Anesth Pain Med 2008; 3: 282 287 임상연구 흉강경수술혹은개흉술시 T 자관을통한대기압산소투여의효과 성균관대학교의과대학삼성서울병원마취통증의학과 안현주ㆍ김지애ㆍ양미경ㆍ김명주ㆍ이대진 The effect of ambient pressure oxygen apply via T-piece in thoracoscopic surgery or thoracotomy Hyun Ju Ahn, M.D., Jie Ae Kim, M.D., Mikyung Yang, M.D., Myung Joo Kim, M.D., and Dae Jin Lee, M.D. Department of Anesthesiology and Pain Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea Background: This prospective, randomized study was to investigate whether ambient pressure oxygen administration via T-piece can be used to reduce arterial desaturation during one-lung ventilation. It can be more beneficial for thoracoscopic surgery, where partial inflation of the non-ventilated lung by continuous positive airway pressure can make the operation itself difficult, delayed, or impossible. Methods: Patients undergoing thoracotomy (Thoracotomy group, n = 50) or video-assisted thoracoscopic surgery (VATS) (VATS group, n = 50) were enrolled into this study. Each group was further divided into two groups: control group (n = 25), and ambient pressure group (n = 25), respectively. Fifteen minutes after two-lung ventilation (TLV1) PaO 2, peak inspiratory pressure, plateau pressure, and tidal volume were measured. Then, in control group, one-lung ventilation was started as usual method while in ambient pressure group, the lumen of the non-ventilated lung was connected to a T-piece with 10 L/min flow rate of oxygen. Same measurements were repeated at 15 minutes and 1 hour after one-lung ventilation (OLV1, OLV2), and 15 minutes after resuming two-lung ventilation (TLV2). Fluid input, urine output, estimated blood loss, operation side/time, and one-lung ventilation time were recorded after operation. Results: In thoracotomy group, there were no significant differences in PaO 2 between control group and ambient pressure group. However, in VATS group, PaO 2 at OLV1 and OLV2 were 논문접수일 :2008 년 8 월 5 일책임저자 : 양미경, 서울시강남구일원동 50 성균관대학교의과대학삼성서울병원마취통증의학과우편번호 : 135-710 Tel: 02-3410-2462, Fax: 02-3410-0361 E-mail: anesyang@skku.edu significantly higher in ambient pressure group than in control group. Conclusions: In patients undergoing VATS, application of ambient pressure oxygen to the non-ventilated lung during one-lung ventilation was effective in increasing PaO 2. (Anesth Pain Med 2008; 3: 282 287) Key Words: ambient pressure oxygen, one-lung ventilation, oxygenation, thoracotomy, VATS. 