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Interventional therapy
Interventional Therapy
R. L. Marks
In the 1960s a gradually increasing number of anaesthetists became involved in the treatment of chronic pain. The naive wish in the early days was that blocking or destroying the conducting pathway would influence the perception of long term pain. Work in the field of cancer pain by Maher, 1 using gravity to control the spread of neurolytic agents, seemed to give support to this view. The pendulum has now swung in the opposite direction. The current view of many practitioners in the field of Pain Management is that interventional methods may have an occasional place, but that the correct approach is one of non-intervention, with the resultant proliferation of Pain Management Programmes both on an in-patient and out-patient basis. The spread of the Hospice movement and its philosophies has also meant that most terminally ill patients can now have their pain controlled pharmacologically. The place for interventional and destructive techniques has therefore diminished and the necessary skills involved in their performance are not as readily available. This is unfortunate because not all patients can be satisfactorily controlled with drugs and destructive procedures such as percutaneous cordotomy 2 can give excellent symptomatic relief without impairing the quality of life. There is usually a place for different approaches in the control of any difficult to manage condition and it is important that the skills involved in some of the techniques to be described are not lost.
Alcohol and phenol were the most popular agents and both are unselective in their mode of action, injuring both large and small nerve fibres as well as interfering with both motor and sensory function. The damage to the axonal membrane which is produced by their action can cause cross fibre connection during the healing process. This may be the reason why painful and inappropriate sensory responses are a late complication of these blocks. If late dysaesthesia does occur it may respond to a repeat block. This reinforces the view that these agents should only be used for pertinent indications in patients with non malignant pain.
Intrathecal injections When used intrathecally for chemical destruction of sensory dorsal roots the lumbar puncture is usually performed at the level of the segment to be blocked, the needle being withdrawn to the edge of the dura just before injection. Absolute alcohol is hypobaric in comparison to cerebrospinal fluid (CSF) and this requires the target to be placed uppermost when it is used intrathecally. The therapeutic effect is related to the accuracy with which the alcohol is placed in relation to the target dorsal roots. 3 An initial burning pain is produced on injection and the maximum dose should be restricted to 1 ml. Relief of pain may take up to two days. Phenol is usually mixed with glycerine for intrathecal use, in a solution varying from 5%-7%. It is hyperbaric in relation to CSF. The target roots should be dependent so the patient is placed in the lateral position and then rotated 45 ° backwards to achieve this. Its injection is not painful and immediate relief occurs if the correct level has been identified. The maximum dose for any one injection should not exceed 0.5 ml. The duration of effect of these blocks in cancer pain
Neurolytie agents The use of neurolytic agents to help relieve the pain in terminal cancer was widespread until the early 1980s. Dr R. L. Marks, District Hospital, Wigginton Road, York, YO3 7HE,
UK Current Anaesthesia and CHtical Care (1993) 4, 83-87
© 1993 Longman Group UK Ltd
83
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CURRENTANAESTHESIAAND CRITICALCARE
is short lived, often only lasting for a few weeks and repeat injections are less successful. They should not be used in patients who are expected to live for more than one year. The main current indication for subarachnoid phenol is intractable perineal pain due to pelvic malignancy. This procedure is performed with the patient in the sitting position and tilted about 25 ° backwards. If this is not successful a bilateral block of the $4 nerve roots through the $4 inter vertebral foramina may be effective and maintain bladder control. 4
Other neurolytic blocks Trigeminal nerve block. Alcohol was commonly used in the treatment of trigeminal neuralgia, both to cause damage to the Gasserian ganglion as well as to the more peripheral branches of the trigeminal nerve. These blocks give initial relief of the neuralgia but rarely last for more than a year. Repeat injections are associated with an increasing rate of complications and a reduced therapeutic effect. There is no control of the degree of hypoalgesia and anaesthesia resulting from the injections and these effects can be extremely unpleasant to the patient. There is no place for this procedure in the current treatment of trigeminal neuralgia. Coeliac plexus block. This is one of the few interventional techniques which is still the treatment of choice in terminally ill patients. In carcinoma of the pancreas 90% of patients will obtain a worthwhile degree of relief. It is less successful in relieving pain in other upper abdominal malignancies. The coeliac plexus surrounds the coeliac artery, lying anterior to the aorta at the level of the first lumbar vertebra. It is a bilateral structure situated in front of the crura of the diaphragm and contains both sympathetic and parasympathetic fibres. Various techniques for approaching the coeliac plexus have been described and they should all be performed using x-ray control. The most frequently used procedure involves placing long needles (150 mm) at either side of the first lumbar vertebra and sliding them off the body of the vertebra into the retroperitoneal space. The patient lies prone. It is common practice to perform a diagnostic block first with local anaesthetic and if this relieves the pain to then use about 20-25 ml of 50% alcohol through each needle. The injection is extremely painful without the prior use of local anaesthesia. A method using one needle through the aorta 5 has simplified the procedure. Only one needle is required and placement of the alcohol in close proximity to the plexus is assured. Whichever method is used it is advisable to inject some contrast first to ensure that the needles are not placed intravascularly or in the renal capsule. The commonest complication is hypotension which occurs in about 20% of patients. It is wise to give intravenous fluids and use elastic stockings for the procedure and to monitor the patients closely when they get out of bed following the block. The hypotension always settles with time, though it can take several days. A much rarer complication is paraplegia, which is believed to be due to
