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발관실패의위험인자및발관후천음과재삽관의예측에있어 Cuff Leak Test 의유용성과의미분석 성균관대학교의과대학내과학교실, 강북삼성병원호흡기내과, 1 삼성서울병원호흡기내과, 2 가천의대길병원호흡기내과, 3 보훈병원호흡기내과임성용, 서지영 1, 경선영 2, 안창혁 2, 박정웅 2, 이상표 2, 정성환 2, 함형석 1, 안영미 3, 임시영, 고원중 1, 정만표 1, 김호중 1, 권오정 1 Risk Factors of Extubation Failure and Analysis of Cuff Leak Test as a Predictor for Postextubation Stridor Seong Yong Lim, M.D., Gee Young Suh, M.D. 1, Sun Yong Kyung, M.D. 2, Chang Hyeok An, M.D. 2, Sang Pyo Lee, M.D. 2, Jung Woong Park, M.D. 2, Sung Hwan Jeong, M.D. 2, Hyoung Suk Ham, M.D. 1, Young Mee Ahn, M.D. 3, Si Young Lim, M.D., Won Jung Koh, M.D. 1, Man Pyo Chung, M.D. 1, Ho Joong Kim, M.D. 1, O Jung Kwon M.D. 1 Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Kangbuk Samsung Hospital, 1 Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea, 2 Division of Pulmonary Medicine, Department of Internal Medicine, Gachon Medical School, Gil Medical Center, Incheon, Korea, 3 Division of Pulmonary Medicine, Department of Internal Medicine, Veterans Hospital, Seoul, Korea Background: Extubation failure was associated with poor prognosis and high hospital mortality. Cuff leak test (CLT) has been proposed as a relatively simple method for detecting laryngeal obstruction that predispose toward postextubation stridor (PES) and reintubation. We examined the risk factors of extubation failure and evaluated the usefulness and limitation of CLT for predicting PES and reintubation. Methods: Thirty four consecutive patients intubated more than 24 hours were examined. The subjects were evaluated daily for extubation readiness, and CLT was performed prior to extubation. Several parameters in the extubation success and failure group were compared. The accuracy and limitation of CLT were evaluated after choosing the thresholds values of the cuff leak volume (CLV) and percentage (CLP). Results: Of the 34 patients studied, 6 (17.6%) developed extubation failure and 3 (8.8%) were accompanied by PES. The patients who had extubation failure were more likely to have a longer duration of intubation and more severe illness. The patients who developed PES had a smaller cuff leak than the others: according to the CLV (22.5±23.8 vs 233.3±147.1ml, p=0.020) or CLP (6.2±7.3 vs 44.3±24.7%, p=0.013). The best cut off values for the CLV and CLP were 50ml and 14.7%, respectively. The sensitivity, negative predictive