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During spontaneous breathing cardiac output lacks major effect on pulmonary shunting in porcine lungs with partial collapse

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Spontaneous breathing (SB) improves oxygenation compared to mechanical ventilation (MV), and does so even without recruit-ing atelectasis [1, 2]. Since it cannot be excluded that cardiac output (CO) impacts on pulmonary shunt, we investigated whether pulmonary shunt correlates with CO in a porcine model of lung collapse.


In 12 anaesthetized and relaxed supine piglets, lung collapse was induced by negative pressure application to the endotracheal tube during MV. Six animals resumed SB after 15 minutes; the other six were kept on MV at a respiratory rate and tidal volume corresponding to SB. All animals were followed over 120 minutes, and repeated measurements were converted to the area under curve and analysed by Mann-Whitney test and linear regression.


PaO2/FiO2 was higher and venous admixture (Qva/Qt) was lower in the SB group. Hemodynamics was stable and CO was similar in both groups. Qva/Qt correlated with CO (r = 0.83, P = 0.04) in the MV group, but not in the SB group (r = 0.08, P = 0.88) (Figure 1).

Figure 1

Venous admixture (Qva/Qt) plotted against CO (pooled data for each group). Solid circles, mechanical ventilation (MV); open circles, spontaneous breathing (SB).


SB achieves higher PaO2/FiO2 and lower Qva/Qt compared to MV. During SB, Qva/Qt seems to be unaffected by CO. This lung collapse model has stable hemodynamics and gas exchange for at least 2 hours irrespective of the mode of ventilation.


  1. 1.

    Carvalho AR, Spieth PM, Pelosi P, et al.: Pressure support ventilation and biphasic positive airway pressure improve oxygenation by redistribution of pulmonary blood flow. Anesth Analg 2009, 109: 856-865. 10.1213/ane.0b013e3181aff245

  2. 2.

    Vimlati L, Kawati R, Hedenstierna G, Larsson A, Lichtwarck-Aschoff M: Spontaneous breathing improves shunt fraction and oxygenation in comparison with controlled ventilation at a similar amount of lung collapse. Anesth Analg 2011, 113: 1089-1095. 10.1213/ANE.0b013e31822ceef8

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Correspondence to L Vimlati.

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Vimlati, L., Larsson, A., Hedenstierna, G. et al. During spontaneous breathing cardiac output lacks major effect on pulmonary shunting in porcine lungs with partial collapse. Crit Care 16, P120 (2012).

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  • Cardiac Output
  • Mechanical Ventilation
  • Tidal Volume
  • Negative Pressure
  • Endotracheal Tube