Many anatomical factors in difficult intubation at direct laryngoscopy have been evaluated. Lateral radiographs were taken of nineteen patients in whom tracheal intubation proved particularly difficult, and fourteen patients whose intubation was reasonably straightforward. Step wise discriminant analysis was used to select the best measurements for distinguishing between the difficult and straightforward groups. The variables which together are most reliable in predicting likely difficulty in intubation are reduced atlanto-occipital extension, reduced mandibular space, and lastly, increased antero-posterior thickness of the tongue. Aformula and graph have been derived to relate these variables with likelihood of difficulty, and a method has been described of applying this information at the bedside, without using X-ray examination, to estimate the likelihood of difficulty in intubating a new patient. Eighteen months' experience of the application of this clinical evaluation have so far found it reliable.
to changes in PaCO 2 between 27-50mmHg remains intact during propofol anaesthesia in healthy individuals. Our absolute CBF values are similar to those previously reported during fixed dose propofol anaesthesia but are lower than those we haye recorded during propofol-N20 anaesthesia ~,z. Similarly, the slope of CBF-PaCO 2 relationship is less than during propofol-N20 anaesthesia. These differences may be explained by either the c e r e b r o v a s o d i l a t i n g e f f e c t of N20 or the quantity of propofol used. During hypocapnia, CBF was low, but there were no changes clinically or in the evoked potentials to suggest ischaemia. Propofol may therefore reduce the CBF threshold for cerebral isohaemia as assessed by evoked potentials.
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