Nicardipine constant rate infusion alleviates the cardiovascular effects of dexmedetomidine infusions without affecting the minimal alveolar concentration in sevoflurane-anesthetized dogs

Two randomized crossover trials evaluated the effects of nicardipine constant rate infusion (CRI) on 1) the anesthetic potency of sevoflurane and 2) the ability to attenuate dexmedetomidine-induced cardiovascular depression in anesthetized dogs. First, six healthy Beagle dogs weighing 11.7 ± 0.9 kg were allocated to one of three treatments that administered a CRI of carrier (saline) or dexmedetomidine 0.5 or 3.0 μg/kg/h following a loading dose. The minimum alveolar concentration (MAC) of sevoflurane was determined utilizing electric stimuli before and after the loading dose of nicardipine (20 μg/kg intravenously for 10 min), followed by CRI at 40 μg/kg/h with 60 min of equilibration. Subsequently, cardiovascular and blood gas variables were evaluated in another trial under sevoflurane anesthesia at the individual 1.5 MAC. After baseline measurements, the dogs were assigned to two treatments (dexmedetomidine CRI at 0.5 or 3.0 μg/kg/h following a loading dose) with sevoflurane doses adjusted to 1.5 times of MAC equivalent, and the measurements were repeated every 15 min for 120 min. After 60 min, nicardipine CRI at 40 μg/kg/h with a loading dose was added to the dexmedetomidine CRI. Dexmedetomidine infusions significantly decreased the sevoflurane MAC but nicardipine did not significantly alter the MAC either with or without dexmedetomidine CRI in dogs. Dexmedetomidine dose-dependently decreased the cardiac index and increased the systemic vascular resistance index; these effects were fully counteracted by concomitant nicardipine CRI. Nicardipine CRI can be useful for controlling the cardiovascular depression elicited by dexmedetomidine in anesthetized dogs without affecting the anesthetic potency of sevoflurane.

Minimal alveolar concentration of sevoflurane in combination with remimazolam in adults during laryngeal mask insertion: an up-down sequential allocation study

BACKGROUND

Remimazolam is a novel ultrashort-acting intravenous benzodiazepine sedative-hypnotic. The combination of remimazolam and sevoflurane does not increase respiratory sensitivity, produce bronchospasm, or cause other adverse conditions. We aimed to observe the effects of different remimazolam doses on the minimum alveolar concentration (MAC) of sevoflurane at end-expiration during laryngeal mask insertion and evaluate the effect of sex on the efficacy of the combination of remimazolam on the suppression of laryngeal mask insertion in adult patients.

METHODS

We included 240 patients undergoing laparoscopic surgery under general anesthesia with elective placement of a laryngeal mask (120 males and 120 females). The patients were randomly divided into four groups according to sex: a control group (randomization for female patients, RF0; randomization for male patients, RM0) and three remimazolam groups (RF1, RM1 / RM2, RF2 / RM3, RF3), with 30 patients in each group. Induction was established by vital capacity rapid inhalation induction (VCRII), using 8% sevoflurane and 100% oxygen (6 L/min) in all patients. The (RF1, RM1), (RM2, RF2), and (RM3, RF3) groups were continuously injected with remimazolam at doses of 1, 1.5, and 2.0 mg/kg/h, respectively, while the (RM0, RF0) group was injected with an equal volume of normal saline. The end-expiratory concentration of sevoflurane was adjusted to a preset value after the patient's eyelash reflex disappeared. After the end-expiratory concentration of sevoflurane was kept stable for at least 15 min, the laryngeal mask was placed, and the patient's physical response to the mask placement was observed immediately and within 30 s of placement. The MAC of sevoflurane was measured using the up-and-down sequential method of Dixon.

RESULTS

The calculated MAC of end-expiratory sevoflurane during laryngeal mask insertion in adult females was (2.94 ± 0.18)%, (2.69 ± 0.16)%, (2.32 ± 0.16)% and (1.83 ± 0.15)% in groups RF0, RF1, RF2 and RF3; (2.98 ± 0.18)%, (2.80 ± 0.19)%, (2.54 ± 0.15)% and (2.15 ± 0.15)% in male groups RM0, RM1, RM2 and RM3, respectively. The MAC values were significantly lower in the (RF1-RF3, RM1-RM3) group when compared to the (RF0, RM0) group. There was no significant difference between (RF0, RF1) and (RM0, RM1), but the MAC value of the RF2-RF3 group was significantly lower than that of the RM2-RM3 group.

