Correspondence / American Journal of Emergency Medicine 36 (2018) 1300-1320 1319

Wojciech Wieczorek, MSc, EMT-P Department of Anaesthesiology, Intensive Care and Emergency Medicine in Zabrze, Medical University of Silesia, Katowice, Poland

Jacek Smereka, PhD, MD

Department of Emergency Medical Service, Wroclaw Medical University,

Wroclaw, Poland

Jerzy R. Ladny, PhD, MD, Prof.

Department of Emergency Medicine and Disaster, Medical University

Bialystok, Bialystok, Poland

Halla Kaminska, PhD, MD

Department of Children’s Diabetology, Medical University of Silesia,

Katowice, Poland

Robert Galazkowski, PhD

Department of Emergency Medical Service, Medical University of Warsaw,

Warsaw, Poland

Lukasz Szarpak, PhD, DPH, EMT-P

Department of Emergency Medicine and Disaster, Medical University

Bialystok, Bialystok, Poland Department of Emergency Medical Service, Medical University of Warsaw,

Warsaw, Poland Corresponding author at: Department of Emergency Medicine, Medical University of Warsaw, 4 Lindleya Str., 02-005Warsaw, Poland.

E-mail address: [email protected]

16 October 2017

First, it seems the estimated confidence interval (CI) for effect of lower fibrinogen on in-hospital mortality in multivariable model is ex- cessively wide, e.g. 1.660 to 18.40. Here it seems that collinearity among the lower fibrinogen and other covariates decline the precision of the estimated odds ratio (OR) for lower fibrinogen. When studying the relatively correlated predictors, it may be wiser to test collinearity among the studied predictors with efficient statistical methods such as variance inflation factor before regression analysis.

Second, the authors recruited a consecutive sample of patients for the study. Such selection of patients can increase risk of selection bias. This bias can occur when the association between predictor and outcome in study population is different from true association between predictor and outcome in target population. Here, the estimated OR for association lower fibrinogen on in-hospital mortality may be different true OR in tar- get population. Fortunately, there are several statistical methods to deter- mine how much the results are influenced by selection bias [2].

Third, the authors reported ORs and area under the curve (AUC) that

have not been corrected for model uncertainty and optimism. Bootstrap resampling is an efficient statistical method for correcting over fitting and quantify optimism in regression models [3].

Conflict of interest

None.

Acknowledgment

This work was not supported by any organization.

https://doi.org/10.1016/j.ajem.2017.11.061

References

Beesems SG, Hardig BM, Nilsson A, Koster RW. Force and depth of mechanical chest com- pressions and their relation to chest height and gender in an out-of-hospital setting. Re- suscitation 2015;91:67-72. https://doi.org/10.1016/j.resuscitation.2015.03.020.

Szarpak L, Filipiak KJ, Ladny JR, Smereka J. Should nurses use mechanical chest com- pression devices during CPR? Am J Emerg Med 2016 Oct;34(10):2044-5. https://doi. org/10.1016/j.ajem.2016.07.057.

Abelairas-Gomez C, Barcala-Furelos R, Szarpak L, Garcia-Garcia O, Paz-Dominguez A, Lopez- Garcia S, et al. The effect of strength training on quality of prolonged basic cardiopulmonary resuscitation. Kardiol Pol 2017;75(1):21-7. https://doi.org/10.5603/KP.a2016.0165.

Wieczorek W, Smereka J, Szarpak L, Kaminska H. Which position for resuscitation should we take? A randomized crossover manikin study. Am J Emerg Med 2017 Sep 29. https://doi.org/10.1016/j.ajem.2017.09.043 (pii: S0735-6757(17)30787-8).

Kurowski A, Szarpak L, Bogdanski L, Zasko P, Czyzewski L. Comparison of the effec- tiveness of cardiopulmonary resuscitation with standard manual chest compressions and the use of TrueCPR and PocketCPR Feedback devices. Kardiol Pol 2015;73(10): 924-30. https://doi.org/10.5603/KP.a2015.0084.

Truszewski Z, Szarpak L, Kurowski A, Evrin T, Zasko P, Bogdanski L, et al. Randomized

trial of the chest compressions effectiveness comparing 3 feedback CPR devices and standard basic life support by nurses. Am J Emerg Med 2016;34(3):381-5. https://doi.org/10.1016/j.ajem.2015.11.003.

Comments on the relationship between fibrinogen and in-hospital mortality in patients with Type A acute aortic dissection

Dear Editor-in-Chief,

We were interested to read the article by Liu et al. that was pub- lished in the American Journal of Emergency Medicine [1]. After reading this article carefully and critically, we noticed some methodological and statistical issues that did not addressed or mentioned as limitations of the study. We therefore wish to highlight these issues as follows:

Saeid Safiri Managerial Epidemiology Research Center, Department of Public Health, School of Nursing and Midwifery, Maragheh University of Medical Sciences,

Maragheh, Iran

Erfan Ayubi

Department of Epidemiology, School of Public Health, Shahid Beheshti

University of Medical Sciences, Tehran, Iran Department of Epidemiology & Biostatistics, School of Public Health, Tehran

University of Medical Sciences, Tehran, Iran Corresponding author at: Department of Epidemiology, School of Public Health, ShahidBeheshti University of Medical Sciences, Tehran, Iran.

E-mail address: [email protected] (E. Ayubi).

25 October 2017

https://doi.org/10.1016/j.ajem.2017.11.063

References

1. Liu J, Sun L-L, Wang J, Ji G. The relationship between fibrinogen and in-hospital mor- tality in patients with type A acute aortic dissection. Am J Emerg Med 2017.
2. Orsini N, Bellocco R, Bottai M, Wolk A, Greenland S. A tool for deterministic and prob- abilistic sensitivity analysis of epidemiologic studies; 2008.
3. Steyerberg E. Clinical prediction models: A practical approach to development, valida- tion, and updating. Springer Science & Business Media; 2008.

   C-reactive protein value is a strong predictor of acute appendicitis in young children

   Dear Editor,

   Acute appendicitis is the one of the most common Surgical emergencies we encounter in daily practice. The diagnosis of AA is based on clinical history, physical examination, laboratory tests