Relationship of inspiratory and expiratory times to upper airway resistance during pulsatile needle cricothyrotomy ventilation with generic delivery circuit.

BACKGROUND: Narrow-bore cricothyrotomy retains a clinical role, due to the availability of its component equipment in acute clinical environments, ease of assembly, and operator preference. However, due to infrequent use, there is a need to model this for research and teaching. We present mathematical and laboratory models. METHODS: Using electrical analogy, we mathematically modelled a generic cannula cricothyrotomy circuit, relating inspiratory and expiratory times to the upper airway resistance (R(u)). We constructed a laboratory model to support our mathematical model. The simulated lung is a smooth-bore tube on a tilting table. The upper airway is simulated by 20 G cannulae. Inspiratory and expiratory times for the water meniscus to travel a preset distance (corresponding to tidal volume) were measured and plotted against the number of cannula. RESULTS: From the mathematical model, inspiratory time increases hyperbolically with decreasing R(u), such that there is a minimum R(u) beyond which most of the fresh gas flow leaks out without inflating the chest. Conversely, as R(u) increases, inspiratory time decreases to a plateau. Expiratory time is limited by respiratory factors at low R(u) and by the resistance of the transtracheal expiratory pathway at high R(u), producing a sigmoid-shaped expiratory curve. The experimental results seem consistent with these predictions, although direct theory-experiment mapping is problematic because of the difficulty in assigning a single value to the dynamically changing upper airway resistance. CONCLUSIONS: We can exploit the contrasting changes in inspiratory and expiratory times with the upper airway resistance to optimize conditions for emergent cannula cricothyrotomy ventilation.

Management of unanticipated difficult intubation: a survey of current practice in the Oxford region.

BACKGROUND AND OBJECTIVE: Unanticipated difficulty in tracheal intubation in an anaesthetized patient has always been a cause of concern to anaesthesiologists. This difficulty may lead to morbidity and mortality. This survey was carried out to determine the technique commonly favoured in centres in the Oxford region in the UK for the management of unanticipated difficult intubation. METHODS: We conducted a clinical scenario-based questionnaire survey of 181 anaesthesiologists in the Oxford region. In this scenario, difficulty in endotracheal intubation is recognized only after induction of anaesthesia. A number of options were available to deal with this situation. We used this scenario as a tool to gain insight into the training and the training needs of anaesthesiologists at various levels of training. RESULTS: Of the 181 questionnaires sent, we received 143 (79%) completed replies. The vast majority (141/143 (99%)) of anaesthesiologists would use a gum-elastic bougie together with head and neck positioning and optimal external laryngeal manipulation to gain the best attempt at intubation. If intubation still failed, overall 129/143 (90%) had a back-up plan, while 14/143 (10%) had no plan. Flexible fibreoptic techniques were more commonly planned by 92/143 (64%) anaesthesiologists compared to blind techniques which were less commonly planned by 37/143 (26%) anaesthesiologists. Differences in choice of technique among anaesthesiologists in teaching and district general hospitals were not significant (P = 0.87). Overall, trainees were less likely to choose fibreoptic techniques compared to consultants (P = 0.0009) and would use blind techniques or ask a more experienced colleague to take over. The main reason for the choice was previous experience with the technique. CONCLUSIONS: Although fibreopric techniques were most commonly planned, these were less often chosen by trainees than consultants due to lack of experience/training, while unavailability of intubating laryngeal mask airway (Intavent) was an additional issue precluding its use as an adjunct to intubation.

Diclofenac vs oxybuprocaine eyedrops for analgesia in paediatric strabismus surgery.

Forty children undergoing strabismus surgery as day patients were randomly allocated to receive oxybuprocaine 0.4% eyedrops or 0.1% diclofenac eyedrops for perioperative analgesia. A non-invasive anaesthetic technique using the reinforced laryngeal mask airway was used. The study demonstrated that both topical analgesics provided good to excellent analgesia and the anaesthetic technique was associated with a relatively low incidence of nausea and vomiting. Complications were limited to two children who were admitted with persistent postoperative nausea and vomiting.

A new hinged tip laryngoscope.

The McCoy laryngoscope undoubtedly improves the view of the vocal cords during difficult tracheal intubation. An inherent design problem with the McCoy blade is the need to relax the grip on the laryngoscope handle at the point when stability is most necessary. A new hinged tip blade is described which is operated by a button mechanism on a secondary handle that runs adjacent to the standard handle. This modification offers the possibility of better stability and ease of manipulation whilst maintaining all the benefits of the McCoy blade.