Risk evaluation for needle-nerve contact related to electrical nerve stimulation in a porcine model.

BACKGROUND: For performing peripheral nerve blocks, the risk for needle-nerve contact (NNC) as an adverse event for low and high current thresholds has not yet been clearly defined when nerve stimulator guided techniques were applied. This experimental study aimed to investigate the risk of NNCs when applying stimulation currents between 0.1 and 2 mA (in increments of 0.1 mA). METHODS: Brachial plexus nerves were exposed surgically in five anesthetized pigs. An insulated needle connected to a nerve stimulator was placed at 10 mm distance to the targeted nerves. Current intensity was adjusted according to randomization (0.1-2.0 mA, increments of 0.1 mA). The needle tip was advanced toward the nerve until a motor response was elicited. The frequencies of NNCs for each of the adjusted current intensities were noted. Risks of NNCs were calculated according to the analysis of 95% confidence intervals (95% CI). RESULTS: We executed 2000 needle placements with stimulation currents ranging from 0.1 to 2.0 mA. The risks for NNC at low current intensities were 0.85 (95% CI, 0.77-0.91) for 0.3 mA and 0.5 (95% CI, 0.4-0.6) for 0.5 mA, respectively. For high current intensities, risks of 0.13 (95% CI, 0.07-0.21) for 0.9 mA and 0.01 (95% CI, 0-0.05) for 1.1 mA were calculated. CONCLUSIONS: In this experimental animal study, a relevant reduction in the risk of NNCs could be observed when high current intensities (0.9-1.1 mA) were applied compared to low current intensities (0.3-0.5 mA).

Clinical effectiveness of a silicone foam dressing for the prevention of heel pressure ulcers in critically ill patients: Border II Trial.

OBJECTIVE: Critically ill patients are at high risk of developing pressure ulcers (PU), with the sacrum and heels being highly susceptible to pressure injuries. The objective of our study was to evaluate the clinical effectiveness of a new multi-layer, self-adhesive soft silicone foam heel dressing to prevent PU development in trauma and critically ill patients in the intensive care unit (ICU). METHOD: A cohort of critically ill patients were enrolled at the Royal Melbourne Hospital. Each patient had the multi-layer soft silicone foam dressing applied to each heel on admission to the emergency department. The dressings were retained with a tubular bandage for the duration of the patients' stay in the ICU. The skin under the dressings was examined daily and the dressings were replaced every three days. The comparator for our cohort study was the control group from the recently completed Border Trial. RESULTS: Of the 191 patients in the initial cohort, excluding deaths, loss to follow-up and transfers to another ward, 150 patients were included in the final analysis. There was no difference in key demographic or physiological variables between the cohorts, apart from a longer ICU length of stay for our current cohort. No PUs developed in any of our intervention cohort patients compared with 14 patients in the control cohort (n=152; p<0.001) who developed a total of 19 heel PUs. CONCLUSION: We conclude, based on our results, that the multi-layer soft silicone foam dressing under investigation was clinically effective in reducing ICU-acquired heel PUs. The findings also support previous research on the clinical effectiveness of multi-layer soft silicone foam dressings for PU prevention in the ICU.

Intrathecal 1% 2-chloroprocaine vs. 0.5% bupivacaine in ambulatory surgery: a prospective, observer-blinded, randomised, controlled trial.

