Blood pressure measurement in special circumstances
The only technique that is practical for widespread clinical application is conventional sphygmomanometry using a well maintained mercury sphygmomanometer. Systolic blood pressure measurements are preferred to those of diastolic blood pressure because of their greater accuracy and consistency.
Use of the correct cuff is crucial. To cover the age range 0-14 years a minimum of three cuffs is necessary, with bladder dimensions 4 x 13 cm, 10 x 18 cm and 12 x 26 cm (adult size). The widest cuff that can be applied to the arm should be used. The length of the bladder should be such as to encircle 80% of the arm circumference. Secure fastening is essential and may not be possible with the Velcro fastenings supplied especially when using the small cuffs.
In some healthy children aged under 5 years and all children under 1 year, measurement of blood pressure by conventional sphygmomanometry is impossible because the Korotkoff sounds cannot be heard reliably. In these and children who are shocked or have a low cardiac output, more sensitive detection systems, such as Doppler ultrasound or oscillometry, should be used.
Circumstances of measurement
Except in acutely ill children, blood pressure should be measured after the child has been sitting quietly (or lying if aged under 2 years) for at least 3 min. Measurements made when the child is eating, sucking or crying will be unrepresentative and usually too high. Management decisions should be taken only on the basis of specialist advice. In older children the indications for ambulatory blood pressure measurement are the same as for adults.
In obese subjects the arm circumference is increased. Use of the "standard" cuff may lead to blood pressure being erroneously elevated - so called "cuff hypertension". All physicians should have a large cuff (bladder dimensions 12 x 40 cm) available, as obesity is quite commonly associated with raised blood pressure. Failure to take arm circumference into account when measuring blood pressure may have serious implications for the management of patients.
The major source of difficulty in blood pressure measurement in arrhythmias is the large variation in blood pressure from beat to beat that occurs in the presence of an irregular cardiac rhythm. In arrhythmias such as atrial fibrillation stroke volume and, as a consequence, blood pressure vary depending on the preceding pulse interval. Blood pressure measurement in atrial fibrillation, particularly when the ventricular rhythm is highly irregular, will at best constitute a rough estimate, the validity of which can perhaps be improved upon only by using repeated measurements.
Between 2% and 5% of pregnancies in Western Europe are complicated by clinically relevant hypertension. In a significant number of these raised blood pressure is a key factor in medical decision-making in the pregnancy. Particular attention must be paid to blood pressure measurement in pregnancy because of the important implications for patient management as well as the fact that it presents some special problems.
Recent studies have resolved the controversy as to whether the muffling or disappearance of sounds should be taken for diastolic blood pressure. Disappearance of sounds (fifth phase) is now recommended for the measurement of diastolic pressure.
The combination of hypertension and ageing is manifest as a decrease in arterial compliance. There is also deterioration in baroreceptor and autonomic function. The consequences are a variety of blood pressure manifestations in elderly hypertensives. These include the following:
© BHS 1999