The Target Plasma Concentration of Propofol Required to Place Laryngeal Mask Versus Cuffed Oropharyngeal Airway

A Potential Mechanism of Sodium Channel Mediating the General Anesthesia Induced by Propofol

General anesthesia has revolutionized healthcare over the past 200 years and continues to show advancements. However, many phenomena induced by general anesthetics including paradoxical excitation are still poorly understood. Voltage-gated sodium channels (Na_V) were believed to be one of the proteins targeted during general anesthesia. Based on electrophysiological measurements before and after propofol treatments of different concentrations, we mathematically modified the Hodgkin–Huxley sodium channel formulations and constructed a thalamocortical model to investigate the potential roles of Na_V. The ion channels of individual neurons were modeled using the Hodgkin–Huxley type equations. The enhancement of propofol-induced GABAa current was simulated by increasing the maximal conductance and the time-constant of decay. Electroencephalogram (EEG) was evaluated as the post-synaptic potential from pyramidal (PY) cells. We found that a left shift in activation of Na_V was induced primarily by a low concentration of propofol (0.3–10 μM), while a left shift in inactivation of Na_V was induced by an increasing concentration (0.3–30 μM). Mathematical simulation indicated that a left shift of Na_V activation produced a Hopf bifurcation, leading to cell oscillations. Left shift of Na_V activation around a value of 5.5 mV in the thalamocortical models suppressed normal bursting of thalamocortical (TC) cells by triggering its chaotic oscillations. This led to irregular spiking of PY cells and an increased frequency in EEG readings. This observation suggests a mechanism leading to paradoxical excitation during general anesthesia. While a left shift in inactivation led to light hyperpolarization in individual cells, it inhibited the activity of the thalamocortical model after a certain depth of anesthesia. This finding implies that high doses of propofol inhibit the network partly by accelerating Na_V toward inactivation. Additionally, this result explains why the application of sodium channel blockers decreases the requirement for general anesthetics. Our study provides an insight into the roles that Na_V plays in the mechanism of general anesthesia. Since the activation and inactivation of Na_V are structurally independent, it should be possible to avoid side effects by state-dependent binding to the Na_V to achieve precision medicine in the future.

Randomized controlled trial comparing the supraglottic airway to use of an endotracheal tube in sinonasal surgery

BACKGROUND

The supraglottic airway (SGA) represents an alternative to endotracheal intubation (endotracheal tube [ETT]) in many types of ambulatory surgery. Adoption of the SGA has progressed slowly in sinonasal surgery due to concerns about airway protection. The purpose of this study was to compare quality of life measures and indices of airway protection between patients undergoing sinonasal surgery who were ventilated via an SGA or ETT.

METHODS

Patients undergoing outpatient sinonasal surgery were enrolled into a randomized, single-blind study in which patients would be ventilated with either an SGA or ETT. At the first postoperative visit, a symptom severity and quality of life questionnaire was completed. Additional objective metrics were extracted from the anesthesia record.

RESULTS

A total of 102 patients were enrolled; 49 assigned to the SGA group and 53 assigned to the ETT group. No significant differences in swallowing function or cough were identified. SGA patients reported more difficulty returning to a normal diet (p = 0.03) with a trend toward reduced throat pain (p = 0.07) and improved phonation (p = 0.06). No significant difference in perioperative oxygen desaturations, emesis, recovery time, or airway blood penetration were identified.

CONCLUSION

While the use of the SGA results in patient diet modification postoperatively, it may also be associated with a reduction in throat pain and dysphonia. SGA use had no appreciable effect on postanesthesia recovery times, oxygen desaturations, or emesis. Use of the SGA in sinonasal surgery appears to be a safe and reliable option for airway management in selected adult patients undergoing routine ambulatory sinonasal surgery.

