5 th year (Control department)

Transcription

1 Benha Faculty of Engineering Benha University 5 th year (Control department) Clinical Equipment Management(E527) Examiner: Dr.Waleed A.A Salem Final Written Examination 2012 / 2013 Time : Three Hours Answer the following questions Question one: Choose the best answer: (YOU CAN SELECT MORE THAN ONE ANSWER){ 10 Marks} 1) The isolation monitor (LIM) on the wall of the operating room is to alert one to d) An excessive electrical leakage from either side of the power line to ground 2) A ground fault circuit interrupter: b) Is never used in OR 3) Determine the safe or not a shock hazard point exists for a person standing on the ground, by touching any one of the points labeled in this faulted circuit e) Point "E" 4) For Electrical Safety Analyzers (as shown), in case of "neutral open",which LED will be on? a) LED 1 b) LED 2 c) LED 3 5) In case of hot /ground reversed,which LED will be on? a) LED 1 b) LED 2 Question two: Complete: [10 Marks] 1. Hospital receptacles should be tested for proper wiring, adequate line voltage, low ground resistance & mechanical tension. 2. Leakage current can be reduced by adding a ground wire from equipment metal chassis to a common ground terminal. 3. The third wire in power systems serves to blow the fuse if hot wire short to equipment metal case,and to drain off leakage current to earth ground. 4. The effect of electrical current passing through the body includes injury to tissues, involuntary muscle contractions,& Fibrillation to the heart. 5. The maximum differential voltage standard in critical care area is 40 mv,& for general care area is 500 mv.

2 Question three: Answer the following question in brief [10 Marks] a) If you scuff your feet across a carpeted surface on a dry day you will produce an electric potential resulting from a static electric charge that may range in order of tens of thousands of volts! Can this pose a danger to you, at least in principle? No, Because this electrostatic discharge is Instantaneous and affect for a very short duration so had no ability to source electric current throughout body Instantaneous b) How to prevent patient shock or electrocution in case of safety ground failure? suggest points 1) Reduce internal equipment leakage current to below standard level. 2) Continuously monitor ground wire continuity. 3) Add an additionally ground wire in parallel with the power cord safety ground. 4) Periodically inspect ground connection integrity. 5) Use a power-isolated system that isolates the equipment, and hence the patient, from neutral ground c) All other factors being equal, which possesses a greater potential for inducing harmful electric shock, DC electricity or AC electricity at a frequency of 60 Hertz? AC has been experimentally proven to possess greater hazard than DC d) Distinguish between macroshock and microshock. Give example for each. Macroshock : a high value current level(ma) which passes arm to arm throughout the body by (skin) contact with a voltage source

3 Microshock : a low level current (µa) which passes directly through the heart via a needle or catheter (bad effect > 10 µa) Question four: [18 Marks] a) Explain with drawing the important susceptibility parameters ( frequency & duration). Frequency Note that the minimal let-go current happens at the precise frequency of commercial power-line, 50-60Hz.

4 Let-go current rises below 10 Hz and above several hundred Hz. Duration The longer the duration, the smaller the current at which ventricular fibrillation occurs Shock must occur long enough to coincide with the most vulnerable period occurring during the T wave.

5 b) What is GFCI? And where it is used in healthcare systems? Explain with aid of drawing its operation. GFCI Used in all circuits serving bathrooms, garages, outdoor receptacles, swimming pools and construction sites also must fitted with GFCI. Patient care areas are typically not fitted with GFCI, since the loss of power to life support equipment can also be equally deadly! GFCIs are used to protect from ground faults by interrupting the circuit and disconnects the faulty instrument. c) How can electrical isolation can be achieved by good: a) Instrument design. b) Circuit design. Give with drawing one example for each case. Instrument design - ECG machines had a fuse - This design is used to prevent a difference of potential a cross the patient body This fuse connected to the right leg of the patient This fuse is leads to limit current to 5mA Disadvantages of this type of ECG: Fuse blow when the current equal to 5mA,this is large value and hazard especially in ICU CCU

6 Circuit design. Isolation amplifiers are devices that break the ohmic continuity of electric signals between the input and output of the amplifier. This isolation includes different supply-voltage sources and different grounds on each side of the isolation barrier. Isolation amplifiers usually consist of an instrumentation amplifier at the input followed by a unity-gain isolation stage.

7 c) "Potentially most damaging leakage is the one with patient leads, since they typically have low impedance patient contacts, current should be restricted to 50µA for non-isolated leads and to 10 µa for isolated leads". What does isolated and non-isolated mean? Explain with drawing the possible tests for leakage current in patient leads to ground. a. Leakage current in patient leads is particularly important because these leads are the most common low-impedance patient contacts. b. Current should be restricted to 50µA for non-isolated leads and to 10 µa for isolated leads (used with catheters / electrodes that make connection to the heart) Test for leakage current from patient leads to ground. Question five: [12 Marks] 1) If the patient is lying on an electrically operated bed in ICU, the ground connection from the wall plug to the bed is faulty. The patient is equipped with a pacing catheter connected to a small battery operated pacemaker; the patient is connected to ECG monitor. The right leg ECG electrode is connected to the hospital grounding system through the monitor. Assume that

8 attendant comes to bedside to adjust the pacing catheter connections and without thinking simultaneously touches the pacemaker terminals and bedrail. If the attendant s resistance is 500 Ω, the patient s resistance is 500 Ω, and the differential voltage between the attendant s right hand and the patient s right leg is 200 mv. a) Does current pass through the attendant? Yes. b) If so, how much? 200 µa c) Is this a macroshock or microshock situation for the attendant? Macroshock situation. d) Is the attendant most probably shocked (above sensation)? No. e) Is the attendant most probably electrocuted (killed) by modern standards? No. f) Does current pass through the patient? Yes. g) If so, how much? 200 µa h) Is this a macroshock or microshock situation for the patient? Microshock situation. i) Is the patient most probably shocked (above sensation)? Yes. j) Is the patient most probably electrocuted (killed) by modern standards? Yes 2) No current pass through the pa ent (pa ent is safe) j à{ Åç uxáà ã á{xá