Ventilation Support and NIV Exam Notes

Question 1: Negative-Pressure Ventilators

• Negative-pressure ventilators increase transthoracic pressure to cause air to enter the lungs.
• Transthoracic Pressure (Ptt): The pressure difference between alveolar pressure (Palv) and body surface pressure (Pbs). Expressed as: Ptt = Palv - Pbs
  • Lowering external pressure increases the transthoracic gradient, drawing air into the lungs.
• Transpulmonary Pressure (Ptp): The pressure difference between alveolar pressure and intrapleural pressure (Ppl). Expressed as: Ptp = Palv - Ppl
  • Incorrect because negative-pressure ventilation manipulates transthoracic pressure, not transpulmonary pressure.
• Transrespiratory Pressure (Ptr): The pressure difference between airway opening pressure (Pao) and body surface pressure (Pbs). Expressed as: Ptr = Pao - Pbs
  • Incorrect because it's overly broad; negative-pressure ventilators specifically target transthoracic pressure.
• Transairway Pressure (Pta): The pressure difference between airway opening and alveolar pressure. Expressed as: Pta = Pao - Palv
  • Incorrect because it reflects pressure needed to overcome airway resistance, not the gradient increased by negative-pressure devices.

Question 2: Acute Cardiogenic Pulmonary Edema (ACPE) Treatment

• For a patient with ACPE (evidenced by pink, frothy secretions) and the following arterial blood gas values on a nonrebreather mask at 15 L/min: pH = 7.50, PaCO2 = 28 mm Hg, PaO2 = 43 mm Hg, SaO2 = 84%, HCO3^- = 24 mEq/L, the respiratory therapist should suggest mask CPAP with supplemental oxygen.
• Postural Drainage: Using patient positioning to facilitate clearance of airway secretions.
  • Incorrect because ACPE involves fluid in alveoli, not retained secretions; postural drainage won’t improve oxygenation or hemodynamics in pulmonary edema.
• IPPB with Supplemental Oxygen: Intermittent Positive-Pressure Breathing delivers positive pressure breaths on a scheduled basis.
  • Incorrect because IPPB provides less continuous alveolar recruitment and hemodynamic benefit than CPAP and is largely outdated for ACPE management.
• Mask CPAP with Supplemental Oxygen: Continuous Positive Airway Pressure via face mask maintains constant distending pressure throughout the respiratory cycle.
  • Mechanism in ACPE:
    • Recruits collapsed alveoli and increases functional residual capacity, improving PaO_2.
    • Increases intrathoracic pressure, reducing venous return (preload) and left ventricular afterload, alleviating pulmonary edema.
  • Correct because it rapidly improves oxygenation and reduces cardiac workload in acute pulmonary edema.
• NIV via Nasal Mask with Postural Drainage: Noninvasive ventilation (e.g., CPAP/BiPAP) delivered through a nasal interface, plus drainage positions.
  • Incorrect because nasal masks often leak and deliver lower effective pressures than full-face CPAP; combined with postural drainage, it’s suboptimal for urgent oxygenation and hemodynamic support in ACPE.

Question 3: Acute Pulmonary Edema and Hypoxemic Respiratory Failure

• For a patient with acute pulmonary edema from left-sided heart failure and acute hypoxemic respiratory failure that has not responded to conventional pharmacologic and oxygen therapy, the respiratory therapist should recommend noninvasive positive-pressure ventilation (NIV).
• Noninvasive Positive-Pressure Ventilation (NIV): Delivery of positive inspiratory and expiratory pressures via a tight-fitting mask (e.g., BiPAP).
  • Mechanism:
    • PEEP component recruits alveoli and improves oxygenation.
    • Pressure support reduces work of breathing and improves ventilation.
  • Correct because it provides both alveolar recruitment and ventilatory support without intubation, rapidly reversing hypoxemia and reducing preload/afterload in cardiogenic pulmonary edema.
• Intubation and Mechanical Ventilation: Invasive airway placement with full ventilatory support.
  • Incorrect because it’s reserved for patients who fail or cannot tolerate NIV; carries higher risks of ventilator-associated complications and hemodynamic instability.
• Continuous Positive Airway Pressure (CPAP): A single, constant distending pressure delivered via mask.
  • Incorrect because while CPAP can improve oxygenation and reduce preload, it provides no pressure support to offload respiratory muscles, making it less effective in acute ventilatory failure compared to full NIV.
• Bronchial Hygiene Therapy: Techniques (e.g., chest physiotherapy, suctioning) to clear airway secretions.
  • Incorrect because pulmonary edema involves alveolar fluid, not thick secretions; these techniques won’t correct hypoxemia or reduce cardiac preload/afterload.

