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D J Sapsford

Publications and source records attributed to D J Sapsford.

18 recordsLinked to original sources
PubMed1996

A method for producing the coherent frequency: a steady-state auditory evoked response in the electroencephalogram.

Transient and steady-state auditory evoked responses in the electroencephalogram are used to study the effect on the brain of graded changes in the concentration of general anesthetics. A method is described using modern signal processing techniques to improve the analysis of steady-state auditory evoked responses (SSAER). The SSAER was obtained using headphones to give 100-200 auditory click stimuli from 6.5 Hz.to 50.5Hz in 1-Hz steps. The resulting electroencephalogram signals were filtered and subject to Fourier analysis, after which a series of coherence indexes were derived based on waves with significant power in the fundamental but with minimal harmonic content. These were plotted against the range of stimuli and fitted with a third-order polynomial. The frequency at which the maximum coherence index was achieved (highest possible value = 1) was derived from polynomial interpolation. The repeatability of the method was examined in 10 awake subjects using runs of ascending then descending stimulating frequencies. The mean maximum coherence index was at 38 Hz, with the 95% confidence interval of 37.3 Hz-38.9 Hz. There was no difference between ascending and descending sweeps. The method provides an automatic analysis of the SSAER that obviates the need to make subjective decisions about which is the dominant wave, a major problem in the analysis of the transient auditory evoked responses.

Acoustic Stimulation↗
PubMed1996

The coherent frequency in the electroencephalogram as an objective measure of cognitive function during propofol sedation.

Ten volunteers were studied during six stages of propofol sedation, namely awake (no propofol), light sedation (small dose of propofol), deep sedation (large dose), deep sedation with stimulation of the ulnar nerve, then light sedation again (small dose), and awake (recovery). Light and deep sedation were defined in terms of performance on a test of cognitive function: the within-list recognition (WLR) test. At each stage, the steady-state auditory evoked potential was measured at different stimulating frequencies to derive the frequency needed to achieve the maximal coherence index. This frequency is called the "maximum coherent frequency". WLR performance correlated with infusion dose (r = -0.71), plasma propofol concentration (r = -0.75), and maximum coherent frequency (r = 0.75). When the correlations were examined for the propofol sedation stages only, there remained a strong correlation between WLR performance and maximum coherent frequency (r = 0.47, P < 0.005), but no significant correlations between infusion dose and WLR (r = -0.11) or infusion dose and plasma concentration (r = 0.13). These data suggest that maximum coherent frequency provides a better measure of depth of sedation than does the dose of propofol alone.

Anesthesia Recovery Period↗
PubMed1996

The effect on the heart of hypoxaemia in patients with severe coronary artery disease.

The aim of the study was to examine the effect of spontaneous nocturnal hypoxaemia on myocardial ischaemia in patients with severe coronary artery disease. This was a prospective study of continuously measured oxygen saturation and ECG overnight in patients prior to coronary artery bypass graft surgery. Fifteen patients with angiographically proved coronary artery disease were studied between October 1992 and September 1993. All patients had episodes of hypoxaemia with oxygen saturation < 94% and eight of the 15 patients had episodes where oxygen saturation < 85%. An episode was defined as a period of hypoxaemia not less than 2.5 min in duration, the longest total duration of hypoxaemia in one patient being 355 min. Twelve of the 15 patients showed a drop in ST segment of 1 mm or more lasting from 5-700 min. The hypoxaemic and ischaemic episodes apparently occurred at random. No causal relationship could be shown between hypoxaemia and ischaemia.

Adult↗
PubMed1995

The PIO2 vs. SpO2 diagram: a non-invasive measure of pulmonary oxygen exchange.

