Objectives: In this study, our aim was to investigate whether bacterial culture growth from donors and recipients is related to early posttransplant complications and to analyze its role in primary graft dysfunction and posttransplant pneumonia in lung transplant recipients.
Materials and Methods: This retrospective cohort study included patients diagnosed with end-stage lung disease who received a lung transplant for treatment. We examined relationships between donor bronchial lavage, pretransplant recipient sputum, and recipient posttransplant serial bronchial lavage culture results, as well as the development of both primary graft dysfunction and pneumonia after lung transplant during the early posttransplant period.
Results: Our study included 77 patients with median age of 48 years (25%-75% IQR, 34-56 years) and who were mostly men (79.2%; n = 61). Donor culture positivity was 62.3% (n = 48), and the positivity of sputum culture from patients before transplant was 20.8% (n = 16). Compared with that shown in those without versus those with primary graft dysfunction, there were significantly more positive sputum cultures from patients before transplant (P = .003). Recipients with donor culture growth had a longer duration of invasive mechanical ventilation (median of 4 days
[IQR, 2-13 days] vs 1 day [IQR, 1-2 days]; P = .001, respectively) than those without. Multivariate logistic analysis identified both donor culture positivity (odds ratio: 3.391; 95% CI, 1.12-20.46; P = .0028) and sputum culture positivity in pretransplant recipient candidates (odds ratio: 6.494; 95% CI, 1.80-36.27; P = .004) as independent predictors of primary graft dysfunction.
Conclusions: Bacterial growth shown in donor bronchial lavage and sputum culture positivity in patients before transplant were found to be independent predictors of primary graft dysfunction in the early posttransplant period. Organism growth in both the donor and the recipient during the pretransplant period are important determinants for the development of primary graft dysfunction.
Key words : Antibiotic treatment, Deceased donor, Early mortality
Lung transplantation has wide acceptance as an effective treatment in patients who have various advanced lung diseases that are refractory to medical treatments, such as obstructive lung disease (OLD), interstitial lung disease (ILD), end-stage infectious lung disease(s) (EILD), and pulmonary vascular diseases.1 Although median survival of lung transplant recipients is 5.7 years with a survival rate of 79% at 1 year, which has increasingly improved over time, it still remains inferior in terms of survival outcomes compared with other solid-organ transplants.2,3 Lung transplantation has a critical process that requires careful perioperative management in terms of preventing the development of serious and even fatal complications during the posttransplant phase. Although improvements in patient management in the perioperative period have resulted in decreased complications and early mortality over the years, primary graft dysfunction (PGD) and post-lung transplant pneumonia (PLTP) are still major causes that are responsible for early mortality after transplant.4,5
Primary graft dysfunction is an acute allograft injury with pulmonary endothelial damage, which is caused by ischemia or reperfusion injury. It is characterized by diffuse parenchymal infiltrates within 72 hours after transplant in the absence of secondary causes, such as cardiogenic pulmonary edema, infection, pulmonary venous anastomotic obstruction, or hyperacute rejection.6 It is seen in 11.8% of transplant recipients and has an early mortality rate of over 50%.7 Several factors for increased risk of PGD are related to both the donor and recipient, including age, smoking history, prolonged mechanical ventilation, trauma, aspiration pneumonia, and donor hemodynamic instability.7,8
Bacterial pneumonia is one of the most frequently encountered complications, with a rate of 82.7% during the early posttransplant period, and it is a major cause of early mortality. The most commonly seen microorganism in lung transplant recipients is Pseudomonas aeruginosa (24.6%).9 Patients may present with this microorganism for various reasons such as by passive transfer of bacterial organisms from the donor or due to the factors related to the recipient, including immunosuppression, prolonged mechanical ventilation, and impaired mucociliary clearance.1 The recognition and preventive approaches for these complications are critical for a successful outcome.
