- Email: [email protected]
Implantable technology for pain management
PAIN
Implantable technology for pain management
Patient selection by clinical group Site of lesion Peripheral nerve • Peripheral nerve lesion
John Hodkinson
Clinical group
Trauma, incision, amputation, stump pain
• Complex regional pain syndrome (CRPS) Spinal cord • Mixed neuropathic nociceptive • Peripheral nerve lesion • Neuralgias • Plexopathies • Radiculopathies • Myelopathies • Polyneuropathies • CRPS • Refractory angina
Implantable devices for managing chronic pain by neuromodulation evolved from spinal regional anaesthesia. In 1998, their use was assessed by the European Federation of Chapters of the International Association for the Study of Pain, and a consensus from this task force stated ‘Neuromodulation procedures offer a non-destructive reversible alternative to the treatment of severe chronic pain where less invasive therapies and/or neurodestructive procedures are not effective or contraindicated’. The procedures involve stimulation of the peripheral nerve, spinal cord, deep brain or motor cortex and drug delivery by the intraspinal or intracerebroventricular route. They should be performed in Pain Treatment Centres by a multidisciplinary team trained in patient selection and education, behavioural and psychological assessments and therapy, surgical implantation of the devices, and continuous aftercare.
Chronic mixed spinal pain, failed back syndromes Entrapment, trauma, amputation Post-herpetic Traumatic avulsion, post-radiation Cervical, lumbar disc, osteoarthritis Spinal cord incomplete lesion, injury Diabetes, post-chemotherapy CRPS type II Occlusive coronary artery disease, syndrome X • Peripheral vascular disease Atherosclerosis, vasospastic, Raynaud’s disease, Buerger’s disease, CRPS type I • Abdominal/pelvic Chronic pancreatitis syndromes
General selection criteria Patients are suitable for an implantable device if other conservative or interventional (surgical) treatments have failed and there is no intention of pursuing those routes. The patient must give informed consent, have a realistic expectation of the outcome and a high degree of cognitive motivation. Patients are unsuitable if they have: a severe coexisting medical disease; a major psychiatric disorder or illness-seeking behaviour; poor understanding, social support or compliance; or if they abuse drugs. In 2004, the Pain Society conducted a national survey of psychological assessments before implantation; guidelines may follow.
Deep brain • Thalamic nuclei
• Periventricular aqueductal grey matter Motor cortex • Neuropathic
Neuromodulation by stimulation In 1965, Melzack and Wall demonstrated the gate control theory of pain. According to the theory, electrical stimulation of large diameter low threshold Aβ proprioceptive sensory nerve fibres causes suppression of small diameter high threshold Aδ and C sensory fibre activity within the dorsal horn of the spinal cord. Antidromic and summation loops are involved following stimulation of the peripheral nerve, spinal cord, deep brain or motor cortex. Targets for stimulation and sensory projection vary with the patient and are unmapped. Stimulation of the spinal cord also influences sympathetic and parasympathetic activity with an autonomic response. Neuromodulation within the CNS by stimulation
Post-herpetic neuralgia, cluster headache, post-stroke, phantom pain
1 is governed by the gene–peptide link and the release and reuptake of neuropeptides within groups of wide dynamic range neurons, particularly of the dorsal horn. Release of vasoactive peptides influences peripheral vascular tone and myocardial perfusion. The types of stimulation required for each clinical group are listed in Figure 1. Specific selection criteria for the most commonly treated conditions are given in Figure 2. Equipment insertion and implantation Stimulation electrodes are cord or paddle shaped, unipolar or multipolar (1–8), single or dual, parallel or in line with anode/ cathode availability (Figure 3). The electrode can be placed perineural (e.g. for peripheral nerve stimulation) or extradural via a percutaneous needle (e.g. for spinal cord or deep brain stimulation) or surgical laminotomy (e.g. spinal cord stimulation) or craniotomy (e.g. motor cortex stimulation). Computer-aided stereotactic imaging and cortical mapping are used to guide the
John Hodkinson is Consultant in Pain Medicine to Morecambe Bay Health Authority NHS Trust, Cumbria, and Director of Furness Pain Management Service. He qualified from Manchester University and pursued a career in anaesthesia and then pain medicine in the UK, Europe and the USA. His research interests include neuromodulation, spinal stimulation and pain management programmes.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
Trigeminal neuralgia, post-herpetic neuralgia, stump or phantom pain, spinal cord lesion, post-stroke pain Chronic mixed failed back, neuropathic pain
61
© 2005 The Medicine Publishing Company Ltd
PAIN
