Acute Pain managementand Intensive care Unit Dr Li Luk Sing 29 May 2010
Definition of Pain • 疼痛? • Pain?
Definition of pain • An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
Problems of unrelieved pain • Patient discomfort & distress • Hyperventilation, resp alkalosis • ↑O2 demand • Thoracic pain impairs lung expansion, ↓thoracic compliance • ↑neuroendocrine stress response • ↓immune function • Gastric stasis/ileus/nausea/vomiting • Delays post-operative mobilization • Venous stasis/platelet aggregation→DVT • Prolongs hospitalization
Predictive factors for chronic post surgical painPerkins & Kehlet 2000 • Pre-op: • Moderate to severe pain lasting > 1 month • Repeat surgery • Psychological vulnerability • Worker’s compensation • Intra-op: • Nerve damage • Post-op : • PAIN (acute-moderate-severe) • Radiation therapy to area • Neurotoxic chemotherapy • Depression • Psychological vulnerability • anxiety
Factors Affecting the Postoperative Pain • A. Surgical factors: • Site of incision and nature of the surgery • upper abdomen > thoracotomy > lower abdomen > limbs • Complications, e.g. wound infection, intraabdominal sepsis, distension • B. Patient factors: • Psychology, genetic, hx of substance abuse, hx of chronic pain
Principles of pain management • History, physical examination, investigation, associated medical problems • Assess the severity of pain • assessment scales • Post op acute pain assessment form : PY/RH • Select appropriate therapy (tx underlying cause) • Assess response to treatment • Detect and treat side effects • Multimodal analgesia • +/- multidisciplinary approach
Common analgesics • Paracetamol • Dologesic (contains paracetamol) • Detropropoxyphene (doloxene) • Doloxene CO (with caffeine/aspirin) • Codeine/ DF118 • Tramadol • NSAIDs • Opioids : pethidine/ morphine/ methadone
Dextropropoxyphene • ? Lack of analgesic effect • QT-interval prolongation and Torsade de pointes. • Metabolite: nordextropropoxyphene. (mean half life 29 hours)
Codeine • Weak mu-receptor agonist. • CYP2D6 P450 isoenzyme
Pethidine • Synthetic opioid. • It was not better than morphine in treatment of renal colic (O’Connor et al 2000 level II) • Metabolite: norpethidine: neuroexcitory effects.
Tramadol • Opioid agonist and a serotoin and noradrenaline reuptake inhibitor. • Lower risk of respiratory depression. • The combination of tramadol with panadol was more effective than either of its two components administered alone (level I)
Ketamine • NMDA receptor antagonists. • Bolus dose of ketamine was an effective ‘rescue analgesic’ in patient with acute postoperative pain that was poorly responsive to morphine (level II) • Perioperative low-dose of ketamine used in conjunction with PCA morphine is opiod-sparing and reduce PONV (level I)
Routes of administration • Oral = preferred route, except in cases of vomiting, delayed gastric emptying, swallowing impairment • Intramuscular – beware: absorption may be impaired in hypovolaemia, shock, hypothermia • Rectal – uptake into venous plexus, bypass hepatic first pass metabolism • Intravascular – bolus/ continuous infusion/ PCA • Neuraxial – epidural/spinal • Topical • Subcutaneous – seldom used in HKEC • Others – intranasal, sublingual, buccal, pulmonary (inhaler)
A word on opioids • Opioids classified into weak/intermediate/strong • According to receptor binding affinity • Can be another lecture • Weak : dextropropoxyphene, codeine • DF118 = synthetic derivative of codeine • Intermediate : pethidine (+/- tramadol) • Equal in strength to pethidine, opioid agonist + 5HT/noradrenaline re-uptake inhibitor • Lower risk of respiratory depression & less G.I. Inhibition than other opioids at equianalgesic doses • Strong : morphine, methadone, fentanyl
Multimodal analgesia • Combinations of analgesics that act by different mechanisms result in additive or synergistic analgesia • reduces the total dose of analgesics required • reduces risk of side effects • Most studies demonstrate a decrease in pain scores or postoperative analgesic requirements with multimodal analgesia • Examples • NSAIDs, panadol, ketamine“morphine sparing effect” • LA infiltration of wound • Epidural analgesia/regional block. • “balanced analgesia”
Patient controlled analgesia PCA • Intravenous morphine bolus administered via a PCA device, activated by a handset operated by the patient • PCA device • Microprocessor-controlled syringe driver • Handset for patient initiates bolus: small, frequent boluses, avoid large swings in plasma concentration, titration by patient • Syringe can be locked • Programme cannot be altered by unauthorized person • Alarms: line occlusion, low battery, empty syringe, max dose exceeded • Meaning of “4 hour limit”
Patient controlled analgesia PCA • Ivi opioid PCA provides better analgesia than conventional parental opioid regimes (level I) • The addition of background infusion to ivi PCA does not improve pain relief or sleep, or reduce the number of PCA demands (level II), but increase risk of respiratory depression.
