A quantitative evaluation of aerosol generation during supraglottic airway insertion and removal

Many guidelines consider supraglottic airway use to be an aerosol-generating procedure. This status requires increased levels of personal protective equipment, fallow time between cases and results in reduced operating theatre efficiency. Aerosol generation has never been quantitated during supraglottic airway use. To address this evidence gap, we conducted real-time aerosol monitoring (0.3–10-µm diameter) in ultraclean operating theatres during supraglottic airway insertion and removal. This showed very low background particle concentrations (median (IQR [range]) 1.6 (0–3.1 [0–4.0]) particles.l⁻¹) against which the patient’s tidal breathing produced a higher concentration of aerosol (4.0 (1.3–11.0 [0–44]) particles.l⁻¹, p = 0.048). The average aerosol concentration detected during supraglottic airway insertion (1.3 (1.0–4.2 [0–6.2]) particles.l⁻¹, n = 11), and removal (2.1 (0–17.5 [0–26.2]) particles.l⁻¹, n = 12) was no different to tidal breathing (p = 0.31 and p = 0.84, respectively). Comparison of supraglottic airway insertion and removal with a volitional cough (104 (66–169 [33–326]), n = 27), demonstrated that supraglottic airway insertion/removal sequences produced <4% of the aerosol compared with a single cough (p < 0.001). A transient aerosol increase was recorded during one complicated supraglottic airway insertion (which initially failed to provide a patent airway). Detailed analysis of this event showed an atypical particle size distribution and we subsequently identified multiple sources of non-respiratory aerosols that may be produced during airway management and can be considered as artefacts. These findings demonstrate supraglottic airway insertion/removal generates no more bio-aerosol than breathing and far less than a cough. This should inform the design of infection prevention strategies for anaesthetists and operating theatre staff caring for patients managed with supraglottic airways.     

The effect of neuromuscular blockade on the efficiency of facemask ventilation in patients difficult to facemask ventilate: a prospective trial

Facemask ventilation of the lungs can be an important rescue intervention in a ‘cannot intubate’ scenario. We assessed the effect of neuromuscular blockade on expiratory tidal volumes in patients with expected difficulty in mask ventilation. The lungs of patients with at least three predictors of difficulty in mask ventilation were ventilated using a facemask held with two hands, with mechanical ventilation set in a pressure‐controlled mode. Tidal volumes were recorded before and after the establishment of complete neuromuscular block. In 113 patients, median (IQR [range]) tidal volume increased from 350 (260–492 [80–850]) ml initially, by 48% to 517 (373–667 [100–1250]) ml 30 s after rocuronium administration, (p < 0.001). After the onset of the complete neuromuscular block, a median tidal volume of 600 (433–750 [250–1303]) ml was observed, corresponding to an increase of 71% from baseline values (p < 0.001), and 16% from values obtained 30 s after rocuronium administration, respectively; p = 0.003). No decrease in the tidal volume during the measurements was observed. We conclude that the administration of rocuronium at a dose of 0.6 mg.kg^?1 was able to improve facemask ventilation in all cases with a potentially clinically relevant increase in tidal volume. The early use of a neuromuscular blocking agent can be considered as a therapeutic option in case of difficulty with mask ventilation.     

A quantitative evaluation of aerosol generation during tracheal intubation and extubation