Specific selection criteria for spinal cord stimulation Chronic low back pain • Failed conservative therapies • Pain experienced correlates with observed pathology • No further surgical intervention indicated • Drug habituation has been treated • Psychological evaluation clearance • No contraindications (e.g. sepsis, coagulopathy) • Successful trial screening
• Optimum medication without adequate pain relief or restoration of function • No planned revascularization procedures • Syndrome X (no occlusive vascular disease) • No implanted demand fibrillation or pacing devices Peripheral vascular disease • Acceptable concomitant disease status • Fontaine Classification Grade III: ulcer > 3 cm2; transcutaneous oxygen pressure 10–30 mm Hg; ankle–brachial index < 0.4 • No peripheral gangrene • No planned or further reconstructive surgery
Refractory angina • Reversible ischaemia of coronary artery disease • Within New York Heart Association classification 3–4
2
Spinal cord stimulation Internal power source
External power source
Electrode lead Extension External antenna Receiver External transmitter Pulse generator
PISCES-Quad Plus Lead
Needle placement – epidural Electrode
Radiopaque marker band Electrode
Tuohy needle
Stylet connector
0
1
2
3
Electrode numbers Stylet Leads contacts
3 placement of deep brain and motor cortex stimulation. Electrode placement for spinal cord stimulation uses continuous fluoroscopy and evoked sensory stimulation (paraesthesia) as experienced by the patient at the time of placement. Figure 4 lists the common electrode placement sites. A trial period of stimulation precedes
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
implantation of the pulse generator, which is usually placed in the abdominal wall within a subcutaneous pocket with a hardwire connection lead to the electrode through a percutaneous tunnel. An aseptic technique with broad-spectrum antibiotic prophylaxis for Staphylococcus is used.
62
© 2005 The Medicine Publishing Company Ltd
PAIN
brain stimulation), 50–85 Hz (spinal cord stimulation), 100–150 Hz (peripheral nerve stimulation), and a pulse width of 200–500 microseconds. Various waveform, operational and cycling modes are available and combinations of stimulation arrays within multipolar channels. Stimulation can be achieved bilaterally with a single electrode placed at the physiological midline. Interesting effects of concentrated stimulation (‘sweet spot’) can be achieved by anode/cathode variation across the dorsal columns with parallel dual electrodes (Figure 5). Follow-up evaluation is essential. Usage guidance is provided by audit of patient experience and demand, and reprogramming of variables is often required. Fully internalized battery-operated electronic systems are reprogrammed by transcutaneous computerized telemetry. Palm computers contain software for downloading and reprogramming devices with on-line wire-less data transfer, which allows remote analysis and reprogramming.
Electrode placement for stimulation Stimulation mapping Spinal cord stimulation • Chronic mixed low back pain • Chronic mixed neck pain • Angina chest wall pain • Peripheral vascular disease of arm • Peripheral vascular disease of leg Deep brain stimulation • Central pain
Motor cortex stimulation • Central pain
T9–L1 C2–T1 C7–T2 C6–T1 T11–L1
Periaqueductal and periventricular thalamic projections Broca motor cortex projections
Complications Wound infection occurs in 5% of cases, and 3% of implants require removal. Epidural abscess or haematoma may require surgical decompression. Electrode migration occurs in 35% of cases, and 23% require re-implantation. Electrode fracture occurs in 5%, and discomfort at the implantation site occurs in 13%.
4
There are various implantable programmable devices activated by internal battery or transcutaneous radiofrequency induction, operated by the patient using a hand set (Figure 3). Operation variables vary widely, some commonly used ranges are amplitude 2–7 volts, frequency range 30–50 Hz (motor cortex or deep
Use of parallel dual electrodes Dual octrodes give broader dermatomal coverage +
+
–
–
Two leads in position
Centre bipoles selected
Stimulation target or 'sweet spot'
Transverse stimulation (cross talk)
Dual quads give less dermatomal coverage
Sample variations in electrode and polarity Physiological midline –
+
+
–
+
–
–
+
–
+
+
–
+ –
– +
5
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
63
© 2005 The Medicine Publishing Company Ltd
PAIN
Implantable drug delivery systems Porta-a-cath® percutaneous portal
Pressure chamber continuous delivery pump Central filling septum
Offset bolus septum
Spinal catheter
Outlet
SynchroMed® programmable infusion system pump
Suture pad AlgoMed® manual peristaltic pump
Catheter port Electronic module
Peristaltic pump
Reservoir tubing
Drug reservoir Catheter
Antenna Control pad
Battery Self-sealing septum
Reservoir
6 Other complications include seroma formation of the pocket, a foreign body immune response causing allergic phenomena either local to the implant or systemically, and CSF leakage. Failure of the implantable device can occur through technical failure or battery failure. Batteries commonly last for 2–6 years depending on use and power delivery; their replacement costs should be included in the budget. Transcutaneous battery recharging facilities are being developed.
