Comparing of rectal and axillary temperature measurements in preterm newborns

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  1. http://orcid.org/0000-0003-0837-4122Lisa K McCarthy1,2,three,
  2. http://orcid.org/0000-0001-7453-5452Colm Patrick Finbarr O'Donnell1,two,three
  1. 1 Department of Neonatology, The National Maternity Hospital, Dublin, Ireland
  2. two The National Children's Research Centre, Crumlin, Dublin 12, Ireland
  3. 3 University College Dublin, Dublin, Republic of ireland
  1. Correspondence to Dr Lisa Thousand McCarthy, Department of Neonatology, The National Maternity Hospital, Dublin D02 YH21, Republic of ireland; lmccarthy{at}nmh.ie

Abstruse

Objective To compare rectal and axillary temperatures in preterm newborns on admission to the neonatal intensive intendance unit of measurement (NICU).

Design Secondary assay of data collected in a randomised controlled trial (RCT).

Setting Maternity hospital, level three NICU.

Patients Seventy-two newborns <31 weeks who were enrolled in the BAMBINO RCT (A randomised trial of exothermic mattresses to prevent oestrus loss in preterm infants at nascence, ISRCTN31707342).

Interventions Newborns were placed in polyethylene bags and were randomised to placement on exothermic mattresses, or not in the delivery room. All infants had rectal and axillary temperatures measured in immediate succession using a digital thermometer on NICU admission.

Outcome measures Admission rectal and axillary temperatures.

Results Hateful (SD) gestational age was 28 (2) weeks and birth weight was 1138 (374) thou. Mean rectal-axillary temperature difference was 0.ane (0.v°C) (range −1.4°C to +one.5°C). Rectal and axillary temperatures differed by ≥0.v°C in 18/72 (25%) infants; axillary temperature was college than rectal in 6 (8%) and lower in 12 (17%). At that place was a positive linear relationship between rectal and axillary measurements (Pearson'south correlation R=0.84). Applying the Bland-Altman technique, the width of 95% prediction interval was one.8°C (−0.8°C to 1.0°C) implying that rectal and axillary measurements may vary by up to 1.0°C. Axillary temperature had a sensitivity of 65% when used to detect rectal hyperthermia and 100% sensitivity for hypothermia.

Conclusion Paired rectal and axillary temperature measurements in preterm newborns on NICU admission vary significantly. Axillary temperature was sensitive at detecting rectal hypothermia but non hyperthermia. Axillary temperature may not exist an accurate proxy for rectal temperature measurement in all preterm newborns on NICU access.

  • infant, newborn
  • preterm
  • temperature
  • hypothermia
  • hyperthermia
  • NICU

Data availability statement

Information are available on reasonable request to LKMC. The identified clinical data are held on password-protected computers at the National Maternity Infirmary, Dublin.

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This is an open access article distributed in accord with the Creative Commons Attribution Not Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adjust, build upon this piece of work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the utilize is not-commercial. Run into: http://creativecommons.org/licenses/by-nc/4.0/.

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  • infant, newborn
  • preterm
  • temperature
  • hypothermia
  • hyperthermia
  • NICU

What is already known on this topic?

  • In preterm newly born infants, abnormal temperature on access to the neonatal intensive intendance unit (NICU) is associated with adverse outcome.

  • The WHO defines normal body temperature for infants equally 36.v°C–37.five°C.

  • In the NICU, temperature is frequently measured at the axilla rather than the rectum equally information technology is more than accessible and less invasive.

What this study adds?

  • Rectal and axillary temperature measurements in preterm newborns on NICU admission may vary considerably.

  • Axillary temperature was sensitive for detecting rectal hypothermia simply not hyperthermia.

  • Axillary temperature may not exist an authentic proxy for rectal temperature measurement in all preterm newborns on admission to the NICU.

Background

Newborn preterm infants lose heat rapidly after birth. Despite measures to foreclose heat loss during stabilisation in the delivery room (DR) many preterm newborns have abnormal temperature on admission to the neonatal intensive care unit (NICU).1 Abnormal temperature on NICU admission is an independent risk factor for morbidity and bloodshed in very preterm newborns.2–4

The WHO defines normal torso temperature for infants as a core temperature of 36.5°C–37.five°C.five There is no gold standard for measuring body temperature, merely temperature measured at the rectum is considered to exist representative of cadre body temperature (temperature around the hypothalamus) and is a more pragmatic approach to measuring infant temperature. Trends in rectal temperature measurements are reflective of changes in core temperature with sufficient accuracy to guide clinical care.half dozen In the NICU, temperature is oft measured at the axilla rather than the rectum every bit it is more attainable and less invasive. Older studies using glass and mercury thermometers take reported complications when measuring rectal temperatures in infants.vii–9 There are conflicting data on how well rectal and axillary temperature measurements correlate when taken with digital thermometers in infants in the NICU.

