Analgesia & Anesthesia for Obstetric Patients - Dr. F Lui Flashcards
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Describe the oxygen consumption & maternal metabolism during pregnancy
- Maternal tissue: ?ml/min
- Fetus + uterus + placenta: ?ml/min
- Oxygen consumption >?ml/min at term
Why is physiological anaemia a common finding in pregnant women?
Physiological increase in red cell volume lags behind physiological increase in plasma volume
What Hb and Hct parameters warrant Ix for specific causes of anaemia in pregnant women at term?
Term
Hb 11.6 g/dL
Hct 35.5
What are the common causes of thrombocytopenia in pregnant women?
- Gestational thrombocytopenia (would not be very low)
- Immune-mediated (much lower count)
- Preeclampsia/HELLP syndrome
Individual assessment on contraindication to regional anaesthesia
For preeclampsia/HELLP syndrome, look at the trend in the drop
- Higher risk of bleeding complications / ICH
What is the trend of fibrinogen in pregnant woman? What do low levels of fibrinogen predict? What can we do about this?
- Fibrinogen is much higher in a term pregnant woman (may increase x3-4)
- Low fibrongen level would predict severity of postpartum haemorrhage
- Give cryoprecipitate or fibrinogen concentrate from blood bank
What are the expected findings of a CVS exam (P/E & ECG) in a term pregnant woman?
P/E:
- Leftward shift of apex beat
- Accentuation of S1
- S3, S4
- Exaggerated physiological split
- ESM
ECG:
- Sinus tachycardia (must determine whether there is pulmonary embolism)
- LAD up to 15º
- Ectopic beats
- T inversion III & aVF
What may different degrees of tachycardia inform us in the assessment of obstetric haemorrhages?
Differentiate if tachycardia is purely due to stress levels or because of actual bleeding
Why does the baby suffer first if the mother starts to bleed?
- There is no autoregulation in uteroplacental blood flow compared to othe regional circulation in the maternal system
- It is the major determinant for oxygen & nutrients to foetus
- Change in foetal heart rate will be the first sign of mother’s suffering from blood loss
How do we avoid aorto-caval compression in pregnant women?
- Left lateral tilting with spine board of at least 30º
- Manually displace uterus by single-handed or double-handed manouvere
What are the respiratory changes in a pregnant woman?
FRC is dropped by 20% = reduce oxygen reserve in spite of increased O2 demand
Clinical significance for respiratory changes in pregnancy
- What respiratory complications are pregnant women prone to developing?
When performing GA for pregnant women, they are prone to quick desaturation
(limited time and attempts of intubation allowed!!!)
Why is intubation required for general anaesthesia?
There is an increased risk of aspiration in pregnant women
- Reduce gastric emptying (hormonal, cephalad stomach)
- Increase gastric acid secretion & acidity
Infant exposure dose
Anything recieved by the baby is less than 10% of the dose recieved by the mother
Breastfeeding concerns if mother is on medication
- What is the transfer of drugs influenced by?
- What are different drug preparations which can help to expose less amount to infants than parenteral administration?
- What can we do to minimise infant exposure?
What are the stages of labour pain divided into?
First stage:
- pain from uterine contraction from lower segment and cervix
- conducted by smaller visceral C + A-delta fibres
Second stage:
- Larger A delta fibres (need to give larger volume of LA to block the pain sensation)
Why is pain control important?
Extreme pain:
- May increase post-natal depression
- Predicts PTSD
- Imapired cognitive function
Non-pharmacological pain relief methods for labour pain
- Moxibustion (burning of dried mugwort on skin to relieve pain)
- Massage
- Support
- Birth ball / positions
- Water bath
- Intracutaneous water papules (inject water into certain locations of lower back to reduce labour pain)
Pharmacological pain relief methods for labour pain
Systemic medication
- Inhalational
– Entonox
– Volatile agents
- Parenteral opioids
– Intramuscular injections
– PCA IV Remifentanil
Neuraxial analgesia
What is entonox gas?
Inhibitor of methionoine synthesase:
- Enzyme involved in DNA synthesis (unsure if there may be harm to baby after prolonged administration)
Systemic opioids for obstetric patients: Intramuscular pethidine
- What are the concerns with this drug?
- Poor efficacy
- Maternal drowsiness and nausea
- Metabolite nor-pethidine has prolonged half-life of 16-20 hours
- Neonatal respiratory depression
- Affect neurovehavioural scores of newborn
Despite the above, it is still commonly used
Other than intramuscular pethidine, what is another options for systemic opioids for pregnant women?
Intravenous patient controlled remifentanil infusion
Downside:
- Require PCA equipment
- Does not escape complicatoins of systemic opioids (Naloxone)
Evidence-based labour analgesia
- What has been proven to work?
- What has been proven to NOT work?
What is the unique advantage of epidural analgesia?
- Efficacious pain relief in experienced hands = gold-standard for comparison
-
Versatility
– Allow top up if operative delivery needed
– Avoid GA & maternal airway manipulation -
Superior maternal haemodynamics
– Preeclampsia
– Maternal heart diseases
[we don’t want to stress these patients, thus we recommend them to have an epidural]
Extra benefits of epidural analgesia (think of maternal plasma catecholamines and ventilation)
