Quantitative evaluation of aerosol generation during manual facemask ventilation

Manual facemask ventilation, a core component of elective and emergency airway management, is classified as an aerosol-generating procedure. This designation is based on one epidemiological study suggesting an association between facemask ventilation and transmission during the SARS-CoV-1 outbreak in 2003. There is no direct evidence to indicate whether facemask ventilation is a high-risk procedure for aerosol generation. We conducted aerosol monitoring during routine facemask ventilation and facemask ventilation with an intentionally generated leak in anaesthetised patients. Recordings were made in ultraclean operating theatres and compared against the aerosol generated by tidal breathing and cough manoeuvres. Respiratory aerosol from tidal breathing in 11 patients was reliably detected above the very low background particle concentrations with median [IQR (range)] particle counts of 191 (77–486 [4–1313]) and 2 (1–5 [0–13]) particles.l^-1, respectively, p = 0.002. The median (IQR [range]) aerosol concentration detected during facemask ventilation without a leak (3 (0–9 [0–43]) particles.l^-1) and with an intentional leak (11 (7–26 [1–62]) particles.l^-1) was 64-fold (p = 0.001) and 17-fold (p = 0.002) lower than that of tidal breathing, respectively. Median (IQR [range]) peak particle concentration during facemask ventilation both without a leak (60 (0–60 [0–120]) particles.l^-1) and with a leak (120 (60–180 [60–480]) particles.l^-1) were 20-fold (p = 0.002) and 10-fold (0.001) lower than a cough (1260 (800–3242 [100–3682]) particles.l^-1), respectively. This study demonstrates that facemask ventilation, even when performed with an intentional leak, does not generate high levels of bioaerosol. On the basis of this evidence, we argue facemask ventilation should not be considered an aerosol-generating procedure.     

Effects of Muscle Relaxants on Mask Ventilation in Anesthetized Persons with Normal Upper Airway Anatomy

BACKGROUND:: Recent studies suggest advantages of muscle relaxants for facemask ventilation. However, direct effects of muscle relaxants on mask ventilation remain unclear because these studies did not control mechanical factors influencing ventilation. We tested a hypothesis that muscle relaxants, either rocuronium or succinylcholine, improve mask ventilation. METHODS:: In anesthetized adult persons with normal upper airway anatomy, tidal volumes during facemask ventilation were measured while maintaining the neutral head and mandible positions and the airway pressures of a ventilator before and during muscle paralysis induced by either rocuronium (n = 14) or succinylcholine (n = 17). Tidal volumes of oral and nasal airway routes were separately measured with a custom-made oronasal portioning full facemask. Behavior of the oral airway was observed by an endoscope in six additional subjects receiving succinylcholine. RESULTS:: Total, oral, and nasal tidal volumes did not significantly change at complete muscle paralysis with rocuronium. In contrast, succinylcholine significantly increased total tidal volumes at 60 s after its administration (mean ± SD; 4.2 ± 2.1 vs. 5.4 ± 2.6 ml/kg, P = 0.02) because of increases of ventilation through both airway routes. Abrupt tidal volume increase occurred more through oral airway route than nasal route. Dilation of the space at the isthmus of the fauces was endoscopically observed during pharyngeal fasciculation in all six subjects. CONCLUSIONS:: Rocuronium did not deteriorate facemask ventilation, and it was improved after succinylcholine administration in association with airway dilation during pharyngeal fasciculation. This effect continued to a lesser degree after resolution of the fasciculation.     

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.     

Evaluation of changes in tidal volume during mask ventilation following administration of neuromuscular blocking drugs

The practice of checking the ability to mask ventilate before administering neuromuscular blocking drugs remains controversial. We prospectively evaluated the changes in the expired tidal volume during pressure‐controlled ventilation (two‐handed mask ventilation technique) as a surrogate marker to assess the ease of mask ventilation following administration of rocuronium. After informed consent, 125 patients were anaesthetised using a standard induction technique consisting of fentanyl, propofol and rocuronium, with anaesthesia then maintained with isoflurane in oxygen. The mean (SD) expired tidal volume before administration of rocuronium increased by 61 (13) ml at 2 min following onset of neuromuscular block (p < 0.001). This supports the concept that neuromuscular blockade induced by rocuronium facilitates mask ventilation.     

