Continuous Positive Airway Pressure at 10 cm H2O During Cardiopulmonary Bypass Improves Postoperative Gas Exchange

Perioperative Care in Cardiac Surgery: A Joint Consensus Statement by the Enhanced Recovery After Surgery (ERAS) Cardiac Society, ERAS International Society, and The Society of Thoracic Surgeons (STS)

Enhanced Recovery After Surgery (ERAS) programs have been shown to lessen surgical insult, promote recovery, and improve postoperative clinical outcomes across a number of specialty operations. A core tenet of ERAS involves the provision of protocolized evidence-based perioperative interventions. Given both the growing enthusiasm for applying ERAS principles to cardiac surgery and the broad scope of relevant interventions, an international, multidisciplinary expert panel was assembled to derive a list of potential program elements, review the literature, and provide a statement regarding clinical practice for each topic area. This article summarizes those consensus statements and their accompanying evidence. These results provide the foundation for best practice for the management of the adult patient undergoing cardiac surgery.

Effect of continuous positive airway pressure on the respiratory system: a comprehensive review

Background

CPAP is characterized by the application of a constant and continuous positive pressure into the patient’s airway. By delivering a constant pressure during both inspiration and expiration, CPAP increases functional residual capacity and opens collapsed or under ventilated alveoli, thus decreasing right to left intrapulmonary shunt and improving oxygenation in obese individuals.

Main body of abstract

Obesity is characterized by several alterations in the mechanics of the respiratory system that tend to further exaggerate impairment of gas exchange rendering these patients prone to perioperative complications, such as hypoxemia, hypercapnia, and atelectasis. Interestingly, CPAP has been advocated as an efficacious modality for prevention and treatment of postoperative atelectasis considered to be the most common postoperative respiratory complication. In OSA, the CPAP device works to splint the airway open and prevent the collapse of the upper airway that is the cardinal event of OSA leading improvement of sleep, quality of life and the reduction of the risks of the cardiovascular and neurocognitive side effects associated with the disease. Besides such a beneficial effect, there are other physiological benefits to CPAP: greater end-expiratory lung volume and consequent increase in oxygen stores, increased tracheal traction to improve upper airway patency and decrease in cardiac after load.

Conclusion

Due to various physiological benefits on the respiratory system CPAP therapy is crucial for the prevention postoperative complications particularly related to obesity and the cornerstone for the treatment of moderate to severe obstructive sleep apnea.

Effect of mechanical ventilation during cardiopulmonary bypass on end-expiratory lung volume in the perioperative period of cardiac surgery: an observational study

BACKGROUND

Many studies explored the impact of ventilation during cardiopulmonary bypass (CPB) period with conflicting results. Functional residual capacity or End Expiratory Lung Volume (EELV) may be disturbed after cardiac surgery but the specific effects of CPB have not been studied. Our objective was to compare the effect of two ventilation strategies during CPB on EELV.

METHODS

Observational single center study in a tertiary teaching hospital. Adult patients undergoing on-pump cardiac surgery by sternotomy were included. Maintenance of ventilation during CPB was left to the discretion of the medical team, with division between "ventilated" and "non-ventilated" groups afterwards. Iterative intra and postoperative measurements of EELV were carried out by nitrogen washin-washout technique. Main endpoint was EELV at the end of surgery. Secondary endpoints were EELV one hour after ICU admission, PaO₂/FiO₂ ratio, driving pressure, duration of mechanical ventilation and post-operative pulmonary complications.

RESULTS

Forty consecutive patients were included, 20 in each group. EELV was not significantly different between the ventilated versus non-ventilated groups at the end of surgery (1796 ± 586 mL vs. 1844 ± 524 mL, p = 1) and one hour after ICU admission (2095 ± 562 vs. 2045 ± 476 mL, p = 1). No significant difference between the two groups was observed on PaO₂/FiO₂ ratio (end of surgery: 339 ± 149 vs. 304 ± 131, p = 0.8; one hour after ICU: 324 ± 115 vs. 329 ± 124, p = 1), driving pressure (end of surgery: 7 ± 1 vs. 8 ± 1 cmH₂O, p = 0.3; one hour after ICU: 9 ± 3 vs. 9 ± 3 cmH₂O), duration of mechanical ventilation (5.5 ± 4.8 vs 8.2 ± 10.0 h, p = 0.5), need postoperative respiratory support (2 vs. 1, p = 1), occurrence of pneumopathy (2 vs. 0, p = 0.5) and radiographic atelectasis (7 vs. 8, p = 1).

CONCLUSION

No significant difference was observed in EELV after cardiac surgery between not ventilated and ventilated patients during CPB.

Lung injury following cardiopulmonary bypass: a clinical update

INTRODUCTION

Cardiopulmonary bypass (CPB) is an integral component of cardiac surgery; however, one of its most critical complications is acute lung injury induced by multiple factors including systemic inflammatory response.

AREAS COVERED

The objective of this review is to investigate the multiple factors that can lead to CPB-induced lung injury. These include contact of blood components with the artificial surface of the CPB circuit, local and systemic inflammatory response syndrome (SIRS), lung ischemia/re-perfusion injury, arrest of ventilation, and circulating endotoxins. We also focus on possible interventions to curtail the negative impact of CPB, such as off-pump surgery, impregnation of the circuit with less biologically active substances, leukocyte depletion filters and ultrafiltration, and pharmacological agents such as steroids and aprotinin.

