The addition of glyceryltrinitrate to capsaicin cream reduces the thermal allodynia associated with the application of capsaicin alone in humans.

The aim of this study was to determine whether topical application of capsaicin cream causes thermal allodynia and the extent to which this is attenuated by the addition of glyceryltrinitrate (GTN). This was a double blind placebo controlled study of 40 consenting adult subjects. Each of four cream combinations (GTN, capsaicin, GTN/capsaicin and vehicle) were applied to the subjects with at least a 1 day interval between each application. Water at a known temperature was applied to the standard area of skin where cream had been applied. Subjects rated the resulting thermal allodynia using a 0-10 Likhert score. Thermal allodynia is usually apparent when warm water is applied to skin containing capsaicin. The thermal allodynia caused by the topical application of capsaicin was significantly reduced by the addition of GTN. The addition of GTN to capsaicin cream significantly reduces the thermal allodynia associated with the application of capsaicin cream alone.

Lamotrigine in the management of neuropathic pain: a review of the literature.

OBJECTIVE: The purpose of this review is to examine the accumulating evidence indicating that lamotrigine is effective in the treatment of neuropathic pain. METHOD: A review of the available literature. RESULTS: Neuropathic pain is a debilitating series of conditions that are often poorly controlled. The molecular action of lamotrigine in terms of its effects in preclinical models of pain and hyperalgesia are considered along with the accumulating evidence suggesting that lamotrigine may be effective in the clinical management of neuropathic pain. CONCLUSION: A review of the literature suggests that lamotrigine may be effective in the management of neuropathic pain.

Intravenous infusion of phenytoin relieves neuropathic pain: a randomized, double-blinded, placebo-controlled, crossover study.

UNLABELLED: Neuropathic pain responds inconsistently to opioids and nonsteroidal antiinflammatory drugs. However, oral anticonvulsants have a proven analgesic effect on neuropathic pain, but may not be practical in an acute flare-up. Phenytoin was the first oral anticonvulsant used as an analgesic for neuropathic pain. There have been few studies on the parenteral analgesic effect of this drug. In this randomized, double-blind, placebo-controlled, crossover study of 20 patients with acute flare-ups of neuropathic pain, we compared a 2-h placebo infusion with a 2-h infusion of 15 mg/kg phenytoin. Overall pain, shooting pain, burning pain, paresthesia, numbness, and sensitivity were measured using a 10-cm linear visual analog score. Numbness and sensitivity were reduced in the placebo group during infusion, but not in the 7 days after infusion. In the phenytoin group, there were significant reductions in burning pain (P < 0.05), shooting pain (P < 0.001), sensitivity (P < 0.001), numbness (P < 0.05), and overall pain (P < 0.005) during the infusion period. The reduction in overall pain persisted for 1 day, in sensitivity for 2 days, and in shooting pain for 4 days after infusion. We conclude that IV infusion of 15 mg/kg phenytoin has an analgesic effect in acute flare-ups of neuropathic pain and that this relief outlives both the infusion time and plasma half-life of phenytoin. IMPLICATIONS: Oral phenytoin can relieve neuropathic pain. The aim of this study was to examine the effect of IV phenytoin on neuropathic pain. The results indicate that IV phenytoin may be used to treat flare-ups of chronic neuropathic pain.

The cholecystokinin antagonist proglumide enhances the analgesic efficacy of morphine in humans with chronic benign pain.

UNLABELLED: The analgesic efficacy of morphine is sometimes only partial in patients with chronic benign pain. Among the possible factors contributing to this limitation are increased levels of cholecystokinin (CCK). We performed this prospective, placebo-controlled, double-blind, cross-over study to examine the effect of proglumide, a nonspecific CCK agonist, on analgesia in patients taking morphine on a chronic basis. Forty patients with intractable pain who were taking sustained-release morphine were recruited, and we obtained results from 36 of these patients. Median visual analog scale scores before the study were 8 and 7 after the addition of placebo for 2 wk (P = 0.16), and 6 after proglumide for 2 wk (P = 0.002). Mobility was unchanged by proglumide or placebo. Of the 36 patients, 13 elected to continue receiving proglumide after the study. We conclude that proglumide enhances the analgesia produced by morphine in some, but not all, patients with chronic benign pain. IMPLICATIONS: The pain-killing effect of morphine is incomplete in some patients. Increasing doses may be needed to maintain the initial effect. The peptide cholecystokinin may be partially responsible for this. In this study, we demonstrated that the cholecystokinin antagonist proglumide increases the analgesic effect of morphine in some patients with chronic benign pain.

Propofol and serum potassium.