damage to the artery of Adamkiewicz which supplies the spinal cord at the level of the 9th-1 lth dorsal vertebra. Problems with ejaculation can occur in males and this could be an important factor if the technique is used for treating non malignant conditions such as chronic pancreatitis. Pituitary gland. The use of alcohol to destroy the pituitary gland in hormone dependent tumours, was first described by Greco 6 in 1957 and popularised by Morrica. 7 The procedure involves the injection of absolute alcohol, using a robust cannula through the nose and then transphenoidally, into the pituitary fossa, with x-ray control. Volumes of alcohol ranging from 1 rnl to 6 ml have been used and varying degrees of success have been claimed for both the relief of pain and regression of tumours. About 70% of patients gain worthwhile relief of pain but generally this is short lived being weeks rather than many months. Tumour regression is uncommon and is not related to relief of pain. The mechanism of action is still unclear. The procedure is now rarely used and cryodestruction has tended to replace alcohol. There are many complications of pituitary alcohol injection because the spread of the alcohol is not controllable and the optic chiasma and the nerves controlling the eye are in close proximity. If the pupil dilates during the procedure immediate intrathecal injection of 25 mg of prednisolone should be given. Miles 8 reports 6 fatalities related to the procedure in 250 injections as well as meningitis, two cases of hypothalamic injury and two permanent visual field losses. Lumbar chemical sympathectomy. Lumbar chemical sympathectomy with phenol is one of the few indications for the use of a neurolytic agent in non cancer pain. The procedure is useful in alleviating pain and hyperpathia in sympathetic dystrophies of the lower limb, rest pain in arteriopaths not considered suitable for surgery, some patients with painful peripheral neuropathies and post amputation pain. It does not usually relieve the pain of intermittent claudication. Phenol is used in preference to alcohol because the injection itself is not associated with pain. It is used in a concentration of 6%-7% in aqueous solution. The procedure should always be performed under biplanar image intensification. Techniques describing the use of up to three needles in the lumbar region are described as well as different positions of the patient? If one needle is used at the level of the second or third lumbar vertebra, 10 centimetres from the mid line, and the phenol is mixed with contrast, the spread can be easily identified and it is rarely necessary to use more than one needle. Contrast should be injected before the phenol to confirm correct placement, eliminate intravascular or subarachnoid injection and make sure tlmt the renal capsule or ureter has not been entered. A volume of up to 10 ml may be required. There are two common complications, after correct placement of the phenol. One is anterior thigh pain usually accompanied by marked hyperaesthesia, which occurs in 20% of patients. It is not related to the technique
INTERVENTIONAL THERAPY
used and can occur after open surgery. It always settles with time and is helped by anticonvulsants and analgesics. The patients should be warned of this possibility. The other complication is genito-femoral neuritis, with a frequency of 5-10%, and is due to the spread of the phenol across the anterior surface of the psoas.
Non n e u r o l y t i e d r u g s Steroids The use of injectable depot preparations of steroids is probably the most widespread interventional practice in pain relief. They can be injected in joint spaces and periarticularly, epidurally, into tendon sheaths and numerous other sites. A lumbar epidural injection of a steroid in the treatment of prolapsed inter vertebral disc is the standard initial treatment in many units. It is probably most effective if used within one month of the onset of symptoms and its benefit may not become apparent for up to 14 days. Nerve damage due to the prolapsed disc will not be improved by the steroid. Some practitioners repeat the injection up to three times. There is no convincing evidence that the use of steroids epidurally causes further nerve root damage. However adrenal function can be suppressed for up to three weeks. There is wide variation in the recommended dose and whether local analgesics should or should not be used. 80 mg of an aqueous suspension of methylprednisolone acetate (Depomedrone) in 10 ml of bupivacaine or saline is a common mixture. It should be noted that Depo-medrone does not have a product licence for epidural use, although there is no documented evidence of any harmful effect from the preparation. This injection can be also be undertaken for the rare occurrence of a cervical disc prolapse. It is also effective in the pain of cervical spondylosis and brachalgia due to foraminal outlet obstruction. As the epidural space terminates rostrally at the level of the foramen magnum the easiest access is by the C7/D1 or C6/7 intervertebral spaces. Other levels are much more difficult to identify and more likely to cause complications such as nerve root trauma. The therapeutic effect of injections of a mixture of local anaesthetic and depot steroid in and around the lumbar facet joints in mechanical low back pain has come under increasing scrutiny. Marks et all ° found that benefits were short lived, only two patients reporting pain relief beyond three months. Most patients with long standing back pain will not be relieved of their symptoms by any procedure and the underlying principle in the management of this group is to enable them to cope with the symptoms and achieve an acceptable quality of life. It is in the management of the acute exacerbation of chronic back pain that facet joint injections are invaluable. Patients come to terms with their condition knowing that if it deteriorates they can gain relief of their symptoms with a simple procedure.
