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Reply to Letter: Prehospital physician involvement and survival after out-of-hospital cardiac arrest
G Model
ARTICLE IN PRESS
RESUS-7054; No. of Pages 1
Resuscitation xxx (2017) xxx.e1
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Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Letter to the Editor Reply to Letter: Prehospital physician involvement and survival after out-of-hospital cardiac arrest Sir, Gunnar H. Laier has questioned whether our findings of prehospital involvement of physicians (PIP) contributing positively to survival after out-of-hospital cardiac arrest (OHCA) were biased by confounding and/or effect modification, especially by the variables “time to first rhythm check” and “calendar year”. We sincerely welcome a discussion of our findings, and are grateful for the thoughtful comments. When analyzing our data, we had concerns similar to those of Dr. Laier. Indeed, and as mentioned in our article, we applied several models and stratified analyses to minimize the risk of drawing biased conclusions. All multivariable models included time to first rhythm check as well as calendar year, and all results pointed in the same direction. One should remember that we found increased survival both in analyses of the full data set as well as in the sub-analysis of cases with less than ten minutes to first rhythm check. This has been discussed in the article. Hence, we disagree with Dr. Laier’s statement that we “discount the bias due to increased survival among PIP patients [because only doctors are allowed to declare a person dead]”. Also mentioned and discussed in the article, the positive association between exposure and outcome was consistent across all strata of the two variables; although the relative effect of PIP was lesser in later years probably due to improvements in survival among the non-exposed. Finally, Dr. Laier mentions the absence of the variable “response time” in our model. Response time measures the time for the vehicle to reach the address, but from here, the time to reach the exact location of the patient within the building, getting access to and assessing the patient, and applying the monitor may vary. We used the clinically more appropriate “time to first rhythm check” in which response time is included which measures the time to when professionals have reached the patient and can begin resuscitation.
As written in our paper we acknowledge the other differences between the two exposure groups, and these potential confounders/effect modifiers have been checked in several multivariable models, and tested for interaction in the propensity score-matched model. In conclusion, we appreciate the time Dr. Laier has taken to read and comment on our study, and hopefully we have addressed his and potentially other readers concerns. Let us lastly mention that the positive effect of physician involvement is rarely questioned elsewhere in the health care system e.g. in-hospital. In most departments such as emergency rooms and intensive care units, physicians are a natural part of the treatment and care teams, even though the presence of a physician even in these settings is strictly speaking not evidence based. So even though it has been difficult to show the positive effect of PIP in previous observational studies in patients with cardiac arrest, our findings should come as no surprise. Conflict of interest statement JS is working as a physician on a physician-staffed mobile critical care unit and receive personal grants for that. AH and NL declare no conflicts of interest. Annika Hamilton ∗ Jacob Steinmetz Nicolai Lohse ∗ Corresponding
author at: Hvidovre, Denmark. E-mail address: [email protected] (A. Hamilton) 24 January 2017
http://dx.doi.org/10.1016/j.resuscitation.2017.01.021 0300-9572/© 2017 Published by Elsevier Ireland Ltd.
Please cite this article in press as: Hamilton A, et al. Reply to Letter: Prehospital physician involvement and survival after out-of-hospital cardiac arrest. Resuscitation (2017), http://dx.doi.org/10.1016/j.resuscitation.2017.01.021
ARTICLE IN PRESS
RESUS-7054; No. of Pages 1
Resuscitation xxx (2017) xxx.e1
Contents lists available at ScienceDirect
Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Letter to the Editor Reply to Letter: Prehospital physician involvement and survival after out-of-hospital cardiac arrest Sir, Gunnar H. Laier has questioned whether our findings of prehospital involvement of physicians (PIP) contributing positively to survival after out-of-hospital cardiac arrest (OHCA) were biased by confounding and/or effect modification, especially by the variables “time to first rhythm check” and “calendar year”. We sincerely welcome a discussion of our findings, and are grateful for the thoughtful comments. When analyzing our data, we had concerns similar to those of Dr. Laier. Indeed, and as mentioned in our article, we applied several models and stratified analyses to minimize the risk of drawing biased conclusions. All multivariable models included time to first rhythm check as well as calendar year, and all results pointed in the same direction. One should remember that we found increased survival both in analyses of the full data set as well as in the sub-analysis of cases with less than ten minutes to first rhythm check. This has been discussed in the article. Hence, we disagree with Dr. Laier’s statement that we “discount the bias due to increased survival among PIP patients [because only doctors are allowed to declare a person dead]”. Also mentioned and discussed in the article, the positive association between exposure and outcome was consistent across all strata of the two variables; although the relative effect of PIP was lesser in later years probably due to improvements in survival among the non-exposed. Finally, Dr. Laier mentions the absence of the variable “response time” in our model. Response time measures the time for the vehicle to reach the address, but from here, the time to reach the exact location of the patient within the building, getting access to and assessing the patient, and applying the monitor may vary. We used the clinically more appropriate “time to first rhythm check” in which response time is included which measures the time to when professionals have reached the patient and can begin resuscitation.
As written in our paper we acknowledge the other differences between the two exposure groups, and these potential confounders/effect modifiers have been checked in several multivariable models, and tested for interaction in the propensity score-matched model. In conclusion, we appreciate the time Dr. Laier has taken to read and comment on our study, and hopefully we have addressed his and potentially other readers concerns. Let us lastly mention that the positive effect of physician involvement is rarely questioned elsewhere in the health care system e.g. in-hospital. In most departments such as emergency rooms and intensive care units, physicians are a natural part of the treatment and care teams, even though the presence of a physician even in these settings is strictly speaking not evidence based. So even though it has been difficult to show the positive effect of PIP in previous observational studies in patients with cardiac arrest, our findings should come as no surprise. Conflict of interest statement JS is working as a physician on a physician-staffed mobile critical care unit and receive personal grants for that. AH and NL declare no conflicts of interest. Annika Hamilton ∗ Jacob Steinmetz Nicolai Lohse ∗ Corresponding
author at: Hvidovre, Denmark. E-mail address: [email protected] (A. Hamilton) 24 January 2017
http://dx.doi.org/10.1016/j.resuscitation.2017.01.021 0300-9572/© 2017 Published by Elsevier Ireland Ltd.
Please cite this article in press as: Hamilton A, et al. Reply to Letter: Prehospital physician involvement and survival after out-of-hospital cardiac arrest. Resuscitation (2017), http://dx.doi.org/10.1016/j.resuscitation.2017.01.021