The laboratory performance of the enFLOW®, buddy lite™ and ThermoSens® fluid warmers

We measured heating of isotonic saline by three fluid warmers in six experiments: saline at 5 °C or 20 °C delivered at 30, 50 or 100 ml.min^?1. At the three flow rates, the enFLOW^®, buddy lite^? and ThermoSens^® systems heated 5 °C saline to mean (SD) temperatures of: 41.1 (0.5) °C, 37.7 (0.6) °C and 39.1 (0.6) °C; to 40.3 (0.8) °C, 33.9 (1.6) °C and 39.3 (0.7) °C; and to 37.1 (0.8) °C, 24.0 (1.3) °C and 37.6 (1.0) °C, respectively, p < 0.0001 for each experiment. The mean (SD) times taken to heat 5 °C saline were: 16.6 (1.7) s, 258.4 (58.9) s and 134.2 (79.6) s; 16.9 (1.8) s, 256.2 (62.2) s and 182.5 (74.5) s; and 21.5 (1.5) s, 275.9 (49.3) s and 313.5 (18.0) s, respectively, p < 0.0003 for each experiment. The results for saline at 20 °C were similar. The enFLOW system heated saline above 36 °C faster than the ThermoSens system, whereas the buddy lite often failed to achieve 36 °C.     

Comparison of portable blood-warming devices under simulated pre-hospital conditions: a randomised in-vitro blood circuit study

Pre-hospital transfusion of blood products is a vital component of many advanced pre-hospital systems. Portable fluid warmers may be utilised to help prevent hypothermia, but the limits defined by manufacturers often do not reflect their clinical use. The primary aim of this randomised in-vitro study was to assess the warming performance of four portable blood warming devices (Thermal Angel, Hypotherm X LG, °M Warmer, Buddy Lite) against control at different clinically-relevant flow rates. The secondary aim was to assess haemolysis rates between devices at different flow rates. We assessed each of the four devices and the control, at flow rates of 50 ml.min⁻¹, 100 ml.min⁻¹ and 200 ml.min⁻¹, using a controlled perfusion circuit with multisite temperature monitoring. Free haemoglobin concentration, a marker of haemolysis, was measured at multiple points during each initial study run with spectrophotometry. At all flow rates, the four devices provided superior warming performance compared with the control (p < 0.001). Only the °M Warmer provided a substantial change in temperature at all flow rates (mean (95%CI) temperature change of 21.1 (19.8–22.4) °C, 20.4 (19.1–21.8) °C and 19.4 (17.7–21.1) °C at 50 ml.min⁻¹, 100 ml.min⁻¹ and 200 ml.min⁻¹, respectively). There was no association between warming and haemolysis with any device (p = 0.949) or flow rate (p = 0.169). Practical issues, which may be relevant to clinical use, also emerged during testing. Our results suggest that there were significant differences in the performance of portable blood warming devices used at flow rates encountered in clinical practice.     

Comparison of fluid warmer performance during simulated clinical conditions

The study evaluated the warming ability and flow rates associated with four fluid warming devices during pressure driven infusion and during wide open gravity driven roller clamp infusion. Warmers tested were the Astotherm, Flotem IIe, Level 1 System 250 and a modified cardioplegia heat exchanger. Fluids tested were crystalloid, red cells diluted with 200 ml, 0.9% saline, and undiluted red cells. The volume of fluid and outlet temperatures (point where iv tubing would be attached to the patient) were measured for each fluid and compared among warmers for each flow rate condition. For pressure driven infusion of red cells and crystalloid, the System 250, and modified heat exchanger delivered warmer fluids (33-35° C) at higher flow rates (160–740 ml · min^{? 1}) than the Astotherm and Flotem (23–31° C, 44–268 ml · min^{? 1}, P< 0.05). For gravity driven infusion, the System 250 delivered the warmest fluids (33–36° C, P < 0.05) compared with the modified heat exchanger (29–35°C), Astotherm (26–32°C) and Flotem (26–27° C). In conclusion, the modified heat exchanger and System 250 were moderately effective (outlet temperture >32°C) in warming crystalloid and red cells at pressure driven flow rates. Only the System 250 warmed red cells >35° C at gravity driven flow rates. The Flotem and Astotherm were not effective in warming rapidly infused solutions. None of the warmers tested was able to deliver fluids at normothermia (>36.5° C).     

