2-12-26 kopp lecture

Respiratory Failure

Overview of Respiratory Failure

  • Definition: Respiratory failure is characterized by inadequate gas exchange in the lungs, leading to insufficient oxygenation of the blood (hypoxemia) and/or retention of carbon dioxide (hypercapnia).

  • Parameters for Definition:

    • P_aO2 (Partial pressure of oxygen): less than 60 mmHg

    • P_aCO2 (Partial pressure of carbon dioxide): greater than 50 mmHg

    • pH: less than 7.3

Types of Respiratory Failure

  • 1. Acute Respiratory Failure (ARF)

    • Onset: Sudden and occurs rapidly with no compensation.

    • Characteristics: Failure of the lungs to perform their gas exchange function correctly.

    • Sequelae: Respiratory rate may increase due to conditions such as fever leading to respiratory fatigue. An example includes patients who breathe rapidly to compensate for acidotic states.

    • Intubation Indication: Understanding two reasons for intubation is crucial for exams.

  • 2. Chronic Respiratory Failure

    • Progression: More gradual and often has renal compensation due to chronic conditions.

    • CO2 Retention: Patients often retain CO2 repeatedly, leading to adjusted normal blood gases that differ from healthy individuals.

    • Example Cases: Patients with severe COPD; they may exhibit high respiratory rates but poor gas exchange due to significant dead space in the lungs.

    • Observation: Patients may exhibit respiratory difficulty, needing to take breaks when walking significant distances.

Common Causes of Acute Respiratory Failure

  • Post-Operative Complications: Patients returning from large surgical procedures may experience ARF due to residual anesthesia and need for ventilation.

  • Sepsis: Identified as an overwhelming infection affecting two or more organ systems. A related protocol in hospitals may include a sepsis alert process.

  • Multisystem Organ Failure: Where multiple organs fail to function properly due to severe sepsis.

  • Trauma: Patients may need airway protection due to traumatic injuries.

  • Pneumonia: Not all pneumonia patients require intubation. Generally, older patients or immunocompromised individuals are more likely to be intubated when they exhibit respiratory failure.

  • Heart Failure: Impaired circulation leads to inadequate oxygen delivery and CO2 removal, contributing to respiratory failure.

  • Acute Respiratory Distress Syndrome (ARDS): Noted as a major challenge for respiratory therapists that can result from various factors including mechanical ventilation, excessive oxygen, and pulmonary injury from events such as trauma or sepsis.

    • Historical Context: Recognized first in the Vietnam War; treatments have evolved since the ARDS NET study in 1980 which established lower tidal volumes during mechanical ventilation.

    • Management: Current tidal volume standards are now at 6-8 mL/kg to prevent lung injury.

Mechanisms of Respiratory Failure

  • What Happens during Respiratory Failure: Gas exchange is inadequate due to factors preventing oxygen or carbon dioxide from passing through the alveolar-capillary membrane efficiently.

  • Acid-Base Balance: Severe derangements occur, leading to acidosis or alkalosis (in the context of respiratory failure, acidosis is common).

Types of Respiratory Failure Based on Mechanism

  • Hypercapnic Respiratory Failure (Type II)

    • Definition: Identified by elevated P_aCO2 due to inadequate alveolar ventilation.

    • Chronic Factors: May include lack of stimulation from drug abuse or other mechanisms leading to hypoventilation.

    • Treatment Needs: Increase in minute ventilation is crucial to manage CO2 levels.

  • Hypoxemic Respiratory Failure (Type I)

    • Definition: Characterized by insufficient oxygen transport. Conditions leading to hypoxemia can include pneumonia, ARDS, and atelectasis.

    • Oxygen Saturation Indicators:

    • Mild Hypoxemia: Less than 80 mmHg

    • Moderate Hypoxemia: Less than 60 mmHg

    • Severe Hypoxemia: Less than 40 mmHg

V/Q Mismatch and Shunting

  • V/Q Mismatch: Refers to ventilation-perfusion coupling issues where ventilated areas may not receive adequate blood flow.

  • True Shunt: Occurs when blood is perfused but not oxygenated due to flooded alveoli with fluids, pus, or inflammatory responses.

  • Refractory Hypoxemia: When increasing FiO2 does not improve saturation, indicating a more severe underlying problem needing interventions like PEEP to recruit collapsed alveoli.

Management Considerations

  • PEEP: Positive End-Expiratory Pressure is crucial for recruiting collapsed lung units without needing full intubation.

    • Distinction: CPAP (Continuous Positive Airway Pressure) is often used in conscious patients or to support spontaneous breathing, while PEEP is a feature of mechanical ventilation.

  • Physiological Monitoring: Understanding changes in blood gas, oxygenation levels, and organ perfusion is necessary for managing perioperative and critical patients.

Summary

  • Be familiar with the types of respiratory failure, the reasons for intubation, and the clinical significance of both hypercapnic and hypoxemic failure.

  • Understand practical implications of managing ventilation, oxygenation, and interventions like PEEP and CPAP during respiratory distress.