Thermometer placement for oral temperature measurement in febrile adults

hf. J. Nurs. Stud. Vol. 13, pp. 199-208, Pergamon Press ,1976. Printed in Great Britain

Thermometer placement for oral temperature measurement in febrile adults ROBERTA

ERICKSON,

Department of Physiological .Nursing-SM-28, School of Nursing, University of Washington, Seattle, Washington 98 195, U.S.A.

temperature is a useful indicator of a person’s state of health when measured accurately and evaluated in the context of related observations about the individual and his environment. Oral temperature measurement is used commonly in clinical settings to screen for febrile states and to document the pattern of fever and whether the course is increasing or diminishing. This study was undertaken to provide additional guidelines for accuracy in oral thermometry technique. BODY

Background

Temperature varies in different parts of the body, and it is difficult to measure directly in the arterial blood or vital organs of the central core areas in the head and trunk. For practical purposes in the clinical setting, measurements are made in accessible locations near large arteries carrying blood which reflects the temperature of the core areas (Tate et al., 1970; Blainey, 1974). Sublingual oral temperature is a reliable indicator of changes in body heat during rapid changes in temperature at the central receptors, such as occur in immersion, exercise, and warm infusions, as well as in the slower changes associated with fever. Rectal temperature fluctuation is similar to concurrent oral measurement in fever, but it tends to lag behind during rapid changes in central body temperature (Mellette, 1950; Gerbrandy et al., 1954; Cranston, 1966). Palpation is unsatisfactory as a screening method for fever (Bergseon, 1974). Sublingual temperature has been shown to correlate well with more direct core measurements made in the esophagus, external auditory meatus, and tympanic membrane (Cranston, 1966). Temperature within the mouth itself can vary more than 3 deg F, from the relatively cool hard palate to the warm sublingual area (Hersh et al., 1943). More specifically, the left and right posterior sublingual pockets of tissue at the base of the tongue have been shown by several investigators to be the points of highest oral 199

200

ROBERTA ERICKS0.N

temperature in afebrile adults, registering O-36-1.6 deg F higher than the area under the front of the tongue in various reports (Bjorn, 1973 ; Jones, 1973 ; Beck and St. Cyr, 1974; Beck and Campbell, 1975; Wironen, 1975). However, many studies involving oral temperature readings have not identified the specific location ‘under the tongue’ where measurements were made, and practitioners in the clinical setting are noted sometimes to interpret ‘sublingual’ as meaning the area beneath the front of the tongue rather than at the base. The two posterior sublingual pockets have a rich blood supply and are in close proximity to their respective carotid arteries (Blainey, 1974). At least in afebrile adults, there seems to be little difference in temperature between the two pockets themselves, with reports of 0*04--0.21 deg F by Tate et al., 1970; Bjbrn, 1973; Jones, 1973; and Wironen, 1975. A literature search revealed no reported studies of oral temperature differences among these three sublingual sites in febrile individuals. A variety of local influences on the mouth may affect sublingual temperature. For example, transitory increases and decreases in local temperature associated with the ingestion of hot and cold fluids have been well-documented (De Nasoquo et al., 1944; Brim and Chandler, 1948; Renbourn, 1963a, p. 19 ; Verhonick and Werley, 1963 ; Woodman et al., 1967; Forster et al., 1970; Lee and Atkins, 1972 ; Breinig, 1975). One factor that has not been adequately documented is whether holding the mouth open or closed while the thermometer is in place has any significant effect on the temperature reading obtained. Manufacturers of electronic thermometers vary in their recommendations on this point, and studies so far have reported conflicting results. Jones (1973) measured open-mouth temperatures with an electronic thermometer at the two posterior sublingual pockets and at the area under the front of the tongue followed by closed-mouth readings in the same locations. Open-mouth temperatures were higher at all three sites. Wironen (1975) replicated Jones’ study, but measured the closed-mouth temperatures first. Generally opposite results were obtained, with the two posterior pockets having higher readings when the mouth was closed. Since neither study randomized the order of the open- and closed-mouth measurements, a possible explanation for the conflicting findings is that the subjects’ body temperature dropped as the measurement sequence proceeded, with the higher readings reflecting an earlier measurement time rather than the effect of mouth position. In both studies, the maximum mean difference between open- and closedmouth readings at any of the three sublingual sites did not exceed 0.14 deg F, a value of little practical clinical importance. However, the conflicting results do leave unresolved the basic question of the effect on oral temperature of holding the mouth in an open or closed position while the thermometer is in place. Electronic instrumentation for oral temperature measurement is coming into use in many clinical settings. While there is controversy as to whether electronic thermometers offer any real advantages in overall time saving, cost reduction, improved client care, or decreased cross-infections, these instruments at the least do provide the convenience of a short measurement time (Ferguson et al., 1971; ‘Mercury vs Electronic Thermometers’, 1972). An oral temperature reading can be obtained in 15-40 set in comparison with the 6-8 min period recommended for optimum registration of a glass-mercury thermometer (Nichols et al., 1969; Nichols and Kucha, 1972; Nichols, 1972). With electronic thermometers coming into wider use, further information is needed to develop guidelines for thermometry technique.

