Influence of air ambulance doctors on on-scene times, clinical interventions, decision-making and independent paramedic practice.

BACKGROUND: Critics of air ambulance doctors question their contribution and believe on-scene time is prolonged. Two helicopter emergency medical service (HEMS) models operate in the West Midlands, one with doctors and the other without. A study was undertaken to compare on-scene time, management and decision-making between the two units. METHOD: Cases were assessed over an 18-month period, identifying on-scene time, incidence of rapid sequence induction (RSI), management of patients with a Glasgow Coma Scale (GCS) score of 3, femoral fracture, pneumothorax or those with myocardial infarction. RESULTS: There were 5275 HEMS activations during the study period. The presence of a doctor had no effect on on-scene time (27 (2) min vs 26 (2) min, p = NS). Advanced management of femoral fractures (nerve block, ketamine or RSI), pneumothorax (chest drain) or RSI (when patients were matched for GCS score) by doctors took no longer than conventional paramedic management. Doctors performed RSI on 38% of trauma patients and 13% of medical patients with a GCS score <15. Patients were more likely to be treated and discharged from the scene when seen by a doctor (8.7% vs 4.6%, p<0.001) and were less likely to be transported to hospital (27% vs 44%, p<0.001). For patients with a GCS score of 3, doctors were more likely to cease resuscitation efforts and confirm death at the scene (70% vs 16%, p<0.001). CONCLUSIONS: Appropriately trained HEMS doctors provide advanced management and decision-making. This is without a negative effect on on-scene time, even when performing complex procedures. They are more likely to declare death or discharge patients at the scene, increasing the availability of this limited resource.

Nucleus- and species-specific properties of the slow (<1 Hz) sleep oscillation in thalamocortical neurons.

The slow (<1 Hz) rhythm is an electroencephalogram hallmark of resting sleep. In thalamocortical neurons this rhythm correlates with a slow (<1 Hz) oscillation comprising recurring UP and DOWN membrane potential states. Recently, we showed that metabotropic glutamate receptor activation brings about an intrinsic slow oscillation in thalamocortical neurons of the cat dorsal lateral geniculate nucleus in vitro which is identical to that observed in vivo. The aim of this study was to further assess the properties of this oscillation and compare them with those observed in thalamocortical neurons of three other thalamic nuclei in the cat (ventrobasal complex, medial geniculate body; ventral lateral nucleus) and two thalamic nuclei in rats and mice (lateral geniculate nucleus and ventrobasal complex). Slow oscillations were evident in all of these additional structures and shared several basic properties including, i) the stereotypical, rhythmic alternation between distinct UP and DOWN states with the UP state always commencing with a low-threshold Ca2+ potential, and ii) an inverse relationship between frequency and injected current so that slow oscillations always increase in frequency with hyperpolarization, often culminating in delta (delta) activity at approximately 1-4 Hz. However, beyond these common properties there were important differences in expression between different nuclei. Most notably, 44% of slow oscillations in the cat lateral geniculate nucleus possessed UP states that comprised sustained tonic firing and/or high-threshold bursting. In contrast, slow oscillations in cat ventrobasal complex, medial geniculate body and ventral lateral nucleus thalamocortical neurons exhibited such UP states in only 16%, 11% and 10% of cases, respectively, whereas slow oscillations in the lateral geniculate nucleus and ventrobasal complex of rats and mice did so in <12% of cases. Thus, the slow oscillation is a common feature of thalamocortical neurons that displays clear species- and nuclei-related differences. The potential functional significance of these results is discussed.

Properties and origin of spikelets in thalamocortical neurones in vitro.

Spikelets, or fast prepotentials as they are frequently referred to, are a common feature of the electrophysiology of central neurones and are invariably correlated with the presence of electrotonic coupling via gap junctions. Here we report that in the presence of the metabotropic glutamate receptor agonists, trans-ACPD or DHPG, thalamocortical neurones of the cat dorsal lateral geniculate nucleus maintained in vitro exhibit stereotypical spikelets that possess similar properties to those described in other brain areas. These spikelets were routinely observed in the presence of antagonists of fast chemical synaptic transmission, were resistant to the application of a variety of voltage-dependent Ca(2+) channel blockers but were abolished by tetrodotoxin. In addition, spikelets were reversibly blocked by the putative gap junction blocker carbenoxolone and were nearly always accompanied by dye-coupling. These results indicate that thalamocortical neurones may be electrotonically coupled via gap junctions with spikelets representing attenuated action potentials from adjoining cells. We suggest that the presence of electrotonic communication between thalamocortical neurones would have major implications for the understanding of both physiological (Steriade et al., 1993; Sillito et al., 1994; Alonso et al., 1996; Neuenschwander and Singer, 1996; Weliky and Katz, 1999) and pathological (Steriade and Contreras, 1995; Pinault et al., 1998) synchronised electrical activity in the thalamus.