Volume 14, Issue 12 , Pages 1385-1393, December 2008
Survival in a Recent Cohort of Mechanically Ventilated Pediatric Allogeneic Hematopoietic Stem Cell Transplantation Recipients
Article Outline
Abstract
There is ongoing discussion whether survival improved for children requiring mechanical ventilation after hematopoietic stem cell transplantation (HSCT). We reviewed the outcomes of 150 children who received an allogeneic HSCT between January 1999 and April 2007, in a pediatric university hospital in The Netherlands. Thirty-five of the 150 patients received mechanical ventilation on 38 occasions. None of the recorded risk factors was significantly associated with the requirement of mechanical ventilation. Sixteen admissions resulted in death in the intensive care unit (ICU), giving a case fatality rate of 42% (95% confidence interval 26%-58%). ICU mortality was associated with multiorgan failure on the second day of admission and with the use of high frequency oscillatory ventilation. Patients had higher pediatric risk of mortality scores than in previous studies, reflecting higher acuity of illness on admission to the ICU. Six-month survival in patients discharged from the ICU was 82%. Compared to previous studies, we found an improvement in ICU survival and survival 6 months after ICU discharge in a recent cohort of ventilated children after allogeneic HSCT, even though our patients were more severely ill. Our results are promising, but they need to be confirmed in larger, preferably multicenter, studies.
Key Words: Mechanical ventilation, Hematopoietic stem cell transplantation, Bone marrow transplantation, Allogeneic transplantation, Outcome, Pediatric
Introduction
Despite all its progress over the years, pediatric hematopoietic stem cell transplantation (HSCT) remains a high risk procedure, which necessitates transfer to the intensive care unit (ICU) in up to 44% of patients [1]. Mortality in ventilated children after HSCT historically was reported to be very high. Whether outcome improved over the years is still a matter of debate: a clear decrease in mortality over time could not be detected in a recent meta-regression analysis [2], mostly because current outcome data in ventilated patients were lacking. Two studies from the United States, published after the inclusion period of the meta-regression analysis, revealed conflicting results: survival had clearly improved over time in 1 study [3], whereas it did not differ by year of study in the other [4]. More outcome data in this population are, therefore, needed.
Only few studies investigated which factors were associated with an increased risk of ICU admission in children after HSCT 5, 6, 7, 8. A considerable proportion of patients in these studies underwent autologous transplantations, which may have limited general applicability of results. Moreover, patients in previous studies often did not require mechanical ventilation during their ICU stay, whereas this specifically is the most uniform ICU treatment, and it is associated with the largest increase in risk of mortality [4].
The main goal of the present study was to assess outcome in a recent cohort of children requiring mechanical ventilation after allogeneic HSCT. Second, we wanted to identify predictors for mortality in this cohort and predictors for the requirement of mechanical ventilation.
Materials and Methods
Setting
This study was performed at the Wilhelmina Children's Hospital, which is part of the University Medical Center Utrecht (Utrecht, The Netherlands). In this hospital, about 30 allogeneic HSCTs in children are performed annually. The multidisciplinary 14-bed pediatric ICU has approximately 650 admissions each year; about 80% of them receive invasive mechanical ventilation. The generally applied ventilation strategies aim to limit tidal volumes to <8 mL/kg and to restrict peak inspiratory pressures to <30 cm H2O, while applying high positive end expiratory pressures. Patients are ventilated in a pressure control or pressure support mode. Patients requiring peak inspiratory pressures above 30 cm H2O or patients with an oxygenation index ([mean airway pressure × FiO2 × 100]/PaO2) >20 proceed to high frequency oscillatory ventilation (HFOV). Ventilation is delivered by a Servo 300 or Servo-i (Maquet, Sweden) for conventional mechanical ventilation and a Sensormedics 3100A or 3100B (Viasys Healthcare, Madison, WI) for HFOV.
Patients
All children younger than 19 years of age, who received an allogeneic HSCT in our hospital between January 1999 and April 2007, were identified from the HSCT database. Patients admitted to the ICU after HSCT were identified from a prospectively maintained ICU database. They were included when they had received invasive mechanical ventilation for more than 24 hours. Prior to the start of the HSCT procedure, all parents, and when appropriate, all patients, gave written informed consent to analyze deidentified clinical data for study purposes.
