Respiratory Dead Space and Shunting

A comprehensive set of flashcards covering key vocabulary and definitions related to respiratory dead space and shunting, their significance, calculations, and monitoring techniques.

Dead Space

Volume of air that does not participate in gas exchange.

Anatomical Dead Space

Volume of air in conducting airways that doesn't reach alveoli, approximately 150 mL in adults.

Alveolar Dead Space

Volume of air reaching alveoli but not participating in gas exchange due to ventilation-perfusion mismatch.

Physiological Dead Space

Total dead space consisting of anatomical and alveolar dead space.

Fowler's method

Calculation method using nitrogen washout to detect and measure dead space in the lungs.

Bohr Equation

Formula used to calculate dead space volume: VD = VT x (PaCO2 - PeCO2) / PaCO2.

VD in Bohr Equation

Represents dead space volume.

VT in Bohr Equation

Tidal volume.

PaCO2

Arterial CO2 partial pressure.

PeCO2

Mixed expired CO2 partial pressure.

Impact of Dead Space

Affects ventilation efficiency and is significant in diseases like COPD and ARDS.

Pulmonary Emboli

Obstruction of a pulmonary artery that can lead to dead space.

Decreased Cardiac Output

A condition that can result in increased dead space.

Tension Pneumothorax

Condition where pressure on vessels leads to dead space.

Shunting

Blood flow that bypasses ventilated alveoli.

Anatomical Shunt

Direct connection between pulmonary and systemic circulation, accounting for 2-5% of cardiac output.

Physiological Shunt

Blood flow through non-ventilated or poorly ventilated lung regions.

Berggren Shunt Equation

QS/QT= (CcO2 – CaO2) /(CcO2 – CvO2) used to calculate shunt fraction.

Oxygen Bound in Arterial Content (CaO2)

(1.34 x Hgb x SaO2) + (PaO2 x 0.003).

Oxygen Bound in Venous Content (CvO2)

(1.34 x Hgb x SvO2) + (PvO2 x 0.003).

Oxygen Content in Capillaries (CcO2)

(1.34 x Hgb) + (PAO2 x 0.003).

Refractory Hypoxemia

Severe hypoxemia that does not respond to oxygen therapy.

V/Q Ratio

Ratio of alveolar ventilation to pulmonary capillary blood flow.

Normal V/Q Ratio

Approximately 0.8 to 1.

Ventilation (V)

Alveolar minute ventilation.

Perfusion (Q)

Cardiac output.

Gravitational Effects on V/Q Ratio

Higher ventilation at lung apex compared to base.

Dead Space in V/Q Mismatch

V/Q = ∞ indicates ventilation without perfusion.

Shunt in V/Q Mismatch

V/Q = 0 indicates perfusion without ventilation.

Low V/Q Ratio

Hypoventilation relative to perfusion.

High V/Q Ratio

Hyperperfused relative to ventilation.

Gas Laws Affecting V/Q Relationships

Includes Boyle's Law, Charles' Law, Dalton's Law, and Henry's Law.

Boyle's Law

Relationship between pressure and volume (P1V1 = P2V2).

Charles' Law

Relationship between volume and temperature (V1T1 = V2T2).

Dalton's Law

The sum of partial pressures equals the total pressure in a gas mixture.

Henry's Law

Solubility of gases in liquids (C = kP).

Mechanical Ventilation and Dead Space

Setting appropriate tidal volumes and PEEP to minimize dead space.

Management for V/Q Mismatch

Strategies include optimizing ventilation and perfusion, and recruitment maneuvers.

Monitoring Dead Space and Shunting

Includes pulse oximetry, arterial blood gas analysis, and end-tidal CO2 monitoring.

Alveolar-Arterial Oxygen Gradient

Used to assess the efficiency of gas exchange.

CT-Pulmonary Angiography

Advanced technique for assessing lung vascular issues.

V/Q Scanning

Diagnostic technique for evaluating lung perfusion and ventilation.

Volumetric Capnography

Technique for measuring CO2 produced in the lungs.

Electrical Impedance Tomography

Advanced imaging technique for pulmonary perfusion assessment.