Aluminium release by coated and uncoated fluid-warming devices

The use of fluid-warming systems is recommended for infusion rates > 500 ml.h⁻¹ to avoid peri-operative hypothermia. Some fluid-warming devices use disposable aluminium-heated plates for heat transfer, but there is no protective coating to separate the fluid from the heated aluminium surface. It is unknown if this could promote release of aluminium into infusion fluids. We investigated a coated (Fluido compact) and an uncoated (enFlow) fluid-warming device using normal saline or balanced electrolyte solution as infusion fluids, pumped through the heated disposables at flow rates of 2, 4 and 8 ml.min⁻¹ for 60 min each. Aluminium concentrations in the fluid samples were analysed using graphite furnace atomic absorption spectrometry. With saline the coated and uncoated devices yielded aluminium concentrations below the level of quantification (< 128 μg.l⁻¹). Similarly, balanced electrolyte solution in the coated device yielded aluminium concentrations < 128 μg.l⁻¹. However, balanced electrolyte solution in the uncoated device yielded aluminium concentrations of up to 6794 (3465–8002 [1868–7421]) μg.l⁻¹. Repeating this last study at a flow rate of 2 ml.min⁻¹ resulted in quite high aluminium concentrations when the uncoated device was not heated (~1000 μg.l⁻¹) and higher concentrations after the device was heated. We conclude that using uncoated aluminium plates in fluid-warming systems can lead to a risk of administering potentially harmful concentrations of aluminium when balanced crystalloid solutions are used. The mechanism is unclear, but heat is in part involved. Coating for aluminium within medical devices in direct contact with infusion fluids should be recommended.     

Cardiopulmonary exercise testing: arm crank vs cycle ergometry

This pilot study compared oxygen consumption during arm crank and cycle ergometer tests in 15 women. The mean (SD) peak oxygen consumption was less with arm cranking (25 (5) ml.kg^?1.min^?1) than with cycling (40 (7) ml.kg^?1.min^?1), p < 0.0001. The mean (SD) anaerobic threshold was less with arm cranking (13 (2) ml.kg^?1.min^?1) than with cycling (20 (4) ml.kg^?1.min^?1), p < 0.0001. There was moderate correlation, r² = 0.60, between the anaerobic thresholds determined by arm and leg exercise, p = 0.0007. This study suggests that arm crank cardiopulmonary exercise testing could be used for pre‐operative assessment in those unable to cycle.     

Evaluation of the utility of the Vigileo FloTrac™, LiDCO™, USCOM and CardioQ™ to detect hypovolaemia in conscious volunteers: a proof of concept study

It is important to detect and treat hypovolaemia; however, detection is particularly challenging in the conscious, spontaneously breathing patient. Eight healthy male volunteers were monitored using four minimally invasive monitors: Vigileo FloTrac^?; LiDCOrapid^?; USCOM 1A; and CardioQ^? oesophageal Doppler. Monitor output and clinical signs were recorded during incremental venesection of 2.5% estimated blood volume aliquots to a total of 20% blood volume removed. A statistically significant difference from baseline stroke volume was detected after 2.5% blood loss using the LiDCO (p = 0.007), 7.5% blood loss using the USCOM (p = 0.019), and 12.5% blood loss using the CardioQ (p = 0.046) and the FloTrac (p = 0.028). Receiver operator characteristic curves for predicting > 10% blood loss had areas under the curve of 0.68–0.82. The minimally invasive cardiac output devices tested can detect blood loss by a reduction in stroke volume in awake volunteers, and may have a role in guiding fluid replacement in conscious patients with suspected hypovolaemia.     

