fetal scalp blood pH
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p421-422
2025-12-13
55
Type of test Blood
Normal findings
pH: 7.25-7.35
O2 saturation: 30%-50%
Po2 : 18-22 mm Hg
Pco2 : 40-50 mm Hg
Base excess: 0 to −10 mEq/L
Test explanation and related physiology
Measurement of fetal scalp blood pH provides valuable information on fetal acid–base status. This test is useful clinically for diagnosing fetal distress. The pH normally ranges from 7.25 to 7.35 during labor; a mild decline within the normal range is noted with contractions and as labor progresses.
Fetal hypoxia causes anaerobic glycolysis, resulting in excess production of lactic acid. This causes an increase in hydrogen ion concentration (acidosis) and a decrease in pH. Acidosis reflects the effect of hypoxia on cellular metabolism. A high correlation exists between low pH levels and low Apgar scores.
Fetal oxygen saturation monitoring (FSpo2 ) also is available to assist the monitoring of fetal well-being during delivery. When the FHR becomes significantly abnormal, C-section is often per formed because of concern for fetal well-being. However, with FSpo2 , an accurate measure of fetal oxygen saturation can be determined. After membranes are ruptured, and if the baby is in vertex position with good cervical dilatation, a specialized probe can be placed on the temple or cheek of the fetus for FSpo2 monitoring. The oxygen saturation is displayed on a monitor screen as a percentage. The normal oxygen saturation for a baby in the womb receiving oxygenated blood from the placenta is usually between 30% and 70%.
Contraindications
• Patients with premature membrane rupture
• Patients with active cervical infection
Potential complications
• Continued bleeding from the puncture site
• Hematoma
• Ecchymosis F
• Infection
Procedure and patient care
Before
* Explain the procedure to the patient.
• Obtain informed consent for this procedure.
* Tell the patient that no fasting or sedation is required.
During
• Note the following procedural steps for fetal scalp pH:
1. Amnioscopy is performed with the mother in the lithotomy position.
2. The cervix is dilated, and the endoscope (amnioscope) is introduced into the cervical canal.
3. The fetal scalp is cleansed with an antiseptic and dried with a sterile cotton ball.
4. A small amount of petroleum jelly is applied to the fetal scalp to cause droplets of fetal blood to bead.
5. After the skin on the scalp is pierced with a small metal blade, beaded droplets of blood are collected in long, heparinized capillary tubes.
6. The tube is sealed with wax and placed on ice to retard cellular respiration, which can alter the pH.
7. The physician performing the procedure applies firm pressure to the puncture site to retard bleeding.
8. Scalp blood sampling can be repeated as necessary.
• Note that this study is performed by a physician in approximately 10 to 15 minutes.
* Tell the patient that she may be uncomfortable during the cervical dilation.
After
* Inform the patient that she may have vaginal discomfort and menstrual-type cramping.
After delivery
• Assess the newborn and document the puncture site(s).
• Cleanse the fetal scalp puncture site with an antiseptic solution and apply an antibiotic ointment.
Abnormal findings
- Fetal distress
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