value, and specificity of CLT were relatively high, but the positive predictive value was low. Conclusion: The likelihood of developing extubation failure increases with increasing severity of illness and duration of intubation. A low CLV or CLP (<50ml or 14.7%) is useful in identifying patients at risk of PES, but the CLT is not an absolute predictor and should not be used an indicator for delaying extubation. (Tuberc Respir Dis 2006; 61: 34-40) Keywords: Extubation failure, Stridor, Cuff leak test. 서 발관실패 (Extubation failure) 는계획된기관내관 론 Address for Crespondence: Gee Young Suh, M.D. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon dong, Kangnam gu, Seoul 135 710, Korea Tel: 822 3410 3426 Fax: 822 3410 3849 E mail: gysuh@smc.samsung.co.kr Received : May. 11. 2006 Accepted : Jul. 4. 2006 발관후 24-72시간내에재삽관과기계환기가필요한경우로이러한환자의예후는불량하여병원내사망률이 30-40% 이상인것으로알려지고있다 1. 발관실패의기도요인중기관내삽관의국소적합병증으로발생한후두기관점막의염증과부종은상기도폐쇄를일으키고발관후천음 (postextubation stridor; 이하 PES) 과호흡부전을유발할수있다. 이러한후두부폐쇄와 PES의발생및이로인한재삽관의위험을발관전에미리예측하기는어려운데, cuff-leak test ( 이하 CLT) 가후두부폐쇄를간접적으로평가하는데유용하다고알려져있다 2,3. 검 34

Tuberculosis and Respiratory Diseases Vol. 61. No.1, Jul. 2006 사의이론적근거는기관내관의부풀려졌던기낭을감압시켰을때정상적으로는기관내관주위로공기의누출이발생하지만후두부폐쇄가있는경우는누출이감소한다는점에착안하여누출되는공기의양을측정함으로써 PES와호흡부전발생가능성을미리예측하는방법이다. 하지만보고자마다 CLT의기준값이다르고일부는 CLT가유용하지않다는연구결과도있어 4 저자들은발관실패환자들의임상적인특성을살펴보고, PES와재삽관을예측하는데있어 CLT의의의와제한점을분석해보고자하였다. 대상및방법 1. 대상환자호흡부전으로강북삼성병원, 삼성서울병원, 길병원의내과계중환자실에입원하여최소 24시간이상삽관과인공호흡기치료후계획된발관을시도한 34명의연속적인환자들을대상으로하였다. 수술후의외과계환자, 기관절개술을시행받거나, 안면부또는기도의외상이나변형, 계획되지않은발관후재삽관을시행받은환자는제외하였다. 2. Protocol 중환자실입원 24시간내연령, 성별, 삽관의원인질환과 Simplified Acute Physiology Score (SAPS II), SOFA score를기록하였고, 7.0-8.0mm 기관내관을사용하여삽관후 24시간이경과된환자에서 Servoί, 또는 Servo 900C (Siemens-Elema, Solna, Sweden) 로인공호흡기치료후각해당기관의방법으로이탈을진행하고 2시간동안의자가호흡관찰 (spontaneous breathing trial) 시도후계획된발관을결정한대상환자에서발관시의 SOFA score, 총삽관기간, 기관내관의크기, 체질량지수, 혈색소, albumin, 전해질, 동맥혈가스검사수치를기록하였고경부단순촬영상튜브의직경 (ɸt) 과기관공기음영의직경 (ɸT) 을측정하여 ɸT/ɸt 를계산하였다. 그후 CLT는용적보조 / 조절환기양식하에서흡기일호흡 량을예상체중당 8-10ml로유지하고인공호흡기에서기록되는호기일호흡량 5회를측정하여평균값 (V1) 을구한후기관내관의부풀려진기낭을감압시키고호기일호흡량 5회를측정하여평균을기록하였다 (V2). 일호흡량은감압시일호흡량이점점감소하여고평부 (plateau) 를이루게되었을때 5회를측정하였다. Cuff leak volume (CLV)= V1-V2로기록하였고 Cuff leak (%) (CLP)= [V1-V2/V1] 100 으로계산하였다. 측정이끝나면기낭을다시부풀리고원래의상태에서관찰하고발관을시행하였으며 24시간동안 PES, 호흡곤란유무를관찰하고재삽관여부를기록하였다. PES는호흡곤란과연관된고음조의흡기시천명음이있을때로정의하였고재삽관은일반적인치료로도호흡곤란이호전되지않는경우담당의사의결정하에시행하였다. 3. 