Shock & critical care echo
Phenotype the shock, measure flow, test fluid responsiveness and tolerance, and find the obstructive causes.
Numbers to remember
- LVOT VTI <15 cm and low SVI are associated with worse outcomes in advanced HF and CICU patients [190,191]
- Cardiac power output was the strongest haemodynamic correlate of death in cardiogenic shock (SHOCK); values ≈0.5–0.6 W or lower mark high risk [114]
- Passive leg raising: a rise in SV or VTI ≥10% predicts fluid responsiveness (pooled sensitivity 85%, specificity 91%) [121]
- Ventilated patients: IVC distensibility >18% predicted fluid response [122]
Questions echo must answer
Echo is recommended to determine the type of shock when clinical examination is not conclusive [153]. It is also the bedside monitor of flow and of the response to treatment [151,152]. The questions are asked in order of lethality:
- Obstructive cause?Tamponade, massive PE (acute RV failure), dynamic LVOT obstruction, tension pneumothorax (lung sliding absent) [124,149,199].
- Is the LV failing?LVEF, LVOT VTI, SVI, CI, cardiac power, filling pressure (E/e′) [114,190].
- Is the RV failing?RV/LV ratio, TAPSE, septal shape, TAPSE/PASP [3,152].
- ValvesAcute severe MR or AR, prosthetic dysfunction, mechanical complications of MI [138].
- VolumeFluid responsiveness (PLR, IVC in ventilated patients) and fluid tolerance (lung B-lines, venous congestion) [121,122,202].
- PhenotypeHypovolaemic, distributive, cardiogenic or obstructive — often mixed [153,154].
Acquisition protocol
- Subcostal 4CFirst look for effusion, RV size and global LV function. This is often the only window in ventilated patients.
- Subcostal IVCDiameter and variation. Spontaneous breathing: collapse; ventilated: distensibility [3,122,169].
- PLAX / PSAXLV size and function, kissing walls (hypovolaemia), septal shape (RV load).
- A5CLVOT VTI (stroke distance) and LVOT diameter → SV, CO, CI; cardiac power = MAP × CO / 451 [114,170,171].
- A4CRV/LV ratio, TAPSE, TR velocity, mitral E, e′, E/e′ [2,3].
- ColourAcute MR or AR, LVOT turbulence (dynamic obstruction), VSD.
- PLRMeasure VTI before and 1 minute into passive leg raising [121,168].
- LungsSliding (pneumothorax), B-lines (oedema), consolidation, pleural effusion [199,202].
- RepeatAfter every intervention: fluid bolus, inotrope, vasopressor, ventilator change.
- Effusion / tamponade
- RV size and function
- LV function, LVOT VTI, SVI, CI
- Dynamic LVOTO
- Valves and mechanical complications
- E/e′ (filling pressure)
- IVC
- PLR response
- Lung ultrasound
- Phenotype and SCAI stage
Diagnosis & severity
| Phenotype | LV | RV | IVC | LVOT VTI | Other |
|---|---|---|---|---|---|
| Hypovolaemic | Small, hyperdynamic, kissing walls | Small | Small, collapsing | Low | Possible dynamic LVOTO |
| Distributive (septic) | Normal or hyperdynamic (may be depressed) | Normal | Variable | Normal or high early | Septic cardiomyopathy possible [155,207] |
| Cardiogenic (LV) | Dilated, low EF | Variable | Dilated | Low | E/e′ high, B-lines [190] |
| Obstructive — tamponade | Small, underfilled | Collapse | Plethoric | Low | Effusion [149] |
| Obstructive — PE | Small D-shaped | Dilated, dysfunctional | Plethoric | Low | McConnell, 60/60 [124] |
Prognostic Doppler haemodynamics in CICU [190,192,193]
Low SVI, low LVOT VTI, high E/e′ and low stroke work index were associated with in-hospital mortality independently of SCAI stage. LV–arterial coupling also stratified risk.
Thresholds that change management
- Tamponade → drainage [149]. Massive PE with RV failure → reperfusion [124]. Tension pneumothorax (no sliding, lung point) → decompression [199].
- Dynamic LVOT obstruction → stop inotropes, give fluid and a beta-blocker or vasopressor (phenylephrine) as tolerated [134].
- Fluid responsive (PLR VTI ≥10%) and not congested → give fluid and re-assess [121].
- Not responsive, or congested (plethoric IVC, B-lines, raised E/e′) → stop fluid; vasopressor, inotrope or de-resuscitation [152,153].
- Cardiogenic shock → SCAI staging with echo-derived flow indices; consider mechanical support in the right setting [114,154].
- Septic shock → early echo for septic cardiomyopathy (systolic and diastolic dysfunction are associated with mortality) [155,207].
Pitfalls & mimics
PitfallThe IVC is poor at predicting fluid response in spontaneously breathing patients and misleading in raised intra-abdominal pressure, RV failure, severe TR and cardiac tamponade [3,152].
- LVOT VTI needs the same sample site and angle on repeated measurements. Use the change, not the absolute value, for PLR.
- Hyperdynamic LV in sepsis ≠ adequate output. Vasoplegia and low afterload flatter EF.
- Mechanical ventilation raises RV afterload and alters all respiratory indices.
- Arrhythmia: average several beats; PLR is still valid in AF [121].