We would like to thank the authors for their valuable comments on our study, wherein we investigated how pre-hospital lactate (P-LACT) measurements could be used to predict the need for (ongoing) in-hospital blood product transfusion in patients attended by HEMS with major traumatic haemorrhage.
As mentioned in our article, the algorithm we developed is a decision support tool, which means that it should be used in conjunction with other parameters, such as clinical gestalt in a heuristic approach to estimate transfusion requirements. The cut-off value of a P-LACT < 2.5 mmol/l used in our population yielded a sensitivity of 80% (corresponding to a low probability of major haemorrhage as the authors rightly mention), and hence was inadequate to be used in isolation. The SOP in our service states that a P-LACT < 2.5 mmol/l is used in conjunction with an SBP > 100mmHg to identify patients who have a low probability of major hemorrhage. This is supported by a recent publication of Gaessler et al. (2023) wherein the authors show that P-LACT and SBP are complimentary in terms of predictive probability [1].
To identify patients with a high likelihood of major haemorrhage requiring in-hospital transfusion, a P-LACT of 6.0 mmol/l was used, as at this this point the predicted probability curve (Fig. 2 in our original article) starts to flatten: using a higher cut-off would not have yielded a higher specificity, whereas a lower cut-off would have dropped specificity whilst not yielding a much higher proportion of the population meeting the cut-off criteria (n = 13, 6.7% for a lactate of 6.0 mmol/l vs. n = 17, 8.7% for a lactate of 5.5 mmol/l). Although we agree that it is likely that many patients with a lactate > 6.0 mmol/l will show clinical signs of shock, 5/13 patients had an SBP > 100 mmHg on first occasion, two of whom also did not exhibit tachycardia. In these patients P-LACT may still be a useful tool. Despite this however, the major challenge remains to identify the bleeding patients in the P-LACT group of 2.5-6 mmol/l, and serial measurements may be the way forward in this group.
Finally, we acknowledge that transfusion requirement is not always a good surrogate to use for outcome, especially not when confounding by indication may be present: using lactate may result in transfusing more patients in the pre-hospital setting, which again may result in a lower threshold to continue transfusion in-hospital. However, as 2/3 of the patients in our cohort received a massive transfusion (> 10 units PRBC within 24 h) rather than a major transfusion, we think transfusion requirement was a reasonable surrogate for risk of death from bleeding in our population. We agree however, that ideally outcome studies should be performed using hard endpoints to confirm this.
Not applicable.
Gaessler H, Helm M, Kulla M, et al. Prehospital predicto
To the editor,
We thank van Veelen and colleagues for their interest in our article on an ascent to high altitude on physical exhaustion during cardiopulmonary resuscitation (CPR) [1].
We wholeheartedly concur with the assessment that performing CPR under such unique circumstances requires greater effort and impairs providers’ ability to adhere to resuscitation guidelines at high altitudes. Whether the ascent was simulated through the use of a hypobaric chamber [2], made by car [3], or through an arduous ascent exceeding 1,200 m as in our case [1], the analysis of vital parameters showed pronounced exhaustion due to the demands of chest compressions at high altitude.
From this perspective, the findings by van Veelen et al. on providers’ struggle to reliably self-evaluate the quality of chest compressions at high altitudes is both interesting and significant. This is in line with our previous findings on the discrepancy between subjective exhaustion and actual quality of CPR at high altitude [4]. We could demonstrate that during ventilation phases, heart rate immediately decreases, even after 14 min of CPR, underlining the importance of frequent resting phases.
We also concur with the assessment of a need for widespread adoption of mechanical chest compression devices in alpine settings, as those have been shown to be viable, even in difficult terrain [5].
We fully endorse the call to adjust the guidelines for CPR in the alpine setting in the light of recent findings. There is a critical need to emphasize the widespread use of mechanical chest compression devices. In their absence, a minute-by-minute rotation of chest compressions might be advocated and should be further studied.
Niederer M, Tscherny K, Burger J, et al. Influence of high altitude after a prior ascent on physical exhaustion during cardiopulmonary resuscitation: a randomised crossover alpine field experiment. Scand J Trauma Resusc Emerg Med. 24. Oktober 2023;31(1):59.
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Vögele A, Van Veelen MJ, Dal Cappello Tet al. Effect of Acute Exposure to Altitude on the Quality of Chest Compression-Only Cardiopulmonary Resuscitation in Helicopter Emergency Medical Services Personnel: A Randomized, Controlled, Single‐Blind Crossover Trial. J Am Heart Assoc. 7. Dezember 2021;10(23):e021090.
Narahara H, Kimura M, Suto T, et al. Effects of Cardiopulmonary Resuscitation at High Altitudes on the Physical Condition of untrained and unacclimatized rescuers. Wilderness Environ Med Juni. 2012;23(2):161–4.
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Egger A, Niederer M, Tscherny K, et al. Influence of physical strain at high altitude on the quality of cardiopulmonary resuscitation. Scand J Trauma Resusc Emerg Med Dezember. 2020;28(1):19.
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