홍상범.hwp

한대학병원내과계중환자실에서장기간기계환기를받은환자들의 3 년예후 울산대학교의과대학서울아산병원호흡기내과전규락, 최익수, 임채만, 고윤석, 오연목, 심태선, 이상도, 김우성, 김동순, 김원동, 홍상범 The 3 years Prognosis of Patients with Long Term Mechanical Ventilation in Medical Intensive Care Unit at a University Hospital Gyu Rak Chon, M.D., Ik Su Choi, M.D., Chae-Man Lim, M.D., Younsuck Koh, M.D., Yeon-Mok Oh, M.D., Tae Sun Shim, M.D., Sang Do Lee, M.D., Woo Sung Kim, M.D., Dong-Soon Kim, M.D., Won Dong Kim, M.D., Sang-Bum Hong, M.D. Division of Pulmonary and Critical Care Medicine, Asan Medical Center, Department of Internal Medicine, University of Ulsan College of Medicine, Seoul, Korea Background: There is little data on the 3 year prognosis and quality of life of patients on long-term (>72 hour) mechanical ventilation in a medical intensive care unit (MICU). Methods: Patients with long-term mechanical ventilation from May 2003 through July 2003 in MICU of Asan Medical Center, Seoul were enrolled in this studay. The survival rates were observed prospectively at 1, 3, 6, 12, 24, 36 months, and the quality of life of survivor was measured at 12 months by using Short Form 36 (SF-36). Results: The survival rate at 1, 3, 6, 12, 24 and 36 months was 54.8% (40/73), 39.7% (29/73), 30.1% (22/73), 20.5% (15/73), 18.3% (13/71) and 16.9% (12/71), respectively. There was a similar survival rate regardless of the diseases that required mechanical ventilation. A neoplasm or chronic liver disease had a worse survival rate than chronic lung or kidney disease (p<0.05). Each SF-36 domain except for the Role-emotional was inferior to the general population. Conclusions: The survival rate of patients with mechanical ventilation more than 72 hours is decreases continuously until 12 months but is relatively constant from 12 to 36 months. In these patients quality of life is also decrased. (Tuberc Respir Dis 2007; 62: 398-405) Key words: Long term mechanical ventilation, Intensive care unit, Survival rate, Quality of life. 서 기계환기는만성폐질환환자의급성악화, 대사적혹은기질적의식장애에의한의식혼수, 신경근육질환에의한호흡부전, 급성호흡곤란증후군, 수술후, 폐부종, 흡인, 폐렴, 패혈증그리고외상등다양한원인들에의한급성호흡부전의중요한보조치료법이다 1-4. 최근인공호흡기의기계적발전과인공호흡기에관련된지식의축적으로인공호흡기치료를받는환자들의사망률이과거에비하여향상되고있다. 이러한인공호흡기치료는대부분중환자실에서수행되는 론 Address for correspondence: Sang-Bum Hong, M.D. Division of Pulmonary and Critical Care Medicine, University of Ulsan College of Medicine, Asan Medical Center, 388-1, Pungnap-2dong, Seoul, 138-736, Korea Phone: 82-2-3010-3893, FAX: 82-2-3010-6968 E-mail: sbhong@amc.seoul.kr Received: Mar. 9. 