Pulmonary atelectasis during paediatric anaesthesia: CT scan evaluation and effect of positive endexpiratory pressure (PEEP).

The case series consisted of ten children, ranged in age from one to three years (median 1.8 yrs), and in body weight from 10.2 to 13.5 kg (median 11.7 kg), in ASA class 1 or 2, all without lung disease. Having undergone general anaesthesia for cranial or abdominal CT scans, the patients were studied for pulmonary morphology. The first pulmonary CT scan was taken five min after induction of general inhalational anaesthesia; preoxygenation was avoided and an intraoperative FiO2相似文献   

全麻中低潮气量机械通气对病人肺泡不张发生的影响

目的 探讨全麻中低潮气量（VT）机械通气对病人肺泡不张发生的影响。方法 择期全麻下行开颅手术病人16例。ASAⅠ级或Ⅱ级，心功能Ⅰ级或Ⅱ级，年龄20-50岁，随机分为2组，每组8例，常规VT（10 ml／kg）组（TV组）和低VT（6 ml／kg）组（LV组）。分别于气管插管后10 min和手术结束后10min采用移动CT行全肺扫描，计算膈上1 cm层面肺不张面积和百分比，同时行动脉血气分析，记录动脉血二氧化碳分压（PaCO2），并计算肺泡．动脉血氧分压差[P（A-a），O2]、氧合指数（PaO2／FiO2）及呼吸指数（RI）。结果 气管插管后10 min和手术结束后10 min时2组病人肺泡不张的发生率、面积、百分比、P（A-a）O2、PaCO2、PaO2／FiO2及RI组内、组间差异均无统计学意义（P〉0．05）。结论 低VT （6 ml／kg）机械通气不增加全麻下开颅手术病人肺泡不张的发生。     

Alveolar recruitment strategy improves arterial oxygenation after cardiopulmonary bypass

Atelectasis occurs during general anaesthesia. This is partly responsible for the impairment of gas exchange that occurs peri-operatively. During cardiopulmonary bypass, this atelectasis is exacerbated by the physical collapse of the lungs. As a result, poor arterial oxygenation is often seen postoperatively. We tested the effect of an 'alveolar recruitment strategy' on arterial oxygenation in a prospective randomised study of 78 patients undergoing cardiopulmonary bypass. Patients were divided equally into three groups of 26. Group 'no PEEP' received a standard post bypass manual lung inflation, and no positive end-expiratory pressure was applied until arrival at intensive care unit. Group '5 PEEP' received a standard post bypass manual inflation, and then 5 cmH2O of positive end-expiratory pressure was applied and maintained until extubation on intensive care. The third group, 'recruitment group', received a pressure-controlled stepwise increase in positive end-expiratory pressure up to 15 cmH2O and tidal volumes of up to 18 ml x kg(-1) until a peak inspiratory pressure of 40 cmH2O was reached. This was maintained for 10 cycles; the positive end-expiratory pressure of 5 cmH2O was maintained until extubation on intensive care. There was a significantly better oxygenation in the recruitment group at 30 min and 1 h post bypass when compared with the no PEEP and 5 PEEP groups. There was no significant difference in any of the groups beyond 1 h. Application of 5 cmH2O positive end-expiratory pressure alone had no significant effect on oxygenation. No complications due to the alveolar recruitment manoeuvre occurred. We conclude that the application of an alveolar recruitment strategy improves arterial oxygenation after cardiopulmonary bypass surgery.     

Prevention of atelectasis formation during the induction of general anesthesia in morbidly obese patients

