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Biomedical subjects

A R Wilkes

Publications and source records attributed to A R Wilkes.

At least 19 recordsLinked to original sources
PubMed2007

Predictive value of IL-18 and SC5b-9 for neurocognitive dysfunction after cardiopulmonary bypass.

BACKGROUND: Neurological injury after cardiopulmonary bypass (CPB) continues to be a major problem after cardiac surgery. The aim of this study was to investigate the predictive value of Interleukin-18 (IL-18) and SC5b-9 as biochemical markers of neurocognitive dysfunction after cardiac surgery. METHODS: A total of 30 patients undergoing elective cardiac surgery using CPB were recruited. Blood samples were obtained for IL-18 and SC5b-9 concentrations before induction, 24, 48, 72, 96 and 120 h post-CPB and 6 weeks after operation. In addition, patients underwent a standard battery of neuropsychometric tests before operation and at day 5 and 6 weeks after operation. RESULTS: Serum concentration of IL-18, but not SC5b-9, was significantly different between patients with and without neurocognitive dysfunction; serum IL-18 concentration significantly increased in patients with neurocognitive dysfunction (P = 0.018). Neurological outcome was significantly dependent on peak difference in IL-18 concentration at day 5 (P = 0.033), but not on peak difference in SC5b-9 concentration (P = 0.16). Eight patients had neurocognitive dysfunction at day 5 and three had neurocognitive dysfunction at 6 weeks. In a very small number of patients, no significant association was demonstrated between IL-18 or SC5b-9 concentrations and neurocognitive dysfunction at 6 weeks. CONCLUSIONS: IL-18 has the potential as a useful marker of neurological dysfunction, requiring further investigation.

Aged↗
PubMed2007

Assessing the efficacy of HME filters at preventing contamination of breathing systems.

Breathing system filters are intended to prevent cross-infection during anaesthesia. However, there is a lack of information on whether filters prevent contamination of the breathing system by the patient. We measured the contamination of 235 used filters of four different types obtained from operating theatres: two pleated hydrophobic (BB25M and BB22/15M, Pall Medical, Portsmouth, UK) used for adult patients and two electrostatic (355/5430 Hygroboy and 355/5427 Hygrobaby, Tyco Healthcare, Gosport, UK) used for paediatric patients. The filters were swabbed over their internal surfaces on both the patient and the machine sides and these were assessed with the use of adenosine triphosphate bioluminescence. Contamination was present on the machine side of 20 (9%) filters. Current standards for testing of filters has no set "pass" level and is performed in the laboratory setting. Bioluminescence may be used in the clinical setting to elucidate factors that might increase the chance of cross-contamination between patients.

Adenosine Triphosphate↗
PubMed2007

Minimum and optimum light output of Macintosh size 3 laryngoscopy blades: a manikin study.

Illumination provided by laryngoscope blades varies widely. It is not known what the optimum level of illumination should be during laryngoscopy. So far, no published standards exist for light intensity provided by laryngoscopes. Fifty anaesthetists were recruited to perform laryngoscopy on a manikin with three different laryngoscopes attached to a variable voltage supply. Anaesthetists were asked to find the minimum and optimum level of light they would wish to have for intubation. This study demonstrated that anaesthetists can see the larynx at very low light levels. The optimum level was significantly greater than the minimum level. The vacuum bulb laryngoscopes provides a significant lower light output than halogen and xenon laryngoscopes. There is a large variation in illumination requirements amongst anaesthetists which may make setting standards difficult. A brighter laryngoscope, as suggested by some manufacturers, may not necessarily be a better one.

Adult↗
PubMed2006

The pressure required to force liquid through breathing system filters.

Liquid in the form of sputum and condensation may be forced through a breathing system filter if sufficient pressure is applied to the filter layer, with the potential for cross-infection. Twenty-three different breathing system filters (12 adult, 11 paediatric) were assessed to determine the pressure causing liquid penetration. Five samples of each were tested by connecting the ventilator end of a breathing system filter to a water-filled U-tube and reservoir. The reservoir was positioned so that the water surface was level with the filter layer and raised until liquid appeared through the filter layer on the patient side and the water-column height recorded. There were substantial differences in performance between models. Liquid penetration occurred at lower pressures for adult electrostatic than adult pleated filters: median [IQR] 1.18 [1.08- 1.32] and 8.04 [4.27-12.80] kPa, respectively, p < 0.0001. Liquid penetration occurred at similar pressures in paediatric electrostatic filters (0.98 [0.74-1.32] kPa) compared to adult electrostatic filters.

