Acute aortic regurgitation due to fibrous strand rupture.

A 60-year-old male presented with sudden onset chest pain and pulmonary edema. The investigation confirmed torrential aortic regurgitation of a bicuspid valve. At surgery, a ruptured fibrous strand was identified which had been supporting the left-right cusp commissure with loss of attachment to the aortic wall. This case demonstrates that fibrous strands may be present as a supporting structure of the aortic valve, and rupture can be a rare cause of torrential aortic regurgitation, similar in pathogenesis to how it may be associated with acute severe mitral regurgitation and chordae tendineae rupture.

Aortic valve replacement in patients over 60: Real-world surgical outcomes.

OBJECTIVE: With the advent of transcatheter aortic valve implantation (TAVI) has come an expectation that there will be a decline in surgical aortic valve replacement (SAVR). This has been fueled by trials comparing outcomes between TAVI and SAVR in lower-risk patients. The aim of this study was to examine outcomes following SAVR in patients over the age of 60. MATERIALS AND METHODS: This retrospective cohort study observed 1005 patients ≥60 who underwent isolated primary SAVR from January 2015 to December 2018. The cohort was stratified by surgical risk, defined as European System for Cardiac Operative Risk Evaluation (EuroSCORE) II < 4 versus ≥4. The cohort was also divided by age (60-69, 70-79, ≥80) for additional comparisons. Outcomes included in-hospital complications and patient survival. RESULTS: The median age and EuroSCORE II were 75 years and 1.6, respectively. The overall 30-day mortality was 1.7% and increased significantly with surgical risk (p = .007). The 30-day mortality of elective patients was 1.1%. Overall, 1- and 2-year survival rates were 94.3% and 91.7%, respectively, which significantly decreased with surgical risk (p < .001) and age (p = .002, p = .003). The rates of postoperative stroke and pacemaker implantations were 1.2% and 3.6%, respectively. CONCLUSIONS: SAVR can be performed in patients ≥60 years old with excellent outcomes, which compare favorably with outcomes from TAVI trials, with their highly selected patient cohorts. SAVR remains a reliable, tried and tested, treatment option in these patients.

Minimally invasive extracorporeal circulation is a cost-effective alternative to conventional extracorporeal circulation for coronary artery bypass grafting: propensity matched analysis.

INTRODUCTION: Minimally invasive extracorporeal circulation has developed with the aim of reducing the impact of the adverse effects associated with conventional extracorporeal circulation. The aim of this study was to compare outcomes for patients undergoing coronary artery bypass grafting using minimally invasive extracorporeal circulation with those performed using conventional extracorporeal circulation. METHODS: A retrospective analysis was performed of patients undergoing minimally invasive extracorporeal circulation coronary artery bypass grafting at a single centre. 2:1 propensity matching was performed to identify control patients undergoing conventional extracorporeal circulation coronary artery bypass grafting. Outcomes were compared using univariate analysis. RESULTS: A total of 354 patients were included in the study, with 118 patients undergoing minimally invasive extracorporeal circulation coronary artery bypass grafting. Patients were well matched on baseline characteristics. The mean logistic EuroSCORE was 3.95 ± 4.20. Operative times (3.31 ± 1.52 vs. 3.56 ± 0.73, p = 0.03) were significantly shorter in minimally invasive extracorporeal circulation cases. Patients who underwent surgery with minimally invasive extracorporeal circulation had significantly less 12-hour blood loss (322.3 ± 13.2 mL vs. 380.8 ± 15.2 mL, p < 0.01). Correspondingly, a significantly lower proportion of patients were transfused (25.8% vs. 36%, p = 0.04), and the mean number of red blood cells transfused was lower (0.45 ± 0.95 vs. 0.97 ± 2.13, p = 0.01). Similarly, the number of coagulation products administered was lower (0.161 ± 0.05 vs. 0.40 ± 0.09, p = 0.05). There was a significantly lower incidence of acute kidney injury (11.0% vs. 19.9%, p = 0.03). Minimally invasive extracorporeal circulation was associated with a £679.50 cost saving per patient. DISCUSSION: Minimally invasive extracorporeal circulation for coronary artery bypass grafting is associated with a reduced requirement for blood transfusion, reduced incidence of acute kidney injury and a significant cost saving. Minimally invasive extracorporeal circulation should be considered as an adjunct for all patients undergoing coronary artery bypass grafting.