The effect of needle dimensions and infusion rates on injection pressures in regional anaesthesia needles: a bench‐top study

Animal studies have shown that injection pressures > 75 kPa indicate probable intrafascicular needle tip position. This study describes the flow/pressure characteristics of seven common needle systems. A syringe pump delivered flow rates of 5, 6.67, 10, 13.3, 15 and 20 ml.min^?1 through these needle systems, while keeping the needle tips open to atmosphere. A pressure transducer connected between the syringe and needle provided a real‐time graphical display for analysis. Mean plateau pressures increased linearly with flow and with decreasing needle diameter (2.7–92 kPa). Flow rates > 17 ml.min^?1 and needle sizes 22 G and smaller produced mean plateau pressures > 75 kPa. Pressure monitors upstream from the needle may produce false‐positive alarms at high flow rates due to needle resistance, and unreliable readings due to non‐laminar flow. We recommend injection rates ≤ 15 ml.min^?1 (0.25 ml.s^?1) to reduce the effect of factors upstream from the needle tip as a cause of high pressure readings.     

The minimally invasive MitraClip™ procedure for mitral regurgitation under general anaesthesia: immediate effects on the pulmonary circulation and right ventricular function

A relatively new minimally invasive cardiological procedure, called the MitraClip^?, does not require sternotomy and may have a number of advantages compared with open mitral valve surgery, but its acute impact on the pulmonary circulation and right ventricular function during general anaesthesia is unclear. We prospectively assessed the effects of the MitraClip procedure in 81 patients with or without pulmonary hypertension (defined as mean pulmonary artery pressure > 25 mmHg), who were anaesthetised using fentanyl (5 μg.kg^?1), etomidate (0.2–0.3 mg.kg^?1), rocuronium (0.5–0.6 mg.kg^?1) and isoflurane. Placement of the MitraClip led to a 60% increase in mean (SD) right ventricular stroke work index (from 512 (321) to 820 (470) mmHg.ml.m^?2, p < 0.0001), while mean (SD) pulmonary vascular resistance index decreased by 24% (522 (330) to 399 (244) dyn.s.cm^?5, p < 0.0001), and mean (SD) pulmonary artery pressure decreased by 10% (30 (8) to 27 (8) mmHg, p < 0.0001). Patients with pulmonary hypertension experienced a similar decrease in mean pulmonary artery pressure compared with those without, and they also had a slight reduction in mean (SD) pulmonary artery occlusion pressure (22 (6) down to 20 (6) mmHg, p = 0.044). We conclude that successful MitraClip treatment for mitral regurgitation acutely improves right ventricular performance by reducing right ventricular afterload, regardless of whether patients have pre‐operative pulmonary hypertension.     

The effect of a forced‐air warming blanket on patients' end‐tidal and transcutaneous carbon dioxide partial pressures during eye surgery under local anaesthesia: a single‐blind,randomised controlled trial

Surgical drapes used during eye surgery are impermeable to air and hence risk trapping air underneath them. We investigated the effect of a forced‐air warming blanket on carbon dioxide accumulation under the drapes in patients undergoing eye surgery under local anaesthesia without sedation. Forty patients of ASA physical status 1 and 2 were randomly assigned to either the forced‐air warmer (n = 20) or a control heated overblanket (n = 20). All patients were given 1 l.min^?1 oxygen. We measured transcutaneous and end‐tidal carbon dioxide partial pressures, heart rate, arterial pressure, respiratory rate, temperature and oxygen saturation before and after draping, then every 5 min thereafter for 30 min. The mean (SD) transcutaneous carbon dioxide partial pressure in the forced‐air warming group stayed constant after draping at 5.7 (0.2) kPa but rose to a maximum of 6.4 (0.4) kPa in the heated overblanket group (p = 0.0001 for the difference at time points 15 min and later). We conclude that forced‐air warming reduces carbon dioxide accumulation under the drapes in patients undergoing eye surgery under local anaesthesia.     

