Background and objective: To compare the application of the cuffed oropharyngeal airway and the laryngeal mask airway on anaesthetized adult patients undergoing minor outpatient surgery.

Methods: One hundred patients received intravenous fentanyl, propofol and N2O for the induction and maintenance of anaesthesia. The patients were randomly divided into two groups: a cuffed oropharyngeal airway group (n = 50) and a laryngeal mask airway group (n = 50). After insertion of the device, fibreoptic laryngoscopy was attempted and the degree of success scored. We then compared the first application success rate of both procedures while judging airway intervention requirement, fibreoptic scores, adverse airway events and haemodynamic tolerance.

Results: Both devices had an almost similar first-time placement rate (cuffed oropharyngeal airway 84% versus laryngeal mask airway 96%). The cuffed oropharyngeal airway required a higher number of airway interventions (P < 0.001). The laryngeal mask airway had a significantly better fibreoptic view compared with the cuffed oropharyngeal airway (P < 0.001). However, the number of adverse airway events was lower in the cuffed oropharyngeal airway group; there were no significant differences in adverse events and haemodynamic variables between the said two groups.

Conclusions: The results suggest that the cuffed oropharyngeal airway was an effective alternative airway in spontaneously breathing patients during short procedures.

Summary

Background and objective: Propofol is a phenol derivative (2,6 di-isopropylphenol) with a unique effect profile including activating effects on GABAA and blocking effects on voltage-operated sodium channels. If the substituents in the 2- and the 6-positions are replaced by tert-butyl groups, the resulting phenol derivative, 2,6 di-tert-butylphenol, despite being a close structural propofol analogue, completely lacks GABAA receptor effects. The aim of this in vitro study was to investigate the effects of 2,6 di-tert-butylphenol on voltage-operated neuronal sodium channels in order to determine whether and, if so, how these structural changes alter the sodium channel-blocking effect seen with propofol.

Methods: Whole-cell sodium inward currents through heterologously expressed rat type IIA sodium channels were recorded in the absence and presence of definite concentrations of 2,6 di-tert-butylphenol and propofol.

Results: When applied at concentrations ≥30 μmol, 2,6 di-tert-butylphenol completely and irreversibly blocked sodium inward currents. The blockade equilibrium time was about 2 min. A partial washout was possible only if the application was stopped before the equilibrium of the blockade was achieved.

Conclusions: 2,6 Di-tert-butylphenol exerts a high-affinity block of neuronal sodium channels. Apparently, the slight structural differences of 2,6 di-tert-butylphenol in comparison with propofol – which account for the lack of GABAA receptor effects – enhance its voltage-operated sodium channel-blocking effects. As 2,6 di-tert-butylphenol is much more potent than most sodium channel blockers in clinical use, it might be of interest in the development of local anaesthetics.

Summary

Background and objective: Perioperative hypothermia is generally regarded as undesirable, but its incidence rate in the elective procedures in our hospital and the effect of the preventative measures taken against it were unknown. An initial audit indicated that postoperative hypothermia occurred. Therefore, changes in practice were implemented to address the problem. A further audit was then undertaken to assess the impact of these measures.

Methods: The first audit recorded data from 177 patients undergoing major elective surgical procedures. Variables recorded were: ASA classification, duration of operation, use and description of preventative measures for hypothermia, blood loss, intravenous fluids, and core and peripheral temperatures on arrival and discharge from the recovery room. The subsequent audit included 158 patients undergoing major general, orthopaedic or vascular surgical procedures. Patients had core temperatures measured preoperatively, immediately upon arrival in the recovery room, and just before discharge back to the ward. Core temperatures in both audits were measured using an infrared temperature probe.

Results: The mean body temperature on arrival in the recovery room of patients in the initial audit was 35.5°C (range 32.2–37.2, SD ± 0.74), and in the subsequent audit 36.6°C (33.6–38.2, ±0.72). These differences reached significance (P < 0.0001). This was despite an average duration of surgery of 133.5 (25–330) min in the initial study compared with 154.7 (90–480) min subsequently.

Conclusions: We found that with simple but consistently implemented changes in practice, postoperative hypothermia in elective patients could largely be eradicated.

Background and objective: The common parameters of the electroencephalogram quantify a shift of its power spectrum towards lower frequencies with increasing anaesthetic drug concentrations (e.g. spectral-edge frequency 95). These ad hoc parameters are not optimized for the content of information with regard to drug effect. Using semilinear canonical correlation, different frequency ranges (bins) of the power spectrum can be weighted for sensitivity to changes of drug concentration by multiplying their power with iteratively determined coefficients, yielding a new (canonical univariate) electroencephalographic parameter.

