9pinions expressed in the Correspondence section are those of the authors, ~nd not necessarily of the editors, ACER or SAEM. The editor reserves the right to edit and 3ublish letters as space permits. Letters not meeting submission criteria will lot be considered for publication. See "Information for Authors."
CORRESPONDENCE Treatment of Hypothermia To the Editor: It was with great interest that I read Drs Shields' and Sixsmith's article, "Treatment of Moderate-to-Severe Hypothermia in an Urban Setting" [October 1990;19:1093-1097]. I had thought that this paper would have helped to support the position that hypothermic patients who are not in cardiac arrest (asystole or ventricular fibrillation) are best managed by minimally invasive therapy, but ['m afraid that problems with this study prevent it from being valid.
Robert J Rothstein, MD, FACEP - Section E d i t o r Bethesda, Maryland
The sample size (16 patients} was too small to allow valuable conclusions about mortality. Although this group of ten moderately hypothermic patients (core temperature, 28 to 32 C) and six severely hypothermic patients (core temperature < 28 C) experienced a 0% mortality,/f a seventeenth patient had been entered in the study and had died, the group's mortality would have been 5.8% (almost exactly the same as in Miller's series of patients who were treated with insulated blankets only}. 1 Can we assume that the addition of warm IV fluids and heated humidified oxygen had any effect on mortality? The authors acknowledge this limitation in the discussion but make no recommendation that a larger series of patients should be studied with randomization to various treatments in hopes of discovering the most appropriate techniques of rewarming. T h e a u t h o r s relied on a r t e r i a l blood gases "corrected for temperature." Although this point is somew h a t controversial, there is good evidence that it is unnecessary to "correct" blood gas results in hypothermia.2, 3 It has never been shown to be clinically useful. The paper did not give enough information to allow the reader to estimate how m u c h heat was actually 20:7: July 1991
delivered to the patients. For example, the IV fluids were heated to 38 C (although some authors recommend 40 to 45 C),4,s but the flow rates (or the total amounts of fluid infused) were not stated. Even if the fluids had been heated to 45 C, a liter would have delivered only 17 Kcal to a patient with a core temperature of 28 C. s Roughly 60 Kcal/hr would be needed to raise this same patient's temperature by 1 C (assuming a 70kg patient with a mean specific heat of body tissue of 0.8 Kcal/kg). 5 The patient's own basal metabolic rate would have supplied half of this requirement {30 Kcal/hr at 28 C).4 By the same token, the temperature of the humidified oxygen was given (40 C), but not the flow rate. Had the flow been 3 L/rain, the patient would have received 9.4 Kcal/ hr. s Had it been delivered at 10 L/min, the patient would have received 23.7 Kcal/hr. s By not providing this information, the authors do not present reproducible study conditions. Finally, the a u t h o r s state that " e l e v e n patients had central vein catheters placed in either the internal jugular or subclavian veins" but later report a rewarming rate for "the ten patients who received warmed fluids by subclavian or internal jugular c a t h e t e r . " Is this an error in the manuscript or did one patient have a central line place d and then not receive the warm IV infusion?
Lee W Shockley, MD, FACEP Emergency Physicians Professional Association Minneapolis, Minnesota
In Reply: We thank Dr Shockley for his recent comments on our article. There is no doubt that the sample size of the study was very small and that the ideal study would be a large, randomized group of hypothermic patients. However, it would have to be a multicenter study to obtain a large number of patients, and there would be difficulty in obtaining the informed consent required in a randomized study. The reason that the blood gases were corrected for temperature was that at the time of study that was the accepted standard. Since that time there have been various articles contesting the need for this, as mentioned by Dr Shockley. The flow rates for both the IV fluids and the humidified oxygen were adjusted according to the patient's clinical condition, and the total a m o u n t delivered in each case was not recorded, making it impossible to calculate the total number of Kcal delivered to the patients. There were 11 patients with central lines; it was a transcription error in the section referring to ten patients with central lines.