THERMOMETER

PLACEMENT

FOR ORAL TEMPERATURE

MEASUREMENT

20 1

This study was done to assess the extent of oral temperature differences in febrile adults among three sublingual sites: left posterior pocket, right posterior pocket, and front sublingual area. A second purpose was to determine the effect of holding the mouth in a closed vs open position when measuring sublingual temperature of febrile adults. The ‘left posterior sublingual pocket’ (left pocket) is the area where the base of the tongue joins the floor of the mouth on the left side of the frenum, and similarly on the other side for the ‘right posterior sublingual pocket’ (right pocket). The ‘front sublingual area’ (front area) is located beneath the tongue at the front of the mouth where the frenum attaches to the mouth floor. For this study, ‘fever’ was defined as an oral temperature reading in at least one of the sublingual sites of 100 deg F or more. ‘Adults’ were persons of either sex who were at least 18 yr of age. Study method The study sample consisted of 50 hospitalized adults, 25 men and 25 women. The age range was 20-81 yr, with a mean age of 52.8 yr. The subjects were fairly evenly distributed among age groups. Fourteen of the 50 were between 20-39 yr of age, 16 were between 40-59, 19 were between 60-79, and one subject was over 80 yr of age. All subjects met the following criteria: an oral temperature reading of 100 deg F or more in at least one sublingual site; no oral pathology, paralysis, or surgery; no treatments involving hot or cold applications to the head or neck; absence of acute pain or discomfort; and ability to cooperate with verbal instructions about keeping the mouth closed or open during temperature measurement. The study sample included all febrile patients available on the six nursing units involved in the study who met the criteria and were willing to participate. Two potential subjects declined to participate in the study.

Indejmdentvariables The two major independent variables were sublingual site and mouth position, closed or open. Six oral temperature measurements were taken on each subject, one reading at each site with the mouth closed and one reading at each site with the mouth open. Background data were obtained to account for other independent variables which might affect oral temperature. These included the subjects’ age, sex, type of dentition, and the presence of oxygen therapy devices and nasogastric tubes. Controlled nariables Several local factors known to affect oral temperature were controlled: ingestion of hot or cold liquids (De Nasaquo et al., 1944; Brim and Chandler, 1948; Renboum, 1963a, p. 19; Verhonick and Werley, 1963; Woodman et al., 1967; Forster et al., 1970; Lee and Atkins, 1972; Breinig, 1975), smoking (Brim and Chandler, 1948; Woodman et al., 1967; B,jiim, 1973) ; therapeutic applications of heat and cold (Hersh et al., 1943), and bathing (Selle, 1952, p. 56; Renbourn, 1963a, p. 25). Activity and body position also are known to affect oral temperature (Mellette, 1950; DuBois, 1951, pp. 480-481; Selle, 1952, p. 56; Cranston et al., 1954, p. 350; Renboum, 1963b, p. 3). However, they were not controlled based on the assumption that a hospitalized febrile person’s activity was likely to be limited and that the subject would be in a bed or chair at the time the readings were made. The effect of gum chewing on oral temperature is questionable and was disregarded (Sercy, 1944; Brim and Chandler, 1948; Verhonik and Werley, 1963). Measurement tool All temperature readings were made by the investigator using the same IVAC 811 predictive electronic thermometer. Oral temperature registered to tenths of a degree Fahrenheit and was displayed on a digital readout. Calibration was done before and after the period ofdata collection

