ObjectiveTo evaluate whether APACHEⅡ score and arterial blood gas (ABG) analysis parameter of elderly patients with severe pneumonia can be improved if low molecular weight heparin (LMWH) was added to conventional therapy.MethodsFrom October 2009 to September 2011, 43 inpatients with severe pneumonia were randomly divided into treatment (n=23) and control (n=20) group. Control group received conventional treatment, and treatment group received conventional treatment plus the LMWH treatment (4 000U q.d.) for 7 days. APACHEⅡ score, and arterial blood gas analysis (pH of blood, partial pressure of oxygen［PaO2］,partial pressure of carbon dioxide［PaCO2］,lactate［Lac］) were compared at 24 h, day 3 and day 7 of treatment.ResultsThe basic data and APACHEⅡ score in two groups were not significantly different before treatment (P>0.05); the difference in incidence of hemorrhage was not significantly different during treatment (P>0.05); At 24 h and day 3 treatment, APACHEⅡ score in two groups was not significantly different (P>0.05),but at day 7,the APACHEⅡ score of treatment group was significantly lower than control group (［13.71±3.65］ vs ［16.95±4.70］, t=2.47, P=0.02). At 24 h, day 3 and day 7, the PH,PaCO2,Lac were not significantly different (P>0.05); at 24 h and day 3, PaO2 was not significantly different (P>0.05),but at day 7, the PaO2 of treatment group was significantly higher than control group(［106.8±32.7］ vs ［88.6±22.2］, t=-2.15,P=0.04).ConclusionLMWH plus conventional treatment for elderly patients with severe pneumonia can improve the oxygenation of patients, and reduce APACHEⅡ score.