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.     

Intra‐operative protective mechanical ventilation in lung transplantation: a randomised,controlled trial

Primary graft dysfunction occurs in up to 25% of patients after lung transplantation. Contributing factors include ventilator‐induced lung injury, cardiopulmonary bypass, ischaemia‐reperfusion injury and excessive fluid administration. We evaluated the feasibility, safety and efficacy of an open‐lung protective ventilation strategy aimed at reducing ventilator‐induced lung injury. We enrolled adult patients scheduled to undergo bilateral sequential lung transplantation, and randomly assigned them to either a control group (volume‐controlled ventilation with 5 cmH₂O, positive end‐expiratory pressure, low tidal volumes (two‐lung ventilation 6 ml.kg^?1, one‐lung ventilation 4 ml.kg^?1)) or an alveolar recruitment group (regular step‐wise positive end‐expiratory pressure‐based alveolar recruitment manoeuvres, pressure‐controlled ventilation set at 16 cmH₂O with 10 cmH₂O positive end‐expiratory pressure). Ventilation strategies were commenced from reperfusion of the first lung allograft and continued for the duration of surgery. Regular PaO₂/F_IO₂ ratios were calculated and venous blood samples collected for inflammatory marker evaluation during the procedure and for the first 24 h of intensive care stay. The primary end‐point was the PaO₂/F_IO₂ ratio at 24 h after first lung reperfusion. Thirty adult patients were studied. The primary outcome was not different between groups (mean (SD) PaO₂/F_IO₂ ratio control group 340 (111) vs. alveolar recruitment group 404 (153); adjusted p = 0.26). Patients in the control group had poorer mean (SD) PaO₂/F_IO₂ ratios at the end of the surgical procedure and a longer median (IQR [range]) time to tracheal extubation compared with the alveolar recruitment group (308 (144) vs. 402 (154) (p = 0.03) and 18 (10–27 [5–468]) h vs. 15 (11–36 [5–115]) h (p = 0.01), respectively). An open‐lung protective ventilation strategy during surgery for lung transplantation is feasible, safe and achieves favourable ventilation parameters.     

A new non-radiological method to assess potential lung recruitability: a pilot study in ALI patients

Introduction: Potentially recruitable lung has been assessed previously in patients with acute lung injury (ALI) by computed tomography. A large variability in lung recruitability was observed between patients. In this study, we assess whether a new non‐radiological bedside technique could determine potentially recruitable lung volume (PRLV) in ALI patients. Methods: Sixteen mechanically ventilated patients with early ALI/ARDS were subjected to a recruitment manoeuvre and decremental PEEP titration. Electric impedance tomography, together with measurements of end‐expiratory lung volume (EELV) and tracheal pressure, were used to determine PRLV. The method defines fully recruited open lung volume (OLV) as the volume reached at the end of two consecutive vital capacity manoeuvres to 40 cmH₂O. It also uses extrapolation of the baseline alveolar pressure/volume curve up to 40 cmH₂O, the volume reached being the non‐recruited lung volume. The difference between the fully recruited and the non‐recruited volume was defined as PRLV. Results: We observed a considerable heterogeneity among the patients in lung recruitability, PRLV range 11–47%. In a post hoc analysis, dividing the patients into two groups, a high and a low PRLV group, we found at baseline before the recruitment manoeuvre that the high PRLV group had lower compliance and a lower fraction of EELV/OLV. Conclusions: Using non‐invasive radiation‐free bedside methods, it may be possible to measure PRLV in ALI/ARDS patients. It is possible that this technique could be used to determine the need for recruitment manoeuvres and to select PEEP level on the basis of lung recruitability.     