통계분석 SPSS (Version 13.0 SPSS Inc) program을이용하였고, 독립적인두군간의비교는 Mann-Whitney U test, 3개이상의비교는 Kruskal-Wallis test, 범주형변수의분석은 Fisher s exact test, 상관분석에는 Pearson s correlation coefficient를이용하였고 receiver-operating characteristic (ROC) curve 분석에는 MedCalc (version 8.1.1 Frank Schoonjans, Belgium) program 으로 PES로인한재삽관을예측할수있는 CLV, CLP의기준값을정하고이값에따른민감도와특이도를구하였으며 P-value가 0.05 미만인경우유의하다고판정하였다. 결과 1. 대상환자의특성총 34명대상환자중발관에성공한환자는 28명, 발관실패로재삽관을받은환자 6명 (17.6%), PES는 3명 (8.8%) 에서관찰되었고 PES 3명은모두재삽관을시행받았다. 평균연령은 60.4±18.3세였고남자가 23 명여자가 11명이었다. 삽관의평균기간은 4.7±3.5일 35

SY Lim et al. : Risk factors of extubation failure and analysis of cuff leak test Table 1. Characteristics of the study subjects and comparison between extubation success and failure group All Cases (n=34) Extubation Success group (n=28) Extubation Failure group (n=6) P-value Age (year) 60.4±18.3 58±18.9 71.5±9.1 0.103 Sex (M/F) 23/11 21/6 2/5 0.070 Days intubated 4.7±3.5 4.0±2.8 8.2±4.6 0.021 SAPS II score 45.2±19.0 41.7±15.5 61.8±26.1 0.027 SOFA Score (adm) * 7.3±3.9 6.6±3.3 10.8±5.1 0.051 SOFA Score (ext) 3.5±2.6 3.0±1.8 5.8±4.2 0.133 BMI (kg/m2) 22.2±3.4 22.2±3.4 20.9±2.4 0.391 Hemoglobin (g/dl) 10.9±1.9 10.9±1.8 11.4±2.7 0.557 Albumin (g/dl) 2.8±0.6 2.8±0.6 2.9±0.6 0.963 ɸT/ɸt 1.79±0.3 1.37±0.3 1.68±0.3 0.378 Definition of Abbreviation: * SOFA score (adm) = SOFA score at admission; SOFA score (ext) = SOFA score at extubation; ɸT/ɸt = diameter of trachea air shadow/ diameter of intubated tube on radiograph 이었고. 삽관의원인질환은폐렴 16예, 패혈증 5예, ARDS 와심부전증각 3예, 천식 2예, 기타 ( 과민성폐장염, 폐색전증, 약물중독, 급성간질성폐렴, 만성폐쇄성폐질환 ) 1예였다 (Table 1). 2. 발관성공군과재삽관군사이의비교분석삽관기간이재삽관군에서 8.2±4.6 일로성공군의 4.0±2.8 일보다길었고 (p=0.021), SAPS II score도재삽관군에서 61.8±26.1로성공군의 41.7± 15.5보다높았다 (p=0.027). 입원시 SOFA score도재삽관군에서 10.8±5.1로성공군의 6.6±3.3보다큰경향을보였다 (p=0.051). 성공군과재삽관군사이에성별, 연령, 체질량지수, albumin, 경부단순촬영상튜브의직경 (ɸt) 과기관공기음영의직경 (ɸT) 으로측정한 ɸT/ɸt 비율은차이를보이지않았다 (Table 1). 3. 재삽관과 PES 유무에따른 cuff-leak test 결과비교재삽관군의평균 CLV은 60.1±79.3ml로발관성공군의 247.8±144.8ml 보다유의하게낮았고 (p=0.004), CLP도재삽관군에서 12.6±14.6% 로발관성공군의 47.0±24.0% 보다유의하게낮았다 (p=0.002). PES 양성군의평균 CLV는 22.5± 23.8ml로음성군의 233.3±147.1ml 보다낮았고 (p=0.020), CLP도양성군에서 6.2±7.3% 로음성군의 44.3±24.7% 보다유의하게낮았다 (p=0.013). Cuff leak volume (ml) 600 500 400 300 200 Intubation Duration (Day) 16 14 12 10 8 6 r= -0.446 P= 0.008 100 0 7.0 7.5 Tube size 8.0 387.5 ± 184.7ml 202.5 ± 128.7ml 151.5 ± 126.9ml 4 2 0 Cuff leak Volume (ml) 0 100 200 300 400 500 600 Figure 1. Cuff leak volume according to the size of endotracheal tube. Large endotracheal tube size was associated with reduction of cuff leak volume (p=0.04). Figure 2. Cuff leak volume according to intubation duration. There was significant negative correlation between cuff leak volume and intubation duration 36