BACKGROUND: This prospective, observer-blinded, randomised, multicentre study aimed at determining the non-inferiority of 50 mg of plain 1% 2-chloroprocaine vs. 10 mg of 0.5% plain bupivacaine in terms of sensory block onset time at T10 after spinal injection. The study hypothesis was that the difference in onset times of sensory block to T10 between the two drugs is ≤ 4 min. METHODS: One hundred and thirty patients undergoing lower abdominal or lower limb procedures (≤ 40 min) were randomised to receive one of two treatments: 50 mg of plain 1% 2-chloroprocaine (Group C, n = 66) or 10 mg of plain 0.5% bupivacaine (Group B, n = 64). Times to sensory and motor block onsets, maximum sensory block level, readiness for surgery, regression of sensory and motor blocks, first analgesic requirements, unassisted ambulation, home discharge, and side effects after 24 h and 7 days were registered blindly. RESULTS: Chloroprocaine was comparable with plain 0.5% bupivacaine in terms of time to sensory block at T10 level. Group C showed faster onsets of motor block (5 vs. 6 min), maximum sensory block level (8.5 vs. 14 min), resolution of sensory (105 vs. 225 min) and motor (100 vs. 210 min) blocks, unassisted ambulation (142.5 vs. 290.5 min), first analgesic requirement (120 vs. 293.5 min), and home discharge (150 vs. 325 min) (all comparisons, P < 0.05). No chloroprocaine patient developed transient neurological symptoms. CONCLUSION: Spinal anaesthesia with 50 mg of plain 1% 2-chloroprocaine is similar to 10 mg of plain 0.5% bupivacaine in terms of onset of sensory block at T10 but shows quicker recovery from anaesthesia than with 0.5% bupivacaine.

Dual guidance improves needle tip placement for peripheral nerve blocks in a porcine model.

BACKGROUND: The objective of the study was to evaluate whether the use of ultrasound (US) together with nerve stimulation (USNST) provides a better needle tip position for performing peripheral regional anaesthesia than the use of US or nerve stimulation (NST) alone. METHODS: Needle placements were applied at the brachial plexus and sciatic nerves in 32 anaesthetised pigs. Following needle placement near the target nerve, using either the USNST or the US or NST, a volume of 0.3 ml synthetic resin was injected mimicking a 'test-dose' injection. The primary outcome was the incidence of close needle-to-nerve placement assessed by injectate localisation in direct contact with the nerve epineurium. Secondary endpoints were the incidences of intraneural injection and haematoma formation in direct contact with the target nerve. RESULTS: A total of 611 punctures were performed. The evaluation for the criterion 'close needle placement' revealed significant differences in favour of the USNST group (98.5%) compared with the NST (90.1%) and the US group (81.6%) (P = 0.001). Significant differences were observed regarding 'intraneural needle placement' between the groups as well (USNST, 0.5%; US, 4%; NST, 2.5%; P = 0.034). The incidence of haematoma formation was significantly higher in the NST group (10.8%) than in the US group (2.5%) and in the USNST group (1.5%) (P = 0.001). CONCLUSION: These findings suggest that the USNST approach combines the benefits of the US and the NST techniques in terms of a higher rate of close needle tip placements and a lower incidence of haematoma formation.

Nerve perforation with pencil point or short bevelled needles: histological outcome.

BACKGROUND: In the case of needle nerve contact during peripheral blocks, pencil point needles are considered less traumatic compared with bevelled needles. However, there are not enough data to prove this notion. Therefore, the aim of this study was to challenge the hypothesis that nerve perforation with short bevelled needles is associated with major nerve damage compared with pencil point needles. METHODS: In five anaesthetised pigs, the brachial plexus was exposed bilaterally. Up to eight nerves underwent needle nerve perforation using a pencil point needles cannula or an short bevelled needle. After 48 h, the nerves were resected. The specimens were processed for visual examination and the detection of inflammatory cells (haematoxylin-eosin, i.e. CD68-immunohistochemistry to detect macrophages), myelin damage (Kluver-Barrera staining) and intraneural haematoma. The grade of nerve injury was characterised by an objective score ranging from 0 (no injury) to 4 (severe injury). RESULTS: Fifty nerves were examined. According to the injury score applied, there was no significant difference between the pencil point needles [median (inter-quartile range) 2.0 (2.0-2.0)] and the short bevelled-needle group [median 2.0 (2.0-2.0) P=0.23]. No myelin damage was observed. Signs of post-traumatic inflammation were equally distributed among both groups. CONCLUSIONS: In the present study, the magnitude of nerve injury after needle nerve perforation was not related to one of the applied needle types. Post-traumatic inflammation rather than structural damage of nerve tissue is the only notable sign of nerve injury after needle nerve perforation with either needle type. However, neither the pencil point- nor the short bevelled needle can be designated a less traumatic device.

