Protection circuit for electromedical device.

p0001The invention is a protective circuit to protect a patient who is connected by conduits to electromedical devices, from a dangerous current flow.

p0002For operations (here eg HF surgical equipment is used), in intensive treatment (here the patients are vital Soffe supplied), when measuring body action potentials (eg ECG, EEG, EMG) and other physical quantities (such as temperature), as well as therapeutic measures (eg Nervstimulator ) are brought lines and / or equipment parts on or in the human body to the application that a critical electrical current can result in case of failure by the body, in particular through the heart. The danger is not just. in electrical patient leads (eg ECG, EEG) given but also in other lines (eg, respiration, blood transfusion), as most of these lines are connected to electrical equipment and cause the lines themselves electrically conductive liquids or may have conductive surfaces.

p0003To protect against these threats, the electrical insulation is applied substantially to the ultimately the separation of circuits (eg isolating transformer, optocoupler) is counting. Metal and not for power circuit [gehärende] equipment (eg housing) are with an additional insulation ( "double insulation") provided with or connected to the grounded protective conductor, however, in case of wrong connection or protective conductor interruption with simultaneous outer conductor circuit a previously BEEN danger is first created , In order to guarantee the necessary protection against the dangers of the latter, the device housings are connected to the protective conductor individually and in addition its own lines, that is, a redundant protection created. This additional protective conductor connection is gleichtzeitig for connection of all in the vicinity of the patient extraneous conductive parts. In this way, a so-called established "potential equalization", ie these parts may assume different and dangerous voltages. however, was first created or increased with the disadvantage that while touching live parts an BEEN not previously or decreased risk.

p0004For certain medical treatments (eg surgery or intensive care) is a power failure for the patient can be fatal. For this reason (eg ground fault) disconnection must be prevented at a first technical fault. This requirement is satisfied by the fact that the supply via an isolation transformer and not the two secondary lines is grounded (isolated power). With ground fault only a disconnection is a visual and audible alarm, however.

p0005Alternatively, the sensitive residual current circuit breaker (EFI) is applied. It allows addition to the usual application of the protective conductor a shutdown when the fault current exceeds a value of generally 30 mA. Therefore, this circuit breaker provides protection not only in direct contact with live parts, but also in spannungfsführendem protective conductor (eg incorrect connection), it offers a protection against electrocution at all (with ground fault), because its release current below the lethal threshold current of 50 mA lies. In case contact the shutdown, however, is associated with a significant power surge, because until that switch off, ie, flows in a period of 10 to 40 ms of the full accident current which can amount to about 1 amp. Through the body.

p0006Since the cited threshold 50 mA only valid when the current crossing points relatively far are from the heart (eg, on the outer skin) and have relatively small areas, the EFI-breaker has particularly no protection if at least one stream crossing point on or in the heart is (eg in cardiac catheter application). Here streams of about 0.08 mA already can be fatal, wenhalb safety's sake, a fault current of max. 0.01 mA is allowed. Currents of the order of 0.08 mA may incidentally occur during normal operation and that is when the operation or a fault current at protective conductor can generate a voltage or when capacitive coupling exists. are allegedly due to these and similar causes two decades ago in the US alone approximately 1,200 patients come annually killed (Bulletin SEV 1971 page 1081).

p0007Also, the above-mentioned IT (isolation transformer with insulation monitoring) can in such cases, the need to protect not offer because an error message erat takes place when the fault current exceeds the value range of 2.2 to 4.4 mA. Moreover, protection is also not given if proposed at least two of the devices connected to a patient's continuous Isolationsfehlervorliegt and both transformer secondary leads a fault current.

p0008The electrocution danger is not only greater, a line is closer to the heart, it grows with the number of leading to the patient cables (eg ECG, EEG, EMG ....) and with the number of additional connected measuring and data processing devices such as computer with monitor and printer.

p0009Since the additional precautions necessary protection can not guarantee this is ultimately the only way to realize that quality insulation is used in all devices. It should also be borne in mind that unavoidable capacitive couplings already generate a non-reducible base current. Since the through the heart flowing Wechatrom (50 Hz) must not be greater than 0.01 mA, the required insulation resistance at least 22 Meg ohm must be.

p0010. To implement this requirement, the relevant medical devices including the periphery [device] high-voltage resistant isolation transformers and optocouplers vorgeschrieben.Wenn these components also meet the high standards for themselves with respect to their dielectric strength, so can other circumstances the existing high insulation resistance negate: The long-term practical operation, by environmental influences (eg moisture) the insulation be affected outside of the components, for example by surface line from port to port. The same effect can occur in that from unforeseen necessity thoughtlessly additional peripherals (eg measuring instruments) are hooked up, do not possess the required dielectric strength.

