Supine Hypotension Syndrome in Pregnancy (Aortocaval Compression Syndrome)
🔹 Definition
Supine hypotension syndrome (SHS), also known as aortocaval compression syndrome, is a clinical condition characterized by hypotension, pallor, sweating, and dizziness when a pregnant woman lies in the supine position, especially during the second and third trimesters.
🔹 Etiopathogenesis
- During pregnancy, the gravid uterus enlarges significantly, especially after 20 weeks of gestation.
- In the supine position, the uterus compresses the inferior vena cava (IVC) and to a lesser extent the abdominal aorta:
- IVC compression → ↓ Venous return to the heart (preload) → ↓ Cardiac output → Hypotension
- Aortic compression → ↓ Uteroplacental blood flow → Fetal compromise
🔹 Pathophysiology
In the Supine Position:
- ↓ Venous return (preload) due to IVC compression.
- Reflex tachycardia may occur to compensate, but this is often inadequate.
- ↓ Stroke volume → ↓ Cardiac output → ↓ BP.
- Uteroplacental perfusion is compromised, potentially affecting fetal oxygenation.
- Some women compensate via collateral venous pathways (azygos and vertebral veins), hence are asymptomatic.
🔹 Clinical Features
|
Maternal Symptoms |
Fetal Effects |
|
Pallor |
Fetal bradycardia |
|
Diaphoresis |
Decreased variability on CTG |
|
Dizziness or light-headedness |
Late decelerations (due to hypoxia) |
|
Nausea or vomiting |
Fetal distress, acidosis |
|
Syncope (in severe cases) |
Intrauterine growth restriction (IUGR) |
|
Hypotension |
Stillbirth (rare, severe, prolonged) |
🔹 Timing and Risk Factors
- Typically occurs in second or third trimester, especially after 20 weeks.
- More common in:
- Polyhydramnios
- Multiple gestations
- Macrosomic fetuses
- Obesity
- Lack of collateral venous compensation
🔹 Diagnostic Clues
- Hypotension when in the supine position and resolution when lateral position is assumed.
- Confirmatory signs include:
- Drop in systolic BP >15-20 mmHg
- Elevated heart rate
- Relief upon left lateral tilt or manual uterine displacement
🔹 Anesthetic Implications
1. During Neuraxial Anesthesia:
- Spinal and epidural anesthesia further decrease systemic vascular resistance and preload.
- Pregnant women are already on the edge of hemodynamic compromise due to SHS.
- SHS can potentiate hypotension post-block.
2. Intraoperative Management:
- Always use a left lateral tilt (15–30°) with a wedge under the right hip.
- Alternatively, perform manual uterine displacement to the left.
- Maintain adequate IV preload, and use vasopressors (phenylephrine is preferred).
- Continuous maternal BP and fetal heart rate (FHR) monitoring is essential.
🔹 Prevention and Management
|
Strategy |
Details |
|
Left Lateral Tilt |
15–30° tilt prevents uterine compression of IVC |
|
Wedge under Right Hip |
Simple, effective method in OR or labour room |
|
Manual Displacement of Uterus |
Useful during C-section under GA or during emergencies |
|
Fluids |
Preloading or coloading with crystalloids to maintain intravascular volume |
|
Vasopressors |
Phenylephrine (preferred), ephedrine in some cases |
|
Avoid Supine Position Prolonged |
Especially after 20 weeks gestation |
|
Oxygen Supplementation |
If symptoms appear or fetal distress is noted |
🔹 Multiple Choice Questions (MCQs)
1. Supine hypotension syndrome is most likely to occur:
- A. In first trimester
- B. After 12 weeks gestation
- ✅ C. After 20 weeks gestation
- D. Before 10 weeks gestation
2. Preferred vasopressor in pregnancy-related hypotension:
- A. Dopamine
- B. Norepinephrine
- ✅ C. Phenylephrine
- D. Epinephrine
3. The primary mechanism of supine hypotension syndrome is:
- A. Increased aortic resistance
- ✅ B. Compression of the inferior vena cava
- C. Compression of iliac veins
- D. Hypovolemia
4. Best position to prevent SHS:
- A. Supine with head-up
- ✅ B. Left lateral tilt
- C. Trendelenburg
- D. Sitting upright
5. Which of the following is NOT a symptom of SHS?
- A. Pallor
- B. Dizziness
- ✅ C. Hypertension
- D. Diaphoresis