Spontaneous diaphragmatic rupture as a complication following lung transplantation.

Spontaneous diaphragm rupture is a rare but potentially life-threatening condition, requiring urgent surgical intervention. Here we present two patients who developed spontaneous right hemidiaphragm rupture with abdominal visceral herniation into the thoracic cavity several days following bilateral lung transplantation, as an unusual complication. Both patients' surgeries were performed through bilateral anterior thoracotomies and were uneventful. There may be an association with this complication and patients suffering with emphysema, typically receiving donor lungs smaller than their native lungs, and with significant pretransplant exposure to steroids, factors that when combined may contribute to an increased risk of spontaneous diaphragmatic rupture in the absence of a significant precipitant. If a similar clinical picture is seen, teams managing lung transplant recipients should be aware of this potential complication and recognize the need for urgent intervention.

Transfer of Patients With Cardiogenic Shock Using Veno-Arterial Extracorporeal Membrane Oxygenation.

OBJECTIVES: The authors describe the experience of patient transfer on veno-arterial extracorporeal membrane oxygenation (VA-ECMO) used as a salvage therapy for refractory cardiogenic shock, examining feasibility and long-term outcomes. DESIGN: A retrospective case series. SETTING: A tertiary referral cardiothoracic transplantation center. PARTICIPANTS AND INTERVENTIONS: Since 2012, the authors' multidisciplinary team has traveled to the referring center of 15 patients referred with refractory cardiogenic shock. Of these, 13 were instituted on VA ECMO support (8 peripheral and 5 central) and subsequently transferred to the authors' center. A further 11 patients were transferred to the authors' institution by the referring team, already having been placed on VA-ECMO (8 peripheral and 3 central). MEASUREMENTS AND MAIN RESULTS: All patients were safely transferred. The distance travelled ranged from 16 to 341 miles. The median duration of support on VA-ECMO was 4 days, ranging from 1 to 24 days. The VA-ECMO support was weaned, or the patient underwent a definitive surgical management (including 4 undergoing cardiac transplantation and 3 pulmonary endarterectomy) in 15 (62.5%) patients. The median intensive care unit stay was 15 days (range 1-109). Overall 30-day survival for this patient cohort was 69.6% with 1-year survival of 59.8%. For patients who were weaned from VA-ECMO, the 30-day survival was 100% and 1-year survival 92.9%. CONCLUSIONS: The authors' experience demonstrates the feasibility and survival benefit of a salvage VA-ECMO retrieval service for carefully selected patients with refractory cardiogenic shock. The authors suggest that a system based on the model of nationally commissioned severe respiratory failure services could be organized to support the transfer of these patients.

Is carotid screening redundant for patients undergoing coronary artery bypass grafting?

OBJECTIVES: Stroke is a devastating complication following coronary artery bypass grafting, which thankfully occurs with low incidence. The role of preoperative carotid ultrasound remains unclear. Whilst it is a cheap and reliable way of diagnosing carotid stenosis (CS), it is unclear if and how this knowledge should impact on subsequent patient management. METHODS: A systematic review of the literature was performed using the PRISMA guideline. A literature search was conducted on the MEDLINE database from 1950 to May 2020 using the OVID interface. Fifteen papers out of a total of 5931 were identified for inclusion. RESULTS: The evidence overall suggests that patients with severe CS are likely to have an increased incidence of postoperative stroke-however, the prevalence of severe CS is low, and even in this cohort of patients, the incidence is not particularly high. CONCLUSION: In screened patients identified to have severe CS, there appears to be a generally low appetite for undertaking carotid intervention internationally either before or concurrently with the coronary artery bypass grafting. Putting this all together, the widespread screening of asymptomatic patients would appear to not be justified.

Impact of stroke on outcomes following cardiac surgery: Propensity matched analysis.