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The procedure is performed under biplanar x-ray control and the painful areas are injected with a mixture of 20 mg of Depo-medrone and local anaesthetic at each site. The volume of the joint space is not more than 0.5 ml and injection of a larger volume may rupture the capsule. The rest of the mixture should be infiltrated around the joint. Relief is usually obtained in from 2 to 7 days but can occasionally take longer. More than 50% of our chronic back pain patients have their symptoms reduced to base line levels for longer than 6 months.
Midazolam Midazolam, an imidazobenzodiazepine, produces antinociceptive effects when injected intrathecally. It has been demonstrated to be effective in the treatment of acute postoperative somatic pain. ~ Serrao et al ~2 have shown that it can be a useful addition to the methods of management of chronic back pain, producing relief of symptoms and reduction of self administered analgesic medication in 50% to 75% of the patients when a dose of 2 mg is mixed with 3 ml of 5% dextrose and injected intrathecally.
Glycerol Glycerol in the form of anhydrous glycerine is a very effective treatment for the distressing condition of trigeminal neuralgia. ~3A spinal needle is introduced into the trigeminal cistern via the foramen ovale. A skin wheel is made about 3 cm from the angle of the mouth and the needle is guided into position using image intensification. Cerebro-spinal fluid should flow back. 0.2 ml to 0.4 ml of the glycerol is then injected through the needle with the patient in the sitting position and the patient maintained in that position for 20 minutes. The injection itself can be painful in some patients, but this is usually short lived. The results are apparent within 2-3 days and are equal to those obtained by radio frequency thermocoagulation. The advantages of this technique are minimal post operative sensory loss and the removal of the need for co-operation fi'om the patient. Glycerol has also proved to be useful for injections around the dorsal root ganglion in cases of root pain. Root pain is common after thoracotomy incisions. Up to 0.5 ml of glycerol placed around the dorsal root gangtion in the intervertebral canal, with the aid of an image intensifier, can often relieve this troublesome pain. A preliminary diagnostic injection with local anaesthetic should be undertaken. Other causes of root pain responding to this form of treatment include renal pain and groin and scrotal pain following hernia repair or testicular surgery.
Radiofrequency lesions The principle of radiofrequency lesioning is the passage, through an electrode, of a high frequency alternating current similar to that used in surgical diathermy, to heat tissue surrounding the electrode tip. Ionic agitation at the
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CURRENT ANAESTHESIA AND CRITICAL CARE
electrode tip produces frictional heating and by using a thermistor or a thermocouple electrode, accurate measurement of the temperature can be made and controlled lesions performed. The size of the lesion created is a function of the electrode diameter, length of the uninsulated tip, temperature and time. Generally the lesion is made for a period of 30-90 s with a tip temperature of 60-85°C. A built in nerve stimulator enables the electrode to be placed in close proximity to the nerve being treated.
Percutaneous cordotomy Percutaneous cordotomy was first popularised by Mullah 14 and Rosomoff. 15 This involves the introduction of an electrode, using a lateral approach and x-ray control, at the interspace between the first and second cervical vertebrae. Local analgesia and some mild sedation are all that is required. The electrode is positioned in the antero-lateral quadrant of the spinal cord on the opposite side to the patient's pain and progressive lesions made, after preliminary stimulation studies have confirmed correct placement, until the area of analgesia to pin prick testing extends two dermatomal segments beyond the pain. The main indication for this method is unilateral somatic pain due to cancer when life expectancy is not more than eighteen months and not less than 4 weeks. The reason for restricting the procedure to terminally ill patients is the development of late onset dysaesthesia which can be worse than the original pain and impossible to relieve. With the correct indications 64% of patients gain complete relief of pain and 25% partial relief, z Complications are problematical motor loss in 10% of patients and occasional patients who have dysaesthesia, impotence, problems with micturition and ataxia. Respiratory difficulties can occur in patients with poor respiratory reserve and a vital capacity of less than 1 1 is an absolute contraindication. Bilateral percutaneous cordotomy at the C 1/2 level can produce sleep apnoea - the so called 'Ondine's curse'. For this reason the second cordotomy is usually performed at the level of C6 and is a much more technically demanding operation. Mortality has been reported at 6%,
Trigeminal neuralgia Radiofrequency lesioning of the preganglionic roots of the trigeminal nerve was the treatment of choice of trigeminal neuralgia which could not be controlled by drugs. Glycerol injection has reduced the need for this mode of treatment. The advantages of radiofrequency lesioning over the earlier methods of treatment are those of control. The electrode, using a combination of X-ray imaging and electrical stimulation at 50-100 Hertz, could be precisely positioned in the affected rootlets. Progressive heat lesions are made until minimal sensory loss to pin prick in the relevant dermatomes is produced. The procedure is time consuming and painful for the
patient so thai intermittent general anaesthesia is used and this can cloud the end point. Excessive numbness can lead to anaesthesia dolorosa. The results are good. 80% of patients gain relief for one year and about 50% for 5 years. Radiofrequency lesions have been, and still are, used in many other situations such as facet nerve thermocoagulation in chronic back pain; coagulation of the dorsal re-entry zone (DREZ) of the spinal cord in the cervical and thoracic regions for post traumatic brachial plexus pain and post herpetic neuralgia; coagulation of the dorsal root ganglion for root pain and destruction of the pituitary gland in cancer pain.