Tuberculosis and Respiratory Diseases Vol. 61. No.1, Jul. 2006 4. Cuff-leak test 와관련인자들간의상관관계 87.1%, 양성예측도 42.9%, 음성예측도 100% 였다. 8.0mm 기관내관을사용한대상군의 CLV의평균은 151.5± 126.9ml로 7.0mm를사용한대상군의평균 387.5±184.7ml보다유의하게작게나타났다 (p=0.04) (Figure 1). 삽관기간과 CLP (r=-0.443, p=0.009), CLV (r=-0.446, p=0.008) 은모두유의한역상관관계를보였다 (Figure 2). 기타연령, 체질량지수, 혈액학적수치, SOFA 및 SAPS II score등은 CLV, CLP와상관관계가없었다. 5. 재삽관과관련된 cuff-leak test의 Receiveroperating characteristic (ROC) curve 본연구의대상환자중 PES와재삽관을시행받은환자는전체의 8.8% 였고이를 ROC curve 분석에서유병율로사용하여분석한결과 95% 의신뢰구간을기준으로하여 area under the curve는 0.957 이었으며, 본연구에서가장신뢰성있는기준값는 CLV은 50ml 였고 CLP는 14.7% 였다 (Fig 3). CLV 50ml 이하를기준값으로할때의민감도는 100%, 특이도 93.5%, 양성예측도 60%, 음성예측도 100% 였고, CLP 14.7% 이하를기준값으로할때의민감도는 100%, 특이도 Sensitivity 1.00.75.50.25 0.00 0.00 Cuff leak 50ml.25 Cuff leak 14.7%.50 1 - Specificity.75 1.00 Figure 3. Receiver operating characteristic (ROC) plot. True positive fraction is plotted on y-axis and the true-negative fraction is plotted on x-axis. 고찰이번연구에서발관실패율은 17.6% 였고재삽관환자에서삽관기간이길고 SAPS II socre로측정한질병의중증도가높았다. 발관실패는후두기관부종등으로인한상기도폐쇄 5, 호흡분비물이많고환자스스로기침과기도보호를할수없는경우 6,7, 심부전과허혈성질환 7, 뇌병증 8, 호흡부전및위장출혈 1, 패혈증 1, 간질 9 등이원인으로실패율은 2-25% 로보고되고있는데 10 본연구결과는기존연구결과의범주내에해당한다. 기존연구에서발관실패율이다양한결과를보이는것은연구대상환자나방법등이다르기때문인데, 대상환자의경우내과계보다는외과계외상환자에서재삽관율이낮고 11, 나이가많고 12,13, 삽관기간이길며 12,13, 빈혈 6, 질병의중증도가크고 13, 진정제의사용 14, 미계획발관환자 15 에서재삽관율이높다고알려져있다. 따라서내과계또는외과계환자중위험인자의포함정도에따라재삽관율결과가달라질것으로예측된다. 재삽관군에서삽관기간이평균 8.2일로길었고 CLV및 CLP와역상관관계를보이고, SAPS II score 가컸던점은삽관기간이길고질병중증도가클수록발관실패위험이높다는기존결과를다시확인한결과로이러한환자의발관시는주의깊은관찰이필요하다. 또한기관내관의크기가커질수록 CLV이작아지는결과를보였는데후두직경에비해크기가큰경우튜브와후두부사이의기계적마찰과압박및플라스틱이나실리콘에대한생화학적반응으로부종등의합병증이많아질것으로예측되며실제위험인자라는보고 16 도있지만그렇지않다는결과 17,18 도많아이에대해서는추가적연구가필요하다. 통계적차이는없었지만연령과성별에있어재삽관군의평균연령이 71.5세로높고, 6명중 4명이여자로노인과여자의비율이높은점은다른연구결과와비슷한경향을보였다고생각되나 BMI, 혈색소는전혀차이가없게나타났는데재삽관환자의수가많지않아결론을내리기에는부족하다고생각된다. 단순촬영 37

