Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-10-13
2002-04-16
Evanisko, George R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06374137
ABSTRACT:
CONTINUING DATA
This application is a continuation-in-part of application Ser. No. 08/775,827 filed Dec. 31, 1996, now abandoned, for “Method and Apparatus for Reducing Defibrillation Energy.”
TECHNICAL FIELD
This invention relates generally to a defibrillation method and apparatus, and more particularly to a method and apparatus for reducing the electrical energy delivered by an external defibrillator. “Defibrillators” include manual defibrillators, semi-automatic defibrillators and automatic defibrillators. This invention also relates to a method and apparatus for dynamically changing the operation of a defibrillator when treating a pediatric patient.
BACKGROUND OF THE INVENTION
Sudden cardiac death is the leading cause of death in the United States. Most sudden cardiac death is caused by ventricular fibrillation (“VF”), in which the heart's muscle fibers contract without coordination, thereby interrupting normal blood flow to the body. The only known effective treatment for VF is electrical defibrillation, in which an electrical pulse is applied to the patient's heart. The electrical pulse must be delivered within a short time after onset of VF in order for the patient to have any reasonable chance of survival. Electrical fibrillation may also be used to treat shockable ventricular tachycardia (“VT”). Accordingly, defibrillation is the appropriate therapy for any shockable rhythm, i.e., VF or shockable VT.
One way of providing electrical defibrillation uses implantable defibrillators, which are surgically implanted in those patients having a high likelihood of experiencing VF. Implanted defibrillators typically monitor the patient's heart activity and automatically supply the requisite electrical defibrillation pulses to terminate VF. Implantable defibrillators are expensive, and are used in only a small fraction of the total population at risk for sudden cardiac death.
External defibrillators send electrical pulses to the patient's heart through electrodes applied to the patient's torso. External defibrillators are typically located and used in hospital emergency rooms, operating rooms, and emergency medical vehicles. Of the wide variety of external defibrillators currently available, automatic and semi-automatic external defibrillators (referred to collectively as “AEDs”) are becoming increasingly popular because they can be used by relatively inexperienced personnel. Such AEDs are also especially lightweight, compact, and portable. AEDs are described in U.S. Pat. No. 5,607,454 to Cameron et al. entitled “Electrotherapy Method and Apparatus” and PCT Publication No. WO 94/27674 entitled “Defibrillator with Self-Test Features”, the specifications of which are incorporated herein.
AEDs provide a number of advantages, including the availability of external defibrillation at locations where external defibrillation is not regularly expected, and is likely to be performed quite infrequently, such as in residences, public buildings, businesses, personal vehicles, public transportation vehicles, etc. Although operators of AEDs can expect to use an AED only very occasionally, they must nevertheless perform quickly and accurately when called upon. For this reason, AEDs automate many of the steps associated with operating external defibrillation equipment, and the operation of AEDs is intended to be simple and intuitive: AEDs are designed to minimize the number of operator decisions required.
Because AEDs have primarily been designed to treat adult VF and shockable VT, AEDs are typically not recommended for treating pediatric patients. One reason is that pediatric VF is not well documented and understood. For example, the optimal energy required for defibrillating infants and children has not yet been established—although currently available information suggests a starting dose of 2 J/kg. Additionally, the criteria used to analyze adult VF would not necessarily be appropriate for pediatric VF because of physiological differences between adults and pediatric patients. Such differences include, for example, heart rate. Finally, the protocol recommended for treating a pediatric victim of sudden cardiac arrest is different than the protocol recommended for treating an adult largely because pediatric VF is typically associated with respiratory failure. (See, Chameides et al. (Eds.) “Pediatric Advanced Life Support” (1997-1999) American Heart Assn).
FIG. 1
is a functional block diagram depicting an AED
20
and an electrode unit
21
. The electrode unit
21
includes defibrillation electrodes
22
which are connected to a connector
23
by electrode wires
25
. In operation, an operator attaches the defibrillation electrodes
22
to a patient
24
, and plugs the connector
23
of the electrode unit
21
into a connector
26
of the AED
20
. The operator then turns on the AED
20
, and ECG signals are gathered by the electrodes
22
and routed to an ECG amplifier
28
within the AED. An A/D converter
30
receives the analog output of the ECG amplifier
28
, and provides corresponding digital samples to a microcomputer
32
for analysis. If the patient
24
is currently experiencing VF, the microcomputer
32
asserts a control signal to cause a high voltage charger
34
to transfer electrical energy from a low voltage source, such as a battery
36
, to a high voltage energy storage device, such as a capacitor
38
. In the case of semi-automatic AEDs, the operator is then prompted by the AED
20
to issue a shock command by depressing a shock control switch
39
. In the case of fully automatic AEDs, the shock command is initiated by the microcomputer
32
, and no shock control switch
39
is provided. In response to the shock command, the microcomputer operates a discharge switch
40
to deliver an electric shock to the patient
24
through the electrodes
22
.
As mentioned above, the use of AEDs for pediatric patients generally has not been considered, primarily because of concerns with potential operator confusion and machine complexity. When defibrillating pediatric patients, the operator must know the appropriate energy dose to deliver, which is based on the pediatric patient's weight or age. In practical terms, this means that an AED must have the necessary circuitry to accurately produce at least two energy levels (adult and child). Because the AED cannot automatically detect the presence of a pediatric patient, the AED must provide the operator with a means, such as an energy selector switch, to choose the proper energy level. It is also necessary that the AED properly analyze VF in pediatric patient. This may require the AED to be informed, via an operator action, that a pediatric patient is present in order to appropriately modify the ECG analysis to account for the differences between heart rhythms of pediatric and adult patients. The need for an operator to select an appropriate energy level, and to indicate to the AED whether a pediatric or adult patient is present, complicates both the AED design and the operator decision making process each time the AED is used. Added complexity is of particular concern for first responder AEDs which are designed for infrequent use, and are typically used by persons whose primary occupation is not lifesaving (such as police officers or flight attendants). Concerns regarding the possible consequences of such complications have outweighed any expected benefits associated with the small utilization rate of AEDs for pediatric patients. Nevertheless, the inability to effectively treat an infant or child near death is difficult to accept.
What is needed is a simple and effective way of reducing the amount of energy delivered to a pediatric patient by an AED. Additionally, what is needed is a device that lowers the defibrillator energy delivered to a pediatric patient as well as enables the defibrillator to modify its behavior to more effectively treat a pediatric patient. Additionally, what is needed is a device that enables the ECG analysis capabilities to dynamically change when the pediatric energy reduction unit i
Gliner Bradford E.
Jorgenson Dawn
Leyde Kent W.
Morgan Carlton B.
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