Spontaneous breathing affects the spatial ventilation and perfusion distribution during mechanical ventilatory support

Uppsala University, Uppsala, Uppsala, Sweden
Critical Care Medicine (Impact Factor: 6.31). 06/2005; 33(5):1090-5. DOI: 10.1097/01.CCM.0000163226.34868.0A
Source: PubMed


In acute respiratory failure, gas exchange improves with spontaneous breathing during airway pressure release ventilation (APRV). The mechanisms for this improvement are not fully clear. We have shown that APRV with spontaneous breathing reopens nonaerated lung tissue in dorsal juxtadiaphragmatic regions. We hypothesized that spontaneous breathing during APRV may redistribute ventilation and perfusion toward these reopened regions.
Prospective, randomized, controlled study.
Animal research laboratory
Twenty controlled mechanically ventilated pigs.
Lung injury was induced by injection of oleic acid into the central circulation; thereafter, pigs were randomized to APRV with or without spontaneous breathing. To induce spontaneous breathing during APRV with spontaneous breathing, the mechanical respiratory rate was decreased by 50% in this group.
We measured respiratory mechanics, hemodynamics, gas exchange including the multiple inert gas elimination technique, and the spatial ventilation and perfusion distribution using single photon emission tomography. At similar minute ventilation and airway pressures, shunt remained stable during APRV with spontaneous breathing, whereas it increased during APRV without spontaneous breathing during the 2-hr study period (p = .006). Single photon emission tomography showed more ventilation (p < .001) and pulmonary blood (p < .025) flow in dorsal, juxtadiaphragmatic lung regions when spontaneous breathing was present.
The beneficial effects of spontaneous breathing on intrapulmonary shunt and oxygenation are explained both by increased ventilation of aerated dependent lung tissue and by opening up nonaerated tissue so that ventilation is distributed to a larger share of the lung. Redistribution of perfusion is possibly secondary to the altered ventilation. The overall effect is a more efficient use of available lung tissue for gas exchange.

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    • "An animal study found less depression of CO and oxygen delivery (DO2) with PCV + SB compared with PCV at similar transpulmonary pressures [40]. In our study, the CO during PCV + SB and PCV – SB was comparable to previously published studies [12,16]., and the more pronounced increase in the PCV – SB group does not lead to a significant increase in DO2. This suggests that the higher CO was required to maintain an adequate DO2. "
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    ABSTRACT: Acute lung injury (ALI) can result from various insults to the pulmonary tissue. Experimental and clinical data suggest that spontaneous breathing (SB) during pressure-controlled ventilation (PCV) in ALI results in better lung aeration and improved oxygenation. Our objective was to evaluate whether the addition of SB has different effects in two different models of ALI. Forty-four pigs were randomly assigned to ALI resulting either from hydrochloric acid aspiration (HCl-ALI) or from increased intra-abdominal pressure plus intravenous oleic acid injections (OA-ALI) and were ventilated in PCV mode either with SB (PCV + SB) or without SB (PCV - SB). Cardiorespiratory variables were measured at baseline after induction of ALI and after 4 hours of treatment (PCV + SB or PCV - SB). Finally, density distributions and end-expiratory lung volume (EELV) were assessed by thoracic spiral computed tomography. PCV + SB improved arterial partial pressure of oxygen/inspiratory fraction of oxygen (PaO2/FiO2) by a reduction in intrapulmonary shunt fraction in HCl-ALI from 27% +/- 6% to 23% +/- 13% and in OA-ALI from 33% +/- 19% to 26% +/- 18%, whereas during PCV - SB PaO2/FiO2 deteriorated and shunt fraction increased in the HCl group from 28% +/- 8% to 37% +/- 17% and in the OA group from 32% +/- 12% to 47% +/- 17% (P < 0.05 for interaction time and treatment, but not ALI type). PCV + SB also resulted in higher EELV (HCl-ALI: 606 +/- 171 mL, OA-ALI: 439 +/- 90 mL) as compared with PCV - SB (HCl-ALI: 372 +/- 130 mL, OA-ALI: 192 +/- 51 mL, with P < 0.05 for interaction of time, treatment, and ALI type). SB improves oxygenation, reduces shunt fraction, and increases EELV in both models of ALI.
    Critical care (London, England) 11/2008; 12(6):R135. DOI:10.1186/cc7108 · 4.48 Impact Factor
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    • "Our results are supported by recent studies that demonstrate that superimposed spontaneous breathing during airway pressure release ventilation redistributes tidal ventilation toward dependent lung regions just near the diaphragm [24]. This conclusion was derived using single photon emission tomography in the pig model. "
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    Critical care (London, England) 02/2007; 11(1):R26. DOI:10.1186/cc5706 · 4.48 Impact Factor
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    • "The net result is an improvement in oxygenation with potentially decreased VALI in these dependent lung regions. These beneficial effects have been confirmed in animal models of ALI/ARDS with spontaneous breathing during APRV [42] [43] [44]. In humans, the oxygenation effects of spontaneous breathing during APRV may accrue over time (ie, 24 hours) because of slow, progressive recruitment of these lung units [45]. "
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    Clinics in Chest Medicine 01/2007; 27(4):615-25; abstract viii-ix. DOI:10.1016/j.ccm.2006.06.008 · 2.07 Impact Factor
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