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.     

Delayed derecruitment after removal of PEEP in patients with acute lung injury

Background: A step decrease in positive end-expiratory airway pressure (PEEP) is not followed by an instantaneous loss of the PEEP-induced increase in end-expiratory lung volume (EELV). Rather, the reduction of EELV is delayed, while adverse PEEP effects on hemodynamics are immediately attenuated upon the drop in airway pressure. Step PEEP increments were applied to the lungs of patients with acute lung injury. It was investigated retrospectively whether enlargement of end-expiratory lung volume and changes in lung mechanics persist 45 min after removal of the PEEP increment.
Methods: In 14 patients with acute lung injury (LIS score 2.7) EELV and volume-dependent dynamic compliance of the respiratory system (C_dyn,rs) were determined 45 min after removal of an additional PEEP increment (0.64 kPa added to baseline PEEP of 1.0 kPa).
Results: Nine patients kept an EELV gain of 13% (SD 7) and showed improved C_dyn,rs. In 5 patients, EELV was reduced (by 9% (SD 6)) and C_dyn,rs unchanged after removal of the PEEP increment compared to baseline.
Conclusion: A subgroup of patients with acute lung injury, the characteristics of which remain to be defined, benefit from prolonged recruitment effects up to 45 min after removal of a PEEP increment, while sequelae of continuously increased airway pressures are minimised.     

Alveolar recruitment strategy and PEEP improve oxygenation,dynamic compliance of respiratory system and end‐expiratory lung volume in pediatric patients undergoing cardiac surgery for congenital heart disease

Objective: Optimizing alveolar recruitment by alveolar recruitment strategy (ARS) and maintaining lung volume with adequate positive end‐expiratory pressure (PEEP) allow preventing ventilator‐induced lung injury (VILI). Knowing that PEEP has its most beneficial effects when dynamic compliance of respiratory system (Crs) is maximized, we hypothesize that the use of 8 cm H₂O PEEP with ARS results in an increase in Crs and end‐expiratory lung volume (EELV) compared to 8 cm H₂O PEEP without ARS and to zero PEEP in pediatric patients undergoing cardiac surgery for congenital heart disease. Methods: Twenty consecutive children were studied. Three different ventilation strategies were applied to each patient in the following order: 0 cm H₂O PEEP, 8 cm H₂O PEEP without an ARS, and 8 cm H₂O PEEP with a standardized ARS. At the end of each ventilation strategy, Crs, EELV, and arterial blood gases were measured. Results: EELV, Crs, and P_aO₂/FiO₂ ratio changed significantly (P < 0.001) with the application of 8 cm H2O + ARS. Mean P_aCO₂– PETCO₂ difference between 0 PEEP and 8 cm H2O PEEP + ARS was also significant (P < 0.05). Conclusion: An alveolar recruitment strategy with relative high PEEP significantly improves Crs, oxygenation, P_aCO₂– PETCO₂ difference, and EELV in pediatric patients undergoing cardiac surgery for congenital heart disease.     

An individualized recruitment maneuver for mechanically ventilated patients after cardiac surgery

Purpose  The recruitment maneuver (RM) has been shown to improve oxygenation for post-cardiopulmonary bypass (CPB) patients; however, sustained inflation of the lung gives rise to hypotension. The primary goal of our study was to evaluate the safety and efficacy of our proposed RM, defined on the basis of dynamic lung compliance (Cdyn). Methods  Twenty-eight patients undergoing elective cardiac surgery with CPB were assigned to two treatment groups: an individualized RM group, in which a pressure equal to 15 ml × real body weight/Cdyn + positive end-expiratory pressure (PEEP) cmH₂O was applied for 15 s; and a control RM group, in which a pressure of 20 cmH₂O was applied for 25 s. Arterial blood pressure, cardiac output, pulmonary artery pressure, and heart rate (HR) were monitored. Tidal volume (V_T), and airway pressure were continuously obtained from an expiratory flow meter and pressure monitor. Blood samples were obtained and analyzed with a blood gas analyzer. Results  The changes in HR, mean arterial pressure, mean pulmonary artery pressure, and cardiac index at the end of the RM were not significantly different between the two groups. The mean airway pressure of sustained inflation was 28.3 ± 1.3 cmH₂O in the individualized RM group. The individualized RM significantly improved the Cdyn and partial pressure arterial oxygen/inspiratory fraction of oxygen (P/F) ratio compared with values in the control RM group (P = 0.026 and P = 0.012, respectively). Conclusion  The present study indicates that the individualized RM resulted in minimum changes of hemodynamics and brought about improvement in oxygenation and lung compliance.     