Drug delivery systems In the late 1970s the first reports started to appear about the analgesic action of opioids on the spinal cord. A new field of clinical research opened and many different drugs are now administered this way. This was the stimulus to the development of fully implantable drug delivery systems for use long term via the epidural and intrathecal routes. The available systems vary from those having a reservoir which needs filling at short intervals by a percutaneous puncture to more sophisticated systems utilising a pump which can have its rate altered telemetrically. Opioids are used in the management of terminally ill patients as well as for conditions such as the 'failed back'. Baclofen, intrathecally, has proved to be invaluable in the management of spasticity in patients suffering from multiple sclerosis and spinal cord injuries. Baclofen is one of a group of drugs, which includes midazolam, which act on the 7-aminobutyric acid (GABA) system in the spinal cord. Administration of GABA-mimetic compounds has been shown to inhibit nociceptive responses in experimental animals and to produce analgesia in man. This may well be the direction from which drugs for the delivery systems of the future will be developed.
Dorsal column stimulation Spinal cord stimulation in the management of chronic intractable pain has been performed for about twenty years. Initially the electrodes were positioned at laminectomy but gradual improvements in the design of electrodes has meant that the percutaneous approach can be utilised for permanent electrode placement. This gives the opportunity for preliminary screening so that the effectiveness of pain relief can be assessed before a full implantation is undertaken. The currently available systems cost about £4500 and the operation should only be undertaken in centres where the appropriate skills can be acquired by performing the procedure regularly. It is not without complications such as electrode slippage and infection and the patients need life time care. Many workers are now reporting long term improvement of more than 50% pain relief in conditions such as the 'failed back', arachnoiditis, phantom limb and stump pain. ~6
INTERVENTIONAL THERAPY
Conclusion Current approaches to the management of non-acute pain are tending to be biased towards the more behavioural models exemplified by Pain Management programmes. There is however still a place for the interventional approach in Pain Management Clinics. This article has outlined the methods that are available and which have proved to be useful in clinical practice, ranging from the injection of depot preparations of steroids to dorsal column stimulation. References 1. Maher R. M. Relief of Pain in incurable cancer. Lancet 1955; 1:18 2. Lahuerta J, Lipton S, Wells JCD Percutaneous cervical cordotomy: results and complications in a recent series of 100 patients. Ann R Coll Surg Eng 1985; 67:41-44 3. Maher R, Mehta M Spinal (intrathecal) and extradural analgesia. In: Lipton S (ed) Persistent pain; modern methods of treatment, vol 1. Academic Press, London, 1977:61-99 4. Robertson DH. Transsacral neurolytic nerve block, an alternative approach to intractable perineal pain. Br J Anaesth 1983; 55:873-875 5. Ischia S, Lozzani A, Ischia A, Faggion S.A new approach to the neurolytic block of the celiac plexus: the transaortic technique. Pain 1983; 16:333-341
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6. Greco T, Sbaragli F, Cammili L L'alcoolizazione della ipofisi per via transfenoidale nella terapia di particolari tumori maligni. Settimana Medicale 1957; 45:355-356 7. Morrica G. Chemical hypophysectomy for cancer pain. In: Bonica JJ (ed) Advances in neurology 4. Raven Press, NewYork, 1974:707-714 8. Miles JB Pituitary destruction. In: Wall PD, Melzack R (eds) Textbook of Pain. Churchill Livingstone, Edinburgh, 1989:860 9. Cotton LT, Cross FW. Lumbar sympathectomy for arterial disease. B r J Surg 1985; 72:678-683 10. Marks RC, Houston T, Thulbourne T. Facet joint injection and facet nerve block: a randomised comparison in 86 patients with chronic low back pain. Pain 1992; 49:325-328 11. Goodchild CS, Noble J. The effects of intrathecal midazolam on sympathetic nervous system reflexes in man - - a pilot study. Br J Clin Pharmacol 1987; 23:273-285 12. Serrao JM, Marks RL, Morley SJ, Goodchild CS. Intrathecal midazolam for the treatment of chronic mechanical low back pain: a controlled comparison with epidural steroid in a pilot study. Pain 1992; 48:5-12 13. Hakansson S. Trigeminal neuralgia treated by the injection of glycerol into the trigeminal cistern. Neurosurgery 1981; 9:638-646 14. Mullan S, Harper PV, Hekmatpanah J, Torres H, Dobbin G. Percutaneous interruption of spinal-pain tracts by means of a Strontium 9° needle. J Neurosurg 1963; 20:931-939 15. Rosomoff HL, Can'ol F, Brown J, Sheptak P Percutaneous radiofrequency cervical cordotomy technique. J Neurosurg 1965; 23:639-644 16. North RB, Ewend MG, Lawton MT, Piantadosi S. Spinal cord stimulation for chronic, intractable pain: superiority of 'multichannel' devices. Pain 1991; 44:119-130
R. L. Marks
In the 1960s a gradually increasing number of anaesthetists became involved in the treatment of chronic pain. The naive wish in the early days was that blocking or destroying the conducting pathway would influence the perception of long term pain. Work in the field of cancer pain by Maher, 1 using gravity to control the spread of neurolytic agents, seemed to give support to this view. The pendulum has now swung in the opposite direction. The current view of many practitioners in the field of Pain Management is that interventional methods may have an occasional place, but that the correct approach is one of non-intervention, with the resultant proliferation of Pain Management Programmes both on an in-patient and out-patient basis. The spread of the Hospice movement and its philosophies has also meant that most terminally ill patients can now have their pain controlled pharmacologically. The place for interventional and destructive techniques has therefore diminished and the necessary skills involved in their performance are not as readily available. This is unfortunate because not all patients can be satisfactorily controlled with drugs and destructive procedures such as percutaneous cordotomy 2 can give excellent symptomatic relief without impairing the quality of life. There is usually a place for different approaches in the control of any difficult to manage condition and it is important that the skills involved in some of the techniques to be described are not lost.
