During calm breathing, the amount of air inhaled or exhaled each time, 5-7ml/kg

VE is the total amount of air inhaled or exhaled per minute at rest, the product of tidal volume and respiratory rate.

VA=(VT-Dead Space Volume)✖Respiratory Rate

When there is no gas involved in gas exchange in mechanical ventilation of 0.2-0.3 tidal volume, VD/VT >0.6 is difficult to wean off the machine.

When trying to breathe deeply and quickly, the maximum volume of air that can be inhaled or exhaled per minute reflects the individual's ventilatory reserve function.

The maximum amount of air that can be exhaled as soon as possible after the maximum inhalation

The volume of air exhaled per unit time as a percentage of FVC

Expressed as the percentage of actual measured value to predicted value, normal is >75%, and the assessment of obstructive ventilatory dysfunction is more sensitive than FEV1% and MVV.

Arterial blood carbon dioxide partial pressure (PaCO2): 35-45mmHg is the best indicator of effective alveolar ventilation.

Transcutaneous partial pressure of carbon dioxide (PtcCO2)

End-tidal carbon dioxide partial pressure (PETCO2)

PaCO2 directly reflects ventilation status and determines acid-base imbalance.

CO2 waveform diagram

Inhaled oxygen concentration (FiO2), exhaled oxygen concentration (FeO2)

Arterial partial pressure of oxygen (PaO2): the only indicator of hypoxemia. Normal value: 80-100mmHg

Mild hypoxemia: 60-79mmHg

Moderate hypoxemia: 40-59mmHg

Severe hypoxemia: <40mmHg

PaO2 varies with age. Over 60 years old, PaO2 is 1mmHg for every 1 year of age. PaO2 is 60mmHg, corresponding to SpO290%

Mild ARDS 200＜PaO2/FiO2≤300 (PEEP or CPAP≥5H2O)

Moderate ARDS 100＜PaO2/FiO2≤200(PEEP≥5H2O)

Severe ARDS PaO2/FiO2≤100(PEEP≥5H2O)

Arterial blood oxygen content (CaO2): 19ml/100ml, oxygen supply

Oxygen uptake rate (O2ER): the percentage of oxygen taken up by tissue cells at capillaries from arterial blood, O2ER=VO2/DO2, 22%-32%

Pulse oxygen saturation (SpO2): Transcutaneous measurement of arterial blood oxygen saturation value to evaluate oxygenation function

Factors Affecting SpO2 Accuracy

There is a good correlation between ScvO2 and SvO2. SO2 of superior vena cava blood or right atrium blood is easy to obtain blood.

Reflect tissue perfusion and oxygenation status

Can detect and treat potential tissue hypoxia early

Normal value 70%-80%

Mixed venous blood specimens obtained from the pulmonary artery with the Swan-Ganz catheter are ideal

Balance between oxygen supply and oxygen consumption Oxygen supply ↓ or oxygen consumption ↑, resulting in SvO2↓ CO↑ and O2↑ uptake from capillaries during hypoxia

Continuous monitoring, continuously reflecting changes in CO, reflecting the balance between systemic oxygen supply and oxygen consumption to determine blood transfusion indications: SvO2 <50%

Normal value 75% (65%-85%); adequate oxygen reserve SvO2>65%; limited oxygen reserve SvO2 50%-60%; insufficient oxygen reserve SvO2 35%-50%

Pulmonary diffusing function, intrapulmonary shunt; air inhalation, 5-10mmHg; pure oxygen inhalation, 40-50mmHg

P(A-a)O2 determines the cause of hypoxemia

Rather right than left, prefer acid to alkali

Move right, dissociate and release oxygen; pH value ↓, PaCO2↑, temperature ↑, 2,3-DPG↑

Exists when >10%, pulmonary edema and poor ventilation↑

>30% require respiratory support to improve hypoxemia

The amount of oxygen the body provides to the tissues through the circulatory system per unit time, that is, the rate at which arterial blood transports oxygen per unit time, 520-720ml/(min*m2)

Circulatory factors, respiratory factors, blood factors

The total amount of oxygen consumed by body tissues per unit time depends on the functional metabolic state. 110-180ml/(min　m2)

When the temperature rises by 1°C, oxygen consumption increases by 10%-15%

Infection or SIRS

Burns, trauma or surgery

Sympathetic excitement, pain, chills (100%) or epilepsy

β2-agonists, amphetamines, tricyclic antidepressants

In a high metabolic state or ingesting a high-sugar diet, sedation, analgesia, and muscle relaxation reduce cell metabolism and oxygen consumption.

The phenomenon that dynamic lung compliance decreases significantly with increasing respiratory rate is called FDC

Inspiratory peak pressure: 20cmH2O

Platform pressure: 9-13cmH2O 10%

End expiratory pressure: 0

Static lung compliance (Cst): lung elasticity 50-100ml/cmH2O

Dynamic lung compliance (Cdyn): Respiratory system elasticity 40-80ml/cmH2O

low break point

High break point

The optimal PEEP is 2-3cmH2O above the low break point

The volume corresponding to the high breakpoint is the high limit of tidal volume