A non-invasive method for measuring pulmonary oxygen exchange is described using a plot of inspired oxygen partial pressure (PIO2) vs. oxygen saturation (SpO2). This method was assessed using nine normal subjects and 35 patients undergoing major surgery, including five thoracotomies. In each patient PIO2 was varied to produce a range of values of SpO2 between 85% and 99%. A model based on the inspired to arterial oxygen difference involving the shunt equation, solved by simultaneous numerical methods, was used to show how the PIO2 vs. SaO2 relationship could be used to derive two parameters of oxygen exchange, the PIO2-Pco2 difference and the Virtual Shunt. The model allows the inspired to arterial difference in PO2 to be divided into (a) an inspired to 'ideal' alveolar difference attributable to the balance between alveolar ventilation and oxygen uptake; (b) an 'ideal' alveolar to end-capillary difference attributable to inhomogeneity in ventilation/perfusion ratios; and (c) end-capillary to arterial difference attributable to true shunt, which was termed 'virtual shunt' because of the uncertainties of assuming fixed values for haemoglobin concentration and arteriovenous oxygen content difference. The coefficient of determination showed that there was a good fit of the model to the data. Because the method is model-based it enables extrapolation to different PIO2 values as well as the study of the evolution of changes in gas exchange under varying conditions.

Adult↗
PubMed1994

Continuous axillary nerve block for chronic pain.

Continuous axillary nerve block was used to relieve pain after a chemical burn to the arm in a child on mechanical ventilation after liver transplantation. The analgesia was sufficient to replace parenteral analgesia and allow extubation.

Aprotinin↗
PubMed1993

Intravenous sedation for handicapped dental patients: a clinical trial of midazolam and propofol.

A double blind, cross-over study to compare intravenous sedation using continuous infusions of midazolam and propofol was carried out in 18 handicapped patients, aged between 5 and 26 years. Using a syringe pump (Ohmeda 9000) midazolam was delivered at 0.4 mg/kg/h with a bolus dose of 0.02 mg/kg and propofol was infused at 4.0 mg/kg/h with a bolus dose of 0.2 mg/kg. Sequential analysis showed that induction and recovery times were shorter with propofol (P < 0.05 and P < 0.01 respectively) and more work was performed over unit time (P < 0.05), with 15.7 units of work being completed per hour on patients under propofol sedation compared to 11.0 units under midazolam. The quality of sedation was assessed as better in patients receiving propofol; eight cases were abandoned under midazolam infusion due to failure of induction, uncontrolled movement and/or emotional outbursts compared with none under propofol. All parents/patients preferred propofol sedation, because recovery was faster and smoother.

Adolescent↗
PubMed1993

A measure of consciousness and memory during isoflurane administration: the coherent frequency.

The coherent frequency (CF) of the auditory evoked response (AER) is derived using auditory clicks presented at frequencies in the range 5-47 Hz. CF and psychological performance were measured while seven subjects breathed isoflurane in doses increasing from 0% to 0.2%, 0.4% and 0.8% end-tidal concentration and then decreasing to 0%. With increasing doses of isoflurane, CF decreased and there was a decrease in within-list recognition (WLR) and category recognition (CR) scores. There was a correlation between changes in CF and WLR (P < 0.05) and between CF and category recognition (CR) (P < 0.05). A painful stimulus given in conjunction with 0.4% isoflurane caused an increase in CF, WLR and CR in some subjects. This did not reach statistical significance for the group as a whole, apart from the short word interval scores in the WLR which indicated an increase in attention (P < 0.01). Subjects did not respond with 0.8% isoflurane, either before or after painful stimulation. Reduction of end-tidal isoflurane from 0.8% to 0% caused an increase in the CF and improved performance on the psychological tests. A category generation task on recovery showed no evidence of implicit learning of words presented in conjunction with 0.8% isoflurane.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMed1992

Continuous measurements of oxygen saturation during haemodialysis.

A new technique for recording and analysing continuous measurements of oxygen saturation (SpO2) by pulse oximeter during haemodialysis was used to compare changes in SpO2 in eight patients during two 4 h periods of dialysis using a cuprophane membrane, once using an acetate dialysate, and once using bicarbonate. The computer-derived patterns of SpO2 show whether hypoxaemia was caused mainly by extrapulmonary abnormalities (ventilatory control) or intrapulmonary abnormalities (V/Q distribution). The patterns of oxygen saturation were analysed for (i) stability, (ii) the lower median 20th centile of SpO2, and (iii) time below a SpO2 of 90%. Not all patients had reduced oxygenation during acetate dialysis. Three of eight patients had a stable pattern with acetate dialysis and six of eight were stable with bicarbonate. Five of eight patients had a lower SpO2 with acetate but one patient had a lower SpO2 with bicarbonate. Four patients had prolonged, clinically significant periods of oxygen desaturation with SpO2 less than 90%; two of these had particularly prolonged periods during acetate (62 min and 12 min), but one patient showed a longer period during bicarbonate than acetate dialysis (7 min). In two patients the SpO2 declined to less than 84%. The patterns of SpO2 suggested that the decrease in oxygen saturation was due more to extrapulmonary abnormalities causing an instability in ventilatory control rather than to venous admixture. It is recommended that pulse oximetry is used to identify patients at risk of hypoxaemia, to monitor these patients during haemodialysis, and to administer oxygen to those whose SpO2 falls below 90%, particularly if they have anaemia or cardiovascular disease.

