10.6 Thoracic Decompression & Chest Drains
Key Takeaways
- In a 3-chamber chest drainage system, tidaling reflects normal respiratory intrapleural pressure swings, while continuous bubbling in the water seal chamber indicates an active patient air leak or circuit disconnection.
- The neonatal spinnaker-sail sign supports pneumomediastinum, while a circumferential pericardial air halo supports pneumopericardium. Hemodynamic tamponade—not the image alone—requires emergency pericardial decompression.
- Suction applied to the pleural space is set by the water depth in the suction control chamber - typically -10 to -20 cmH2O in children and -5 to -10 cmH2O in neonates - not by the wall regulator dial.
- Emergency needle decompression for tension pneumothorax precedes radiography; a 20-gauge catheter is placed in the second intercostal space at the midclavicular line over the superior margin of the third rib.
10.6 Thoracic Decompression & Chest Drains
The Three-Chamber Chest Drainage System
Modern wet-suction chest drainage units combine three interconnected chambers in a single sterile canister.
+-------------------------------------------------------------------------------------------------------------+
| THREE-CHAMBER CHEST DRAINAGE SYSTEM |
+------------------------------------+------------------------------------+-----------------------------------+
| Chamber 1: Collection Chamber | Chamber 2: Water Seal Chamber | Chamber 3: Suction Control Chamber|
+------------------------------------+------------------------------------+-----------------------------------+
| - Receives drainage fluid, blood, | - Acts as a one-way valve: gas | - Regulates negative pressure |
| and exudate from pleural space. | escapes, but air cannot re-enter.| applied to pleural cavity. |
| - Calibrated for volume, rate, and | - Filled with sterile water to the | - Determined by WATER DEPTH |
| fluid character assessment. | 2 cmH2O line. | (-10 to -20 cmH2O in pediatrics;|
| - Fluid does not affect suction or | - Shows TIDALING with respiration. | -5 to -10 cmH2O in neonates). |
| water seal function. | - Bubbling = AIR LEAK. | - Gentle continuous bubbling. |
+------------------------------------+------------------------------------+-----------------------------------+
1. Water Seal Chamber: Tidaling vs. Bubbling
- Tidaling (Respiratory Fluctuation): The water level in the narrow column normally fluctuates with intrapleural pressure swings during breathing:
- Spontaneous Breathing: During inspiration, negative intrapleural pressure pulls the water column UP; during expiration, positive pressure pushes the water column DOWN.
- Positive Pressure Ventilation: During mechanical inspiration, positive pressure pushes the water column DOWN; during exhalation, the water column rises UP.
- Absence of Tidaling: Indicates either that the lung has completely re-expanded and sealed against the parietal pleura, OR the chest tube is occluded by a blood clot, kinked, or clamped.
- Air Leak Bubbling: Air exiting the pleural space bubbles through the water seal column:
- Intermittent Bubbling: Bubbling only during exhalation, coughing, or Valsalva maneuvers is normal while an active pneumothorax is evacuating.
- Continuous Bubbling: Bubbling throughout both inspiration and expiration signifies a large, continuous air leak: either a persistent bronchopleural fistula / parenchymal tear, or an external system leak.
2. Suction Control Chamber
The negative pressure applied to the patient's pleural space is strictly determined by the depth of the water column in the suction control chamber, NOT by the wall suction regulator!
- Prescribed Levels: Typically $-10\text{ to } -20\text{ cmH}_2\text{O}$ in pediatric patients, and $-5\text{ to } -10\text{ cmH}_2\text{O}$ in neonates.
- Bubbling Mechanics: The wall suction regulator should be dialed until gentle, slow bubbling appears in the suction chamber. Turning the wall regulator higher does not increase suction to the patient; it merely generates loud noise and rapidly evaporates the water column, dangerously lowering suction depth.
