Comparing outcomes in patients with end-stage chronic obstructive pulmonary disease: single versus bilateral lung transplants

Abstract

 

OBJECTIVES

Debate continues on whether a bilateral (BLT) or a single lung transplantation (SLT) is preferred for patients with end-stage chronic obstructive pulmonary disease (COPD). The purpose of this study is to examine the interplay between patient age and transplant type on survival outcomes.

METHODS

We performed a retrospective study of lung transplants for COPD at our centre from February 2012 to March 2020 (n = 186). Demographics and clinical parameters were compared between patients based on their age (≤65 vs >65 years old) and type of transplant (single vs bilateral). Cox proportional hazards regression was also performed. P-values <0.05 were considered significant.

RESULTS

Of the 186 patients with COPD who received lung transplants, 71 (38.2%) received BLTs and 115 (61.8%) received SLTs. There was no significant difference in survival outcomes when looking at patients with single versus BLTs (P = 0.870). There was also no difference in survival between the 2 age groups ≤65 versus > 65 years (P = 0.723). The Cox model itself also did not show a statistically significant improvement in survival outcomes (P = 0.126).

CONCLUSIONS

Lung transplant outcomes in patients with end-stage COPD demonstrated non-inferior results in patients with an SLT compared to patients with a BLT. When we compared the age groups, neither transplant type showed superior survival benefits, suggesting there may be some utility in an SLT in younger recipients.

Chronic obstructive pulmonary disease (COPD) with end-stage disease remains a major indication for a lung transplant, accounting for over a third of all lung transplants globally [1].

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) with end-stage disease remains a major indication for a lung transplant, accounting for over a third of all lung transplants globally [1]. However, it remains controversial whether a single lung transplantation (SLT) or a bilateral lung transplantation (BLT) is the superior therapeutic option for a patient with end-stage COPD.

Early publications demonstrated similar survival in older patients receiving SLT or BLT for COPD, with inferior survival in SLT for patients younger than 60 [2, 3, 4]. Studies evaluating survival after the change in organ prioritization with the lung allocation score (LAS) algorithm in the USA suggested reduced 5-year mortality with BLT [5], whereas others suggested no survival difference [6].

From a physiological perspective, BLT may be superior because it prevents early ventilation and perfusion mismatching, avoiding the hyperinflation in the native lung seen after SLT [7]. This outcome and the idea that younger patients can better survive the longer surgical duration of a BLT have led to a preference for BLT in the younger population [8]. This preference may also have contributed to selection bias, driving more robust patients towards BLT and consequently leaving more at-risk patients to the SLT cohorts, affecting retrospective survival results.

If there is no survival benefit to BLT, SLTs, by their very nature, offer greater benefit from a population perspective, supplying more recipients from the same globally limited donors pools. We evaluated the survival trends in SLT and BLT between younger and older patients at our high-volume urban transplant centre. We hypothesized that, with the technological and technical advancements in modern lung transplant procedures, we may not see the survival benefit of BLT as previously suggested.

MATERIALS AND METHODS

This study was a retrospective chart review and was approved by the Temple University Hospital Institutional Review Board on 21 August 2020 (ID number: 27207). Lung transplant recipient data for 186 adult patients with COPD from February 2012 to March 2020 were obtained from our medical centre’s internal patient records. All analyses were performed with SPSS 26.0 (IBM-SPSS Inc., Armonk, NY, USA). Patients were classified by lung transplant type (single vs bilateral). The distribution of recipient sex, race, height, LAS and hospital length of stay (LOS) was evaluated for statistical significance across the type of transplant. Extracorporeal support, approach, induction and donor age, sex and height were also analysed. The approach was also included in the survival analysis due to the variability of the surgical approach in both the SLT and the BLT groups. Predicted total lung capacity (TLC) values were calculated per existing regression equations and ratios of donor-predicted TLC/recipient-predicted TLC were statistically analysed [9]. For categorical variables, Pearson’s χ² test was used. For continuous variables, a Shapiro–Wilk test was used to assess normality, and a Fisher’s F-test was used to assess homogeneity of variance. In cases of non-normality, a Mann–Whitney U-test pooled over strata was performed to evaluate significance in distribution. Otherwise, a two-sample t-test was used. If the F-test showed non-significance, then the t-test was performed with an equal variance assumption. Otherwise, a two-sample t-test with unequal variances was used. The median and mean ± standard deviation were obtained as well. A P-value below 0.05 was considered statistically significant.