The potential aerosolised transmission of severe acute respiratory syndrome coronavirus-2 is of global concern. Airborne precaution personal protective equipment and preventative measures are universally mandated for medical procedures deemed to be aerosol generating. The implementation of these measures is having a huge impact on healthcare provision. There is currently a lack of quantitative evidence on the number and size of airborne particles produced during aerosol-generating procedures to inform risk assessments. To address this evidence gap, we conducted real-time, high-resolution environmental monitoring in ultraclean ventilation operating theatres during tracheal intubation and extubation sequences. Continuous sampling with an optical particle sizer allowed characterisation of aerosol generation within the zone between the patient and anaesthetist. Aerosol monitoring showed a very low background particle count (0.4 particles.l⁻¹) allowing resolution of transient increases in airborne particles associated with airway management. As a positive reference control, we quantitated the aerosol produced in the same setting by a volitional cough (average concentration, 732 (418) particles.l⁻¹, n = 38). Tracheal intubation including facemask ventilation produced very low quantities of aerosolised particles (average concentration, 1.4 (1.4) particles.l⁻¹, n = 14, p < 0.0001 vs. cough). Tracheal extubation, particularly when the patient coughed, produced a detectable aerosol (21 (18) l⁻¹, n = 10) which was 15-fold greater than intubation (p = 0.0004) but 35-fold less than a volitional cough (p < 0.0001). The study does not support the designation of elective tracheal intubation as an aerosol-generating procedure. Extubation generates more detectable aerosol than intubation but falls below the current criterion for designation as a high-risk aerosol-generating procedure. These novel findings from real-time aerosol detection in a routine healthcare setting provide a quantitative methodology for risk assessment that can be extended to other airway management techniques and clinical settings. They also indicate the need for reappraisal of what constitutes an aerosol-generating procedure and the associated precautions for routine anaesthetic airway management.     

Aerosol generation with the use of positive pressure ventilation via supraglottic airway devices: an observational study

The amount of aerosol generation associated with the use of positive pressure ventilation via a supraglottic airway device has not been quantified. We conducted a two-group, two-centre, prospective cohort study in which we recruited 21 low-risk adult patients scheduled for elective surgery under general anaesthesia with second-generation supraglottic airway devices. An optical particle sizer and an isokinetic sampling probe were used to record particle concentrations per second at different size distributions (0.3–10 μm) during use as well as baseline levels during two common activities (conversation and coughing). There was a median (IQR [range]) peak increase of 2.8 (1.5–4.5 [1–28.1]) and 4.1 (2.0–7.1 [1–18.2]) times background concentrations during SAD insertion and removal. Most of the particles generated during supraglottic airway insertion (85.0%) and removal (85.3%) were < 3 μm diameter. Median (IQR [range]) aerosol concentration generated by insertion (1.1 (0.6–5.1 [0.2–22.3]) particles.cm⁻³) and removal (2.1 (0.5–3.0 [0.1–18.9]) particles.cm⁻³) of SADs were significantly lower than those produced during continuous talking (44.5 (28.3–70.5 [2.0–134.5]) particles.cm⁻³) and coughing (141.0 (98.3–202.8 [4.0–296.5]) particles.cm⁻³) (p < 0.001). The aerosol levels produced were similar with the two devices. The proportion of easily inhaled and small particles (<1 μm) produced during insertion (57.5%) and removal (57.5%) was much lower than during talking (99.1%) and coughing (99.6%). These results suggest that the use of supraglottic airway devices in low-risk patients, even with positive pressure ventilation, generates fewer aerosols than speaking and coughing in awake patients.     

A quantitative evaluation of aerosol generation during awake tracheal intubation

Aerosol-generating procedures are medical interventions considered high risk for transmission of airborne pathogens. Tracheal intubation of anaesthetised patients is not high risk for aerosol generation; however, patients often perform respiratory manoeuvres during awake tracheal intubation which may generate aerosol. To assess the risk, we undertook aerosol monitoring during a series of awake tracheal intubations and nasendoscopies in healthy participants. Sampling was undertaken within an ultraclean operating theatre. Procedures were performed and received by 12 anaesthetic trainees. The upper airway was topically anaesthetised with lidocaine and participants were not sedated. An optical particle sizer continuously sampled aerosol. Passage of the bronchoscope through the vocal cords generated similar peak median (IQR [range]) aerosol concentrations to coughing, 1020 (645–1245 [120–48,948]) vs. 1460 (390–2506 [40–12,280]) particles.l^-1 respectively, p = 0.266. Coughs evoked when lidocaine was sprayed on the vocal cords generated 91,700 (41,907–166,774 [390–557,817]) particles.l^-1 which was significantly greater than volitional coughs (p < 0.001). For 38 nasendoscopies in 12 participants, the aerosol concentrations were relatively low, 180 (120–525 [0–9552]) particles.l^-1, however, five nasendoscopies generated peak aerosol concentrations greater than a volitional cough. Awake tracheal intubation and nasendoscopy can generate high concentrations of respiratory aerosol. Specific risks are associated with lidocaine spray of the larynx, instrumentation of the vocal cords, procedural coughing and deep breaths. Given the proximity of practitioners to patient-generated aerosol, airborne infection control precautions are appropriate when undertaking awake upper airway endoscopy (including awake tracheal intubation, nasendoscopy and bronchoscopy) if respirable pathogens cannot be confidently excluded.     