Alcohol and phenol were the most popular agents and both are unselective in their mode of action, injuring both large and small nerve fibres as well as interfering with both motor and sensory function. The damage to the axonal membrane which is produced by their action can cause cross fibre connection during the healing process. This may be the reason why painful and inappropriate sensory responses are a late complication of these blocks. If late dysaesthesia does occur it may respond to a repeat block. This reinforces the view that these agents should only be used for pertinent indications in patients with non malignant pain.
Intrathecal injections When used intrathecally for chemical destruction of sensory dorsal roots the lumbar puncture is usually performed at the level of the segment to be blocked, the needle being withdrawn to the edge of the dura just before injection. Absolute alcohol is hypobaric in comparison to cerebrospinal fluid (CSF) and this requires the target to be placed uppermost when it is used intrathecally. The therapeutic effect is related to the accuracy with which the alcohol is placed in relation to the target dorsal roots. 3 An initial burning pain is produced on injection and the maximum dose should be restricted to 1 ml. Relief of pain may take up to two days. Phenol is usually mixed with glycerine for intrathecal use, in a solution varying from 5%-7%. It is hyperbaric in relation to CSF. The target roots should be dependent so the patient is placed in the lateral position and then rotated 45 ° backwards to achieve this. Its injection is not painful and immediate relief occurs if the correct level has been identified. The maximum dose for any one injection should not exceed 0.5 ml. The duration of effect of these blocks in cancer pain
Neurolytie agents The use of neurolytic agents to help relieve the pain in terminal cancer was widespread until the early 1980s. Dr R. L. Marks, District Hospital, Wigginton Road, York, YO3 7HE,
UK Current Anaesthesia and CHtical Care (1993) 4, 83-87
© 1993 Longman Group UK Ltd
83
84
CURRENTANAESTHESIAAND CRITICALCARE
is short lived, often only lasting for a few weeks and repeat injections are less successful. They should not be used in patients who are expected to live for more than one year. The main current indication for subarachnoid phenol is intractable perineal pain due to pelvic malignancy. This procedure is performed with the patient in the sitting position and tilted about 25 ° backwards. If this is not successful a bilateral block of the $4 nerve roots through the $4 inter vertebral foramina may be effective and maintain bladder control. 4
Other neurolytic blocks Trigeminal nerve block. Alcohol was commonly used in the treatment of trigeminal neuralgia, both to cause damage to the Gasserian ganglion as well as to the more peripheral branches of the trigeminal nerve. These blocks give initial relief of the neuralgia but rarely last for more than a year. Repeat injections are associated with an increasing rate of complications and a reduced therapeutic effect. There is no control of the degree of hypoalgesia and anaesthesia resulting from the injections and these effects can be extremely unpleasant to the patient. There is no place for this procedure in the current treatment of trigeminal neuralgia. Coeliac plexus block. This is one of the few interventional techniques which is still the treatment of choice in terminally ill patients. In carcinoma of the pancreas 90% of patients will obtain a worthwhile degree of relief. It is less successful in relieving pain in other upper abdominal malignancies. The coeliac plexus surrounds the coeliac artery, lying anterior to the aorta at the level of the first lumbar vertebra. It is a bilateral structure situated in front of the crura of the diaphragm and contains both sympathetic and parasympathetic fibres. Various techniques for approaching the coeliac plexus have been described and they should all be performed using x-ray control. The most frequently used procedure involves placing long needles (150 mm) at either side of the first lumbar vertebra and sliding them off the body of the vertebra into the retroperitoneal space. The patient lies prone. It is common practice to perform a diagnostic block first with local anaesthetic and if this relieves the pain to then use about 20-25 ml of 50% alcohol through each needle. The injection is extremely painful without the prior use of local anaesthesia. A method using one needle through the aorta 5 has simplified the procedure. Only one needle is required and placement of the alcohol in close proximity to the plexus is assured. Whichever method is used it is advisable to inject some contrast first to ensure that the needles are not placed intravascularly or in the renal capsule. The commonest complication is hypotension which occurs in about 20% of patients. It is wise to give intravenous fluids and use elastic stockings for the procedure and to monitor the patients closely when they get out of bed following the block. The hypotension always settles with time, though it can take several days. A much rarer complication is paraplegia, which is believed to be due to
