Midazolam enhances the analgesic properties of dexmedetomidine in the rat

Evaluating the Physiologic Effects of Alfaxalone, Dexmedetomidine, and Midazolam Combinations in Common Blue-Tongued Skinks (Tiliqua scincoides)

Common blue-tongued skinks (Tiliqua scincoides) are popular pet reptiles; however, there has been limited research to investigate sedatives for this species. The purpose of this study was to measure the physiologic effects of four combinations of alfaxalone, dexmedetomidine, and midazolam for minor procedures such as intubation and blood collection. Eleven common blue-tongued skinks (Tiliqua scincoides) were used for this prospective, randomized cross-over study. The subcutaneous combinations were used as follows: 20 mg/kg alfaxalone (A); 10 mg/kg alfaxalone and 1 mg/kg midazolam (AM); 0.1 mg/kg dexmedetomidine and 1 mg/kg midazolam (DM); and 5 mg/kg alfaxalone, 0.05 mg/kg dexmedetomidine, and 0.5 mg/kg midazolam (ADM). Heart rate, respiratory rate, palpebral reflex, righting reflex, escape reflex, toe pinch withdrawal reflex, tongue flicking, and the possibility of intubation were recorded at baseline and every 5 min for 60 min. Venous blood gases were measured at baseline, full sedation, and recovery. Heart and respiratory rates decreased significantly in all groups, but the reductions were most prominent in DM and ADM. Analgesic effects, as measured by the toe pinch withdrawal reflex, were only observed in DM and ADM. Intubation was possible in all four protocols; however, it was not possible in two DM skinks. Based on these trials, ADM and AM are recommended for minor procedures in blue-tongue skinks.

Dexmedetomidine as a Short-Use Analgesia for the Immature Nervous System

Pain management in neonates continues to be a challenge. Diverse therapies are available that cause loss of pain sensitivity. However, because of side effects, the search for better options remains open. Dexmedetomidine is a promising drug; it has shown high efficacy with a good safety profile in sedation and analgesia in the immature nervous system. Though dexmedetomidine is already in use for pain control in neonates (including premature neonates) and infants as an adjunct to other anesthetics, the question remains whether it affects the neuronal activity patterning that is critical for development of the immature nervous system. In this study, using the neonatal rat as a model, the pharmacodynamic effects of dexmedetomidine on the nervous and cardiorespiratory systems were studied. Our results showed that dexmedetomidine has pronounced analgesic effects in the neonatal rat pups, and also weakly modified both the immature network patterns of cortical and hippocampal activity and the physiology of sleep cycles. Though the respiration and heart rates were slightly reduced after dexmedetomidine administration, it might be considered as the preferential independent short-term therapy for pain management in the immature and developing brain.

Treatment of Pain in Rats, Mice, and Prairie Dogs

Recent myomorph and scuiromorph rodent analgesia studies are reviewed and evaluated for potential clinical application. Differences between laboratory animal studies and clinical use in diseased animals are discussed. Analgesia classes reviewed include local anesthetics, nonsteroidal anti-inflammatories, acetaminophen, opioids, and adjuvants such as anticonvulsants. Routes of administration including sustained-release mechanisms are discussed, as are reversal agents. Drug interactions are reviewed in the context of beneficial multimodal analgesia as well as potential adverse effects. Dosage recommendations for clinical patients are explored.

Comparison of two injectable anaesthetic protocols in Egyptian fruit bats (Rousettus aegyptiacus) undergoing gonadectomy

Egyptian fruit bats have gained increasing interest being a natural reservoir for emerging zoonotic viruses. Anaesthesia is often required to allow safe handling of bats. We aimed to compare the sedative and cardiopulmonary effects of two balanced anaesthetic protocols in bats undergoing gonadectomy. Group DK (n = 10) received intramuscular dexmedetomidine (40 µg/kg) and ketamine (7 mg/kg), whereas group DBM (n = 10) received intramuscular dexmedetomidine (40 µg/kg), butorphanol (0.3 mg/kg) and midazolam (0.3 mg/kg). Induction time and cardiopulmonary parameters were recorded. If anaesthetic plan was inadequate, isoflurane was titrated-to-effect. At the end of surgery venous blood gas analysis was performed and atipamezole or atipamezole-flumazenil was administered for timed and scored recovery. In DBM group heart rate and peripheral oxygen saturation were significantly higher (p = 0.001; p = 0.003 respectively), while respiratory rate was significantly lower (p = 0.001). All bats required isoflurane supplementation with no significant differences between groups. Induction and recovery times showed no significant differences. In group DK a better recovery was scored (p = 0.034). Sodium and chloride were significantly higher in DBM group (p = 0.001; p = 0.002 respectively). Both anaesthetic protocols were comparable and can be recommended for minor procedures in bats.