Pooled data from a review of twenty studies of 3201 term infants and children showed a wide variation in rectal and axillary temperatures across studies. The pooled, random effects mean temperature difference (rectal minus axillary temperature) for electronic thermometers in this meta-analysis was 0.85°C (−0.19°C to 1.ninety°C). At that place was less variability in the pooled mean temperature difference for newborns: 0.17°C (−0.15°C to 0.fifty°C); however, most of the included studies used mercury thermometers.10 In a written report of 63 term infants >1 60 minutes of historic period admitted to the NICU, Cusson et al observed moderate correlation betwixt rectal and axillary temperatures measured with the IVAC digital thermometer.11 Hissink Muller et al reported a wide variation between paired rectal and axillary temperature measurements using digital thermometers (Thermoval Waterproof) in 33 infants (25–42 weeks' gestation) in the NICU. The authors concluded that the two measurements should not be used interchangeably every bit infants in their study had significantly lower axillary temperatures (0.27°C±0.twenty°C) and the 95% limits of agreement ranged from −0.13°C to 0.67°C.12 Roll et al compared rectal and axillary temperatures in 20 very preterm and unstable term neonates in the NICU. In their subgroup analysis, hateful axillary temperature was merely 0.06°C lower than rectal temperature in infants <1000 g compared with 0.37°C lower at the axilla in infants >2500 g.thirteen

Most studies report information on rectal-axillary temperature correlations in non-newborn, stable, normothermic infants at unlike stages during their NICU access. There are little data on the correlation betwixt rectal and axillary temperatures in newborn very preterm infants on admission post-obit stabilisation in the DR. Many of these infants are not normothermic and are not clinically stable. Abnormal temperature at this time, in this population, is associated with agin outcome.2–iv

The objective of this study was to compare rectal and axillary temperatures in newborn very preterm infants <31 weeks' gestation measured with digital thermometers on admission to the NICU.

Patients and methods

Written report design

This is secondary analysis of data collected prospectively in accomplice of newborn preterm infants enrolled in a randomised controlled trial (RCT) conducted at the National Maternity Hospital, Dublin, Ireland, between Feb 2011 and February 2012.

Participants

Infants in this report were enrolled in the BAMBINO RCT (A randomised trial of exothermic mattresses to prevent heat loss in preterm infants at nascence, ISRCTN31707342).14 Inborn infants <31 weeks' gestation were eligible for inclusion. We compared rectal temperature on NICU admission in preterm newborns wrapped in polyethylene bags (Pb) to infants wrapped in PB and placed on exothermic mattresses (EM) in the DR. Nosotros found that more infants who were placed on EM had temperatures outside the range of 36.5°C–37.5°C and were more likely to exist hyperthermic on admission to the NICU. The trial was stopped early due to the high rate of hyperthermia detected in infants in the EM grouping, every bit measured by rectal temperature.14

DR care

Later birth, all infants were transferred to a CosyCot Babe Warmer. They were placed without drying in a bag with a hat placed on their caput. Infants randomised to treatment with an EM were placed on an activated TransWarmer mattress (Cooper Surgical, Trumbull, Connecticut, USA). Stabilisation was otherwise carried out in accordance with international recommendations.15 sixteen Infants in both groups were transferred to the NICU in transport incubators. All infants remained in their Atomic number 82 and those randomised to the EM grouping remained on their mattress for transfer.

Temperature on NICU admission

On arrival to the NICU, all infants had a rectal and axillary temperature measurement taken in firsthand succession using the Vicks V900F-EE SmartTemp Digital Thermometer (Procter & Risk, Ohio, USA). This thermometer was the standard digital thermometer used in the NICU at that time and is licensed for oral, axillary and rectal use in children and infants. The manufacturer states that the accuracy of the thermometer is ±0.1°C between 35.5°C and 41.half dozen°C at room temperature of 21.6°C; and its temperature range is 32.0°C–42.8°C. They say that the thermometer is calibrated at the time of industry and if the instructions are followed, the accuracy of measurements will non be affected.

Rectal temperature was measured kickoff in all cases. Caregivers were instructed to plow the thermometer on, wait for it to signal before opening the incubator portholes, then open up the Pb and gently insert the tip of the thermometer into the rectum to ane cm. The thermometer displayed the temperature continuously until it signalled over again (eight beeps) that peak temperature was reached (~xxx southward). For axillary readings the thermometer was placed in the axilla with the tip touching the peel and the reading awaited every bit previously described. The same thermometer was used for both measurements and was cleaned with an booze wipe betwixt readings. Infants remained within the ship incubator, wrapped in a Lead with or without an EM until the temperature was measured. Demographic data on gestational age, birth weight, gender, multiple births, mode of delivery, maternal fever, respiratory support in the DR, proportion of infants placed on EM in the DR and time from birth to NICU admission were recorded.

