Spinal Anesthesia and Maternal Hypotension (Low blood pressure during labor)

Hypotension commonly occurs as a complication of spinal anesthesia (1, 2). One study on 511 mothers who received spinal anesthesia for a C-section found that 20% had mild hypotension, 35% had moderate hypotension, and 40% had severe hypotension (1).

Women who have received spinal anesthesia often lie in the supine position (flat on their backs), which can create pressure-related issues affecting various veins (3).

The height of the block, the mother’s position, and prophylactic measures taken may all influence the severity of maternal hypotension. Hypotension is more frequent when mothers are placed in the tilted supine position than when they are in the left lateral position (3, 4, 5).

Women are more likely to experience maternal hypotension as a side effect of spinal anesthesia if they have the following risk factors:

• Advanced maternal age (over 35)
• Body mass index (BMI)  ≥25 kg/m2
• 11-20 kg weight gain
• Gravidity ≥4 (Gravidity refers to the number of times a woman has previously been pregnant. A similar measure is parity, which refers to the number of times she has previously given birth)
• History of hypotension
• Baseline systolic blood pressure (SBP) < 120 mmHg
• Baseline heart rate >100 beats/min
• Fluid preloading  ≥1000 ml
• Adding sufentanil to bupivacaine
• Sensory block height >T4 in anaesthesia-related modelling (P < 0.05) (1)

For more information on these risk factors, please click here.

Prolonged maternal hypotension frequently causes nausea and vomiting in the mother, and can also be harmful to the fetus. Even brief episodes of maternal hypotension can result in fetal acidosis, lower Apgar scores (6), and hypoxic-ischemic encephalopathy (HIE).

Hypotension during pregnancy is associated with an increased risk of stillbirth (7), as well as pregnancy complications such as preterm birth, intrauterine growth restriction (IUGR), meconium stained  fluid, and postpartum hemorrhage (8). The lower the blood pressure, the higher the risk of poor pregnancy outcome.

The negative effects on fetuses are likely due to poor placental perfusion (9). Supporting this idea is the observation that diastolic hypotension and low mean arterial pressure (MAP) seem to be more likely to result in poor pregnancy outcome than is systolic hypotension (10). Diastolic hypotension refers to low pressure in the blood vessels when the heart rests between beats. Systolic hypotension is low pressure in the blood vessels while the heart is beating (11). MAP calculates overall blood flow to various organs (12).

If a mother has spinal anesthesia, her doctor must be vigilant for signs of hypotension. If promptly addressed, hypotension can often be improved by repositioning the mother or using a vasopressor. Physicians must also record the baby’s heart rate with a fetal monitor up until the point of abdominal prepping for C-section. In some cases, monitoring may also be required after preparation for surgery. A fetal heart rate monitor can show signs of fetal distress, which are indications that a baby is being deprived of oxygen. A baby in distress is in need of immediate medical attention and delivery. If medical professionals do not respond appropriately to signs of fetal distress, the outcomes can be serious and permanent. The baby may develop lifelong conditions such as hypoxic-ischemic encephalopathy (HIE), cerebral palsy (CP), seizure disorders, and developmental disabilities.