Data Collection
Patient data were collected from medical charts and from the HSCT database. Data that were abstracted included demographic information, preexisting diagnosis requiring HSCT, number and type of transplantations, type of donor and source of stem cells. For those patients admitted to the ICU for mechanical ventilation, the following additional information was recorded: presence of neutropenia, grade of graft-versus-host disease (GVHD), cytomegalovirus status (CMV), time interval between HSCT and admission to the ICU, reason for intubation, duration of intubation, use of HFOV, pediatric risk of mortality (PRISM) score [9], highest oxygenation index during the first day of admission, and severity of organ dysfunction during the first 3 days of admission to the ICU.
Definitions
Indications for HSCT were categorized in the following groups: malignancy, inborn error of metabolism, immunodeficiency, bone marrow failure syndrome, and miscellaneous inborn error (including thalassemia, Morbus Glanzmann). GVHD was diagnosed and graded according to Glucksberg et al. [10]. CMV status at admission to the ICU was categorized as negative, infection (including reactivation), or carrier. Neutropenia was defined as a polymorphonuclear leukocyte count of <500 cells per cubic millimeter of blood. Reasons for admission to the ICU were grouped in the following categories: respiratory failure, neurologic deterioration, sepsis, arrest, bleeding, and postoperative [11]. Number and severity of organ dysfunction was assessed following the criteria of Wilkinson et al. [12]. The PRISM score [9] was used to assess severity of illness on admission to the ICU. It is a validated scoring system, applied by pediatric ICUs worldwide. It is based on deteriorations of a number of physiologic variables measured during the first 24 hours of ICU admission. Human leukocyte antigen (HLA) matching was based on high-resolution typing for class I and class II antigens for bone marrow and peripheral blood stem cell (PBSC) donors (10 antigens: A, B, C, DR, and DQ). For cord blood donors intermediate resolution criteria were used (Loci A and B serologically and DRB1 by high-resolution typing) [13]. A DPB1 mismatch was not taken into account. For the analyses, patients were simply divided into a matched or mismatched group. Identical cord blood grafts according to the intermediate resolution criteria mentioned above were regarded as matched.
Primary endpoint of the study was outcome (survival or death) at discharge from the ICU; secondary endpoint was outcome (survival or death) 6 months after discharge from the ICU.
Statistical Analysis
Differences in categoric demographic and clinical variables were analyzed using Fisher's exact test. Continuously distributed data were evaluated using Student's t-tests. The association between potential risk factors and ICU admission or ICU mortality was quantified using univariable logistic regression analysis. This was followed by stepwise multiple logistic regression analysis to identify those factors independently associated with ICU admission or ICU mortality. A value of P < .05 was considered to indicate statistical significance. Data were analyzed using SPSS version 12.0.2 (SPSS, Chicago, IL).
Results
A flow chart of HSCTs and ICU admissions is given in Figure 1. During the inclusion period, 175 HSCTs were performed in 150 patients: a second transplantation was done in 23 patients, and 1 patient received 3 transplantations. Fifty-one patients were admitted to the ICU on 56 occasions: 2 patients were admitted twice, 1 patient was admitted to the ICU on 5 occasions. Eighteen admissions (16 patients) did not receive mechanical ventilation for more than 24 hours and they were excluded. Three of the excluded patients died in the ICU: 1 patient was admitted because of a sepsis, which rapidly deteriorated. Despite intubation and resuscitation he died within 1 hour after admission. In 2 patients it was decided (in agreement with the patients' and parents' wishes) to give maximum support, but refrain from mechanical ventilation. Both patients died within 3 days after ICU admission.
Figure 1
Flow chart of ICU admissions and outcomes of children after allogeneic hematopoietic stem cell transplantation. HSCT, hematopoietic stem cell transplantation; ICU, intensive care unit; MV, mechanical ventilation.
