When should we measure blood pressure?

There is no evidence that screening normal children for hypertension is rewarding; essential hypertension does not ‘track’ reliably through childhood, and severe secondary hypertension is too infrequent to justify screening. However, all children with symptoms or signs that could be associated with hypertension or with conditions or on drugs that could cause hypertension should have their blood pressure measured.

These include:

In practice we suggest that all children attending a paediatric department whether as an outpatient, day case or in-patient should have their blood pressure measured at least once.

How should we measure blood pressure?

The best non-invasive way to measure blood pressure is to have a relaxed child and use a sphygmomanometer and have a well applied large cuff and accurate detection of systolic flow.

Cuff The bladder should be the largest that can be applied to the limb. A cuff that is too small may overestimate blood pressure, but the evidence is that an extra large cuff will not underestimate blood pressure. We believe that the standard teaching of a cuff two-thirds the length of the upper arm is simply wrong.

A common error is to use a smallish bladder in a wide cloth cuff - do not be fooled; the bladder size is all that matters.

The bladder must be closely applied to the limb, especially in smaller cuffs. Loosely applied cuffs become round in cross-section when inflated so only a small area is in contact with the arm, giving a falsely high blood pressure reading.
Measurement Although a stethoscope is fine for detecting systolic flow in the arms of older children it has limited value in an active small child, and cannot be used for leg measurements.

The doppler vascular flow detector is the most sensitive instrument and the easiest to use. It can be used in the arm or the leg and will detect even the smallest of blood flows. Our standard technique now is to use a very large upper arm cuff (which may cover the antecubital fossa) and to detect the flow at the radial pulse.

You may hear the doppler referred to as "Thomas"; this is a wonderful technique for anxious two to five year olds. Simply find the sound of Thomas the Tank Engine at their wrist and then pump the cuff up to stop him in the station, and deflate it to make him go again!

Although palpation is often unreliable (under-reading), in some children with very full pulses it can be useful.

The flush method is very crude and always underestimates blood pressure.

Automatic blood pressure machines are very convenient and if properly used and maintained may be very useful for quickly screening older children who attend outpatients or are admitted. They should not be relied on to detect hypotension and if an abnormally high reading is obtained it should be checked using a sphygmomanometer or doppler/stethoscope. Many studies and our own experience have shown that they can be very unreliable in some cases, especially in small infants with very low blood presumes when they tend to over read. Before relying on automatic blood pressure rnachine measurements for repeated measurements in any particular child we therefore calibrate the machine for that child using doppler, and repeat the calibration if the blood pressure appears to change markedly.

The leg can be used to measure blood pressure if the patient is lying down; apply a large cuff to the calf and use a doppler over the dorsalis pedis or posterior tibial artery. A common cause of false hypertension is to continue to use the leg with the patient sat up (when the reading is the blood pressure plus the distance below the heart).

What is normal blood pressure?

There is a massive amount of evidence that systolic blood pressure is the best indicator of hypertension in children (there is good evidence that it is as good or better than diastolic blood pressure in adults, but old habits die hard!). This is partly because it is much more reliable to measure. On Ward 8 North at the RVI we only chart systolic blood pressure readings; this emphasises our belief that they are the only values reliable enough to base management on.

Blood pressure increases with age (Note: preterm babies have much lower normal values; these are not included here). Centiles are available separately for boys and girls, systolic and diastolic values.

To simplify management we suggest the following guidelines of systolic blood pressure are used:

  1 month 1 year 5 years 10 years 15 years
Mean systolic BR 60 80 90 105 115
Upper limit of normal 80 100 110 120 130
*needs urgent treatment* 110 130 140 150 160

What is the management of hypertension?

The first line management of severe hypertension is almost always with hypotensive drug treatment. However, the specific treatment needed depends on

Any child with severe hypertension should be discussed urgently with a specialist centre; most need to be transferred.

Cause Most significant hypertension in childhood is due to renal causes; only occasionally drug treatment (eg steroids) or excess catechol drive is responsible.

In renal patients, most hypertension is probably renin-driven, eg in renal artery stenosis, glomerulonephritis, reflux nephropathy, polycystic kidney disease, etc, and is treated with hypotensive drugs. However, some cases are due completely or in part to salt and water overload, eg glomerulonephritis, acute and chronic renal failure. In these cases management must also be directed at correcting salt and water balance, which may include a low salt intake, furosemide, dialysis, haemofiltration etc.

Note* Beware of hypovolaemia as a cause of hypertension, especially seen in severely nephrotic children. These patients have poor peripheral circulation (ice cold hands and feet) and usually have abdominal pain; their paradoxical hypertension is due to their gross life-saving hyper-reninaemic response. Treatment is with lg/kg albumin iv over two hours, followed by furosemide.
Duration If a child who was known to have been normotensive recently presents with acute hypertension, it is safe to control his blood pressure quickly. An example would be a transplant recipient becoming suddenly hypertensive due to a rejection episode. The treatment should be discussed with the consultant, but could include sub-lingual nifedipine or intravenous diazoxide, hydralazine, labetalol or nitroprusside. Immediate treatment is urgent: severe acute hypertension is a medical emergency.

In many cases the duration of hypertension can only be guessed at; eg a child presenting with a UTI found to be severely hypertensive. In these circumstances blood pressure control should be achieved slowly. Chronic hypertension leads to a protective cerebral vasospasm; a rapid fall in blood pressure can result in acute underperfusion of the brain, presenting clinically as fitting, encephalopathy and sudden blindness. The vasospasm will reverse in about 48 hours; hence aim to lower blood pressure over two to three days. If the hypertension itself is causing blindness, cerebral oedema, encephalopathy, etc then it may be appropriate to control it more quickly. Two or three days can sometimes feel like a lifetime!
Severity Mild hypertension can be managed by the gentle introduction of oral hypotensive agents. Severe acute hypertension needs to be managed promptly by sublingual or intravenous bolus treatment.

Severe hypertension of long or unknown duration must be managed by controlled intravenous infusion under very strict supervision. Ideally the hypertension should be corrected by about one-third for 24 hours, by two-thirds for 24 hours, and completely by day three. Labetalol, a combined alpha and beta blocker, is currently the drug of choice.