서 개흉술에서일측폐환기는수술편의를위한상대적적응증으로여겨지지만, 1) 최근그시행횟수가급격히증가하고있는흉강경수술에서의 2,3) 일측폐환기는수술시야의확보를위해반드시필요한사항이되고있다. 일측폐환기시가장큰문제점은저산소혈증이고이에대해가장많이사용하고있는효과적인방법은비환기폐에지속적기도양압을가하는것이다. 4) 하지만지속적기도양압을사용하였을경우개흉술에서는팽창된폐를견인기로누르면서수술을진행할수있지만, 흉강경수술에서는팽창된폐의견인도쉽지않고폐의팽창이수술시야를방해하는정도가수술진행자체를지연시키거나곤란하게할수있어그적용에어려움이있다. Pfitzner 등은 5) 측와위에서흉강이닫혀있는상태에서아래쪽폐에양압환기를시행하게되면종격동이동으로인해반대편흉강에일시적인압력변화를유발하게되고이는비환기폐에연결된이중기공관을통해공기의드나듦을유발할수있다는것을증명해보였다. 비환기폐의이중기공관을통해대기가드나드는대신, 어떤장치를사용하여산소가드나들수있도록해준다면, 이러한산소의드나듦은비환기폐의션트를줄여줄수있을것이다. 6) Baraka 등은 7) 5명의흉강경수술을받는환자들을대상으로일측폐환기시비환기폐에 T자관 (T-piece) 을이용하여 10 L/min의산소를투여함으로써비환기폐를대기에노출시켰을때에비해동맥혈산소분압을유의하게높게유지할수있었다고보고하였다. 하지만이연구들은실험적단계에서소수의환자들을 론 282
안현주외 4 인 : 대기압산소투여의효과 283 대상으로 15분정도짧은시간동안의효과만을관찰한것이어서그임상적유용성을입증하기에는어려움이있다. 반면 Pitzner 등은 6) 흉강경수술을받는환자들에게비환기폐에호흡낭 (reservoir bag) 을연결하여대기압산소를투여함으로써저산소혈증을예방하였다고보고하였다. 하지만이들은호흡낭에달린입구판막 (inlet valve) 오작동으로인한위험성도함께지적하였다. 이에저자들은호흡낭대신 T자관을사용하여대기압의산소를투여할경우, Pitzner 등의연구에 6) 비해대기가들어갈기회를차단할가능성은낮아지지만그래도동맥혈산소분압을효과적으로증가시킬수있는지조사해보고자한다. 비슷한결과를도출할수있다면사용하기에훨씬간편하고기구사용에따른위험이거의없는 T자관으로대기압산소투여를하는것이훨씬효율적일것이다. 그리고이론적으로흉강이열리면이중기공관을통한공기의드나듦은사라지게되는데이러한대기압산소투여의효과가일측폐환기시흉강이열린후어느정도까지지속될수있는지도알아보고자한다. 또한흉강경수술과달리흉강이크게열려있어환기폐의양압환기가비환기폐의공기드나듦을유발하기어려운개흉술의경우대기압산소투여의효과에대해논란이많다. 4,8,9) 이연구들은흉강이열리고폐허탈이일어난후대기압산소투여를시행하였기때문에본연구에서는흉강이닫혀있을때일측폐환기시작과함께대기압산소를미리투여하면그효과가다른지도아울러살펴보고자한다. 대상및방법개흉술및흉강경수술이예정되어있는 100명의환자들을대상으로하였다. 병원윤리위원회의승인을받았으며환자에게설명후동의를얻었다. 중등도이상의심, 폐기능 이상을지닌환자, 75세이상의환자는제외하였다. 개흉술을시행받는환자 50명, 흉강경수술을시행받는환자 50명을대상으로각수술별로밀봉된봉투법을이용하여무작위로대조군과대기압산소투여군 25명씩을배정하였다. 개흉술군과흉강경수술군각각에서대조군과대기압산소투여군간에성별, 연령, 체중, 신장, 미국마취과학회신체등급분류, 폐기능검사치는의미있는차이가없었다 (Table 1). 모든환자들에게 thiopental sodium 5 mg/kg을정주하여마취를유도하였고 vecuronium 0.1 mg/kg, fentanyl 2μg/kg를투여한후좌측이중기공관 (Broncho-Cath TM, Mallinckrodt, Athlone, Ireland) 을삽관하였다. 이중기공관의위치는청진및굴곡성기관지경 (BF-3C30, Olympus, Japan) 을이용하여점검및교정하였고마취유지는산소 2 L/min에 sevoflurane 2 4 vol% 로유지하였다. 흡입산소분율 1.0, 일회호흡량 9 ml/kg, 호흡횟수 10회 / 분으로양압환기를시작하였으며 (GE Datex-Ohmeda Model Aestiva 5, GE Healthcare, USA) 호기말이산화탄소분압이 35 40 mmhg로유지되도록호흡횟수를조절하였다. 