Blood Pressure & Neonatal Hypotension

Blood pressure is a product of the cardiac output and systemic vascular resistance, therefore hypotension occurs due to a decrease in CO or SVR. The "normal" range of blood pressure in NICU babies is really not known, primarily because it is affected by additional factors (e.g. disease severity, presence of infection, perinatal insults, ductal shunting, etc.). In practice, hypotension is often defined as either:

• a mean BP <30 mmHg

• a mean BP less than the babies gestational age in weeks

• or a BP value accompanied by clinical evidence of circulatory compromise (e.g. decreased urine output, poor peripheral perfusion, decreased urine output, and/or lactic acidosis).

Hypotension can result from many different causes... hypovolemia, cardiac dysfunction, capillary leak, and many others. I find that understanding what the systolic, diastolic, and mean values are indicative of and can help us to evaluate our patient in an effort to identify the problem.

• The systolic blood pressure is a measure of left ventricular (LV) stroke volume. Systolic hypotension can be the result of:

  • Compromised preload (e.g. volume depletion)

  • Compromised contractility (e.g. myocardial dysfunction)

  • Increased afterload (e.g. post PDA closure, cold septic shock)

• The diastolic blood pressure is a measure of systemic vascular resistance. Diastolic hypotension can occur:

  • When there is a problem with SVR

    • Examples include: sepsis, capillary leak, and hemodynamically significant PDA, and arteriovenous malformations

• The mean arterial blood pressure (MAP) is a calculated time weighted average of the systolic and diastolic blood pressure over a cardiac cycle

Evaluating systolic and diastolic pressures individually will provide more information on cardiac output and SVR. Combined systolic and diastolic hypotension indicate failure of the entire cardiovascular system.

More about BP in the Neonatal Blood Pressure Blog

Treatment for Hypotension

The therapy that is selected for management of neonatal hypotension is based on an individual patient assessment. 

The drugs used to support blood pressure primarily act on the alpha and beta adrenergic receptors. I can never remember exactly what they do, so let's review them really quick...

• Alpha 1 and alpha 2 adrenergic receptors cause systemic vasoconstriction

• Beta 1 receptors increase cardiac output by increasing the heart rate (chronotropy), contractility (inotropy), and conduction velocity (dromotropy)

• Beta 2 receptors cause smooth muscle relaxation and vasodilation

• Dopaminergic receptors in the kidney improve diuresis, and myocardial dopaminergic receptors improve contractility without increasing the heart rate

Volume

Ensuring the patient has enough circulating volume is important when addressing hypotension. Administration of crystalloids or colloids can improve preload, (crystalloids are preferred). While historically volume expansion has been a first line treatment for hypotension, it is not without risk (especially in preterm babies). 

If there is a history of blood loss, volume replacement with blood products may be necessary to restore oxygen carrying capacity.

Inotropic & Vasoactive Medications

What’s the difference between an inotrope and a vasopressor??

Inotropes are medications that primarily act on the cardiac myocyte to increase contractility. Improving contractility improves perfusion by increasing the cardiac output. Examples of inotropes include dobutamine and epinephrine. Some inotropes also have vasodilator effects (e.g. low dose epi) and are used to decrease vessel wall tension, improving stroke volume and cardiac output. 

Vasopressors induce vasoconstriction which increases SVR (thus increasing MAP). Examples of vasopresssors include epinephrine, norepinephrine, dopamine, and vasopressin.

Some drugs we give have both inotropic and vasodilatory effects. Let's review a few of these medications together...

Dopamine: is the most commonly prescribed medication for the treatment of neonatal hypotension and shock. The mechanism of action is dose dependent.

• Low doses (2-5mcg/kg/min) activate the dopaminergic receptors resulting in an increase in renal perfusion.

• Moderate dose dopamine activates beta-1 adrenergic receptors resulting in increased cardiac contractility and heart rate.

• High dose dopamine activates alpha-1 adrenergic receptors resulting in increased peripheral vasoconstriction.

Dobutamine: is a synthetic catecholamine that promotes direct stimulation of adrenergic receptors in the myocardium. Similar to Dopamine, the effect of dobutamine is dose dependent.

• Lower doses (<5mcg/kg/min) activate beta-1 and beta-2 receptors resulting in increased stroke volume, contractility, and cardiac output with decreased SVR.

• Improved LV performance in preterm infants is seen at doses of 5-10mcg/kg/min.

• Higher doses (5-15mcg/kg/min) primarily act on alpha-1 receptors, increasing SVR. 

Epinephrine: is an endogenous hormone secreted by the adrenal medulla. Epi is a potent stimulator of both alpha and beta adrenergic receptors and the effects it has are also dose dependent.

• Low doses (0.01-0.1mcg/kg/min) stimulate the cardiac and vascular beta-1 and beta-2 receptors leading to increased contractility, HR, conduction velocity, and peripheral vasodilation.