The remaining 35 patients (23% of all HSCT recipients) were included in the study. Because 3 patients required 2 episodes of mechanical ventilation, mechanical ventilation was given on 38 occasions. Readmissions for mechanical ventilation occurred 2 days, 214 days, and 219 days after the first admission. They were considered to be separate treatment episodes and were analyzed accordingly. None of the included patients had received noninvasive ventilation before intubation or during weaning. The reasons to start mechanical ventilation were respiratory failure (n = 26), neurologic deterioration (n = 6), sepsis (n = 4), cardiac arrest (n = 1), and postoperative (n = 1).
Sixteen patients died in the ICU, resulting in a case fatality rate of 42% (95% confidence interval (CI) 26% to 58%). The cause of death for patients in the ICU was respiratory failure (n = 6), multiple organ system failure (n = 7), sepsis (n = 1), Epstein Barr encephalitis (n = 1), and posttransplantation lymphoproliferative disorder (n = 1). All 3 patients who received 2 episodes of mechanical ventilation died in the ICU. During ICU treatment 2 patients received renal replacement therapy; both died in the ICU. The observed ICU mortality (42%) corresponded to PRISM-based predicted mortality (37%). However, there was a wide variation between annually observed and predicted ICU mortality (Figure 2).
Figure 2
Predicted mortality rates (based on PRISM scores) and observed mortality rates in children requiring mechanical ventilation after allogeneic hematopoietic stem cell transplantation. ObsMort, observed ICU mortality rate; PredMort, predicted ICU mortality rate based on PRISM score [9].
Three patients who were discharged from the ICU died shortly afterward: 1 patient after 10 days (refractory GVHD), 1 after 20 days (refractory GVHD, Epstein Barr reactivation, and pulmonary aspergillosis), and 1 patient died 34 days after ICU discharge (idiopathic pneumonia syndrome, multiple viral infections). Early mortality rate (ie, death on the ICU or shortly after discharge from the ICU), therefore, was 50% (95% CI 34% to 66%). Eighteen patients who were discharged from the ICU were still alive 6 months later. Altogether, therefore, 18 of 38 ICU admissions (47%) could be discharged from the ICU and lived at least 6 months afterward.
Risk Factors for the Requirement of Mechanical Ventilation
Characteristics of all HSCT recipients are summarized in Table 1. In this table, a comparison is made between ventilated and nonventilated children. Data are analyzed per patient. When data were analyzed with each transplantation as a separate event (ie, n = 175 instead of n = 150), comparable results were found (data not shown).
Table 1. Characteristics of Pediatric Allogeneic Hematopoietic Stem Cell Transplantation Recipients
| All HSCT Recipients | HSCT Recipients Who Did Not Receive MV | HSCT Recipients Requiring MV | ||
|---|---|---|---|---|
| (n = 150) | (n = 115) | (n = 35) | P -Value | |
| Gender (female) | 39% | 37% | 46% | .43 |
| Median Age (years) | 6.5 | 6.6 | 4.7 | .56 |
| Diagnosis | ||||
 Malignancy | 54% | 56% | 49% | .56 |
| Immunodeficiency | 17% | 17% | 20% | .62 |
| Bone marrow failure | 13% | 16% | 6% | .16 |
| Inborn error of metabolism | 10% | 8% | 17% | .12 |
| Miscellaneous inborn error | 5% | 4% | 9% | .39 |
| Type of Transplant | ||||
| Bone marrow | 69% | 70% | 63% | .41 |
| Cord blood | 17% | 15% | 23% | .30 |
| Peripheral blood stem cells | 16% | 17% | 14% | 1.00 |
| Type of donor (related) | 43% | 47% | 29% | .06 |
| HLA mismatch | 33% | 32% | 31% | .68 |
| More than 1 Transplantation | 15% | 17% | 6% | .11 |
| Year of Transplantation | 1999-2007 | 1999-2007 | 1999-2007 | .05 |
In the univariable analysis, year of transplantation and type of donor were associated with the risk of requiring mechanical ventilation (see Table 1). In the multiple regression analysis, both year of transplantation (odds ratio 1.15, 95% CI 0.94-1.39, P = .17) and type of donor (odds ratio 0.56, 95% CI 0.24-1.35, P = .20) lost significance.