SY Lim et al. : Risk factors of extubation failure and analysis of cuff leak test 을통하여기관내관의직경 (ɸt) 과기관공기음영의직경 (ɸT) 을측정하여후두부폐쇄정도를 ɸT/ɸt로계산하여평가해보고자하였지만차이를보이지않았고측정시육안으로하기때문에오류가생길수있어 PES의예측에있어유용성은낮다고생각된다. 성공적인발관에있어후두부의개방성이중요하며과다한기낭압, 외상성삽관, 긴삽관기간, 기관감염, 여성에서후두부협착이잘생긴다 10. 이로인한 PES의발생율은 2-16% 로보고 18 되고있고본연구에서는 8.8% 로기존과비슷한결과를보였다. PES로인한호흡일의증가는발관실패로이어지는데후두부의폐쇄여부를발관전에미리예측하기위한방법으로제안된것이 CLT이다. Marik등 19 은정성적인방법으로공기누출이전혀없는경우와있는경우로분류하고누출이있는환자에서는 PES가생기지않았다고하였다. 이후누출양을정량적인방법으로측정한연구가보고되었고 Miller 등 2 은 PES 양성환자에서 CLV이 180±157ml로대조군의 316±176ml보다낮았고 110ml 이하를기준값으로했을때 PES 발생의양성예측율이 80% 였다고하여 CLV 기준값이처음으로제시되었다. 하지만일부연구에서는 CLV 절대값보다는 CLP로평가하였는데 De Bast 등 17 은 15.5%, Sandhu 등3은 10%, Jaber 등 18 은 12% 이하를기준으로 PES와재삽관의위험이높아진다고하였다. 이와같이 CLT가여러연구에서유용성이있다고알려졌지만일부연구에서는유용하지않다는결론을보고하였는데, Engoren 등 4 은 531예의발관중 3예만 PES가생겼고이들의 CLV은 489±216 ml로높았고 1예만이재삽관을받았으며 20예는기준값 110ml 미만이었지만 PES가생기지않아민감도와양성예측도가 0% 로 CLT가부정확하며유용성이없다고주장하였으며, Erginel 등 20 도 CLV값이 283ml, CLP 57% 로기준값을보고해기존연구와큰차이를보였다. De Bast 등의기준값으로는민감도 75%, 특이도 72.1%, 양성예측도 25%, 음성예측도 96.1% 였고, Jaber 등의기준값으로는민감도 85%, 특이도 95%, 양성예측도 69%, 음성예측도 98% 를보였으며여러연구에서도검사의정확도가다양하게보고되고있다. 본연구결과에서는 PES 양성군의평균 CLV은 22.5ml로음성군의 233.3ml보다낮았고, CLP도 PES 양성군이평균 6.2% 로음성군의 7.3% 보다의미있게낮았으며 PES를기준으로가장신뢰할수있는기준값을분석한결과 CLV 50ml, CLP 14.7% 로나타났다. 또한 CLV 50ml, CLP 14.7% 이하를기준값으로할때의민감도와특이도및음성예측도는비교적높게나타났지만양성예측도는낮게나타났다. CLV, CLP 기준값은기존연구와조금씩차이를보이지만 PES 환자에서누출양이감소함을다시확인하는결과로생각된다. 그러나, CLV, CLP 모두양성예측도가낮다는점으로보아나머지 40-60% 의환자에서는 cuff leak 값이낮더라도성공적인발관을할가능성이있다는것으로 CLT 결과만으로발관을제한할필요는없음을의미하며위험요인이많은환자에서주의깊은관찰을하는것이더타당하다. 또한음성예측도가높다는점으로검사가정상이면재삽관을일으키는후두부손상의가능성을배제할수있다는점에서검사의중요성이있다고생각된다. CLT 결과는대상군의선택, PES의발생빈도, CLV 또는 CLP 중어떤방식으로측정하는가에따라기준값이매우다양할것으로예측된다. 또한기준값을결정할때는위음성과위양성율중어느쪽에중점을둘것인가가중요한데즉, 발관실패의위험을낮추기위한임상적목적이큰경우에는위음성의위험도를줄이고결국특이도가낮아짐을감수해야하며불필요하게삽관을오래하는것을방지하는목적이큰경우에는위양성의위험도를줄이고결국민감도가낮아짐을감수해야한다. CLT는삽관기간이길어짐을방지하는목적보다발관실패의위험도를줄이기위한것이므로기준값을높이게되면특이도가감소되고실제로는발관이가능한환자도불필요하게오래삽관이될가능성이높다. 따라서기준값을어떻게정하든지 CLT 결과는재삽관의위험에대한지표로고려해야하고발관시도자체를배제하는측정법은아니다고생각된다. Adderley 등 21 도감압시기관내관주위로공기누출이있다는것이성공적인발관의예측에도움을주지만절대적인예후인자는아니라고하였다. 38

Tuberculosis and Respiratory Diseases Vol. 61. No.1, Jul. 2006 결론적으로이번연구에서는삽관기간이길고중증질환환자에서발관실패의가능성이높고, CLV 50ml, CLP 14.7% 이하인경우 PES로인한재삽관위험이높아지므로주의깊은관찰이필요하지만 CLT 결과를발관에대한유일한기준으로삼고발관자체를배제하는결과로인식할필요는없다고생각된다. 이번연구의제한점은여러기관에서연속적인환자를대상으로했지만 PES와재삽관환자수가적었고, 발관시후두경을통한직접적인평가가되지않았고, CLT전충분히기관내분비물을흡인했지만튜브밖에존재하는분비물에의해 CLV 수치에영향을주었을가능성이있다. 향후에는 PES와발관실패의위험인자가큰환자만을대상으로한전향적인연구가필요할것으로생각된다. 요약연구배경 : 발관실패와관련된위험인자를살펴보고, 기관내삽관의합병증으로인한후두부폐쇄와 PES로인한재삽관의위험성을발관전에미리예측하기위한 CLT 검사의의의및제한점을알아보고자하였다. 방법 : 24시간이상삽관과인공호흡기치료후발관을시도한 34명의연속적인환자들을대상으로발관실패군에서성공군과차이를보이는인자를살펴보고 CLT 를시행해서 PES와재삽관을예측하는 CLV, CLP의기준값을구하였다. 