Blockade of the T6-T11 intercostal nerves gives good results after unilateral abdominal incisions, e.g. for cholecystectomy. Using 0.5% bupivacaine 6-12 h of analgesia can be obtained (see p. 144).
Cryoanalgesia of the intercostal nerves performed while the thorax is open has been used for pain relief after thoracotomy. Good relief is obtained particularly after the intercostal drain has been removed, but there have been reports of troublesome neuropathy.
Cryoanalgesia of the intercostal nerves performed while the thorax is open has been used for pain relief after thbracotomy. Good relief is obtained particularly after the intercostal drain has been removed, but there have been reports of troublesome neuropathy.
Interpleural injection
(See p. 150). This is particularly effective after subcostal (Kocher) incisions for cholecystecto-my, but it has also been used for thoracotomy, fractured ribs, renal surgery and mastectomy.
Bupivacaine is the preferred drug. Several dosage regimes have been used and only seem to differ in regard to the duration of effect, the more local anaesthetic used, the longer being the duration. Thus 20 ml of 0.25% will last on average about 4 h, 20 ml 0.375% 6 h and 20 ml 0.5% 8 h. Individual variations are quite wide and top-ups should be given as required. The plasma concentrations that have been measured indicate a slow uptake from the pleural cavity and toxic levels are not seen. Epineph-rine 1:200.000 is usually added to the solution.
To avoid top-up injections, continuous infusions have been used, e.g. 5-10 ml/h of 0.25% or 0.5% bupivacaine.
Central nerve blocks
Epidural block
Although the effectiveness of epidural block in relieving postoperative pain is undoubted and the use of a catheter technique allows for continuous use over many hours or days, this technique has not achieved the popularity in postoperative analgesia that it has with the relief of pain in labour.
Advantages
Nevertheless, excellent results can be obtained, and the following advantages may accrue from its use:
1. Excellent pain relief without central depression
2. Protection from the surgical stress reaction
3. Increase in lower limb blood flow with a decrease in the incidence of deep venous thrombosis and pulmonary embolus
4. Avoidance of postoperative hypertension, e.g. after major arterial surgery
5. Ability to passively move replaced joints and institute physiotherapy without pain
6. Better gastrointestinal function as the inhibitory effects of opioids can be avoided
Side-effects
The most feared side-effects are:
Hypotension
This is seldom a problem if patients are properly hydrated, the block is restricted to the segments required for analgesia, and sudden movement to the sitting up position is avoided. Arterial blood pressure is easy to monitor and hypotension is easy to treat, e.g. by giving IV fluids and/or a vasopressor.
Prolonged paralysis of the lower limbs
This is disliked by the patients but can be avoided by proper selection of the concentration of local anaesthetic.
Catheter migration to the subarachnoid space
This has been described but it must be extremely rare. Plastic catheters used in epidural blocks cannot be pushed through normal dura mater. Apparent migration can often be explained by the use of a multiple hole catheter which may have been inserted in such a way that the distal hole is within the subarachnoid space while the proximal holes are in the epidural space. In such an eventuality, a slow injection would deposit drug in the epidural space while a fast injection would force it into the subarachnoid space.
Urinary retention
This is common with epidural blocks that involve the sacral nerve roots containing the sacral parasympathetic nerves. It does necessitate catheterisation of the bladder and prophylactic antibiotic is a prudent precaution.
Principles
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