Avoid common mistakes on your manuscript.
Dear Editor,
During the coronavirus disease 2019 (COVID-19) outbreak in the Netherlands, a serious lack of intensive care unit (ICU) beds arose. ICU patients were distributed nationwide by ground-based Mobile Intensive Care Units. In addition, we used an EC-145 Airbus helicopter for long-distance inter-hospital transport, staffed by experienced Helicopter Emergency Medical Service anesthesiologists.
Clinical guidelines from the United Kingdom Intensive Care Society assert that, during helicopter transport, vibration and acceleration/deceleration forces significantly adversely affect patient hemodynamics and monitoring [1]. However, evaluation of the impact of helicopter transport on physiological variables is scarce [2] and frequent serial measurements are lacking. Accordingly, we undertook a prospective observational cohort study in mechanically ventilated patients with COVID-19 to determine whether changes in physiological variables occurred during helicopter transport.
Between March 2020 and March 2021, we measured invasive mean arterial blood pressure (MAP), arterial oxygen saturation (SpO2), heart rate (HR) and end-tidal carbon dioxide partial pressure (PET CO2) with 1-min intervals during transport. Three time spans were defined: the last 10 min before helicopter take-off (Tref), time spent airborne (Tair), and the first 10 min after landing (Tground). Tref served as reference for Tair and Tground. Our longitudinal study has the distinguishing feature that the physiological variables are measured numerous times on each patient. To account for the within-subject correlation of repeated measurements, we used generalized linear mixed-effects models. Such a model allows to analyse the effect of time span on the physiological response variables. Critical thresholds were defined for MAP, SpO2 and HR [3, 4].
In 117 patients, we obtained a total of 32,664 measurements (8166 per variable) (Fig. 1). Supplementary Material shows details on transfers and patients.
Patients were airborne for 50 (SD = 15) min. During Tref, average MAP, SpO2, HR and PET CO2 were 84 (95% CI = 82–86) mmHg, 93.8 (93.5–94.2) %, 83 (79–87) bpm and 42 (40–43) mmHg, respectively. During Tair, these values decreased with 1.8 (1.2–2.5) mmHg, 0.2 (0.1–0.3) %, 1.7 (1.4–2.1) bpm and 1.4 (1.3–1.6) mmHg, respectively. All differences between Tref and Tair, and between Tref and Tground may be qualified as clinically irrelevant. This applies to the point estimates as well as to the entire range of the 95% confidence intervals (Table S3).
Potentially harmful events, such as MAP < 65 mmHg or SpO2 < 90% for more than 5 min, occurred only in a minority of patients (Fig. S2). More importantly, these events were less likely to occur during the time spent airborne than on firm ground before take-off (Table S3). For Tair:Tref, odds ratios were 0.34 (95% CI = 0.26–0.43) and 0.23 (0.16–0.35) for MAP and SpO2, respectively. For Tground:Tref, these odds ratios were 0.49 (0.35–0.68) and 0.21 (0.12–0.39).
No life-threatening complications occurred. The number of minor adverse events per hour was lowest during Tair (Table S4).
In conclusion, being airborne aboard a helicopter had minimal and clinically irrelevant impact on the physiological variables, compared with the reference period prior to take-off. Noteworthy, a simulation study showed that variations in invasive blood pressure readings during accelerations or decelerations can be artifacts resulting from inevitable physical phenomena [5]. The time courses of physiological variables and absence of complications suggest that helicopter transport can contribute to safe inter-hospital transfers of ventilated COVID-19 patients. Although we cannot exclude that sicker patients may have been triaged away from air transport, our findings may be of relevance in deciding how to transport critically ill patients.
Data availability
All the data that support the findings of this study will be available from the corresponding author upon reasonable request.
References
Intensive Care Society (2019) Guidance on: the transfer of the critically ill adult. The faculty of intensive care medicine. https://www.gmccmt.org.uk/wp-content/uploads/2019/10/ICS-2019-Transfer-Guidance.pdf. Accessed 7 Jan 2022
Seymour CW, Kahn JM, Schwab CW, Fuchs BD (2008) Adverse events during rotary-wing transport of mechanically ventilated patients: a retrospective cohort study. Crit Care 12:R71. https://doi.org/10.1186/cc6909
Asfar P, Radermacher P, Ostermann M (2018) MAP of 65: target of the past? Intensive Care Med 44:1551–1552. https://doi.org/10.1007/s00134-018-5292-8
Alhazzani W, Moller MH, Arabi YM, Loeb M, Gong MN, Fan E, Oczkowski S, Levy MM, Derde L, Dzierba A, Du B, Aboodi M, Wunsch H, Cecconi M, Koh Y, Chertow DS, Maitland K, Alshamsi F, Belley-Cote E, Greco M, Laundy M, Morgan JS, Kesecioglu J, McGeer A, Mermel L, Mammen MJ, Alexander PE, Arrington A, Centofanti JE, Citerio G, Baw B, Memish ZA, Hammond N, Hayden FG, Evans L, Rhodes A (2020) Surviving Sepsis Campaign: guidelines on the management of critically ill adults with Coronavirus Disease 2019 (COVID-19). Intensive Care Med 46:854–887. https://doi.org/10.1007/s00134-020-06022-5
Droogh JM, Reinke L, Snel GJ, Mouthaan B, Struys MM, Ligtenberg JJ, Keus F, Zijlstra JG (2014) Arterial blood pressure changes induced by acceleration during mobile intensive care unit patient transport are not patient related: beware of misinterpretation. Intensive Care Med 40:460–461. https://doi.org/10.1007/s00134-013-3195-2
Acknowledgements
We would like to thank Hans van der Hoeven and Patrick Schober for their critical remarks on earlier versions of the manuscript.
Funding
None.
Author information
Authors and Affiliations
Contributions
All the authors have contributed substantially to the conception and design of the study, the acquisition of data, or the analysis and interpretation of the data. All the authors drafted or provided critical revision of the article. All the authors approved the final version submitted for publication. Detailed contributions: conception and design: ES, CS, GJG, JL, and EB. Data collection: ES, CS, and GJG. Analysis and interpretation of data: ES, GJG, JL, and EB. Critical revision of the manuscript for important intellectual content and approval of the final version to be published: all the authors.
Corresponding author
Ethics declarations
Conflicts of interest
The authors have no conflict of interest.
Compliance with ethical standards
Permission to use the data collected during this new operation was granted by the Medical Ethics Committee Arnhem-Nijmegen (file 2020-6822) on 29 July, 2020. Additional approval was granted 10 February 2021 (file 2021-7313) and 22 November 2021 (amendment date), including a waiver for informed consent.
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Information
Below is the link to the electronic supplementary material.
134_2022_6686_MOESM1_ESM.pdf
The online version of this research letter contains supplementary material that is available to authorized users. (PDF 727 KB)
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, which permits any non-commercial use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc/4.0/.
About this article
Cite this article
Spoelder, E.J., Lerou, J., Bronkhorst, E. et al. Time course of physiological variables during inter-hospital helicopter transport of ventilated COVID-19 patients. Intensive Care Med 48, 756–758 (2022). https://doi.org/10.1007/s00134-022-06686-1
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00134-022-06686-1