There are no strict protocols in place regarding the rejection of a donor as a result of growth of bacterial microorganisms detected in results from microbi-ological samples taken from the donor. In fact, this situation may vary from center to center. The same is true for recipient bacterial microorganism results. In addition, data are limited on the utility of microorganism growth results from donor or recipient candidate airways to assess transplant suitability. From the early lung transplant era, culture examinations from donor airways have been used to identify donors with occult bacterial growth. Fiberoptic bronchoscopy to obtain bronchoalveolar lavage (BAL) specimens is a critical tool for evaluating airway injury and for sampling to identify culture growth in donors and recipients.10 However, data from previous studies that have analyzed the relationship between bacterial growth (from airways of donors or recipients) during the pretransplant period versus patient outcomes in the early posttransplant period have been so far inconsistent and unclear.6,10,11
In this study, we aimed to investigate whether the presence of bacterial culture growth in samples from donors and recipients is related to complications observed during the early posttransplant period and to identify whether bacterial growth has a role in the development of PGD and PTLP in lung transplant recipients.
Materials and Methods
We evaluated 77 patients with end-stage lung disease who underwent transplant in our clinic between December 1, 2016, and April 1, 2021. The study was ap-proved by the local ethics committee. Ethical approval was in accordance with the Declaration of Helsinki.
We reviewed medical records to identify clinical characteristics and posttransplant outcomes of donors and recipients. Respiratory samples of donors and recipients, cultures before and after transplant, lavage cultures obtained by the bronchoscopic method, and the presence of bacteria up to 1 month after transplant were assessed.
Definition of post-lung transplant pneumonia and primary graft dysfunction
Recipients who developed pneumonia within the first 30 days after lung transplant were included in the PLTP group. Post-lung transplant pneumonia was diagnosed according to the Centers for Disease Control and Prevention criteria for hospital-acquired pneumonia on the basis of clinical and laboratory indexes of respiratory tract infections (productive airway secretion, fever, leukocytosis/leukopenia, and growth in medium) and supported by abnormal findings observed in chest radiography results.12 The risk factors for the development of PLTP were analyzed by comparing the clinical features between patients with and without PLTP. In 2005, the International Society for Heart and Lung Transplantation standardized the definition of PGD, with PGD determined according to ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2) and when diffuse parenchymal infiltrates are present in the allograft on chest radiography in the first 72 hours posttransplant.13 In this study, we did not compare or evaluate the demographic and clinical parameters between patients with and without PGD.
Selection of recipients and donors
The first consensus report on the patient selection criteria was published by the International Society for Heart and Lung Transplantation in 1998; it was renewed intermittently with increases in experience over time and has been updated. The donors included in our study were accepted according to the current criteria, which included review of the following features: donor lungs, age, sex, cause of death, duration of mechanical ventilation, arterial blood gas values, radiographic changes, ABO mismatch, and organ size match.14
All donors included in the study had PaO2/FiO2 ratios greater than 300 mm Hg (positive end-expiratory pressure of 5 cmH2O) and normal or close to normal chest radiographs. All bronchoscopy evaluations performed before retrieval of lungs from donors revealed absent airway secretions. At the time of organ procurement, all donors were younger than 55 years old; for donors with smoking history, it was checked that the number of years of smoking was less than 20 years. There are definite rules in place for donor acceptance. Therefore, all donors included in the study were determined to be in compliance with these rules and protocols. None of the donors had signs of chest trauma or previous heart-lung surgery. Furthermore, none of the donors had past signs of aspiration/sepsis.15
Before organ acceptance, the donor’s medical history, physical examination, radiology, and bronchoscopy findings are evaluated in detail by the procurement team. Thus, our transplant team, consisting of pulmonologists, infectious disease specialists, and thoracic surgeons, has sufficient information to make a decision about the donor’s condition. Bronchial lavage samples and bronchial swab and blood cultures are also obtained to identify any infection in the donor.
Patients listed for lung transplant had inter-mittent control sampling of sputum. In this manner, optimal antibiotic agents were selected according to the sputum culture status. Sputum cultures in patient samples before transplant were taken after the donor was accepted, with the patient taken to our intensive care unit (ICU) and a sputum sample obtained. All identified organisms were defined as either recipient- or donor-derived bacteria.