PCA Prescription • Loading dose • Bolus dose • Lockout interval • Background infusion • Dose limit
Bolus dose • The amount of analgesic drug the patient receives after a successful demand. • 0.5mg, 1.0mg, 1.5mg and 2.0mg morphine • Optimal dose: 1mg morphine
Lockout interval • The time following the end of the delivery of one dose until the patient is able to successfully obtain another dose • Safety mechanism • 5-10 minutes.
Dose limit • Limits to the maximum amount of opioid that can be delivered over a certain period • 1 hour or 4 hours
Complication of PCA • Operator-related error • Patient-related errors • Problems due to equipment used • Side effects of PCA opioid
Operator errors • Those related to programming. • Wrong drug • Inappropriate prescription of concurrent medications.
Patient related errors • Failure to understand the technique • PCA by proxy
Complications related to PCA opioid • Respiratory depression(1.2-11.5%) • Nausea (32%) • Vomiting (20.7%) • Pruritus (13.8%)
Epidural analgesia 硬膜外麻醉 • Central neuraxial block • Small catheter inserted into epidural space, where nerve roots come out from the spinal cord • Drugs used: local anaesthetic +/- fentanyl +/- morphine • Target delivery of opioid to spinal cord opioid receptors, less dose required → less systemic side effects, better analgesia • EA dose = 10% of IV dose
Level I evidence • Epidural analgesia • Provide superior analgesia than PCA. • Improve oxygenation and reduce pulmonary infection and other pulmonary complication compared with ivi opioid. • Is not assoicated with increase risk of anastomotic leakage after bowel surgery
Level I evidence-thoracic epidural analgesia • For open abdominal aortic surgery reduces the duration of tracheal intubation and mechanical ventilation and incidence of MI. • Used for CABG reduces postoperative pain, risk of dyrhythmias, pulmonary complications and time to extubation compared with ivi opioid analgesia. • Improves bowel recovery after abdominal surgery and colorectal surgery. • Extended > 24 hours reduces the incidence of postoperative MI. • Reduces need for ventilation in patient with muliple rib fracture and reduce incidence of pneumonia.
Removing epidural catheters • Acute pain management protocols available on HKEC website • “protocols/guidelines” • Anaesthesia • Acute pain management • Check with anaesthetist – no contra-indications (e.g.. hepatectomy, clotting derangement) • Don’t pull hard if resistance felt • Make sure “blue tip” (catheter end) intact after removal • documentation
Minimum effective length of epidural catheter in Space • Expert opinion = 2cm
Shift out 2cm at marking 11cm • Should we inform oncall pain team if patient control is satisfactory?
Shift out 2cm at marking 11cm • Catheter in space =11cm-8cm (catheter in space) = 3cm • The minimum effective length of epidural catheter in Space = 2cm. • 3cm > 2cm
Pain team consensus • If satisfactory pain control and • The minimum effective length of epidural catheter in Space = 2cm. • Can inform us next morning/pm pain round.
Any doubt • Inform pain team or anaes 2nd call
Adverse effects of epidural analgesia • Neurological injury • Epidural haematoma • Epidural abscess • Respiratory depression • Hypotension • Postural puncture headache • Treatment failure
Neurological injury • 1: 3600 • Transient neuropathy • Permanent neurological deficit
Epidural haematoma • With subsequent potentially permanent spinal cord injury. • 0.0005% • Immediate decompression (<8 hrs after the onset of neurological signs increase the likelihood of partial or good neurological recovery (level IV)
Epidural abscess • 0.015% to 0.05% • 71% of all patient had back pain as the initial presenting symptoms. • Only 66% were febrile. • The classic triad of symptoms (back pain, fever and neurological changes) was present in only 13% of patient.
Epidural morphine-induced Pruritus • 60%. • ? Non-dose dependent • Itch Centre in medulla • Piriton • Propofol • Naloxone • Droperidol • 5 HT3 recepton antagonist- ondansetron