Comparative study of effective-site target controlled infusion with standard bolus induction of propofol for laryngeal mask airway insertion

Several studies demonstrated induction of anesthesia with different plasma target-controlled infusion (TCI) of propofol for LMA insertion. However, there has been no study to compare the standard bolus propofol induction with the effective site TCI for LMA insertion. Objective: Compare the efficacy of induction of anesthesia with propofol for LMA insertion between the effective-site TCI, using 6 μg/mL, and the standard bolus propofol dose of 2.5 mg/kg in elective surgical patients. Methods: A randomized, prospective, single-blinded, clinical study was used for this study. Seventy-eight unpremedicated patients, American Society of Anesthesiologists (ASA) physical status I and II undergoing elective surgical procedure were randomly allocated between two groups. Group 1 received the standard bolus propofol dose of 2.5 mg/kg. Group 2 received effective site TCI (Schnider model) dose of 6 μg/mL for LMA insertion. The hemodynamics and anesthetic depth (Bispectral index score) were monitored and recorded during and immediately after LMA insertion. The number of insertion attempted, insertion quality score, induction time, and propofol doses used were recorded and compared between groups. Results: The success rate of first insertion attempt was equal in both groups (92.3%). There was no significant hemodynamic response difference between the groups during pre-induction, induction, insertion, and post insertion period. The BIS score was significantly lower during post insertion period in group 1 (51.4+11.0) than group 2 (58.4+3.2) (p=0.013). The propofol doses in group 2 were significantly lower than in group 1 (110.6+14.8 vs. 153.5+21.5) (p <0.001). Patients in group 2 required significantly more induction time than group 1 (146.9+42.3 vs. 103.4+33.6 (p <0.001). Conclusion: Propofol induction with TCI provided equal success rate as compared with standard bolus propofol induction for LMA insertion and insertion quality score. TCI significantly lowered the propofol consumption when compared with the standard 2.5 mg/kg propofol dose.

Propofol, but not ketamine or midazolam, exerts neuroprotection after ischaemic injury by inhibition of Toll-like receptor 4 and nuclear factor kappa-light-chain-enhancer of activated B-cell signalling: A combined in vitro and animal study

BACKGROUND

Propofol, midazolam and ketamine are widely used in today's anaesthesia practice. Both neuroprotective and neurotoxic effects have been attributed to all three agents.

OBJECTIVE

To establish whether propofol, midazolam and ketamine in the same neuronal injury model exert neuroprotective effects on injured neurones in vitro and in vivo by modulation of the Toll-like receptor 4-nuclear factor kappa-light-chain-enhancer of activated B cells (TLR-4-NF-κB) pathway.

DESIGN AND SETTING

Cell-based laboratory (n = 6 repetitions per experiment) and animal (n = 6 per group) studies using a neuronal cell line (SH-SY5Y cells) and adult Sprague-Dawley rats.

INTERVENTIONS

Cells were exposed to oxygen-glucose deprivation before or after treatment using escalating, clinically relevant doses of propofol, midazolam and ketamine. In animals, retinal ischaemia (60 min) was induced followed by reperfusion and randomised treatment with saline or propofol.

MAIN OUTCOME MEASURES

Neuronal cell death was determined using flow-cytometry (mitochondrial membrane potential) and lactate dehydrogenase (LDH) release. Nuclear factor NF-κB and hypoxia-inducible factor 1 α-activity were analysed by DNA-binding ELISA, expression of NF-κB-dependent genes and TLR-4 by luciferase-assay and flow-cytometry, respectively. In animals, retinal ganglion cell density, caspase-3 activation and gene expression (TLR-4, NF-κB) were used to determine in vivo effects of propofol. Results were compared using ANOVA (Analysis of Variance) and t test. A P value less than 0.05 was considered statistically significant.

RESULTS

Post-treatment with clinically relevant concentrations of propofol (1 to 10 μg ml) preserved the mitochondrial membrane potential in oxygen-glucose deprivation-injured cells by 54% and reduced LDH release by 21%. Propofol diminished TLR-4 surface expression and preserved the DNA-binding activity of the protective hypoxia-inducible factor 1 α transcription factor. DNA-binding and transcriptional NF-κB-activity were inhibited by propofol. Neuronal protection and inhibition of TLR-4-NF-κB signalling were not consistently seen with midazolam or ketamine. In vivo, propofol treatment preserved rat retinal ganglion cell densities (cells mm, saline 1504 ± 251 vs propofol 2088 ± 144, P = 0.0001), which was accompanied by reduced neuronal caspase-3, TLR-4 and NF-κB expression.

CONCLUSION

Propofol, but neither midazolam nor ketamine, provides neuroprotection to injured neuronal cells via inhibition of TLR-4-NF-κB-dependent signalling.

