Anaesthesia and Pregnant Woman Flashcards
What are the major CV physiological changes at 32w pregnancy?
- CO inc 40%
- HR inc 15%
- SV inc 35%
- TPR dec 35%
- Heart displaced up and left
- Louder heart sounds
- +/- flow murmur
What are the ECG changes of pregnancy?
- ECG: inverted T in II, V1, V2
- L axis deviation
- Some ST depression
What is the compensation that occurs following aorto-caval compression?
- Tachycardia
- Vasoconstriction
- Diversion of blood through epidural and azygous system
Why is aorto-caval compression significant in the setting of anaesthetics?
Compensation usually occurs unless there is an epidural in when decompensation may result: bradycardia, nausea, sweating, pallor, fainting
what are the major Resp physiological changes with pregnancy?
- Tidal volume inc 40%
- RR inc 15%
- Airway resistance dec 35%
- Alveolar ventilation inc 70%
- FRC dec 20%
- In 1/3-1/2 at term, CC > FRC
- Diaphragm elevated 4cm
- Capillary and soft tissue engorgement upper airway
Haem physiolgoical changes with pregnancy?
- Total volume inc 40%
- Plasma volume inc 50%
- RBC volume in 30%
- Hb dec to 120
- Hct dec to 35%
- Platelets dec 20%
- Clotting factors inc 800%
- Plasminogen and anti-thrombin III dec
GIT physiological changes with pregnancy?
- GIT tone and motility dec
- Gastric emptying delayed
- Acid production inc
- LOS pressure dec
- Reflux present in >80%
CNS physiolgoical changes with pregnancy relevant to anaesthetics?
sensitivity increased to: -narcotics -local anaesthetics -GA gases Endorphins increased
What occurs short term post delivery which confers high risk for CV events during this period?
- Loss of placental shunt
- Auto transfusion with uterine contraction
When is the highest risk period for thromboembolic events?
During the 5days following delivery when physiological changes of pregnancy being reversed
What are the clinical implications of physiological pregnancy changes for anaesthetics?
Most systems are at end of reserve point.
- Risk of hypoxia:
- O2 consumption inc 20%
- FRC decreased
- CC > FRC
- Risk of failed intubation
- Risk of acid aspiration
- Risk of thromboembolism
What is the respiratory manifestation of pain physiology during labour? implications?
Hyperventilation = hypocarbia and alkalemia.
- hypoventilation between contractions > maternal and foetal hypoxemia and acidosis
- uteroplacental and foetaplacental vasoconstriction
- left shift of O2 curve compromised transplacental O2 transfer to foetus
What are the visceral pathways of pain transmission in labour?
- Paracervical region
- Through pelvis: inferior, middle and superior hypogastric plexuses
- Lumber sympathetics
- T10-L1 synapse with interneurons in dorsal horn
What are the somatic pathways of pain transmission in labour?
- Pudendal nerve (S2, 3, 4)
- Ilioinguinal nerve
- genitofemoral nerve (genital branch)
- Posterior femoral cutaneous nerve
What is the predominant pain transmission pathways in the first stage of labour?
T10 - L1/2
-Referred to lower back, abdomen, upper thigh.
What is the predominant pain transmission pathway in the second stage of labour?
- Distension of outlet, vagina, vulva, perineum
- S2-4
- Well localised
What are the non-pharm methods of pain relief during labour?
- Preparation (classes, knowledge reduces anxiety)
- Hypnosis
- Acupuncture (infxn, bleeding risk)
- TENS
What are the broad pharmacological categories of labour pain relief?
- NO
- Opioids
- Regional anaesthesia (epidural, spinal, combined)
What are the characteristics of NO?
- Potent analgesic gas
- Low solubility = rapid uptake
- Inspired concentration 30-70%
- Takes ~50s to attain effective analgesic concentration
- Start using before contraction starts
What is the most common opioid used in labour?
Pethidine
Dose pethidine in labour?
100mg IM 2-3h
What are the pros and cons of pethidine?
- Cheap, safe, easy to use
- Maternal N/V, dysphoria; foetal effects
Fentanyl long or short acting?
Shorter
Fentanyl characteristics?
- shorter acting synthetic opioid
- highly lipophilic with rapid analgesia
- 50-100ug IV
- PCA