ROBERTA

202

ERKXSON

with the IVAC probe and a National Bureau of Standards thermometer suspended in a wellstirred Haake water bath. Calibration was carried out with probe cover in place and in accordance with the IVAC manufacturer’s instructions for the test mode (IVAC Corporation). In both tests, the mean error of the IVAC thermometer was 0.17 deg F or less over a range of 94-106 deg F as well as over the narrower range of 98-104 deg F, which was inclusive of all readings made in the study. Readings made with 10 different probe covers at a bath temperature of 98.6 deg F showed a variation of O-1 deg F, which was the smallest difference the thermometer could register. Data collection The temperature measurements were made between 3:30-4:30 p.m. and 7:30-8:30 p.m. These periods corresponded with the hospital’s routine temperature monitoring times which were closest to the expected daily peak temperature that occurs between approximately 5 and 7 p.m. (Selle, 1952, p. 9). Febrile patients were identified from temperature records on the nursing units; also noted were persons who potentially might be febrile due to their diagnosis, therapy, or recent temperature trend. Other study criteria were verified from patient records or, when necessary, by direct assessment. The study was explained to potential subjects and their verbal consent to participate was obtained. They were then requested not to eat, drink, rinse their mouths, brush their teeth, bathe, or smoke until the investigator returned and made the temperature readings some 30-45 min later. The measurement technique recommended in the thermometer manufacturer’s instructions was used, inserting the probe at the front of the mouth under the tongue and slowly sliding it back along the gum line to the back of the mouth, taking 3-7 set to reach the posterior sublingual pocket (IVAC Corporation). For the front sublingual area, the probe was moved inward slowly from the gum line toward the frenum, taking 3-7 set to reach the point where it joined the floor of the mouth. Special care was taken to insure slow probe insertion, careful placement at each site, and maintaining constant contact of the probe with mouth tissue. The six measurements were taken one immediately after the other in a predetermined randomized order derived from a table of random numbers. Only one set of readings was made on each subject, and no two sequences were alike. For readings in the open-mouth position, the subject was asked to hold his mouth open until the probe was removed. For closed-mouth readings, the subject was instructed to keep his mouth open until the probe was in the proper position; then he was asked to close hi lips snugly around the probe until told that the reading was completed. Resulta and discussion

100.6 u. z

100.4

xl

100.2

J

100.0

1; e X

99.6

E f

99.4

99.6

99.2

Left pccket

Right pocket

Front area

Mouth closed

Mouth open

FIG. 1. Mean temperatures at the three sublingual sites and for closed and open-mouth positions.

Figure 1 shows the mean temperatures measured at the three sublingual sites and for the closed and open mouth positions. An analysis of variance for repeated

THERMOMETER

PLACEMEsNT FOR ORAL TEMPERATURE

MEASUREMENT

203

TABLE 1. ANALYHSOF VARIANCE FORSUBLINGUAL SITEANDMOUTHPOSITION Sum of squares

df

Variance estimate

F

Probability

Sublingual site

8.5213

2

4.261

73.466

< 0.01*

Mouth position

0464 1

1

0464

8.000

< 0.01**

Site X position

0.2609

2

0.130

2.241

N.S.

14.2904

245

0.058

Source

Pooled error

* P < 0.01 with df either 1,245 or 1,49 (conservative). ** P < 0.01 with df either 2,245 or 1,49 (conservative). measures

was applied to the temperature differences associated with the variables of sublingual site and mouth position. Both variables were shown to be statistically significant at the 0.01 level with no interaction between them (see Table 1). There were no significant differences associated with the background variables examined: age, sex, type of dentition. That is, they did not make a significant difference, either individually or by interaction with each other or with site and position, in the temperature readings obtained. The small number of subjects who had an oxygen cannula (one) or nasogastric tube (three) precluded statistical analysis of the effects of these devices on oral temperature. The temperature variations shown by the four subjects were similar to those in the rest of the study sample. Sublingual site

The Bonferoni t-test was used to determine which mean temperature differences among the paired sublingual sites were significant. The Bonferoni t-test is an appropriate statistic to use in a repeated measures design to determine which mean values are significantly different and to avoid the increased chance of error that exists when repeated Student’s t-tests are used for analysis (Wike, 197 1, pp. 72-73). Figure 2 shows the mean temperature differences among the paired sublingual sites and the ranges of individual differences that existed in the study sample. The mean temperature differences between the left pocket and the front area was 0.37 deg F, with individual differences ranging from -0.5-1.7 deg F. (Negative values indicate that the first-named site was lower in temperature, positive values that it was higher.) The mean difference between the right pocket and front area was 0.34 deg F, with a range of individual differences of -0.6-1.4 deg F. The Bonferoni t-test was significant at the 0.01 level for both means, indicating that significantly higher temperatures were found in the two posterior pockets than in the front sublingual area Values of the magnitude of 0.3-0.4 deg F also begin to have practical clinical importance, as they may affect the intensity of patient evaluation and decisions about the treatment plan. Temperature differences between the left and right posterior pockets themselves ranged from -0.7-0.6 deg F. The mean difference was only 0.04 deg F, slightly higher on the left side. This value was of neither statistical nor clinical significance (P > 0.05).

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- ROBERTA

&TRIC&TO.N

FIG. 2. Mean temperature differences and ranges among the three sublingual sites and between closed and open-mouth positions.

