Paroxysmal Nocturnal Dyspnea (PND) — 5 Marks (Physiotherapy in CVTS)

Definition

Mechanism / Pathophysiology

1. On lying supine, blood that has pooled in the dependent extremities and splanchnic (abdominal) circulation during the day is redistributed back into the central circulation.
2. This increases venous return and raises left ventricular preload.
3. In a failing left ventricle that cannot accommodate the extra volume, pulmonary venous and pulmonary capillary hydrostatic pressures rise sharply.
4. This drives fluid into the pulmonary interstitium and alveoli (pulmonary congestion/interstitial edema), reducing lung compliance and increasing the work of breathing - Goldman-Cecil Medicine, p. 2320.
5. Additional contributing factors: during sleep, the respiratory center's sensitivity is depressed, and there is reduced adrenergic (sympathetic) support to the failing myocardium, both of which allow congestion to build up unnoticed until it becomes severe enough to abruptly wake the patient (Fuster and Hurst's The Heart, p. 1406-1407).

Clinical Features

• Sudden violent attack of breathlessness and coughing, usually 1-2 hours after falling asleep.
• Patient wakes up gasping for air, often sits up, dangles legs over the bed, or moves to a window for air.
• May be accompanied by wheeze ("cardiac asthma"), anxiety, diaphoresis, and cough (sometimes with pink, frothy sputum in severe pulmonary edema).
• Symptoms characteristically improve within 10-30 minutes of assuming the upright position, as gravity redistributes fluid away from the lungs - unlike orthopnea, which resolves almost immediately on sitting up.
• Associated symptoms of heart failure: orthopnea, dyspnea on exertion, fatigue, peripheral edema, bilateral basal crackles - Goldman-Cecil Medicine, p. 3465-3472.

Distinction from Orthopnea

Relevance in Physiotherapy / CVTS Assessment and Management

• Subjective assessment: PND is a key history-taking marker of decompensated left heart failure; number of pillows used and history of PND/orthopnea help grade severity and guide safe positioning for treatment.
• Positioning: Patients with PND should be treated and positioned in a semi-recumbent or upright/high Fowler's position rather than fully supine, to minimize venous return and pulmonary congestion during physiotherapy sessions (chest physiotherapy, breathing exercises, mobilization).
• Exercise prescription: Indicates a need for cautious, graded exercise progression and closer monitoring of vital signs, SpO2, and fatigue in cardiac rehabilitation.
• Precaution/red flag: A worsening history of PND signals decompensating heart failure - physiotherapists should communicate this to the medical team before intensifying exercise or chest physiotherapy techniques (e.g., postural drainage in head-down tilt is contraindicated).
• Post-cardiac surgery (CVTS) relevance: In post-CABG/valve surgery patients, new or worsening PND may indicate fluid overload or early left ventricular dysfunction, requiring modification of the physiotherapy plan and prompt medical reporting.

Effects of Anesthesia on the Cardiorespiratory System (4 Key Effects)

1. Decreased Functional Residual Capacity (FRC) and Atelectasis

• The supine position itself reduces FRC by 0.8-1.0 L, and induction of general anesthesia further reduces it by another 0.4-0.5 L - Morgan and Mikhail's Clinical Anesthesiology, 7e, p. 908.
• This drop is caused by loss of inspiratory muscle (diaphragmatic) tone, an upward shift of the diaphragm, and increased chest wall rigidity, which together produce compression atelectasis (alveolar collapse), especially in dependent lung zones.
• Physiotherapy relevance: This is the primary rationale for early post-op deep breathing exercises, incentive spirometry, and positioning to re-expand collapsed alveoli and restore FRC.

2. Ventilation-Perfusion (V/Q) Mismatch and Increased Intrapulmonary Shunting

• General anesthesia commonly increases venous admixture (shunt) to 5-10%, because desaturated blood passes through poorly ventilated/collapsed alveolar units without being oxygenated - Morgan and Mikhail's Clinical Anesthesiology, 7e, p. 908.
• The reduced FRC relative to closing capacity is the most common cause of hypoxemia seen after general anesthesia and in the post-anesthesia care unit (PACU).
• Physiotherapy relevance: Explains why postural drainage, mobilization, and breathing exercises are used to improve oxygenation and prevent hypoxemia in the immediate post-op period.

3. Myocardial Depression and Reduced Cardiac Contractility

• Potent inhalational (volatile) anesthetic agents directly depress myocardial contractility by decreasing calcium entry into cells during depolarization and reducing the sensitivity of contractile proteins to calcium - Morgan and Mikhail's Clinical Anesthesiology, 7e, p. 638.
• They also depress sinoatrial (SA) node automaticity and slow atrioventricular (AV) conduction, which can predispose to bradycardia or junctional rhythms.
• Physiotherapy relevance: Patients, especially those with pre-existing cardiac impairment, are more vulnerable to acute cardiac decompensation after induction (due to withdrawal of sympathetic/catecholamine support) - this guides cautious, graded mobilization and continuous hemodynamic monitoring during early post-op physiotherapy.

4. Vasodilation, Hypotension, and Altered Hemodynamics

• Anesthetic agents cause systemic vasodilation and reduce sympathetic vasomotor tone, leading to a fall in systemic vascular resistance and blood pressure.
• Combined with reduced venous return (from positioning and positive-pressure ventilation) and depressed contractility, this can significantly lower cardiac output, particularly in patients with poor ventricular reserve.
• Physiotherapy relevance: Explains the importance of slow position changes (e.g., gradual sit-up rather than abrupt standing) to avoid orthostatic hypotension, and close monitoring of blood pressure and heart rate before starting exercise or ambulation post-surgery.

