Evaluation Of Curative Effect Of Dead Space Fraction In Patients With Ards Undergoing Prone Position Ventilation

Objective(s):To investigate whether the dead space fraction(VD/VT)can be used as a effective index to judge the treatment of acute respiratory distress syndrome(ARDS)patients with prone position ventilation(PPV).Methods:30 patients with ARDS(PaO2/FiO2<200mmHg)were divided into the pulmonary group and the extra-pulmonary group according to different etiology.Both groups were implemented with prone position ventilation therapy for 2 hours.Their arterial oxygen tension(PaO2),inhaled oxygen concentration(FiO2)and arterial carbon dioxide partial pressure(PaCO2)were recorded in supine position,prone position 1,2 hours and recovery supine position for 1,2,3 hours.At the same time,the end tidal carbon dioxide partial pressure(ETCO2)was measured by ventilator.Finally,the oxygenation index(PaO2/FiO2)and dead space fraction(VD/VT)were calculated.Results:prone position ventilation can make VD/VT and PaO2/FiO2 improved significantly:VD/VT in the prone position ventilation 2 hours appear the biggest drop(from 0.62 + 0.02 to 0.52 + 0.02,P<0.05).and PaO2/FiO2 delay to restore supine 1 hours after the biggest change value(from 120.30 + 8.60 to 167.49 + 6.26.P<0.05).There was a negative correlation between VD/VT and PaO2/FiO2 by Pearson correlation analysis(r=-0.89,P=0.012).For group ARDSp,VD/VT have improved to some extent in the prone position ventilation for 1 hours,then 2 hours in the prone position ventilation reached the maximum drop value(from 0.62 + 0.06 to 0.53 + 0.01,P<0.05),and PaO2/FiO2 after gradually rise;the delay to the prone position ventilation 2 hours began to appear significantly improved,before it reaches the maximum value of changes in the recovery supine position ventilation 1 hours(from 119.72+4.32 to 169.17+3.80,P<0.05),then gradually decreased.For group ARDSexp,in the prone position ventilation 1 hours,dead space fraction(VD/VT)began to decline significantly improved,reathed the maximum value(from 0.61 + 0.08 to 0.50+0.01,P<0.05),then gradually increased,and the oxygenation index(PaO2/FiO2)although started to improve,but was delayed until 2 hours before it reaches the prone position ventilation the maximum change value(from 120.88 + 5.20 to 173.21 + 5.49,P<0.05),then gradually decreased;Conclusion(s):VD/VT and PaO2/FiO2 are closely related,which can be used as an index to evaluate the efficacy of ARDS patients with mechanical ventilation in prone position.VD/VT and PaO2/FiO2 show a certain degree of difference among ARDS patients with different etiologies.