A comparison of the laryngeal mask airway with the facemask and oropharyngeal airway for manual ventilation by first responders in children

In adults, first responders to a cardiopulmonary arrest provide better ventilation using a laryngeal mask airway than a facemask. It is unclear if the same is true in children. We investigated this by comparing the ability of 36 paediatric ward nurses to ventilate the lungs of 99 anaesthetised children (a model for cardiopulmonary arrest) using a laryngeal mask airway and using a facemask with an oropharyngeal airway. Anteroposterior chest wall displacement was measured using an ultrasonic detector. Nurses achieved successful ventilation in 74 (75%) of cases with the laryngeal mask airway and 76 (77%) with facemask and oropharyngeal airway (p = 0.89). Median (IQR [range]) time to first breath was longer for the laryngeal mask airway (48 (39–65 [8–149])) s than the facemask/airway (35 (25–53 [14–120]) s; p < 0.0001). In 10 cases (10%) the lungs were ventilated using the laryngeal mask airway but not using the facemask/oropharyngeal airway. We conclude that ventilation is achieved rapidly using a facemask and oropharyngeal airway, and that the laryngeal mask airway may represent a useful second line option for first responders.     

The effect of neuromuscular blockade on mask ventilation

We wished to test the hypothesis that neuromuscular blockade facilitates mask ventilation. In order reliably and reproducibly to assess the efficiency of mask ventilation, we developed a novel grading scale (Warters scale), based on attempts to generate a standardised tidal volume. Following induction of general anaesthesia, a blinded anaesthesia provider assessed mask ventilation in 90 patients using our novel grading scale. The non-blinded anaesthesiologist then randomly administered rocuronium or normal saline. After 2 min, mask ventilation was reassessed by the blinded practitioner. Rocuronium significantly improved ventilation scores on the Warters scale (mean (SD) 2.3 (1.6) vs 1.2 (0.9), p<0.001). In a subgroup of patients with a baseline Warters scale value of >3 (i.e. difficult to mask ventilate; n=14), the ventilation scores also showed significant improvement (4.2 (1.2) vs 1.9 (1.0), p=0.0002). Saline administration had no effect on ventilation scores. Our data indicate that neuromuscular blockade facilitates mask ventilation. We discuss the implications of this finding for unexpected difficult airway management and for the practice of confirming adequate mask ventilation before the administration of neuromuscular blockade.     

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.     

Airway obstruction with cricoid pressure and lateral tilt

We studied the effect of cricoid pressure and lateral tilt on airway patency during ventilation by facemask in a simulated obstetric setting. The lungs of 50 patients were ventilated by facemask and Guedel airway using a Nuffield Penlon 200 ventilator and Bain system with standard settings. Expired tidal volumes and peak inspiratory pressures were recorded for 10 breaths in each of four combinations: supine with no cricoid pressure, supine with cricoid pressure, 15 degrees lateral tilt with no cricoid pressure and 15 degrees lateral tilt with cricoid pressure. The timing of cricoid pressure was randomised and blinded to all observers. In both supine and tilted positions, cricoid pressure produced a reduction in tidal volume (p < 0.001) and an increase in peak inspiratory pressure (p < 0.001). Cricoid pressure with lateral tilt did not produce any additional airway obstruction to that in the supine position. Complete airway obstruction (tidal volume < 200 ml) resulted on three occasions, all with cricoid pressure applied.     

The effect of neuromuscular blockade on the efficiency of mask ventilation of the lungs

We conducted a two-part study to assess the practice of withholding neuromuscular blockade until the ability to ventilate the lungs using a bag and face mask (mask ventilation) has been established following induction of anaesthesia. The first part of the study consisted of a postal survey (71% response rate) of 188 anaesthetists in the Oxford region to assess their current practice. Thirty per cent of respondents always checked mask ventilation before administering a neuromuscular blocking drug, whereas 39% of respondents (all them consultants) never did this. A further 31% only did so in the case of known or anticipated difficulty with the airway. In the second part of the study, we measured inspired (V(TI)) and expired (V(TE)) tidal volumes before and after neuromuscular blockade in 30 patients undergoing general anaesthesia. The ratio V(TE)/V(TI) was used as a measure of the efficiency of ventilation. There was no difference in V(TE)/V(TI) before [mean (SD) 0.47 (0.13)] and after [0.45 (0.13)] neuromuscular blockade. We conclude that neuromuscular blockade does not affect the efficiency of mask ventilation in patients with normal airways.     

