Patent Application
20130284168
This invention relates to the field of analgesia and conscious sedation. More particularly, this invention provides an apparatus and method for the delivery of halogenated ethers for producing analgesia in a patient.
Since the mid-1800's conscious sedation/analgesia has been used in hospital and pre-hospital settings to relieve pain. Nitrous oxide (N2O) has been the primary inhalant agent in this regard. Sedative hypnotics such as diazepam and midazolam have been used as alternatives as have any number of barbitutes, opioids and agonist/antagonist agents.
Dentistry and oral surgery were the first applications of nitrous oxide conscious sedation and gained wide-spread acceptance following successful use on Queen Victoria. Subsequently, the use of conscious sedation spread throughout the hospital, to emergency rooms, in ambulances, and in other doctor offices.
Conscious sedation is a pain-blocking technique that allows a patient to remain partially alert during an invasive procedure. Analgesia is provided but, unlike anesthesia, the patient maintains awareness and recall. Specifically, the method is unique because patients do not perceive pain, but preserve their protective reflexes, maintain airways independently, and arouse in response to stimuli. Thus the risks of reduced or suppressed respiration associated with anesthesia are mitigated.
There are many benefits associated with conscious sedation. In particular, conscious sedation reduces anxiety in patients, particularly children. Accordingly, medical procedures are easier for the patient and the health care provider, as conscious sedation reduces patient tension and resistance to treatment. Furthermore, the technique has the potential for expansive applications. Studies have shown success with patient controlled analgesia.
The inhaled halogenated ethers offer a number of advantages in critical categories versus nitrous oxide conscious sedation or conscious sedation employing the sedative hypnotics. An example of some of the comparison with these agents is shown in Table 1.
The combination of these features makes the halogenated ethers attractive candidates for conscious sedation. However, there is also a need for a safe, accurate and cost effective delivery system.
The use of nitrous oxide based conscious sedation has declined in recent years principally reflecting the issues with the safety profile of the gas including those items listed above, but also because of its interference with methionine synthesis in prolonged exposure. Thhese factors are particularly relevant to female health care professionals of childbearing age who face increased risk of spontaneous abortion due to nitrous oxide's teratogenetic profile.
N2O is relatively impotent. As discussed in the description of the invention below, this impotence requires that limits are placed on the inspired percentage of N2O to insure patients receive sufficient oxygen. The concentration of oxygen in the atmosphere approximates 21%. As a result, most international regulatory agencies, including the United States Food and Drug Administration (“FDA”) established oxygen delivery guidelines to avoid hypoxia. The most common ratio is 70% N2O/30% oxygen, although some delivery systems maintain 50% oxygen. At a 70% mixture of N2O, conscious sedation occurs in most patients. The 70% N2O/30% oxygen mixture, on a sustained basis at the delivery level has a Minimum Alveolar Content (“MAC”) of 0.636 MAC.
Six inhaled ethers are in use today: halothane, methoxyflurane, enflurane, isoflurane, sevoflurane and desflurane. (Terrell, then of Airco, Inc., synthesized enflurane, isoflurane and desflurane.) These compounds were developed focusing on being non-flammable, non-addictive, potent, having rapid induction properties and cardiovascular stability. Traditionally these products have been packaged in 100 ml and 250 ml brown glass bottles and vaporized using an agent specific, temperature compensated system.
These drugs were developed for anesthesia. None of the inhaled ethers was developed as an inhalant analgesic. This reflected industry perceptions that either there was no need for an inhalant analgesic or there was the absence of cost-effective specialized equipment to administer these agents as analgesics. The equipment developed for anesthesia use in hospital settings was both sophisticated and expensive, frequently costing over $100,000. The combination of these factors virtually eliminated the ability to use these drugs as conscious sedation agents, particularly in the pre-hospital setting.
