Mechanical Ventilation and Airway resistance
Mechanical ventilation is a type of life support. A mechanical ventilator is a device that takes over the work of breathing when a person is not able to respire enough on their own. The mechanical ventilator is also known as a respirator, ventilator, or breathing machine. There are certain factors on which mechanical ventilation functions depend. Among them, airway resistance is one. Let’s discuss airway resistance in this article.
Airway resistance is the degree of airflow obstruction in the airways. It is determined by the patency or diameter of the airway. Other causes of airflow resistance are changes inside the airway eg. Secretions, changes in the airway wall, i.e. bronchiole tumor, changes outside the airway I.e. enlarged lymph node. According to Poiseuille’s law, the driving pressure [P] to maintain the same airflow [V] must increase by the factor of 16 times when the radius [r] of the airway reduces by half of its original state. is the formula. Normal airway resistance is 0.5-2.5 cm H2O/L/ sec.
Some clinical conditions where airway resistance increases are:
| Type | Clinical Conditions |
| COPD | Emphysema
Asthma |
| Mechanical Obstruction | Endotracheal tube
Foreign body Condensation in the ventilator circuit Ventilatory tube |
| Infection | Croup
Epiglottitis Bronchitis |
Airway resistance is higher in intubated patients. It is directly related to the length and inversely related to the radius of the endotracheal tube. It is also related to the work of breathing.
Airway resistance is calculated by:
Raw=P/V [ Raw- Airway resistance , V- airflow , P- pressure change] Pressure Change = Peak inspiratory pressure - plateau pressure.
Pressure Change reflects the work of breathing. So, an increase in resistance causes an increase in the work of breathing. An increase in work of breathing always has a detrimental effect on ventilation and oxygenation. This leads to fatigability. Airflow resistance in ventilation patients can be access by using a pressure-volume loop.
To know more about the pressure-volume loop, you may enroll in the course ‘Mechanical Ventilation (A Case-based Approach)’ by Dr. Sanjith Saseedharan (HOD- Critical Care, S.L.Raheja Hospital), here, https://docmode.org/mechanical-ventilation-a-case-based-approach/