Question 4: Physiological Goals of NIV in Acute Respiratory Failure

• One of the physiological goals of NIV in acute respiratory failure used to improve gas exchange is resting the respiratory muscles.
• Resting the Respiratory Muscles: Unloading inspiratory muscles by providing pressure support.
  • Mechanism: Reduces work of breathing and muscle fatigue, allowing more efficient ventilation and improved gas exchange.
• Decreasing the Effect of Secretions: Enhancing mucus clearance.
  • Incorrect because NIV does not directly clear secretions; bronchial hygiene techniques address that.
• Decreasing the Functional Residual Capacity (FRC): Lowering the lung volume at end-expiration.
  • Incorrect because NIV actually increases FRC via PEEP to recruit alveoli and reduce shunt.
• Increasing Right Ventricular Preload: Elevating venous return to the right heart.
  • Incorrect because NIV raises intrathoracic pressure, which decreases venous return (preload) and can reduce left ventricular afterload—beneficial in cardiogenic edema but not a goal to increase preload.

Question 5: Primary Goal of NIV in Acute Care

• The primary goal of NIV in the acute care setting is to avoid invasive ventilation.
• Avoid Invasive Ventilation: Prevent the need for endotracheal intubation and its associated risks (e.g., ventilator-associated pneumonia, airway trauma).
  • Correct because by providing timely positive-pressure support, NIV can reverse respiratory failure early, reducing the necessity for invasive mechanical ventilation.
• Eliminate Nocturnal Hypopnea: Prevent shallow breathing episodes during sleep.
  • Incorrect because this is a goal in chronic sleep apnea management, not the acute care use of NIV.
• Decrease Muscle Fatigue: Unload respiratory muscles via pressure support.
  • Incorrect because while NIV does reduce work of breathing, this is a secondary benefit rather than the primary acute-care objective.
• Improve Sleep Quality: Enhance sleep architecture and continuity.
  • Incorrect because improving sleep is relevant in chronic NIV for sleep-disordered breathing, not the immediate goal in acute respiratory failure.

Question 6: Minimum NIV Hours for Chronic Hypoventilation

• Patients with chronic hypoventilation disorders typically need a minimum of 4–6 hours of NIV to experience improved quality of life.
• Clinical studies show at least 4-6 hours of nightly NIV use is needed to achieve measurable improvements in daytime gas exchange, sleep quality, and overall quality of life in chronic hypoventilation (e.g., obesity hypoventilation syndrome, neuromuscular weakness).
• Shorter durations (e.g., 2–4 hours) do not consistently yield these benefits, while longer use further consolidates them.

Question 7: Standard of Care for COPD Exacerbation

• NIV is considered the standard of care for the treatment of COPD exacerbation.
• In acute COPD exacerbations, NIV delivers pressure support that unloads fatigued respiratory muscles, improves alveolar ventilation, and corrects hypercapnia.
• By providing both inspiratory assistance and PEEP, it enhances tidal volume, reduces work of breathing, and reverses CO_2 retention—thereby lowering the need for endotracheal intubation, decreasing ICU stays, and improving survival.

Question 8: COPD Patient in Emergency Department

• For a 75-year-old man with a long history of COPD brought to the emergency department with shortness of breath, a persistent, productive cough with green purulent sputum, cyanosis of the lips and extremities, and is uncooperative, with arterial blood gas values on 2 L/min by nasal cannula: pH = 7.25; PaCO2 = 90 mm Hg; PaO2 = 38 mm Hg; SaO2 = 59%; HCO3^- = 38 mEq/L, the most appropriate action at this time is invasive mechanical ventilation.
• Mask CPAP
  • Provides a constant distending pressure (PEEP) to improve oxygenation.
  • Inappropriate because it does not deliver pressure support for ventilation—insufficient to correct severe hypercapnia.
• Nasal Cannula
  • Delivers low-flow oxygen (up to ~6 L/min).
  • Inappropriate because the patient is already failing on 2 L/min; cannot correct profound hypoxemia or hypercapnia.
• Invasive Mechanical Ventilation
  • Secures airway and delivers controlled ventilatory support (tidal volume, rate, PEEP).
  • Appropriate because:
    • Corrects acute on chronic respiratory acidosis (PaCO_2 90, pH 7.25).
    • Ensures adequate oxygenation and ventilation in an uncooperative patient.
• NIV via Full-Face Mask
  • Provides pressure support and PEEP noninvasively.
  • Inappropriate because the patient’s agitation/uncooperativeness makes mask seal and synchrony unreliable; risk of NIV failure is high.

