Anaesthetics and Pregnancy

Question 1

Describe the cardiovascular changes relevant to anaesthetics that occur in pregnancy

Answer 1

• SV (blood volume increase), HR, CO increase
• LVH and dilation
• Upward displacement of the diaphragm
  
  • ECG changes slowly from 20 weeks due to this displacement of the heart - LAD, ST depression, T flattening or inversion in III
• Aortocaval compression
  
  • Compensation occurs to an extent through the azygos and epidural venous plexuses in a normal situation. General and regional anaesthesia turns off this ability.
  • Pregnant women need to be tilted to the left

Question 2

Describe the haematological changes that occur during pregnancy

Answer 2

• Increased blood volume > increased RBC volume - dilutional, physiological anaemia
  
  • Lower Hb decreases viscosity - compensating for increase in clotting factors
• Hypercoagulability: increased fibrinogen, clotting factors (except XI, XIII)
  
  • Increased platelet production but decreased count (dilutional)

Question 3

Describe the respiratory and GI cahnges that occur during pregnancy as applicable to anaesthetics

Answer 3

• Reduced FRC (elevated diaphragm and capillary engorgement and oedema), with compensatory chest wall expansion and flaring.
  
  • Predisposes to airway and lung collapse when supine (increases closing capacity) and creates intubation difficulties
• LOS relaxation from stomach compression with resultant reflux (80%) - major risk of aspiration

Question 4

Describe the change sin drug hadling that occur during pregnancy as applicable to anaesthetics

Answer 4

• Compression of the epidural and spinal areas leads to reduced space and CSF - require a smaller dose for anaesthesia
• CNS is more sensitive to all drugs

Question 5

Describe the genitourinary and musculoskeletal changes that occur during pregnancy

Answer 5

• Dilated ureters, increase in renal blood flow and GFR, decrease in renal glucose threshold, increase in aldosterone
• Progesterone-mediated relaxation of ligaments

Question 6

What are the main anaesthetic risks during pregnancy?

Answer 6

• Risk of hypoxia, failed intubation, acid aspiration, VTE

Question 7

Describe the pain physiology of the first stage of labour

Answer 7

• T10-L1/2, mostly visceral pain (dilation, uterine contraction). Referred to abdomen, lower back, upper thigh

Question 8

Describe the pain physiology of the second stage of labour

Answer 8

• S2-4, distension of outlet, vagina, vulva, perineum. Well localised

Question 9

Describe the features of lumbar epidurals and spinal anaesthetics in terms of volume, continuous use, and space injected into

Answer 9

• Lumbar
  
  • 10-20mL into potential epidural space, can be one-off or infusion
• Spinal
  
  • 3mL into subarachnoid space, one-off only

Question 10

What are the contraindications to lumbar epidural anaesthesia?

Answer 10

• Refusal
• Coagulopathy - increased epidural abscess risk
• Sepsis - increased epidural abscess risk
• Hypovolaemia - also a complication
• Relative - neurological conditions, foetal distress, late stage of labour

Question 11

What are the early and late complications of epidural anaesthesia?

Answer 11

• Early
  
  • Hypotension (+/- bradycardia - due to sympathetic block)
  • Total spinal block
  • Local anaesthetic toxicity (injection into a vessel)
  • Foetal distress (hypotension)
  • Spinal headache
  • Motor block
  • Urinary retention
  • Pruritus (opiates)
• Late
  
  • Permanent neurological harm
  • Paraplegia
  • Death (very rare)

Question 12

What are the difficulties in delivering a general anaesthetic to a pregant woman? Are the GA drugs damaging to the foetus

Answer 12

• Intubation is more difficult (congested airway)
• Preoxygenation is more difficult (decreased FRC)
• Aspiration is more likely (LOS relaxation)
• Not damaging to foetus