CONCLUSIONS

Remimazolam can effectively reduce end-expiratory sevoflurane MAC values during laryngeal mask placement in adults. When remimazolam was measured above 1.5 mg/kg/h, the effect of inhibiting laryngeal mask implantation in female patients was stronger than that in male patients. Remimazolam at a dose of 1-2 mg/kg/h combined with sevoflurane induction can be safely and effectively used in these patients.

Anesthetic management of a patient with an electroencephalogram phenotype for a "vulnerable brain": a case report

BACKGROUND

Low frontal alpha power is an electroencephalogram phenotype suggesting vulnerability to anesthetics. This phenotype for a "vulnerable brain" carries risks for burst suppression at lower-than-expected anesthetic concentrations and therefore for postoperative delirium.

CASE PRESENTATION

A 73-year-old man underwent a laparoscopic Miles' operation. He was monitored with a bispectral index monitor. Before the skin incision, the fraction of age-adjusted minimum alveolar concentration of desflurane was 0.48, and a spectrogram showed slow-delta oscillation despite a bispectral index value of 38-48. Although the fraction of age-adjusted minimum alveolar concentration of desflurane decreased to 0.33, the EEG signature remained unchanged, along with a similar bispectral index value. No burst suppression patterns were observed throughout the whole procedure, and he did not experience postoperative delirium.

CONCLUSIONS

This case suggests that monitoring of electroencephalogram signatures is helpful for detecting patients with a "vulnerable brain" and for providing optimal anesthetic depth in such patients.

Effects of isoflurane, remifentanil and dexmedetomidine on selected EEG parameters derived from a Narcotrend Monitor before and after nociceptive stimulation at different MAC multiples in cats

Background

The aim of this prospective and complete cross-over study was to evaluate the effects of isoflurane, remifentanil and dexmedetomidine on EEG parameters derived from the Narcotrend® Monitor before and after nociceptive stimulation at different isoflurane MAC (minimal alveolar concentration) multiples. Seven adult European Domestic Short Hair cats were used. Each cat went through 3 experimental treatments. Group I received isoflurane, group IR received isoflurane and a constant rate infusion (CRI) of remifentanil (18 μg/kg/h IV), and group ID received isoflurane and a CRI of dexmedetomidine (3 μg/kg/h IV). The isoflurane MAC in each group was determined via supramaximal electrical stimulation. The EEG parameters were derived by a Narcotrend Monitor at specific time points before and after nociceptive stimulation at 0.75, 1.0 and 1.5 MAC.

The depth of anaesthesia was also assessed by a clinical score.

Results

The mean MAC sparing effects in group IR and group ID were 9.8 and 55.2%, respectively. The best correlation of EEG and MAC multiples was found for the Narcotrend Index (NI) in group I (r = − 0.67). The NI was also able to differentiate between 0.75 MAC and 1.5 MAC in group IR. Spectral edge frequency had a lower correlation with MAC multiples in group I (r = − 0.62) but was able to differentiate between 0.75 MAC and 1.5 MAC in groups I and IR, and between 1.0 MAC and 1.5 MAC in group IR. Narcotrend Index, SEF 95 and MF increased significantly after nociceptive stimulation at 1.0 MAC in group I, and SEF 95 increased significantly at 0.75 MAC in group ID. The clinical score correlated closer than any of the EEG parameters with MAC in all groups, with highest correlation values in group I (r = − 0.89). Noxious stimulation led to a significant increase of the clinical score at 0.75 MAC and 1.0 MAC in group I.

Conclusions

The EEG parameters derived from the Narcotrend Monitor show correlation to isoflurane MAC multiples in cats, but the anaesthetic protocol and especially the addition of dexmedetomidine have great influence on the reliability. The Narcotrend Monitor can be used as an additional tool to assess anesthetic depth in cats.

Preoperative education improves the preparedness for extubation at emergence from general anaesthesia!

