Torsten Eken

Functional role of plateau potentials in vertebrate motor neurons.

The expression of plateau potentials in spinal motor neurons is regulated by neuromodulatory substances. Recent experiments have shed new light on this regulation at the cellular level. It is now possible to evaluate the existence of plateau potentials in intact organisms, including humans, and to address the functional role of plateau potentials in motor control, as well as in information transfer in the brain.

Electrical stimulation resembling normal motor-unit activity: effects on denervated fast and slow rat muscles.

1. The slow‐twitch soleus muscle and the fast‐twitch extensor digitorum longus muscle (EDL) were denervated and stimulated directly with implanted electrodes for 33‐82 days. Four different stimulation patterns were used in order to mimic important characteristics of the natural motor‐unit activity in these muscles. In addition, to compare the effects of direct stimulation to other experimental models, some EDLs were stimulated through the nerve or cross‐innervated by soleus axons. 2. After 33‐82 days of stimulation the contractile properties were measured under isometric and isotonic conditions. 3. ‘Native’ stimulation patterns could maintain normal contractile speed in both EDL and soleus. In the EDL, normal isotonic shortening velocity was maintained only by a stimulation pattern consisting of very brief trains with an initial short interspike interval (doublet), and not by the other ‘native’ high‐frequency patterns. 4. The contractile properties of both EDL and soleus muscles receiving a ‘foreign’ stimulation pattern were transformed in the direction of the muscle normally receiving that type of activity. The transformations were not complete, and soleus and EDL muscles stimulated with the same stimulation pattern remained different. This suggests that adult muscle fibres in rat EDL and soleus are irreversibly differentiated into different fibre types earlier in development. 5. The three high‐frequency stimulation patterns used differed in their ability to change or maintain various contractile properties in the soleus and the EDL. The results indicate that the following qualities of a stimulation pattern might be of importance for the control of contractile properties: instantaneous frequency, total amount of stimulation, train length, interval between trains and presence of an initial doublet. 6. With the exception of the EDL shortening velocity, changes in contractile speed induced by a ‘foreign’ stimulation pattern were quantitatively similar to the effects of cross‐innervation both in the EDL and the soleus. We thus suggest that the change in activity pattern is the mechanism behind most of the changes induced by cross‐innervation.

Precision of field triage in patients brought to a trauma centre after introducing trauma team activation guidelines

BackgroundField triage is important for regional trauma systems providing high sensitivity to avoid that severely injured are deprived access to trauma team resuscitation (undertriage), yet high specificity to avoid resource over-utilization (overtriage). Previous informal trauma team activation (TTA) at Ulleval University Hospital (UUH) caused imprecise triage. We have analyzed triage precision after introduction of TTA guidelines.MethodsRetrospective analysis of 7 years (2001–07) of prospectively collected trauma registry data for all patients with TTA or severe injury, defined as at least one of the following: Injury Severity Score (ISS) > 15, proximal penetrating injury, admitted ICU > 2 days, transferred intubated to another hospital within 2 days, dead from trauma within 30 days. Interhospital transfers to UUH and patients admitted by non-healthcare personnel were excluded. Overtriage is the fraction of TTA where patients are not severely injured (1-positive predictive value); undertriage is the fraction of severely injured admitted without TTA (1-sensitivity).ResultsOf the 4 659 patients included in the study, 2 221 (48%) were severely injured. TTA occurred 4 440 times, only 2 002 of which for severely injured (overtriage 55%). Overall undertriage was 10%. Mechanism of injury was TTA criterion in 1 508 cases (34%), of which only 392 were severely injured (overtriage 74%). Paramedic-manned prehospital services provided 66% overtriage and 17% undertriage, anaesthetist-manned services 35% overtriage and 2% undertriage. Falls, high age and admittance by paramedics were significantly associated with undertriage. A Triage-Revised Trauma Score (RTS) < 12 in the emergency department reduced the risk for undertriage compared to RTS = 12 (normal value). Field RTS was documented by anaesthetists in 64% of the patients compared to 33% among paramedics.Patients subject to undertriage had an ISS-adjusted Odds Ratio for 30-day mortality of 2.34 (95% CI 1.6–3.4, p < 0.001) compared to those correctly triaged to TTA.ConclusionTriage precision had not improved after TTA guideline introduction. Anaesthetists perform precise trauma triage, whereas paramedics have potential for improvement. Skewed mission profiles makes comparison of differences in triage precision difficult, but criteria or the use of them may contribute. Massive undertriage among paramedics is of grave concern as patients exposed to undertriage had increased risk of dying.