Precautions During Suctioning (For Physiotherapy Students)

1. Pre-Procedure Precautions

• Monitoring setup: Attach continuous pulse oximetry, cardiac monitoring, and capnography (if available) before starting.
• Positioning: Awake, alert patients should sit upright with the head in a neutral position; mechanically ventilated patients should have the head of the bed elevated to 30 degrees to optimize respiratory mechanics.
• Preoxygenation: Preoxygenate for 30-60 seconds before suctioning - increase FiO2 to 100% in ventilated patients, or give 10-15 L high-flow oxygen in non-ventilated patients, to buffer against suction-induced hypoxia.
• Aseptic technique: Use sterile, single-use catheters and a no-touch/aseptic technique throughout to prevent introducing infection.
• Backup equipment ready: Have emergency airway equipment immediately available in case of complications.

2. Precautions During the Procedure

• Catheter size: Use the correct catheter size (French size = 2 x [tracheal tube size - 2]) to avoid excessive occlusion of the airway.
• Suction pressure: Keep vacuum pressure as low as possible - do not exceed 80 mmHg in infants or 150 mmHg in adults - to minimize mucosal trauma and atelectasis.
• Duration: Limit each suction pass to no more than 10-15 seconds to avoid significant hypoxia, especially in children.
• Technique: Insert the catheter without suction, withdraw 1-2 cm from the point of resistance/cough, then apply suction while gently rotating and slowly withdrawing the catheter - never suction on insertion.
• Avoid routine saline instillation: Routine normal saline instillation before suctioning has no proven benefit and is no longer recommended.
• Continuous monitoring: Watch for cardiac dysrhythmia, hypoxia (falling SpO2), or rising end-tidal CO2 throughout - stop suctioning immediately if any of these develop.

3. Key Complications to Watch For (Rationale for Precautions)

• Hypoxemia - from interruption of oxygen delivery and removal of air along with secretions.
• Cardiac dysrhythmias/bradycardia - caused by vagal stimulation, hypoxia, increased myocardial oxygen demand, or catecholamine release; bradycardia with hypoxia can potentiate dangerous ventricular arrhythmias - Roberts and Hedges' Clinical Procedures in Emergency Medicine, p. 207.
• Increased intracranial pressure - relevant in neuro patients, so suction duration and frequency must be minimized.
• Mucosal injury and bleeding - from catheter tip trauma or invagination of mucosa into catheter side ports, which also impairs mucociliary clearance and predisposes to infection/tracheitis.
• Atelectasis - from excessive negative pressure removing too much air from the lungs.
• Patient agitation/discomfort - explain the procedure to a conscious patient beforehand where possible.

4. General Rule for Physiotherapy Practice

Precautions During Suctioning (For Physiotherapy Students)

1. Pre-Procedure Precautions

• Monitoring setup: Attach continuous pulse oximetry, cardiac monitoring, and capnography (if available) before starting.
• Positioning: Awake, alert patients should sit upright with the head in a neutral position; mechanically ventilated patients should have the head of the bed elevated to 30 degrees to optimize respiratory mechanics.
• Preoxygenation: Preoxygenate for 30-60 seconds before suctioning - increase FiO2 to 100% in ventilated patients, or give 10-15 L high-flow oxygen in non-ventilated patients, to buffer against suction-induced hypoxia.
• Aseptic technique: Use sterile, single-use catheters and a no-touch/aseptic technique throughout to prevent introducing infection.
• Backup equipment ready: Have emergency airway equipment immediately available in case of complications.

2. Precautions During the Procedure

• Catheter size: Use the correct catheter size (French size = 2 x [tracheal tube size - 2]) so it does not excessively occlude the airway.
• Suction pressure: Keep vacuum pressure as low as possible - not exceeding 80 mmHg in infants or 150 mmHg in adults - to minimize mucosal trauma and atelectasis.
• Duration: Limit each suction pass to no more than 10-15 seconds to avoid significant hypoxia, especially in children.
• Technique: Insert the catheter without applying suction, withdraw 1-2 cm from the point of resistance/cough, then apply suction while gently rotating and slowly withdrawing the catheter - never suction on insertion.
• Avoid routine saline instillation: Routine normal saline instillation before suctioning has no proven clinical benefit and is no longer recommended.
• Continuous monitoring: Watch for cardiac dysrhythmia, hypoxia (falling SpO2), or rising end-tidal CO2 throughout the procedure - stop immediately if any of these develop.

3. Key Complications to Watch For (Rationale for the Above Precautions)

• Hypoxemia - from interrupting oxygen delivery and removing air along with secretions.
• Cardiac dysrhythmias/bradycardia - caused by vagal stimulation, hypoxia, increased myocardial oxygen demand, or catecholamine release; bradycardia combined with hypoxia can potentiate dangerous ventricular arrhythmias - Roberts and Hedges' Clinical Procedures in Emergency Medicine, p. 207.
• Increased intracranial pressure - important in neuro patients, so suction duration and frequency must be minimized.
• Mucosal injury and bleeding - from catheter tip trauma or mucosal invagination into catheter side ports, which also impairs mucociliary clearance and predisposes to infection/tracheitis.
• Atelectasis - from excessive negative pressure removing too much air from the lungs.
• Patient agitation/discomfort - explain the procedure to a conscious patient beforehand where possible.

4. General Rule for Physiotherapy Practice