Donor gender, height and age data were directly compared with the respective recipient data by calculating the net difference between the 2 as recipient data subtracted from donor data. For the gender variable, this net difference was calculated by assigning men a value of 1 and women a value of 0. The averages of all these variables were evaluated as well as the standard deviations for continuous variables.

Recipient selection for a lung transplant was indicated for patients with chronic end-stage lung disease who were failing maximal medical and surgical therapy, including smoking cessation, maximal bronchodilating treatment, rehabilitation, long-term oxygen therapy and endoscopic or surgical lung volume reduction where feasible. Guidelines for a transplant included patients with a BODE (Body mass index, airflow Obstruction, Dyspnoea and Exercise) index of 7–10 or with a history of hospitalization for exacerbation associated with acute hypercapnia, pulmonary hypertension or cor pulmonale despite oxygen therapy or forced expiratory volume in 1 s of <20% and either a diffusion capacity of the lung for carbon monoxide of <20% or homogeneous distribution of emphysema. All donor lungs were O₂ challenged and checked for parenchymal infiltration, with the quality of the lung being assessed by the procurement surgeon. Assessing the quality of the lungs is a standard part of the protocol at our institution. Lungs were not deemed marginal in the study and were not supported by the ex vivo perfusion technique. Selection of the type of transplant was primarily dependent on the preference of the surgeon, although BLT was indicated based on infectious disease status (such as cystic fibrosis and bronchiectasis), morbidities (such as severe pulmonary hypertension with pulmonary artery pressure > 35 mmHg) and the size-match standpoint. Thus, if a patient were found to have significant comorbidities along with an age over 70 years, the surgeon might decide that the patient would not be a good candidate for a BLT.

The patient was evaluated before extubation and before leaving the hospital to assess the viability of the airways and the anastomosis. Patients were continually evaluated at ∼2, 4, 6 and 12 months. Routine pulmonary function tests were also performed on all patients before discharge. These tests were repeated approximately every month. Complications were not based on any universal grading system but were recorded if they were deemed severe by our thoracic department. Interventions included stents, balloon dilatation and ablation of granulation tissue. Patients with airway complications were followed up with greater frequency as deemed necessary.

Survival outcomes were assessed using Kaplan–Meier survival curves with log-rank tests to assess significance at 1, 3 and 5 years post-transplant by transplant type. Three survival analyses were performed using 1-, 3- and 5-year survival data. A log-rank test was performed on each of these models. Three additional Kaplan–Meier curves were also made to examine survival variance by age. The first curve compared the survival of both transplant types by recipient age (≤65 vs >65). The second curve examined recipient survival within the ≤65 cohort, and the third curve examined recipient survival within the >65 cohort.

We also chose to perform regression modelling using stratified Cox proportional hazards by transplant type to evaluate the impact of significant covariates. The hazard ratios (HRs) at years 1, 3 and 5 were independently obtained. The Cox regression model assumes that the effects of covariates on survival outcomes are not time-dependent. To test whether this assumption was met, a hierarchical regression strategy was used. First, a Cox regression was individually performed with the original set of covariates. Then, a potential time-dependent interaction with each covariate was modelled, and the change in fit between the original model and the interaction model was evaluated using a likelihood ratio test for statistical significance. If any covariate was found to be time-dependent, then the final survival model included both the original covariate and its time-dependent interaction term. This approach provides especially strong statistical evidence for derived conclusions on survival outcomes.