A physiological study to determine the mechanism of carbon dioxide clearance during apnoea when using transnasal humidified rapid insufflation ventilatory exchange (THRIVE)

Clinical observations suggest that compared with standard apnoeic oxygenation, transnasal humidified rapid-insufflation ventilatory exchange using high-flow nasal oxygenation reduces the rate of carbon dioxide accumulation in patients who are anaesthetised and apnoeic. This suggests that active gas exchange takes place, but the mechanisms by which it may occur have not been described. We used three laboratory airway models to investigate mechanisms of carbon dioxide clearance in apnoeic patients. We determined flow patterns using particle image velocimetry in a two-dimensional model using particle-seeded fluorescent solution; visualised gas clearance in a three-dimensional printed trachea model in air; and measured intra-tracheal turbulence levels and carbon dioxide clearance rates using a three-dimensional printed model in air mounted on a lung simulator. Cardiogenic oscillations were simulated in all experiments. The visualisation experiments indicated that gaseous mixing was occurring in the trachea. With no cardiogenic oscillations applied, mean (SD) carbon dioxide clearance increased from 0.29 (0.04) ml.min⁻¹ to 1.34 (0.14) ml.min⁻¹ as the transnasal humidified rapid-insufflation ventilatory exchange flow rate was increased from 20 l.min⁻¹ to 70 l.min⁻¹ (p = 0.0001). With a cardiogenic oscillation of 20 ml.beat⁻¹ applied, carbon dioxide clearance increased from 11.9 (0.50) ml.min⁻¹ to 17.4 (1.2) ml.min⁻¹ as the transnasal humidified rapid-insufflation ventilatory exchange flow rate was increased from 20 l.min⁻¹ to 70 l.min⁻¹ (p = 0.0014). These findings suggest that enhanced carbon dioxide clearance observed under apnoeic conditions with transnasal humidified rapid-insufflation ventilatory exchange, as compared with classical apnoeic oxygenation, may be explained by an interaction between entrained and highly turbulent supraglottic flow vortices created by high-flow nasal oxygen and cardiogenic oscillations.     

Heating capabilities of the Hotline and Autoline at low flow rates

BACKGROUND: At low flow rates, fluid warmers using coaxial warming tubes are superior in preventing heat loss. This laboratory investigation was performed in order to compare the heating capabilities of two coaxial fluid warmers. METHODS: The Hotline and the Autoline were investigated by using normal saline at various flow rates (10-99 ml x h(-1)). Final infusion temperatures were measured six times in a row at the end of the tubing by using a rapid-response thermometer. Final temperatures were compared with those of infusions, which passed through disposable i.v. tubing covered and warmed using an 'off label' convective air warming system (WarmTouch). Measurements were performed at two different room temperatures (20 and 24 degrees C). Each group was analyzed with respect to differences between various flow rates as well as differences between the groups at comparable flow rates by using a three-way anova with multiple comparisons according to Tukey's procedure. Significance was defined at P < 0.05. RESULTS: Both devices heat infusions at low flow rates efficiently above 34 degrees C, with the Hotline being more effective than the Autoline (P < 0.0001). Except for the lowest flow rate (10 ml x h(-1)), the Hotline delivered infusion temperatures between 38 and 39 degrees C, while the Autoline warmed the infusions upto 36 degrees C. While heating capability of the Hotline was improved with elevated room temperatures at low flow rates (10-60 and 80 ml x h(-1)), the Autoline demonstrated lower infusion temperatures throughout elevated room temperature at flow rates between 20 and 90 ml x h(-1). Both devices heated infusions more efficiently compared with 'off label used' convective air warmer (each with P < 0.0001). CONCLUSIONS: Both the Hotline and the Autoline heated infusions sufficiently at low flow rates. However, the heating capability of the Hotline was superior and can further be increased at low flow rates by increasing the room temperature.     