BACKGROUND

Preoperative patient education is an essential responsibility of any healthcare provider, especially an anaesthetist, and is beneficial for perioperative outcome. A smooth emergence and extubation is a clinical skill that needs to be mastered by an anaesthetist. The aim of this study was to analyse whether a detailed preoperative patient education improves the quality of and preparedness for extubation at emergence from general anaesthesia.

METHODS

One hundred patients were randomly assigned to two groups. The study group received a detailed preoperative patient education and counselling about the mode of anaesthesia, extubation process and their expected response at extubation while the control group received the routine counselling. The Extubation Quality Scale at emergence and the recovery profile in the post anaesthesia care unit were assessed for both groups.

RESULTS

The primary outcome was a better quality of extubation in the patients who received a detailed preoperative patient education. The Extubation Quality Scale was found to be better for patients in the study group (p < 0.001). The endotracheal tube tolerance at a minimum alveolar concentration of ≤0.2 and response to verbal commands at extubation were better for the study group (p < 0.05) besides an earlier discharge from post anaesthesia care unit (p < 0.005).

CONCLUSION

Preoperative patient education improves the patients' preparedness for and quality of extubation and recovery from general anaesthesia .

Experimental study on the effects of isoflurane with and without remifentanil or dexmedetomidine on heart rate variability before and after nociceptive stimulation at different MAC multiples in cats

BACKGROUND

Heart rate variability (HRV) provides information about autonomic nervous system (ANS) activity and is therefore a possible tool with which to assess anaesthetic depth. The aim of the present study was to evaluate the effects of isoflurane, remifentanil and dexmedetomidine on HRV before and after nociceptive stimulation at different anaesthetic depths. Seven healthy domestic short-hair cats were used, and each cat was anaesthetized three times - group I with isoflurane alone, group IR with isoflurane and a constant rate infusion (CRI) of remifentanil (18 μg/kg/h), and group ID with isoflurane and a CRI of dexmedetomidine (3 μg/kg/h). Minimum alveolar concentration (MAC) values were determined via electrical supramaximal nociceptive stimulation for each treatment group. Nociceptive stimulation was repeated at 3 different MAC multiples (0.75, 1.0 and 1.5 MAC), and electrocardiographic recordings were performed for 3 min before and after stimulation. Only the 1 min epochs were used for further statistical analysis. Electrocardiographic data were exported for offline HRV analysis.

RESULTS

The mean isoflurane MAC ± standard deviation (SD) was 1.83 ± 0.22 vol% in group I, 1.65 ± 0.13 vol% in group IR and 0.82 ± 0.20 vol% in group ID. Nociception was indicated by several HRV parameters, however, with high variability between treatments. The best correlation with MAC was found for the SD of heart rate (STD HR) in group I (r_s = - 0.76, p = 0.0001, r² = 0.46). STD HR was also able to distinguish 0.75 MAC from 1.5 MAC and 1.0 MAC from 1.5 MAC in group I, as well as 0.75 MAC from 1.5 MAC in group ID.

CONCLUSIONS

The choice of anaesthetic protocol influences the HRV parameters in cats. Frequency domain parameters respond to nociception at lower MAC levels. The STD HR has the potential to provide additional information for the assessment of anaesthetic depth in isoflurane-anaesthetized cats. The utility of HRV analysis for the assessment of anaesthetic depth in cats is still questionable.

The triple variable index combines information generated over time from common monitoring variables to identify patients expressing distinct patterns of intraoperative physiology

Background

Mean arterial pressure (MAP), bispectral index (BIS), and minimum alveolar concentration (MAC) represent valuable, yet dynamic intraoperative monitoring variables. They provide information related to poor outcomes when considered together, however their collective behavior across time has not been characterized.

Methods

We have developed the Triple Variable Index (TVI), a composite variable representing the sum of z-scores from MAP, BIS, and MAC values that occur together during surgery. We generated a TVI expression profile, defined as the sequential TVI values expressed across time, for each surgery where concurrent MAP, BIS, and MAC monitoring occurred in an adult patient (≥18 years) at the University of Pittsburgh Medical Center between January and July 2014 (n = 5296). Patterns of TVI expression were identified using k-means clustering and compared across numerous patient, procedure, and outcome characteristics. TVI and the triple low state were compared as prediction models for 30-day postoperative mortality.

