Computer simulation clarifies mechanisms of carbon dioxide clearance during apnoea

BackgroundApnoeic oxygenation can come close to matching the oxygen demands of the apnoeic patient but does not facilitate carbon dioxide (CO2) elimination, potentially resulting in dangerous hypercapnia. Numerous studies have shown that high-flow nasal oxygen administration prevents hypoxaemia, and appears to reduce the rate of increase of arterial CO2 partial pressure (PaCO2), but evidence is lacking to explain these effects.MethodsWe extended a high-fidelity computational simulation of cardiopulmonary physiology to include modules allowing variable effects of: (a) cardiogenic oscillations affecting intrathoracic gas spaces, (b) gas mixing within the anatomical dead space, (c) insufflation into the trachea or above the glottis, and (d) pharyngeal pressure oscillation. We validated this model by reproducing the methods and results of five clinical studies on apnoeic oxygenation.ResultsSimulated outputs best matched clinical data for model selection of parameters reflecting: (a) significant effects of cardiogenic oscillations on alveoli, both in terms of strength of the effect (4.5 cm H2O) and percentage of alveoli affected (60%), (b) augmented gas mixing within the anatomical dead space, and (c) pharyngeal pressure oscillations between 0 and 2 cm H2O at 70 Hz.ConclusionsCardiogenic oscillations, dead space gas mixing, and micro-ventilation induced by pharyngeal pressure variations appear to be important mechanisms that combine to facilitate the clearance of CO2 during apnoea. Evolution of high-flow oxygen insufflation devices should take advantage of these insights, potentially improving apnoeic gas exchange

Visuospatial ability as a predictor of novice performance in ultrasound–guided regional anesthesia

Background: Visuospatial ability correlates positively with novice performance of simple laparoscopic tasks. The aims of this study were to identify if visuospatial ability could predict technical performance of an ultrasound–guided needle task by novice operators, and to describe how emotional state, intelligence and fear of failure impact on this. Methods: Sixty medical student volunteers enrolled in this observational study. We used an instructional video to standardize training for ultrasound-guided needle advancement in a turkey breast model and assessed volunteers’ performance independently by two assessors using composite error score (CES) and global rating scale (GRS). We assessed their ‘visuospatial ability’ with mental rotation test (MRT), group embedded figures test (GEFT) and Alice Heim group ability (AH4) test. ‘Emotional state’ was judged with UWIST mood adjective checklist (UMACL) and fear of failure, and ‘general cognitive ability’ with numerical reasoning test (NRT-20). Results: High CES scores (high error rate) were associated with low MRT scores (= −0.54; P<0.001). Better GRS scores were associated with better MRT scores (= 0.47; P<0.001). Regarding emotions, GRS scores were low when anxiety levels were high (= −0.35; P= 0.005) and CES scores (errors) were low when individuals reported feeling vigorous and active (= −0.30; P= 0.01). Conclusions: MRT predicts novice performance of an ultrasound-guided needling task on a turkey model, and as a trait measure could be used as a tool to focus training resources on less able individuals. Anxiety adversely affects performance. Both may therefore prove useful in directing targeted training in USGRA

Simultaneous temperature and humidity measurements in a mechanical ventilator using an optical fibre sensor

An optical fibre sensor for simultaneous temperature and humidity measurements consisting of one fibre Bragg grating (FBG) to measure temperature and a mesoporous film of bilayers of Poly(allylamine hydrochloride)(PAH) and silica (SiO2) nanoparticles deposited onto the tip of the same fibre to measure humidity is reported. The hygroscopic film was created using the layer-by-layer (LbL) method and the optical reflection spectra were measured up to a maximum of 23 bilayers. The temperature sensitivity of the FBG was 10 pm/°C while the sensitivity to humidity was (-1.4x10-12 W / %RH) using 23 bilayers. The developed sensor was tested in the mechanical ventilator and temperature and humidity of the delivered artificial air was simultaneously measured. Once calibrated, the optical fibre sensor has the potential to control the absolute humidity as an essential part of critical respiratory care. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Characterization and use of a fiber optic sensor based on PAH/SiO2 film for humidity sensing in ventilator care equipment

Objective: To develop a compact probe that can be used to monitor humidity in ventilator care equipment. A mesoporous film of alternate layers of Poly(allylamine hydrochloride) (PAH) and silica (SiO2) nanoparticles (bilayers), deposited onto an optical fibre was used. The sensing film behaves as a Fabry-Perot cavity of low-finesse where the absorption of water vapour changes the optical thickness and produces a change in reflection proportional to humidity. Methods: The mesoporous film was deposited upon the cleaved tip of an optical fibre using the layer-by-layer method. The sensor was calibrated in a bench model against a commercially available capacitive sensor. The sensitivity and response time were assessed in the range from 5 % relative humidity (RH) to 95 %RH for different numbers of bilayers up to a maximum of nine. Results: The sensitivity increases with the number of bilayers deposited; sensitivity of 2.28 mV/%RH was obtained for nine bilayers. The time constant of the response was 1.13 s ± 0.30 s which is faster than the commercial device (measured as 158 s). After calibration, the optical fibre humidity sensor was utilised in a bench top study employing a mechanical ventilator. The fast response time enabled changes in humidity in individual breaths to be resolved. Conclusion: Optical fibre sensors have the potential to be used to monitor breath to breath humidity during ventilator care. Significance: Control of humidity is an essential part of critical respiratory care and the developed sensor provides a sensitive, compact and fast method of humidity monitoring

Validity and reliability of an objective structured assessment tool for performance of ultrasound-guided regional anaesthesia

