Pulmonary abnormalities after coronary arterial bypass grafting operation: cardiopulmonary bypass versus mechanical stabilization

BACKGROUND: Cardiopulmonary bypass has been implicated in causing poor pulmonary gas exchange postoperatively in patients undergoing coronary artery bypass grafting procedures. This randomized prospective study was conducted to determine whether patients undergoing coronary artery bypass grafting operations using cardiac stabilization and thereby avoiding cardiopulmonary bypass will have improved pulmonary function postoperatively. METHODS: Fifty-eight patients were randomized to one of two groups: coronary artery bypass grafting operation with stabilization or coronary artery bypass grafting operation with cardiopulmonary bypass. Preoperative and postoperative pulmonary gas exchange measurements were performed on intubated patients, including the arterial partial pressure of oxygen on 100% inspired oxygen, the alveolar-arterial oxygen gradient, and pulmonary shunt. Static and dynamic lung compliance measurements were performed postoperatively. Hemodynamic variables (including creatine kinase-MB and troponin levels), intubation time, postoperative bleeding, and blood transfusions were compared. RESULTS: Both study groups had a large decrease in arterial partial pressure of oxygen on 100% inspired oxygen (p < 0.0001) and a significant postoperative increase in the alveolar-arterial oxygen gradient (p < 0.0001). There was no statistical difference in the postoperative gas exchange between the two groups; however, the postoperative pulmonary shunt was significantly better in the stabilization group (24% versus 31%, p = 0.03). The patients were extubated in the intensive care unit earlier in the stabilization group (8.2 hours versus 9.2 hours, not significant). The mean static and dynamic lung compliance postoperatively was lower in the stabilization group, although not statistically significant (p = 0.06). CONCLUSIONS: Coronary artery bypass grafting operation using cardiac stabilization technique is safe and avoids the risk of cardiopulmonary bypass. The pulmonary gas exchange postoperatively is comparable to standard cardiopulmonary bypass procedures, but a reduced postoperative pulmonary shunt was seen in the stabilization group.     

Effects of Oxygen on Central Haemodynamics and Va/Q Distribution after Coronary Bypass Surgery

Central haemodynamics and ventilation-perfusion (VA/Q) distribution were studied in 16 patients, 21 h after coronary bypass surgery, during ventilation with FIO2 = 0.3 and 1.0. VA/Q distributions were determined by the multiple inert gas elimination technique. In 15 patients with normal preoperative lung function, there was a significant shunt of 7.5% of cardiac output and perfusion of regions with VA/Q between 0.005-0.1 of 2.4% (FIO2 = 0.3). Mean VA/Q for the Q-distribution was 0.89 with log s.d. of 0.92. Ventilation of regions with VA/Q above 100 was 0.22. After 30 min of ventilation with FIO2 = 1.0, there was a slight increase in cardiac output while pulmonary arterial mean pressure and pulmonary vascular resistance showed slight decreases. There was a marked increase of the shunt in three patients but the increase for the whole group was not significant. Perfusion of regions with low VA/Q (0.005-0.1) increased significantly to 8.7% while the distribution of ventilation remained unchanged. The changes in distribution of Q were probably due to a release of hypoxic vasoconstriction in combination with complete or incomplete alveolar collapse. One patient with obstructive lung disease showed only minor changes in perfusion distribution.     

The effect of positive end expiratory pressure on the respiratory profile during one-lung ventilation for thoracotomy

Summary In this randomised controlled trial we examined the effects of four different levels of positive end expiratory pressure (PEEP at 0, 5, 8 or 10 cmH(2)O), added to the dependent lung, on respiratory profile and oxygenation during one lung ventilation. Forty-six patients were recruited to receive one of the randomised PEEP levels during one lung ventilation. We did not find significant differences in lung compliance, intra-operative or postoperative oxygenation amongst the four different groups. However, the physiological deadspace to tidal volume ventilation ratio was significantly lower in the 8 cmH(2)O PEEP group compared with the other levels of PEEP (p < 0.0001). We concluded that the use of PEEP (< or =10 cmH(2)O) during one lung ventilation does not clinically improve lung compliance, intra-operative or postoperative oxygenation despite a statistically significant reduction in the physiological deadspace to tidal volume ratio.     