Atelectasis caused by general anesthesia is increased in morbidly obese patients. We have shown that application of positive end-expiratory pressure (PEEP) during the induction of anesthesia prevents atelectasis formation in nonobese patients. We therefore studied the efficacy of PEEP in morbidly obese patients to prevent atelectasis. Twenty-three adult morbidly obese patients (body mass index >35 kg/m(2)) were randomly assigned to one of two groups. In the PEEP group, patients breathed 100% oxygen (5 min) with a continuous positive airway pressure of 10 cm H(2)O and, after the induction, mechanical ventilation via a face mask with a PEEP of 10 cm H(2)O. In the control group, the same induction was applied but without continuous positive airway pressure or PEEP. Atelectasis, determined by computed tomography, and blood gas analysis were measured twice: before the induction and directly after intubation. After endotracheal intubation, patients of the control group showed an increase in the amount of atelectasis, which was much larger than in the PEEP group (10.4% +/- 4.8% in control group versus 1.7% +/- 1.3% in PEEP group; P < 0.001). After intubation with a fraction of inspired oxygen of 1.0, PaO(2) was significantly higher in the PEEP group compared with the control group (457 +/- 130 mm Hg versus 315 +/- 100 mm Hg, respectively; P = 0.035) We conclude that in morbidly obese patients, atelectasis formation is largely prevented by PEEP applied during the anesthetic induction and is associated with a better oxygenation. IMPLICATIONS: Application of positive end-expiratory pressure during induction of general anesthesia in morbidly obese patients prevents atelectasis formation and improves oxygenation. Therefore, this technique should be considered for anesthesia induction in morbidly obese patients.     

The effect of positive airway pressure during pre-oxygenation and induction of anaesthesia upon duration of non-hypoxic apnoea

Positive end-expiratory pressure (PEEP) applied during induction of anaesthesia may prevent atelectasis formation in the lungs. This may increase the duration of non-hypoxic apnoea by increasing the functional residual capacity. We studied the benefit of PEEP applied during the induction of anaesthesia on the duration of apnoea until the SpO2 reached 90%. Forty ASA I-II patients were randomly allocated to one of two groups. In the PEEP group (n = 20) patients were pre-oxygenated using 100% O2 administered using a CPAP device (6 cmH2O) for 5 min. Following induction of anaesthesia, patients were mechanically ventilated (PEEP 6 cm H2O) for a further 5 min. In the ZEEP group (n = 20), no CPAP or PEEP was used. The duration of apnoea until SpO2 reached 90% was measured. Non-hypoxic apnoea duration was longer in the PEEP group compared to ZEEP group (599 +/- 135 s vs. 470 +/- 150 s, p = 0.007). We conclude that the application of positive airway pressure during induction of anaesthesia in adults prolongs the non-hypoxic apnoea duration by > 2 min.     

Correlation between extravascular lung water and oxygenation in ALI/ARDS patients in septic shock: possible role in the development of atelectasis?

This study aimed to evaluate the relationship between PaO2/FiO2 ratio and extravascular lung water in septic shock-induced acute respiratory distress syndrome in a prospective observational clinical trial. Twenty-three patients suffering from sepsis induced acute respiratory distress syndrome were recruited. All patients were ventilated in pressure control/support mode. Haemodynamic parameters were determined by arterial thermodilution (PiCCO) eight hourly for 72 hours. At the same time blood gas analyses were done and respiratory parameters were also recorded. Data are presented as mean +/-SD. For statistical analysis Pearson's correlation test, and analysis of variance (ANOVA) was used respectively. Significant negative correlation was found between extravascular lung water and PaO2/FiO2 (r = -0.355, P < 0.001), and significant positive correlation was shown between extravascular lung water and PEEP (r=0.557, P<0.001). A post-hoc analysis was performed when "low" PEEP: < 10 cmH2O and "high" PEEP: (10 cmH2O PEEP was applied, and neither the oxygenation, nor the driving pressure or the PaCO2 differed significantly, but the extravascular lung water showed significant difference when "high" or "low" PEEP was applied (13+/-5 vs 9+/-2 ml/kg respectively, P=0.001). This study found significant negative correlation between extravascular lung water and PaO2/FiO2. The mechanism by which extravascular lung water affects oxygenation is unknown but the significant positive correlation between PEEP and extravascular lung water shown in this trial suggests that the latter may have a role in the development of alveolar atelectasis.     