RESULTS

Of the 186 patients with COPD who had lung transplants whose data were collected, 71 (38.2%) had BLTs and 115 (61.8%) had SLTs. A total of 99 (53.2%) were ≤65, 96 (51.6%) were men, 154 (82.8%) were White, 31 (16.7%) were African American and 1 (0.5%) was Hispanic. Twelve (6.5%) had cardiopulmonary bypass extracorporeal support (10 patients in the BLT group and 2 in the SLT group), 3 (1.6%) had venoarterial extracorporeal membrane oxygenation, 1 (0.5%) had venovenous extracorporeal membrane oxygenation and 170 (91.4%) were off extracorporeal support. A total of 74 (93.5%) were anteroaxillary incisions, 8 (4.3%) were clamshell incisions and 4 (2.2%) were median sternotomies. Ninety-nine (53.2%) received alemtuzumab (Campath, Leverkusen, Germany) induction, and 87 (46.8%) received basiliximab (Simulect, East Hanover, NJ, USA) induction. A total of 166 (89.2%) of the donors were male.

There was no statistical significance detected in the distribution of transplant type by age (P = 0.10), induction (P = 0.20), body mass index (P = 0.90), recipient height (P = 0.42), donor sex (P = 0.10) and donor age (P = 0.99). However, recipient sex (P = 0.001), recipient race (P = 0.018), extracorporeal support (P = 0.005), surgical approach (P = 0.004), LAS (P < 0.001), LOS (P < 0.001), donor height (P = 0.026) and the ratio of donor-predicted TLC to recipient-predicted TLC (P < 0.001) showed significance in distribution for transplant type. Table 1 notes the frequencies of all categorical variables and mean ± standard deviation for numerical variables as well as the significance in distribution. Average net difference calculations for gender, height and age were all positive. For all 3 variables, the net difference was more positive for SLTs than for BLTs. The mean ± standard deviations are listed in Table 2. Overall, a total of 16 pretransplant complications and 9 post-transplant complications were reported. Pretransplant complications included multiple pneumothoraxes, venoarterial extracorporeal membrane oxygenation, lung volume reduction surgery, ventilation-dependent respiratory failure and tricuspid valve repair. Post-transplant complications included venovenous extracorporeal membrane oxygenation (n = 3), cerebrovascular accident post-transplant (n = 4) and retransplants (n = 1). Due to the small number of pre- and post-transplant complications, they were not included in the statistical analyses because there would be little statistical power behind the analyses.

Table 1:

Frequencies and descriptions of variables used in study

Category	SLT	BLT	Significance (P-value)
Total	115	71
Recipient age cohort	≤65: 59 (51.3) >65: 56 (48.7)	≤65: 40 (56.3) >65: 31 (43.7)	0.30
Recipient agea (years)	65.3 ± 5.9	63.2 ± 7.1	0.10
Recipient sex	Male: 48 (41.7)	Male: 48 (67.6)	0.001
	Female: 67 (58.3)	Female: 23 (32.4)
Recipient race	African American: 13 (11.3)	African American: 18 (25.4)	0.018
	Hispanic: 0 (0.0)	Hispanic: 1 (1.4)
	White: 102 (88.7)	White: 52 (73.2)
Recipient height (cm)	64.3 ± 3.4	66.1 ± 3.6	0.42
LOS (days)	18.4 ± 16.1 (15.0)a	25.0 ± 20.5 (19.0)a	<0.001
LASb	33.5 ± 2.6	38.3 ± 10.4	<0.001
BMIc	25.8 ± 4.5	26.2 ± 4.5	0.90
Extracorporeal support	Off: 111 (96.5)	Off: 59 (83.1)	0.005
	CPB: 2 (1.7)	CPB: 10 (14.1)
	VA ECMO: 2 (1.7)	VA ECMO: 1 (1.4)
	VV ECMO: 0 (0.0)	VV ECMO: 1 (1.4)
Approach	Anteroaxillary: 113 (98.3)	Anteroaxillary: 61 (85.9)	0.004
	Mediastinal sternotomy: 1 (0.9)	Mediastinal sternotomy: 3 (4.2)
	Clamshell: 1 (0.9)	Clamshell: 7 (9.9)
Induction	Alemtuzumab: 57 (49.6)	Alemtuzumab: 42 (59.2)	0.20
	Basiliximab: 58 (50.4)	Basiliximab: 29 (40.8)
Donor agea (cm)	36.4 ± 12.8	36.3 ± 11.8	0.99
Donor sex (years)	Male: 106 (92.2)	Male: 60 (84.5)	0.10
	Female: 9 (7.8)	Female: 11 (15.5)
Donor heighta	70.7 ± 3.4	69.2 ± 3.7	0.026
Donor-predicted TLC/recipient-predicted TLC	1.35 ± 0.2	1.14 ± 0.1	<0.001