2007 Accepted: May. 4. 2007 데중환자실은많은인력과기계장비및시설들이집중되어있어치료비용이크게발생되는곳이다. 국가적으로도인력의손실과경제적부담을초래하게된다. 그러므로중환자실에서치료받는환자들의예후평가에대한중요성이부각되고있다. 이중에서장기간기계환기가필요한환자에서사망률이높으며, 퇴원후에도지속적인치료또는요양을요하며이에따른비용의증가가문제가되고있다 5. 중환자실예후측정에대해서는아직우수한도구가없는실정이다. 예후평가로는 1개월생존여부를조사하는것이가장많이사용되고있으며, 6개월, 혹은 12개월째측정하는연구도있으나이에대한지침은없는실정이다. 1개월째생존여부측정이가장간편하지만장기간기계환기를하는중환자실환자의경우는보다장기적으로예후를측정해야될필요성이있다. 그외예후평가로는중환자실환자들을대상으로삶의질을조사하는방법이있다. 국내는중환자실에서기계환기치료를받는환자들의예후및삶 398

Tuberculosis and Respiratory Diseases Vol. 62. No.5, May. 2007 의질에대한전향적인자료가부족한실정이다. 외국에서도장기간기계환기치료를받은환자에서의 1년예후및삶의질에대한자료가보고 5-10 는되고있으나기저질환별, 기계환기적응증별로 1년예후에대한연구보고가없고병원획득성폐렴 11, 중증패혈증 12, 급성호흡곤란증후군 13 등각각의사망률에대한보고가있다. 본연구는국내의한대학병원내과계중환자실에서 72시간이상장기간기계환기를받은환자들의자료를수집, 분석하여기저질환별, 기계환기적응증별로 1, 3, 6, 12, 24, 36개월째예후를관찰하여예후판정에적절한시점을보고자하였으며, 1년째에는이환자들의삶의질상태를평가하고자하였다. 대상및방법 1. 연구대상 2003년 5월 1일부터 2003년 7월 31일까지서울아산병원내과계중환자실에서 72시간이상기계환기치료를받은 18세이상성인 74명을대상으로하였다. 기계환기가필요했던원인질환은만성폐질환자의급성악화, 의식혼수, 신경근육질환, 급성호흡부전의 4가지로구분하였다. 만성폐질환자의급성악화는기저폐쇄성혹은제한성폐질환자 ( 만성폐쇄성폐질환, 기관지천식, 결핵후유증, 기관지확장증, 폐섬유화증, 기타로분류 ) 가감염, 기관지수축, 심부전혹은다른급성악화로기계환기가필요한경우로, 의식혼수는대사성혹은기질적이상으로인한의식장애에의해기계환기가필요한경우로, 신경근육질환은말초신경, 신경근육접합부, 혹은근육질환에의해기계환기가필요한경우로, 급성호흡부전은기저폐쇄성혹은제한성폐질환이없었던환자에서폐렴, 패혈증, 급성심부전, 급성호흡곤란증후군, 수술후, 흡인및외상으로기계환기가필요한경우로정의하였다. 2. 연구방법환자들이기계환기가 72시간이상경과되었을때 연구대상에포함되어나이, 성별, 기저질환, 기계환기가필요했던원인질환, 병원입원기간, 중환자실입원기간, 총기계환기시간, 기계환기이탈시간, 질병의중증도평가를위한입원첫날 Acute Physiology And Chronic Health Evaluation Ⅱ(APACHE Ⅱ) 점수와 1, 3, 6, 12, 24, 36개월생존여부를조사하였다. 삶의질평가는설문지의타당도가입증된 Short- Form 36(SF-36) 설문지 14 를이용하여 12개월생존자 15명중연구동의서에동의한 7명을대상으로전화, 면담을통해조사하였다. SF-36 설문지는총 35개의문항으로구성되어있으며신체적건강영역과정신적건강영역으로구분되고각각신체적건강영역은 Physical functioning(10문항 ), Role limiting due to physical problem(4 문항 ), Bodily pain(2 문항 ), General health perception(5문항 ) 4항목, 정신적건강영역에는 Vitality, energy or fatigue(4문항 ), Social functioning(2문항 ), Role limiting due to emotional problem(3 문항 ), General mental health(5문항 ) 4항목으로이루어져있다. Ware 15 가제시한방법에따라각문항들의점수는일부가중치를두어합산되었고합산된점수는 100점만점으로환산되었다 (0점은가장나쁜건강상태, 100점은가장좋은건강상태를의미 ). Cha 등 16 이보고한근로자들에서의건강수준조사자료를정상대조군으로삶의질평가비교를하였다. 이군의각항목별자료는평균 ± 표준편차로기술되어다음과같다 : Physical functioning 85.7±15.4, Role limiting due to physical problem 72.2±32.3, Bodily pain 68.2±18.1, General health perception 58.1±16.4, Vitality, energy or fatigue 61.8±19.7, Social functioning 80.0±16.8, Role limiting due to emotional problem 73.3±36.0, General mental health 60.0±19.7. 3. 통계분석통계처리는 SPSS 12.0 프로그램을사용하였으며, 조사된수치는평균 ± 표준편차형식으로기술하였다. 단변수분석은두군간의평균치비교를위해서 Student's t-test를사용하였고두군이상의빈도비교를위해 Chi-square test를사용하였다. 다변수분 399