The diagnostic yield and clinical impact of a chest X-ray after percutaneous dilatational tracheostomy: a prospective cohort study

A chest X-ray (CXR) is routinely performed after percutaneous dilatational tracheostomy (PDT). The purpose of this study was to evaluate the diagnostic yield of routine CXR following PDT and its impact on patient management and to identify predictors of post-PDT CXR changes. Two-hundred-and-thirty-nine patients who underwent PDT in a 21-bed intensive care unit were included prospectively in the study. The following data were collected: patient demographics, APACHE III scores, pre-PDT FiO2 and PEEP, PDT technique, perioperative complications and the use of bronchoscopic guidance. We compared post-PDT CXR with the last pre-PDT CXR. We documented any post-PDT new radiographic findings including atelectasis, pneumothorax, pneumomediastinum, surgical emphysema, pulmonary infiltrates or tracheostomy tube malposition. We also recorded management modifications based on post-PDT radiographic changes, including increased PEEP, chest physiotherapy, therapeutic bronchoscopy or chest tube insertion. Atelectasis was the only new finding detected on post-PDT CXRs of 24 (10%) patients. The new radiographic findings resulted in a total of 14 modifications of management in 10 (4%) patients including increased PEEP in six, chest physiotherapy in six and bronchoscopy in two patients. Trauma and pre-PDT PEEP >5 cmH2O were independent predictors of post-PDT CXR changes. Routine CXR following PDT has a low diagnostic yield, detecting mainly atelectasis and leading to a change in the management in only a minority ofpatients. Routine CXR after apparently uncomplicated PDT performed by an experienced operator may not be necessary and selective use may improve its diagnostic yield. Further studies are required to validate the safety of selective versus routine post-PDT CXR.     

Prevention of atelectasis formation during induction of general anesthesia

General anesthesia promotes atelectasis formation, which is augmented by administration of large oxygen concentrations. We studied the efficacy of positive end-expiratory pressure (PEEP) application during the induction of general anesthesia (fraction of inspired oxygen [FIO(2)] 1.0) to prevent atelectasis. Sixteen adult patients were randomly assigned to one of two groups. Both groups breathed 100% O(2) for 5 min and, after a general anesthesia induction, mechanical ventilation via a face mask with a FIO(2) of 1.0 for another 5 min before endotracheal intubation. Patients in the first group (PEEP group) had continuous positive airway pressure (CPAP) (6 cm H(2)O) and mechanical ventilation via a face mask with a PEEP of 6 cm H(2)O. No CPAP or PEEP was applied in the control group. Atelectasis, determined by computed radiograph tomography, and analysis of blood gases were measured twice: before the beginning of anesthesia and directly after the intubation. There was no difference between groups before the anesthesia induction. After endotracheal intubation, patients in the control group showed an increase of the mean area of atelectasis from 0.8% +/- 0.9% to 4.1% +/- 2.0% (P = 0.0002), whereas the patients of the PEEP group showed no change (0.5% +/- 0.6% versus 0.4% +/- 0.7%). After the intubation with a FIO(2) of 1.0, PaO(2) was significantly higher in the PEEP group than in the control (591 +/- 54 mm Hg versus 457 +/- 99 mm Hg; P = 0.005). Atelectasis formation is prevented by application of PEEP during the anesthesia induction despite the use of large oxygen concentrations, resulting in improved oxygenation. IMPLICATIONS: Application of positive end-expiratory pressure during the induction of general anesthesia prevents atelectasis formation. Furthermore, it improves oxygenation and probably increases the margin of safety before intubation. Therefore, this technique should be considered for all anesthesia induction, at least in patients at risk of difficult airway management during the anesthesia induction.     

Elastic pressure-volume curves indicate derecruitment after a single deep expiration in anaesthetised and muscle-relaxed healthy man

BACKGROUND: In acute respiratory distress syndrome, lung volume is lost immediately after positive end-expiratory pressure (PEEP) is removed and is not immediately regained when PEEP is restored to its original value. The aim of this study was to investigate whether the same phenomenon also occurs in cardiopulmonary healthy individuals during anaesthesia and muscle relaxation. METHODS: In 13 anaesthetised and muscle-relaxed patients, inspiratory elastic pressure-volume (Pel-V) curves were, after lung recruitment, obtained from zero end-expiratory airway pressure (ZEEP) and from a PEEP of 5 cmH2O. The curves were aligned on a common volume axis. Differences in lung volumes and compliance (Crs) were calculated at the different airway pressures. RESULTS: At comparable pressures the ZEEP curve showed significantly lower volumes up to an airway pressure of 25 cmH2O. Maximum Crs was similar on the curves obtained from ZEEP and PEEP. However, the lower segments of the curve recorded from PEEP showed lower Crs compared to the curve recorded from ZEEP. CONCLUSION: During anaesthesia and muscle paralysis, the Pel-V relations change immediately when 5 cmH2O of PEEP is removed. This phenomenon is probably mainly caused by closure of small airways and only in a minor part, if any, by formation of atelectasis. This study indicates that under these conditions lung volume might easily be normalised by a large breath producing an airway pressure of 20 cmH2O.     