Evaluation of a recruitment maneuver with positive inspiratory pressure and high PEEP in patients with severe ARDS

BACKGROUND: To evaluate the effect of a recruitment maneuver (RM) with constant positive inspiratory pressure and high positive end-expiratory pressure (PEEP) on oxygenation and static compliance (Cs) in patients with severe acute respiratory distress syndrome (ARDS). METHODS: Eight patients with ARDS ventilated with lung-protective strategy and an arterial partial pressure of oxygen to inspired oxygen fraction ratio (PaO2/FIO2) < or =100 mmHg regardless of PEEP were prospectively studied. The RM was performed in pressure-controlled ventilation at FIO2 of 1.0 until PaO2 reached 250 mmHg or a maximal plateau pressure/PEEP of 60/45 cmH2O was achieved. The RM was performed with stepwise increases of 5 cmH2O of PEEP every 2 min and thereafter with stepwise decreases of 2 cmH2O of PEEP every 2 min until a drop in PaO2 >10% below the recruitment PEEP level. Data was collected before (preRM), during and after 30 min (posRM). RESULTS: The PaO2/FIO2 increased from 83 +/- 22 mmHg preRM to 118 +/- 32 mmHg posRM (P = 0.001). The Cs increased from 28 +/- 10 ml cmH2O(-1) preRM to 35 +/- 12 ml cmH2O(-1) posRM (P = 0.025). The PEEP was 12 +/- 3 cmH2O preRM and was set at 15 +/- 4 cmH2O posRM (P = 0.025). The PEEP of recruitment was 36 +/- 9 cmH2O and the collapsing PEEP was 13 +/- 4 cmH2O. The PaO2 of recruitment was 225 +/- 105 mmHg, with five patients reaching a PaO2 > or = 250 mmHg. The FIO2 decreased from 0.76 +/- 0.16 preRM to 0.63 +/- 0.15 posRM (P = 0.001). No major complications were detected. CONCLUSION: Recruitment maneuver was safe and useful to improve oxygenation and Cs in patients with severe ARDS ventilated with lung-protective strategy.     

Pressure-volume relationships in acute lung injury: methodological and clinical implications

BACKGROUND: Pressure-volume relationships (PV curves) are the only available method for bedside monitoring of respiratory mechanics. Alveolar recruitment modifies the results obtained from the PV curves. We hypothesized that method-related differences may influence PV-curve guided ventilatory management. METHODS: Twelve acute lung injury (ALI) patients [PaO2/FiO2 13.0 +/- 1.5 kPa (97.6 +/- 11.3 mmHg), bilateral pulmonary infiltrates] were studied. Two PV curves [one at variable, and another at constant level of positive end-expiratory pressure (PEEP)] were obtained from each patient using constant inspiratory flow and end-inspiratory and -expiratory occlusions. Upper and lower inflection points (UIP, LIP) were estimated. Recruitment due to PEEP and during inflation was assessed by respiratory inductive plethysmography (RIP). RESULTS: (1) Pressure-volume curves at constant PEEP tended to provide higher LIP values compared with curves at variable PEEP (mean difference +/- SEM 5.1 +/- 1.9 cmH2O); and (2) recruitment occurred throughout the PV curve with no relationship with LIP or UIP. CONCLUSION: Pressure-volume curves obtained using variable PEEP translate a different physiological reality and seem to be clinically more relevant than curves constructed at constant PEEP. If curves constructed at constant PEEP are used to set the ventilator, unnecessarily high PEEP levels may be used. Respiratory inductive plethysmography technology may be used for monitoring of recruitment at the bedside.     