A performance comparison of the paediatric i‐gel™ with other supraglottic airway devices

We performed a review of published literature comparing the i‐gel^? with other supraglottic airway devices in children. Sixty‐two articles were identified following a literature search; we included data from 14 randomised controlled trials and eight observational studies that compared i‐gel sizes 1–2.5 with other commonly used, equivalently‐sized, devices. The primary outcome in most studies was oropharyngeal leak pressure. In the 14 randomised trials the i‐gel performed the same as the comparator device in five trials, significantly better in eight studies (p < 0.05) and significantly worse in one (p < 0.01). Seven studies assessed fibreoptic views of the larynx through the device; two found significantly better views through the i‐gel. Three studies reported a shorter insertion time for the i‐gel, whereas two reported a longer time. Insertion success rate, gastric tube placement and complications were similar for all the devices. Seven of the eight observational studies measured average oropharyngeal leak pressures of 20–27 cmH₂O and all had first‐time insertion success rates exceeding 90%. We conclude that the i‐gel is at least equivalent to other supraglottic airway devices currently available for use in children, and may enable a higher oropharyngeal leak pressure and an improved fibreoptic view of the glottis.     

Performance of three systems for warming intravenous fluids at different flow rates

This study compared the intravenous fluid warming capabilities of three systems at different flow rates. The devices studied were a water-bath warmer, a dry-heat plate warmer, and an intravenous fluid tube warmer Ambient temperature was controlled at 22 degrees to 24 degrees C. Normal saline (0.9% NaCl) at either room temperature (21 degrees to 23 degrees C) or at ice-cold temperature (3 degrees to 5 degrees C) was administered through each device at a range of flow rates (2 to 100 ml/min). To mimic clinical conditions, the temperature of the fluid was measured with thermocouples at the end of a one metre tube connected to the outflow of the warmer for the first two devices and at the end of the 1.2 m warming tubing for the intravenous fluid tube warmer The temperature of fluid delivered by the water bath warmer increased as the flow rate was increased up to 15 to 20 ml/min but decreased with greater flow rates. The temperature of the fluid delivered by the dry-heat plate warmer significantly increased as the flow rate was increased within the range tested (due to decreased cooling after leaving the device at higher flow rates). The temperature of fluid delivered by the intravenous fluid tube warmer did not depend on the flow rate up to 20 ml/min but significantly and fluid temperature-dependently decreased at higher flow rates (>30 ml/min). Under the conditions of our testing, the dry heat plate warmer delivered the highest temperature fluid at high flow rates.     

A randomised crossover comparison of manikin ventilation through Soft Seal®, i‐gel™ and AuraOnce™ supraglottic airway devices by surf lifeguards

Forty surf lifeguards attempted to ventilate a manikin through one out of three supraglottic airways inserted in random order: the Portex^® Soft Seal^®; the Intersurgical^® i‐gel?; and the Ambu^® AuraOnce?. We recorded the time to ventilate and the proportion of inflations that were successful, without and then with concurrent chest compressions. The mean (SD) time to ventilate with the Soft Seal, i‐gel and AuraOnce was 35.2 (7.2)s, 15.6 (3.3)s and 35.1 (8.5) s, respectively, p < 0.0001. Concurrent chest compression prolonged the time to ventilate by 5.0 (1.3–8.1)%, p = 0.0072. The rate of successful ventilations through the Soft Seal (100%) was more than through the AuraOnce (92%), p < 0.0001, neither of which was different from the i‐gel (97%). The mean (SD) tidal volumes through the Soft Seal, i‐gel and AuraOnce were 0.65 (0.14) l, 0.50 (0.16) l and 0.39 (0.19) l, respectively. Most lifeguards (85%) preferred the i‐gel. Ventilation through supraglottic airway devices may be considered for resuscitation by surf lifeguards.     

Influence of a modified propofol equilibration rate constant (ke0) on the effect‐site concentration at loss and recovery of consciousness with the Marsh model

This study compared the predicted effect‐site concentration of propofol at loss and recovery of consciousness when using target‐controlled infusion devices with the same pharmacokinetic model (Marsh) but a different plasma effect‐site equilibration rate constant (k_e0), the Diprifusor^TM (k_e0 0.26 min^?1) and Base Primea? (k_e0 1.21 min^?1). We studied 60 female patients undergoing minor gynaecological surgery under general anaesthesia. Although the total dose of propofol and time until loss of consciousness were comparable, the effect‐site concentration at loss of consciousness was significantly lower with the Diprifusor than with the Base Primea (1.2 (0.3) μg.ml^?1 vs 4.5 (0.9) μg.ml^?1, respectively, p < 0.001). The effect‐site concentration at recovery of consciousness was significantly higher with the Diprifusor than with the Base Primea (1.8 (0.4) μg.ml^?1 vs 1.5 (0.2) μg.ml^?1, respectively, p = 0.01). In conclusion, the effect‐site concentration of propofol differs depending on the k_e0, despite the use of the same pharmacokinetic model. Therefore, the k_e0 should be considered when predicting loss and recovery of consciousness based on the effect‐site concentration of propofol.     

