OBJECTIVE: To investigate the effects of medialization laryngoplasty on laryngeal airway resistance at various clinically relevant flow rates. STUDY DESIGN: This study was conducted using a total of 13 laboratory experiments. Two of the experiments were used to validate the cadaveric model employed. Eleven experiments were used to quantify airway resistance relative to increasing medialization laryngoplasty stent size. METHODS: With autopsy consent the authors obtained 13 consecutive and anatomically complete larynges for experimentation. A thyrotomy window measuring 8 x 6 mm was made on the left side of the thyroid cartilage. A #4 laryngeal mask was secured to the pharyngeal airway with sutures. Eleven experiments were conducted at the same flow rates using increasingly larger stents from 1 mm to 11 mm in size. Using the Bernoulli equation, the pressure measured at the proximal end of the laryngeal mask is representative of the pressure drop across the airway. The experimental model was validated in two experiments using flow rates between 5 and 50 L/min and stents measured at 5, 10, 15, and 20 mm. RESULTS: Average results from the 11 experiments indicate that at increasing levels of medialization, from 0 to 11 mm, there is essentially the same pressure drop across the larynx at a given flow rate. CONCLUSION: At physiologic airflow rates in a cadaveric model, medialization laryngoplasty implants of 11 mm or less seem to have no obvious effect on airway resistance.

Aged↗

PubMed1999

Mendelson's syndrome: a contrarian perspective.

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Cesarean Section↗

PubMed1998

Jehovah's Witnesses and blood transfusions.

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Blood Transfusion↗

PubMed1998

The unanticipated difficult airway with recommendations for management.

PURPOSE: To review the current literature and generate recommendations on the role of newer technology in the management of the unanticipated difficult airway. METHODS: A literature search using key words and filters of English language and English abstracted publications from 1990-96 contained in the Medline, Current Contents and Biological Abstracts databases was carried out. The literature was reviewed and condensed and a series of evidence-based recommendations were evolved. CONCLUSIONS: The unanticipated difficult airway occurs with a low but consistent incidence in anaesthesia practice. Difficult direct laryngoscopy occurs in 1.5-8.5% of general anaesthetics and difficult intubation occurs with a similar incidence. Failed intubation occurs in 0.13-0.3% general anaesthetics. Current techniques for predicting difficulty with laryngoscopy and intubation are sensitive, non-specific and have a low positive predictive value. Assessment techniques which utilize multiple characteristics to derive a risk factor tend to be more accurate predictors. Devices such as the laryngeal mask, lighted stylet and rigid fibreoptic laryngoscopes, in the setting of unanticipated difficult airway, are effective in establishing a patient airway, may reduce morbidity and are occasionally lifesaving. Evidence supports their use in this setting as either alternatives to facemask and bag ventilation, when it is inadequate to support oxygenation, or to the direct laryngoscope, when tracheal intubation has failed. Specifically, the laryngeal mask and Combitube have proved to be effective in establishing and maintaining a patent airway in "cannot ventilate" situations. The lighted stylet and Bullard (rigid) fibreoptic scope are effective in many instances where the direct laryngoscope has failed to facilitate tracheal intubation. The data also support integration of these devices into strategies to manage difficult airway as the new standard of care. Training programmes should ensure graduate physicians are trained in the use of these alternatives. Continuing medical education courses should allow physicians in practice the opportunity to train with these alternative devices.

Education, Medical, Continuing↗

PubMed1998

Medical equipment reuse: some principles.

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Disposable Equipment↗

PubMed1998

Applying human factors to the design of medical equipment: patient-controlled analgesia.

OBJECTIVE: Medical instruments commonly have poorly designed user interfaces that promote human errors with life-threatening consequences. The primary hypothesis of this study was that a specific user interface could be made safer and more efficient if redesigned using human factors techniques and principles. METHODS: The user interface of a commercially available patient-controlled analgesia (PCA) pump, the Abbott Lifecare 4100 PCA Plus II infuser, was evaluated using a cognitive task analysis of bench tests and field observations. Based on this analysis, the user interface was redesigned. Important elements of the new design include a dialog structure with fewer steps, a dialog overview showing the user's location in the programming sequence, better command feedback, easier error recovery, and clearer labels and messages. The changes were evaluated by comparing a computer prototype of the new interface with a computer simulation of the old one. Twelve student nurses performed six programming tasks with each interface. Task completion time, number of errors, and subjective mental workload were collected for each trial. RESULTS: The results showed significantly faster programming times (F(1,11) = 6.85, P < 0.025), lower mental workload ratings (chi2(1) = 4.45, p < 0.025, one-tailed), and fewer errors (chi2(1) = 3.33, p < 0.05, one-tailed) with the new interface. CONCLUSION: Adopting a human factors approach to redesigning the PCA interface led to significantly faster, easier, and more reliable performance. These findings have important implications for improving the design of other computer-based medical equipment.

Analgesia, Patient-Controlled↗

PubMed1998