Results

The median frequency MAP, BIS, and MAC were recorded was one measurement every 3, 5, and 5 min. Three expression patterns were identified: elevated, mixed, and depressed. The elevated pattern displayed the highest average MAP, BIS, and MAC values (86.5 mmHg, 45.3, and 0.98, respectively), while the depressed pattern displayed the lowest values (76.6 mmHg, 38.0, 0.66). Patterns (elevated, mixed, depressed) were distinct across the following characteristics: average patient age (52, 53, 54 years), American Society of Anesthesiologists Physical Status 4 (6.7, 16.1, 27.3%) and 5 (0.1, 0.6, 1.6%) categories, cardiac (2.2, 6.5, 16.1%) and emergent (5.8, 10.5, 12.8%) surgery, cardiopulmonary bypass use (0.3, 2.6, 9.8%), intraoperative medication administration including etomidate (3.0, 7.3, 12.6%), hydromorphone (47.6, 26.3, 25.2%), ketamine (11.2, 4.6, 3.0%), dexmedetomidine (18.4, 16.6, 13.6%), phenylephrine (74.0, 74.8, 83.0), epinephrine (2.0, 6.0, 18.0%), norepinephrine (2.4, 7.5, 21.2%), vasopressin (3.4, 7.6, 21.0%), succinylcholine (74.0, 69.0, 61.9%), intraoperative hypotension (28.8, 33.0, 52.3%) and the triple low state (9.4, 30.3, 80.0%) exposure, and 30-day postoperative mortality (0.8, 2.7, 5.6%). TVI was a better predictor of patients that died or survived in the 30 days following surgery compared to cumulative triple low state exposure (AUC 0.68 versus 0.62, p < 0.05).

Conclusions

Surgeries that share similar patterns of TVI expression display distinct patient, procedure, and outcome characteristics.

Electronic supplementary material

The online version of this article (10.1186/s12874-019-0660-9) contains supplementary material, which is available to authorized users.

Part 2

OBJECTIVE

To outline the major components of the minimum alveolar concentration (MAC) and review the literature regarding pharmacological manipulation of the MAC of halothane, isoflurane, sevoflurane, enflurane, and desflurane in dogs. The pharmacological agents included are alpha-2 agonists, benzodiazepines, propofol, opioids, lidocaine, acepromazine, non-steroidal anti-inflammatory agents (NSAIDs), maropitant, and NMDA antagonists. Part 2 of this review will focus on the effect of opioids, lidocaine, NSAIDs, maropitant, acepromazine, and NMDA antagonists on MAC.

DATABASES USED

PubMed, Google Scholar, CAB Abstracts. Search terms used: minimum alveolar concentration, MAC, dog, canine, inhaled anesthetic potency, isoflurane, sevoflurane, desflurane, enflurane, and halothane.

CONCLUSIONS

Opioids, lidocaine, NSAIDs, maropitant, acepromazine, and NMDA antagonists have been shown to reduce the MAC of inhaled anesthetics in dogs and allow for clinically important decreases in inhalant anesthetic use. Thus, the use of these agents potentially decrease the adverse cardiovascular and pulmonary effects associated with the use of high concentrations of inhaled anesthetics.

Intravenous dexmedetomidine pre-medication reduces the required minimum alveolar concentration of sevoflurane for smooth tracheal extubation in anesthetized children: a randomized clinical trial

Background

It has been known that Dexmedetomidine pre-medication enhances the effects of volatile anesthetics, reduces the need of sevoflurane, and facilitates smooth extubation in anesthetized children. This present study was designed to determine the effects of different doses of intravenous dexmedetomidine pre-medication on minimum alveolar concentration of sevoflurane for smooth tracheal extubation (MAC_EX) in anesthetized children.

