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The challenge of establishing a correct serum potassium cutoff for inhospital triage after avalanche-induced cardiac arrest
Correspondence / American Journal of Emergency Medicine 34 (2016) 1300–1319
The challenge of establishing a correct serum potassium cutoff for inhospital triage after avalanche-induced cardiac arrest☆
To the Editor, We read with interest the article of Cohen et al [1], where they investigated possible association between clinical and biological parameters and signs of brain hypoxia on brain computed tomographic scan in 19 patients with avalanche-induced cardiac arrest (CA) (12 with brain hypoxia and 7 without). The authors did not find any association between prehospital clinical parameters (eg, burial time, core temperature, airway obstruction, air pocket, and prehospital cardiac rhythm) and brain hypoxia. However, the 2 groups showed a significant difference in serum potassium and some biological parameters associated with coagulation disorders. Most importantly, the authors highlighted that a threshold of 4.35 mmol/L serum potassium had 100% specificity to predict brain hypoxia on brain computed tomographic scan after avalanche-induced CA and thereby suggested to lower the serum potassium cutoff for inhospital triage. We raise some doubts as to whether these results and this suggestion may be considered clinically meaningful. First, the median burial time was 30 minutes (25-75th percentiles, 20-45 minutes) with a median maximum duration of no flow of 25 minutes (25-75th percentiles, 20-40 minutes). In the subgroup of patients with brain hypoxia, median burial time was even 27.5 minutes (2575th percentiles, 20-42.5 minutes), which strongly suggests that at least some patients were not severely hypothermic. The time to first prehospital body core temperature measurement was not defined in the study [1], but the highest cooling rate reported in a completely buried avalanche victim is 9°C per hour and was measured at extrication in a patient with stable circulation and a carotid pulse [2]. The median prehospital core temperature of 28°C (25-75th percentiles, 26°C-30°C) in the study [1] could be attributed to postextrication cooling when victims with no or low flow were exposed to low ambient temperature and received cardiopulmonary resuscitation. These results imply that the authors are extrapolating a conclusion about hypothermic avalanche victims in CA based mostly on cases of normothermic CA. Current international guidelines suggest using the parameter airway obstruction and serum potassium only in avalanche victims with CA at extrication with (i) burial time greater than 60 minutes or (ii) the initial core temperature less than 30°C, if duration of burial is unknown [3–4]. Second, the aim of hospital triage is to select and determine the priority of patient's treatments based on their conditions. Therefore, in avalanche victims, triage should exclude those patients with no or a very low probability of survival but include all others. This implies a low sensitivity (ie, only the most probable nonsurvivors would be excluded) and, therefore, a high false-negative rate (ie, many nonsurvivors will be included). On the other side, specificity must be very high, possibly close to 100%, as all survivors should be included. With a threshold of 4.35 mmol/L, a sensitivity of 67% (n = 12) and specificity of 100% (n = 7) were observed in 19 patients [1]. The currently recommended triage criteria to terminate resuscitation with respect to serum potassium is greater than 8 mmol/L [3], and therefore, the authors suggest a lower threshold [1]. However, the proposed new threshold of 4.35 mmol/L is within the physiological range (ie, serum potassium in adults between 3.5 and 5.1 mmol/L), and the exact 95% confidence intervals for the given sensitivity and specificity are 35% to 90% and 59% to 100%, respectively. Hence, specificity can be as low as 59%, and therefore, there is no guarantee that only nonsurvivors are excluded. The given threshold therefore is unreliable. Lastly, it should be considered that the highest potassium in an avalanche patient who survived with good neurologic outcome was 6.4 mmol/L [5]. Reviewing ☆ Conflict of interest statement: No conflict of interest to declare.