A cohort evaluation of the paediatric i-gel(™) airway during anaesthesia in 120 children

We studied the i‐gel? in 120 anaesthetised children (92 boys, 28 girls; median (IQR [range]) age (3 ‐7 [0.4 ‐13]) years and weight 19 (15–26 [7–35]) kg) to assess efficacy and usability. Insertion was successful on the first/second/third attempt in 110/8/1 children and failed in one child. Median (IQR [range]) insertion time was 14 (9–16 [6–200]) s. Manual ventilation was possible in all cases, although excess leak precluded a tidal volume above 7 ml.kg^?1 in three children. Fibreoptic inspection through the i‐gel revealed a clear view of the vocal cords in 40 out of 46 cases (87%). Median (IQR [range]) leak pressure was 20 (16–26 [8–30]) cmH₂O. During maintenance of anaesthesia, 16 manipulations were required in 11 children to improve the airway. One child regurgitated without aspirating. Other complications and side effects were infrequent. The i‐gel was inserted without complications, establishing a clear airway and enabling spontaneous and controlled ventilation, in 113 (94%) children. You can respond to this article at http://www.anaesthesiacorrespondence.com     

Facemask ventilation and vocal cord angle following neuromuscular blockade: a prospective observational study#

Numerous studies support the idea that neuromuscular blockade facilitates facemask ventilation after induction of anaesthesia. Although improved airway patency or pulmonary compliance and a resolution of laryngospasm have been suggested as possible causes, the exact mechanism remains unclear. We aimed to assess whether neuromuscular blockade improves facemask ventilation and to clarify whether this phenomenon is associated with the vocal cord angle. This prospective observational study included patients aged between 20 and 65 years scheduled for elective surgery under general anaesthesia. After induction of anaesthesia, patients' lungs were ventilated with pressure-controlled ventilation using a facemask. During facemask ventilation, a flexible bronchoscope was inserted through a self-sealing diaphragm at the elbow connector attached to the facemask and breathing circuit and positioned to allow a continuous view of the vocal cords. The mean tidal volume and vocal cord angle were measured before and after administration of neuromuscular blocking drugs. Of 108 patients, 100 completed the study. Mean (SD) tidal volume ((11.0 (3.9) ml.kg^-1 vs. 13.6 (2.6) ml.kg^-1; p < 0.001) and mean (SD) vocal cord angle (17° (10°) vs. 26° (5°); p < 0.001) increased significantly after neuromuscular blockade. The proportional increase in mean tidal volume after neuromuscular blockade was positively correlated with vocal cord angle (Spearman's ρ = 0.803; p < 0.001). In conclusion, neuromuscular blockade facilitated facemask ventilation, and the improvement was correlated with further opening of the vocal cords.     

