An assessment of introducers used for airway management.

Different introducers are available to assist with tracheal intubation. Subtle differences in the design of introducers can have a marked effect on safety and performance. The Difficult Airway Society's Airway Device Evaluation Project Team proposal states that devices should only be purchased for which there is at least a case-control study on patients assessing airway devices. However, resources are not currently available to carry out a case-control study on all introducers available on the market. This study comprised a laboratory and manikin-based investigation to identify introducers that could be suitable for clinical investigation. We included six different introducers in laboratory-based assessments (design characteristics) and manikin-based assessments involving the participation of 30 anaesthetists. Each anaesthetist attempted placement in the manikin's trachea with each of the six introducers in a random order. Outcomes included first-time insertion success rate; insertion success rate; number of attempts; time to placement; and distance placed. Each anaesthetist also completed a questionnaire. First-time insertion success rate depended significantly on the introducer used (p = 0.0016) and varied from 47% (Armstrong and P3) to 77% (Intersurgical and Frova). Median time to placement (including oesophageal placement) varied from 10 s (Eschmann and Frova) to 20 s (P3) (p = 0.0025). Median time to successful placement in the trachea varied from 9 s (Frova) to 22 s (Armstrong) (p = 0.037). We found that the Armstrong and P3 devices were not as acceptable as other introducers and, without significant improvements to their design and characteristics, the use of these devices in studies on patients is questionable. The study protocol is suitable for differentiating between different introducers and could be used as a basis for assessing other types of devices.

Ergonomics in the anaesthetic workplace: Guideline from the Association of Anaesthetists.

Ergonomics in relation to anaesthesia is the scientific study of the interaction between anaesthetists and their workspace environment in order to promote safety, performance and well-being. The foundation for avoiding pain or discomfort at work is to adopt and maintain a good posture, whether sitting or standing. Anaesthetists should aim to keep their posture as natural and neutral as possible. The successful practice of anaesthesia relies on optimisation of ergonomics and lack of attention to detail in this area is associated with impaired performance. The anaesthetic team should wear comfortable clothing, including appropriately-sized personal protective equipment where necessary. Temperature, humidity and light should be adequate at all times. The team should comply with infection prevention and control guidelines and monitoring as recommended by the Association of Anaesthetists. Any equipment or machinery that is mobile should be positioned where it is easy to view or reach without having to change the body or head position significantly when interacting with it. Patients who are supine should, whenever possible, be raised upwards to limit the need to lean towards them. Any item required during a procedure should be positioned on trays or trolleys that are close to the dominant hand. Pregnancy affects the requirements for standing, manually handling, applying force when operating equipment or moving machines and the period over which the individual might have to work without a break. Employers have a duty to make reasonable adjustments to accommodate disability in the workplace. Any member of staff with a physical impairment needs to be accommodated and this includes making provision for a wheelchair user who needs to enter the operating theatre and perform their work.

Multicentre clinical simulation evaluation of the ISO 80369-6 neuraxial non-Luer connector.

To avoid potentially fatal wrong-route neuraxial drug errors, international standard ISO 80369-6 specifying a non-Luer neuraxial connector design was published in 2016. We describe usability studies used in development of the design. Thirty-eight doctors and 17 nurses performed simulated procedures on manikins, using devices fitted with Luer connectors or draft ISO 80369-6 'non-Luer' connectors. The procedures included spinal anaesthesia; intrathecal chemotherapy; lumbar puncture, cerebrospinal fluid collection and pressure measurement; epidural catheter placement with bolus injection and critical care use. Participants attempted cross connection between neuraxial connectors and a range of other medical device connectors, including those from the ISO 80369 small-bore connector series. Video recording analysis was used for all assessments. Participants subjectively assessed performance of the draft non-Luer connector, including suitability for routine clinical use. Participants performed 198 procedures. The connector achieved easy, leak-free connections. The willingness of participants to use the non-Luer connectors were: spinal anaesthesia 100%; intrathecal chemotherapy 88%; lumbar puncture, cerebrospinal fluid collection and pressure measurement 93%; epidural catheter placement with bolus injection 78%; critical care use 100%. Concerns raised were generally device related, rather than connector related. Most cross-connection attempts failed, even using above clinical forces and, when successful, were judged of low clinical risk potential; the exception was a malaligned connection between the non-Luer slip and female Luer connectors. This led to revision of the dimensional tolerances of the non-Luer connector to reduce this risk, before publication of the final specification in 2016. We conclude that the ISO 80369-6 neuraxial non-Luer connector is suitable for clinical use.

