Infectious Disease · Medical Literature
Inter-hospital ICU-to-ICU transfer of critically ill COVID-19 patients is not associated with increased mortality: a systematic review with exploratory meta-analysis.
Abstract
During the COVID-19 pandemic, inter-hospital transfer of critically ill patients between intensive care units was widely used to manage capacity shortages. While several individual studies have compared outcomes of transferred and non-transferred patients, no systematic synthesis of this evidence exists. This systematic review aims to determine whether inter-hospital ICU-to-ICU transfer of adult COVID-19 patients is associated with increased mortality or other adverse clinical outcomes. We systematically searched PubMed, Web of Science, and Scopus for observational studies comparing clinical outcomes of adult COVID-19 patients who underwent inter-hospital ICU-to-ICU transfer with non-transferred ICU patients. Two reviewers screened, selected, and extracted data independently and in duplicate. Risk of bias was assessed using the Newcastle-Ottawa Scale and ROBINS-I, and certainty of evidence using GRADE. Exploratory random-effects meta-analyses were performed separately for each effect measure, with Hartung-Knapp and crude-effect sensitivity analyses. Nine observational studies from seven countries were included (approximately 6,100 transferred and 29,200 non-transferred ICU patients). None of the adjusted effect estimates showed a statistically significant mortality disadvantage for transferred patients. Pooled adjusted subgroup estimates were an odds ratio of 1.29 (95% CI 0.84 to 1.98; k = 3) and a hazard ratio of 0.71 (95% CI 0.34 to 1.46; k = 2). Length of stay was longer in transferred patients in most studies. The available observational evidence did not show a clear increase in mortality among transferred compared with non-transferred COVID-19 ICU patients. These findings support the use of inter-hospital transfer as a safe strategy for managing ICU surge capacity. PROSPERO CRD420261356915.
Clinical relevance
Among critically ill adult COVID-19 patients, is inter-hospital ICU-to-ICU transfer associated with increased mortality or other adverse clinical outcomes compared with non-transferred ICU patients? __SNAPSHOT__ {"studyDesign":"Systematic review with exploratory random-effects meta-analysis of observational studies","setting":"Multi-national; studies drawn from seven countries; affiliated with Jena University Hospital and the Leibniz Centre for Photonics in Infection Research (LPI), Jena, Germany","sampleSize":"Nine observational studies; approximately 6,100 transferred and 29,200 non-transferred ICU patients (total ~35,300)","population":"Adult patients with confirmed COVID-19 admitted to an ICU who either underwent inter-hospital ICU-to-ICU transfer or remained at the admitting ICU","intervention":"Inter-hospital ICU-to-ICU transfer (capacity-driven, non-clinical indication)","comparator":"Non-transferred ICU patients at the admitting facility","primaryOutcome":"Mortality (all-cause; specific time-point definitions varied across included studies); secondary outcomes described as 'other adverse clinical outcomes' (specific endpoints not further detailed in the abstract)","followUp":"Variable across included studies; not uniformly reported in the abstract","fundingSource":"Not reported in the abstract"}
Key findings
Across nine observational studies enrolling approximately 6,100 transferred and 29,200 non-transferred critically ill COVID-19 ICU patients from seven countries, the pooled findings of the exploratory random-effects meta-analyses did not demonstrate an association between inter-hospital ICU-to-ICU transfer and increased mortality. Specific pooled effect estimates (odds ratios, hazard ratios, risk ratios), confidence intervals, p-values, I² heterogeneity statistics, and NNT/NNH are not reported in the available abstract and therefore cannot be presented here. The meta-analyses were conducted separately for each effect measure, with Hartung-Knapp adjustment (a more conservative variance estimation method) and crude-effect sensitivity analyses performed to assess robustness. Risk of bias was assessed using both the Newcastle-Ottawa Scale and ROBINS-I; certainty of evidence was graded using the GRADE framework. No specific adverse event or safety data (e.g., transfer-related complications, adverse events during transport) are described in the abstract. The title's conclusion — that transfer 'is not associated with increased mortality' — reflects the direction and statistical non-significance of the pooled estimates, but absolute and relative effect sizes cannot be verified from the abstract alone.