BACKGROUND: Stroke remains a devastating complication of cardiac surgery. The aim of this study was to characterize the incidence of stroke and analyze the impact of stroke on patient outcomes and survival. METHODS: A retrospective analysis was performed of patients with a computed tomography-confirmed stroke diagnosis between 1 January 2015 and 31 March 2019 at a single center. 2:1 propensity matching was performed to identify a control population. RESULTS: Over the period 165 patients suffered a stroke (1.99%), with an incidence ranging from 0.85% for coronary artery bypass grafting to 8.14% for aortic surgery. The mean age was 70.3 years and 58.8% were male. 18% had experienced a previous stroke or transient ischemic attack. Compared to the comparison group, patients experiencing postoperative stroke had a significantly prolonged period of intensive care unit admission (8.0 vs 1.1 days P < .001) and hospital length of stay (12.94 vs 8.0 days P < .001). Patient survival was also inferior. In-hospital mortality was almost three times as high (17.0% vs 5.9%; P < .001). Longer-term survival was also inferior to Kaplan-Meier estimation (P < .001). The 1-year and 3-year survival were 61.5% and 53.8% respectively compared to 89.4% and 86.1% for the comparison group. CONCLUSION: Perioperative stroke is a devastating complication following cardiac surgery. Perioperative stroke is associated with significantly inferior outcomes in terms of both morbidity and mortality. Notably a 28% reduction in 1-year survival. Efforts should focus on identifying strategies aimed at reducing the incidence, morbidity, and mortality of perioperative stroke following cardiac surgery.

Emergency valve-in-valve transcatheter aortic valve implantation for endocarditis degeneration.

The use of transcatheter aortic valve implantation (TAVI) in the emergency setting has not been widely reported, and TAVI is generally contraindicated in the context of endocarditis. Here we describe a patient developing acute cardiogenic shock due to prosthetic aortic valve degeneration with free-flow aortic regurgitation 8 months after receiving treatment for confirmed infective endocarditis. Due to his clinical status, he was deemed unfit for redo surgery, and he underwent salvage valve-in-valve (ViV)-TAVI. The patient made an excellent recovery. Postprocedure he was treated with a 6-week course of antibiotics, and at 18-months follow-up remains very well with no evidence of reinfection. This case may demonstrate that for selected patients with degenerative prosthetic aortic valve disease, despite a history of infective endocarditis, ViV-TAVI may be considered an alternative to redo surgery in the emergency setting.

Catastrophic sickling crisis in patient undergoing cardiac transplantation with sickle cell trait.

There is debate in the literature regarding management of patients with sickle cell trait (SCT) undergoing cardiac surgery, since it is recognized that cardiopulmonary bypass presents many precipitating risk factors for a sickling crisis. Despite this, many report successful outcomes without any modification to perioperative management. A 49-year-old woman with SCT (HbS 38%) with postpartum cardiomyopathy underwent cardiac transplantation. The patient was cooled to 34.0°C and retrograde cold blood cardioplegia was infused continuously. The cold ischemic time was 219 minutes and warm ischemic time 46 minutes. After weaning from bypass, she developed global cardiac dysfunction requiring veno-arterial extracorporeal membrane oxygenation. The circuit suddenly stopped, requiring emergency reinstitution of bypass; the circuit had clotted. Transesophageal-echocardiogram revealed thrombus within the left atrium and ventricle. There was no recovery of cardiac function and the patient developed multiorgan failure. At postmortem there was extensive myocardial infarction with evidence of widespread catastrophic intravascular red-cell sickling. This case highlights the danger of complacency in patients with SCT, offering a learning opportunity for the cardiothoracic community to highlight the most serious complication that can occur in this group of patients. We have learned that SCT and cardiac surgery is not a benign combination.

Germinal center humoral autoimmunity independently mediates progression of allograft vasculopathy.

The development of humoral autoimmunity following organ transplantation is increasingly recognised, but of uncertain significance. We examine whether autoimmunity contributes independently to allograft rejection. In a MHC class II-mismatched murine model of chronic humoral rejection, we report that effector antinuclear autoantibody responses were initiated upon graft-versus-host allorecognition of recipient B cells by donor CD4 T-cells transferred within heart allografts. Consequently, grafts were rejected more rapidly, and with markedly augmented autoantibody responses, upon transplantation of hearts from donors previously primed against recipient. Nevertheless, rejection was dependent upon recipient T follicular helper (TFH) cell differentiation and provision of cognate (peptide-specific) help for maintenance as long-lived GC reactions, which diversified to encompass responses against vimentin autoantigen. Heart grafts transplanted into stable donor/recipient mixed haematopoietic chimeras, or from parental strain donors into F1 recipients (neither of which can trigger host adaptive alloimmune responses), nevertheless provoked GC autoimmunity and were rejected chronically, with rejection similarly dependent upon host TFH cell differentiation. Thus, autoantibody responses contribute independently of host adaptive alloimmunity to graft rejection, but require host TFH cell differentiation to maintain long-lived GC responses. The demonstration that one population of helper CD4 T-cells initiates humoral autoimmunity, but that a second population of TFH cells is required for its maintenance as a GC reaction, has important implications for how autoimmune-related phenomena manifest.