^aData are expressed as the mean ± standard deviation (median).

^bThe LAS (range 0–100) is based on risk factors associated with either wait-list or post-transplantation mortality. A higher score implies a higher-acuity patient who would benefit from a lung transplant; patients with higher scores are given preference for organs.

^cCalculated as weight in kilograms divided by height in metres squared.

BMI: body mass index; CPB: cardiopulmonary bypass; BLT: bilateral lung transplantation; LAS: lung allocation score; LOS: length of hospital stay; SLT: single lung transplantation; TLC: total lung capacity; VA ECMO: venoarterial extracorporeal membrane oxygenation; VV ECMO: venovenous extracorporeal membrane oxygenation.

Table 2:

Net differences (donor–recipient) of sex, height and age

Characteristics	SLT	BLT	Significance
Sex	0.50	0.17	P < 0.001
Height (cm)	6.35 ± 2.92	3.10 ± 3.19	P < 0.001
Age (years)	−28.85 ± 14.89	−26.93 ± 13.64	P = 0.35

BLT: bilateral lung transplantation; SLT: single lung transplantation.

The Kaplan–Meier survival curve by transplant type (Fig. 1) did not show statistical significance at 1 year (P = 0.65), 3 years (P = 0.91) and 5 years (P = 0.87). Another Kaplan–Meier survival curve comparing ≤65 and >65 cohorts (Fig. 2) also showed no statistical significance (P = 0.72). Finally, Kaplan–Meier survival curves examining transplant type within each age cohort (Fig. 3: ≤65 and Fig. 4: >65) had no statistical significance (≤65: P = 0.89; >65: P = 0.95). The Cox proportional hazards regression model created to assess the impact of significant covariates on transplant type using a log-rank test showed no significance in survival outcomes at 5 years (P = 0.84). The covariates assessed included recipient height, recipient sex, recipient race, LAS, LOS, extracorporeal support, approach, induction and donor height. All covariates were time-independent. The Cox model itself did not show a statistically significant improvement in evaluating survival outcomes when compared to its related Kaplan–Meier curve when evaluated by the χ² Omnibus Tests of Model Coefficients (P = 0.13), and no individual covariate had a significant effect on survival outcomes. The HRs at 1, 3 and 5 years for each covariate are listed in Table 3, as well as the significance of each covariate.

Figure 1:

KM curve showing no survival differences in transplant types compared for significance (P < 0.05) between the groups. Patients with a bilateral lung transplantation had a median survival of 4.11 years, with 56 alive 5 years post-transplant patients. Patients with a single lung transplantation had a median survival of 4.05 years, with 95 alive at 5 years post-transplant. COPD: chronic obstructive pulmonary disease; KM: Kaplan–Meier.

Figure 2:

KM curve showing no survival differences in cohort age compared for significance (P < 0.05) between the groups. A total of ≤65 patients had a median survival of 4.15 years, with 81 alive at 5 years post-transplant; >65 patients had a median survival of 4.11 years, with 70 alive at 5 years post-transplant. COPD: chronic obstructive pulmonary disease; KM: Kaplan–Meier.

