1.1 Airway Clearance & Suctioning

Airway Clearance & Suctioning

Proper airway clearance is paramount in critical care to prevent mucous plugging, maintain patency, and optimize gas exchange. In mechanically ventilated patients, the artificial airway bypasses the normal upper airway anatomy, which is responsible for heating, humidifying, and filtering inspired gas. This disruption paralyzes the mucociliary escalator and impairs the patient's ability to clear secretions through coughing. Consequently, the clinician must intervene using endotracheal suctioning.

Clinical Indications for Suctioning

Suctioning must be based on clinical assessment, never performed routinely. Key indications include:

• Auscultation of coarse rhonchi or crackles over the large airways.
• Visible secretions in the endotracheal or tracheostomy tube.
• A 'sawtooth' pattern on the ventilator's flow-volume loop.
• A sudden increase in PIP during volume-controlled ventilation, or a decrease in Vt during pressure-controlled ventilation.
• Patient-ventilator dyssynchrony.
• Acute respiratory distress or unexplained deterioration in SpO2.
• Suspected aspiration of gastric contents.

Open vs. Closed-Circuit Suctioning Systems

Suctioning can be performed using either an open-circuit or a closed-circuit (in-line) system. The clinical differences are significant:

In patients requiring high levels of positive end-expiratory pressure (PEEP > 10 cm H2O) or high fraction of inspired oxygen (FiO2 > 0.50), closed-circuit suctioning is mandatory to prevent severe alveolar derecruitment and refractory hypoxemia.

Suction Pressure Regulation

Suction pressure must be adjusted to the lowest effective level to minimize complications. The recommended ranges are:

• Adults: 100 to 120 mmHg (absolute maximum of 150 mmHg).
• Pediatrics: 80 to 100 mmHg.
• Neonates: 60 to 80 mmHg.

Exceeding these limits increases the risk of tracheal mucosal trauma, severe atelectasis, and vagal-mediated bradycardia.

Catheter Sizing Calculations

To prevent airway obstruction, the suction catheter's outer diameter (OD) must not exceed 50% of the ETT's internal diameter (ID) in adults. The sizing formula is:

$\text{Catheter Size (Fr)} = (\text{ETT Size (mm)} - 1) \times 2$

For example, an 8.0 mm ID ETT: $(8 - 1) \times 2 = 14 \text{ Fr}$

For a 7.0 mm ID ETT: $(7 - 1) \times 2 = 12 \text{ Fr}$

French size represents outer circumference. Dividing by 3 yields OD in millimeters. A 12 Fr catheter has an OD of 4.0 mm, which is exactly 50% of an 8.0 mm ID ETT. A 14 Fr catheter has an OD of approximately 4.67 mm; it is clinically standard but slightly exceeds 50%.

Step-by-Step Clinical Procedure

1. Assess the Patient: Verify clinical indications.
2. Pre-oxygenate: Deliver 100% FiO2 for 1-2 minutes. Modern ventilators have a 'Suction Support' button to automate this.
3. Catheter Insertion: Gently advance the catheter without suction until resistance is met (the carina), then withdraw 1-2 cm. This prevents tracheal injury.
4. Suction Application: Apply suction continuously or intermittently while rotating and withdrawing.
5. Duration Limit: Limit the suction pass to less than 15 seconds to prevent hypoxia.
6. Post-oxygenate: Re-administer 100% FiO2 for at least 1 minute.
7. Reassess: Check heart rate, rhythm, SpO2, and breath sounds.

The Normal Saline Instillation (Lavage) Controversy

Historically, instilling 3 to 5 mL of sterile normal saline (0.9% NaCl) into the ETT was common to thin secretions. Evidence-based guidelines strongly discourage this because saline is immiscible with mucus; it sits on top, forming droplets. Airflow can propel these droplets (carrying ETT biofilm) deeper into the lungs, increasing Ventilator-Associated Pneumonia (VAP) risk. Saline also triggers bronchospasm, desaturation, elevated ICP, and distress.

Instead, maximize humidification (heated humidifiers set to 37°C with 44 mg H2O/L), maintain hydration, or utilize nebulized acetylcysteine (10%) or hypertonic saline (3%) to mobilize thick secretions.

Complications and Clinical Interventions

• Vagal Response (Bradycardia): Direct mechanical stimulation of the carina can trigger the vagus nerve, causing a sudden drop in heart rate, heart blocks, or asystole. Action: Stop suctioning immediately, withdraw the catheter, and hyperoxygenate the patient with 100% oxygen. If bradycardia persists, administer atropine (0.5 mg IV) and initiate BLS/ACLS.
• Atelectasis: Prevented by maintaining closed-circuit suctioning, limiting suction duration, and ensuring the catheter size does not exceed the 50% ID rule.
• Mucosal Damage: Indicated by bloody secretions. Prevented by keeping suction pressure below 120 mmHg and ensuring the catheter is pulled back off the carina before suction is applied.

ACCS Exam Traps

• Trap 1: Choosing to instill normal saline to help mobilize thick secretions. The NBRC exam will penalize this choice; instead, select non-invasive humidification optimization or systemic hydration.
• Trap 2: Using an oversized catheter (e.g., a 14 Fr catheter for a 6.5 mm ETT). Always perform the formula calculation to ensure compliance with the 50% internal diameter safety limit.