Impaired O2 unloading from stored blood results in diffusion-limited O2 release at tissues: evidence from human kidneys.

ABSTRACT: The volume of oxygen drawn from systemic capillaries down a partial pressure gradient is determined by the oxygen content of red blood cells (RBCs) and their oxygen-unloading kinetics, although the latter is assumed to be rapid and, therefore, not a meaningful factor. Under this paradigm, oxygen transfer to tissues is perfusion-limited. Consequently, clinical treatments to optimize oxygen delivery aim at improving blood flow and arterial oxygen content, rather than RBC oxygen handling. Although the oxygen-carrying capacity of blood is increased with transfusion, studies have shown that stored blood undergoes kinetic attrition of oxygen release, which may compromise overall oxygen delivery to tissues by causing transport to become diffusion-limited. We sought evidence for diffusion-limited oxygen release in viable human kidneys, normothermically perfused with stored blood. In a cohort of kidneys that went on to be transplanted, renal respiration correlated inversely with the time-constant of oxygen unloading from RBCs used for perfusion. Furthermore, the renal respiratory rate did not correlate with arterial O2 delivery unless this factored the rate of oxygen-release from RBCs, as expected from diffusion-limited transport. To test for a rescue effect, perfusion of kidneys deemed unsuitable for transplantation was alternated between stored and rejuvenated RBCs of the same donation. This experiment controlled oxygen-unloading, without intervening ischemia, holding all non-RBC parameters constant. Rejuvenated oxygen-unloading kinetics improved the kidney's oxygen diffusion capacity and increased cortical oxygen partial pressure by 60%. Thus, oxygen delivery to tissues can become diffusion-limited during perfusion with stored blood, which has implications in scenarios, such as ex vivo organ perfusion, major hemorrhage, and pediatric transfusion. This trial was registered at www.clinicaltrials.gov as #ISRCTN13292277.

A randomized trial of normothermic preservation in liver transplantation.

Liver transplantation is a highly successful treatment, but is severely limited by the shortage in donor organs. However, many potential donor organs cannot be used; this is because sub-optimal livers do not tolerate conventional cold storage and there is no reliable way to assess organ viability preoperatively. Normothermic machine perfusion maintains the liver in a physiological state, avoids cooling and allows recovery and functional testing. Here we show that, in a randomized trial with 220 liver transplantations, compared to conventional static cold storage, normothermic preservation is associated with a 50% lower level of graft injury, measured by hepatocellular enzyme release, despite a 50% lower rate of organ discard and a 54% longer mean preservation time. There was no significant difference in bile duct complications, graft survival or survival of the patient. If translated to clinical practice, these results would have a major impact on liver transplant outcomes and waiting list mortality.

Risks for donors associated with living kidney donation: meta-analysis.

BACKGROUND: Living kidney donation risk is likely to differ according to donor's demographics. We aimed to analyse the effects of age, sex, body mass index (BMI) and ethnicity. METHODS: A systematic review and meta-analysis was undertaken of the effects of preoperative patient characteristics on donor kidney function outcomes, surgical complications, and hypertension. RESULTS: 5129 studies were identified, of which 31 met the inclusion criteria, mainly from the USA and Europe. The estimated glomerular filtration rate (eGFR) in donors aged over 60 years was a mean of 9.54 ml per min per 1.73 m2 lower than that of younger donors (P < 0.001). Female donors had higher relative short- and long-term survival. BMI of over 30 kg/m2 was found to significantly lower the donor's eGFR 1 year after donation: the eGFR of obese donors was lower than that of non-obese patients by a mean of -2.70 (95 per cent c.i. -3.24 to -2.15) ml per min per 1.73 m2 (P < 0.001). Obesity was also associated with higher blood pressure both before and 1 year after donation, and a higher level of proteinuria, but had no impact on operative complications. In the long term, African donors were more likely to develop end-stage renal disease than Caucasians. CONCLUSION: Obesity and male sex were associated with inferior outcomes. Older donors (aged over 60 years) have a larger eGFR decline than younger donors, and African donors have a higher incidence of ESRD than Caucasians.

Is Preemptive Kidney Transplantation Associated With Improved Outcomes when Compared to Non-preemptive Kidney Transplantation in Children? A Systematic Review and Meta-Analysis.

