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Biomedical subjects

S E Milne

Publications and source records attributed to S E Milne.

12 recordsLinked to original sources
PubMed2003

Relationship between bispectral index, auditory evoked potential index and effect-site EC50 for propofol at two clinical end-points.

BACKGROUND: Many anaesthetists are deterred from using total i.v. anaesthesia because of uncertainty over the concentration of propofol required to prevent awareness. We predicted blood and effect-site concentrations of propofol at two clinical end-points: loss of consciousness and no response to a painful stimulus. METHODS: Forty unpremedicated Caucasian patients were anaesthetized with i.v. propofol delivered by a Diprifusor target-controlled infusion (TCI). Bispectral index (BIS) and auditory evoked potential index (AEPex) were measured and blood and effect-site propofol concentrations were predicted. Logistic regression was used to estimate population values for predicted blood and effect-site propofol concentrations at the clinical end-points and to correlate these with BIS and AEPex. RESULTS: The effect-site EC(50) at loss of consciousness was 2.8 micro m ml(-1) with an EC(05) and an EC(95) of 1.5 and 4.1 micro m ml(-1), respectively. The predicted EC(50) when there was no response to a tetanic stimulus was 5.2 micro m ml(-1) with an EC(05) and an EC(95) of 3.1 and 7.2 micro m ml(-1), respectively. CONCLUSIONS: Unconsciousness and lack of response to a painful stimulus occur within a defined range of effect-site concentrations, predicted by Diprifusor TCI software.

Adult↗
PubMed2003

Propofol sparing effect of remifentanil using closed-loop anaesthesia.

BACKGROUND: General anaesthesia is a balance between hypnosis and analgesia. We investigated whether an increase in remifentanil blood concentration would reduce the amount of propofol required to maintain a comparable level of anaesthesia in 60 patients undergoing ambulatory surgery. METHODS: Patients were allocated randomly to receive remifentanil to a target blood concentration of 2 ng ml(-1) (low), 4 ng ml(-1) (medium), or 8 ng ml(-1) (high), administered by target-controlled infusion (TCI). After equilibration, propofol TCI was commenced in closed-loop control, with auditory evoked potentials (AEPex) as the input signal, aiming for an AEPex of 35. This was to ensure a comparable and unbiased level of anaesthesia in all patients. RESULTS: We found a dose-dependent decrease in propofol requirements with increasing remifentanil concentrations. The mean (95% CI) propofol target blood concentration during adequate anaesthesia was 4.96 (3.85-6.01) micro g ml(-1) in the low, 3.46 (2.96-3.96) micro g ml(-1) in the medium, and 3.01 (2.20-3.38) micro g ml(-1) in the high group. There was no significant difference when recovery end points were achieved between the groups. Cardiovascular changes were moderate, but most pronounced in the high concentration group, with a decrease in heart rate of 21% compared with baseline. The mean calculated effect site propofol concentration at loss of consciousness was 2.08 (1.85-2.32) micro g ml(-1), and at recovery of consciousness was 1.85 (1.68-2.00) micro g ml(-1). CONCLUSIONS: This study confirms a synergistic interaction between remifentanil and propofol during surgery, whereas the contribution of remifentanil in the absence of stimulation seems limited. In addition, our results suggest that the propofol effect site concentration provides a guide to the value at which the patient recovers consciousness.

Adolescent↗
PubMed2002

Propofol effective concentration 50 and its relationship to bispectral index.

Sixty unpremedicated healthy adult patients were studied during induction of anaesthesia with intravenous propofol delivered by a 'Diprifusor' target-controlled infusion. Bispectral index (BIS) and spectral edge frequency (SEF95) were measured concurrently with the predicted blood and effect site propofol concentrations. Logistic regression was used to calculate the predicted propofol blood and effect site concentrations required to produce unconsciousness and no response to a noxious stimulus in 50% and 95% of patients and to correlate BIS with these end-points. The Diprifusor TCI software produces anaesthesia at consistent target concentrations. Bispectral index correlates well with clinical end-points and may be useful during propofol anaesthesia.

Adolescent↗
PubMed1998

Feedback control of anaesthesia.

Feedback control of anaesthesia can improve the quality of patient care while reducing the administration and cost of anaesthetic drugs. Systems have been available for several years to control blood pressure and neuromuscular blockade. Control of anaesthetic depth has been reported using the median frequency of the electroencephalogram. Recently, the monitoring of anaesthetic depth using the bispectral index or auditory evoked potentials has greatly improved feedback control of the depth of anaesthesia.

Journal Article↗
PubMed1998

Future applications for TCI systems.

Infusion pumps incorporating 'Diprifusor' for the administration of propofol by target controlled infusion are now commercially available and are becoming more widely used. This paper considers possible future applications of target controlled infusion and summarises results obtained using prototype systems as a component of other control techniques and with other drugs. These include studies with patient-controlled systems for the administration of analgesia or sedation and a closed loop control system for the administration of propofol. Among currently available analgesic drugs, alfentanil and remifentanil are considered to be the most suitable for administration by target controlled infusion, but commercial systems for these agents are not yet available.

Analgesia↗
PubMed1989

Factors affecting the accuracy of position matching at the proximal interphalangeal joint in human subjects.

1. The ability of normal subjects to match finger position at the proximal interphalangeal (PIP) joint was tested under a number of different conditions. One finger (target finger) was passively displaced in a pseudorandom manner whilst the other (matching) finger was actively positioned by the subject. 2. Digital nerve block of the target finger resulted in the matching finger only being displaced through a small range ('range compression') whilst anaesthesia of the matching finger produced the opposite effect ('range expansion'). 3. When the finger is unanaesthetized, the velocity of displacement of the target finger from one position to the next does not affect the accuracy of position matching. However, during digital nerve block of the target finger, matching errors increase with decreasing velocity. 4. The impairment of matching performance during digital nerve block is due specifically to loss of input from receptors in and around the PIP joint, as anaesthesia of the tip of the finger to produce any significant decrement in matching accuracy. 5. The results show that muscle receptors contribute to position sense at this joint but are not the exclusive source of proprioceptive sensations.

Fingers↗
PubMed1978

Incomplete anaerobiosis as a cause of metronidazole 'resistance'.

Clostridium welchii, used as a control, was found to grow well in a microaerophilic jar used for campylobacters but appeared resistant to a metronidazole disc although the campylobacter was sensitive. Minimum inhibitory concentrations for six strains of Cl. welchii were up to 64-fold higher in these conditions than when grown anaerobically. Zones of inhibition with both Cl. welchii and Bacteroides fragilis varied with the amount of air admitted to anaerobic jars.

Anaerobiosis↗