Methods

A total of seventy-five pediatric patients, aged 3–7 years, ASA physical status I and II, and undergoing tonsillectomy were randomized to receive intravenous saline (Group D₀), dexmedetomidine 1 μg∙kg⁻¹ (Group D₁), or dexmedetomidine 2 μg∙kg⁻¹ (Group D₂) approximately 10 min before anesthesia start. Sevoflurane was used for anesthesia induction and anesthesia maintenance. At the end of surgery, the initial concentration of sevoflurane for smooth tracheal extubation was determined according to the modified Dixon’s “up-and-down” method. The starting sevoflurane for the first patient was 1.5% in Group D₀, 1.0% in Group D₁, and 0.8% in Group D₂, with subsequent 0.1% up or down in next patient based on whether smooth extubation had been achieved or not in current patient. The endotreacheal tube was removed after the predetermined concentration had been maintained constant for ten minutes. All responses (“smooth” or “not smooth”) to tracheal extubation and respiratory complications were assessed.

Results

MAC_EX values of sevoflurane in Group D₂ (0.51 ± 0.13%) was significantly lower than in Group D₁ (0.83 ± 0.10%; P < 0.001), the latter being significantly lower than in Group D₀ (1.40 ± 0.12%; P < 0.001). EC₉₅ values of sevoflurane were 0.83%, 1.07%, and 1.73% in Group D₂, Group D₁, and Group D₀, respectively. No patient in the current study had laryngospasm.

Conclusion

Dexmedetomidine decreased the required MAC_EX values of sevoflurane to achieve smooth extubation in a dose-dependent manner. Intravenous dexmedetomidine 1 μg∙kg⁻¹ and 2 μg∙kg⁻¹ pre-medication decreased MAC_EX by 41% and 64%, respectively.

Trial registration

Chinese Clinical Trial Registry (ChiCTR): ChiCTR-IOD-17011601, date of registration: 09 Jun 2017, retrospectively registered.

Part 1

OBJECTIVE

To outline the major components of the minimum alveolar concentration (MAC) and review the literature in regard to pharmacological manipulation of the MAC of halothane, isoflurane, sevoflurane, enflurane, and desflurane in dogs. The pharmacologic agents included are alpha-2 agonists, benzodiazepines, propofol, maropitant, opioids, lidocaine, acepromazine, non-steroidal anti-inflammatory agents, and NMDA antagonists. Part 1 will focus on summarizing the relevance, measurement, and mechanisms of MAC and review the effects of alpha-2 agonists, benzodiazepines, and propofol on MAC.

DATABASES USED

PubMed, Google Scholar, CAB Abstracts. Search terms used: minimum alveolar concentration, MAC, dog, canine, inhaled anesthetic potency, isoflurane, sevoflurane, desflurane, enflurane, and halothane.

CONCLUSIONS

Many drugs reduce the MAC of inhaled anesthetics in dogs, and allow for a clinically important decrease in inhalant anesthetic use. A decrease in MAC may decrease the adverse cardiovascular and pulmonary effects associated with the use of high concentrations of inhaled anesthetics.

Effect of single-dose dexmedetomidine on postoperative recovery after ambulatory ureteroscopy and ureteric stenting: a double blind randomized controlled study

BACKGROUND

Ambulatory surgery has recently gain popularity, as it is a good method of optimizinghospital resources utilization. To support ambulatory surgery, anaesthetic goals nowrevolve around patients' early recovery with minimal pain and nausea, expedientdischarge home and prompt resumption of activities of daily living. In this study, weevaluated the effect of a single pre-induction dose of dexmedetomidine on anaestheticrequirements, postoperative pain and clinical recovery after ambulatory ureteroscopy andureteric stenting under general anaesthesia.

METHODS

Sixty patients were randomised to receive IV dexmedetomidine 0.5 μg.kg-¹ (Group DEX, n = 30) or IV saline (Group P, n = 30). General anaesthesia was maintained with Sevoflurane: oxygen: air, titrated to BIS 40-60. Pain intensity, sedation, rescue analgesics, nausea/vomiting and resumption of daily activities were recorded at 1 h, and postoperative day (POD) 1-5.

