Provided the detector is responsive to cyclical changes of C02 concentrations and is not permanently discolored by gastric aspirate or by drugs, it is useful for verifying endotracheal tube position in children weighing more than 2 kg with spontaneous circulation. A positive result during CPR confirms endotracheal tube position while a negative result requires an alternative means of confirmation.

Mananda S Bhende, MD, FAAP, FACEP Ann E Thompson,MD, FAAP,FCCM University of Pittsburgh School of Medicine Children's Hospitalof Pittsburgh Pittsburgh, Pennsylvania 1. Muir JD, Randalls PB, Smith GB: End tidal carbon dioxide monitoring for cardiopulmonary resuscitation (letter). Br Med J 1990;301:41-42. 2. Hayes M, Higgins D, Yau EHS, et al: End tidal carbon dioxide monitoring for cardiopulmonary resuscitation (letter). Br Med J 1990;301:41-42. 3. Wright RE, Smith KW, Hayes JK, et al: Evaluation of the Fenem endtidal CO2 detector in a dog model of cardiopulmonary resuscitation. Anesth Analg 1990;70(suppl 2):$443. 4. Bhende MS, Gavula DP, Menegazzi J J: Comparison of an endtidal C02 detector with capnometry during CPR in a pediatric asphyxial arrest model (abstract). Pediatr Emerg Care 1991;7:383. 5. Fluid therapy and medications, in Chameides L (ed): Textbook of Pediatric Advanced Life Support. Dallas, American Heart Association, 1990, p 47-59.

Topical Antibiotics for All Wounds? To the Editor. In their article "Controversial Issues in Clinical Management of the Simple Wound" [January 1992;21: 72-80], Berk et al discussed the use of topical antimicrobials in traumatic surface wounds. Two studies 1,2" were cited as. demonstrating lower infection rates among surface lacerations in animals treated with topical antimicrobials. In fact, the paper by Bergamini et a[1 was unable to detect such a difference


at a statistically significant level. The other cited article 2 concluded that topical antimicrobials were ineffective if applied more than three hours after wounding. That is, the window of opportunity for using topical antimicrobials is quite brief because many patients with traumatic wounds wait hours to receive definitive care. This information is supported by Burke,s who documented a threehour limit on the effectiveness of "prophylactic" parenteral antimicrobials. Edlich et at2 examined this temporal phenomenon and posited a preteinaceous coagulum on the wound surface acting as a barrier to antimicrobial penetration. Rodeheaver et al4verified this concept by extending the effective period of topical antibiotics to eight hours by applying topical proteolytic enzymes before administering antimicrobials. Our unpublished data support the idea that simple irrigation with antimicrobial solution is not effective in older wounds. We used quantitative bacteriology in a guinea pig model and could detect no difference from control in number of bacteria per gram of tissue among 12-hour-old wounds irrigated with either normal saline, 1% povidoneiodine, or cefazolin solution. We had a statistical power of 0.8 to detect approximately a 2 log (10) difference. The clinical study by Lindsey et al 5 identified a significant improvement in infection rates after penicillin irrigation. However, wound age, degree of contamination, and method of wound preparation and closure (aside from irrigation) were not described for the treatment groups, although wound care was standardized. This begs the question: are topical antibiotics effective and safe for all wounds? Experimental animal literature2,3 supports the use of topical antibiotics on contaminated wounds less than three hours after wounding. This seems to be confirmed by Dr Lindsey's study, although time from wounding to treatment is not clear. We agree with the authors that tissue effects of, topical antimicrobials have not been studied. Further, the use of topical antimicrobials is not proven

effective more than three hours after wounding. Safe, inexpensive methods of removing surface coagulum may atlow the use of topical antimicrobials in older injuries. However, before widespread use of this modality is instituted, its safety and effectiveness must be documented. Using topical antimicrobials on all simple wounds is an expensive proposition. We should wait for research to define the indications and limitations of this therapy.

John M Howell, MD, FACEP Thomas0 Stair, MD, FACEP Departmentof EmergencyMedicine Georgetown UniversityHospital Washington, DC I. Bergamini TM, Lament PM, Cheadle WG, et al: Combined topical attd systemic antibiotic prophylaxis in experimental wound infection. Am J Surg 1984;147:753-756. 2. Edlich RF, Smith QT, Edgerton MT: Resistance of the surgical wo und to antimicrobial prophylaxis and its mechanisms of development. Am J Surg 1973;126:583-591. 3. Burke JF: The effective period of preventive antibiotic action in experimental incisions and dermal lesions. Surgery 1961 ;50:161-168. 4. Rodeheaver G, Marsh D, Edgerton MT, et al: Proteolytic enzymes as adjuncts to antimicrobial prophylaxis of contaminated wounds. Am J Surg 1975;129:537-544. 5. Lindsey D, Nava C, Martin M: Effectiveness of penicillin irrigation in control of infection in sutured lacerations. J Trauma 1982;22:186-189.

Usefulness of a Diagnostic Test To the Editor. The article by McAnena et al "Contributions of Peritoneal Lavage Enzyme Determinations to the Management of Isolated Hollow Visceral Abdominal Wounds [August 1991;20:834-837] raises several issues pertaining to study design and results reporting. The study design and lack of important results do not allow conclusions to be drawn concerning the diagnostic use of peritoneal lavage enzyme levels in hollow viscus abdominal injury.

A study that evaluates the usefulness of a diagnostic test should contain eight specific elements before the reader considers applying the findings to clinical practice.~ One basic element includes providing all data that are required to construct a "two-by-two" or fourfold table. These data are needed to calculate a test's sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and prevalence, which are important when evaluating a diagnostic test's usefulness. Because the current study did not provide peritoneal enzyme data on patients without hollow viscus injury, only sensitivity could be calculated. Therefore the abstract statement "...elevation of LAM is highly specific for small bowel injury" is incorrect. Also, because accuracy cannot be calculated, the conclusion statement, "Lavage amylase and lavage alkaline phosphatase are accurate predictors of isolated small bowel pathology...," is also incorrect. It is not appropriate to study a patient population with a disease prevalence of 100% when evaluating a diagnostic test's usefulness. The patient population should have a disease prevalence similar to that seen in clinical practice. In addition, it is important to include patients with varying degrees of disease, including disease-free patients. The study patient population consisted of those with known hollow viscera injuries as determined by laparotomy (100% prevalence)! It is not surprising that abnormalities in lavage enzyme levels were found. The study population had an artificial prevalence and lacked patients without disease (hollow viscera injury), which does not reflect the true prevalence or spectrum of disease in emergency department patients who undergo diagnostic peritoneal lavage. Therefore, these findings cannot be applied to the ED population. Another element that must be present when evaluating an article about a diagnostic test is a sensible definition of "normal." The materials and methods section should have included details on how the cutoffs


Topical antibiotics for all wounds?

CORRESPONDENCE Provided the detector is responsive to cyclical changes of C02 concentrations and is not permanently discolored by gastric aspirate or...
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