M04.07.05 Positive-Pressure Ventilation

Positive-pressure ventilation is a method of mechanical ventilation where air is pushed into the lungs to aid in breathing. This document focuses on three specific modes of positive-pressure ventilation: Assisted Control Mode Ventilation (ACMV), Positive End-Expiratory Pressure (PEEP), and Continuous Positive Airway Pressure (CPAP). Each of these plays a crucial role in managing patients with respiratory conditions.

1. Assisted Control Mode Ventilation (ACMV)

ACMV is a mode of mechanical ventilation where the inspiratory cycle can be initiated by the patient or automatically if no signal is detected within a specified time window. This ensures that the patient receives a breath even if they are unable to initiate one on their own. Expiration in ACMV is not assisted and occurs naturally through the passive recoil of the lungs.

2. Positive End-Expiratory Pressure (PEEP)

PEEP involves the application of positive pressure at the end of the expiratory cycle to prevent alveolar collapse. This technique is particularly useful in treating the hypoxemia associated with Acute Respiratory Distress Syndrome (ARDS).

Key Points:

• Alveolar Collapse Prevention: Small alveoli tend to collapse, leading to atelectasis. PEEP helps keep these alveoli open.
• Improved Oxygenation: Larger, better-ventilated alveoli improve oxygen exchange, aiding in the maintenance of normal arterial PO2 levels.
• Cardiovascular Considerations: A potential downside of PEEP is the reduction in venous return, which can decrease cardiac output.

3. Continuous Positive Airway Pressure (CPAP)

CPAP is a non-invasive ventilation method where continuous positive pressure is applied to the airways. This method is commonly used to treat Obstructive Sleep Apnea (OSA) by maintaining lung and upper airway volume throughout the respiratory cycle.

Key Points:

• Non-invasive: Administered via a mask, without the need for intubation.
• Spontaneous Breathing: The patient breathes independently while the positive pressure prevents airway collapse.

Points to Remember

• ACMV ensures that patients receive a breath even if they cannot initiate one, with expiration occurring naturally.
• PEEP is essential in treating ARDS by preventing alveolar collapse but may reduce cardiac output.
• CPAP is beneficial for patients with OSA by keeping airways open during the respiratory cycle.

References

1. Lung Mechanics. Positive-Pressure Ventilation. Chapter 1.
2. “Hypoxemia and ARDS.” Respiratory Medicine.
3. “Positive End-Expiratory Pressure (PEEP).” Pulmonary Health Journal.
4. “Continuous Positive Airway Pressure (CPAP) in Obstructive Sleep Apnea.” Sleep Disorders Review.