GR Chon et al: The prognosis of patients with long term mechanical ventilation Table 1. Demographics and clinical characteristics of patients with long term mechanical ventilation(n=73) Table 3. Underlying diseases of long term mechanical ventilator patients(n=68) Characteristic Underlying disease n(%) Gender, male/female 54/19 Age (years) (mean±sd) 60.0±19.7 Length of hospital stay (days) (mean±sd) 60.3±82.8 Length of ICU* stay (days) (mean±sd) 18.7±14.7 Admission APACHE II score (mean±sd) 23.8±8.9 Length of MV (days) (mean±sd) 15.2±13.7 Length of weaning (days) (mean±sd) 9.9±11.2 *Intensive care unit, Acute physiologic and chronic health evaluation, Mechanical ventilation. Table 2. Indications of long term mechanical ventilation(n=73) Indication n(%) Acute respiratory failure 49(67) Pneumonia 16 Sepsis 12 Acute heart failure 7 Others 14 Acute exacerbation of chronic respiratory failure 11(15) Coma 8(11) Neuromuscular disease 5(7) 석은 1년생존에영향을미치는요인을보기위해로지스틱회귀분석을사용하였다. 95% 신뢰구간을사용하여 p값이 0.05보다낮을때통계학적인의미를부여하였다. 결 과 1. 대상환자의인구역학적특성 추적관찰에실패한 1명을제외한연구대상에포함된 73명의기본특성은 Table 1에기술되어있다. 환자들의총기계환기시간은 15.2±13.7일, 중환자실입원기간은 18.7±14.7일이었고, 그리고병원입원기간은 60.3±82.8일이었다 (Table 1). 기계환기가필요했던 Chronic lung disease 19(28) Neoplasm 15(22) Chronic kidney disease 10(15) Chronic liver disease 4(6) DM complications 4(6) Peripheral disease 4(6) Heart failure 3(4) Acute abdominal disease 3(4) Neuromuscular disease 2(3) Postoperative state 2(3) Trauma 2(3) 원인질환은급성호흡부전 49명 (67%), 만성폐질환자의급성악화 11명 (15%), 의식혼수 8명 (11%), 신경근육질환 5명 (7%) 명이었다 (Table 2). 연구대상 73명중기저질환이있는환자수는 68명 (93%) 으로만성폐질환 19명 (28%), 신생물 15명 (22%), 만성신장질환 10명 (15%), 만성간질환 4명 (6%) 명순으로조사되었다 (Table 3). 연구에포함된환자들의기계환기방식과호흡역학은 Table 4에기록되어있다. 조절환기양식은대부분이압력조절환기양식을사용하였고이탈은대부분압력보조환기양식을사용하였다. 2. 72시간이상기계환기치료를받은환자들의예후대상환자들의 1개월생존율은 54.8%(40/73), 3개월생존율은 39.7%(29/73), 6개월생존율은 30.1% (22/73), 12개월생존율은 20.5%(15/73), 24개월생존율은 18.3%(13/71), 그리고 36개월생존율은 16.9% (12/71) 였다. 12개월까지는지속적으로생존율이감소하다가그이후부터 36개월까지비교적생존율이유지되는것으로조사되었다. 24개월부터 2명은추적관찰을할수없었다. 기저질환별과기계환기가필요했던주요질환별로분석을했을때도역시비슷한경향을관찰할수있었다 (Figure 1, 2). 기저질환별 3, 6, 400