마취유도후요골동맥에동맥로를개설하였고자세를측와위로바꾼후이중기공관의위치는굴곡성기관지경을이용하여다시확인하였다. 환자의상태가안정된후양측폐환기상태에서 15분이경과한후 (two lung ventilation:tlv1) 최고흡기압, 고평부기도압, 일회호흡량을측정하고혈액가스분석을실시하였다. 개흉술을시행받는군에서는늑간근을절제하기직전에일측폐환기를시작하였으며흉강경수술을시행받는군에서는투관침을삽관하기직전에일측폐환기를시작하였다. 각군의대조군들은통상하는방법대로비환기폐로연결된이중기공관을대기에노출시켜두었고, 각군의대기압산소투여군들은산소 10 L/min의유량이흐르는 T자관을비환기폐의이중기공관에연결시킨상태로폐를허탈시켰다. 일측폐환기를시작한지 15분이경과한후 (one lung ve Table 1. Demographic Data of Each Group Thoracotomy (n = 50) VATS (n = 50) Control group (n = 25) Ambient pr. gr. (n = 25) Control group (n = 25) Ambient pr. gr. (n = 25) Sex (M/F) Age (yr) Body weight (kg) Height (cm) ASA class (I/II) FEV1 (L) FVC (L) 19/6 61.1 ± 9.2 61.1 ± 10.3 163.8 ± 6.7 17/8 2.64 ± 0.51 3.71 ± 0.61 19/6 56.4 ± 10.4 64.5 ± 10.4 164.9 ± 7.8 20/5 2.65 ± 0.55 3.76 ± 0.70 12/13 57.8 ± 10.0 62.0 ± 8.6 161.5 ± 6.6 11/14 2.62 ± 0.45 3.49 ± 0.78 10/15 55.6 ± 7.7 62.2 ± 10.0 160.3 ± 7.7 16/9 2.59 ± 0.41 3.45 ± 0.73 Values are mean ± SD or number of patients. VATS: video-assisted thoracoscopic surgery, Ambient pr. gr.: ambient pressure group, ASA: American Society of Anesthesiologists, FEV1: forced expiratory volume in 1 second, FVC: forced vital capacity. There are no significant differences between control group and ambient pressure group, respectively.
284 Anesth Pain Med Vol. 3, No. 4, 2008 Table 2. Operation Data Thoracotomy (n = 50) VATS (n = 50) Control group (n = 25) Ambient pr. gr. (n = 25) Control group (n = 25) Ambient pr. gr. (n = 25) Side (R/L) Crystalloid (ml) Colloid (ml) U/O (ml) EBL (ml) Operation (min) OLV (min) 17/8 1169 ± 372 528 ± 207 335 ± 150 454 ± 153 190 ± 43 142 ± 31 15/10 1150 ± 456 506 ± 259 327 ± 200 448 ± 170 185 ± 41 139 ± 39 15/10 1198 ± 332 320 ± 284 368 ± 256 357 ± 160 148 ± 39 128 ± 39 13/12 1218 ± 456 380 ± 303 368 ± 205 362 ± 167 142 ± 40 129 ± 39 Values are mean ± SD. VATS: video-assisted thoracoscopic surgery, Ambient pr. gr.: ambient pressure group, Side (R/L): operation side (right/left), Crystalloid: amount of infused crystalloid, Colloid: amount of infused colloid, U/O: urine output, EBL: estimated blood loss, Operation: duration of operation, OLV: duration of one lung ventilation. There are no significant differences between control group and ambient pressure group, respectively. 