CD8 T-cell recognition of acquired alloantigen promotes acute allograft rejection.

Adaptive CD8 T-cell immunity is the principal arm of the cellular alloimmune response, but its development requires help. This can be provided by CD4 T cells that recognize alloantigen "indirectly," as self-restricted allopeptide, but this process remains unexplained, because the target epitopes for CD4 and CD8 T-cell recognition are "unlinked" on different cells (recipient and donor antigen presenting cells (APCs), respectively). Here, we test the hypothesis that the presentation of intact and processed MHC class I alloantigen by recipient dendritic cells (DCs) (the "semidirect" pathway) allows linked help to be delivered by indirect-pathway CD4 T cells for generating destructive cytotoxic CD8 T-cell alloresponses. We show that CD8 T-cell-mediated rejection of murine heart allografts that lack hematopoietic APCs requires host secondary lymphoid tissue (SLT). SLT is necessary because within it, recipient dendritic cells can acquire MHC from graft parenchymal cells and simultaneously present it as intact protein to alloreactive CD8 T cells and as processed peptide alloantigen for recognition by indirect-pathway CD4 T cells. This enables delivery of essential help for generating cytotoxic CD8 T-cell responses that cause rapid allograft rejection. In demonstrating the functional relevance of the semidirect pathway to transplant rejection, our findings provide a solution to a long-standing conundrum as to why SLT is required for CD8 T-cell allorecognition of graft parenchymal cells and suggest a mechanism by which indirect-pathway CD4 T cells provide help for generating effector cytotoxic CD8 T-cell alloresponses at late time points after transplantation.

Global Cardioplegia Practices: Results from the Global Cardiopulmonary Bypass Survey.

Despite the ubiquitous use of cardioplegia in cardiac surgery, there is a lack of agreement on various aspects of cardioplegia practice. To discover current cardioplegia practices throughout the world, we undertook a global survey to document contemporary cardiopulmonary bypass practices. A 16-question, Internet-based survey was distributed by regional specialist societies, targeting adult cardiac anesthesiologists. Ten questions concerned caseload and cardioplegia practices, the remaining questions examined anticoagulation and pump-priming practices. The survey was available in English, Spanish, and Portuguese. The survey was launched in June 2015 and remained open until May 2016. A total of 923 responses were analyzed, summarizing practice in Europe (269), North America (334), South America (215), and Australia/New Zealand (105). Inter-regional responses differed for all questions asked (p < .001). In all regions other than South America, blood cardioplegia was the common arrest technique used. The most commonly used cardioplegia solutions were: St. Thomas, Bretschneider, and University of Wisconsin with significant regional variation. The use of additives (most commonly glucose, glutamate, tris-hydroxymethyl aminomethane, and aspartate) varied significantly. This survey has revealed significant variation in international practice with regards to myocardial protection, and is a reminder that there is no clear consensus on the use of cardioplegia. It is unclear why regional practice groups made the choices they have and the clinical impact remains unclear.

Robotic Camera Assistance: The Future of Laparoscopic and Thoracoscopic Surgery?

INTRODUCTION: Minimally invasive techniques have become the standard for a variety of procedures across all surgical specialties. There has been a recent move to integrate robotic technology into standard laparoscopic and thoracoscopic surgery with the aim of improving stability of the visual field with the use of robotic camera assistance. The aim of this study was to report on and examine the use of a headset-controlled robotic camera holder, FreeHand. METHODS: Between May 2013 and Dec 2016, 105 procedures were observed where the FreeHand robotic camera assistant was used. Observations were made of 43 consultant surgeons in 30 hospitals performing 21 different surgical procedures. During the surgery, the number of scope cleans and collisions were quantified, and surgeons were asked to score from 0 to 5 the setup, ergonomics, usability, and overall experience in a questionnaire. RESULTS: Overall surgeon satisfaction was rated as "good" for setup (4.29), ergonomics of the system (4.12), usability (4.39), and overall experience of the system (4.34). In 8 operations (7.6%), there was a conversion from robotic camera assistant to manual assistant. There were no reported adverse events attributable to the use of the system. CONCLUSION: This study demonstrates the breadth of surgical procedures that can be performed with a robotic camera assistant. The robotic camera assistant was found to be safe and simple to use and was positively perceived on assessment in multiple procedures spanning several surgical specialties. This work suggests that robotic camera assistants may offer significant benefits to laparoscopic and thoracoscopic surgeons.

