Articles: mechanical-ventilation.
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Mechanical ventilation to alter and improve respiratory gases is a fundamental feature of critical care and intraoperative anesthesia management. The range of inspired O2 and expired CO2 during patient management can significantly deviate from values in the healthy awake state. It has long been appreciated that hyperoxia can have deleterious effects on organs, especially the lung and retina. Recent work shows intraoperative end-tidal (ET) CO2 management influences the incidence of perioperative neurocognitive disorder (POND). The interaction of O2 and CO2 on cerebral blood flow (CBF) and oxygenation with alterations common in the critical care and operating room environments has not been well studied. ⋯ Human CBF responds dramatically to alterations in ET gas tensions commonly seen during anesthesia and in critical care. Such alterations may contribute to delirium following surgery and under certain circumstances in the critical care environment.
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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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Our Cooling to Help Injured Lungs (CHILL) trial of therapeutic hypothermia in ARDS includes neuromuscular blockade (NMB) as an inclusion criterion to avoid shivering. NMB has been used to facilitate mechanical ventilation in ARDS and was shown to reduce mortality in the ACURASYS trial. To assess the feasibility of a multi-center CHILL trial, we conducted a survey of academic intensivists about their NMB use in patients with ARDS. ⋯ We conclude that NMB is frequently used by academic intensivists to facilitate mechanical ventilation in patients with moderate to severe ARDS.
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The combination of general anaesthesia with low tidal volume and moderate-to-high PEEP reduces post-operative pulmonary complications in the general surgical population.
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Randomized Controlled Trial
Effects of ventilation mode and manual chest compression on flow bias during the positive end- and zero end-expiratory pressure manoeuvre in mechanically ventilated patients: a randomised crossover trial.
To investigate the effects of ventilation mode and manual chest compression (MCC) application on the flow bias generated during positive end-expiratory pressure-zero end-expiratory pressure (PEEP-ZEEP) in mechanically ventilated patients. PEEP-ZEEP is an airway clearance manoeuvre with the potential to exceed the flow bias required to remove secretions. However, the ventilation mode applied during the manoeuvre has not been standardised. ⋯ http://www.ensaiosclinicos.gov.br/rg/RBR-223xv8/.