Tuberculosis and Respiratory Diseases Vol. 62. No.5, May. 2007 Table 4. The ventilator modes and settings at the time of 72 hours according to the reason for initiating mechanical ventilation Ventilation mode Total Pneumonia Sepsis CRF* Heart failure PCV 46(63%) 10(62.5%) 7(58.3%) 5(45.5%) 5(71.4%) PS 20(27.3%) 4(25%) 5(41.7%) 1(9.1%) 2(28.6%) NPPV 6(8.2%) 1(6.3%) 0(0%) 5(45.5%) 0(0%) Other 1(1.4%) 1(6.3%) 0(0%) 0(0%) 0(0%) Monitored variables TV (ml) 434.9±100.2 407.7±93.6 435.8±72.8 451.4±158.5 515.7±97.9 PEEP (cmh2o) 4.7±2.8 4.2±2.7 4.0±2.7 3.9±3.5 5.0±3.2 RR** 23.1±4.1 25.2±3.7 21.5±4.7 21.6±2.8 23.1±4.2 PIP (cmh2o) 19.8±6.2 20.0±5.7 17.5±4.3 19.0±5.9 22.4±6.4 *Acute exacerbation of chronic respiratory failure, Pressure controlled ventilation, Pressure support, Noninvasive positive pressure ventilation, Tidal volume, Positive end expiratory pressure, **Respiration rate, Peak inspiratory pressure. Figure 1. Survival rates according to major disease that needed mechanical ventilation during observation period. There was no difference in survival rate among diseases that needs mechanical ventilation at 1, 3, 6, 12, 24, 36 month(p>0.05). Figure 2. Survival rates according to underlying disease during observation period. Neoplasm or chronic liver disease were worse than chronic lung or kidney disease in survival rate at 3, 6, 12, 24, 36 month(p<0.05). 12, 24, 36개월생존율은신생물또는만성간질환이만성신장질환이나만성폐질환, 기저질환이없는군에비해예후가좋지않았다 (p<0.05). 12개월이후생존율이유지되는점으로 12개월에서단변수분석을실시한결과, 12개월생존에영향을미치는변수는성별 (p=0.017), 최고흡기압력 (p=0.044) 으로분석되었다 (Table 5). 그러나교란변수를보정하기위해로지스 틱회귀분석을사용한다변수분석에서는 12개월생존에영향을미치는변수가없었다. 3. 삶의질평가연구동의서에동의한 7명을대상으로 SF-36 설문지로조사한결과, Physical functioning 항목이최저 401

GR Chon et al: The prognosis of patients with long term mechanical ventilation Table 5. Predictors affecting 1 year survival rate in univariate analysis Variables Death (n=58) Survival (n=15) p-value Age (years) (mean SD) 65.3±15.1 60.3±10.8 0.236 Gender, male/female 47/11 7/8 0.011 Length of hospital stay (days) (mean±sd) 59.1±88.9 64.9±55.3 0.809 Length of ICU* stay (days) (mean±sd) 18.2±14.6 20.7±15.4 0.554 Admission APACHE II score (mean±sd) 23.9±9.1 23.6±8.4 0.893 72h PIP (cmh2o) (mean±sd) 20.6±6.4 16.5±4.2 0.044 Length of MV (days) (mean±sd) 15.3±13.4 15.0±15.1 0.945 Length of weaning (days) (mean±sd) 10.3±11.3 9.15±11.2 0.752 *Intensive