Prolonged Treatment with Propofol Transiently Impairs Proliferation but Not Survival of Rat Neural Progenitor Cells In Vitro

Neurocognitive dysfunction is common in survivors of intensive care. Prolonged sedation has been implicated but the mechanisms are unclear. Neurogenesis continues into adulthood and is implicated in learning. The neural progenitor cells (NPC) that drive neurogenesis have receptors for the major classes of sedatives used clinically, suggesting that interruption of neurogenesis may partly contribute to cognitive decline in ICU survivors. Using an in vitro system, we tested the hypothesis that prolonged exposure to propofol concentration- and duration-dependently kills or markedly decreases the proliferation of NPCs. NPCs isolated from embryonic day 14 Sprague-Dawley rat pups were exposed to 0, 2.5, or 5.0 μg/mL of propofol, concentrations consistent with deep clinical anesthesia, for either 4 or 24 hours. Cells were assayed for cell death and proliferation either immediately following propofol exposure or 24 hours later. NPC death and apoptosis were measured by propidium iodine staining and cleaved caspase-3 immunocytochemistry, respectively, while proliferation was measured by EdU incorporation. Staurosporine (1μM for 6h) was used as a positive control for cell death. Cells were analyzed with unbiased high-throughput immunocytochemistry. There was no cell death at either concentration of propofol or duration of exposure. Neither concentration of propofol impaired NPC proliferation when exposure lasted 4 h, but when exposure lasted 24 h, propofol had an anti-proliferative effect at both concentrations (P < 0.0001, propofol vs. control). However, this effect was transient; proliferation returned to baseline 24 h after discontinuation of propofol (P = 0.37, propofol vs. control). The transient but reversible suppression of NPC proliferation, absence of cytotoxicity, and negligible effect on the neural stem cell pool pool suggest that propofol, even in concentrations used for clinical anesthesia, has limited impact on neural progenitor cell biology.

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.

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

BACKGROUND

Dexmedetomidine is a useful anesthetic adjuvant for general anesthesia. We determined whether preoperative dexmedetomidine administration could reduce the half maximal effective concentration (EC50) of propofol for successful i-gel insertion without muscle relaxants.

METHODS

Thirty-seven patients were randomly allocated to one of two groups. In the dexmedetomidine group (n = 19), dexmedetomidine (1 µg/kg) was loaded for 10 min preoperatively. In the control group (n = 20), the same volume of 0.9% normal saline was administered in the same manner. The EC50 of propofol for successful i-gel insertion was determined using Dixon's up-and-down method. The EC50 of propofol was calculated as the midpoint concentration after at least six crossover points had been obtained. For successful i-gel insertion, all of the following four factors were required—(1) no major movement of the body within 1 min of insertion, (2) no significant resistance to mouth opening, (3) cough ≤2, and (4) visible square wave capnogram without air leakage at a peak airway pressure of <10 cmH2O. Mean blood pressure (MBP) and heart rate (HR) were monitored during the peri-insertion period of i-gel.

RESULTS

The EC50 of propofol for successful i-gel insertion was 3.18 μg/mL in the dexmedetomidine group and 6.75 μg/mL in the control group (p < 0.001). The incidence of hypotension (MBP <80% of the baseline) during the peri-insertion period of i-gel was higher in the control group (p = 0.001), whereas the incidence of bradycardia (HR <80% of the baseline) was higher in the dexmedetomidine group (p = 0.001).

CONCLUSIONS

Preoperative dexmedetomidine reduced the EC50 of propofol for successful i-gel insertion without muscle relaxants.

Lidocaine given intravenously improves conditions for laryngeal mask airway insertion during propofol target-controlled infusion

BACKGROUND AND OBJECTIVE

Patient response to laryngeal mask airway insertion during propofol induction depends on many factors. Lidocaine has been used to reduce cardiovascular responses, coughing, and bucking induced by tracheal intubation. The aim of this study was to determine the effects of intravenous lidocaine on laryngeal mask airway insertion conditions during the induction of anaesthesia with propofol target-controlled infusion.

