Advanced Stats exam

Original Article. . . . . . . . . . . . . . Preterm Infant Thermal Responses to Caregiving Differ by Incubator Control Mode

Karen A. Thomas, PhD, RN

OBJECTIVE:

To determine the influence of caregiving on preterm infant and incubator

temperature and to investigate incubator control mode in thermal responses

to caregiving.

STUDY DESIGN:

The intensive within-subject design involved continuous recording of

infant and incubator temperature and videotaping throughout a 24-hour

period in 40 hospitalized preterm infants. Temperature at care onset was

compared with care offset, and 5, 10, 15, and 20 minutes following care

offset using ANOVA-RM.

RESULTS:

Following caregiving, infant and incubator temperature differed

significantly over time by incubator control mode. In air servo-control,

infant temperature tended to decrease after caregiving, while in skin

servo-control infant temperature remained relatively stable. With

caregiving, incubator temperature remained consistent in air servo-

control and increased in skin servo-control.

CONCLUSIONS:

The temperature effects of caregiving should be considered relative to

maintenance of thermoneutrality and unintentional thermal stimulation.

Journal of Perinatology (2003) 23, 640 – 645. doi:10.1038/sj.jp.7211002

INTRODUCTION

The purpose of this study was to determine the influence of caregiving activities on preterm infant and incubator temperature.

Specific research questions included: (1) What is the effect of caregiving, defined as care clusters, on infant and incubator temperature at care offset, and at 5, 10, 15, and 20 minutes following care offset compared with temperature at care onset? (2) Does incubator control mode effect infant and/or incubator temperature responses to caregiving?

Thermal care has been termed the cornerstone of neonatal care.

1 Simulation models have demonstrated infants’ profound capacity to exchange body heat with the environment.2 Provision of a supportive thermal environment minimizes metabolic requirements, a basic objective of neonatal care.3 Because thermal capability is exponentially correlated with gestational age,4

management of the thermal environment requires close attention in preterm infants who are particularly prone to both hyper- and hypothermia. Temperature management is related to infant outcomes. In one study of six neonatal intensive-care units hypothermia (body temperature <961F) was statistically significant factor increasing neonatal illness severity.5

Incubators provide a micro-environment suited to the infant’s thermoregulatory abilities. Incubators are operated in skin servo- or air servo-control modes and these operation modes produce differing patterns of incubator and infant temperature.6

While incubator control appears straightforward, the regulation of incubator and infant temperature is complex. External thermal perturbations, such as initiation of phototherapy, produce large, sustained changes in incubator thermal environment requiring up to 3 hours to reach new equilibrium.7 Aside from the thermal control of the ambient room temperature, three control systems are in effect: the infant’s thermoregulatory control, the incubator’s set point, and the caregiver making adjustments to the incubator set point. The ongoing interaction of these control systems is further complicated by one extremely important condition: the incubator is not a closed system. Caregiving involves opening the incubator, potentially disrupting incubator temperature. In addition to shifting infant temperature, alterations in incubator temperature also produce wide-ranging responses. In a study of the effects of cool exposure in preterm infants (34±2 weeks gestational age, 22±1 days postnatal age), air temperature 1.51C less than thermoneutrality resulted in state change.

8

Neonatal care providers have struggled with balancing needed caregiving against the physiologic costs of disrupting infants. Caregiving has been shown to produce a variety of physiological responses including hypoxia, heart and respiratory changes,

Address correspondence and reprint requests to Karen A. Thomas, PhD, RN, Department of

Family and Child Nursing, University of Washington, Box 357262, Seattle, WA 98195-7262, USA.

Research supported by a grant awarded from the National Center for Nursing Research, R29

NR02420.

Statistical consultant: Robert Burr, PhD, MSEE, Department of Biobehavioral Nursing and Health

Systems, University of Washington.

Department of Family and Child Nursing, University of Washington, Seattle, WA, USA.