Figure 3:

KM curve showing no survival differences in transplant types compared for significance (P < 0.05) in recipients at or under 65 years. Patients with a single lung transplantation had a median survival of 4.18 years, with 49 alive at 5 years post-transplant. Patients with a bilateral lung transplantation had a median survival of 4.18 years, with 32 alive at 5 years post-transplant. COPD: chronic obstructive pulmonary disease; KM: Kaplan–Meier.

Figure 4:

KM curve showing no survival differences in transplant types compared for significance (P < 0.05) in recipients over 65 years. Patients with a single lung transplantation had a median survival of 3.25 years, with 46 alive at 5 years post-transplant. Patients with a bilateral lung transplant had a median survival of 4.02 years, with 24 alive at 5 years post-transplant. COPD: chronic obstructive pulmonary disease; KM: Kaplan–Meier.

Table 3:

Hazard ratios of variables used in Cox regression

Covariate	1-Year hazard ratio	Sig.	3-Year hazard ratio	Sig.	5-Year hazard ratio	Sig.
Recipient sex (female vs male)	2.368	0.167	1.593	0.328	1.455	0.43
Recipient race (African American vs White)	1.040	0.912	0.616	0.130	0.643	0.24
Recipient height (cm)	0.932	0.407	0.953	0.486	0.983	0.81
LOS (days)	0.988	0.569	0.999	0.955	0.998	0.86
LASa	0.912	0.311	0.949	0.167	0.954	0.21
Extracorporeal support (off vs all other)	1.557	0.620	1.684	0.371	2.156	0.14
Approach (anteroaxillary vs all other)	1.260	0.797	0.526	0.451	0.579	0.53
Induction (alemtuzumab vs basiliximab)	1.566	0.361	1.582	0.208	1.499	0.26
Donor height	0.924	0.407	0.890	0.167	0.887	0.075

^aThe LAS (range 0–100) is based on risk factors associated with either wait-list or post-transplant mortality. A higher score implies a higher-acuity patient who would benefit from a lung transplant, and patients with higher scores are given preference for organs.

LAS: lung allocation score; LOS: length of hospital stay; Sig.: significance.

DISCUSSION

Our results indicate that there is no significant survival benefit to a BLT in patients with end-stage COPD regardless of patient age (≤65 vs >65). There was also no significant survival difference between the 2 age groups in recipients of an SLT. Furthermore, patients who had an SLT had a significantly shorter LOS (15 vs 19 days) in the hospital, which may have been associated with fewer perioperative deaths. These findings support the surprising idea that we should consider pursuing SLT instead of BLT in younger patients. Part of this result may also be due to the fact that the sizes of the lungs being received in an SLT may be larger than the lungs being received in a double lung transplant as indicated by the donor height as well as by the ratio of the donor’s predicted TLC/recipient’s predicted TLC, both being higher in the SLT group.

The notion of using SLT in young patients has long been met with apprehension due to the increased risk of early ventilation/perfusion mismatch and the risk of hyperinflation in the non-transplanted native lung [10]. Our results contradicted findings in the International Society for Heart and Lung Transplantation registry, which found post-transplant survivability to be significantly higher with a BLT (7 years) than with an SLT (5 years) between January 1995 and June 2018 [11]. These results may be prone to treatment selection bias and combined data from patients prior to LAS algorithm implementation, which may explain why our results differ. We did not find any significant differences in post-transplant survival between patients in our cohort with BLT and SLT.