The invention may be embodied as a method or system, such as:
1. A method for delivery of a mixture to a patient effective to produce analgesia without loss of consciousness in a patient wherein the method comprises:
For a fuller understanding of the nature and objects of the invention, reference should be made to the accompanying drawings and the subsequent description. Briefly, the drawings are:
Modern inhalation agents are halogenated ethers. They are generally characterized by a specific gravity between 1.0 and 2.0, low molecular weights (165.0-200.0), a low boiling point (22 degrees C. to 104 degrees C.), and significant potency—0.16%-7.8% of an agent on oxygen will put 99% of adults into anesthesia. These particular variables are important in the characterization of this invention as the drugs are converted from liquid to gas and delivered with a carrier gas—usually oxygen hut sometimes a combination of oxygen and another gas or gases including oxygen, nitrous oxide and/or air.
However, the agents vary in many important respects. Some agents including methoxyflurane, halothane and sevoflurane are known to react to metals. To some extent these same agents decompose in the presence of “soda lime” (calcium hydroxide) and/or UV light. To a greater or lesser extent, all halogenated agents are solvents. A delivery system for conscious sedation must be compatible with the agent in use.
The potency of anesthetic agents is measured by the minimum alveolar concentration of an anesthetic producing immobility in 50% of patients, defined as 39 year old males, undergoing surgical incision (“MAC”). The MAC of potent inhaled agents varies significantly. The MAC of nitrous oxide, the leading inhalant conscious sedation drug, can only be determined under unusual conditions of temperature and pressure, such as a hyper barie chamber, when additional dosages can be provided without creating hypoxia. Research suggests the MAC of nitrous oxide to be 110%. Thus, to create anesthesia, most patients would suffocate. Conversely, the MAC of methoxyflurane, an early-halogenated ether is only 0.16%. In present inhalant conscious sedation systems, nitrous oxide is delivered in conjunction with a minimum of 30% oxygen to insure the patient maintains a sufficient level of oxygen. In the United States, the Food and Drug Administration (“FDA”) has set 70% nitrous oxide as the limit for delivery in a conscious sedation unit. For this description a MAC equivalent of 70% nitrous oxide will be used for comparison with other inhalants, as shown in Table 2.
For patients who would benefit from higher levels of oxygen delivery including, but not limited to those with Coronary Artery Disease (CAD)), replacement of nitrous oxide with an inhalant analgesia could provide improvement in myocardial oxygenation.
To deliver a concentration of the relevant agent that creates analgesia but not loss of awareness (either amnesia or loss of consciousness) requires a finely calibrated instrument through which the agent can flow with very minimal risk of overdose or delivery of hypoxic mixture (
As shown in
Clinical utilization of conscious sedation system is possible in a wide ranging number of procedures including but not limited to dental and oral surgery procedures, burn debridement, pain relief in emergency and trauma situations, administration in the intensive care, cardiac care or critical care units, in examination or work on the extremities including podiatric procedures, labor and delivery, to reduce anxiety in individuals with fear of needle insertion, and where prolonged immobilization would be difficult without the delivery of a sedation agent.
Additionally, the invention has the following attributes. The invention increases oxygenation of blood, an important feature for individuals with poor myocardial or cerebral oxygenation. The invention increases occupational safety when analgesics described herein are substituted for nitrous oxide, an important feature for women of child-bearing age. The invention can reduce claustrophobia-associated anxiety and relieve pain in patients facing prolonged periods of inactivity, such as during nuclear magnetic resonance imaging (MRI) when used with an MR-safe (1.5 tesla) version of the delivery system. Similarly, the invention may be used for sedation in Intensive Care Units (ICU), Critical Care Units (CCU), or during cardiac catheterization, implantable defibrillator or pacemaker adjustments, and in general pain relief. The device may be provided in alternative configurations, such as with a stand or method for holding patient monitors, including integration of the monitors with the system. Additionally, the device may be provided with a regulator system that senses the depth of a patient's inhalation to allow safe patient controlled analgesia administration.
Having provided an overview of systems that are in keeping with the invention, descriptions will now be given of features that may be found in a system according to the invention.
Active Scavenging:
Inhalation analgesics are fluorocarbons and greenhouse gases. See Table 3. Regulatory and environmental legislation have been enacted in a number of markets, particularly Canada and Western Europe, to protect operating room staff from repeated exposure to these agents. Further, some groups have counseled their members to include potential greenhouse gas impact of the agents if the choice does not impact therapeutic outcome.