Partial liquid ventilation with perfluorodecalin following unilateral canine lung allotransplantation in non-heart-beating donors.

BACKGROUND: The purpose of this study was to evaluate canine lungs obtained from non-heart-beating donors after unilateral lung transplantation subjected to partial liquid ventilation with perfluorodecalin. METHODS: Twelve donor dogs were killed and kept under mechanical ventilation for 3 hours. Heart-lung blocks were harvested after retrograde pulmonary hypothermic flush with Perfadex. Left lung grafts were randomly transplanted into 12 weight-matched recipient animals. Animals were divided into 2 groups: control (standard mechanical ventilation, n = 6) and PLV (partial liquid ventilation, n = 6). Forty-five minutes after transplantation, the animals in the PLV group received perfluorodecalin (15 ml/kg) via orotracheal tube. All animals received volume-controlled ventilation (FIO2) 1.0, PEEP 5 cm H(2)O) over 6 consecutive hours. Thereafter, blood-gas analysis, ventilatory mechanics and hemodynamics were registered at 30-minute intervals. After 6 hours of reperfusion the animals were killed and the transplanted lungs were extracted to obtain the wet/dry weight ratio. RESULTS: There were significant differences in pulmonary arterial pressure, which were higher in control group animals (p < 0.009). The control animals also showed higher arterial PaO(2) than those in the PLV group (p < 0.00001), but lower PaCO(2) (p < 0.008). The peak and plateau pressures were higher in the PLV group (p < 0.00001). Neither static compliance nor wet/dry weight ratios were different in between groups. CONCLUSIONS: PLV with perfluorodecalin yields functional results compatible with life in this model. Nonetheless, pulmonary gas exchange and mechanics were superior after reperfusion in animals given conventional mechanical ventilation up to 6 hours after left lung allotransplantation.     

Effects of ventilatory techniques during cardiopulmonary bypass on post-bypass and postoperative pulmonary compliance and shunt.

Pulmonary compliance and shunt were evaluated preoperatively, 30 minutes after cardiopulmonary bypass, and two hours postoperatively in 132 calves undergoing open-heart surgery with halothane and oxygen anesthesia. The calves were divided into 11 groups with respect to maintenance of the lungs during bypass. In Group 1 the lungs were collapsed during bypass. In all other groups the lungs were mechanically ventilated, statically inflated, or both, with either pure oxygen or nitrous oxide, 50 per cent, in oxygen. All groups had similar compliance and shunt values before operation and sustained significant decreases in compliance and increases in shunt 30 minutes after bypass. Calves exposed to positive-pressure breathing during bypass had higher shunt and lower compliance values after bypass and postoperatively than those not exposed to mechanical ventilation, irrespective of the inflating gas or presence or absence of any amount of static airway pressure. Animals not ventilated during bypass had compliance and shunt values that were not significantly different from preoperative values, while calves that were ventilated had compliance and shunt values that were still significantly altered two hours postoperatively. These data demonstrate that positive-pressure breathing during bypass decreases pulmonary compliance after bypass and postoperatively and increases intrapulmonary shunt, but that the gas inflating the lungs during bypass does not influence either of these variables. The findings also suggest that static pulmonary inflation during bypass offers no advantage over allowing the lungs to remain collapsed.     

