Variable groups and operational definitions

As previously mentioned, each variable was given a specific operational definition, to prevent misinterpretation within variables. There were 46 variables in this study, divided into five groups purely for ease of classification and grouping. These five groups were:

1. Variables that describe ward / patient condition.

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3. Variables that describe PUs (no., category, location etc.).

4. Glamorgan RAS’ sub-items.

5. Braden Q RAS’ sub-items.

These variables were subjected to different statistical tests, both descriptive and inferential. The type of test used depended on the nature of the variable and its relatedness to the observed outcome (whether PU developed or not). Also, some variables were tested based on univariate analyses while others were tested on both univariate and multivariate statistics. This choice depended on many factors, such as level of measurement, level of significance, whether or not they violated multivariate statistics assumptions and others, which will be explained later in this chapter.

 Group one: Variables which describe ward / patient condition

This group includes variables which describe patients’ condition during ICU/ hospital admission, namely age, gender, medical diagnosis, Glasgow coma scale score (GCS), gestational age, development of any adhesive injury, need for MV, and positive end expiratory pressure (PEEP) level. It also includes variables related to the admission ward (type of ward/speciality), and other variables related to patients’ residence in the ward, such as length of stay (LOS), number of follow-up assessments, and the reason for follow-ups being discontinued.

Age was sub-divided into two groups. The first dealt with children aged less than one

year, whose ages were entered into SPSS as ‘age in days’. The second group included children from 1 to 18 years old, who were labelled according to ‘age in years’. This was done to facilitate data entry and analysis where such a wide age range existed, and also in view of the fact that the vast majority of the sample were infants of less than one year of age. Both variables were continuous.

Gender was a dichotomous variable (male/ female). Medical diagnosis was entered

under ‘case classification’, a categorical variable which included six sub-categories (Respiratory, Cardiac and Circulatory, Metabolic, Infectious, Neurological, and Other).

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‘Other’ diagnoses included gastric, morphologic and growth problems. The recorded diagnosis was the primary medical diagnosis of patients when admitted to the ICU (incidence study) or hospital (prevalence study). Gestational Age was entered both as a continuous variable (weeks in uterus prior to delivery), and categorical (Full Term, if GA ≥ 37 weeks or Preterm, if GA < 37 weeks).

Data related to patients being on mechanical ventilators was also gathered. There was one dichotomous variable, describing whether a patient was on an MV at the first assessment (assessment no. = 0) (yes/no). The level of PEEP on MV settings was also observed (in this sample measured by H2O level), as was the duration the patient had

spent on the MV in days (continuous variable). A GCS score was also calculated

based on the paediatric/ infant GCS criteria which were used in the hospital where the data collection was undertaken. This score ranged from a minimum score of 3 (unconscious) up to a maximum of 15 (fully conscious). This continuous variable was important for measuring the motor, verbal and sensory responses of patients.

The final variable related to ‘adhesive injury’. The decision to collect information on this variable was only taken once the data collection process was underway and it was added because it was seen to be a highly prevalent problem, especially in NICU. It is a dichotomous variable which establishes whether or not a child has sustained a skin injury from plaster stripping or the application of adhesive products.

Other variables in this group were connected to the admission ward. In the incidence study, the admission ward was one of 4 ICUs (PICU, GICU, NICU, and GIMU). In the prevalence study, admission wards were grouped into four major categories (medical, surgical, critical units, and newborn). Patients’ length of stay (LOS) in the ICU was recorded as a continuous variable in days. However, LOS in the prevalence study refers to the patient’s entire hospital stay, and not in a particular ward/ unit, up until the day the survey commenced.

The number of observations carried out for each patient during the follow-up period in

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could not be less than two and not more than twelve observations, including the initial observation on admission).

The reason for discontinuing the study was recorded as a categorical variable as follows: the patient was discharged, died, or the follow-up period (8 weeks) was ended.

 Group two: Biological/ laboratory test related variables

This group of variables covers all important factors related to the patient’s physiological condition during the relevant ICU admission. They include biological measures such as the vital signs blood pressure (BP) and temperature, and other key indicators of a patient’s condition such as acidemia, hypoxemia, and body weight. Also noted were the results of certain laboratory tests which have been shown to be associated with PU development in previous literature. Such diagnostic tests are: serum Potassium level (K), Sodium (Na), Urea and Creatinine, glucose level, C reactive protein (CRP), and Bilirubin level. All these were considered based on Pillitteri (2010).

Blood pressure reading (BP) means the non-invasive arterial blood pressure first

reading recorded on the initial assessment (assessment 0) on admission. It is measured in mm Hg and recorded both as systolic and diastolic measures. This variable is continuous.

Body temperature (Temp) refers to the external body temperature taken during the

initial assessment (0) on admission. It is a continuous variable measured in degrees Celsius (C˚).

This variable was intended to be omitted from the multivariate analysis when the regression model combined all risk factors with the Glamorgan sub-items. This was in order to reduce the Multicollinearity effect (discussed later) when Temp was combined with Hyperthermia sub-score on the Glamorgan scale.

Acidemia and Hypoxemia were measured based on the arterial blood gases (ABGs)

readings. This was done by documenting PH, PCO2, PO2, and HCO3 levels. Both of the variables were recorded as dichotomous as the actual values were used to demonstrate simply whether Acidemia/Hypoxemia existed or not (Yes/No). Acidemia

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was considered to exist if (PH < 7.35; PCO2 > 45 mmhg or HCO3 < 22). Hypoxemia was considered to occur if PO2 (< 80 mmhg).

Body weight was recorded as a continuous variable in Kilograms (Kgs). This was

omitted from the multivariate analysis to reduce duplication with the weight sub-item in the Glamorgan RAS, and the weight changes in nutrition sub-item in the Braden Q RAS. For the multivariate analysis, weight was taken into consideration based on the weight centile charts as recommended by the Glamorgan risk scale. It was classed as a categorical variable, recorded as either below 10th centile or 10th centile and above (Appendix 3.4).

All laboratory tests were conducted on blood serum. The results were measured as actual values and entered into the SPSS as continuous variables, except in the case of the CRP value which was a dichotomous (negative/ positive) test. All of these tests were recorded in the initial assessment (0), within 24 hours of admission.

 Group three: Variables which describe PUs.

These variables involve descriptions related to the observed outcome (dependent variable DV), which is PU development (Yes/ No). The descriptors include the number of ulcers developed by each patient in the study and the category and location of the most severe ulcers of each patient. Whether the patient had single or multiple ulcers was also noted.

Categorising PUs was based on the EPUAP and NPUAP classification system, as previously mentioned in the methodology chapter. All these variables were dealt with through descriptive analysis, as they only describe the outcome (PU development) and are not considered predictors of the outcome. Therefore, none were analysed by inferential statistics.

 Group four: Glamorgan RAS sub-items.

This group contains the Glamorgan RAS sub-items. There are nine sub-items (Appendix 1.10), which were dichotomous variables - except for one ordinal variable (mobility) – and were entered in both univariate and multivariate analyses. All,

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however, were dealt with as ordinal variables, since they all originated from a continuous measurement scale (risk scores). A description of each item was provided in the methodology chapter.

 Group five: Braden Q RAS’ sub-items.

This group contains the Braden Q RAS’ sub-items. There are 7 sub-items in total (Appendix 1.11), which were all ordinal variables. They were entered in both univariate and multivariate analyses. A description of each item was included in the methodology chapter.