Hemodynamic Monitoring

Hemodynamic monitoring asks three questions: is the pump working, is the tank full enough, and are the pipes holding tone? It uses arterial, central venous and pulmonary artery pressures, cardiac output and derived values to answer them. The answers guide the next intervention.

Key Components

Flow Path

1. Pressure is generated by the heart in whichever chamber or vessel holds the catheter tip.
2. Pressure is transmitted along a column of fluid in the line until it reaches the transducer.
3. The transducer converts it to an electrical signal. The monitor draws the waveform and shows the mean.
4. Derived values come from the arithmetic, not from the transducer. Cardiac output, SVR and oxygen delivery are worked out from measured pressures, cardiac output and hemoglobin.

Think of the circulation as three parts. The pump is cardiac output. The tank is preload, the filling volume and compliance of the venous system. The pipes are vascular resistance. MAP − CVP = CO × SVR ÷ 80. The same MAP can come from high flow through open pipes or from low flow through clamped ones.

What It Does

What It Depends On

• In shock, preload, afterload and contractility often shift together.
• Rhythm: losing atrial contraction or running a rapid atrial fibrillation rate both lower stroke volume.
• Valve and wall function: regurgitation, stenosis and ischemia all change how pressures reflect volume.
• Device position: transducer level, catheter tip position and lung volume

Every access route asks a different question. Begin with the least invasive measurement that still answers yours.

Pulmonary Artery Catheter Ports

• Distal lumen: PA pressure and the PAOP wedge trace when the balloon is inflated
• Proximal (RA) lumen: CVP, and the injectate for thermodilution
• Thermistor near the tip: temperature change for thermodilution CO
• Thermal filament: continuous CO on catheters that have one
• Balloon inflation valve: the labeled maximum volume is printed on the catheter
• Optional connectors: fiberoptic SvO₂ and a pacing lumen, when fitted

Indications

• Arterial line: vasoactive therapy that you titrate to a MAP target (initial shock target ≥65 mmHg per SSC 2021), or frequent blood gas sampling. SSC 2021 suggests invasive arterial pressure monitoring as soon as practical in septic shock, when resources allow.
• CVC: vasoactive infusions that should not run peripherally. Central venous access also serves other therapies.
• PA catheter: selected shock or pulmonary hypertension, when CVP, PAOP, CO and SVR together will change what you do next.
• Pulmonary hypertension: A mean PAP above 20 mmHg is the definition. PVR above 2 Wood units points to a precapillary component (per the 2022 ESC/ERS guideline).

Contraindications

Limitations

• PAOP is not LVEDP in mitral disease, pulmonary venous obstruction, a stiff ventricle, high PEEP or severe ARDS
• CVP does not reliably predict fluid responsiveness. Read it against the trend and the rest of the data.
• Thermodilution CO gets less reliable with significant tricuspid regurgitation, an intracardiac shunt or an irregular rhythm.

Key Evidence

The targets below are typical adult values. Each unit sets its own, so follow institutional protocol. Units are in every cell.

The 70% ScvO₂ target comes from the 2001 early goal-directed therapy trial, and it is historical. ProCESS found no mortality benefit from protocolized ScvO₂ care. Treat ScvO₂ as a trend.

Initial Settings

• Leveling: transducer at the phlebostatic axis (4th intercostal space, mid-axillary line); re-level after every position change
• Zeroing: open the stopcock to air, zero, then turn it to the patient; re-zero whenever the numbers do not fit
• Damping (fast-flush test): One or two oscillations, then a quick return to baseline, means the damping is adequate.
• Reading: invasive pressures at end-expiration on the ventilator; average the trace over the breathing cycle if the patient breathes spontaneously
• Wedge: use the smallest balloon volume that gives a wedge trace, never above the volume printed on the catheter (typically 1.5 mL on adult catheters; the printed label governs), and keep each wedge brief
• Flush system: pressurized continuous flush through a pressure bag (commonly 300 mmHg) at a set rate (commonly 3 mL/hr) (typical; follow institutional protocol)

Sizing & Positioning

Check collateral flow before you pick the arterial site. Then confirm a waveform before you trust any number. Insertion depth for central and PA catheters depends on the site and the manufacturer's markings. Position the patient for the measurement you plan, and document the transducer level.

These derived values turn pressures into flow, resistance and oxygen delivery. Run the math only once the waveforms and zeros look right.

Dynamic Fluid Responsiveness

• Static pressures (CVP, PAOP) predict poorly whether a fluid bolus will raise output. SSC 2021 prefers dynamic measures for fluid decisions.
• Pulse-pressure or stroke-volume variation can be read only in controlled mechanical ventilation, with a regular rhythm and no spontaneous breaths. Check the monitor's stated requirements.
• Passive leg raise is a bedside test. A CO rise of 10% or more during the test predicts fluid responsiveness (a 2016 meta-analysis of 21 studies found sensitivity 0.85 and specificity 0.91). Confirm the threshold and measurement method with your protocol.