The Tulip GT® airway versus the facemask and Guedel airway: a randomised,controlled, cross‐over study by Basic Life Support‐trained airway providers in anaesthetised patients

We performed a randomised, controlled, cross‐over study of lung ventilation by Basic Life Support‐trained providers using either the Tulip GT^® airway or a facemask with a Guedel airway in 60 anaesthetised patients. Successful ventilation was achieved if the provider produced an end‐tidal CO₂ > 3.5 kPa and a tidal volume > 250 ml in two of the first three breaths, within 60 sec and within two attempts. Fifty‐seven (95%) providers achieved successful ventilation using the Tulip GT compared with 35 (58%) using the facemask (p < 0.0001). Comparing the Tulip GT and facemask, the mean (SD) end‐tidal CO₂ was 5.0 (0.7) kPa vs 2.5 (1.5) kPa, tidal volume was 494 (175) ml vs 286 (186) ml and peak inspiratory pressure was 18.3 (3.4) cmH₂O vs 13.6 (7) cmH₂O respectively (all p < 0.0001). Forty‐seven (78%) users favoured the Tulip GT airway. These results are similar to a previous manikin study using the same protocol, suggesting a close correlation between human and manikin studies for this airway device. We conclude that the Tulip GT should be considered as an adjunct to airway management both within and outside hospitals when ventilation is being undertaken by Basic Life Support‐trained airway providers.     

Cuffed vs. uncuffed tracheal tubes in children: a randomised controlled trial comparing leak,tidal volume and complications

Cuffed tracheal tubes are increasingly used in paediatric anaesthetic practice. This study compared tidal volume and leakage around cuffed and uncuffed tracheal tubes in children who required standardised mechanical ventilation of their lungs in the operating theatre. Children (0–16 years) undergoing elective surgery requiring tracheal intubation were randomly assigned to receive either a cuffed or an uncuffed tracheal tube. Assessments were made at five different time‐points: during volume‐controlled ventilation 6 ml.kg^?1, PEEP 5 cmH₂O and during pressure‐controlled ventilation 10 cmH₂O / PEEP 5 cmH₂O. The pressure‐controlled ventilation measurement time‐points were: just before a standardised recruitment manoeuvre; just after recruitment manoeuvre; 10 min; and 30 min after the recruitment manoeuvre. Problems and complications were recorded. During volume‐controlled ventilation, leakage was significantly less with cuffed tracheal tubes than with uncuffed tracheal tubes; in ml.kg^?1, median (IQR [range]) 0.20 (0.13–0.39 [0.04–0.60]) vs. 0.82 (0.58–1.38 [0.24–4.85]), respectively, p < 0.001. With pressure‐controlled ventilation, leakage was less with cuffed tracheal tubes and stayed unchanged over a 30‐min period, whereas with uncuffed tracheal tubes, leakage was higher and increased further over the 30‐min period. Tidal volumes were higher in the cuffed group and increased over time, but in the uncuffed group were lower and decreased over time. Both groups showed an increase in tidal volumes following recruitment manoeuvres. There were more short‐term complications with uncuffed tracheal tubes, but no major complications were recorded in either group at long‐term follow‐up. With standardised ventilator settings, cuffed tracheal tubes produced better ventilation characteristics compared with uncuffed tracheal tubes during general anaesthesia for routine elective surgery.     

