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New methods for optimization of mechanical ventilation
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mechanical ventilation saves lives, but it is an intervention fraught with the potential for serious complications. Prevention of these complications has become the focus of research and critical care in the last twenty years. This thesis presents the first use, or the application under new conditions, of three technologies that could contribute to optimization of mechanical ventilation.

Optoelectronic plethysmography was used in Papers I and II for continuous assessment of changes in chest wall volume, configuration, and motion in the perioperative period. A forced oscillation technique (FOT) was used in Paper III to evaluate a novel positive end-expiratory pressure (PEEP) optimization strategy. Finally, in Paper IV, FOT in conjunction with an optical sensor based on a self-mixing laser interferometer (LIR) was used to study the oscillatory mechanics of the respiratory system and to measure the chest wall displacement.

In Paper I, propofol anesthesia decreased end-expiratory chest wall volume (VeeCW) during induction, with a more pronounced effect on the abdominal compartment than on the rib cage. The main novel findings were an increased relative contribution of the rib cage to ventilation after induction of anesthesia, and the fact that the rib cage initiates post-apneic ventilation. In Paper II, a combination of recruitment maneuvers, PEEP, and reduced fraction of inspired oxygen, was found to preserve lung volume during and after anesthesia. Furthermore, the decrease in VeeCW during emergence from anesthesia, associated with activation of the expiratory muscles, suggested that active expiration may contribute to decreased functional residual capacity, during emergence from anesthesia.

In the lavage model of lung injury studied in Paper III, a PEEP optimization strategy based on maximizing oscillatory reactance measured by FOT resulted in improved lung mechanics, increased oxygenation, and reduced histopathologic evidence of ventilator-induced lung injury.

Paper IV showed that it is possible to apply both FOT and LIR simultaneously in various conditions ranging from awake quiet breathing to general anesthesia with controlled mechanical ventilation. In the case of LIR, an impedance map representing different regions of the chest wall showed reproducible changes during the different stages that suggested a high sensitivity of the LIR-based measurements.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 62 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1102
Keyword [en]
mechanical ventilation, optoelectronic plethysmography, forced oscillation technique, laser interferometry
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care
Identifiers
URN: urn:nbn:se:uu:diva-249172ISBN: 978-91-554-9238-0 (print)OAI: oai:DiVA.org:uu-249172DiVA: diva2:802192
Public defence
2015-06-03, Enghoffsalen, Entrance 50, Akademiska sjukhuset, Uppsala, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2015-05-13 Created: 2015-04-11 Last updated: 2015-07-07
List of papers
1. Effects of propofol anaesthesia on thoraco-abdominal volume variations during spontaneous breathing and mechanical ventilation
Open this publication in new window or tab >>Effects of propofol anaesthesia on thoraco-abdominal volume variations during spontaneous breathing and mechanical ventilation
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2011 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 55, no 5, 588-596 p.Article in journal (Refereed) Published
Abstract [en]