Repeated vital capacity manoeuvres after cardiopulmonary bypass: effects on lung function in a pig model

Respiratory failure following cardiopulmonary bypass (CPB) is a major complication after cardiac surgery. A vital capacity inflation of the lungs, performed before the end of CPB, may improve gas exchange, but the necessity to repeat it is unclear. Therefore, we studied 18 pigs undergoing hypothermic CPB. A vital capacity manoeuvre (VCM) was performed in two groups and consisted of inflating the lungs for 15 s to 40 cm H2O at the end of CPB. In one group, VCM was repeated every hour. The third group served as controls. Atelectasis was studied by CT scan. Intrapulmonary shunt increased after bypass in the controls and improved spontaneously 3 h later without returning to baseline values. From 3 to 6 h after CPB, there was no more improvement and more than 10% atelectasis remained at 6 h. In contrast, the two groups treated before termination of CPB with VCM showed only minor atelectasis and no abnormal changes in gas exchange directly after bypass or later. We conclude that the protective effect of VCM remained for 6 h after bypass, and there was no extra benefit on gas exchange by repeating the VCM.      

Effects of positive end expiratory pressure on oxygen transport

Fifteen patients admitted at the ICU of our hospital suffering from respiratory failure and submitted to mechanical ventilation were included in a study upon the influence of positive end expiratory pressure (PEEP) on oxygen transport. When the PaO2/FiO2 index was less than 300, 200, and 150, PEEP of +5, +10, and +15 cmH2O respectively was introduced. A Swan-Ganz catheter in the pulmonary artery and a catheter in a radial artery were inserted with the aim to obtain mixed venous blood samples and determine cardiac output, and vascular pulmonary resistances for each PEEP value. When PEEP increased from 5 cmH2O to 15 cmH2O, oxygen supply decreased a 12.4% (p less than 0.05), oxygen extraction from the tissues increased a 21.4% (p less than 0.025) and cardiac output decreased a 7.9% (p less than 0.02) while vascular pulmonary resistances increased a 6.6% (p = NS). We conclude that a PEEP of 5 cmH2O impairs tissue oxygenation when compared with PEEP of 5 cmH2O and that oxygen supply decrease with cardiac output.     

Positive end-expiratory pressure improves arterial oxygenation during prolonged pneumoperitoneum

BACKGROUND: Laparoscopic surgery usually requires the use of a pneumoperitoneum by insufflating gas in the peritoneal space. The gas most commonly used for insufflation is carbon dioxide. Increased intra-abdominal pressure causes cephalad displacement of the diaphragm resulting in compressed lung areas, which leads to formation of atelectasis, especially during mechanical ventilation. The aim of this prospective study was to investigate the effect of prolonged intraperitoneal gas insufflation on arterial oxygenation and hemodynamics during mechanical ventilation with and without positive end-expiratory pressure (PEEP). METHODS: Twenty patients undergoing totally endoscopic robot-assisted radical prostatectomy were randomly allocated to one of two groups. In the PEEP group (n = 10) a constant PEEP of 5 cmH(2)O was used, whereas in the ZPEEP group (n = 10) no PEEP was used. RESULTS: Application of PEEP (5 cmH(2)O) resulted in significantly higher P(a)O(2) levels after 3 h (182 +/- 49 vs. 224 +/- 35 mmHg) and 4 h (179 +/- 48 vs. 229 +/- 29 mmHg) of pneumoperitoneum; after desufflation, P(a)O(2) values decreased significantly below preinsufflation values. While there were no significant differences in heart rate, central venous pressure (CVP) and mean arterial blood pressure (MAP) during pneumoperitoneum between both groups, baseline values in CVP and MAP differed significantly between both groups with higher levels in the ZPEEP group. CONCLUSION: The application of a constant positive airway pressure of 5 cmH(2)O preserves arterial oxygenation during prolonged pneumoperitoneum.     

