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  • Effects of subanaesthetic sevoflurane on ventilation. 2: Response to acute and sustained hypoxia in humans.

    2 February 2018

    We have determined the influence of 0.1 minimum alveolar concentration (MAC) of sevoflurane on the acute ventilatory response to hypoxia (AHVR), hypoxic ventilatory decline (HVD) and the magnitude of the rapid decline in ventilation on relief of sustained hypoxia (the off-response) in eight healthy adult volunteers. The following design was used with and without 0.1 MAC of sevoflurane: end-tidal PO2 was maintained at 13.3 kPa for 5 min, at 7.9 kPa for 20 min and at 13.3 kPa for 5 min. End-tidal PCO2 was held constant throughout at 1.3 kPa above the subject's normal value. A dynamic end-tidal forcing system was used to generate these gas changes. Sevoflurane reduced AHVR from 14.5 (SEM 1.2) to 11.6 (1.6) litre min-1, and the off-response at cessation of hypoxia from 7.1 (1.1) to 6.3 (1.4) litre min-1. The magnitude of HVD was slightly increased by sevoflurane from 8.2 (1.1) to 10.6 (2.8) litre min-1. None of these changes was significant (ANOVA). These results suggest that 0.1 MAC of sevoflurane had very little effect on the AHVR, and that it did not markedly alter the processes underlying HVD during sustained hypoxia.

  • Physiology and pharmacology of spinal and epidural anaesthesia

    27 October 2017

    Delivering drugs into the spinal and epidural spaces are frequently used techniques in modern anaesthesia. Historically, they carried significant morbidity and fell out of favour. Their safety profile has improved and now they have been shown to convey a safety benefit for patients and often form part of 'enhanced recovery' programmes. With over 300,000 blocks performed, it is important for surgeons to be aware of the postoperative sequelae when patients return to the ward. With subtle differences between spinal and epidural anaesthesia and a wide variety of drugs and doses used, here we review the physiological consequences of neuraxial blocks and the pertinent pharmacology. © 2012 Elsevier Ltd. All rights reserved.

  • Using mean duration and variation of procedure times to plan a list of surgical operations to fit into the scheduled list time.

    6 February 2018

    BACKGROUND AND OBJECTIVE: It is important that a surgical list is planned to utilise as much of the scheduled time as possible while not over-running, because this can lead to cancellation of operations. We wished to assess whether, theoretically, the known duration of individual operations could be used quantitatively to predict the likely duration of the operating list. METHODS: In a university hospital setting, we first assessed the extent to which the current ad-hoc method of operating list planning was able to match the scheduled operating list times for 153 consecutive historical lists. Using receiver operating curve analysis, we assessed the ability of an alternative method to predict operating list duration for the same operating lists. This method uses a simple formula: the sum of individual operation times and a pooled standard deviation of these times. We used the operating list duration estimated from this formula to generate a probability that the operating list would finish within its scheduled time. Finally, we applied the simple formula prospectively to 150 operating lists, 'shadowing' the current ad-hoc method, to confirm the predictive ability of the formula. RESULTS: The ad-hoc method was very poor at planning: 50% of historical operating lists were under-booked and 37% over-booked. In contrast, the simple formula predicted the correct outcome (under-run or over-run) for 76% of these operating lists. The calculated probability that a planned series of operations will over-run or under-run was found useful in developing an algorithm to adjust the planned cases optimally. In the prospective series, 65% of operating lists were over-booked and 10% were under-booked. The formula predicted the correct outcome for 84% of operating lists. CONCLUSION: A simple quantitative method of estimating operating list duration for a series of operations leads to an algorithm (readily created on an Excel spreadsheet, that can potentially improve operating list planning.

  • Determination of the site of tracheal tube impingement during nasotracheal fibreoptic intubation.

    1 February 2018

    This study examines the incidence and site of tracheal tube impingement during nasotracheal fibreoptic intubation, and the efficacy of anticlockwise tube rotation to overcome the problem. Forty-three patients underwent fibreoptic-assisted nasotracheal intubation using a preformed nasal tube, and a second fibrescope was used to observe any obstruction to passage of the tracheal tube. Impingement occurred in 10 cases, with the most common site being the right arytenoid cartilage. Rotation resulted in successful intubation in all 10 cases, but proximal rotation did not always result in an equal degree of rotation at the tube tip. We conclude that the site of impingement for nasotracheal intubation with preformed nasal tubes is located at the posterior structures of the laryngeal inlet and that anticlockwise rotation is a simple and effective solution.

  • Day of surgery cancellations after nurse-led pre-assessment in an elective surgical centre: the first 2 years.

    28 January 2018

    We describe a nurse-led pre-assessment system at an elective surgical centre. A targeted referral system was used by trained nurses to direct referrals to a supervising consultant anaesthetist or to the surgical team. Of 2726 patients pre-assessed in the first 2 years, 105 patients (3.9%) were cancelled or postponed for medical optimisation after pre-assessment. There were 137 cancellations (5.0%) on the day of surgery, despite pre-assessment, but only 36 were for anaesthetic or medical reasons. Only eight of these 36 were considered a 'failure' of the pre-assessment system. These results are much better than the cancellation rate of about 11% in the Trust as a whole. There were 18 transfers of patients postoperatively from the elective centre to another hospital. A review suggested that four of these transfers could have been reasonably predictable from the patients' medical history. We conclude that a pre-assessment clinic has an important role to play in minimizing cancellations on the day of surgery and also in reducing the number of patients transferred to other hospitals. This last conclusion has an important implication for the planning of systems in hospitals that perform only elective surgery.