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potassium levels of survivors in other studies could help to strengthen or weaken the statement of this study. Unsurprisingly, also 70% of nonsurvivors in another case series of avalanche victims also had a plasma potassium concentration less than 8 mmol/L [6]. In conclusion, the present study shows that serum potassium is a valid predictor for brain hypoxia, but it is not possible to establish a threshold due to inclusion criteria and limited sample size. Moreover, prehospital triage could have lead to a patient preselection bias that did not allow to find an association between prehospital clinical parameters and brain hypoxia. Giacomo Strapazzon, MD, PhD* Markus Falk, MSc EURAC Institute of Mountain Emergency Medicine, Bolzano, Italy *Corresponding author. EURAC Institute of Mountain Emergency Medicine Viale Druso 1, 39100 Bolzano, Italy Tel.: +39 0471055 543; fax: +39 0471055 549 E-mail address: [email protected] Peter Paal, MD, MBA Department of Anaesthesiology and Critical Care Medicine Innsbruck University Hospital, Innsbruck, Austria Barts Heart Centre, St Bartholomew's Hospital, Barts Health NHS Trust Queen Mary University of London, London EC1A 7BE, United Kingdom Hermann Brugger, MD EURAC Institute of Mountain Emergency Medicine, Bolzano, Italy http://dx.doi.org/10.1016/j.ajem.2016.04.040 References [1] Cohen JG, Boué Y, Boussat B, Reymond E, Grand S, Blancher M, et al. Serum potassium concentration predicts brain hypoxia on computed tomography after avalancheinduced cardiac arrest. Am J Emerg Med 2016;34:856–60. [2] Oberhammer R, Beikircher W, Hormann C, Lorenz I, Pycha R, Adler-Kastner L, et al. Full recovery of an avalanche victim with profound hypothermia and prolonged cardiac arrest treated by extracorporeal re-warming. Resuscitation 2008;76:474–80. [3] Truhlar A, Deakin CD, Soar J, Khalifa GE, Alfonzo A, Bierens JJ, et al. European Resuscitation Council guidelines for resuscitation 2015: section 4. Cardiac arrest in special circumstances. Resuscitation 2015;95:148–201. [4] Brugger H, Durrer B, Elsensohn F, Paal P, Strapazzon G, Winterberger E, et al. Resuscitation of avalanche victims: evidence-based guidelines of the International Commission for Mountain Emergency Medicine (ICAR MEDCOM): intended for physicians and other advanced life support personnel. Resuscitation 2013;84(5):539–46. [5] Althaus U, Aeberhard P, Schupbach P, Nachbur BH, Muhlemann W. Management of profound accidental hypothermia with cardiorespiratory arrest. Ann Surg 1982;195: 492–5. [6] Mair P, Brugger H, Mair B, Moroder L, Ruttmann E. Is extracorporeal rewarming indicated in avalanche victims with unwitnessed hypothermic cardiorespiratory arrest? High Alt Med Biol 2014;15:500–3.
Blood potassium after avalanche-induced cardiac arrest: sampling method and interpretation
To the Editor, We thank Dr Monneret and Dr Strapazzon et al for their comments about our contribution [1]. They indicated their concern over the interpretation of serum potassium on hospital admission after avalancheinduced cardiac arrest. They also provided pertinent preanalytical recommendations for the adequate sampling method. This gives us the opportunity to discuss this parameter in light of our expertise for the in-hospital management of avalanche victims. First, Dr Monneret elegantly discussed preanalytical conditions that might interfere with serum potassium concentration. We totally agree with their recommendations, which apply to the measurement of
The challenge of establishing a correct serum potassium cutoff for inhospital triage after avalanche-induced cardiac arrest☆
To the Editor, We read with interest the article of Cohen et al [1], where they investigated possible association between clinical and biological parameters and signs of brain hypoxia on brain computed tomographic scan in 19 patients with avalanche-induced cardiac arrest (CA) (12 with brain hypoxia and 7 without). The authors did not find any association between prehospital clinical parameters (eg, burial time, core temperature, airway obstruction, air pocket, and prehospital cardiac rhythm) and brain hypoxia. However, the 2 groups showed a significant difference in serum potassium and some biological parameters associated with coagulation disorders. Most importantly, the authors highlighted that a threshold of 4.35 mmol/L serum potassium had 100% specificity to predict brain hypoxia on brain computed tomographic scan after avalanche-induced CA and thereby suggested to lower the serum potassium cutoff for inhospital triage. We raise some doubts as to whether these results and this suggestion may be considered clinically meaningful. First, the median burial time was 30 minutes (25-75th percentiles, 20-45 minutes) with a median maximum duration of no flow of 25 minutes (25-75th percentiles, 20-40 minutes). In the subgroup of patients with brain hypoxia, median burial time was even 27.5 minutes (2575th percentiles, 20-42.5 minutes), which strongly suggests that at least some patients were not severely hypothermic. The time to first prehospital body core temperature measurement was not defined in the study [1], but the highest cooling rate reported in a completely buried avalanche victim is 9°C per hour and was measured at extrication in a patient with stable circulation and a carotid pulse [2]. The median prehospital core temperature of 28°C (25-75th percentiles, 26°C-30°C) in the study [1] could be attributed to postextrication cooling when victims with no or low flow were exposed to low ambient temperature and received cardiopulmonary resuscitation. These results imply that the authors are extrapolating a conclusion about hypothermic avalanche victims in CA based mostly on cases of normothermic CA. Current international guidelines suggest using the parameter airway obstruction and serum potassium only in avalanche victims with CA at extrication with (i) burial time greater than 60 minutes or (ii) the initial core temperature less than 30°C, if duration of burial is unknown [3–4]. Second, the aim of hospital triage is to select and determine the priority of patient's treatments based on their conditions. Therefore, in avalanche victims, triage should exclude those patients with no or a very low probability of survival but include all others. This implies a low sensitivity (ie, only the most probable nonsurvivors would be excluded) and, therefore, a high false-negative rate (ie, many nonsurvivors will be included). On the other side, specificity must be very high, possibly close to 100%, as all survivors should be included. With a threshold of 4.35 mmol/L, a sensitivity of 67% (n = 12) and specificity of 100% (n = 7) were observed in 19 patients [1]. The currently recommended triage criteria to terminate resuscitation with respect to serum potassium is greater than 8 mmol/L [3], and therefore, the authors suggest a lower threshold [1]. However, the proposed new threshold of 4.35 mmol/L is within the physiological range (ie, serum potassium in adults between 3.5 and 5.1 mmol/L), and the exact 95% confidence intervals for the given sensitivity and specificity are 35% to 90% and 59% to 100%, respectively. Hence, specificity can be as low as 59%, and therefore, there is no guarantee that only nonsurvivors are excluded. The given threshold therefore is unreliable. Lastly, it should be considered that the highest potassium in an avalanche patient who survived with good neurologic outcome was 6.4 mmol/L [5]. Reviewing ☆ Conflict of interest statement: No conflict of interest to declare.