일회호흡량, 동맥혈산소분압은 two-way repeated measures ANOVA를사용하여비교하였다. 성별, 미국마취과학회신체등급분류등의범주형변수의경우 Fisher s exact test를이용하여비교하였다. 모든자료는평균 ± 표준편차로표시하였으며사용한통계프로그램은 Jandel Sigma Stat (version 3.1, Jandel Corporation, USA) 이었다. P < 0.05인경우통계적으로유의하다고판정하였다. 결 과 Fig. 1. T connector used in this experiment (diameter 2.5 cm, length 30 cm). ntilation:olv1) 기도압측정과혈액가스분석을실시하였고일측폐환기시행 1시간이되는시점에 (OLV2) 다시반복하였다. 양측폐환기를시작한후 15분후에 (TLV2) 위의측정들을다시반복하였다. 수술이끝난후수술위치, 수술시간, 일측폐환기시간, 정질액투여량, 교질액투여량, 뇨량, 추정실혈량등을기록하였다. 사용한 T자관은 Pitzner의실험결과를 5) 참고하여드나드는일회공기량 (tidal volume) 을 150 ml로추정하고이부피를충분히보유할수있도록하기위해파형튜브를직경 2.5 cm, 길이 30 cm로재단하여 T자연결자 (T connector) 에연결하여제작하였다 (Fig. 1). 대조군과대기압산소투여군간의동맥혈산소분압차가 100 mmhg 이상차이가나는것을임상적으로의미있는차이로규정하여표준편차가 100 mmhg이고 α를 0.05 로하였을때 0.8의검정력을갖기위한최소한의표본수는 17명이었다. 환자들의연령, 체중, 신장등연속변수들은 t-test 혹은 Wilcoxon rank sum test를사용하였고기도압, 대조군과대기압산소투여군간의수술위치, 수액투여량, 요량, 추정실혈량, 수술시간, 일측폐환기시간은개흉술군과흉강경수술군모두에서유의한차이가없었다 (Table 2). 양측폐환기시와 (TLV1, 2) 일측폐환기시에 (OLV1, 2) 측정한최고흡기압, 고평부기도압, 일회호흡량은개흉술군과흉강경수술군모두에서대조군과대기압산소투여군간에유의한차이가없었다 (Table 3, 4). 개흉술군에서는대조군과대기압산소투여군간에일측폐환기 15분, 1시간에측정한동맥혈산소분압의유의한차이를관찰할수없었다 (Fig. 2). 반면흉강경수술군에서는일측폐환기 15분, 1시간에측정한동맥혈산소분압이대기압산소투여군에서대조군에비해유의하게높음을관찰할수있었다 (Fig. 3). 고찰본연구의의의는흉강경수술을받는환자에서일측폐환기시작과동시에비환기폐의이중기공관에 T자관을이용하여대기압산소를투여하면동맥혈산소분압을의미있게증가시킬수있다는것이며, 이러한현상은개흉술을시행받는환자들에서는관찰할수없었다.
안현주외 4 인 : 대기압산소투여의효과 285 Table 3. Ventilation Data of Thoracotomy Group Control group (n = 25) Ambient pr. gr. (n = 25) TLV 1 OLV 1 OLV 2 TLV 2 TLV 1 OLV 1 OLV 2 TLV 2 PIP (cmh 2O) Plateau (cmh 2O) Tidal volume (ml) 16.8 ± 2.1 13.0 ± 2.0 516 ± 77 23.8 ± 3.6 17.6 ± 2.8 500 ± 70 24.4 ± 3.4 18.0 ± 2.8 502 ± 73 17.3 ± 2.4 13.1 ± 2.4 514 ± 74 17.0 ± 2.3 13.2 ± 2.2 520 ± 48 24.5 ± 3.3 17.9 ± 3.1 511 ± 56 24.7 ± 3.1 18.2 ± 2.6 507 ± 56 17.4 ± 2.5 13.5 ± 2.8 515 ± 57 Values are mean ± SD. Ambient pr. gr.: ambient pressure group, TLV 1: 15 minutes after two lung ventilation before one lung ventilation, OLV 1: 15 minutes after one lung ventilation, OLV 2: 1 hour after one lung ventilation, TLV 2: 15 minutes after two lung ventilation after one lung ventilation, PIP: peak