Two methods of predicting difficult laryngoscopy were compared prospectively. Mallampati class and Wilson risk-sum were determined before operation and laryngeal view graded in 675 patients. Both tests identified five of 12 difficult laryngoscopies; twice as many patients were predicted to be difficult by Mallampati classification than by Wilson risk-sum. Inter-observer variation was minimal using Wilson risk-sum, but considerable for Mallampati classification. We prefer the Wilson risk-sum for assessment of the airway, while noting that both tests have poor sensitivities.

The Effective Blood Concentration (EC) of propofol required to prevent response to surgical incision was determined in 65 ASA I or II female patients breathing either 100% oxygen or 67% N2O in oxygen. Propofol was administered via a microcomputer-controlled infusion system programmed to maintain the blood propofol concentration at predetermined target values. The blood propofol concentrations predicted by the micro-computer were validated by measurement of whole blood propofol concentration. Predicted and measured concentrations differed during infusion of propofol, but became similar after discontinuing the infusion for at least 90 s, suggesting that equilibration within the central compartment was incomplete during infusion. The response to the initial incision was observed and probit analysis used to determine the predicted blood concentration at which 50% of patients responded. The predicted EC50 for propofol/N2O/O2 and propofol/O2 was 4.5 micrograms ml-1 and 6.0 micrograms ml-1 respectively, and the measured EC50 propofol/N2O/O2 and propofol/O2 was 5.36 micrograms ml-1 and 8.1 micrograms ml-1, 67% nitrous oxide in oxygen reducing the predicted EC50 by 25% and the measured EC50 of propofol by 33%. The predicted EC may be more representative of the equilibrated concentration in the central compartment and thus reflective of tissue propofol concentrations.

SummaryA study was undgrtaken to investigate the use of fentanyl by aerosol for postoperative analgesia. Seven patients hadplacebo, six received fentanyl 100 pg and seven were given fentanyl300 pg. A Key wordsAnalgesics, narcotic; fentanyl. Aerosols.A simple method of analgesia which is rapidly effective with the minimum of complex apparatus would be useful for the postoperative patient and for self administration by those suffering severe pain at home. Such systems were developed with infusion pumps, but their widespread use is limited by cost and complexity. Delivery of drugs by aerosol into the respiratory tract is simple and has become widely accepted for the prophylaxis and treatment of asthma, in migraine and in angina pectoris. Modern nebulisers, using hospital compressed gases, or electrically driven air nebulisers, are capable of reliably producing aerosols of fine particle size which penetrate the bronchial tree and are deposited in airways and alveoli.'.2 Drug is deposited in sites drained by both the bronchial and pulmonary circulations, and will enter the systemic circulation and reach the brain. There is recent interest in the administration of morphine in this way. '-5 Fentanyl is a synthetic narcotic analgesic which is highly lipid soluble, has a rapid onset of action, is potent, does not release histamine, and which, in a single dose, has a short duration of action. It is an effective analgesic agent for pain relief. We have therefore undertaken a pilot study to look at the use of nebulised fentanyl as a method of postoperative analgesia. MethodsThirty patients in a single-blind study were randomly allocated to receive a standard volume (6 ml) that contained placebo (0.9% saline), 100 p g or 300 pg fentanyl given by nebuliser. Patients were aged 18-65 years, were ASA 1-2, and undergoing a variety of elective surgical procedures (Table 1). Those with known respiratory or hepatic disease, or who were receiving drugs known to interfere with drug metabolism were not studied. Ten patients were allocated to each group. Ethics committee approval and informed written consent were obtained.Premedication consisted of morphine and cyclizine. Anaesthesia was induced with thiopentone and maintained with nitrous oxide and halothane in oxygen. Additional analgesia was provided with morphine, and muscle relaxants were used where indicated.Patients who complained of pain in the recovery room were asked to assess its severity on a 10-cm linear visual analogue (LVA) scale which had been explained the day before. Fentanyl or placebo was then administered in a single-blind fashion via an Acorn I1 nebuliser driven by compressed oxygen and nebulised to dryness in oxygen at a flow of 8-10 litres/ minute to produce a particle size of 2 p

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