Effect of ultrasound-guided lung recruitment manoeuvre on perioperative atelectasis during laparoscopy in young infants: A randomised controlled trial

BackgroundPneumoperitoneum is a risk factor for perioperative atelectasis in infants. This research aimed to investigate whether lung recruitment manoeuvres guided by ultrasound are more effective for young infants (<3 months) during laparoscopy under general anaesthesia.MethodsYoung infants (<3 months) undergoing general anaesthesia during laparoscopic surgery (>2 h) were randomised to either conventional lung recruitment (control group) or ultrasound-guided lung recruitment (ultrasound group) once per hour. Mechanical ventilation was started with a tidal volume of 8 mL·kg⁻¹, positive end-expiratory pressure of 6 cm H₂O and 40% inspired oxygen fraction. Lung ultrasound (LUS) was performed four times (T1 was performed 5 min after intubation and before pneumoperitoneum set, T2 was performed after pneumoperitoneum, T3 was performed 1 min after surgery, and T4 was performed before being discharged from post-anaesthesia care unit [PACU]) in each infant. The primary outcome was the incidence of significant atelectasis at T3 and T4 (defined by LUS consolidation score ≥ 2 in any region).Results62 babies were enrolled in the experiment and 60 infants were included in the analysis. Before the recruitment, atelectasis was similar between infants randomised to the control or ultrasound group at T1 (83.3% vs 80.0%; P = 0.500) and T2 (83,3% vs 76.7%; P = 0.519). The incidence of atelectasis at T3 and T4 were lower in the ultrasound group (26.7% and 33.3%), compared with infants randomised to conventional lung recruitment (66.7% and 70%) (P = 0.002; P = 0.004; respectively).ConclusionsUltrasound-guided alveolar recruitment reduced the perioperative incidence of atelectasis in infants <3 months during laparoscopy under general anaesthesia.     

Effect of informational internet web pages on patients’ decision‐making: randomised controlled trial regarding choice of spinal or general anaesthesia for orthopaedic surgery

This study explored whether patients’ preference for particular types of anaesthesia could be influenced pre‐operatively by giving them the addresses of various relevant websites. Patients at an orthopaedic pre‐assessment education clinic completed a questionnaire, which included a short multiple‐choice general knowledge quiz about anaesthesia, and also questioned them as to their choice of anaesthesia (general or neuraxial). Patients were randomly assigned to intervention or control groups. Intervention group members were given the addresses of three relevant anaesthesia and health related websites to access at home. All patients were asked to complete the questionnaires on a second occasion, before surgery. Initially, most patients stated a preference for general anaesthesia. Subsequently, the intervention group altered their preference towards neuraxial anaesthesia compared to the control group (p ≤ 0.0001). The increase in median (IQR [range]) anaesthesia knowledge test score was greater in the intervention group (from 10.0 (9.0–12.0 [5.0–14.0]) to 13.0 (11.0–14.0 [6.0–14.0])) than in the control group (from 10.0 (9.0–11.5 [3.0–13.0]) to 11.0 (9.0–12.0 [4.0–14.0]); p = 0.0068).     

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.     

Efficacité d’une manœuvre de recrutement alvéolaire associée à une pression expiratoire positive sur la mécanique respiratoire en cœliochirurgie bariatrique

Objective

To evaluate recruitment manoeuvre (RM) efficiency associated with a 10 cmH₂O positive end expiratory pressure (PEEP) on respiratory mechanic estimated by lung compliance (Ctp) and PEEP to ZEEP expiratory volume delta (Δ VTE) during laparoscopic bariatric surgery in patients with morbid obesity.

Study design

Prospective randomized study.

Methods

Twenty-six obese patients (BMI > 40 kg/m²) undergoing laparoscopic bariatric surgery. The recruitment group received an RM followed by a 10 cmH₂O PEP versus only 10 cmH₂O PEP in the control group. Ctp was measured during the intervention and functional residual capacity (FRC) was estimated measuring Δ VTE during a PEP to ZEP manoeuvre. Mann and Whitney tests as well as a t-test were used (significance p < 0.05).

Results

In the RM group, a significant improvement of 52 ± 14 ml/cmH₂O was noted versus a 36 ± 10 ml/cmH₂O in the PEP group (p = 0,004). This improvement was transitory and no statistically significant Δ VTE difference was noted between the groups at the end of the intervention (360 [90–770] ml [MRA] and 310 [190–450] ml [PEP]).