RESULTS

Group DEX patients had significant reduction in sevoflurane minimum alveolar concentration (MAC), mean (SD) DEX vs. Placebo 0.6 (0.2) vs. 0.9 (0.1), p = 0.037; reduced postoperative resting pain at 1 h (VAS 0-10) (mean (SD) 1.00 (1.84) vs. 2.63 (2.78), p = 0.004), POD 1 (mean (SD) 1.50 (1.48) vs. 2.87 (2.72), p = 0.002), POD 2 (0.53 (0.97) vs. 1.73 (1.96), p = 0.001) and POD 3 (0.30 (0.75) vs. 0.89 (1.49), p = 0.001). DEX patients also had less pain on movement POD 1 (3.00 (2.12) vs. 4.30 (3.10), p = 0.043) and POD 2 (2.10 (1.98) vs. 3.10 (2.46), p = 0.040), with higher resumption of daily activities by 48 h compared to placebo, 87% vs. 63%, p = 0.04.

CONCLUSIONS

We conclude that a single dose of dexmedetomidine was a useful adjuvant in reducing MAC and postoperative pain (at 1 h and POD 1-3), facilitating faster return to daily activities by 48 h.

TRIAL REGISTRATION

The Australian New Zealand Clinical Trials Registry (ANZCTR), ACTRN12617001120369 , 31st July 2017, retrospectively registered.

Effect of the severity of liver dysfunction on the minimum alveolar concentration of sevoflurane responding to an electronic stimulation in cirrhotic patients

BACKGROUND

It has been observed that patients with liver dysfunction need lower dose anesthetic compared patients with normal liver function. The minimum amount of volatile anesthetic to achieve an optimal depth of anesthesia for these patients is still unclear. In this study, Minimum alveolar concentration (MAC) of the sevoflurane was determined using an electric stimulation and the effect of severity of liver dysfunction on the MAC was observed in cirrhotic patients.

METHODS

Thirty patients undergoing upper abdominal surgery were divided into the following groups: group N (normal liver function), group A (Child-Pugh grade A) and group B (Child-Pugh grade B-C). Neuropsychological tests were performed before surgery. We measured MAC_electric (minimum alveolar concentration that prevents movement in response to an electric stimulation in 50 % of patients) of sevoflurane in cirrhotic patients with liver dysfunction using an electrical stimulation of 80 mA at 50 Hz, and analyzed factors that associated change of MAC.

RESULTS

According to the neuropsychological tests, there were 7 and 4 patients with minimal hepatic encephalopathy in Groups B and A, respectively. MAC_electric in cirrhotic patients with liver dysfunction decreased significantly compared to that in healthy liver patients (1.51 ± 0.16 vol. %, 1.33 ± 0.14 vol. % and 1.17 ± 0.13 vol. % in Group N, A and B, respectively), while MAC_electric was comparable between the cirrhotic patients with different Child-Pugh grade. The Alanine Aminotransferase (ALT) and baseline values of bispectral index (BIS) were risk factors associated with the lowering of MAC_electric (p < 0.05).

CONCLUSION

MAC_electric of sevoflurane in cirrhotic patients was significantly lower than that of patients with a healthy liver. The severity of liver dysfunction had no effect on the MAC_electric of sevoflurane in cirrhotic patients.

TRIAL REGISTRATION

This study has been registered in the Chinese Clinical Trial Register in August 3, 2011 (No. ChiCTR-TRC-11001507 ).

Potent Inhalational Anesthetics for Dentistry

Nitrous oxide and the volatile inhalational anesthetics have defined anxiety and pain control in both dentistry and medicine for over a century. From curious experimentation to spectacular public demonstrations, the initial work of 2 dentists, Horace Wells and William T. G. Morton, persists to this day in modern surgery and anesthesia. This article reviews the history, similarities, differences, and clinical applications of the most popular inhalational agents used in contemporary dental surgical settings.

The effect of remifentanil on the minimum alveolar concentration of isoflurane in children

STUDY OBJECTIVE

To evaluate the effect of remifentanil on the isoflurane end-tidal concentration required to eliminate movement reaction upon surgical incision in children.

DESIGN

Prospective, double blinded, serial study.

SETTING

Operating room of a university-affiliated hospital.

PATIENTS

Patients of ASA status 1 or 2, aged 4 to 7 years, scheduled for either inguinal hernia repair or orchidopexy surgery with general anesthesia.