Christopher P Shields, MD Diane M Sixsmith, MD, FACEP The New York Infirmary Beekman Downtown Hospital New York
Temperature Measurement in Children To the Editor:
1. Miller JW, Danzl DF, Thomas DM: Urban accidental hypothermia: 135 cases. Ann Emerg Med 1980;9: 456-461. 2. Delaney KA, Howland MA, Vassallo S, et al: Assessment of acid-base disturbances in hypothermia and their physiologic consequences. Ann Emerg Med 1989;18:72-82. 3. Swain JA: Hypothermia and blood pH. Arch Intern Med 1988;146:1643-1646. 4. O'Keefe KM: Treatment of accidental hypothermia and rewarming techniques, in Roberts JR~ Hedges JR (eds): Clinical Procedures in Emergency Medicine, ed 1. Philadelphia, WB Saunders Co, 1985, p 1040-1055, 5. Bangs C, Hamlet MP: Hypothermia and cold injuries, in Auerbach PS, Geehr EC (eds]: Management of Wilderness and Environmental Emergencies, ed 1. New York, Macmillan Publishing Co, 1983, p 27-63.
Annals of Emergency Medicine
I am writing regarding the article "Comparison of Rectal, Axillary, and Tympanic Membrane Temperatures in Infants and Young Children" by Muma et al [January 1991~20:41-44]. Although it implicitly purports to provide new information of an evaluative nature, we note from the sidenotes that the work was performed nearly five years ago, precisely at the time this revolutionary technology was being introduced to clinicians. Indeed, it was submitted for publication almost three years after data were collected. The widespread expe829/193
CORRESPONDENCE
rience of other clinicians, encompassing nearly 400 million temperatures in infants, children, and adults since that time bears dramatic testimony to the value, precision, and rel i a b i l i t y of F i r s t T e m p ® t y m p a n i c thermometry. In their paper, "Evaluation of an Infrared Tympanic Membrane Thermometer in Pediatric Patients" [Pediatrics, May 1990;85:854-858], Kenney et al present perhaps the best single example of a recent, well-controlled, and documented evaluation approximating the M u m a study's experience. A thorough reading of both studies appears to indicate a number of inadequacies in Muma's work that may perhaps be attributable primarily to the investigators' inexperience with the t e c h n o l o g y and u n f a m i l i a r i t y with the techniques for properly obt a i n i n g i n f r a r e d signals f r o m the smaller ears of infants and children. Additional aspects of this paper that are of concern include the following. 1. Use of a standard (ie, DIATEK® oral/rectal} electronic t h e r m o m e t e r as comparison for both rectal and axillary measurements. No mention is made of the method by which axillary temperatures were actually obtained; because the oral/rectal predict i v e device depends on a m o i s t , highly vascularized area for reproducible results, its use in the dry, skinlined axilla fails to accommodate its own use-parameters (unless it was switched from Predictive to Monitor mode and kept in place for six minutes). We mention this factor only as it relates to an apparent unfamiliarity with the recommendations and limitations for alternate site temperature measurement. 2. The authors' definition of "fever" may be interpreted as artificially low, as most texts and several review articles continue to suggest that ... "temperatures as low as 36.2 C (97 F) and as high as 38 C {100.4 F) are considered n o r m a l in p e d i a t r i c t e x t books." [Roberts JR: Emergency Med-
icine and Ambulatory Care News, November 1987.] 3. The " n e w classification rule" 194/830
employed by the authors to predict a rectal temperature of 38 C using a " s i m p l e linear regression between the two devices (ie, tympanic and axillary instruments)" may be a major contributing factor to the anomalous sensitivity and specificity data that they say is then " e s t i m a t e d using these new fever definitions." No discussion of this new method is presented. 4. The relatively high specificity and sensitivity quoted by the authors for overall correlation of temperatures taken on the entire study population suggest that the authors' expressed inability to enter the smaller ear openings rather than to properly seal the outer opening of the ear canal in infants and younger children (as directed in the operator's brochure) is most likely responsible for the lower recordings they reported for this group. The FirstTemp ® t h e r m o m e t e r receives naturally emitted infrared signals exiting the ear canal opening, and does not, as the authors imply, depend primarily on entrance or deep penetration of the canal to perform in its measurement. Indeed, the authors' failure to seal the opening would very heavily contribute to consistently, lower-thanactual temperatures recorded in the youngest of the subjects. 5. Emphasis, in the investigators' conclusion, on the difference in speculum size between the FirstTemp ® (8 mm) and a pediatric otoscope (4 mm) further illustrates the authors' lack of understanding of the technology, because the FirstTemp ® doesn't depend on v i s u a l i z a t i o n of the t y m p a n i c membrane for its accuracy.
