Oxygen concentration and characteristics of progressive atelectasis formation during anaesthesia (original) (raw)
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Upsala Journal of Medical Sciences
Background: Following preoxygenation and induction of anaesthesia, most patients develop atelectasis. We hypothesized that an immediate restoration to a low oxygen level in the alveoli would prevent atelectasis formation and improve oxygenation during the ensuing anaesthesia. Methods: We randomly assigned 24 patients to either a control group (n ¼ 12) or an intervention group (n ¼ 12) receiving an oxygen washout procedure directly after intubation. Both groups were, depending on body mass index, ventilated with a positive end-expiratory pressure (PEEP) of 6-8 cmH 2 O during surgery. The atelectasis area was studied by computed tomography before emergence. Oxygenation levels were evaluated by measuring blood gases and calculating estimated venous admixture (EVA). Results: The atelectasis areas expressed as percentages of the total lung area were 2.0 (1.5-2.7) (median [interquartile range]) and 1.8 (1.4-3.3) in the intervention and control groups, respectively. The difference was non-significant, and also oxygenation was similar between the two groups. Compared to oxygenation before the start of anaesthesia, oxygenation at the end of surgery was improved in the intervention group, mean (SD) EVA from 7.6% (6.6%) to 3.9% (2.9%) (P ¼ .019) and preserved in the control group, mean (SD) EVA from 5.0% (5.3%) to 5.6% (7.1%) (P ¼ .59). Conclusion: Although the oxygen washout restored a low pulmonary oxygen level within minutes, it did not further reduce atelectasis size. Both study groups had small atelectasis and good oxygenation. These results suggest that a moderate PEEP alone is sufficient to minimize atelectasis and maintain oxygenation in healthy patients.
Dynamics of re-expansion of atelectasis during general anaesthesia
British Journal of Anaesthesia, 1999
A major cause of impaired gas exchange during general anaesthesia is atelectasis, causing pulmonary shunt. A 'vital capacity' (VC) manoeuvre (i.e. inflation of the lungs up to 40 cm H 2 O, maintained for 15 s) may re-expand atelectasis and improve oxygenation. However, such a manoeuvre may cause adverse cardiovascular effects. Reducing the time of maximal inflation may improve the margin of safety. The aim of this study was to analyse the change over time in the amount of atelectasis during a VC manoeuvre in 12 anaesthetized adults with healthy lungs. I.v. anaesthesia with controlled mechanical ventilation (VT 9 (SD 1) ml kg -1 ) was used. For the VC manoeuvre, the lungs were inflated up to an airway pressure (Paw) of 40 cm H 2 O. This pressure was maintained for 26 s. Atelectasis was assessed by analysis of computed x-ray tomography. The amount of atelectasis, measured at the base of the lungs, was 4.0 (SD 2.7) cm 2 after induction of anaesthesia. The decrease in the amount of atelectasis over time during the VC manoeuvre was described by a negative exponential function with a time constant of 2.6 s. At an inspired oxygen concentration of 40%, Pa O 2 increased from 17.2 (4.0) kPa before to 22.2 (6.0) kPa (Pϭ0.013) after the VC manoeuvre. Thus in anaesthetized adults undergoing mechanical ventilation with healthy lungs, inflation of the lungs to a Paw of 40 cm H 2 O, maintained for 7-8 s only, may re-expand all previously collapsed lung tissue, as detected by lung computed tomography, and improve oxygenation. We conclude that the previously proposed time for a VC manoeuvre may be halved in such subjects.
A ventilation strategy during general anaesthesia to reduce postoperative atelectasis
Upsala Journal of Medical Sciences, 2014
Background. Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy, without recruitment manoeuvres, using a combination of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and a reduced end-expiratory oxygen fraction (F ET O 2) before ending mask ventilation with CPAP after extubation would reduce the area of postoperative atelectasis. Methods. Thirty patients were randomized into three groups. During induction and emergence, inspiratory oxygen fractions (F I O 2) were 1.0 in the control group and 1.0 or 0.8 in the intervention groups. No CPAP/PEEP was used in the control group, whereas CPAP/PEEP of 6 cmH 2 O was used in the intervention groups. After extubation, F I O 2 was set to 0.30 in the intervention groups and CPAP was applied, aiming at F ET O 2 < 0.30. Atelectasis was studied by computed tomography 25 min postoperatively. Results. The median area of atelectasis was 5.2 cm 2 (range 1.6-12.2 cm 2) and 8.5 cm 2 (3-23.1 cm 2) in the groups given F I O 2 1.0 with or without CPAP/PEEP, respectively. After correction for body mass index the difference between medians (2.9 cm 2) was statistically significant (confidence interval 0.2-7.6 cm 2 , p = 0.04). In the group given F I O 2 0.8, in which seven patients were ex-or current smokers, the median area of atelectasis was 8.2 cm 2 (1.8-14.7 cm 2). Conclusion. Compared with conventional ventilation, after correction for obesity, this ventilation strategy reduced the area of postoperative atelectasis in one of the intervention groups but not in the other group, which included a higher proportion of smokers.
