Lennart Edmark

Optimal oxygen concentration during induction of general anesthesia.

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.

The effects of anesthesia and muscle paralysis on the respiratory system.

BackgroundOxygenation is impaired in almost all subjects during anesthesia, and hypoxemia for shorter or longer periods is a common finding. Moreover, postoperative lung complications occur in 3–10% after elective abdominal surgery and more in emergency operations.DiscussionRapid collapse of alveoli on induction of anesthesia and more widespread closure of airways seem to explain the oxygenation impairment and may also contribute to postoperative pulmonary infection. Causative mechanisms to atelectasis and airway closure seem to be loss of respiratory muscle tone and gas resorption.ConclusionAvoiding high inspired oxygen fractions during both induction and maintenance of anesthesia prevents or reduces atelectasis, while intermittent “vital capacity” maneuvers recruit atelectatic lung regions.

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.

Effects of anesthesia on the respiratory system

Most anesthetics cause a loss of muscle tone that is accompanied by a fall in the resting lung volume. The lowered lung volume promotes cyclic (tidal) or continuous airway closure. High inspired oxygen fractions cause rapid absorption of gas behind closed airways, resulting in atelectasis. This chapter deals with these mechanisms in more detail, and it addresses possible measures to keep the lung open with the use of recruitment maneuvers, continuous and/or end-expiratory positive pressure, as well as the interaction with different oxygen concentrations. The effects on ventilation/perfusion matching and pulmonary gas exchange are also discussed.

A ventilation strategy during general anaesthesia to reduce postoperative atelectasis

Abstract 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 (FETO2) 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 (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, aiming at 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. After correction for body mass index the difference between medians (2.9 cm2) was statistically significant (confidence interval 0.2–7.6 cm2, p = 0.04). In the group given FIO2 0.8, in which seven patients were ex- or current smokers, the median area of atelectasis was 8.2 cm2 (1.8–14.7 cm2). 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.

Protective Ventilation during Anesthesia Is It Meaningful

Protective Ventilation during Anesthesia: Is It Meaningful? Goran Hedenstierna;Lennart Edmark; Anesthesiology

Preserved oxygenation in obese patients receiving protective ventilation during laparoscopic surgery: a randomized controlled study.

Venous admixture from atelectasis and airway closure impedes oxygenation during general anaesthesia. We tested the hypothesis that continuous positive airway pressure (CPAP) during pre‐oxygenation and reduced fraction of inspiratory oxygen (FIO2) during emergence from anaesthesia can improve oxygenation in patients with obesity undergoing laparoscopic surgery.

Postoperative lung complications: have multicentre studies been of any help?

1 Overton E. Studien über die Narkose zugleich ein Beitrag zur allgemeinen Pharmakologie. Jena, Germany: Verlag von Gustav Fischer, 1901 2 Thunberg T. Ernest Overton. Skandinavisches Archiv Für Physiologie 1934; 70: 1–9 3 Overton CE. Beobachtungen und Versuche über das Auftreten von rothem Zellsaft bei Pflanzen. Jahrb Fuer Wissenschaftliche Botanik 1899; 33: 171–233 4 Overton CE. On the reduction of chromosomes in the nuclei of plants. Annals of Botany 1893; 7: 139–43 5 Kanna A. Membrane Permeability: 100 Years Since Ernest Overton. San Diego: Academic Press, 1999 6 Kepner GR. From Oil Layer to Bilayer. Liposome Letters. London, New York: Academic Press, 1983; 15–27 7 Höber R. Physikalische Chemie der Zelle und der Gewebe, 5th Edn. Leipzig, Germany: Verlag Wilhelm Engelmann, 1924 8 Lepeschkin WW. My opinion about protoplasm. Protoplasma 1930; 9: 269–97 9 Perouansky M. Coagulation, flocculation, and denaturation: a century of research into protoplasmic theories of anesthesia. Anesth Analg 2014; 119: 311–20 10 Overton CE. Über die allgemeinen osmotischen Eigenschaften der Zelle, ihre vermutlichen Ursachen und ihre Bedeutung für die Physiologie. Vierteljahresschr D Naturforsch Ges in Zürich 1899; 64: 87–136 11 Kleinzeller A. Charles Ernest Overton’s concept of a cell membrane. In: Deamer DW, KleinzellerFambrough ADM, eds. Membrane Permeability: 100 Years Since Ernest Overton. San Diego: Academic Press, 1999; 1–22 12 Overton CE. Studies of Narcosis. Schaumburg, IL: Chapman and Hall, Wood Library-Museum of Anesthesiology, 1991 13 Overton E. Studien über die Narkose Zugleich ein Beitrag zur Allgemeinen Pharmakologie. Jena, Germany: Verlag von Gustav Fischer, 1901; III–IV 14 McCormick DA. Action potential. In: Squire LRB, McConnell SK, Roberts JL, Spitzer NC, Zigmond MJ, eds. Fundamental Neuroscience. Waltham, MA: Academic Press, 2003 15 Overton CE. Über den Mechanismus der Resorption und der Sekretion. In: Nagel WA, ed. Handbuch der Physiologie des Menschen. Braunschweig, Germany: Druck und Verlag von Friedrich Vieweg und Sohn, 1905–1910; 743–898 16 Plowe JQ. Membranes in the plant cell I. Morphological membranes at protoplasmic surfaces. Protoplasma 1931; 12: 196–221 17 Lipnick RL. Charles Ernest Overton: narcosis studies and a contribution to general pharmacology. Trends Pharmacol Sci 1986; 7: 161–4 18 Lipnick RL. A QSAR studyof Overton’s tadpole data. Prog Clin Biol Res 1989; 291: 421–4 19 Collander PR. Ernest Overton (1865–1933): a pioneer to remember. Leopoldina 1962–3; 8–9: 242–54

Post-operative atelectasis – a randomised trial investigating a ventilatory strategy and low oxygen fraction during recovery

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 concentration during recovery would reduce post‐operative atelectasis.

Minimizing atelectasis formation during general anaesthesia-oxygen washout is a non-essential supplement to PEEP

Abstract 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 = 12) or an intervention group (n = 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 cmH2O 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 = .019) and preserved in the control group, mean (SD) EVA from 5.0% (5.3%) to 5.6% (7.1%) (P = .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.