Negative feedback regulation of thyrotropin subunits and pituitary deiodinases in red drum, Sciaenops ocellatus.

Thyroxine (T4) undergoes dynamic daily cycles in the perciform fish the red drum, Sciaenops ocellatus, that are inversely timed to cycles of thyrotropin (TSH) subunit mRNA expression in the pituitary gland. We have proposed that these daily cycles are regulated by negative feedback of circulating T4 on expression of pituitary thyroid hormone deiodinase type 3 (Dio3), such that elevated circulating T4 results in diminished pituitary thyroid hormone catabolism and consequent increased negative feedback on expression of TSH subunits during the day. To determine whether thyroid hormones function to modulate expression of pituitary deiodinase enzymes we developed an immersion technique to administer physiological doses of T3 and T4in vivo. Immersion in T4 or T3 significantly inhibited the mRNA expression of the TSH α and ß subunits from 4 to 66h of immersion. Pituitary Dio3 expression was significantly diminished by T3 and T4 at 22h. These results indicate that both T4 and T3 are capable of negative feedback regulation of TSH subunit expression in red drum at physiological concentrations and on a time scale consistent with the T4 daily cycle. Furthermore, thyroid hormones negatively regulate Dio3 expression in the pituitary in a manner suggesting that negative thyroxine feedback on Dio3 promotes the release of TSH subunits from TH inhibition and may be an important mechanism for generating daily thyroid hormone cycles. These results highlight a potentially important role for D3 in mediating thyroid hormone feedback on TSH expression, not previously described in other species.

Laboratory evaluation of a novel anaesthesia delivery device.

Here, we describe proof of concept of a novel method for delivering volatile anaesthetics, where the liquid anaesthetic (sevoflurane or isoflurane) is formulated into an emulsion that is contained in a compact, lightweight device through which carrier gas flows. Release of anaesthetic is achieved by stirring of the formulation, allowing controlled and responsive release of anaesthetic at a variety of fixed flow rates between 0.5 l.min-1 and 5 l.min-1 , with ventilated, non-ventilated and draw-over breathing systems. Anaesthetic release was evaluated using target anaesthetic concentrations ranging from 0.5% v/v to 8% v/v to mimic those typically required for induction and maintenance of anaesthesia, and lower concentrations suitable for sedation. Under all conditions, output could be maintained within 0.1% v/v of the intended setting, and the device could deliver a controlled level of anaesthetic for at least 60 min, with compensation for different ambient temperatures (10-30 °C) and carrier gas flow rates. This device offers a simple, inexpensive method of delivering safe concentrations of volatile anaesthetics for a wide range of applications.

Effect of early tracheostomy on resource utilization and clinical outcomes in critically ill patients: meta-analysis of randomized controlled trials.