The results of our study were more in accordance with findings in recent studies of lung transplants in patients with COPD. Schaffer et al. [6] analysed the United Network of Organ Sharing (UNOS) thoracic registry and initially found median survival in patients with end-stage COPD to be 58.6 months after an SLT and 69.3 months after a BLT in an unadjusted analysis. After adjusting for confounders with a propensity score-based inverse probability of treatment weighting estimator, there was no significant survival advantage between the SLT (64.0 months) and the BLT (67.7) groups (log-rank P = 0.23). However, the study was limited by missing data that required multiple imputations that could introduce residual bias. Similarly, Bennett et al. [12] analysed patients in a single institution and found comparable survival at 5 years between SLT (53%) and BLT (57%, log-rank P = 0.75). The study further compared their single-institution outcomes with those in the UNOS registry and found 46% survival probability at 5 years after SLT and 56% after BLT (log-rank P < 0.0001) [12]. After adjusting for covariates in a Cox proportional hazards model, they did not observe an increased hazard for death between patients from the single institution who had an SLT versus patients from the UNOS registry who had a BLT. Benvenuto et al. [13] recently expanded on the results of Schaffer et al. by having a larger study size and longer study follow-up and were unable to reproduce similar results when they adhered to the parameters of their study. Instead, Benvenuto et al. [13] found that patients who received a right-lung transplant had survival outcomes to similar those of patients who received BLTs. Although our study did not analyse the difference in survival outcomes between right-lung and left-lung transplants, we similarly found SLTs to have non-inferior outcomes relative to BLTs.

Contrary to the results of these studies and our centre’s results, Crawford et al. [5] found that the 5-year survival probability was significantly worse in patients with an SLT (51%) than in those with a BLT (59%, log-rank P < 0.001). Even so, in the Cox proportional hazards model, a BLT was not associated with an increased hazard of mortality in the 1-year (HR = 0.89; P = 0.36) and 3-year (HR = 0.90; P = 0.16) mortality models. At 5 years, although a BLT was associated with a decreased hazard of mortality (HR = 0.88), there was only a mild statistical significance (P = 0.04). The authors acknowledged that the study may be underpowered because the HR of BLT to SLT at 5 years did not meet their effect size determination. Not only did our study not find any decreased hazard of mortality with a BLT, but we also had significantly higher 5-year survival probabilities than the previously mentioned studies (BLT: 77.1% vs SLT: 71.6%; P = 0.87). This finding also contrasts with that from the UNOS registry, which found the 5-year survival probability in the BLT group to be 60.8% and 50.43% in the SLT group [11].

The present study also demonstrated no survival benefit of BLT in patients younger than 65 years. This outcome appears to be a novel finding that other studies did not share. An older study from Meyer et al. [3] recommended SLT for older recipients with COPD who have poorer expected post-lung transplant survival. However, this study comes from a pre-LAS era, and its findings may no longer be as applicable to modern transplant recipients. Recent studies such as Schaffer et al. [6] cite Meyer et al. to recommend SLT in older patients. In the post-LAS era, Crawford et al. [5] found that older recipient age was associated with an independent increase in the hazard of mortality (HR = 1.03; P < 0.001) in patients with COPD. These findings may be confounded due to some selection bias in the SLT group because they have stated that the group tended to be older (62 vs 60 years) with worse LAS (33 vs 34, rank-sum P < 0.01) [5]. Although our study had a similar SLT group that tended to be older (65 vs 64 years) with worse LAS (33.5 vs 38.3, rank-sum P < 0.0001), we did not see worse survival outcomes in these patients relative to the BLT group in either age group (≤65 vs >65). Crawford et al. [5] was one of few groups who analysed the association between older recipient age and transplant type. The number of studies that delve into the differences in survival outcomes between transplant types stratified by age has been limited since the implementation of the LAS algorithm.

More broadly, Biswas Roy et al. [14] analysed all patients in the UNOS registry receiving lung transplants. When they focused on post-LAS era patients, they found that BLT did not significantly affect the 3-year survival probability of patients in the UNOS registry aged 65–69 (63% vs 57%; P = 0.059), 70–74 (57% vs 49%; P = 0.079) and 75–79 groups (26% vs 45%; P = 0.14) but did affect patients aged below 65 (68% vs 64%; P < 0.0001). The fact that the study results were not specific to any particular diagnosis limits the applicability of the results to other studies because each diagnosis can have different results.