Main Problem: Preemptive kidney transplantation (PKT) is performed prior to dialysis initiation to avoid dialysis-related morbidity and mortality in children and adolescents. We undertook a systematic review to compare clinical outcomes in PKT versus kidney transplantation after dialysis initiation in paediatric patients. Methods: The bibliographic search identified studies that compared paediatric recipients of a first or subsequent, living or deceased donor PKT versus non-preemptive kidney transplant. Methodological quality was assessed for all studies. Data were pooled using the random-effects model. Results: Twenty-two studies (n = 22,622) were included. PKT reduced the risk of overall graft loss (relative risk (RR) .57, 95% CI: .49-.66) and acute rejection (RR: .81, 95% CI: .75-.88) compared to transplantation after dialysis. Although no significant difference was observed in overall patient mortality, the risk of patient death was found to be significantly lower in PKT patients with living donor transplants (RR: .53, 95% CI: .34-.83). No significant difference was observed in the incidence of delayed graft function. Conclusion: Evidence from observational studies suggests that PKT is associated with a reduction in the risk of acute rejection and graft loss. Efforts should be made to promote and improve rates of PKT in this group of patients (PROSPERO). Systematic Review Registration: https://clinicaltrials.gov/, CRD42014010565.

Tracheal Stent Buckling and In-stent Stenosis: A Proposed Airway Management Algorithm for Airway Obstruction for Patients With Tracheal Stents.

EMERGENCY AIRWAY management strategies for patients with complications due to tracheobronchial stents are of growing interest to anesthesiologists. Although tracheal stenting increasingly is used to manage tracheobronchial stenosis of both benign and malignant conditions,1-3 official guidelines for the perioperative airway management of patients with tracheobronchial stents in situ are lacking.3 Here, the authors discuss the management of airway obstruction from a tracheal stent strut protrusion and in-stent stenosis in a patient with a self-expanding nitinol tracheal stent in situ. They discuss the airway management strategy employed and outline a pragmatic airway management algorithm for patients with tracheal stents presenting with airway obstruction.

Oxygenated versus standard cold perfusion preservation in kidney transplantation (COMPARE): a randomised, double-blind, paired, phase 3 trial.

BACKGROUND: Deceased donor kidneys are preserved in cold hypoxic conditions. Providing oxygen during preservation might improve post-transplant outcomes, particularly for kidneys subjected to greater degrees of preservation injury. This study aimed to investigate whether supplemental oxygen during hypothermic machine perfusion (HMP) could improve the outcome of kidneys donated after circulatory death. METHODS: This randomised, double-blind, paired, phase 3 trial was done in 19 European transplant centres. Kidney pairs from donors aged 50 years or older, donated after circulatory death, were eligible if both kidneys were transplanted into two different recipients. One kidney from each donor was randomly assigned using permuted blocks to oxygenated hypothermic machine perfusion (HMPO2), the other to HMP without oxygenation. Perfusion was maintained from organ retrieval to implantation. The primary outcome was 12-month estimated glomerular filtration rate (eGFR) using the Chronic Kidney Disease Epidemiology Collaboration equation in pairs of donated kidneys in which both transplanted kidneys were functioning at the end of follow-up. Safety outcomes were reported for all transplanted kidneys. Intention-to-treat analyses were done. This trial is registered with the ISRCTN Registry, ISRCTN32967929, and is now closed. FINDINGS: Between March 15, 2015, and April 11, 2017, 197 kidney pairs were randomised with 106 pairs transplanted into eligible recipients. 23 kidney pairs were excluded from the primary analysis because of kidney failure or patient death. Mean eGFR at 12 months was 50·5 mL/min per 1·73 m2 (SD 19·3) in the HMPO2 group versus 46·7 mL/min per 1·73m2 (17·1) in HMP (mean difference 3·7 mL/min per 1·73m2, 95% CI -1·0 to 8·4; p=0·12). Fewer severe complications (Clavien-Dindo grade IIIb or more) were reported in the HMPO2 group (46 of 417, 11%, 95% CI 8% to 14%) than in the HMP group (76 of 474, 16%, 13% to 20%; p=0·032). Graft failure was lower with HMPO2 (three [3%] of 106) compared with HMP (11 [10%] of 106; hazard ratio 0·27, 95% CI 0·07 to 0·95; p=0·028). INTERPRETATION: HMPO2 of kidneys donated after circulatory death is safe and reduces post-transplant complications (grade IIIb or more). The 12-month difference in eGFR between the HMPO2 and HMP groups was not significant when both kidneys from the same donor were still functioning 1-year post-transplant, but potential beneficial effects of HMPO2 were suggested by analysis of secondary outcomes. FUNDING: European Commission 7th Framework Programme.