Question 9: Shortness of Breath and Pulmonary Congestion

• For a 61-year-old female admitted with shortness of breath, alert and oriented but very anxious, latest arterial blood gas values on a nasal cannula at 3 L/min show: pH = 7.39; PaCO2 = 41 mm Hg; PaO2 = 40 mm Hg; SaO2 = 74%; HCO3^- = 24 mEq/L, breath sounds are decreased throughout with fine late crackles on inspiration, and the current chest X-ray shows an enlarged heart with bilateral vascular congestion, the most appropriate therapy for this patient is mask CPAP.
• Invasive Ventilation
  • Endotracheal intubation with full ventilatory support.
  • Incorrect because the patient is cooperative and has normal ventilation (PaCO_2 41, pH 7.39); intubation is premature and carries greater risk.
• Mask CPAP (Continuous Positive Airway Pressure)
  • Applies a constant distending pressure throughout the respiratory cycle.
  • Correct because:
    • Improves oxygenation by recruiting alveoli and increasing FRC.
    • Reduces preload and afterload, beneficial in cardiogenic pulmonary edema.
    • Avoids intubation in a patient who is alert and ventilating adequately.
• Nasal Cannula
  • Delivers low-flow oxygen (up to ~6 L/min).
  • Incorrect because patient is already failing at 3 L/min; cannot correct severe hypoxemia or provide positive pressure.
• Nonrebreather Mask
  • Delivers high FiO_2 (~60–90%).
  • Incorrect because it provides no PEEP; fails to recruit alveoli or reduce cardiac preload—key in pulmonary edema management.

Question 10: Delivered Tidal Volume in Bilevel Positive-Pressure Ventilation

• The gradient between the IPAP and EPAP determines the patient’s delivered tidal volume in all modes of bilevel positive-pressure ventilation.
• The gradient between the IPAP and EPAP
  • The pressure support level (\Delta P = IPAP - EPAP).
  • This pressure difference is the driving force that inflates the lungs; a larger gradient delivers a larger tidal volume for a given patient effort and lung mechanics.
• IPAP (Inspiratory Positive Airway Pressure)
  • IPAP alone sets the inspiratory pressure but does not account for the baseline EPAP; without subtracting EPAP, it doesn’t define the true pressure support.
• EPAP (Expiratory Positive Airway Pressure)
  • EPAP maintains airway patency and FRC but does not directly drive volume; its role is to set the baseline from which IPAP provides additional support.
• Patient’s Respiratory Rate
  • Respiratory rate affects minute ventilation but does not determine the volume delivered with each breath; tidal volume in bilevel modes is set by pressure support, not by rate.

Question 11: COPD Patient with Dyspnea and Hypersomnolence

• For a 62-year-old male patient with COPD being seen in the pulmonary clinic for dyspnea at rest and daytime hypersomnolence, who has been hospitalized three times in the past year for COPD exacerbations and once for pneumonia, currently uses 2 L/min oxygen from a concentrator all the time, reports that he is able to sleep only about 2 hours each night and that he has a headache every morning, nocturnal NIV should be recommended to the physician.
• Tracheostomy and Ventilation
  • Surgical creation of an airway with chronic invasive mechanical ventilation.
  • Incorrect because it's reserved for end-stage ventilatory failure or neuromuscular disease unresponsive to noninvasive measures; overly invasive given this patient’s stable airway and cooperative status.
• Nocturnal NIV (Bilevel Positive Airway Pressure)
  • Delivery of inspiratory and expiratory positive pressures via a mask during sleep.
  • Correct because:
    • Provides pressure support to unload respiratory muscles and improve alveolar ventilation.
    • Corrects nocturnal hypoventilation, alleviating morning headaches and daytime hypersomnolence.
    • Reduces hospitalizations in COPD with chronic hypercapnia.
• Chest Cuirass
  • Negative-pressure ventilation via a shell around the chest.
  • Incorrect because it is rarely used in COPD; cumbersome, limited to specialized centers, and less effective for chronic ventilatory support compared to NIV.
• Nocturnal CPAP
  • Continuous positive pressure throughout the respiratory cycle.
  • Incorrect because while CPAP can improve oxygenation and upper-airway patency, it provides no inspiratory pressure support—insufficient to correct hypoventilation and hypercapnia in COPD.