Using intranasal dexmedetomidine with buccal midazolam for magnetic resonance imaging sedation in children: A single-arm prospective interventional study

OBJECTIVE

Although numerous intravenous sedative regimens have been documented, the ideal non-parenteral sedation regimen for magnetic resonance imaging (MRI) has not been determined. This prospective, interventional study aimed to investigate the efficacy and safety of buccal midazolam in combination with intranasal dexmedetomidine in children undergoing MRI.

METHODS

Children between 1 month and 10 years old requiring sedation for MRI examination were recruited to receive buccal midazolam 0.2 mg⋅kg^-1 with intranasal dexmedetomidine 3 μg⋅kg^-1. The primary outcome was successful sedation following the administration of the initial sedation regimens and the completion of the MRI examination.

RESULTS

Sedation with dexmedetomidine-midazolam was administered to 530 children. The successful sedation rate was 95.3% (95% confidence interval: 93.5-97.1%) with the initial sedation regimens and 97.7% (95% confidence interval: 96.5-99%) with a rescue dose of 2 μg⋅kg^-1 intranasal dexmedetomidine. The median sedation onset time was 10 min, and a significant rising trend was observed in the onset time concerning age (R = 0.2491, P < 0.001). The wake-up and discharge times significantly correlated with the duration of the procedure (R = 0.323, P < 0.001 vs. R = 0.325, P < 0.001). No oxygen deficiency nor medication intervention due to cardiovascular instability was observed in any of the patients. History of a prior failed sedation was considered a statistically significant risk factor for failed sedation in the multivariate logistic regression model [odds ratio = 4.71 (95% confidence interval: 1.24-17.9), P = 0.023].

CONCLUSION

In MRI examinations, the addition of buccal midazolam to intranasal dexmedetomidine is associated with a high success rate and a good safety profile. This non-parenteral sedation regimen can be a feasible and convenient option for short-duration MRI in children between 1 month and 10 years.

Sedation and Anesthesia in Rodents

Sedation and anesthesia in rodent species are complex due to their wide species variation, small size, and metabolism. This review article covers recent advances in sedation and anesthesia as well as an updated drug formulary for sedation protocols. Setup, equipment, monitoring, maintenance, and recovery are reviewed as well as species-specific anatomy.

ANESTHETIC EFFECT OF DEXMEDETOMIDINE-KETAMINEMIDAZOLAM COMBINATION ADMINISTERED INTRAMUSCULARLY TO ZOO-HOUSED NAKED MOLE-RATS (HETEROCEPHALUS GLABER)

In this study, adult intact male and female (n = 10) naked mole-rats (Heterocephalus glaber) were anesthetized using a combination of dexmedetomidine (0.06 mg/kg intramuscularly [IM]), ketamine (20 mg/kg IM), and midazolam (1.0 mg/kg IM). Atipamezole (1.0 mg/kg IM) and flumazenil (0.1 mg/kg IM) were administered 40 min after induction. Induction and recovery times were monitored and recorded. Vital parameters, including heart rate, respiratory rate, and SpO₂, and reflexes were monitored every 5 min during the anesthetic period. Anesthetic induction was smooth and rapid. All monitored reflexes were lost within a median time of 60 sec (interquartile range, 15 sec). Heart rate and respiratory rate were significantly decreased from baseline, whereas there was no difference in SpO₂ over the anesthetic period. The mean time to recovery was 15 ± 7 min (mean ± SD). One animal was found dead 40 min after apparent recovery, which is suspected to be an anesthetic-related death. Based on these findings, dexmedetomidine-ketamine-midazolam anesthesia is an effective anesthetic protocol in naked mole rats that provides a consistent anesthetic plane but should be used with caution in animals with underlying conditions.

