Labour pain and anaesthesia Flashcards

Question

How does the local anaesthetic in an epidural work?

Answer 1

Blocks voltage-gated sodium channels in nerves, preventing propagation of action potentials Thus prevents transmission of nociceptive impulses in small diameter nerves entering the spinal canal →Also affect the nerves leaving the spinal canal such as: - Sympathetic nerves innervating blood vessels: vasodilatation and hypotension - Motor nerves which innervate muscles, causing motor blockade It is possible to use opioids and local anaesthetic drugs on their own for epidural analgesia, but combining the two drugs gives a synergistic effect with minimal side-effects.

Answer 2

2018 Cochrane review 40 trials, 11000 women. - Secondary outcome (v opioid) (34 trials involving 10,440 women) Both first and second stages of labour were shorter for the women who received opioids First stage: MD 32.28 minutes, Second stage: MD 15.38 minutes, Heterogeneity high especially for the second stage Secondary outcome (v placebo/no analgesia): There was no clear difference between the groups for length of first stage of labour (minutes)

Answer 3

Caesarean section? - Opioids The caesarean section rate was no different between the groups - no analgesia/placebo: Fewer women in the epidural group underwent caesarean section compared to women in the placebo or no-treatment group Operative Vaginal Birth - Opioids: The assisted vaginal birth rate was higher in the epidural group (RR1.44,). - no analgesia/placebo There was no clear difference in this outcome between the groups

Answer 4

- Lower concentrations of local anaesthetic are associated with lower motor blockade 1mg/mL bupivacaine - Although overall there appears to be an increase in assisted vaginal birth when women have epidural analgesia, a post hoc subgroup analysis shows that this effect is not seen in recent studies (after 2005), suggesting that modern approaches to epidural analgesia in labour do not affect this outcome.

Answer 5

- Caesarean rate not higher but more Caesarean sections are done for fetal distress - Prolonged second stage - Urinary retention Opioid Group - More women in the epidural group had urinary retention compared with the opioid group Placebo: There was no clear difference in this outcome between the groups

Answer 6

1. Hypotension: Spinal anesthesia blocks small, unmyelinated sympathetic fibers first. Sympathectomy from spinal or epidural analgesia ==\> to a ↓ in blood pressure. ==\> ↑ adrenaline ==\>uterine artery constriction ==\>↓ placental blood flow. ==\> fetal bradycardia. Both arteries and veins vasodilate, however the venous effect is more pronounced, leading to substantial decreases in preload 2. Opioids: Intrathecal opioids ==\> to a ↓ in sympathetic nervous system output + ↓ adrenaline levels. Adrenaline is in itself an effective tocolytic due to β2 activity. Therefore, the ↓ adrenaline levels ==\> to unopposed noradrenaline activity, which ↑ uterine tone and ==\> ↓ placental blood flow. If placental blood flow is ↓ enough ==\> fetal bradycardia due to fetal compromise.

Answer 7

1) Local Anaesthetic Systemic Toxicity (LAST) 2) Total/high spinal blockade

Answer 8

1. Send for help: Red Bell, including alerting the anaesthetist, senior obstetrician and neonatal provider 2. Disconnect epidural 3. Start Resuscitation 100% oxygen, woman on side, ensure 2 wide bore IV access and IV Fluids Continually reassess ABC 4. Assess woman - Block height - Other symptoms 5. Assess baby - Continuous CTG 6. Definitive management - Definitive airway - ICU involvement / transfer - BP support - fluids +/- inotropes and vasopressors - Consider 20% Intralipid IV - Prepare for delivery if required to optimise maternal rescusitation

Answer 9

Cardiorespiratory: * Hypotension * Bradycardia * Respiratory compromise / reduced respiratory effort * Reduced oxygen saturations * Difficulty speaking/coughing * Apnoea * Cardiac arrest (asystole) Neurological: * Nausea + vomiting * Nausea and anxiety * Arm/hand paraesthesia or paralysis\* * High sensory level block * Cranial nerve involvement * Loss of consciousness

Answer 10

Drug factors a. Dose/concentration - Block height more dependent on dose than volume (higher dose gives higher risk) b. Baricity – cephalad spread easier to control with hyperbaric solution c. Prior drug administration – such as epidural local anaesthetic diffusion (unrecognised/sub-clinical block gives higher risk) Patient factors a. Body morphology – higher BMI or abdominal girth (including pregnancy) may reduce thecal volume and increase the risk of high block b. Anatomical or pathological factors – compressed thecal sack (epidural fluid & dilated vessels), spinal canal abnormality can give higher risk 3. Technique factors a. Higher lumbar insertion may increase final block height b. Position at and following injection – sitting may minimise cephalad spread c. Spinal needle – finer gauge and cephalad direction of needle hole may increase risk of higher block

Answer 11

- Bradycardia: Vagolytics e.g. atropine Sympathomimetics e.g. ephedrine, adrenaline - Hypotension: Vasopressors e.g. metaraminol, phenylephrine Fluid bolus Leg elevation - Respiratory dysfunction: Oxygenation, definitive airway, NIV/ventilation - Loss of consciousness: Secure airway Supportive measures

Answer 12

Cardiovascular: * Initial Phase: Hypertension + tachycardia * Intermediate Phase: bradycardia + hypotension * Terminal phase: severe hypotension, arrhythmias e.g. sinus bradycardia, ventricular tachyarrhythmias, respiratory depression / apnoea, cardiac arrest / asystole. Neurological: * Excitatory phase: Perioral tingling, tinnitus, slurred speech, lightheadedness, tremor. May progress to generalized convulsions * Depressive phase: Coma + respiratory depression NB. cardiovascular collapse can occur before ANY neurological symptoms occur

Answer 13

In ml/kg: Lidocaine: 3, Adr: 7 Bupivocaine: 2 Adr: 2 Rupivocaine: 3 Adr: 3 Prilocaine: 6 Adr: -

Answer 14

Patient factors: * Severe renal impairment: reduced clearance * Liver disease: reduced clearance * Severe cardiac failure: susceptible to LA induced myocardial depression and arrhythmias. * Pregnancy: a low α1-acid glycoprotein (AAG) titre results in a higher concentration of free LA

Answer 15

* Miscarriage risk 5-10% (highest in first trimester and if peritonitis) * LBW * preterm labour * stillbirth No convincing evidence of teratogenicity anaesthetic agents - large scale trials do not show increased rates of birth defects above baseline 3%. NB. Benzodiazepines may increase cleft palate and cardiac abnormalities.

Answer 16

Cardiovascular: Uterine perfusion not autoregulated Decreased SVR/PVR - Hypotension common under RA + GA Aortocaval compression requires LLT Respiratory: Increased minute ventilation = Faster inhalation induction Increased oxygen consumption, V/Q mismatch - Potential hypoxaemia, rapid desaturation Upward displacement of diaphragm - difficult ventilation Mucosal oedema - Difficult laryngoscopy + intubation Gastrointestinal: Reduced cardiac sphincter tone and delayed gastric emptying - ↑ Aspiration risk → Antacid prophylaxis, RSI after 18/40