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Influence of Carbon Dioxide on Hypoxic Pulmonary Vasoconstriction during Pneumoperitoneum
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background: Pneumoperitoneum (PP) by CO2-inflation may result in acid-base alterations such ashypercarbia and respiratory acidosis. We studied in an animal preparation the effect of abdominal inflation by carbon dioxide (CO2) and air on gas exchange during PP.

Methods: 27 anesthetized pigs were allocated to 3 groups. PP was maintained either with 1/ CO2 or 2/ air or 3/ CO2 during intravenous natriumprusside infusion (SNP) (n=9 in each group). In 3 pigs in each group, SPECT was used for analysis of ventilation and perfusion distributions, in another 6 pigs MIGET was used for assessing V/Q matching. MIGET, SPECT and central haemodynamics and pulmonary gas exchange were recorded during anaesthesia and after 60 minutes of PP.

Results: CO2-PP but not Air-PP caused a shift of blood flow away from collapsed to aerated regions. SNP-PP shifted blood flow towards atelectatic areas of the lung. V/Q analysis by MIGET showed a decrease in shunt during CO2-PP (6±1% compared to baseline 9±2%, p<0.001) but an increase during SNP-PP (16±2%, p< 0.001) and no changes during Air-PP (10±2%). PaO2 increased from 266±21 to 305±20 mmHg (baseline to CO2-PP/p<0.01) and decreased to 240±24 mmHg during Air-PP and to 200±22 mmHg during SNP-PP. Arterial carbon dioxide (PCO2) increased only during CO2 and SNP- PP.

Conclusion: CO2-PP enhanced the shift of blood flow towards better ventilated areas of the lung compared to Air-PP. Moreover, SNP worsened the ventilation-perfusion match even more and blunted the effects previously seen with CO2. CO2 should therefore be the mediator of enhanced HPV during PP.

National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-150211OAI: oai:DiVA.org:uu-150211DiVA: diva2:406645
Available from: 2011-03-29 Created: 2011-03-28 Last updated: 2011-05-04Bibliographically approved
In thesis
1. The Effect of CO2-Pneumoperitoneum on Ventilation Perfusion Distribution of the Lung
Open this publication in new window or tab >>The Effect of CO2-Pneumoperitoneum on Ventilation Perfusion Distribution of the Lung
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Laparoscopic operations are a common and popular way for abdominal procedures. They are usually performed by insufflation of carbon dioxide (CO2) into the abdominal cavity. However, insufflation of CO2 may interfere with cardiac and circulatory as well as respiratory functions. The CO2-pneumoperitoneum (PP) may cause hypercarbia and acidosis. The direct effects of CO2 and acidosis lead to decreased cardiac contractility, sensitization of the myocardium to arrhythmogenic effects of catecholamines and systemic vasodilatation. There may even be long-lasting post-operative effects on breathing control.

The pneumoperitoneum may also cause several respiratory changes, e.g. decreased functional residual capacity (FRC) and vital capacity (VC), formation of atelectasis, reduced respiratory compliance and increased airway pressure. Still, arterial oxygenation is mostly maintained or even improved during PP.

In view of the apparently contradictory results in respiratory mechanics and gas exchange, the present studies were performed to evaluate respiratory changes on gas exchange and ventilation-perfusion distributions during PP in a porcine model. It was demonstrated that atelectasis during anaesthesia and PP may be estimated by an increased arterial to endtidal PCO2-gradient (study I). Perfusion was redistributed away from dorsal, collapsed lung regions when PP was established. This resulted in a better ventilation-perfusion match (study II). Increasing abdominal pressure shifted blood flow more and more away from collapsed lung tissue, decreased pulmonary shunt and improved oxygenation from 8 to 16 mmHg PP, despite an increase of atelectasis formation (study III). CO2-PP enhanced the shift of blood flow towards better ventilated parts of the lung compared to Air-PP. Moreover, sodium natriumprusside worsened the ventilation-perfusion match even more and blunted the effects previously seen with carbon dioxide. CO2 should therefore be the mediator of enhancing HPV during PP.

In conclusion, pneumoperitoneum with CO2 causes atelectasis with elimination of ventilation in the dependent lung regions. However, an efficient shift of blood flow away from collapsed, non-ventilated regions results in a better ventilation-perfusion matching and better oxygenation of blood than without PP. A prerequisite for the beneficial effect is the use of carbon dioxide for the abdominal inflation, since it enhances HPV.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 662
Keyword
lung, atelectasis; computed tomography; multiple inert gas elimination technique; model, pig; Pa–ECO2 ratio; surgery, laparoscopy; lung, blood flow; single photon emission computed tomography; ventilation/perfusion distribution; gas exchange; hypoxic pulmonary vasoconstriction
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-149746 (URN)978-91-554-8045-5 (ISBN)
Public defence
2011-05-11, Enghoff Salen, Akademiska Hospital, Entrance 30, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-04-20 Created: 2011-03-22 Last updated: 2011-05-05Bibliographically approved

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