This topic hasn't yet been a CRQ question, though the curriculum asks for knowledge of 'the management of incomplete or failed regional blockade including, where appropriate, the use of rescue blocks '.
There is no current universal definition of block failure, though overall describes any block where there is inadequate analgesia or anaesthesia within a suitable time frame to allow the planned procedure to take place, without the need for additional intervention
The incidence varies on the type of block performed:
Contributory Factors
Hurdles to communication e.g. language barrier, visual or hearing impairment
Improper expectation management
Obesity
Sarcopaenia
Factors affecting positioning e.g. arthritis, limb contractures
Ehlers-Danlos syndrome i.e. LA resistance
Inadequate knowledge of appropriate dermatome, myotome and osteotome distribution
Inadequate knowledge of ultrasound anatomy
Patient anatomical variations e.g. pre-fixed or post-fixed plexus
Anatomy obscured by presence of implants at intended injection site e.g. pacemaker, VP shunt
Lack of familiarity with equipment inc. ultrasound
Reduced experience
Poor ergonomics
Incorrect LA choice for required onset and duration
Inadequate time given for block to work
Incorrect deposition of LA - some suggestion circumferential and/or longitudinal spread is superior
Changing surgical approach e.g. different incision, lengthening incision
Longer-than-anticipated duration of surgery
Tourniquet pain; not covered by the block or refractory to block
Block assessment
There's no consensus on the best method for formal block testing
One should be mindful that altered nerve function appears sequentially: sympathetic first, then sensory, then motor
Methods include:
Temperature sensation over relevant dermatomes vs. contralateral side
Altered sensation to pain
This may include cessation or reduction of existing pain
Reduced soft-touch sesnation
Motor block
Management of failure
In all cases, appropriate communication between the surgical & anaesthetic teams and the patient is necessary
One should plan interventions in case of failure ahead of time e.g. top-ups, rescue block, GA or even abandoning surgery
Inadequate anaesthesia or analgesia prior to surgery starting may necessitate:
Allowing more time for the existing block to work
Top-up existing block if maximum LA dose hasn't been exceeded
If surgery has already begun, the intervention required will depend on exact nature of symptoms:
Those with no pain but anxiety/discomfort can be offered reassurance and (if appropriate) procedural sedation e.g. midazolam, propofol
Those with tourniquet pain may benefit from short-acting opioid or low-dose ketamine analgesia
Those with surgical site pain may benefit from surgical LA top-up (if maximum dose not reached) ± short-acting opioids
If none of the above is working, either GA may be required or abandonment of surgery if GA is contra-indicated