Hyperbaric oxygen therapy attenuates central sensitization induced by a thermal injury in humans.

BACKGROUND: Hyperbaric oxygen (HBO2 ) treatment has in animal experiments demonstrated antinociceptive effects. It was hypothesized that these effects would attenuate secondary hyperalgesia areas (SHAs), an expression of central sensitization, after a first-degree thermal injury in humans. METHODS: Seventeen healthy volunteers were examined during two sessions using a randomized crossover design. Volunteers were studied during control conditions (ambient pressure, FI O2 = 0.21) and during HBO2 (2.4 standard atmosphere, FI O2 = 1.0, 90 min) conditions in a pressure chamber. Quantitative sensory testing, including assessment of SHAs was performed. RESULTS: A statistically significant overall attenuation of SHAs was seen during the HBO2 sessions compared with the control-sessions (P = 0.011). In the eight volunteers starting with the HBO2 session, no difference in SHAs compared with control was demonstrated. However, in the nine volunteers starting with the control session, a statistical significant attenuation of SHAs was demonstrated in the HBO2 session (P = 0.004). CONCLUSIONS: The results indicate that HBO2 therapy in humans attenuates central sensitization induced by a thermal skin injury, compared with control. These new and original findings in humans corroborate animal experimental data. The thermal injury model may give impetus to future human neurophysiological studies exploring the central effects of hyperbaric oxygen treatment.

Chronic pain and the development of a symptom checklist: a pilot study.

BACKGROUND: There is currently no instrument to systematically assess the range of symptoms/problems and their bothersomeness in patients with chronic non-cancer pain (CNPN). Systematic assessment and prioritizing may target treatments and improve outcomes. METHODS: The authors developed a checklist of symptoms and problems, the Copenhagen Symptom Checklist (CSC), presented clinically by patients. Fifty-three items representing biological, psychological and social areas were selected. Symptom/problem severity was rated on a 5-point scale anchored at 0 = 'not at all' and 4 = 'severe'. Patients ranked the five most bothersome symptoms/problems and could add five open-ended items. Patients completed the CSC after the first visit at the multidisciplinary pain centre. RESULTS: One hundred and twelve consecutive patients completed the CSC. Eighty-nine percent scored pain as rather severe or very severe (score = 3 plus score = 4), followed by reduction in physical activity (67%), fatigue (66%) and sleep disturbance (53%). Pain and fatigue, but not reduction in physical activity, were given highest priority. Cognitive problems were important to a third of the patients. Depressive symptoms, cognitive problems and worry explained 17.5% of the total variance. Patients filled in the CSC without important loss of information, but a minority prioritized more than three areas or used the free text alternative. CONCLUSIONS: Patients prioritized pain and fatigue as the most burdensome symptoms, but reduction in physical activity and sleep problems were also highly ranked. Patients were positive to the idea of symptom reporting; however, the 53-item number in this version of CSC is larger than may be necessary.

Humidity affects the performance of von Frey monofilaments.

BACKGROUND: Assessment of tactile and nociceptive thresholds of the skin with calibrated polyamide monofilaments is an established testing method both in animal and in human research. It is known that changes in relative humidity may affect the physical properties of the monofilaments. As this effect has only been studied in very small diameter monofilaments, used in neonatal research, we therefore studied complete sets of polyamide monofilaments. METHODS: The effects were studied in a controlled climate chamber during six incremental changes in relative humidity from 20% to 79% (22-24°C). Following 24 h of equilibration at each humidity level, calibration with a precision scale was performed. RESULTS: A highly significant linear correlation between the natural logarithm (In) of the bending force and the von Frey number was observed at all humidity levels (r(2)>0.99, P<0.0001). An inverse linear relationship between relative humidity and In of the bending force for each monofilament was found (r(2)=0.95, P<0.0001). One percent increase in relative humidity corresponded to a 1-4% relative decrease in numerical bending force, depending on the diameter of the monofilament. A significant linear relationship was observed between the coefficient of variation and the relative humidity (r(2)=0.87, P<0.001). CONCLUSIONS: The data indicate that the hygroscopic properties of polyamide monofilaments must be taken into account for their reliable use in quantitative sensory testing.

Patients' experiences with multiple stimulation axillary block for fast-track ambulatory hand surgery.