clinical distribution includes failed back syndrome (42%), cancer (32%), complex regional pain syndrome (5%), post-herpetic neuralgia (5%), peripheral nerve injury (3.7%), multiple sclerosis (2.1%), spinal cord injury (1.4%) and others (8%). Equipment, insertion and implantation A trial epidural, intrathecal or intraventricular catheter is percutaneously inserted using an aseptic technique. Reductions of systemic drug doses by up to 300:1 are achieved in some cases. When titration to effect and pain control are acceptable, re-insertion of a long-term indwelling silastic catheter is performed percutaneously, tunnelled and connected to the implanted delivery device. An aseptic technique and broad-spectrum antibiotic prophylaxis is essential for the trial and implant procedures, and the immediate aftercare period. The various systems used include a subcutaneous portal for continuous or bolused treatments via needle access (Porta-a-cath), or totally implantable pumps consisting of a primed chamber with a reservoir manually operated by patient palpation for refill and delivery of a fixed volume and dose (AlgoMed). The IsoMed is fully internalized with a primed reservoir under
Neuromodulation by implantable drug delivery systems Delivery routes are intraspinal (epidural or intrathecal) and less commonly intracerebroventricular. The general indications for use are a failure of conventional treatments (including stimulation) or if the oral and systemic administration of analgesic drug(s) at appropriate dose as recommended by the World Health Organization ladder (see page 66) does not control pain or is associated with unmanageable side-effects. A good response to a screening trial and life expectancy over 3 months is necessary. The types of pain treated include somatic, visceral, neuropathic and mixed. The
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
64
© 2005 The Medicine Publishing Company Ltd
PAIN
pressure giving constant flow delivery, and the SynchroMed has a primed reservoir with a battery-operated, electronically programmable, constant flow pump. All the devices are accessible percutaneously for priming the pump or reservoir, changing the drug or concentration and for a test bolus, sometimes through a separate portal (Figure 6). Drugs in common use include opioids (e.g. diamorphine, morphine, hydromorphone, fentanyl, sufentanyl, buprenorphine), local anaesthetics (e.g. bupivacaine) and α2-agonists (e.g. clonidine). Combinations of opioid drugs, local anaesthetic and α2-agonists are used synergistically for their dosesparing effect, though all drugs have an analgesic property and can also be used separately. The devices require continual patient monitoring, repriming, dose re-adjustments or re-programming of battery-operated devices, which can be performed by transcutaneous computerized telemetry.
Management of severe pain in terminal care Michael Bennett
Cancer pain occurs in about 30% of patients at diagnosis, but increases in prevalence with advanced disease. Recent surveys suggest that over 80% of patients with advanced cancer have pain and about half of them experience pain that is inadequately controlled. This suggests that despite the 80% efficacy of standardized management approaches to cancer pain, many patients with severe pain are likely to be encountered in clinical practice. This is often due to a combination of factors including inadequate pain assessment, under-dosing of medication, failure to educate and monitor patients and their carers, and failure of the medication to relieve pain. Patients with cancer often experience more than one pain; one study showed that 80% have two or more pains and 34% have four or more pains. Common causes of pain in this context are described in Figure 1.
Complications Complications can occur with surgery or the implantation procedure as described above. Drug overdose, tolerance and postural hypotension may occur. Side-effects of the drugs include constipation, micturition disturbance, nausea, vomiting, dysfunction of sexual potency and libido, pruritus, sweating, oedema, weakness, weight gain and nightmares. Catheter complications include migration of catheter tip, fibrosis at the delivery site and nerve root irritation. Mechanical or electrical failure of the pump device can also occur.