inspiratory pressure, Plateau: plateau pressure. There are no significant differences between control group and ambient pressure group, respectively. Table 4. Ventilation Data of VATS Group Control group (n = 25) Ambient pr. gr. (n = 25) TLV 1 OLV 1 OLV 2 TLV 2 TLV 1 OLV 1 OLV 2 TLV 2 PIP (cmh 2O) Plateau (cmh 2O) Tidal volume (ml) 16.7 ± 2.0 12.8 ± 1.8 511 ± 68 24.8 ± 3.3 18.2 ± 2.2 490 ± 65 25.1 ± 3.0 18.6 ± 2.3 483 ± 66 17.0 ± 2.8 13.1 ± 2.9 500 ± 64 17.0 ± 2.5 13.1 ± 2.2 509 ± 82 24.2 ± 2.7 18.1 ± 2.2 494 ± 86 24.1 ± 2.7 17.9 ± 2.5 482 ± 86 17.5 ± 3.2 13.4 ± 2.8 500 ± 80 Values are mean ± SD. VATS: video-assisted thoracoscopic surgery, Ambient pr. gr.: ambient pressure group, TLV 1: 15 minutes after two lung ventilation before one lung ventilation, OLV 1: 15 minutes after one lung ventilation, OLV 2: 1 hour after one lung ventilation, TLV 2: 15 minutes after two lung ventilation after one lung ventilation, PIP: peak inspiratory pressure, Plateau: plateau pressure. There are no significant differences between control group and ambient pressure group, respectively. Fig. 2. PaO 2 changes in thoracotomy group. There are no significant differences between control group and ambient pressure oxygen group. Alfery 등은 9) 개에서개흉술후일측폐환기시지속적기도양압혹은폐동맥혈류제한은동맥혈산소분압을증가시켰지만압력없이산소만을흘려보낸경우에는산소화개선의효과가없었다고보고하였다. 저자들의연구에서도개흉술을시행받은환자에서는대조군과대기압산소투여군간에동맥혈산소분압의의미있는차이를발견할 Fig. 3. PaO 2 changes in thoracotomy group. There are no significant differences between control group and ambient pressure oxygen group.pao 2 changes in VATS group. There are significant differences between control group and ambient pressure oxygen group during one lung ventilation period. *: P < 0.05 compared to control group. VATS: video assisted thoracoscopic surgery. 수없었다. 한편개흉술을받는환자에서 14 Fr. 카테터를비환기폐에연결된이중기공관내에거치하여 1 L/min의산소를지속적으로흘려보냈더니대조군에비해산소화가개선되었다는보고도 8) 있고고빈도제트환기를한경우에효
