Pulmonary

Fundamental Concepts to Keep in Mind:

  • The diaphragm is the primary muscle responsible for breathing.
  • PCO₂ levels serve as a key measure for assessing ventilation needs.
  • Standard PCO₂ range: 35-45 mmHg
  • Expected mixed venous oxygen saturation (SvO₂): 60-75%
  • Normal arterial oxygen levels (PaO₂): 80-100 mmHg (Values below 80 indicate hypoxemia.)
  • Tidal volume (Vt) standard range: 8-10 mL/kg
  • Positive End-Expiratory Pressure (PEEP) helps keep alveoli open and enhances lung recruitment.
  • Positioning: Place the healthier lung downward to reduce the risk of hypoxemia.

Arterial Blood Gas (ABG) Reference Ranges (ROME Method):

  • pH: 7.35-7.45
  • Carbon dioxide (CO₂): 35-45 mmHg
  • Bicarbonate (HCO₃): 22-26 mEq/L
  • Partial pressure of oxygen (PaO₂): 80-100 mmHg

Acid-Base Abnormalities

There are four primary categories:
a. Respiratory alkalosis (excessive CO₂ elimination)
b. Respiratory acidosis (CO₂ retention)
c. Metabolic alkalosis (increased bicarbonate or acid loss)
d. Metabolic acidosis (bicarbonate depletion or acid buildup)

  • Respiratory system compensates rapidly (minutes to hours).
  • Metabolic system adjusts gradually (hours to days).
  • Anion gap (normal: 5-15) helps track metabolic acidosis, reducing frequent ABG testing.

Carbon Monoxide Toxicity

  • Pulse oximetry is unreliable for assessing oxygen levels in CO poisoning.
  • SpO₂ readings cannot distinguish CO from oxygen.
  • Management: Administer 100% FiO₂ until symptoms resolve and CO levels drop below 10%.

Lung Compliance

  • Static compliance measures lung elasticity.
  • Dynamic compliance evaluates airway resistance.
  • Decreased lung flexibility leads to increased breathing effort.

Severe Asthma (Status Asthmaticus)

  • Progressive airway tightening causes:
    • Wheezing → diminished breath sounds → total silence (ominous).
    • Intubation is required for: absent breath sounds, altered consciousness, critical hypoxia, or respiratory acidosis.
  • Ventilation strategy:
    • Lower respiratory rate to allow full exhalation.
    • Reduce tidal volume to avoid air trapping and auto-PEEP.
  • Treatment: Bronchodilators, steroids, and hydration.

Chronic Obstructive Pulmonary Disease (COPD)

  • Leading cause: smoking.
  • Key issue: difficulty exhaling, leading to air trapping.
  • V/Q imbalance due to ventilatory impairment and CO₂ retention.
  • May progress to right-sided heart failure.
  • Symptoms: Breathlessness at rest or exertion, rapid breathing, small tidal volumes, barrel chest.
  • Management:
    • Increase FiO₂ to maintain O₂ saturation above 90%.
    • Use corticosteroids, bronchodilators, BiPAP, or mechanical ventilation if needed.

Pulmonary Fibrosis

  • Scarring of lung tissue leads to stiffness, reducing lung expansion and oxygen exchange.
  • Scar tissue does not allow gas exchange.
  • Supportive care includes oxygen therapy, medications, and rehabilitation.

Pulmonary Embolism (PE)

  • Creates ventilated but non-perfused lung areas (dead space).
  • Oxygen therapy is effective.
  • Best diagnostic tool: pulmonary angiography.
  • Common signs: Fast heart rate, shortness of breath, rapid breathing, crackles, cough, respiratory alkalosis, anxiety.
  • Treatment:
    • Airway, breathing, circulation support (ABCs).
    • 100% oxygen, pain control, IV fluids, anticoagulation, IVC filter, or surgical embolectomy.
    • Fat embolism: Recognized by petechiae.
    • Air embolism: Position Trendelenburg, left side down.

