210 Microamps and a Pulmonary Artery Catheter
A 62-year-old after CABG is in the CTICU with a pulmonary artery catheter and temporary epicardial pacing wires in place. The nurse reports "pins and needles" when she touches the bed rail and the monitor housing at the same time. You measure AC leakage current: bed chassis 210 µA with the ground pin intact, monitor chassis 60 µA, and receptacle ground resistance 0.4 Ω. The room has standard grounded receptacles; there is no isolated power. A patient-controlled analgesia pump was added this morning and its line cord has a section wrapped in electrical tape. The patient is stable but has had two runs of non-sustained VT in the last hour and the team is discussing starting an antiarrhythmic.
1. Which of these measurements actually explains a perceived shock, and which do not? Reason through the current paths involved.
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The numbers do not add up to what the nurse felt, and that is the important finding.
- 210 µA chassis leakage is below the commonly cited 500 µA earth-leakage limit for Class I equipment in normal condition, and it is roughly at or below the threshold at which 60 Hz current is even perceptible (on the order of 0.5–1 mA for a brief touch). A 210 µA chassis-to-ground leakage reading by itself does not comfortably explain a tingle.
- 60 µA monitor chassis is likewise not perceptible on its own.
- 0.4 Ω ground resistance is within the usual acceptable range for a patient-care-area grounding path, so the receptacle ground is probably not the defect.
A perceived shock means current actually flowed through a person. The plausible explanations are: (a) the taped cord on the PCA pump is leaking far more than the measured devices - a damaged cord is a fault waiting to be quantified; (b) the two surfaces the nurse bridged are at different ground potentials because of a compromised ground connection somewhere in the chain, so the current is a touch current between two "grounded" objects, not a single device's leakage; (c) an intermittent fault that a single steady-state reading missed.
Bottom line: treat the sensation as real and unexplained, not as an over-sensitive nurse and not as a 210 µA problem.
2. The patient has an intracardiac catheter and epicardial pacing wires. How does that change your risk assessment and your immediate actions?
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It changes the threshold from "uncomfortable" to "potentially lethal."
A conductor in contact with the myocardium bypasses the protective resistance of skin. Current on the order of tens of microamps - far below perception - delivered through an intracardiac electrode can precipitate ventricular fibrillation. That is why Type CF applied parts carry the tightest limits (commonly cited as 10 µA patient leakage in normal condition and 50 µA under single-fault condition, versus 100 µA for Type B/BF). Macroshock limits are irrelevant to this patient; microshock limits are everything.
Immediate actions, in order:
- Remove the PCA pump with the taped cord from service immediately - unplug it, tag it, and quarantine it. Do not tape, splice, or "make it work" for the shift.
- Verify that every device with an applied part on this patient (monitor, pacing generator/analyzer, PA transducer, bed) is Type CF rated for the connections in use, and check that the pacing wires and catheter connections are dry, capped, and not contacting other metal.
- Have the room's receptacles and equipotential ground Bus checked and take the bed out of service pending its own leakage test.
- Tell nursing not to bridge metal surfaces at the bedside until the fault is found, and consider relocating the patient to a room with known-good wiring.
- Document the event and report it - two runs of NSVT in the last hour make the timeline clinically relevant, and the care team should know an electrical fault is being investigated.
The tempting shortcut - "the leakage is within limits, so nothing is wrong" - is exactly the error this situation punishes.
3. The PCA pump's leakage measures 480 µA after removal. What do you do with it, and what do you document about the whole event?
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480 µA on the PCA pump: measurable and far above what should reach a patient-connected device, and combined with visible cord damage it is a clear failure regardless of which clause of which standard it technically satisfies. Action: keep it out of service, do not repair field-damaged line cords by taping, route it for authorized repair or retirement, and check whether other units from the same purchase/fleet have the same cord design or damage pattern. If the same model shows a pattern, that is a fleet-level issue for the vendor and for materials management, not a one-off.
Document:
- The nurse's reported sensation, time, and which surfaces she bridged.
- Every measurement with instrument, method, and the conditions under test (normal vs single-fault).
- The devices removed from service and their disposition.
- The patient's rhythm events and the notification made to the care team.
- The corrective actions and the verification test after repair.
If the event involved patient contact with a device that failed, handle it through the facility's medical device reporting process rather than closing it as a maintenance ticket. The record should let a reviewer reconstruct why each decision was made, not just what the numbers were.