Hypotension

Hypotension and hemodynamic instability in the early postnatal period are common diagnoses within preterm population and has been associated with adverse short-term and long-term outcomes. There are a number of compensatory responses that occur to maintain perfusion and oxygen delivery to the most vital organs, which include peripheral vasoconstriction to maintain blood pressure (BP).

Stable preterm infants with lower BP often have no biochemical or clinical signs of shock, and have normal systemic blood flow and sufficient tissue oxygen delivery (‘permissive hypotension’). These infants probably do not require therapy despite BP lower then their respective gestational age (in weeks).

Brief overview of hemodynamic control

Etiology of Hypotension (first 72 hours)

• Multifactorial
• Myocardial dysfunction
• Persistent ductus arteriosus (PDA)
• Respiratory distress syndrome (RDS)
• Sepsis
• Abnormal vasoregulation
• Hypovolemia
• Relative adrenal insufficiency

Diagnosis

Clinical Signs

• Mean arterial BP (MABP, mmHg)
  → maintain > gestational age (in weeks)
  → poor relationship to morbidities
• End-organ blood flow
  → absolute BP values
  → cardiac output
  → peripheral vascular resistance
• Tachycardia
• Oliguria
• Weak peripheral pulses
• Low systolic-diastolic difference
• Impaired consciousness

Laboratory Findings

• Blood gas (lactic metabolic acidosis)

Imaging

• Echocardiography (see below)
• Intra-arterial BP monitoring
• NIRS (near infrared spectroscopy)
• Chest X-ray

Echocardiography

ECHO signs of hemodynamically significant PDA (HS-PDA)

PDA diameter (as measured in the narrowest part)

• small PDA < 1.5 mm
• medium PDA 1.5 – 3.0 mm
• large PDA > 3.0 mm

PDA flow pattern

• restrictive (end-diastolic velocity > 2 m/s)
• non-restrictive (end-diastolic velocity < 2 m/s)

Pulmonary artery flow turbulence

• indirect sign of HS-PDA

Left atrium dilatation

• Left atrium to Aorta (LA/Ao) ratio > 1.5
• LA/Ao measured by M-mode at LA and Aortic valve

Organ perfusion alterations

• a. mesenterica superior, a. renalis, ao. abdominalis
• decreased, absent or retrograde diastolic blood flow (“steal phenomenon”)

Diastolic flow in the left pulmonary artery (LPA)

• small PDA < 0.3 m/s
• medium PDA < 0.5 m/s
• large PDA > 0.5 m/s

PDA to LPA

• PDA/LPA diameter ratio > 1 signifies HS-PDA

Therapy

General

• Ventilation
• Fluid boluses (10 – 20 ml/kg)

Pharmacology

DOPAMINE

• Usual dose: 2 – 20 μg/kg/min

DOBUTAMINE

• Usual dose: 4 – 40 μg/kg/min

NORADRENALINE

• Usual dose: 0.1 – 1 μg/kg/min

ADRENALINE

• Resuscitation: 10 – 30 μg/kg/dose

References

① Dionne JM, Flynn JT. Management of severe hypertension in the newborn. Arch Dis Child. 2017;102(12):1176-1179. doi:10.1136/archdischild-2015-309740

② Dempsey EM, Barrington KJ, Marlow N, et al. Management of hypotension in preterm infants (The HIP Trial): a randomised controlled trial of hypotension management in extremely low gestational age newborns. Neonatology. 2014;105(4):275-281. doi:10.1159/000357553