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MBBS VI - SpC - Obstetrics and Gynaecology > Analgesia and Anesthetics during labor > Flashcards

Analgesia and Anesthetics during labor Flashcards

1
Q

Oxygen consumption and maternal metabolism requirement

A

Maternal tissue: 4ml/min
Fetus+ uterus+ placenta: 12ml/min
At term: oxygen consumption >20ml/min

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2
Q

List normal haematological changes during pregnancy

A

Physiological haemodilution and anaemia
Thrombocytopenia: due to physiological changes, or pathologies e.g. pre-eclampsia causing HELLP
Pro-coagulative outisde utero-placental unit

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3
Q

Common CVS changes during pregnancy

A

 Sinus tachycardia

 JVP: height remain unchanged

 Peripheral pulses: ↑volume

 Atrial and ventricular ectopic beats, T wave inversion in lead III and aVF

 Loud ± split S1, S3, ejection systolic murmur (flow murmur, from 2T onwards and disappear upon delivery)

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4
Q

Explain why pregnant women masks hypotension due to blood loss

A

Physiological increase in cardiac output masks blood loss and hypotension until 30-35% blood loss

  • ↑cardiac output: by 40-50%
     Mostly during 1st trimester, can reach 7L/min at rest by 24w
     Reaching plateau during 3rd trimester
     Further ↑during labor
  • ↑heart rate: by 10-15bpm cf baseline
  • ↑stroke volume: by 10-20mL/beat

Need to differentiate cause of tachycardia during delivery between stress vs blood loss

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5
Q

Non-pharmacological measures for pain relief during labor

A

 One-to-one care in labor from midwife or effective birth partner
 Relaxation and breathing exercise
 Massage (esp by husband) and acupuncture
 Birth ball
 Water bath
 Intracutaneous water papules
 Moxibustion

Low-risk, but difficult to perform RCT and evaluate efficacy

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5
Q

Pharmacological options for pain relief during labor

A
  1. Transcutaneous electrical nerve stimulator (TENS)
  2. Narcotic analgesia - IM pethidine 50-75mg up to Q3-4h
  3. Inhalation analgesia - self-administration by Entonox facemask (1:1 mixture of N2O:O2)
  4. Epidural analgesia - mixture of low concentration LA + opioid
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6
Q

Prevention of aortocaval compression

A

Left uterine displacement by:
- Left tilt with spine board
- Manual displacement and manipulation

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7
Q

Ventilatory parameter changes during pregnancy

Relevance for anaesthesia use

A

Physiological changes
* * ↑ventilation by 40%
* ↑tidal volume by 40%
* ↓expiratory reserve by 20% but unchanged inspiratory reserve
* ↓lung residual volume
* NO change in respiratory rate
* NO change in vital capacity overall

Pregnant women: prone to develop hypoxaemia
- reduced oxygen reserve and increased demand
- Hyperventilation due to pain/ bear down effort/ anxiety during delivery
- Further decrease FRC by atelectasis, shunting, Increased O2 A-a gradient
- High metabolism and O2 consumption at term
- Quick desaturation, meaning limited time and attempts of intubation allowed

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8
Q

GI changes during pregnancy

Relevance to anaesthesia use

A

Relevance:
- High risk of aspiration due to decreased gastric motility, increased gastric secretion and acidity, increase intra-gastric pressure
- Intubation is required for GA, airway adjuncts are inadequate

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9
Q

Infant drug exposure dose calculation

A
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10
Q

Determinants of drug toxicity to infants

A

Starting feeding before dose may help minimise infant exposure

Poorly developed BBB and liver enzymes in fetus increases risk of toxicity

Parenteral drugs present much higher bioavailability than topical solutions

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11
Q

Physiology of labor pain

A

First stage:
- Visceral C and A-delta fibers in lower uterine segment and cervix
- Pain signal travels via paracervical ganglion > hypogastric nerve > lumbar sympathetic chain > T10-L1 > higher center

Second stage
- Large A-delta fibers at vagina and perineum > pedendal nerve > S2-S4 > higher center
- Larger fibers require higher concentration of analgesia for second stage
- Non-epidural analgesia might not be able to target pain in both stages

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12
Q

Reason for pain relief during labor

A

Pain associated:
- Impaired cognitive function
- Predicts PTSD
- Increase postnatal depression

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13
Q

Transcutaneous electrical nerve stimulator (TENS)
- MoA
- C/I
- Procedure
- Use

A
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14
Q

Narcotic analgesia
- MoA
- S/E
- Disadvantage

A

Drug of choice: usu IM pethidine 50-75mg up to Q3-4h
Alternative: Intravenous PCAA Remifentanil infusion

