3.5 Airway Suctioning Technique & Safety
Key Takeaways
- Set the lowest suction pressure that clears secretions and follow neonatal or pediatric device policy; commonly taught starting ranges are about 60–80 mmHg in neonates and 80–100 mmHg in older infants and children.
- Choose a catheter whose external diameter occupies no more than about half the ETT lumen; (ETT ID in mm − 1) × 2 is a practical French-size estimate.
- Prefer measured shallow suction to the tube tip, apply suction during withdrawal, limit each pass, and reassess heart rate, saturation, ventilation, and secretions. Deep suction is reserved for a specific indication and protocol.
3.5 Airway Suctioning Technique & Safety
Endotracheal suctioning and bronchopulmonary hygiene are essential interventions to maintain artificial airway patency, eliminate retained tracheobronchial secretions, and treat atelectasis. However, in neonatal and pediatric patients, improper technique carries severe risks of hypoxemia, cardiac arrhythmias, airway mucosal denudation, and intracranial hemorrhage. Strict adherence to age-specific clinical parameters is tested rigorously on the NBRC NPS examination.
Endotracheal Suctioning Pressures, Duration & Pre-Oxygenation
1. Suction Vacuum Pressures
Subatmospheric vacuum pressures must be calibrated with the suction tubing occluded prior to catheter insertion:
- Neonates (Preterm and Term): 60 to 80 mmHg
- Infants and Pediatric Patients: 80 to 100 mmHg
- (Adult vacuum pressures range from 100 to 120 mmHg for comparison).
Pathophysiology of Excessive Vacuum: Applying vacuum pressures exceeding these thresholds does not improve secretion clearance. Instead, excessive negative pressure rapidly exhausts functional residual capacity (FRC), collapses unstable alveolar units, avulses delicate respiratory ciliated epithelium, and produces transmural mucosal petechiae and hemorrhage.
2. Duration of Vacuum Application
Negative pressure application must be strictly time-limited:
- Neonates: ≤5 seconds
- Pediatric Patients: ≤5 to 10 seconds Total procedure time (from catheter insertion to withdrawal) should never exceed 10 to 15 seconds. Suction must be applied intermittently or continuously only during catheter withdrawal, never during catheter insertion.
3. Pre-Oxygenation
Do not increase oxygen automatically for every suction pass. For a patient who predictably desaturates, pre-oxygenate using the smallest temporary increase that achieves the prescribed saturation target, then return promptly to baseline. Avoid both suction-related hypoxemia and unnecessary hyperoxemia, especially in preterm infants; the exact FiO2 and duration depend on baseline oxygen need and local protocol.
Catheter Sizing Formulas and the 50% to 70% Rule
Using an oversized suction catheter is a primary cause of severe clinical atelectasis during artificial airway suctioning.
1. French Sizing Formula
To determine the appropriate external suction catheter size based on endotracheal tube (ETT) internal diameter (ID):
Worked Sizing Calculations:
- For a 3.0 mm ETT: $(3.0 - 1) \times 2 = 2 \times 2 = \mathbf{4\text{ Fr}}$ (or 5–6 Fr based on availability).
- For a 3.5 mm ETT: $(3.5 - 1) \times 2 = 2.5 \times 2 = \mathbf{5\text{ Fr}}$ (or 6 Fr).
- For a 4.0 mm ETT: $(4.0 - 1) \times 2 = 3 \times 2 = \mathbf{6\text{ Fr}}$.
- For a 5.0 mm ETT: $(5.0 - 1) \times 2 = 4 \times 2 = \mathbf{8\text{ Fr}}$.
- For a 6.0 mm ETT: $(6.0 - 1) \times 2 = 5 \times 2 = \mathbf{10\text{ Fr}}$.
2. The 50% to 70% Internal Diameter Rule
The French gauge scale measures external circumference (where $1\text{ French} = 1/3\text{ mm}$ outer diameter). To prevent airway obstruction during suctioning:
- Neonatal Airways: The outer diameter (OD) of the suction catheter should not exceed 50% of the ETT internal diameter.
- Pediatric Airways: The outer diameter of the suction catheter should not exceed 70% of the ETT internal diameter.
Mechanical Principles: When vacuum is applied, air must be entrained from the atmosphere into the lungs through the annular space between the catheter's exterior and the ETT's interior wall. If the catheter occupies $>70%$ of the lumen, it acts as a mechanical piston. The vacuum draws directly from alveolar gas volume, plunging intrathoracic pressure to subatmospheric levels, collapsing airways, and causing immediate, severe hypoxemia and bilateral microatelectasis.