p0011The only protection against the aforementioned risks, the periodic review of electromedical equipment is prescribed in the Federal Republic of Germany since 1986 and carried out. These revisions are associated with considerable Persona Lund Financial expenses (BRD: schätzungsweiae DM 1.5 billion annually). It also should be that the achievable risk reduction is relatively low; because an insulation damage generally occurs suddenly. An accident is then only a matter of time, the next test date usually then no longer matters.

p0012Proposals for more effective protection measures have become known. For example, it is proposed to eliminate the influence of capacitive couplings by using direct current (Bio-Medical Technology Volume 34, Supplement 1989, p 134). proposed Next If dervermehrte use of isolation transformers (eg for each individual device) (Biomedical Engineering Volume 35, Supplement, 1990, page 272). The implementation of these proposals would only apply to new devices in question and would not provide a solution for the equipment in operation. Next, the first proposal would bring no equivalent improvement despite additional expenditure. In the second proposal, the improvement would be better, but still insufficient.

p0013The present invention is based, with little effort to realize a protection of the patient, is independent of the insulation condition of the connected devices, and without the faulty plant must be shut down fully effective the task.

p0014The invention achieves the object according to claim 1, characterized in that there are voltage-limiting components between all lines leading to the patient's body. The following sub-claims contain advantageous developments of the invention.

p0015In the drawings, the problems given and the inventions formation solution according to examples shown.

p0016In Fig. 1, the patient P is connected to the line 1 of the ECG device. For clarity, is located no further discharge in addition to the ground line E. The device is powered via the earthed socket St directly from the general power transformer T via the lines L and N. R is the load resistance of the device EKG and A is the exit point for the patient line 1. The device housing itself is connected to the protective conductor SL.

p0017If the unit from the conductor L, a circuit for Geräteauslaßstelle A, ie the intervening insulation resistance Ris inadmissible small (eg 2000 ohms), then there is for the patient Danger (88 mA accident current at 220 volts and 500 ohms body resistance).

p0018In FIG. 2, the same situation as in FIG. 1 is illustrated, except that in addition, the protection circuit according to the invention (G1, G2) is applied. When a hazardous, ie low Isolatiönswiderstand Ris, for example 2000 ohms, falls on the voltage limiter, that is at the opposite polarity connected in parallel rectifiers G1 and G2, only a voltage of 0.5 volts, with the consequence that flow through the patient's body than 1 mA , The current is completely harmless when the current crossing points are, as here, on the body outer surface and sufficiently far from the heart away.

p0019Since the human body outwardly emitted and, measured body action potentials (eg ECG, EEG, EMG) are barely above 2 mV (in exceptional cases in ECG measurements in heart nearby to 7 mV), disturbs the voltage limiter, where the limiting capacity in the best begins Fallerst at 80 mV, the measurements are not, as it in such small landing voltages an intrinsic resistance of several 100 Meg-ohms. The to the current sources in the human body (eg, heart, muscle) parallel body resistances are lower by several orders of magnitude. Also indicated in Fig. 4 current limiting resistors (Rs and Rv) hardly affect the measurement results, if they do not exceed eg 10 K-Ohm.

p0020In Fig. 3 a cardiac catheter device HK in addition to the ECG connected. As long as the insulation resistance of the device Ris does not fall below the value of 22 Meg-ohm at grounding of the patient, the current flowing through the patient leakage current exceeds the value of 0.01 mA not know what freedom means danger.

p0021Suppose the insulation resistance in the cardiac catheterization device HK is Ris1 = 2 Meg ohm, then flows from the past in the heart catheter, a current of 0.11 mA through the body to the ground E, which is associated with a death. The risk was not significantly lower in omitting the ground line E because a zuzätzlicher insulation fault in another device (eg RIS2), or / and the body contact by a second person (eg doctor, who must feel no electricity itself!), And / or produce capacitive coupling to ground an unavoidable relatively low impedance connection to the earth.

p0022In FIG. 4 the same situation as in FIG. 3 is shown, except that in addition, the protection circuit according to the invention is applied. If dangerous for cardiac catheter application insulation resistance as Ris = 2 Meg-ohm falls on voltage limiter G5 and G6 still a voltage of eg 0.4 volts, but the resistors Rvl and RvE (eg with 10 K-ohms) limit by the heart flowing current to a safe value, then 0.02 mA.

p0023As apparent from the circuit, the patient is not only protected with a dual-circuit conductor, but also in direct contact with a live conductor or direct contact of the earth.

p0024In FIG. 5, the protection circuit is shown in improved performance. A cascade connection, here Ga and Gb, the voltage limit may be reduced in connection with Ras on an even deeper level. In addition, (eg short circuit) cause no harm, because in this case, the upstream fuse Si interrupts the power supply by a suitable choice of the first voltage limiter Ga seeking a low-resistance insulation resistance.