Respiratory Failure and Ventilatory Support

Vocabulary practice flashcards covering respiratory failure classification, diagnostic blood gas criteria, bedside pulmonary function testing, lung expansion modalities, and mechanical ventilation adjustments from Egan's Chapters 45 and 50.

Respiratory Failure

The inability to maintain normal oxygen delivery to the tissues (oxygenation) or normal carbon dioxide removal from the tissues (ventilation), clinically diagnosed by a $\text{PaO}_2 < 60\text{ mm Hg}$ and/or a $\text{PaCO}_2 > 45\text{ mm Hg}$ while breathing room air at sea level.

Hypoxemic Respiratory Failure (Type I)

A form of respiratory failure characterized primarily by an abnormally low arterial oxygen level ($\text{PaO}_2$) resulting from conditions such as shunt or V/Q mismatch.

Hypercapnic Respiratory Failure (Type II)

A form of ventilatory failure characterized primarily by an elevated arterial carbon dioxide level ($\text{PaCO}_2 > 45\text{ mm Hg}$) accompanied by respiratory acidemia ($\text{pH} < 7.35$).

Ventilation/Perfusion (V/Q) Mismatch

An imbalance between alveolar ventilation and pulmonary capillary blood flow; it represents the most common cause of hypoxemia and is characterized by a significant improvement in $\text{PaO}_2$ in response to supplemental oxygen.

Right-to-Left Shunt

A physiological defect where blood moves from the right side of the heart to the left side without participating in gas exchange, producing refractory hypoxemia that shows minimal to no change in $\text{PaO}_2$ with supplemental oxygen.

Diffusion Impairment

A cause of hypoxemia arising from thickened or scarred alveolar membranes (as seen in pulmonary fibrosis or asbestosis) or alveolar wall destruction (as in emphysema).

Perfusion/Diffusion Impairment

A specialized mechanism of impaired oxygenation specifically observed in liver disease complicated by hepatopulmonary syndrome.

Simple Hypoventilation Rule

A clinical calculation indicating that respiratory failure is due to pure hypoventilation when the sum of $\text{PaO}_2 + \text{PaCO}_2$ breathing room air falls between $110\text{ mm Hg}$ and $130\text{ mm Hg}$.

Lung Dysfunction Calculation Rule

A diagnostic calculation indicating underlying pulmonary pathology (such as shunt, V/Q mismatch, or diffusion impairment) when the sum of $\text{PaO}_2 + \text{PaCO}_2$ breathing room air is $< 110\text{ mm Hg}$.

Alveolar-arterial Gradient ($P(A\text{-}a)O_2$)

A calculation measuring the difference between alveolar and arterial oxygen tensions (normal on room air: $10\text{ to }15\text{ mm Hg}$); an elevated gradient points to intrinsic lung dysfunction rather than simple hypoventilation.

Platypnea and Orthodeoxia

Clinical signs characterized by dyspnea and arterial oxygen desaturation that worsen when transitioning from a recumbent to an upright position, commonly associated with right-to-left shunts or hepatopulmonary syndrome.

Vital Capacity (VC)

A bedside pulmonary function parameter measuring the maximum volume exhaled after maximal inhalation (normal: $65\text{--}75\text{ mL/kg}$); values $< 10\text{--}15\text{ mL/kg}$ indicate inadequate reserve and the need for ventilatory support.

Negative Inspiratory Force (NIF) / Maximum Inspiratory Pressure (MIP)

A test measuring inspiratory muscle strength (normal: $-50\text{ to }-100\text{ cm H}_2\text{O}$); a value weaker than $-20\text{ to }-30\text{ cm H}_2\text{O}$ indicates respiratory muscle fatigue and signals the need for ventilatory support.

Non-Invasive Ventilation (NIV)

Positive pressure ventilatory support delivered without an invasive artificial airway; it is the gold standard, first-line therapy for acute exacerbations of COPD with hypercapnic respiratory failure.

Positive End-Expiratory Pressure (PEEP)

A mechanical ventilation modality that maintains positive pressure during expiration to recruit collapsed alveoli, increase surface area, and improve refractory hypoxemia caused by shunting.

Inspiratory Positive Airway Pressure (IPAP)

The higher pressure setting delivered during inhalation in non-invasive ventilation (BiPAP) that governs ventilation and aids in decreasing $\text{PaCO}_2$ by increasing tidal volume ($V_T$).

Expiratory Positive Airway Pressure (EPAP)

The baseline pressure setting delivered during exhalation in non-invasive ventilation (BiPAP) that acts similarly to PEEP to recruit alveoli, increase functional residual capacity, and improve $\text{PaO}_2$.

Driving Pressure (Pressure Support)

The mathematical difference between inspiratory and expiratory pressures ($\text{IPAP} - \text{EPAP}$) that directly determines the size of the delivered tidal volume ($V_T$).

Incentive Spirometry (IS)

A lung expansion therapy coaching patients to perform a sustained maximal inspiratory (SMI) maneuver held for $5\text{ to }10\text{ seconds}$ to decrease pleural pressure ($P_{pl}$) and increase lung volume.

Positive Expiratory Pressure (PEP) Therapy

A lung expansion and airway clearance modality utilizing threshold, resistor, or flutter valves to generate positive expiratory pressure, increasing functional residual capacity and mobilizing secretions.

Continuous Positive Airway Pressure (CPAP)

A ventilatory therapy that applies constant positive pressure throughout both inhalation and exhalation, primarily utilized for treating atelectasis and cardiogenic pulmonary edema.

Intermittent Positive Pressure Breathing (IPPB)

A specialized non-invasive lung expansion therapy providing short-term, machine-assisted positive pressure breaths to patients who cannot perform incentive spirometry or have not responded to other therapies.

Open Suctioning

A tracheobronchial clearance technique performed through an artificial airway using a single-use suction catheter, clinically indicated for copious secretions ($20\text{--}30\text{ mL/day}$) or an ineffective cough.