The aim of this study was to examine the effect of propofol and propofol with suxamethonium on serum potassium concentration during induction of general anaesthesia. Forty patients were studied during elective surgery and serum electrolytes were measured before and after the induction of anaesthesia. Patients were allocated at random into two groups to receive either propofol alone or with suxamethonium. The serum potassium fell by 0.04 mmol.l-1 by 5 min after induction with propofol alone but had recovered to the pre-induction level by 10 min. The serum potassium rose by 0.23 mmol.l-1 when a combination of propofol and suxamethonium was used for the induction of anaesthesia.

Factors that influence the induction dose of propofol.

Factors that influence the induction of anaesthesia with propofol were investigated in a prospective study of 1000 patients. Pre-operative albumin and urea concentrations correlated with the minimum induction dose of propofol, but less strong correlations were found with haemoglobin, globulin and total protein concentrations. Age was an important influence on the induction dose of propofol (r = -0.34) which was also closely related to ASA grade. Induction of anaesthesia with propofol is dependent on a number of variables, and this study suggests that pre-operative albumin and urea concentrations are important.

Preoperative measurement of haemoglobin concentration.

Haemoglobin concentrations were estimated in 1158 patients admitted to hospital for elective surgical procedures. Haemoglobin concentration below 10 g/dl was not seen in male patients who were fit and healthy, or had mild or severe non life threatening systemic diseases. In female patients haemoglobin concentration below 10 g/dl was seen in 0.3% of normal fit healthy patients, 2% of patients with mild systemic diseases, 6.4% of patients with severe, non life threatening diseases, and 18.7% of those with severe incapacitating diseases. Routine haemoglobin measurement is unnecessary in fit healthy patients, or in those with mild systemic disease (American Society of Anesthesiologists grades 1 or 2), but should be done in those with more severe systemic diseases (American Society of Anesthesiologists grades 3, 4 or 5).

Pre-operative anxiety and serum potassium.

Small decreases in serum potassium in a study of 200 pre-operative patients were demonstrated in those who had an increase in anxiety, as measured on a linear analogue anxiety scale, in the 24 hours before anaesthesia. The possible aetiology and implications of this change are discussed. The combination of temazepam and a pre-operative visit by the anaesthetist effectively reduced pre-anaesthetic anxiety in 60% of patients.

Routine pre-operative electrocardiography.

In a study of 877 patients presenting for anaesthesia with an ECG, 45 per cent of the ECGs were found to be abnormal. The incidence of abnormal ECGs was found to be highest in the over-40 age group, and also in those patients of ASA Grades II, III, IV and V, and this investigation is therefore recommended in these patients.

The nature of pre-operative anxiety.

In a study of 247 patients who had general anaesthesia for dental procedures, the incidence of individual anxieties was noted using a questionnaire completed by the patient. The most common anxieties related to the period before transfer to the operating theatre, intra-operative awareness and postoperative pain. These anxieties were present in over half the patients questioned. The follow-up questionnaire was completed by 207 patients in order to indicate which anxieties they would expect to have if they needed anaesthesia in the future. All anxieties were less frequent than found before operation.

Pre-operative investigations--the anaesthetist's perspective.

The information gained when abnormalities are detected by pre-operative investigations is of interest to the anaesthetist as it may change the anaesthetic technique and anaesthetic drugs used. Tests should not be routinely used in all patients, but only in those over the age of 50 or in those with an increased chance of abnormalities being detected.

Electroconvulsive therapy and serum potassium.

In 54 patients presenting for electroconvulsive therapy, the concentration of serum potassium was measured before and after the induced convulsion modified with a standard anaesthetic technique of methohexitone and suxamethonium. It was found that there was a statistically significant rise in serum potassium, but that the duration of convulsion had no significant effect on that rise in serum potassium. In a further 11 patients, methohexitone alone was administered without ECT, and it was found that serum potassium fell. Methohexitone, suxamethonium and ECT in combination cause a rise in serum potassium which is not clinically important unless pre-induction level is abnormally high, and prolonged convulsion does not exaggerate this rise.

Routine preoperative chest X-rays.

687 patients presenting for routine and emergency anaesthesia were studied. 297 were found to have a chest X-ray. Abnormalities on chest X-ray were scattered amongst most age groups. Patients in American Society of Anaesthesiologists grade I were found to have abnormalities in only 4% of cases, and the abnormalities were of no anaesthetic significance. The incidence of abnormalities increased to 25% in grade II, 52% in grade III and 81% in grades IV and V. Patients in American Society of Anaesthesiologists grades III, IV and V, and those suffering from trauma should have a preoperative chest X-ray.