Transplant Trial Watch.

To keep the transplantation community informed about recently published level 1 evidence in organ transplantation ESOT (https://esot.org/) the Centre for Evidence in Transplantation (www.transplantevidence.com) has developed the Transplant Trial Watch. The Transplant Trial Watch is a monthly overview of 10 new randomized controlled trials (RCTs) and systematic reviews. This page of Transplant International offers commentaries on methodological issues and clinical implications on two articles of particular interest from the CET Transplant Trial Watch monthly selection. For all high-quality evidence in solid organ transplantation, visit the Transplant Library: www.transplantlibrary.com.

Transplant Trial Watch.

To keep the transplantation community informed about recently published level 1 evidence in organ transplantation, ESOT (https://esot.org/) and the Centre for Evidence in Transplantation have developed the Transplant Trial Watch (www.transplantevidence.com). The Transplant Trial Watch is a monthly overview of 10 new randomized controlled trials (RCTs) and systematic reviews. This page of Transplant International offers commentaries on methodological issues and clinical implications on two articles of particular interest from the CET Transplant Trial Watch monthly selection. For all high-quality evidence in solid organ transplantation, visit the Transplant Library: www.transplantlibrary.com.

Transplant Trial Watch.

To keep the transplantation community informed about recently published level 1 evidence in organ transplantation, ESOT (https://esot.org/) and the Centre for Evidence in Transplantation (www.transplantevidence.com) have developed the Transplant Trial Watch. The Transplant Trial Watch is a monthly overview of 10 new randomized controlled trials (RCTs) and systematic reviews. This page of Transplant International offers commentaries on methodological issues and clinical implications on two articles of particular interest from the CET Transplant Trial Watch monthly selection. For all high-quality evidence in solid organ transplantation, visit the Transplant Library: www.transplantlibrary.com.

Transplant Trial Watch.

To keep the transplantation community informed about recently published level 1 evidence in organ transplantation ESOT and the Centre for Evidence in Transplantation (www.transplantevidence.com) have developed the Transplant Trial Watch. The Transplant Trial Watch is a monthly overview of 10 new randomised controlled trials (RCTs) and systematic reviews. This page of Transplant International offers commentaries on methodological issues and clinical implications on 2 articles of particular interest from the CET Transplant Trial Watch monthly selection. For all high quality evidence in solid organ transplantation, visit the Transplant Library (www.transplantlibrary.com).

A systematic review and meta-analyses of regional perfusion in donation after circulatory death solid organ transplantation.

In donation after circulatory death (DCD), (thoraco)abdominal regional perfusion (RP) restores circulation to a region of the body following death declaration. We systematically reviewed outcomes of solid organ transplantation after RP by searching PubMed, Embase, and Cochrane libraries. Eighty-eight articles reporting on outcomes of liver, kidney, pancreas, heart, and lung transplants or donor/organ utilization were identified. Meta-analyses were conducted when possible. Methodological quality was assessed using National Institutes of Health (NIH)-scoring tools. Case reports (13/88), case series (44/88), retrospective cohort studies (35/88), retrospective matched cohort studies (5/88), and case-control studies (2/88) were identified, with overall fair quality. As blood viscosity and rheology change below 20 °C, studies were grouped as hypothermic (HRP, ≤20 °C) or normothermic (NRP, >20 °C) regional perfusion. Data demonstrate that RP is a safe alternative to in situ cold preservation (ISP) in uncontrolled and controlled DCDs. The scarce HRP data are from before 2005. NRP appears to reduce post-transplant complications, especially biliary complications in controlled DCD livers, compared with ISP. Comparisons for kidney and pancreas with ISP are needed but there is no evidence that NRP is detrimental. Additional data on NRP in thoracic organs are needed. Whether RP increases donor or organ utilization needs further research.