BACKGROUND: Early tracheostomy may decrease the duration of mechanical ventilation, sedation exposure, and intensive care stay, possibly resulting in improved clinical outcomes, but the evidence is conflicting. METHODS: Systematic review and meta-analysis of randomized trials in patients allocated to tracheostomy within 10 days of start of mechanical ventilation was compared with placement of tracheostomy after 10 days if still required. Medline, EMBASE, the Cochrane Controlled Clinical Trials Register, and Google Scholar were searched for eligible trials. The co-primary outcomes were mortality within 60 days, and duration of mechanical ventilation, sedation, and intensive care unit stay. Secondary outcomes were the number of tracheostomy procedures performed, and incidence of ventilator-associated pneumonia (VAP). Outcomes are described as relative risk or weighted mean difference with 95% confidence intervals. RESULTS: Of note, 4482 publications were identified and 14 trials enrolling 2406 patients were included. Tracheostomy within 10 days was not associated with any difference in mortality [risk ratio (RR): 0.93 (0.83-1.05)]. There were no differences in duration of mechanical ventilation [-0.19 days (-1.13-0.75)], intensive care stay [-0.83 days (-2.05-0.40)], or incidence of VAP. However, duration of sedation was reduced in the early tracheostomy groups [-2.78 days (-3.68 to -1.88)]. More tracheostomies were performed in patients randomly assigned to receive early tracheostomy [RR: 2.53 (1.18-5.40)]. CONCLUSION: We found no evidence that early (within 10 days) tracheostomy reduced mortality, duration of mechanical ventilation, intensive care stay, or VAP. Early tracheostomy leads to more procedures and a shorter duration of sedation.

A comparison of fibreoptic-guided tracheal intubation through the Ambu ® Aura-i ™, the intubating laryngeal mask airway and the i-gel ™: a manikin study.

We compared the Aura-i(™) , intubating laryngeal mask airway and i-gel(™) as conduits for fibreoptic-guided tracheal intubation in a manikin. Thirty anaesthetists each performed two tracheal intubations through each device, a total of 180 intubations. The median (IQR [range]) time to complete the first intubation was 40 (31-50 [15-162]) s, 37 (34-48 [25-75]) s and 28 (22-35 [14-59]) s for the Aura-i, intubating laryngeal mask airway and i-gel, respectively. Tracheal intubation through the i-gel was the quickest (p < 0.01). Resistance to railroading of the tracheal tube over the fibrescope was significantly greater through the Aura-i compared with the intubating laryngeal mask airway and the i-gel (p = 0.001). There were no failures to intubate through the intubating laryngeal mask airway or the i-gel but six intubation attempts through the Aura-i were unsuccessful, in five owing to a railroading failure and in one owing to accidental oesophageal intubation. We conclude that the Aura-i does not perform as well as the intubating laryngeal mask airway or the i-gel as an adjunct for performing fibreoptic-guided tracheal intubation.

Bougie-related airway trauma: dangers of the hold-up sign.

The bougie is a popular tool in difficult intubations. The hold-up sign is used to confirm tracheal placement of a bougie. This study aimed to establish the potential for airway trauma when using this sign with an Eschmann re-usable bougie or a Frova single-use bougie. Airways were simulated using a manikin (hold-up force) and porcine lung model (airway perforation force). Mean (SD) hold-up force (for airway lengths over the range 25-45 cm) of 1.0 (0.4) and 5.2 (1.1) N were recorded with the Eschmann and Frova bougies, respectively (p < 0.001). The mean (SD) force required to produce airway perforation was 0.9 (0.2) N with the Eschmann bougie and 1.1 (0.3) N with the Frova bougie (p = 0.11). It is possible to apply a force at least five times greater than the force required to produce significant trauma with a Frova single-use bougie. We recommend that the hold-up sign should no longer be used with single-use bougies. Clinicians should be cautious when eliciting this sign using the Eschmann re-usable bougie.

Investigation of phthalate release from tracheal tubes.

Phthalates are chemicals used extensively in the manufacture of plastics for their desirable physical characteristics. In addition to enhancing the performance of plastics, phthalates have a number of undesirable effects, principally endocrine disruptor effects, that may have adverse effects on reproductive development and functioning. As a result, they have been banned from the manufacture of children's toys. Despite this, they continue to be used in the manufacture of medical devices, including anaesthetic equipment. This study aimed to assess phthalate release from five brands of tracheal tube. Using gas chromatography-mass spectrometry, we analysed phthalate concentrations from samples of ultra pure water in which tracheal tubes had been submerged. Phthalate concentration increased from 6.7 to 149 µg.l(-1) over a period of 4.8 days. Phthalate release from anaesthetic equipment has not previously been documented over short time periods and raises the possibility of iatrogenic endocrine disruption with routine anaesthesia.