Changes in cardiac index and blood pressure on positioning children prone for scoliosis surgery

In this prospective observational study we investigated the changes in cardiac index and mean arterial pressure in children when positioned prone for scoliosis correction surgery. Thirty children (ASA 1–2, aged 13–18 years) undergoing primary, idiopathic scoliosis repair were recruited. The cardiac index and mean arterial blood pressure (median (IQR [range])) were 2.7 (2.3–3.1 [1.4–3.7]) l.min^?1.m^?2 and 73 (66–80 [54–91]) mmHg, respectively, at baseline; 2.9 (2.5–3.2 [1.7–4.4]) l.min^?1.m^?2 and 73 (63–81 [51–96]) mmHg following a 5‐ml.kg^?1 fluid bolus; and 2.5 (2.2–2.7 [1.4–4.8]) l.min^?1.m^?2 and 69 (62–73 [46–85]) mmHg immediately after turning prone. Turning prone resulted in a median reduction in cardiac index of 0.5 l.min^?1.m^?2 (95% CI 0.3–0.7 l.min^?1.m^?2, p = 0.001), or 18.5%, with a large degree of inter‐subject variability (+ 10.3% to ? 40.9%). The changes in mean arterial blood pressure were not significant. Strategies to predict, prevent and treat decreases in cardiac index need to be developed.     

Transthoracic echocardiographic assessment of haemodynamics in severe pre‐eclampsia and HIV in South Africa

Haemodynamic and cardiac structural changes in severe pre‐eclampsia and in pregnant women with human immunodeficiency virus (HIV) infection have not been clearly established. We performed transthoracic echocardiography on 105 women. Women with pre‐eclampsia demonstrated (mean (SD), untreated vs treated) preserved fractional shortening (40 (7.1)% vs 41 (8.6)%), a non‐dilated left ventricle (4.5 (0.49) cm vs 4.4 (0.44) cm), increased mitral valve E/septal e′ (10.5 (3.3) vs 10.6 (2.8)), and preserved tricuspid annular plane systolic exertion (2.6 (0.36) cm vs 2.4 (0.51) cm). Women with HIV infection demonstrated (mean (SD), HIV‐positive vs healthy) a reduced cardiac index (2.8 (0.64) ml.min^?1.m^?2 vs 3.1 (0.7) ml.min^?1.m^?2, p = 0.029), reduced septal s′ tissue Doppler velocity (8.5 (1.5) cm.s^?1 vs 9.3 (1.7) cm.s^?1, p = 0.042), increased left ventricular end‐diastolic area (7.6 (2.1) cm² vs 6.3 (1.7) cm²_, p = 0.004), and reduced right ventricular s′ and e′ velocity (s′ velocity 14.7 (3.1) cm.s^?1 vs 7.0 (2.9) cm.s^?1 p = 0.001, e′ velocity 16.3 (4.1) cm.s^?1 vs 18.7 (3.4) cm.s^?1, p = 0.013). The mitral value E/septal e′ was > 8 in 39% of patients with HIV. Fractional shortening (< 28%) was reduced in 10% of healthy women, and mitral valve E/septal e′ ratios were > 8 in 38% of that group. Women with pre‐eclampsia demonstrated preserved systolic function, with diastolic dysfunction. Women with HIV demonstrated reduced left and right ventricular systolic function, with increased ventricular dilatation.     

