[The significance of non invasive cardiac output monitoring system on evaluating circulatory and respiratory function in pig with acute respiratory distress syndrome].

OBJECTIVE: To investigate the effect of non invasive cardiac output monitoring (NICO) system in pig model with acute respiratory distress syndrome (ARDS), and to provide experimental basis for clinical application.

METHODS: Eleven anaesthetized and ventilated ARDS male pig models were induced by intravenously infusing 0.2 mL/kg oleic acid. Lung recruitment was condocted by pressure control ventilation on pigs with ARDS. The optimal positive end-expiratory pressure (PEEP) was determined by optimal dead space fraction [the ratio of dead space to tidal volume (VD/VT)]. Cardiac output (CO) was determined by NICO, the respiratory function was monitored, and the VD/VT, dynamic compliance (Cdyn), oxygenation index (PaO₂/FiO₂), the volume of alveolar ventilation (Valv) and arterial blood oxygen saturation (SaO₂) were recorded before infusing oleic acid, after stabilization of ARDS model and at optimal PEEP level, and the intrapulmonary shunt fraction (Qs/Qt) was calculated. CO was also determined by application of pulse indicated continuous cardiac output (PiCCO), and the linear regression analysis between CO determined by NICO and CO determined by PiCCO was conducted.

RESULTS: Seven experimental ARDS pigs model were successfully established. The optimal PEEP identified by the lowest VD/VT method was (15.71 ± 1.80) cmH₂O (1 cmH₂O = 0.098 kPa). Compared with before infusing oleic acid, VD/VT and Qs/Qt after stabilization of ARDS model were significantly increased [VD/VT: (72.29 ± 8.58)% vs. (56.00 ± 11.06)%, Qs/Qt: (21.04 ± 15.05)% vs. (2.00 ± 1.32)%, both P<0.05], and SaO₂and Valv were significantly decreased [SaO₂: 0.888 ± 0.108 vs. 0.999 ± 0.053, Valv (mL): 92.06 ± 35.22 vs. 146.11 ± 45.43, both P<0.05]. VD/VT, Qs/Qt, SaO₂and Cdyn at optimal PEEP level were improved to the levels before infusing oleic acid [(61.07 ± 9.30)%, (3.21 ± 6.10)%, 0.989 ± 0.025, (117.14 ± 41.14)mL]. Cdyn and PaO₂/FiO₂after stabilization of ARDS model were significantly lowered compared with those before infusing oleic acid [Cdyn (mL/cmH₂O): 14.43 ± 5.50 vs. 38.14 ± 6.72, PaO₂/FiO₂(mmHg, 1 mmHg = 0.133 kPa): 78.71 ± 23.22 vs. 564.37 ± 158.85, both P < 0.05]. Cdyn and PaO₂/FiO₂at optimal PEEP level [(19.71 ± 4.86)%, (375.49 ± 141.30) mmHg] were elevated compared with the levels after stabilization of ARDS model (both P <0 .05), but still lower than those before infusing oleic acid (both P < 0.05). Compared with the levels after stabilization of ARDS model, CO at optimal PEEP level showed obvious decrease from (4.18 ± 2.46) L/min to (3.95 ± 2.69) L/min without significant difference (P > 0.05). There was linear correlation between CO determined by NICO and CO determined by PiCCO (r²=0.925, P < 0.001).

CONCLUSIONS: NICO technique provides a useful and accurate non invasive estimation of CO and respiratory function.VD/VT provided by NICO can titrate the optimal PEEP in patients with ARDS.