Anaesthetics in Pregnancy

Question 1

What are some things to consider in pregnant ladies for anaesthetic that complicate it in terms physiology?

Answer 1

• CVD
  
  • increased demand (increased CO 40%)
  • ECG
    
    • inverted T in 2, V1 and V2
    • Left axis deviation
    • some ST depression
  • Aortio-caval compression
    
    • ​aorta + IVC compression by gravid uterus.
    • compensation - increased HR, vasocontriction, diversion of blood through azygous system
    • decompensation - nausea, decreased HR, pallor, fainting - under anaesthetic sympathetic system gets suppressed.
• Resp:
  
  • diaphragm 4cm elevated
  • increased airway resistance
• Haem
  
  • increased plasma proteins
    
    • increase total amount, decreased concentration
    • plasma pseudocholinesterase levels decreased - prolonged effects of suxamethonium (delayed breakdown)
• GI
  
  • reflux by >80%
  • reduced tone and motility, increased acid.
• UTI
  
  • increased GFR - renal threshold for glucose lower.
• CNS
  
  • increased sensitivity to narcotics/anaesthetic gases/local anaesthetics
  • increased beta endorphins - suffer less pain. Fall asleep after epidurals - removal of pain sedative effect.

Question 2

What are some things that happen post-delivery?

Answer 2

• Short term
  
  • loss of placental shunt (been getting 20% of CO)
  • auto-transfusion with uterine contractions. Blood squeezed. Going into venous volume
  • highest risk for CV events
• Long term
  
  • high risk time for TE - triad
    
    • immobility
    • intrinsic hypercoagulability (pregnancy - plasma)
    • vessel damage - sheared off whole organ.

Question 3

Anaesthetics Airway considerations when thinking about intubation in pregnancy?

Answer 3

• rapid desaturation - increased metabolic rate, lower store
• increased aspiration
• risk of failed intubation (10x increased risk)
  
  • fluid retention - laryngeal oedema
  • weight gain
  • breast enlargement

Question 4

What are the pain transmission pathways during the stages of labour?

Answer 4

• Visceral
  
  • first stage of labour
    
    • paracervical = via sympathetic nervous system
    • lower uterine segment contraction = T10-T12.
    • referred to lower back, abdomen, upper thigh
• Somatic
  
  • second stage
    
    • stretch of structures
    • S2-S4 in the pelvis
      
      • pudendal nerve
      • ilioinguinal nerve
      • genitofemoral nerve
      • posterior femoral cutaneous nerve
• need a method that is across a wide range

Question 5

What are some non-pharmacological methods?

Answer 5

• being prepared
  
  • antenatal classes
  • knowing reduces anxiety
• hypnosis
  
  • trance-like state - sessions prior to labour
• acupuncture
  
  • risk infection and bleeding.
• TENS
  
  • good placebo - high frequency

Question 6

General systemic pharmacological interventions in labour?

Answer 6

• Nitric oxide
  
  • rapid uptake in the brain
  • 60-70% effective
  • difficult to use - before contractions start. Timed to use it before contraction.
• Opioids
  
  • pethidine - no longer used
  • in UK using dimorphine
  • morphine - most common, cheap/safe
    
    • N/V
    • resp depression
    • dysphoria - state of unease
    • fetal effects (resp, N/V)
• Fentanyl
  
  • PCA - often used in epidural
  • rapid onset
• Remifentanil - not used
  
  • ultra short acting synthetic opioid.

Question 7

Talk through epidurals as a regional anaesthetics that can be used in labour?

Answer 7

Types:

• Epidural
  
  • between dura and spinal canal
  • spinal cord ends L1/L2 - second fused vertebrae.
  • continous infusion
  • indications
    
    • pain relief
    • medical (cardiac disease - prevent CO going up, pre-eclampsia - HTN and epidural helps control BP)
  • contraindications:
    
    • hypovolemia
    • coagulopathy or heparin
    • sepsis
    • active neurlogical condition (relative) - MS relaspe post-pregnancy (residual block)
    • fetal distress (relative) - urgent delivery it takes too long
  • advantages:
    
    • effective - reducing pain but with it
    • no sedation
    • improve placental blood flow in some cases (pre-eclampsia)
    • allows instrumental delivery/LUSCS
  • complications:
    
    • Immediate:
      
      • hypotension
      • high block
      • total spinal (dural puncture)
      • intravascular injection - don’t recognise toxicity. Not something that happens with mixes now. One of causes of death.
    • Delayed:
      
      • postdural puncture headache (1% women)
      • infective, haematoma, neurological (paralysis)
  • drugs:
    
    • bupivacaine + ropivacaine
    • fentanyl
  • PCEA - patient controlled - continous

Question 8

Spinal regional anaesthetics advantages and disadvantages?

Answer 8

• spinal - first obstetric technique
  
  • rapid onset of analgesia
  • not titratable
  • post-dural puncture headache. Not routine in old days but nowadays needles are very fine.

Question 9

How do you decide an anaesthetic for a C-section?

Answer 9

• degree of urgency
  
  • GA>spinal>epidural
• if its already in in Aus hospitals epidurals just as fast.
• want to avoid GA if you can for procedures.

Spinal C-section:

• Heavy bupivicaine - want them lying down
• more reliable than an epidural
• less local anaesthetic

Epidural - not empty space - unilateral block, lie on left and hoping some will sink.