• Higher doses (>0.1mcg/kg/min) stimulate vascular and cardiac alpha-1-receptors leading to vasoconstriction and increased contractility. Epinephrine has been shown to increase coronary artery blood flow, cerebral perfusion, SVR to PVR in a 1:1 ratio or less.

Norepinephrine: is an endogenous hormone with diverse functions as a hormone and neurotransmitter. Norepinephrine produces systemic vasoconstriction by stimulating both alpha-1 and alpha-2 receptors. It’s impact on alpha-2 receptors may be responsible for the preferential systemic vasoconstriction (over pulmonary) making it useful for patients with PPHN. 

Milrinone: is a selective type III phosphodiesterase inhibitor that enhances LV filling, preload, contractility, and cardiac output. Milrinone assists with systemic and pulmonary vasodilation. 

Vasopressin: is an endogenous neuropeptide from the posterior pituitary gland that controls fluid homeostasis and osmolarity. Vasopressin activates the V1a and V2 receptors leading to increases in SVR as well as vasodilation of the kidneys to increase water reabsorption.

Hydrocortisone: Corticosteroids are often prescribed as an adjunct for neonates with hypotension and shock. Hydrocortisone increases adrenergic receptor expression causing vasoconstriction and increase cardiac output. By up-regulating these receptors, there is improved responsiveness to endogenous and exogenous catecholamines. In addition, hydrocortisone inhibits the production of endogenous nitric oxide and prostaglandins. Hydrocortisone also increases the conversion of norepinephrine to epinephrine and inhibits catecholamine metabolism. 

Nursing Considerations

Caring for critically ill newborns receiving continuous infusions of inotropic or vasoactive drugs for blood pressure support requires meticulous monitoring and nursing expertise.

Key nursing responsibilities include:

• Promote comfort and pain management: Ensure the infant's comfort while minimizing stress and pain.

• Respiratory support: Monitor for signs of respiratory distress and optimize oxygenation and ventilation.

• Circulatory assessment: Closely monitor blood pressure, pulses, and overall perfusion.

• Urine output: Evaluate kidney perfusion and fluid balance.

• Skin integrity: Reposition the infant regularly and assess the skin to prevent pressure injuries.

• Family support: Provide ongoing education, reassurance, and emotional support to families during this critical time.

In addition nurses must:

• Closely Monitor IV sites: Central lines are preferred for infusing inotropic and vasoactive drugs. If a peripheral IV must be used, the nurse must closely monitor for infiltration or extravasation. These complications can cause significant tissue damage or burns. In the event of infiltration, phentolamine—an alpha-adrenergic blocking agent—should be administered as an antidote. This medication promotes vasodilation, reversing ischemia caused by vasopressor infiltration.

• Check medication compatibility: Ensure that vasoactive drugs are compatible with other medications being administered to prevent drug interactions or precipitation.

• Follow titration protocols: Gradually adjust drug dosages as the infant stabilizes to avoid abrupt changes that could lead to hemodynamic instability.

Ongoing assessment and monitoring are essential:

• Laboratory monitoring: Regularly evaluate electrolyte levels, as medications may cause shifts in potassium, sodium, or calcium. Monitor lactate levels to detect signs of impaired tissue perfusion.

• Prevent infection: Use strict aseptic technique when accessing lines or changing dressings to reduce the risk of nosocomial infection.

Collaboration is key:

• Interdisciplinary communication: Work closely with neonatologists, neonatal nurse practitioners, respiratory therapists, physical and occupational therapists, pharmacists, and social workers to provide comprehensive care.

• Family-centered rounding: Include families in care discussions to enhance understanding and participation.

Finally, consider the infant's overall well-being:

• Developmental care: Minimize environmental stress by reducing noise and light exposure. Cluster care to allow for periods of uninterrupted rest. Involve the family as much as possible, use developmental aides to provide comfort and promote neurodevelopment.

These considerations ensure a safe and holistic approach to caring for newborns requiring inotropic or vasoactive drug support. By staying vigilant and proactive, nurses can optimize outcomes for these critically ill infants while supporting their families through challenging times.

I hope this was a helpful review on hypotension and vasopressors for you. What do you want to learn about next? Email me with your suggestions, I always love hearing from you!

Happy Holidays!
Amanda

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Reference:

Kalish B. T. (2017). Management of Neonatal Hypotension. Neonatal network : NN, 36(1), 40–47. https://doi.org/10.1891/0730-0832.36.1.40

Noori, S. & Seri, I. (2024). Cardiovascular Compromise in the Newborn Infant in Avery’s Diseases of the Newborn. Elsevier

Rios, D., Vasquez, A., & McPherson, C. (2024). Neonatal Cardiovascular Drugs in Neonatology Questions and Controversies: Neonatal Hemodynamics. Elsevier

Barnes, J., Jnah, A., Dias, P. (2024) Hypotension and Shock in Fetal and Neonatal Pharmacology for the Advanced Practice Nurse. Springer Publishing Company