EXPERT OPINION

Although many aspects of CPB are proposed to contribute to lung injury, its overall role is still not clear. Multiple interventions have been introduced to reduce the risk of pulmonary dysfunction, with many of these interventions having shown promising results, significantly attenuating inflammatory mediators and improving post-operative outcome. However, since lung injury is multifactorial and affected by inextricably linked components, multiple interventions tackling each of them is required.

Year in Review 2021: Noteworthy Literature in Cardiothoracic Anesthesia

In 2021, progress in clinical science related to Cardiac Anesthesiology continued, but at a slower rate due to the ongoing pandemic and disruptions to clinical research. Most progress was incremental and addressed persistent questions related to our field. To identify articles for this review, we completed a structured review using our previously reported methods (1). Specifically, we used the search terms: "cardiac anesthesiology and outcomes" (n = 177), "cardiothoracic anesthesiology" (n = 34), "cardiac anesthesia," and "clinical outcomes" (n = 42) filtered on clinical trials and the year 2021 in PubMed. We also reviewed clinical trials from the most prominent clinical journals to identify additional studies for a narrative review. We then selected the most noteworthy publications for inclusion in this review and identified key themes.

Effectiveness of postural lung recruitment on postoperative atelectasis assessed by lung ultrasound in children undergoing lateral thoracotomy cardiac surgery with cardiopulmonary bypass

OBJECTIVES

To assess the effects of postural lung recruitment maneuvers on the postoperative atelectasis assessed by lung ultrasound (LUS) compared with supine position recruitment maneuvers in children undergoing right lateral thoracotomy cardiac surgery with cardiopulmonary bypass.

METHODS

In this randomized and controlled trial, 84 patients aged 3 years or younger, scheduled for right lateral thoracotomy cardiac surgery with cardiopulmonary bypass (CPB) were randomly allocated to postural lung recruitment group or control group. The first LUS exam was performed immediately upon completion of the cardiac surgery (T1), and a repeat ultrasound exam started 1 min after lung recruitment maneuvers (T2). The primary outcome was the incidence of significant atelectasis at T2.

RESULTS

The incidence of significant atelectasis at T2 in the postural lung recruitment maneuver group was lower compared with that in the control group (30.2% vs. 58.1%; odds ratio: 0.31; 95% confidence interval: 0.13-0.76; p = .009). The LUS scores for consolidations and B-lines of the left lung were higher than those of the right lung in both groups at T1. More significant reduction of the left LUS scores and sizes of atelectatic areas were found in the postural lung recruitment group than those in the control group.

CONCLUSIONS

Postoperative postural recruitment maneuver was more effective to improve reaeration of lung than supine position recruitment maneuver in children undergoing right lateral thoracotomy cardiac surgery with CPB.

Low Tidal Volume Mechanical Ventilation Against No Ventilation During Cardiopulmonary Bypass in Heart Surgery (MECANO): A Randomized Controlled Trial

BACKGROUND

Postoperative pulmonary complications are common after cardiac surgery and have been related to lung collapse during cardiopulmonary bypass (CPB). No consensus exists regarding the effects of maintaining mechanical ventilation during CPB to decrease these complications.

RESEARCH QUESTION

To determine whether maintaining low-tidal ventilation (3 mL/kg 5 times/min, with positive end expiratory pressure of 5 cm H₂O) during CPB (ventilation strategy) was superior to a resting-lung strategy with no ventilation (no ventilation strategy) regarding postoperative pulmonary complications, including mortality.

STUDY DESIGN AND METHODS

In a randomized controlled trial, patients undergoing cardiac surgery at a single center from May 2017 through August 2019 were randomized to the ventilation or no ventilation strategy during CPB (1:1 ratio). Apart from the CPB phase, perioperative ventilation procedures were standardized.

RESULTS

The study included 1,501 patients (mean age, 68.8 ± 10.3 years; 1,152 (76.7%) men; mean EuroSCORE II, 2.3 ± 2.7). Seven hundred fifty-six patients were in the ventilation strategy group, and no differences existed in baseline characteristics and types of procedures between the two groups. An intention-to-treat analysis yielded no significant difference between the ventilation and no ventilation groups regarding incidence of the primary composite outcome combining death, early respiratory failure, ventilation support beyond day 2, and reintubation, with 112 of 756 patients (14.8%) in the ventilation group vs 133 of 745 patients (17.9%) in the no ventilation group (OR, 0.80; 95% CI, 0.61-1.05; P = .11). Strict per-protocol analyses of 1,338 patients (89.1%) with equally distributed preoperative characteristics yielded similar results (OR, 0.81; 95% CI, 0.60-1.09; P = .16). Post hoc analysis of the subgroup who underwent isolated coronary artery bypass graft procedures (n = 725) showed that the ventilation strategy was superior to the no ventilation strategy regarding the primary outcome (OR, 0.56; 95% CI, 0.37-0.84; P = .005).

INTERPRETATION

Among patients undergoing cardiac surgery with CPB, continuation of low tidal volume ventilation was not superior to no ventilation during CPB with respect to postoperative complications, including death, early respiratory failure, ventilation support beyond day 2, and reintubation.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT03098524; URL: www.clinicaltrials.gov.