3. Systematic Troubleshooting of an Air Leak
When unexpected continuous bubbling appears in the water seal chamber, the clinician must systematically locate the source:
Continuous Bubbling in Water Seal Chamber
|
[ FIRST: Inspect patient, insertion site, tubing, and connections ]
|
+------------+------------+
| |
Bubbling STOPS Bubbling PERSISTS
| |
Source is PATIENT Source is EXTERNAL
(Parenchymal leak, (Tubing or canister leak)
bronchopleural fistula) |
[ THEN: Use supervised protocol-directed isolation only if safe ]
|
+------------+------------+
| |
Bubbling STOPS Bubbling PERSISTS at canister
| |
Connection loose Canister cracked / defective
(Tape or replace) (Replace drainage unit)
Pneumomediastinum, Pneumopericardium, and Subcutaneous Emphysema
| Condition | Anatomical Location & Mechanism | Hallmark Radiographic Sign | Clinical Manifestations & Management |
|---|---|---|---|
| Pneumomediastinum | Air dissects along bronchovascular sheaths into mediastinum. | "Spinnaker Sail Sign" (Angel Wing Sign): Thymic lobes elevated and pushed laterally/superiorly by retrosternal air. | Usually benign and asymptomatic. Auscultation reveals Hamman's sign (precordial crunching synchronous with heartbeat). Supportive care; rarely requires drainage. |
| Pneumopericardium | Air enters pericardial sac, completely encircling the myocardium. | Continuous radiolucent halo completely outlining the pericardial perimeter, not extending beyond great vessel reflections. | Causes cardiac tamponade: distant/muffled heart tones, narrow pulse pressure, severe hypotension, electrical alternans. Emergency subxiphoid needle pericardiocentesis. |
| Subcutaneous Emphysema | Gas dissects through soft tissue planes of neck, chest, and face. | Streaky radiolucency in subcutaneous tissue planes; soft tissue swelling. | Palpable cutaneous crepitus ("Rice Krispies" sensation). Benign resorptive course; manage underlying airway leak. |
Worked Clinical Case: Thoracic Emergency in the NICU
A 3-day-old full-term infant ($3,400\text{ g}$) with severe meconium aspiration syndrome is ventilated on conventional volume-targeted ventilation (PIP $28\text{ cmH}_2\text{O}$, PEEP $7\text{ cmH}_2\text{O}$, $FiO_2\ 0.55$). Suddenly, the ventilator high-pressure alarm sounds, and the infant's heart rate plummets from $145\text{ bpm}$ to $62\text{ bpm}$. Blood pressure drops to $32/16\text{ mmHg}$, and $SpO_2$ falls from $95%$ to $58%$.
Stepwise Emergency Management:
- Immediate Bedside Triage: The patient is in acute obstructive shock. Auscultation reveals completely absent breath sounds over the right hemithorax with hyperresonance. The trachea is deviated to the left. A cold-light examination in a dimmed room produces an unusually broad glow over the right hemithorax, supporting the already evident tension physiology.
- Emergency Needle Decompression: Without waiting for a chest radiograph, the respiratory therapist and neonatologist perform emergent needle thoracostomy. A $20\text{-gauge}$ angiocatheter attached to a saline-filled syringe is inserted into the 2nd intercostal space at the right midclavicular line directly over the superior margin of the 3rd rib. Pressurized air escapes and the team reassesses heart rate, pressure, oxygenation, breath sounds, and catheter function while preparing definitive drainage.
- Definitive Tube Thoracostomy: An age-appropriate pleural drain is placed at the protocol-selected lateral site and connected to the prescribed drainage system and suction setting.
- Drainage Assessment: Tidaling is observed in the water seal column. Intermittent bubbling occurs with exhalation, confirming successful evacuation of the pneumothorax. Post-procedure radiograph confirms full re-expansion of the right lung with the chest tube positioned apically.
NPS Exam Traps
Exam Trap 1: The "Wait for the X-Ray" Trap
On clinical simulation and multiple-choice questions, when a patient displays acute hypotension, bradycardia, cyanosis, and asymmetrical breath sounds following positive pressure ventilation, examiners will offer "Order a STAT portable chest radiograph" as a distractor. Never pick the radiograph in an unstable patient. The correct answer is immediate needle decompression. Obtaining a radiograph in tension pneumothorax results in cardiac arrest before the film can be developed.
Exam Trap 2: Increasing Wall Suction for Water Seal Bubbling
Continuous water-seal bubbling suggests an air leak; increasing wall suction does not locate it. A trained clinician may briefly use a padded clamp during supervised troubleshooting when the protocol permits, but never leave the tube clamped and avoid clamping when a continuing air leak could recreate tension physiology. Inspect connections and the insertion site first.
Exam Trap 3: Positioning PIE With the "Good Lung Down"
For unilateral PIE, affected-side-down positioning can reduce ventilation to the diseased lung and is a monitored option alongside pressure/volume reduction and specialist high-frequency ventilation. Response is variable; reassess oxygenation, ventilation, perfusion, and imaging rather than treating position as mandatory or assuming ordinary “good lung down” physiology applies unchanged.
A 7-year-old child with severe necrotizing pneumonia has a 16-Fr chest tube connected to a 3-chamber water-seal drainage system set to -15 cmH2O suction following drainage of an empyema and pneumothorax. The respiratory therapist observes vigorous, continuous bubbling in the water seal chamber throughout both inspiration and expiration. Tidaling in the water seal chamber is present. The therapist briefly applies a padded clamp to the chest tube at the patient's thoracic insertion site, and the continuous bubbling in the water seal chamber immediately ceases. What does this clinical finding indicate, and what is the appropriate interpretation?