Lecture Notes. Chapter 2: Introduction to Respiratory Failure

Transcription

1 Lecture Notes Chapter 2: Introduction to Respiratory Failure

2 Objectives Define respiratory failure, ventilatory failure, and oxygenation failure List the causes of respiratory failure Describe the effects of respiratory failure on the lung, heart, and other body systems Recognize the clinical features associated with respiratory failure Describe the treatment of respiratory failure

3 Introduction Respiratory failure Failure of the lungs to provide adequate oxygenation or ventilation Oxygenation failure PaO 2 < 60 mm Hg at FiO 2 >.50 Ventilatory failure Inadequate ventilation between the lungs and atmosphere that results PaCO 2 > 45 mm Hg

4 Introduction The amount of oxygen consumed and CO2 produced each minute is dictated by the metabolic rate of the patient. Exercise and fever are examples of factors that increase the metabolic rate Patients with acute respiratory failure have inadequate oxygenation of the arterial blood or elevation of CO2 levels or both.

5 Etiology: Oxygenation Failure Hypoxemia has potentially serious consequences because it can lead to inadequate tissue oxygenation (hypoxia). Tissue hypoxia of the heart complicates the problem by causing dysrhythmias and poor contractility. V/Q mismatch Shunt is the movement of blood from the right side of the heart to the left side of the heart without coming into contact with ventilated Alveoli Anatomical congenital heart defect Physiologic collapsed or unventilated alveoli Hypoxemia Mild: PaO mm Hg Moderate: PaO mm Hg Severe: PaO 2 < 40 mm Hg

6 Etiology: Ventilatory Failure Depression of respiratory centers by drugs Cerebral disease Spinal cord abnormalities Muscular disease Thoracic cage abnormalities Upper and lower airway obstruction Malnutrition and electrolyte disturbances

7 Pathophysiology: Oxygenation Failure Patient s response to hypoxemia depends on Pre-existing condition (cardiopulmonary patient, healthy). Severity of hypoxemia Tachypnea and tachycardia are the most common responses

8 Pathophysiology: Oxygenation Failure Hypoxemia stimulates the pulmonary capillaries to constrict in the affected regions. pulmonary vasoconstriction Increase pulmonary vascular resistance (PVR) Increased right ventricular workload Increased pulmonary vascular resistance Right ventricular failure Cor pulmonale abnormal enlargement of the right side of the heart as a result of disease of the lungs or the pulmonary blood vessels Cardiac muscles contraction and rate are increased as result of hypoxemia which is can lead to ischemia and irreversible damage (infarction).

9 Pathophysiology: Ventilatory Failure Ventilatory failure is defined as a change in respiration resulting in an elevated PaCO2. e.g. Drug overdose Change in respiration Elevated PaCO 2 Acidosis

10 Clinical Features: Oxygenation Failure Physical exam Central cyanosis Tachycardia, tachypnea, hypertension Altered mental status PVCs Cor pulmonale: hepatomegaly, JVD, pedal edema

11 Clinical Features: Oxygenation Failure Laboratory abnormalities Low PaO2 Low SaO2 Low CaO2 Polycythemia if chronic Chest radiograph Often normal if extrapulmonary cause

12 Clinical Features: Ventilatory Failure Clinical findings (nonspecific) Headache Diminished alertness Warm and flushed skin Bounding peripheral pulses Hypothermia and altered mental status = drug OD Tachycardia and hypertension = tricyclics Respiratory alternans or abdominal paradox = diaphragmatic fatigue

13 Clinical Features: Ventilatory Failure Laboratory abnormalities High PaCO2 Acidosis Elevated total CO2 on electrolyte panel

14 Treatment: Oxygenation Failure Supplemental oxygen (V/Q mismatching) Positive pressure ventilation-cpap (shunt) If PaO2 < 60 mm Hg at FiO2 >.50 Mechanical ventilation If mask CPAP unsuccessful

15 Treatment: Ventilatory Failure Mechanical ventilation VT 5 10 ml/kg IBW Keep Pplateau < 35 cm H2O Respiratory rate according to age and metabolic rate FiO2 adjusted with pulse oximetry

16 Treatment: Ventilatory Failure Weaning criteria Etiology of ventilatory failure resolved Patient s condition stable and improving Vital capacity > ml/kg Resting minute volume < 10 L/min MIP > -20 cm H2O Adequate oxygenation on FiO2 <.50 Spontaneous respiratory rate < 35 breaths/min Spontaneous tidal volume > 325 ml

17 Treatment: Ventilatory Failure Weaning methods IMV Decrease number of mechanical breaths until support is no longer necessary Pressure Support Set to acceptable tidal volume and rate without use of accessory muscles and wean thereafter T-Piece Temporary discontinuation of mechanical ventilation Blow-by of appropriate FiO2