Compartment syndrome and rhabdomyolysis and pain management Flashcards
Scenario: 28 yr old male, leg crushed for a few hours, left unobserved on orthopaedic ward. Bloods: AKI. Urine dip: blood.
What are the complications?
-Compartment syndrome
-Rhabdomyolysis
What is the clinical picture of compartment syndrome?
-Worsening pain: this may be out of proportion to the injury
-Paraesthesia: especially the loss of two point tactile discrimination
Clinical signs
–> tense and swollen compartments
–> sensory loss
–> pain on passive stretching
Loss of regional pulses which is a LATE sign
How to diagnose compartment syndrome in a patient with altered sensorium or sensorimotor deficit
This can be achieved by:
–> measurement of intercompartmental pressure, tissue pressures of >30mmhg suggest decreased capillary blood flow, which can result in muscle and nerve damage from anoxia
–> blood pressure: the lower the systemic pressure, the lower the compartment pressure that causes compartment syndrome
What is a normal compartment pressure?
0-15mmhg
If >30, indication for fasciotomy
What is the treatment for compartment syndrome?
Emergency fasciotomy e.g. in lower leg 4 compartment fasciotomies through 2 incisions as an emergency procedure
What will you say to the patient when you consent for fasciotomies?
-Explain operation, complications (permanent nerve damage, permanent muscle damage, permanent scarring, loss of affected limb, infection, kidney failure, in rare cases death
Why would you get acute renal failure in compartment syndrome?
–>Rhabdomyolysis
–>accumulation of myoglobin in renal tubules leads to tubular obstruction
–> formation of obstructive casts with uric acid
–> low blood pressure can lead to renal arteriole vasoconstriction and relative reduced blood flow
–> together these processes lead to ATN
–> nephrotic effect of myoglobulin precipitating in renal tubules
–> decrease extracellular volume –> vasoconstriction
–> renal tubular ischaemia and necrosis
–> myoglobulin, uric acid –> obstructive cast formation
What is myoglobin?
-O2 binding protein found in muslces
What is the definition of rhabdomyolysis?
-The release of potentially toxic muscle cell components into the systemic circulation
What are the causes of rhabdomyolysis?
-Blunt trauma to skeletal muscle e.g. crush injury
-Massive burns
-Hypothermia or hyperthermia
-Ischaemic reperfusion injury e.g. clamp on artery during surgery
-Prolonged immobilisation on hard surface
-Strenuous and prolonged spontaneous excercise e.g. marathon running
-Drugs e.g. statins, fibrates, alchohol
What are the biochemical results in rhabdomyolysis?
-Increased CK >5 times normal
-Increased lactate, LDH, creatinine
-Electrolyte disturbances:
—> hyperkalaemia (and metabolic acidosis with increased anion gap)
—> hypocalcaemia(myocyte necrosis is associated with calcium influx into cell)
–> hyperphosphataemia
–> hyperuricaemia
-Myoblobinuria suggested by positive dipstick to blood in abscence of haemoglobinuria (red cells on microscopy)
What is the managementof rhabdomyolysis
-ABC
-> fluid resus: ensure good hydration to support UO >300ml/hr using IV crystalloid until myoglobinuria has ceased
–> diuretics (manittol) may be used
–> alkalinisation of urine: NaHCO3 to prevent renal damage
–> treat electrolyte disturbance (hyperkalaemia
–> monitor ECG, electrolytes,
NaHCO3:
–> tamm horsfall protein precipitates at lower ph, so prevents cast formation
Define pain
Unpleasant sensory and emotional experience associated with actual or potential tissue damage
What are the side effects of opioids?
-Respiratory depression
-Nausea/vomiting
-Constipation
-Urinary retentaion
Chronic use
-Hypogonadism
-Immunosuppression
-Withdrawal
What is the pain pathway?
Pain is tramsmitted via fast A-delta fibers (sharp pain) and slower C fibers (dull pain) to lateral spinothalamic tract and then to thalamus
What is patient controlled analgesia?
-Syringe pump connected IV to allow patient to self-administer boluses of morphine
-Overdosage is avoided by limiting size of bolus and frequency of administration
-Lock out time is set within which pressing the button again will not result in a bolus of analgesia
-One way valve preventing backflow of opiates into the infusion chamber which may lead to overdose when redelivered
What is normal dose of morphine pca?
0.5-2mg bolus
What are the disadvantages of a PCA?
-Patient has to be alert and orientated to use it
-Can break down, run out of battery
-Sleep disturbance
-Limits patient mobility
What are the complications of pain?