Systematic evaluation of the highest current threshold for regional anaesthesia in a porcine model.

BACKGROUND: The purpose of this study was to determine systematically the highest minimal stimulation current threshold for regional anaesthesia in pigs. METHODS: In an established pig model for regional anaesthesia, needle placements applying electric nerve stimulation were performed. The primary outcome was the frequency of close needle to nerve placements as assessed by resin injects and subsequent anatomical evaluation. Following a statistical model (continual reassessment method), the applied output currents were selected to limit the necessary number of punctures, while providing guidance towards the highest output current range. RESULTS: Altogether 186 punctures were performed in 11 pigs. Within the range of 0.3-1.4 mA, no distant needle to nerve placement was found. In the range of 1.5-4.1 mA, 43 distant needle to nerve placements occurred. The range of 1.2-1.4 mA was the highest interval that resulted in a close needle to nerve placement rate of > or =95%. CONCLUSIONS: In the range of 0.3-1.4 mA, all resin deposition was found to be adjacent to nerve epineurium. The application of minimal current intensities up to 1.4 mA does not obviously lead to a reduction of epineural injectate contacts in pigs. These findings suggest that stimulation current thresholds up to 1.4 mA result in equivalent needle tip localisation in pigs.

Nerve injury by needle nerve perforation in regional anaesthesia: does size matter?

BACKGROUND: In regional anaesthesia, there is a risk of direct nerve injury. The purpose of this study was to determine whether the diameter of the applied needle is associated with the magnitude of nerve injury after needle nerve perforation. METHODS: In five anaesthetized pigs, the brachial plexus were exposed bilaterally. Up to eight nerves underwent needle nerve perforation using a 24 G pencil-point cannula (small diameter) or a 19 G pencil-point needle (large diameter). After 48 h, the nerves were resected during anaesthesia. The specimens were processed for visual examination and the detection of inflammatory cells, myelin damage and intraneural haematoma. The grade of nerve injury was scored ranging from 0 (no injury) to 4 (severe injury). RESULTS: Forty-eight nerves were examined. The applied injury score was significantly lower in the small-diameter group [median (inter-quartile range) 2.0 (2.0-2.0)] compared with the large-diameter group [3.5 (3.0-4.0) P<0.01]. Myelin damage and intraneural haematoma occurred predominantly in the large-diameter group. Signs of post-traumatic regional inflammation were comparable among both groups. CONCLUSIONS: The severity of nerve injury after needle nerve perforation was related to the diameter of the applied cannula. However, no such difference exists for regional inflammation. Functional consequences of these findings need to be determined. Currently, small-diameter cannulae may be advisable for peripheral nerve blocks to minimize the risk of nerve injury in the case of nerve perforation.

High or low current threshold for nerve stimulation for regional anaesthesia.

BACKGROUND: The purpose of this study was to determine whether the application of high stimulation current thresholds (SCT) leads to a distant needle to nerve proximity (NNP) compared with low SCT during nerve localization for regional anaesthesia in pigs. METHODS: A minimal motor response to the stimulation of femoral or brachial plexus nerves in 16 anaesthetized pigs was triggered either by a minimal SCT of a low (0.01-0.3 mA) or a high (0.8-1.0 mA) current in a random order. After eliciting a motor response with a predetermined SCT, synthetic resin was injected via the needle. After postmortem dissection of the injection site, the localization of the resin deposition was determined verifying the final position of the needle tip. Depending on the proximity of resin deposition to the nerve epineurium, the needle tip placement was considered either as a close or a distant NNP. RESULTS: A total of 235 punctures were performed. Ninety-one punctures were carried out with low SCT and 92 with a high SCT. Fifty-two punctures served as a control (1.8-2.0 mA). All injectates following both high or low SCT were considered 'close needle tip to nerve placement', whereas 27 of 52 injectates of the control group appeared distant to nerve epineurium. CONCLUSION: Regardless of the applied SCT, i.e. high or low, all resin deposition was found adjacent to nerve epineurium. These findings suggest that high and low SCT result in equivalent needle tip localization in pigs.