Risk Factors for Mortality in Ventilated Patients
Clinical characteristics of ventilated patients who survived to ICU discharge are summarized in Table 2. Clinical characteristics of ventilated patients who died during their ICU admission are summarized in Table 3.
Table 2. Clinical Characteristics of the 22 Ventilated Pediatric Hematopoietic Stem Cell Transplantation Recipients Who Survived to ICU Discharge
| Primary Diagnosis | Indication for MV | Diagnosis Necessitating MV | Time Between ICU and HSCT (days) | Duration of MV (days) | Survival after ICU discharge | Grade of aGvHD | Neutropenia admission to ICU | Viral infection on admission to ICU | |
|---|---|---|---|---|---|---|---|---|---|
| 1 | GM1-gangliosidosis | resp. failure | idiopathic pneumonia syndrome | 7 | 9 | > 6 months | 1 | yes | no |
| 2 | AML | resp. failure | engraftment syndrome, hepatic VOD | 10 | 12 | > 6 months | 1 | no | no |
| 3 | MPS I | resp. failure | diffuse alveolar hemorrhage | 11 | 19 | > 6 months | 0 | yes | adenovirus reactivation |
| 4 | beta thalassemia major | resp. failure | hepatic VOD with pulmonary edema | 14 | 8 | > 6 months | 0 | yes | no |
| 5 | MDS | resp. failure | idiopathic pneumonia syndrome, hepatic VOD | 24 | 20 | > 6 months | 0 | no | no |
| 6 | MDS | resp. failure | hepatic VOD with pulmonary edema, acute GVHD | 25 | 15 | 10 days | 4 | no | no |
| 7 | AML | resp. failure | intoxication cyclosporine with pleural effusions and multi-organ failure | 29 | 2 | > 6 months | 0 | no | CMV reactivation |
| 8 | Niemann-Pick disease | resp. failure | idiopathic pneumonia syndrome, pulmonary VOD | 66 | 31 | > 6 months | 3 | no | no |
| 9 | alpha-mannosidose | resp. failure | idiopathic pneumonia syndrome | 82 | 17 | 34 days | 1 | no | adenovirus reactivation |
| 10 | MDS | resp. failure | interstitial pneumonitis, only rhinovirus isolated | 90 | 9 | > 6 months | 1 | no | rhinovirus isolated |
| 11 | MPS VI | resp. failure | bronchiolitis obliterans, no microorganism identified | 94 | 11 | > 6 months | 1 | no | no |
| 12 | CID | resp. failure | idiopathic pneumonia syndrome, subglottic stenosis | 117 | 8 | > 6 months | NA | no | no |
| 13 | SAA | resp. failure | lobar pneumonia, no microorganism identified | 171 | 21 | > 6 months | NA | no | no |
| 14 | T-cell ALL | neur. det. | Guillain-Barré syndrome | 68 | 50 | > 6 months | 0 | no | no |
| 15 | cartilage hair hypoplasia | neur. det. | Acinetobacter sepsis with encephalopathy | 71 | 5 | 144 days | 0 | yes | systemic adenoviral infection |
| 16 | relapsed AML | neur. det. | central nervous system toxoplasmosis | 171 | 37 | > 6 months | NA | no | no |
| 17 | AML | neur. det. | CNS, pulmonary and intestinal aspergillosis | 244 | 39 | > 6 months | NA | no | no |
| 18 | AML | sepsis | Klebsiella pneumoniae sepsis with ARDS | 69 | 17 | > 6 months | 0 | no | CMV reactivation |
