Obstetrics Book

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Fetal Scalp pH

Aka: Fetal Scalp pH, Fetal Scalp Blood Sampling
  1. Indications
    1. Assess degree of Fetal Hypoxia
  2. 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)
  3. 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
  4. Technique
    1. Amnioscope tube passed via dilated Cervix
    2. Guarded knife produces blood droplets for sample
  5. Adverse Effects
    1. Fetal scalp Hemorrhage
      1. Bleeding may be difficult to control
  6. 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
  7. Efficacy
    1. Reduces number of unnecessary Cesarean Sections
    2. False Positive Rate if scalp pH <7.20: <20%

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