Obstetrics Flashcards
(19 cards)
Outline the respiratory changes during pregnancy.
FRC decreased by 20% - worse when lying down
Ventilation increased (progesterone) - at term, minute ventilation has increased by 50%
O2 consumption increases by 40-60% and 100% in labour
Blood gas - compensatory respiratory alkalosis
O2 dissociative curve shifted to right
What are the consequences of the respiratory changes that occur in a woman during pregnancy?
Greater risk of hypoanemia - decreased O2 stores, increased O2 demand (may desaturate rapidly after induction of GA even with adequate pre oxygenation due to reduced FRC and increased metabolism)
Airway difficulties - oedema, worse Mallampati score
Outline the cardiovascular changes during pregnancy.
CO increased up to 50%
SVR decreased by 20%
During labour, CO increased a further 40%, esp due to pain
Aortocaval compression (supine hypotension syndrome) when lying down
Delivery - auto transfusion of up to 500ml
Outline the haematological changes during pregnancy.
Blood volume increases 30-40%
Plasma protein concentration decreases
Hypercoagulable state
Outline the GIT changes during pregnancy.
Increase gastric acid production
Delayed gastric emptying from 12+ weeks (increased even further during labour - pain, anxiety, opiates may be used)
Decreased lower oesophageal sphincter tone
Increased risk of gastro reflux (returned to normal > 48 hours after delivery)
Increased aspiration risk (prophylactic measure NB)
What are the challenges of providing anaesthesia in obstetrics?
Airway at risk of both aspiration and difficult intubation
Respiratory capacity decreased - raid desaturation
Increased metabolic demands
Two patients to bear in mind
C/section is major surgery with potentially major blood loss
What are options available for analgesia for labour?
Entonox (50/50 mixture of O2 + N2O) - self administered and needs to be timed with contractions
Opioids - pethidine, morphine - can result in respiratory distress
Epidural anaesthesia
Mother may choice no analgesia if desired
What is the standard option of anaesthesia in the case of c-sections? And why?
Spinal
Best outcomes in terms of safety where no contraindications exist
Avoids problems with airway in GA (hypoxia, aspiration, difficult airway)
Awake mother - present at birth, early bonding
Mortality + morbidity occur with both GA and regional
What are the common obstetric contraindications to neuraxial blockade?
Haemorrhage + hypovolaemia
Major placenta praevia (even if planned c/s)
Thrombocytopenia in pre-eclampsia
CVS coorbidities (stenosis lesion, cardiomyopathies)
Provide details of what needs to be done when performing a typical obstretric spinal.
Regular hx + examination and consent checking
Antacid prophylaxis - sodium citrate solution
Good IV access
Co loading of isotonic crystal loads at time of block
Spinal at L3/L4, using pencil point needle
Typical dose 2ml 0.5% bupivacaine with dextrose (added opioid - 10ug fentanyl)
T4 block is achieved in most cases
Supine with 15 degree left lateral tilt
What is the vasopressor of choice when anticipating hypotension during a spinal? Which one is second line?
1st: Phenylephrine
2nd: Ephedrine
If the spinal block is inadequate, what should be done?
Inhaled N2O
Alfentanil or fentanyl post delivery (if baby born, but patient needs to be closed up still)
BZD small dose
LA infiltration
Convert to GA
Patient with epidural now needing c/section?
Two options:
- Convert epidural into spinal like block (high dose + volume LA top up)
- Remove epidural and do spinal OR keep epidural for post op analgesia, spinal 1 level lower
What are the obstetric indications for a GA?
Severe fetal distress (fatal bradycardia)
Obstetric hemorrhage (placenta praevia, abruptio placentae)
HELLP syndrome / severe pre eclampsia
How does one balance the risk of prevention aspiration and also prevent difficult airway?
Oxygenation is paramount, you can survive aspiration but you cannot survive without oxygen
Obstetric GA always a rapid sequence induction, but if difficulty encountered and patient becomes hypoxic, it is essential to provide oxygen
If BMV is necessary, it must be done
And/or a temporary airway (SGA/LMA)
Outline the general technique with an obstetric GA.
Antacid prophylaxis and good IV access
Preoxygenation 100% for 5 minutes, end tidal O2 > 80%
Rapid sequence induction (classically thiopentone + suxamethonium, propofol fine if no haemodynamic instability, no poisons until delivery of baby)
Which pre-delivery analgesia can be given?
Nitrous oxide
Volatile (isoflurance or sevoflurane good choices)
Which agents need to be given at delivery, after clamping of cord?
Oxytocin as per spinal (bolus + infusion)
Opioid can now be given (fentanyl / morphine)
IV paracetamol
Continue N2O
Carefully titrate volatile, too much can cause uterine hypotonia