Assessment of patients with cancer pain: the experience of pain is influenced by physical, emotional, social and spiritual factors. The concept of total pain acknowledges the importance of all these dimensions of suffering, and that good pain relief is unlikely without attention to all of them. Assessment of a patient with cancer who is in pain should not differ from the assessment of any other patient with pain. This relies on a comprehensive pain history (Figure 2) and examination.
Clinical efficacy stimulation and pumps Data on clinical efficacy are derived from personal and clinical practice supported by case reports and internal audit. Patient series longtitudinal data and retrospective non-randomized and randomized controlled trials have been performed, and repeated measures of sensory, psychological and qualitative dimensions show improvement of quality of life with less social dependence. The usual measurement tools and outcome predictors are visual analogue scores and psychometric questionnaires. Implantable devices are cost-effective because they reduce hospitalization and the use of medication.
Causes of pain in patients with cancer • The cancer (e.g. direct pressure on or invasion of somatic structures) • Cancer treatment (e.g. post-surgical scar pain, painful neuropathies from chemotherapy or radiotherapy) • Debility (e.g. pressure sores, constipation, aphthous ulceration) • Comorbid diseases (e.g. osteoarthritis, post-herpetic neuralgia)
FURTHER READING Bennett G, Serafini M, Burchiel K et al. Evidence-based review of the literature on intrathecal delivery of pain medication. J Pain Symptom Manage 2000; 20: S12–36. Melzack R, Wall P D. Pain mechanisms: A new theory. Science 1965; 150: 971–9. Melzack R, Wall P D. Textbook of pain. 4th ed. Edinburgh: Churchill Livingstone, 1999. Turner J A, Loeser J D, Bell K G. Spinal cord stimulation for chronic low back pain: a systematic literature synthesis. Neurosurgery 1995; 37(6): 1088–96. Turner J A, Loeser J D, Deylo R A, Sanders S B. Spinal cord stimulation for patients with failed back surgery syndrome or complex regional pain syndrome. A systematic review of effectiveness and complications. Pain 2004; 108: 137–47.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
1
Michael Bennett is Senior Clinical Lecturer in Palliative Medicine at St Gemma’s Hospice and the University of Leeds. He qualified from Birmingham University and trained in general and palliative medicine. His research interests include neuropathic pain assessment and management and prognostic factors in advanced disease.
65
© 2002 2005 The Medicine Publishing Company Ltd
Implantable technology for pain management
Patient selection by clinical group Site of lesion Peripheral nerve • Peripheral nerve lesion
John Hodkinson
Clinical group
Trauma, incision, amputation, stump pain
• Complex regional pain syndrome (CRPS) Spinal cord • Mixed neuropathic nociceptive • Peripheral nerve lesion • Neuralgias • Plexopathies • Radiculopathies • Myelopathies • Polyneuropathies • CRPS • Refractory angina
Implantable devices for managing chronic pain by neuromodulation evolved from spinal regional anaesthesia. In 1998, their use was assessed by the European Federation of Chapters of the International Association for the Study of Pain, and a consensus from this task force stated ‘Neuromodulation procedures offer a non-destructive reversible alternative to the treatment of severe chronic pain where less invasive therapies and/or neurodestructive procedures are not effective or contraindicated’. The procedures involve stimulation of the peripheral nerve, spinal cord, deep brain or motor cortex and drug delivery by the intraspinal or intracerebroventricular route. They should be performed in Pain Treatment Centres by a multidisciplinary team trained in patient selection and education, behavioural and psychological assessments and therapy, surgical implantation of the devices, and continuous aftercare.
Chronic mixed spinal pain, failed back syndromes Entrapment, trauma, amputation Post-herpetic Traumatic avulsion, post-radiation Cervical, lumbar disc, osteoarthritis Spinal cord incomplete lesion, injury Diabetes, post-chemotherapy CRPS type II Occlusive coronary artery disease, syndrome X • Peripheral vascular disease Atherosclerosis, vasospastic, Raynaud’s disease, Buerger’s disease, CRPS type I • Abdominal/pelvic Chronic pancreatitis syndromes
General selection criteria Patients are suitable for an implantable device if other conservative or interventional (surgical) treatments have failed and there is no intention of pursuing those routes. The patient must give informed consent, have a realistic expectation of the outcome and a high degree of cognitive motivation. Patients are unsuitable if they have: a severe coexisting medical disease; a major psychiatric disorder or illness-seeking behaviour; poor understanding, social support or compliance; or if they abuse drugs. In 2004, the Pain Society conducted a national survey of psychological assessments before implantation; guidelines may follow.