Acetates↗
PubMed1992

A study to compare the effectiveness of temazepam and a chloral hydrate/hydroxyzine combination in sedating paediatric dental patients.

The study compared the effectiveness of temazepam and a mixture of chloral hydrate and hydroxyzine in sedating 20 young children aged 20 to 60 months (mean age 38.7 months). All the children exhibited negative behaviour during a screening visit and required at least two visits for restorative treatment with the use of sedation. The children were assigned randomly to receive either 50 mg/kg of chloral hydrate with 25 mg of hydroxyzine or 0.3 mg/kg of temazepam for the first visit, and the alternate regimen for the second visit, in a double-blind manner. Pulse rate and blood oxygen saturation levels were monitored before, during and after the operative procedures. All the treatment sessions were video-recorded and evaluated independently by three paediatric dentists for the degree of crying, movement, sleep and overall behaviour during specific procedures and at specific time intervals. The results showed no statistically significant differences between the two pharmacologic regimens with regard to crying, movement, sleep and overall behaviour. No significant difference in behaviour was found related to either the order of administration of the drugs or to the sex of the patients. It was concluded that 0.3 mg/kg temazepam and a mixture of 50 mg/kg chloral hydrate with 25 mg hydroxyzine had similar sedative effects on the children receiving dental treatment.

Anesthesia, Dental↗
PubMed1991

Nitrous oxide sedation causes post-hyperventilation apnoea.

We have studied, in six normal subjects, the effect of nitrous oxide sedation on the ventilatory pattern and oxygen saturation using pulse oximetry (SpO2) after hyperventilation to an end-tidal carbon dioxide partial pressure (PE'CO2) of 3 kPa. This value of PE'CO2 was shown to be less than the apnoeic threshold of all these subjects when their ventilation vs PE'CO2 response curves were plotted. All subjects became apnoeic when told to relax following hyperventilation while breathing 75% nitrous oxide for 90 s. Apnoea was defined as cessation of breathing for 20 s or more. The mean duration of apnoea was 78 s (range 29-130 s). All subjects demonstrated arterial desaturation (mean SpO2 75%, range 44-87%). In contrast, following hyperventilation with air, no apnoea was seen in any subject, although there was some evidence of desaturation (mean SpO2 92.5%, range 88-98%). It was concluded that subjects who are sedated with nitrous oxide behave similarly to those who are anaesthetized rather than to those who were fully conscious, in that they become apnoeic below the apnoeic threshold point. The reduction in SpO2 after hyperventilation was explained almost entirely by apnoea and may explain abnormalities of respiratory control and hypoxaemia in patients recovering from general anaesthesia or sedation accompanied by hypocapnia. This mechanism may be of importance in obstetric patients after breathing Entonox, when apnoea and hypoxaemia may reduce oxygen delivery to the fetus.

Adult↗
PubMed1991

Changes in amplitude and latency of the P300 component of the auditory evoked potential with sedative and anaesthetic concentrations of nitrous oxide.

The P300 component of the auditory evoked response was recorded from six subjects whilst they listened via headphones to a series of clicks which were interrupted unpredictably by a tone burst. They were instructed to press a button as quickly as possible after hearing the tone whilst breathing first air and then a series of increasing concentrations of nitrous oxide. Both the amplitude and the latency of the P300 changed in a dose-dependent manner with nitrous oxide, as did minimum reaction time. At nitrous oxide concentrations which prevented recall of any events that occurred whilst breathing the gas, four subjects continued to respond to the tone by pressing the button. In three subjects, the P300 wave was still detectable with a nitrous oxide concentration at which the task was no longer performed. These results show that there is retention of the ability to perform a reaction time task when there is a complete loss of recall of the task. There may be some recognition of an auditory stimulus, as manifest by a P300 wave, albeit reduced greatly in amplitude, in the absence of a motor response to it. The P300, therefore, merits investigation as a tool for studying conscious awareness under anaesthesia.

