Principles of Mechanical Ventilation Mazen Kherallah, M.D., FCCP Internal Medicine, Critical Care Medicine, and Infectious Diseases Initial Ventilatory Settings

Modes of Mechanical Ventilation Volume-Cycled Control Mode Ventilation

Indicated for patients who are unable to ventilate: –Drug intoxication –CNS disorders –Peripheral neurological disorders –Pharmacological Paralysis Limitations: –Patient-ventilator dysynchrony secondary to aborted ventilatory cycles when patient exhales during ventilator inspiratory cycle –Hypercapnea

Modes of Mechanical Ventilation Assist-Control Ventilation

Indications: – for patients who are awake, moderately sedated or paralyzed and able to initiates ventilation –increase metabolic demands: infection, burns, multisystem organ failure –Respiratory muscle strengthening and weaning Limitations: –patient-ventilator dysynchrony –ventilator assisted hyperventilation in agitated patients with increased inspiratory drive –auto-PEEP in COPD patients

Modes of Mechanical Ventilation Intermittent Mandatory Ventilation

Modes of Mechanical Ventilation Synchronized Intermittent Mandatory Ventilation

Indications: –patients with minimal spontaneous respiratory efforts –respiratory muscle conditioning –ventilator weaning Limitations: –patient-ventilator dysynchrony especially in agitated patients –nonphysiologic way of respiratory muscle conditioning

Modes of Mechanical Ventilation Pressure Support Ventilation

Indications: –weaning –more physiologic conditioning of respiratory muscles: low pressure-high volume load –improved patient- ventilator dysynchrony Limitations:

Modes of Mechanical Ventilation Inverse Ratio Ventilation

Distribution of Normal Ventilation-Perfusion Ratios

Oxygen-carbon dioxide diagram

The Effect of Increasing Ventilation-Perfusion Inequality on Arterial Po2 and Pco2

Ventilation-Perfusion Inequality Acute Exacerbation of COPD

Ventilation-Perfusion Inequality Asthma

Ventilation-Perfusion Inequality Pulmonary Embolism

Shunting Process ARDS

The effect of changing the inspired oxygen concentration on arterial Po2 for lung’s shunts of 10 to 50%

Pulmonary Mechanics Peak pressure Plateau pressure IE Airway Resistance

Static Pressure-volume curve in ARDS with PEEP of 0 and PEEP 0 PEEP

Auto-PEEP

Normal Lung Mechanics and Gas Exchange

Severe Airflow Obstruction

Acute on Chronic Respiratory Failure

Acute Hypoxemic Respiratory Failure