肺复张策略对健侧肺氧合及顺应性的影响

目的 评价肺复张策略(lung recruitment maneuvers,LRM)对健侧肺氧合及顺应性的影响. 方法 ASA分级Ⅱ级择期行胸腔镜辅助下肺切除术患者40例,采用随机数字表法分为对照组(C组)和实验组(L组),每组20例.C组术中常规单肺通气(one lung ventilation,OLV),L组OLV 20 min后进行1次LRM,两组均在OLV结束关闭胸腔前进行1次肺复张.分别于患者麻醉前(T0),OLV后20 min(T1),LRM后15 min(T2)、30 min(T3)、45 min(T4)及OLV结束(T5)时,采集患者生命体征数据并采集动脉血样本进行血气分析,根据公式计算肺顺应性(dynamic compliance,Cdyn). 结果 与C组相比,L组PaO2在T2[(150±11) mmHg比(204±21) mmHg,1 mmHg=0.133 kPa]、T3[(154±12) mmHg比(176±14) mmHg]、T5[(442±20) mmHg比(473±15) mmHg]时点均升高(P＜0.05),Cdyn在T2[(21±3) ml/cmH2O比(25±3) ml/cmH2O,1 cmH2O=0.098 kPa]和T5[(26±3) ml/cmH2O比(31±5)ml/cmH2O)]时点提高(P＜0.05). 结论 LRM可以有效改善OLV期间氧合及Cdyn,单次LRM提高PaO2有效时间为30 min,在15 min左右PaO2改善最为明显.     

Effects of PEEP on extra vascular lung water and central blood volume in the dog

Twenty-four mongrel dogs were anaesthetized and ventilated mechanically in the supine position. Extravascular lung water (EVLW) and central blood volume (CBV) were measured with a double indicator (dye/cold) dilution technique. Both indicators were detected intravascularly in the aortic root with a fibreoptic thermistor catheter. Seven dogs ventilated with a positive end-expiratory pressure (PEEP) of 1.0 kPa (10 cmH2O) for a short period of time (less than 20 min) displayed no significant change in EVLW as measured with the indicator dilution technique (= EVLWi), while reductions were seen in both CBV (15%, P less than 0.01) and cardiac output (CO-thermodilution technique) (10%, P less than 0.05). Another seven dogs ventilated with a PEEP of 1.0 kPa for 8 h showed a gradual increase in EVLWi. After 8 h, a mean increase of 34% (P less than 0.01) was recorded, and the increase was also verified by post-mortem gravimetric determination of EVLW (= EVLWg), displaying an increase of 61% (P less than 0.01). In five dogs ventilated with zero end-expiratory pressure (ZEEP) for 8 h, no changes in EVLWi, CO, and CBV were observed, and EVLWg was mean 4.39 g/kg body weight (BW). Five additional dogs were sacrificed after 15 min of anaesthesia without catheterization and EVLWg was found to be 4.24 g/kg BW. It is concluded that EVLWi does not change measurably during ZEEP or short periods of PEEP. However, long periods (8 h) of PEEP result in elevated EVLWi values. Gravimetry supports these conclusions.(ABSTRACT TRUNCATED AT 250 WORDS)     

不同通气方式对小儿心内直视手术期间Crs改变的初步观察

目的 小儿心内直视手术麻醉期间应用ＰＥＥＰ和转流期间肺泡低压,寻找此类手术麻醉中改善肺表面活性物质（ＰＳ）生成和呼吸系统总顺应性（Ｃｒｓ）的途径。方法 ４０例左向右分流型先心病患儿随机分为４组,Ｉ组为ＩＰＰＶ通气组,ＩＩ组ＰＥＥＰ应用组,Ⅲ组为ＩＰＰＶ通气且转流期间肺泡低压组,ＩＶ组为ＰＥＥＰ及转流期间肺泡低压组,测定各组各时点的Ｃｒｓ及ＰＳ生化指标,结果 Ｉ组手术结束时Ｃｒｓ,饱和磷／总磷及饱和     