CVS
-Increased HR, BP, myocardial consumption –> increased risk of MI
-DVT from immobility
GIT
-delayed gastric emptying
-Reduced bowel motility
-Paralytic ileus
Respiratory
-Limits chest movements leading to atelectasis, retained secretions, pneumonia
How would you manage patient in post op pain?
-A-E assessment
-Assess severity with pain scale
-Give analgesics according to WHO ladder with regular assessment
Non pharmacological methods:
–> cold or heat
–> Immobilisation of injured limbs
–> TENS`
Give examples of opioids in common use. Which are synthetic and which are non synthetic?
-Non synthetic: morphine, codeine (10% metabolised to morphine)
-Semi-synthetic: diamorphine, dihydrocodeine
-Synthetic: pethidine, fentanyl
Why is codeine bad?
-Drowsiness, constipation, orthostatic hypotension
-CYP2D6 enzyme converts codeine into morphine in the liver
-Some patients have high levels of this enzyme, resulting in rapid metabolisation to morphine, causing over-intoxication which can cause respiratory depression
-Some patients have less of this enzyme and therefore lose analgesic affect while still suffering side effects
What is the mechanism of action of paracetamol?
-Mechanism poorly understood
-Generally considered to be weak inhibitor of prostaglandin production
-In vivo effects similar to COX 2 inhibitors
How would you manage paracetamol toxicity?
-Activated charcoal 30mins-2 hrs ingestion
-Acetylcysteine: antidote replenishing body stores of antioxidant glutathione
-Liver transplant in acute liver failure
What different pain scoring systems are there?
-Verbal numerical rating scale 0-10
-Visual anaglogue scale (mark on 10cm line no pain to worst imaginable)
-Wong-baker FACES (children)
What is epidural anaesthesia?
Epidural anaesthesia is a form of regional anaesthesia that involves injection/infusion of anaesthetic medidcation into epidural space
What are features of an epidural?
-Drug injected into epidural space
-Can be performed at any level along spinal column
-Slow onset (15-25 minutes)
-Large volume (10-20ml) LA +/- opioids
-Large needle (16G) used
-Usually epidural catheter is inserted for repeated doses or infusions
Spinal features:
-Drug injected into subarachnoid space
-Can be performed at level below termination of spinal cord
-Rapid onset (usually <5 minutes)
-Small volume (2-4ml) LA +/- opioids
-Single shot given with thin needle (25G)
What are diffeneces between epidural and spinal?
-Space injected (Epidural vs subarachnoid)
-Level performed (any level vs below termination)
-Onset (slow vs rapid)
-Volume injected (large vs small)
-Needle used (large vs small)
-Number of infusions (multiple vs few)
Describe layers encountered when inserting needle into epidural space
-Skin
-Subcut fat
-Supraspinous ligament
-Interspinous ligament
-Ligamentum flavum
Describe the effects of epidural analgesia
Sympathetic block of transmission of signals through nerve roots near the spinal cord
How can epidurals cause bradycardia?
-‘High epidural block’: spread of LA affecting spinal nerves above T4
-blocks cardio-accelerator fibres
-Leads to unopposed parasympathetic action of vagus nerve
What is a high epidural block?
-Results from excessively large dose of local being injected into epidural space
-Spread of LA affecting nerve roots above T4
-Hypotension, sensory loss or paraesthesia high thoracic/cervical nerve roots
-Bradycardia: blocking of cardio-accelerator fibres leading to unopposed parasympathetic cardiac innervation via vagus nerve
-Dyspnoea due to blockade of nerve supply to intercostals + diaphgragm
How would you assess level of epidural blockade?
-Pain and temp are conducted by same nerve fibre types
-Therefore the only appropariate test is to assess ability to detect cold stimulus which is impaired in blocked dermatomes with either ice or ethyl chloride spray
How do you treat hypotension resulting from epidural block? What is mechanism behind hypotension?
-Pt is hypotensive due to vasodilatation secondary to sympathetic block
-Stop epidural
-IV fluid resuscitation
-Vasoconstrictor drugs: metaraminol
What is the mechanism of high epidural block induced bradycardia? How is it treated?
-Cardio-accelerator fibres originate between T1-T3. Epidural/spinal blockade results in bradycardia from unopposed parasympathetic (vagal) tone
-This is treated with atropine or glycopyrrolate
-Sometimes adrenaline, dobutamine or isoprenaline may be needed
Describe the WHO analgesic ladder
-Mild pain: simple oral analgesics e.g. paracetamol, NSAIDs
-Moderate pain: combined therapies, oral weak opioids eg. tramadol, codeine
-Strong pain: opioids +/- oral analgesics e.g. IV/IM opioids, PCA
-Epidural
