3/9/2023 0 Comments Tidal volumeIt is trotted out whenever tidal volume selection is discussed, viewed as relevant even in the modern day (it appears in the 2016 edition of Egan’s Fundamentals of Respiratory care, for example). Speaking of monolithic messages passed down from ancient civilisations, another such ancient artefact is the Radford nomogram. Tidal volume selection for mechanical ventilation of normal lungs This makes the 7ml/kg tidal volume a fundamental tenet it may as well be carved on a granite plinth dating back to the Silurian. If his measurements are converted into ml/kg, one finds that they agree with Needham et al. Going back further, Hutchinson (1846) described tidal volume measurement (he called this pulmonary volume “breathing air” ), measuring his subjects’ capacities in cubic inches and their weight in pounds. ![]() For example, we have studies such as Needham et al (1954) whose tables reveal a range of resting tidal volumes in the range of 570-780ml for adult males and 500-550 for adult females, which gave about 7ml/kg taking into account the weight of these volunteers. As usual, it is impossible to track down where Brandis got this from, but only the briefest begooglement reveals that the origins of this information are ancient. If anaesthetic trainees are expected to regurgitate it, it must be true. Tidal volume is 7 ml/kg in a normally breathing subject, according to Kerry Brandis' "The Physiology Viva". Tidal volume in the spontaneous breathing patient For patients with severe bronchospasm and gas trapping, the respiratory rate should be lower.For ARDS, poorly compliant lungs and other patients with necessarily small tidal volumes, the respiratory rate should be higher.This initial setting is relatively safe for patients with no lung disease.To achieve this, one typically requires 12-16 breaths (using 6-8ml/kg as a tidal volume).The minute volume for a normal adult is 70-110ml/kg/min.For non-ARDS patients, 6-8ml/kg is also recommended by most sources.The ARMA trial (2000) found that 6ml/kg of ideal body weight was safer in patients with ARDS.Historical tidal volume settings had been 12-15ml/kg. ![]() A spontaneously breathing person has a tidal volume of 7ml/kg.
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