Correspondencc

Orthostatic Vital Signs Bernard L Lopez, MD/ Jane Koziol-McLain, RN, MS Steve Lowenstein, MD, MPH Pharmacotherapy of PregnancyRelated SVT Peter J Mariani, MD, FACEP Using ACE-lnhibitors AJ SmaUy, MD/ James R Roberts, MD, FACEP Richard C Waerz, MD

FEBRUARY1992

Orthostatic Vital Signs To the Editor. KozioI-McLain et al are to be commended for their study, "Orthostatic Vital Signs in Emergency Department Patients" [June 1991;20:606-6t0], as they have added to the sparsely researched topic of orthostatic vital signs in the ED. Many measurements signifying a "positive" tilt test can be found in various textbooks of medicine, yet few of these are referenced to scientific studies. It is unfortunate that a test considered by many to be the standard of care in the evaluation of the hypevolemic patient has little in the way of true scientific support. As of now, there are only two studies in which orthostatic vital signs were tested against known quantities of volume depletion.l.2 Most of the measurements found in textbooks are "facts" that have been passed down through the generations without validation. Several questions arise from the study by KozioI-McLain et ah First, how are we to be sure that the patients in the study were truly euvolemic? If the tilt test is a truly accurate measure of hypovolemia, then even mild degrees of fluid depletion could affect the measurements of the test. Second, in the ovulation of orthostatic heart rate and age, an rof-0.36 is really not large enough to be considered significant. If an ton the order of 0.50 were used, then this relation-

21:2 ANNALS OF EMERGENCY MEDICINE

ship is actually insignificant, and therefore the orthostatic measurements are not significantly related to any of the variables. This further underscores the conclusions that orthestatic measurements are widely variable. Finally, the authors state that "examination of orthostatic diastolic blood pressure should receive priority attention, being the most reliable of the orthostatic vital signs." This is not a true statement. Diastolic blood pressure may be the least variable of the vital signs, but there is no documented correlation between diastolic blood pressure measurements and degree of hypovolemia. Until any correlation is established, it cannot be considered "reliable." Our study looking at the tilt test in the ED patient examined 202 patients using a forward, stepwise linear regression model for dehydration percentage using measured serum osmolality and body weight.3 We found such a large variation in the orthestatic vital sign measurements in both the control (healthy volunteers) and the study group that the measurements were not clinically useful. Our findings are in agreement with KozioI-McLain et al. The problem with evaluating orthostatic vital signs as a useful indicator of hypovolemia is that there is no good way to accurately determine fluid or volume depletion in patients, and until a reliable method of accurately determining true body fluid or blood deficit is discovered, there is really no way to assign certain changes in orthostatic

measurements to degree of hypovolemia. Physicians have used a number of laboratory tests such as blood urea nitrogen, creatinine, and serum osmolality; some have used "traditional criteria" from the physical examination. However, none has ever been validated by scientific studies. 4 KozioI-McLain et al state correctly that more research is needed to identify reliable and valid screening tools for identifying the volumedeficient ED patient. If a reliable method is found, it needs to be applicable not only to healthy volunteers, but also to diseased patients as well. Once this is done, orthostaic measurements can then be assigned to levels of hypovolemia. Not until this occurs can orthostatic vital signs be useful. One probable, accurate method would be to perform Swan-Ganz catheterization on normal subjects over a wide age range, do orthostatics, then remove known quantities of blood or fluid and repeat the orthostatics to give "normal" parameters. Once these are known, the same testing could be done for ED patients with a wide variety of illnesses and medications to see how orthostatic measurements are affected. Does anyone know of an institutional review board that might approve this?

