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

Recruitment maneuvers to reduce pulmonary atelectasis after cardiac surgery: A meta-analysis of randomized trials

BACKGROUND

Pulmonary atelectasis is a common postoperative complication that may lead to intrapulmonary shunt, refractory hypoxemia, and respiratory distress. Recruitment maneuvers may relieve pulmonary atelectasis in patients undergoing cardiac surgery. We conducted a meta-analysis of randomized controlled trials to evaluate the effectiveness of recruitment maneuvers in these patients.

METHODS

We conducted a search in PubMed, Embase, Cochrane Library, and the ClinicalTrials.gov registry for trials published before March 2020. Individual effect sizes were standardized, and a meta-analysis was performed to calculate a pooled effect size by using random-effects models. Pulmonary atelectasis was assessed postoperatively. Secondary outcomes included hypoxic events, arterial oxygen tension (Pao₂)/inspired oxygen fraction (Fio₂) ratio, cardiac index, mean arterial pressure, and postoperative complications including pneumothorax and pneumonia.

RESULTS

We reviewed 16 trials involving 1455 patients. Patients receiving recruitment maneuvers had a reduced incidence of pulmonary atelectasis (group with recruited pressure >40 cmH₂O: risk ratio [RR], 0.20; 95% confidence interval [CI], 0.07-0.57; group with recruited pressure <40 cmH₂O: RR, 0.54; 95% CI, 0.33-0.89), reduced incidence of hypoxic events (RR, 0.23; 95% CI, 0.14-0.37), reduced incidence of pneumonia (RR, 0.42; 95% CI, 0.18-0.95), and improved Pao₂/Fio₂ ratio (weighted mean difference [WMD]; 58.87, 95% CI, 31.24-86.50) without disturbing the cardiac index (WMD, 0.22; 95% CI, -0.18 to 0.61) or mean arterial pressure (WMD, -0.30, 95% CI, -3.19 to 2.59) as compared with those who received conventional mechanical ventilation. The incidence of pneumothorax was nonsignificant between the groups.

CONCLUSIONS

Recruitment maneuvers may reduce postoperative pulmonary atelectasis, hypoxic events, and pneumonia and improve Pao₂/Fio₂ ratios without hemodynamic disturbance in patients undergoing cardiac surgery.

Ventilation strategies with different inhaled Oxygen conceNTration during CardioPulmonary Bypass in cardiac surgery (VONTCPB): study protocol for a randomized controlled trial

Background

There is no consensus on the ventilation management during cardiopulmonary bypass (CPB), and the anesthesiologists or the surgeons usually ventilate the lungs with different ventilation strategies or keep them static. Better outcomes are more likely to occur when the ventilation is administered during CPB according to the existing literatures. However, the use of high fraction of inspired oxygen (FiO₂) is debatable in cardiac surgery. And the potential effects of strategies combining low tidal volume (V_T) ventilation with different FiO₂ during CPB on postoperative pulmonary complications (PPCs) are unclear.

Design

The VONTCPB trial is a single-center, prospective, double-blinded, randomized, controlled trial. We are going to recruit total 420 elective cardiac surgery patients with median sternotomy under CPB, who will be equally randomized into three different ventilation strategy groups: NoV, LOV and HOV. (1) The NoV group receives no mechanical ventilation during CPB; (2) the LOV group receives a low V_T of 3-4 ml/kg of ideal body weight (IBW) with the respiratory rate (RR) of 10–12 acts/min, and the positive end-expiratory pressure (PEEP) of 5–8 cmH₂O during CPB; the FiO₂ is 30%; (3) the HOV group receives a low V_T of 3-4 ml/kg of IBW with the RR of 10–12 acts/min, and the PEEP of 5–8 cmH₂O during CPB; the FiO₂ is 80%. The primary endpoints are the incidence of the composite of PPCs and the PPCs score. The secondary endpoints refer to the incidence of the oxygenation index (PaO₂/FiO₂ ratio) < 300 mmHg at three time points (the moment arriving in the ICU, 6 and 12 h after arrival in the ICU), the surgical incision healing grade, the intubation time, the stay of ICU, the length of hospital stay, and mortality at 30 days after the surgery.

Discussion

The VONTCPB trial is the first study to assess the effects of strategies combining low tidal volume (V_T) ventilation with different FiO₂ during CPB on patients’ outcomes.

Trial registration

ChiCTR1800015261. Registered on 20 March 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3335-2) contains supplementary material, which is available to authorized users.

Perioperative lung protective ventilation

Perioperative lung injury is a major source of postoperative morbidity, excess healthcare use, and avoidable mortality. Many potential inciting factors can lead to this condition, including intraoperative ventilator induced lung injury. Questions exist as to whether protective ventilation strategies used in the intensive care unit for patients with acute respiratory distress syndrome are equally beneficial for surgical patients, most of whom do not present with any pre-existing lung pathology. Studied both individually and in combination as a package of intraoperative lung protective ventilation, the use of low tidal volumes, moderate positive end expiratory pressure, and recruitment maneuvers have been shown to improve oxygenation and pulmonary physiology and to reduce postoperative pulmonary complications in at risk patient groups. Further work is needed to define the potential contributions of alternative ventilator strategies, limiting excessive intraoperative oxygen supplementation, use of non-invasive techniques in the postoperative period, and personalized mechanical ventilation. Although the weight of evidence strongly suggests a role for lung protective ventilation in moderate risk patient groups, definitive evidence of its benefit for the general surgical population does not exist. However, given the shift in understanding of what is needed for adequate oxygenation and ventilation under anesthesia, the largely historical arguments against the use of intraoperative lung protective ventilation may soon be outdated, on the basis of its expanding track record of safety and efficacy in multiple settings.

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.

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.

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.