Methods: Electroencephalographic data obtained during application of volatile anaesthetics were used: isoflurane (n = 6), desflurane (7), sevoflurane (7), desflurane during surgical stimulation (12). Volatile anaesthetic end-tidal concentrations varied between 0.5 and 1.6 minimum alveolar concentration (MAC). The canonical univariate parameter and spectral-edge frequency 95 were determined and their correlation with the volatile anaesthetic effect compartment concentration, obtained by simultaneous pharmacokinetic—pharmacodynamic modelling, were compared.

Results: The canonical univariate parameter with individually optimized coefficients, but not with mean coefficients, was superior to the spectral-edge frequency 95 as a measure of anaesthetic drug effect. No significant differences of the coefficients were found between the three volatile anaesthetics or between the data with or without surgical stimulus. The coefficients for volatile anaesthetics were similar to the coefficients for opioids, but different from coefficients for propofol and midazolam.

Conclusions: The canonical univariate parameter calculated with individually optimized coefficients, but not with mean coefficients, correlates more accurately and consistently with the effect site concentrations of volatile anaesthetics than with spectral-edge frequency 95.

Masseter muscle rigidity after suxamethonium, usually occurring in children induced with halothane,is associated with malignant hyperthermia. A case is reported in which masseter muscle rigidity occurred in an adult following vecuronium. From the limited data available, this and two similar reported cases, it appears that non-depolarizing muscle relaxants can, very rarely, cause masseter muscle rigidity in adults. This masseter muscle rigidity may complicate airway management, but is unlikely to progress to generalized rigidity and malignant hyperthermia.

Summary

Background and objectives: Teaching is an important responsibility of non-consultant hospital doctors. In Ireland, specialist registrars (SpRs) in anaesthesia are contractually obliged to teach medical students, other doctors and nurses. Both medical students and fellow non-consultant hospital doctors attribute between 30 and 40% of their knowledge gain to non-consultant hospital doctors.

Methods: We carried out a confidential telephone survey of anaesthetic SpRs in Ireland regarding their current teaching practices and the perceptions of their role as undergraduate teachers. All the SpRs currently working in clinical practice in Ireland were eligible.

Results: Fifty-five of the 79 (70%) SpRs responded to the questionnaire. Only 7 (12.7%) of the respondents said they had been well trained as a teacher. The majority of the respondents stated that they would attend a learning-to-teach course/workshop if one was available, and felt that such a course would improve their ability as a teacher. Only 8 (14.5%) agreed that adequate emphasis is placed on commitment to teaching in the assessment of SpRs, both by individual departments and by the College of Anaesthetists. Anaesthetic SpRs in Ireland spend a considerable amount of time each day teaching undergraduate medical students, the majority (68.9%) stated that they had inadequate time to prepare for teaching.

Conclusion: The majority of the respondents stated that they enjoy teaching, feel that they play an important role in undergraduate teaching but have inadequate time to prepare for teaching. An adequate emphasis is not placed on their commitment to teaching.

Summary

Background and objective: This prospective, randomized, observer-blinded study compared onset time and duration of epidural anaesthesia produced by with levobupivacaine and ropivacaine for lower limb surgery.

Methods: ASA I–III adult patients undergoing elective lower limb procedures were randomized to receive epidural levobupivacaine 0.5% 15 mL (n = 30) or epidural ropivacaine 0.75% 15 mL (n = 35). A blinded observer evaluated onset time and regression of motor and sensory block, and intraoperative needs for fentanyl supplementation (0.1 mg intravenously).

Results: With levobupivacaine, onset time was 29 ± 24 min, with ropivacaine it was 25 ± 22 min (P = 0.41). Complete resolution of motor block required 105 ± 63 min with levobupivacaine and 95 ± 48 min with ropivacaine (P = 0.86). The time for regression of sensory block to T12 was 185 ± 77 min with levobupivacaine and 201 ± 75 min with ropivacaine (P = 0.46). Analgesic supplementation was required in one patient receiving levobupivacaine (3.5%) and in two patients receiving ropivacaine (5.7%) (P = 0.99).

Conclusions: In adults undergoing lower limb surgery, levobupivacaine 0.5% 15 mL produces an epidural block with the same clinical profile as ropivacaine 0.75% 15 mL.

Summary

Background and objective: Initial distribution volume of glucose (IDVG) reliably measures the central extracellular fluid volume in the presence of fluid gain or loss. We hypothesized that IDVG has a close relationship with intrathoracic blood volume (ITBV), which has recently been used as an indicator of cardiac preload. We therefore examined whether IDVG can correlate with ITBV in various fluid volume states.

Methods: Fourteen anaesthetized mongrel dogs were mechanically ventilated. ITBV and cardiac output were measured by single transpulmonary thermodilution technique. IDVG and indocyanine green derived plasma volume (PV-ICG) were determined by the administration of 100 mg kg−1 glucose and 0.5 mg kg−1 indocyanine green solutions, respectively, and calculated by applying a one-compartment model. Three sets of measurements were performed before and after haemorrhage (30 mL kg−1) and subsequent fluid volume loading (90 mL kg−1 of lactated Ringer's solution).

