Anaesthesia
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Measurement of left ventricular stroke volume and cardiac output is very important for managing haemodynamically unstable or critically ill patients. The aims of this study were to compare stroke volume measured by three-dimensional transoesophageal echocardiography with stroke volume measured using a pulmonary artery catheter, and to examine the ability of three-dimensional transoesophageal echocardiography to track stroke volume changes induced by haemodynamic interventions. This study included 40 cardiac surgery patients. ⋯ The concordance rate in the 4-quadrant analysis after phenylephrine and ephedrine administration was 75% and 84%, respectively. In the polar-plot analysis, the angular concordance rate was 66% and 73% after phenylephrine and ephedrine administration, respectively. Three-dimensional transoesophageal echocardiography was clinically acceptable for measuring stroke volume; however, it was not sufficiently reliable for tracking stroke volume changes after haemodynamic interventions.
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The risk of accidental over-dosing of obese children poses challenges to anaesthetists during dose calculations for drugs with serious side-effects, such as analgesics. For many drugs, dosing scalars such as ideal body weight and lean body mass are recommended instead of total body weight during weight-based dose calculations. However, the complex current methods of obtaining these dosing scalars are impractical in the peri-operative setting. ⋯ A nomogram was created and its performance compared with the standard calculation method by volunteers using measurements from 108 obese children. The nomogram was as accurate (bias 0.12 kg vs -0.41 kg, respectively, p = 0.4), faster (mean (SD) time taken 2.8 (1.0) min (vs 3.3 (0.9) min respectively, p = 0.003) and less likely to result in mistakes (significant errors 3% vs 19%, respectively, p = 0.001). We present a system that simplifies estimation of ideal body weight and lean body mass in obese children, providing foundations for safer drug dose calculation.
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Epidural blood patches may be used to treat post-dural puncture headache following accidental dural puncture in parturients. Their mode of action and the optimum volume of blood for injection remain controversial, with the interaction between injected blood and cerebrospinal fluid unknown. We aimed to establish the effects of serial haemodilution of whole blood with cerebrospinal fluid from 34 pregnant patients compared with serial haemodilution with Hartmann's solution, using the thromboelastogram. ⋯ Cerebrospinal fluid led to a mean (95% CI) decrease in r-time by 2.4 (1.6-3.2) min, a decrease in k-time by 0.6 (0.4-0.8) min, an increase in alpha angle by 7.3 (5.5-9.0)°, and a decrease in maximum amplitude by 2.0 (0.6-3.4) mm. This may have implications for epidural blood patch, as success may be reduced near the time of dural puncture when cerebrospinal fluid leak is at its greatest, and large volumes of blood may be required to reduce haemodilution and clot destabilisation by cerebrospinal fluid. In addition, blood patching should be performed at the level of the dural puncture in order to ensure that the maximum volume of blood comes into contact with the cerebrospinal fluid.
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Animal studies have shown that injection pressures > 75 kPa indicate probable intrafascicular needle tip position. This study describes the flow/pressure characteristics of seven common needle systems. A syringe pump delivered flow rates of 5, 6.67, 10, 13.3, 15 and 20 ml.min(-1) through these needle systems, while keeping the needle tips open to atmosphere. ⋯ Flow rates > 17 ml.min(-1) and needle sizes 22 G and smaller produced mean plateau pressures > 75 kPa. Pressure monitors upstream from the needle may produce false-positive alarms at high flow rates due to needle resistance, and unreliable readings due to non-laminar flow. We recommend injection rates ≤ 15 ml.min(-1) (0.25 ml.s(-1) ) to reduce the effect of factors upstream from the needle tip as a cause of high pressure readings.