The Value of Systematic Reviews and Meta-Analyses in Surgery.

BACKGROUND: Systematic reviews and meta-analyses are generally regarded as sitting atop the hierarchy of clinical evidence. The unbiased summary of current evidence that a systematic review provides, along with the increased statistical power from larger numbers of patients, is invaluable in guiding clinical decision-making and development of practice guidelines. Surgical specialties have historically lagged behind other areas of medicine in the application of evidence-based medicine, perhaps due to the unique challenges faced in the conduct of surgical clinical trials. These challenges extend to the conduct of systematic reviews, due to issues with the quality and heterogeneity of the underlying literature. SUMMARY: Recent years have seen an improvement in the quality of randomized controlled trials in surgical topics and an explosion in the publication of systematic reviews. This review explores recent trends in systematic reviews in surgery and discussed some of the aspects in conducting and interpreting reviews that are unique to surgical topics, including blinding, surgical heterogeneity and learning curves, patient and clinician preference, and industry involvement. Key Messages: Clinical trials, and therefore systematic reviews, of surgical interventions pose unique challenges which are important to consider when conducting them or applying the findings to clinical practice. Despite the challenges, systematic reviews still represent the best level of evidence for development of surgical practice guidelines.

Using Artificial Intelligence for Predicting Survival of Individual Grafts in Liver Transplantation: A Systematic Review.

The demand for liver transplantation far outstrips the supply of deceased donor organs, and so, listing and allocation decisions aim to maximize utility. Most existing methods for predicting transplant outcomes use basic methods, such as regression modeling, but newer artificial intelligence (AI) techniques have the potential to improve predictive accuracy. The aim was to perform a systematic review of studies predicting graft outcomes following deceased donor liver transplantation using AI techniques and to compare these findings to linear regression and standard predictive modeling: donor risk index (DRI), Model for End-Stage Liver Disease (MELD), and Survival Outcome Following Liver Transplantation (SOFT). After reviewing available article databases, a total of 52 articles were reviewed for inclusion. Of these articles, 9 met the inclusion criteria, which reported outcomes from 18,771 liver transplants. Artificial neural networks (ANNs) were the most commonly used methodology, being reported in 7 studies. Only 2 studies directly compared machine learning (ML) techniques to liver scoring modalities (i.e., DRI, SOFT, and balance of risk [BAR]). Both studies showed better prediction of individual organ survival with the optimal ANN model, reporting an area under the receiver operating characteristic curve (AUROC) 0.82 compared with BAR (0.62) and SOFT (0.57), and the other ANN model gave an AUC ROC of 0.84 compared with a DRI (0.68) and SOFT (0.64). AI techniques can provide high accuracy in predicting graft survival based on donors and recipient variables. When compared with the standard techniques, AI methods are dynamic and are able to be trained and validated within every population. However, the high accuracy of AI may come at a cost of losing explainability (to patients and clinicians) on how the technology works.

A systematic review to identify whether perfusate biomarkers produced during hypothermic machine perfusion can predict graft outcomes in kidney transplantation.

There is good evidence to support the use of hypothermic machine perfusion (HMP) over static cold storage as the favoured preservation method for deceased donor kidneys. However, the utility of HMP as a tool to assess the viability of kidneys for transplant is unclear. There is a need to determine whether perfusate biomarkers produced during HMP can predict post-transplant outcomes and assess the suitability of organs for transplantation. Three different databases (MEDLINE, Embase, Transplant Library) were screened to 31 May 2019. Articles were included if a relationship was reported between one or more perfusate biomarkers and post-transplant outcomes. Studies were assessed and graded for methodological quality and strength of evidence. Glutathione S-transferase was the most promising biomarker for predicting delayed graft function, but its predictive ability was at best moderate. Analysis of primary nonfunction rates was challenging due to low occurrence rates and small sample sizes. Existing studies are limited in quality and have not yielded biomarkers for kidneys undergoing HMP that are able to predict post-transplant outcomes with sufficient accuracy to support routine clinical use. Further studies with larger samples and more robust methodology are needed. (PROSPERO registration: CRD42019121161).