286 Anesth Pain Med Vol. 3, No. 4, 2008 과가있다는보고도 10) 있다. 이연구들은흉강이열리고폐허탈이일어난후의상태에서실험을하였고폐허탈이전이나폐가허탈된상태에서비환기폐가대기에노출되어비환기폐내에질소가잔존해있을가능성을배제할수없다는점이본연구의개흉술을시행받은환자들의경우와다른점이다. 저자들은마취유도시부터흡입산소분율 1.0 을사용하여질소잔존가능성을배제하였으며흉강이열리기전일측폐환기를시작하였으며이와동시에대기압산소를투여하여비환기폐가대기에노출될가능성을최소화하였다. 이처럼시행방법에차이를두었음에도불구하고개흉술군에서는대기압산소투여가산소화개선에효과가없었다. 하지만흉강경군에서는대기압산소투여가산소화개선에효과가있는것으로나타났다. Pitzner 등도 6) 3 L 호흡낭을사용한환자에서지속적기도양압사용이나양측폐환기가필요한경우는없었다고보고하였다. 한편이들은호흡낭의입구판막이없다면흉강내흡입으로인해과도한음압이걸릴경우호흡낭이허탈되면서비환기폐가급격히팽창할가능성이있고이로인해폐부종이나손상이발생할수있음을지적하며환자의안전이가장중요하다고강조하였다. 이에저자들은호흡낭대신 T자관을사용하였는데실제임상사용면에서는 T자관이더간단하고익숙한장비이며입구판막오작동으로인한위험성이없어더뛰어난것으로생각된다. 흉강이열리기전비환기폐의이중기공관을대기에노출시키면환기폐의양압환기에의해종격동이동이발생하고이로인해비환기폐의흉강에압력변화가발생하여공기의수동적인움직임을유발하게된다. 이런공기의드나드는양은이중기공관및연결자등으로이루어진기구사강의용적을훨씬초과하며평균 134 (65 265) ml 정도라고보고되고있다. 5) 이런공기의드나듦은흉강이열리게되면이론상압력변화가사라지게되어소실되게되지만실제로는그렇지않은경우도있다. 공기드나듦의원인중흉강내압력변화외에비환기폐를지나가는혈관에서여전히산소섭취가진행중인것도작지만한요인이될수있기때문이다. 그리고외과의들이공기밀착형구멍 (airtight port) 을사용하거나늑막유착이심한경우에는흉강이열린후에도상당한기간동안이런공기의드나듦을관찰할수있다. 즉, 일측폐환기시비환기폐의이중기공관이대기에노출되어있으면대기의폐내유입이가능하며이때드나드는공기의양이상당하고또한비환기폐를지나가는혈관에서는여전히산소섭취가진행중이므로그결과폐포내질소농도가점진적으로증가하고저산소혈증을유발할수있다. 이경우대기압산소투여는비환기폐로부터질소를씻어냄으로써일측폐환기시의산소화개선만이아니라비환기폐의허탈도더촉진시키는것으로 알려져있다. 본연구에서는처음부터흡입산소분율을 1.0으로하였고폐허탈은모두문제가없었으므로양군간폐허탈정도의차이는발견할수없었다. 개흉술에서는일측폐환기시저산소혈증이발생하면비환기폐에지속적기도양압을가하는것이표준치료처럼되어있지만, 1) 흉강경수술의경우는지속적기도양압을비환기폐에가하면일부팽창된폐가시야를방해하여수술이더힘들어지고시간이연장되는불편이있으며, 말기폐기종환자의폐용적감소술처럼지속적기도양압을사용할수없는경우도있다. 11) 또한지속적기도양압은저산소혈증발생시교정하는의미가있다면, 대기압산소투여는저산소혈증을미리예방한다는점에서차이가있다. 흉강경수술에서저산소혈증의발생가능성이높은환자들의경우미리대기압산소투여를하면서일측폐환기를시작하거나혹은예상치못한환자에게서저산소혈증이발생할경우일시적으로양측폐환기를실시하여동맥혈산소분압을증가시키고질소도씻어낸후다시일측폐환기를시작할때대기압산소투여를동시에시작하면유용할것으로생각된다. 즉, 흉강경수술에서는대기압산소투여가개흉술에서의지속적기도양압과같은역할을해낼수있을것으로기대한다. 비환기폐의산소화개선여부를실험할경우대상환자각각이대조군과실험군을겸하게되는경우가많은데이는동맥혈산소분압의개인차가너무커의미있는결과를얻기힘들기때문이다. 저자들은일측폐환기 1시간후까지장기적인영향을조사하려고대조군을따로설정하였다. 두군간동맥혈산소분압에영향을미칠만한교란인자유무를확인하기위해인구학적자료외에수술전폐기능검사치, 수술위치, 수술중최고흡기압, 고평부기도압, 일회호흡량, 수액투여및실혈량, 뇨량, 수술시간, 일측폐환기시간등을조사하였는데양군간의미있는차이를발견할수없어대기압산소투여외에동맥혈산소분압에영향을미칠만한다른인자들은없었던것으로추정된다. 저자들의연구에서한계점을살펴보도록하겠다. 첫째, 저산소혈증이유발될가능성이높은중증의환자들을대상으로하지않아산소화개선의임상적효용성이검증되지않았다는것이다. 이미다른연구에서효과를증명하기는했지만사용하는장비가조금달랐고수술방법이나환자군등의특성이다를수있어이연구를통해확인후중증의환자들을대상으로적용하기위해미루었기때문이다. Pitzner 등은 6) 주로장비의소개와사용상주의점에초점을맞추어기술하였고또한이장비를사용하지않은대조군과의비교가없었으며, Baraka 등은 7) 앞서언급한바와같이소수의환자에게각각대조군과실험군을겸하게하여짧은기간의효과를살핀실험적연구라는것이이연구와의차이점일것이다. 둘째, 폐내션트량과심박출량을계산