Anesthetic effects of dexmedetomidine-ketamine-midazolam administered intramuscularly in five-striped palm squirrels (Funambulus pennantii)

OBJECTIVE

To evaluate efficacy and safety of anesthesia with dexmedetomidine-ketamine-midazolam (DKM) in five-striped palm squirrels (Funambulus pennantii).

ANIMALS

8 male squirrels.

PROCEDURES

Squirrels were anesthetized with DKM (dexmedetomidine, 0.1 mg/kg; ketamine hydrochloride, 30 mg/kg; and midazolam, 0.75 mg/kg) administered IM. Atipamezole (0.15 mg/kg) and flumazenil (0.1 mg/kg) were administered IM 40 minutes after induction of anesthesia. Vital signs and responses were recorded every 5 minutes during anesthesia.

RESULTS

Anesthetic induction and recovery from anesthesia were rapid and without complications in all squirrels. Median anesthetic induction time was 67.5 seconds (interquartile [25th to 75th percentile] range, 5.5 seconds), and mean ± SD recovery time after drug reversal was 147 ± 79 seconds. Heart rate, respiratory rate, and rectal temperature significantly decreased during the anesthetic period. All squirrels became hypothermic by 40 minutes after induction. The righting reflex was absent during the 40-minute anesthetic period in all squirrels, with variable responses for the palpebral reflex, jaw tone, forelimb withdrawal reflex, and hind limb withdrawal reflex. Only 2 of 8 squirrels had loss of the limb withdrawal reflex in both the forelimbs and hind limbs from anesthetic induction to 25 minutes after induction.

CONCLUSIONS AND CLINICAL RELEVANCE

DKM appeared to provide safe and effective anesthesia in five-striped palm squirrels, but oxygen and thermal support were indicated. At the doses administered, deep surgical anesthesia was not consistently achieved, and anesthetic depth of individual squirrels must be determined before surgical procedures are performed in palm squirrels anesthetized with this drug combination.

Evaluation of sedative and antinociceptive effects of dexmedetomidine, midazolam and dexmedetomidine-midazolam in tegus (Salvator merianae)

OBJECTIVE

To evaluate dexmedetomidine, midazolam and dexmedetomidine-midazolam for sedation and antinociception in tegus.

STUDY DESIGN

Prospective, crossover, randomized, blinded study.

ANIMALS

Six healthy tegus (Salvator merianae) weighing 1.6±0.3 kg.

METHODS

Tegus were administered intramuscularly saline (0.5 mL; CON), dexmedetomidine (0.2 mg kg^-1; DX), midazolam (1 mg kg^-1; MZ) and dexmedetomidine-midazolam (same doses; DM). Heart rate (HR) and respiratory frequency (f_R) were recorded before treatment (baseline) and 15, 30 minutes, 1, 2, 3, 4, 6, 8, 12 and 24 hours after the treatments. Sedation scores were recorded according to resistance to manual restraint, posture and response to noxious stimulus, at baseline and 5, 10, 15, 30 minutes, 1, 2, 3, 4, 6, 8, 12 and 24 hours after the treatments. Antinociception was evaluated by measurement of latency of limb withdrawal reflex (LWR) to thermal stimulus, recorded at baseline and 15 minutes, 1, 2, 4, 8, 12 and 24 hours after the treatments.

RESULTS

Lower HR (DX and DM) and f_R (MZ, DX and DM) than CON were measured 15 minutes after the treatment and for up to 6 hours. Sedation was mild to moderate in MZ, deep in DM and absent in DX, although animals showed behavioral changes in DX, with increase in aggressiveness. Median (interquartile range) duration of sedation were 170 (50; 235) minutes in MZ and 230 (115; 235) minutes in DM. Recovery period was prolonged in both treatments, surpassing the duration of the experiment. Higher LWR than CON was detected from 15 minutes until 12 hours in DX and DM.

CONCLUSIONS AND CLINICAL RELEVANCE

Midazolam provided sedation without antinociception, and dexmedetomidine provided antinociception without sedation. Drug combination increased the duration of sedation but not antinociception. Due to increased duration of sedation, reversal of effects with flumazenil and atipamezole should be considered after conclusion of clinical procedures.

