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Biomedical subjects

P Charters

Publications and source records attributed to P Charters.

At least 37 records · Page 2Linked to original sources
PubMed1993

An analysis of laryngoscope blade shape and design: new criteria for laryngoscope evaluation.

Laryngoscope blade design has tended to be relatively arbitrary and so far scientific analysis has not allowed useful comparisons between blade shapes. A new theoretical method of analysing laryngoscope blades is introduced and uses the depth of insertion profiles of two angular measurements. One represents eyeline displacement and the other the forward space that the blade occupies at the level of the mandible. Photographs of straight and curved blades were studied on Cartesian graphs with the tip T, at the origin and handle fittings parallel to the x-axis of the graph. Then, IT is any line from the origin to the incisor surface and represents a point of contact with the upper incisors for a given depth of blade insertion. Angle EIT (eyeline displacement) is to a tangent from I along the lower lingual surface of the blade. Point M is on the upper lingual surface of the blade, at right angles to IT, 1/3 of the distance from I along IT. Angle MIT (forward space) may be positive or negative depending on whether M is in front of or behind IT. The angles EIT, MIT and their additive combination are used in blade analysis. Negative MIT compensates for eyeline displacement as Macintosh size 3 and 4 blades have better combination scores than Miller size 3. All three are superior to the straight Soper size 3 blade. The Macintosh size 1 and 2 blades are quite different from the larger Macintosh blades. This theoretical basis for blade analysis is consistent with commonly expressed clinical opinions and may influence blade design in the future.

Equipment Design↗
PubMed1992

The role of mucosal receptors in the nasal sensation of airflow.

50 subjects were admitted into a randomized double-blind placebo controlled cross-over trial with 4% lignocaine as the active drug and normal saline as the placebo. Each subject had 2 ml of solution sprayed into each nasal cavity and all subjects had both sprays but on different occasions. The order in which the sprays were administered was randomized. The subjective sensation of nasal airflow was measured using a visual analogue scale before and after the spray. These measurements were made under conditions of the same airflow rate, which was monitored throughout the experiment using a reprogrammed NR6 rhinomanometer. Objective nasal patency was measured as peak nasal inspiratory flow rate. It was found that the nasal sensation of airflow decreased slightly after both lignocaine (difference between medians 5.0; 95% confidence interval -2.91 to 6.11) and normal saline (difference between medians 6.0; 95% confidence interval -1.02 to 7.21). Nonparametric analysis of variance showed this difference to be non-significant (P = 0.73). In addition there was no significant change in objective nasal patency. The results suggest that nerve endings in the nasal mucosa play no part in sensing nasal airflow during respiration.

Adolescent↗
PubMed1991

The objective assessment of nasal patency.

Nasal patency was measured by five techniques in 24 subjects and the results compared. In addition three pulmonary parameters were measured as well as height and weight. Nasal resistance to airflow measured by active anterior rhinomanometry was found to be highly correlated with peak nasal inspiratory flow rate. Other correlations were also noted. Peak nasal inspiratory flow was itself highly correlated with pulmonary peak expiratory flow rate as well as with several other parameters. The possible reasons for these correlations are discussed in terms of fluid mechanics.

Adult↗
PubMed1990

Pivoting larynx--an unusual clinical observation at laryngoscopy.

Rigid oesophagoscopy was planned in the investigation of a young patient with dysphagia. During laryngoscopy for tracheal intubation an unusual pivoting manoeuvre was required to see the vocal cords. Although the initial diagnostic investigations were unhelpful, follow up directed at explaining the clinical observations led to an eventual diagnosis of anterior tubercles of C6, which explained the observation and accounted for the dysphagia.

Adult↗
PubMed1990

Factor analysis in difficult tracheal intubation: laryngoscopy-induced airway obstruction.

We have studied eight patients with a history of difficult tracheal intubation, using x-ray laryngoscopy and local anaesthesia, a curved Macintosh blade and a standard intubating position. The view obtained was better than recorded previously during general anaesthesia in two patients, and in a third the x-ray showed that positioning the blade tip beneath the epiglottis would have improved vision, suggesting that reproducibility of the assessment may not be consistent. The "ease of intubation" and "complementary" angles may be helpful in the assessment of such patients. A "peardrop" effect is described whereby during laryngoscopy, the epiglottis became pressed against the posterior pharyngeal wall as a result of tongue compression. In the absence of muscle paralysis, removal of the blade caused immediate correction. However, during anaesthesia with neuromuscular block it is suggested that this not only occurs more readily but, may not correct when the blade is removed. Iatrogenic airway obstruction during moderately difficult tracheal intubation may be common and should be anticipated.