Practice implications
This systematic review provides the first formal pooled synthesis of observational evidence on inter-hospital ICU-to-ICU transfer for COVID-19 patients, addressing a clinically and logistically important question that arose during pandemic surge management. The central finding — absence of a statistically significant association between transfer and increased mortality — is directionally reassuring for critical care networks that utilized or may consider similar capacity-redistribution strategies in future mass-casualty or surge scenarios. However, several important caveats limit the strength of inference. All included studies are observational, meaning unmeasured confounding is a persistent concern: patients selected for transfer are likely systematically different (e.g., more hemodynamically stable, younger, fewer comorbidities, or conversely more resource-intensive) than those retained at the originating ICU, introducing substantial healthy-transferee or selection bias. The GRADE framework was applied, and given the observational study design and likely risk of bias, certainty of evidence is expected to be low to very low, though the specific GRADE ratings are not available in the abstract. The findings may not generalize to non-COVID critical illness, to health systems with different transport infrastructure, or to resource-limited settings. The population studied reflects the specific epidemiology and care standards of the COVID-19 pandemic period, potentially limiting applicability to future non-COVID surge events. Secondary outcomes (e.g., ICU length of stay, days alive and out of ICU, long-term functional status) are referenced but not quantified in the abstract. IMPORTANT NOTE: This summary is based solely on the published abstract; full-text review is required to evaluate effect sizes, heterogeneity, individual study risk-of-bias profiles, GRADE certainty ratings, and secondary outcome data before applying findings to clinical or policy decisions. __LIMITATIONS__ 1. All included studies are observational (cohort designs); no randomized evidence exists or is likely feasible in this context, creating an inherent ceiling on certainty. 2. Selection bias (healthy-transferee bias): patients chosen for inter-hospital transfer are not randomly selected — they are typically more physiologically stable, which may systematically underestimate transfer-associated risk; this may not have been fully adjusted for in all included studies. 3. Residual confounding: even with statistical adjustment in individual studies, unmeasured confounders (e.g., severity trajectory, time-to-deterioration, institutional expertise, transport distance and mode, staffing ratios at receiving ICU) likely persist. 4. Heterogeneity: with nine studies from seven countries spanning a pandemic with multiple waves, treatment eras, and variant-specific mortality profiles, clinical and methodological heterogeneity is expected to be substantial, limiting the interpretability of any single pooled estimate. 5. Small number of included studies (n=9) limits statistical power and the reliability of heterogeneity estimation in random-effects models. 6. Outcome definition inconsistency: mortality time-points (in-hospital, 30-day, 90-day, 180-day, ICU) likely varied across studies, making meta-analytic pooling inherently imprecise. 7. Secondary outcome reporting: adverse clinical outcomes beyond mortality are referenced but not detailed in the abstract, limiting assessment of the full risk-benefit profile of transfer. 8. Publication and language bias: observational studies with null or negative findings may be underrepresented; language restrictions (if any) are not reported in the abstract. 9. Temporal and contextual specificity: findings reflect COVID-19 pandemic conditions (specific pathogen, specific treatment protocols, system-level surge responses) and may not generalize to other critical illness populations or future pandemic scenarios. 10. Funding source not reported, precluding assessment of potential sponsor influence. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ This first systematic review with meta-analysis of inter-hospital ICU-to-ICU transfer for critically ill COVID-19 patients (nine observational studies; ~6,100 transferred vs. ~29,200 non-transferred patients from seven countries) found no statistically significant association between transfer and increased mortality. The evidence base is exclusively observational, and substantial selection bias, residual confounding, and heterogeneity mean that certainty of evidence is likely low by GRADE standards. These findings provide preliminary, hypothesis-supporting reassurance that capacity-driven ICU-to-ICU transfer during pandemic surges does not appear to confer a mortality penalty, but they are not sufficient to independently guide transfer policy without full-text review and integration with local system-level safety and logistics data.