Using PET/CT imaging to characterize 18 F-fluorodeoxyglucose utilization in fish.

Fish are becoming an increasingly important research species as investigators seek alternatives to mammalian models. Combined positron emission tomography/computed tomography with ¹8F-fluorodeoxyglucose (FDG-PET/CT) is a powerful new technology that has been extensively applied for high-resolution imaging in mammals but not fish. CT scanning provides detailed anatomical three-dimensional imaging. PET scanning detects areas of cellular activity using radio-labelled molecular probes with specific uptake rates appropriate to the tissue involved. FDG-PET is used in oncology because tissues with high glucose uptake, such as neoplasms, are intensely radio-labelled. PET/CT combines the two technologies, so that images acquired from both devices are merged into one superimposed image, thus more precisely correlating metabolic activity with anatomical three-dimensional imaging. Our objective was to determine if fish can be viable replacement animals in cancer studies using this technique by analysing the similarities between fish and humans in glucose uptake in select organs across multiple fish species. Rapid, quantifiable glucose uptake was demonstrated, particularly in brain, kidneys and liver in all imaged fish species. Standard uptake values for glucose uptake in the major organ systems of fish were more similar to those of humans than mice or dogs, indicating that fish may serve as effective alternative animal models using this technology. Applications for this technique in fish may include oncogenesis and metabolism studies as well as screening for environmental carcinogenesis.

Epidural catheter connectors: a laboratory-based comparison of the Portex Tuohy-Borst and EpiFuse™ designs.

Disconnection of an epidural catheter from its connector may result in patient harm and commonly requires resiting of the epidural. Clamp-connector designs such as the novel Portex EpiFuse™ potentially offer an improved safety profile over screw-cap designs such as the Tuohy-Borst, but comparative studies are limited. We therefore compared the tensile strength of EpiFuse and Tuohy-Borst connectors in a laboratory setting. We further sought to establish whether operator modification of the EpiFuse increased its vulnerability to disconnection. The median (IQR [range]) force to induce disconnection was 8.0 (4.1-12.8 [0.0-22.6]) N for Tuohy-Borst connectors and 16.4 (15.2-17.7 [5.7-18.9]) and 15.9 (15.0-16.9 [5.8-18.1]) N for standard and modified EpiFuse connectors, respectively (p<0.0001). The Tuohy-Borst was also less likely to meet British Standard requirements (13/20 sets vs 19/20 and 20/20, p=0.002). Modification of the EpiFuse did not affect lumen patency or connection strength. We conclude that under controlled conditions, EpiFuse connectors are superior to Tuohy-Borst connectors.

A randomised crossover trial comparing a single-use polyvinyl chloride laryngeal mask airway with a single-use silicone laryngeal mask airway.

We compared insertion rates of single-use polyvinyl chloride laryngeal mask airways (LMAs) vs single-use silicone LMAs in 72 anaesthetised patients. Both airways were produced by Flexicare Medical. Laryngeal mask airway insertion was successful on the first attempt in 68/72 (94%) polyvinyl chloride LMAs vs 64/72 (89%) silicone LMAs (p = 0.39). Overall insertion rates were 72/72 (100%) for the polyvinyl chloride LMAs and 71/72 (99%) for the silicone LMAs (p = 1.0). Mean (SD) insertion times were similar for polyvinyl chloride and silicone LMAs: 24.3 (5.1)s vs 24.8 (7.8)s (p = 0.64). Laryngeal mask airway position, as assessed using a fibrescope, was not different (p = 0.077). The median (IQR [range]) leak pressure was 16 (12-20 [6-30]) cmH(2) O for the polyvinyl LMA and 18 (13-22 [6-30]) cmH(2) O or the silicone LMA (p = 0.037). In conclusion, we did not find any important differences between polyvinyl chloride and silicone laryngeal mask airways.

Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 2 - practical use, including problems, and their use with paediatric patients.