Outcomes of primary arteriovenous fistulas in patients older than 70 years.

BACKGROUND: The population of elderly hemodialysis patients is increasing, yet the most suitable approach for providing permanent hemodialysis access remains unclear. Here we report outcomes using an approach aimed predominantly at creating radiocephalic (RC) fistulas. METHODS: A single-center retrospective cohort study was performed in which access outcomes for primary arteriovenous fistulas created between January 1, 2005, and December 31, 2012, in patients aged 70 years or older were compared. RESULTS: During the study period, 204 RC, 1 brachiobasilic, and 9 brachiocephalic (BC) primary fistulas were created initially for patients requiring dialysis. Immediate failure rates for RC fistulas were lower than for BC fistulas but not significantly so (12% vs 22%; Fisher's exact text, P = .319). One-year primary and secondary patency for RC fistulas was 54% and 66%, respectively, and similar for those created in patients between 70 and 80 years old and in those older than 80 years. The secondary patency rate at 1 year for RC fistulas using cephalic vein of diameter <2.5 mm was lower than for fistulas created with cephalic vein >2.5 mm (49% vs 72%; log-rank test, P = .005). Creation of a BC fistula was associated with a significantly higher incidence of steal syndrome than with an RC fistula (10% vs 2%; Fisher's exact text, P = .009). CONCLUSIONS: RC fistulas formed in the elderly carry a lower risk of steal syndrome than BC fistulas and offer the potential for further revision surgery, such that acceptable secondary patency is achieved for RC fistulas formed using even small (<2.5 mm) cephalic veins.

Workplace-based assessment: a review of user perceptions and strategies to address the identified shortcomings.

Workplace based assessments (WBAs) are now commonplace in postgraduate medical training. User acceptability and engagement is essential to the success of any medical education innovation. To this end, possessing an insight into trainee and trainer perceptions towards WBAs will help identify the major problems, permitting strategies to be introduced to improve WBA implementation. A review of literature was performed to identify studies examining trainee and trainer perceptions towards WBAs. Studies were excluded if non-English or sampling a non-medical/dental population. The identified literature was synthesised for the purpose of this critical narrative review. It is clear that there is widespread negativity towards WBAs in the workplace. This has negatively impacted on the effectiveness of WBA tools as learning aids. This negativity exists in trainees but also to an extent in their trainers. Insight gained from the literature reveals three dominant problems with WBA implementation: poor understanding as to the purpose of WBAs; insufficient time available for undertaking these assessments; and inadequate training of trainers. Approaches to addressing these three problems with WBA implementation are discussed. It is likely that a variety of solutions will be required. The prevalence of negativity towards WBAs is substantial in both trainees and trainers, eroding the effectiveness of learning that is consequent upon them. The educational community must now listen to the concerns being raised by the users and consider the range of strategies being proposed to improve the experiences of trainees, and their trainers.

Analysis of ischemia/reperfusion injury in time-zero biopsies predicts liver allograft outcomes.

Ischemia/reperfusion injury (IRI) that develops after liver implantation may prejudice long-term graft survival, but it remains poorly understood. Here we correlate the severity of IRIs that were determined by histological grading of time-zero biopsies sampled after graft revascularization with patient and graft outcomes. Time-zero biopsies of 476 liver transplants performed at our center between 2000 and 2010 were graded as follows: nil (10.5%), mild (58.8%), moderate (26.1%), and severe (4.6%). Severe IRI was associated with donor age, donation after circulatory death, prolonged cold ischemia time, and liver steatosis, but it was also associated with increased rates of primary nonfunction (9.1%) and retransplantation within 90 days (22.7%). Longer term outcomes in the severe IRI group were also poor, with 1-year graft and patient survival rates of only 55% and 68%, respectively (cf. 90% and 93% for the remainder). Severe IRI on the time-zero biopsy was, in a multivariate analysis, an independent determinant of 1-year graft survival and was a better predictor of 1-year graft loss than liver steatosis, early graft dysfunction syndrome, and high first-week alanine aminotransferase with a positive predictive value of 45%. Time-zero biopsies predict adverse clinical outcomes after liver transplantation, and severe IRI upon biopsy signals the likely need for early retransplantation.

