1 Participants and procedure
In this prospective observational study, performed at the Princess Máxima Center for pediatric oncology in Utrecht, the Netherlands, families were eligible for inclusion if the child was aged 2–18 years and admitted for a scheduled course of chemotherapy or immunotherapy, requiring at least one overnight stay. The study was also open to the inrooming caregiver. Since most caregivers are the parents, the term parents will be used hereafter. If parents alternated rooming-in during the child’s hospital stay, both parents were given the opportunity to participate. Families were not eligible during the child’s first course of therapy, to eliminate the additional stress accompanying a first admission. Another exclusion criterion was insufficient mastery of the Dutch language.
The Empatica E4 wristwatch was attached on the day of admission. The wristwatch and other measures are described in detail below. Study duration lasted until hospital discharge, unless admission exceeded seven nights, patients developed a fever/fell ill during admission, or elected to stop prior to that time.
Following regular hospital policy, patients were admitted to a private or a double room and one parent slept in a bed directly next to the child. Patients also occasionally moved between rooms, meaning they could sleep a part of their admission in a private room, and part in a double room. Infusion pumps were situated next to the patients’ bed in a docking station and alarms were audible in the patients’ room. The alarm sound levels could manually be regulated by the nurse, and could range from 59 to 74 dB, though pumps were mostly set at the lowest level. The infusion pumps were not automatically connected to the nurse call system (NCS), patients / parents needed to manually alert the nurse by activating the NCS.
2 Outcomes
2.1 Sociodemographic and medical information of children and parents
Parents filled out a general questionnaire about their child and themselves containing information on demographic variables, history of sleep problems, and use of medication. Information on cancer diagnosis and therapy was obtained from hospital records.
2.2 Infusion pump alarms of children and parents
Information on timing and duration of infusion pump alarms was collected by a cable-connection to the hospital server. If the infusion pumps were disconnected from the hospital server (e.g. bathroom visits), data was retrieved from the pump itself after the treatment course was completed. Both methods led to similar information on date, time, and duration of alarms. Bed and wake times from the sleep diary were used to determine the timeframe in which the participants attempted nighttime sleep. The number and duration of infusion pump alarms during these timeframes were extracted. When admitted in a double room, alarms of both the participants’ pump and the other patients’ pump were combined. In case bed and wake times were missing from the sleep diaries (five nights), sleep onset and offset were extracted from the Empatica data (described below).
2.3 Sleep quantity of children and parents
Sleep quantity was measured in children and parents using the Empatica E4 wristwatch (Empatica Inc., Cambridge, United States) referred to as E4[20]. The participants were asked to wear the E4 on their non-dominant wrist day and night during the study period. The E4 uses a three axes accelerometer to measure wrist movement at a rate of 32 Hz. An accelerometer has the capability to measure sleep and wake minutes from the absence/presence of wrist movement, movement is captured by the device and subsequently translated to sleep and wake minutes through an algorithm on a computer: actigraphy. Actigraphy is generally accepted as a valid and reliable method to measure sleep in both children and adults[21, 22]. To support the accelerometer data, bedtime, waketime and non-wear time were reported in a sleep diary.
The raw data from the E4 was divided into epochs with one minute intervals. For each epoch, zero-crossings for all three axis were summed. The Cole-Kripke algorithm was then applied to label each epoch as ‘sleep’ or ‘wake’. This algorithm is mostly used for adults,[23, 24] who are most represented in our study sample, but the algorithm has also successfully been used in children[25–27]. Since participant characteristics and type of device can influence the performance of the algorithm, we first analyzed the performance of the original Cole-Kripke algorithm in our study population. This original algorithm considers an epoch ‘wake’ when crossing a threshold of 1.0. The original algorithm significantly over-classified sleep in our population, therefore we altered the study threshold to 0.4. This value was determined by analyzing Cole-Kripke scores of a subset of participants during their wake and sleep periods and selecting the value that maximized the classification accuracy, as visualized in Fig. 1. Sleep onset and offset was determined by a partly automated algorithm used with the support of the sleep diary. First, the algorithm looked for 8 minutes of continuous sleep within 45 minutes of the sleep diary times. If the device was not worn during this time, sleep onset and offset were manually reviewed through the scored files, to prevent misclassification (since not wearing the device looks similar to sleep for the algorithm). Once each night and morning had sleep onset and offset times, epochs between the determined timings were spliced and the sleep outcomes were calculated: total sleep time (TST), defined as number of minutes scored as sleep between sleep onset and offset; wake after sleep onset (WASO), defined as number of minutes scored as wake between sleep onset and offset; sleep efficiency (SE), defined as percentage of sleep between sleep onset and offset; and night awakenings (NA), defined as number of wake blocks interrupting one or more minutes of continuous sleep.