Question 12: Amyotrophic Lateral Sclerosis (ALS) Patient

• For a patient who was diagnosed 1 year ago with amyotrophic lateral sclerosis complaining of fatigue and inability to concentrate at work, FVC is 45% of predicted, the PaCO2 is 47 mm Hg, and the MIP is 54 cmH2O, nocturnal NIV should be considered for this patient.
• Supplemental Home Oxygen
  • Delivery of low-flow oxygen to correct hypoxemia.
  • Incorrect because this patient’s problem is hypoventilation (elevated PaCO_2, reduced FVC), not isolated hypoxemia. Oxygen alone can worsen hypercapnia by reducing respiratory drive.
• Continuation of Current Therapy
  • Maintaining status quo without adding ventilatory support.
  • Incorrect because progressive respiratory muscle weakness (FVC < 50%, rising PaCO2) indicates early ventilatory failure; delaying support risks further fatigue and CO2 retention.
• Nocturnal CPAP
  • Continuous positive airway pressure throughout the respiratory cycle.
  • Incorrect because it provides alveolar recruitment and keeps airways open but offers no inspiratory assistance—insufficient to unload weakened respiratory muscles in ALS.
• Nocturnal NIV (Bilevel Positive Airway Pressure)
  • Delivery of both inspiratory (IPAP) and expiratory (EPAP) pressures via mask during sleep.
  • Correct because:
    • Supports inspiratory effort by providing pressure support, reducing work of breathing.
    • Improves alveolar ventilation (reduces PaCO_2), alleviates fatigue and cognitive impairment.
    • Recommended when FVC < 50% or PaCO_2 ≥ 45 mm Hg in neuromuscular disease.

Question 13: Requirements for Successful CPAP

• To use CPAP successfully, a patient must have adequate spontaneous ventilation.
• Secure Artificial Airway
  • An endotracheal tube or tracheostomy.
  • Incorrect because CPAP can be delivered noninvasively via mask; an artificial airway is not required and may actually be avoided using CPAP.
• Adequate PaO_2
  • Sufficient arterial oxygen tension.
  • Incorrect because while CPAP improves oxygenation, there is no minimum PaO_2 needed to initiate CPAP; patients with severe hypoxemia often benefit most.
• PaCO_2 >40 mm Hg
  • Elevated arterial carbon dioxide tension.
  • Incorrect because CPAP is not indicated based on PaCO2 level alone; in fact, CPAP does not provide ventilatory support (pressure support)—it may worsen CO2 retention in hypoventilators.
• Adequate Spontaneous Ventilation
  • The patient’s ability to initiate and maintain breathing efforts without ventilator-delivered tidal volumes.
  • Correct because CPAP provides continuous distending pressure but does not assist inspiration; patients must breathe spontaneously to generate tidal volumes and benefit from alveolar recruitment.

Question 14: Variable Ending Pressure Support Breaths

• Flow is the variable that ends pressure support breaths from a pressure-supported breath.
• Pressure
  • The set inspiratory pressure level in pressure support.
  • Incorrect because pressure is held constant during inspiration; it does not trigger breath termination.
• Flow
  • The patient’s inspiratory flow decays below a set threshold (commonly 25–30% of peak flow).
  • Correct because pressure support breaths are “flow-cycled,” ending when inspiratory flow falls to the cycling sensitivity.
• Time
  • A fixed inspiratory time.
  • Incorrect because time cycling applies to some modes (e.g., pressure control), but pressure support uses variable timing based on flow decay, not a preset duration.
• Volume
  • A target tidal volume.
  • Incorrect because volume is not measured to terminate support breaths; pressure support provides variable volume depending on patient effort and mechanics.

Question 15: Leading Cause of Patient Discomfort and Noncompliance with NIV

• Mask type and fit is the leading cause of patient discomfort and noncompliance with NIV.
• Mask Type and Fit
  • The design and seal of the interface (nasal, oronasal, full-face mask).
  • Correct because poorly fitting or uncomfortable masks cause air leaks, skin breakdown, pressure sores, and claustrophobia, leading patients to remove the mask and refuse therapy.
• Lack of an Oxygen Blender
  • Absence of a device to mix precise FiO_2 with pressurized air.
  • Incorrect because while accurate FiO_2 delivery is important, blender availability does not directly cause mask discomfort or interface intolerance.
• Drying of Nasal Mucosa
  • Desiccation of the nasal passages due to unhumidified gas flow.
  • Incorrect because it can cause discomfort and nasal congestion, but humidification systems and heated circuits typically mitigate this; it’s a less common reason for outright NIV refusal.
• Type of PTV (Positive-Pressure Ventilation)
  • The ventilator mode (e.g., CPAP vs. BiPAP).
  • Incorrect because choice of mode can affect efficacy but is rarely the primary driver of discomfort—interface issues dominate patient tolerance.