Bernard L Lopez, MD Division of Emergency Medicine Thomas Jefferson University Hospital Philadelphia •

2 2 8 / 1 69

CORRESPONDENCE

l. Knopp R, Claypool R, Leonardi D: Use of the tilt test in measuring acute blood loss. Ann Emerg Med 1980;9:72-75. 2. Green DM, Metheny D: The estimation of acute blood loss by the tilt test. Surg Gynecol Obstet t948;8:145-150. 3. Levitt MA, Lieberman M, Lopez B: Evaluation qf the tilt test in an adult emergency department population (abstract). Ann Emerg Med 1989;18:439. 4, Poole SR: Criteria for measurement of dehydration (letter). Ann Emerg Med 1990;19.'730-731.

In Reply: We thank Dr Lopezfor his comments. We would like to respond to two of his remarks. First, he asserts that the correlation coefficient of-.36 for the relationship between orthostatic heart rate and age is "not large enough to be significant." We plotted the raw data to allow the reader to judge the significance of the correlation. The clinical significance is a matter of judgment. However, using regression analysis, age is a statistically significant predictor of orthostatic heart rate (P= .0001; re= .13). Age explained 13% of the variation in orthostatic heart rate. Second, Dr Lopez questions our use of the term "reliable" with respect to orthostatic diastolic blood pressure (DBP). Reliability describes the reproducibility or precision of a measurement and can be assessed by the magnitude of the standard deviation or the coefficient of variation. Thus, in our study orthostatic diastolic blood pressure was a more reliable measure than ortbostatic systolic blood pressure or heart rate. "Validity" measures whether orthostatic vital signs are a "true" measure of volume status. We did net comment on the validity of the orthostatic diastolic blood pressure as a measure of volume status. Indeed, we agree with Dr Lopez that the diastolic blood pressure may not be a valid measure.Validity must measured by comparing orthostatic diastolic blood pressure to a g01d standard. Jane Kozio/-McLain,RN, MS Steve Lowenstein, MD, MPH EmergencyMedicine Research Center University of ColoradoHealth Sciences Center Denver

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Pharmacotherapy of PregnancyRelated SVT To the Editor: In their paper, "Verapamil in the Treatment of Maternal Paroxysmal Supraventricular Tachycardia" [May 1991;20:552-554], Byerly et al correctly state that previously reported experience with the use of verapamil in such a setting is limited. It is not, however, limited to the single case that they cite. Shortly before the resubmission of their manuscript, a report appeared wherein I recounted an experience with a patient of similar age, parity, gestation, symptoms, and physical examination. 1 Interestingly, this patient also failed to respond to 10 mg IV verapamil (as did the authors' patient on second presentation) but rather converted to sinus rhythm immediately following a strong fetal kick. The reported experience for verapamil, in the pregnant patient with SVT therefore amounts to four episodes, two of which constituted treatement failures. While I agree with the author's conclusion that verapamil "may be useful" in this setting, the shorter half-lives of adenosine and esmo@ (approximately ten seconds2 and ten minutes9 respectively) offer theoretical advantage over verapamii (5.3 hours4) for both pregnant and nonpregnant patients. The 2,00g-fold shorter half-life of adenosine is less than the normal blood circulation time; placental exposure to the agent is thereby minimized. In one animal study in which placental exposure was controlled by uterine artery perfusion, adenosine recovered from the fetal circulation amounted to only 12% of the perfused dose.5 In an in utero chronically instrumented fetal sheep model, an infusion of 0.25 mg/kg/min of adenosine directly into the fetal carotid artery produced no significant effect on fetal blood gases or mean arterial pressure A 30% increase in heart rate was, however, observed following one hour of infusion.s Human pregnancy serum concentrations of adenosine deaminase,