Pulmonary abnormalities after cardiac surgery are better explained by atelectasis than by increased permeability oedema

BACKGROUND: Cardiac surgery can be complicated by pulmonary abnormalities, but it is unclear how various manifestations interrelate. METHODS: A prospective study in the intensive care unit was performed on 26 mechanically ventilated patients without cardiac failure within 3 h after elective cardiac surgery involving cardiopulmonary bypass. Oedema (extravascular lung water, EVLW) was measured by the thermal-dye technique and permeability by a dual radionuclide technique, yielding a pulmonary leak index (PLI). Radiographic, mechanical and gas exchange features were used to calculate the lung injury score (LIS), ranging between 0 and 4. Evidence for left lower lobe atelectasis was obtained from plain radiographs. The plasma colloid osmotic pressure (COP) was measured by an oncometer. RESULTS: The EVLW (normal, <7 ml/kg) was elevated in 36% of patients and the PLI (normal, <14.1 x 10(-3)/min) in 44%, but the variables did not interrelate directly. Patients with a supranormal EVLW had a lower COP than patients with normal EVLW. The duration of mechanical ventilation was prolonged in patients (20%) with EVLW > 10 ml/kg. There was no difference in EVLW and PLI in patients with LIS < 1 and LIS > 1 (31% of patients). In patients with radiographic evidence for atelectasis (46%), the positive end-expiratory pressure and inspiratory O2 fraction to maintain oxygenation were higher than in those without. CONCLUSIONS: After cardiac surgery, mild pulmonary oedema is relatively common, even in the absence of high filling pressures, and is mainly attributable to a low COP, irrespective of increased permeability in about one-half of patients. It may prolong mechanical ventilation at EVLW > 10 ml/kg. However, pulmonary radiographic and ventilatory abnormalities may result, at least in part, from atelectasis rather than increased permeability oedema.     

Continuous positive airway pressure and lung separation during cardiopulmonary bypass to facilitate congenital heart surgery via the right thorax in children

We describe a fast track anesthesia technique that facilitates congenital heart surgery via right axillary thoracotomy in children. Continuous positive airway pressure on the dependent lung, before and during cardiopulmonary bypass, approximates the heart towards the chest wall incision, and significantly improves the surgeon's access to the heart.     

Effect of fluid loading with saline or colloids on pulmonary permeability, oedema and lung injury score after cardiac and major vascular surgery

Background. The optimal type of fluid for treating hypovolaemiawithout evoking pulmonary oedema is still unclear, particularlyin the presence of pulmonary vascular injury, as may occur aftercardiac and major vascular surgery. Methods. In a single-centre, prospective, single-blinded clinicaltrial 67 mechanically ventilated patients were randomly assignedto receive saline, gelatin 4%, HES 6% or albumin 5%, accordingto a 90 min fluid loading protocol with target central venouspressure of 13 and pulmonary capillary wedge pressure of 15mm Hg, within 3 h after cardiac or major vascular surgery. Beforeand after the protocol, we recorded haemodynamics and ventilatoryvariables and took chest radiographs. The pulmonary vascularinjury was evaluated using the ⁶⁷Ga-transferrin pulmonary leakindex (PLI) and extravascular lung water (EVLW). Plasma colloidosmotic pressure (COP) was determined and the lung injury score(LIS) was calculated. Results. More saline was infused than colloid solutions (P<0.005).The COP increased in the colloid groups and decreased in patientsreceiving saline. Cardiac output increased more in the colloidgroups. At baseline, PLI and EVLW were above normal in 60 and30% of the patients, with no changes after fluid loading, exceptfor a greater PLI decrease in HES than in gelatin-loaded patients.The oxygenation ratio improved in all groups. In the colloidgroups, the LIS increased, because of a decrease in total respiratorycompliance, probably associated with an increase in intrathoracicplasma volume. Conclusions. Provided that fluid overloading is prevented, thetype of fluid used for volume loading does not affect pulmonarypermeability and oedema, in patients with acute lung injuryafter cardiac or major vascular surgery, except for HES thatmay ameliorate increased permeability. During fluid loading,changes in LIS (and respiratory compliance) do not representchanges in pulmonary permeability or oedema.      