Low tidal volume mechanical ventilation against no ventilation during cardiopulmonary bypass heart surgery (MECANO): study protocol for a randomized controlled trial

Background

Postoperative pulmonary complications are a leading cause of morbidity and mortality after cardiac surgery. There are no recommendations on mechanical ventilation associated with cardiopulmonary bypass (CPB) during surgery and anesthesiologists perform either no ventilation (noV) at all during CPB or maintain low tidal volume (LTV) ventilation. Indirect evidence points towards better pulmonary outcomes when LTV is performed but no large-scale prospective trial has yet been published in cardiac surgery.

Design

The MECANO trial is a single-center, double-blind, randomized, controlled trial comparing two mechanical ventilation strategies, noV and LTV, during cardiac surgery with CPB. In total, 1500 patients are expected to be included, without any restrictions. They will be randomized between noV and LTV on a 1:1 ratio. The noV group will receive no ventilation during CPB. The LTV group will receive 5 breaths/minute with a tidal volume of 3 mL/kg and positive end-expiratory pressure of 5 cmH2O. The primary endpoint will be a composite of all-cause mortality, early respiratory failure defined as a ratio of partial pressure of oxygen/fraction of inspired oxygen <200 mmHg at 1 hour after arrival in the ICU, heavy oxygenation support (defined as a patient requiring either non-invasive ventilation, mechanical ventilation or high-flow oxygen) at 2 days after arrival in the ICU or ventilator-acquired pneumonia defined by the Center of Disease Control. Lung recruitment maneuvers will be performed in the noV and LTV groups at the end of surgery and at arrival in ICU with an insufflation at +30 cmH20 for 5 seconds. Secondary endpoints are those composing the primary endpoint with the addition of pneumothorax, CPB duration, quantity of postoperative bleeding, red blood cell transfusions, revision surgery requirements, length of stay in the ICU and in the hospital and total hospitalization costs. Patients will be followed until hospital discharge.

Discussion

The MECANO trial is the first of its kind to compare in a double-blind design, a no-ventilation to a low-tidal volume strategy for mechanical ventilation during cardiac surgery with CPB, with a primary composite outcome including death, respiratory failure and postoperative pneumonia.

Trial registration

ClinicalTrials.gov, NCT03098524. Registered on 27 February 2017.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2321-9) contains supplementary material, which is available to authorized users.

Different strategies for mechanical VENTilation during CardioPulmonary Bypass (CPBVENT 2014): study protocol for a randomized controlled trial

Background

There is no consensus on which lung-protective strategies should be used in cardiac surgery patients. Sparse and small randomized clinical and animal trials suggest that maintaining mechanical ventilation during cardiopulmonary bypass is protective on the lungs. Unfortunately, such evidence is weak as it comes from surrogate and minor clinical endpoints mainly limited to elective coronary surgery. According to the available data in the academic literature, an unquestionable standardized strategy of lung protection during cardiopulmonary bypass cannot be recommended. The purpose of the CPBVENT study is to investigate the effectiveness of different strategies of mechanical ventilation during cardiopulmonary bypass on postoperative pulmonary function and complications.

Methods/design

The CPBVENT study is a single-blind, multicenter, randomized controlled trial. We are going to enroll 870 patients undergoing elective cardiac surgery with planned use of cardiopulmonary bypass. Patients will be randomized into three groups: (1) no mechanical ventilation during cardiopulmonary bypass, (2) continuous positive airway pressure of 5 cmH₂O during cardiopulmonary bypass, (3) respiratory rate of 5 acts/min with a tidal volume of 2–3 ml/Kg of ideal body weight and positive end-expiratory pressure of 3–5 cmH₂O during cardiopulmonary bypass. The primary endpoint will be the incidence of a PaO₂/FiO₂ ratio <200 until the time of discharge from the intensive care unit. The secondary endpoints will be the incidence of postoperative pulmonary complications and 30-day mortality. Patients will be followed-up for 12 months after the date of randomization.

Discussion

The CPBVENT trial will establish whether, and how, different ventilator strategies during cardiopulmonary bypass will have an impact on postoperative pulmonary complications and outcomes of patients undergoing cardiac surgery.

Trial registration

ClinicalTrials.gov, ID: NCT02090205. Registered on 8 March 2014.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2008-2) contains supplementary material, which is available to authorized users.

Effects of pulmonary static inflation with 50% xenon on oxygen impairment during cardiopulmonary bypass for stanford type A acute aortic dissection: A pilot study

BACKGROUND

The goal of this study was to investigate the effects of pulmonary static inflation with 50% xenon on postoperative oxygen impairment during cardiopulmonary bypass (CPB) for Stanford type A acute aortic dissection (AAD).

METHODS

This prospective single-center nonrandomized controlled clinical trial included 100 adult patients undergoing surgery for Stanford type A AAD at an academic hospital in China. Fifty subjects underwent pulmonary static inflation with 50% oxygen from January 2013 to January 2014, and 50 underwent inflation with 50% xenon from January 2014 to December 2014. During CPB, the lungs were inflated with either 50% xenon (xenon group) or 50% oxygen (control group) to maintain an airway pressure of 5 cm H2O. The primary outcome was oxygenation index (OI) value after intubation, and 10 minutes and 6 hours after the operation. The second outcome was cytokine and reactive oxygen species levels after intubation and 10 minutes, 6 hours, and 24 hours after the operation.

