Contents
Respiratory Anatomy & Physiology
Upper Airway
- Functions: Filtration, warming, humidification of inspired air
- Protective reflexes: Gag reflex, swallow reflex (CN IX & X)
- Impaired reflexes (stroke, sedation) increase aspiration risk
- Structures: Nose, pharynx, larynx (vocal cords)
Lower Airway
- Trachea: Shares posterior wall with esophagus (risk of TE fistula)
- Carina: Bifurcation of trachea, rich in cough receptors
- Right mainstem bronchus: Straighter, larger - common aspiration site
- Bronchioles: Smooth muscle, responsive to beta-2 agonists
- Alveoli: Gas exchange units (~300 million, ~800 sq ft surface area)
- Type I pneumocytes: Gas exchange
- Type II pneumocytes: Produce surfactant (reduces surface tension)
Pulmonary Circulation
- Low-pressure system compared to systemic circulation
- Pulmonary arteries carry deoxygenated blood
- Hypoxic pulmonary vasoconstriction: Redirects blood away from poorly ventilated areas
- Pulmonary capillaries: Single RBC width for optimal gas diffusion
Ventilation & Oxygenation
Ventilation Parameters
- Tidal Volume (Vt): Volume per breath (~500 mL or 6-8 mL/kg IBW)
- Respiratory Rate (RR): Normal 12-20 breaths/min
- Minute Ventilation (MV) = Vt × RR (normal 5-10 L/min)
- Alveolar Ventilation = (Vt - Dead Space) × RR
- Dead space: Areas ventilated but not perfused (normal ~150 mL)
Oxygenation Concepts
- FiO2: Fraction of inspired oxygen (room air = 21%)
- PaO2: Partial pressure of oxygen in arterial blood (normal 80-100 mmHg)
- SaO2/SpO2: Oxygen saturation (normal >95%)
- P/F Ratio: PaO2 ÷ FiO2 - assesses oxygenation efficiency
- Normal P/F: ~500, Mild ARDS: 200-300, Moderate: 100-200, Severe: <100
Oxyhemoglobin Dissociation Curve
- Shows relationship between PaO2 and hemoglobin saturation
- Right shift (releases O2 easier): Acidosis, fever, increased 2,3-DPG, hypercapnia
- Left shift (holds O2 tighter): Alkalosis, hypothermia, decreased 2,3-DPG
- Remember: "Right = Release" for conditions that increase oxygen delivery to tissues
Hypoxemia vs Hypoxia
- Hypoxemia: Low oxygen in blood (PaO2 <60 mmHg)
- Hypoxia: Inadequate oxygen at tissue level
- Types of hypoxia: Hypoxemic, Anemic, Circulatory, Histotoxic (cyanide)
- Hypoxemia causes: V/Q mismatch, shunt, diffusion impairment, hypoventilation
ABG Interpretation
Normal ABG Values
- pH: 7.35-7.45
- PaCO2: 35-45 mmHg (respiratory component)
- HCO3: 22-26 mEq/L (metabolic component)
- PaO2: 80-100 mmHg
- Base excess: -2 to +2
Step-by-Step ABG Analysis
- Step 1: Look at pH - Acidemia (<7.35) or Alkalemia (>7.45)?