2.4 Sleep satisfaction of children and parents
Participants were asked to rate daily how satisfied they were with their sleep in the sleep diary. A visual analogue scale (VAS) ranging from one to ten was used for parental sleep and for children below 8 years of age (proxy-report). A VAS with a range from one to five, illustrated with five faces was used for children 8 to 18 years (self-report). Both scales were then converted to a categorical variable ranging from one to five. A higher score indicated better sleep quality.
2.5 Sleep quality and daytime impairment of parents
Sleep and fatigue of parents was assessed by self-reported questionnaires on the last day of parents’ study participation. Similar to previous studies on sleep during hospital admissions, recall time was the current hospital admission, instead of the original recall time of the questionnaires[28].
Insomnia severity index (ISI): A reliable and valid, 7-item self-report questionnaire assessing the nature, severity, and impact of insomnia. Questions were answered on a 5-point Likert scale (0 ´no problem´ to 4 ´very severe problem´). The total score ranges from 0 to 28 and is interpreted as follows; absence of insomnia (0–7); sub-threshold insomnia (8–14); moderate insomnia (15–21); and severe insomnia (22–28). Questionnaires with ≥ one missing item could not be scored (n = 4)[29].
Patient Reported Outcomes Measurement Information System (PROMIS) Sleep Disturbance item bank: A reliable and valid 27-item questionnaire, reflective of insomnia-like symptoms[30, 31]. PROMIS Sleep-Related Impairment item bank: A valid and reliable 16-item questionnaire, containing items related to sleepiness, fatigue, and cognitive difficulties during waking hours[30, 31]. PROMIS short form Fatigue: A valid and reliable 8-item questionnaire, containing items on the experience of fatigue and the impact of on daily activities[32, 33]. PROMIS´ items were measured on a 5-point Likert scale (1 ´not at all´/´never´ to 5 ´very much´/´always´). The official Health Measures scoring service tool was used to calculate T-scores using the US calibration parameters for all participants who filled out at least one item. T-scores are anchored on the US general population, with a mean of 50 and a standard deviation of 10. Higher scores indicate more sleep disturbances.
3 Statistical analyses
To describe sleep quantity and satisfaction during hospital admissions, mean sleep satisfaction and E4 outcomes (TST, SE, WASO, NA) were calculated for all participants. Norm scores are not available for comparison of these outcomes. Self-reported sleep and the daytime consequences parents experienced were described by comparing T-scores to norm scores by using one sample T-tests. A P-value of < .05 was considered significant. In addition, we reported the number of parents in each category of the ISI.
To determine the association between sleep satisfaction and quantity and nightly infusion pump alarms in children and parents, linear mixed models were performed using maximum likelihood estimation. As the models could include multiple nights per participant, and parents and children were combined in one model, two random intercepts were included to account for dependency; on individual subject level and on family level. Since it is plausible that children and adults react differently to alarming sounds,[34] secondary analyses were performed separately for children (random intercept on individual subject level) and parents (random intercept on individual subject level and on family level). Models were constructed for the outcomes sleep satisfaction, WASO, SE and NA, with number of alarms per night and total duration of alarms per night as independent variables. As a longer sleep duration would automatically infer a greater opportunity for alarms to sound, TST was not included as an outcome. All analyses were performed with SPSS Statistics 25.0.0.2.