Journal of Perinatology 2003; 23:640 – 645 r 2003 Nature Publishing Group All rights reserved. 0743-8346/03 $25

www.nature.com/jp640

distress cues, and sleep – wake state disturbance.9,10 – 15 A considerable portion of the infant’s day is spent in caregiving activities and the pattern of caregiving frequently involves repetitive interruption. In one of the earliest studies of neonatal caregiving, nursing interventions were the most frequent source of infant contact, with an average of 1.68 interventions occurring per hour.

16 The pattern of caregiving has been documented in hospitalized preterm infants (mean gestational age 31.7 weeks) using 24-hour video recording.17 In total, 70% of care occurred in clusters (three or more activities), 11% in paired occurrences (two activities), and 19% in single activities. The mean duration of clustered care was 8.31 minutes while the mean duration of single care activities was 0.48 minutes. In another study of low-risk preterm infants (31 to 36 weeks gestational age, postnatal age 3 to 16 days), caregiving was found to be the predominant factor, producing cyclic influences based on pattern of caregiving.

18

Although caregiving procedures differ across nurseries, in general studies of care patterns have demonstrated significant amounts of disruption as well as changeable pattern of caregiving. Although the thermal disruption produced by caregiving is clinically recognized, there have been few studies of the effect of caregiving on infant and incubator and infant temperature.

The consequences of caregiving on temperature involve two general areas of concern. The first concern is the direct effect of caregiving on incubator and/or infant temperature. In preterm infants less than 1500 g, decreases in both peripheral (sole of foot, mean 1.31C, range 0.2 to 3.0) and central (abdominal skin, mean 0.71C, range 0.0 to 1.71C) temperature occurred with caregiving episodes that lasted 15 to 45 minutes; temperature recovery required up to a 2-hour period.19 The decline in body temperature was negatively correlated with body weight. Using an intervention protocol to improve thermal environment stability in fragile ELBW infants (23 to 29 weeks gestational age) during the first days of life, one nurse investigator demonstrated less variability in ambient temperature, less peripheral vasoconstriction (heel temperature <35.21C), and decreased gradient between heel and abdominal skin temperature.

20 In this experimental study, approximately 10 to 11 caregiving disruptions occurred in a 10-hour period.20

The second area of concern related to temperature effects of caregiving is related to sensory stimulation. Although not widely studied in preterm infants, thermal stimulation is a powerful form of sensory input. In a study of temperature stimulation, heart rate variability was entrained by differing frequencies of skin (palm) temperature; this entrainment varied with age.21 Thus, preterm infants are sensitive to thermal stimulation and this stimulation potentially affects multiple functions.

MATERIALS AND METHODS

Infant and incubator temperature were recorded continuously over a 24-hour period in 40 hospitalized preterm infants using an

intensive within-subject design. Selection criteria included: gestational age 26 to 33 weeks and postnatal age 14 to 28 days, housed in an incubator, weight average for gestational age, absence of major congenital anomalies and surgical interventions, intraventricular hemorrhage rGrade II, and not receiving phototherapy at the time of study. Infants receiving >28 days of ventilatory assistance were excluded from the study. Given the selection criteria, infants were medically stable, experiencing the typical problems of prematurity. The study was conducted in the NICU of a large Northwestern metropolitan hospital in which average nursery ambient temperature was 231C.

Infant abdominal skin and incubator temperature were recorded at minute intervals using a battery-operated monitor (Vitalog PMS8, Redwood, CA). A skin probe (YSI427, Yellow Springs, OH) was adhered to the infant’s right lateral abdomen, at the point of intersection of perpendicular lines drawn from the anterior axilla and the umbilicus, using a reflective probe cover (Accutemp Plus, Kentec Medical, Irvine, CA) which was then covered with an air and moisture permeable tape (Tegaderm, 3M, St. Paul, MN). An ambient air temperature probe (YSI405, Yellow Springs, OH) was suspended 10 cm from the center of the incubator ceiling. The recorded air temperatures reflected the central portion of the incubator where the infant was positioned. Temperature probes were calibrated against a certified thermometer to assess accuracy (r>o.99).