Heat and moisture exchangers and breathing system filters are intended to replace the normal warming, humidifying and filtering functions of the upper airways. The first part of this review considered the history, principles of operation and efficiency of these devices. The aim of this part of the review is to summarise recent guidelines on the use of these devices and outline the problems that can occur. In particular, the effect of these devices on gas analysis, dead space, resistance to gas flow and blockage of the breathing system is considered. In children, it is important to consider the addition of dead space and resistance to gas flow. A body weight of 2.5 kg is probably the lower weight limit for use with heat and moisture exchangers, and 3 kg for filters. The resistance to gas flow of a heat- and moisture-exchanging filter added to a Mapleson F breathing system can cause a delay in the induction of anaesthesia.

Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 1 - history, principles and efficiency.

Heat and moisture exchangers and breathing system filters are intended to replace the normal warming, humidifying and filtering functions of the upper airways when these structures are bypassed during anaesthesia and intensive care. Guidance on their use continues to evolve. The aim of this part of the review is to describe the principles of their action and efficiency and to summarise the findings from clinical and laboratory studies. Based on previous studies, an appropriate minimum target for moisture output is 30 and 20 g.m⁻³ for long-duration use in intensive care and short-duration use in anaesthesia, respectively. The practice of reusing a breathing system in anaesthesia, provided it is protected by a filter, assumes that the filter is effective. However, there is wide variation in the gas-borne filtration performance, and contaminated condensate can potentially pass through some filters under typical pressures encountered during mechanical ventilation.

Comparison of the manoeuvrability and ease of use of the Ambu aScope and Olympus re-usable fibrescope in a manikin.

In this study, we compared the manoeuvrability and ease of use of the single-use Ambu aScope and Olympus re-usable fibrescope in a manikin set to simulate difficult fibrescope placement. A total of 75 anaesthetists took part in this randomised crossover non-inferiority study. We recorded the time to task completion, tip surface collision count and participants' impression of ease of use. For the Ambu aScope and Olympus fibrescope, the mean (SD) first attempt time to task completion was 63 (31) s and 53 (23) s, respectively (95% CI of the difference 3-17 s), p = 0.008. This rejected the null hypothesis of a difference of > 30 s. The mean (SD) number of tip surface collisions was 2.7 (1.9) and 2.5 (1.8), respectively, (95% CI of the difference -0.4 to 0.7) p = 0.56. However, the participants found the Olympus easier to use (p < 0.001). Mean (SD) visual analogue scores for the perceived ease of use (0 mm = extremely difficult and 100 mm = extremely easy) were 65 (18) mm and 77 (14) mm for the Ambu aScope and Olympus scopes, respectively. This study found that the single-use Ambu aScope is as easy to manoeuvre as the Olympus re-usable fibrescope. This single-use device appears to be an acceptable alternative to the re-usable fibrescope.

The history of anaesthetic equipment evaluation in the United Kingdom: lessons for developing future strategy.

Recent guidance published by the Association of Anaesthetists of Great Britain and Ireland encourages the purchase of equipment based on evidence of safety and performance. For many years, evidence of the safety and performance of anaesthetic equipment was published by various government departments and agencies. However, these schemes were gradually eroded over time such that many devices entered the market with little or no clinical evidence of their efficacy. This recently led to the Difficult Airway Society's issuing guidance to its members on how best to select new airway devices; guidance that was based on the available evidence. This article provides a short history of the evaluation of anaesthetic equipment in the United Kingdom.

The Difficult Airway Society 'ADEPT' guidance on selecting airway devices: the basis of a strategy for equipment evaluation.

Faced with the concern that an increasing number of airway management devices were being introduced into clinical practice with little or no prior evidence of their clinical efficacy or safety, the Difficult Airway Society formed a working party (Airway Device Evaluation Project Team) to establish a process by which the airway management community within the profession could itself lead a process of formal device/equipment evaluation. Although there are several national and international regulations governing which products can come on to the market and be legitimately sold, there has hitherto been no formal professional guidance relating to how products should be selected (i.e. purchased). The Airway Device Evaluation Project Team's first task was to formulate such advice, emphasising evidence-based principles. Team discussions led to a definition of the minimum level of evidence needed to make a pragmatic decision about the purchase or selection of an airway device. The Team concluded that this definition should form the basis of a professional standard, guiding those with responsibility for selecting airway devices. We describe how widespread adoption of this professional standard can act as a driver to create an infrastructure in which the required evidence can be obtained. Essential elements are that: (i) the Difficult Airway Society facilitates a coherent national network of research-active units; and (ii) individual anaesthetists in hospital trusts play a more active role in local purchasing decisions, applying the relevant evidence and communicating their purchasing decisions to the Difficult Airway Society.