METHODS

Eighty patients, 16-54 years of age, weighing between 45 and 100 kg, who underwent minor surgery, were randomly divided into two groups (the lidocaine and control groups). Anaesthesia was induced with propofol target-controlled infusion at a target plasma concentration of 6 microg ml. The lidocaine group received 1.5 mg kg of lidocaine 50 s after starting target-controlled infusion and the control group received an equivalent volume of saline. Laryngeal mask airways were inserted when propofol effect-site concentrations reached 2.5 microg ml. Laryngeal mask airway insertion conditions (mouth opening, gagging, coughing, movements, laryngospasm, overall ease of insertion, and hiccups) were assessed, and haemodynamic responses were monitored for 3 min after laryngeal mask airway insertion.

RESULTS

No significant differences were observed between the two groups in terms of haemodynamic responses. However, the lidocaine group showed lower incidences of coughing (5 vs. 22.5%), gagging (25 vs. 55%), and laryngospasm (2.5 vs. 17.5%) (P < 0.05).

CONCLUSION

Pretreatment with intravenous lidocaine 1.5 mg kg during induction with propofol target-controlled infusion improves laryngeal mask airway insertion conditions.

Comparison of the anaesthetic requirement with target-controlled infusion of propofol to insert the laryngeal tube vs. the laryngeal mask

BACKGROUND AND OBJECTIVE

The target effect-site concentration of propofol to insert a laryngeal mask airway was recently reported as almost 5 microg mL(-1). The present study aimed to determine the target effect-site concentration with target-controlled infusion of propofol to place classical larnygeal mask airway or current laryngeal tube in adult patients.

METHODS

We included 40 patients scheduled for short gynaecological and radiological procedures under general anaesthesia in a randomized, double-blind manner using the Dixon's up-and-down statistical method. Monitoring included standard cardiorespiratory monitors, and bispectral index monitoring was used for all patients. Anaesthesia was conducted with a target-controlled infusion system: Diprifusor. The initial target plasma concentration of propofol was 5 microg mL(-1), and was changed stepwise by 0.5 microg mL(-1) increments according to Dixon's up-and-down method. Criteria for acceptable insertion were: Muzi's score < or = 2, and mean arterial blood pressure, heart rate or bispectral index variation <20% the baseline values.

RESULTS

Target effect-site concentration of propofol required to insert laryngeal tube was 6.3 +/- 0.3 microg mL(-1) with Dixon method and ED50 was 6.1 microg mL(-1) (5.9-6.4) with logistic regression method. In the case of larnygeal mask airway they were 7.3 +/- 0.2 microg mL(-1) (Dixon method) and 7.3 microg mL(-1) (7.1-7.5; with logistic regression) respectively (P < 0.05). ED95 (logistic regression) was 6.8 microg mL(-1) (5.9-7.6) for laryngeal tube and 7.7 microg mL(-1) (7.3-8.0) for larnygeal mask airway (P < 0.05). Haemodynamic incidents were 55% in the larnygeal mask airway group vs. 30% in the laryngeal tube group (P < 0.05).

CONCLUSIONS

The target effect-site concentration of propofol for insertion of laryngeal tube was lower than for larnygeal mask airway (P < 0.05), with a consequent reduction of the propofol induced haemodynamic side-effects.

Predicted values of propofol EC50 and sevoflurane concentration for insertion of laryngeal mask Classic and ProSeal

BACKGROUND

A new laryngeal mask airway, the ProSeal (PLMA), is said to be more difficult to insert than the laryngeal mask airway Classic (CLMA) using propofol anaesthesia. Therefore, we expected a greater dose of propofol and sevoflurane to be required to insert the PLMA compared with the CLMA. We determined the effective concentration 50% (EC(50)) of propofol and end-tidal sevoflurane to allow insertion of the PLMA and the CLMA.

METHODS

Seventy-six elective female patients (aged 20-60 yr and ASA I-II) were randomly assigned to one of four groups. Either a PLMA or a CLMA was inserted using either propofol target controlled infusion or sevoflurane. Both propofol and sevoflurane targets were determined with a modified Dixon's up-and-down method. After equilibration between the predetermined blood and effect site concentrations, which had been held steady for more than 10 min, LMA insertion was attempted without neuromuscular block.

RESULTS

The predicted EC(50CLMA) and EC(50PLMA) for propofol were 3.14 (0.33) and 4.32 (0.67) micro g ml(-1). E'(CLMA) and E'(PLMA) of sevoflurane (mean (SD)) were 2.36 (0.22) and 2.82 (0.45)% (P<0.01 and 0.05, respectively).