RESULTS

Patients treated with xenon had lower OI levels compared to the control group before surgery (P = 0.002); however, there was no difference in postoperative values between the 2 groups. Following surgery, mean maximal OI values decreased by 18.8% and 33.8%, respectively, in the xenon and control groups. After surgery, the levels of interleukin-6 (IL-6), tumor necrosis factor alpha, and thromboxane B2 decreased by 23.5%, 9.1%, and 30.2%, respectively, in the xenon group, but increased by 10.8%, 26.2%, and 26.4%, respectively, in the control group. Moreover, IL-10 levels increased by 28% in the xenon group and decreased by 7.5% in the control group. There were significant time and treatment-time interaction effects on methane dicarboxylic aldehyde (P = 0.000 and P = 0.050, respectively) and myeloperoxidase (P = 0.000 and P = 0.001 in xenon and control groups, respectively). There was no difference in hospital mortality and 1-year survival rate between the 2 groups.

CONCLUSION

Pulmonary static inflation with 50% xenon during CPB could attenuate OI decreases at the end of surgery for Stanford type A AAD. Thus, xenon may function by triggering anti-inflammatory responses and suppressing pro-inflammatory and oxidative effects.

Ventilation during cardiopulmonary bypass for prevention of respiratory insufficiency: A meta-analysis of randomized controlled trials

BACKGROUND

Cardiopulmonary bypass (CPB) is necessary for most cardiac surgery, which may lead to postoperative lung injury. The objective of this paper is to systematically evaluate whether ventilation during CPB would benefit patients undergoing cardiac surgery.

METHODS

We searched randomized controlled trials (RCTs) through PubMed, Embase, and Cochrane Library from inception to October 2016. Eligible studies compared clinical outcomes of ventilation versus nonventilation during CPB in patients undergoing cardiac surgery. The primary outcome includes oxygenation index (PaO2/FiO2 ratio) or alveolar to arterial oxygen tension difference (AaDO2) immediately after weaning from bypass. The secondary outcomes include postoperative pulmonary complications (PPCs), shunt fraction (Qs/Qt), hospital stay, and AaDO2 4 hours after CPB.

RESULTS

Seventeen trials with 1162 patients were included in this meta-analysis. Ventilation during CPB significantly increased post-CPB PaO2/FiO2 ratio (mean difference [MD] = 21.84; 95% confidence interval [CI] = 1.30 to 42.37; P = 0.04; I = 75%) and reduced post-CPB AaDO2 (MD = -50.17; 95% CI = -71.36 to -28.99; P <0.00001; I = 74%). Qs/Qt immediately after weaning from CPB showed a significant difference between groups (MD = -3.24; 95% CI = -4.48 to -2.01; P <0.00001; I = 0%). Incidence of PPCs (odds ratio [OR] = 0.79; 95% CI = 0.42 to 1.48; P = 0.46; I = 37%) and hospital stay (MD = 0.09; 95% CI = -23 to 0.41; P = 0.58; I = 37%) did not differ significantly between groups.

CONCLUSION

Ventilation during CPB might improve post-CPB oxygenation and gas exchange in patients who underwent cardiac surgery. However, there is no sufficient evidence to show that ventilation during CPB could influence long-term prognosis of these patients. The beneficial effects of ventilation during CPB are requisite to be evaluated in powerful and well-designed RCTs.

Variable Definitions: Implications for the Prediction of Pulmonary Complications after Adult Cardiac Surgery

AIM

The aim of this paper was to review the implications that variable definitions have for the prediction of post-operative pulmonary complications after cardiac surgery.

METHOD

A review of the literature from 1980 to 2002. Selected studies demonstrated an original attempt to examine multivariate associations between pre, intra or post-operative antecedents and pulmonary outcomes in patients undergoing coronary artery bypass grafting (CABG). Reports that described the validation of established clinical prediction rules, testing interventions or research conducted in non-human cohorts were excluded from this review.

RESULTS

Consistently, variable factor and outcome definitions are combined for the development of multivariate prediction models that subsequently have limited clinical value. Despite being prevalent there are very few attempts to examine post-operative pulmonary complications (PPC) as endpoints in isolation. The trajectory of pulmonary dysfunction that precedes complications in the post-operative context is not clear. As such there is little knowledge of post-operative antecedents to PPC that are invariably excluded from model development.

CONCLUSION

Multivariate clinical prediction rules that incorporate antecedent patient and process factors from the continuum of cardiovascular care for specific pulmonary outcomes are recommended. Models such as these would be useful for practice, policy and quality improvement.