The effect of respiratory activity,non-invasive respiratory support and facemasks on aerosol generation and its relevance to COVID-19

Respirable aerosols (< 5 µm in diameter) present a high risk of SARS-CoV-2 transmission. Guidelines recommend using aerosol precautions during aerosol-generating procedures, and droplet (> 5 µm) precautions at other times. However, emerging evidence indicates respiratory activities may be a more important source of aerosols than clinical procedures such as tracheal intubation. We aimed to measure the size, total number and volume of all human aerosols exhaled during respiratory activities and therapies. We used a novel chamber with an optical particle counter sampling at 100 l.min^-1 to count and size-fractionate close to all exhaled particles (0.5–25 µm). We compared emissions from ten healthy subjects during six respiratory activities (quiet breathing; talking; shouting; forced expiratory manoeuvres; exercise; and coughing) with three respiratory therapies (high-flow nasal oxygen and single or dual circuit non-invasive positive pressure ventilation). Activities were repeated while wearing facemasks. When compared with quiet breathing, exertional respiratory activities increased particle counts 34.6-fold during talking and 370.8-fold during coughing (p < 0.001). High-flow nasal oxygen 60 at l.min^-1 increased particle counts 2.3-fold (p = 0.031) during quiet breathing. Single and dual circuit non-invasive respiratory therapy at 25/10 cm.H₂O with quiet breathing increased counts by 2.6-fold and 7.8-fold, respectively (both p < 0.001). During exertional activities, respiratory therapies and facemasks reduced emissions compared with activities alone. Respiratory activities (including exertional breathing and coughing) which mimic respiratory patterns during illness generate substantially more aerosols than non-invasive respiratory therapies, which conversely can reduce total emissions. We argue the risk of aerosol exposure is underappreciated and warrants widespread, targeted interventions.     

A comparison of gastric gas volumes measured by computed tomography after high-flow nasal oxygen therapy or conventional facemask ventilation*

High-flow nasal oxygen therapy is increasingly used to improve peri-intubation oxygenation. However, it is unknown whether it may cause or exacerbate insufflation of gas into the stomach. High-flow nasal oxygen therapy is now standard practice in our hospital for adult patients undergoing percutaneous thermal ablation of liver cancer under general anaesthesia with tracheal intubation. We compared gastric gas volumes measured from computed tomography images that had been acquired immediately after intubation in two series of patients: 50 received peri-intubation high-flow nasal oxygen therapy and another 50 received conventional facemask pre-oxygenation and ventilation before intubation and before high-flow nasal oxygen therapy became standard practice in our unit. Median (IQR [range]) gastric gas volume was 24.0 (14.2–59.9 [3–167]) cm³ in the high-flow nasal oxygen therapy group and 23.8 (12.6–38.8 [0–185]) cm³ in the facemask group. There was no difference between the two groups in the volume of gastric gas measured by computed tomography imaging (Mann–Whitney U-test, U = 1136, p = 0.432, n₁ = n₂ = 50). Our results demonstrate that a small volume of gastric gas is commonly present after induction of anaesthesia, but that the use of peri-intubation high-flow nasal oxygen therapy for pre-oxygenation and during apnoea does not increase this volume compared with conventional facemask pre-oxygenation and ventilation. This is clinically relevant, as high-flow nasal oxygen therapy is increasingly being used in a peri-intubation context and in patients at higher risk of aspiration.     

Pulse pressure variation to predict fluid responsiveness in spontaneously breathing patients: tidal vs forced inspiratory breathing

We evaluated whether pulse pressure variation can predict fluid responsiveness in spontaneously breathing patients. Fifty‐nine elective thoracic surgical patients were studied before induction of general anaesthesia. After volume expansion with hydroxyethyl starch 6 ml.kg^?1, patients were defined as responders by a ≥ 15% increase in the cardiac index. Haemodynamic variables were measured before and after volume expansion and pulse pressure variations were calculated during tidal breathing and during forced inspiratory breathing. Median (IQR [range]) pulse pressure variation during forced inspiratory breathing was significantly higher in responders (n = 29) than in non‐responders (n = 30) before volume expansion (18.2 (IQR 14.7–18.2 [9.3–31.3])% vs 10.1 (IQR 8.3–12.6 [4.8–21.1])%, respectively, p < 0.001). The receiver‐operating characteristic curve revealed that pulse pressure variation during forced inspiratory breathing could predict fluid responsiveness (area under the curve 0.910, p < 0.0001). Pulse pressure variation measured during forced inspiratory breathing can be used to guide fluid management in spontaneously breathing patients.     