BACKGROUND: Ambulatory axillary block by multiple nerve stimulation (MNS) is effective and time efficient, but may be rejected by patients because of block pain. This prospective study assessed patients' anxiety and acceptance of this block, identified which of the components of blocking procedure is most painful (i.v. line insertion, repeated needle passes, local anesthetic injection, or electrical stimulation) and recorded patients' anesthetic preferences for the future hand surgery. METHODS: Upon arrival at the day unit, 100 unpremedicated adult patients without previous experience of peripheral nerve stimulation indicated on the visual analog scale (VAS; 0-100) their anxiety about the block. The blocking procedure was then explained step-by-step. After inserting the i.v. line and freezing the skin in axilla, four terminal nerves (musculocutaneous, median, ulnar, radial) were electrolocated using an initial current of 2 mA and a target current of 0.1-0.5 mA. Pain caused by the individual components of blocking procedure was assessed on VAS before the start of surgery. On the day after the operation, the patients reassessed their anxiety for the next axillary block and indicated which anesthetic method (block alone, block plus sedation, or general anesthesia) they would prefer for the future hand surgery. RESULTS: Before the block, 59 patients admitted being anxious about regional block (median anxiety VAS=27), compared with 42 patients (anxiety VAS=10) postoperatively: P<0.01. Median intensity of electrical stimulation pain was significantly higher (VAS=16) than pain of local anesthetic injections (VAS=8), i.v. line insertion (VAS=6) and multiple needle passes (VAS=5). However, only 53 patients categorized electrolocation as painful. Twenty-seven reported discomfort but not pain, and 20 patients described the sensation as 'funny' or 'strange'. None of the patients had surgical pain during operation. Mean duration of surgery was 77 min, and of hospital stay 166 min. Ninety-eight patients would choose the same block for the future hand surgery, 13 of which would like sedation before the block, and two patients did not wish to be awake during any surgery. Ninety-five patients were satisfied with fast-tracking. CONCLUSIONS: Fear of block pain is diminished after experiencing the blocking procedure. Electrical stimuli was perceived as painful by 53% of patients, and this pain was more intense than with other block components. The majority of our patients would choose axillary block without sedation for future hand surgery and are satisfied with fast-tracking.

A comparison of coracoid and axillary approaches to the brachial plexus.

BACKGROUND: Brachial plexus block by the coracoid approach does not require arm abduction and may be more effective than the axillary approach because of a more proximal injection of local anaesthetic. However, the clinical usefulness of the coracoid approach has not been tested in prospective controlled trials. The present randomized, observer-blinded study compared success rates, time to obtain a complete block, frequency of adverse effects and block discomfort in two groups of 30 patients, anaesthetized for hand surgery using either the coracoid or the axillary approach to the brachial plexus. METHODS: After subcutaneous infiltration with 5 ml of 1% mepivacaine/adrenaline the brachial plexus was located using a nerve stimulator and an insulated pencil-point needle. Ropivacaine 0.75%, 20-40 ml, depending on body weight, was used for the initial block. In the coracoid (C) group two plexus cords, and in the axillary (A) group four terminal nerves were electrolocated and the volume of ropivacaine was divided equally between them. Spread of analgesia to the arm was assessed every 5 min, by an anaesthetist unaware of the block technique. The block was defined as effective (complete) when analgesia was present in all five sensory nerve areas distal to the elbow. Incomplete blocks were supplemented 30 min after the initial block. RESULTS: In the C group a median 11 min was required for block performance as compared to 12 min in the A group (NS). Onset of block was shorter and the frequency of incomplete blocks lower in the A group (median 17 min and 17%) than in the C group (30 min and 47%, respectively). Lack of analgesia of the ulnar nerve was the main cause of incomplete initial blocks in the C group. All incomplete blocks were successfully supplemented. However, total time to obtain complete block was shorter in the A group than in the C group (29 min vs. 41 min, P<0.05). Accidental arterial puncture occurred in seven patients (five in C and two in A group), which resulted in two haematomas, both in the C group (NS). No permanent sequelae were observed. CONCLUSION: The axillary approach to the brachial plexus using four injections of ropivacaine results in a faster onset of block and a better spread of analgesia than the coracoid approach using two injections.

Low dose axillary block by targeted injections of the terminal nerves.

PURPOSE: To compare anesthetic time, success rate and adverse effects of axillary block by single or multiple injections of local anesthetic. METHODS: Two groups of patients were studied. In group T (targeted injections, n = 53) the four terminal nerves were located by electrical stimulation, and anesthetized with 5 ml mepivacaine 1% with epinephrine 5 microg x ml(-1) (MEPE). In group S (single injection, n = 53) 80 mL MEPE 1% were injected into the neurovascular sheath, transarterially or after eliciting paresthesia. Patchy blocks were supplemented after 30 min. The patient was ready for surgery when analgesia was present in all areas distal to the elbow. RESULTS: The block was complete at 11 min (6-15) in Group T and 7 min (5-13) in group S, P<0.01. Supplementation was required in 46% in group S compared with 13% in group T P<0.001: anesthesia time was 32 min (19-52) in group T, and 39 min (16-58) in group S, P = 0.02. The average doses of MEPE were 3.5 mg x kg(-1) (2.4-5.6) in T group and 12.0 mg x kg(-1) (8.9-16.4), in S group. However, 22% of patients in group T and 4% in group S reported tourniquet pain, P = 0.02. Paresthesia was elicited in 42% of patients in group S and 8% in group T, P<0.001. CONCLUSIONS: Small targeted injections of MEPE reduce total anesthetic time, give better spread of analgesia in the hand and forearm, and may be safer than a single large injection.