Definition

Hypertension is not commonly diagnosed in newborn infants. The incidence in infants discharged from neonatal units ranges from 0.7% to 2.0%

Hypertension is defined by a systolic blood pressure in a neonate which is ≥95^th percentile for age and sex on 3 separate occasions.

The gold standard for blood pressure measurement is an appropriately calibrated intra-arterial catheter.  However, for babies who do not have or require invasive monitoring, the most frequently used technique is via an oscillometric manometer (e.g Dinamap).  Blood pressure should be taken when babies are quiet and not feeding (systolic BP is 5mmHg lower in sleeping babies) with an appropriate sized cuff.

Hypertension detected on oscillometry (Dinamap) must be confirmed with another modality such as Doppler sphygmomanometry

Normal Data ¹

Causes

1. Renal
   • Renal artery thrombosis (particularly if a UAC has been in place)
   • Renal vein thrombosis
   • Renal artery stenosis or compression (e.g. from tumour)
   • Parenchymal renal disease
   • Severely obstructed urinary tract
2. Cardiovascular
   • Coarctation of the aorta
   • Interrupted aortic arch
   • Distal aortic thrombosis (particularly if a UAC has been in place)
   • Fluid overload
3. Endocrine
   • Congenital Adrenal Hyperplasia
   • Hyperaldosteronism
   • Hyperthyroidism
   • Adrenal haemorrhage
   • Hypercalcaemia
4. Neonatal Chronic Lung Disease
   • May manifest late after discharge from NICU
5. Drugs
   • Dexamethasone
   • Adrenergic agents
   • Caffeine
6. Neurological
   • Pain
   • Seizures
   • Intracranial hypertension
   • Drug Withdrawal

Investigations

First Line Investigations:

1. Repeat your clinical examination:
   • Are there any abdominal masses?  Can you feel the kidneys?
   • Feel the pulses!  Are the femoral pulses the same as the brachial pulses?
   • Are the fontanelle and sutures normal?
2. 4-limb blood pressures
   • Note:  Dinamap BP can be normal in the lower limbs in a baby with coarctation in. 
   • Do not rely on four limb Dinamap BP measurement to exclude coarctation - use fingers or ideally Doppler sphygmomanometry
3. Electrolytes, urea, and creatinine
4. Urinalysis
5. Renal ultrasound scan
6. Chest radiograph (if cardiac murmur or signs of congestive cardiac failure)

Second Line Investigations (when history suggests):

1. Echocardiogram to exclude coarctation or interrupted aortic arch.
   • Also useful to assess cardiovascular function and complications in long-standing or severe hypertension.
2. Plasma renin activity
   • Renin levels are higher in newborn infants than in older children and adults and an elevated PRA may not indicate underlying renal disease
3. Plasma cortisol, aldosterone, or thyroxine (as indicated)
4. Cranial ultrasound or MRI if any suspicion of an intracranial cause
5. Renal radionucleotide study

Treatment

1. Treatment will depend on the underlying cause and should be commenced only after discussion with either a paediatric nephrologist or a paediatric cardiologist (depending on underlying cause).
   • In general, Labetalol is the first-line treatment of hypertension severe enough to require treatment (once coarctation is excluded).
   • Second line agents include calcium channel blockers (however, not Nifedipine) or Hydrallazine.

References