Pulmonary Complications After Cardiac Surgery

Over the past two decades there has been a steady evolution in the practice of adult cardiac surgery with the introduction of “off-pump” surgery. However, respiratory complications remain a leading cause of postcardiac surgical morbidity and can prolong hospital stays and increase costs. The high incidence of pulmonary complications is in part due to the disruption of normal ventilatory function that is inherent to surgery in the thoracic region. Furthermore, patients undergoing such surgery often have underlying illnesses such as intrinsic lung disease (e.g., chronic obstructive pulmonary disease) and pulmonary dysfunction secondary to cardiac disease (e.g., congestive heart failure) that increase their susceptibility to postoperative respiratory problems. Given that many patients undergoing cardiac surgery are thus susceptiple to pulmonary complications, it is remarkable that more patients do not suffer from them during and after cardiac surgery. This is to a large degree because of advances in anesthetic, surgical and critical care that, for example, have reduced the physiological insults of surgery (e.g., better myocardial preservation techniques) and streamlined care in the immediate postoperative period (e.g., early extubation). Moreover, the development of minimally invasive surgery and nonbypass techniques are further evidence of the attempts at reducing the homeostatic disruptions of cardiac surgery. This review examines the available information on the incidences, consequences, and treatments of postcardiac surgery respiratory complications.

Pulmonary Protection Strategies in Cardiac Surgery: Are We Making Any Progress?

Pulmonary dysfunction is a common complication of cardiac surgery. The mechanisms involved in the development of pulmonary dysfunction are multifactorial and can be related to the activation of inflammatory and oxidative stress pathways. Clinical manifestation varies from mild atelectasis to severe respiratory failure. Managing pulmonary dysfunction postcardiac surgery is a multistep process that starts before surgery and continues during both the operative and postoperative phases. Different pulmonary protection strategies have evolved over the years; however, the wide acceptance and clinical application of such techniques remain hindered by the poor level of evidence or the sample size of the studies. A better understanding of available modalities and/or combinations can result in the development of customised strategies for the different cohorts of patients with the potential to hence maximise patients and institutes benefits.

Perioperative ventilatory strategies in cardiac surgery

Recent data promote the utilization of prophylactic protective ventilation even in patients without acute respiratory distress syndrome (ARDS), and especially after cardiac surgery. The implementation of specific perioperative ventilatory strategies in patients undergoing cardiac surgery can improve both respiratory and extra-pulmonary outcomes. Protective ventilation is not limited to tidal volume reduction. The major components of ventilatory management include assist-controlled mechanical ventilation with low tidal volumes (6-8 mL kg(-1) of predicted body weight) associated with higher positive end-expiratory pressure (PEEP), limitation of fraction of inspired oxygen (FiO2), ventilation maintenance during cardiopulmonary bypass, and finally recruitment maneuvers. In order for such strategies to be fully effective, they should be integrated into a multimodal approach beginning from the induction and continuing over the postoperative period.

Protection strategies during cardiopulmonary bypass: ventilation, anesthetics and oxygen

PURPOSE OF REVIEW

To provide an update of research findings regarding the protection strategies utilized for patients undergoing cardiopulmonary bypass (CPB), including perioperative ventilatory strategies, different anesthetic regimens, and inspiratory oxygen fraction. The article will review and comment on some of the most important findings in this field to provide a global view of strategies that may improve patient outcomes by reducing inflammation.

RECENT FINDINGS

Postoperative complications are directly related to ischemia and inflammation. The application of lung-protective ventilation with lower tidal volumes and higher positive end-expiratory pressure reduces inflammation, thereby reducing postoperative pulmonary complications. Although inhalation anesthesia has clear cardioprotective effects compared with intravenous anesthesia, several factors can interfere to reduce cardioprotection. Hyperoxia up to 0.8 FiO(2) may confer benefits without increasing oxidative stress or postoperative pulmonary complications. During the early postoperative period, inhalation anesthesia prior to extubation and the application of preventive noninvasive ventilation may reduce cardiac and pulmonary complications, improving patients' outcomes.

SUMMARY

Lung-protective mechanical ventilation, inhalation anesthesia, and high FiO(2) have the potential to reduce postoperative complications in patients undergoing CPB; however, larger, well powered, randomized control trials are still needed.

Postoperative pulmonary dysfunction and mechanical ventilation in cardiac surgery

Postoperative pulmonary dysfunction (PPD) is a frequent and significant complication after cardiac surgery. It contributes to morbidity and mortality and increases hospitalization stay and its associated costs. Its pathogenesis is not clear but it seems to be related to the development of a systemic inflammatory response with a subsequent pulmonary inflammation. Many factors have been described to contribute to this inflammatory response, including surgical procedure with sternotomy incision, effects of general anesthesia, topical cooling, and extracorporeal circulation (ECC) and mechanical ventilation (VM). Protective ventilation strategies can reduce the incidence of atelectasis (which still remains one of the principal causes of PDD) and pulmonary infections in surgical patients. In this way, the open lung approach (OLA), a protective ventilation strategy, has demonstrated attenuating the inflammatory response and improving gas exchange parameters and postoperative pulmonary functions with a better residual functional capacity (FRC) when compared with a conventional ventilatory strategy. Additionally, maintaining low frequency ventilation during ECC was shown to decrease the incidence of PDD after cardiac surgery, preserving lung function.

Pulmonary pathophysiology and lung mechanics in anesthesiology: a case-based overview

Anesthesia, surgical requirements, and patients' unique pathophysiology all combine to make the accumulated knowledge of respiratory physiology and lung mechanics vital in patient management. This article take a case-based approach to discuss how the complex interactions between anesthesia, surgery, and patient disease affect patient care with respect to pulmonary pathophysiology and clinical decision making. Two disparate scenarios are examined: a patient with chronic obstructive pulmonary disease undergoing a lung resection, and a patient with coronary artery disease undergoing cardiopulmonary bypass. The impacts of important concepts in pulmonary physiology and respiratory mechanics on clinical management decisions are discussed.

