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Haemodynamic stability and pulmonary shunt during spontaneous breathing and mechanical ventilation in porcine lung collapse
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.
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, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
2012 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 56, no 6, 748-754 p.Article in journal (Refereed) Published
Abstract [en]

Background

We investigated the haemodynamic stability of a novel porcine model of lung collapse induced by negative pressure application (NPA). A secondary aim was to study whether pulmonary shunt correlates with cardiac output (CO).

Methods

In 12 anaesthetized and relaxed supine piglets, lung collapse was induced by NPA (−50 kPa). Six animals resumed spontaneous breathing (SB) after 15 min; the other six animals were kept on mechanical ventilation (MV) at respiratory rate and tidal volume (VT) that corresponded to SB. All animals were followed for 135 min with blood gas analysis and detailed haemodynamic monitoring.

Results

Haemodynamics and gas exchange were stable in both groups during the experiment with arterial oxygen tension (PaO2)/inspired fraction of oxygen (FiO2) and pulmonary artery occlusion pressure being higher, venous admixture (Qva/Qt) and pulmonary perfusion pressure being lower in the SB group. CO was similar in both groups, showing slight decrease over time in the SB group. During MV, Qva/Qt increased with CO (slope: 4.3 %min/l; P < 0.001), but not so during SB (slope: 0.55 %min/l; P = 0.16).

Conclusions

This porcine lung collapse model is reasonably stable in terms of haemodynamics for at least 2 h irrespective of the mode of ventilation. SB achieves higher PaO2/FiO2 and lower Qva/Qt compared with MV. During SB, Qva/Qt seems to be less, if at all, affected by CO compared with MV.

Place, publisher, year, edition, pages
2012. Vol. 56, no 6, 748-754 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-175676DOI: 10.1111/j.1399-6576.2012.02700.xISI: 000305070400012PubMedID: 22524589OAI: oai:DiVA.org:uu-175676DiVA: diva2:532469
Available from: 2012-06-11 Created: 2012-06-11 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Benefits of Spontaneous Breathing: Compared with Mechanical Ventilation
Open this publication in new window or tab >>Benefits of Spontaneous Breathing: Compared with Mechanical Ventilation
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

When spontaneous breathing (SB) is allowed during mechanical ventilation (MV), atelectatic lung areas are recruited and oxygenation improves thereby. Whether unsupported SB at its natural pattern (without PEEP and at low pressure/small tidal volume) equally recruits and improves oxygenation, and if so by which mechanism, has not been studied.

A porcine lung collapse model was designed to study this question. The cardiac output dependency of the pulmonary shunt was investigated with healthy lungs and with major shunt (during one-lung ventilation) and with SB, MV and continuous positive airway pressure (CPAP). The hypoxic pulmonary vasoconstriction (HPV) was blocked with sodium nitroprusside (SNP) to see whether HPV is the only mechanism available for ventilation/perfusion (VA/Q) matching during MV and SB. In all experiments, respiratory rate and tidal volume during MV were matched to SB. Oxygenation was assessed by serial blood gas measurements, recruitment by thoracic CTs; pulmonary shunt was assessed by multiple inert gas elimination or venous admixture.

SB attained better oxygenation and lower pulmonary shunt compared with MV, although it did not recruit collapsed lung. Pulmonary shunt did not correlate with cardiac output during SB, whereas a correlation was found during MV and CPAP. With blocked HPV, pulmonary shunt was considerably lower during SB than MV.

In conclusion, SB improves VA/Q matching as compared with MV, even when no recruitment occurs. In contrast to MV and CPAP, cardiac output has no major effect on pulmonary shunt during SB. The improved VA/Q matching during SB despite a blocked HPV might indicate the presence of a SB-specific mechanism that improves pulmonary blood flow redistribution towards ventilated lung regions independent of or supplementary to HPV.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 47 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 824
Keyword
spontaneous breathing, mechanical ventilation, pulmonary shunt, oxygenation, hypoxic pulmonary vasoconstriction
National Category
Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care
Identifiers
urn:nbn:se:uu:diva-182564 (URN)978-91-554-8498-9 (ISBN)
Public defence
2012-11-23, Enghoffsalen, Entrance 50, Akademiska sjkhuset, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2012-11-01 Created: 2012-10-11 Last updated: 2013-01-23Bibliographically approved

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Vimláti, LaszloLarsson, AndersHedenstierna, GöranLichtwarck-Aschoff, Michael

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