![]() The equation to transform FCO 2 into PCO 2 is PCO 2 = FCO 2 multiplied by the difference between barometric pressure minus water-vapour pressure. Ī device that measures partial pressures (PCO 2) or fractions (FCO 2) of CO 2 during the breathing cycle is called a capnograph. Physiologic dead space (Vd phys) is comprised of Vd aw (instrumental and anatomic dead space) and Vd alv and it is usually reported in mechanical ventilation as the portion of tidal volume (Vt) or minute ventilation that does not participate in gas exchange. This instrumental dead space is considered to be part of the Vd aw. ![]() Mechanical ventilation, if present, adds additional Vd as part of the ventilator equipment (endotracheal tubes, humidification devices, and connectors). The volume of dead space (Vd) reflects the sum of two separate components of lung volume: 1) the nose, pharynx, and conduction airways do not contribute to gas exchange and are often referred to as anatomical Vd or herein as airway Vd (Vd aw) 2) well-ventilated alveoli but receiving minimal blood flow comprise the alveolar Vd (Vd alv). The concept of dead space accounts for those lung areas that are ventilated but not perfused. Positive pressure ventilation (i.e.The homogeneity between ventilation and perfusion determines normal gas exchange.Neck extension and jaw protrusion (can increase it twofold).General anesthesia – multifactorial, including loss of skeletal muscle tone and bronchoconstrictor tone.The ratio of physiologic dead space to tidal volume is usually about 1/3. Alveolar dead space is the volume of gas within unperfused alveoli (and thus not participating in gas exchange either) it is usually negligible in the healthy, awake patient. Anatomic dead space is the volume of gas within the conducting zone (as opposed to the transitional and respiratory zones) and includes the trachea, bronchus, bronchioles, and terminal bronchioles it is approximately 2 mL/kg in the upright position. Physiologic or total dead space is the sum of anatomic dead space and alveolar dead space. ![]() ![]() Dead space is the volume of a breath that does not participate in gas exchange. ![]()
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