Anesthesia Recovery Period↗
PubMed1991

Patterns of oxygenation after thoracotomy.

We have studied patterns of oxygen saturation (SpO2) before and after thoracotomy in 20 patients monitored nightly from the preoperative night to the fourth postoperative night. After operation, 10 patients received paravertebral bupivacaine (PVB) infusion and 10 received paravertebral saline (PVS) infusion. Papaveretum was given as required. Before operation the SpO2 profiles formed two groups: stable with SpO2 greater than 94% and stable with a median SpO2 less than 94% (hypoxaemia). During the first night after operation SpO2 profiles formed four groups: stable, not hypoxaemic (2/20); stable, hypoxaemic but improving (8/20); stable and constant hypoxaemia (5/20); unstable, hypoxaemic and deteriorating (5/20). Eleven patients remained hypoxaemic as late as the fourth night after operation. All patients who were hypoxaemic before operation were hypoxaemic after operation. Postoperative hypoxaemia was predicted in only 50% of cases. Papaveretum requirement was reduced in the PVB group, but regional analgesia did not affect the proportion of patients showing each SpO2 profile. Papaveretum caused a decrease in SpO2 in both analgesic groups.

Adult↗
PubMed1990

Postoperative hypoxaemia: comparison of extradural, i.m. and patient-controlled opioid analgesia.

Arterial oxygen saturation (SaO2) was analysed continuously before and for 24 h after lower abdominal surgery in 30 patients breathing air using one of three postoperative analgesic regimens: i.v. diamorphine using a patient-controlled analgesia system (PCAS), extradural diamorphine or i.m. morphine. Hypoxaemia was defined as SaO2 less than 94% for more than 6 min h-1. Before operation there was no difference between the three analgesia groups assessed by the duration when SaO2 was less than 94%. After operation the pattern of SaO2 vs time distribution was either stable, with little variation from hour to hour with no hypoxaemia, or unstable with large variation with 30% of patients hypoxaemic. Thus three patterns of SaO2 distribution were seen in the postoperative period: stable without hypoxaemia (4/10 PCAS, 0/10 extradural, and 1/10 i.m. patients), unstable without hypoxaemia (4/10 PCAS, 5/10 extradural and 7/10 i.m. patients) and unstable with prolonged nocturnal periods with SaO2 less than 94% for a mean of 17.7 min h-1, 95% confidence limits (CL) 10-25 min h-1, (2/10 PCAS, 2/10 i.m. and 5/10 extradural patients). Before operation, the unstable group with hypoxaemia spent longer at less than 94% SaO2 (mean 4.8 min h-1, 95% CL 1.0-8.6 min h-1) than the stable group (mean 0.4 min h-1, 95% CL 0.17-0.61 min h-1) and this was a predictor of postoperative hypoxaemia. Hypoxaemia occurred in all analgesia groups, but extradural diamorphine tended to cause longer periods. Some patients at risk of postoperative hypoxaemia may be predicted by preoperative monitoring of SaO2 although extradural diamorphine boluses were associated with hypoxaemia in patients with normal preoperative values.

Abdomen↗
PubMed1990

Postoperative hypoxaemia: mechanisms and time course.

Postoperative hypoxaemia results predominantly from two mechanisms. Gas exchange is impaired during anaesthesia as a result of reduced tone in the muscles of the chest wall and probably alterations in bronchomotor and vascular tone, and the resulting changes persist into the postoperative period. In addition, there is an abnormality of control of breathing, which results in episodic obstructive apnoea. These episodes continue for several days after operation and are related to sleep pattern and analgesic administration, although the precise effects of different analgesic regimens have not been evaluated. Oxygen administration is effect in reducing the degree of hypoxaemia.

Anesthesia, General↗