Independent lung ventilation in patients with unilateral pulmonary contusion. Monitoring with compliance and EtCO2
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Objective: a) to describe a non-barotraumatic ventilatory setting for independent lung ventilation (ILV); b) to determine the utility of single lung end-tidal CO2 (EtCO2) monitoring to evaluate the ventilation to perfusion (V/Q) matching in each lung during ILV and for ILV weaning. Design: prospective study. Setting: general intensive care unit in a university teaching hospital. Patients: twelve patients with unilateral thoracic trauma needing ILV. Interventions and results: ILV was started with each lung ventilated with the same tidal volume (Vt): plateau airway pressure (Pplat) was 34.2±3.2 cmH2O in diseased lungs (DL) and 18.1±1.9 cmH2O in normal lungs (NL) (P<0.01). Static compliance (Cst) was 9.9±1.1 ml/cmH2O in DL and 19.3±1.7 ml/cmH2O in NL (P<0.01). EtCO2 was 22.5±2.2 mmHg in DL and 36.6±1.9 mmHg in NL (P<0.01). PaO2/FiO2 was at 151±20. PEEP was applied on the DL and each lung was ventilated with a Vt that developed Pplat ≤26 cmH2O. With this setting, Vt given to the NL was unchanged, whereas it was reduced in the DL (238±30 ml vs 350±31 ml; P<0.01). Cst and EtCO2 were still significantly lower in the DL (P<0.01, respectively), while the PaO2/FiO2 ratio remained unchanged. Vt was then progressively increased in the DL as Pplat decreased, but remained unchanged in the NL. ILV was discontinued when Vt, Cst and EtCO2 were the same in each lung. PaO2/FiO2 ratio had then increased to 295±18. Conclusions: a) during ILV, adequate oxygenation and a reduction in V/Q mismatch can be obtained by setting Vt and PEEP to keep Pplat below a safe threshold for barotrauma; b) measurement of single lung EtCO2 can be useful to evaluate progressive V/Q matching.
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