damage to the artery of Adamkiewicz which supplies the spinal cord at the level of the 9th-1 lth dorsal vertebra. Problems with ejaculation can occur in males and this could be an important factor if the technique is used for treating non malignant conditions such as chronic pancreatitis. Pituitary gland. The use of alcohol to destroy the pituitary gland in hormone dependent tumours, was first described by Greco 6 in 1957 and popularised by Morrica. 7 The procedure involves the injection of absolute alcohol, using a robust cannula through the nose and then transphenoidally, into the pituitary fossa, with x-ray control. Volumes of alcohol ranging from 1 rnl to 6 ml have been used and varying degrees of success have been claimed for both the relief of pain and regression of tumours. About 70% of patients gain worthwhile relief of pain but generally this is short lived being weeks rather than many months. Tumour regression is uncommon and is not related to relief of pain. The mechanism of action is still unclear. The procedure is now rarely used and cryodestruction has tended to replace alcohol. There are many complications of pituitary alcohol injection because the spread of the alcohol is not controllable and the optic chiasma and the nerves controlling the eye are in close proximity. If the pupil dilates during the procedure immediate intrathecal injection of 25 mg of prednisolone should be given. Miles 8 reports 6 fatalities related to the procedure in 250 injections as well as meningitis, two cases of hypothalamic injury and two permanent visual field losses. Lumbar chemical sympathectomy. Lumbar chemical sympathectomy with phenol is one of the few indications for the use of a neurolytic agent in non cancer pain. The procedure is useful in alleviating pain and hyperpathia in sympathetic dystrophies of the lower limb, rest pain in arteriopaths not considered suitable for surgery, some patients with painful peripheral neuropathies and post amputation pain. It does not usually relieve the pain of intermittent claudication. Phenol is used in preference to alcohol because the injection itself is not associated with pain. It is used in a concentration of 6%-7% in aqueous solution. The procedure should always be performed under biplanar image intensification. Techniques describing the use of up to three needles in the lumbar region are described as well as different positions of the patient? If one needle is used at the level of the second or third lumbar vertebra, 10 centimetres from the mid line, and the phenol is mixed with contrast, the spread can be easily identified and it is rarely necessary to use more than one needle. Contrast should be injected before the phenol to confirm correct placement, eliminate intravascular or subarachnoid injection and make sure tlmt the renal capsule or ureter has not been entered. A volume of up to 10 ml may be required. There are two common complications, after correct placement of the phenol. One is anterior thigh pain usually accompanied by marked hyperaesthesia, which occurs in 20% of patients. It is not related to the technique
INTERVENTIONAL THERAPY
used and can occur after open surgery. It always settles with time and is helped by anticonvulsants and analgesics. The patients should be warned of this possibility. The other complication is genito-femoral neuritis, with a frequency of 5-10%, and is due to the spread of the phenol across the anterior surface of the psoas.
Non n e u r o l y t i e d r u g s Steroids The use of injectable depot preparations of steroids is probably the most widespread interventional practice in pain relief. They can be injected in joint spaces and periarticularly, epidurally, into tendon sheaths and numerous other sites. A lumbar epidural injection of a steroid in the treatment of prolapsed inter vertebral disc is the standard initial treatment in many units. It is probably most effective if used within one month of the onset of symptoms and its benefit may not become apparent for up to 14 days. Nerve damage due to the prolapsed disc will not be improved by the steroid. Some practitioners repeat the injection up to three times. There is no convincing evidence that the use of steroids epidurally causes further nerve root damage. However adrenal function can be suppressed for up to three weeks. There is wide variation in the recommended dose and whether local analgesics should or should not be used. 80 mg of an aqueous suspension of methylprednisolone acetate (Depomedrone) in 10 ml of bupivacaine or saline is a common mixture. It should be noted that Depo-medrone does not have a product licence for epidural use, although there is no documented evidence of any harmful effect from the preparation. This injection can be also be undertaken for the rare occurrence of a cervical disc prolapse. It is also effective in the pain of cervical spondylosis and brachalgia due to foraminal outlet obstruction. As the epidural space terminates rostrally at the level of the foramen magnum the easiest access is by the C7/D1 or C6/7 intervertebral spaces. Other levels are much more difficult to identify and more likely to cause complications such as nerve root trauma. The therapeutic effect of injections of a mixture of local anaesthetic and depot steroid in and around the lumbar facet joints in mechanical low back pain has come under increasing scrutiny. Marks et all ° found that benefits were short lived, only two patients reporting pain relief beyond three months. Most patients with long standing back pain will not be relieved of their symptoms by any procedure and the underlying principle in the management of this group is to enable them to cope with the symptoms and achieve an acceptable quality of life. It is in the management of the acute exacerbation of chronic back pain that facet joint injections are invaluable. Patients come to terms with their condition knowing that if it deteriorates they can gain relief of their symptoms with a simple procedure.
