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Open lung concept in high risk anaesthesia: Optimizing mechanical ventilation in morbidly obese patients and during one lung ventilation with capnothorax
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
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 [en]
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: urn:nbn:se:uu:diva-268498ISBN: 978-91-554-9440-7 (print)OAI: oai:DiVA.org:uu-268498DiVA: diva2:881127
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
List of papers
1. Prevention of atelectasis in morbidly obese patients during general anesthesia and paralysis: a computerized tomography study
Open this publication in new window or tab >>Prevention of atelectasis in morbidly obese patients during general anesthesia and paralysis: a computerized tomography study
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2009 (English)In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 111, no 5, 979-987 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Morbidly obese patients show impaired pulmonary function during anesthesia and paralysis, partly due to formation of atelectasis. This study analyzed the effect of general anesthesia and three different ventilatory strategies to reduce the amount of atelectasis and improve respiratory function. METHODS: Thirty patients (body mass index 45 +/- 4 kg/m) scheduled for gastric bypass surgery were prospectively randomized into three groups: (1) positive end-expiratory pressure of 10 cm H2O (PEEP), (2) a recruitment maneuver with 55 cm H2O for 10 s followed by zero end-expiratory pressure, (3) a recruitment maneuver followed by PEEP. Transverse lung computerized tomography scans and blood gas analysis were recorded: awake, 5 min after induction of anesthesia and paralysis at zero end-expiratory pressure, and 5 min and 20 min after intervention. In addition, spiral computerized tomography scans were performed at two occasions in 23 of the patients. RESULTS: After induction of anesthesia, atelectasis increased from 1 +/- 0.5% to 11 +/- 6% of total lung volume (P < 0.0001). End-expiratory lung volume decreased from 1,387 +/- 581 ml to 697 +/- 157 ml (P = 0.0014). A recruitment maneuver + PEEP reduced atelectasis to 3 +/- 4% (P = 0.0002), increased end-expiratory lung volume and increased Pao2/Fio2 from 266 +/- 70 mmHg to 412 +/- 99 mmHg (P < 0.0001). PEEP alone did not reduce the amount of atelectasis or improve oxygenation. A recruitment maneuver + zero end-expiratory pressure had a transient positive effect on respiratory function. All values are presented as mean +/- SD. CONCLUSIONS: A recruitment maneuver followed by PEEP reduced atelectasis and improved oxygenation in morbidly obese patients, whereas PEEP or a recruitment maneuver alone did not.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-113069 (URN)10.1097/ALN.0b013e3181b87edb (DOI)000271172500009 ()19809292 (PubMedID)
Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2016-02-12Bibliographically approved
2. Preoperative lung function tests as a predictor for atelectasis in morbidly obese patients during anesthesia
Open this publication in new window or tab >>Preoperative lung function tests as a predictor for atelectasis in morbidly obese patients during anesthesia
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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:nbn:se:uu:diva-268621 (URN)
Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2016-02-12
3. Real-time ventilation and perfusion distributions by electrical impedance tomography during one-lung ventilation with capnothorax
Open this publication in new window or tab >>Real-time ventilation and perfusion distributions by electrical impedance tomography during one-lung ventilation with capnothorax
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2015 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 59, no 3, 354-368 p.Article in journal (Refereed) Published
Abstract [en]

Background: Carbon dioxide insufflation into the pleural cavity, capnothorax, with one-lung ventilation (OLV) may entail respiratory and hemodynamic impairments. We investigated the online physiological effects of OLV/capnothorax by electrical impedance tomography (EIT) in a porcine model mimicking the clinical setting.

Methods: Five anesthetized, muscle-relaxed piglets were subjected to first right and then left capnothorax with an intra-pleural pressure of 19cm H2O. The contra-lateral lung was mechanically ventilated with a double-lumen tube at positive end-expiratory pressure 5 and subsequently 10cm H2O. Regional lung perfusion and ventilation were assessed by EIT. Hemodynamics, cerebral tissue oxygenation and lung gas exchange were also measured.

Results: During right-sided capnothorax, mixed venous oxygen saturation (P=0.018), as well as a tissue oxygenation index (P=0.038) decreased. There was also an increase in central venous pressure (P=0.006), and a decrease in mean arterial pressure (P=0.045) and cardiac output (P=0.017). During the left-sided capnothorax, the hemodynamic impairment was less than during the right side. EIT revealed that during the first period of OLV/capnothorax, no or very minor ventilation on the right side could be seen (33% vs. 97 +/- 3%, right vs. left, P=0.007), perfusion decreased in the non-ventilated and increased in the ventilated lung (18 +/- 2% vs. 82 +/- 2%, right vs. left, P=0.03). During the second OLV/capnothorax period, a similar distribution of perfusion was seen in the animals with successful separation (84 +/- 4% vs. 16 +/- 4%, right vs. left).

Conclusion: EIT detected in real-time dynamic changes in pulmonary ventilation and perfusion distributions. OLV to the left lung with right-sided capnothorax caused a decrease in cardiac output, arterial oxygenation and mixed venous saturation.

National Category
Anesthesiology and Intensive Care
Identifiers
urn:nbn:se:uu:diva-248178 (URN)10.1111/aas.12455 (DOI)000349604000010 ()25556329 (PubMedID)
Note

De 2 första författarna delar förstaförfattarskapet.

Available from: 2015-04-12 Created: 2015-03-30 Last updated: 2017-12-04Bibliographically approved
4. Optimal PEEP during one lung ventilation with capnothorax. An experimental study
Open this publication in new window or tab >>Optimal PEEP during one lung ventilation with capnothorax. An experimental study
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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:nbn:se:uu:diva-268620 (URN)
Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2016-02-12

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