How do you monitor cardiac function in patients under anesthesia in a Magnetic Resonance Imaging (MRI) environment?

Cardiac Monitoring in Anesthetized Patients During MRI

The same minimum standards of monitoring used in the operating theatre must be applied in the MRI environment, including continuous ECG monitoring with MR Safe electrodes, non-invasive blood pressure (NIBP) monitoring with plastic connections, pulse oximetry using fibreoptic devices, and capnography, with all equipment positioned to allow remote monitoring from the control room during scanning. 1

Essential MRI-Compatible Cardiac Monitoring Equipment

ECG Monitoring Requirements

• Use only MR Safe ECG electrodes specifically designed for the MRI environment to prevent thermal burns from induced currents during scanning 1
• Standard ECG electrodes must be removed before scanning as they can cause serious burns 1
• Position monitoring equipment according to magnetic fringe field safety zones, typically marked on the floor, with guidance from the local MR Safety Expert 1
• Be prepared to interpret field strength-dependent ECG artifacts during scanning, including T-wave elevation that may exceed QRS amplitude and R-wave reduction or inversion—these changes are harmless and resolve when scanning stops 1

Blood Pressure Monitoring

• Non-invasive blood pressure monitoring requires plastic rather than ferromagnetic connections to function safely in the MRI environment 1
• For invasive arterial pressure monitoring, minimize line length to reduce damping and ensure the pressure bag contains no metallic components 1
• Invasive monitoring can be safely performed in critically ill patients undergoing high-field MRI examinations 2

Pulse Oximetry

• Fibreoptic pulse oximeters must be used exclusively as standard oximeters have caused burns from induction currents 1
• Continuous pulse oximetry with plethysmograph waveform is mandatory throughout the procedure 1

Capnography

• Continuous waveform capnography is required for all anesthetized patients 1
• Minimize the length of the capnograph sampling line to reduce time-lag in waveform changes 1

Remote Monitoring Setup

Control Room Configuration

• The MRI unit setup must allow remote monitoring from the control room while scanning is in progress 1
• This is critical because MRI-safe equipment is often more basic with poor alarm accessibility, making the MRI environment inherently high-risk 1
• The anaesthetist should remain in the control room with continuous visual and electronic monitoring during scanning 1

Equipment Positioning

• All monitoring equipment must be assessed for safe placement relative to magnetic fringe fields 1
• Floor markers typically identify safety ranges for equipment positioning 1
• Consult the local MR Safety Expert (often a clinical scientist) for equipment placement decisions 1

Additional Monitoring Considerations

Temperature Monitoring

• Both peripheral and central temperature can be measured using specifically designed MR-compatible probes 1

Advanced Hemodynamic Monitoring

• For high-risk patients with cardiovascular comorbidity, consider additional cardiac output monitoring or echocardiography 1
• Transesophageal echocardiography (TOE) should be considered if acute severe hemodynamic instability develops during or after the procedure 1

Critical Safety Protocols

Equipment Classification

• All equipment must be formally classified as MR Safe (no hazard at any field strength) or MR Conditional (safe under specified conditions) before entering the MRI environment 3
• MR Unsafe equipment presents unacceptable risk and must never enter the scanner room 3

Pre-Procedure Checklist

• Complete an MR safety checklist immediately before entering the scanner room 3
• Remove all unlabeled equipment, including standard stethoscopes 3
• Verify equipment is formally labeled as MR Safe or meets MR Conditional requirements 3

Anaesthetic Machine Requirements

• Only MR Safe vaporizers and gas cylinders should be used within the scanning room 1
• MR Conditional anaesthetic machines and ventilators must be positioned according to the individual magnet's field specifications 1
• Standard equipment may lead to serious accidents if brought into the MRI environment 1

Emergency Preparedness

Cardiac Arrest Protocol

• During diagnostic scanning, immediately evacuate the patient from the MRI environment to allow resuscitation with standard equipment and wider team support 1
• Roles of the radiographer and anaesthetist during patient evacuation must be clearly defined in a standard operating procedure and regularly reviewed 1
• For interventional procedures where patient movement is difficult, establish a clear protocol defining which personnel and equipment may enter during emergencies 1

Common Pitfalls to Avoid

• Never rely on standard operating room monitoring equipment—it poses projectile risk and can cause patient burns 1, 3
• Do not dismiss ECG changes during scanning as artifact without considering the expected field-dependent patterns 1
• Avoid positioning monitoring equipment too close to the magnet, which can cause malfunction or become projectile hazards 1
• Ensure specific training with MRI-compatible equipment before use, as it differs significantly from standard hospital equipment 1
• Do not assume alarm systems will function adequately—the anaesthetist must maintain continuous vigilance from the control room 1