Evaluation of the use of midazolam as a co-induction agent with ketamine for anaesthesia in sedated ponies undergoing field castration

BACKGROUND

There are limited investigations comparing ketamine to a ketamine-midazolam co-induction.

OBJECTIVES

To compare quality and safety of general anaesthesia induced using ketamine alone with anaesthesia co-induced using ketamine and midazolam.

STUDY DESIGN

Randomised, double blinded, placebo controlled trial.

METHODS

After i.v. detomidine (20 μg/kg) thirty-eight ponies undergoing field castration received either 0.06 mg/kg (0.6 mL/50 kg) midazolam (group M) or 0.6 mL/50 kg placebo (group P) with 2.2 mg/kg ketamine i.v. for anaesthetic induction. Quality of anaesthetic induction, endotracheal intubation, surgical relaxation and recovery were scored using combinations of simple descriptive and visual analogue scales. Time of sedation, induction, start of endotracheal intubation, first movement, sternal recumbency and standing were recorded, as were time, number and total quantity of additional i.v. detomidine and ketamine injections. Cardiorespiratory variables were assessed every 5 min. Adverse effects were documented. Data were tested for normality and analysed with a mixed model ANOVA, Fisher's exact test, unpaired Students' t test and Wilcoxon Rank-sum as appropriate; P<0.05 was considered significant.

RESULTS

Group M had better scores for induction (P = 0.005), intubation (P<0.001) and surgical relaxation (P<0.001) and required fewer additional injections of detomidine and ketamine (P = 0.04). Time (minutes) from induction to first movement (P<0.001), sternal recumbency (P =< 0.001) and standing was longer (P = 0.05) in group M. Recoveries were uneventful with no difference in quality between groups (P = 0.78).

MAIN LIMITATIONS

Clinical study with noninvasive monitoring undertaken in field conditions.

CONCLUSIONS

Ketamine-midazolam co-induction compared to ketamine alone improved quality of induction, ease of intubation and muscle relaxation without impacting recovery quality.

Behavioral and cardiopulmonary effects of dexmedetomidine-midazolam and dexmedetomidine-midazolam-butorphanol in the silver fox (Vulpes vulpes)

OBJECTIVE

To evaluate the behavior and some cardiopulmonary variables of dexmedetomidine-midazolam or dexmedetomidine-midazolam-butor-phanol in the silver fox (Vulpes vulpes).

STUDY DESIGN

Blinded, randomized design.

ANIMALS

Sixteen adult silver foxes, aged 7-9 months, weighting 6.0-9.2 kg.

METHODS

Animals were randomly assigned to dexmedetomidine (50 μg kg^-1) and midazolam (0.45 mg kg^-1) (group DM) or to dexmedetomidine (30 μg kg^-1), midazolam (0.45 mg kg^-1) and butorphanol (0.25 mg kg^-1) (group DMB), administered intramuscularly. Pulse rate (PR), respiratory rate (f_R), noninvasive arterial pressures, oxygen saturation (SpO₂), rectal temperature (T) and behavioral scores (posture, sedation, antinociception, jaw relaxation and auditory response) were measured at 5, 10, 20, 30, 40, 50 and 60 minutes after injection. Time from drug injection to recumbency with no response to stimuli (IT) and time from administration of atipamezole (0.2 mg kg^-1) to standing with coordination (RT) were recorded. The occurrences of adverse events were recorded. Data were analyzed by two-tailed unpaired t-tests and Bonferroni post hoc tests. Significant differences were accepted at p<0.05.

RESULTS

There were no statistically significant differences between the groups for IT or RT. Arterial pressures were higher in DMB at each time point except at 5 minutes. PR was lower in DM at each time point except at 10 and 60 minutes. No significant difference was found between the groups for f_R, SpO₂ and T. The behavioral scores were significantly lower (lower quality immobilization) in DMB at 5,10 and 60 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

IT and RT were not different between the groups. Both protocols provided immobilization for 30-40 minutes with excellent muscle relaxation and analgesia adequate for clinical examinations and some simple surgical procedures.

Preemptive Epidural Analgesia for Postoperative Pain Relief Revisited: Comparison of Combination of Buprenorphine and Neostigmine with Combination of Buprenorphine and Ketamine in Lower Abdominal Surgeries, A Double-blind Randomized Trial

Context:

Postoperative pain relief provides subjective comfort to patient in addition to blunting of autonomic and somatic reflex responses to pain, subsequently enhancing restoration of function by allowing the patient to breathe, cough, and move easily.