Comparison of the intubating laryngeal mask airway and laryngeal tube placement during manual in-line stabilisation of the neck

We compared the placement of the laryngeal tube (LT) with the intubating laryngeal mask airway (ILMA) in 51 patients whose necks were stabilised by manual in-line traction. Following induction of anaesthesia and neuromuscular blockade, the LT and ILMA were inserted consecutively in a randomised, crossover design. Using pressure-controlled ventilation (20 cmH(2)O inspiratory pressure), we measured insertion attempts, time to establish positive-pressure ventilation, tidal volume, gastric insufflation, and minimum airway pressure at which gas leaked around the cuff. Data were compared using Wilcoxon signed-rank tests; p < 0.05 was considered significant. Insertion was found to be more difficult with the LT (successful at first attempt in 16 patients) than with the ILMA (successful at first attempt in 42 patients, p < 0.0001). Time required for insertion was longer for the LT (28 [23-35] s, median [interquartile range]) than for the ILMA (20 [15-25] s, p = 0.0009). Tidal volume was less for the LT (440 [290-670] ml) than for the ILMA (630 [440-750] ml, p = 0.013). Minimum airway pressure at which gas leak occurred and incidence of gastric insufflation were similar with two devices. In patients whose necks were stabilised with manual in-line traction, insertion of the ILMA was easier and quicker than insertion of the LT and tidal volume was greater with the ILMA than the LT.     

Transfer of airway skills from manikin training to patient: success of ventilation with facemask or LMA‐SupremeTM by medical students

During emergency care, the ability to ventilate the patient's lungs is a crucial skill. Supraglottic airway devices have an established role in emergency care, and manikin trials have shown that placement is easy even for inexperienced users. However, there is current discussion as to what extent these results can be transferred to patients. We studied the transfer of skills learnt on a manikin to the clinical situation in novice medical students during their anaesthesia rotation. They were required to ventilate the lungs of a manikin using a facemask and then position a supraglottic airway device (LMA‐Supreme?) and ventilate the lungs. This process was then repeated on anaesthetised patients, with standard ventilator settings to assess adequacy of ventilation. Sixty‐three students participated in the manikin study. The success rate for ventilating the lungs was 100% for both devices, but the mean (SD) time to achieve successful ventilation was 27.8 (24.4) s with the facemask compared with 38.6 (22.0) s with the LMA‐Supreme (p = 0.008). Fifty‐one of the students progressed to the second part of the study. In anaesthetised patients, the success rate for ventilating the lungs was lower for the facemask, 27/41 (66%) compared with the LMA‐Supreme 37/41 (90%, p = 0.006). For 26 students who succeeded with both devices, the tidal volume was lower using the facemask, 431 (192) ml compared with the LMA‐Supreme 751 (221) ml (p = 0.001), but the time to successful ventilation did not differ, 60.0 (26.2) s vs 57.3 (26.6) s (p = 0.71). We conclude that the results obtained in manikin studies cannot be transferred directly to the clinical situation and that guidelines should take this into account. Based on our findings, a supraglottic airway device may be preferable to a facemask as the first choice for inexperienced emergency caregivers.     

Difficult mask ventilation: does it matter?

We discuss the relevance of finding a patient's lungs difficult to ventilate by facemask during the course of anaesthetic induction. In particular, we discuss the issue of whether it is advisable or unnecessary to check the ability to ventilate by facemask before administering a neuromuscular blocking agent. In the light of advances in supraglottic airway technology it has become possible to insert these devices very soon after induction and in a wider variety of patients. Similarly, the development of videolaryngoscopes and rapidly acting drugs such as rocuronium have raised the possibility of earlier, and possibly more successful, tracheal intubation, with the potential result that mask ventilation becomes redundant. However, we conclude by reaffirming its value in airway management strategies.     

Sniffing position combined with mouth opening improves facemask ventilation in children with adenotonsillar hypertrophy