This study of COPD lung transplant outcomes had several inherent limitations of a retrospective review. First, although we are a very high-volume transplant centre, implicit in a single-centre design is a limitation of sample size that can introduce variability that may be difficult to control for. The study was also limited in its ability to control for survival confounders such as socioeconomic status, which were not captured at our centre. In general, we treat an underserved urban population. Furthermore, our major outcome parameter to compare the study group was overall survival, and so outcomes such as primary graft dysfunction, time to chronic lung allograft dysfunction, chronic lung allograft dysfunction-free survival, exercise capacity, pulmonary function and quality of life were not included in this study. Neither were calculations of predicted TLC included. Finally, due to the retrospective nature of the study, it is difficult to know why a surgical decision was made because the circumstances as to why the decision was made to perform an SLT are difficult to analyse. And the fact that the decision to perform SLT versus BLT was surgeon dependent introduces bias. However, our results may be helpful, potentially more so than the gross UNOS findings, in identifying potential breakthrough changes to the status quo with the unique conditions, techniques and surgeons at our centre.

We traditionally have had to make the philosophical decision, well described by Yusen et al. [1], of offering BLT with better palliation to fewer patients or SLT with poorer survival to a greater number of patients. Our results suggest this way of thinking may be outdated, because there may not necessarily be a survival benefit to BLT, and if there is, it may not functionally warrant halving our potential recipient pool. With more studies finding worse survival outcomes for patients on wait lists than for patients receiving SLT, there may be some validity to SLT as a procedure choice in the post-LAS era [19]. Our results may warrant a paradigm shift and require further investigation into the consideration of SLT in younger patients.

Our multivariable analysis did not show statistically significant improvement in survival outcomes in any variable. This finding is also in contrast with the results of the other previously mentioned studies. Schaffer et al. [6] had a substantial number of variables that were associated with lower post-transplant survival, such as recipient age. The absence of any statistically significant variable in our multivariable analysis and overall strong survival may be a result of modern transplant technology and of surgical techniques used at our institution. Alongside surgeon skill, we believe that careful donor selection may have played a role in our unusual recipient survival outcomes. Many studies have shown that an oversized allograft is associated with improved survival after a lung transplant [15]. Studies show that larger lungs are closely associated with greater height [16]. Men also tend to have larger lungs (10–12%) than women of the same age and height [17]. Finally, some studies suggest that younger donors may lead to improved recipient survival in many instances [18]. As indicated in Table 2, a much greater proportion of single rather than BLTs were male to female. The average net difference in height of recipients of SLTs was more than twice as great as that for recipients of BLTs, and the net difference in age also slightly favoured SLTs. We hypothesize that these differences may have contributed to the improved survival outcomes of our patients receiving SLTs.

Conflict of interest: none declared.

Author contributions

Sudeep Mutyala: Data curation; Formal analysis; Investigation; Software; Writing—original draft; Writing—review & editing. M. Abul Kashem: Conceptualization; Project administration; Supervision; Validation. Jay Kanaparthi: Investigation; Writing—original draft; Writing—review & editing. Gengo Sunagawa: Investigation; Methodology. Manish Suryapalam: Data curation; Formal analysis; Writing—original draft. Eros Leotta: Investigation; Methodology. Kenji Minakata: Investigation; Methodology. Stacey Brann: Investigation; Methodology. Norihisa Shigemura: Investigation; Methodology. Yoshiya Toyoda: Conceptualization; Investigation; Methodology; Supervision; Validation.

Reviewer information

Interactive CardioVascular and Thoracic Surgery thanks Mohammad Behgam Shadmehr, Milton Saute and the other, anonymous reviewer(s) for their contribution to the peer review process of this article.

ABBREVIATIONS

BLT

Bilateral lung transplantation

COPD

Chronic obstructive pulmonary disease

HR

Hazard ratio

LAS

Lung allocation score

LOS

Length of stay

SLT

Single lung transplantation

TLC

Total lung capacity

UNOS

United Network of Organ Sharing

 

Presented at the 34th Annual Meeting of the European Association for Cardio-Thoracic Surgery, Barcelona, Spain, 8–10 October 2020.