Aims:

The aim is to evaluate and compare the effects of neostigmine + buprenorphine and ketamine + buprenorphine for preemptive epidural analgesia for postoperative pain relief in patients undergoing abdominal surgeries under general anesthesia (GA).

Settings and Design:

A double-blind randomized trial.

Subjects and Methods:

A total of 60 American Society of Anesthesiologists physical status Classes I and II patients undergoing abdominal surgeries under GA were taken up for the study. They were randomly allocated into two groups, Group A and Group B of thirty patients each. Preemptive epidural analgesia for postoperative pain relief was provided by a combination of neostigmine 1 μg/kg + buprenorphine 2 μg/kg in Group A patients and ketamine 1 mg/kg + buprenorphine 2 μg/kg in Group B patients after induction of GA but before surgical incision. Postoperatively, vital parameters, pain score, requirement of top up doses, and side effects in the two groups were observed and recorded at 2, 4, 6, 10, 18, and 22 h.

Statistical Analysis Used:

Mean values within each of the Group A and Group B were compared using one-way analysis of variance (one-way ANOVA). Mean values between Group A and Group B were compared using double analysis of variance (two-way ANOVA).

Results:

Group A patients had a significant analgesia (visual analog scale [VAS] pain scores reduced significantly from 54.6 ± 6.3 at 2 h to 8.1 ± 8.9 at 22 h postoperatively). Group B patients had significant analgesia too (VAS pain scores reduced significantly from 36 ± 12.5 at 2 h to 5.3 ± 10.9 at 22 h postoperatively). There was however no significant difference between the two groups with respect to the degree of postoperative analgesia on comparison of VAS scores, effect on vital parameters, and incidence of side effects.

Conclusions:

Either of the two combinations, neostigmine 1 μg/kg + buprenorphine μg/kg or ketamine 1 mg/kg + buprenorphine 2 μg/kg can be safely used for preemptive epidural analgesia for postoperative pain relief in patients undergoing abdominal surgeries under GA.

Dexmedetomidine-midazolam versus Sufentanil-midazolam for Awake Fiberoptic Nasotracheal Intubation: A Randomized Double-blind Study

BACKGROUND

Awake fiberoptic intubation (AFOI) is usually performed in the management of the predicted difficult airway. The aim of this study was to evaluate the feasibility of dexmedetomidine with midazolam (DM) and sufentanil with midazolam (SM) for sedation for awake fiberoptic nasotracheal intubation.

METHODS

Fifty patients with limited mouth opening scheduled for AFOI were randomly assigned to two groups (n = 25 per group) by a computer-generated randomization schedule. All subjects received midazolam 0.02 mg/kg as premedication and airway topical anesthesia with a modified "spray-as-you-go" technique. Group DM received dexmedetomidine at a loading dose of 0.5 μg/kg over 10 min followed by a continuous infusion of 0.25 μg·kg-1·h-1, whereas Group SM received sufentanil at a loading dose of 0.2 μg/kg over 10 min followed by a continuous infusion of 0.1 μg·kg-1·h-1. As necessary, since the end of the administration of the loading dose of the study drug, an additional dose of midazolam 0.5 mg at 2-min intervals was given to achieve a modified Observers' Assessment of Alertness/Sedation of 2-3. The quality of intubation conditions and adverse events were observed.

RESULTS

The scores of ease of the AFOI procedure, patient's reaction during AFOI, coughing severity, tolerance after intubation, recall of the procedure and discomfort during the procedure were comparable in both groups (z = 0.572, 0.664, 1.297, 0.467, 0.895, and 0.188, respectively, P > 0.05). Hypoxic episodes similarly occurred in the two groups, but the first partial pressure of end-tidal CO2after intubation was higher in Group SM than that in Group DM (45.2 ± 4.2 mmHg vs. 42.2 ± 4.3 mmHg, t = 2.495, P < 0.05).

CONCLUSIONS

Both dexmedetomidine and sufentanil are effective as an adjuvant for AFOI under airway topical anesthesia combined with midazolam sedation, but respiratory depression is still a potential risk in the sufentanil regimen.