Background: We aimed to examine the validity and reliability of previously developed criterion-referenced assessment checklist (AC) and global rating scale (GRS) to assess performance in ultrasound-guided regional anaesthesia (UGRA). Methods: Twenty-one anaesthetists’ single, real-time, UGRA procedures (total: 21 blocks) were assessed using 22-item AC and 9-item GRS scored on a 3-point and 5-point Likert scales respectively. We used one-way ANOVA to compare assessment scores between 3 groups (group I: ≤30 blocks in the preceding year; group II: 31–100; group III: >100). Concurrent validity was evaluated using Pearson’s correlation (r). We calculated type-A intra- class correlation coefficient (ICC) using an absolute agreement definition in two-way random effects model, and inter-rater reliability (IRR) using absolute agreement between raters. The inter-item consistency was assessed by Cronbach’s alpha (α). Results: Greater UGRA experience in the preceding year was associated with better AC [F (2,18) 12.01; p <0.001] and GRS [F (2,18) 7.44; p =0.004] scores. There was strong correlation between mean AC and GRS scores [r=0.73 (p <0.001)] and strong inter-item consistency for AC (α = 0.94) and GRS (α = 0.83). The ICC (95% CI) and IRR (95% CI) for AC was 0.96 (0.95 – 0.96) and 0.91 (0.88 – 0.95) respectively and 0.93 (0.90 – 0.94) and 0.80 (0.74 – 0.86) for GRS. Conclusions: Both assessments differentiated between individuals who have performed fewer (≤30) and many (>100) blocks in the preceding year, supporting construct validity. It also established concurrent validity and overall reliability. We recommend both tools may be used in UGRA assessment

Validity and reliability of an objective structured assessment tool for performance of ultrasound-guided regional anaesthesia

Background: We aimed to examine the validity and reliability of previously developed criterion-referenced assessment checklist (AC) and global rating scale (GRS) to assess performance in ultrasound-guided regional anaesthesia (UGRA). Methods: Twenty-one anaesthetists’ single, real-time, UGRA procedures (total: 21 blocks) were assessed using 22-item AC and 9-item GRS scored on a 3-point and 5-point Likert scales respectively. We used one-way ANOVA to compare assessment scores between 3 groups (group I: ≤30 blocks in the preceding year; group II: 31–100; group III: >100). Concurrent validity was evaluated using Pearson’s correlation (r). We calculated type-A intra- class correlation coefficient (ICC) using an absolute agreement definition in two-way random effects model, and inter-rater reliability (IRR) using absolute agreement between raters. The inter-item consistency was assessed by Cronbach’s alpha (α). Results: Greater UGRA experience in the preceding year was associated with better AC [F (2,18) 12.01; p <0.001] and GRS [F (2,18) 7.44; p =0.004] scores. There was strong correlation between mean AC and GRS scores [r=0.73 (p <0.001)] and strong inter-item consistency for AC (α = 0.94) and GRS (α = 0.83). The ICC (95% CI) and IRR (95% CI) for AC was 0.96 (0.95 – 0.96) and 0.91 (0.88 – 0.95) respectively and 0.93 (0.90 – 0.94) and 0.80 (0.74 – 0.86) for GRS. Conclusions: Both assessments differentiated between individuals who have performed fewer (≤30) and many (>100) blocks in the preceding year, supporting construct validity. It also established concurrent validity and overall reliability. We recommend both tools may be used in UGRA assessment

High PEEP in ARDS: quantitative evaluation between improved oxygenation and decreased oxygen delivery

Background: Positive end-expiratory pressure (PEEP) is widely used to improve oxygenation and prevent alveolar collapse in mechanically ventilated patients with the acute respiratory distress syndrome (ARDS). While PEEP predictably improves arterial oxygenation, high PEEP strategies have demonstrated equivocal improvements in ARDS mortality. The effect of PEEP on tissue oxygen delivery is poorly understood and is difficult to quantify or investigate in the clinical environment. Methods: We investigated the effects of PEEP on tissue oxygen delivery in ARDS using a novel, high-fidelity, computational model with highly integrated respiratory and cardiovascular systems. The model was configured to replicate published clinical trial data on the responses of individual ARDS patients to changes in PEEP. These virtual patients were subjected to increasing PEEP levels during a lung-protective ventilation strategy (0 - 20 cmH2O). Measured variables included arterial oxygenation, cardiac output, peripheral oxygen delivery and alveolar strain. Results: As PEEP increased, tissue oxygen delivery decreased in all subjects (mean reduction 25% at 20 cmH2O PEEP), despite an increase in arterial oxygen tension (mean increase 6.7 kPa, at 20 cmH2O PEEP). Changes in arterial oxygenation and tissue oxygen delivery differed between subjects, but showed a consistent pattern. Static and dynamic alveolar strain decreased in all patients as PEEP increased. Conclusions: Incremental PEEP in ARDS appears to protect alveoli and improve arterial oxygenation, but also appears to significantly impair tissue oxygen delivery due to reduced cardiac output. We propose why this trade-off may explain the poor improvements in mortality associated with high PEEP ventilation strategies

Professionalism, Golf Coaching and a Master of Science Degree: A commentary

As a point of reference I congratulate Simon Jenkins on tackling the issue of professionalism in coaching. As he points out coaching is not a profession, but this does not mean that coaching would not benefit from going through a professionalization process. As things stand I find that the stimulus article unpacks some critically important issues of professionalism, broadly within the context of golf coaching. However, I am not sure enough is made of understanding what professional (golf) coaching actually is nor how the development of a professional golf coach can be facilitated by a Master of Science Degree (M.Sc.). I will focus my commentary on these two issues