Physiological dead space (Vd/Vt)

Each part of the inhaled gas remains in the respiratory tract from the upper respiratory tract to the respiratory bronchi. This part of the gas does not participate in the gas exchange between the alveolar and the blood, which is called an anatomical void or dead space. Its volume is approximately 150 ml. The gas entering the alveoli can also be distributed due to the uneven distribution of blood flow in the lungs. This part of the alveolar volume is called the alveolar ineffective cavity. The alveolar null cavity is collectively referred to as a physiologically ineffective cavity together with the anatomical void. The physiologically ineffective cavity of a healthy person lying down is equal to or close to the anatomical cavity. Basic Information Specialist classification: Respiratory examination classification: pulmonary function test Applicable gender: whether men and women apply fasting: not fasting Analysis results: Below normal: No clinical significance. Normal value: Normal value: 25-33% Above normal: Increase the disease that can be seen in the ineffective cavity of the alveoli, such as pulmonary vascular bed reduction caused by various reasons such as emphysema, pulmonary blood flow reduction and pulmonary vascular embolism. negative: Positive: Reminder: Quiet rest before the determination of resting ventilation, should be completely under the basal metabolic state, the surrounding environment is quiet, requiring a steady breathing. Normal value The normal person Vd/Vt is 25% to 33%. Clinical significance Vd/Vt helps to understand dead space ventilation and assist in the diagnosis and evaluation of pulmonary vascular disease. Scope of application: 1 pulmonary embolism, shock and other pulmonary blood flow reduction diseases. 2 pulmonary vascular bed destructive diseases such as emphysema, tuberculosis, and pulmonary cysts. 3 respiratory monitoring during mechanical ventilation. Analysis of inspection results: (1) Vd/Vt increase can be seen in diseases with increased alveolar voids, such as pulmonary vascular bed reduction caused by various causes such as emphysema, pulmonary blood flow reduction and pulmonary vascular embolism. (2) Vd/Vt increase is also seen in mechanical ventilation when the breathing tube is too long, the tracheal intubation is too long and other iatrogenic anatomical voids increase. High results may be diseases: pulmonary embolism, emphysema precautions (1) Before the examination, the subjects should be explained in detail about the inspection methods and essentials, and adaptive training should be done. (2) Quiet rest before the measurement of resting ventilation, should be carried out completely under the basal metabolic state, the surrounding environment is quiet, and the breathing is required to be stable. (3) Since the dead volume can not be directly measured, the dead air volume can be calculated by measuring the minute resting ventilation and the exhaled CO 2 partial pressure, thereby obtaining alveolar ventilation. Clinically, PaCO2 is often used to reflect the adequacy of alveolar ventilation. (4) Due to the difference in measurement methods and instruments, and the degree of cooperation of the subjects, the maximum range of maximum ventilation is large. The normal range is generally taken as a percentage of the predicted value of ±20%. (5) The forced vital capacity and the maximum expiratory mid-flow volume were all affected by the degree of forced exhalation during the examination. The former had a greater impact. (6) The sex, age, height and muscle strength of the subject may affect the results of the above examination. (7) Contraindications: 1 severe heart and lung disease, physical weakness. 2 mental disorders or can not be well coordinated. Inspection process The internal jugular vein, subclavian vein or anterior elbow vein were used for intubation. After the catheter reached the superior vena cava, the pressure curve should be observed. When the pressure curve changes with breathing and coughing, it can be confirmed that the catheter has reached the superior vena cava even without fluoroscopy. When the catheter reaches the pulmonary artery, the pulmonary artery pressure (PAP) waveform appears on the monitor. If the pulmonary artery pressure waveform does not appear after the catheter reaches the right ventricle and then advances for about 15 cm, the catheter should be considered to be curled in the right ventricle. Exit the catheter to the right atrium to prevent the catheter from knotting and then re-advance the catheter. Not suitable for the crowd Contraindications: 1 severe heart and lung disease, weak body. 2 mental disorders or can not be well coordinated. Adverse reactions and risks Generally no complications and harm.