S/E:
* N/V in mother → often given tgt with anti-emetics
* Maternal drowsiness and sedation
* Delayed gastric emptying → ↑risk if GA is subsequently required
* Neonatal respiratory depression: esp if ≤2h of delivery

Disadvantage:
- Poor efficacy
- Affect neurobehavioral score of newborn
- Require extensive monitoring e.g. waveform capnography

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15
Q

Inhalation analgesia
- MoA
- Advantage
- S/E
- Use

A

MoA: self-administration by Entonox facemask (1:1 mixture of N2O:O2)

Advantages: quick onset, short duration of effect, more effective than pethidine

S/E: light-headedness, nausea, inhibition of methionine synthase after prolonged administration (unsure DNA synthesis disruption)

Use: most suitable later in labor or while awaiting epidural analgesia as hyperventilation may result in hypocapnia, dizziness, tetany and fetal hypoxia when used early in labor

16
Q

Analgesia methods that work vs do not work during labor

A
17
Q

Epidural analgesia

Indication
Absolute and relative contraindication

A

 Indication: joint decision between mother, midwife, obstetric team and anesthetist → for effective pain relief esp in prolonged labor, maternal HT, multiple gestation, ↑risk of OT

 Absolute C/I: coagulopathy, local or systemic sepsis, hypovolemia, ↑ICP, patient refusal

 Relative C/I: difficult anatomy (e.g. scoliosis, previous spinal surgery), pre-existing neurological deficits

18
Q

Epidural analgesia

Procedure
Care during epidural analgesia

A

Procedure: prefer in later stages of labor as it limit mobility, but should not defer when requested
- Aseptic technique: cleansing of women’s back, with LA infiltration
- Fine epidural catheter inserted by anesthesiologist at L3-4 interspace until epidural space reached
- Injection of test dose to check position (diluted LA → should NOT have any effect on sensation unless punctured dural space)
- Injection of epidural solution into epidural space: usu a mixture of low concentration LA + opioid → addition of opioid ↓motor blockade and peripheral ANS effects of epidural

Care during the duration of epidural analgesia:
- Pt in lateral or wedged position (avoid aortocaval compression)
- IV drip in situ before and throughout duration of epidural
- Frequent BP monitoring esp after each ‘top-up’ bolus

19
Q

Epidural analgesia/ Regional analgesia during labor

Possible complications

A
  • Accidental dural puncture (<1%): may result in postural headache due to CSF leakage
  • Accidental total SA: severe hypotension, resp failure, unconsciousness, death
  • Spinal hematoma and neurological Cx: rare, usu a/w bleeding disorder
  • LA toxicity if inadvertent injection into blood vessels, N/V, pruritis, sedation
  • Bladder dysfunction: if bladder allowed to overfill → should catheterize bladder during labor
  • Hypotension: uncommon, Tx by fluid boluses ± vasopressors
  • Neonatal respiratory depression due to opioid content
20
Q

Epidural analgesia

Advantages

A
  • Gold standard in terms of efficacy
  • Versatile: Allow increase dose if operative delivery needed
  • Avoids GA and maternal airway manipulation
  • Improves maternal haemodynamics: can be used for maternal heart disease/ Pre-eclampsia
  • Maintains haemodynamics: Decreases maternal plasma catecholamines, maternal hyperventilation due to painful uterine contractions, improves uterine blood flow with stable plasma CO2 level
21
Q

Comparison between epidural vs spinal analgesia

A
22
Q

Commonly used epidural and spinal mixtures in QMH

A
23
Q

Common obstetric operations that require analgesia

A
24
Q

Advantages of regional anaesthesia vs GA during labor

A

General advantages:
- Flexible in operation duration
- Flexible in significant blood loss
- Easier for invasive monitoring
- Airway: avoid airway manupulation and aspiration
- Haemodynamic: avoid surges in BP, avoid uteroplacental blood flow drop with catecholamines
- Neonatal benefits: decrease neonatal depression, neurotoxicity
- Post-op: decrease analgesia use, better neurological monitoring, earlier post-op mobilisation
- Encourages breast feeding

25
Q

General anaesthesia during labor

Indications
Preparation
Assessment

A

Indications:
- Crash delivery
- C/I or failed regional anaesthesia

Preparation:
- Supplemental 100% O2 for pre-oxygenation
- IV access
- Standard vitals monitoring
- Sniffing air position for intubation
- Ramping up head position tp open airway

Assessments:
- Thyromental distance, incisor gap, dentition, Head and neck movement, obesity, craniofacial abnormalities, mallampati classification…etc
- Airway edema during labor

MBBS VI - SpC - Obstetrics and Gynaecology (42 decks)

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