from T2 up to T5 timepoint (P < .05). The differences in RR among the 3 groups were significant at T2 and T3 timepoints (P < .05).

CLINICAL RELEVANCE

Dexmedetomidine pre-injection reduces the amount of propofol required for endotracheal intubation response in Beagles, thereby reducing the respiratory inhibition induced by propofol.

Comparison of sedation between dexmedetomidine and propofol during transesophageal echocardiography: A randomized controlled trial

Background:

This study aimed to compare sedation characteristics of dexmedetomidine (Dex) and propofol during transesophageal echocardiography (TEE) in cardiac patients.

Methods:

This clinical trial was conducted on 65 cardiac patients, who underwent TEE in a referral heart hospital. The patients were randomly divided into two groups: Dex (n = 34) and propofol (n = 31). The depth of sedation in the patients was assessed at 5-min intervals until the end of the TEE examination. The patient, physicians’ satisfaction was recorded. Furthermore, blood pressure, heart and respiratory rates, peripheral oxygen saturation, and the bispectral index (BIS) of the patients were measured. The occurrence of apnea, hypotension or bradycardia was documented.

Results:

Demographic variables were similar in both groups. Time from the beginning of sedation to the start of TEE was significantly longer in the Dex group (P = 0.01). Duration of the TEE examination was not different between the two groups. Interestingly, the recovery time was shorter in the Dex group than in the propofol group. There were no significant differences regarding patient and physician satisfaction with sedation quality. Hemodynamic profile was mainly similar in both groups. There was a significantly lower BIS level in the Dex group. There was no significant difference in the incidence of apnea or hypotension between the groups.

Conclusions:

Time from the beginning of sedation with Dex was longer than that with propofol. However, Dex was able to provide satisfactory sedation levels, hemodynamic stability, short recovery time, and acceptable patient and practitioner satisfaction during TEE in our cardiac patients.

Comparative evaluation of i-gel® insertion conditions using dexmedetomidine-propofol versus fentanyl-propofol - A randomised double-blind study

Background and Aims:

i-gel^® insertion necessitates adequate depth of anaesthesia to prevent laryngospasm, gagging or limb movements. We aimed to compare i-gel^® insertion conditions with propofol induction after pre-treatment with dexmedetomidine or fentanyl.

Methods:

Eighty ASAI/II patients undergoing general anaesthesia were randomised into Groups D (n = 40) and F (n = 40). Group D received 1 μg/kg dexmedetomidine over 10 minutes followed by 5ml of 0.9%normal saline (NS) over 2 minutes. Group F received 10 ml of 0.9%NS over 10 minutes followed by fentanyl 1 μg/kg over 2 minutes. Thirty seconds after study drugs, propofol 2 mg/kg was given. Ninety seconds after propofol, i-gel^® was inserted. Overall insertion conditions were assessed by Modified Scheme of Lund and Stovener. Heart-rate (HR) and mean arterial pressure (MAP) were noted at baseline, after study drug, propofol induction and 1,3,5,10 minutes after i-gel^® insertion. Respiratory rate and apnoea times were recorded.

Results:

Insertion conditions were comparable between both groups. Moderately relaxed jaw, coughing and movement was observed in more patients of Group F. Incidence of apnoea was significantly higher (P < 0.0001) in group F (18/40) than group D (3/40).Mean duration of apnoea in group F (284.5 ± 11.19 sec) was significantly higher than group D (217.17 ± 16.48 sec). Percentage drop in MAP from baseline after propofol was more in group F (10.3%) than group D (5.6%). MAP after induction was significantly lower in group F compared to group D (P = 0.002), but similar after i-gel^® insertion, 1,3,5 and 10 minutes after insertion. After propofol (P = 0.003) and i-gel^® insertion (P < 0.001), HR was significantly lower with dexmedetomidine.

Conclusion:

Dexmedetomidine and fentanyl provide comparable conditions for i-gel^® insertion with propofol.

Pharmacodynamic Interaction of Remifentanil and Dexmedetomidine on Depth of Sedation and Tolerance of Laryngoscopy

BACKGROUND

Dexmedetomidine is a sedative with modest analgesic efficacy, whereas remifentanil is an opioid analgesic with modest sedative potency. Synergy is often observed when sedative-hypnotics are combined with opioid analgesics in anesthetic practice. A three-phase crossover trial was conducted to study the pharmacodynamic interaction between remifentanil and dexmedetomidine.