Adult↗
PubMed2006

Flexibility and light emission of disposable paediatric Miller 1 laryngoscope blades*.

With the emergence of Creutzfeldt-Jakob disease and the discovery of prions in tonsillar material, there has been an increase in the number of available disposable laryngoscope blades. This has led to non-conformity over many aspects of blade design. Miller 1 disposable blades have been produced in both metal and plastic and appear to have different properties of rigidity. We examined the rigidity of 11 disposable Miller 1 blades in three different axes of force. There was a significant difference in flexibility between metal and plastic blades in both primary and torsional axis (p = 0.006). We also studied the blades' light intensity and angle of light emission, finding up to an eightfold difference in the level of illumination provided at a distance of 10 mm from the tips of the blades. The area of maximal illumination varied, with some blades providing narrow beams of light, and others provided a more dispersed field of illumination. In addition, the angle of maximal illumination varied between the blade types from a central position to one directed to the right-hand side.

Disposable Equipment↗
PubMed2005

A comparison of 20 laryngoscope blades using an intubating manikin: visual analogue scores and forces exerted during laryngoscopy.

Fifty anaesthetists were recruited to use 20 different laryngoscope blades (one metal re-usable blade, five metal single-use blades and 14 plastic single-use blades, of which eight were bulb-type and 12 were fibreoptic-type) in a manikin to achieve a grade I Cormack and Lehane view. The anaesthetists were asked to provide visual analogue scores (VAS) for: ease of attachment of the blade to the handle; illumination; view of the larynx; and satisfaction for clinical use. The peak force applied and time to achieve the grade I Cormack and Lehane view were also measured. A cluster analysis method was used to group together blades with similar scores or measures. Ease of attachment, illumination, view, clinical use, force and duration were all significantly affected by the blade used (p < 0.0001 for all six). The mean peak force applied and mean duration for the 20 blades were 32-39 N and 4.4-9.5 s, respectively. All five metal single-use and four plastic single-use blades were always placed in the 'best' group in the cluster analysis. Two plastic blades provided a poor view and increased the duration of laryngoscopy.

Cluster Analysis↗
PubMed2005

Effect of breathing low concentrations of volatile anaesthetic agents on incidence of adverse airway events.

The effect of breathing 0.1 minimum alveolar concentrations (MAC) of desflurane or isoflurane for three minutes on the incidence of adverse airway events on a subsequent breath of 2 MAC was investigated. Twenty-five volunteers known to develop an adverse airway event to desflurane or isoflurane took part in the study. Each volunteer was exposed to isoflurane and desflurane at least 24 h apart. Volunteers were assessed for adverse airway events while breathing 2 MAC inhalational anaesthetic following breathing 100% O(2) for 3 min. This was repeated with 0.1 MAC inhalational anaesthetic in oxygen instead of 100% O(2). Adverse airway events decreased from 88% to 40% when tests were conducted with desflurane (p = 0.002). With isoflurane, the reduction from 60% to 52% was not statistically significant (p = 0.774). Breathing low concentrations of desflurane decreases the incidence of adverse airway events on subsequent inhalation of higher concentration of desflurane.

Adult↗
PubMed2005

Sevoflurane (12% and 8%) inhalational induction in children.

BACKGROUND: Sevoflurane induction of anesthesia is frequently used in children. Rapidly performed inhalational induction may reduce excitation during early anesthesia. Increasing the total anesthetic MAC delivered to patients can be achieved by increasing volatile concentration or adding nitrous oxide. The latter reduces inspired oxygen concentration delivered, which may not be desirable. Even 8% sevoflurane induction is associated with excitation. A system capable of delivering 12% sevoflurane using two tandem vaporizers has been developed. METHODS: A randomized double blind study was undertaken to assess whether 12% sevoflurane offered any advantage over 8% in time and quality of induction. Sixty children aged 5-10 years were recruited and received either 12 or 8% sevoflurane. Time to loss of eyelash reflex, central pupils, incidence of adverse events, induction quality, systolic blood pressure and heart rate were recorded. RESULTS: Twelve percent sevoflurane reduced time to loss of eyelash reflex compared with 8% [mean (sd): 35 (12) and 46 (14) P<0.05], but the reduction was only 10% higher than the error in the measurement (assessment every 10 s). Twelve percent sevoflurane offered significantly better quality of induction (P<0.05). There was no difference in cardiovascular stability between groups, although heart rate rose significantly in both groups. Maintaining sevoflurane at 12% for 4 min caused significant amounts of apnea (69% with 12% and 38% with 8%, P<0.05). CONCLUSION: Twelve percent sevoflurane offers a smoother anesthesia induction than 8% in children of this age with no additional consequences for the cardiovascular system.