the enzyme responsible for the nucleoside's rapid degradation, have been shown to be approximately 75% of those of nonpregnant women.7 The potential need for a downward adjustment in adenosine dosing for SW in pregnancy may, however, be offset by normal gestational increases in vascular volume. Current evidence suggests that standard clinical use of !3-blocking agents in pregnancy poses little risk to the fetus8 In a case in which esmolol was used successfully in the management of a pregnant woman with thyrotoxicosis, no maternal or fetal adverse effects were evident.9 While animal studies have demonstrated transplacental passage of esmolol with resultant fetal homodynamic effects, disagreement exists as to their extent and significanceJo,ll Verapamil, adenosine, and esmolel are each FDA-classified for pregnancy as "Category C." Due to the infrequent incidence of pregnancy-related maternal SVT,a prospective, controlled clinical comparison of the agents in this setting is unlikely to be forthcoming. Pharmacokinetic considerations, combined with increasing clinical familiarity, have brought adenosine and esmolol (particularly the former) closer to achieving "drug of choice" status for the general treatment of SVT, thus challenging verapamii in this regard. Additional evidence from basic science and clinical investigation as discussed aboved suggests the same end for the rapidly metabolized, natural product adenosine in the particular treatment of SVT in pregnancy.

PeterJ MarianL MD, FACEP Departmentof EmergencyMedicine SUNYHealth ScienceCenter Syracuse I. :!,lariani PJ, Mitchell BK: The littlest cardiologist. JAMA 1990:263:3258-3259. 2. DiMarco JP, Miles W, Akhtar M, et ah Adenosine for paroxy*rnal supraventricular tachycardia: Dose ranging and comparison with verapamil. Ann Intern Med 1990;113:104-i l O. 3. Gorczynski RJ: Basic pharmacology of esmolnl. Am ] Cardinl f985;56:3F-]IF. 4. McTavish D, Sorkin EM: I/brapamil~ An updated review of its pharmacodynamic" and pharmacokinetic properties and therapetuc use in hypertension. Drags 38;1989:I 9- 76.

5. Wheeler C, Yudilevish DL: Transport and metabolism of adenosine in the per~hsed guinea-pig placenta. J Physiol ] 988;405:511-525. 6. Koos BJ, Matsuda K: Fetal breathing, sleep state, and cardiovascular responses to adenosine in sheep. J Appl Physiol 1990;68:489-495. 7. Jaqueti J, Martinez-Hernandez D, Hernandez-Garcia R, et al: Adenosine deaminase in pregnancy serum. Ciin Chem 1990;36:2144. 8. Frishman V/H, Chesner M: Betaadrenergic blockers in pregnancy. Am Head J 1988;115(Part 1):i47-152. 9. lsley V/L, DahI S, Gibbs H: Use of esmolol in managaging a thyrotoxic patient needing emergency surgery. Am J Med 1990:89:I22-123. lO. Ostman PL, Chestnut DH, Robillard JE, et ah Transplacental passage and hemodynamic ef/bcts of esmolol in the gravid ewe. Anesthesio11988;69:738-741. l 1. Eisenach JC, Castro Mh Maternally administered esmolol produces fetal betaadrenergie blockade and hypoxemia in sheep. Anesthesiol 1989;71:718-722.

Using ACE-Inhibitors To the Editor. Roberts and Wuerz, in their article, "Clinical Characteristics of Angiotensin-Converting Enzyme Inhibitor-Induced Angioedema" [May 1991;20:555-558], make the statement that "individuals with a history of idiopathic angioedema or urticaria may be at increased risk and probably should not be treated with ACE inhibitors." Their reference 16 provides no substantiation of this factJ What is referenced is that patients with a history of angloedema (often accompanied by urticaria) should probably not be treated with ACE inhibitors5 AJ Smelly, MD Departmentof EmergencyMedicine University of Connecticut School of Medicine Farmington 1. Or/an N, Patterson R, D~4~ewiezMS: Severe angioedema related to ACE inhibitors in patients with a history of idiopathic angioedema. JAMA 1990;264:128Z

In Reply. Dr Smally is correct that a history of urticaria alone does not necessarily contraindicate the use of ACEinhibitors, although there are •

ANNALS OF EMERGENCY MEDICINE 2 1 : 2 FEBRUARY1992

Orthostatic vital signs.

Correspondencc Orthostatic Vital Signs Bernard L Lopez, MD/ Jane Koziol-McLain, RN, MS Steve Lowenstein, MD, MPH Pharmacotherapy of PregnancyRelated...
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