Background: This study evaluates the influence of sniffing position combined with mouth opening on the effectiveness of facemask ventilation in paralyzed pediatric patients undergoing adenotonsillectomy during sevoflurane‐N₂O anesthesia. Methods: After Institutional Ethics Committee approval, 40 children 5–11 years of age who were scheduled for an elective adenotonsillectomy operation were enrolled in this prospective randomized study. After routine monitoring and pre‐oxygenation, anesthesia was induced with sevoflurane 8% in a mixture of 50% N₂O‐O₂. Three minutes after the administration of vecuronium, the sequence of the positions was randomized. Three positions were applied during facemask ventilation: Position CN (closed mouth – neutral head and neck position), position CS (closed mouth‐sniffing position) and position OS (opened mouth‐sniffing position). Volume‐controlled ventilation was started. Peak inspiratory pressure (PIP), tidal volume (V_T), expired tidal volume (V_Texp) and end‐tidal CO₂ pressure were recorded. The percent of leakage was calculated. The primary endpoint of this study was the expired tidal volume (V_Texp). Results: There was a statistically significant difference among the three positions for V_Texp and PIP values. The OS resulted in higher V_Texp values when compared with CN (P=0.022). The OS was significantly better than the other two positions, resulting in lower PIP values (P<0.001 and P=0.004, for CN and CS, respectively). The OS also resulted in less leakage during facemask ventilation when compared with CN and CS. Conclusions: Sniffing position combined with mouth opening improves V_Texp and PIP values during facemask ventilation during sevoflurane‐N₂O anesthesia in paralyzed pediatric patients with adenotonsillar hypertrophy.     

A comparison of the laryngeal mask airway with facemask and oropharyngeal airway for manual ventilation by critical care nurses in children

The laryngeal mask airway is included as a first line airway device during adult resuscitation by first responders. However, there is little evidence for its role in paediatric resuscitation. Using anaesthetised children as a model for paediatric cardiopulmonary arrest, we compared the ability of critical care nurses to manually ventilate the anaesthetised child via the laryngeal mask airway compared with the facemask and oropharyngeal airway. The airway devices were inserted in random order and chest expansion was measured using an ultrasound distance transducer. The critical care nurses were able to place the laryngeal mask airway and achieve successful ventilation in 82% of children compared to 70% using the facemask and oropharyngeal airway, although the difference was not statistically significant (p = 0.136). The median time to first successful breath using the laryngeal mask airway was 39 s compared to 25 s using the facemask (p < 0.001). In this group of nurses, we did not show a difference in ventilation via a laryngeal mask airway or facemask, although facemask ventilation was achieved more quickly.     

Rocuronium versus vecuronium during fentanyl induction in patients undergoing coronary artery surgery.

OBJECTIVE: To evaluate the neuromuscular, ventilatory, and cardiovascular effects of rocuronium and vecuronium. DESIGN: Randomized, prospective, blinded study. SETTING: Tertiary care teaching center, single institution. PARTICIPANTS: Patients undergoing elective coronary artery bypass graft procedure. INTERVENTIONS: Patients received rocuronium, 1.0 mg/kg (n = 17), or vecuronium, 0.15 mg/kg (n = 15), during fentanyl induction of anesthesia. MEASUREMENTS AND MAIN RESULTS: Measures consisted of time to visual loss of orbicularis oculi twitches in response to facial nerve stimulation, ease of mask ventilation, hemodynamics, need for vasoactive drugs, and tracheal intubating conditions. Median time to twitch loss was faster (p < 0.05) after rocuronium (60 s) than after vecuronium (>84 s). Within 45 seconds, only 3 of 17 patients in the rocuronium group had moderate-to-severe difficulty with mask ventilation versus 12 of 15 patients in the vecuronium group (p < 0.05). Tracheal intubating conditions were excellent in all patients after rocuronium. In the vecuronium group, intubating conditions were excellent in 46%, good in 27%, and poor in 27% (p < 0.05 vrocuronium). Patients receiving vecuronium were more likely to require ephedrine and phenylephrine for hypotension (10/15 patients v 5/17 patients for rocuronium, p < 0.05). There were no clinically important differences in hemodynamic variables, oxygen metabolism, or myocardial ischemia between groups. CONCLUSION: During narcotic induction of anesthesia, rocuronium was associated with lower requirement for vasopressors, faster onset of neuromuscular blockade, and better conditions for mask ventilation and tracheal intubation compared with vecuronium.     