Activity of single motor units in attention-demanding tasks: firing pattern in the human trapezius muscle

Activity of single motor units in relation to surface electromyography (EMG) was studied in 11 subjects in attention-demanding work tasks with minimal requirement of movement. In 53 verified firing periods, single motor units fired continuously from 30 s to 10 min (duration of the experiment work task) with a stable median firing rate in the range of 8–13 Hz. When the integrated surface EMG were stable, the motor units identified as a rule were continuously active with only small modulations of firing rate corresponding to low-amplitude fluctuations in surface EMG. Marked changes in the surface EMG, either sudden or gradual, were caused by recruitment or derecruitment of motor units, and not by modulations of the motor unit firing rate. Motor unit firing periods (duration 10 s-35 s) in low-level voluntary contractions (approximately 1%–5% EMGmax) performed by the same subjects showed median firing rates (7–12 Hz) similar to the observations in attention-related activation.

Prevalence, predictors and outcome of hypofibrinogenaemia in trauma: a multicentre observational study

IntroductionExsanguination due to trauma-induced coagulopathy is a continuing challenge in emergency trauma care. Fibrinogen is a crucial factor for haemostatic competence, and may be the factor that reaches critically low levels first. Early fibrinogen substitution is advocated by a number of authors. Little evidence exists regarding the indications for fibrinogen supplementation in the acute phase. This study aims to estimate the prevalence of hypofibrinogenaemia in a multi-center trauma population, and to explore how initial fibrinogen concentration relates to outcome. Also, factors contributing to low fibrinogen levels are identified.MethodsPatients arriving in hospital less than 180 minutes post-injury requiring full trauma team activation in four different centers were included in the study. Time from injury, patient demographics, injury severity scores (ISS) and 28 days outcome status were recorded. Initial blood samples for coagulation and blood gas were analyzed. Generalized additive regression, piecewise linear regression, and multiple linear regression models were used for data analyses.ResultsOut of 1,133 patients we identified a fibrinogen concentration ≤1.5g/L in 8.2%, and <2 g/L in 19.2%. A non-linear relationship between fibrinogen concentration and mortality was detected in the generalized additive and piecewise linear regression models. In the piecewise linear regression model we identified a breakpoint for optimal fibrinogen concentration at 2.29 g/L (95% confidence interval (CI): 1.93 to 2.64). Below this value the odds of death by 28 days was reduced by a factor of 0.08 (95% CI: 0.03 to 0.20) for every unit increase in fibrinogen concentration. Low age, male gender, lengthened time from injury, low base excess and high ISS were unique contributors to low fibrinogen concentrations on arrival.ConclusionsHypofibrinogenaemia is common in trauma and strongly associated with poor outcome. Below an estimated critical fibrinogen concentration value of 2.29 g/L a dramatic increase in mortality was detected. This finding indicates that the negative impact of low fibrinogen concentrations may have been previously underestimated. A number of clinically identifiable factors are associated with hypofibrinogenaemia. They should be considered in the management of massively bleeding patients. Interventional trials with fibrinogen substitution in high-risk patients need to be undertaken.

Selective depletion of spinal monoamines changes the rat soleus EMG from a tonic to a more phasic pattern.

1. To assess the role of descending monoaminergic pathways for motor activity long‐lasting EMG recordings were performed from the adult soleus muscle before and after selective depletion of spinal monoamines. 2. Rats were chronically implanted with an intrathecal catheter placed in the lumbar subarachnoid space and gross‐EMG recording electrodes in the soleus muscle. EMG recordings were performed in control conditions and at different times after intrathecal administration of either 40‐55 micrograms 5,6‐dihydroxytryptamine (5,6‐DHT) and 40‐55 micrograms 6‐hydroxydopamine (6‐OHDA) or 80 micrograms 5,7‐dihydroxytryptamine (5,7‐DHT) alone. The depletions were evaluated biochemically in brains and spinal cords after recordings. 3. In agreement with previous studies the intrathecal administration of neurotoxins caused a reduction of the noradrenaline (NA) and serotonin (5‐HT) content of the lumbar spinal cord to about 2‐3% of control, with little or no changes in the monoamine content of the cortex. 4. In non‐treated chronically catheterized rats the integrated rectified gross EMG displayed long‐lasting EMG episodes composed of phasic high‐amplitude events and tonic segments of varying duration and amplitude. 5. After intrathecal administration of neurotoxins the number of long‐lasting gross‐EMG episodes, the mean episode duration, and the total EMG activity per 24 h, were reduced. These changes were accompanied by a simultaneous increase both in the number of short‐lasting EMG episodes and the total number of EMG episodes per 24 h period. The changes were apparent 5‐6 days after drug administration and fully developed after 2‐3 weeks. 6. No changes in general movement ability were observed, except that the denervated animals had a tendency to a less errect posture. 7. These results indicate that descending monoaminergic pathways are important for the maintained motor output in tonic hindlimb muscles.

Refining the role of splenic angiographic embolization in high-grade splenic injuries.