Ronald M Benincasa Sales and Marketing Intelligent Medical Systems, Inc Carlsbad, California
In Reply: We are happy to respond to Mr Benincasa's remarks. He raises some interesting points. We fail to understand why the passage of time should affect our data or the conclusions that follow from it; nor should the Annals of Emergency Medicine
widespread use of this device be used to validate its clinical or scientific merit. Validity should be confirmed with thoughtful scientific study. As to the use of the Diatek ® device, we simply were using the device as it is used thousands of time a day in clinical practices around the country. It is unlikely that anyone uses the device as they suggest, holding under the arm for a full six minutes in a young child. This would obviate its simplicity and convenience. The definition of fever in children is controversial; we used the one found in The Textbook of Pediatric Emergency Medicine. Clearly, what designates a fever varies from person to person and clinical circumstances. However, we accounted for this and calculated sensitivity and specificity based on several fever definitions, although only one is reported in the paper. If fever is defined as a temperature of more than 38.3 C, then the sensitivity for FirstTemp® rose to 59%, still quite low. We used linear regression to determine which tympanic m e m b r a n e t e m p e r a t u r e best predicted a rectal t e m p e r a t u r e of more than 38.0 C. Using this definition, ie, a tympanic membrane temperature of more than 37.3 C, sensitivity rose to 81%. Even using this later example, 20% of fevers would be missed with the FirstTemp ® thermometer. The FirstTemp ® device cannot be inserted fully nor can a seal be reliably obtained; the problem lies with the design of the probe, which is l a r g e a n d inflexible. The suggestion t h a t a seal could be ensured in a frightened, moving child seems again to ignore clinical' realities. In addition, the canal is tortuous at the entrance; this usually requires manipulation of an otoscope during an exa m i n a t i o n . T h e r e is no w a y of k n o w i n g w h e t h e r the F i r s t T e m p ® probe is actually in the ear canal or simply sensing the outer portion of the external auditory canal. T h e r e l a t i o n s h i p b e t w e e n core temperature sites is complex and not efltirely understood, particularly in children. It follows that the prediction of one core temperature from another w i t h o u t taking into account 20:7 July 1991
CORRESPONDENCE Treatment of Hypothermia To the Editor: It was with great interest that I read Drs Shields' and Sixsmith's article, "Treatment of Moderate-to-Severe Hypothermia in an Urban Setting" [October 1990;19:1093-1097]. I had thought that this paper would have helped to support the position that hypothermic patients who are not in cardiac arrest (asystole or ventricular fibrillation) are best managed by minimally invasive therapy, but ['m afraid that problems with this study prevent it from being valid.
Robert J Rothstein, MD, FACEP - Section E d i t o r Bethesda, Maryland
The sample size (16 patients} was too small to allow valuable conclusions about mortality. Although this group of ten moderately hypothermic patients (core temperature, 28 to 32 C) and six severely hypothermic patients (core temperature < 28 C) experienced a 0% mortality,/f a seventeenth patient had been entered in the study and had died, the group's mortality would have been 5.8% (almost exactly the same as in Miller's series of patients who were treated with insulated blankets only}. 1 Can we assume that the addition of warm IV fluids and heated humidified oxygen had any effect on mortality? The authors acknowledge this limitation in the discussion but make no recommendation that a larger series of patients should be studied with randomization to various treatments in hopes of discovering the most appropriate techniques of rewarming. T h e a u t h o r s relied on a r t e r i a l blood gases "corrected for temperature." Although this point is somew h a t controversial, there is good evidence that it is unnecessary to "correct" blood gas results in hypothermia.2, 3 It has never been shown to be clinically useful. The paper did not give enough information to allow the reader to estimate how m u c h heat was actually 20:7: July 1991
delivered to the patients. For example, the IV fluids were heated to 38 C (although some authors recommend 40 to 45 C),4,s but the flow rates (or the total amounts of fluid infused) were not stated. Even if the fluids had been heated to 45 C, a liter would have delivered only 17 Kcal to a patient with a core temperature of 28 C. s Roughly 60 Kcal/hr would be needed to raise this same patient's temperature by 1 C (assuming a 70kg patient with a mean specific heat of body tissue of 0.8 Kcal/kg). 5 The patient's own basal metabolic rate would have supplied half of this requirement {30 Kcal/hr at 28 C).4 By the same token, the temperature of the humidified oxygen was given (40 C), but not the flow rate. Had the flow been 3 L/rain, the patient would have received 9.4 Kcal/ hr. s Had it been delivered at 10 L/min, the patient would have received 23.7 Kcal/hr. s By not providing this information, the authors do not present reproducible study conditions. Finally, the a u t h o r s state that " e l e v e n patients had central vein catheters placed in either the internal jugular or subclavian veins" but later report a rewarming rate for "the ten patients who received warmed fluids by subclavian or internal jugular c a t h e t e r . " Is this an error in the manuscript or did one patient have a central line place d and then not receive the warm IV infusion?