Statistical analysis

Information were analysed using SPSS Five.18.0. Continuous event variables with a normal distribution were expressed as mean (SD) and variables with an abnormal distribution as median (IQR). Differences between temperature readings were analysed using a Student's paired t-examination. A p value <0.05 was taken to exist statistically significant. Dichotomous variables were expressed every bit numbers and percentages. We determined the Pearson'due south correlation (R) between rectal and axillary temperatures and presented the data in a scatterplot. The degree of understanding betwixt temperature measurements recorded at the axilla and rectum was assessed using the Bland-Altman technique. The deviation between their measurements was plotted against their average. Two SDs around the mean difference represented the upper and lower limits of agreement.17 18

Results

Seventy-2 infants <31 weeks' gestation were enrolled in the BAMBINO trial. All 72 infants enrolled in the trial at the time of stopping were included for assay in this report. All infants had a rectal and axillary temperature measured on admission to the NICU. In the DR, all infants were wrapped in Atomic number 82 and 37 (51%) were placed on EM. The mean (SD) gestational age was 28 (two) weeks and the mean (SD) nascency weight was 1138 (374) one thousand. Twenty-ix infants were <28 weeks' gestation. All 72 infants received respiratory support and 10 (fourteen%) were intubated in the DR. The median (IQR) age at the time of admission was 20 (17, 26) min (table one).

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Tabular array 1

Results: characteristics of 72 infants enrolled in the study

The mean (SD) rectal-axillary temperature difference was 0.1 (1.5)°C, with a range of −1.4°C to +ane.5°C. Rectal and axillary temperatures differed past ≥0.5°C in xviii/72 (25%) infants; axillary temperature was higher in six (8%) infants and lower in 12 (17%). Using the Bland-Altman technique, we plotted the difference between each pair of readings confronting the average rectal and axillary temperatures (figure 1). Overall, the temperature readings correlated well (Pearson's correlation R=0.84, figure ii) but our analysis showed that the width of the 95% prediction interval was ane.8°C (from –0.viii°C to 1.0°C). This suggests that individual rectal and axillary temperature measurements may vary by up to 1.0°C.

Figure 1

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Figure 1

Results: Bland-Altman plot for rectal and axillary temperature measurements on neonatal intensive intendance unit access. The solid line represents the mean (rectal-axillary) difference and dashed lines represent the 95% limits of agreement.

Figure 2

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Figure ii

Results: scatterplot of rectal and axillary temperatures on access to the neonatal intensive care unit of measurement (n=72). The vertical and horizontal lines represent the normal temperature range (36.5°C–37.five°C). Pearson'southward correlation R=0.84, R2=0.69.

Hyperthermia is divers every bit a temperature >37.5°C and hypothermia <36.5°C.5 In this accomplice, 42 infants had a normal rectal temperature, and of these 34 infants had a normal axillary temperature (effigy two). Axillary temperature measurements were a reasonably sensitive marking for rectal normothermia (sensitivity: 81% (34/42), positive predictive value (PPV): 81% (34/42)) and although the numbers were small (northward=vii), axillary temperature was an excellent marker for rectal hypothermia (sensitivity: 100% (7/vii), negative predictive value: 100% (threescore/sixty)). Even so, when axillary temperature was used to observe rectal hyperthermia it had low sensitivity of 65% (15/23) (effigy 2).

Discussion

In this report, mean rectal temperature was 0.one°C higher than axillary temperature in newborn preterm infants on admission to the NICU. This, withal, does not adequately describe the agreement between the two measurements. We applied the Bland-Altman method of analysis to further assess the relationship between rectal and axillary temperatures and institute that although the mean deviation appeared small-scale (0.1°C), the width of the 95% prediction limits for the difference between rectal and axillary temperatures was ±0.nine°C. This suggests that in some cases there was wide variability betwixt the paired readings of up to 1.0°C. The normal temperature range for infants is narrow, between 36.five°C and 37.5°C, therefore a departure of up to 1°C in temperature readings may be the difference betwixt normal and aberrant temperatures. This may have significant implications for agin event.