Differential effects of volatile and intravenous anesthetics on the activity of human TASK-1.

Volatile anesthetics have been shown to activate various two-pore (2P) domain K(+) (K(2P)) channels such as TASK-1 and TREK-1 (TWIK-related acid-sensitive K(+) channel), and mice deficient in these channels are resistant to halothane-induced anesthesia. Here, we investigated whether K(2P) channels were also potentially important targets of intravenous anesthetics. Whole cell patch-clamp techniques were used to determine the effects of the commonly used intravenous anesthetics etomidate and propofol on the acid-sensitive K(+) current in rat ventricular myocytes (which strongly express TASK-1) and selected human K(2P) channels expressed in Xenopus laevis oocytes. In myocytes, etomidate decreased both inward rectifier K(+) (K(ir)) current (I(K1)) and acid-sensitive outward K(+) current at positive potentials, suggesting that this drug may inhibit TASK channels. Indeed, in addition to inhibiting guinea pig Kir2.1 expressed in oocytes, etomidate inhibited human TASK-1 (and TASK-3) in a concentration-dependent fashion. Propofol had no effect on human TASK-1 (or TASK-3) expressed in oocytes. Moreover, we showed that, similar to the known effect of halothane, sevoflurane and the purified R-(-)- and S-(+)-enantiomers of isoflurane, without stereoselectivity, activated human TASK-1. We conclude that intravenous and volatile anesthetics have dissimilar effects on K(2P) channels. Human TASK-1 (and TASK-3) are insensitive to propofol but are inhibited by supraclinical concentrations of etomidate. In contrast, stimulatory effects of sevoflurane and enantiomeric isoflurane on human TASK-1 can be observed at clinically relevant concentrations.

Randomised, controlled outcome study of active mobilisation compared with collar therapy for whiplash injury.

OBJECTIVES: Standard therapy in Germany for acute whiplash injury has traditionally included a soft collar (cervical orthosis), an approach that is passive compared with early exercise and mobilisation. The purpose of this study is to examine the recovery in the first six weeks of groups of acute whiplash injury patients subjected to two different treatment approaches, the traditional approach of a collar compared with active, early mobilisation. METHODS: Between August 1997 and February 2000 a randomised clinical trial with a total of 200 patients was performed. A total of 97 were randomly assigned to a collar therapy group, and 103 to the exercise group, treated by a physiotherapist. Study participants recorded average pain and disability twice (baseline and six week follow up) during a one week period by diary, using numeric visual analogue (VAS) rating scales ranging from 0 to 10. RESULTS: The initial mean VAS pain intensity and VAS disability reported by the collar therapy group and the exercise group showed no statistical difference. The mean VAS pain rating reported by the collar therapy group after six weeks was 1.60 and mean VAS disability rating was 1.56. The mean VAS pain intensity of the exercise group was 1.04 and mean VAS disability was 0.92. These differences between the groups were both significant, as was the reduction in the prevalence of symptoms in the exercise therapy group compared with the collar group at six weeks. CONCLUSIONS: Early exercise therapy is superior to the collar therapy in reducing pain intensity and disability for whiplash injury.

[Diagnosis and therapy of acute complaints after "whiplash injury" in Germany. Results of a representative survey at surgical and trauma departments in Germany]. / Diagnostik und Therapie akuter Beschwerden nach "HWS-Distorsion" in Deutschland. Ergebnisse einer Umfrage an chirurgischen und unfallchirurgischen Kliniken in Deutschland.