Anesthesia, Inhalation↗
PubMed2004

Bougie-assisted difficult airway management in a manikin - the effect of position held on placement and force exerted by the tip.

In a randomised cross-over study, 50 anaesthetists attempted to place a multiple-use bougie in the trachea of a manikin, when holding it at either 20 cm or 30 cm from the tip. A grade 3 laryngoscopic view was simulated. The anaesthetists were blinded to success (tracheal placement) or failure (oesophageal placement). The success rates when held at 20 and 30 cm distance from the tip were 68 and 62%, respectively (p = 0.55). In a separate experiment, multiple and single-use bougies were held at four different positions and pressed onto a disc attached to a force transducer. The peak force exerted by the single-use bougies was two to three times greater than that which could be exerted by the multiple-use bougies (p < 0.0001). Holding the bougie at either 20 or 30 cm distance from the tip is unlikely to influence bougie placement. The single-use bougie is much more likely to cause trauma to tissue during placement, particularly if held close to the tip.

Cross-Over Studies↗
PubMed2004

The moisture-conserving performance of breathing system filters during the first three minutes of simulated use.

Breathing system filters are recommended for use during anaesthesia to protect the patient from inhaling gas-borne particles. Filters placed at the patient connection port of the breathing system can also humidify the inspired gases. The end-inspired moisture content was measured when using five different filters with two different ventilatory test conditions on a patient model during a typical pre-oxygenation period of 3 min. The moisture content of the end-inspired air at the end of the 3-min period varied from 6.4 to 27.8 and from 4.4 to 25.9 g.m-3 for tidal volumes of 0.5 and 1.0 l, respectively (p < 0.0001 for all pairwise comparisons of the five filters and for the two tidal volumes). Those breathing system filters that have at least an adequate level of performance (at least 20 g.m-3) will generally achieve this level within the 3-min pre-oxygenation period.

Anesthesia, Closed-Circuit↗
PubMed2004

The moisture-conserving performance of breathing system filters in use with simulated circle anaesthesia breathing systems.

Breathing system filters can be used to humidify gases delivered to patients. Performance can be determined by measuring the net moisture loss (the difference between expired and inspired levels of humidity) from a patient model. The net moisture loss should be decreased by increasing the level of humidity in the breathing system by, for example, using a circle breathing system. The effect of four different filters, three different levels of humidity in the breathing system (7, 13 and 19 g.m-3) and two tidal volumes (0.5 l and 1.0 l) on the net moisture loss from a patient model was measured. The net moisture loss decreased as the humidity in the breathing system increased and was less for the lower tidal volume. Adequate levels of humidity (>/= 20 g.m-3) will be delivered to patients by most filters provided they are used in conjunction with circle breathing systems and low fresh gas flows.

Anesthesia, Closed-Circuit↗
PubMed2004

The effect of gas flow on the filtration performance of breathing system filters.

When tested according to the European standard, the performance of breathing system filters is determined at a flow of 15 or 30 l.min-1 for filters intended for use with paediatric or adult patients, respectively. However, higher flows of gas may pass through a filter in some circumstances. The penetration of sodium chloride particles through seven different breathing system filters (three pleated hydrophobic and four electrostatic) was measured at five different flows ranging from 15 to 75 l.min-1. Penetration varied from 0.004% to 24.4% for the various filters at the different flows. Penetration increased by between 2 and 40 times for the different filters as the flow increased by a factor of five but this did not markedly alter the rank order of the filters in terms of performance. Testing to the standard provides a useful indication of relative performance at any flow.