1317
potassium levels of survivors in other studies could help to strengthen or weaken the statement of this study. Unsurprisingly, also 70% of nonsurvivors in another case series of avalanche victims also had a plasma potassium concentration less than 8 mmol/L [6]. In conclusion, the present study shows that serum potassium is a valid predictor for brain hypoxia, but it is not possible to establish a threshold due to inclusion criteria and limited sample size. Moreover, prehospital triage could have lead to a patient preselection bias that did not allow to find an association between prehospital clinical parameters and brain hypoxia. Giacomo Strapazzon, MD, PhD* Markus Falk, MSc EURAC Institute of Mountain Emergency Medicine, Bolzano, Italy *Corresponding author. EURAC Institute of Mountain Emergency Medicine Viale Druso 1, 39100 Bolzano, Italy Tel.: +39 0471055 543; fax: +39 0471055 549 E-mail address: [email protected] Peter Paal, MD, MBA Department of Anaesthesiology and Critical Care Medicine Innsbruck University Hospital, Innsbruck, Austria Barts Heart Centre, St Bartholomew's Hospital, Barts Health NHS Trust Queen Mary University of London, London EC1A 7BE, United Kingdom Hermann Brugger, MD EURAC Institute of Mountain Emergency Medicine, Bolzano, Italy http://dx.doi.org/10.1016/j.ajem.2016.04.040 References [1] Cohen JG, Boué Y, Boussat B, Reymond E, Grand S, Blancher M, et al. Serum potassium concentration predicts brain hypoxia on computed tomography after avalancheinduced cardiac arrest. Am J Emerg Med 2016;34:856–60. [2] Oberhammer R, Beikircher W, Hormann C, Lorenz I, Pycha R, Adler-Kastner L, et al. Full recovery of an avalanche victim with profound hypothermia and prolonged cardiac arrest treated by extracorporeal re-warming. Resuscitation 2008;76:474–80. [3] Truhlar A, Deakin CD, Soar J, Khalifa GE, Alfonzo A, Bierens JJ, et al. European Resuscitation Council guidelines for resuscitation 2015: section 4. Cardiac arrest in special circumstances. Resuscitation 2015;95:148–201. [4] Brugger H, Durrer B, Elsensohn F, Paal P, Strapazzon G, Winterberger E, et al. Resuscitation of avalanche victims: evidence-based guidelines of the International Commission for Mountain Emergency Medicine (ICAR MEDCOM): intended for physicians and other advanced life support personnel. Resuscitation 2013;84(5):539–46. [5] Althaus U, Aeberhard P, Schupbach P, Nachbur BH, Muhlemann W. Management of profound accidental hypothermia with cardiorespiratory arrest. Ann Surg 1982;195: 492–5. [6] Mair P, Brugger H, Mair B, Moroder L, Ruttmann E. Is extracorporeal rewarming indicated in avalanche victims with unwitnessed hypothermic cardiorespiratory arrest? High Alt Med Biol 2014;15:500–3.
Blood potassium after avalanche-induced cardiac arrest: sampling method and interpretation
To the Editor, We thank Dr Monneret and Dr Strapazzon et al for their comments about our contribution [1]. They indicated their concern over the interpretation of serum potassium on hospital admission after avalancheinduced cardiac arrest. They also provided pertinent preanalytical recommendations for the adequate sampling method. This gives us the opportunity to discuss this parameter in light of our expertise for the in-hospital management of avalanche victims. First, Dr Monneret elegantly discussed preanalytical conditions that might interfere with serum potassium concentration. We totally agree with their recommendations, which apply to the measurement of