Comparison between remifentanil and dexmedetomidine for sedation during modified awake fiberoptic intubation

Cricothyroid membrane injections and the application of a coarse fiberoptic bronchoscope (FOB) below the vocal cords for topical anesthesia have a number of limitations for certain patients. Thus, the aim of the present observational study was to assess the effect of a novel modified topical anesthesia method using the effective sedation drugs, remifentanil (Rem) or dexmedetomidine (Dex), during awake fiberoptic orotracheal intubation (AFOI). In total, 90 adult patients, who had been classified as American Society of Anesthesiologists I-II, were included in the study. The patients had anticipated difficult airways and were to undergo orotracheal intubation for elective surgery. The patients were enrolled in the double-blinded randomized pilot study and received Rem or Dex for sedation during the modified AFOI procedure. The two groups received 2% lidocaine for topical anesthesia via an epidural catheter, which was threaded through the suction channel of the FOB. The main clinical outcomes were evaluated by graded scores representing the conditions for intubation and post-intubation. Additional parameters analyzed included airway obstruction, hemodynamic changes, time required for intubation, amnesia level and subjective satisfaction. All 90 patients were successfully intubated using the modified AFOI technique. The comfort scores and airway events during intubation did not significantly differ between the two groups. However, the Rem group experienced less coughing, and less time was required for tracheal intubation when compared with the Dex group. No statistically significant differences were observed in the changes to the mean arterial pressure and heart rate at any time point between the two groups. Therefore, the current study demonstrated that the modified AFOI method is feasible and effective for difficult airway management, and that Dex and Rem exhibit similar efficacy as adjuvant therapies.

Dexmedetomidine pretreatment alleviates propofol injection pain

OBJECTIVE

The incidence of propofol injection pain during induction of general anesthesia varies from 28% to 90%. This prospective, randomized, double-blind, placebo-controlled study evaluated the effect of dexmedetomidine (DEX) for reducing the incidence and severity of propofol injection pain.

METHODS

Patients undergoing elective surgical procedures were randomly allocated into seven groups of 30 patients each. Experimental treatments were intravenously administered over 10 min (total volume 10 mL) prior to intravenous propofol injection, as follows: group I, the control group, was given isotonic saline. Patients in groups II, III, and IV received DEX 0.25 µg/kg, 0.5 µg/kg, or 1.0 µg/kg, respectively, mixed with isotonic saline immediately before propofol injection. Patients in groups V, VI, and VII received DEX as above, but 5 minutes before propofol injection. Propofol consisted of 1% long-chain triglyceride propofol (2.5 mg/kg) injected at 1 mL/s.

RESULTS

Median propofol injection pain score was 0.00 (IQR 0.00-3.00) in patients who received 1.0 µg/kg DEX 5 min before the propofol injection (group VII), and only 1 patient (of 30) in this group received a pain score >2. The median pain score and number of patients with pain scores >2 in group VII were both significantly less than in the control (group I; p = 0.000, both). There were no differences in either mean arterial pressure or heart rate at any time point after DEX injection among the groups.

CONCLUSIONS

Pretreatment with intravenous DEX 1 µg/kg 5 min prior to injection of long-chain triglyceride propofol is effective and safe in reducing the incidence and severity of pain due to propofol injection.

Effects of dexmedetomidine and midazolam on motor coordination and analgesia: a comparative analysis

Objective

We compared the effects of 2 sedative drugs, dexmedetomidine and midazolam, on motor performance and analgesic efficacy in a rat model.

Materials and methods

Rats were randomly divided into the following 4 groups on the basis of the treatment received. The first group received 83 µg/kg/min midazolam; the second, 1 µg/kg/min dexmedetomidine; the third, 83 µg/kg/min morphine; and the fourth was a control group. The rats were measured motor coordination and pain reflexes by using rotarod, accelerod, hot plate, and tail flick tests.

Results

At all the tested speeds, the midazolam-injected rats remained on the rotarod longer than did the dexmedetomidine-injected rats. Furthermore, in the 10-minute accelerod test, the midazolam-injected rats remained for a longer duration than did the dexmedetomidine-injected rats. The latency time for the hot plate test was significantly higher at 10 minutes and 20 minutes in the dexmedetomidine group than in the midazolam group. Further, the latency time at 10 minutes for the tail flick test was greater in the dexmedetomidine group than in the midazolam group.