Observational study of pre-operative intravenous iron given to anaemic patients before elective cardiac surgery

Cardiac surgical patients with anaemia experience increased morbidity and mortality. Iron deficiency is the most common cause of pre-operative anaemia in this group. We designed and implemented the Cardiff Pathway, a pre-assessment and treatment pathway to identify cardiac surgical patients with anaemia and iron deficiency. Patients identified with anaemia and/or iron deficiency (Hb < 130 g.l^-1 and ferritin < 100 μg.l^-1) were offered intravenous iron infusion 20 mg.kg^-1 pre-operatively. Treatment success was defined as Hb ≥ 130g.l^-1 on the day of surgery. We analysed data from 447 patients: 300 (67%) were not anaemic; 75 (17%) were anaemic and treated with intravenous iron; and 72 (16%) were anaemic and not treated. Haemoglobin concentration increased in successfully treated anaemic patients by a mean (95%CI) of 17 (13–21) g.l^-1 and they received a median (IQR [range]) of 0 (0–2 [0–15]) units of blood peri-operatively. Transfusion was avoided in 54% of the successfully treated anaemic patients, which was significantly more than the unsuccessfully treated anaemic (22%, p = 0.005) and untreated anaemic (28%, p = 0.018) patients and similar to non-anaemic patients who received a median (IQR [range] of 0 (0–1 [0–16])) units of blood and, 63% avoided transfusion). Mean (95%CI) Hb fell between pre-assessment and surgery in the untreated anaemic (-2 (0 to -4) g.l^-1) and non-anaemic groups (-2 (-1 to -3) g.l^-1). Twenty-one (7%) of the non-anaemic group became newly anaemic waiting for surgery. The Cardiff Pathway reliably identified patients with anaemia and iron deficiency. Anaemic patients who had their Hb restored to normal after treatment required less blood peri-operatively and over half of them required no transfusion at all.     

Effect of iron deficiency without anaemia on days alive and out of hospital in patients undergoing valvular heart surgery

Comprehensive evidence regarding the treatment of non-anaemic iron deficiency in patients undergoing valvular heart surgery is lacking. This study aimed to investigate the association between non-anaemic iron deficiency and postoperative outcomes in these patients. We retrospectively analysed 321 patients of which 180 (56%) had iron deficiency (defined as serum ferritin < 100 ng.ml^-1 or < 300 ng.ml^-1 with transferrin saturation < 20%). While the iron-deficient group had lower pre-operative haemoglobin levels than the non-iron deficient group (median (IQR [range]) 134 (127–141 [120–172]) g.l^-1, 143 (133–150 [120–179]) g.l^-1, p = 0.001), there was no between-group difference in allogeneic red blood cell transfusion. Median (IQR [range]) days alive and out of hospital at postoperative day 90 was 1 day shorter in the iron-deficient group (80 (77–82 [9–85]) days vs. 81 (79–83 [0–85]) days, p = 0.026). In multivariable analysis, only cardiopulmonary bypass duration (p = 0.032) and intra-operative allogeneic red blood cell transfusion (p = 0.011) were significantly associated with reduced days alive and out of hospital at postoperative day 90. Iron deficiency did not exert any adverse influence on secondary outcomes except length of hospital stay. Our findings indicate that non-anaemic iron deficiency alone is not associated with adverse effects in patients undergoing valvular heart surgery when it does not translate into an increased risk of allogeneic transfusion.     