Shock Profiles at a Glance

Normal

• Arterial: a sharp upstroke and a dicrotic notch on the downslope. The MAP on screen is the integrated mean.
• Right atrium: low-amplitude trace with a, c and v waves and x and y descents
• Right ventricle: tall systolic peaks with near-zero diastolic pressure and no dicrotic notch
• Pulmonary artery: systolic peak with a clear dicrotic notch; diastolic pressure above the wedge value
• Wedge (PAOP): small, venous-looking trace with a mean at or slightly below the PA diastolic pressure

Abnormal Patterns

At the bedside, monitoring is routine. The waveform, the site and the trend matter more than any one number.

Positioning & Mobility

• Keep the transducer leveled to the phlebostatic axis whenever the patient moves; re-zero after any change
• Secure lines and tubing at every position change, and keep the arterial limb in view
• Head-of-bed position and hip-flexion limits follow the unit protocol and the catheter site

Doses vary by protocol; follow local protocols and medical direction. Infusion rates are weight-based unless stated. Check the units on the pump before you start.

Pattern to Drug

Pediatric doses are in Special Populations. For more dosing detail, use the linked medication pages.

Look at the patient first and the machine second. Before you blame the monitor, confirm the patient is perfused.

Aseptic insertion, a brief wedge and a daily check on need prevent most complications.

Each scenario below starts with the life-saving action. Steps beyond EMS or general RN scope are marked, and each follows local protocol.

Readiness to Remove

Remove each catheter once its measurement stops changing management, or once the catheter itself is causing harm. Document why it stays in.

Removal Steps

1. Confirm the indication and get team agreement.
2. PA catheter: deflate the balloon fully before any movement, then withdraw slowly with the waveform in view.
3. Arterial line: hold firm pressure until hemostasis; check distal perfusion.
4. Central line: remove per protocol; apply an occlusive dressing.
5. Afterward: check the site and limb for bleeding and hematoma, and document.

Before You Move

1. Power: confirm battery charge and backup power for the monitor.
2. Flush and pressure bag: confirm the pressure bag and flush supply are working.
3. Balloon: confirm the PA balloon is deflated and the catheter is secured.
4. Lines: secure and label every catheter and tubing; spare transducer and cable if available.
5. Team: brief the receiving team on the device, the last numbers and the trigger points.

If You Are Not the Device Specialist

EMS and general RN guidance

• Watch the limb with the arterial line; report a cold, pale or numb hand or foot
• Do not wedge, inflate or flush the PA lumen; do not move or disconnect a PA catheter
• If an arterial line bleeds, apply direct pressure; if a line is disconnected, close the stopcock
• If the trace is lost, report it; use the cuff for BP and call for help
• ACLS governs CPR and defibrillation. The lines stay in place.

During Transport

• Re-level and re-zero after every move that changes the patient's position
• Check the pressure bag, the flush and the tubing security at every handoff
• Watch for air in the tubing and any change in the trace

Air Medical & Altitude

Boyle's law explains why: gas in a closed line expands as ambient pressure falls. Before flight, and during ascent or descent, check every connection for air.

Handoff

• Monitoring type, site and insertion date
• Last MAP, CVP or PAOP, and CI with the time measured
• Vasoactive drugs and doses, and the target MAP
• Damping status and the last zero and level
• Limb checks, recent alarms and complications
• Anticoagulation and the latest labs (lactate, hemoglobin, platelets)

Pediatric & Neonatal

Pediatric MAP targets and normal values depend on age and size, so do not use adult numbers for children. Arterial lines are common in pediatric intensive care. PA catheters are rarely used in children because of their size. For normal vital signs, shock and vascular access, use the pediatric pages: /pediatrics/vital-signs.html, /pediatrics/shock.html and /pediatrics/vascular-access.html. Pediatric hypotension is defined by age. Use the thresholds on the pediatric shock page, not adult values. Neonatal and infant lines run at lower flush rates than adult lines, so follow the unit's pediatric flush protocol.

Pregnancy & Peripartum

Pregnancy raises cardiac output and lowers SVR, so adult normal values can mislead you. Late in pregnancy, lying supine compresses the aorta and vena cava and lowers preload. Use left lateral tilt or uterine displacement, and hold the same position for serial readings. PA catheter use in pregnancy is uncommon. It is a team decision made with the obstetric team.

Other

Indexed values (CI, SVRI, SV index) depend on which body surface area formula you use. Keep the same formula across serial measurements.

• Obesity: use a correctly sized cuff for noninvasive MAP, and confirm invasive readings on the waveform
• ECMO or ventricular assist devices: the arterial waveform may be reduced or absent. Follow the device team's monitoring plan.

Systematic Walk-Through

1. Trust the hardware: check level, zero, damping and the waveform.
2. Look at the pump: MAP, CI and SvO₂ or ScvO₂ against the target.
3. Look at the tank: CVP and PAOP, and whether a fluid challenge is likely to help.
4. Look at the pipes: SVR and PVR.
5. Integrate: lactate, urine output, skin, mental status and echo.
6. Decide and reassess: fluid, vasopressor, inotrope or mechanical support, then trend the result.

Pearls

• The trend beats any single number.
• Full and failing, with high PAOP and low CI, is not the same as empty and failing, with low PAOP and low CI.
• Read the waveform before you read the number.
• One MAP, many causes.
• A catheter only answers the question someone asks it.