| 19 | HLH | sepsis | Stenotrophomonas sepsis | 72 | 5 | > 6 months | 0 | no | VZV, adenovirus reactivation |
| 20 | ALL high risk | sepsis | septic shock, no microorganism identified | 412 | 6 | > 6 months | NA | no | no |
| 21 | AML | postop. | external CSF drainage for hydrocephalus, BAL | 12 | 3 | 20 days | 0 | yes | EBV, HHV6 reactivation |
| 22 | AML | arrest | pulmonary VOD with pulmonary hypertension | 94 | 23 | > 6 months | 0 | no | no |
Table 3. Clinical Characteristics of the 16 Ventilated Pediatric Hematopoietic Stem Cell Transplantation Recipients Who Died during their ICU Admission
| Primary Diagnosis | Indication for MV | Diagnosis Necessitating MV | Time between ICU and HSCT (days) | Duration of MV (days) | Grade of aGvHD | Neutropenia admission to ICU | Viral infection on admission to ICU | |
|---|---|---|---|---|---|---|---|---|
| 1 | Relapsed ALL | resp. failure | acute GVHD, hepatic VOD | 7 | 29 | 3 | yes | no |
| 2 | MDS | resp. failure | idiopathic pneumonia syndrome | 9 | 26 | 4 | no | no |
| 3 | Lymphoproliferative syndrome | resp. failure | pulmonary microbacterial and nocardia infection | 10 | 34 | 0 | no | no |
| 4 | Morbus Glanzmann | resp. failure | idiopathic pneumonia syndrome, diffuse alveolar hemorrhage | 13 | 42 | 1 | yes | no |
| 5 | Osteopetrosis | resp. failure | idiopathic pneumonia syndrome | 22 | 33 | 0 | no | no |
| 6 | SAA | resp. failure | pulmonary aspergillosis | 23 | 11 | 0 | no | no |
| 7 | Morbus Wolman | resp. failure | idiopathic pneumonia syndrome, diffuse alveolar hemorrhage | 25 | 30 | 1 | no | CMV infection |
| 8 | Cartilage Hair Hypoplasia | resp. failure | CMV pneurmonia | 40 | 17 | 2 | yes | CMV pneumonia, adenovirus and EBV reactivation |
| 9 | CVID | resp. failure | EBV PTLD | 56 | 3 | 2 | no | EBV PTLD |
| 10 | relapsed ANLL | resp. failure | adenovirus infection | 60 | 7 | 0 | yes | adenovirus infection |
| 11 | Wiskott-Aldrich syndrome | resp. failure | CMV, EBV infection | 64 | 11 | 0 | no | CMV, EBV infection |
| 12 | Alpha-mannosidose | resp. failure | idiopathic pneumonia syndrome | 104 | 30 | 1 | no | adenovirus reactivation |
| 13 | Niemann-Pick disease | resp. failure | candida sepsis with ARDS | 319 | 6 | NA | no | no |
| 14 | Relapsed AML | neur. det. | RPLS | 118 | 3 | NA | yes | EBV and adenovirus reactivation |
| 15 | AML | neur. det | cerebral EBV infection | 248 | 11 | NA | no | EBV infection |
| 16 | Relapsed ALL | sepsis | septic shock, no microorganism identified | 4 | 3 | 0 | yes | no |
Results from the statistical comparison between survivors and nonsurvivors are given in Table 4. In the univariate analysis, number of organs failing on day 2 and HFOV were significantly related with ICU mortality. Both organ failure on day 2 (odds ratio 3.45, 95% CI 1.12-10.63, P = .03) and HFOV (odds ratio 6.28, 95% CI 1.16-34.12, P = .03) remained significantly associated with mortality in the multivariate analysis.
