Statistical Analysis Needed in Catheter Flow

To the Editor." We found the a r t i c le by Dula and col leagues [April

1985;14:303-306] to be interesting. The catheter flow rate achieved roughly correlates to that of our previous work,2-4 but we have some serious problems with the data and sta- t ist ical analysis.

First, in looking at the table we note that the baseline means of the cardiac output are substantial ly different. In fact, because the baseline means for the experimental ani- maps cardiac outputs are stat ist ically different (P < .05), any subsequent data are invali& Second, the standard deviations (43.65, 30.64, 28.28, 34.72) noted in Groups 1 and 2 for the mean arterial pressure are out of proportion to the small sample size (n = 3). Because of these problems, these data alone are inadequate to substant ia te the authors ' conclu- sions.

Any study wi th clear group comparisons calls for statis- t ical "significance" testing to support the conclusions.

Kenneth V Iserson, MD, FACEP Alan Reeter, MSEE Elizabeth Criss, RN Section of Emergency Medicine University of Arizona Health Sciences Center Tucson, Arizona

1. Iserson KV, Retter AK: Rapid fluid replacement: A new meth- odology. Ann Emerg Med 1984;13:97-100.

Rate Study

2. Reeter AK, Iserson KV: A new device for rapid fluid replace- ment. J Clin Engineer 1984;9:37-41.

3. Iserson KV, Reeter AK, Criss E: Comparison of flow rates for standard and large bore tubing. West J Med 1985;143:183-185.

4. Iserson KV, Reeter AK, Woods W, et al: Pressurization of IV Bags: A new configuration and evaluation for use. J Emerg Med 1985;3:89-92.

In Reply: I agree wi th the problems incurred with performing sta-

t istical analysis on the data of my study of rapid flow. It was a small sample size of each study group, and I was unable to demons t ra te s ta t i s t ica l ly significant results. Despi te this flaw, we felt it sti l l was worthwhile to report the data we collected as suggestive evidence of what may be encoun- tered clinically.

I agree wi th the correspondents' conclusion that further testing wi th a larger sample size is necessary to determine if the results are stat ist ically significant.

David J Dula, MD Department of Emergency Medicine Geisinger Medical Center Danville, Pennsylvania

Use of Large.Bore Catheter

To the Editor: The article by Aeder, et al enti t led "Technical Limitat ions

in t he R a p i d I n f u s i o n of I n t r a v e n o u s F l u i d s " [Apr i l 1985; 14:307-310] discussed the l imitat ions of rapid fluid de- livery. The results described by these authors agree roughly wi th those of our own work in this area.l-a We have taken this further and developed a large-bore catheter capable of delivering 850 mL/min with gravity drainage in vitro and 650 mL/min in vivo. Use of this catheter in animals and human beings has caused no untoward vein wall damage.

More important ly, we have found that in pract ice the average flow rate to a pat ient is strongly affected by the abil- i ty of the staff to mainta in IV bag pressure and rapidly re- place empty bags. 4 As the catheter and tubing increase in size, these other factors become increasingly important . A catheter tubing combina t ion that increases flow rate by 30% in the laboratory often will increase "in-practice" flow rates by o n l y 10% unless the external factors also are ad- dressed.

Kenneth V Iserson, MD, FACEP Alan Reeter, MSEE Elizabeth Criss, RN Section of Emergency Medicine University of Arizona Health Sciences Center Tucson, Arizona

1. Iserson KV, Reeter AK: Rapid fluid replacement: A new meth- odology. Ann Emerg Med 1984;13:97-100.

2. Reeter AK, Iserson KV: A new device for rapid fluid replace- ment. J Clin Engineer 1984;9:37-41.

3. Iserson KV, Reeter AK, Criss E: Comparison of flow rates for standard and large bore tubing. West J Med 1985;143:183-185.

4. Iserson KV, Reeter AK, Woods W, et al: Pressurization of IV bags: A new configuration and evaluation for use. J Emerg Med 1985;3:89-92.

15:1 January 1986 Annals of Emergency Medicine 109/167