PERI-OPERATIVE PAIN MANAGEMENT

Dr P Chalmers

CP4004 2010 - 2011

IASP definition

“Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”

Mechanism of Pain

Cell Injury→Cytokines,prostanoids→Plasma

Leakage→macrophages, monocytes, mast cells, platelets→Cytokines,prostanoids→

nociceptive nerve endings (C and Aδfibres)

IASP definition

“Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”

Process of Nociception

1. Transduction conversion of pain stimulus into a nerve impulse by sensory receptors

2. Transmission of nerve impulses from the periphery to the brain and spinal cord

3.Perception the recognition of these impulses or signals as pain

4.Modulation whereby descending neuronal tracts from the brain modify the nociceptive transmission in the spinal cord

Opioid system, noradrenergic, GABA, serotonin

Effects of PainNeurohumoral

• Psychological Anxiety• Resp:hypoventilation →hypercarbia and hypoxia hyperventilation• CVS: tachycardia, hypertension, subendocardial

ischaemia• Nausea and vomiting• Sweating• Increased stress response → catabolism

• Outcome:• Prolonged immobilisation and recovery• Prolonged hospital stay

Effects of Analgesia

• Reduces anxiety and stress response• Reduces respiratory complications• Reduces cardiovascular complications• Reduces autonomic effects

• Outcome:• Earlier mobilisation• Shorter hospital stay

Factors influencing pain

• Age

• Site of surgery

• Quality of care

• Patient autonomy

• Patient motivation

Assessment of pain

Intraop: Monitoring CVS, RS

Postop:• Visual cues facial expression body language• Psychological anxiety, restlessness, withdrawal• Verbal response• VAS• Imagery• Universal

Categorical Scale

• Mild

• Moderate

• Severe

• Verbal 1-10

Visual Analogue Scale

Facial Scale

Management of Acute Pain

• Multimodal

• Pharmacological

• Neural Blockade

Why multimodal

• Synergism

• Opioid sparing

• Reduced risk of tolerance and morphine sensitisation

• Reduced side effects and complications

• Pre-emptive

Pharmacological

• Opiods

• Paracetemol

• NSAIDS

Mode of Administration

• Oral

• IM

• IV Boluses continuous infusion PCA

• PR

0 4 8 Hours

Pla

sma

conc

→

PCAIM

Advantages and disadvantages of im v PCA administration

IM PCA

Delayed onset Rapid onset

Fixed dose Dose matches pain

Painful Painless

Fluctuating plasma levels Continuous plasma levels

Gradual onset of Technical error or failure

side effects may be fatal

Enhances patient autonomy

Neural Blockade

Neural Blockade

Neuroaxial: Spinal

Epidural

Regional Blockade

Skin Infiltration

Local anaesthetics

Adjuvants

Requirementsfor Neural Blockade

• Consent

• Sterile condition

• Vascular access

• Monitoring

• Resuscitation equipment

• No clinical contraindications (coag,infections,allergies)

Epidural procedure

Epidural procedure

Spinal

Epidural

Epidural Infusion Pump

Effects of Neural Blockade

• Sensory Loss

• Muscle Paralysis

• Autonomic Effects (spinal, epidural)

ALWAYS aspirate before injection

beware of accidental intravascular administration

Complications Neuro-axial Block(spinal/epidural)

• Hypotension• Backache• Spinal cord/nerve root compression

(haematoma/abscess)• Dural headache (epidural)• Overextensive block • Total Spinal Block • Accidental Intravascular injection• Side Effects of drugs LA’s Opiods

Advantages of epidural analgesia

• Excellent analgesia for 72hrs or longer

• Avoids side effects of opiods

• Improves postop respiratory function

• Reduces thromboembolic phenomena

• Reduces incidence of persistent post surgical pain

Local anaesthetics

• Lignocaine

• Bupivicaine

• Levobupivicaine

• www.4um.com/tutorial/anaesth/Locals.htm

Lignocaine Bupivicaine

Onset of Action Fast Medium

Pka 7.9 8.1

% unionised 25 15

Weak bases mostly ionised at pH 7.4

Lignocaine Bupivicaine

Potency 1 4

Lipid solubility 150 1000

Lignocaine Bupivicaine

Duration of action medium Long

% protein bound 70 95

Vasoactivity Dilatation at lo doses ++

Constriction at hi doses+

Dilatation at lo doses +

Constriction at hi doses++

Lignocaine Bupivicaine Laevo-bupivicaine

Onset of action

2-4 min

rapid

10 min

Duration 30-90min

medium

3-7hrs (16hrs)

Long

3-7hrs (16hrs)

Dosage 3mg/kg/4hrs

(adr 6mg/kg)

2mg /kg/4hrs

(adr 2 mg/kg)

Max dose 150mg; 400mg/24hrs

Local anaesthetics

Adrenaline 1:200,000=5micrograms/ml

Never used in spinals and epidurals

Max dose 8ug/kg/hr = 20mls of 1in 200,000/hr

Lignocaine Bupivicaine Laevo-bupivicaine

Toxic plasma conc ug/ml

>5 >1.5

Toxicity CNS +++ Cardiac +++

Cardiac +

Management of toxicity

• R/Lipid emulsion 20% a bolus of 100mls followed by an infusion of 400mls over 20min (approx 0.25mls /kg/min) Repeat if necessary

• PLUS supportive measures anticonvulsants, inotropes etc

Adjuvants in neural blocks

• Opiods→pruritus,delayed onset resp depression, nausea, vomiting

• Clonidine

Pain Syndromes

• Sensitisation occurs in response to repeated or prolonged noxious stimuli: lower activation threshold ,increased rate of firing

a. peripheral: Increased sensitivity and excitability of nociceptive receptors and damaged nerves

b.central: hyperexcitability of spinal neurones and descending modulating pathways

Activation of NMDA receptors

Pain Syndromes

• Opioid Induced Hyperalgesia : the use of opioid paradoxically increases the patient’s perception of pain excitatory descending modulating pathways

• Persistent Post Surgical Pain Syndrome The response outlives the initiating stimulus and lasts for 3 months or more

Risk Factors • History of poorly controlled pain (preoperatively and perioperatively)• Intraoperative nerve damage (surgical, anaesthetic)• History of preoperative neuropathic pain• Co-morbidities associated with neuropathy:Diabetes, alcohol abuse, uraemiaDrug induced neuropathyNutritional deficiency,vitB12, B6,• Malignancy• Chem/radiotherapy• Impaired immune system• Fibromyalgia• Major trauma• Depression/anxiety (the unemployed)

Prevention of Pain Syndromes

• Efficient and effective pain management in the perioperative period

• Multimodal analgesia with neuroblockade regular acetaminophan and Nsaids and opioids

• On going research regarding perioperative use of antihyperalgesic agents:

Pregabalin gabapentin NMDA receptor antagonists eg Ketamine Alpha agonists eg clonidine

Any questions ???