Conclusion

In patients with morbid obesity undergoing laparoscopic bariatric surgery, an RM conducted prior the pneumoperitoneum temporarily improves lung mechanics but without any change of the end expiratory lung volume at the end of the surgery in comparison with PEP alone. The RM was well tolerated.     

Oxygen concentration and characteristics of progressive atelectasis formation during anaesthesia

Background: Atelectasis is a common consequence of pre‐oxygenation with 100% oxygen during induction of anaesthesia. Lowering the oxygen level during pre‐oxygenation reduces atelectasis. Whether this effect is maintained during anaesthesia is unknown. Methods: During and after pre‐oxygenation and induction of anaesthesia with 60%, 80% or 100% oxygen concentration, followed by anaesthesia with mechanical ventilation with 40% oxygen in nitrogen and positive end‐expiratory pressure of 3 cmH₂O, we used repeated computed tomography (CT) to investigate the early (0–14 min) vs. the later time course (14–45 min) of atelectasis formation. Results: In the early time course, atelectasis was studied awake, 4, 7 and 14 min after start of pre‐oxygenation with 60%, 80% or 100% oxygen concentration. The differences in the area of atelectasis formation between awake and 7 min and between 7 and 14 min were significant, irrespective of oxygen concentration (P<0.05). During the late time course, studied after pre‐oxygenation with 80% oxygen, the differences in the area of atelectasis formation between awake and 14 min, between 14 and 21 min, between 21 and 28 min and finally between 21 and 45 min were all significant (P<0.05). Conclusion: Formation of atelectasis after pre‐oxygenation and induction of anaesthesia is oxygen and time dependent. The benefit of using 80% oxygen during induction of anaesthesia in order to reduce atelectasis diminished gradually with time.     

Ultrasound‐guided catheterisation of the subclavian vein: freehand vs needle‐guided technique

The objective of this prospective, randomised study was to examine the impact of a multi‐angle needle guide for ultrasound‐guided, in‐plane, central venous catheter placement in the subclavian vein. One hundred and sixty patients were randomly allocated to two groups, freehand or needle‐guided, and then 159 catheterisations were analysed. Cannulation of the first examined access site was successful in 96.9% of cases with no significant difference between groups. There were three arterial punctures and no other severe injuries. Catheter misplacements did not differ between the groups. Higher success rates within the first and second attempts in the needle‐guided group were observed (p = 0.041 and p = 0.019, respectively). Use of the needle guide reduced the access time from a median (IQR [range]) of 30 (18–76 [6–1409]) s to 16 (10–30 [4–295]) s; p = 0.0001, and increased needle visibility from 31.8% (9.7%–52.2% [0–96.67]) to 86.2% (62.5%–100% [0–100]); p < 0.0001. A multi‐angle needle guide significantly improved aligning the needle and ultrasound plane compared with the freehand technique when cannulating the subclavian vein. Use of the guide resulted in faster access times and increased success at the first and second attempts.     

A randomised controlled trial comparing meat‐based with human cadaveric models for teaching ultrasound‐guided regional anaesthesia

The aim of this prospective, blinded, randomised controlled study was to compare novices' acquisition of the technical skills of ultrasound‐guided regional anaesthesia using either a meat phantom model or fresh‐frozen human cadavers. The primary outcome was the time taken to successfully perform an ultrasound‐guided sciatic nerve block on a cadaver; secondary outcomes were the cumulative score of errors, and best image quality of the sciatic nerve achieved. After training, the median (IQR [range]) time taken to perform the block was 311(164–390 [68–600]) s in the meat model trained group and 210 (174–354 [85–600]) s in the fresh‐frozen cadaver trained group (p = 0.24). Participants made a median (IQR [range]) of 18 (14–33 [8–55]) and 15 (12–22 [8–44]) errors in the two groups respectively (p = 0.39). The image quality score was also not different, with a median (IQR [range]) of 62.5 (59.4–65.6 [25.0–100.0])% vs 62.5 (62.5–75.0 [25.0–87.5])% respectively (p = 0.58). The training and deliberate feedback improved all participants' block performance, the median (IQR [range]) times being 310 (206–532 [110–600]) s before and 240 (174–354 [85–600]) s after training (p = 0.02). We conclude that novices taught ultrasound scanning and needle guidance skills using an inexpensive and easily constructed meat model perform similarly to those trained on a cadaveric model.     