The temperature differences shown among the three sublingual sites in this study concur with the findings of previous oral temperature studies with afebrile subjects (Tate et al., 1970; Bjiirn, 1973; Jones, 1973; Beck and St. Cyr, 1974; Beck and Campbell, 1975 ; Wironen, 1975). Therefore, a general conclusion can be drawn that for both febrile and afebrile individuals, oral temperature is significantly higher in either of the two posterior sublingual pockets than in the area under the front of the tongue. No significant temperature difference exists between the left and right posterior pockets themselves. Mouth position Temperature differences with the mouth closed vs open at the three sublingual sites ranged from -0.7 to 1.0 deg F. The mean difference was 0.08 deg F. While this value was statistically significant by analysis of variance, the actual size of the value makes it of little clinical importance. Therefore, although holding the mouth closed during measurement resulted in a slightly higher reading, the temperature-lowering effect of holding the mouth open was quite small. Subject comfort during measurement was not formally assessed. However, more discomfort and tenseness seemed to be associated with holding the mouth open during the approximately 30-set measurement period than during a like time with the mouth closed. On the other hand, maintaining accurate probe placement was facilitated by being able to see the area when the subject’s mouth was open. As stated earlier, there was no interaction between the variables of sublingual site and mouth position. That is, the posterior pockets had significantly higher temperature readings than the front area regardless of whether the mouth was closed or open. Likewise, measurements made with the mouth closed were slightly higher than those with the mouth open, irrespective of which particular sublingual site was involved.

THERMOMETER

Site

pocket

F G. 3. Frequency

PLACEMENT

of highest

FOR ORAL TEMPERATURE

temperature

pot ket

pocket

Site

pocket

of lowest

pocket

with which the highest and lowest temperature site.

MEASUREME.NT

205

temperature

pot ket

readings occurred at each sublingual

Sites of highest and lowest readings

Figure 3 shows the frequency with which each sublingual site was the location of the subjects’ highest and lowest readings in the six-temperature measurement sequence. One or both of the posterior pockets was the site of the high reading in 48 out of 50 subjects, with the left pocket high in 31 measurement sequences and the right pocket in 30. Only 2 subjects had a high reading in the front area. Since the same high reading sometimes occurred in more than one site, the total number of high readings is greater than the total number of subjects. As might be expected, opposite results occurred for the site of lowest temperature. In 46 out of 50 subjects, the front area provided the low reading. The left pocket temperature was low in 8 measurement sequences and the right pocket temperature in 9. These findings give further reinforcement to the conclusion that the two posterior sublingual pockets are most likely to be the sites of highest oral temperature. Dentition

An interesting finding came from comparing the mean difference between the highest and lowest temperatures in each measurement sequence with the subject’s type of dentition. The 30 subjects who had both upper and lower natural teeth showed a mean difference of O-73 deg F between their highest and lowest temperatures. The 16 subjects with either full or partial artificial dentures had a mean difference of 0.62 deg F. The 4 subjects who were edentulous at the time of measurement showed the greatest difference between the highest and lowest readings, l-18 deg F. Because the latter group is small, little can be concluded from the greater extent of temperature variation demonstrated. However, the finding may be of interest for future study about the effect on oral temperature of the type of dentition. Implications for practice

Based on the study findings, the following guidelines temperature measurement technique :

are recommended

for oral

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ROBERTA

ERICKSON

1. Oral temperature should be measured in either the left or right posterior sublingual pocket at the base of the tongue, and not in the area under the front of the tongue. 2. The decision of which posterior sublingual pocket to use, left or right, should be based on selecting the side of the mouth into which the operator can most accurately place the thermometer probe tip into the pocket. At times, the client may have local oral discomfort or pathology that will contraindicate using one side. 3. Having the client close his mouth once the thermometer is in place generally is preferable and probably will be more comfortable for him as well. However, the open-mouth position may be indicated occasionally when the operator needs to see the site to insure that the thermometer probe tip remains in place. In the event that the client is unable to hold his mouth closed during measurement, the effect on lowering the temperature reading is likely to be quite small and clinically unimportant.

Recommendations

for study

There are other questions about oral temperature measurement that need to be answered. Recommendations for further study include determining whether there are differences in local oral temperature and in more direct central measurements associated with : use of oxygen therapy devices of various kinds, at various flow rates, over various periods of time; use of nasogastric tubes; presence of dental plates or absence of teeth; and occurrence of longer than transitory periods of mouth breathing. The conclusions reached in this study and others that have used electronic thermometers are based on measurements of tissue temperature. Therefore, it seems logical that they would apply to the use of glass-mercury thermometers as well. That is, for taking a measurement at the site of highest oral temperature, either type of instrument would be placed in one of the posterior sublingual pockets. However, since the glass-mercury thermometer requires a 6-8 min measurement period, there possibly could be some evening-out of local oral temperature differences over time. Additional study of different types of thermometers is needed to develop guidelines for oral thermometry specific to each type of instrument and to delineate those principles that are common to all. Acknowledgemmts-The author would like to thank Louise W. Mansfield and Nancy W. their consultation. The study was supported by the Action Program for Nursing Research Facilitation, NU00369 and by General Research Support Grant, DHEW, RR05758.

King

for

DHEW,

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TEMPERATURE

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