It is essential that patient selection is according to not only the criteria specified in international guidelines but also according to national and local epidemiological data, such as the number of patients on the wait list in the centers and donor presentation.
Pre- and posttransplant management with antibiotics and immunosuppression
Recipients received a standard triple-drug immuno-suppressive regimen consisting of a calcineurin inhibitor (tacrolimus), a cell cycle inhibitor (mycophenolate mofetil), and steroids.16 The target tacrolimus through level was set at 12 to 15 μg/L in the first 6 months after lung transplant, according to the protocol in our transplant unit.
Pretransplant screening of sputum, urine, blood and axillary, and inguinal and rectal swab samples from recipient candidates is routinely performed in our center. The same screening methods are repeated on the day of transplant. At the time of organ procurement, BAL and bronchial swab screening cultures from donor bronchoscopy are also collected. These findings were obtained from patient records and the hospital’s electronic database. Micro-biological typing and antibiogram were obtained by the VITEK 2 automated system. Multiresistance and pan-resistance characteristics of microbiological strains were recorded per the use of previous definitions.17
Donor screening results are available within 24 hours after transplant. We routinely administer broad-spectrum antibiotic therapy (meropenem + fosfomycin + inhaled gentamycin + vancomycin) for 10 to 14 days whether susceptible microorganisms are detected or whether culture results are negative.
Data were analyzed using IBM SPSS Statistics for Windows version 23.0.18 Descriptive statistics were used to illustrate the demographic and clinical characteristics of the patients. Nonparametric variables are presented as medians and 25% to 75% interquartile ranges (IQR), and parametric variables are presented as means ± standard deviations. In addition, Kruskal-Wallis analysis was used because the underlying diseases of OLD, ILD, and EILD comprised more than 2 independent groups. The chi-square test was used to compare categorical variables such as comparisons between PGD and non-PGD or PLTP and non-PLTP. To better understand the development of PGD, an algorithm was used to analyze parameters first in the univariant regression model and to determine the P < .25 as the candidate variable. Variables that were significant at P < .25 were selected as variables for multiple logistic regression. For the multivariable logistic regression model, 4 candidate predictors were chosen, in which outcomes were present in 21 patients (21/4 = 5.2). Therefore, we preferred to use the penalized multivariable logistic regression method to reduce the overfitting risk.19 The results of the final logistic regression models are presented as odds ratio (OR), 95% confidence interval (95% CI), and P values. Statistical significance was at P < .05.
In a total of 77 patients, the median age was 48 years (IQR, 34-56 years) and 79.2% (n = 61) of the patients were male. Donor culture positivity was 62.3%
(n = 48), and sputum culture positivity in recipient candidates before transplant was 20.8% (n = 16). Culture positivity from BAL was 42.9% (n = 33) at days 1 to 3, 24.7% (n = 19) at day 7, 32.5% (n = 25) at day 14, and 22.1% (n = 17) at month 1 posttransplant. Among total recipients in the study, 21 patients (27.3%) had PGD and 22 patients (28.6%) had PTLP.
When we analyzed patients by disease group, 41.6% (n = 32) were in the ILD group, 35.1% (n = 27) were in the EILD group, and 20.8% (n = 16) were in the OLD group. Two patients (2.6%) had other underlying lung diseases (1 had idiopathic pulmonary arterial hypertension and 1 had lung malignancy).
In our comparison of underlying lung disease groups, patients with idiopathic pulmonary arterial hypertension and malignancy (n = 2) were not included in the analysis because of insufficient sample size. Compared with the other groups, there were significantly more younger patients (P = .003) and more female patients (P = .003) in the EILD group. There were fewer patients with sputum culture positivity pretransplant (P = .025) and fewer patients with day 7 BAL culture positivity (P = .046) in the ILD group compared with the other groups. As shown in (Table 1), other demographic, clinical, and culture results were similar between the groups.