Results: A linear correlation was observed between IDVG and ITBV (r2 = 0.52, n = 42, P < 0.001) and between PV-ICG and ITBV (r2 = 0.44, n = 42, P < 0.001) throughout the procedures. A linear correlation was also observed between changes in IDVG and those in ITBV (r2 = 0.76, n = 28, P < 0.001). The ITBV/IDVG ratio during normovolaemia was 0.26 ± 0.04, which remained unchanged during the procedure.

Conclusion: Results showed that that IDVG has a linear correlation with ITBV, and support the concept that IDVG measurement has potential as a surrogate measure of ITBV in various fluid volume states.

In this double-blind placebo controlled study the preoperative cardiovascular and metabolic effects of intramuscular (i.m.) clonidine and midazolam are assessed. Forty-five ASA Grade I patients (n = 15 per group) undergoing plastic surgical procedures were randomly allocated to receive either placebo, clonidine 4 μg kg−1 or midazolam 70 μg kg−1. Drugs were administered into the deltoid muscle [thkap ]90 min prior to the scheduled induction of anaesthesia. The metabolic measurements were performed using an indirect calorimetry device. Heart rate and blood pressure were measured noninvasively. Pre-operative subjective anxiety, dryness of mouth and tiredness were assessed using visual analogue scales (VAS). Clonidine increased subjective tiredness significantly more than placebo. Clonidine also induced moderate decreases in blood pressure and heart rate. Oxygen consumption (̇VO2), CO2) production and energy expenditure (EE) decreased significantly after clonidine and midazolam. The decrease in ̇VO2) and EE was maximally 11–14% on average from the base-lines after clonidine and midazolam. These effects were of longer duration after clonidine and lasted until the end of the 90 min study period. In conclusion, both clonidine and midazolam are effective as a means of decreasing pre-operative ̇VO2) and EE.

Chronic heart failure is known to be an important risk factor for adverse perioperative outcome in patients undergoing non-cardiac surgery. A promising new form of electric therapy is currently being used in a phase III trial in patients with severe chronic heart failure (cardiac contractility modulation). Cardiac contractility modulation is a non-pharmacological approach to improve Ca2+ effect on cardiac myofilaments using electric currents. The cardiac contractility modulation system used at present (OPTIMIZER™ III, Impulse Dynamics, Orangeburg, NY, USA) consists of a subcutaneously implanted pulse generator and three electrodes. As far as we know, cardiac contractility modulation therapy is a safe and feasible way of improving the systolic function of the heart in congestive heart failure patients. No pro-arrhythmic effects of this new therapy have been reported. The technique shows promise as an additive treatment for severe chronic heart failure. The perioperative and intraoperative management of patients should follow current cardiac pacemaker/implantable cardioverter defibrillator guidelines.

Summary

Background and objective: The LMA-ProSeal® laryngeal mask airway is a new laryngeal mask airway with a modified cuff and drainage tube. We compared oropharyngeal leak pressure, intracuff pressure and anatomical position (assessed fibreoptically) for the Size 5 LMA-ProSeal® laryngeal mask airway and the classic laryngeal mask airway in different head–neck positions and using different intracuff inflation volumes.

Methods: Thirty paralysed anaesthetized adult male patients were studied. The LMA-ProSeal® laryngeal mask airway and the classic laryngeal mask airway were inserted into each patient in random order. The oropharyngeal leak pressure, intracuff pressure, and anatomical position of the airway tube and drainage tube (LMA-ProSeal® laryngeal mask airway only) were documented in four head and neck positions (neutral first, then flexion, extension and rotation in random order), and at 0–40 mL cuff volumes in the neutral position in 10 mL increments.

Results: Compared with the neutral position, the oropharyngeal leak pressure for both the LMA-ProSeal® laryngeal mask airway and the classic laryngeal mask airway was higher in flexion and rotation (all P ≤ 0.02), but lower in extension (all P ≤ 0.01). Changes in head–neck position did not alter the anatomical position of the airway tube or the drainage tube. The oropharyngeal leak pressure was always higher for the LMA-ProSeal® laryngeal mask airway (all P ≤ 0.005) and anatomical position better for the classic laryngeal mask airway (all P ≤ 0.04).

Conclusions: The anatomical position of the LMA-ProSeal® and the classic laryngeal mask airway is stable in different head–neck positions, but head–neck flexion and rotation are associated with an increase, and head–neck extension a decrease, in oropharyngeal leak pressure and intracuff pressure. The Size 5 LMA-ProSeal® laryngeal mask airway is capable of forming a more effective seal than the Size 5 classic laryngeal mask airway in males.