Deep brain • Thalamic nuclei
• Periventricular aqueductal grey matter Motor cortex • Neuropathic
Neuromodulation by stimulation In 1965, Melzack and Wall demonstrated the gate control theory of pain. According to the theory, electrical stimulation of large diameter low threshold Aβ proprioceptive sensory nerve fibres causes suppression of small diameter high threshold Aδ and C sensory fibre activity within the dorsal horn of the spinal cord. Antidromic and summation loops are involved following stimulation of the peripheral nerve, spinal cord, deep brain or motor cortex. Targets for stimulation and sensory projection vary with the patient and are unmapped. Stimulation of the spinal cord also influences sympathetic and parasympathetic activity with an autonomic response. Neuromodulation within the CNS by stimulation
Post-herpetic neuralgia, cluster headache, post-stroke, phantom pain
1 is governed by the gene–peptide link and the release and reuptake of neuropeptides within groups of wide dynamic range neurons, particularly of the dorsal horn. Release of vasoactive peptides influences peripheral vascular tone and myocardial perfusion. The types of stimulation required for each clinical group are listed in Figure 1. Specific selection criteria for the most commonly treated conditions are given in Figure 2. Equipment insertion and implantation Stimulation electrodes are cord or paddle shaped, unipolar or multipolar (1–8), single or dual, parallel or in line with anode/ cathode availability (Figure 3). The electrode can be placed perineural (e.g. for peripheral nerve stimulation) or extradural via a percutaneous needle (e.g. for spinal cord or deep brain stimulation) or surgical laminotomy (e.g. spinal cord stimulation) or craniotomy (e.g. motor cortex stimulation). Computer-aided stereotactic imaging and cortical mapping are used to guide the
John Hodkinson is Consultant in Pain Medicine to Morecambe Bay Health Authority NHS Trust, Cumbria, and Director of Furness Pain Management Service. He qualified from Manchester University and pursued a career in anaesthesia and then pain medicine in the UK, Europe and the USA. His research interests include neuromodulation, spinal stimulation and pain management programmes.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
Trigeminal neuralgia, post-herpetic neuralgia, stump or phantom pain, spinal cord lesion, post-stroke pain Chronic mixed failed back, neuropathic pain
61
© 2005 The Medicine Publishing Company Ltd
PAIN
Specific selection criteria for spinal cord stimulation Chronic low back pain • Failed conservative therapies • Pain experienced correlates with observed pathology • No further surgical intervention indicated • Drug habituation has been treated • Psychological evaluation clearance • No contraindications (e.g. sepsis, coagulopathy) • Successful trial screening
• Optimum medication without adequate pain relief or restoration of function • No planned revascularization procedures • Syndrome X (no occlusive vascular disease) • No implanted demand fibrillation or pacing devices Peripheral vascular disease • Acceptable concomitant disease status • Fontaine Classification Grade III: ulcer > 3 cm2; transcutaneous oxygen pressure 10–30 mm Hg; ankle–brachial index < 0.4 • No peripheral gangrene • No planned or further reconstructive surgery
Refractory angina • Reversible ischaemia of coronary artery disease • Within New York Heart Association classification 3–4
2
Spinal cord stimulation Internal power source
External power source
Electrode lead Extension External antenna Receiver External transmitter Pulse generator
PISCES-Quad Plus Lead
Needle placement – epidural Electrode
Radiopaque marker band Electrode
Tuohy needle
Stylet connector
0
1
2
3
Electrode numbers Stylet Leads contacts
3 placement of deep brain and motor cortex stimulation. Electrode placement for spinal cord stimulation uses continuous fluoroscopy and evoked sensory stimulation (paraesthesia) as experienced by the patient at the time of placement. Figure 4 lists the common electrode placement sites. A trial period of stimulation precedes
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
implantation of the pulse generator, which is usually placed in the abdominal wall within a subcutaneous pocket with a hardwire connection lead to the electrode through a percutaneous tunnel. An aseptic technique with broad-spectrum antibiotic prophylaxis for Staphylococcus is used.
