Respiratory Physiology: Lung Function

Lung Compliance

• Lung compliance refers to the lungs' ability to inflate easily.
• Three factors impact lung compliance:
  • Elastin and collagen fibers: Elastin makes inflation easier, while collagen makes it harder. In pulmonary diseases, elastin is replaced by scar tissue.
  • Water content: Influences lung elasticity.
  • Surface tension: The force that holds fluid together, impacting inflation.

Airway Resistance

• Airway resistance is the opposition to gas flow in the airways.
• Factors influencing airway resistance include:
  • Length of the airway: Longer airways offer more resistance.
  • Diameter of the airway: Narrower airways have higher resistance.
  • Flow rate of gases: Faster flow creates more resistance.

Pulmonary Perfusion

• Pulmonary perfusion is the movement of blood through the pulmonary capillaries.

Hypoxia-Induced Vasoconstriction

• Pulmonary blood vessels react strongly to alveolar oxygen levels.
• Vasoconstriction occurs in response to low oxygen levels.
• This redirects blood flow away from poorly oxygenated areas of the lungs and toward well-ventilated areas.

Arterial Blood Gas (ABG)

• ABG tests assess:
  • Acid-base balance
  • Ventilation (how well the lungs are removing carbon dioxide)
  • Oxygenation (how well oxygen is being delivered to the blood)

Nursing Responsibility for ABG Samples:

• Before Obtaining Sample: Indicate whether the patient is using oxygen and its flow rate. Avoid recent changes in oxygen therapy or interventions like suctioning or position changes for 15 min.
• During Obtaining Sample: Assist with positioning the patient correctly to obtain the sample. Collect blood using a heparinized syringe and ensure no air bubbles remain.
• After Obtaining Sample: Apply direct pressure to the puncture site for at least 5 minutes to prevent hematoma formation.

Arterial Blood Gas Analysis:

• Interpreting ABG results: Label all values PACO2, HCO3, pH as acidic or alkalotic. Compare the results to the normal ranges, identify whether it's fully compensated (normal pH), partially compensated (opposite PACO2 and HCO3), or uncompensated (normal value in one component).

Sputum Studies

• Sputum studies are crucial for identifying and treating pulmonary infections.
• Sputum can be collected by:
  • Expectoration (coughing up)
  • Tracheal suction
  • Bronchoscopy (with a flexible tube inserted through the nose or mouth into the airways)

Collecting Sputum Specimens from Endotracheal (ET) or Tracheostomy Tubes

• Requires sterile techniques .

CT Scan

• CT scans diagnose suspicious lesions.
• Advantages: They provide more detailed images than conventional X-rays.
• Types of CT scans:
  • High-resolution CT (HRCT) provides detailed images of the lungs.
  • Spiral/helical CT is used to diagnose pulmonary embolism (blood clots in the lungs).

Nursing Responsibility for CT Scans

• Before the scan:
  • Evaluate renal function if contrast media will be used since it's iodine-based.
• Assess for shellfish allergies.
  • The patient might need to be NPO (nothing by mouth) for 4 hours prior to the scan.
• During the scan:
  • Warn the patient that the contrast may cause warmth and flushing.
  • The patient must lie still throughout the scan.
• After the scan:
  • Encourage fluid intake to flush out the contrast.

Magnetic Resonance Imaging (MRI)

• MRIs provide in-depth imaging for lesions that are difficult to visualize using CT scans, as well as for differentiating vascular and nonvascular structures.
• IV contrast agent (gadolinium) may be given.

Nursing Responsibility for MRIs

• Before the scan:
• Check for pregnancy, allergies, and renal function.
• Ensure the patient removes all metal objects.
• Ask about implanted metallic devices or surgical insertions.
• The patient might need to be fasting.
• Assess for claustrophobia and the need for antianxiety medication.
• During the scan: The patient must lie still.

Positron Emission Tomography (PET) Scan

• PET scans use a glucose-containing nuclear tracer substance that's injected and taken up by metabolically active cells.
• Cancer cells have a high glucose uptake, causing "hot spots" on the scan that indicate active cancer.
• PET scans distinguish between benign and cancerous lung nodules.

Nursing Responsibility for PET Scans

• Before the scan:
  • Establish an IV line to inject the tracer substance.
  • The patient must be NPO (nothing by mouth) except for water and medications for 4-6 hours prior.
  • Hold glucose-containing IV solutions and change to normal saline.
  • Check blood glucose levels, which should be between 60-140 mg/dL.
• During the scan: The patient must lie still.
• After the scan: Encourage fluids to excrete the radioactive substance.

Oxygen Therapy

• The goal of oxygen therapy is to supply enough inspired oxygen to maximize the oxygen-carrying capacity of the arterial blood and ensure adequate cellular oxygenation.

Complications of Oxygen Therapy

• Oxygen toxicity:
• Caused by prolonged exposure to high oxygen concentrations.
• Pathophysiology: Overproduction of damaging oxygen free radicals.
• Signs and symptoms (early): Substernal chest pain, dry cough, tracheal irritation, nasal stuffiness, sore throat.
• Signs and symptoms (late): Chest X-ray changes (atelectasis, pneumonia), decreased vital capacity.
• Prevention: Utilize the lowest possible FiO2 to achieve SaO2 of 90%. Limit the duration of 100% FiO2 to 2-3 days and 60% FiO2 to 2-3 days. Monitor ABG if FiO2 is above 40% to assess the need for high concentrations.

Artificial Airways

• Oropharyngeal airway (OPA): Used for upper airway obstruction caused by tongue relaxation, secretions, seizures, or biting down on oral ETs. Only use in unconscious patients.
• Nasopharyngeal airway (NPA): Used when OPA is contraindicated, or in conscious patients.
• Laryngeal mask airway (LMA): Provides ventilation in the case of a difficult airway insertion.
• Endotracheal tube (ETT): The most widely used artificial airway; inserted through the mouth and into the trachea.
• Tracheostomy tube: A long-term airway inserted directly into the trachea through an opening made in the neck; used when an ETT is not suitable.

Tracheostomy Care

• Important steps include:
  • Confirming proper tube placement.
  • Inflating the tracheostomy cuff.
  • Securing the tube with ties, tapes, or a Velcro strap.
  • Monitoring vital signs and checking for any signs of complications.

Nursing Management for Patients with Tracheostomies

• Assessment is vital: Check the tracheostomy site for redness, inflammation, edema, ulceration, and signs of infection.
• Sterile care: Perform sterile dressing changes every 12-24 hours.
• Cuff management: Maintain cuff inflation pressure at 20-30 mmHg every 8 hours with a manometer.
• Suctioning: Suction the tracheostomy as needed, but try to avoid suctioning for a few hours after tracheostomy placement.
• Tracheostomy tapes: Change the tapes after the first 24 hours and as needed.

Types of Suctioning

• Closed suctioning: The suction catheter is enclosed in a plastic sleeve connected directly to the patient-ventilator circuit.
• Open suctioning: Performed when sterile sputum samples are needed or a closed suctioning system isn't available.

Decannulation

• De-cannulation is the process of removing the tracheostomy tube.
• Indications for decannulation:
  • The condition that required the tracheostomy has resolved.
  • The patient is hemodynamically stable.
  • The patient has a stable, intact respiratory drive.
  • The patient can independently exchange air and expectorate secretions.

Pre-procedure for Decannulation

• Explain the process to the patient.
• Monitor vital signs.
• Suction the airway and clear any oral secretions.
• Loosen or cut the tracheostomy ties.
• Remove any visible sutures.
• Deflate the cuff.
• Pull the tube straight out.