CONCLUSIONS

The estimated concentration of propofol and the sevoflurane concentration needed to allow insertion of the ProSeal are respectively 38 and 20% greater than those needed for insertion of the Classic LMA.

Relation between fentanyl dose and predicted EC 50 of propofol for laryngeal mask insertion

BACKGROUND

This study sought to determine the effective concentration for 50% of the attempts to secure laryngeal mask insertion (predicted EC(50LMA)) of propofol using a target-controlled infusion (Diprifusor) and investigated whether fentanyl influenced these required concentrations, respiratory rate (RR) and bispectral index (BIS).

METHODS

Sixty-four elective unpremedicated patients were randomly assigned to four groups (n = 16 for each group) and given saline (control) or fentanyl 0.5, 1 or 2 micro g kg(-1). Propofol target concentration was determined by a modification of Dixon's up-and-down method. Laryngeal mask airway insertion was attempted without neuromuscular blocking drugs after equilibration had been established for >10 min. Movement was defined as presence of bucking or gross purposeful muscular movement within 1 min after insertion. EC(50LMA) values were obtained by calculating the mean of 16 patients in each group.

RESULTS

Predicted EC(50LMA) of the control, fentanyl 0.5, 1 and 2 micro g kg(-1) groups were 3.25 (0.20), 2.06 (0.55), 1.69 (0.38) and 1.50 (0.54) micro g ml(-1) respectively; those of all fentanyl groups were significantly lower than that of control. RR was decreased in relation to the fentanyl dose up to 1 micro g kg(-1). BIS values after fentanyl 1 and 2 micro g kg(-1) were significantly greater than in the control and 0.5 micro g kg(-1) groups.

CONCLUSIONS

A fentanyl dose of 0.5 micro g kg(-1) is sufficient to decrease predicted EC(50LMA) with minimum respiratory depression and without a high BIS value.

Target-controlled infusion of propofol for fibreoptic intubation

BACKGROUND AND OBJECTIVE

In a retrospective study, we examined the suitability of a departmental clinical protocol for anaesthesia induction with target-controlled infusion of propofol developed for fibreoptic intubation in spontaneously breathing patients scheduled for outpatient oral surgery at the dental clinic of the Vienna University Hospital.

METHODS

Propofol was administered using target-controlled infusion (Diprifusor) at increasing target plasma concentrations starting at 2.5 microg mL(-1). After 10 min, an intravenous dose of alfentanil (5-10 microg kg(-1)) was given for pain reduction. After a further 2 min, the patient was evaluated for response to auditory stimulation. If unresponsive, fibreoptic intubation was performed, otherwise the target concentration was increased by 0.2 microg mL(-1) every 2 min until non-responsiveness was attained.

RESULTS

Tracheal intubation was successful in all patients without any haemodynamic instability. However, one patient required facemask ventilation for 2 min. No patient was aware of intubation. The plasma concentration required for non-responsiveness was 2.8 +/- 0.4 microg mL(-1) (mean +/- SD).

CONCLUSIONS

When using a target-controlled infusion of propofol, fibreoptic intubation can be performed with complete amnesia of the procedure for the patient. However, assisted ventilation of the lungs may be necessary as spontaneous ventilation may cease.

Fentanyl decreases propofol requirement for laryngeal mask airway insertion

BACKGROUND

Since fentanyl is a potent depressant of the upper airway reflex, preadministration of fentanyl may facilitate insertion of the laryngeal mask airway (LMA) using propofol. Accordingly, we tested the hypothesis that fentanyl pretreatment would reduce the dose of propofol required for the LMA insertion.

METHODS

Forty-one healthy patients without sedative premedication were randomly assigned to either fentanyl group, receiving fentanyl 2 microg kg-1 intravenously, or control group, receiving equal volumes of normal saline. Then, 3 ml of 2% lidocaine was given intravenously to alleviate pain associated with propofol administration. Thirty s after the fentanyl or saline injection, a predetermined dose of 1% propofol was given at a rate of 100 mg min-1. Insertion of the LMA was attempted 90 s after the completion of the propofol injection. The dose of propofol given to a particular patient was determined by the response of the preceding patient in that group to a higher or lower dose, using the up-and-down method. The first patient in each group received 2.5 mg kg-1 of propofol, while the step-size was 0.25 mg kg-1. Patients responses were assessed by a blinded observer.