62
© 2005 The Medicine Publishing Company Ltd
PAIN
brain stimulation), 50–85 Hz (spinal cord stimulation), 100–150 Hz (peripheral nerve stimulation), and a pulse width of 200–500 microseconds. Various waveform, operational and cycling modes are available and combinations of stimulation arrays within multipolar channels. Stimulation can be achieved bilaterally with a single electrode placed at the physiological midline. Interesting effects of concentrated stimulation (‘sweet spot’) can be achieved by anode/cathode variation across the dorsal columns with parallel dual electrodes (Figure 5). Follow-up evaluation is essential. Usage guidance is provided by audit of patient experience and demand, and reprogramming of variables is often required. Fully internalized battery-operated electronic systems are reprogrammed by transcutaneous computerized telemetry. Palm computers contain software for downloading and reprogramming devices with on-line wire-less data transfer, which allows remote analysis and reprogramming.
Electrode placement for stimulation Stimulation mapping Spinal cord stimulation • Chronic mixed low back pain • Chronic mixed neck pain • Angina chest wall pain • Peripheral vascular disease of arm • Peripheral vascular disease of leg Deep brain stimulation • Central pain
Motor cortex stimulation • Central pain
T9–L1 C2–T1 C7–T2 C6–T1 T11–L1
Periaqueductal and periventricular thalamic projections Broca motor cortex projections
Complications Wound infection occurs in 5% of cases, and 3% of implants require removal. Epidural abscess or haematoma may require surgical decompression. Electrode migration occurs in 35% of cases, and 23% require re-implantation. Electrode fracture occurs in 5%, and discomfort at the implantation site occurs in 13%.
4
There are various implantable programmable devices activated by internal battery or transcutaneous radiofrequency induction, operated by the patient using a hand set (Figure 3). Operation variables vary widely, some commonly used ranges are amplitude 2–7 volts, frequency range 30–50 Hz (motor cortex or deep
Use of parallel dual electrodes Dual octrodes give broader dermatomal coverage +
+
–
–
Two leads in position
Centre bipoles selected
Stimulation target or 'sweet spot'
Transverse stimulation (cross talk)
Dual quads give less dermatomal coverage
Sample variations in electrode and polarity Physiological midline –
+
+
–
+
–
–
+
–
+
+
–
+ –
– +
5
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
63
© 2005 The Medicine Publishing Company Ltd
PAIN
Implantable drug delivery systems Porta-a-cath® percutaneous portal
Pressure chamber continuous delivery pump Central filling septum
Offset bolus septum
Spinal catheter
Outlet
SynchroMed® programmable infusion system pump
Suture pad AlgoMed® manual peristaltic pump
Catheter port Electronic module
Peristaltic pump
Reservoir tubing
Drug reservoir Catheter
Antenna Control pad
Battery Self-sealing septum
Reservoir
6 Other complications include seroma formation of the pocket, a foreign body immune response causing allergic phenomena either local to the implant or systemically, and CSF leakage. Failure of the implantable device can occur through technical failure or battery failure. Batteries commonly last for 2–6 years depending on use and power delivery; their replacement costs should be included in the budget. Transcutaneous battery recharging facilities are being developed.
clinical distribution includes failed back syndrome (42%), cancer (32%), complex regional pain syndrome (5%), post-herpetic neuralgia (5%), peripheral nerve injury (3.7%), multiple sclerosis (2.1%), spinal cord injury (1.4%) and others (8%). Equipment, insertion and implantation A trial epidural, intrathecal or intraventricular catheter is percutaneously inserted using an aseptic technique. Reductions of systemic drug doses by up to 300:1 are achieved in some cases. When titration to effect and pain control are acceptable, re-insertion of a long-term indwelling silastic catheter is performed percutaneously, tunnelled and connected to the implanted delivery device. An aseptic technique and broad-spectrum antibiotic prophylaxis is essential for the trial and implant procedures, and the immediate aftercare period. The various systems used include a subcutaneous portal for continuous or bolused treatments via needle access (Porta-a-cath), or totally implantable pumps consisting of a primed chamber with a reservoir manually operated by patient palpation for refill and delivery of a fixed volume and dose (AlgoMed). The IsoMed is fully internalized with a primed reservoir under
Neuromodulation by implantable drug delivery systems Delivery routes are intraspinal (epidural or intrathecal) and less commonly intracerebroventricular. The general indications for use are a failure of conventional treatments (including stimulation) or if the oral and systemic administration of analgesic drug(s) at appropriate dose as recommended by the World Health Organization ladder (see page 66) does not control pain or is associated with unmanageable side-effects. A good response to a screening trial and life expectancy over 3 months is necessary. The types of pain treated include somatic, visceral, neuropathic and mixed. The
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
64
© 2005 The Medicine Publishing Company Ltd
PAIN
pressure giving constant flow delivery, and the SynchroMed has a primed reservoir with a battery-operated, electronically programmable, constant flow pump. All the devices are accessible percutaneously for priming the pump or reservoir, changing the drug or concentration and for a test bolus, sometimes through a separate portal (Figure 6). Drugs in common use include opioids (e.g. diamorphine, morphine, hydromorphone, fentanyl, sufentanyl, buprenorphine), local anaesthetics (e.g. bupivacaine) and α2-agonists (e.g. clonidine). Combinations of opioid drugs, local anaesthetic and α2-agonists are used synergistically for their dosesparing effect, though all drugs have an analgesic property and can also be used separately. The devices require continual patient monitoring, repriming, dose re-adjustments or re-programming of battery-operated devices, which can be performed by transcutaneous computerized telemetry.