Effect of rate and inspiratory flow on ventilator-induced lung injury

BACKGROUND: We examined the effects of decreasing respiratory rate (RR) at variable inspiratory times (It) and reducing inspiratory flow on the development of ventilator-induced lung injury. METHODS: Forty sheep weighing 24.6+/-3.2 kg were ventilated for 6 hours with one of five strategies (FIO2 = 1.0, positive end-expiratory pressure = 5 cm H2O): (1) pressure-controlled ventilation (PCV), RR = 15 breaths/min, peak inspiratory pressure (PIP) = 25 cm H2O, n = 8; (2) PCV, RR = 15 breaths/min, PIP = 50 cm H2O, n = 8; (3) PCV, RR = 5 breaths/min, PIP = 50 cm H2O, It = 6 seconds, n = 8; (4) PCV, RR = 5 breaths/min, PIP = 50 cm H2O, It = 2 seconds, n = 8; and (5) limited inspiratory flow volume-controlled ventilation, RR = 5 breaths/min, pressure-limit = 50 cm H2O, flow = 15 L/min, n = 8. RESULTS: Decreasing RR at conventional flows did not reduce injury. However, limiting inspiratory flow rate (LIFR) maintained compliance and resulted in lower Qs/Qt (HiPIP = 38+/-18%, LIFR = 19+/-6%, p < 0.001), reduced histologic injury (HiPIP = 14+/-0.9, LIFR = 2.2+/-0.9, p < 0.05), decreased intra-alveolar neutrophils (HiPIP = 90+/-49, LIFR = 7.6+/-3.8,p = 0.001), and reduced wet-dry lung weight (HiPIP = 87.3+/-8.5%, LIFR = 40.8+/-17.4%,p < 0.001). CONCLUSIONS: High-pressure ventilation for 6 hours using conventional flow patterns produces severe lung injury, irrespective of RR or It. Reduction of inspiratory flow at similar PIP provides pulmonary protection.     

Impact of changes in operating pressure during high-frequency jet ventilation

Fifteen critically ill patients with acute respiratory failure were ventilated with high-frequency jet ventilation (HFJV; frequency 100 breaths/min; I/E ratio 0.43; 1.8-mm internal diameter injector cannula). The patients were divided into two groups according to their initial PaO2 during intermittent positive pressure ventilation at FIO21: in eight patients (group I) the mean PaO2 was 141 +/- 34 mm Hg, and in seven patients (group II) mean PaO2 was 376 +/- 75 mm Hg. During HFJV three different operating pressures were used at random: 1.3, 1.8, and 2.3 bars. Increase in operating pressures significantly decreased PaCO2 and significantly increased mean lung volume above apneic FRC, mean airway pressure, and mean alveolar pressure in both groups. A close relationship was found between variations in mean airway pressure and mean alveolar pressure (r = 0.99, P less than 0.001). Significant increases in PaO2 with increasing operating pressures were observed only in group I. In group II, PaCO2 was significantly lower than in group I for a given operating pressure. We conclude that operating pressure is a main determinant of arterial oxygenation during HFJV because of the concomitant increases in intrathoracic pressures and lung volume. Operating pressure also influences carbon dioxide clearance, PaCO2 varies inversely with operating pressure.     

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.     

The impact of heparin-coated cardiopulmonary bypass circuits on pulmonary function and the release of inflammatory mediators

Reduction of the inflammatory reaction with the use of heparin coating has been found during and after cardiopulmonary bypass (CPB). The question remains whether this reduced reaction also decreases the magnitude of CPB-induced pulmonary dysfunction. We therefore evaluated the effects of a heparin-coated circuit versus a similar uncoated circuit on pulmonary indices as well as on inflammatory markers of complement activation (C3b/c), elastase-alpha(1)-antitrypsin complex, and secretory phospholipase A(2) (sPLA(2)) during and after CPB. Fifty-one patients were randomly assigned into two groups undergoing coronary artery bypass grafting with either a heparin-coated (Group 1) or an uncoated (Group 2) circuit. During CPB, a continuous positive airway pressure of 5 cm H(2)O and a fraction of inspired oxygen (FIO(2)) of 0.21 were maintained. Differences in favor of the coated circuit were found in pulmonary shunt fraction (P < 0.05), pulmonary vascular resistance index (P < 0.05), and PaO(2)/FIO(2) ratio (P < 0.05) after CPB and in the intensive care unit. During and after CPB, the coated group demonstrated lower levels of sPLA(2). After CPB, C3b/c and the elastase-alpha(1)-antitrypsin complex were significantly less in the coated group (P < 0.001). The coated circuit was associated with a reduced inflammatory response, decreased pulmonary vascular resistance index and pulmonary shunt fraction, and increased PaO(2)/FIO(2) ratio, suggesting that the coated circuit may have beneficial effects on pulmonary function. The correlation with sPLA(2), leukocyte activation, and postoperative leukocyte count suggests reduced activation of pulmonary capillary endothelial cells. IMPLICATIONS: Heparin coating of the extracorporeal circuit reduces the inflammatory response during cardiopulmonary bypass. Analysis of indices of pulmonary function indicates that use of heparin coating may result in less impaired gas exchange.     