A randomised comparison of the self-pressurised air-Q(TM) intubating laryngeal airway with the LMA Unique(TM) in children*

We conducted a randomised trial comparing the self‐pressurised air‐Q^TM intubating laryngeal airway (air‐Q SP) with the LMA‐Unique in 60 children undergoing surgery. Outcomes measured were airway leak pressure, ease and time for insertion, fibreoptic examination, incidence of gastric insufflation and complications. Median (IQR [range]) time to successful device placement was faster with the air‐Q SP (12 (10–15 [5–18])) s than with the LMA‐Unique (14 (12–17 [6–22]) s; p = 0.05). There were no statistically significant differences between the air‐Q SP and LMA‐Unique in initial airway leak pressures (16 (14–18 [10–29]) compared with 18 (15–20 [10–30]) cmH₂O, p = 0.12), an airway leak pressures at 10 min (19 (16–22 [12–30]) compared with 20 (16–22 [10–30]) cmH₂O, p = 0.81); fibreoptic position, incidence of gastric insufflation, or complications. Both devices provided effective ventilation without the need for airway manipulation. The air‐Q SP is an alternative to the LMA‐Unique should the clinician prefer a device not requiring cuff monitoring during anaesthesia.     

Supplementation of standard pre‐oxygenation with nasal prong oxygen or machine oxygen flush during a simulated leak scenario

The presence of a facemask leak significantly reduces the effectiveness of pre‐oxygenation and increases the risk of post‐induction hypoxia. We randomly assigned 24 healthy volunteers to a six‐period crossover trial with and without a simulated facemask leak. Pre‐oxygenation was performed using a standard anaesthesia machine circuit supplemented either by nasal prong oxygen or by anaesthesia machine flush oxygen. Each intervention was completed with both 3‐min tidal breathing and 8 deep breath techniques: end‐tidal oxygen fraction was used as the measure of pre‐oxygenation effectiveness. The presence of a stimulated mask leak significantly reduced the effectiveness of pre‐oxygenation regardless of the breathing method used. With a simulated facemask leak introduced, the mean (SD) end‐tidal oxygen fraction with the 3‐min tidal breath technique was 74.7 (9.3)% compared with 57.5 (6.2%) for the 8 deep breath technique with 3‐min tidal breathing and a leak. End‐tidal oxygen fractions increased by 11.0% (95% CI 7.8–14.3%) (p < 0.0001) with the addition of nasal prong oxygenation and 16.8% (13.6–20.0%) (p < 0.0001) with machine oxygen flush compared with standard pre‐oxygenation. When a leak is present, 3‐min tidal breathing with either nasal prong or anaesthesia machine flush oxygenation is an effective pre‐oxygenation method, and preferable to the 8 deep breath method.     

Borderline anaemia and postoperative outcome in women undergoing major abdominal surgery: a retrospective cohort study

Pre-operative anaemia is typically diagnosed with a haemoglobin concentration < 120 g.l⁻¹ for women and < 130 g.l⁻¹ for men on the basis of limited evidence. This retrospective cohort study stratified women undergoing elective, major abdominal surgery based on pre-operative haemoglobin concentration: anaemic (< 120 g.l⁻¹); borderline anaemic (120–129 g.l⁻¹); and non-anaemic (> 130 g.l⁻¹). Data from 1554 women were analysed. Women with borderline anaemia had a greater incidence of postoperative complications (55 (16%) vs. 110 (11%); p = 0.026), longer duration of hospital stay (median (IQR [range]) 3 (1–6 [0–69]) days vs. 2 (1–5 [0–80]) days; p = 0.017) and fewer days alive and out of hospital at postoperative day 30 (median (IQR [range]) 27 (23–29 [0–30]) vs. 28 (25–29 [0–30]) days; p = 0.017) compared with non-anaemic women. However, after matched cohort analysis, these outcome differences no longer remained statistically significant. After multivariable adjustment for procedure, Charlson comorbidity index and patient age, a negative relationship between logarithmic pre-operative haemoglobin concentration and duration of stay was found (parameter estimate (standard error) −0.006 (0.003) vs. 0.003 (0.003) for a haemoglobin concentration < 130 g.l⁻¹ vs. > 130 g.l⁻¹, respectively; p = 0.03); the difference in duration of stay was approximately 50% greater for women with a haemoglobin concentration of 120 g.l⁻¹ compared with those with a haemoglobin concentration of 130 g.l⁻¹. Although the contribution of borderline anaemia to the incidence of postoperative complications is uncertain, the current diagnostic criteria should be re-assessed.     