肺保护性通气所致呼吸性酸血症对罗库溴铵神经肌肉阻滞持续时间的影响

目的探讨肺保护性通气所致呼吸性酸血症是否增加罗库溴铵神经肌肉阻滞的持续时间。方法选择择期全麻手术的患者114例,男57例,女57例,年龄20～79岁, BMI 19～28 kg/m~2,ASAⅠ或Ⅱ级。随机分为两组:S组和L组,每组57例。麻醉诱导后,所有患者给予罗库溴铵0.6 mg/kg;S组患者根据预测体重V_T 10 ml/kg,不实施呼气末正压通气(PEEP);L组患者根据预测体重V_T 6 ml/kg,PEEP 5 cmH_2O。第一次抽搐后,立即给予罗库溴铵0.15 mg/kg。采用拇内收肌成串刺激加速度成像监测神经肌肉阻滞程度。记录静注罗库溴铵即刻到第一次抽搐的首次自发恢复时间(T1),从第一次抽搐后首次自发恢复到第二次恢复的时间(T2)。检测首次自发恢复和第二次自发恢复时动脉血pH值、PaCO_2、BE和体温。结果与S组比较,L组T1和T2均明显延长(P0.05)。与S组比较,首次自发恢复和第二次自发恢复时L组pH明显降低,PaCO_2明显升高(P0.01)。两组BE和体温差异无统计学意义。结论肺保护性通气所致呼吸性酸血症可延长罗库溴铵神经肌肉阻滞的持续时间。     

The association of postoperative pulmonary complications in 109,360 patients with pressure‐controlled or volume‐controlled ventilation

We thought that the rate of postoperative pulmonary complications might be higher after pressure‐controlled ventilation than after volume‐controlled ventilation. We analysed peri‐operative data recorded for 109,360 adults, whose lungs were mechanically ventilated during surgery at three hospitals in Massachusetts, USA. We used multivariable regression and propensity score matching. Postoperative pulmonary complications were more common after pressure‐controlled ventilation, odds ratio (95%CI) 1.29 (1.21–1.37), p < 0.001. Tidal volumes and driving pressures were more varied with pressure‐controlled ventilation compared with volume‐controlled ventilation: mean (SD) variance from the median 1.61 (1.36) ml.kg^?1 vs. 1.23 (1.11) ml.kg^?1, p < 0.001; and 3.91 (3.47) cmH₂O vs. 3.40 (2.69) cmH₂O, p < 0.001. The odds ratio (95%CI) of pulmonary complications after pressure‐controlled ventilation compared with volume‐controlled ventilation at positive end‐expiratory pressures < 5 cmH₂O was 1.40 (1.26–1.55) and 1.20 (1.11–1.31) when ≥ 5 cmH₂O, both p < 0.001, a relative risk ratio of 1.17 (1.03–1.33), p = 0.023. The odds ratio (95%CI) of pulmonary complications after pressure‐controlled ventilation compared with volume‐controlled ventilation at driving pressures of < 19 cmH₂O was 1.37 (1.27–1.48), p < 0.001, and 1.16 (1.04–1.30) when ≥ 19 cmH₂O, p = 0.011, a relative risk ratio of 1.18 (1.07–1.30), p = 0.016. Our data support volume‐controlled ventilation during surgery, particularly for patients more likely to suffer postoperative pulmonary complications.     

Gas leakage and the laryngeal mask airway: A comparison with the tracheal tube and facemask during spontaneous ventilation using a circle breathing system

The ability of the laryngeal mask airway, tracheal tube and facemask to provide a leak free seal in a clinical setting was assessed by measuring the minimal fresh gas flows needed in a closed circle system during spontaneous ventilation on 60 subjects. The fresh gas flow was reduced until no spillage occurred from the pop-off valve. This fresh gas flow was taken to represent the sum of gas uptake by the subject and gas leakage from the circuit. The median fresh gas flow after 20 minutes was 350 ml. min⁻¹ in the laryngeal mask airway group, 350 ml. min⁻¹ in the tracheal tube group and 450 ml. min⁻¹ in the facemask group. The fresh gas flow required for the facemask group was significantly higher than that for the laryngeal mask airway or tracheal tube groups (p < 0.01). There was no significant difference between the fresh gas flows required for the tracheal tube and laryngeal mask airway groups. We conclude that the laryngeal mask airway provides as good a gas tight seal as a tracheal tube in this context and would be of benefit in reducing anaesthetic gas pollution.