Culture positivity results are shown in (Figure 1). As shown in (Table 2), the most common bacterial species were methicillin-susceptible Staphylococcus aureus in BAL from donors (n = 13; 16.9%) and in day 1 to 3 posttransplant BAL in recipients (n = 8; 10.4%). Pseudomonas putida from sputum of recipient candidates pretransplant (n = 9; 11.7%), Acinetobacter baumannii from BAL at day 7 posttransplant (n = 8, 10.4%), Klebsiella pneumoniae from BAL at day 14 posttransplant (n = 11, 14.3%), and Pseudomonas aeruginosa from BAL at month 1 posttransplant (n = 7, 9.1%) were the most detected microorganisms.
In pretransplant recipient candidates, we observed no significant differences when we compared donor culture positivity versus sputum culture positivity pretransplant. Furthermore, there were no differences observed regarding culture positivity of the serial BAL and the presence of PGD between patients with and without PTLP. These results are shown in (Table 3).
In comparison with patients without PGD, sputum culture positivity in the pretransplant recipient candidates was significantly more frequent in patients with PGD (P = .003). There were no differences in patients with and without PGD with regard to culture positivity results in donor BAL samples or in recipient day 1 to 3 posttransplant BAL samples (Table 4).
Patients with donor culture growth had longer duration of invasive mechanical ventilation (median 4 days [IQR, 2-13 days] vs 1 day [IQR, 1-2 days]) than those without donor culture growth (P = .001). The length of hospital stay (median 19 days [IQR, 9-31 days] vs 21 days [IQR, 14-36 days]) and the length of ICU stay (median 6 days [IQR, 3-16 days] vs 4 days [3-9 days]) were similar in patients with and without donor culture growth (P > .05). The duration of invasive mechanical ventilation, length of hospital stay, and length of ICU stay were similar in patients with or without sputum culture positivity in samples from pretransplant recipient candidates (P > .05).
In the logistic regression analysis, univariate predictors were donor culture positivity, sputum culture positivity in pretransplant recipient candidates, and patients with ILD and EILD. Multivariate analyses identified both donor culture positivity (OR, 3.931; 95% CI, 1.146-17.654; P = .028) and sputum culture positivity in pretransplant samples from recipient candidates (OR, 6.494; 95% CI, 1.147-29.645; P = .004) as independent predictors of PGD (Table 5).
In this study, our primary finding was the observation that bacterial culture positivity in sputum samples taken before transplant was associated with PGD development in transplant recipients. However, we also observed that the bacterial culture growth was not associated with PTLP development in these patients. In addition, positive bacterial culture results shown in donors and positive sputum results from pretransplant recipient candidates were independent predictors for the development of PGD in the early posttransplant period. Furthermore, we found that culture growth in consecutive airway samples from recipients and donors was not related to PTLP.
In the first years after the introduction of lung transplant, donor-derived microorganisms were shown to be associated with posttransplant pneumonia in recipients.11 However, more recent findings have revealed that bacterial culture positivity in BAL samples from donors did not predict the development of early postoperative pneumonia under prophylactic antibiotic coverage in donors and recipients, similar to the results of our study.10 The upper airways of the intubated and mechanically ventilated donors are predisposed to contamination. Therefore, there are reports that positive cultures from donor BAL can identify pneumonia better, as it can provide information about the microorganisms colonizing the donor’s lower respiratory tract, unlike tracheal aspirates obtained from the upper airway.20,21
Because samples from donors were obtained from BAL in our study, the microbiological status of donors may not sufficiently reflect the lung parenchyma. However, in general, there was minimized constraint of upper airway contamination.