CPAP of 10 cmH2O during cardiopulmonary bypass followed by an alveolar recruitment manoeuvre does not improve post-bypass oxygenation compared to a recruitment manoeuvre alone in children

This randomised controlled study assessed whether continuous positive airway pressure (CPAP) of 10 cmH2O during cardiopulmonary bypass improves post-bypass oxygenation in children compared with no CPAP during bypass. We studied children with a ventricular septal defect. CPAP of 10 cmH2O was applied during bypass in the CPAP group (n=24), whereas the lungs were left deflated in the control group (n=20). In both groups, an alveolar recruitment maneuver was performed by applying positive pressure of 30 to 40 cmH2O for five seconds before weaning from bypass. Postoperative ventilation had the peak inflation pressure set to produce an expired tidal volume of 8 ml/kg with positive end expiratory pressure of 5 cmH2O. Arterial blood gas and haemodynamic measurements were performed at skin incision, five minutes after weaning from bypass, five minutes after chest closure and four hours after arrival in the intensive care unit. In four children CPAP was discontinued because it adversely affected the operating field. There was no difference in demographic characteristics, haemodynamic data, bypass time and operation time. No difference was observed between the groups with respect to pH, PaO2, P(A-a) DO2, PaCO2, and ETCO2 at each time. Variability in the data was greater than expected, leading to a decrease in the expected power of the study. CPAP at 10 cmH2O during bypass was not found to improve the post-bypass oxygenation as compared with leaving the lung deflated during bypass in children undergoing ventricular septal defect repair who had an alveolar recruitment maneuver at the end of bypass.

Partitioning of exhaled NO in ventilated patients undergoing cardiac surgery

The change in exhaled NO after cardio-pulmonary bypass remains controversial. The aims were to determine whether exhaled NO sources (alveolar or bronchial) are modified after bypass, and whether mechanical ventilation (MV) settings during bypass modify exhaled NO changes. Thirty-two patients were divided into three groups: without MV during bypass and positive end-expiratory pressure (PEEP) (n=12), dead space MV without PEEP (n=10) and dead space MV with PEEP (n=10). Alveolar NO concentration and bronchial NO flux were calculated before and 1h after surgery using a two-compartment model of NO exchange developed in spontaneous breathing patients. Whereas a significant decrease in bronchial NO was found after bypass in the two groups without PEEP during bypass, this decrease was not observed in patients with dead space ventilation with PEEP. Alveolar NO was not significantly modified whatever the ventilation settings. In conclusion, the impairment of bronchial NO seemed related to airway closure since dead space mechanical ventilation with PEEP prevented its decrease.

[Comparison of three ventilatory modes during immediate postoperative transfer of cardiac surgical patients]

OBJECTIVE

Compare three ventilatory strategies during the immediate postoperative transfer of cardiac surgical patient.

STUDY DESIGN

Prospective, comparative and observational study.

PATIENTS AND METHODS

After approval by our local ethical committee, 330 patients undergoing on-pump cardiac surgery were consecutively included. Patients suffering from chronic obstructive pulmonary disease, exhibiting intraoperative hypoxemia or requiring nitric oxide were excluded. The ventilatory mode was left at the discretion of the anesthesiologist and included: controlled mechanical ventilation (FiO(2)=1, N=124) or (FiO(2)=0.6, N=106), and manual ventilation using rebreathing bag (N=100). A blood gas analysis was performed immediately prior to connecting patient at ventilator at the arrival in ICU.

RESULTS

The mean duration of transfer was 3.9+/-1.4 min. Invasive pressure monitoring was used in all patients. The pulse oxymetry and electrocardiogram were respectively used in 78% and 24% of patients. PaO(2) values less than 100 mmHg and those more than 300 mmHg were more frequently found in patients ventilated by rebreathing bag (42%) and mechanical ventilation FiO(2)1 (52%), respectively. No significant difference was found between groups regarding PaCO(2) values.

CONCLUSION

When rebreathing bag is used for transfer in ICU, severe decrease in PaO(2) may be observed. In absence of intraoperative hypoxemia, a mechanical ventilation with FiO(2)0.6 seems to be the most suitable ventilatory strategy for such short immediate postoperative transfer.

Alveolar recruitment strategy during cardiopulmonary bypass does not improve postoperative gas exchange and lung function

Pulmonary dysfunction with impairment of lung function and oxygenation is one of the most serious problems in the early postoperative period after cardiac surgery. In this study we investigated the effect of alveolar recruitment strategy during cardiopulmonary bypass on postoperative gas exchange and lung function. This prospective randomized study included 32 patients undergoing elective myocardial revascularization with cardiopulmonary bypass. In 16 patients 5 cm H(2)O of positive end-expiratory pressure was applied after intubation and maintained until extubation (Group I). In the other 16 patients (group II) a positive end expiratory pressure (PEEP) of 5 cm H(2)O was maintained as well but was increased to 14 cm H(2)O every 20 min for 2 min during cross clamp. Measurements were taken preoperatively, before skin incision, before and after (3, 24, 48 h) cardiopulmonary bypass and before discharge (6th postoperative day). Postoperative gas exchange, extravascular lung water and lung function showed no significant difference between the groups. Postoperative pulmonary function variables were lower in both groups compared to baseline values. In patients with normal preoperative pulmonary function, application of an alveolar recruitment strategy during cardiopulmonary bypass does not improve postoperative gas exchange and lung function after cardiac surgery.