- Step 2: Identify primary disorder
- - If pH and CO2 move opposite: Respiratory cause
- - If pH and HCO3 move together: Metabolic cause
- Step 3: Check for compensation
- - Respiratory compensation happens in hours
- - Metabolic compensation takes 3-5 days
Common ABG Patterns
- Respiratory Acidosis: pH↓, CO2↑ (hypoventilation, COPD, sedation)
- Respiratory Alkalosis: pH↑, CO2↓ (hyperventilation, anxiety, PE)
- Metabolic Acidosis: pH↓, HCO3↓ (DKA, lactic acidosis, renal failure)
- Metabolic Alkalosis: pH↑, HCO3↑ (vomiting, diuretics, NG suction)
Anion Gap
- Formula: Na - (Cl + HCO3) = Normal 8-12
- Elevated AG acidosis: MUDPILES - Methanol, Uremia, DKA, Propylene glycol, INH/Iron, Lactic acid, Ethylene glycol, Salicylates
- Normal AG acidosis: Diarrhea, RTA, saline administration
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Berlin Definition Criteria
- Timing: Within 1 week of known insult or new/worsening symptoms
- Imaging: Bilateral opacities not explained by effusion, collapse, or nodules
- Origin: Not fully explained by cardiac failure or fluid overload
- Oxygenation (P/F ratio on PEEP ≥5): Mild 200-300, Moderate 100-200, Severe <100
Pathophysiology
- Direct injury: Pneumonia, aspiration, inhalation injury, pulmonary contusion
- Indirect injury: Sepsis, pancreatitis, trauma, transfusion (TRALI)
- Inflammatory cascade damages alveolar-capillary membrane
- Increased permeability → non-cardiogenic pulmonary edema
- Surfactant dysfunction → alveolar collapse → refractory hypoxemia
ARDS Management
- Low Tidal Volume Ventilation (LTVV): 6 mL/kg IBW
- Plateau pressure goal: <30 cmH2O
- Higher PEEP to recruit alveoli and improve oxygenation
- Permissive hypercapnia acceptable if pH >7.20
- Prone positioning: For moderate-severe ARDS (P/F <150), 16+ hours/day
- Conservative fluid management once hemodynamically stable
- Neuromuscular blockade in severe cases first 48 hours
COPD & Asthma
COPD Overview
- Chronic airflow limitation that is not fully reversible
- Two phenotypes: Chronic bronchitis ("Blue bloater"), Emphysema ("Pink puffer")
- Risk factors: Smoking (#1), occupational exposure, alpha-1 antitrypsin deficiency
- Diagnosis: Spirometry showing FEV1/FVC <70%
COPD Exacerbation Management
- Bronchodilators: Short-acting beta agonists (albuterol), anticholinergics (ipratropium)
- Corticosteroids: Reduce inflammation, shorten recovery
- Antibiotics: If increased sputum purulence or volume
- Oxygen: Target SpO2 88-92% (avoid suppressing hypoxic drive)
- NIV (BiPAP): First-line for respiratory acidosis, reduces intubation rate
Asthma & Status Asthmaticus
- Reversible airway obstruction, inflammation, hyperresponsiveness
- Triggers: Allergens, exercise, cold air, infections, aspirin
- Status asthmaticus: Severe attack unresponsive to initial treatment
- Danger signs: Silent chest, altered mental status, cyanosis
- Treatment: Continuous nebs, IV steroids, magnesium sulfate, possibly intubation
- If intubating: Low RR, long expiratory time to prevent air trapping
Pulmonary Embolism
Pathophysiology
- Obstruction of pulmonary vasculature (usually thrombus from DVT)
- Virchow's Triad: Stasis, Endothelial injury, Hypercoagulability
- Results in V/Q mismatch (ventilated but not perfused = dead space)
- Large PE can cause right heart strain and cardiogenic shock
Clinical Presentation
- Dyspnea (most common), pleuritic chest pain, tachycardia, tachypnea
- Hemoptysis, syncope (suggests massive PE)
- Signs of DVT: Unilateral leg swelling, calf tenderness
- Massive PE: Hypotension, right heart failure
Diagnosis
- D-dimer: Sensitive but not specific (rules out PE if low probability)
- CT Pulmonary Angiography (CTPA): Gold standard diagnostic test
- V/Q scan: Alternative if contrast contraindicated
- ECG findings: Sinus tachycardia, S1Q3T3 pattern, right heart strain
- Echo: RV dilation, McConnell sign
Treatment
- Anticoagulation: Heparin, then warfarin or DOAC
- Thrombolytics: For massive PE with hemodynamic instability