A randomised controlled trial of intrathecal blockade versus peripheral nerve blockade for day‐case knee arthroscopy

We allocated 100 patients scheduled for day‐case knee arthroscopy to unilateral spinal anaesthesia with 40 mg intrathecal hyperbaric prilocaine or to ultrasound‐guided femoral‐sciatic nerve blockade with 25 ml mepivacaine 2%, 50 participants each. The median (IQR [range]) time to walk was 285 (240–330 [160–515]) min after intrathecal anaesthesia vs 328 (280–362 [150–435]) min after peripheral nerve blockade, p = 0.007. The median (IQR [range]) time to home discharge was 310 (260–350 [160–520]) min after intrathecal anaesthesia vs 335 (290–395 [190–440]) min after peripheral nerve blockade, p = 0.016. There was no difference in time from anaesthetic preparation to readiness for surgery.     

Recruitment manoeuvres dislodge mucus towards the distal airways in an experimental model of severe pneumonia

Background

Recruitment manoeuvres generate a transient increase in trans-pulmonary pressure that could open collapsed alveoli. Recruitment manoeuvres might generate very high inspiratory airflows. We evaluated whether recruitment manoeuvres could displace respiratory secretions towards the distal airways and impair gas exchange in a porcine model of bacterial pneumonia.

Assessment of block height for satisfactory spinal anaesthesia for caesarean section

We investigated block heights that anaesthetists considered adequate for caesarean section to proceed under spinal anaesthesia. During 3 months, 15 obstetric anaesthetists recorded block height to touch, pinprick or cold when spinal anaesthesia was considered satisfactory for caesarean section to proceed. Median (IQR [range]) block height for touch, pinprick, first cold and icy were: T10 (T7–T12 [T3–L1]); T5 (T4–T6 [C7–L1]); T5 (T4–T6 [C7–L1]); and T3 (T2–T4 [C7–L1]), respectively. Modalities were significantly correlated for: touch and cold, p = 0.0001; touch and icy, p = 0.0007; touch and pinprick, p = 0.0018; cold and icy, p < 0.0001; cold and pinprick, p = 0.0001; icy and pinprick, p < 0.0001. Pairwise comparisons showed differences between all modalities (p < 0.001) apart from pinprick and first cold (p = 0.94). All women had satisfactory anaesthesia despite 76 (81%) having a block to touch below T6. Single modality assessment of block height, particularly using touch, may erroneously indicate inadequate anaesthesia for caesarean section.     

Visualization of alveolar recruitment in a porcine model of unilateral lung lavage using 3He-MRI

Background: In the acute respiratory distress syndrome potentially recruitable lung volume is currently discussed. ³He‐magnetic resonance imaging (³He‐MRI) offers the possibility to visualize alveolar recruitment directly. Methods: With the approval of the state animal care committee, unilateral lung damage was induced in seven anesthetized pigs by saline lavage of the right lungs. The left lung served as an intraindividual control (healthy lung). Unilateral lung damage was confirmed by conventional proton MRI and spiral‐CT scanning. The total aerated lung volume was determined both at a positive end‐expiratory pressure (PEEP) of 0 and 10 mbar from three‐dimensionally reconstructed ³He images, both for healthy and damaged lungs. The fractional increase of aerated volume in damaged and healthy lungs, followed by a PEEP increase from 0 to 10 mbar, was compared. Results: Aerated gas space was visualized with a high spatial resolution in the three‐dimensionally reconstructed ³He‐MR images, and aeration defects in the lavaged lung matched the regional distribution of atelectasis in proton MRI. After recruitment and PEEP increase, the aerated volume increased significantly both in healthy lungs from 415 ml [270–445] (median [min–max]) to 481 ml [347–523] and in lavaged lungs from 264 ml [71–424] to 424 ml [129–520]. The fractional increase in lavaged lungs was significantly larger than that in healthy lungs (healthy: 17% [11–38] vs. lavage: 42% [14–90] (P=0.031). Conclusion: The ³He‐MRI signal might offer an experimental approach to discriminate atelectatic vs. poor aerated lung areas in a lung damage animal model. Our results confirm the presence of potential recruitable lung volume by either alveolar collapse or alveolar flooding, in accordance with previous reports by computed tomography.     