Adult↗
PubMed2004

Evaluation of Frova, single-use intubation introducer, in a manikin. Comparison with Eschmann multiple-use introducer and Portex single-use introducer.

In a randomised cross-over study, 48 anaesthetists attempted to place a Frova single-use introducer, an Eschmann multiple-use introducer and a Portex single-use introducer in the trachea of a manikin set up to simulate a grade 3 laryngoscopic view. The anaesthetists were blinded to success (tracheal placement) or failure (oesophageal placement). Successful placement (proportion, 95% confidence interval) of either the Frova introducer (65%, 50-77%) or the Eschmann introducer (60%, 46-73%) was significantly more likely than with the Portex introducer (8%, 3-20%). There were no significant differences between the success rates for the Frova and the Eschmann introducers. A separate experiment revealed that the peak force exerted by the Frova and Portex introducers was two to three times greater than that which could be exerted by the Eschmann introducer, p < 0.0001, indicating that the single-use introducers are more likely to cause tissue trauma during placement.

Analysis of Variance↗
PubMed2003

Cricoid yoke: the effect of surface area and applied force on discomfort experienced by conscious volunteers.

BACKGROUND AND OBJECTIVE: The application of cricoid force is central to techniques that reduce the risk of gastric regurgitation and the subsequent pulmonary aspiration associated with obstetric and emergency anaesthesia. The discomfort associated with cricoid force in awake preoperative patients increases the incidence of coughing, struggling and pain during induction of anaesthesia. This study determined if increasing the surface area of a cricoid yoke reduced the associated discomfort in volunteers. METHODS: Fifty volunteers participated in a randomized single-blinded study. The cricoid yoke was positioned using standard anatomical landmarks and forces of 10, 20, 30 and 40 N were applied in a random order for 20s, using two different yoke attachments with surface areas of 3 and 10 cm2. A rest of 30s was allowed between the application of forces. Discomfort was graded by volunteers on a scale from 0 to 10 (0: no discomfort; 10: worse discomfort imaginable). A score of 10 was allocated if the volunteers could not tolerate the applied force for 20s. RESULTS: Median scores for the small yoke were always higher than those for the large yoke at each force. There were significant differences between the scores for the small and large yokes at 10 and 20 N (P < 0.001) and 30 N (P = 0.0233), but there was no significant difference at 40 N. CONCLUSIONS: The larger yoke was tolerated better by volunteers when clinically relevant cricoid forces were applied.

Adult↗
PubMed2003

A comparison of simulated difficult intubation with multiple-use and single-use bougies in a manikin.

In a randomised cross-over study, 20 anaesthetists attempted to place a multiple- or single-use bougie in the trachea of a manikin, in which a grade 3 Cormack and Lehane laryngoscopic view was simulated. The anaesthetists made two attempts at placement with each bougie and were blinded to success (tracheal placement) or failure (oesophageal placement). The success rates for the first attempts with the multiple- and single-use bougies were 85 and 15%, respectively [mean (95% CI) difference between the two bougies 70% (40-84%); p < 0.001]. The success rates for the second attempts were similar to those for the first attempts with both bougies. There is an increased risk of failure to intubate the trachea when using a single-use bougie, and this must be weighed against the unquantified risk of cross-infection from prions when using a multiple-use bougie.

Clinical Competence↗
PubMed2003

Adverse airway events during brief nasal inhalations of volatile anaesthetics: the effect of humidity and repeated exposure on incidence in volunteers preselected by response to desflurane.

Twelve volunteers known to have airways that responded adversely to 2.0 MAC desflurane were recruited. Each volunteer inhaled three single breaths of each of 0.5, 1.0 and 2.0 MAC of sevoflurane, halothane, isoflurane, desflurane and balance air, with breaths of air between, whilst breathing nasally through a face mask attached to one of three filters that provided three different levels of humidification. The incidence of any adverse airway events was recorded. The anaesthetic inhaled significantly affected the incidence of adverse airway events (p < 0.001), with the least to most irritant being sevoflurane, halothane, isoflurane and desflurane. Increasing the concentration of anaesthetic also significantly increased the incidence of adverse airway events (p < 0.001). The filter used, and hence the level of humidification, did not affect the incidence of adverse airway events (p = 0.09), but repeated exposure caused a significant reduction in the incidence of adverse airway events (p < 0.001).

Adult↗