Infants were videotaped throughout the 24-hour data collection period using a lapse time video recording system with 12:1 reduction (Panasonic AG-6030). A mini-camera (Toshiba) was suspended from the incubator ceiling, providing a view of the infant and incubator interior. Caregiving was defined as all health- related entrances to the incubator. Caregiving was coded from the videotapes in 1-minute epochs using a dichotomous code (absent, present). Type of caregiving was not recorded. Inter-rater reliability of coding, determined by percent agreement, was maintained at >85%. The time stamp on the video recording was synchronized with the computer used in programming the temperature monitor; the time difference between the two systems was <5 seconds over a 24-hour period.

Care clusters were determined from the caregiving code and care onset and offset were then determined. As caregiving was coded yes/no and care of preterm infants often involves multiple incubator entrances, a care cluster was operationally defined as an episode of care lasting at least 1 minute and preceded by an interval of greater than 20 minutes without caregiving. This definition was based on visual analysis of tapes as well as consultation with neonatal nursing experts. Duration of care clusters and the interval between clusters were calculated. Infant and incubator temperature at care onset, offset, and at 5, 10, 15, and 20 minutes following care offset were then identified. Differences in temperature from care onset to offset and the time following as well as the effect of incubator control mode were

Temperature and Caregiving Thomas

Journal of Perinatology 2003; 23:640 – 645 641

analyzed using analysis of variance for repeated measures (ANOVA-RM).

Informed consent for participation was obtained from parents. Following application of temperature recording and video equipment, infants received typical nursery care. Selection of incubator operation mode as well as set point for air servo- or skin servo-control was based on unit procedures and nurses’ clinical judgment. Incubators were the same model (Air Shields C-200). Study procedures were approved by human subjects review committees at both the investigator’s home institution and the study clinical setting.

RESULTS

Subject characteristics and temperature-descriptive statistics are provided in Tables 1 and 2. Mean gestational age of the 40 subjects was 30.3 (SD 2.5) weeks and mean postnatal age at time of study was 16.6 (SD 4.8) days. The sample distribution of race and ethnicity was Black, 2; Hispanic, 3; Asian, 2; White, 33. The description of caregiving clusters is provided in Table 3. Infants received caregiving during 11 to 46% of the 24 hour recording period, mean 23%. The mean number of clusters per 24 hours was 12.6 and mean interval between care was 87.9 minutes. The mean duration of care clusters was 25.6 minutes; however, the caregiving mode was 1. For 16.7% of all care clusters, care duration was 1 minute, and care duration of 1 to 2 minutes accounted for 25% of all care clusters. Thus, there was considerable variability both within and across subjects, with frequent very short-term care as well as long bouts of care.

There were no significant differences (t-test) between incubator control mode in mean cluster duration or interval, number of care clusters, percent of time in caregiving, and Apgar scores at 1 and 5 minutes. There was no association (w2) between incubator control mode and gender, oxygen therapy, treatment of sepsis, continuous or intermittent gavage feeding, and receipt of antibiotics or caffeine. No infants were receiving analgesics or propranalol. Five infants in skin servo-control incubators were receiving lorazapam. Infants in skin servo-control incubators differed from those in air

servo-control (t-test, 38 df) by gestational age (28.12 vs 30.30 weeks, p ¼ 0.002), postconceptional age (30.18 vs 32.67 weeks, p<0.000), and study weight (1060.53 vs 1545.17 g, p<0.000). Using w2, there was an association between incubator control mode and IV therapy (skin, 13; air, 6, p ¼ 0.002) and ventilatory support (skin, 8; air, 4, p ¼ 0.053). Mean abdominal skin temperature for all subjects at onset of care cluster was 36.401C (SD 0.726) and mean incubator air temperature was 30.721C (SD 2.45). Changes in temperature following caregiving were highly variable, with increase and/or decrease in both infant and incubator temperature following care. Duration of care cluster did not correlate with temperature changes following care (r<0.10). As the set points for incubator control differ based on type of control, control mode was examined in relationship to temperature changes in infant and incubator following care (Table 4, Figure 1).

