# How do you calculate anatomic dead space?

## How do you calculate anatomic dead space?

Many respiratory and medical textbooks state that anatomic dead space can be estimated from the patient’s weight by assuming there is approximately 1 mL of dead space for every pound of body weight.

### What is the relationship between anatomical and alveolar dead space?

Alveolar dead space is defined as the difference between the physiologic dead space and the anatomic dead space. It is contributed to by all the terminal respiratory units that are over-ventilated relative to their perfusion.

#### What is the formula for alveolar minute ventilation?

Alveolar minute ventilation is less than minute ventilation and is calculated as ([tidal volume − dead space] × respiratory rate) or ([500 mL − 150 mL] × 12 breaths/min) = 4200 mL/min.

How do you calculate PAO2?

At sea level without supplemented inspired oxygenation, the alveolar oxygen partial pressure (PAO2) is: PAO2 = (760 – 47) 0.21 – 40 / 0.8 = 99.7 mm Hg.

How does anatomical dead space affect ventilation?

Dead space is the volume not taking part in gas exchange and, if increased, could affect alveolar ventilation if there is too low a delivered volume. We determined if there were differences in dead space and alveolar ventilation in ventilated infants with pulmonary disease or no respiratory morbidity.

## What is anatomical dead space ventilation?

Anatomic dead space specifically refers to the volume of air located in the respiratory tract segments that are responsible for conducting air to the alveoli and respiratory bronchioles but do not take part in the process of gas exchange itself.

### How is patient dead space ventilation calculated?

Physiologic dead space (VDphys) is the sum of the anatomic (VDana) and alveolar (VDalv) dead space. Dead space ventilation (VD) is then calculated by multiplying VDphys by the respiratory rate (RR). Total ventilation (VE) is, therefore, the sum of alveolar ventilation (Valv) and VD.

#### What factors determine dead space?

• General anesthesia – multifactorial, including loss of skeletal muscle tone and bronchoconstrictor tone.
• Anesthesia apparatus/circuit.
• Artificial airway.
• Neck extension and jaw protrusion (can increase it twofold)
• Positive pressure ventilation (i.e. increased airway pressure)

What is the difference between SaO2 and PaO2?

PaO2 is a major determinant of SaO2, and the relationship is the familiar sigmoid-shaped oxygen dissociation curve. SaO2 is the percentage of available binding sites on hemoglobin that are bound with oxygen in arterial blood.

Is PaO2 and SpO2 the same?

PaO2 values are always much lower than oxygen saturation values. This is simply a reflection of the oxygen saturation curve (figure above). For example, a saturation of 88% correlates to a PaO2 of ~55mm. We’re generally comfortable with a saturation of 88%, but a PaO2 of 55mm may cause concern.