RESULTS

ED50 and ED95 of propofol requirements were significantly less in the fentanyl group (0.82, 1.17 mg kg-1, respectively) than those in the control group (2.39, 2.62 mg kg-1, P < 0.001).

CONCLUSION

Our results indicate that preadministration of fentanyl 2 microg kg-1 decreases the propofol requirement for the LMA insertion.

Bispectral index in patients with target-controlled or manually-controlled infusion of propofol

In this prospective, randomized study we compared bispectral index (BIS), hemodynamics, time to extubation, and the costs of target-controlled infusion (TCI) and manually-controlled infusion (MCI) of propofol. Forty patients undergoing first-time implantation of a cardioverter-defibrillator were included. Anesthesia was performed with remifentanil (0.2-0.3 micro g. kg(-1). min(-1)) and propofol. Propofol was used as TCI (plasma target concentration, 2.5-3.5 micro g/mL; n = 20) or MCI (3.0-4.0 mg. kg(-1). h(-1); n = 20). BIS, heart rate, and arterial blood pressure were measured at six data points: T1, before anesthesia; T2, after intubation; T3, after skin incision; T4, after first defibrillation; T5, after third defibrillation; and T6, after extubation. There were no significant hemodynamic differences between the two groups. BIS was significantly lower at T3 and T4 in the TCI group than in the MCI group. The mean dose of propofol was larger in TCI patients (5.8 +/- 1.4 mg. kg(-1). h(-1)) than in the MCI patients (3.7 +/- 0.6 mg. kg(-1). h(-1)) (P < 0.05), whereas doses of remifentanil did not differ. Time to extubation did not differ between the two groups (TCI, 13.7 +/- 5.3 min; MCI, 12.3 +/- 3.5 min). One patient in the MCI group had signs of intraoperative awareness without explicit memory after first defibrillation (BIS before shock, 49; after shock, 83). Costs were significantly less in the MCI group (34.83 US dollars) than in the TCI group (39.73 US dollars). BIS failed to predict the adequacy of anesthesia for the next painful stimulus.

IMPLICATIONS

In this prospective, randomized study, bispectral index (BIS), hemodynamics, time to extubation, and costs of target-controlled infusion (TCI) and manually-controlled infusion of propofol were compared. TCI increased the amount of propofol used. BIS failed to predict the adequacy of anesthesia for the next painful stimulus.

Oral clonidine premedication reduces the EC50 of propofol concentration for laryngeal mask airway insertion in male patients

BACKGROUND

Oral clonidine, an alpha2-adrenergic receptor agonist, reduces the dose of propofol required for laryngeal mask airway (LMA) insertion. Target-controlled infusion (TCI) is becoming increasingly popular for propofol infusion. There is no information, however, on the propofol blood concentrations required for LMA insertion and the effect of oral clonidine premedication on these values.

METHODS

Propofol at target effect-site concentrations from 4.0 to 12.0 microg/ml were randomly administered using TCI in three groups of healthy male patients (n=35 each) who were undergoing elective orthopedic surgery: control, 2.5 microg/kg clonidine, and 5.0 microg/kg clonidine groups. Nothing was administered to the control group. Clonidine(2.5 microg/kg or 5.0 microg/kg) was administered orally 90 min before arrival at the operating room in the clonidine groups. After equilibration between the blood- and effect-site for 15 min, insertion of the LMA was attempted. The EC50 for LMA insertion (measured propofol serum concentration in equilibrium with the effect-site at which 50% of patients do not respond to the insertion of the LMA) was determined by logistical regression.

RESULTS

EC50+/-standard error values in the control, 2.5 microg/kg clonidine, and 5.0 microg/kg clonidine groups were 8.72+/-0.55, 7.76+/-0.60, and 5.84+/-0.58 microg/ml, respectively. The EC50 in the 5.0 microg/kg clonidine group was significantly lower than that in the control group (P < 0.01).

CONCLUSIONS

The propofol concentration required for LMA insertion in healthy male patients is reduced by premedication with 5.0 microg/kg oral clonidine.