A randomised comparison of free‐handed vs air‐Q™ assisted fibreoptic‐guided tracheal intubation in children < 2 years of age

We prospectively compared free‐handed and air‐Q? assisted fibreoptic‐guided tracheal intubation in children < 2 years of age. Eighty healthy children were enrolled and randomly assigned to a technique (free‐handed or air‐Q assisted) and operator (trainee or attending). Time, number of attempts and manoeuvres required were assessed. There was no difference in median (IQR [range]) time to successful tracheal intubation between the free‐handed (52.2 (34.8–67.7 [19.7–108.0]) s), and the air‐Q assisted (60.3 (45.5–75.1 [28.1–129.0]) s; p = 0.13) groups, or the number of attempts needed. The air‐Q assisted group required fewer manoeuvres to optimise the laryngeal view (median (IQR [range]) 0 (0–1 [0–2])) than the free‐handed group (1 (1–1 [0–3]); p < 0.001). In conclusion, fibreoptic‐guided tracheal intubation times were similar with and without the use of the air‐Q, but supraglottic airway devices may be a consideration for their other practical advantages.     

A randomised comparison of the LMA SupremeTM and LMAProSealTM in children

We conducted a randomised trial comparing the size‐2 LMA Supreme? with the LMA ProSeal? in 60 children undergoing surgery. The outcomes measured were airway leak pressure, ease and time for insertion, fibreoptic examination, incidence of gastric insufflation, ease of gastric tube placement, quality of the airway during anaesthetic maintenance and complications. There were no statistically significant differences between the LMA Supreme and LMA ProSeal in median (IQR [range]) insertion time (12 (10–15 [7–18]) s vs 12 (10–13 [8–25]) s; p = 0.90), airway leak pressures (19 (16–21 [12–30]) cmH₂O vs 18 (16–24 [10–34]) cmH₂O; p = 0.55), fibreoptic position of the airway or drain tube, ease of gastric access and complications. Both devices provided effective ventilation requiring minimal airway manipulation. The LMA Supreme can be a useful alternative to the LMA ProSeal when single‐use supraglottic devices with gastric access capabilities are required.     

Digital palpation of the pilot balloon vs. continuous manometry for controlling the intracuff pressure in laryngeal mask airways

This study compared two methods of controlling the intracuff pressure in laryngeal mask airways. One hundred and eighty patients were randomly assigned into two groups. In the first group (n = 90), after training, the intracuff pressure was controlled using digital palpation of the pilot balloon. In the second group (n = 90), continuous manometry was used to control the intracuff pressure. An upper pressure limit of 60 cmH₂O was set. The median (IQR [range]) intracuff pressure in the palpation group was 130 (125–130 [120–130]) cmH₂O compared with 29 (20–39 [5–60]) cmH₂O in the manometry group (p < 0.001). In the palpation group, 37% of patients experienced pharyngolaryngeal complications vs. 12% in the manometry group (p < 0.001). We conclude that the digital palpation technique is not a suitable alternative to manometry in controlling the intracuff pressure in laryngeal mask airways.     