Changes in intrathoracic pressures induced by positive end-expiratory pressure ventilation after cardiac surgical procedures

The consequences of controlled ventilation with positive end-expiratory pressure (PEEP) were studied, after cardiac surgical procedures, in two groups of patients supposed to have different lung and chest wall mechanical properties. The first group included 6 patients who had undergone coronary artery graft surgical procedures (CGS). The second group included 5 patients who had undergone a mitral valve replacement (MVR). Postoperatively, static lung and chest wall compliance was measured by stepwise inflation and deflation of the thorax. Esophageal, pericardial, and pleural pressures were then measured, and cardiac output was determined while PEEP was increased from 0 to 20 cm H2O. Lung and chest wall compliance values sharply decreased in MVR patients. This accounts for the lower values for pleural and pericardial pressures in this group than in the CGS patient group, but the transmission of airway pressure was identical in the two groups when PEEP was increased. The decrease in cardiac output induced by PEEP was similar in the two groups. The results suggest that the opposing influences of lung and chest wall compliance on airway pressure transmission could at least partly explain the hemodynamic effects of PEEP in patients in whom the mechanical properties of the lung and thorax are impaired. PEEP ventilation should be used cautiously in patients suspected of having thoracic rigidity.     

Hemodynamic and oxygenation changes of combined therapy with inhaled nitric oxide and inhaled aerosolized prostacyclin

OBJECTIVE: To evaluate hemodynamic and oxygenation changes of combined therapy with inhaled nitric oxide (iNO) and inhaled aerosolized prostcyclin (IAP) during lung transplantation. DESIGN: Prospective study. SETTING: University hospital. PARTICIPANTS: Ten patients scheduled for lung transplantation. INTERVENTIONS: Ten patients, with a mean age of 38 years (range, 24 to 56 years), were scheduled for lung transplantation (2 single-lung transplantations and 8 double-lung transplantations). During first lung implantation with single-lung perfusion and ventilation, hemodynamic and oxygenation data were analyzed in 3 phases: (1) baseline, 5 minutes after pulmonary artery clamping; (2) inhaled NO phase, 15 minutes after inhaled NO administration (20 ppm) in 100% oxygen; and (3) IAP-inhaled NO phase, 15 minutes after combined administration of inhaled NO (20 ppm) and IAP (10 ng/kg/min) in 100% oxygen. MEASUREMENTS AND MAIN RESULTS: During the inhaled NO phase, reductions of mean pulmonary arterial pressure (p < 0.05) and intrapulmonary shunt (p < 0.05) were noted. After the start of prostacyclin inhalation, a further decrease in mean pulmonary arterial pressure (p < 0.05) was observed. PaO2/FIO2 increased during the IAP-inhaled NO phase (p < 0.05), whereas intrapulmonary shunt decreased (p < 0.05). CONCLUSION: This study confirms the action of inhaled NO as a selective pulmonary vasodilator during lung transplantation. Combined therapy with IAP and inhaled NO increases the effects on pulmonary arterial pressure and oxygenation compared with inhaled NO administered alone without any systemic changes.     