The use of the cuffed oropharyngeal airway in paediatric patients

BACKGROUND

The cuffed oropharyngeal airway (COPA) is a device which has already been demonstrated to be suitable for anaesthetized adult patients undergoing either spontaneous or mechanical ventilation. There are few reports on the use of the COPA in children. In this study, the authors assessed the COPA in paediatric patients undergoing minor surgery.

METHODS

The same anaesthesiologist inserted the COPA in 40 consecutive paediatric patients, ASA I and II, aged 1.8-15.3 years. (7.4 +/- 3.9), after induction of anaesthesia with N2O/O2/sevoflurane. COPA size was chosen by measuring the distal tip of the device at the angle of the jaw with the COPA perpendicular to the patient's bed. The proper positioning of the COPA was assessed by observing thoracoabdominal movements, regular capnograph trace, the reservoir bag movements and SpO2 > 94% with a fraction of inspired oxygen of 0.5. Anaesthesia was maintained with 1 MAC halothane, sevoflurane, or isoflurane in N2O/O2 (50%) and the patients were spontaneously breathing. The stability of the COPA following changes in head, neck and body position was tested. We recorded the duration time for COPA insertion, the side-effects of placement of the COPA and during the intraoperative period, the number of attempts, the type of manipulation in order to provide an effective airway and postoperative symptoms, such as the presence of blood on the device, sore throat, neckache, jaw pain and PONV.

RESULTS

Successful COPA insertion at the first attempt was 90% and at the second attempt in the remaining 10%. The most frequent airway manipulations were head tilt in 27.5% (obtained by a pillow under shoulders) and chin lift in 5%. No complications both at COPA placement nor during the intraoperative period were observed. On the basis of weight and age, the COPA size was no. 8 in 50%, no. 9 in 30%, no. 10 in 12.5%, and no. 11 in 7.5%. The COPA demonstrated stability after changes in head, neck and body position. Postoperative complications were the presence of blood stains in one case and PONV in six cases (15%).

CONCLUSIONS

The COPA is an extratracheal airway device suitable in paediatric patients undergoing general anaesthesia with spontaneous ventilation for minor surgery and other painful procedures. This study shows that for paediatric patients: (i) complications seem to be rare; (ii) the COPA allows hands free anaesthesia; (iii) specific indication for the COPA could be obese patients with a small mouth; and (iv) COPA sizing can be easily established by the weight or age of the patients.

Facilitation of laryngeal mask airway insertion: effects of remifentanil administered before induction with target-controlled propofol infusion

Eighty-six adult day-case patients were recruited into a prospective, randomised study and allocated to one of two groups. Patients received either intravenous remifentanil 0.3 microg.kg(-1) or an equivalent volume of sodium chloride 0.9% followed by induction of anaesthesia with propofol target-controlled infusion until the effect (brain) site calculated concentration was 2 microg.ml(-1). Jaw opening and ease of laryngeal mask insertion were assessed immediately after mask insertion. A higher incidence of failure of induction of anaesthesia was observed in the control group compared with the remifentanil group [15 (35%) vs. 3 (7%); p < 0.01] and addition of remifentanil significantly increased the ease and success of laryngeal mask insertion, with grade 1 (no coughing/gagging) conditions observed in 29 (68%) of the remifentanil group and 21 (49%) of the control group (p < 0.01). The doses of remifentanil and propofol used were not associated with any significant cardiorespiratory instability. In conclusion, when combined with propofol target-controlled infusion, remifentanil 0.3 microg.kg(-1) facilitates laryngeal mask insertion with minimal adverse haemodynamic changes.

Target-controlled infusion or manually controlled infusion of propofol in high-risk patients with severely reduced left ventricular function

OBJECTIVE

To compare hemodynamics, time to extubation, and costs of target-controlled infusion (TCI) with manually controlled infusion (MCI) of propofol in high-risk cardiac surgery patients.

DESIGN

Prospective, randomized.

SETTING

Major community university-affiliated hospital.

PARTICIPANTS

Twenty patients undergoing first-time implantation of a cardioverter-defibrillator with severely reduced left ventricular function (left ventricular ejection fraction <30%).

INTERVENTIONS

Anesthesia was performed using remifentanil, 0.2 to 0.3 microg/kg/min, and propofol. Propofol was used as TCI (plasma target concentration, 2 to 3 microg x mL; n = 10) or MCI (2.5 to 3.5 mg/kg/hr; n = 10).