The donor is under the risk of lung injury due to trauma, aspiration, mechanical ventilation, infection, and the process of brain death. Brain death causes a systemic inflammatory response with an increase in cytokines.22 In an in vitro study, bacterial growth was enhanced by the presence of high concentrations of cytokines.23 Bacteria can damage the donor lung, which aggravates the ischemia/reperfusion time, and this may cause adverse outcomes such as premature graft dysfunction in the recipient.10 Previous studies that have investigated the effects of culture growth on early posttransplant PGD are limited in number. In addition, the reported results for PGD and other early adverse events are inconsistent. A study by Avlonitis and associates demonstrated that the presence of bacteria in donor lungs was associated with increased acute rejection, prolonged mechanical ventilation, and length of ICU stay.20 On the other hand, Ahmad and colleagues reported that bacterial growth in donor BAL was associated with prolonged mechanical ventilation but not with PGD in recipients.6 Weill and colleagues suggested that culture positivity did not affect oxygenation or the duration of mechanical ventilation.10
In our study, we found that culture growth shown in the donor’s BAL and positive sputum results from recipient candidates before transplant were predictors of the occurrence of PGD after transplant. Similar to previous reports, our results demonstrated that donor culture growth associated with a 3.931-fold increased risk and growth in sputum from pretransplant candidates was associated with a 6.494-fold increased risk in the occurrence of PGD. In our center, the recipient is routinely given prophylactic broad-spectrum antibiotic treatment before transplant, and this treatment is arranged after transplant according to the donors’ culture results, with length of treatment modified according to the subsequent culture results. However, despite prophylactic antibiotic coverage, we observed a greater incidence of posttransplant PGD in patients who had growth in donor lavage and growth in sputum in pretransplant samples. These results indicate the need to optimize the approach of prophylactic antibiotic treatment, and we suggest that patients in the ICU who are potential donors may need antibiotic treatment to be started as soon as possible. In other words, if a deceased patient is identified as a donor, then antibiotics should be started quickly according to the microorganism detected. The same situation may indicate the necessity of early antibiotic treatment according to the culture samples taken from the recipient.
According to the microorganism culture samples detected in the donor after brain death, the early initiation of antibiotic therapy may prevent the development of PGD in recipients. Similar to previous studies, we found that patients with a positive donor culture needed a significantly longer mechanic ventilation period.6,20
Posttransplant serial BAL culture results from recipients did not differ in terms of either PGD or PTLP occurrence. As expected, we found more bacterial growth in the pretransplant sputum and in day 7 samples from transplant recipients with infectious end-stage lung disease compared with other underlying disease groups.
One of the important limitations of our study was the preference in sampling bronchial specimens from donors and sputum from recipient candidates before transplant instead of BAL sampling.
Our lung transplant department is one of the 2 main centers in our country. However, the small number of transplants led to a limited number of patients, which limited our analyses.
Growth in bacterial culture from BAL obtained from the donor and growth in bacterial culture from sputum obtained from recipient candidates before transplant were independent predictors for the occurrence of PGD in recipients during the early posttransplant period. Our study pointed out the determinative importance of organism growth in the donor and recipient before transplant for the development of graft dysfunction in the early period posttransplant. Our study suggests the need to optimize the approach of antibiotherapy prophylaxis. Considering our results, we suggest that starting an antibiotic treatment without delay (that is, at brain death and/or at donor identification) according to the culture samples may prevent the development of PGD in the recipient.
Volume : 20
Issue : 10
Pages : 930 - 936
DOI : 10.6002/ect.2021.0496
From the Kartal Kosuyolu Training and Research Hospital, Department of Lung Transplantation, Istanbul, Turkey
Acknowledgements: The authors have not received any funding or grants in support of the presented research or for the preparation of this work and have no declarations of potential conflicts of interest.
Corresponding author: Pinar Atagun Guney, Kartal Kosuyolu Training and Research Hospital, Department of Lung Transplantation, Istanbul, Turkey
Phone: +90 216 421 4200, +90 5359674490
Figure 1. Alluvial Plot Demonstrating Changes in Culture Positivity Over Time
Table 1. Demographic and Clinical Parameters of Study Patients
Table 2. Microorganisms Shown in Donors and Recipients
Table 3. Comparison of Culture Results and Incidence of Graft Failure in Patients With and Without Post-Lung Transplant Pneumonia
Table 4. Comparison of Culture Results in Patients With and WithoutPrimary Graft Dysfunction
Table 5. Logistic Regression Analysis for Primary Graft Dysfunction