Anaesthesia is used to
allow the performance of surgery or interventional procedures
Anaesthesia is a combo of
- Analgesia (pain control)
- Amnesia (loss of memory)
- Muscle relaxation (loss of movement)
Anaesthesia types
general
Neuroaxial- spinal/ epidural
– Peripheral nerve block
– Intravenous regional block
General Anaesthesia 3 stages
- Induction
- Maintenance
- Emergence
General Anaesthesia induction stage
from administration of anesthesia to
ready for incision
General Anaesthesia maintanence stage
- From incision to near completion of procedure
- Volatile or intravenous anaesthetics used (volatile gases are cold & drying)
General Anaesthesia emergence stage
Starts when the person emerges from anaesthesia & is ready to leave the operating room (waking up)
Effects of GA on the Respiratory System
Related to secretion movement
- Reduced cilial activity
- Drying of secretions (atropine)
- increased secretion production
- Loss of cough reflex
Effects of GA on the Respiratory System
Related to gas movement
- Reduced minute ventilation (reduces RR, VT or both)
- Decreased respiratory drive
- reduces FRC (atelectasis -> hypoxaemia)
- Loss of hypoxic vasoconstriction (hypoxaemia)
FRC progressively reduces with:
- Supine position
- Induction of anaesthesia
- Paralysis (diaphragm)
- Certain positions for surgery
(eg HDT)
Neuroaxial Anaesthesia
- With the patient awake, local anaesthetic is introduced via the ‘spine’
- Blocks pain +/- motor and sensation
- Smaller volume of local anaesthetic required than GA
Effects of GA on the Cardiovascular System
- Myocardial depression
– Drugs may reduce contractility (SV) and therefore CO - Abnormal rates & rhythms
- Reduced blood pressure
Spinal vs epidural anaesthesia
– SPINAL:
* small gauge needle inserted into the subarachnoid space
– EPIDURAL:
* small gauge catheter placed into the epidural space
Neuroaxial Anaesthesia
* Benefits
– Reduced incidence of thrombotic complications such as
DVT, PE
– Beneficial for patients with chronic respiratory conditions
by avoiding detrimental respiratory effects of GA
Neuroaxial Anaesthesia complications
– Post-dural puncture headache
– Spinal haematoma
– Vasodilation
Peripheral Nerve block used for
procedures involving theextremities
Intravenous Regional block
Local anaesthetic and double tourniquet
Post-operative pain influenced by
– Site and duration of the surgery
– Extent of incision and surgical trauma
– Physiological and psychological aspects of the patient \previous experience of pain
NSAIDs site of action
Peripheral action – act at the site of injury to reduce the pain associated with an inflammation
Epidurals site of action
Act at the spinal cord level
Local anaesthetics site of action
Alter nerve conduction to act locally
Opioids and some antidepressants site of action
Alter central perception of pain by modifying signal transmission in the dorsal horn. Can also effect the emotional aspects of pain
- Patient Controlled Analgesia (PCA)
– Self administration of small doses of IV analgesics by the patient
– Immediate and effective
– Useful for incident pain eg
* Before physiotherapy, eg coughing
– Tailored to the needs of the individual
Epidural aim PCEA
– Aim to provide pain relief with no loss of power or sensation