INTERVENTIONS AND MEASUREMENTS

After endotracheal intubation, 108 children serially received 1 of 6 dose (nil, 0.05, 0.10, 0.15, 0.20, or 0.25 μg kg(-1) min(-1)) of remifentanil. End-tidal isoflurane concentration was adjusted according to a Dixon's up-and-down approach. Twenty-five minutes after starting the remifentanil infusion, the surgical incision was performed. The response of patients was classified as either "response" or "no response." Response was defined as a purposeful response in response to skin incision.

MAIN RESULTS

The MAC of isoflurane were 1.50 ± 0.16%, 1.33 ± 0.27%, 0.93 ± 0.13%, 0.73 ± 0.27%, 0.63 ± 0.19%, and 0.60 ± 0.15% for remifentanil infusion rates of nil, 0.05, 0.10, 0.15, 0.20, and 0.25 μg kg(-1) min(-1), respectively.

CONCLUSION

The MAC of isoflurane decreased with increasing infusion rate of remifentanil, showing an initial step reduction followed by a ceiling effect.

Intranasal dexmedetomidine premedication reduces the minimum alveolar concentration of sevoflurane for tracheal intubation in children: a randomized trial

STUDY OBJECTIVE

To determine the effects of dexmedetomidine premedication on the minimum alveolar concentration of sevoflurane for tracheal intubation (MACTI) in children.

DESIGN

Prospective, randomized, clinical comparison study.

SETTING

Operating room of an academic hospital.

PATIENTS

90 pediatric, ASA physical status 1 patients, aged 3 to 7 years, scheduled for minor elective surgery.

INTERVENTIONS

Patients were randomized to three groups to receive placebo, dexmedetomidine 1 μg/kg, or dexmedetomidine 2 μg/kg approximately 60 minutes before anesthesia. Anesthesia was induced with sevoflurane. Each concentration of sevoflurane for which a tracheal intubation was attempted was predetermined according to modification of the Dixon's up-and-down method, with 0.25% as a step size and held constant for at least 15 minutes before tracheal intubation. All responses ("movement" or "no movement") to tracheal intubation were assessed.

MEASUREMENTS AND MAIN RESULTS

The MACTI of sevoflurane was 2.82% ± 0.17% in the control group, 2.26% ± 0.18% in the 1 μg/kg dexmedetomidine group, and 1.83% ± 0.16% in the 2 μg/kg dexmedetomidine group. Dexmedetomidine premedication (1 and 2 μg/kg) decreased the MACTI of sevoflurane by 20% and 35%, respectively. There were no clinically significant episodes of hypotension or bradycardia in any patients.

CONCLUSION

Intranasal dexmedetomidine premedication produces a dose-dependent decrease in the concentration of sevoflurane needed for tracheal intubation in children.

Minimum alveolar concentrations and hemodynamic effects of two different preparations of sevoflurane in pigs

BACKGROUND

Original sevoflurane (Sevo A) is made with water, while a generic sevoflurane (Sevocris) is produced with propylene glycol as a stabilizing additive. We investigated whether the original and generic sevoflurane preparations differed in terms of their minimum alveolar concentration (MAC) values and hemodynamic effects.

METHODS

Sixteen pigs weighing 31.6+/-1.8 kg were randomly assigned to the Sevo A or Sevocris groups. After anesthesia induction via mask with the appropriate sevoflurane preparation (6% in 100% oxygen), the MAC was determined for each animal. Hemodynamic and oxygenation parameters were measured at 0.5 MAC, 1 MAC and 1.5 MAC. Histopathological analyses of lung parenchyma were performed.

RESULTS

The MAC in the Sevo A group was 4.4+/-0.5%, and the MAC in the Sevocris group was 4.1+/-0.7%. Hemodynamic and metabolic parameters presented significant differences in a dose-dependent pattern as expected, but they did not differ between groups. Cardiac indices and arterial pressures decreased in both groups when the sevoflurane concentration increased from 0.5 to 1 and 1.5 MAC. The oxygen delivery index (DO(2)I) decreased significantly at 1.5 MAC.

CONCLUSION

Propylene glycol as an additive for sevoflurane seems to be as safe as a water additive, at least in terms of hemodynamic and pulmonary effects.