9.1 Obstructive Shock
Key Takeaways
- Obstructive shock is a mechanical block to inflow or outflow—volume will not fix tension pneumothorax, tamponade, massive PE, or aortocaval compression.
- Treat tension pneumothorax with needle or finger decompression and an unclamped chest tube before climb; Boyle expands residual pleural air.
- Tamponade shows Beck signs, electrical alternans, and FAST fluid; pericardiocentesis is last-ditch and the destination is an OR or window-capable ED.
- Massive PE needs RV support and avoidance of high PEEP; a gravid uterus needs left uterine displacement, not another unthinking liter.
- Do not clamp a bubbling chest tube for flight; use ultrasound if carried to separate obstruction from hypovolemia.
Obstructive shock is a plumbing problem: the tank is full and the pump can squeeze, but a block to inflow or outflow collapses stroke volume. Domain 2.C.2.b of the August 2026 Board of Certification for Emergency Nursing (BCEN) Certified Flight Registered Nurse (CFRN) outline tests obstructive shock because Boyle's law makes several of those blocks worse on climb. Volume will not fix a mechanical obstruction. Treat it on the ground, then fly to a destination that can finish it.
Tension pneumothorax: treat before climb
Why altitude turns a small leak into a crisis
A tension pneumothorax is pressurized pleural air that collapses the lung, shifts the mediastinum, and kinks venous return. Expect progressive distress, unilateral chest rise, late tracheal deviation, jugular venous distention (JVD), falling saturation of peripheral oxygen (SpO2) and end-tidal carbon dioxide (ETCO2), and shock that looks like hypovolemia until you notice the neck veins and the asymmetric chest. Trust the chest wall, the trend, and point-of-care ultrasound (POCUS) if carried: absent lung sliding and a barcode M-mode pattern support pneumothorax. Auscultation will not help.
Boyle's law says gas volume rises as ambient pressure falls. Residual pleural air that is barely tolerated at the dock expands on an unpressurized climb. Treat before takeoff. Do not watch a borderline pneumothorax at 6,000 feet.
Needle, finger, then a real tube
Decompress on the ground:
- Needle thoracostomy is a bridge: a long large-bore catheter in the second intercostal space, midclavicular line, or the fifth intercostal space, midaxillary line. A hiss helps; a silent short catheter proves nothing.
- Finger (simple) thoracostomy is the more reliable field decompression in many programs: incision, blunt dissection, finger into the pleura, then a tube.
- A chest tube is the durable fix. Use an unclamped underwater seal or a Heimlich / flutter valve, with extra collection volume because residual gas and output increase with altitude.
Do not clamp a bubbling chest tube for flight. A bubbling tube is venting expanding pleural gas. Clamping it recreates tension as cabin altitude rises.
Tamponade and the operating room, not the needle first
Beck, electrical alternans, and FAST
Cardiac tamponade is intrapericardial pressure that equalizes filling and starves the right heart of preload. Beck's triad—hypotension, JVD, and muffled heart sounds—is classic and incomplete. You will not hear muffled tones in a helicopter. Look for a narrow pulse pressure, pulsus paradoxus on an arterial line, electrical alternans (beat-to-beat QRS amplitude change), and a low-voltage QRS. Focused Assessment with Sonography in Trauma (FAST) or a cardiac window, if you are trained, shows pericardial fluid and right-chamber collapse.
A small fluid bolus can buy minutes if the patient is empty and tamponaded; it is not the therapy. Pericardiocentesis is last-ditch when the patient is peri-arrest and an operating room is not immediately available. Destination is an operating room (OR) or a capable emergency department that can do a window or thoracotomy, not a clinic.
Massive pulmonary embolism, abdomen, and the gravid uterus
Right-ventricular strain and the ventilator
Massive pulmonary embolism (PE) obstructs the pulmonary arteries. The right ventricle (RV) dilates, the septum bows left, and output falls with a relatively clear left lung. Hypotension plus RV strain on ultrasound or a right-strain electrocardiogram (ECG) (right bundle-branch block, T-wave inversion in V1–V4, or S1Q3T3) is the picture. Support first: oxygen, cautious fluid only if the RV looks empty, and norepinephrine for coronary perfusion to the strained RV. Thrombolysis is a destination-and-risk conversation with the receiving team. Avoid high positive end-expiratory pressure (PEEP)—it starves RV preload and raises RV afterload.
Abdominal compartment and aortocaval compression
Abdominal compartment syndrome and a gravid uterus both obstruct the inferior vena cava (IVC). A tense post-resuscitation abdomen kinks venous return the way tamponade does from below—stop flooding it and fly to a surgeon who can decompress. In the third trimester, aortocaval compression is positional: the uterus sits on the IVC and aorta when the patient is packaged supine. Left uterine displacement (LUD)—manual displacement or a left tilt that still protects the spine—restores preload. If she snaps back when you move the uterus, that was obstruction, not missing volume.
| Obstruction | Hallmark | First move | Destination |
|---|---|---|---|
| Tension pneumothorax | Asymmetric chest, JVD, no sliding | Needle or finger, then unclamped tube, before climb | Thoracic-capable ED |
| Tamponade | Beck signs, electrical alternans, FAST fluid | Limited fluid; pericardiocentesis if peri-arrest | OR or window-capable ED |
| Massive PE | Shock plus RV strain, clearer lungs | Support, norepinephrine, avoid high PEEP | PE-capable center |
| Abdominal or gravid IVC | Tense abdomen or supine gravid hypotension | Stop flooding; LUD | Surgical or obstetric OR |
Not hypovolemia, and what ultrasound adds
Obstructive and hypovolemic shock both look hypotensive on a cuff. Distinguishing them keeps you from drowning a tamponaded or PE-strained RV.
- Neck veins and ultrasound: full veins plus a dilated RV or a pericardial stripe mean obstruction; flat veins and an empty hyperdynamic heart mean volume loss (Chapter 8).
- Small-bolus response: hypovolemia improves; tamponade and massive PE often stay flat or worsen.
- Asymmetry: a silent, ballooning hemithorax is not a blood-only problem.
- Altitude: pleural air and a clamped tube worsen on climb; hemorrhage does not expand with Boyle.
Use ultrasound on the ramp if you carry it: lung sliding, a subxiphoid window, and an IVC glance beat another failed stethoscope exam. Leave tubes open, refuse to climb through an untreated pneumothorax, and fly to the room that can cut, lyse, or decompress.
A scene patient develops progressive shock, jugular venous distention, and a silent hyper-expanded left chest while you package for an unpressurized climb. What is the priority action?
A penetrating-chest patient has hypotension, distended neck veins, electrical alternans, and pericardial fluid on FAST. The aircraft is ten minutes from a community clinic and twenty-five minutes from a trauma operating room. What is the correct plan?
An intubated patient with massive pulmonary-embolism shock is loaded for flight. Which ventilator and destination decision is most appropriate?