Acute Respiratory Distress Syndrome (ARDS)

  • Causes significant oxygenation failure (shunting).
  • Inflammation increases permeability in lung capillaries.
  • Damage to Type II alveolar cells leads to surfactant loss and lung collapse.
  • Does not improve with oxygen alone—requires PEEP.

Stages of ARDS:

  1. Exudative Phase (0-4 days) – Fluid buildup in alveoli.
  2. Proliferative Phase (3-10 days) – Tissue repair and worsening lung stiffness.
  3. Fibrotic Phase (7-14 days) – Scar tissue formation, poor prognosis.

Symptoms: Fluid-filled lungs, crackles, low lung compliance, reduced residual capacity, and bilateral infiltrates on chest X-ray.

Treatment:

  • Intubation and mechanical ventilation with high PEEP (>15 cm H₂O).
  • Monitor for reduced cardiac output and barotrauma.
  • Low tidal volume (4-6 mL/kg) to prevent lung injury.
  • Consider prone positioning for improved oxygenation.

Tension Pneumothorax

  • The mediastinum shifts away from the affected lung.
  • Symptoms: Seen on X-ray, fast heart rate, bulging neck veins, and low blood pressure.
  • Treatment:
    • Chest tube placement to restore negative pressure.
    • Needle decompression, followed by a chest tube (inserted high for pneumothorax, low for hemothorax).
    • Oxygen therapy for support.

Chest Tube Management

  • Air bubbles in the water seal chamber with breathing? ABNORMAL – indicates a leak.
  • Fluid moving up and down (tidaling)? EXPECTED – shows normal pleural pressure changes.

Pneumonia

  • Findings: Chest X-ray shows solid lung areas (consolidation) or scattered infiltrates.
  • Symptoms: Dehydration, rapid heart rate, chest pain, fever, chills, weakness, and confusion (in elderly patients).
  • Lab results: High white blood cell count, positive sputum or blood cultures.
  • Treatment:
    • Maximize oxygenation—place the healthy lung down.
    • Administer the first dose of antibiotics within 4 hours.
    • Ensure proper nutrition and hydration.

Aspiration Pneumonia

  • Most cases occur in the right lung due to its larger, straighter bronchus.
  • Symptoms: Fast heart rate, low blood pressure, low oxygen levels, and crackling lung sounds.
  • Treatment:
    • Mechanical ventilation if necessary.
    • Antibiotics.
    • Trendelenburg positioning with the right side down to aid drainage.

Respiratory Failure

  • Low oxygen levels (PaO₂ <60 mmHg):
    • Signs: Rapid breathing, use of accessory muscles, blue skin, anxiety, and restlessness.
  • High carbon dioxide levels (PaCO₂ >50 mmHg):
    • Signs: Shallow, slow breathing, low consciousness.
  • Management:
    • Ensure open airways (keep the patient upright, maintain oxygen saturation above 90%).
    • Stabilize circulation (treat low blood pressure and abnormal heart rhythms).

Noninvasive Ventilation (NIV)

  • CPAP: Used for low oxygen levels (hypoxemia) by keeping airways open with continuous pressure.
  • BiPAP: Helps with both hypoxemia and high CO₂ levels (hypercapnia) by providing different pressures for inhaling and exhaling.
  • Not recommended if the patient:
    • Has an altered mental state or can’t protect their airway.
    • Produces excessive secretions.
    • Can’t tolerate the mask.
    • Has life-threatening low oxygen that doesn’t improve.
    • Is unstable (low blood pressure, irregular heart function).

Mechanical Ventilation

Modes:

  • SIMV (Synchronized Intermittent Mandatory Ventilation): Provides a set tidal volume and rate with the option for the patient to breathe independently.
  • Pressure Support (PS): Delivers preset pressure, not volume; often used during the weaning process.

Ventilator Weaning Criteria:

  • Minute ventilation <10 L/min
  • Spontaneous tidal volume >5 mL/kg
  • Negative inspiratory force (NIF) > -25
  • Vital capacity 3-5 L

Stop the Spontaneous Breathing Trial (SBT) if:

  • Respiratory rate >35 or <8
  • Oxygen saturation drops below 88%
  • Patient shows distress or decreased consciousness → Weaning failed.

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