EDT Patient Preparation & Safety 2 — Questions and Answers
Question 1: When applying surface electrodes for an EMG study, which skin preparation step is most critical for obtaining low-impedance recordings?
- Applying electrode gel without abrasion
- Lightly abrading the skin with fine sandpaper or abrasive pad (Correct answer)
- Warming the skin with a heat lamp for 10 minutes
- Shaving the area and applying alcohol only
Correct answer: Lightly abrading the skin with fine sandpaper or abrasive pad
Light skin abrasion removes the high-resistance dead-cell layer of the stratum corneum, reducing inter-electrode impedance to acceptable levels (below 5 kΩ).
Question 2: A patient with a pacemaker is referred for nerve conduction studies. What is the primary safety concern?
- The pacemaker will interfere with EMG amplifier gain settings
- Electrical stimulation current may inhibit or reset the pacemaker (Correct answer)
- Repetitive stimulation will drain the pacemaker battery
- The patient cannot lie still long enough for accurate recordings
Correct answer: Electrical stimulation current may inhibit or reset the pacemaker
External electrical stimulation can be sensed by a pacemaker's sensing circuit and may trigger inappropriate inhibition or mode-switching, posing a cardiac risk.
Question 3: Which grounding principle is essential during nerve conduction studies to minimize electrical shock hazard to the patient?
- The ground electrode must be placed distal to the recording electrode
- The ground electrode should be placed between the stimulating and recording electrodes (Correct answer)
- Ground is optional when using modern digital amplifiers
- The ground electrode must always be placed on the patient's chest
Correct answer: The ground electrode should be placed between the stimulating and recording electrodes
Placing the ground electrode between the stimulator and recording electrodes reduces stimulus artifact and provides a common reference, improving both safety and signal quality.
Question 4: Before performing electrodiagnostic studies on a patient taking anticoagulant therapy (e.g., warfarin), what specific precaution applies to needle EMG?
- Needle EMG is absolutely contraindicated in all anticoagulated patients
- Superficial muscles should be prioritized; deep muscles carry higher bleeding risk (Correct answer)
- INR must be below 1.0 before any needle insertion
- The needle gauge must be larger to allow faster withdrawal
Correct answer: Superficial muscles should be prioritized; deep muscles carry higher bleeding risk
In anticoagulated patients, needle EMG can still be performed, but examination of deep or paraspinal muscles with abundant blood supply increases hematoma risk and should be approached cautiously.
Question 5: A patient reports a latex allergy before the start of an electrodiagnostic study. What is the most appropriate immediate action?
- Proceed normally as latex is not used in EDX equipment
- Verify that all supplies (gloves, electrode adhesives) are latex-free before proceeding (Correct answer)
- Postpone the study until the allergy is medically treated
- Use extra alcohol wipes to neutralize any latex residue
Correct answer: Verify that all supplies (gloves, electrode adhesives) are latex-free before proceeding
Latex can be present in gloves and some electrode adhesives; confirming all materials are latex-free is mandatory to prevent anaphylaxis.
Question 6: During a nerve conduction study, a patient suddenly complains of dizziness and diaphoresis after electrode placement. The most likely cause is:
- Electrode impedance mismatch causing artifact
- A vasovagal response triggered by anxiety or pain (Correct answer)
- Electrical leakage current from the stimulator
- Hypersensitivity to electrode gel chemicals
Correct answer: A vasovagal response triggered by anxiety or pain
Vasovagal syncope is the most common acute patient reaction in the EDX lab, caused by anxiety or pain-induced vagal activation resulting in bradycardia and hypotension.
Question 7: What is the recommended minimum distance between a nerve stimulation site and an implanted deep brain stimulator (DBS) lead?
- No minimum distance applies if current is under 10 mA
- At least 10 cm from any lead or pulse generator (Correct answer)
- Stimulation ipsilateral to the DBS device is completely safe
- At least 30 cm, and contralateral limbs only should be studied
Correct answer: At least 10 cm from any lead or pulse generator
Current guidelines recommend keeping stimulation sites at least 10 cm from DBS leads and pulse generators to avoid device interaction or tissue heating.
EDT Patient Preparation & Safety 2
When applying surface electrodes for an EMG study, which skin preparation step is most critical for obtaining low-impedance recordings?