Performance of a new oxygen delivery device for potentially infectious critically ill patients

In patients with highly contagious diseases that are spread by respiratory droplets or air‐borne particles, the use of high‐flow oxygen may carry a significant risk of nosocomial transmission. We tested a new oxygen delivery device designed to address these problems by simulating 108 patients with sepsis and respiratory failure. The device being tested consisted of an airtight mask, a bacterial and viral filter, a T‐shaped reservoir (50 and 100 ml) and oxygen delivery tubing connected directly to the mask. When tested with a 50‐ml reservoir, a high fractional oxygen concentration was achieved: mean (SD) 0.83 (0.11) at a flow of 15 l.min^?1 oxygen. The 50‐ml reservoir, when compared with the 100‐ml reservoir, was associated with reduced carbon dioxide rebreathing (mean (SD) inspired fractional carbon dioxide concentration 2.5 (1.0) vs 3.0 (1.1), respectively, p = 0.009) and reduced inspiratory resistive work of breathing (mean (SD) 1.0 (0.6) J.l^?1 vs 1.2 (0.5) J.l^?1, respectively, p = 0.028). However, rebreathing and work of breathing were relatively high if a high respiratory rate was simulated. We conclude that the novel oxygen device we describe, equipped with the 50‐ml T‐shaped reservoir, is suitable for potentially infectious patients with type‐1 respiratory failure but without marked tachypnoea.     

Comparative efficacy and safety of the Ambu® AuraOnce™ laryngeal mask airway during general anaesthesia in adults: a systematic review and meta‐analysis

Previous comparisons between the Ambu^® AuraOnce^? and other laryngeal mask airways have revealed different results across various clinical studies. We aimed to perform a systematic review with meta‐analysis on the efficacy and safety of the AuraOnce compared with other laryngeal mask airways for airway maintenance in adults undergoing general anaesthesia. Our search of PubMed, PubMed Central, Scopus and the Central Register of Clinical Trials of the Cochrane Collaboration yielded nine randomised controlled trials eligible for inclusion. Comparator laryngeal mask airways were the LMA Unique^? (four trials), the LMA Classic^® (five trials) and the Portex^® Soft Seal^® (three trials). The AuraOnce provided an oropharyngeal leak pressure higher than the LMA Unique (304 participants, mean (95% CI) difference 3.1 (1.6–4.7) cmH₂O, p < 0.0001) and equivalent to the LMA Classic. The Soft Seal provided a higher leak pressure than the AuraOnce (229 participants, mean (95% CI) difference 3.5 (0.4–6.7) cmH₂O, p = 0.03). Insertion was significantly faster with the AuraOnce than the LMA Unique (304 participants, mean (95% CI) difference 5.4 (2.1–8.71) s, p = 0.001) and Soft Seal (229 participants, mean (95% CI) difference 9.5 (3.0–15.9) s, p = 0.004), but similar to the LMA Classic. The first‐insertion success rate of the AuraOnce was equivalent to the LMA Unique, LMA Classic and Soft Seal. We found a higher likelihood of bloodstaining on the cuff with the Soft Seal and a higher incidence of sore throat with the LMA Classic. We conclude that the AuraOnce is an effective alternative to the LMA Classic and LMA Unique, and easier to insert than all three other devices studied.     

Induction of general anaesthesia by effect‐site target‐controlled infusion of propofol: influence of pharmacokinetic model and ke0 value

We studied the use of a new k_e0 value (0.6 min^?1) for the Marsh pharmacokinetic model for propofol. Speed of induction and side‐effects produced were compared with three other target‐controlled infusion systems. Eighty patients of ASA physical status 1–2 were studied in four groups in a prospective, randomised study. Median (IQR [range]) induction times were shorter with the Marsh model in effect‐site control mode with a k_e0 of either 0.6 min^?1 (81 (61–101 [49–302])s, p < 0.01), or 1.2 min^?1 (78 (68–208 [51–325])s, p < 0.05), than with the Marsh model in blood concentration control (132 (90–246 [57–435])). The Schnider model in effect‐site control produced induction times that were longer (298 (282–398 [58–513])s) than those observed with the Marsh model in blood control (p < 0.05), or either effect‐site control mode (p < 0.001). There were no differences in the magnitude of blood pressure changes or frequency of apnoea between groups.