小潮气量肺保护性通气策略与压力通气模式对妇科腹腔镜手术患者氧合功能的影响

目的:评价小潮气量肺保护性通气策略(protective lung ventilation mode,PLV)与压力通气模式(pressure con-trolled ventilation,PCV)在妇科腹腔镜手术中应用的有效性及安全性。方法:拟于我院择期行妇科腹腔镜手术的患者共计144例,按随机序列号分为PLV组和PCV组,每组72例。PLV组潮气量6 ml/kg,吸呼比1∶2,呼吸频率16次/min,呼气末正压5 cmH 2O(1 cmH 2O=0.098 kPa);PCV组设定通气压力维持潮气量8 ml/kg,吸呼比1∶2,呼吸频率12~16次/min。分别于气管插管后5 min(T1)、气腹后10 min(T2)、气腹后20 min(T3)、撤除气腹后10 min(T4)记录患者气道峰压(airway peak pressure,Ppeak)、平均气道压(mean airway pressure,Pmean),并计算动态肺顺应性(dynamic lung compliance,Cdyn)。于T3、T4时点行血气分析记录PaO 2、PaCO 2、肺泡-动脉氧分压差(alveoli-arterial oxygen partial pressure,A-aDO 2),并计算氧合指数(oxygenation index,OI)。结果:PLV组T3时点Ppeak、Pmean显著高于PCV组,但Cdyn低于PCV组,差异有统计学意义(P<0.05)。PLV组T4时点Ppeak显著高于PCV组,差异有统计学意义(P<0.05)。两组T2、T3时点Ppeak、Pmean较T1时点显著升高,而Cdyn显著低于T1时点,差异有统计学意义(P<0.05)。PLV组T3时点Ppeak、Pmean显著高于T2时点,Cdyn显著低于T2时点,差异有统计学意义(P<0.05)。PLV组T3时点PaO 2、OI显著高于PCV组,而PaCO 2、A-aDO 2显著低于PCV组,差异有统计学意义(P<0.05)。两组T4时点PaO 2、OI较T3时点显著升高,而PaCO 2、A-aDO 2较T3时点显著降低,差异有统计学意义(P<0.05)。两组T4时点PaO 2、PaCO 2、A-aDO 2、OI差异无统计学意义(P>0.05)。两组间各呼吸系统并发症发生情况及住院天数差异均无统计学意义(P>0.05)。结论:对妇科腹腔镜手术患者而言,PCV有助于维持患者呼吸动力学稳定,而小潮气量PLV有助于维持患者术中氧合功能,二者安全性差异无统计学意义。     

单肺通气期间连续气道正压通气对胸腔镜房间隔缺损修补术患者肺功能的影响

目的 探讨单肺通气期间连续气道正压通气(CPAP)对胸腔镜房间隔缺损修补术患者肺功能的影响.方法 拟行房间隔缺损修补术的患者20例,年龄16～30岁,体重41～64 kg,性别不限,ASA分级Ⅱ级,随机分为2组(n=10):对照组和CPAP组.两组单肺通气时VT 8 ml/kg,呼吸频率12～16次/min,吸呼比1:2,维持PET CO2 35～40 mm Hg.CPAP组单肺通气期间,非通气侧肺采用CPAP,压力为6 cm H2O.术中监测氧合指数、肺顺应性和气道压,记录拔管时间、单肺通气期间心血管事件和低氧血症的发生情况.结果 与对照组比较,CPAP组氧合指数和肺顺应性升高,拔管时间缩短,低氧血症发生率低(P＜0.01),两组患者气道压力在正常范围且未发生心血管事件.结论 单肺通气期间行CPAP(6 cm H2O)可改善胸腔镜房间隔缺损修补术患者的肺功能.     