care unit, Acute physiologic and chronic health evaluation, Peak inspiratory pressure, Mechanical ventilation. Table 6. Comparison of quality of life (SF-36) between study group and control group Domains Study group (n=7) Control group (n=296) Physical functioning 29.3±32.2 85.7±15.4 Role physical 60.7±37.8 72.2±32.3 Bodily pain 51.8±27.4 68.2±18.1 General health perception 47.1±18.4 58.1±16.4 Vitality, energy or fatigue 39.3±9.7 61.8±19.7 Social functioning 41.1±26.7 80.0±16.8 Role emotional 81.0±25.2 73.3±36.0 General mental health 46.8±16.1 60.0±19.7 값 (29.3±32.2) 을보였고 Role limiting due to emotional problem 항목이최고값 (81.0±25.2) 을보였으며정상대조군과비교시정신적건강영역에서 Role limiting due to emotional problem을제외하고낮은값을보였다 (Table 6). SF-36의각항목별로남녀간의차이는없었다 (p>0.05). 고 중환자실에서장기간기계환기치료후회복된환자들의예후및삶의질을적절하게평가하는것은환자, 보호자, 의사, 및의료보험정책입안자모두에게필수적인부분이다. 중환자치료에서예후에대한지 찰 표로생존율이가장흔하게사용되고있다. 몇연구에서중환자실에서회복된환자들의 1년생존율에대해낮게는 27% 에서높게는 75% 까지보고 5-7,9,10 하고있지만장기간기계환기를받은환자에서기저질환별, 기계환기가필요했던원인질환별로 1년생존율을보고한전향적인연구는적다. 본연구에서는 12개월생존율이 20.5% 로외국의보고보다생존율이낮은데이점은기저질환을가진환자가 93% 포함되고장기간기계환기를시행한중증환자를포함한결과로생각된다. 하지만이부분에대해서는향후대규모연구가필요할것이다. 본연구에서주목할만한점은중환자들의생존율이 12개월까지는지속적으로감소하다가그이후부터 36개월까지비교적일정하게유지되는점이다. 기저질환별과기계환기가필요했던주요질환별로분석을했을때도역시비슷한경향을보여주었다. Eddleston 등 6 은 6개월이후환자들의생존율이유지되는것으로보고하였는데, 이연구에서는기계환기를시행하지않은환자들을포함하였다. 연구마다포함된환자들의기저질환및기계환기기간등이차이가많아기존연구들과비교는어려운편이다. 장기예후를보는시점에대한연구가부족한상황에서본연구의결과는향후연구에있어중증환자들을포함한연구에서는 12개월까지생존율을평가하는것에대한근거를제시하였다고볼수있겠다. 특히기저 402

Tuberculosis and Respiratory Diseases Vol. 62. No.5, May. 2007 질환을중심으로조사하였을때종양과중증간질환환자의생존율은 0% 로조사되었다. 본연구에서 1년이후생존율이유지되는이유로중환자들의기능적회복이 1년이걸리는것으로판단할수있으나, 사망원인분석및지속적병원치료등에대해서는향후연구를통해서확인해야될것으로사료된다. Douglas 등 5 은장기간기계환기치료를받은환자에서지속적인병원치료와비용증가를제시하였다. 장기간기계환기의정의는견해차이가있는부분이지만, 기계환기이탈시 72시간을기준으로이탈방식을다르게접근하므로본연구자들은 72시간으로임의로설정해서연구를진행하였다. 연구결과에서중환자실및병원재원기간, 기계환기시간, 그리고사망률등모두장기중환자실중증환자들의특성을보여준것으로사료된다. Djaiani 등 7 의보고에따르면나이, 진단, 질병의중증도가 1년생존에영향을미치는요인이었는데본연구에서는 1년생존의예후인자로통계적유의성을보인것은없었다. 저자들은연구에포함된대상자가적어서통계적유의성을보이지못했다고추정하였다. 중환자의학치료의예후지표로생존여부만으로는부족하다는인식이높아지면서급성호흡곤란증후군 17,18, 장기간치료를받은중환자실생존자 6,19,20, 심장수술후에장기간기계환기치료를받은중환자실생존자 21 에서삶의질평가에대한여러논문들이보고되었다. 삶의질평가를위한 SF-36의사용은 Garratt 등 22 의보고에서처럼많은연구에서광범위하게사용되고있고환자가자가작성하기에편리하다는점, 중환자군에서접근성과타당도가보고된점 23, 그리고국내와외국에서타당도가증명이된점 14,24,25 등으로다른평가도구보다낫다고생각된다. 본연구는국내중환자실에서장기간기계환기치료를받은환자들을대상으로삶의질평가를시행한최초의연구라는점에서의의가있다고할수있으며 Eddleston 등 6 의보고와달리 SF-36 각항목별로남녀간의차이를보이지않았다. 