Table 3.3.1: Airway Sizing, Catheter Selection, and Suction Settings
| ETT Size (mm ID) | Formula Calculated Size | Recommended Catheter | Catheter OD (mm) | Ratio (OD / ID) | Vacuum Setting Limit |
|---|---|---|---|---|---|
| 2.5 mm | 3.0 Fr | 5.0 Fr | 1.67 mm | 67% (use short duration) | 60–80 mmHg |
| 3.0 mm | 4.0 Fr | 5.0 or 6.0 Fr | 1.67–2.0 mm | 55–66% | 60–80 mmHg |
| 3.5 mm | 5.0 Fr | 6.0 Fr | 2.0 mm | 57% | 60–80 mmHg |
| 4.0 mm | 6.0 Fr | 6.0 or 8.0 Fr | 2.0–2.67 mm | 50–67% | 80–100 mmHg |
| 5.0 mm | 8.0 Fr | 8.0 or 10.0 Fr | 2.67–3.33 mm | 53–67% | 80–100 mmHg |
| 6.0 mm | 10.0 Fr | 10.0 Fr | 3.33 mm | 55% | 80–100 mmHg |
Suctioning Technique: Shallow vs. Deep & The Saline Lavage Controversy
1. Shallow (Measured) Suctioning Technique
Routine artificial-airway suction should use a measured shallow technique:
- Advance only to the premeasured tube-tip depth specified by the airway and suction protocol; adapter length and catheter markings must be accounted for.
- Avoid unnecessary contact with the carina or distal mucosa.
- Apply suction during withdrawal for the shortest effective pass, then reassess ventilation, heart rate, saturation, and secretions.
2. Dangers of Deep Suctioning
Deep suctioning involves advancing the catheter until physical resistance is encountered at the carina or mainstem bronchus, withdrawing 1 cm, and applying vacuum.
- Deep suction is not routine: It increases mucosal-trauma, bleeding, bradycardia, hypoxemia, and airway-injury risk. Reserve it for a specific indication—such as retained secretions not cleared by shallow suction—and follow the neonatal or pediatric protocol with careful depth and response monitoring.
3. The Normal Saline Lavage Controversy
Historically, clinicians instilled 0.5 to 2.0 mL of sterile 0.9% normal saline (NaCl) into the endotracheal tube prior to suctioning under the assumption that it thinned thick secretions.
Current Evidence and AARC Clinical Practice Guidelines strongly condemn routine saline instillation:
- Immiscibility: Mucus is a complex viscoelastic glycoprotein gel, whereas saline is an aqueous electrolyte solution. Saline does not mix with, dilute, or thin inspissated mucus; instead, it simply forms droplets that roll over sputum plugs.
- Biofilm Dislodgement and VAP: In intubated patients, an extensive bacterial biofilm lines the internal lumen of the ETT within 48 hours. Instilling saline flushes dislodged bacterial aggregates deep into the sterile lower respiratory tract and distal alveoli, dramatically increasing the incidence of ventilator-associated pneumonia (VAP).
- Severe Gas Exchange Deterioration: Saline instillation washes out endogenous pulmonary surfactant, precipitates ventilation-perfusion ($\dot{V}/\dot{Q}$) mismatch, and induces prolonged drops in arterial oxygen saturation ($SpO_2$) lasting up to 30 minutes.
- Adverse Reflexes: Saline triggers severe paroxysmal coughing, acute bronchospasm, and sharp spikes in intracranial pressure (ICP).
Clinical standard: Optimize systemic hydration when appropriate, active humidification, and disease-specific clearance or mucolytic therapy. Routine normal-saline instillation before suctioning is not recommended because it can worsen desaturation, discomfort, and contamination; a protocol may reserve small-volume saline for selected tenacious plugs after other causes are addressed.
A neonatal respiratory therapist is preparing to perform endotracheal suctioning on a mechanically ventilated 2-week-old infant intubated with a 3.5 mm internal diameter (ID) endotracheal tube. What suction catheter size and maximum suction vacuum pressure should be selected to ensure safe secretion clearance?
A 27-week gestational age neonate (current weight 920 grams) intubated for respiratory distress syndrome develops left lower lobe atelectasis on day 4 of life. A junior clinician suggests placing the neonate in a steep Trendelenburg (head-down) position for postural drainage and chest percussion. What is the primary clinical rationale for withholding this position in this infant?