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  • Title: Haemodynamic stability and pulmonary shunt during spontaneous breathing and mechanical ventilation in porcine lung collapse.
    Author: Vimláti L, Larsson A, Hedenstierna G, Lichtwarck-Aschoff M.
    Journal: Acta Anaesthesiol Scand; 2012 Jul; 56(6):748-54. PubMed ID: 22524589.
    Abstract:
    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 (V(T) ) 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 (PaO(2) )/inspired fraction of oxygen (FiO(2) ) and pulmonary artery occlusion pressure being higher, venous admixture (Q(va) /Q(t) ) 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, Q(va) /Q(t) 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 PaO(2) /FiO(2) and lower Q(va) /Q(t) compared with MV. During SB, Q(va) /Q(t) seems to be less, if at all, affected by CO compared with MV.
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