Hemodynamic monitoring and critical care concepts

Invasive monitoring provides continuous, real-time data in critically ill clients.

Common invasive devices

• Arterial lines
• Central venous catheters
• Pulmonary artery catheters (less common)

Maintaining an arterial line

An arterial line gives continuous, beat-to-beat blood pressure and easy access for blood sampling, but the reading is only as trustworthy as the setup that produces it. Key nursing priorities:

• Level and zero the transducer to the phlebostatic axis (roughly the fourth intercostal space, midaxillary line). A transducer that sits too high reads falsely low, and one that sits too low reads falsely high.
• Assess the waveform. A normal arterial waveform has a sharp upstroke and a dicrotic notch; a damped (flattened) waveform suggests a clot, air bubble, kink, or loose connection.
• Monitor the insertion site for bleeding, hematoma, and signs of impaired distal circulation (color, temperature, and pulse of the limb).
• When a reading looks abnormal, verify the equipment and the client before acting — re-level and re-zero the transducer and assess the client rather than treating the number alone.

Managing pacing, telemetry, and renal replacement clients

Several critical care clients are monitored with devices whose nursing priorities appear on the exam:

• Pacing device: Confirm the pacemaker is capturing — each pacing spike should be followed by a QRS complex (ventricular pacing) or a P wave (atrial pacing). Report failure to capture, failure to sense, or a heart rate below the set rate.
• Telemetry: Keep leads and skin contact intact, respond to alarms with client assessment rather than silencing them, and correlate any dysrhythmia on the monitor with how the client actually looks.
• Hemodialysis / continuous renal replacement therapy (CRRT): Monitor fluid and electrolyte shifts, blood pressure (hypotension is common during fluid removal), and the vascular access site for bleeding and patency. CRRT removes fluid slowly and continuously, which is better tolerated by hemodynamically unstable clients than intermittent hemodialysis.

Cardiac rhythm abnormalities

Telemetry and bedside monitors display the client’s heart rhythm, so recognizing a few key dysrhythmias by their defining features is essential. Read each strip for three things: the rate, the regularity, and whether normal P waves precede each QRS complex. As always, treat the client, not just the strip — a rhythm matters most when it changes how the client looks and perfuses.

• Sinus bradycardia: Regular rhythm, rate below $60$ bpm, with a normal P wave before every QRS. Often benign in athletes or during sleep; it needs intervention only when it causes symptoms of low output such as dizziness, hypotension, or altered mental status.
• Premature ventricular contractions (PVCs): Early, wide, bizarre QRS complexes with no P wave in front of them. Occasional PVCs are often harmless, but frequent or multifocal PVCs can be a warning sign, especially in an ischemic heart.
• Ventricular tachycardia (VT): A run of wide QRS complexes at a rate above $100$ bpm, usually regular, with no identifiable P waves. This is a medical emergency — assess the client immediately for a pulse, because pulseless VT is treated like cardiac arrest.
• Atrial fibrillation: An irregularly irregular rhythm with no distinct P waves; the QRS complexes are usually narrow but spaced unevenly. The main risks are a rapid ventricular response and clot formation in the fibrillating atria, which raises stroke risk.
• Ventricular fibrillation (VF): A chaotic, disorganized waveform with no identifiable P waves or QRS complexes and no measurable rate. The heart is quivering rather than pumping — this is pulseless cardiac arrest requiring immediate CPR and defibrillation.

Key hemodynamic parameters (high-yield)

Blood pressure and mean arterial pressure (MAP)

MAP ≥65 mmHg is generally required for adequate organ perfusion

MAP = (SBP + 2 × DBP) ÷ 3

SBP: Systolic blood pressure; DBP: Diastolic blood pressure

• Diastole counts twice because the heart spends more time there.
• Low MAP suggests inadequate tissue perfusion.
• A normal systolic BP does not guarantee adequate perfusion.

Example: Calculating MAP

A client’s blood pressure is $90/50$ mmHg. Using MAP = (SBP + 2 × DBP) ÷ 3:

$$\text{MAP}=\frac{90+2\times 50}{3}=\frac{190}{3}\approx 63\text{ mmHg}$$

Answer: A MAP of about $63$ mmHg is below the $65$ mmHg threshold, so despite a seemingly adequate systolic reading, this client’s organs may already be underperfused.

Central venous pressure (CVP)

The CVP reflects the right ventricular preload (how much blood is returning to the heart). It is measured directly via a central venous catheter and reported in mmHg (or cm H₂O)

• Low CVP → hypovolemia
• High CVP → fluid overload or right-sided heart failure

Cardiac output and cardiac index

Cardiac output (CO) = heart rate × stroke volume

Where:

• Heart rate (HR) = beats per minute
• Stroke volume (SV) = amount of blood ejected per beat

Cardiac index (CI) = CO ÷ body surface area (BSA)

The cardiac index adjusts cardiac output for client size and provides a more accurate comparison between clients.

Low CO/CI leads to:

• Hypotension
• Decreased urine output (oliguria)
• Altered mental status
• Cool extremities

Hemodynamic patterns in shock

Hypovolemic shock

• Low CVP
• Low cardiac output
• Low MAP

Common causes: Hemorrhage, dehydration, burns

Cardiogenic shock

• High CVP
• Low cardiac output
• Pulmonary congestion

Common causes: Myocardial infarction, severe heart failure

Septic shock

• Early (compensated):
  • Normal or high cardiac output
  • Low systemic vascular resistance (SVR)
  • Warm, flushed skin
• Late (decompensated):
  • Low cardiac output
  • Hypotension
  • Oliguria