Whiplash injury of the cervical spine is a relevant medical and socioeconomic problem, which is still the subject of controversy. We performed a survey to evaluate the current status of diagnostics, classification, treatment, and doctors' subjective opinions at surgical and trauma departments in Germany. A total of 1568 hospitals were addressed to answer a standardized questionnaire on their proceedings and opinions concerning whiplash injury. We received 540 (34.44%) completed questionnaires. There was overall agreement concerning the need for physical examination. The radiological assessment included an a.p. and a lateral plain X-ray of the cervical spine in 82.6%. The indication for functional X-rays in flexion/extension was inconsistent. On average they were performed in 39.1% of all patients. In most cases (68.9%) whiplash injury was not classified; 13.2% of doctors used the classification according to the Quebec Task Force and 13.9% according to Erdmann. A cervical collar was prescribed in 85%. While 30% of patients received only a cervical collar, 55.6% underwent additional physiotherapy. Only 8.3% were treated by physiotherapy without immobilization. The doctors' subjective opinions indicated psychological factors to be important for long-lasting problems, but not for the acute period of complaints. There is no homogeneous concept for diagnostics, classification, and treatment of patients who suffered a whiplash injury in Germany. This situation reflects the current problems in management of this condition. Scientific evidence for functional treatment to avoid adverse influence of immobilization by cervical collars has not yet been transferred to our daily routine in Germany.

[Results of early mobilisation of acute whiplash injuries]. / Ergebnisse der frühfunktionellen krankengymnastischen Ubungsbehandlung nach HWS-Distorsion.

BACKGROUND: Diagnostic evaluation and therapeutic management of acute neck pain after whiplash is a frequent but unsolved clinical problem. Long-lasting symptoms and disability are common. Former studies proposed beneficial effects of physiotherapy in the early management of whiplash injury. The purpose of this study was to assess the effects of early active mobilization versus standard treatment with a soft cervical collar. METHODS: Between August 1997 and February 2000 a prospective randomized clinical trial with a total of 168 patients was performed. Of these patients 81 (31 male, 50 female; average age 28,78 years) were randomly assigned to the standard therapy group, which received a soft cervical collar, and 87 (31 male, 56 female; average age 29,62 years) to the early mobilization group, treated by physiotherapy. Study participants documented pain and disability twice (baseline and six week follow-up) during a one week period by diary, using numeric rating scales ranging from 0 to 10. RESULTS: The initial mean pain intensity (4,75) reported by the standard therapy group was similar to disability (4,76). There were no significant differences to initial pain (4,50) and disability (4,39) reported by the early mobilization group. The mean pain intensity reported by the standard therapy group after 6 weeks was 2,66 and disability was 2,40. The mean pain intensity indicated by physiotherapy group was 1,44 and mean disability was 1,29. The differences between the groups were both significant. CONCLUSIONS: Early mobilization is superior to the standard therapy regarding pain intensity and disability. We conclude that mobilization should be recommended as the new adequate standard-therapy in the acute management of whiplash injury.

[Selection of subjects: a problem of clinical trials in traumatology. Selection effects and the problem of representation as exemplified by a prospective randomized trial on whiplash injuries]. / Selektionseffekte--Ein Problem unfallchirurgischer Studien? Stichprobenselektionseffekte und das Problem der Repräsentativität am Beispiel einer prospektiven randomisierten Studie zur HWS-Beschleunigungsverletzung.

INTRODUCTION: The internal and external validity of studies is endangered by many factors, such as selection of subjects for inclusion. Selection bias itself is a major problem, but remains unmentioned and probably unexamined in the majority of published clinical trials in traumatology. AIM OF THE STUDY: The aim of this investigation was to detect effects of subject selection which occurred during our own prospective intervention study. The clinical trial compared subjects with whiplash injury who were either treated by early mobilization or immobilization (soft collar). MATERIAL AND METHODS: Source population, eligible subjects, study participants and final study participants were compared for differences on various items like age, gender and further sociodemographic as well as crash related factors and clinical findings. RESULTS: Between 21.08.1997 and 30.04.1999 a total of 732 patients was examined and treated after whiplash in our trauma department. The options for inclusion were met by 453 patients. While 346 escaped from the study, 107 agreed to participate. Of these another 39 patients dropped out of the study. Selection effects were detected on two different levels, leading to distinct statistical procedures from those proposed in the study protocol. CONCLUSIONS: Uncontrolled selection effects could undermine the interpretability of the results of clinical trials. Awareness of selection effects is mandatory regarding the applicability of these results to subjects, other than those in the group of the final study participants.