안현주외 4 인 : 대기압산소투여의효과 287 하지않았다는것이다. 실제임상상황에서동맥혈산소분압을개선할수있는가가보고자하는목표였기때문에생략하였지만산소화개선의기전을설명할수있는기회를배제하여아쉽다. 하지만많은수의환자들을대상으로폐동맥카테터를삽입하기에는윤리적인문제가제기될수있어포함시키지않았다. 또한심박출량을측정하진않았지만양군간에혈압과맥박은유의한차이를발견할수없었다. 결론적으로흉강경수술을받는환자들에서일측폐환기시작시점에비환기폐의이중기공관에 T자관을이용한대기압산소투여는동맥혈산소분압을일측폐환기시작 1 시간후까지의미있게증가시켰으며, 이는흉강경수술시저산소혈증을겪는환자들에게수술시야를방해하지않으면서산소화를개선시킬수있는좋은방법으로여겨진다. 반면, 개흉술을받는환자들에서는대기압산소투여로인한산소화개선효과는관찰할수없었다. 참고문헌 1. Benumof JL: Anesthesia for thoracic surgery. 2nd ed. Pennsylvania, W.B. Saunders Company. 1995, pp 330-427. 2. Mack MJ, Aronoff RJ, Acuff TE, Douthit MB, Bowman RT, Ryan WH: Present role of thoracoscopy in the diagnosis and treatment of diseases of the chest. Ann Thorac Surg 1992; 54: 403-9. 3. Landreneau RJ, Mack MJ, Hazelrigg SR, Dowling RD, Acuff TE, Magee MJ, et al: Video-assisted thoracic surgery: basic technical concepts and intercostal approach strategies. Ann Thorac Surg 1992; 54: 800-7. 4. Capan LM, Turndorf H, Patel C, Ramanathan S, Acinapura A, Chalon J: Optimization of arterial oxygenation during one-lung anesthesia. Anesth Analg 1980; 59: 847-51. 5. Pfitzner J, Peacock MJ, McAleer PT: Gas movement in the nonventilated lung at the onset of single-lung ventilation for video-assisted thoracoscopy. Anaesthesia 1999; 54: 437-43. 6. Pfitzner J, Peacock MJ, Daniels BW: Ambient pressure oxygen reservoir apparatus for use during one-lung ventilation. Anaesthesia 1999; 54: 454-8. 7. Baraka A, Lteif A, Nawfal M, Taha S, Maroun M, Khoury S, et al: Ambient pressure oxygenation via the nonventilated lung during video-assisted thoracoscopy. Anaesthesia 2000; 55: 602-3. 8. Rees DI, Wansbrough SR: One-lung anesthesia: percent shunt and arterial oxygen tension during continuous insufflation of oxygen to the nonventilated lung. Anesth Analg 1982; 61: 507-12. 9. Alfery DD, Benumof JL, Trousdale FR: Improving oxygenation during one-lung ventilation in dogs: the effects of positive end-expiratory pressure and blood flow restriction to the nonventilated lung. Anesthesiology 1981; 55: 381-5. 10. Noh GJ, Jeon WJ: The effects of high frequency jet ventilation to the collapsed lung on systemic oxygenation during one lung ventilation. Korean J Anesthesiol 2001; 40: 728-32. 11. Krucylak PE, Naunheim KS, Keller CA, Baudendistel LJ: Anesthetic management of patients undergoing unilateral videoassisted lung reduction for treatment of end-stage emphysema. J Cardiothorac Vasc Anesth 1996; 10: 850-3.