Conclusions

In this rat model, midazolam results in faster recovery of motor coordination performance when compared with dexmedetomidine.

Dexmedetomidine versus Remifentanil for Sedation during Awake Fiberoptic Intubation

This study compared remifentanil and dexmedetomidine as awake fiberoptic intubation (AFOI) anesthetics. Thirty-four adult ASA I-III patients were enrolled in a double-blinded randomized pilot study to receive remifentanil (REM) or dexmedetomidine (DEX) for sedation during AFOI (nasal and oral). Thirty patients completed the study and received 2 mg midazolam IV and topical anesthesia. The REM group received a loading dose of 0.75 mcg/kg followed by an infusion of 0.075 mcg/kg/min. The DEX group received a loading dose of 0.4 mcg/kg followed by an infusion of 0.7 mcg/kg/hr. Time to sedation, number of intubation attempts, Ramsay sedation scale (RSS) score, bispectral index (BIS), and memory recall were recorded. All thirty patients were successfully intubated by AFOI (22 oral intubations/8 nasal). First attempt success rate with AFOI was higher in the REM group than the DEX group, 72% and 38% (P = 0.02), respectively. The DEX group took longer to attain RSS of ≥3 and to achieve BIS <80, as compared to the REM group. Postloading dose verbal recall was poorer in the DEX group. Dexmedetomidine seems a useful adjunct for patients undergoing AFOI but is dependent on dosage and time. Further studies in the use of dexmedetomidine for AFOI are warranted.

Revisiting the isobole and related quantitative methods for assessing drug synergism

The isobole is well established and commonly used in the quantitative study of agonist drug combinations. This article reviews the isobole, its derivation from the concept of dose equivalence, and its usefulness in providing the predicted effect of an agonist drug combination, a topic not discussed in pharmacology textbooks. This review addresses that topic and also shows that an alternate method, called "Bliss independence," is inconsistent with the isobolar approach and also has a less clear conceptual basis. In its simplest application the isobole is the familiar linear plot in cartesian coordinates with intercepts representing the individual drug potencies. It is also shown that the isobole can be nonlinear, a fact recognized by its founder (Loewe) but neglected or rejected by virtually all other users. Whether its shape is linear or nonlinear the isobole is equally useful in detecting synergism and antagonism for drug combinations, and its theoretical basis leads to calculations of the expected effect of a drug combination. Numerous applications of isoboles in preclinical testing have shown that synergism or antagonism is not only a property of the two agonist drugs; the dose ratio is also important, a fact of potential importance to the design and testing of drug combinations in clinical trials.

Combining sevoflurane anesthesia with fentanyl-midazolam or s-ketamine in laboratory mice

Laboratory mice typically are anesthetized by either inhalation of volatile anesthetics or injection of drugs. Here we compared the acute and postanesthetic effects of combining both methods with standard inhalant monoanesthesia using sevoflurane in mice. After injection of fentanyl-midazolam or S-ketamine as premedication, a standard 50-min anesthesia was conducted by using sevoflurane. Addition of fentanyl-midazolam (0.04 mg/kg-4 mg/kg) induced sedation, attenuation of aversive behaviors at induction, shortening of the induction phase, and reduced the sevoflurane concentration required by one third (3.3% compared with 5%), compared with S-ketamine (30 mg/kg) premedication or sevoflurane alone. During anesthesia, heart rate and core body temperature were depressed significantly by both premedications but in general remained within normal ranges. In contrast, with or without premedication, substantial respiratory depression was evident, with a marked decline in respiratory rate accompanied by hypoxia, hypercapnia, and acidosis. Arrhythmia, apnea, and occasionally death occurred under S-ketamine-sevoflurane. Postanesthetic telemetric measurements showed unchanged locomotor activity but elevated heart rate and core body temperature at 12 h; these changes were most prominent during sevoflurane monoanesthesia and least pronounced or absent during fentanyl-midazolam-sevoflurane. In conclusion, combining injectable and inhalant anesthetics in mice can be advantageous compared with inhalation monoanesthesia at induction and postanesthetically. However, adverse physiologic side effects during anesthesia can be exacerbated by premedications, requiring careful selection of drugs and dosages.