Negative predictive value of drain amylase concentration for development of pancreatic fistula after pancreaticoduodenectomy.

BACKGROUND: Post-operative pancreatic fistula (POPF) is the major source of morbidity following pancreaticoduodenectomy. A predictive indicator would be highly advantageous. One potential marker is drain amylase concentration (DAC). However, its predictive value has not been fully established. METHODS: 405 patients undergoing pancreaticoduodenectomy at our centre over a 10 year period were reviewed to determine the value of DAC as a predictive indicator for the development of POPF. RESULTS: POPF developed in 58 patients (14%). These patients suffered greater morbidity. Overall 30-day mortality was 1.5%. Male gender (OR: 5.1; p = 0.0082) and age > 70 (OR 2; p = 0.0372) were independent risk factors for POPF, whilst Type 2 diabetes (OR: 0.2321; p = 0.0090) and pancreatic ductal-adenocarcinoma (OR: 0.3721; p = 0.0039) decreased POPF risk. The DACs post-operatively were significantly higher in those developing POPF, but with significant overlap. ROC curves revealed optimal threshold values for differentiating POPF and non-POPF patients. A DAC°<°1400 U/ml on day 1 and <768 U/ml on day 2, although having a poor positive predictive value (32-44%), had a very strong negative predictive value (97-99%). CONCLUSION: Our data suggest that post-operative DAC below the determined optimal threshold values on day 1 and 2 following pancreaticoduodenectomy carries high negative predictive value for POPF development and identifies patients in whom early drain removal, and enhanced recovery may be considered, with simultaneous assessment of operative and clinical factors.

The predictive and prognostic value of risk factors in patients receiving hybrid coronary revascularization with postoperative pulmonary complications.

Background: The mortality rate of coronary artery disease ranks first in developed countries, and coronary revascularization therapy is an important cornerstone of its treatment. The postoperative pulmonary complications (PPCs) in patients receiving one-stop hybrid coronary revascularization (HCR) aggravate the dysfunction of multiple organs such as the heart and lungs, therefore increasing mortality. However, the risk factors are still unclear. The objective of this study was to explore the risk factors of PPCs after HCR surgery. Methods: In this study, the perioperative data of 311 patients undergoing HCR surgery were reviewed. All patients were divided into two groups according to whether the PPCs occurred. The baseline information and surgery-related indicators in preoperative laboratory examination, intraoperative fluid management, and anesthesia management were compared between the two groups. Results: Advanced age [odds ratio (OR): 1.065, 95% confidence interval (CI): 1.030-1.101, P<0.001], high body mass index (BMI; OR: 1.113, 95% CI: 1.011-1.225, P=0.02), history of percutaneous coronary intervention (PCI) surgery (OR: 2.831, 95% CI: 1.388-5.775, P=0.004), one-lung volume ventilation (OR: 3.804, 95% CI: 1.923-7.526, P<0.001), inhalation of high concentration oxygen (OR: 3.666, 95% CI: 1.719-7.815, P=0.001), the application of positive end-expiratory pressure (PEEP; OR: 2.567, 95% CI: 1.338-4.926, P=0.005), and long one-lung ventilation time (OR: 1.015, 95% CI: 1.006-1.023, P=0.001) may be risk factors for postoperative PPCs in patients undergoing one-stop coronary revascularization surgery. Using the above seven factors to jointly predict the risk of PPCs in patients undergoing one-stop coronary revascularization surgery, the receiver operating characteristic (ROC) curve showed an area under the curve (AUC) =0.873, 95% CI: 0.835-0.911, sensitivity: 84.81%, and specificity: 75.82%; the predictive model was shown to be effective. Conclusions: Patients undergoing HCR surgery with advanced age, high BMI, a history of PCI surgery, one-lung volume ventilation, inhalation of high concentration oxygen, use of PEEP, and prolonged single lung ventilation are more prone to PPCs.