In an embodiment of the invention, active scavenging devices are used to recover the inhalation analgesics exhaled by the patient.
Inhalation agents offer real therapeutic benefits when used as sedatives or analgesics including profound pain relief, very rapid recovery, lower incidence of drug interaction reflecting their primary pathway of respiratory excretion and minimized risk of post procedure delirium, particularly in the elderly. A challenge in using these drugs in non-traditional settings (examples include but are not limited to: ICU/CCU and diagnostic rooms in the hospital; doctor and dental offices, and field emergency locations) is that these settings frequently do not have waste gas scavenging systems.
Thus the patient, theatre staff and environment are exposed to the low levels of agent the conscious sedation system patient scavenging system captures. In an embodiment of the invention, an active scavenger is included. The active scavenger captures waste agent, separates the waste agent from the exhaled gases, principally carbon dioxide, and accumulates the waste agent for either appropriate incineration or recycle back to an analgesic when appropriate recovery technology is developed and approved by informed regulatory agencies, such as the United States Food & Drug Administration (“FDA”).
Monitored Care:
In 2011, the American Society of Anesthesiologists (“ASA”) approved guidelines for the administration of mild and moderate sedation to include different types of patient monitoring. These monitors included non-invasive blood pressure (“NIPB”), pulse oximetry (“SaO2”), EKG, and respiration monitoring. An example of respiration monitoring would be capnography. A system according to the invention may include systems for monitoring these aspects of the patient.
Oxygen Concentrator:
The need for sedation and pain relief is not limited to hospitals, free standing surgical, or doctor office settings. The use of an oxygen and/or an air cylinder provide only limited periods of portability in a conscious sedation system. Smaller cylinders allow greater portability but have limited useful life. It is a further challenge to replace these cylinders in rural, field or emergency settings. As such, there is a demand for a self-generating oxygen system that can be incorporated in the device to allow its on-going use in these field and trauma situations. An embodiment of the invention may include an oxygen concentration device into the system.
Drug Identification:
A system according to the invention may include systems for assuring that the correct drug is used. Because the physical properties (density, viscosity, vapor pressure, heat content, etc) and the medical properties (potency, minimum alveolar concentration, ease of induction, side effects, etc.) of the individual inhalation agents differ, the device must correspond to the agent that is being delivered. Engineering standards (i.e., ISO, ASTM standards) dictate that precautions be taken to ensure that the correct drug is used with the correct device.
One way to identify drugs is by RFID (radio frequency identification) labeling. See
Another way to identify drugs is by bar scan labeling. A label (See
For example, a conscious sedation device that is designed and built to deliver sevoflurane to patients must only allow sevoflurane to enter. The sevoflurane conscious sedation device may have an RFID or bar code reader installed on it. The sevoflurane bottles may have labels that include RFID or bar codes on them that uniquely identify them as containing sevoflurane. The software on the sevoflurane conscious sedation device may be programmed to read the drug bottle RFID tag or bar code. If the RFID tag or bar code identifies the drug as sevoflurane, then the sevoflurane conscious sedation device would operate normally, and allow liquid sevoflurane from the bottle to enter the sevoflurane conscious sedation device, flow into a reservoir, be metered into a flow of oxygen where it vaporizes, and then conveyed to the patient to effect conscious sedation.
Note that conscious sedation devices can potentially be used with a single agent (sevoflurane, enflurane, desflurane, isoflurane, halothane) or potentially with a multiple of these agents. The drug labeling and device programming would fit the specific case. For example, for a conscious sedation device that operates with sevoflurane, halothane, and isoflurane, the reader would identify that these three drugs could be suitable for use with the device, whereas other drugs (or other liquids in bottles) are not suitable for use.
If the RFID tag or bar code identified the drug or liquid as different than a drug permitted for that system, then the conscious sedation device would indicate an error code, notify the user that the wrong drug or liquid is attempting to be used, and would not allow the drug to enter the system.
Data Gathering:
Documentation of patient monitoring, drug usage data, and procedure duration during medical or dental procedures is important for patient safety and billing purposes. Patient monitoring, such as ECG, blood pressure, oxygen saturation levels, pulse, breathing, and/or exhaled carbon dioxide provide medical practitioners with the ability to monitor the health of the patient when sedated. Actions can be taken to ensure that the patient remains healthy during a procedure. The duration of the procedure and the amount of drug used for a patient also can be used to bill patients.
