Cause of Device-Related Incident
Device factors; External factors

Clinical Specialty or Hospital Department
Anesthesia; Cardiology / Cardiac Catheterization; Clinical/Biomedical Engineering; Obstetrics and Gynecology; OR / Surgery

Device Factors
Device interaction

Document Type
User Experience Network (UEN) reports

External Factors
Electromagnetic or radio-frequency interference (EMI and RFI)

Mechanism of Injury or Death
Misdiagnosis; Monitoring failure

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
*Not stated

UMDNS
ECG Monitors [12-599]; Heart-Lung Bypass Units [11-969]; Hemodialysis Units [11-969]; Infusion Pumps, General Purpose [13-215]; Pacemakers Cardiac [12-911]

ECG Artifact in the OR



User Experience Network [Health Devices Mar-Apr 1991;20(3-4):140-1]

ECG Artifact in the OR

Hospital

During open-heart surgery, we often face the problem of artifact on ECGs. The artifact is periodic and looks somewhat like QRS or pacemaker spikes. What is the likely cause, and how can it be corrected?

ECRI

In the OR, spike-like interference can be produced by two common sources: fluid delivery systems and line isolation monitors (LIMs). In Health Devices, we have published reports of artifact associated with fluid delivery systems, including infusion controllers and heart-lung bypass pumps (Health Devices 7[4]:111, Feb 1978 and 12[1]:27, Nov 1982, respectively). Artifact has also been associated with infusion pumps and hemodialysis machine pumps. The rate of the spikes changes as the pumping rate is varied, and turning off the pump causes the artifact to stop. ECG artifact is caused by the cyclic pinching and releasing of the polyvinyl chloride (PVC) tubing (or possibly other plastic parts) in the pump, which can generate electricity through piezoelectric or static electricity effects. The resulting electrical signal flows into the patient through the fluid in the tubing and may be picked up by the ECG electrodes. The currents associated with this signal pose no electrical safety risk.

Isolated power supply LIMs may also produce ECG artifact, which can occur about once per second or at line frequency (60 Hz); recent LIM designs have greatly reduced this problem. This source of interference can be identified by momentarily removing the LIM fuses and looking to see whether the artifact disappears.

Although less common, electrical signals from other devices can also cause artifact. In one case, for example, an atrial fibrillation-like artifact seen during bronchoscopy was associated with the automatic light intensity control in a fiberoptic light source (see Health Devices 15[1]:24, Jan 1986).

Artifact from pumps and LIMs can be exacerbated by ECG electrode characteristics and application, monitor performance, and environmental factors. When experiencing such a problem, consider the following.

ECG electrodes: Discuss the problem with your ECG electrode supplier, and verify that the most appropriate foam-backed electrode designed for OR applications is being used. Obtain samples for trial use from a manufacturer whose product might be superior, even if the cost is greater, to see whether this eliminates or reduces the noise problem.

ECG electrode cables and lead wires: Periodically inspect cables and lead wires for breaks and cracks and replace as needed (e.g., if broken or cracked) or, primarily for lead wires, prophylactically (e.g., weekly, monthly).

Skin preparation and application: Correct skin preparation and electrode application are essential. Follow the electrode manufacturer's recommendations. Generally, the only skin preparation required is a brisk, dry rub. In "wet" procedures (i.e., chest and abdominal surgery), it may be advisable to apply an adhesive covering over the electrode to protect it from exposure to solutions.

Isolated power systems: Historically, the primary purpose of an isolated power system in the OR was to reduce the fire and explosion risks associated with the use of flammable anesthetics. As long as only nonflammable anesthetics are used in the OR, isolated power systems are not needed; this is consistent with national codes and standards. Thus, removing or disabling isolated power systems that are causing noise problems is justified (unless their use is dictated by local requirements).

Disabling these systems can be accomplished in a number of ways, including simply grounding one side of the secondary to a suitable ground (e.g., water pipe). It is advisable to connect each of the isolated power secondaries within one room to a single grounding point, to identify the now "neutral" wiring at the circuit panel and behind each outlet with a band of white tape, and to verify that all outlets are wired in correct polarity. We also recommend replacing the explosion-proof outlets with Hospital Grade conventional (parallel-blade) duplex receptacles.

ECG monitors: Many monitors have two frequency-response modes (e.g., Monitor and Diagnostic). The mode with the lower cutoff frequency (e.g., Monitor) may help reduce noise and artifact, while still providing adequate response for monitoring applications.

The common mode rejection ratio (CMRR) is affected both by monitor design and the ECG cable. This is not a problem with most monitors today, but CMRR can be evaluated using the tests described in the ECG monitor acceptance testing procedures in ECRI's Inspection and Preventive Maintenance (IPM) System.) CMRR should exceed 10,000:1 (80 dB).

Relative humidity: In one published case, a problem of intermittent artifact was associated with cardiopulmonary bypass; this was not resolved by the normal attention to ECG electrodes and cables.(1) The problem occurred predominantly during the winter when the relative humidity (RH) in the OR was low (below 50%). An aerosol spray of tap water applied to the pump tubing in the roller heads provided partial, temporary relief, but was an unsatisfactory solution for a number of reasons.

Users should attempt to maintain the RH near 50%, although this is not possible in some facilities (especially older ones). (NFPA 99, 1990, Section 5-4.1.1 calls for a RH of at least 35% and notes that several advantages have been claimed, including avoidance of hypothermia, possible reduction in floating particulate matter, and minimization of wound infection following procedures in ORs in which the RH is maintained at 50% to 55%.) Adequate RH may also increase personnel comfort.

Note

  1. Wald AW, Khambatta HJ, Tone JG, et al. Plastic induced ECG interference on cardiopulmonary bypass: An adventure in clinical engineering. Clin Eng 1990 Jul-Aug;15:301-7.

UMDNS Terms

  • ECG Monitors [12-599]
  • Heart-Lung Bypass Units [11-969]
  • Hemodialysis Units [11-969]
  • Infusion Pumps, General Purpose [13-215]
  • Pacemakers Cardiac [12-911]

Cause of Device-Related Incident

Device factor: Device interaction

External factor: Electromagnetic or radio-frequency interference (EMI, RFI) 

Mechanism of Injury or Death

Misdiagnosis; Monitoring failure


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