Fio2 Estimation Calculator

Oxygen delivery devices split into two classes, and the distinction governs how much the numbers in this table can be trusted. Low-flow systems such as nasal cannulae and simple masks supply less gas than a patient draws during inspiration, so every breath entrains room air and the delivered fraction depends on tidal volume, respiratory rate, and inspiratory flow. The familiar rule of thumb that each litre per minute adds about 4 percentage points above the 21 percent of room air, giving roughly 24 percent at 1 L/min and 44 percent at 6 L/min, assumes a settled adult breathing pattern; in a tachypnoeic patient the real value can be 10 to 15 points lower. A simple mask needs at least 5 L/min purely to flush its own volume, or exhaled carbon dioxide is rebreathed from the mask dead space. Fixed-performance devices avoid that dependence. An air-entrainment mask uses a calibrated jet to draw in a set volume of room air per volume of oxygen, delivering total flow above peak inspiratory demand and holding the fraction near 24, 28, 35, 40, or 60 percent whatever the patient does. High-flow nasal cannula achieves the same stability by brute force, warming and humidifying 20 to 60 L/min so the set fraction between 21 and 100 percent is actually what reaches the airway, while generating a modest positive pressure of roughly 1 cmH2O per 10 L/min with the mouth closed and flushing nasopharyngeal dead space. British Thoracic Society guidance targets saturations of 94 to 98 percent in most acutely unwell adults and 88 to 92 percent in those at risk of hypercapnic failure, and sustained fractions above 60 percent risk absorption atelectasis and pulmonary oxygen toxicity.

Oxygen was isolated independently by Carl Wilhelm Scheele and Joseph Priestley in the 1770s, and Thomas Beddoes was already trying it therapeutically at his Pneumatic Institution in Bristol before 1800, but delivery remained crude for well over a century. Practical clinical oxygen therapy dates to the 1910s and 1920s, when John Scott Haldane, drawing on his work on gas poisoning during the First World War, argued for continuous administration at controlled concentrations, and Alvan Barach in New York developed oxygen tents and studied their effects in pneumonia and cardiac failure through the 1920s and 1930s. Nasal catheters and simple masks became standard hospital equipment in that period, delivering concentrations nobody could specify with any precision. The decisive advance was the air-entrainment mask introduced by the physician E. J. Moran Campbell around 1960. Campbell was working on patients with chronic bronchitis and emphysema in whom uncontrolled oxygen provoked carbon dioxide retention, and he applied the Venturi principle, named for the Italian physicist Giovanni Battista Venturi and described in 1797, to build a mask that delivered a known, low, and reproducible concentration. Colour-coded entrainment adapters followed and remain in use. High-flow nasal cannula systems with active humidification arrived from neonatal practice in the 2000s and moved into adult critical care after trials in acute hypoxaemic respiratory failure, notably the FLORALI study published in 2015.