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Optimal PEEP during one lung ventilation with capnothorax. An experimental study
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 Surgical Sciences, Hedenstierna laboratory.
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 Surgical Sciences, Anaesthesiology and Intensive Care.
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(English)Article in journal (Other academic) Submitted
Abstract [en]

Background: One-lung ventilation (OLV) with capnothorax is used to facilitate thoracoscopic surgery and carries the risk of hypotension, hypoxemia, carbon dioxide retention and ventilator induced lung injury. The optimal positive end-expiratory pressure (PEEP) during these circumstances is unknown and the PEEP level chosen in clinical praxis is often a compromise between hemodynamic and respiratory considerations. We therefore investigated the physiological effects of a recruitment maneuver followed by a decremental PEEP trial in order to find the optimal PEEP level.

Methods: Eight anesthetized, muscle relaxed piglets were subjected to right sided OLV with a CO2-insufflation pressure of 16 cm H2O into the contralateral pleural cavity. Following a recruitment maneuver, a decremental PEEP trial from PEEP 20 cm H2O to zero end-expiratory pressure (ZEEP), was performed. Regional pulmonary ventilation and perfusion were recorded with electrical impedance tomography. End expiratory lung volume (EELV) and hemodynamics were also recorded. Computerized tomography (CT) was used to confirm EIT- and EELV measurements and visualize the effects of the decremental PEEP trial.

Results: The best arterial oxygenation was reached at a PEEP level of 12 cm H2O (49 ± 14 kPa) and then gradually deteriorated to ZEEP (11 ± 5 kPa) (p <0.001). The lowest driving pressures were recorded at PEEP 14 cm H2O (19.6 ± 5.8 cm H2O) and then increased to (38.3 ± 6.1 cm H2O at ZEEP (p <0.001). EIT maps showed that ventilation shifted from the dorsal parts of the ventilated lung and perfusion shifted from the ventilated to the non-ventilated lung with down titration of PEEP from 12-14 cm H2O to lower PEEP-levels (p = 0.003, p = 0.02, respectively). Arterial CO2-levels increased and pH decreased at initiation of OLV with capnothorax but were then stable during down titration of PEEP to 12 cm H2O. With further decrement of PEEP, the hypercapnic acidosis worsened from pH 7.19 ± 0.06 to 7.04 ± 0.09 (p = 0.002). Optimal hemodynamic condition was also found at 12 -16 cm H2O, with mean arterial pressure significantly higher at PEEP 12 cm H2O (84 ± 9 mm Hg) compared to ZEEP (63 ± 15 mm Hg) (p = 0.005).

Conclusion: 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.

National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care
Identifiers
URN: urn:nbn:se:uu:diva-268620OAI: oai:DiVA.org:uu-268620DiVA: diva2:878190
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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