Biologically variable ventilation prevents deterioration of gas exchange during prolonged anaesthesia

We have studied the time course of changes in gas exchange and respiratory mechanics using two different modes of ventilation during 7 h of isoflurane anaesthesia in pigs. One group received conventional control mode ventilation (CV). The other group received biologically variable ventilation (BVV) which simulates the breath-to-breath variation in ventilatory frequency (f) that characterizes normal spontaneous ventilation. After baseline measurements with CV, animals were allocated randomly to either CV or BVV (FIO2 1.0 with 1.5% end- tidal isoflurane). With BVV, there were 376 changes in f and tidal volume (VT) over 25.1 min. Ventilation was continued over the next 7 h and blood gases and respiratory mechanics were measured every 60 min. The modulation file used to control the ventilator for BVV used an inverse power law frequency distribution (I/fa with a = 2.3 +/- 0.3). After 7 h, at a similar delivered minute ventilation, significantly greater PaO2 (mean 72.3 (SD 4.0) vs 63.5 (6.5) kPa) and respiratory system compliance (1.08 (0.08) vs 0.92 (0.16) ml cm H2O-1 kg-1) and lower PaCO2 (6.5 (0.7) vs 8.7 (1.5) kPa) and shunt fraction (7.2 (2.7)% vs 12.3 (6.2)%) were seen with BVV, with no significant difference in peak airway pressure (16.3 (1.2) vs 15.3 (3.7) cm H2O). A deterioration in gas exchange and respiratory mechanics was seen with conventional control mode ventilation but not with BVV in this experimental model of prolonged anaesthesia.      

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.     

Alveolar recruitment prevents rapid-reperfusion-induced injury of lung transplants.

BACKGROUND: Physical factors play an important role in ischemia-reperfusion-induced injury of lung transplants. For example, rapid restoration of reperfusion resulted in severe pulmonary edema and deterioration of pulmonary function of lung explants in an ex vivo reperfusion system. This type of injury can be prevented by a stepwise increase in the perfusion flow rate, or by adding prostaglandin E1 (PGE1) to the blood perfusate during the first 10 minutes. However, the mechanisms of these protective effects are unknown. We noted a dramatic decrease in airway pressure rather than pulmonary arterial pressure in these studies, suggesting that lung recruitment may be an important factor in minimizing injury. METHODS: In the present study, we examined the importance of alveolar recruitment in preventing rapid-reperfusion-induced lung injury. Rat lungs were flushed preserved with low potassium dextran solution for 12 hours at 4 degrees C. Lung explants were randomly divided into three groups: 1) untreated control; 2) lungs inflated to total lung capacity for 2 minutes; and 3) lungs ventilated for 10 minutes prior to reperfusion. Postpreservation lung function was assessed in an isolated rat lung reperfusion model. RESULTS: Rapid initiation of reperfusion led to severe pulmonary edema and significant pulmonary dysfunction. In inflation or ventilation groups, the injury was significantly attenuated. The PaO2 and shunt fractions in these lungs were comparable to normal lungs. A significant drop in airway pressure was observed in these two groups and the lung compliance in the inflation group was significantly better than other two groups. CONCLUSIONS: These results suggest that overcoming alveolar collapse with inflation or ventilation, may protect the lung from mechanical-stress-induced injury during reperfusion.     

Pulmonary artery perfusion with protective solution reduces lung injury after cardiopulmonary bypass