Alveolar recruitment maneuver in refractory hypoxemia and lobar atelectasis after cardiac surgery: A case report

ABSTRACT: OBJECTIVE: This case report describes an unusual presentation of right upper lobe atelectasis associated with refractory hypoxemia to conventional alveolar recruitment maneuvers in a patient soon after coronary artery bypass grafting surgery. METHOD: Case-report. RESULTS: The alveolar recruitment with PEEP = 40cmH2O improved the patient's atelectasis and hypoxemia. CONCLUSION: In the present report, the unusual alveolar recruitment maneuver with PEEP 40cmH2O showed to be safe and efficient to reverse refractory hypoxemia and uncommon atelectasis in a patient after cardiac surgery.     

Effects of lung recruitment maneuver and positive end-expiratory pressure on lung volume,respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery

BACKGROUND: It is unclear whether positive end-expiratory pressure (PEEP) is needed to maintain the improved oxygenation and lung volume achieved after a lung recruitment maneuver in patients ventilated after cardiac surgery performed in the cardiopulmonary bypass (CPB). METHODS: A prospective, randomized, controlled study in a university hospital intensive care unit. Sixteen patients who had undergone cardiac surgery in CPB were studied during the recovery phase while still being mechanically ventilated with an inspired fraction of oxygen (FiO2) 1.0. Eight patients were randomized to lung recruitment (two 20-s inflations to 45 cmH2O), after which PEEP was set and kept for 2.5 h at 1 cmH2O above the pressure at the lower inflexion point (14+/-3 cmH2O, mean +/-SD) obtained from a static pressure-volume (PV) curve (PEEP group). The remaining eight patients were randomized to a recruitment maneuver only (ZEEP group). End-expiratory lung volume (EELV), series dead space, ventilation homogeneity, hemodynamics and PaO2 (oxygenation) were measured every 30 min during a 3-h period. PV curves were obtained at baseline, after 2.5 h, and in the PEEP group at 3 h. RESULTS: In the ZEEP group all measures were unchanged. In the PEEP group the EELV increased with 1220+/-254 ml (P<0.001) and PaO2 with 16+/-16 kPa (P<0.05) after lung recruitment. When PEEP was discontinued EELV decreased but PaO2 was maintained. The PV curve at 2.5 h coincided with the curve obtained at 3 h, and both curves were both steeper than and located above the baseline curve. CONCLUSIONS: Positive end-expiratory pressure is required after a lung recruitment maneuver in patients ventilated with high FiO2 after cardiac surgery to maintain lung volumes and the improved oxygenation.     

Effect of vital capacity manoeuvres on arterial oxygenation in morbidly obese patients undergoing open bariatric surgery

BACKGROUND: Arterial oxygenation may be compromised in morbidly obese patients undergoing bariatric surgery. The aim of this study was to evaluate the effect of a vital capacity manoeuvre (VCM), followed by ventilation with positive end-expiratory pressure (PEEP), on arterial oxygenation in morbidly obese patients undergoing open bariatric surgery. METHODS: Fifty-two morbidly obese patients (body mass index >40 kg m-2) undergoing open bariatric surgery were enrolled in this prospective and randomized study. Anaesthesia and surgical techniques were standardized. Patients were ventilated with a tidal volume of 10 mL kg-1 of ideal body weight, a mixture of oxygen and nitrous oxide (FiO2 = 40%) and respiratory rate was adjusted to maintain end-tidal carbon dioxide at a level of 30-35 mmHg. After abdominal opening, patients in Group 1 had a PEEP of 8 cm H2O applied and patients in Group 2 had a VCM followed by PEEP of 8 cm H2O. This manoeuvre was defined as lung inflation by a positive inspiratory pressure of 40 cm H2O maintained for 15 s. PEEP was maintained until extubation in the two groups. Haemodynamics, ventilatory and arterial oxygenation parameters were measured at the following times: T0 = before application of VCM and/or PEEP, T1 = 5 min after VCM and/or PEEP and T2 = before abdominal closure. RESULTS: Patients in the two groups were comparable regarding patient characteristics, surgical, haemodynamic and ventilatory parameters. In Group 1, arterial oxygen partial pressure (PaO2) and arterial haemoglobin oxygen saturation (SaO2) were significantly increased and alveolar-arterial oxygen pressure gradient (A-aDO2) decreased at T2 when compared with T0 and T1. In Group 2, PaO2 and SaO2 were significantly increased and A-aDO2 decreased at T1 and T2 when compared with T0. Arterial oxygenation parameters at T1 and T2 were significantly improved in Group 2 when compared with Group 1. CONCLUSION: The addition of VCM to PEEP improves intraoperative arterial oxygenation in morbidly obese patients undergoing open bariatric surgery.     