Background Anaesthesia based on inhalational agents has profound effects on chest wall configuration and breathing pattern. The effects of propofol are less well characterised. The aim of the current study was to evaluate the effects of propofol anaesthesia on chest wall motion during spontaneous breathing and positive pressure ventilation. Methods We studied 16 subjects undergoing elective surgery requiring general anaesthesia. Chest wall volumes were continuously monitored by opto-electronic plethysmography during quiet breathing (QB) in the conscious state, induction of anaesthesia, spontaneous breathing during anaesthesia (SB), pressure support ventilation (PSV) and pressure control ventilation (PCV) after muscle paralysis. Results The total chest wall volume decreased by 0.41 +/- 0.08 l immediately after induction by equal reductions in the rib cage and abdominal volumes. An increase in the rib cage volume was then seen, resulting in total chest wall volumes 0.26 +/- 0.09, 0.24 +/- 0.10, 0.22 +/- 0.10 l lower than baseline, during SB, PSV and PCV, respectively. During QB, rib cage volume displacement corresponded to 34.2 +/- 5.3% of the tidal volume. During SB, PSV and PCV, this increased to 42.2 +/- 4.9%, 48.2 +/- 3.6% and 46.3 +/- 3.2%, respectively, with a corresponding decrease in the abdominal contribution. Breathing was initiated by the rib cage muscles during SB. Conclusion Propofol anaesthesia decreases end-expiratory chest wall volume, with a more pronounced effect on the diaphragm than on the rib cage muscles, which initiate breathing after apnoea.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-152944 (URN)10.1111/j.1399-6576.2011.02413.x (DOI)000289365000014 ()
Available from: 2011-05-03 Created: 2011-05-03 Last updated: 2017-12-11Bibliographically approved
2. Active expiration may contribute to the reduction in end-expiratory volume during emergence from anesthesia and in the immediate post-operative period.
Open this publication in new window or tab >>Active expiration may contribute to the reduction in end-expiratory volume during emergence from anesthesia and in the immediate post-operative period.
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(English)Manuscript (preprint) (Other academic)
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care
Identifiers
urn:nbn:se:uu:diva-248627 (URN)
Available from: 2015-04-05 Created: 2015-04-05 Last updated: 2015-07-07
3. Positive end-expiratory pressure optimization with forced oscillation technique reduces ventilator induced lung injury: a controlled experimental study in pigs with saline lavage lung injury
Open this publication in new window or tab >>Positive end-expiratory pressure optimization with forced oscillation technique reduces ventilator induced lung injury: a controlled experimental study in pigs with saline lavage lung injury
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2011 (English)In: Critical Care, ISSN 1364-8535, E-ISSN 1466-609X, Vol. 15, no 3, R126- p.Article in journal (Refereed) Published
Abstract [en]

Introduction: Protocols using high levels of positive end-expiratory pressure (PEEP) in combination with low tidal volumes have been shown to reduce mortality in patients with severe acute respiratory distress syndrome (ARDS). However, the optimal method for setting PEEP is yet to be defined. It has been shown that respiratory system reactance (Xrs), measured by the forced oscillation technique (FOT) at 5 Hz, may be used to identify the minimal PEEP level required to maintain lung recruitment. The aim of the present study was to evaluate if using Xrs for setting PEEP would improve lung mechanics and reduce lung injury compared to an oxygenation-based approach.

Methods: 17 pigs, in which acute lung injury (ALI) was induced by saline lavage, were studied. Animals were randomized into two groups: in the first PEEP was titrated according to Xrs (FOT group), in the control group PEEP was set according to the ARDSNet protocol (ARDSNet group). The duration of the trial was 12 hours. In both groups recruitment maneuvers (RM) were performed every 2 hours, increasing PEEP to 20 cmH(2)O. In the FOT group PEEP was titrated by monitoring Xrs while PEEP was reduced from 20 cmH(2)O in steps of 2 cmH(2)O. PEEP was considered optimal at the step before which Xrs started to decrease. Ventilatory parameters, lung mechanics, blood gases and hemodynamic parameters were recorded hourly. Lung injury was evaluated by histopathological analysis.

Results: The PEEP levels set in the FOT group were significantly higher compared to those set in the ARDSNet group during the whole trial. These higher values of PEEP resulted in improved lung mechanics, reduced driving pressure, improved oxygenation, with a trend for higher PaCO(2) and lower systemic and pulmonary pressure. After 12 hours of ventilation, histopathological analysis showed a significantly lower score of lung injury in the FOT group compared to the ARDSNet group.

Conclusions: In a lavage model of lung injury a PEEP optimization strategy based on maximizing Xrs attenuated the signs of ventilator induced lung injury. The respiratory system reactance measured by FOT could thus be an important component in a strategy for delivering protective ventilation to patients with ARDS/acute lung injury.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-162094 (URN)10.1186/cc10236 (DOI)000295799700008 ()
Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2017-12-08Bibliographically approved
4. The application of forced oscillation technique and self-mixing laser interferometers during anesthesia and mechanical ventilation.
Open this publication in new window or tab >>The application of forced oscillation technique and self-mixing laser interferometers during anesthesia and mechanical ventilation.
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(English)Manuscript (preprint) (Other academic)
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care
Identifiers
urn:nbn:se:uu:diva-248628 (URN)
Available from: 2015-04-05 Created: 2015-04-05 Last updated: 2015-07-07

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