Letters to the Editor: Letter to the Editor
To the Editor:
We were intrigued by the article by Yang et al.,1 “Trends of hemoglobin oximetry: Do they help predict blood transfusion during trauma patient resuscitation.” We have 3 questions for the authors.
The first concerns the clinicians’ judgment, which seemed to play a large role in the results. Of the 1191 patients enrolled in the study, only 677 were included for analysis because 34 had incomplete laboratory data, and in 480, the hemoglobinometry pulse oximeter was not placed because of the “interruption of patient care.” The hemoglobin oximetry cohort had 20 (3%) patients receiving packed red blood cells (pRBCs) within 3 hours of arrival, 29 (4.3%) within 6 hours of arrival, and 36 (5.3%) within 12 hours of arrival. Twelve patients (1.8%) died. Assuming that none of the 34 patients who had incomplete laboratory data received a transfusion or died, this would mean that in the nonhemoglobin oximetry cohort, the 480 cases in which placement of the monitor was deferred to avoid interruption of patient care, 60 (12.5%) patients received pRBC within 3 hours of arrival, 77 (16.0%) patients received pRBC within 6 hours of arrival, and 85 (17.7%) patients received pRBC within 12 hours of arrival. Forty-nine (10.2%) patients died. That is an approximately 5-fold increase in mortality potentially based on the clinician’s judgment during the first 15 minutes of the patient’s arrival (Table 1). Could the authors clarify, because this finding seems significant?
Second, could the authors comment further on the cutoff for the shock index (SI) as inclusion criteria? The authors reference Vandromme et al2 and Olaussen et al,3 who studied a wider range of the SI, with neither group giving a reason for using a 0.62 as a cutoff for the need for transfusion. Both references describe the normal range for the SI to be between 0.5 and 0.7 and the utility of this number being to help triage patients in the prehospital setting for the possible need for a large-volume transfusion. Excluding patients with a greater SI seems paradoxical for determining the need for transfusion. Therefore, as expected, few patients needed transfusions, and Yang et al state “…because relatively few of the patients were transfused, the data were skewed, so the AUROC curve was used to evaluate the transfusion discriminant capability of each classification model.”1 Would the authors have preferred to study the whole spectrum of patient SIs to determine the correlation between hemoglobinometry and transfusion?
Finally, according to Figure 4,1 only 8 of the cases had hemoglobin values <10 g/dL, and only 2 of the cases had a hemoglobin <9 g/dL. All of these patients would have an average or a better than average SI. The Society of Critical Care Medicine and the Eastern Association for the Surgery of Trauma would place the trigger for transfusion closer to 7.0 g/dL in the absence of hemorrhagic shock, evidence of acute hemorrhage, hemodynamic instability, inadequate oxygen delivery, or acute myocardial ischemia.4 Understandably, the transfusions were given at 3, 6, and 12 hours, whereas the laboratory values in this study were drawn at the first 15 minutes. Rice et al5 suggested that the clinically significant range that hemoglobinometry should study would be between 6 and 10 g/dL. Referring back to Figure 4 from Yang et al., 7 data points fall into region C in the 6 to 10 g/dL range where there are significant differences between the hemoglobinometry and laboratory values that would affect therapeutic decision making. Only 2 of 677 data points reside in the narrow isthmus of region A, which would guide accurate decision making. Can the authors comment on the significance of their findings in light of so few points in the 6 to 10 g/dL transfusion range?
Joshua W. Sappenfield, MDDepartment of AnesthesiologyUniversity of Florida College of MedicineGainesville, Floridajsappenfield@anest.ufl.edu
Mark J. Rice, MDDepartment of AnesthesiologyVanderbilt University Medical CenterNashville, Tennessee
Nikolaus Gravenstein, MDTimothy E. Morey, MDDepartment of AnesthesiologyUniversity of Florida College of MedicineGainesville, Florida
1. Yang S, Hu PF, Anazodo A, Gao C, Chen H, Wade C, Hartsky L, Miller C, Imle C, Fang R, Mackenzie CF. Trends of hemoglobin oximetry: do they help predict blood transfusion during trauma patient resuscitation? Anesth Analg 2016;122:11525.
2. Vandromme MJ, Griffin RL, Kerby JD, McGwin G Jr, Rue LW III, Weinberg JA. Identifying risk for massive transfusion in the relatively normotensive patient: utility of the prehospital shock index. J Trauma 2011;70:3848; discussion 38890.
3. Olaussen A, Blackburn T, Mitra B, Fitzgerald M. Review article: shock index for prediction of critical bleeding post-trauma: a systematic review. Emerg Med Australas 2014;26:2238.
4. Napolitano LM, Kurek S, Luchette FA, Corwin HL, Barie PS, Tisherman SA, Hebert PC, Anderson GL, Bard MR, Bromberg W, Chiu WC, Cipolle MD, Clancy KD, Diebel L, Hoff WS, Hughes KM, Munshi I, Nayduch D, Sandhu R, Yelon JA; American College of Critical Care Medicine of the Society of Critical Care Medicine; Eastern Association for the Surgery of Trauma Practice Management Workgroup. Clinical practice guideline: red blood cell transfusion in adult trauma and critical care [Erratum in: Crit Care Med 2010;38:1621]. Crit Care Med 2009;37:312457.
5. Rice MJ, Gravenstein N, Morey TE. Noninvasive hemoglobin monitoring: how accurate is enough? Anesth Analg 2013;117:9027.