Blood pressure - hypotension in neonates
Blood pressure (BP) increases over the first hours, then days after birth. Very low birth weight babies often have a low blood pressure, especially on the first day.
Normal blood pressure
Blood pressure (BP) increases over the first hours, then days after birth. Very low birth weight babies often have a low blood pressure, especially on the first day. Infants with low Apgar scores or requiring assisted ventilation tend to have lower BPs, while those whose mothers were hypertensive or who received antenatal steroids have higher BPs. There are poor relationships between blood pressure and either cardiac output or blood volume in preterm infants¹,². Systemic vascular resistance is of great importance.
In very low birth weight infants, patent ductus arteriosus may contribute to low blood pressure, even in the first few days, and its closure may result in an increase in BP³,⁴,⁵
Importance of low blood pressure
Cardiac output and end organ perfusion cannot be directly measured as yet in neonatal patients. Blood pressure is widely accepted as one of a set of parameters used in assessing cardiovascular stability. Reduced SVC flow (as a measure of cerebral blood flow) is associated with a significant increase in mortality, NEC and neurodevelopmental impairment (small study) in infants of <30 weeks⁶,⁷,⁸
There is controversy as to how active to be in treating a low blood pressure in a small sick baby. There are several publications linking low BP with poor outcome. There may be reporting bias in these publications. It is possible that the duration of low blood pressure (perfusion) is more relevant than the actual point measurement. No-one hasyetshown that treating low blood pressure improves outcome.
Some have found a correlation between periods of hypotension and IVH⁹,¹⁰. Miall-Allen also showed an association between MBP <30 and IVH, ischaemic lesions or death¹¹. Low found a relationship between low BP and hypoxaemia and a poor neuro-developmental outcome¹². The association between a low BP and IVH was not supported by D'Souza¹³.
Blood pressure to aim for
Miall-Allen¹¹used a mean BP of 30mm as her cut off irrespective of size or gestational age. Watkins⁹used his 10th centiles, which were:
For very low birth weight infants, a good rule of thumb is to aim for the baby's gestational age as the desired minimum mean blood pressure.
Fluctuation in blood pressure
Blood pressure fluctuation may be as important as its absolute value in the development of cerebral lesions and the long term outcome of infants. Blood pressure variability should be minimised as much as possible in the first days of life in very preterm infants. This involves strategies of minimal handling, careful and gradual management changes and avoiding interventions that can cause changes in catecholamine levels and blood pressure.
Blood pressure in Persistent Pulmonary Hypertension (PPH)
PPHN is associated with poor cardiac function. The ductus arteriosus is often patent so that, with supra-systemic pulmonary artery pressure there is R-L ductal shunting. If systemic pressure can be increased without a corresponding increase in pulmonary pressure, the shunt will lessen and oxygenation improve. There is not much information on the effect of inotropes on pulmonary vascular resistance in sick newborn infants. What there is suggests that dopamine does not produce a selective increase in systemic pressure.¹⁴
However:
Attempt to keep systemic blood pressure high.
Treat initially with volume (judicious) and then with inotropic support.
See the PPHN guidelines.
Assessment of end organ perfusion
Review mean, systolic and diastolic blood pressure (see 'blood pressure to aim for').
Is the baby clinically stable or unstable?
Are other observations normal?
Is there any acidosis? (What is the lactate?)
Is skin perfusion normal?
Is the urinary output normal?
Consider the need for Echocardiography
Treatment of low blood pressure
Consider the underlying cause:
| Normal Saline | Give one to two boluses of 10-15ml/kg over 20 minutes. Equal response to 5% albumin infusion but fewer repeat doses of volume were needed and a lower weight gain was seen over 48 hours, with no difference in serum [Na+] in the one trial15. Saline similar to albumin/FFP in effect16. Volume (albumin in the published paper) is less consistent at increasing BP than dopamine and starting dopamine should not be delayed if hypotension persists17. |
| Dopamine | Start at 5mcg/kg/min and increase incrementally to a maximum of 20mcg/kg/min. Increases BP. More consistent response, at a lower dose with a bigger increase in BP than dobutamine18,19,20. |
| Dobutamine | Start at 5mcg/kg/min and increase incrementally to a maximum of 20mcg/kg/min. Dobutamine is added to dopamine in persistently hypotensive infants, when the dopamine dose has been increased to 10-20mcg/kg/min. Some evidence that improves systemic blood flow better than dopamine20. |
| 4% Albumin | This is an alternative to Normal saline. There is limited data on the relative merits of each in the treatment of neonatal hypotension. A small study showed a trend towards increased mortality in those treated with albumin consistent with the findings in larger adult studies21. |
| Blood | Use 'whole' blood as volume support if the baby is also relatively anaemic. If volume expansion is desired, do not give furosemide with the blood. |
| Hydrocortisone | 2.5mg/kg IV 4hrly x 2 then 6hrly x 48 hrs then 1.25mg/kg 6hrly x 48 hrs, then 0.625 mg/kg 6hrly x 48 hrs. Not for routine use. Consider in preterm infants with refractory hypotension who may have relative adrenocortical insufficiency 22. Increases BP a little less consistently but to a greater extent than with dopamine23. |
| Dexamethasone | 0.1-0.25mg/kg/dose. Studies of dexamethasone for ventilator dependence shows a fairly rapid increase in BP and ability to wean off inotropes24,25. |
| Adrenaline | 100-300 nanograms/kg/minute, incrementally, higher doses occasionally required. May be considered as additional therapy in refractory hypotension such as septic shock or asphyxial cardiac compromise. As effective as dopamine as single therapy at low doses but with increased side effects26. Use with caution and only after a decision by a specialist. |
| Noradrenaline | 0.05-0.5mcg/kg/min, incrementally. Primarily raises systemic vascular resistance. It may produce a reflex reduction in cardiac output and can produce coronary artery changes. Very little (if anything) published on its use in the newborn. Use with caution and only after a decision by a specialist27. |