Table 4. Demographic and Clinical Data of the Children Requiring Mechanical Ventilation after Allogeneic Hematopoietic Stem Cell Transplantation; Comparison between Survivors and Nonsurvivors
| Patients Requiring MV | 95% Confidence Interval for OR | |||||
|---|---|---|---|---|---|---|
| Survivors n = 22 | Nonsurvivors n = 16 | OR | Lower bound | Upper bound | p-Value | |
| Gender (female) | 59% | 31% | 0.32 | 0.08 | 1.22 | .11 |
| Median age (years) | 4.3% | 8.7 | 1.00 | 1.00 | 1.00 | .29 |
| Diagnosis | ||||||
| Malignancy | 55% | 38% | 0.50 | 0.13 | 1.86 | .34 |
| Immunodeficiency | 14% | 25% | 2.11 | 0.40 | 11.13 | .43 |
| Bone marrow failure | 5% | 6% | 1.40 | 0.08 | 24.20 | 1.00 |
| Inborn error of metabolism | 18% | 25% | 1.50 | 0.31 | 7.19 | .70 |
| Miscellaneous inborn error | 9% | 6% | 0.67 | 0.06 | 8.06 | 1.00 |
| Type of Transplant | ||||||
| Bone marrow | 59% | 69% | 1.52 | 0.39 | 5.91 | .74 |
| Cord blood | 23% | 31% | 1.55 | 0.36 | 6.61 | .71 |
| Peripheral blood stem cells∗ | 18% | 0% | .12 | |||
| HLA mismatch | 27% | 44% | 2.07 | 0.53 | 8.10 | .32 |
| Type of donor (related) | 27% | 25% | 0.89 | 0.20 | 3.87 | 1.00 |
| CMV status | ||||||
| Negative | 59% | 56% | 0.89 | 0.24 | 3.28 | 1.00 |
| Infection/reactivation | 14% | 25% | 2.11 | 0.40 | 11.13 | .43 |
| Carrier | 27% | 19% | 0.62 | 0.13 | 2.95 | .71 |
| Days o mechanical ventilation (range) | 14 (2-50) | 14 (3-42) | 1.01 | 0.96 | 1.06 | .66 |
| Days between Tx and ICU admission (range) | 70 (7-412) | 32 (4-319) | 1.00 | 0.99 | 1.01 | .54 |
| Oxygenation index at admission (range) | 10 (2-36) | 11 (2-37) | 0.99 | 0.92 | 1.07 | .87 |
| HFOV | 14% | 44% | 4.93 | 1.03 | 23.63 | .05 |
| Neutropenia at ICU admission | 23% | 42% | 2.04 | 0.49 | 8.45 | .47 |
| GVHD >grade 2 | 9% | 12% | 3.33 | 0.53 | 21.03 | .20 |
| PRISM score at admission (range) | 20 (4-40) | 21 (9-36) | 1.02 | 0.95 | 1.10 | .64 |
| Predicted risk of mortality-PRISM (range) | 35% (2-97) | 37% (5-94) | ||||
| Number of organs failing on ICU day 1 (range) | 2 (1-3) | 2 (1-4) | 1.95 | 0.86 | 4.41 | .11 |
| Number of organs failing on ICU days 2 (range) | 2 (1-3) | 2 (1-5) | 3.10 | 1.06 | 9.05 | .04 |
| Number of organs failing on ICU days 3 (range) | 2 (1-4) | 3 (1-6) | 2.45 | 0.98 | 6.13 | .06 |
| Indication for MV | ||||||
| Respiratory failure | 59% | 81% | 3.00 | 0.66 | 13.66 | .18 |
| Neurological deterioration | 18% | 13% | 0.64 | 0.10 | 4.03 | 1.00 |
| Sepsis | 14% | 6% | 0.42 | 0.04 | 4.48 | .62 |
| Ppostoperative∗ | 5% | 0% | ||||
| Arrest∗ | 5% | 0% | ||||
∗Odds ratio and 95% confidence interval could not be calculated because no patients died in the ICU with specified risk factor. |
Discussion
We assessed risk factors for and outcomes of mechanical ventilation in a recent cohort of children after allogeneic HSCT. The main finding is that ICU mortality rate was considerably lower than in previous studies. ICU discharge was followed by a low medium-term mortality rate. Our results are promising, but they need to be confirmed in larger multicenter studies.
There is ongoing discussion whether ICU outcome improved over time for children after HSCT. A recent meta-regression analysis [2] could not detect a significant improvement over the years, but conclusions were hampered by the limited availability of current data. After the inclusion period of the meta-regression analysis, 2 additional studies on this subject were published. Bratton et al. [4] found a decrease over the years in complications requiring ICU transfer in children after HSCT. However, once mechanical ventilation was necessary, mortality remained unchanged in the years studied. This study benefited from a very large sample size from a database of over 3000 hospitals in the United States, but it did not focus on ICU treatment or ICU outcomes. It therefore included only limited information on the reason for ICU transfer, or the acuity of illness on admission to the ICU, which limits interpretation of their results. Tamburro et al. [3] reviewed outcomes of mechanical ventilation in a large cohort of pediatric HSCT recipients between 1996 and 2004, and found a significant improvement over the years. Our findings are in line with their results, and even suggest an ongoing improvement in outcomes in more recent years, both for ICU survival (40% in the study of Tamburro et al. versus 58% in our study) and for 6-month survival (25% in the study of Tamburro et al. versus 47% in our study).
