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Eur J Cardiothorac Surg 2007;31:75-82. doi:10.1016/j.ejcts.2006.10.024
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved
a Department of Pathology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
b Division of Lung Transplantation, The Heart Centre, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
c Department of Thoracic Anesthesiology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
d Department of Thoracic Surgery, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
e Department of Clinical Physiology and Nuclear Medicine, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
Received 15 August 2006; received in revised form 18 October 2006; accepted 23 October 2006.
* Corresponding author. Address: Hjertecentret 2141, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark. Tel.: +45 35 45 29 06; fax: +45 35 45 26 48. (Email: cmburton{at}doctors.net.uk).
| Abstract |
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Key Words: Lung transplantation Primary graft dysfunction Diffuse alveolar damage Bronchiolitis obliterans organizing pneumonia Acute cellular rejection Bronchiolitis obliterans syndrome
| 1. Introduction |
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To co-ordinate future research and facilitate the exchange of data, the International Society of Heart and Lung Transplantation (ISHLT) Working Group on Primary Lung Graft Dysfunction has recently defined and graded reperfusion edema as primary graft dysfunction (PGD) based on radiological appearances and the PaO2:FiO2 ratio [8]. Although ARDS is manifest as a pattern of diffuse alveolar damage (DAD) histologically, the ISHLT consensus report does not incorporate histological findings into the definition.
The objectives of the present study were to describe the outcome of these patients in relation to survival, long-term lung function, and histological findings.
| 2. Materials and methods |
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12), body temperature >36 °C, stable hemodynamic condition without inotropic medication, PaO2 >10 kPa, PaCO2 <8 kPa, FiO2 <40%, and acceptable post-operative hemorrhage [10]. All transplanted patients received induction therapy with either antithymocyte globulin (ATG) or daclizumab (an IgG1 monoclonal antibody for interleukin-2 receptor). Thereafter, patients received triple maintenance immunosuppressive therapy consisting of cyclosporine, azathioprine and prednisolone. Blood cyclosporine concentration was maintained in the range 145245 µg/l. Acute rejection (
A2) episodes were treated with intravenous methylprednisolone 1 g daily for 3 days, followed by prednisolone tapered to maintenance dose over a 3-week period.
2.3 Histological surveillance
Protocol flexible bronchoscopy surveillance with routine transbronchial biopsy (TBB) and broncho-alveolar lavage (BAL) was performed in all patients at 2, 4, 6, 12, 26, 52, 78 and 104 weeks. Three biopsies consisting predominantly of alveolar tissue were considered sufficient for histological evaluation, but in most cases at least five biopsies were obtained. Histological grading of all allograft material with respect to acute cellular infiltrate, lymphocytic bronchiolitis, bronchiolitis obliterans, and vasculitis was performed by a single pathologist according to the standard criteria [11]. The presence of additional inflammatory interstitial patterns such as DAD, bronchiolitis obliterans organizing pneumonia (BOOP), and interstitial pneumonitis were also noted [12]. Patients with histological evidence of diffuse alveolar damage, bronchiolitis obliterans organizing pneumonia, or obstructive pneumonitis were re-classified as a single group with histological features of organizing pneumonia.
2.4 Statistical analysis
For the analysis of histological data, the time from transplantation for all transbronchial biopsies was calculated for each patient. These calculated time intervals were subsequently grouped together according to the closest of the scheduled surveillance windows (for example, if a patient had biopsies taken at 3.5 and 4.9 weeks, both biopsies would be grouped in the 4 weeks surveillance window). If, as in the aforementioned example, two or more transbronchial biopsies were performed within the same surveillance window, the most severe histological grade of acute cellular rejection was recorded for analysis.
Forced expiratory volume in 1 s (FEV1) values obtained within the 3 months prior to death were excluded from calculation of the BOS grade. The BOS grade was otherwise calculated in accordance with the criteria proposed by Estenne et al. [13]. FEV1 and forced vital capacity (FVC) values were presented as percent predicted which were calculated using formulas published by the European Respiratory Society [14].
