Study design: This was a hospital-based, observational, descriptive, cross-sectional study.
Study location: The study was carried out in the Department of Paediatrics, Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC), Ile-Ife and the Bethesda Heart Centre located in Bodija in Ibadan North Local Government area, Ibadan, Nigeria. The OAUTHC, Ile-Ife, is a tertiary health center that serves the township which has a population of 355,341 at the 2006 population census.107 It also serves as a referral centre not only for Osun state but also for neighbouring states of Ondo and Ekiti. However, at the time of this study there was no functioning Echocardiography machine at OAUTHC, Ile-Ife, hence, an alternative was sought at the Bethesda Heart Center (BHC) in Bodija, Ibadan. The BHC is a hospital dedicated to the management of both congenital and acquired heart diseases in children. It is owned by a nongovernmental organization called Save-a-Child’s Heart Foundation, Nigeria and receives patients from all over the country. It has staff strength of ten including two doctors and three registered nurses.
Study period: The study was carried out between February 2011 and July 2011.
Subjects and Controls Subjects
The subjects were recruited from the Paediatric Sickle Cell Out Patient Clinic of the OAUTHC, Ile-Ife. This clinic is run on a weekly basis by a Consultant Paediatric Haematologist assisted by two to three resident doctors and staff nurses. The study subjects comprised children, aged one to fifteen years with sickle cell anaemia in steady state. This age group was chosen
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because the children seen in the Paediatric Sickle cell Out Patient Clinic of our hospital are aged fifteen years and below. Children above this age are referred to the adult haematology clinic.
Steady state means they were free of infection, pain, or other disease processes.2
Sample size determination: The following formula for comparing two means was used to determine the sample size.108
n= (u+v)2 (σ12 + σ02 ) ( μ1 –μ0 )2
Where n = The desired sample size u = 1.28, for power of 90%
v = 1.96 at a level of significance of 5%
σ = Standard deviation of the mean
μ1 –μ0 = The difference of the means of two population Using values obtained from a previous study,17
µ1 = 108.7 (Mean of the left ventricular mass in the SCA patients)
µ0 = 76.0 (Mean of the left ventricular mass (LVM) in the controls σ1 = 44.0 (Standard deviation of the LVM among the SCA subjects)
σ0= 31.6 (Standard deviation of the LVM among the Hb AA subjects) n = (1.28+1.96)2 ((44.0)2+(31.6)2) = 29
(108.7- 76.0)2
The minimum sample size is 29. However, 50 subjects with sickle cell anaemia and 50 healthy Hb AA controls were studied.
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Subject inclusion criteria: Children aged one to fifteen years with sickle cell anaemia confirmed by haemoglobin electrophoresis and who were in steady state were studied after informed consent to participate in the study was obtained. The lower limit of one year was chosen in order to ensure cooperation of the subjects during echocardiography. The upper age limit was set at 15 years because children older than 15 years of age are referred to the adult haematology clinic where they are attended to.
Subject exclusion criteria included the following:
1. Children in any form of sickle cell crises.
2. Children with congenital or acquired heart diseases.
3. Children with evidence of acute infections.
4. Children with chronic renal failure or hypertension.
5. Children who had received blood transfusion within three months prior to the time of the study.
6. Refusal of consent by parent(s) or caregiver.
Controls
The controls were age- and sex-matched children with haemoglobin genotype AA, who were recruited from the general Paediatric Out Patient Department (POPD) of the hospital. These children were on follow-up after recovering from minor illnesses unrelated to the cardiovascular, respiratory and renal systems. Haemoglobin electrophoresis was carried out on each recruited control in the Haemotology Department of the same hospital using the cellulose acetate strips at pH of 8.6.
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The total number of controls recruited into the study was set similarly to that of the subjects on a ratio of 1: 1. Hence, 50 age- and sex-matched children were recruited as controls.
Control inclusion criteria:
1. Age one to 15 years 2. Haemaoglobin type AA.
3. Venous haematocrit of at least 30 percent – this was done to ensure that the children did not have anaemia from other causes.