METHODS

After institutional review board approval, 30 age- and sex- stratified healthy volunteers were studied. The subjects received consecutive stepwise increasing target-controlled infusions of dexmedetomidine, remifentanil, and remifentanil with a fixed dexmedetomidine background concentration. Drug effects were measured using binary (yes or no) endpoints: no response to calling the subject by name, tolerance of shaking the patient while shouting the name ("shake and shout"), tolerance of deep trapezius squeeze, and tolerance of laryngoscopy. The drug effect was measured using the electroencephalogram-derived "Patient State Index." Pharmacokinetic-pharmacodynamic modeling related the administered dexmedetomidine and remifentanil concentration to these observed effects.

RESULTS

The binary endpoints were correlated with dexmedetomidine concentrations, with increasing concentrations required for increasing stimulus intensity. Estimated model parameters for the dexmedetomidine EC50 were 2.1 [90% CI, 1.6 to 2.8], 9.2 [6.8 to 13], 24 [16 to 35], and 35 [23 to 56] ng/ml, respectively. Age was inversely correlated with dexmedetomidine EC50 for all four stimuli. Adding remifentanil did not increase the probability of tolerance of any of the stimuli. The cerebral drug effect as measured by the Patient State Index was best described by the Hierarchical interaction model with an estimated dexmedetomidine EC50 of 0.49 [0.20 to 0.99] ng/ml and remifentanil EC50 of 1.6 [0.87 to 2.7] ng/ml.

CONCLUSIONS

Low dexmedetomidine concentrations (EC50 of 0.49 ng/ml) are required to induce sedation as measured by the Patient State Index. Sensitivity to dexmedetomidine increases with age. Despite falling asleep, the majority of subjects remained arousable by calling the subject's name, "shake and shout," or a trapezius squeeze, even when reaching supraclinical concentrations. Adding remifentanil does not alter the likelihood of response to graded stimuli.

Clinical Pharmacokinetics and Pharmacodynamics of Propofol

Propofol is an intravenous hypnotic drug that is used for induction and maintenance of sedation and general anaesthesia. It exerts its effects through potentiation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) at the GABAA receptor, and has gained widespread use due to its favourable drug effect profile. The main adverse effects are disturbances in cardiopulmonary physiology. Due to its narrow therapeutic margin, propofol should only be administered by practitioners trained and experienced in providing general anaesthesia. Many pharmacokinetic (PK) and pharmacodynamic (PD) models for propofol exist. Some are used to inform drug dosing guidelines, and some are also implemented in so-called target-controlled infusion devices, to calculate the infusion rates required for user-defined target plasma or effect-site concentrations. Most of the models were designed for use in a specific and well-defined patient category. However, models applicable in a more general population have recently been developed and published. The most recent example is the general purpose propofol model developed by Eleveld and colleagues. Retrospective predictive performance evaluations show that this model performs as well as, or even better than, PK models developed for specific populations, such as adults, children or the obese; however, prospective evaluation of the model is still required. Propofol undergoes extensive PK and PD interactions with both other hypnotic drugs and opioids. PD interactions are the most clinically significant, and, with other hypnotics, tend to be additive, whereas interactions with opioids tend to be highly synergistic. Response surface modelling provides a tool to gain understanding and explore these complex interactions. Visual displays illustrating the effect of these interactions in real time can aid clinicians in optimal drug dosing while minimizing adverse effects. In this review, we provide an overview of the PK and PD of propofol in order to refresh readers' knowledge of its clinical applications, while discussing the main avenues of research where significant recent advances have been made.

Clinical Pharmacokinetics and Pharmacodynamics of Dexmedetomidine

Dexmedetomidine is an α₂-adrenoceptor agonist with sedative, anxiolytic, sympatholytic, and analgesic-sparing effects, and minimal depression of respiratory function. It is potent and highly selective for α₂-receptors with an α₂:α₁ ratio of 1620:1. Hemodynamic effects, which include transient hypertension, bradycardia, and hypotension, result from the drug’s peripheral vasoconstrictive and sympatholytic properties. Dexmedetomidine exerts its hypnotic action through activation of central pre- and postsynaptic α₂-receptors in the locus coeruleus, thereby inducting a state of unconsciousness similar to natural sleep, with the unique aspect that patients remain easily rousable and cooperative. Dexmedetomidine is rapidly distributed and is mainly hepatically metabolized into inactive metabolites by glucuronidation and hydroxylation. A high inter-individual variability in dexmedetomidine pharmacokinetics has been described, especially in the intensive care unit population. In recent years, multiple pharmacokinetic non-compartmental analyses as well as population pharmacokinetic studies have been performed. Body size, hepatic impairment, and presumably plasma albumin and cardiac output have a significant impact on dexmedetomidine pharmacokinetics. Results regarding other covariates remain inconclusive and warrant further research. Although initially approved for intravenous use for up to 24 h in the adult intensive care unit population only, applications of dexmedetomidine in clinical practice have been widened over the past few years. Procedural sedation with dexmedetomidine was additionally approved by the US Food and Drug Administration in 2003 and dexmedetomidine has appeared useful in multiple off-label applications such as pediatric sedation, intranasal or buccal administration, and use as an adjuvant to local analgesia techniques.