Lee W Shockley, MD, FACEP Emergency Physicians Professional Association Minneapolis, Minnesota
In Reply: We thank Dr Shockley for his recent comments on our article. There is no doubt that the sample size of the study was very small and that the ideal study would be a large, randomized group of hypothermic patients. However, it would have to be a multicenter study to obtain a large number of patients, and there would be difficulty in obtaining the informed consent required in a randomized study. The reason that the blood gases were corrected for temperature was that at the time of study that was the accepted standard. Since that time there have been various articles contesting the need for this, as mentioned by Dr Shockley. The flow rates for both the IV fluids and the humidified oxygen were adjusted according to the patient's clinical condition, and the total a m o u n t delivered in each case was not recorded, making it impossible to calculate the total number of Kcal delivered to the patients. There were 11 patients with central lines; it was a transcription error in the section referring to ten patients with central lines.
Christopher P Shields, MD Diane M Sixsmith, MD, FACEP The New York Infirmary Beekman Downtown Hospital New York
Temperature Measurement in Children To the Editor:
1. Miller JW, Danzl DF, Thomas DM: Urban accidental hypothermia: 135 cases. Ann Emerg Med 1980;9: 456-461. 2. Delaney KA, Howland MA, Vassallo S, et al: Assessment of acid-base disturbances in hypothermia and their physiologic consequences. Ann Emerg Med 1989;18:72-82. 3. Swain JA: Hypothermia and blood pH. Arch Intern Med 1988;146:1643-1646. 4. O'Keefe KM: Treatment of accidental hypothermia and rewarming techniques, in Roberts JR~ Hedges JR (eds): Clinical Procedures in Emergency Medicine, ed 1. Philadelphia, WB Saunders Co, 1985, p 1040-1055, 5. Bangs C, Hamlet MP: Hypothermia and cold injuries, in Auerbach PS, Geehr EC (eds]: Management of Wilderness and Environmental Emergencies, ed 1. New York, Macmillan Publishing Co, 1983, p 27-63.
Annals of Emergency Medicine
I am writing regarding the article "Comparison of Rectal, Axillary, and Tympanic Membrane Temperatures in Infants and Young Children" by Muma et al [January 1991~20:41-44]. Although it implicitly purports to provide new information of an evaluative nature, we note from the sidenotes that the work was performed nearly five years ago, precisely at the time this revolutionary technology was being introduced to clinicians. Indeed, it was submitted for publication almost three years after data were collected. The widespread expe829/193
CORRESPONDENCE
rience of other clinicians, encompassing nearly 400 million temperatures in infants, children, and adults since that time bears dramatic testimony to the value, precision, and rel i a b i l i t y of F i r s t T e m p ® t y m p a n i c thermometry. In their paper, "Evaluation of an Infrared Tympanic Membrane Thermometer in Pediatric Patients" [Pediatrics, May 1990;85:854-858], Kenney et al present perhaps the best single example of a recent, well-controlled, and documented evaluation approximating the M u m a study's experience. A thorough reading of both studies appears to indicate a number of inadequacies in Muma's work that may perhaps be attributable primarily to the investigators' inexperience with the t e c h n o l o g y and u n f a m i l i a r i t y with the techniques for properly obt a i n i n g i n f r a r e d signals f r o m the smaller ears of infants and children. Additional aspects of this paper that are of concern include the following. 1. Use of a standard (ie, DIATEK® oral/rectal} electronic t h e r m o m e t e r as comparison for both rectal and axillary measurements. No mention is made of the method by which axillary temperatures were actually obtained; because the oral/rectal predict i v e device depends on a m o i s t , highly vascularized area for reproducible results, its use in the dry, skinlined axilla fails to accommodate its own use-parameters (unless it was switched from Predictive to Monitor mode and kept in place for six minutes). We mention this factor only as it relates to an apparent unfamiliarity with the recommendations and limitations for alternate site temperature measurement. 2. The authors' definition of "fever" may be interpreted as artificially low, as most texts and several review articles continue to suggest that ... "temperatures as low as 36.2 C (97 F) and as high as 38 C {100.4 F) are considered n o r m a l in p e d i a t r i c t e x t books." [Roberts JR: Emergency Med-