Table 1 Sample Characteristics by Incubator Control Mode

Variable Air servo-control

(n=23)

Skin servo-control

(n=17)

Total

(N=40)

fr (%) Fr (%) fr (%)

Gender

Male 15 (65.2) 8 (47.1) 23 (57.5)

Female 8 (34.8) 9 (52.9) 17 (42.5)

Oxygen 7 (30.4) 10 (58.8) 17 (42.5)

Ventilation* 4 (17.4) 8 (47.1) 12 (30)

IV fluids 6 (26.1) 13 (76.5) 19 (47.5)

IVH 1 (4.3) 2 (11.8) 3 (7.5)

Sepsis 5 (21.7) 6 (35.3) 11 (27.5)

Intermittent gavage 14 (60.9) 6 (35.3) 20 (50)

Continuous gavage 7 (30.4) 10 (58.8) 17 (42.5)

Nipple fed 6 (35.3) 0 6 (15)

Antibiotics 3 (13.0) 3 (17.6) 6 (15)

Bronchodilator 4 (17.4) 1 (5.9) 5 (12.5)

Caffeine 8 (34.8) 8 (47.1) 16 (40)

Lorazepam 0 5 (29.4) 5 (12.5)

Steriods 4 (17.4) 5 (29.4) 9 (22.5)

Note: IV=intravenous, IVH=intraventricular hemorrhage. * Ventilation includes continuous positive airway pressure.

Table 2 Descriptive statistics by incubator control mode

Air servo-control (n=23) Skin servo-control (n=17) Total (N=40)

Variable Mean (SD) Min/Max Mean (SD) Min/Max Mean (SD) Min/Max

Gestational age (weeks) 30.3 (2.5) 26/30 28.1 (1.6) 26/31 29.4 (2.4) 26/33

Birth weight (g) 1506.0 (409.1) 910/2220 1098.5 (237.2) 566/1500 1332.8 (398.9) 566/2220

Apgar 1 minute 5.6 (2.4) 2/9 4.7 (2.3) 1/9 5.2 (2.3) 1/9

Apgar 5 minute 7.3 (1.5) 4/9 7.3 (1.2) 5/9 7.3 (1.3) 4/9

PCA (weeks) 32.7 (2.1) 29.1/35.3 30.2 (1.4) 28.1/32.8 31.6 (2.2) 28.1/35.3

PNA (day) 16.6 (4.8) 13/29 14.5 (2.1) 11/18 15.7 (4.0) 11/29

Study weight (g) 1545.2 (414.5) 906/2300 1060.5 (220.1) 625/1390 1339.2 (419.1) 625/2300

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642 Journal of Perinatology 2003; 23:640 – 645

Infant and incubator temperature across time were analyzed separately using ANOVA-RM (Table 5) and the Greenhouse – Geisser epsilon correction for F test degrees of freedom. For infant temperature there was a significant time and time � control main effect. Within subject contrasts demonstrated significant polynomial time and time � control effects. ANOVA-RM for incubator temperature also revealed significant main effects for time and time � control with significant polynomial components for time and time � control. Using t-test comparisons, abdominal temperature at care onset did not differ between control modes, although mean air temperature in skin servo-control was slightly

higher than in air servo-control (36.44 vs 36.371C). In air servo- control incubators, mean infant temperature tended to decrease during care, continued to decrease after care offset, and then rose slightly, however at 20 minutes following care offset precare temperature was not re-established. In skin servo-control, mean infant temperature tended to increase slightly throughout care and after.

Summarizing infant temperature data using the mean does not portray clinically significant changes occurring within infants. Change in infant temperature following caregiving was further examined in those infants whose abdominal skin temperature at care onset was within normal ranged, defined as 36.2 to 36.81C. Infant temperature at care onset was compared with temperature at 20 minutes following care offset. In air servo-control incubators, of the 71 care clusters (representing 23 infants) that started with infant temperature within normal range, temperature was below normal range in 21 (30%) and above normal range in 14 (20%), 20 minutes following care offset. In skin servo-control incubators, there were 90 care clusters (representing 17 infants), initiated while infant temperature was within normal range, that resulted in temperature below normal range in 10 instances (11%) and above