The effect of dexmedetomidine pretreatment on the median effective bolus dose of propofol for facilitating laryngeal mask airway insertion

BACKGROUND

We designed this study to investigate the effect of dexmedetomidine (1 μg/kg) pretreatment on the median effective dose (ED50) of propofol for facilitating successful laryngeal mask airway (LMA) insertion compared to propofol alone.

METHODS

Forty patients were randomized to either the control group (n = 21) or the dexmedetomidine group (n = 19). After infusion of normal saline or dexmedetomidine 1 µg/kg over 10 min, 1 % lidocaine 0.5 mg/kg, followed by propofol 2.5 mg/kg was administered and the laryngeal mask airway was inserted without muscle relaxants. The ED50 of propofol for successful LMA insertion was determined by the modified Dixon's up-and-down method. The ED50 and ED95 were also calculated using an isotonic regression method, based on the pooled adjacent-violators algorithm-adjusted response rate, and the confidential interval (CI) was estimated using a bootstrap approach.

RESULTS

The ED50 of propofol for smooth insertion of the LMA was significantly higher in the control group than in the dexmedetomidine group (3.1 ± 0.4 vs 1.9 ± 0.3 mg/kg, P < 0.001). From isotonic regression analysis using a bootstrap approach, the ED50 and ED95 of propofol was 2.9 mg/kg (83 % CI 2.5-3.3 mg/kg) and 3.9 mg/kg (95 % CI 3.5-4.0 mg/kg) in the control group, and 1.8 mg/kg (83 % CI 1.8-2.1 mg/kg) and 2.4 mg/kg (95 % CI 2.0-2.5 mg/kg) in the dexmedetomidine groups, respectively. The apnea time was not significantly different between the two groups.

CONCLUSIONS

Pretreatment with dexmedetomidine 1 μg/kg could reduce the propofol requirement by 38 % for facilitating LMA insertion without prolonged respiratory depression and hemodynamic instability.

Male patients require higher optimal effect-site concentrations of propofol during i-gel insertion with dexmedetomidine 0.5 μg/kg

BACKGROUND

The pharmacokinetics and pharmacodynamics of an anesthetic drug may be influenced by gender. The purpose of this study was to compare effect-site half maximal effective concentrations (EC50) of propofol in male and female patients during i-gel insertion with dexmedetomidine 0.5 μg/kg without muscle relaxants.

METHODS

Forty patients, aged 20-46 years of ASA physical status I or II, were allocated to one of two groups by gender (20 patients per group). After the infusion of dexmedetomidine 0.5 μg/kg over 2 min, anesthesia was induced with a pre-determined effect-site concentration of propofol by target controlled infusion. Effect-site EC50 values of propofol for successful i-gel insertion were determined using the modified Dixon's up-and-down method.

RESULTS

Mean effect-site EC50 ± SD of propofol for successful i-gel insertion was significantly higher for men than women (5.46 ± 0.26 μg/ml vs. 3.82 ± 0.34 μg/ml, p < 0.01). The EC50 of propofol in men was approximately 40% higher than in women. Using isotonic regression with a bootstrapping approach, the estimated EC50 (95% confidence interval) of propofol was also higher in men [5.32 (4.45-6.20) μg/ml vs. 3.75 (3.05-4.43) μg/ml]. The estimated EC95 (95% confidence interval) of propofol in men and women were 5.93 (4.72-6.88) μg/ml and 4.52 (3.02-5.70) μg/ml, respectively.

CONCLUSIONS

During i-gel insertion with dexmedetomidine 0.5 μg/kg without muscle relaxant, male patients had higher effect-site EC50 for propofol using Schnider's model. Based on the results of this study, patient gender should be considered when determining the optimal dose of propofol during supraglottic airway insertion.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02268656. Registered August 26, 2014.