icine and Ambulatory Care News, November 1987.] 3. The " n e w classification rule" 194/830
employed by the authors to predict a rectal temperature of 38 C using a " s i m p l e linear regression between the two devices (ie, tympanic and axillary instruments)" may be a major contributing factor to the anomalous sensitivity and specificity data that they say is then " e s t i m a t e d using these new fever definitions." No discussion of this new method is presented. 4. The relatively high specificity and sensitivity quoted by the authors for overall correlation of temperatures taken on the entire study population suggest that the authors' expressed inability to enter the smaller ear openings rather than to properly seal the outer opening of the ear canal in infants and younger children (as directed in the operator's brochure) is most likely responsible for the lower recordings they reported for this group. The FirstTemp ® t h e r m o m e t e r receives naturally emitted infrared signals exiting the ear canal opening, and does not, as the authors imply, depend primarily on entrance or deep penetration of the canal to perform in its measurement. Indeed, the authors' failure to seal the opening would very heavily contribute to consistently, lower-thanactual temperatures recorded in the youngest of the subjects. 5. Emphasis, in the investigators' conclusion, on the difference in speculum size between the FirstTemp ® (8 mm) and a pediatric otoscope (4 mm) further illustrates the authors' lack of understanding of the technology, because the FirstTemp ® doesn't depend on v i s u a l i z a t i o n of the t y m p a n i c membrane for its accuracy.
Ronald M Benincasa Sales and Marketing Intelligent Medical Systems, Inc Carlsbad, California
In Reply: We are happy to respond to Mr Benincasa's remarks. He raises some interesting points. We fail to understand why the passage of time should affect our data or the conclusions that follow from it; nor should the Annals of Emergency Medicine
widespread use of this device be used to validate its clinical or scientific merit. Validity should be confirmed with thoughtful scientific study. As to the use of the Diatek ® device, we simply were using the device as it is used thousands of time a day in clinical practices around the country. It is unlikely that anyone uses the device as they suggest, holding under the arm for a full six minutes in a young child. This would obviate its simplicity and convenience. The definition of fever in children is controversial; we used the one found in The Textbook of Pediatric Emergency Medicine. Clearly, what designates a fever varies from person to person and clinical circumstances. However, we accounted for this and calculated sensitivity and specificity based on several fever definitions, although only one is reported in the paper. If fever is defined as a temperature of more than 38.3 C, then the sensitivity for FirstTemp® rose to 59%, still quite low. We used linear regression to determine which tympanic m e m b r a n e t e m p e r a t u r e best predicted a rectal t e m p e r a t u r e of more than 38.0 C. Using this definition, ie, a tympanic membrane temperature of more than 37.3 C, sensitivity rose to 81%. Even using this later example, 20% of fevers would be missed with the FirstTemp ® thermometer. The FirstTemp ® device cannot be inserted fully nor can a seal be reliably obtained; the problem lies with the design of the probe, which is l a r g e a n d inflexible. The suggestion t h a t a seal could be ensured in a frightened, moving child seems again to ignore clinical' realities. In addition, the canal is tortuous at the entrance; this usually requires manipulation of an otoscope during an exa m i n a t i o n . T h e r e is no w a y of k n o w i n g w h e t h e r the F i r s t T e m p ® probe is actually in the ear canal or simply sensing the outer portion of the external auditory canal. T h e r e l a t i o n s h i p b e t w e e n core temperature sites is complex and not efltirely understood, particularly in children. It follows that the prediction of one core temperature from another w i t h o u t taking into account 20:7 July 1991