呼气末正压通气具有提高大剂量肾上腺素心肺复苏模型大鼠生存率的作用

背景 在心肺复苏(cardiopulmonary resuscitation,CPR)的模型上曾经验证过多种干预措施,目的是改良用药、完善胸外按压的手法及通气参数的设置,但呼气末正压通气(positive end-expiratory pressure,PEEP)对CPR的影响则未曾有研究涉及.鉴于PEEP能逆转肺不张...     

Influence of Gas Composition on Recurrence of Atelectasis after a Reexpansion Maneuver during General Anesthesia

Background: Atelectasis, an important cause of impaired gas exchange during general anesthesia, may be eliminated by a vital capacity maneuver. However, it is not clear whether such a maneuver will have a sustained effect. The aim of this study was to determine the impact of gas composition on reappearance of atelectasis and impairment of gas exchange after a vital capacity maneuver.

Methods: A consecutive sample of 12 adults with healthy lungs who were scheduled for elective surgery were studied. Thirty minutes after induction of anesthesia with fentanyl and propofol, the lungs were hyperinflated manually up to an airway pressure of 40 cmH2 O. FI sub O2 was either kept at 0.4 (group 1, n = 6) or changed to 1.0 (group 2, n = 6) during the recruitment maneuver. Atelectasis was assessed by computed tomography. The amount of dense areas was measured at end-expiration in a transverse plane at the base of the lungs. The ventilation-perfusion distributions (V with dot A/Q with dot) were estimated with the multiple inert gas elimination technique. The static compliance of the total respiratory system (Crs) was measured with the flow interruption technique.

Results: In group 1 (FIO2 = 0.4), the recruitment maneuver virtually eliminated atelectasis for at least 40 min, reduced shunt (V with dot A/Q with dot < 0.005), and increased at the same time the relative perfusion to poorly ventilated lung units (0.005 < V with dot A/Q with dot < 0.1; mean values are given). The arterial oxygen tension (PaO2) increased from 137 mmHg (18.3 kPa) to 163 mmHg (21.7 kPa; before and 40 min after recruitment, respectively; P = 0.028). In contrast to these findings, atelectasis recurred within 5 min after recruitment in group 2 (FIO2 = 1.0). Comparing the values before and 40 min after recruitment, all parameters of V with dot A/Q with dot were unchanged. In both groups, Crs increased from 57.1/55.0 ml *symbol* cmH2 O sup -1 (group 1/group 2) before to 70.1/67.4 ml *symbol* cmH2 O sup -1 after the recruitment maneuver. Crs showed as low decrease thereafter (40 min after recruitment: 61.4/60.0 ml *symbol* cmH2 O sup -1), with no difference between the two groups.     

