What is the definition and treatment of hypotension in infants?

Definition and Treatment of Hypotension in Infants

For infants under 12 years of age, hypotension is best defined as systolic blood pressure below the fifth percentile for age, with the Pediatric Advanced Life Support (PALS) definition providing the most accurate reference values. 1

Definition of Hypotension in Infants

Age-Based Definitions

The definition of hypotension in infants varies across different guidelines, with significant variability in clinical cut-offs:

• Preterm Infants: A commonly used clinical definition is mean arterial pressure (MAP) less than the infant's gestational age in weeks 2

  • For extremely low birth weight infants (≤600g), MAP values at 10th percentile are approximately:
    • 1 hour of life: 22 mmHg
    • 3 hours: 24 mmHg
    • 6 hours: 25 mmHg
    • 24 hours: 28 mmHg 3

• Term Infants and Older Children: The fifth percentile of systolic blood pressure for age is the most evidence-based definition 1

  • PALS definition shows the best agreement with population-based values for children under 12 years
  • For children over 12 years, Parshuram's early warning score provides better reference values 1

Key Considerations in Defining Hypotension

• Population-based centiles show limited studies in infants under 1 year of age 1
• Current clinical guidelines show variable agreement with population-based blood pressure centiles 1
• Clinical cut-offs that exceed the fifth centile may incorrectly classify too many infants as hypotensive 1
• Reference values from healthy children may not be accurate for acutely ill infants due to factors like pain and distress 1

Treatment of Hypotension in Infants

Initial Assessment

• Evaluate for signs of adequate perfusion despite low blood pressure:
  • Urine output >1 mL/kg/h
  • Normal mental status
  • Normal oxygen saturation (>95%)
  • Normal glucose and ionized calcium concentrations 1

Fluid Resuscitation (First Line)

• Crystalloid is the fluid of choice in neonates with hemoglobin >12 g/dL 1
• Packed red blood cells should be transfused in newborns with hemoglobin <12 g/dL 1
• Fluid replacement should be directed at clinical endpoints including perfusion and central venous pressure 1
• Ongoing fluid replacement may be needed for days due to capillary leak 1

Pharmacologic Interventions

For persistent hypotension despite adequate fluid resuscitation:

1. Vasopressors/Inotropes:

   • Epinephrine (0.05–0.3 μg/kg/min) is effective in newborns with poor left ventricle function 1
   • Norepinephrine can be used for refractory hypotension (maintain ScvO2 >70%) 1
   • In very low birth weight babies, pentoxifylline (5-day course) may be considered 1

2. Hormonal Therapy:

   • Hydrocortisone for suspected adrenal insufficiency (peak cortisol after ACTH <18 μg/dL) 1
   • Triiodothyronine for newborns with thyroid insufficiency 1

3. Rescue Therapies (with adequate cardiac output monitoring):

   • Vasopressin, terlipressin, or angiotensin may be considered 1
   • For term newborns with persistent pulmonary hypertension, inhaled nitric oxide (typically at 20 ppm) 1

Special Considerations

• Extremely preterm infants receiving vasopressors have higher risk of severe intraventricular hemorrhage 2

  • Risk factors for vasopressor use include lower birth weight, low 5-minute Apgar scores, and admission hypothermia 2

• Monitoring should include:

  • Continuous intra-arterial blood pressure
  • Central venous pressure/oxygen saturation
  • Urine output
  • Blood gas analysis
  • Glucose and calcium concentrations 1

Refractory Shock Management

For newborns with refractory shock, consider:

1. Rule out unrecognized conditions requiring specific treatment:

   • Pericardial effusion, pneumothorax, ongoing blood loss
   • Hypoadrenalism, hypothyroidism
   • Inborn errors of metabolism
   • Congenital heart disease 1

2. ECMO (Extracorporeal Membrane Oxygenation):

   • Consider for term newborns with refractory shock
   • Current survival rate for newborn sepsis on ECMO is 80%
   • Most centers accept refractory shock or PaO2 <40 mm Hg after maximal therapy as indication 1

3. CRRT (Continuous Renal Replacement Therapy):

   • Consider in newborns with inadequate urine output and 10% fluid overload despite diuretics 1

Pitfalls to Avoid

• Relying solely on blood pressure values without assessing perfusion and end-organ function
• Using adult definitions of hypotension for infants
• Failure to recognize that MAP normally increases with gestational age and postnatal age 3
• Failure to increase MAP between 3-6 hours of life should raise concern 3
• Overtreatment of "numerical hypotension" in the absence of clinical signs of poor perfusion