Intra‐operative correction of acidosis,coagulopathy and hypothermia in combat casualties with severe haemorrhagic shock

We assessed acidosis, coagulopathy and hypothermia, before and after surgery in 51 combat troops operated on for severe blast injury. Patients were transfused a median (IQR [range]) of 27 (17–38 [5–84]) units of red cell concentrate, 27 (16–38 [4–83]) units of plasma, 2.0 (0.5–3.5 [0–13.0]) units of cryoprecipitate and 4 (2–6 [0–17]) pools of platelets. The pH, base excess, prothrombin time and temperature increased: from 7.19 (7.10–7.29 [6.50–7.49]) to 7.45 (7.40–7.51 [7.15–7.62]); from ?9.0 (?13.5 to ?4.5 [?28 to –2]) mmol.l^?1 to 4.5 (1.0–8.0 [?7 to +11]) mmol.l^?1; from 18 (15–21 [9–24]) s to 14 (11–18 [9–21]) s; and from 36.1 (35.1–37.1 [33.0–38.1]) °C to 37.4 (37.0–37.9 [36.0–38.0]) °C, respectively. Contemporary intra‐operative resuscitation strategies can normalise the physiological derangements caused by haemorrhagic shock.     

Apnoeic oxygenation with high‐flow nasal oxygen for laryngeal surgery: a case series

Surgery under apnoeic conditions with the use of high‐flow nasal oxygen is novel. Between November 2016 and May 2017, 28 patients underwent tubeless laryngeal or tracheal surgery under apnoeic conditions with high‐flow nasal oxygen as the sole method of gas exchange. Patients received total intravenous anaesthesia and neuromuscular blocking agents for the duration of their surgery. The median (IQR [range]) apnoea time was 19 (15–24 [9–37]) min. Four patients experienced an episode of oxygen desaturation to a value between 85% and 90%, lasting less than 2 min in each case. Median (IQR [range]) end‐tidal carbon dioxide (ETCO₂) level following apnoea was 8.2 (7.2–9.4 [5.8–11.8]) kPa. The mean (SD) rate of ETCO₂ increase was 0.17 (0.07) kPa.min^?1 from an approximated baseline value of 5.00 kPa. Venous blood sampling from 19 patients demonstrated a mean (SD) partial pressure of carbon dioxide (P_VCO₂) of 6.29 (0.71) kPa at baseline and 9.44 (1.12) kPa after 15 min of apnoea. This equates to a mean (SD) P_VCO₂ rise of 0.21 (0.08) kPa.min^?1 during this period. Mean (SD) pH was 7.40 (0.03) at baseline and 7.23 (0.04) after 15 min of apnoea. Mean (SD) standard bicarbonate was 26.7 (1.8) mmol.l^?1 at baseline and 25.4 (1.8) mmol.l^?1 at 15 min. We conclude that high‐flow nasal oxygen under apnoeic conditions can provide satisfactory gas exchange in order to allow tubeless anaesthesia for laryngeal surgery.     

Pre‐operative anaemia,intra‐operative hepcidin concentration and acute kidney injury after cardiac surgery: a retrospective observational study