- Embolectomy: Surgical or catheter-based for massive PE
- IVC filter: If anticoagulation contraindicated or recurrent PE despite therapy
- Supportive: Oxygen, pressors if needed, avoid fluid overload
Mechanical Ventilation
Ventilator Modes
- Volume Control (VC): Set Vt, flow; variable pressure
- Pressure Control (PC): Set pressure, inspiratory time; variable Vt
- Assist-Control (AC): Delivers set breath for every patient trigger + backup rate
- SIMV: Set number of mandatory breaths, patient can breathe between
- Pressure Support (PS): Patient-triggered, pressure-augmented spontaneous breaths
Initial Ventilator Settings
- Tidal Volume: 6-8 mL/kg ideal body weight
- Rate: 12-16 breaths/min (adjust for PaCO2)
- FiO2: Start 100%, wean to <60% to avoid oxygen toxicity
- PEEP: 5 cmH2O baseline, increase for hypoxemia/ARDS
- Goal: Plateau pressure <30 cmH2O to prevent barotrauma
Ventilator Troubleshooting
- High peak pressure + Normal plateau = Airway resistance (secretions, bronchospasm, kinked tube)
- High peak + High plateau = Decreased compliance (ARDS, pneumothorax, edema)
- Fighting the vent: Check synchrony, sedation, pain, underlying cause
- Auto-PEEP: Incomplete exhalation, reduce rate or increase expiratory time
Weaning & Extubation
- Prerequisites: Underlying cause resolved, hemodynamically stable, adequate oxygenation
- Spontaneous Breathing Trial (SBT): T-piece or low PS for 30-120 minutes
- RSBI (Rapid Shallow Breathing Index): RR/Vt - <105 predicts success
- Cuff leak test: Assesses for laryngeal edema before extubation
- Post-extubation: Monitor for stridor, respiratory distress
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PaO2 is 60 on FiO2 1.0 (100%). PEEP is 10. According to the Berlin criteria, what severity of ARDS does this represent?
- Mild ARDS (P/F Ratio 200-300)
- Moderate ARDS (P/F Ratio 100-200)
- Severe ARDS (P/F Ratio < 100)
- Acute Respiratory Distress Syndrome is not present
Rationale: P/F Ratio = 60 / 1.0 = 60. Ratios < 100 are Severe; 100-200 Moderate; 200-300 Mild....
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Patient is acidotic, hyperthermic, and hypercarbic. Which way does the oxyhemoglobin dissociation curve shift?
- Left Shift
- Right Shift
- No Shift
- Cannot be determined
Rationale: "Right release." The hemoglobin has lower affinity for O2, releasing it easily to the tissues (good for tissues, bad for saturation)....
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High Pressure Alarm sounds on a ventilator. Patient is biting the tube. What is the most likely cause?
- Patient disconnection
- Obstruction / Kinked Tube
- Apnea
- Decreased tidal volume
Rationale: High pressure = Resistance. Other causes: secretions, pneumothorax, coughing, reduced compliance....
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Take Respiratory Quiz →Frequently Asked Questions
What percentage of the CCRN exam is respiratory?
Respiratory (pulmonary) makes up 15% of the Adult CCRN exam — about 19 of the 125 scored questions, making it the second-largest clinical category after cardiovascular.
What respiratory topics are tested on the CCRN exam?
High-yield topics include ARDS and lung-protective ventilation, ABG interpretation, ventilator modes and weaning readiness, acute respiratory failure, pulmonary embolism, pneumothorax and chest tube management, and oxygenation versus ventilation problems.
How do I interpret ABGs quickly on the CCRN?
Use a consistent three-step method: check the pH (acidosis or alkalosis), match it to the PaCO2 (respiratory cause) or HCO3 (metabolic cause), then assess compensation. Practicing 20–30 ABGs with this method makes exam interpretation nearly automatic.
What ventilator settings does the CCRN test?
Know lung-protective ventilation for ARDS — tidal volume 4–8 mL/kg of ideal body weight with plateau pressure under 30 cmH2O — plus PEEP titration, recognizing auto-PEEP and dyssynchrony, and weaning criteria such as an RSBI below 105.