Documentation of this data may be facilitated by downloading data to a patient chart, a hospital information system, personal digital assistant, or similar device. An embodiment of the invention may include one or more devices for receiving, storing and subsequently providing such data, for example by hardcopy, communication ports, or wirelessly.
A system according to the invention may incorporate a printer and/or electronics to enable these capabilities. The device may periodically record data from each of the patient monitors (ECG, blood pressure, oxygen saturation levels, pulse, breathing, and/or exhaled carbon dioxide) and/or variables from the micro-flow titration system (oxygen flowrate, agent concentration). Such a system may calculate or measure the amount of agent and oxygen that is used and record that data periodically.
The data may be retained in memory and/or printed periodically or at the end of each procedure, or day, or week. The data can be downloaded from memory through cables attached to a communication port, such as USB, RS-232, firewire, serial ports, parallel ports, specialized ports, etc. The data can be downloaded from memory wirelessly using Bluetooth, wireless modem, infrared, and/or Wi-Fi, or equivalent technology. Preferably such data can be formatted expeditiously to fit into patient electronic records, paper records, and/or hospital information systems.
Bottle Holder:
The bottle containing the inhalant analgesic may be held in position by a multifunctional bottle holder system. An example of such a system is depicted in
Pressurized Tank:
For accurate and reproducible micro liter dispensed volumes of liquid analgesic into a flow stream, several system constraints along with pressure characterize system performance may be implemented. A reliable means of controlling flow can be obtained by combining, a micro-flow titration system with a reservoir pressurized by a regulated oxygen source. The amount of pressure needed will depend on the fluid properties of the liquid being dispensed (viscosity, density, etc), gas flow rates (1-10 LPM) as well as, the dispenser mechanism being used. It may be that the amount of pressure for a particular system may need to be determined experimentally. Too little or too much pressure may result in inaccurate liquid metering. In the first instance the liquid may collect in the micro-dispensing valve and accumulates. In the second instance the liquid may splatter. We determined that a pressurized reservoir at between 0.5 and 20 psig is advantageous to accurately dispense the inhalant agent into the oxygen flow stream. Figure depicts a system having a pressurized reservoir.
Masks:
A conscious sedation system according to the invention may be used to deliver an inhalant analgesic agent, such as sevoflurane, along with oxygen in order to produce analgesia and/or conscious sedation so that acute care procedures may be carried out. The choice of delivery devices for oxygen and the inhalation agent depends on many factors, such as the application for which the delivery device is being used, efficacy of the delivery device, and patient acceptance.
Centralized Systems:
The invention may have redundant handling of the inhalant drug, oxygen, and/or of waste gases for the safety of both the patient and the user. The device may be equipped with a sub-sized oxygen tank and with a portable scavenging system. This improves portability of the invention, while maintaining usability in non-traditional settings (examples include but are not limited to: ICU/CCU and diagnostic rooms in the hospital; doctor and dental offices, and field emergency locations), where a centralized waste gas scavenging system and/or an oxygen line are unavailable. However, the invention may be able to interface to the centralized/wall-mounted oxygen/scavenging lines, if they are available. In this case, the on-board oxygen tank will serve as a backup in case of failure of the main line.
To further improve safety and redundancy it is possible to add a small reservoir of inhalant drug within the manifold itself.
Although the present invention has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present invention may be made without departing from the spirit and scope of the present invention. Hence, the present invention is deemed limited only by the appended claims and the reasonable interpretation thereof.
This application is a continuation-in-part of U.S. patent application Ser. No. 10/272,794, which was filed on Oct. 17, 2002. Ser. No. 10/272,794 claims the benefit of priority to U.S. provisional patent application 60/330,063. This continuation-in-part patent application claims the benefit of priority of Ser. No. 10/272,794 and Ser. No. 60/330,063.
| Number | Date | Country | |
|---|---|---|---|
| 60330063 | Oct 2001 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10272794 | Oct 2002 | US |
| Child | 13794733 | US |