[Atelectasis in general anesthesia and alveolar recruitment strategies]

Atelectasis occurs in most patients during general anesthesia and is the main cause of hypoxemia. The objective of this review is to examine the causes and diagnosis of atelectasis and the different strategies for reducing or preventing this complication and improving oxygenation. Pulmonary atelectasis is mainly caused by 3 factors: compression, gas absorption, and lack of surfactant. Compression and gas absorption are, however, the 2 most commonly implicated factors. Lung collapse is accentuated if pure oxygen is inhaled during induction or if the patient is morbidly obese. Laparoscopic, thoracic, and upper abdominal interventions also carry risk of lung collapse. Various techniques may be used to prevent atelectasis or to reopen collapsed lung tissue. These include using positive end-expiratory pressure or a high tidal volume-thus providing a higher airway pressure (vital capacity maneuver)-or both in combination. Alveolar recruitment strategies have been tried in bariatric surgery, single-lung ventilation, laparoscopy, and adult respiratory distress syndrome. Their application has reduced or prevented atelectasis, thereby reducing postoperative pulmonary complications.

Pulmonary injury after cardiopulmonary bypass: beneficial effects of low-frequency mechanical ventilation

OBJECTIVE

Pulmonary dysfunction is a frequent postoperative complication after cardiac surgery with cardiopulmonary bypass, and atelectasis is thought to be one of the main causes. The aim of this study was to evaluate whether low-frequency ventilation and continuous positive airway pressure during cardiopulmonary bypass reduce postcardiopulmonary bypass lung injury.

METHODS

Eighteen Yorkshire pigs were subjected to 120 minutes of cardiopulmonary bypass (1 hour of cardioplegic arrest) followed by 90 minutes of recovery before being sacrificed. Six animals served as control with the endotracheal tube open to atmosphere during cardiopulmonary bypass. The remaining animals were divided into 2 groups of 6: One group received continuous positive airway pressure of 5 cm H(2)O, and one group received low-frequency ventilation (5/minutes) during cardiopulmonary bypass. Lung tissue biopsy and bronchoalveolar lavage samples were obtained before and 90 minutes after discontinuation of cardiopulmonary bypass for measurement of adenine nucleotide (adenosine-5'-triphosphate, adenosine diphosphate, adenosine monophosphate), lactate dehydrogenase, DNA levels, and histology. Hemodynamic data and arterial blood gases were also collected through the study.

RESULTS

The hemodynamic parameters were similar in the 3 groups. After cardiopulmonary bypass, the low-frequency ventilation group showed significantly better oxygen tension and alveolar arterial oxygen gradient, higher adenine nucleotide, lower lactate dehydrogenase levels, and reduced histologic damage in lung biopsy, as well as lower DNA levels in bronchoalveolar lavage compared with the control group. The continuous positive airway pressure group showed only significantly reduced lactate dehydrogenase levels compared with control.

CONCLUSION

Low-frequency ventilation during cardiopulmonary bypass in a pig experimental model reduces tissue metabolic and histologic damage in the lungs and is associated with improved postoperative gas exchange.

Pulmonary protection during cardiac surgery: systematic literature review

Ischemia-reperfusion injury occurs during heart surgery in which cardiopulmonary bypass is used. Current knowledge of the factors contributing to postoperative pulmonary dysfunction and the measures to avoid it are reviewed.

Development of post-pump syndrome in a sheep after mitral valve stenting

Summary

A one-year-old healthy sheep received an implant stenting the mural (‘posterior’) leaflet of the mitral valve. The experiment was authorized by the Cantonal Ethical Committee. The surgery was performed on the open, beating heart during cardiopulmonary bypass (CPB). Management of anaesthesia was based on isoflurane with mechanical intermittent positive pressure ventilation (IPPV) of the lungs, combined with intercostal nerve blocks and intravenous fentanyl and lidocaine. Marked cardiovascular depression occurred towards the end of CPB time and required high doses of dopamine, dobutamine, lidocaine and ephedrine to allow for weaning off the CPB pump. Moreover, severe pulmonary dysfunction developed when IPPV was re-initiated after CPB. Hypoxaemia persisted throughout the recovery from general anaesthesia. Multiple organ failure developed gradually during the three postoperative days, leading to euthanasia of the animal. As described in this case, marked lung injury associated with some degree of failure of other vital organs may occur in sheep after CPB. Intraoperative cardiorespiratory complications when weaning-off may indicate the development of ‘post-pump 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.

