Anaesthesia
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Case Reports Randomized Controlled Trial
Incidence of clinically symptomatic pneumothorax in ultrasound-guided infraclavicular and supraclavicular brachial plexus block.
The use of periclavicular brachial plexus block as regional anaesthesia for surgical procedures on the upper extremity is common. However, the proximity of the pleura results in a risk of pneumothorax. Without ultrasound monitoring, the pneumothorax risk has been reported to be as high as 6.1%. ⋯ Ultrasound guidance does therefore appear to reduce the risk of pneumothorax. Although all of the anaesthesiologists involved in the complications had previously performed fewer than 20 blocks, we are not able to confirm that a block experience ≤ 20 is a significant risk factor. Faulty image-setting, inability to obtain a view of the needle tip and inadequate supervision are likely to be important risk factors.
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Randomized Controlled Trial Comparative Study
A randomised comparison of the i-gel™ and the Laryngeal Mask Airway Classic™ in infants.
We performed a randomised comparison of the i-gel™ and the Laryngeal Mask Airway (LMA) Classic™ in children aged less than a year who were undergoing general anaesthesia for elective surgery. Fifty-four infants were randomly allocated to either the i-gel or the LMA Classic. We measured performance characteristics, fibreoptic views through the device and complications. ⋯ Insertion of the device was considered easy in 26/27 (96%) patients in the i-gel group compared with 18/26 (69%) patients in the LMA Classic group (p = 0.009). There were no differences between the groups in insertion times, fibreoptic views through the device, airway leak pressures or complications. We conclude that the i-gel was considered easier to insert than the LMA Classic in infants.
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Observational Study
A prospective observational study of stroke volume responsiveness to a passive leg raise manoeuvre in healthy non-starved volunteers as assessed by transthoracic echocardiography.
Current guidelines for intra-operative fluid management recommend the use of increments in stroke volume following intravenous fluid bolus administration as a guide to subsequent fluid therapy. To study the physiological premise of this paradigm, we tested the hypothesis that healthy, non-starved volunteers would develop an increment in their stroke volume following a passive leg raise manoeuvre. Subjects were positioned supine and stroke volume was measured by transthoracic echocardiography at baseline, 30 s, 1 min, 3 min and 5 min after passive leg raise manoeuvre to 45°. ⋯ Of the 11 volunteers evaluated, five (45%) had stroke volume increases of greater than 10%. Mean (SD) maximum percentage change in cardiac index was 14.8 (9.7)% (p = 0.004). A wide variation in baseline stroke volume and response to the passive leg raise manoeuvre was seen, suggesting greater heterogeneity in the normal population than current clinical guidelines recognise.
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Ropivacaine plasma levels following local infiltration analgesia for primary total hip arthroplasty.
We measured total and free plasma concentrations of ropivacaine following high-volume, high-dose local infiltration analgesia in 19 patients aged 65 years or over undergoing unilateral total hip arthroplasty. The patients received 180 ml ropivacaine 0.2% (360 mg), which was injected into the deep and peri-capsular tissues, the gluteal muscles and fascia lata, and the subcutaneous tissues and skin. Patients were monitored for clinical symptoms and signs of systemic local anaesthetic toxicity. ⋯ No samples reached the toxic threshold for venous ropivacaine concentration, although four patients exhibited mild symptoms consistent with local anaesthetic toxicity. One patient had episodes of complete heart block on ECG monitoring, but plasma ropivacaine levels were below toxic levels. We conclude that plasma levels for ropivacaine associated with toxicity in a volunteer population (total 2.2 μg.ml(-1) , free 0.15 μg.ml(-1) ) are not reached during local infiltration analgesia for hip arthroplasty in elderly patients.
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Using a simple surface nerve stimulation system, I examined the effects of general anaesthesia on rheobase (the minimum current required to stimulate nerve activity) and chronaxie (the minimum time for a stimulus twice the rheobase to elicit nerve activity). Nerve stimulation was used to elicit a motor response from the ulnar nerve at varying pulse widths before and after induction of general anaesthesia. ⋯ Under anaesthesia, rheobase values increased by an average of 20% (p = 0.05), but chronaxie values did not change significantly (p = 0.39). These results suggest that threshold currents used for motor response from nerve stimulation under general anaesthesia might be higher than those used in awake patients.