Postoperative pulmonary complications and lung function in high-risk patients: a comparison of three physiotherapy regimens after upper abdominal surgery in general anesthesia

The effect of three postoperative regimens of respiratory therapy on pulmonary complications and lung function was compared in high-risk patients. Fifty-one patients were randomized to: 1) conventional chest physiotherapy alone (PHYS), 2) chest physiotherapy and positive expiratory pressure (PEP), or 3) chest physiotherapy with both positive expiratory pressure and inspiratory resistance (RMT). Treatments were given twice daily by a physiotherapist and self-administered. The incidence of postoperative pulmonary complications (PPC) was respectively, 71%, 76% and 65% in the PHYS-, PEP- and RMT-groups. The incidence of PPC requiring treatment with antibiotic, bronchodilator or supplementary oxygen according to the existing clinical practice was 47%, 47% and 29%. The incidence of atelectasis was 65%, 64% and 60% and of pneumonia 29%, 35% and 6%. There was no difference between the groups, except for a tendency to a lower frequency of pneumonia in the RMT-group. Postoperatively forced vital capacity (FVC) decreased to mean 54%, forced expired volume in 1 s to 48% and functional residual capacity to 76% of preoperative values. Arterial oxygen tension (PaO2) declined to mean 8.1 kPa and arterial saturation (SaO2) to 89%. There was no difference between the groups except for FVC, PaO2 and SaO2 (P = 0.008, P = 0.008 and P = 0.002), which showed the least decrease in the RMT-group. None of the regimens could be considered as satisfactory concerning the prevention of PPC, but RMT seemed to be the most efficient. Insufficient self-administration of treatment was probably one of the causes of the overall high incidence of PPC in this study.     

The effect of driving pressure-guided versus conventional mechanical ventilation strategy on pulmonary complications following on-pump cardiac surgery: A randomized clinical trial

Study objectivePostoperative pulmonary complications occur frequently and are associated with worse postoperative outcomes in cardiac surgical patients. The advantage of driving pressure-guided ventilation strategy in decreasing pulmonary complications remains to be definitively established. We aimed to investigate the effect of intraoperative driving pressure-guided ventilation strategy compared with conventional lung-protective ventilation on pulmonary complications following on-pump cardiac surgery.DesignProspective, two-arm, randomized controlled trial.SettingThe West China university hospital in Sichuan, China.PatientsAdult patients who were scheduled for elective on-pump cardiac surgery were enrolled in the study.InterventionsPatients undergoing on-pump cardiac surgery were randomized to receive driving pressure-guided ventilation strategy based on positive end-expiratory pressure (PEEP) titration or conventional lung-protective ventilation strategy with fixed 5 cmH₂O of PEEP.MeasurementsThe primary outcome of pulmonary complications (including acute respiratory distress syndrome, atelectasis, pneumonia, pleural effusion, and pneumothorax) within the first 7 postoperative days were prospectively identified. Secondary outcomes included pulmonary complication severity, ICU length of stay, and in-hospital and 30-day mortality.Main resultsBetween August 2020 and July 2021, we enrolled 694 eligible patients who were included in the final analysis. Postoperative pulmonary complications occurred in 140 (40.3%) patients in the driving pressure group and 142 (40.9%) in the conventional group (relative risk, 0.99; 95% confidence interval, 0.82–1.18; P = 0.877). Intention-to-treat analysis showed no significant difference between study groups regarding the incidence of primary outcome. The driving pressure group had less atelectasis than the conventional group (11.5% vs 17.0%; relative risk, 0.68; 95% confidence interval, 0.47–0.98; P = 0.039). Secondary outcomes did not differ between groups.ConclusionAmong patients who underwent on-pump cardiac surgery, the use of driving pressure-guided ventilation strategy did not reduce the risk of postoperative pulmonary complications when compared with conventional lung-protective ventilation strategy.