Considerations

MAGUIRE Enterprises, Inc.

1-800-548-9686

Considerations When 'Slaving' Monitors and Defibrillators

"Slaving" The defibrillator/monitor

Some hospital customers may wish to interface the defibrillator/monitor to other medical equipment, such as bedside or central station monitors. Commonly referred to as "slaving", the patient's ECG signal is cabled from one device to another, for the purposes of therapy or remote monitoring. This document describes typical interconnection schemes, patient risks that may be incurred, and how to decrease these risks.

Review: What is Synchronized Cardioversion?

In patients with certain arrhythmia, administering a random counter shock carries the risk of inducing ventricular fibrillation(1). In such cases, synchronized cardioversion is usually indicated. A defibrillation shock delivered during the vulnerable period of the cardiac cycle, identified in FIGURE 1, may actually cause ventricular fibrillation.

FIGURE 1: Timing A Synchronized Counter Shock to the Cardiac Cycle

With the SYNC mode on the defibrillator/monitor selected, each QRS complex the patient produces is identified and marked. The defibrillator only allows delivery of a shock immediately after a QRS complex is detected. The Association for the Advancement of Medical Instrumentation (AAMI) recommends that defibrillators operating in synchronized mode deliver the synchronized shock within 60 ms after the peak of the R wave(2). Since the vulnerable period immediately follows this60 ms "window", delivery of the shock must not occur more than 60 ms after the peak of the R wave.

"Slaving" A Bedside Monitor From The defibrillator/monitor (crash Cart)

When a defibrillator/monitor is used in conjunction with a bedside monitor, the clinical staff may want to view the patient's ECG signal on both units. A typical connection would allow the patient to be connected to the defibrillator/monitor plus have the ability to quickly interconnect a cable to the bedside monitor and it's associated central station. This is the preferred method for synchronized cardioversion as delay time is not an issue.

When a patent requiring synchronized cardioversion is already connected to another bedside monitor, it may be impractical or undesirable to place additional monitoring electrodes on the patient's chest. To monitor with the defibrillator/monitor during the cardioversion procedure, the clinical staff may elect to "slave" an ECG signal from the bedside monitor to the defibrillator/monitor, as shown in FIGURE 2. The delivery of defibrillation therapy with devices interconnected in this fashion can result in specific patient risks that must be understood and managed by the hospital's clinical and biomedical staff.

"Slaving" The Defibrillator/monitor From Another Monitor For Synchronized Cardioversion

If the defibrillator/monitor is to be "slaved" from a bedside monitor as shown in FIGURE 2, it is critical that the ECG signal obtained from the bedside monitor is real time; that is, with minimal delay introduced by the bedside monitor. The hospital's biomedical engineering staff should perform sync delay measurements on the system as a whole to ensure that the 60 ms limit for sync delay is not exceeded. For equipment designed to easily measure sync delay, contact MAGUIRE Enterprises, Inc. or go to our on-line catalog.

FIGURE 2: Slaving aA LIFEPAK 12 defibrillator/monitor From A Bedside Monitor For Synchronized Cardioversion

Cable Availability

For assistance in acquiring the appropriate cables, contact MAGUIRE Enterprises, Inc. at 1-800-548-9686 or go to our on-line catalog. Be prepared to provide the manufacturer and model number of the bedside monitor and defibrillator to be used. Patient cable input adapters are also available allowing the monitor cable to be plugged into the defibrillator, even if the original connectors were non compatible.

Patient Risk Current

When interconnecting medical equipment as shown in FIGURE 2, chassis leakage or risk currents may be increased. To ensure patient safety, the hospital biomedical staff should perform electrical safety testing on the complete system to ensure that safe current limits are not exceeded.

Noninvasive Pacing

IMPORTANT: The defibrillator/monitor should not be slaved from another monitor for pacing?

The defibrillator/monitor is primarily used as a demand-mode pacer, which delivers pacing therapy based on the ECG signal acquired through it's patient cable. Placing another monitor in the ECG signal path (as shown in FIGURE 2) may result in unexpected distortions of the pacer-driven ECG waveform, which may, in turn, affect pacing therapy. When pacing, the defibrillator/monitor must be connected directly to the patient through the patient cable.