BACKGROUND: The inflammatory response and higher temperature of lung tissue during cardiopulmonary bypass can result in lung injury. This study was to evaluate the protective effect of pulmonary perfusion with hypothermic antiinflammatory solution on lung function after cardiopulmonary bypass. METHODS: Twelve adult mongrel dogs were randomly divided into two groups. The procedure was carried out through a midline sternotomy, cardiopulmonary bypass was established using cannulas placed in the ascending aorta, superior vena cava, and right atrium near the entrance of the inferior vena cava. After the ascending aorta was clamped and cardioplegic solution infused, the right lung was perfused through a cannula placed in the right pulmonary artery with 4 degrees C lactated Ringer's solution in the control group (n = 6) and with 4 degrees C protective solution in the antiinflammation group (n = 6). Antiinflammatory solution consisted of anisodamine, L-arginine, aprotinin, glucose-insulin-potassium, and phosphate buffer. Plasma malondialdehyde, white blood cell counts, and lung function were measured at different time point before and after cardiopulmonary bypass; lung biopsies were also taken. RESULTS: Peak airway pressure increased dramatically in the control group after cardiopulmonary bypass when compared with the antiinflammation group at four different time points (24 +/- 1, 25 +/- 2, 26 +/- 2, 27 +/- 2 cm H2O versus 17 +/- 2, 18 +/- 1, 17 +/- 1, 18 +/- 1 cm H2O; all p < 0.01). Pulmonary vascular resistance increased significantly in the control group than in the antiinflammation group at 5 and 60 minutes after cardiopulmonary bypass (1,282 +/- 62 dynes x s x cm(-5) versus 845 +/- 86 dynes x s x cm(-5) and 1,269 +/- 124 dynes x s x cm(-5) versus 852 +/- 149 dynes x s x cm(-5), p < 0.05). Right pulmonary venous oxygen tension (PvO2) in the antiinflammation group was higher than in the control group at 60 minutes after cardiopulmonary bypass (628 +/- 33.3 mm Hg versus 393 +/- 85.9 mm Hg, p < 0.05). The ratio of white blood cells in the right atrial and the right pulmonary venous blood was lower in the antiinflammation group than in the control group at 5 minutes after the clamp was removed (p < 0.05). Malondialdehyde were lower in the antiinflammation group at 5 and 90 minutes after the clamp was removed (p < 0.01 and p < 0.05, respectively). Histologic examination revealed that the left lung from both groups had marked intraalveolar edema and abundant intraalveolar neutrophils, whereas the right lung in the control group showed moderate injury and the antiinflammation group had normal pulmonary parenchyma. CONCLUSIONS: Pulmonary artery perfusion using hypothermic protective solution can reduce lung injury after cardiopulmonary bypass.     

Percutaneous extracorporeal arteriovenous carbon dioxide removal improves survival in respiratory distress syndrome: a prospective randomized outcomes study in adult sheep

OBJECTIVE: Arteriovenous carbon dioxide removal (AVCO(2)R) uses a simple arteriovenous shunt for CO(2) removal to minimize barotrauma/volutrauma from mechanical ventilation. We performed a prospective randomized outcomes study of AVCO(2)R in our new, clinically relevant model of respiratory distress syndrome. METHODS: Adult sheep (n = 18) received an LD(50) severe smoke inhalation and 40% third-degree burn. When respiratory distress syndrome developed (PaO (2)/FIO (2) < 200 at 40 to 48 hours), animals were randomized to the AVCO(2)R (n = 9) or sham group (n = 9) for 7 days. Ventilator management protocols mandated reductions in minute ventilation, first tidal volume to peak inspiratory pressure less than 30 cm H(2)O, then respiratory rate when PaCO (2) was less than 40 mm Hg. PaO (2) was kept above 60 mm Hg by adjusting FIO (2). When FIO (2) was 0.21, animals were weaned. RESULTS: The study required 2946 animal-hours of critical care with 696 AVCO(2)R hours. One died in each group during model development. AVCO(2)R flow from 820 mL/min to 970 mL/min (11% to 14% cardiac output) removed CO(2) at a rate of 92 to 116 mL/min (mean 103 mL/min; 93%-97% of CO(2) production). Heart rate, mean arterial pressure, cardiac output, and pulmonary arterial wedge pressure remained relatively constant. Within 48 hours, AVCO(2)R allowed significant ventilator reductions versus baseline in the following measurements: tidal volume (420 to 270 mL), peak inspiratory pressure (25 to 14 cm H(2)O), minute ventilation (13 to 5 L/min), respiratory rate (26 to 16 breaths/min), and FIO (2) (0.88 to 0.35). Ventilator-free days with AVCO(2)R were 3.9 versus 0.2 (P <.01) for sham animals, and ventilator-dependent days with AVCO(2)R were 2.4 versus 6.2 (P <.01) for the 3 sham survivors. All 8 AVCO(2)R animals and 3 of 8 sham animals survived 7 days after randomization. CONCLUSIONS: Percutaneous AVCO(2)R achieved significant reduction in airway pressures, increased ventilator-free days, decreased ventilator-dependent days, and improved survival in a sheep model of respiratory distress syndrome.     

