Anaesthesia
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Observational Study
Effects of tracheal intubation and tracheal tube position on regional lung ventilation: an observational study.
Take me back to the First Part
This study confirmed the well-known observation of the ventral ventilation shift under positive pressure ventilation, and quantified the contribution from the endotrachial tube itself, versus from muscle relaxation and IPPV.
This ventral shift under IPPV has also been shown to occur during pressure support ventilation with an LMA, when compared with spontaneous breathing under GA (Radke 2012).
Using electrical impedance tomography Lumb et al. confirmed this ventral shift in supine IPPV subjects, and demonstrated that this is primarily due to IPPV rather than the ETT itself, – although they found tube presence contributed to ~16% of the change.
"The generally accepted physiological explanation ... is that of greater cephalad movement of the diaphragm in dependent vs. non‐dependent lung regions during anaesthesia, resulting in changes in regional lung compliance."
"...regional ventilation with positive pressure ventilation during anaesthesia, even with no tracheal tube in place, is grossly different when compared with spontaneous ventilation, with greater ventilation of the left lung and ventral regions of both lungs. These effects are exacerbated by ventilation through a tracheal tube, leading to a greater degree of inhomogeneity of overall ventilation compared with when awake.
Take-home message
The authors note that while anaesthetists understand the detrimental effect of inadvertent endobronchial intubation, simply having the ETT tip close to the carina also worsens V/Q mismatch and is not as well appreciated. In these situations, tube withdrawal and/or 90o rotation may improve V/Q match.
Although this may be clinical insignificant for most patients, it should be considered when needing to improve gas exchange, particularly in critical care patients.
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Randomized Controlled Trial
Carbetocin at elective caesarean section: a sequential allocation trial to determine the minimum effective dose in obese women.
Postpartum haemorrhage is a leading cause of maternal death during childbirth. There is an increasing incidence of atonic postpartum haemorrhage in developed countries, and maternal obesity has been proposed as a contributing factor. The dose-response relationship of carbetocin in obese women has not yet been determined. ⋯ The estimated blood loss was 880 (621-1178 [75-2442]) ml. The overall rates of hypotension and hypertension after delivery were 40% and 6.7%, respectively, while nausea occurred in 26.7% of women. The ED90 for carbetocin in obese women at elective caesarean section is lower than the dose of 100 μg currently recommended by the Society of Obstetricians and Gynaecologists of Canada, but is approximately four times higher than the previously demonstrated ED90 of 14.8 μg in women with body mass index < 40 kg.m-2 .
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Pulmonary aspiration of gastric content is a significant cause of anaesthesia-related morbidity and mortality. High-quality prospective randomised evidence to support prevention strategies, such as rapid sequence intubation, is difficult to generate due to well-described practical, ethical and methodological barriers. We aimed to generate an understanding of worldwide practice through surveying clinically practicing anaesthetists and airway experts. ⋯ Respondents from lower income countries were more likely to prefer [OR (95%CI]: the supine position 2.33 (2.00-2.63), p < 0.001; nasogastric tube insertion 1.29 (1.09-1.51), p = 0.002; and cricoid force application 2.54 (2.09-3.09), p < 0.001 as compared with respondents from higher income countries for a hypothetical patient with intestinal obstruction. This survey, which we believe is the largest of its kind, demonstrates that preferences for positioning, nasogastric tube use and cricoid force application during rapid sequence intubation vary substantially. Achieving agreed consensus may yield better training in the principles of rapid sequence intubation.