BMJ open, 2017
To assess the diagnostic accuracy of peripheral capillary oxygen saturation (SpO2) while breathing room air for 5 min (the 'Air-Test') in detecting postoperative atelectasis. Prospective cohort study. Diagnostic accuracy was assessed by measuring the agreement between the index test and the reference standard CT scan images. Postanaesthetic care unit in a tertiary hospital in Spain. Three hundred and fifty patients from 12 January to 7 February 2015; 170 patients scheduled for surgery under general anaesthesia who were admitted into the postsurgical unit were included. The Air-Test was performed in conscious extubated patients after a 30 min stabilisation period during which they received supplemental oxygen therapy via a venturi mask. The Air-Test was defined as positive when SpO2 was ≤96% and negative when SpO2 was ≥97%. Arterial blood gases were measured in all patients at the end of the Air-Test. In the subsequent 25 min, the presence of atelectasis was evaluated by perf...
Optimal Oxygen Concentration during Induction of General Anesthesia
Anesthesiology, 2003
Background The use of 100% oxygen during induction of anesthesia may produce atelectasis. The authors investigated how different oxygen concentrations affect the formation of atelectasis and the fall in arterial oxygen saturation during apnea. Methods Thirty-six healthy, nonsmoking women were randomized to breathe 100, 80, or 60% oxygen for 5 min during the induction of general anesthesia. Ventilation was then withheld until the oxygen saturation, assessed by pulse oximetry, decreased to 90%. Atelectasis formation was studied with computed tomography. Results Atelectasis in a transverse scan near the diaphragm after induction of anesthesia and apnea was 9.8 +/- 5.2 cm2 (5.6 +/- 3.4% of the total lung area; mean +/- SD), 1.3 +/- 1.2 cm2 (0.6 +/- 0.7%), and 0.3 +/- 0.3 cm2 (0.2 +/- 0.2%) in the groups breathing 100, 80, and 60% oxygen, respectively (P < 0.01). The corresponding times to reach 90% oxygen saturation were 411 +/- 84, 303 +/- 59, and 213 +/- 69 s, respectively (P < ...
BJA: British Journal of Anaesthesia, 2020
Background: General anaesthesia is increasingly common in elderly and obese patients. Greater age and body mass index (BMI) worsen gas exchange. We assessed whether this is related to increasing atelectasis during general anaesthesia. Methods: This primary analysis included pooled data from previously published studies of 243 subjects aged 18e78 yr, with BMI of 18e52 kg m À2. The subjects had no clinical signs of cardiopulmonary disease, and they underwent computed tomography (CT) awake and during anaesthesia before surgery after preoxygenation with an inspired oxygen fraction (FIO 2) of >0.8, followed by mechanical ventilation with FIO 2 of 0.3 or higher with no PEEP. Atelectasis was assessed by CT. Results: Atelectasis area of up to 39 cm 2 in a transverse scan near the diaphragm was seen in 90% of the subjects during anaesthesia. The log of atelectasis area was related to a quadratic function of (ageþage 2) with the most atelectasis at~50 yr (r 2 ¼0.08; P<0.001). Log atelectasis area was also related to a broken-line function of the BMI with the knee at 30 kg m À2 (r 2 ¼0.06; P<0.001). Greater atelectasis was seen in the subjects receiving FIO 2 of 1.0 than FIO 2 of 0.3e0.5 (12.8 vs 8.1 cm 2 ; P<0.001). A multiple regression analysis, including a quadratic function of age, a broken-line function of the BMI, and dichotomised FIO 2 (0.3e0.5/1.0) adjusting for ventilatory frequency, strengthened the association (r 2 ¼0.23; P<0.001). PaO 2 decreased with both age and BMI. Conclusions: Atelectasis during general anaesthesia increased with age up to 50 yr and decreased beyond that. Atelectasis increased with BMI in normal and overweight patients, but showed no further increase in obese subjects (BMI !30 kg m À2). Therefore, greater age and obesity appear to limit atelectasis formation during general anaesthesia. Clinical trial registration: ▪.
Positive End-expiratory Pressure and Postoperative Atelectasis
Anesthesiology
Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background Positive end-expiratory pressure (PEEP) increases lung volume and protects against alveolar collapse during anesthesia. During emergence, safety preoxygenation preparatory to extubation makes the lung susceptible to gas absorption and alveolar collapse, especially in dependent regions being kept open by PEEP. We hypothesized that withdrawing PEEP before starting emergence preoxygenation would limit postoperative atelectasis formation. Methods This was a randomized controlled evaluator-blinded trial in 30 healthy patients undergoing nonabdominal surgery under general anesthesia and mechanical ventilation with PEEP 7 or 9 cm H2O depending on body mass index. A computed tomography scan at the end of surgery assessed baseline atelectasis. The study subjects were thereafter allocated to either maintained PEEP (n = 16) or zero PEEP (n = 14) during emergence preoxygenation. The prim...