결과 : 총 34명중발관실패는 6명 (17.6%), PES는 3명 (8.8%) 이었고 PES가있던 3명은모두재삽관을받았다. 발관실패환자에서삽관기간이길었고, SAPS II score가컸으며, 삽관기간은 CLV, CLP와역상관관계를보였다. PES 양성환자의평균 CLV은 22.5± 23.8ml로음성환자의 233.3±147.1ml보다낮았고, CLP도양성군에서 6.2±7.3% 로음성군의 44.3±24.7% 보다유의하게낮았다. 가장신뢰성있는 CLV, CLP의기준값은 50 ml, 14.7% 였고 CLV의민감도는 100%, 특이도 93.5%, 양성예측도 60%, 음성예측도 100% 였고, CLP의민감도는 100%, 특이도 87.1%, 양성예측도 42.9%, 음성예측도 100% 였다. 결론 : 삽관기간이길고중증질환환자에서발관실패의가능성이높다. CLV, CLP가감소되어있을경우 PES로인한재삽관위험이높아지므로발관시주의가필요하지만발관의불필요한연기나시도자체에대한기준은아닐것으로생각된다 참고문헌 1. Epstein SK, Ciubotaru RL. Independent effects of etiology of failure and time to reintubation on outcome for patients failing extubation. Am J Respir Crit Care Med 1998;158:489-93. 2. Miller RL, Cole RP. Association between reduced cuff leak volume and postextubation stridor. Chest 1996;1 10:1035-40. 3. Sandhu RS, Pasquale MD, Miller K, Wasser TE. Measurement of endotracheal tube cuff leak to predict postextubation stridor and need for reintubation. J Am Coll Surg 2000;190:682-7. 4. Engoren M. Evaluation of the cuff-leak test in a cardiac surgery population. Chest 1999;116:1029-31. 5. Colice GL, Stukel TA, Dain B. Laryngeal complications of prolonged intubation. Chest 1989; 96:877-84. 6. Khamiees M, Raju P, DeGirolamo A, Amoateng-Adjepong Y, Manthous CA. Predictors of extubation outcome in patients who have successfully completed a spontaneous breathing trial. Chest 2001; 120:1262-70. 7. Srivastava S, Chatila W, Amoateng-Adjepong Y, Kanagasegar S, Jacob B, Zarich S, et al. Myocardial ischemia and weaning failure in patients with coronary artery disease: an update. Crit Care Med 1999; 27:2109-12. 8. Namen AM, Ely EW, Tatter SB, Case LD, Lucia MA, Smith A, et al. Predictors of successful extubation in neurosurgical patients. Am J Respir Crit Care Med 2001;163:658-64. 9.DeHaven CB, Kirton OC, Morgan JP, Hart AM, Shatz DV, Civetta JM. Breathing measurement reduces false-negative classification of tachypneic preextubation trial failures. Crit Care Med 1996; 24:976-80. 10. Rothaar RC, Epstein SK. Extubation failure: magnitude of the problem, impact on outcomes, and prevention. Curr Opin Crit Care 2003;9:59-66. 11. Daley BJ, Garcia-Perez F, Ross SE. Reintubation as an outcome predictor in trauma patients. Chest 1996; 110:1577-80. 12. Rady MY, Ryan T. Perioperative predictors of extubation failure and the effect on clinical outcome after 39

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