Airway Obstruction↗
PubMed1990

Factor analysis in patients with a history of failed tracheal intubation during pregnancy.

Eight patients with a history of failed tracheal intubation during pregnancy were investigated by x-ray laryngoscopy after delivery. Partial elevation of the epiglottis with no view of glottic structures was found in five patients who were therefore considered to still present difficulty. In each of these five patients the blade tip failed to make contact with the hyoid and in four this was explained by the tongue being compressed into a pear shape such that it prevented sight of the larynx. Relatively few abnormal anatomical indices were seen in these patients and this was in keeping with the level of difficulty encountered. An angular measure of jaw protrusion from a line joining the upper incisors and a point just above and anterior to the vocal cords, to the mid-point on the inner surface of the mandible was useful: the lower angle of this triangle was as important as the angle at the incisors.

Adult↗
PubMed1989

Defining a standard intubating position using "angle finder".

Study of patients who exhibit only limited morphological abnormality yet present difficulty with direct laryngoscopy is facilitated by a standard intubating position. The "Angle Finder" instrument allows implementation of a simple reproducible geometric standard which is applied easily in formal research work and in clinical practice and teaching. The proposed standard relates to the curved (Macintosh) laryngoscope blade and a supine patient. The lower neck flexion is 35 degrees and extension of the plane of the face 15 degrees, each angle measured relative to horizontal. Initially, the standard was derived from a review of the literature, then validated in a study of the intubating practices of 10 senior anaesthetists. A more detailed study of 10 normal volunteers confirmed reproducibility and, for nine patients with a history of difficult direct laryngoscopy, the standard was shown to be appropriate.

Head↗
PubMed1989

Disposition of cervical vertebrae, atlanto-axial joint, hyoid and mandible during x-ray laryngoscopy.

Ten healthy volunteers underwent direct laryngoscopy using topical anaesthesia and a curved Macintosh laryngoscope blade. A lateral x-ray was performed during laryngoscopy in a standard intubating position. In this position the lower neck was relatively straight and increasing curvature occurred from the mid cervical spine upwards. Extension at the atlanto-axial joint was probably near maximum; this has implications for conditions associated with laxity of this joint. The position of the mandible was influenced by the direction of pull on the laryngoscope handle. The hyoid was drawn forward and its body tilted downwards so as to lie halfway between the lower border of the mandible and the glottis. The relative length of epiglottis projecting above the hyoid was variable.

Adult↗
PubMed1988

An additional tactile test. Further developments in tactile tests to confirm laryngeal placement of tracheal tubes.

An additional clinical test to confirm laryngeal placement of tracheal tubes is described. Using the new test, placement was confirmed in all of 50 patients studied in whom difficulty would have been anticipated using previously described tactile tests (male patients with lower molar teeth). Two anaesthetists with small hands averaged 98% confirmations in two series each of 100 consecutive unselected intubations. A simple modification of the tests enables their application after nasotracheal intubation; even with small hands, a confirmation rate of 96% in 50 consecutive cases was found. The three tactile tests are reviewed and analysed. In the authors' combined experience of 14 cases of difficult laryngoscopy the tests gave reliable confirmation in 12 patients. Familiarity with these tests is stressed to be important for their reliable implementation.

Adult↗
PubMed1987

Tactile orotracheal tube placement test. A bimanual tactile examination of the positioned orotracheal tube to confirm laryngeal placement.

The development of a tactile clinical test of the positioned orotracheal tube is described which allows confirmation of its location within the larynx. It was possible, after preliminary experience with the test, to confirm laryngeal placement confidently in an average of 97% of cases in two concurrent series each of which consisted of 100 patients. Inevitably, there are limitations to its usefulness but it has the advantage that no special apparatus is required for its performance. The implications of this test are discussed in relation to difficult intubation, obstetric anaesthesia, the teaching of applied anatomy and checking by their trainers of intubations performed by very junior anaesthetists. Familiarity with this test should be considered essential for its reliable implementation.

Adult↗