Anaesthesia
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Drawing samples from an indwelling arterial line is the method of choice for frequent blood analysis in adult critical care areas. Sodium chloride 0.9% is the recommended flush solution for maintaining the patency of arterial catheters, but it is easy to confuse with glucose-containing bags on rapid visual examination. The unintentional use of a glucose-containing solution has resulted in artefactually high glucose concentrations in blood samples drawn from the arterial line, leading to insulin administration causing hypoglycaemia and fatal neuroglycopenic brain injury. ⋯ We also make recommendations about storage, arterial pressure monitoring and sampling systems and techniques. Finally, we make recommendations about glucose monitoring and insulin administration. It is intended that adherence to these guidelines will reduce the frequency of sample contamination errors in arterial line use and capture events, when they do occur, before they cause patient harm.
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We measured the pulsatility indices in the inferior collateral and posterior recurrent ulnar arteries, which supply the ulnar nerve at the elbow, in 38 conscious adults. Compared with a straight 30° abducted arm, elbow flexion to 120° reduced the mean (SD) pulsatility index in the inferior artery and increased the pulsatility index in the posterior artery: from 3.36 (0.86) to 3.04 (0.94), p = 0.001, and from 3.14 (0.81) to 3.64 (1.05), p < 0.0005, respectively. The mean (95% CI) pulsatility index in the inferior artery was unaffected by shoulder abduction to 120°, but it was decreased in the posterior artery in men, from 3.06 (2.76-3.36) to 2.64 (2.34-2.95), but not women, from 3.22 (2.94-3.50) to 3.25 (2.97-3.53), p = 0.01 for men vs women. Researchers should measure arterial pulsatility indices under general anaesthesia and associate them with measures of nerve function.
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In the presence of single-use airway filters, we quantified anaesthetic circuit aerobic microbial contamination rates when changed every 24 h, 48 h and 7 days. Microbiological samples were taken from the interior of 305 anaesthetic breathing circuits over a 15-month period (3197 operations). ⋯ Annual savings for one hospital (six operating theatres) were $AU 5219 (£3079, €3654, $US 4846) and a 57% decrease in anaesthesia circuit steriliser loads associated with a yearly saving of 2760 kWh of electricity and 48 000 l of water. Our findings suggest that extended circuit use from 24 h up to 7 days does not significantly increase bacterial contamination, and is associated with labour, energy, water and financial savings.
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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.