4. Absence of intercurrent illness.
Control exclusion criteria:
1. History or evidence of protein energy malnutrition.
2. History or evidence of congenital heart disease.
3. History or evidence of acquired heart disease.
Ethical clearance
Ethical clearance was sought and obtained from the Ethics and Research Committee of the OAUTHC, Ile-Ife (Appendix I) prior to commencement of the study.
Study methods and Instrumentation
The subjects and the controls were recruited at the OAUTHC, Ile-Ife with informed written consent from the parents/ caregivers (Appendix II). The details of their history including demographic and socio-economic data was obtained from the parent/ guardian and the patient (where appropriate) and entered into a study-specific proforma (Appendix III).
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Each child was thoroughly examined. The temperature (oC), weight (kg), height (cm) and blood pressure (mmHg) of each child were recorded in the proforma. Temperature was measured using a mercury-in-glass thermometer. The bulb of the thermometer was placed at the apex of the axilla, half way between the anterior and posterior margins of the axilla and read after four minutes.109
For the measurement of the height a fixed stadiometer, Spirit Height® was used. Each child was asked to stand erect with the back against the wall with the fixed stadiometer in place.
During the measurement the child was barefoot, with the scapulae and buttocks in contact with the wall, the legs were placed together bringing the ankles or the knees together. The child was instructed to stand erect and look straight ahead with head placed in Frankfort plane.110 In this position, an imaginary line can be drawn from the bottom of the eye socket (orbital margin) to the external opening of the ear (external auditory canal).
The moveable headpiece was brought onto the upper most (superior) point on the head with sufficient pressure to compress the hair.110 The height was measured to the nearest one decimal place. The values obtained were recorded in the study proforma.
Each child was weighed wearing only light underwear using a SECA® scale. Weight was read to the nearest 0.5 kg. Before each reading the scale was checked for zero error. Weight was measured with the child’s arms hanging freely by the sides of the body, with palms facing the thighs, the head held up and facing forward.110 The scale was calibrated with a standard weight at periodic intervals or whenever it was moved from place to place. These values were also recorded on the study proforma for each child.
From these measurements, the body surface area (BSA) was derived using the Mosteller formula: 111
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Pulse was taken from the right radial artery and counted over 60 seconds and recorded in the study proforma. Blood pressure was measured for each subject using the Accuson® mercurial sphygmomanometer. Measurements were taken with the child seated and well rested. The right arm was supported on a horizontal surface at the level of the heart. The appropriate cuff was selected for each child. Two readings were taken at one minute interval deflating the cuff completely between readings. The average of the two readings was taken as the patient’s blood pressure. The systolic blood pressure corresponded to the first Korotkoff sound (K1) while the diastolic blood pressure corresponded to the fourth Korotkoff sound (K4).84
Thereafter, a venous haematocrit check was carried out on each subject by the investigator using aseptic technique. The procedure was explained to each of the participants and they were assured that utmost care would be taken in ensuring that the procedure was as gentle as possible. The investigator wore a pair of gloves and applied a tourniquet to the forearm of each child. A suitable vein was identified. The skin surface was wiped repeatedly with a piece of wet spirit swab until the investigator was sure that the skin surface was clean. A sterile hypodermic needle was carefully introduced into the chosen vein and blood gently drawn. The samples were collected into heparinized capillary tubes; two capillary tubes per child. The tourniquet was released, the hypodermic needle was gently withdrawn and a clean dry piece of cotton wool was applied to the site. The investigator applied firm pressure to the site until haemostasis was secured. The capillary tubes were then placed in the groves of the bench centrifuge in the Paediatric Ward side laboratory, one on opposite sides. The samples were spun for a period of five minutes at 10,000 revolutions per second.112 When the centrifuge came to a
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halt the capillary tubes were taken out of the bench centrifuge and read using a microhaematocrit reader and values were recorded on the study proforma.