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Positive End-expiratory Pressure Alone Minimizes Atelectasis Formation in Nonabdominal Surgery: A Randomized Controlled Trial
Västerås & Köping Hosp, Dept Anesthesia & Intens Care, Västerås, Sweden.ORCID iD: 0000-0002-7449-3907
Västerås & Köping Hosp, Dept Radiol, Västerås, Sweden.
Clin Res Ctr, Västerås, Sweden.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
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2018 (English)In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 128, no 6, p. 1117-1124Article in journal (Refereed) Published
Abstract [en]

Background: Various methods for protective ventilation are increasingly being recommended for patients undergoing general anesthesia. However, the importance of each individual component is still unclear. In particular, the perioperative use of positive end-expiratory pressure (PEEP) remains controversial. The authors tested the hypothesis that PEEP alone would be sufficient to limit atelectasis formation during nonabdominal surgery. Methods: This was a randomized controlled evaluator-blinded study. Twenty-four healthy patients undergoing general anesthesia were randomized to receive either mechanical ventilation with PEEP 7 or 9 cm H2O depending on body mass index (n = 12) or zero PEEP (n =12). No recruitment maneuvers were used. Hie primary outcome was atelectasis area as studied by computed tomography in a transverse scan near the diaphragm, at the end of surgery, before emergence. Oxygenation was evaluated by measuring blood gases and calculating the ratio of arterial oxygen partial pressure to inspired oxygen fraction (Pao(2)/Fio(2) ratio). Results: At the end of surgery, the median (range) atelectasis area, expressed as percentage of the total lung area, was 1.8 (0.3 to 9.9) in the PEEP group and 4.6 (1.0 to 10.2) in the zero PEEP group. Tire difference in medians was 2.8% (95% CI, 1.7 to 5.7%; A = 0.002). Oxygenation and carbon dioxide elimination were maintained in the PEEP group, but both deteriorated in the zero PEEP group. Conclusions: During nonabdominal surgery, adequate PEEP is sufficient to minimize atelectasis in healthy lungs and thereby maintain oxygenation. Titus, routine recruitment maneuvers seem unnecessary, and the authors suggest that they should only be utilized when clearly indicated.

Place, publisher, year, edition, pages
LIPPINCOTT WILLIAMS & WILKINS , 2018. Vol. 128, no 6, p. 1117-1124
National Category
Anesthesiology and Intensive Care
Identifiers
URN: urn:nbn:se:uu:diva-363070DOI: 10.1097/ALN.0000000000002134ISI: 000441172900012PubMedID: 29462011OAI: oai:DiVA.org:uu-363070DiVA, id: diva2:1255557
Available from: 2018-10-12 Created: 2018-10-12 Last updated: 2019-04-08Bibliographically approved
In thesis
1. Pulmonary Atelectasis in General Anaesthesia: Clinical Studies on the Counteracting Effects of Positive End-Expiratory Pressure
Open this publication in new window or tab >>Pulmonary Atelectasis in General Anaesthesia: Clinical Studies on the Counteracting Effects of Positive End-Expiratory Pressure
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Partial lung collapse, i.e., pulmonary atelectasis, is common during general anaesthesia. The main causal mechanism is reduced lung volume with airway closure and subsequent gas absorption from preoxygenated alveoli. Atelectasis impairs oxygenation and forms the pathophysiological basis for postoperative pulmonary complications. Positive end-expiratory pressure (PEEP) counteracts the loss in lung volume, but its role in preventing atelectasis during anaesthesia is not clear.

All studies included in this thesis were prospective randomized clinical trials. In the first study, oxygenation was used as a surrogate measure of atelectasis in obese patients undergoing laparoscopic gastric bypass. The subsequent studies used single-slice computed tomography (CT) to evaluate atelectasis in healthy patients undergoing non-abdominal surgery.

Paper I: We studied the use of continuous positive airway pressure (CPAP) and PEEP during induction of anaesthesia and a reduced inspired oxygen fraction (FiO2) during emergence. Oxygenation was maintained in the group that received CPAP during induction, followed by a PEEP of 10 cmH2O. Postoperative oxygenation was impaired in the group that received a high FiO2 during emergence.

Paper II: An early oxygen washout manoeuvre to quickly restore nitrogen levels and thus stabilize the alveoli, had no effect on atelectasis at the end of surgery. Both study groups exhibited small atelectasis after being ventilated with a moderate PEEP of 6-8 cmH2O during anaesthesia.

Paper III: The effect of PEEP versus zero PEEP on atelectasis formation and oxygenation at the end of surgery was compared. The PEEP group maintained oxygenation better and exhibited less atelectasis than the zero-PEEP group, with atelectasis involving a median 1.8% of total lung area compared with 4.6% in the zero-PEEP group (P = 0.002).

Paper IV: Postoperative atelectasis was compared between a group in which PEEP was maintained during emergence preoxygenation with FiO2 1.0 and a group in which PEEP was withdrawn just before the start of emergence preoxygenation with FiO2 1.0. The two groups had small atelectasis when fully awake at 30 min after extubation, with no statistically significant difference between them.  

In conclusion, preserved end-expiratory lung volume is the key to avoiding atelectasis, in particular when an increased oxygen reserve is required during airway manipulation. PEEP is both necessary and sufficient to minimize atelectasis in healthy patients undergoing non-abdominal surgery.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 63
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1566
Keywords
General anaesthesia, pulmonary atelectasis, positive end-expiratory pressure, oxygen, computed tomography, continuous positive airway pressure, mechanical ventilation
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care
Identifiers
urn:nbn:se:uu:diva-380317 (URN)978-91-513-0635-3 (ISBN)
Public defence
2019-05-31, Vårdskolans aula, ingång 21, Västmanlands sjukhus Västerås, 13:15 (Swedish)
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Supervisors
Available from: 2019-05-10 Created: 2019-04-08 Last updated: 2019-06-18

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Zetterström, HenrikHedenstierna, Göran

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