In our study, we showed that COVID-19 ICU patients who were initially hospitalized for respiratory failure and who required interhospital transport did not suffer higher mortality rates when compared to COVID-19 ICU patients admitted locally. However, the length of mechanical ventilation was increased in the transferred group.
Worldwide, the Sars-CoV-2 pandemic led ICU bed capacities to be exceeded. Urgent solutions such as treating patients with respiratory distress in conventional units using noninvasive respiratory support appeared feasible yet with a higher risk of staff contamination . Other temporary measures included telecritical care service to support newly formed ICU personnel . Consequently, health authorities set up two main long-term strategies: relocate work forces and construct new medical capacities and/or transfer critically ill patients to less busy areas [6, 7, 18]. The occurrence of a second and possible third wave of COVID-19 necessitated a rapid evaluation of these strategies.
Patients’ transfers between ICUs are not risk-free and can increase ICU and hospital length of stay [10, 19, 20]. Similarly, intrahospital transfer of critically ill patients is associated with pneumothorax, atelectasis, ventilator-associated pneumonia, dysglycemia, and a longer ICU length of stay in a French cohort of 6000 patients . Conversely, mortality does not seem to be impacted by intra- and inter-hospital transfers [11, 19, 20]. In France, authorities opted for medical transfer of ICU patients, predominantly via train, due to France large rail network: indeed, it operates the second-largest European railway network, with a total of 29,900 km of railway of which 2600 km are high-speed lines . Moreover, this transfer strategy was also feasible because of the network of 32 tertiary centres covering French territory, all of them being located and served by an airport and train station .
Regarding specific medical transport of COVID-19 ventilated patients, the literature is scant and most of it describes the process and the means of transporting COVID-19 patients rather than exploring their clinical and biological features [23, 24]. One study by Boutonnet et al. described the procedure of evacuating 36 COVID-19 patients via French Air Force military planes. They described that two-thirds of their patients received catecholamine infusion, yet none encountered life-threatening event during flight .
In our study the ICU mortality rate was 11%, far lower than from recent studies with large populations where the mortality rate oscillated between 30 and 50% [1, 3, 4]. Several factors could explain this discrepancy. Firstly, Rennes, Poitiers, and Tours Intensive Care Units (and by extension hospitals), were far from being overwhelmed during the study period compared to other regions in France. In fact, transferred patients accounted for nearly half of the COVID-19 patients’ admission during the study period. It enabled doctors and staff to promptly admit patients, to take time to make critical decisions such as the decision to intubate, initiate treatments, or extubate. Secondly, transferred patients were admitted in real ground concrete medical and surgical ICUs, with highly trained staff, nurses, and physicians. Thirdly, selection bias is likely to play a role in the low ICU mortality rate as most transferred patients were clinically stable before departure. Finally, because of a delay in surge of COVID-19 cases in Rennes, Poitiers, and Tours ICU, clinicians benefited from other centres experience regarding COVID-19 management, complications, and care.
Along these lines, in a recent study by Taccone et al., ICU overflow and having a high proportion of created ICU beds were independently associated with in-hospital mortality . One solution to face the next pandemic may be to increase the average number of ICU beds per inhabitant ensuring homogenous distributions across territories .
In addition to our main result, we showed that in the transferred group, PaO2/FiO2 ratio and SOFA score were similar immediately before and after transport. These findings highlight that in the COVID-19 patient population, treated for predominant respiratory illness with underlying ARDS, medical transfer did not appear to worsen their general state and specifically their respiratory function.
Furthermore, acquired infection, length of ICU and hospital stay were similar in both groups. However, length of mechanical ventilation was increased in the transferred group. This could be explained by a stop in the invasive mechanical ventilation weaning process because of the upcoming interhospital transfer and the necessity for sedation during transfer. These results may lead to the hypothesis that the need to sedate patients during transport will therefore increase the length of stay without worsening the outcome.
Following the analysis and reflections surrounding our study results, we can state that transport of COVID-19 ICU patients is safe and constitutes a possible management to face urgent and locally overwhelmed hospitals and ICU capacities. Transferring patients into non-overwhelmed areas or transferring healthcare workers into overwhelmed areas are both valuable strategies to face the pandemic. Unfortunately, efficacy, cost, and results of these two strategies have not been evaluated yet.
Our study has several limitations, including data being collected retrospectively, small number of patients and the transfer of patients’ medical file with the risk of loss of information. Furthermore, selection bias may have been introduced in choosing which patients were transferred. It is noteworthy that transferred patients have probably been selected and that the ideal control group should have been non-transferred patients from the same areas. However, at their initial admission, severity scores were identical between both groups of patients. Next, due to missing information, calculation of neuromuscular blockers duration did not include transferred patients’ pre-transportation data, hence comparison of this value between the two groups must be undertaken cautiously.
In conclusion, we found that interhospital medical transfer of mechanically ventilated COVID-19 critically ill patients did not result in a higher mortality, but did increase length of mechanical ventilation. This could be proposed as a safe strategy to manage the surge of ICU needs in the future.