Management of severe pain in terminal care Michael Bennett
Cancer pain occurs in about 30% of patients at diagnosis, but increases in prevalence with advanced disease. Recent surveys suggest that over 80% of patients with advanced cancer have pain and about half of them experience pain that is inadequately controlled. This suggests that despite the 80% efficacy of standardized management approaches to cancer pain, many patients with severe pain are likely to be encountered in clinical practice. This is often due to a combination of factors including inadequate pain assessment, under-dosing of medication, failure to educate and monitor patients and their carers, and failure of the medication to relieve pain. Patients with cancer often experience more than one pain; one study showed that 80% have two or more pains and 34% have four or more pains. Common causes of pain in this context are described in Figure 1.
Complications Complications can occur with surgery or the implantation procedure as described above. Drug overdose, tolerance and postural hypotension may occur. Side-effects of the drugs include constipation, micturition disturbance, nausea, vomiting, dysfunction of sexual potency and libido, pruritus, sweating, oedema, weakness, weight gain and nightmares. Catheter complications include migration of catheter tip, fibrosis at the delivery site and nerve root irritation. Mechanical or electrical failure of the pump device can also occur.
Assessment of patients with cancer pain: the experience of pain is influenced by physical, emotional, social and spiritual factors. The concept of total pain acknowledges the importance of all these dimensions of suffering, and that good pain relief is unlikely without attention to all of them. Assessment of a patient with cancer who is in pain should not differ from the assessment of any other patient with pain. This relies on a comprehensive pain history (Figure 2) and examination.
Clinical efficacy stimulation and pumps Data on clinical efficacy are derived from personal and clinical practice supported by case reports and internal audit. Patient series longtitudinal data and retrospective non-randomized and randomized controlled trials have been performed, and repeated measures of sensory, psychological and qualitative dimensions show improvement of quality of life with less social dependence. The usual measurement tools and outcome predictors are visual analogue scores and psychometric questionnaires. Implantable devices are cost-effective because they reduce hospitalization and the use of medication.
Causes of pain in patients with cancer • The cancer (e.g. direct pressure on or invasion of somatic structures) • Cancer treatment (e.g. post-surgical scar pain, painful neuropathies from chemotherapy or radiotherapy) • Debility (e.g. pressure sores, constipation, aphthous ulceration) • Comorbid diseases (e.g. osteoarthritis, post-herpetic neuralgia)
FURTHER READING Bennett G, Serafini M, Burchiel K et al. Evidence-based review of the literature on intrathecal delivery of pain medication. J Pain Symptom Manage 2000; 20: S12–36. Melzack R, Wall P D. Pain mechanisms: A new theory. Science 1965; 150: 971–9. Melzack R, Wall P D. Textbook of pain. 4th ed. Edinburgh: Churchill Livingstone, 1999. Turner J A, Loeser J D, Bell K G. Spinal cord stimulation for chronic low back pain: a systematic literature synthesis. Neurosurgery 1995; 37(6): 1088–96. Turner J A, Loeser J D, Deylo R A, Sanders S B. Spinal cord stimulation for patients with failed back surgery syndrome or complex regional pain syndrome. A systematic review of effectiveness and complications. Pain 2004; 108: 137–47.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:2
1
Michael Bennett is Senior Clinical Lecturer in Palliative Medicine at St Gemma’s Hospice and the University of Leeds. He qualified from Birmingham University and trained in general and palliative medicine. His research interests include neuropathic pain assessment and management and prognostic factors in advanced disease.
65
© 2002 2005 The Medicine Publishing Company Ltd