CORRESPONDENCE

cial technology of external cardiac pacing to the current t rea tment . In this s i tua t ion i t appears unnecessary to sta- t i s t ica l ly rule out a de t r imenta l effect. If the more appro- priate one-tai led test is appl ied to Dr Maio 's example, only 121 pa t ien ts are needed in each s tudy arm to detect his desired 10% benefit . ~ In view of this, our s tudy does have appropriate s ta t is t ica l power to address the re levant clini- cal quest ion: does prehospi ta l external cardiac pacing im- prove survival in this pa t ien t populat ion?

Of note is that we did f ind a s ta t i s t ica l ly significant dif- ference in the bradycardic group, and the authors feel this

may be the mos t impor tan t resul t (taken in context of the l i m i t a t i o n d iscussed in the paper) of the study. As we s ta ted in the paper, we encourage further s tudy of this is- sue to del ineate all potent ia l benefits of external pacing.

Edward Barthell, MD Department of Emergency Medicine Medical College of Wisconsin Milwaukee

1. Meinert CL, Tonaseia S: Clinical Trials: Design, Conduct and Analysis. New York, Oxford University Press, 1986, p 71-89.

Of Mice and Men

To the Editor: Lest our fel low emergency physic ians despair over the

cont inuing bat t le for p r imary board recogni t ion status, I would l ike to po in t out that the Advisory Board on Veter- inary Specia l t ies r ecen t ly granted p rov i s iona l A m e r i c a n Veter inary Medica l Assoc ia t ion (AVMA) recogn i t ion to the A m e r i c a n Col lege of Ve te r ina ry Emergency Medi - cine. 1 Can h u m a n beings be far behind?

Marc S Nelson, MD, FACEP Division of Emergency Medicine Stanford University School of Medicine Stanford, California

1. Jordan CS: Specialty board recognizes emergency medicine and critical care. J Am Vet Med Assoc 1989;194:1397.

Progress in Blood Warming

To the Editor: Drs Flancbaum, Trooskin, and Pedersen present inter-

es t ing data in their ar t ic le "Evaluat ion of Blood-Warming Devices W i t h the Apparen t T h e r m a l C lea rance" [April 1989;18:355-359]. However, in their discussion, they con- fuse the issues related to rapid blood warming by repeat- ing the fallacy that "contac t w i th tempera tures of more than 40 C leads to hemolys i s of red blood cells and de- n a t u r a t i o n of p r o t e i n s . " T h i s s t a t e m e n t is b a s e d on studies of prolonged incubat ion (more than 15 minutes) at higher tempera tures (more than 45 C), rather than rapid blood warming. 1

T h e m i s i n t e r p r e t a t i o n of th i s i n f o r m a t i o n has done more to hold back progress in blood warming than any one other factor. It is unfor tuna te that i t should be perpet- ua ted here, espec ia l ly s ince several recen t pub l i ca t ions have d e m o n s t r a t e d the efficacy of us ing m u c h warmer , but very short contact , t empera tures to successful ly warm b lood by a d m i x t u r e A -4 In add i t ion , w h i l e the a u tho r s men t i on problems that have been encountered wi th some techniques of prewarming blood, they fail to men t ion this h ighly promis ing me thod of admix ture blood warming.

It should be emphas ized that, un l ike the b lood-warming devices tested, 37 C blood can be infused by the admix- ture t echn ique as rap id ly as the f luid de l ivery sy s t em (catheter, tubing, pressure device) wi l l allow. It is also in- expensive enough to be used in v i r tua l ly any hospital .

Kenneth V Iserson, MD, FACEP Section of Emergency Medicine University of Arizona College of Medicine Tucson

1. Chalmers C, Russell WJ: When does blood hemolyse? A temperature study. Br J Anaesth 1974;46:742-746. 2. Wilson EB, Iserson KV: Admixture blood warming: A technique for rapid warming of erythrocytes. Ann Emerg Med 1987;16:4:413-416. 3. Wilson EB, Knauf MA, Iserson KV: Red cell tolerance of admixture with heated saline. Transfusion 1988i28:2:170-172. 4. Wilson EB, Knauf MA, Donohoe K, et al: Red blood cell survival follow- ing admixture with heated saline: Evaluation of a new blood warming method for rapid transfusion. [ Trauma 1988;28:8:1274-1277.

In Reply: In his letter, Dr Iserson correct ly points out that hemo-

lysis and denatura t ion of prote ins in warmed blood occur fol lowing exposure to tempera tures of more than 45 C for more than 15 minutes . We are grateful and acknowledge that use of the t e rm "prolonged" might have been better. However, the s t a tement in our art icle to which he refers was part of a descr ipt ion of factors and concepts tha t have inf luenced the deve lopment and design of blood warming devices to date, and in that context remains accurate and could hardly be said to hamper progress in blood warming.

Our ar t ic le dealt specifical ly wi th the appl ica t ion of a theoret ica l model for the design of blood warmers to com- merc ia l ly available uni ts in order to provide a useful stan- dard (the apparent thermal clearance) for evaluat ion and comparison. It did not deal wi th warming blood per se, and for that reason a discussion of techniques such as ad- m ix tu r e blood w a r m i n g was no t warranted . The refer-

184/1024 Annals of Emergency Medicine 18:9 September 1989