RE-EXPANSION OF ATELECTASIS DURING GENERAL ANAESTHESIA: A COMPUTED TOMOGRAPHY STUDY

Formation of atelectasis is one mechanism of impaired gas exchangeduring general anaesthesia. We have studied manoeuvres to re-expandsuch atelectasis in 16 consecutive, anaesthetized adults withhealthy lungs. In group 1 (10 patients), the lungs were inflatedstepwise to an airway pressure (Paw) of 10, 20, 30 and 40 cmH₂O In group 2 (six patients), three repeated inflations upto Paw = 30 cm H₂O were followed by one inflation to 40 cm H₂O.Atelectasis was assessed by analysis of computed x-ray tomography(CT). In group 1 the mean area of atelectasis in the CT scanat the level of the right diaphragm was 6.4 cm² at Paw = 0 cmH₂O, 5.9 cm² at 20 cm H₂O, 3.5 cm ² at 30 cm H₂O and 0.8 cm²at 40 cm H₂O, A Paw of 20 cm H₂O corresponds approximately toinflation with twice the tidal volume. In group 2 the mean areaof atelectasis was 9.0 cm² at Paw = 0 cm H₂O and 4.2 cm² afterthe first inflation to 30 cm H₂O. Repeated inflations did notadd to re-expansion of atelectasis. The final inflation (Paw= 40 cm H₂O) virtually eliminated the atelectasis. We concludethat, after induction of anaesthesia, the amount of atelectasiswas not reduced by inflation of the lungs with a conventionaltidal volume or with a double tidal volume ("sigh"). An inflationto vital capacity (Paw = 40 cm H₂O, however, re-expanded virtuallyall atelectatic lung tissue. (Br. J. Anaesth. 1993; 71: 788–795)     

经胸腔镜肺大泡切除术中应用单肺通气对血气及血液动力学的影响

目的　观察胸腔镜手术中单肺通气时应用不同水平的呼气末正压通气 (PEEP)对血气及血液动力学的影响。方法　随机选择胸腔镜肺大泡切除术病人 36例 ,均分为三组 :A组为单肺间歇正压通气 (IPPV)通气 ;B组为单肺IPPV加PEEP 5cmH2 O通气 ;C组为单肺IPPV加PEEP10cmH2 O通气。分别记录平卧位双肺通气、侧卧位双肺通气、单肺通气 10min和 30min四个时点的血气和血液动力学参数。结果　各组病人SpO2 始终维持在 99%～ 10 0 %。动脉血氧分压 (PaO2 )也在正常范围 ,但B、C组明显高于A组 (P <0 .0 5 )。其余血气指标无明显变化。三组病人HR、MAP、左心室射血时间 (LVET)及体循环血管阻力 (SVR)均无明显变化。B、C组在单肺通气 10min及 30min后 ,每搏量 (SV)及心输出量 (CO)下降明显 ,但均在正常范围 ,且无组间差异。体位改变时血液动力学稳定。结论　经胸腔镜肺大泡切除术中单肺IPPV、PEEP 5cmH2 O均能维持满意的PaO2 和动脉血二氧化碳分压 (PaCO2 ) ,血液动力学变化不显著 ;但PEEP 5cmH2 O较IPPV能进一步提高PaO2 ,PEEP 10cmH2 O不能较PEEP 5cmH2 O进一步提高PaO2 。     

The effect of timing of application of positive end-expiratory pressure on oxygenation during one-lung ventilation

Many studies have confirmed that applying positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation (OLV) improves oxygenation. Our purpose was to investigate the best time and level of PEEP application. Thirty patients undergoing thoracic surgery were randomised into three groups. After 20 minutes of two-lung ventilation (TLV) in the lateral position, all patients received OLV for one hour During OLV, 0, 5, 10 cmH2O PEEP were applied in order in group A, with each level sustained for 20 minutes. Group B had 5 cmH2O PEEP applied and maintained for one hour Patients in group C received PEEP with levels set in the opposite order to that of group A. The ventilation model was then converted to TLV. PaO2, PaCO2 and respiratory mechanical variables were compared at five different time points among groups, 20 minutes after TLV (T1), 20 (T2), 40 (T3) and 60 minutes (T4) after OLV and 20 minutes after conversion to TLV (T5). We found that PaO2 was lower in group A than the other two groups at T2 (P <0.05). PaO2 decreased significantly at T5 compared with T1 (P <0.05) in group A only. When PEEP was set to 10 cmH2O, the airway pressure increased significantly (P <0.05). These findings indicate that PEEP applied at the initial time of OLV improves oxygenation most beneficially. Five cmH2O PEEP may produce this beneficial effect without the increase in airway pressure associated with 10 cmH2O PEEP.