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Spontaneous Breathing Improves Shunt Fraction and Oxygenation in Comparison with Controlled Ventilation at a Similar Amount of 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.
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2011 (English)In: Anesthesia and Analgesia, ISSN 0003-2999, E-ISSN 1526-7598, Vol. 113, no 5, 1089-1095 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Spontaneous breathing (SB), when allowed during mechanical ventilation (MV), improves oxygenation in different models of acute lung injury. However, it is not known whether oxygenation is improved during mechanically unsupported SB. Therefore, we compared SB without any support with controlled MV at identical tidal volume (V(T)) and respiratory rate (RR) without positive end-expiratory pressure in a porcine lung collapse model.

METHODS: In 25 anesthetized piglets, stable lung collapse was induced by application of negative pressure, and animals were randomized to either resume SB or to be kept on MV at identical VT (5 mL/kg; 95% confidence interval: 3.8 to 6.4) and RR (65 per minute [57 to 73]) as had been measured during an initial SB period. Oxygenation was assessed by blood gas analysis (n = 15) completed by multiple inert gas elimination technique (n = 8 of the 15) for shunt measurement. In addition, possible lung recruitment was studied with computed tomography of the chest (n = 10).

RESULTS: After induction of lung collapse, PaO(2)/FIO(2) decreased to 90 mm Hg (76 to 103). With SB, PaO(2)/FIO(2) increased to 235 mm Hg (177 to 293) within 15 minutes, whereas MV at identical VT and RR did not cause any improvement in oxygenation. Intrapulmonary shunt by 45 minutes after induction of lung collapse was lower during SB (SB: 27% [24 to 30] versus MV: 41% [28 to 55]; P = 0.017). Neither SB nor MV reduced collapsed lung areas on computed tomography.

CONCLUSIONS: SB without any support improves oxygenation and reduces shunt in comparison with MV at identical settings. This seems to be achieved without any major signs of recruitment of collapsed lung regions.

Place, publisher, year, edition, pages
2011. Vol. 113, no 5, 1089-1095 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-161927DOI: 10.1213/ANE.0b013e31822ceef8ISI: 000296236200025OAI: oai:DiVA.org:uu-161927DiVA: diva2:458537
Available from: 2011-11-23 Created: 2011-11-21 Last updated: 2017-12-08Bibliographically 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
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Available from: 2012-11-01 Created: 2012-10-11 Last updated: 2013-01-23Bibliographically approved

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Vimlati, LaszloKawati, RafaelHedenstierna, GöranLarsson, AndersLichtwarck-Aschoff, Michael

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