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The procedure is performed under biplanar x-ray control and the painful areas are injected with a mixture of 20 mg of Depo-medrone and local anaesthetic at each site. The volume of the joint space is not more than 0.5 ml and injection of a larger volume may rupture the capsule. The rest of the mixture should be infiltrated around the joint. Relief is usually obtained in from 2 to 7 days but can occasionally take longer. More than 50% of our chronic back pain patients have their symptoms reduced to base line levels for longer than 6 months.
Midazolam Midazolam, an imidazobenzodiazepine, produces antinociceptive effects when injected intrathecally. It has been demonstrated to be effective in the treatment of acute postoperative somatic pain. ~ Serrao et al ~2 have shown that it can be a useful addition to the methods of management of chronic back pain, producing relief of symptoms and reduction of self administered analgesic medication in 50% to 75% of the patients when a dose of 2 mg is mixed with 3 ml of 5% dextrose and injected intrathecally.
Glycerol Glycerol in the form of anhydrous glycerine is a very effective treatment for the distressing condition of trigeminal neuralgia. ~3A spinal needle is introduced into the trigeminal cistern via the foramen ovale. A skin wheel is made about 3 cm from the angle of the mouth and the needle is guided into position using image intensification. Cerebro-spinal fluid should flow back. 0.2 ml to 0.4 ml of the glycerol is then injected through the needle with the patient in the sitting position and the patient maintained in that position for 20 minutes. The injection itself can be painful in some patients, but this is usually short lived. The results are apparent within 2-3 days and are equal to those obtained by radio frequency thermocoagulation. The advantages of this technique are minimal post operative sensory loss and the removal of the need for co-operation fi'om the patient. Glycerol has also proved to be useful for injections around the dorsal root ganglion in cases of root pain. Root pain is common after thoracotomy incisions. Up to 0.5 ml of glycerol placed around the dorsal root gangtion in the intervertebral canal, with the aid of an image intensifier, can often relieve this troublesome pain. A preliminary diagnostic injection with local anaesthetic should be undertaken. Other causes of root pain responding to this form of treatment include renal pain and groin and scrotal pain following hernia repair or testicular surgery.
Radiofrequency lesions The principle of radiofrequency lesioning is the passage, through an electrode, of a high frequency alternating current similar to that used in surgical diathermy, to heat tissue surrounding the electrode tip. Ionic agitation at the
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CURRENT ANAESTHESIA AND CRITICAL CARE
electrode tip produces frictional heating and by using a thermistor or a thermocouple electrode, accurate measurement of the temperature can be made and controlled lesions performed. The size of the lesion created is a function of the electrode diameter, length of the uninsulated tip, temperature and time. Generally the lesion is made for a period of 30-90 s with a tip temperature of 60-85°C. A built in nerve stimulator enables the electrode to be placed in close proximity to the nerve being treated.
Percutaneous cordotomy Percutaneous cordotomy was first popularised by Mullah 14 and Rosomoff. 15 This involves the introduction of an electrode, using a lateral approach and x-ray control, at the interspace between the first and second cervical vertebrae. Local analgesia and some mild sedation are all that is required. The electrode is positioned in the antero-lateral quadrant of the spinal cord on the opposite side to the patient's pain and progressive lesions made, after preliminary stimulation studies have confirmed correct placement, until the area of analgesia to pin prick testing extends two dermatomal segments beyond the pain. The main indication for this method is unilateral somatic pain due to cancer when life expectancy is not more than eighteen months and not less than 4 weeks. The reason for restricting the procedure to terminally ill patients is the development of late onset dysaesthesia which can be worse than the original pain and impossible to relieve. With the correct indications 64% of patients gain complete relief of pain and 25% partial relief, z Complications are problematical motor loss in 10% of patients and occasional patients who have dysaesthesia, impotence, problems with micturition and ataxia. Respiratory difficulties can occur in patients with poor respiratory reserve and a vital capacity of less than 1 1 is an absolute contraindication. Bilateral percutaneous cordotomy at the C 1/2 level can produce sleep apnoea - the so called 'Ondine's curse'. For this reason the second cordotomy is usually performed at the level of C6 and is a much more technically demanding operation. Mortality has been reported at 6%,
Trigeminal neuralgia Radiofrequency lesioning of the preganglionic roots of the trigeminal nerve was the treatment of choice of trigeminal neuralgia which could not be controlled by drugs. Glycerol injection has reduced the need for this mode of treatment. The advantages of radiofrequency lesioning over the earlier methods of treatment are those of control. The electrode, using a combination of X-ray imaging and electrical stimulation at 50-100 Hertz, could be precisely positioned in the affected rootlets. Progressive heat lesions are made until minimal sensory loss to pin prick in the relevant dermatomes is produced. The procedure is time consuming and painful for the
patient so thai intermittent general anaesthesia is used and this can cloud the end point. Excessive numbness can lead to anaesthesia dolorosa. The results are good. 80% of patients gain relief for one year and about 50% for 5 years. Radiofrequency lesions have been, and still are, used in many other situations such as facet nerve thermocoagulation in chronic back pain; coagulation of the dorsal re-entry zone (DREZ) of the spinal cord in the cervical and thoracic regions for post traumatic brachial plexus pain and post herpetic neuralgia; coagulation of the dorsal root ganglion for root pain and destruction of the pituitary gland in cancer pain.
