RESP

Overview of the Autonomic Nervous System (ANS)

  • The autonomic nervous system (ANS) consists of two main divisions: the sympathetic and parasympathetic nervous systems.

    • Sympathetic Nervous System: Responsible for the 'fight or flight' response.

    • Parasympathetic Nervous System: Promotes 'rest and digest' and homeostasis.

Receptors and Neurotransmitters in the ANS

  • Different receptors and neurotransmitters are involved in the sympathetic and parasympathetic divisions.

  • Medications can target specific receptors to produce desired effects with regard to these systems.

Sympathetic Nervous System Stimulus

  • Activation can be due to stress or fear (e.g., facing a scary tiger).

  • Example medication: beta receptor agonist.

    • Effects:

    • Increased airway diameter, beneficial for patients with asthma or COPD.

    • Potential adverse effects include increased heart rate and blood pressure.

Agonists vs. Antagonists

  • Agonists: Enhance receptor effects.

  • Antagonists: Block receptor effects.

    • In cases where dilation of bronchi is the desired effect, a medication blocking the parasympathetic effects may be used.

Parasympathetic Nervous System and Neurotransmitter

  • Main neurotransmitter: Acetylcholine.

    • Stimulates muscarinic and nicotinic receptors.

  • Anticholinergics: Medications that block parasympathetic effects to increase airway diameter.

    • Mechanism: Block the effect of acetylcholine in the parasympathetic nervous system, promoting bronchodilation.

Beta-2 Receptors in the Lungs

  • Beta-2 receptors located in the lungs.

    • Stimulation leads to relaxation of bronchial smooth muscle and bronchodilation, improving airflow.

Administration of Medications

  • Inhalation: Preferred method of administering respiratory medications.

    • Delivers medication directly to the lungs and requires smaller doses, reducing adverse effects.

  • Devices used: Metered dose inhalers (MDIs) with or without a spacer, and nebulizers for specific cases.

    • Nebulizers: Risk of infection; used cautiously for patients who struggle to use MDIs effectively.

Types of Beta-2 Agonists

Short-Acting Beta-2 Agonists (SABAs)

  • Characteristics:

    • Quick onset of action (within 5 minutes).

    • Duration approximately 3 hours.

    • Used as reliever medications for fast symptom relief.

    • Example: Salbutamol (Trade name: Ventolin).

Long-Acting Beta-2 Agonists (LABAs)

  • Characteristics:

    • Slower onset (up to 20 minutes).

    • Duration lasts at least 12 hours.

    • Used as preventative medications to manage symptoms over time.

    • Example: Salmeterol.

  • Combination with anti-inflammatory corticosteroids for daily preventive treatment.

  • Patients using SABAs excessively (three or more times a week) may require LABAs for management.

    • Example of combination medication: Fluticasone and Salmeterol (Trade name: Seravent).

Adverse Effects of Beta-2 Agonists

  • Common adverse effects:

    • Tremor

    • Palpitations

    • Headaches

    • Insomnia

  • High doses can lead to hypokalemia, risk exacerbated by corticosteroids and diuretics.

  • Coadministration with beta blockers can block therapeutic effects of beta agonists, potentially triggering asthma.

    • Warning: Beta blockers contraindicated for patients with asthma or COPD.

Anticholinergics

  • Function by blocking acetylcholine action in the parasympathetic system, resulting in long-acting bronchodilation.

    • Example medication: Ipratropium (Trade name: Atrovent).

    • Duration: Approximately 6 hours; used for acute asthma and COPD exacerbations.

  • Common adverse effects:

    • Dry mouth

    • Throat irritation

  • Patient education: Avoid contact with eyes to prevent blurred vision and discomfort; report any vision issues or urinary retention.

Corticosteroids

  • Administered inhaled, intravenously, or orally to reduce airway inflammation and bronchial hypersensitivity.

  • Mechanism of inhaled corticosteroids (ICS):

    • Enter the cell and affect protein synthesis regulating inflammation, preventing an inflammatory response.

    • Maintain control of bronchial hyperreactivity to triggers.

  • Examples of ICS include Beclomethasone and Fluticasone.

Adverse Effects of Inhaled Corticosteroids

  • Common adverse effects:

    • Dysphonia: Changes in voice due to irritation of vocal cords.

    • Oral pharyngeal candidiasis (thrush).

    • Bruising.

  • Concerns with high doses:

    • Potential for systemic absorption leading to adrenal suppression, bone density loss, glaucoma, etc.

Patient Education for Inhaled Corticosteroids

  • Use of a spacer recommended to reduce systemic absorption.

  • Patient should rinse mouth after inhalation to remove residue.

Systemic Corticosteroids

  • Used in acute exacerbations; may be orally administered or intravenously.

  • Examples include Prednisolone (oral) and Hydrocortisone (IV).

  • Effects:

    • Decrease inflammation and enhance beta-2 agonist actions, aiding bronchodilation.

    • Suppress immune response, reducing bronchoconstriction and airway edema/mucus production.

Risks of Systemic Corticosteroids

  • Risks increase with prolonged use:

    • Adrenal suppression

    • Sodium and water retention

    • Hypertension

    • Hyperglycemia and diabetes risk

    • Osteoporosis

    • Delayed wound healing

  • Adrenal Crisis: Occurs if corticosteroids are stopped suddenly after prolonged use; adrenal glands reduce cortisol production, leading to insufficiency during stress.

    • Important discussion topic for seminar on ceasing systemic corticosteroids safely.

References Used

  • [Resources from Asthma Australia and NPS on inhalers and medication administration]