Reference — Critical Care
Hemodynamic Parameters Reference
The hemodynamic numbers an RT encounters in the ICU, in one place — pressures, flows, resistances, and the venous oxygen saturations — with their normal ranges, what each reflects, and the oxygen-delivery equations that connect them to the gas.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
Hemodynamic parameters describe the pressures, flows, and resistances of the circulation, plus the venous oxygen saturations that report the balance between oxygen delivery and consumption. Normal ranges vary modestly between references and with the patient’s size and physiology; the values below are the commonly cited adult ranges. They are most useful read as a pattern and trended over time — this table is the quick lookup, not a substitute for interpreting them in context.
Normal Values
| Parameter | Normal Range | Reflects |
|---|---|---|
| MAP | 70–100 mmHg (target ≥ 65 in shock) | Organ perfusion pressure |
| CVP / RAP | 2–6 mmHg | Right-heart (RV) preload |
| PA pressure (systolic/diastolic) | ~15–30 / 8–15 mmHg | Pulmonary artery pressure |
| PCWP (wedge) | 8–12 mmHg | Left-heart (LV) preload surrogate |
| Cardiac output (CO) | 4–8 L/min | Total blood flow per minute |
| Cardiac index (CI) | 2.5–4.0 L/min/m² | CO indexed to body surface area |
| Stroke volume (SV) | 60–100 mL | Volume ejected per beat |
| SVR | 800–1200 dynes·s·cm⁻⁵ | Systemic (LV) afterload |
| PVR | 37–250 dynes·s·cm⁻⁵ | Pulmonary (RV) afterload |
| SvO₂ (mixed venous) | 60–80% | Global oxygen supply/demand balance |
| ScvO₂ (central venous) | ≥ 70% | Central venous surrogate for SvO₂ |
Oxygen Delivery Equations
These equations tie the hemodynamic numbers to oxygenation — the link between the monitor and the blood gas.
Arterial oxygen content (CaO₂)
CaO₂ = (1.34 × Hb × SaO₂) + (0.003 × PaO₂)
Oxygen carried per 100 mL of arterial blood — mostly hemoglobin-bound.
Oxygen delivery (DO₂)
DO₂ = CaO₂ × CO × 10
The supply side of the balance; normal is roughly 1000 mL/min.
Systemic vascular resistance (SVR)
SVR = [(MAP − CVP) / CO] × 80
Quantifies left-ventricular afterload from the pressure gradient and flow.
Oxygen extraction ratio (O₂ER)
O₂ER ≈ 25%
Fraction of delivered oxygen the tissues extract; rises when delivery falls.
Clinical Notes
- Trend over time, don’t fix on one number. A single reading is noisy; the direction of travel across serial measurements carries far more meaning than any isolated value.
- Level and zero the transducer at the phlebostatic axis. Every transduced pressure depends on it; a transducer that is not referenced correctly gives systematically wrong CVP and wedge values.
- Positive-pressure ventilation alters preload-dependent values. PEEP and ventilator pressures raise intrathoracic pressure, which inflates transduced pressures and reduces venous return — read the values against the ventilator settings.
- A low SvO₂ / ScvO₂ means more oxygen is being extracted. The tissues are pulling a greater fraction of what is delivered because delivery is inadequate or demand is up — a signal to examine cardiac output, hemoglobin, arterial saturation, and metabolic load.
Related Resources
Sources
- Cecconi M, De Backer D, Antonelli M, et al. Consensus on circulatory shock and hemodynamic monitoring. Intensive Care Med. 2014;40(12):1795-1815.
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.