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Reducing Atelectasis during General Anaesthesia – the Importance of Oxygen Concentration, End-Expiratory Pressure and Patient Factors: A Clinical Study Exploring the Prevention of Atelectasis in Adults
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Medicinska och farmaceutiska vetenskapsområdet, centrumbildningar mm, Centre for Clinical Research, County of Västmanland. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: The use of pure oxygen during preoxygenation and induction of general anaesthesia is a major cause of atelectasis. The interaction between reduced lung volume, resulting in airway closure, and varying inspiratory fractions of oxygen (FIO2) in determining the risk of developing atelectasis is still obscure.

Methods: In this thesis, computed tomography (in studies I and II during anaesthesia, in studies III and IV postoperatively) was used to investigate the area of atelectasis in relation to FIO2 and varying levels of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP).

Study I investigated the short-term influence of reducing FIO2 during preoxygenation and induction of general anaesthesia, and the time to hypoxia during apnoea.

Study II focused on the long-term effect of an FIO2 of 0.8 for preoxygenation.

Study III applied CPAP/PEEP with an FIO2 of 1.0 or 0.8 for pre- and postoxygenation until extubation. After extubation, CPAP with an FIO2 of 0.3 was applied before the end of mask ventilation.

Study IV compared two groups given CPAP/PEEP during anaesthesia and an FIO2 of 1.0 or 0.3 during postoxygenation, but without CPAP after extubation.

Results: Study I showed a reduction in atelectasis with an FIO2 of 0.8 or 0.6, compared with 1.0, but the time to hypoxia decreased. In study II, atelectasis evolved gradually after preoxygenation. In study III, atelectasis was reduced with an FIO2 of 1.0 and CPAP/PEEP compared with an FIO2 of 1.0 without CPAP/PEEP. The intervention failed in the group given an FIO2 of 0.8, this group had more smokers. Atelectasis and age were correlated. In study IV, no difference was found between the groups. Post hoc analysis showed that smoking and ASA class increased the risk for atelectasis.

Conclusion, the effect of reducing FIO2 during preoxygenation to prevent atelectasis might be short-lived. A lower FIO2 shortened the time to the appearance of hypoxia. Increasing lung volume by using CPAP/PEEP also decreased the risk of atelectasis, but the method might fail; for example in patients who are heavy smokers. In older patients care must be taken to reduce a high FIO2 before ending CPAP.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 954
Keyword [en]
Anaesthesia, general. Lung: Atelectasis; CPAP; Oxygen; PEEP; Ventilation, mechanical; Tomography, X-ray computed.
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology; Physiology
Identifiers
URN: urn:nbn:se:uu:diva-209714ISBN: 978-91-554-8808-6 (print)OAI: oai:DiVA.org:uu-209714DiVA: diva2:661744
Public defence
2013-12-18, Vårdskolans aula, Ingång 21, Västmanlands sjukhus Västerås, Västerås, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2013-11-27 Created: 2013-10-24 Last updated: 2013-11-27
List of papers
1. Optimal Oxygen Concentration during Induction of General Anesthesia
Open this publication in new window or tab >>Optimal Oxygen Concentration during Induction of General Anesthesia
2003 (English)In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 98, no 1, 28-33 p.Article in journal (Other academic) Published
Abstract [en]

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 < 0.01).

CONCLUSION:

During routine induction of general anesthesia, 80% oxygen for oxygenation caused minimal atelectasis, but the time margin before unacceptable desaturation occurred was significantly shortened compared with 100% oxygen.

National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology
Identifiers
urn:nbn:se:uu:diva-63695 (URN)12502975 (PubMedID)
Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-11-30Bibliographically approved
2. Oxygen concentration and characteristics of progressive atelectasis formation during anaesthesia
Open this publication in new window or tab >>Oxygen concentration and characteristics of progressive atelectasis formation during anaesthesia
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2011 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 55, no 1, 75-81 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-140148 (URN)10.1111/j.1399-6576.2010.02334.x (DOI)000284898500012 ()21039356 (PubMedID)
Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2017-12-11Bibliographically approved
3. Reduction in postoperative atelectasis by continuous positive airway pressure and low oxygen concentration after endotracheal extubation
Open this publication in new window or tab >>Reduction in postoperative atelectasis by continuous positive airway pressure and low oxygen concentration after endotracheal extubation
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background. Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy using a combination of 1) continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and 2) a reduced end-expiratory oxygen fraction (FETO2) before commencing 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 (FIO2) 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 cmH2O was used in the intervention groups. After extubation, FIO2 was set to 0.30 in the intervention groups and CPAP was applied via a facemask, aiming at a FETO2 < 0.30. Atelectasis was studied by computed tomography 25 min postoperatively.

Results. The median area of atelectasis was 5.2 cm2 (range 1.6–12.2 cm2) and 8.5 cm2 (3–23.1 cm2) in the groups given FIO2 1.0 with or without CPAP/PEEP, respectively. In the group given FIO2 0.8, in which 7 patients were ex- or current smokers, the median area of atelectasis was 8.2 cm2 (1.8–14.7 cm2). After correction for body mass index and age, the difference between the two groups given FIO2 1.0 was statistically significant (P = 0.016).

Conclusion. Compared with conventional ventilation, 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.

Keyword
Atelectasis, CPAP, PEEP, Oxygen fraction, Ventilation, General Anaesthesia, Smoking
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology
Identifiers
urn:nbn:se:uu:diva-209961 (URN)
Available from: 2013-10-29 Created: 2013-10-29 Last updated: 2013-10-29
4. Atelectasis after anaesthesia: a randomised trial of positive airway pressure and low oxygen
Open this publication in new window or tab >>Atelectasis after anaesthesia: a randomised trial of positive airway pressure and low oxygen
Show others...
2013 (English)Article in journal (Other academic) Submitted
Abstract [en]

Background:

Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy with a combination of 1) continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and 2) a reduced end-expiratory oxygen fraction (FETO2) before extubation would reduce postoperative atelectasis.

Methods:

Sixty patients were randomized into two groups. During anaesthesia induction, inspiratory oxygen fractions (FIO2) were 1.0, and depending on weight, CPAP 6–8 cm H2O was applied in both groups via face mask. During maintenance of anaesthesia, a laryngeal mask airway was used, and depending on weight, PEEP was 6–8 cm H2O in both groups. Before extubation, FIO2 was set to 0.3 in the intervention groups and 1.0 in the control group. Atelectasis was studied by computed tomography approximately 13 min postoperatively.

Results:

The area of atelectasis was 5.5, 0–16.9 cm2 (median and range), and 6.8, 0–27.5 cm2 in the groups given FIO2 0.3 or FIO2 1.0 before extubation, a difference that was not statistically significant.

Conclusion:

Inducing anaesthesia with CPAP/PEEP and FIO2 1.0 and deliberately reducing FIO2 before extubation did not reduce postoperative atelectasis compared with FIO2 1.0 before extubation.

Keyword
Atelectasis, CPAP, PEEP, Oxygen fraction, Smoking, ASA, Postoperative complications
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology; Clinical Physiology
Identifiers
urn:nbn:se:uu:diva-209736 (URN)
Available from: 2013-10-29 Created: 2013-10-25 Last updated: 2013-11-04Bibliographically approved

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