Prehospital Therapeutic Hypothermia in Patients With Out-Of-Hospital Cardiac Arrest 1

To the Editor Dr Kim and colleagues investigated the benefits of prehospital therapeutic hypothermia in patients successfully resuscitated from out-of-hospital cardiac arrest when compared with standard in-hospital cooling. Although this study confirmed2 that prehospital cooling is effective in reducing patients’ temperature and in achieving the target of 34°C earlier, Kim et al1 found no differences either in survival rates or in intact neurological outcomes between the 2 strategies. Some important issues should be further discussed to better interpret the results. First, not all randomized patients were treated with therapeutic hypothermia during the study period; only 435 patients (74%) of 583 with a shockable rhythm and 461 patients (59%) of 776 with a nonshockable rhythm eventually reached the target temperature (based on eTable 2 in the Supplement). Thus, the benefits from prehospital hypothermia may have been blunted because cooling procedures were not continued after hospital admission. In another study,3 the use of prehospital hypothermia (although intra-arrest) increased the number of patients achieving a return to spontaneous circulation and being admitted alive to the hospital; however, only 13% of the cohort received in-hospital therapeutic hypothermia and there was no increase in survival. Second, we question the use of cold fluids to induce prehospital hypothermia. Although easy to use and inexpensive, cold fluids have been associated with several complications, including pulmonary edema, as discussed by Kim et al.1 In a systematic review4 of experimental studies comparing cold fluids with other strategies to induce intra-arrest hypothermia, cold fluids were associated with a poorer outcome. This may be related to a reduction in the coronary perfusion pressure; negative hemodynamic effects could be even more evident in patients with moderate to severe heart disease. As such, hemodynamic monitoring may be useful to better understand the effect of fluids administered in the prehospital setting. Moreover, the use of saline solutions may produce detrimental effects on blood pH and renal function,5 with worsening circulatory instability that could contribute to rearrest. Third, temperature at the time of hospital admission was similar between groups (difference

Prehospital therapeutic hypothermia in patients with out-of-hospital cardiac arrest--reply.

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