Maintenance schedule for different equipment and their records in a hospital By Mr. Rahul kumar

 Most commonly used electric equipments in the hospitals are : Computers Refrigerators Cardiac monitors Pulse oxymeter Nebulizer Syringe pump Glucometer Ultrasound CT & MRI machines Ventilator Defibrillator  Proper care and maintenance is very important for proper functioning of equipment.

Physiological effects of current

Ventricular fibrillation In cases of shock due to unwanted connection to power grid voltage, current passing through the heart is considered the most dangerous effect and can cause ventricular fibrillation (ventricles) with fatal consequences Ventricular fibrillation is completely irregular, asynchronous heartbeat; no synchronism in ventricular contractions, blood flow stops and if such heart work does not stop, it leads to death within a few minutes

 Body weight and fibrillation, duration of the current Several studies using animals of various sizes have shown that the fibrillation threshold increases with body weight Fibrillating current increases from 50 mA rms for 6 kg dogs to 130 mA rms for 24 kg dogs.

Leakage currents Occur between conductors that are not in direct contact (touch) and are at different potentials For devices that are powered from the grid, leakage currents are: – capacitive character (spreading capacity) – operative character (current through the insulation, dust, humidity...)

Leakage currents

Leakage currents pathways Pathways of leakage current through the patient a) Intact ground lead b) Broken protective ground lead, patien connected to ground through a catheter c) Broken protective ground lead, patien connected to ground by an electrode or unintentianally.

Point of entry (macroshock and microshock) Microshock:- Macroshock:- All the current applied through an intracardiac catheter flows through the heart small currents called microshocks can induce Ventricle fibrillation Current of about 20 µA can cause microshock. The widely accepted safety limit to prevent microshocks is 10 mA. When current is applied at two points on the surface of the body, only a small fraction of the total current flows through the heart (macroshock). The magnitude of current needed to fibrillate the heart is far greater when the current is applied on the surface of the body than it would be if the current were applied directly to the heart

Isolated-power systems Any ground faults can posses hazard. A ground fault :- Is a short circuit between the hot conductor and ground that injects large currents into the grounding system.  Isolation of both conductors from ground is commonly achieved with an isolation transformer isolation transformer + line isolation monitor Measures the total possible resistive and capacitive leakage current (total hazard current) that would flow through a low impedance if it were connected between either isolated conductor and ground. When the total hazard current exceeds 3.7 to 5.0 mA for normal line voltage, a red light and an audible alarm are activated Checking the lines by the LIM can interfere with (ECG,EEG,ect.),or it can trigger synchronized defibrillators

Limits on Leakage Current Limits on Leakage Current for Electric Appliances

Basic approaches to protection against shock Reliable grounding for equipment Reduction of leakage current Double-insulated equipment Operation at low voltages Electrical isolation There are two fundamental methods of protecting patients against shock:- 1. The patient should be completely isolated and insulated from all grounded objects. 2. All sources of electric current and all conductive surfaces within reach of the patient can be maintained at the same potential, which is not Isolated heart connections  For the power distribution For the equipment necessarily ground potential  In practical neither of these approaches can be fully achieved so we used :-  Grounding system  solated pow distribution system  Groun fault circuit interrupters (GFCI)

Protection: power distribution Grounding system - A grounding system protects patients by keeping all conductive surfaces and receptacle grounds in the patient ’s environment at the same potential The grounding system has 1. a patient-equipment grounding point 2. a reference grounding point 3. and connections

Isolated-power systems A ground fault :- Is a short circuit between the hot conductor and ground that injects large currents into the grounding system.  Isolation of both conductors from ground is commonly achieved with an isolation transformer isolation transformer + line isolation monitor Measures the total possible resistive and capacitive leakage current (total hazard current) that would flow through a low impedance if it were connected between either isolated conductor and ground. When the total hazard current exceeds 3.7 to 5.0 mA for normal line voltage, a red light and an audible alarm are activated Checking the lines by the LIM can interfere with (ECG,EEG,ect.),or it can trigger synchronized defibrillators

Protective grounding Generally, patients are only occasionally and accidentally exposed to risk of getting in touching with devices whose conductive parts may be energized In hospitals, especially in intensive care units, patients are deliberately connected to the diagnostic and/or therapeutic electrical devices/equipment – particularly careful with the isolation of any conductive parts connected to the heart or its vicinity from all other conductive parts – all conductive parts in the vicinity of the patient must be connected to a single point grounding (eg, metal bed, cupboard, etc.) – periodic testing of the grounding impedance must be provided Tolerable difference in potential between the grounded conductive parts in clinical areas: – in the general - of 500 mV – intensive care and other critical cases- of 40 mV

Determination of device categorie