본연구에서일부중환자들은신체여건상삶의질평가를시행할수가없었기때문에이를고려하면점수는더낮을것으로사료된다. 본연구의제한점은첫째, 장기간기계환기를 72시간으로임의로설정해서연구를진행한것이다. 이부분에대해서는기계환기시간과합병증간의명확한연관성에관한연구가필요할것이다. 둘째, 72시간미만기계환기를적용받았던환자군과의 1년예후및삶의질평가비교가없는점이다. 셋째, 삶의질평가에서 1년동안의연구기간동안 3개월, 혹은 6개월시점의반복적인측정이이루어지지않아서삶의질이어느정도개선되는지에대한평가를할수없었다. 넷째, 삶의질평가에서정상군으로인용된자료는공단의근로자들을대상으로조사된부분으로실제선택비뚤림이작용해서 Role limiting due to emotional problem 항목에서차이가나지않은것으로생각해볼수있겠다. 결론적으로한내과계중환자실에서 72시간이상장기간기계환기를받은환자들의 3년간생존율은낮았으며, 기저질환별로차이를보였다. 또한환자들의생존율이 12개월까지지속적으로낮아지나 12개월부터 36개월까지유지되었다. 1년시점에서삶의질평가시이환자들의삶의질상태가낮음을보여주었다. 요약연구배경 : 내과계중환자실에서 72시간이상장기간기계환기를받은환자들의자료가부족하여기저질환별, 기계환기가필요했던원인질환별로장기예후를관찰하며, 또한 1년째에는삶의질평가를같이수행하여이환자들의삶의질상태를평가하고자하였다. 방법 : 2003년 3월부터 2003년 7월까지서울아산병원내과계중환자실에서 72시간이상기계환기치료를받은환자 73명을대상으로 1, 3, 6, 12, 24, 36개월생존율을전향적으로관찰하고 1년생존자를대상으로 Short Form 36(SF-36) 을이용하여삶의질을측정하였다. 결과 : 대상환자들의 1개월생존율은 54.8%(40/73), 3개월생존율은 39.7%(29/73), 6개월생존율은 30.1% (22/73), 12개월생존율은 20.5%(15/73), 24개월생존 403

GR Chon et al: The prognosis of patients with long term mechanical ventilation 율은 18.3%(13/71), 그리고 36개월생존율은 16.9% (12/71) 이었다. 3년간생존율은기계환기가필요했던원인질환별로는차이가없었고, 기저질환별로는신생물또는만성간질환이만성폐질환이나만성신장질환에비해예후가불량하였다 (p<0.05). SF-36을이용한삶의질평가에서정상대조군과비교시정신적건강영역에서 Role limiting due to emotional problem을제외하고모두낮은값을보였다. 결론 : 한대학병원내과계중환자실에서 72시간이상장기간기계환기를받은환자들의 3년간생존율은낮았으며, 12개월까지지속적으로낮아지나 12 개월부터 36개월까지는유지되었다. 1년시점에서삶의질평가시이환자들의삶의질상태가낮음을보여주었다. 감사의글 환자들의생존여부와삶의질평가설문지면담으로노력해주신윤아영, 조은미연구간호사분들께이지면을빌어서깊은감사를드립니다. 아울러삶의질평가에대해아낌없는조언을해주신연세대학교의과대학신촌세브란스병원호흡기내과김영삼교수님께도깊은감사를드립니다. 참고문헌 1. Knaus WA, Wagner DP, Zimmerman JE, Draper EA. Variations in mortality and length of stay in intensive care units. Ann Intern Med 1993;118:753-61. 2.Thomsen GE, Morris AH. Incidence of the adult respiratory distress syndrome in the State of Utah. Am J Respir Crit Care Med 1995;152:965-71. 3. Connors AF, Dawson NV, Thomas C, Harrell FE, Desbiens N, Fulkerson WJ, et al. Outcomes following acute exacerbation of severe chronic obstructive lung disease. Am J Respir Crit Care Med 1996;154:959-67. 4. Pontoppidan, H, Geffin B, Lowenstein E. Acute respiratory failure in the adult. N Engl J Med 1972;287:799-806. 5. Douglas SL, Daly BJ, Gordon N, Brennan PF. Survival and quality of life: short-term versus longterm ventilator patients. Crit Care Med 2002;30: 2655-62 6. Eddleston JM, White P, Guthrie E. Survival, morbidity, and quality of life after discharge from intensive care. Crit Care Med 2000;28:2293-9. 