MEASUREMENTS AND MAIN RESULTS

Hemodynamics were measured at 6 data points: T1, before anesthesia; T2, after intubation; T3, after skin incision; T4, after first defibrillation; T5, after third defibrillation; and T6, after extubation. There were no significant hemodynamic differences between the 2 groups. Dobutamine was required to maintain cardiac index >2 L/min/m(2) in significantly more patients of the TCI group than of the MCI group. Mean dose of propofol was higher in the TCI patients (6.0 +/- 1.0 mg/kg/hr) than in the MCI patients (3.0 +/- 0.4 mg/kg/hr) (p < 0.05), whereas doses of remifentanil did not differ. Time to extubation was significantly shorter in the MCI (11.9 +/- 2.4 min) versus the TCI group (15.6 +/- 6.8 min). Costs were significantly lower in MCI patients (34.73 dollars) than in TCI patients (44.76 dollars).

CONCLUSIONS

In patients with severely reduced left ventricular function, TCI and MCI of propofol in combination with remifentanil showed similar hemodynamics. TCI patients needed inotropic support more often than MCI-treated patients. Although extubation time was longer in TCI patients and costs were higher, both anesthesia techniques can be recommended for early extubation after implantation of a cardioverter-defibrillator.

Laryngeal mask insertion during target-controlled infusion of propofol

STUDY OBJECTIVE

To compare the Laryngeal Mask Airway (LMA; The Laryngeal Mask Airway Co., Ltd., Nicosia, Cyprus) insertion conditions produced by 6 and 8 microg/mL of target plasma concentrations (Cpt) during the induction of anesthesia with target-controlled infusion (TCI) of propofol.

DESIGN

Randomized, prospective, single-blind, clinical study.

SETTING

University hospital.

PATIENTS

44 ASA physical status I and II patients, 16 to 54 years of age, weighing between 45 and 100 kg, undergoing minor surgery in which the use of LMA was indicated.

INTERVENTIONS

Patients were randomly divided into two groups (1 and 2) of 22 to compare the effects of different propofol concentrations. Three minutes after intravenous (IV) injection of midazolam 0.04 mg/kg, group 1 and 2 received TCI of propofol with 6 and 8 microg/mL of Cpt, respectively. LMA was inserted when the effect-site concentration (EC) reached 2.5 microg/mL, which was displayed on the infusion pump.

MEASUREMENTS

The LMA insertion conditions (mouth opening, gagging, coughing, head or limb movement, laryngospasm, overall ease of insertion) were assessed, and hemodynamic responses were evaluated until 3 minutes after LMA insertion. Total dose of propofol, EC, and elapsed time since the start of TCI were recorded at five times: at the loss of consciousness and eyelash reflex, at 2.5 microg/mL of EC, and immediately, 1 minute, and 3 minutes after the insertion of LMA.

MAIN RESULTS

There was no significant difference between the two groups in insertion conditions, despite the significantly larger total dose and shorter elapsed time (2.6 +/- 0.08 mg/kg and 109 +/- 5.0 s) in Group 2 than those (2.1 +/- 0.02 mg/kg and 140 +/- 4.1 s) in Group 1 at 2.5 microg/mL of EC (p < 0.05). Systolic and diastolic blood pressure decreased and heart rate increased significantly throughout the study period in both groups (p < 0.05). But there was a significant decrease in arterial pressure in Group 2 compared with Group 1 1 and 3 minutes after the insertion (p < 0.05).

CONCLUSIONS

Induction with 8 microg/mL of Cpt, compared with 6 microg/mL, allowed earlier LMA insertion but, could not improve the conditions for LMA insertion and required more careful attention to the decrease in blood pressure after LMA insertion.

Simulation in anesthesia: the merits of large simulators versus small simulators

Anesthesia simulation is generally perceived as involving large simulators that provide a limited number of operating room scenarios, especially crisis management. The scope of both anesthesia and flight simulation is much wider, and this review summarizes the range of the former. The areas where simulation has been used include training, education and science. The diversity of its uses may surprise the reader. The models that are used in simulations are important, and these are discussed in part of the discussion. As a result of the current imbalance in perception, I emphasize the merits of small simulators at the expense of large simulators.