Data analyses were performed using Statistical Analysis Software (SAS®) version 9.1 and Statistical Package for the Social Sciences (SPSS®) 11.2. Continuous data are described as mean ± standard deviation (±SD) or median and quartiles for normal and skewed distributions, respectively. Two group comparisons were performed by Student's t-test or MannWhitney test, as appropriate. Comparisons between categorical data were performed by Chi square test. Holm's correction method was employed for multiple pair-wise comparisons. Survival data was assessed by KaplanMeier method, and group comparisons were made by log rank test. Hazard ratios (HR) are given with 5% and 95% confidence intervals (CI).
| 3. Results |
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PGD as defined by the presence of diffuse radiological infiltrate was recorded in 63% (n = 113) patients (Table 1 ). Inter-observer and intra-observer kappa coefficients for the presence or absence of infiltrates were 0.51 and 0.72, respectively. The inter-observer weighted kappa coefficient for the sub-classification of patients according to the severity of infiltrate was 0.49.
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The distribution of patients with and without PGD according to recipient and donor demographic, and operative and postoperative variables is shown in Table 2 .
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Patients with PGD had a worse prognosis in terms of 90-day postoperative mortality (14% versus 3%, p = 0.03, HR = 5.0, CI 1.121.7) and 3-year survival (55% versus 77%, p = 0.003, HR = 2.5, CI 1.34.7), respectively (Fig. 2 ). There was a significant survival trend between patient subgroups according to the presence and extent of radiological infiltrate (p = 0.002), but not comparing ISHLT grades 03 according to the PaO2:FiO2 ratio (p = 0.07).
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3.3 Histology
A total of 875 post-transplant transbronchial biopsy specimens pertaining to 65 (97%) PGD and 110 (97%) PGD+ patients were available for analysis. Excluding patients with missing transbronchial biopsies, a mean number of 9 ± 3 and 8 ± 3 histological specimens were obtained from patients with and without PGD, respectively (p
= 0.5). The median number of completed transbronchial biopsy surveillance time points (maximum of 8) was 6 in the PGD group and 7 in the PGD+ group.
Fig. 4
demonstrates the cumulative proportion of patients free from acute cellular rejection (
A2), organizing pneumonia, interstitial pneumonitis, and bronchiolitis obliterans according to presence or absence of PGD. During follow-up, PGD+ patients were more likely to develop histological evidence organizing pneumonia (p
= 0.0004), comprising either DAD and/or BOOP (p
= 0.009 and p
= 0.01, respectively). The cumulative incidence of interstitial pneumonitis (which included non-specific, desquamative and unclassified types) was also higher in patients with PGD (p
= 0.02), however, the cumulative incidence of acute cellular rejection was highest in the group without PGD (p
= 0.07). The cumulative incidence of bronchiolitis obliterans was similar in both PGD groups (p
= 0.3).
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| 4. Discussion |
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Employing the new ISHLT consensus definitions, we demonstrate that patients with PGD (1) experienced a longer duration intensive care stay, an increased risk of perioperative mortality and a lower 3-year survival, (2) had a lower baseline FEV1 after lung transplantation despite no change in the rate of decline in lung function, and (3) a higher cumulative incidence of organizing pneumonia (particularly DAD) on subsequent surveillance protocol transbronchial biopsy. In addition, the study demonstrates that grading PGD in terms of the extent of radiological infiltration rather than PaO2:FiO2 ratio was sufficient in illustrating trends between the severity of PGD and the decline in baseline FEV1, the increasing cumulative incidence of organizing pneumonia (particularly DAD), and worsening patient survival.
Prior to the new ISHLT consensus definition of PGD, the reported incidence of reperfusion edema varied widely. The highest incidences of reperfusion injury were reported in series employing solely radiological definitions [15]. Other series have employed both radiographic criteria in combination with measures of oxygenation [1,3,5,7,16]. Although Christie et al. [1] reported that all patients in their 1998 cohort had histological evidence of DAD, only the study by Fisher et al. in 2002 [17], defined PGD solely on the presence of this histological finding either by TBB at 7 days or by autopsy.
As the presence of PGD is now essentially a radiological diagnosis, it is not surprising that the finding of PGD in 63% of the SLTX recipient population at this center is similar to the incidence of reperfusion edema reported by other centers using only radiographic criteria [15]. The radiological findings of isolated peri-hilar infiltrate were not classified as PGD in this study. Indeed, peri-hilar infiltrate was a common finding as has been reported previously [18], and was identified in almost all SLTX recipients. The incidence of moderate to severe radiological infiltrate in our cohort of patients (13%) is similar to the incidence of PGD as defined by more stringent criteria by King et al. [5] and Christie et al. [3]. King et al. reported an incidence of 22% in 120 patients whereby PGD was defined as a severe radiological infiltrate in association with a PaO2:FiO2 ratio <200 during the first 48 h after transplantation. Using a more stringent definition whereby the PaO2:FiO2 ratio <200 should persist beyond 48 h after transplantation; Christie et al reported an overall PGD incidence of 11.8% in their study of 255 patients.