BACKGROUND The justification and safety of splenic angiographic embolization (SAE) as an adjunct to nonoperative management (NOM) in high-grade splenic injuries are matters of controversy. At Oslo University Hospital-Ulleval, mandatory SAE was introduced in hemodynamically stable Organ Injury Scale (OIS) Grades 3 to 5 injuries in 2002. From October 2008, mandatory SAE was restricted to OIS Grade 4 injuries or higher. The aim of the present study was to evaluate clinical outcome in patients with high-grade splenic injuries and further define the role of SAE. METHODS All patients 17 years or older with splenic injury admitted from August 1, 2002, to July 31, 2010, were included. Patient charts, computed tomographic scans, and trauma registry data were reviewed. The OIS Grade 3 protocol was amended on October 1, 2008. RESULTS A total of 296 patients with splenic injuries (mean splenic OIS grade, 3.0) resulted in a 70% attempted NOM rate, with 96% success rate. NOM was attempted in 64 (70%) of 91 patients with Grades 4 and 5 injuries, with a 95% success rate. Comparing OIS Grade 3 injuries admitted before (n = 81) and after (n = 35) October 2008, we found similar admission physiology and Injury Severity Score (ISS). Despite the reduction in SAE rate (from 49% to 26%), the NOM rate remained unchanged, as did NOM failure rate (3% vs. 4%), rate of rebleeding, complications, and mortality. CONCLUSION A protocol with mandatory SAE in OIS Grades 4 and 5 injuries resulted in an overall 95% success rate among the 70% eligible for NOM. In OIS Grade 3 splenic injuries, mandatory SAE does not seem justified. LEVEL OF EVIDENCE Therapeutic study, level IV.

Efficacy of a two-tiered trauma team activation protocol in a Norwegian trauma centre

A registry‐based analysis revealed imprecise informal one‐tiered trauma team activation (TTA) in a primary trauma centre. A two‐tiered TTA protocol was introduced and analysed to examine its impact on triage precision and resource utilization.

Long-Lasting Performance Improvement After Formalization of a Dedicated Trauma Service

BACKGROUND Few studies have evaluated intrainstitutional improvement of trauma care. We hypothesized that the formalization of a dedicated multidisciplinary trauma service in a major Scandinavian trauma center in 2005 would result in improved outcome. METHODS Institutional trauma registry data for 7,243 consecutive patients from the years 2002-2008 were retrospectively evaluated using variable life-adjusted display (VLAD) as one of several performance indicators. VLAD is a refinement of the cumulative sum method that adjusts death and survival by each patients risk status (probability of survival) and provides a graphical display of performance over time. Probability of survival was calculated according to Trauma and Injury Severity Score (TRISS) methodology with National Trauma Data Bank 2005 coefficients. RESULTS VLAD demonstrated a sharp increase in cumulative survival starting at the beginning of 2005 and continuing linearly throughout the study period, amounting to 68 additional saved lives. The increase was mainly caused by improved survival among the critically injured (injury severity score 25-75). A cutoff point t0 for analysis of differences between time periods was set at January 1, 2005, coinciding with the formalization of a dedicated trauma service. Mortality in the whole trauma population showed a 33% decrease after t0. W-statistics confirmed the increased survival to be significant. There were no significant changes in age, gender, or injury mechanism. Injury severity score decreased, but differences in case mix were adjusted for in the survival prediction model. CONCLUSION We have shown that the start of the long-lasting performance improvement coincided with formalization of a dedicated trauma service, providing increased multidisciplinary focus on all aspects of trauma care.

Calculating trauma triage precision: effects of different definitions of major trauma

BackgroundTriage is the process of classifying patients according to injury severity and determining the priority for further treatment. Although the term “major trauma” represents the reference against which over- and undertriage rates are calculated, its definition is inconsistent in the current literature. This study aimed to investigate the effects of different definitions of major trauma on the calculation of perceived over- and undertriage rates in a Norwegian trauma cohort.MethodsWe performed a retrospective analysis of patients included in the trauma registry of a primary, referral trauma centre. Two “traditional” definitions were developed based on anatomical injury severity scores (ISS >15 and NISS >15), one “extended” definition was based on outcome (30-day mortality) and mechanism of injury (proximal penetrating injury), one ”extensive” definition was based on the “extended” definition and on ICU resource consumption (admitted to the ICU for >2 days and/or transferred intubated out of the hospital in ≤2 days), and an additional four definitions were based on combinations of the first four.ResultsThere were no significant differences in the perceived under- and overtriage rates between the two “traditional” definitions (NISS >15 and ISS >15). Adding “extended” and “extensive” to the “traditional” definitions also did not significantly alter perceived under- and overtriage. Defining major trauma only in terms of the mechanism of injury and mortality, with or without ICU resource consumption (the “extended” and “extensive” groups), drastically increased the perceived overtriage rates.ConclusionAlthough the proportion of patients who were defined as having sustained major trauma increased when NISS-based definitions were substituted for ISS-based definitions, the outcomes of the triage precision calculations did not differ significantly between the two scales. Additionally, expanding the purely anatomic definition of major trauma by including proximal penetrating injury, 30-day mortality, ICU LOS greater than 2 days and transferred intubated out of the hospital at ≤2 days did not significantly influence the perceived triage precision. We recommend that triage precision calculations should include anatomical injury scaling according to NISS. To further enhance comparability of trauma triage calculations, researchers should establish a consensus on a uniform definition of major trauma.