7. Djaiani G, Ridley S. Outcome of intensive care in the elderly. Anaesthesia 1997;52:1130-6. 8. Hurel D, Loirat P, Saulnier F, Nicolas F, Brivet F. Quality of life 6 months after intensive care: Results of a prospective multicenter study using a generic health status scale and a satisfaction scale. Intensive Care Med 1997;23:331-7. 9. Konopad E, Noseworthy TW, Johnston R, Shustack A, Grace M. Quality of life measures before and one year after admission to an intensive care unit. Crit Care Med 1995;23:1653-9. 10. Dragsted L, Qvist J, Madsen M. Outcome from intensive care. Ⅳ. A 5-year study of 1308 patients: long-term outcome. Eur J Anaesthesiol 1990;7:51-62. 11. Heyland DK, Cook DJ, Griffith L, Keenan SP, Brun-Buisson C. The attributable morbidity and mortality of ventilator associated pneumonia in the critically ill patients. Am J Respir Crit Care Med 1999;159:1249-56. 12. Angus DC, Linde-Zwirble WT, Lidicker J, Clermont G, Carcillo J, Pinsky MR. Epidemiology of severe sepsis in the United States: Analysis of incidence, outcome, and associated costs of care. Crit Care Med 2001;29:1303-10. 13. Vincent JL, Sakr Y, Ranieri VM. Epidemiology and outcome of acute respiratory failure in intensive care unit patients. Crit Care Med 2003;31:S296-99. 14. Nam BH, Lee SW. Testing the validity of the Korean SF-36 health survey. J Korean Soc Health Stat 2003;28:3-24. 15. Ware JE. SF-36 health survey. Manual & Interpretation Guide. Boston, MA: Quality Metric, Inc.; 1993. 16. Cha BS, Koh SB, Chang SJ, Park JK, Kang MG. The assessment of worker's health status by SF-36. Korean J Occup Med 1998;10:9-19. 17. Herridge MS, Cheung AM, Tansey CM, Matte-Martyn A, Diaz-Granados N, Al-Saidi F, et al. One year outcomes in survivors of the acute respiratory distress syndrome. N Engl J Med 2003;348:683-93. 18. Davidson TA, Caldwell ES, Curtis JR, Hudson LD, Steinberg KP. Reduced quality of life in survivors of acute respiratory distress syndrome compared with critically ill control patients. JAMA 1999;281:354-60. 19. Chatila W, Kreimer D, Criner G. Quality of life in survivors of prolonged mechanical ventilatory support. Crit Care Med 2001;29:737-42. 20. Niskanen M, Ruokonen E, Takala J, Rissanen P, Kari A. Quality of life after prolonged intensive care. Crit 404

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