Acute kidney after cardiac surgery is more common in anaemic patients, whereas haemolysis during cardiopulmonary bypass may lead to iron‐induced renal injury. Hepcidin promotes iron sequestration by macrophages: hepcidin concentration is reduced by anaemia and increased by inflammation. We analysed the associations in 525 patients between pre‐operative anaemia (haemoglobin < 130 g.l^?1 in men and < 120 g.l^?1 in women), intra‐operative hepcidin concentration and acute kidney injury (dialysis or > 26.4 μmol.l^?1 or > 50% creatinine increase during the first two days after cardiac surgery. Rates of pre‐operative anaemia and postoperative kidney injury were 109/525 (21%) and 36/525 (7%), respectively. The median (IQR [range]) intra‐operative hepcidin concentration was 20 (10–33 [0–125]) μg.l^?1 and was lower in anaemic patients than those who were not: 15 (4–28 [0–125]) μg.l^?1 vs. 21 (12–33 [0–125]) μg.l^?1, respectively, p = 0.002. Four variables were independently associated with postoperative kidney injury, for which the beta‐coefficients (SE) were: minutes on cardiopulmonary bypass, 0.016 (0.004), p < 0.001; intra‐operative hepcidin concentration, 0.032 (0.008), p < 0.001; pre‐operative anaemia, 1.97 (0.56), p < 0.001; and Cleveland clinic risk score, 0.88 (0.35), p = 0.005. Contrary to generally increased rates of kidney injury in patients with higher hepcidin concentrations, rates of kidney injury in anaemic patients were lower in patients with higher hepcidin concentrations, beta‐coefficient (SE) ?0.037 (0.01), p = 0.007. In cardiac surgical patients the rate of postoperative acute kidney injury predicted by the Cleveland risk score might be adjusted for pre‐operative anaemia and intra‐operative cardiopulmonary bypass time and hepcidin concentration. Pre‐operative correction of anaemia, reduction in intra‐operative bypass time and modification of iron homeostasis and hepcidin concentration might reduce acute kidney injury.     

A randomised comparison of the Ambu® AuraGain™ and the LMA® supreme in infants and children

We conducted a randomised trial in 100 children in order to compare the clinical performance of the Ambu^® AuraGain^? and the LMA^® Supreme^* for airway maintenance during mechanical ventilation. The primary outcomes were initial and 10‐min airway leak pressures. Ease, time and success rates for device and gastric tube insertion, fibreoptic grades of view, airway quality during anaesthetic maintenance, and complications were also assessed. There were no differences in the initial and ten min airway leak pressures between the Ambu AuraGain and LMA Supreme, median (IQR [range]) initial: 19 (16–22 [10–34]) vs 18 (14–24 [8–40]) cmH₂O, p = 0.4; and ten min: 22 (18–26 [11–40]) vs 20 (16–26 [12–40]) cmH₂O, p = 0.08, respectively. Ease, time and success rates for device placement, gastric tube insertion and complications were also not significantly different. Children receiving the LMA Supreme required more airway manouevers (7 vs 1 patient, p = 0.06) to maintain a patent airway. Our results suggest that the Ambu AuraGain may be a useful alternative to the LMA Supreme, as demonstrated by comparable overall clinical performance in children.     

High-flow nasal oxygen vs. standard flow-rate facemask pre-oxygenation in pregnant patients: a randomised physiological study

High-flow nasal oxygen has been shown to provide effective pre-oxygenation and prolong apnoeic time during intubation attempts in non-pregnant patients. We aimed to compare pre-oxygenation using high-flow nasal oxygen (30–70 l.min⁻¹ oxygen flow) via nasal prongs with standard 15 l.min⁻¹ oxygen breathing via a tight-fitting facemask. Forty healthy parturients were randomly allocated to these two groups, and furthermore each patient underwent the selected pre-oxygenation method with both 3-min tidal volume breathing and 30s tidal breathing followed by eight vital capacity breaths. With 3-min tidal volume breathing, the respective estimated marginal means for high-flow nasal oxygen and standard flow rate facemask pre-oxygenation were 87.4% (95%CI 85.5–89.2%) and 91.0% (95%CI 89.3–92.7%), p = 0.02; with eight vital capacity breaths the estimated marginal means were 85.9% (95%CI 84.1–87.7%) and 91.8% (95%CI 90.1–93.4%, p < 0.0001). Furthermore, high-flow nasal oxygen did not reliably achieve a mean end-tidal oxygen concentration ≥ 90% compared with the standard flow rate facemask. In this physiological study, high-flow nasal oxygen pre-oxygenation performed worse than standard flow rate facemask pre-oxygenation in healthy term parturients.