Lab

Fetal Scalp pH

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Fetal Scalp pH, Fetal Scalp Blood Sampling

  • Indications
  1. Assess degree of Fetal Hypoxia
  • Scalp Stimulation Test
  1. Positive Scalp stimulation response
    1. Fetal Heart Rate increases 15 beats for 15 seconds
  2. Positive Response implies no acidosis (pH > 7.20)
  • Fetal Scalp Blood Sample Analysis
  1. Normal
    1. pH: 7.25-7.35 (mean 7.33)
    2. pCO2: 40-50 mmHg
    3. pO2: 20-30 mmHg
    4. Base: <10
  2. Non-reassuring findings (see interpretation below)
    1. pH <7.20
    2. Base Excess < -12 mmol/liter
  3. Metabolic Acidosis
    1. pH: <7.25
    2. pCO2: 45-55 mmHg
    3. pO2: <20 mmHg
    4. Base: >10
  4. Respiratory Acidosis
    1. pH: <7.25
    2. pCO2: >50 mmHg
    3. pO2: Varies
    4. Base: <10
  • Technique
  1. Amnioscope tube passed via dilated Cervix
  2. Guarded knife produces blood droplets for sample
  • Adverse Effects
  1. Fetal scalp Hemorrhage
    1. Bleeding may be difficult to control
  • Interpretation
  1. Scalp pH >= 7.25 and FHT remains non-reassuring
    1. Continue to observe labor
    2. Repeat scalp sampling every 2-3 hours
  2. Scalp pH >= 7.20 and FHT remains non-reassuring
    1. Repeat Scalp sample in 15-30 minutes
  3. Scalp pH < 7.20
    1. Repeat Scalp sample immediately
    2. If no change in pH then immediate delivery
  • Efficacy
  1. Reduces number of unnecessary Cesarean Sections
  2. False Positive Rate if scalp pH <7.20: <20%