Abstract： Objective To compare the effect of slight and usual sedation on the prognosis and inflammatory marker levels in patients receiving mechanical ventilation in ICU.Methods We enrolled 78 critically ill adult patients who were undergoing mechanical ventilation and were expected to need ventilation for more than 48 h.The patients were prospectively and randomly assigned to receive:slight sedation(Richmond Agitation Sedation Score-1 to 0,n =38 patients) or usual sedation (Richmond Agitation Sedation Score-3 to-2,n =40 patients).Sedative dosages,duration of mechanical ventilation,length of ICU stay,complications (ventilator-associated pneumonia,tracheotomy),adverse reactions (accidental extubation,reintubation,barotrauma) and levels of inflammatory markers on the day of sedation time for 48 h were recorded.Results When compared with the usual sedation group,duration of mechanical ventilation(d)(8 ± 5 vs 13 ± 8,P ＜0.05) and length of ICU stay(d)(12 ± 10 vs 22 ±9,P ＜ 0.05) were significantly shorter in the slight sedation group.The total doses of midazolam (mg),propofol (mg) and fentany(μg) were lower in the slight sedation group than those in the usual sedation group(275 ±85 vs575±142,4 562±1 128 vs 7 434±1 712 and 2 332±1 458 vs 4 124±2 743,P＜0.05).Accidental extubation(5％ vs 3％),reintubation(5％ vs 10％) and barotraumas(3％ vs 8％) showed no differences between the 2 groups (P ＞ 0.05).In the slight sedation group,the incidences of ventilatorassociated pneumonia (26％ vs 53％) and tracheotomy (18％ vs 48％) were significantly decreased compared with those in the usual group.The levels of IL-1 (35 ± 12 vs 47 ± 18,P ＜ 0.05) rg/L,IL-6(49 ±21 vs 62 ±27,P＜0.05) ng/L,TNF-α(39 ±16 vs 52 ±25,P＜0.05) ng/L and CRP (95 ±41 vs 125 ± 45,P ＜ 0.05) mg/L were also lower in the slight sedation group than those in the conventional group.There were no differences in ICU mortality and 28 d-survival rate between the 2 groups.Conclusion Slight sedation was shown to reduce the length of mechanical ventilation and ICU stay.It also decreased the levels of inflammatory markers while didn' t increase the incidence of adverse reactions.