Lecture Notes Chapter 3: Asthma
Objectives Define asthma and status asthmaticus List the potential causes of asthma attacks Describe the effect of asthma attacks on lung function List the clinical features of patients having an asthma attack List the treatments and indications for mechanical ventilation in asthma
Introduction Obstructive pulmonary disease Diffuse airway inflammation and narrowing Entirely or partially reversible Excessive airway secretions Status asthmaticus Asthma attack refractory to conventional treatment Occupational asthma (work place) Stable asthma (4 weeks no symptoms) Unstable asthma (increasing symptoms) Between attacks, the asthmatic often has normal lung function.
Etiology Genetic Atopy (allergic to specific allergens) Triggers Infection Exercise Dust Pollens Cold air Air pollution
Pathophysiology Bronchospasm - Mucus plugging - Mucosal edema airway resistance V/Q mismatching hypoxemia pulmonary vascular resistance Airway obstruction primarily affects exhalation. This results in air trapping and progressive hyperinflation of the lungs.
Clinical Features: History Chief complaints Chest tightness Difficulty breathing Wheezing Coughing Rapid onset may disappear rapidly with appropriate treatment
Clinical Features: Physical Exam Inadequate assessment = insufficient treatment and monitoring. Tachypnea Use of accessory muscles Prolonged exhalation Increased A-P chest diameter Expiratory polyphonic wheezing Diaphoresis Intercostal retractions https://www.youtube.com/watch?v=hv68eq3tcbi
Clinical Features: Physical Exam in Severe Asthma Pronounced use of accessory muscles https://www.youtube.com/watch?v=kpwovh4fpfg Paradoxical pulse decrease in systolic blood pressure. Inability to speak Inspiratory and expiratory wheezing Decreased peak flows (maximum speed of expiration) Diaphoresis Abdominal paradox Abnormal sensorium (late finding)
Clinical Features: Chest Radiograph Often normal or hyperinflation In presence of complications Pneumonia Atelectasis Pneumothorax
Clinical Features: Pulmonary Function Studies (Severe Asthma) Peak flows < 100 L/min FEV1 < 1.0 L Methacholine provocation (will cause bronchospasm) To determine degree of airway reactivity if normal PFTs FEV1 decreased by 20%
Clinical Features: Arterial Blood Gases Degree of hypoxemia and hypercapnia = reliable indicators of severity of airway obstruction PaCO2 initially decreased Normal or increased PaCO2 suggests Severe degree of obstruction Respiratory muscle fatigue
Treatment: Pharmacological Agents Beta-adrenergics Rapid onset of action Lower dose requirements Lower incidence of systemic effects Albuterol Q3 to Q6 hours Q 20 minutes x 3 in acute attack Continuous therapy when refractory (10 mg/h) Small-volume nebulizer (SVN) Metered-dose inhaler (MDI)
Treatment Pharmacological Agents Anticholinergics Combination with β-agonists Safe and may be more effective than either drug alone Small-volume nebulizer (SVN) Metered-dose inhaler (MDI)
Treatment: Pharmacological Agents IV Corticosteroids With failure of inhaled β-agonists Anti-inflammatory effects may take hours Methylprednisolone 100 500 mg IV Prednisone 60 80 mg PO
Treatment IV Aminophylline Not used for therapy of acute attack high incidence of adverse effects. Heliox Low density gas Severe acute asthma
Treatment: Pharmacological Agents Magnesium sulfate Smooth muscle relaxant Severe asthma Medications to avoid in acute attack Sedatives can induce ventilatory failure Acetylcysteine Cromolyn sodium Dense aerosols These agents tend to be irritating to the airways
Treatment: Pharmacological Agents Anti Ig-E antibodies Ig-E plays major role in pathogenesis of allergic diseases Omalizumab (Xolair) Reduces number of exacerbations Reduces use of corticosteroids Improves overall quality of life
Treatment: Indications for Endotracheal Intubation Fatigue Rising PaCO2 Deteriorating sensorium Abdominal paradox Decreased peak flow Respiratory failure Refractory hypoxemia Severe acidemia (ph < 7.25) Central cyanosis Cardiac arrest
Treatment: Mechanical Ventilation Sedative agents Reduce oxygen consumption Improve patient comfort Ventilatory strategy Tidal volume < 8 ml/kg Rate 8 12 breaths/min Flow 80 100 L/min Keep Pplateau < 35 cm H2O Adequate expiratory time Permissive hypercapnia acceptance higher values of arterial CO2 tension (Paco2)
Prevention Assess asthma severity Careful history PFTs Investigate provoking agents Patient education Avoid provoking agents Use of medications and side effects Use of peak flow meter Cromolyn sodium stabilizing the mast cells to prevent the release of mediators, such as histamine, that can cause bronchospasm.
Prognosis predicting the outcome Excellent if patient has a good response to conventional treatment Prior history of respiratory failure and intubation increases mortality Adult patients with asthma at greater risk for bronchitis and emphysema