Anaesthesia + Analgesia Flashcards
What is full cervical dilation?
10 cm
Describe pain transmission in the first stage of labour
Repetitive uterine contractions
Visceral - crampy, poorly localised
Slow, unmyelinated C fibres
- paracervical ganglion
- lumbar sympathetic chain
Uterus: T10-L1
Describe pain transmission in the second stage of labour
Repetitive uterine contractions + distension of pelvic + perineal structures
Somatic - well localised, sharp pain
Fast, myelinated A delta fibres - lumbo-sacral plexus
- pudendal nerves
- ilio-inguinal
- genito-femoral
- perforating branch posterior cutaneous nerve of thigh
Perineum: S2-S4
How is pain modulated in the spinal cord?
- Afferent pain neurones enter dorsal horn
- Synapse in substantia gelatinosa
- Interneurones effect sensitivity of secondary afferents
- Secondary afferents cross + ascend in spino-thalamic tract
What role do C fibres play in spinal cord pain modulation?
- C fibres stim secondary afferents
- Inhibitory interneuron suppressed
- Strong pain stimulus transmitted via 2nd order neurone
- Pain gate = open
What role do AB fibres play in spinal cord pain modulation?
- AB fibres stim inhibitory interneurones
- Reduced transmission of pain to secondary afferents
- Pain gate = closed
How is Entonox used and what are the side effects?
- Gas & air
- Analgesic, sedative, euphoric
- Rapid on/offset
- Nausea + vomiting
- B12 inactivation
How do opiates (e.g. Naloxone) work and what are their side effects?
- Widespread in CNS
- GPC
- Hyperpolarize neurones, reduce excitability
- Analgesic + Euphoria
- Nausea, Sedation, Resp depression
- IV/IM
- Readily cross placenta
What is the most commonly used opiate for labour pain management in the UK?
- Pethidine
- IM
- Analgesic
- Sedative
- Nausea + vomiting
What are the types of neuraxial analgesia?
Epidural
Spinal
What is the route of epidural anaesthesia administration?
Skin > Subcut tissue > Supraspinous L > Interspinous L > L Flavum > Epidural space
Compare the onset of epidural vs spinal anaesthesia
Epidural
- Slow as local anaesthetic outside dura
- Catheter - prolonged effect
Spinal
- Rapid onset
- Dense block
- Single injection
What is the route of spinal anaesthesia administration?
Skin > Subcut tissue > Supraspinous L > Interspinous L > L flavum > Epidural space > Dura
Below conus L1-2
Pierce dura + aspirate CSF
What are the contraindications for neuraxial anaesthesia?
- Abnormal spinal anatomy - spina bifida + lumbar fusion
- Impaired coagulation - risk spinal haematoma
- Infection - risk abscess/meningitis
- Fixed CO - severe aortic stenosis, massive haemorrhage
What are the complication of nauraxial anaesthesia?
- Failure - incorrect placement/anatomical
- Dural puncture headache - CSF leak, low pressure headache
- High block - total spinal
- Nerve damage - direct-connus, nerve root, indirect - haematoma, abscess
- Meningitis
- LA toxicity - wrong route administration
