Mil-Std-461G
Specified for Surgical Suite Lighting
What is the purpose of Mil-Std-416G in surgical suites? If you follow along you will understand how it was chosen and why it is important to patient safety. During surgery, the patient's health is monitored using sensitive electronic medical devices. Some of these devices measure very small voltages taken from the outer surface of the body to indicate things like heart (ECG) or brain activity (EEG) as well as levels of sedation and respiration. These devices are connected to the patient with conductive pads and leads. The typical measurements are in microvolts (1V= .000001 volt) and are very small indeed.
Patient Safety
The patient's health and safety is crucial during surgery and is monitored accordingly.
These values are displayed over time on a graph. This is what creates that pattern we are all familiar with from hospitals. However, there is much more information gathered and if it's accurate, it can help the medical staffunderstand patient health moment by moment throughout the surgical procedure. Accuracy is improved without interference from electrical equipment.
EMI and RFI
Electrical devices can radiate and conduct electrical noise to other electronics, especially those designed to sense electrical signals. As an example, radios and TVs are designed to receive broadcast signals and can have interference from nearby running motors or distant lightning. This is called EMI or electromagnetic interference. RFI or radio frequency interference is the higher frequency noise. A similar situation existed in the surgical suite. High power lighting loads are running just a few feet above a patient. The patient and their connections to the ECG or EEG can act like an antenna, receiving both signals and noise. The lighting fixtures are identified as a source of RF noise in the surgical suite, creating interference with the proper measurement of the patient. There are two types of interference, conducted and radiated. Conducted interference are emissions which travels back from the fixture power wiring into the hospital electrical system and to the electrical equipment used during surgery. This noise can affect many kinds of equipment, not just devices like ECG and EEG. Radiated interference emissions travel from the fixture, through the air, like a transmitter. The patient and their leads are the antenna, and the equipment is the receiver. The receiver must separate the noise from the signal. It would be far better if there were less noise. Because the lighting fixtures are using high frequency switch-mode power supplies to drive LEDs. that are placed just over the patient, they create both conducted and radiated emissions. Proper care needs to be taken in fixture selection to be sure that the fixture has arrested conducted and radiated emissions. The care comes in the form of testing to relevant standards.
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