In our cohort, the axillary temperature was a reasonably sensitive marker for rectal normothermia and highly sensitive for hypothermia. In all vii cases, infants with axillary hypothermia had a low rectal temperature. These infants are at increased chance of decease every bit a result of their access hypothermia.2 three Conversely, our analysis suggests that axillary temperature is quite insensitive at detecting admission temperature >37.5°C; and misses up to 35% of infants with rectal hyperthermia. In the past, this was less relevant every bit most infants were hypothermic on access and few had temperatures >37.5°C.19–21 Due to improved awareness and more effective warming strategies the number of infants with high temperatures on admission is increasing.1 14 22 23 Compared with hypothermia, less is known about the long-term consequences of hyperthermia subsequently birth in preterm newborns. Hyperthermia in asphyxiated term infants is associated with adverse neurodevelopmental outcomes.24 25 In their study of >9000 infants <33 weeks, the Canadian Neonatal Network demonstrated a U-shaped relationship between admission temperature and adverse neonatal outcomes. Both hypothermia and hyperthermia were associated with college rates of complications of prematurity; complications were lowest at admission temperatures ranging from 36.5°C to 37.2°C.4 The newborn resuscitation guidelines emphasise the importance of maintaining normothermia and avoiding hyperthermia.15 16

The mean rectal-axillary temperature deviation of 0.1°C that nosotros observed is less than the mean deviation reported in previous studies (0.17°C,ten 0.27°C,12 0.16°C13 and 0.7°C26). This may be considering the infants in our study were a more than homogenous group; they were all preterm and their temperatures were measured at the same time point. One written report included infants up to six months of historic period in hospital and at dwelling house,26 others monitored temperature at different times during infant's NICU admission13 and some analysed term and preterm infants together.x 12 Results of the subgroup analysis in preterm infants in one study suggest that the correlation between rectal and axillary temperatures is closer in preterm infants than in larger term infants.xiii There is besides testify that this correlation is strongest in the days closest to nativity and weakens equally infants mature.27 28

Few studies report data on very preterm newborns on admission to the NICU. One of the strengths of our written report is that nosotros report prospective data in a relatively homogenous, reasonably big group of preterm newborns at the aforementioned point in time. Nosotros measured the rectal and axillary temperatures for each infant using the aforementioned thermometer in immediate succession. No interventions were carried out between readings to adjust the babe's temperature then it is unlikely that changes in trunk temperature were responsible for the differences in temperature readings.

There are a number of limitations to our study. Although nosotros used the aforementioned thermometer to measure the rectal and axillary temperatures, different nurses with varying degrees of experience carried out measurements in different infants. However, the thermometers and the techniques used were the same as are routine in clinical care and the manufacturer'south instructions were followed. There are a number of potential issues with temperature readings at both sites and fault can occur depending on the placement of the probe. At the axilla temperature readings may differ depending on adequate closure of the axillary fold, blood flow to the axillary region and potentially activation of not-shivering thermogenesis.27 28 Rectal temperature readings may also vary depending on the depth of insertion of the probe and whether faeces are present. Nosotros performed additional subgroup assay to examine the sensitivity and PPV of axillary temperature for rectal temperature in infants in the 'Pb' group, 'EM' group and for infants <28 weeks' gestation. A similar positive linear correlation was observed between axillary and rectal temperature readings in the subgroups but the numbers were too small to report sensitivity and PPV meaningfully. The additional assay, with its small-scale numbers, did non suggest that in sure circumstances (ie, in a purse and on a mattress, or only in a bag, or <28 weeks) axillary temperature is more accurate.

In that location is sometimes a reluctance to carry out rectal temperature measurements in newborn infants because it is deemed to be invasive, and in the by was associated with rectal perforation. The gamble of rectal injury caused by rectal temperature measurement is extremely small26 and most of the published example reports of rectal injury refer to mercury-in-glass thermometers that are no longer used. Mercury thermometers have been replaced past plastic, digital thermometers with narrow, smoothen probes that only take xxx s to read and are less likely to break or crusade trauma. A potential benefit of taking rectal temperature, in improver to being more accurate, is the early identification of anal patency.

Determination

Paired rectal and axillary temperature measurements in preterm newborns on NICU admission may vary significantly. Axillary temperature was sensitive at detecting rectal hypothermia but non hyperthermia. Axillary temperature may not be an accurate proxy for rectal temperature measurement in all preterm newborns on admission to the NICU.

Data availability statement

Information are available on reasonable request to LKMC. The identified clinical information are held on countersign-protected computers at the National Maternity Hospital, Dublin.

Ethics statements

Ethics approving

The trial was approved by the NMH Enquiry and Ideals Commission and written informed consent was obtained from a parent or guardian before delivery.

Acknowledgments

We give thanks Ricardo Segurado, consultant biostatistician, at the Center for Support and Training in Analysis and Research (CSTAR), University College Dublin, for his help with the statistical analysis of our data. Nosotros also offering sincere thanks to the families of all babies who participated in our study.

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