Continuous positive airway pressure does not improve lung function after cardiac surgery

PURPOSE: Despite the well-documented impairment of pulmonary function after cardiopulmonary bypass, effective precautions and ideal management strategies for this problem are still under debate. This study aimed to evaluate the effects of continuous positive airway pressure (CPAP) applied during cardiopulmonary bypass on respiratory and hemodynamic variables. METHODS: In this randomized, prospective, controlled trial, 120 male patients, aged 45 to 70 yr undergoing first-time elective bypass surgery, were randomly assigned to receive either 10 cm H2O of CPAP (Group I; n = 60) during cardiopulmonary bypass, or serve as control (Group II; n = 60), where the patient's lungs were vented to atmosphere during the bypass period. RESULTS: Alveolar-arterial oxygen partial pressure difference and shunt fraction were significantly higher in the control group compared with the CPAP group after cardiopulmonary bypass (T2) and after closure of sternum (T3), (P < 0.05). No differences between groups with respect to hemodynamic variables were observed at any time. Postoperative pulmonary function variables were lower in both groups compared to baseline values. CONCLUSIONS: Continuous positive airway pressure administered during cardiopulmonary bypass decreased shunt fraction and alveolar-arterial oxygen partial pressure difference during surgery, but had no sustained effect on either variable postoperatively. We conclude that, in patients with normal preoperative pulmonary function, application of 10 cm H2O CPAP does not improve lung function after cardiac surgery.     

Improved flow and pressure capabilities of the Datex-Ohmeda SmartVent anesthesia ventilator

STUDY OBJECTIVE: To compare the flow and pressure capabilities of the Datex-Ohmeda SmartVent (Ohmeda 7900, Datex-Ohmeda, Madison, WI) to previous Ohmeda (7810 and 7000, Datex-Ohmeda, Madison, WI) anesthesia ventilators. To determine airway pressure and minute ventilation thresholds for intraoperative use of a critical care ventilator. DESIGN: Three anesthesia ventilators and one critical care ventilator (Siemens Servo 900C, Siemens, Solna, Sweden) were studied in a lung model. Retrospective medical record review. SETTING: Research Laboratory and Critical Care Unit of a Level I Trauma Center. PATIENTS: 145 mechanically ventilated patients treated for acute respiratory failure who underwent 200 surgical procedures. INTERVENTIONS: The effect of increasing pressure on mean inspiratory flow was determined by cycling each ventilator through increasing restrictors. Maximum minute ventilation was measured at low compliance (10-30 mL/cm H2O), positive end-expiratory pressure (PEEP) (0-20 cm H2O), and increased airway resistance (approximately 19 and approximately 36 cm H2O/L/sec) in a mechanical lung model. MEASUREMENTS AND MAIN RESULTS: Flow, volume, and pressure were measured with a pulmonary mechanics monitor (BICORE CP-100, Thermo Respiratory Group, Yorba Linda, CA). Preoperative peak airway pressure and minute ventilation (VE) were extracted from the medical record. Mean inspiratory flow declined with increasing pressure in all anesthesia ventilators. The SmartVent and the 7810 produced greater mean inspiratory flow than did the 7000 ventilator. As compliance progressively decreased, the Siemens, the SmartVent, and the 7810 ventilators maintained VE compared to the 7000 ventilator. The Siemens and the SmartVent maintained VE with PEEP, compared to the 7810 and 7000 ventilators. During increased airway resistance, maximal VE was lower for all ventilators. The SmartVent met the ventilation requirements in 90% of the patients compared to 67% of patients with the 7000 ventilator. CONCLUSION: The improved pressure and flow capabilities of the SmartVent increase the threshold for using a critical care ventilator intraoperatively to a peak airway pressure > 65 cm H2O and/or VE > 18 L/min.