Postoperative Pulmonary Dysfunction in Adults After Cardiac Surgery With Cardiopulmonary Bypass: Clinical Significance and Implications for Practice

Postoperative pulmonary complications are the most frequent and significant contributor to morbidity, mortality, and costs associated with hospitalization. Interestingly, despite the prevalence of these complications in cardiac surgical patients, recognition, diagnosis, and management of this problem vary widely. In addition, little information is available on the continuum between routine postoperative pulmonary dysfunction and postoperative pulmonary complications. The course of events from pulmonary dysfunction associated with surgery to discharge from the hospital in cardiac patients is largely unexplored. In the absence of evidence-based practice guidelines for the care of cardiac surgical patients with postoperative pulmonary dysfunction, an understanding of the pathophysiological basis of the development of postoperative pulmonary complications is fundamental to enable clinicians to assess the value of current management interventions. Previous research on postoperative pulmonary dysfunction in adults undergoing cardiac surgery is reviewed, with an emphasis on the pathogenesis of this problem, implications for clinical nursing practice, and possibilities for future research.

Surgical repair of acute type A aortic dissection: continuous pulmonary perfusion during retrograde cerebral perfusion prevents lung injury in a pilot study

OBJECTIVE

Postoperative respiratory failure is a frequent and serious complication in patients with type A acute aortic dissection operated on with deep systemic hypothermia. Interaction between neutrophils and pulmonary endothelium along with ischemic insult and reperfusion are the major determinants of lung injury. The aim of this prospective study was to evaluate the effect of continuous pulmonary perfusion during retrograde cerebral perfusion on lung function.

METHODS

Twenty-two patients referred for acute type A aortic dissection, who were free from preoperative respiratory dysfunction, were assigned prospectively and alternately to one of 2 treatment groups. Pulmonary perfusion was performed during retrograde cerebral perfusion in group B (11 patients), whereas the conventional Ueda technique was applied in group A (11 patients). Lung function was evaluated on the basis of intubation time, scoring of chest radiographs at 12 hours after cardiopulmonary bypass, and Pao(2)/fraction of inspired oxygen ratio assessed from immediately before the operation to 72 hours after termination of cardiopulmonary bypass.

RESULTS

Study groups were homogeneous for age, sex, interval between symptom onset and surgical operation, previous aortic surgery, preoperative ejection fraction and pulmonary gas exchange function, extent of aortic repair, and concomitant procedures. Cardiopulmonary bypass time, length of retrograde cerebral perfusion, operation time, need for blood substitutes, and surgical revision for bleeding did not differ between treatment groups. Postoperative Pao(2)/fraction of inspired oxygen ratios were higher in group B than in group A, and the difference remained statistically significant throughout the study period. The incidence of prolonged ventilator support (>72 hours) and the severity of the radiographic pulmonary infiltrate score were lower in the perfused group (18.2% vs 72.7% [P =.015] and 0.81 +/- 0.75 vs 1.8 +/- 0.78 [P =.028], respectively).

CONCLUSIONS

Continuous pulmonary perfusion provided a better preservation of lung function in patients operated on with deep systemic hypothermia.

The effect of high-frequency ventilation of the lungs on postbypass oxygenation: A comparison with other ventilation methods applied during cardiopulmonary bypass

OBJECTIVE

To compare the effect of high-frequency ventilation versus other ventilation methods applied during cardiopulmonary bypass on postbypass oxygenation.

DESIGN

Prospective, randomized study.

SETTING

University hospital.

PARTICIPANTS

Seventy-five patients undergoing coronary artery bypass graft surgery.

INTERVENTIONS

Patients were allocated to 5 equal groups of different ventilation methods during bypass. Groups 1 and 2 received high-frequency, low-volume ventilation with 100% and 21% oxygen, respectively. Groups 3 and 4 received 5 cm H(2)O of continuous positive airway pressure (CPAP) with either 100% or 21% oxygen. Patients from group 5 were disconnected from the ventilator during the bypass period.

MEASUREMENTS AND MAIN RESULTS

Spirometry data, blood gas analysis, oxygen saturation as measured by pulse oximetry, and end-tidal carbon dioxide were recorded 5 minutes before chest opening, 5 minutes before bypass, 5 minutes after bypass, 5 minutes after chest closure and 6, 12, 18, and 24 hours after surgery. There were no differences in compliance and mean airway pressures. Alveolar-to-arterial oxygen gradients increased, and PaO(2) decreased significantly (p < 0.05) in all groups 5 minutes after bypass and this trend continued in the postoperative period. Patients from group 3 had higher PaO(2) and lower alveolar-to-arterial oxygen gradients, 5 minutes after weaning from bypass (p < 0.05). Extubation times were similar in all groups.

CONCLUSIONS

The alveolar-arterial oxygen gradient was lower, and the PaO(2) was higher 5 minutes after bypass in patients receiving CPAP (100% O(2)) as compared with those ventilated with high-frequency ventilation.

Pulmonary dysfunction after cardiac surgery

Postoperative lung injury is one of the most frequent complications of cardiac surgery that impacts significantly on health-care expenditures and largely has been believed to result from the use of cardiopulmonary bypass (CPB). However, recent comparative studies between conventional and off-pump coronary artery bypass grafting have indicated that CPB itself may not be the major contributor to the development of postoperative pulmonary dysfunction. In our study, we review the associated physiologic, biochemical, and histologic changes, with particular reference to the current understanding of underlying mechanisms. Intraoperative modifications aiming at limiting lung injury are discussed. The potential benefits of maintaining ventilation and pulmonary artery perfusion during CPB warrant further investigation.