Shock physiology: educational interpretation
Educational work by a pre-medical student — not medical advice. Not a clinical protocol, prescription, or patient handout, and not for patient care. See DISCLAIMER. Shock is inadequate tissue perfusion or oxygen utilization in context; a blood pressure cutoff alone is insufficient. Mechanisms can coexist and change over time.
| Mechanism | Educational features and caveats |
|---|---|
| Hypovolemic | Reduced effective circulating volume may limit flow. Low CVP or a small IVC alone does not establish fluid need. |
| Distributive | Altered vascular tone and microcirculatory dysfunction can occur with apparently preserved output; myocardial dysfunction may coexist. |
| Cardiogenic | Cardiac dysfunction can limit forward flow, often with congestion. Preserved EF does not exclude important cardiac pathology. |
| Obstructive | Mechanical impairment of filling or outflow can limit circulation; interpretation depends on the cause. |
| Mixed | More than one mechanism is common, particularly after surgery and in complex critical illness. |
Assessment integrates history, examination, serial perfusion observations, appropriately interpreted imaging, and relevant measurements. Lactate is influenced by production and clearance and is not specific for tissue hypoxia. ScvO2 and SvO2 cannot be interchanged or interpreted as universal treatment thresholds.
Static filling pressures are not sufficient to choose fluids. Dynamic tests, when valid in the clinical context, address responsiveness; they do not independently establish fluid tolerance or indicate treatment. The current sepsis guideline and its patient-specific qualifications should be consulted rather than treating an older summary as a protocol.
No drug sequence, resuscitation dose, or device escalation rule is supplied here. The synthetic scenarios are study exercises, not clinical instructions.
Sources and applicability
- SCCM/ESICM 2026 adult sepsis guideline (Prescott et al.; co-published in Intensive Care Med, DOI, and Crit Care Med, DOI): the current guideline supersedes the 2021 edition. For ongoing fluid decisions, dynamic responsiveness assessment is preferable to isolated filling pressures.
- ATS 2024 ARDS guideline: conditionally favors higher PEEP without recruitment maneuvers in moderate-to-severe ARDS and recommends against prolonged recruitment maneuvers.
- ATS/ESICM/SCCM 2017 ventilation guideline: lower tidal volumes use predicted body weight, not actual body weight. Its PEEP, recruitment-maneuver and ECMO questions were re-addressed and are superseded by the ATS 2024 update; the low-tidal-volume/predicted-body-weight and prone-positioning recommendations remain in use.
- ESICM 2023 ARDS guideline (Grasselli et al., Intensive Care Med 2023;49:727-759): a European comparator whose recommendations on PEEP and other adjuncts differ in places from ATS 2024.
- ESICM 2025 circulatory shock and hemodynamic monitoring guideline (Monnet et al., Intensive Care Med 2025;51:1971-2012): current society guidance on shock assessment, including dynamic over static preload markers, echocardiography as first-line imaging for shock type, and cardiac-output monitoring in patients not responding to initial therapy. It updates the 2014 ESICM consensus.
These summaries are educational and do not reproduce the full guideline, its exceptions, or its implementation requirements.