Obstetrical Anesthesia 

Physiological Changes – Cardiovascular System (CVS)

Changes are largely due to high progesterone levels:

• ↑ Total blood volume by 35%
  
  

• ↑ Heart rate by 15 bpm
  
  

• ↑ Cardiac Output (CO) by 40%
  
  

• ↑ Stroke Volume (SV) by 30%
  
  

• ↓ Systemic Vascular Resistance (SVR) by 15%
  
  

• ↑ Uterine blood flow by 500 ml/min
  
  

• ↓ Venous return from lower limbs (due to gravid uterus)
  
  

• Aortocaval compression: mechanical obstruction of IVC/aorta in supine position
  
  

Impact of CVS Changes

• Decompensation risk in patients with pre-existing cardiac disease (especially during labor/postpartum when CO peaks)
  
  

• Blood loss at delivery: 400–600 ml
  
  

• Supine hypotensive syndrome: due to aortocaval compression, leading to ↓ venous return → hypotension, bradycardia, fetal hypoxia
  
  

Aortocaval Compression

• Caused by gravid uterus compressing inferior vena cava and aorta when lying supine
  
  

• Leads to reduced preload, hypotension, syncope, and fetal compromise
  
  

• Prevented by left lateral tilt (15–30°) using a wedge
  
  

Physiological Changes – Respiratory System

• ↑ Oxygen consumption by 20% (up to 100% during labor)
  
  

• ↑ Minute ventilation by 50% (due to increased tidal volume)
  
  

• ↓ Arterial PaCO₂
  
  

• ↓ Functional Residual Capacity (FRC) → decreased oxygen reserve
  
  

Impact of Respiratory Changes

• Faster uptake of inhaled anesthetics
  
  

• ↑ risk of hypoxia during apnea (due to ↓ FRC and ↑ O₂ demand)
  
  

• Preoxygenation less effective in general anesthesia
  
  

Physiological Changes – Airway

• Mucosal venous engorgement
  
  

• Edema of airway tissues
  
  

• Worsening Mallampati score in labor
  
  

Impact of Airway Changes

• Difficult/failed intubation risk increased ×10
  
  

• Trauma during suctioning or intubation
  
  

• Requires smaller endotracheal tubes (ETTs) (e.g., 6.0–6.5 mm ID)
  
  

Physiological Changes – Central Nervous System (CNS)

• ↓ Minimum Alveolar Concentration (MAC) by 25–40%
  
  

• ↓ Local anesthetic (LA) dose requirement
  
  

• Faster onset of neuraxial blocks (spinal/epidural)
  
  

Impact of CNS Changes

• ↓ Inhalation agent requirement
  
  

• ↑ Risk of LA toxicity (due to enhanced sensitivity)
  
  

• Use lower doses in regional anesthesia
  
  

Physiological Changes – Gastrointestinal Tract (GIT)

• ↑ Gastric volume and acidity
  
  

• ↓ Lower esophageal sphincter tone
  
  

Impact of GIT Changes

• ↑ Risk of aspiration
  
  

• All pregnant women = full stomach
  
  

• Aspiration prophylaxis recommended for Cesarean Section (C/S):
  
  

  • Sodium citrate 30 mL orally
    
    

  • Ranitidine 50 mg IV
    
    

  • Metoclopramide 10 mg IV
    
    

Anesthesia for Cesarean Section

Key considerations:

• Preparation
  
  

• Preventing complications
  
  

• Choosing anesthetic technique
  
  

• Fetal safety
  
  

Preparation

• Premeds: antacids
  
  

• IV access and preload (avoid glucose solutions)
  
  

• Left lateral tilt (wedge under right pelvis)
  
  

• Monitors:
  
  

  • ECG
    
    

  • NIBP
    
    

  • Pulse oximetry
    
    

  • Fetal heart rate monitoring
    
    

• GA: Add ETCO₂, nerve stimulator, temperature probe
  
  

Preventing Complications

• Aspiration prophylaxis
  
  

• Airway evaluation
  
  

• Fluid resuscitation
  
  

• Safe neuraxial anesthesia practice
  
  

• Maintain left lateral tilt to prevent hypotension
  
  

Anesthetic Techniques

• Regional Anesthesia (preferred):
  
  

  • Spinal
    
    

  • Epidural
    
    

  • Combined Spinal-Epidural (CSE)
    
    

• General Anesthesia (when regional is contraindicated)
  
  

Spinal Anesthesia

• Also called Subarachnoid Block (SAB)
  
  

• LA injected into subarachnoid space
  
  

• Acts on spinal nerves, not spinal cord substance
  
  

Spinal Anesthesia – Advantages

• Simple and rapid
  
  

• Single shot
  
  

• Profound block
  
  

• Preferred for elective and many emergency C/S
  
  

Indications for Spinal Anesthesia

• Cesarean delivery
  
  

• Hernia repair, gynecological, urologic (e.g., TURP), lower limb surgeries
  
  

• Manual removal of placenta (if not hypovolemic)
  
  

• Suitable for elderly/systemic disease patients
  
  

Spinal Anesthesia – Complications

• Hypotension
  
  

• Post-dural puncture headache (~1 in 100)
  
  

• Temporary backache
  
  

• Nausea/vomiting (↓ BP or opioids)
  
  

• Rare: neurological injury, anaphylaxis
  
  

General Anesthesia – Indications

• Patient declines regional anesthesia
  
  

• Contraindications to regional block
  
  

• Emergency C/S without time for adequate neuraxial block
  
  

General Anesthesia – Preparation

• Assess airway and obtain consent
  
  

• Administer antacid
  
  

• Complete pre-anesthetic checklist
  
  

• Monitor SpO₂ and BP
  
  

• Large-bore IV access + fluids
  
  

• Left lateral tilt
  
  

• Position head to optimize intubation (e.g., ramping in obese)
  
  

General Anesthesia – Technique

• Preoxygenate 3 minutes
  
  

• Rapid Sequence Induction (RSI)
  
  

• Use suxamethonium for muscle relaxation
  
  

• Avoid opioids/volatile agents until baby is delivered
  
  

• Administer antibiotics before incision
  
  

• Be cautious with halothane (uterine atony risk)
  
  

• Administer 5–10 IU oxytocin IV at delivery
  
  

  • Follow with 40 IU in 500 mL NS over 4 hrs if uterine atony risk
    
    

• Extubate only when fully awake
  
  

General Anesthesia – Complications

• Failed intubation
  
  

• Failed ventilation → death or hypoxic brain injury
  
  

• Awareness under GA
  
  

• Aspiration pneumonia
  
  

More in the document above.

END