An analysis of the association between older recipient age and outcomes after whole-organ pancreas transplantation - a single-centre, retrospective study.

Older people are increasingly being referred for consideration for pancreas transplantation (PT). We investigated the outcomes after PT in our older recipient cohort. A prospectively maintained database was interrogated. The cohort was analysed for associations between outcome and older recipient age. A total of 444 transplants were performed in patients aged 23-54 years and 83 transplants in patients aged 55-67 years. There was no difference in death-censored pancreas or kidney graft survival between the groups. Patient death was associated with older recipient age (HR 1.63 per 10-year increase). In multivariate Cox regression, risk of mortality was also associated with post-transplant myocardial infarction (HR 7.25, P = 0.006), pancreas failure (HR 1.91, P = 0.003) and kidney failure (HR 3.55, P < 0.001). About 40% of recipients who died in the first year post-transplant suffered early graft loss. Those alive at a year post-transplant had inferior survival if they had lost their kidney graft (P < 0.001). Mortality is higher in older patients and is strongly associated with pancreas and kidney graft failure. This suggests that pancreas transplantation is feasible in older recipients, and careful selection of donor organs is important to optimize survival.

Transient Cold Storage Prior to Normothermic Liver Perfusion May Facilitate Adoption of a Novel Technology.

Clinical adoption of normothermic machine perfusion (NMP) may be facilitated by simplifying logistics and reducing costs. This can be achieved by cold storage of livers for transportation to recipient centers before commencing NMP. The purpose of this study was to assess the safety and feasibility of post-static cold storage normothermic machine perfusion (pSCS-NMP) in liver transplantation. In this multicenter prospective study, 31 livers were transplanted. The primary endpoint was 30-day graft survival. Secondary endpoints included the following: peak posttransplant aspartate aminotransferase (AST), early allograft dysfunction (EAD), postreperfusion syndrome (PRS), adverse events, critical care and hospital stay, biliary complications, and 12-month graft survival. The 30-day graft survival rate was 94%. Livers were preserved for a total of 14 hours 10 minutes ± 4 hours 46 minutes, which included 6 hours 1 minute ± 1 hour 19 minutes of static cold storage before 8 hours 24 minutes ± 4 hours 4 minutes of NMP. Median peak serum AST in the first 7 days postoperatively was 457 U/L (92-8669 U/L), and 4 (13%) patients developed EAD. PRS was observed in 3 (10%) livers. The median duration of initial critical care stay was 3 days (1-20 days), and median hospital stay was 13 days (7-31 days). There were 7 (23%) patients who developed complications of grade 3b severity or above, and 2 (6%) patients developed biliary complications: 1 bile leak and 1 anastomotic stricture with no cases of ischemic cholangiopathy. The 12-month overall graft survival rate (including death with a functioning graft) was 84%. In conclusion, this study demonstrates that pSCS-NMP was feasible and safe, which may facilitate clinical adoption.

Noninvasive biomarkers in monitoring kidney allograft health.

PURPOSE OF REVIEW: A key aspect of posttransplant management is to identify and treat graft injury before it becomes irreversible. The gold-standard for detection is histology, but biopsy is uncomfortable for the patient and carries a risk of complications. Detection of changes at a molecular level may preempt histological injury, and thereby identify injury earlier. RECENT FINDINGS: Indicators of immune system activation, such as candidate chemokines CXCL9 and CXCL10, and by-products of neutrophil activity, have been related to acute rejection and early allograft function. Transcriptomic studies of multiple-gene panels have identified candidate combinations that have proven very promising in risk-stratification and prediction of acute rejection, as well as diagnosis of both T-cell-mediated and antibody-mediated rejection. Serum and urine cell-free DNA is also a promising area of investigation, particularly in antibody-mediated rejection. SUMMARY: Noninvasive, rapid, and accurate tests for risk-prediction and diagnosis in renal transplant allografts are urgently required. The ideal candidate is one that can be measured in either urine or blood, is cheap, and is both sensitive and specific for the condition of interest. Numerous strategies have been proposed, with varying degrees of clinical and preclinical success. A few that meet the essential criteria have been evaluated; a few have made it as far as clinical testing.