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.
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.
SummaryA study has been undertaken to compare the induction characteristics of the new intravenous anaesthetic agent 2,6 di-isopropyl phenol, newly prepared in a lipid emulsion (propofol) with those of thiopentone. Despite a signijicantly higher incidence of pain on injection and spontaneous movement, the new agent "as felt to perform comparably to thiopentone as an induction agent. Unfortunately, propofol caused decreases in blood pressure which were signijicantly greater than those seen after thiopentone. This feature may prove to be a considerable hurdle to the general acceptance of propofol.
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.
Maternal venous (MV), umbilical venous (UV) and umbilical arterial (UA) blood samples were obtained for assay of atracurium, laudanosine and monoquaternary alcohol concentrations in 22 healthy patients undergoing elective Caesarean section under general anaesthesia. At delivery (at a mean time of 8.2 min after atracurium 0.3 mg kg-1), the mean UV concentrations were 103 ng ml-1 (range 44-189 ng ml-1) for atracurium, 26 ng ml-1 (range 6-60 ng ml-1) for laudanosine and 59 ng ml-1 (range 21-148 ng ml-1) for monoquaternary alcohol. The ratios of UV:MV, UA:MV and UA:UV blood concentrations were related positively to time since injection of atracurium for all three substances (P less than 0.01 in each instance). The UV:MV ratio at delivery was greatest for laudanosine: mean 19.4% (range 1-35%), compared with 7% (range 2-21%) for atracurium and 10% (range 0-15%) for monoquaternary alcohol. These low values confirm that, although atracurium crosses the placental barrier and its metabolites may be found in the fetus, the drug is safe to use during Caesarean section.
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