Our results need to be interpreted cautiously: they are limited by the retrospective nature of the study and by the relatively small number of patients included from only a single center. This is especially important, because ventilated children after HSCT form a heterogeneous population, which makes it difficult to compare results between studies. Moreover, we do not know in which patients ICU admission was denied because it was considered futile. Triage decisions can influence ICU outcome, as has been shown in adult cancer patients [14]. With these limitations in mind, we can conclude that results are promising, but need to be confirmed in other, preferably multicenter, studies. Because transplantation and critical care medicine are rapidly evolving, future research on ICU treatment in HSCT recipients would be helped with a prospectively collected database by a group of dedicated ICUs. Only then can some of the remaining questions in this complex group of patients be answered.
There may be several explanations for the improved survival we found. First, it is likely that advancements in medical care contributed to better outcomes. Second, improvements in outcome can be explained by a lower threshold to start mechanical ventilation, and by intubating less severely ill patients. In our study, 23% of transplanted children required mechanical ventilation, which is comparable to the proportion of patients after allogeneic HSCT in previous European studies 6, 8, 15. However, in the study of Bratton et al. [4], only 10% of children after allogeneic HSCT received mechanical ventilation. In this study, 45% of nonsurvivors died without receiving mechanical ventilation, which may suggest a restrictive use of ICU care in a considerable number of children. Patients in our study had higher PRISM scores than patients in other studies 1, 7, 16, 17, and their PRISM-based risk of mortality (37%) was considerably higher than in previous studies (18% [11], 19% [18], and 26% [19]). It is, therefore, unlikely that a lower threshold to start mechanical ventilation or a lower severity of illness explains the improved outcome in our patients.
An interesting finding in the present study is that the duration of mechanical ventilation (median 14 days, range: 2-50 years) was considerably longer than reported in previous studies. This may coincide with a higher severity of illness on admission to the ICU. Furthermore, therapeutic options for complications after HSCT have extended, which may lead to prolonged treatment in patients who would have already died previously. The shorter duration of mechanical ventilation in other studies may reflect withdrawal or limitation of ICU treatment, because the need for prolonged mechanical ventilation has been considered predictive for death by many physicians 11, 20, 21, 22, 23. However, the results from the current study emphasize that the decision to stop or limit ICU treatment should not be based solely on the duration of mechanical ventilation.
Organ failure was associated with ICU mortality, but only on the second day of admission. This suggests that lack of improvement or even progression of organ failure despite ICU treatment gives the largest increase in risk of mortality. The relation between organ failure and ICU mortality is a consistent finding in nearly all other ICU studies in HSCT recipients. It is also reflected in the association between HFOV and mortality, because HFOV is used in patients with the most severe form of respiratory failure. On the other hand, 30% of patients who received HFOV in our study survived, as did the patient with the highest PRISM score, and the patient with the highest oxygenation index. This underscores the difficulty of identifying survivors and nonsurvivors in a way accurate enough to guide clinical decision making.
In conclusion, there is ongoing discussion whether ICU outcome improved over time for ventilated children after HSCT. Compared to previous studies, we found significantly better outcomes. This holds true both for ICU survival as for survival 6 months after discharge from the ICU. The ICU survival rate of more than 50% in the present study is promising, but needs to be confirmed in other, preferably multicenter, studies.
Acknowledgments
Financial disclosure: The authors have nothing to disclose.
The authors state that their work is original and has not been published previously. Part of this work has been presented at the annual congress of the European Group for Blood and Marrow Transplantation in Florence, Italy (March 30 to April 2, 2008). All authors have contributed substantially in the conception and design of the study. They all participated actively in the writing of the manuscript. All authors approve to submit this version of the manuscript to Biology of Blood and Marrow Transplantation. No reprints will be ordered.
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Financial disclosure: See Acknowledgments on page 1392.
PII: S1083-8791(08)00419-9
doi:10.1016/j.bbmt.2008.09.020
© 2008 American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.
Volume 14, Issue 12 , Pages 1385-1393, December 2008
