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Preoperative lung function tests as a predictor for atelectasis in morbidly obese patients during anesthesia
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Medicinska och farmaceutiska vetenskapsområdet, centrumbildningar mm, UCR-Uppsala Clinical Research Center.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
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(English)Article in journal (Other academic) Submitted
Abstract [en]

Rationale: Pulmonary function is regularly impaired during general anesthesia and paralysis in morbidly obese patients. The aim of this study was to compare preoperative lung function with the alterations in respiratory function after induction of anesthesia in patients with BMI > 40 kg/m2.

Methods: 23 women and 7 men (38 ± 9 years, (mean ± SD)), with a body mass index of 45 ± 4 kg/m2 were studied. 20 patients were active smokers (20 ± 12 pack years). All patients underwent preoperative lung functiontests. Arterial blood gases were collected before and after induction of anesthesia and either a single slice CT or a spiral CT was made for assessment of the amount of lung collapse. Respiratory system compliance was measured during anesthesia.

Results: Lung volumes were within normal limits, however forced expiratory gas flow was reduced during the latter part of expiration. The arterial oxygen tension divided by the inspired O2 fraction (PaO2/FIO2 ratio) decreased from 409 ± 47 mmHg awake to 238 ± 80 mmHg after induction of anesthesia. The higher FEV1 was, the larger was the fall in oxygenation during anesthesia. At 5 min after induction, atelectasis in a CT cut 1 cm above the diaphragm was 7 ± 2 % of the lung area. The amount of atelectasis during anesthesia correlated with FEF75 in a regression analysis (p = 0.03).

Conclusion: In morbidly obese patients without clinical signs of pulmonary disease a preoperative spirometry with mild signs of airway obstruction (reduced late expiratory flow) may predict reduced formation of atelectasis during anesthesia.

National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care
Identifiers
URN: urn:nbn:se:uu:diva-268621OAI: oai:DiVA.org:uu-268621DiVA: diva2:878197
Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2016-02-12
In thesis
1. Open lung concept in high risk anaesthesia: Optimizing mechanical ventilation in morbidly obese patients and during one lung ventilation with capnothorax
Open this publication in new window or tab >>Open lung concept in high risk anaesthesia: Optimizing mechanical ventilation in morbidly obese patients and during one lung ventilation with capnothorax
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Formation of atelectasis, defined as reversible collapse of aerated lung, often occurs after induction of anaesthesia with mechanical ventilation. As a consequence, there is a risk for hypoxemia, altered hemodynamics and impaired respiratory system mechanics. In certain situations, the risk for atelectasis formation is increased and its consequences may also be more difficult to manage. Anesthesia for bariatric surgery in morbidly obese patients and surgery requiring one-lung ventilation (OLV) with capnothorax are examples of such situations.

In Paper I (30 patients with BMI > 40 kg/m2 scheduled for bariatric surgery) a recruit­ment maneuver followed by positive end-expiratory pressure (PEEP) re­duced the amount of atelectasis and improved oxygenation for a prolonged period of time. PEEP or a recruitment maneuver alone did not reduce the amount of atelectasis.

In paper II we investigated whether it is possible to predict respiratory function impairment in morbidly obese patients without pulmonary disease from a preoperative lung function test. Patients with mild signs of airway obstruction (reduced end-expiratory flow) in the preoperative spirometry developed less atelectasis during anaesthesia.

In paper III we developed an experimental model of sequential OLV with capnothorax using electrical impedance tomography (EIT) that in real-time detected lung separation and dynamic changes in pulmonary ventilation and perfusion distributions. OLV to the left side caused a decrease in cardiac output, arterial oxygenation and mixed venous saturation.

In paper IV we used our model of OLV with capnothorax and applied a CO2-insufflation pressure of 16 cm H2O. We demonstrated that a PEEP level of 12-16 cm H2O is needed for optimal oxygenation and lowest possible driving pressure without compromising hemodynamic variables. Thus, the optimal PEEP was closely related to the level of the capnothorax insufflation pressure. With insufficient PEEP, ventilation/perfusion mismatch in the ventilated lung and redistribution of blood flow to the non-ventilated lung occurred.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 77 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1169
Keyword
Anaesthesia, mechanical ventilation, atelectasis, morbidly obese, one-lung ventilation, PEEP, recruitment maneuver, spirometry, EIT
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care
Identifiers
urn:nbn:se:uu:diva-268498 (URN)978-91-554-9440-7 (ISBN)
Public defence
2016-02-12, Grönwallssalen, Ing. 70, Akademiska sjukhuset, Uppsala, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2016-01-22 Created: 2015-12-06 Last updated: 2016-02-12

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