Despite the discrepancies in the definition of reperfusion injury, there is some agreement that these patients have a prolonged requirement for ventilatory support (and by inference, delayed discharge from intensive care) [1,4,5,15], and a higher post-operative mortality [4,5]. In our own series, PGD was documented as the primary cause of death in 41%, and a contributory cause of death in 18% of all lung transplanted patients not surviving until hospital discharge [9]. This is similar to the findings reported from an analysis of 5262 patients from the United Network for Organs Sharing (UNOS) registry whereby 43.6% of patients dying in the first 30 days had PGD [6]. The same study also showed that for patients surviving more than 1 year, patients with earlier PGD had significantly worse survival over ensuing years than for patients without PGD. The results of the present study corroborate with these earlier observations.
In the most severe cases PGD resembles ARDS, the histological hallmark of which is a pattern of DAD [1,17]. The results of the present study support a temporal association between clinical PGD and histological DAD. In addition, the findings support a correlation between the extent of radiographic infiltration and the cumulative incidence of DAD. There was also a significantly higher cumulative incidence of BOOP in the group of patients with PGD.
BOOP is usually identified in association with other medical conditions and rarely occurs in the idiopathic form [19], and has been reported in the context of lung, bone marrow, and other solid organ transplantation [20], and also in association with the use of immunosuppressive therapy with sirolimus and tacrolimus [21,22]. All patients in this study-received cyclosporine based triple immunosuppressive therapy, exclusively. We believe that early BOOP is likely to be the result of non-specific epithelial injury of multiple etiology.
We were unable to demonstrate a relationship between the development of BOS and earlier PGD in a sub-analysis of patients surviving more than 3 months. However, patients with PGD had a lower median maximal FEV1, which decreased with increasing radiographic severity. The median maximal FEV1 is approximately 39% lower in recipients with severe PGD compared to patients without PGD, which perhaps, would be sufficient to explain the observed effects on morbidity [4] and survival.
As with all retrospective studies, we are unable to exclude the possibility of bias. In addition, the inter- and intra-observer agreement was lower than anticipated; although, the higher intra-observer agreement suggests that training may improve consistency. With hindsight, radiographic sub-classification into four groups of severity based on the percentage of lung affected may have been too ambitious. Firstly, because of the introduction of human error in visually identifying such proportions; and secondly because more severely involved edematous parenchyma may shrink and appear as a smaller proportion of the whole lung when imaged by CXR. However, other underlying components of the proposed radiological sub-classification, such as the distinction between infiltration and consolidation may be a more important reflection of the severity of PGD.
We chose to study SLTX patients exclusively primarily in order to reduce potential misdiagnosis of PGD in double lung-transplanted patients with fluid overload. In addition, one would expect the patient cohort to be a more homogeneous in terms of age, preoperative functional NYHA status, and pre-transplant diagnosis; and that both PGD+ and PGD groups would be subject to the same degree of confounding relating to intra- and post-operative donor organ stress. Indeed, this approach appears to have been validated in a recent study by Oto et al. [23] recommending that studies of PGD in DLTX and SLTX should be considered separately. In this study, possible artifacts related to earlier extubation and the effects of the native lung in SLTX recipients contributed to the apparently paradoxical outcomes of more severe PGD (graded according to the PaO2:FiO2 ratio) but shorter intubation requirements and a tendency to better short-term outcomes than was seen in the DLTX group. Certainly, extubation would be expected to reflect a less severe clinical manifestation in patients with PGD. In the present study, the grading of the severity of PGD based on the PaO2:FiO2 ratio was also problematic. Accurate determination of the PaO2:FiO2 ratio requires the patient to be on a sealed ventilatory system. Since 57% of the SLTX recipients were extubated in the operating room, a proportion of patients with PGD were not receiving a known FiO2. In non-ventilated patients receiving supplementary oxygen, several large assumptions would be required to estimate the FiO2, the true value of which is respiratory rate dependent.
Despite these limitations we were able to demonstrate the reproducibility and prognostic reliability of radiologically defined PGD in terms of early and late survival, and demonstrate a correlation between the extent of radiological infiltrate and histological findings consistent with organizing pneumonia, particularly DAD pattern.
| 5. Conclusions |
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| References |
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