Table 3 Description of Daily Caregiving (N=503 Care Clusters,

40 Infants)

Variable Mean SD Minimum Maximum

Clusters/infant 12.6 2.6 9 17

Cluster duration (min) 25.6 27.3 1 224

Cluster interval (min) 87.9 53.2 10 316

Caregiving (%) 23 8 11 46

Table 4 Effect of Caregiving on Infant and Incubator Temperatures by Incubator Control Mode (N=40)

Air servo-control (n=23) Skin servo-control (n=17)

Infant Incubator Infant Incubator

Time T1C D T1C D T1C D T1C D

Onset

Mean (SD) 36.37 (0.77) 30.25 (1.60) 36.44 (0.67) 31.31 (3.14)

Min/max 33.63/38.25 27.10/33.50 33.17/38.75 22.51/37.25

Offset

Mean (SD) 36.29 (0.75) 0.08 (0.57) 30.37 (1.55) �0.11 (0.43) 36.46 (0.61) �0.02 (0.52) 31.76 (3.38) �0.45 (1.79) Min/max 33.47/37.99 �1.89/2.72 27.10/34.24 �2.11/1.59 34.60/37.85 �2.62/2.47 22.73/38.57 �7.78/4.32

5 minutes

Mean (SD) 36.26 (0.76) 0.12 (0.59) 30.33 (1.57) �0.08 (0.39) 36.45 (0.65) �0.01 (0.52) 31.92 (3.55) �61 (2.01) Min/max 34.17/37.99 �1.79/2.75 27.10/34.13 �1.54/1.50 34.04/37.85 �2.54/2.29 22.37/39.84 �8.75/4.70

10 minutes

Mean (SD) 36.26 (0.75) 0.12 (0.59) 30.27 (1.59) �0.02 (0.35) 36.46 (0.65) �0.03 (0.54) 31.99 (3.64) �0.70 (2.20) Min/max 34.28/38.07 �1.79/1.96 27.10/33.60 �1.56/1.35 33.85/37.85 �2.75/2.35 22.23/40.35 �9.65/5.09

15 minutes

Mean (SD) 36.27 (0.77) 0.04 (0.61) 30.25 (1.60) 0.01 (0.33) 36.47 (0.63) �0.04 (0.56) 31.96 (3.70) �0.68 (2.34) Min/max 34.17/38.17 �1.79/1.92 27.03/34.13 �1.46/1.29 33.78/37.85 �2.94/2.50 22.80/40.49 �10.24/5.38

20 minutes

Mean (SD) 36.29 (0.77) 0.08 (0.62) 30.24 1.62 0.02 (0.35) 36.49 (0.63) �0.06 (0.56) 31.95 (3.64) �0.63 (2.40) Min/max 33.97/38.17 �1.83/1.83 27.03/34.34 �2.38/1.43 33.89/37.82 �3.08/2.64 22.73/40.49 �10.47/5.66

Note: T1C=temperature; D=temperature difference: onset – offset, and offset-value at 5, 10, 15, and 20 minutes, respectively. Positive value=temperature decrease after care, negative value=temperature increases after care.

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Journal of Perinatology 2003; 23:640 – 645 643

normal range in 21 instances (23%). For those care clusters that began when infants’ temperature was within normal range, the minimum and maximum temperature change following care was �1.07 to 1.711C in air servo-control mode and �1.35 to 0.961C in skin servo-control mode.

Incubator temperature differed between control mode at all time points and skin servo-control demonstrated greater variability. Air servo-control incubators showed little change in air temperature during care and following. In skin servo incubators, air temperature increased with care giving and remained elevated 20 minutes following care offset.

Infants in servo-control were less than 33 weeks postconceptional age. To examine the possible confounding of postconceptional age and incubator control mode, the sample was divided into two subgroups, <33 and Z33 weeks postconceptional age and compared. There were no statistically significant differences by age group in abdominal temperature at care onset or offset. Air temperatures were generally warmer in infants less than 33 weeks PCA compared to those 33 weeks and older (31.19 vs 29.461C, p ¼ 0.018) and remained warmer after care offset. Owing to subject numbers and limited statistical power, postconceptional age could not be entered as a covariate in the ANOVA-RM reported above. A modified model, using only infants less than 33 weeks (n ¼ 27) and comparing temperature at care onset, care offset, and 15 and 20 minutes following care offset also demonstrated a significant main effect of control (3, 23 df, p ¼ 0.048) and significant within subject time � control effect.