The effect of lung deflation on the position of the pleura during subclavian vein cannulation in infants receiving mechanical ventilation: an ultrasound study

We evaluated the effect of lung deflation on the relative position of the pleura compared with a reference line during supra‐ and infraclavicular approaches to the right subclavian vein. The reference line was drawn relative to the predicted pathway of the needle. The distances between the pleura and the reference line for supra‐ and infraclavicular approaches were measured during inspiration and expiration in 41 infants. Measurements were repeated with the application of 5 cmH₂O positive end‐expiratory pressure (PEEP) and in the Trendelenburg position. Lung deflation during the supraclavicular approach significantly decreased the volume of lung crossing the reference line by a median (IQR [range]) of 1.0 (0.6 to 1.3 [0.0 to 4.8]) mm, p < 0.001, irrespective of the application of PEEP or patient position. However, during the infraclavicular approach, lung deflation showed no change in the distance of the pleura from the reference line regardless of PEEP or patient position. We conclude that lung deflation moves the lung apex caudally and can reduce the potential risk of pneumothorax during a supraclavicular approach to the right subclavian vein in infants.     

Prolonged moderate pressure recruitment manoeuvre results in lower optimal positive end-expiratory pressure and plateau pressure

Background: In acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), recruitment manoeuvres (RMs) are used frequently. In pigs with induced ALI, superior effects have been found using a slow moderate‐pressure recruitment manoeuvre (SLRM) compared with a vital capacity recruitment manoeuvre (VICM). We hypothesized that the positive recruitment effects of SLRM could also be achieved in ALI/ARDS patients. Our primary research question was whether the same compliance could be obtained using lower RM pressure and subsequent positive end‐expiratory pressure (PEEP). Secondly, optimal PEEP levels following the RMs were compared, and the use of volume‐dependent compliance (VDC) to identify successful lung recruitment and optimal PEEP was evaluated. Patients and methods: We performed a prospective randomised cross‐over study where 16 ventilated patients with early ALI/ARDS each were subjected to the two RMs, followed by decremental PEEP titration. Volume‐dependent initial, middle and final compliance (C_ini, C_mid and C_fin) were determined. Electric impedance tomography and end‐expiratory lung volume measurements were used to follow lung volume changes. Results: The maximum response in compliance, PaO₂/FIO₂, venous admixture and C_ini/C_fin after recruitment, during decremental PEEP, was at significantly lower PEEP and plateau pressure after SLRM than VICM. Fewer patients responded in gas exchange after the SLRM, which was not the case for lung mechanics. The response in C_ini was more pronounced than in conventional compliance. Conclusions: The same compliance increase is achieved with SLRM as with VICM, and lower PEEP can be used, with correspondingly lower plateau pressures. VDC seems promising to identify successful recruitment and optimal PEEP.     

Positive end-expiratory pressure prevents atelectasis during general anaesthesia even in the presence of a high inspired oxygen concentration

BACKGROUND: General anaesthesia impairs the gas exchange in the lungs, and moderate desaturation (SaO2 86-90%) occurred in 50% of anaesthetised patients in a blinded pulse oximetry study. A high FiO2 might reduce the risk of hypoxaemia, but can also promote atelectasis. We hypothesised that a moderate positive end-expiratory pressure (PEEP) level of 10 cmH2O can prevent atelectasis during ventilation with an FiO2 = 1.0. METHODS: Atelectasis was evaluated by computed tomography (CT) in 13 ASA I-II patients undergoing elective surgery. CT scans were obtained before and 15 min after induction of anaesthesia. Then, recruitment of collapsed lung tissue was performed as a "vital capacity manoeuvre" (VCM, inspiration with Paw = 40 cmH2O for 15 s), and a CT scan was obtained at the end of the VCM. Thereafter, PEEP = 0 cmH2O was applied in group 1, and PEEP = 10 cmH2O in group 2. Additional CT scans were obtained after the VCM. Oxygenation was measured before and after the VCM. RESULTS: Atelectasis (> 1 cm2) was present in 12 of the 13 patients after induction of anaesthesia. At 5 and 10 min after the VCM, atelectasis was significantly smaller in group 2 than group 1 (P < 0.005). A significant inverse correlation was found between PaO2 and atelectasis. CONCLUSIONS: PEEP = 10 cmH2O reduced atelectasis formation after a VCM, when FiO2 = 1.0 was used. Thus, a VCM followed by PEEP = 10 cmH2O should be considered when patients are ventilated with a high FiO2 and gas exchange is impaired.