Influence of patient factors on the efficacy of breathing system filters at preventing contamination of breathing systems.

We measured the level of contamination in 207 breathing system filters of five different models. The median (IQR [range]) levels of contamination measured in relative light units on the machine side of the filters were: HMEF 750/S 27 (16-56 [4-13 615]); Ultipor BB25 26 (13-40 [9-66]); Humid-vent filter pedi 19 (15-34 [11-48]); Hygroboy 11 (7-19 [3-113]); and Hygrobaby 9 (6-14 [4-21]). A total of 41/138 (30%) of the HMEF 750/S (the most commonly used filter) had measured values > 50, indicating excessive contamination on the machine side of the filter. The incidence of coughing and duration of the case were significantly associated with the incidence of excessive contamination on the machine side (p = 0.034 and p = 0.024, respectively). Excessive contamination on the machine side of the filter could be from the patient or from the re-used breathing system and could result in cross-infection. The level of contamination may need to be checked routinely during each list.

The effect of desflurane on filtration performance of breathing system filters.

This study assessed the effect of desflurane on the filtration performance of six breathing system filters intended for use with adults. Three filters contained an electrostatic filter material and three contained a pleated glass fibre filter material. Five samples of each model of filter were exposed to 6% v/v of desflurane for 1 h, 12% v/v of desflurane for 1 h, 12% v/v of desflurane for 4 h and air only for 1 h. Five samples of each filter were also tested without exposure to any vapour or air. The filtration performance was measured by challenging each filter with an aerosol of sodium chloride particles using a Moore's test rig. Penetration of particles through the electrostatic filters increased following exposure to a higher concentration of desflurane for a longer duration (p < 0.001). The effect on two of the pleated filters was not significant (p = 0.55 and p = 0.64). The effect on the remaining pleated filter was significant (p < 0.001) but small. The efficiency of some filters decreases when they are exposed to high concentrations of desflurane for a long duration. This effect appears more marked in electrostatic filters compared with pleated filters.

Comparison of fibrescope guided intubation via the classic laryngeal mask airway and i-gel in a manikin.

We compared the classic laryngeal mask airway and i-gel as adjuncts to fibrescope guided intubation in a manikin. Two methods of intubation were compared with each device: the tracheal tube directly over the fibrescope; and the tracheal tube over an Aintree Intubation Catheter. Thirty-two anaesthetists took part in this randomised crossover study. Each anaesthetist performed two intubations with each method via each device. The mean (SD) time for the first intubation using the tracheal tube over the fibrescope was 43 (24) s with the classic laryngeal mask airway and 22 (9) s with the i-gel (95% CI for the difference 12-30 s, p < 0.0001). The mean (SD) times for the first intubation when using the Aintree Intubation Catheter was 46 (24) s with the classic laryngeal mask airway and 37 (9) s with the i-gel (95% CI for the difference 5-12 s, p < 0.0001). We recorded five (5/64, 8%) oesophageal intubations when using the classic laryngeal mask airway and none when using the i-gel. The participants rated the ease of railroading of the tracheal tube and railroading the Aintree Intubation Catheter over the fibrescope to be significantly easier (p < 0.0001 and p = 0.002 respectively) when using the i-gel than when using the classic laryngeal mask airway. Furthermore, 30/32 (94%) of anaesthetists reported preference for the i-gel over the classic laryngeal mask airway for fibrescope guided tracheal intubation when managing a difficult airway. We conclude that the i-gel is likely to be a more appropriate conduit than the classic laryngeal mask airway for fibrescope guided intubation irrespective of the intubation method used.