DISCUSSION

The findings illustrate that caregiving is associated with changes in infant and incubator temperature and incubator control mode is a factor governing these changes. Synthesizing the results of five research articles in which either (1) oxygen consumption was used

to define TNZ, or (2) skin temperature was recorded when core body temperature was carefully controlled within normal range, abdominal skin temperature between 36.2 and 36.81C is used to define TNZ.

22 – 26 While the magnitude of mean change in infant temperature is relatively small, decreasing temperature following care in air servo-control incubators results in unacceptably low temperatures in some infants. Caregiving resulted in significant change in incubator temperature, with particularly large variation in skin servo-control incubators. The higher skin servo-control air temperatures following caregiving indicate the ambient temperature required to sustain infant temperature following this disruption. Again, the mean values do not adequately portray the experiences of some infants with extremely large changes in incubator temperature following caregiving. While the changes in incubator temperature support maintenance of infant temperature, they also reflect considerable thermal stimulation. The effect of thermal stimulation in preterm infants is incompletely understood; however, temperature has been related to respiratory control.

27

Table 5 Analysis of Variance for Repeated Measures for Infant and

Incubator Temperature at Care Onset, Offset, and 5, 10, 15, and 20

Minutes Following Offset (n=40)

Source F df p

Infant

Multivariate test Time 3.483 5, 34 0.012

Time � control 3.012 5, 34 0.023 Within subjects contrast Time 11.092 1, 38 0.002

Time � control 9.039 1, 38 0.005

Incubator

Multivariate test Time 7.903 5, 34 0.000

Time � control 7.792 5, 34 0.000 Within subjects contrast Time 13.863 1, 38 0.001

Time � control 25.927 1, 38 0.000 Incubator Control Method

Skin servoAir servo

In cu

b a

to r

°C

33.0

32.5

32.0

31.5

31.0

30.5

30.0

29.5

onset

offset

5 min after offset

10 min after offset

15 min after offset

20 min after offset

Incubator Control Method

Skin servoAir servo

In fa

n t

°C

36.7

36.6

36.5

36.4

36.3

36.2

36.1

onset

offset

5 min after offset

10 min after offset

15 min after offset

20 min after offset

Figure 1. Incubator and infant temperature following caregiving (95% confidence intervals).

Thomas Temperature and Caregiving

644 Journal of Perinatology 2003; 23:640 – 645

In a previous study, differing thermal environments were produced by skin and air servo-incubator control modes.6 Skin servo-control resulted in more variable air but more stable infant temperature, while air servo-control resulted in more stable air and more variable infant temperature.6 In a Cochrane review of incubator control mode, skin servo-control reduced neonatal death rate among low-birth-weight infants, particularly among VLBW (relative risk 0.72, 95% CI 0.54 to 0.97).28 The current study shows that the thermal effects of caregiving also differ by incubator control mode. The study was not designed to determine superiority of incubator control mode. Rather, results highlight the need for further study of incubator control.

Videotaping may have influenced caregiving pattern and hence the thermal responses observed. Only the hands of caregivers were visible and caregivers were not identifiable. The camera was unobtrusive and did not physically interfere with the infants care. Nursery staff were accepting the research study and did not express discomfort with the videotaping procedures.

In summary, preterm infant caregiving activities altered both infant and incubator temperature. These changes in temperature were dependent on mode of incubator control. In general, air servo-control resulted in reduction of mean infant temperature with caregiving, while in skin servo-control mean infant temperature tended to rise with caregiving. Within infants, however, caregiving produced variable effects, with body temperature both increasing and decreasing following caregiving. Incubator regulation in response to caregiving produces wide variability in air temperature. Further investigation of the effect of this thermal stimulation is needed.

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