Drug delivery systems In the late 1970s the first reports started to appear about the analgesic action of opioids on the spinal cord. A new field of clinical research opened and many different drugs are now administered this way. This was the stimulus to the development of fully implantable drug delivery systems for use long term via the epidural and intrathecal routes. The available systems vary from those having a reservoir which needs filling at short intervals by a percutaneous puncture to more sophisticated systems utilising a pump which can have its rate altered telemetrically. Opioids are used in the management of terminally ill patients as well as for conditions such as the 'failed back'. Baclofen, intrathecally, has proved to be invaluable in the management of spasticity in patients suffering from multiple sclerosis and spinal cord injuries. Baclofen is one of a group of drugs, which includes midazolam, which act on the 7-aminobutyric acid (GABA) system in the spinal cord. Administration of GABA-mimetic compounds has been shown to inhibit nociceptive responses in experimental animals and to produce analgesia in man. This may well be the direction from which drugs for the delivery systems of the future will be developed.
Dorsal column stimulation Spinal cord stimulation in the management of chronic intractable pain has been performed for about twenty years. Initially the electrodes were positioned at laminectomy but gradual improvements in the design of electrodes has meant that the percutaneous approach can be utilised for permanent electrode placement. This gives the opportunity for preliminary screening so that the effectiveness of pain relief can be assessed before a full implantation is undertaken. The currently available systems cost about £4500 and the operation should only be undertaken in centres where the appropriate skills can be acquired by performing the procedure regularly. It is not without complications such as electrode slippage and infection and the patients need life time care. Many workers are now reporting long term improvement of more than 50% pain relief in conditions such as the 'failed back', arachnoiditis, phantom limb and stump pain. ~6
INTERVENTIONAL THERAPY
Conclusion Current approaches to the management of non-acute pain are tending to be biased towards the more behavioural models exemplified by Pain Management programmes. There is however still a place for the interventional approach in Pain Management Clinics. This article has outlined the methods that are available and which have proved to be useful in clinical practice, ranging from the injection of depot preparations of steroids to dorsal column stimulation. References 1. Maher R. M. Relief of Pain in incurable cancer. Lancet 1955; 1:18 2. Lahuerta J, Lipton S, Wells JCD Percutaneous cervical cordotomy: results and complications in a recent series of 100 patients. Ann R Coll Surg Eng 1985; 67:41-44 3. Maher R, Mehta M Spinal (intrathecal) and extradural analgesia. In: Lipton S (ed) Persistent pain; modern methods of treatment, vol 1. Academic Press, London, 1977:61-99 4. Robertson DH. Transsacral neurolytic nerve block, an alternative approach to intractable perineal pain. Br J Anaesth 1983; 55:873-875 5. Ischia S, Lozzani A, Ischia A, Faggion S.A new approach to the neurolytic block of the celiac plexus: the transaortic technique. Pain 1983; 16:333-341
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6. Greco T, Sbaragli F, Cammili L L'alcoolizazione della ipofisi per via transfenoidale nella terapia di particolari tumori maligni. Settimana Medicale 1957; 45:355-356 7. Morrica G. Chemical hypophysectomy for cancer pain. In: Bonica JJ (ed) Advances in neurology 4. Raven Press, NewYork, 1974:707-714 8. Miles JB Pituitary destruction. In: Wall PD, Melzack R (eds) Textbook of Pain. Churchill Livingstone, Edinburgh, 1989:860 9. Cotton LT, Cross FW. Lumbar sympathectomy for arterial disease. B r J Surg 1985; 72:678-683 10. Marks RC, Houston T, Thulbourne T. Facet joint injection and facet nerve block: a randomised comparison in 86 patients with chronic low back pain. Pain 1992; 49:325-328 11. Goodchild CS, Noble J. The effects of intrathecal midazolam on sympathetic nervous system reflexes in man - - a pilot study. Br J Clin Pharmacol 1987; 23:273-285 12. Serrao JM, Marks RL, Morley SJ, Goodchild CS. Intrathecal midazolam for the treatment of chronic mechanical low back pain: a controlled comparison with epidural steroid in a pilot study. Pain 1992; 48:5-12 13. Hakansson S. Trigeminal neuralgia treated by the injection of glycerol into the trigeminal cistern. Neurosurgery 1981; 9:638-646 14. Mullan S, Harper PV, Hekmatpanah J, Torres H, Dobbin G. Percutaneous interruption of spinal-pain tracts by means of a Strontium 9° needle. J Neurosurg 1963; 20:931-939 15. Rosomoff HL, Can'ol F, Brown J, Sheptak P Percutaneous radiofrequency cervical cordotomy technique. J Neurosurg 1965; 23:639-644 16. North RB, Ewend MG, Lawton MT, Piantadosi S. Spinal cord stimulation for chronic, intractable pain: superiority of 'multichannel' devices. Pain 1991; 44:119-130