Analgesia & Anesthesia for Obstetric Patients - Dr. F Lui Flashcards
Online Videos / Web-based Learning Modules
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)
What are the different regional techniques for analgesia / anaesthesia?
“Spinal” or
- Intrathecal or
- Subarachnoid
Epidural or
- Extradural
Combined spinal-epidural
What do we mean by spinal injection?
Injecting drug directly into CSF
Use small amount of drug, which acts locally (quick effect)
As we are injecting drug into extradural space, we need to place a plastic catheter
Drug either works by direct diffusion to the nerve roots or it can be absorbed by the epidural fat which acts as a deport for the slow release of drugs
Can also be absorbed into the maternal circulation (much larger volume is used, far higher risk of inducing toxicity)
Epidural analgesia vs spinal analgesia
Epidural analgesia
- Flexible in duration as drug is given through plastic cathteter
- Epidural cannot be removed shortly after the administration of anticoagulants (i.e. LMWH)
Commonly used regimes in QMH for anaesthesia in CS
Commonly used regimes in QMH for labour pain relief
Absolute and relative contraindications to regional anaesthesia/analgesia
Absolute:
- Coagulopathy
- Systemic septicaemia
- Hypovolaemia/antepartum haemorrhage (as S/E of anaesthesia is maternal hypotension)
- Raised intracranial pressure
- Patients’ refusal
Relative:
- Difficult anatomy (scoliosis)
- Pre-existing neurological deficits
S/E related to procedure of regional anaesthesia/analgesia
- Treat maternal hypotension with vasopressin
- Motor block may develop if concentration of LA used is too high
S/E related to drugs given in regional anaesthesia/analgesia
Most effects are opioids-related
What are common operations performed in obstetrics?
- Caesarean section
- Manual removal of placenta
- Cerclage
- Perineal tear repair
- Instrumental deliveries
- Non-obstetric operations (appendectomy, endoscopy)
What are the advantages of regional anaesthesia?
If feasible, regional anaesthesia is always preferred
Reduce drug exposure to baby and reduce surges in maternal plasma catecholamines
What are the advantages of general anaesthesia?
- Flexible in operation duration
- Flexible in significant blood loss
- Easier for invasive monitoring
When is general anaesthesia inevitable?
- Crash delivery
- Contraindications to regional techniques
- Failed regional techniques
What is the preparation for all before intubation?
- Supplemental 100% oxygen with tight sealing mask
- Intravenous access
- Standard monitoring
- Patient positioning - sniffing air position unless contraindicated (align oropharyngeal axis and laryngeal axis for easy intubation)
- Start CPR and resuscitation if arrested
In term-pregnant woman, perform:
- Left lateral tilt
- Manual displacement of uterus
Prevent aorto-caval compression
What must we look for during airway assessment?
Relationship between airway edema and progress. oflabour
What can we do to optimise the head and neck position of the patient?
open up her airway + better intubation attempts
Difference between Macintosh and McCoy blade
Always hold with your L hand
McCoy blade = can elevate epiglottis using the tip of the blade = better view of larynx
What are the different types of laryngeal mask airways for intubation/rescue
- 2nd gen LMA has 2nd lumen = can pass orogastric tube = reduce stomach contents after passage of orogastric tube
- Shape of laryngeal mask is more tailor-made for PPV
- However, dose not eliminate risk of aspiration in term pregnant women
What should we inform the anaesthesist if we see a patient with difficult airway?
Inform them early that there may be complication in intubation
Preparation for haemorrhages
What are these?
- Plasma
- Drugs
- Warming devices
- Central lines
Preparation for haemorrhages
What is this?
Intra-operative red cell recovery
Blood shed by patients has been suctioned by suctioning devices. After going through processing devices by centrifugation and haemodilution
What are these?
Bair hugger prevent heat loss by evaporation
Hot line is a co-axial circuit (reun warm fluid around fluid being administered to patient)
