Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
2000-04-05
2004-02-24
Lo, Weilun (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S913000, C128S201130, C128S203260, C128S207140
Reexamination Certificate
active
06694977
ABSTRACT:
RELATED APPLICATIONS
The present invention relates to ventilator and heat exchange systems and, more particularly, to a “mixed-mode” gas-plus-liquid ventilator system using an endotracheal catheter to add and remove liquid ventilation or heat-exchange medium from the lungs continuously and/or cyclically, with delivery of gas to the lungs at a rate and volume independent of addition and removal of liquid.
FIELD OF THE INVENTION
The present invention relates to ventilator and heat exchange systems and, more particularly, to a “mixed-mode” gas-plus-liquid ventilator system using an endotracheal catheter to add and remove liquid ventilation or heat-exchange medium from the lungs continuously and/or cyclically, with delivery of gas to the lungs at a rate and volume independent of addition and removal of liquid.
BACKGROUND OF THE INVENTION
There are many situations in both human and veterinary medicine where it is desirable to rapidly induce or reverse hypothermia. There are also many clinical situations where it is essential to be able to rapidly reduce dangerously elevated body temperatures to near normal, as in the case of hyperthermia from heat stroke, drug or surgical anesthetic reaction, and febrile illness secondary to stroke, infection or other illnesses. In fact, it has been demonstrated in a number of studies that patient mortality is directly dependent on high temperature exposure time, and inversely dependent on the rapidity with which core temperature-is normalized.
Heretofore, the only clinically available means of achieving very rapid reduction in body temperature (or conversely, of re-warming from hypothermic temperatures) has been the use of invasive methods of heat exchange, such as cardiopulmonary bypass (circulating blood over a heat exchanger), or peritoneal and/or pleural lavage. A third, slower alternative for changing body temperature involves immersing the patient in a bath of heated or chilled liquid or gas (e.g. helium). The problems with these approaches are many:
1) External means of chilling or re-warming are relatively slow (<0.01° C. to 0.20° C./min), and produce a host of undesirable and sometimes lethal complications. In the case of cooling, the chilling of external body tissues results in vasoconstriction which interferes with the delivery and removal of oxygen, nutrients, and wastes from the peripheral tissues.
2) Re-warming from hypothermia by external means can cause a peripheral vaso-relaxation, hypotension, and effective hypovolemia, for which the cold-impaired heart and autonomic nervous system cannot compensate. Profound hypotension may develop, causing cardiac arrest and death, sometimes paradoxically in people presenting for apparently non-critical conditions.
3) Peripheral tissues being re-warmed recover the need for oxygen and metabolic substrates before the circulatory system and other organs can deliver them (since these organs are still cold and functioning marginally). This resulting imbalance between metabolic supply and demand results in the generation of large amounts of anaerobic waste products, including carbon dioxide and lactate, which decrease blood and tissue pH and result in severely disturbed homeostasis.
4) If external re-warming proceeds without inducing cardiac arrest, a second phase of risk occurs when “after-drop” is experienced. After-drop is a reduction in body core temperature during slow external re-warming. After-drop occurs as a result of peripheral vasodilation during patient re-warming, thus allowing large amounts of blood to flow through deeply chilled peripheral tissues, resulting in a seemingly paradoxical drop in body core temperature. After-drop can result in cardiac arrest during patient re-warming if the heart is cooled below its critical threshold for fibrillation. Though some controversy exists about the relative importance of this process in humans, it still remains of great concern to specialists in the field.
5) The use of invasive temperature modifying techniques such as peritoneal and pleural lavage, extracorporeal perfusion, or central venous cooling, are either not very effective (e.g. lavage techniques), or can be performed only in a medical setting by highly skilled, licensed practitioners (e.g. physicians). Most importantly, these techniques cannot be safely or reliably performed in the field by paramedics or other non-physician emergency medical personnel. In the case of techniques which require vascular access, many medical facilities possess neither the complex and costly equipment required to carry out such procedures, nor the highly skilled personnel necessary to perform such procedures. A particular problem with these methods is the need for bulky, complicated, failure-prone equipment which may be difficult to store in states of readiness (e.g. cardiopulmonary bypass apparatus). Technical errors and mechanical failures associated with extracorporeal techniques carry a high risk of morbidity, with such errors frequently resulting in neurological damage or loss of life.
The Lungs as a Gas Exchanger and Heat Exchanger
An alternative to invasive temperature modifying techniques would be to use the large surface area of the lungs as a heat exchanger. Nearly all of the cardiac output (i.e., all blood flowing to the body) flows through the lungs, and since the lungs possess a surface area of at least 70 square meters, they form an ideal heat exchanger that would allow for rapid core cooling and re-warming of the patient without the problems associated with the techniques previously discussed. In addition, since the lungs are accessible via the trachea, the relatively benign maneuver of endotracheal intubation (a skill universally possessed by paramedics) allows for quick field access to this powerful heat exchanger. The potential utility of the lungs as a heat exchanger was first recognized by Clark and Gollan in the 1960's, when they used the perfluorochemical FX-80 to demonstrate the concept of total liquid breathing in mice. The concept of using the lungs as a heat exchanger for therapeutic purposes was first proposed by Shaffer et al. in 1984, using total liquid ventilation and the fluorocarbon “Rimar 101” (Rimar Chimica S.p.A., Vincenza, Italy).
Heat exchange in the lungs using liquid ventilation is superior to gas ventilation because at standard temperature and pressure, gases such as oxygen and air have only approximately a 2200th of the volumetric specific heat capacity of water. Thus, under ordinary circumstances the lungs serve as a relatively poor heat exchanger if only gaseous media are used. This includes the use of the highly conductive—low viscosity gas mixture of oxygen and helium (Heliox). The high conductivity of Heliox makes it far more efficacious as a heat exchange medium under high pressure conditions where its specific heat capacity is greater that at normal pressures; however these conditions are of little relevance to most clinical situations.
The Basics of Liquid Ventilation
Liquid ventilation involves the breathing of gas-carrying liquid as the medium of gas exchange within the lungs. Since the first liquid ventilation experiments (1950's) in mice using super-oxygenated saline, several liquid media for ventilation have been studied. The class of agents currently optimized to function as liquid breathing media are the fluorocarbons (containing only fluorine and carbon), and the organic perfluorochemicals. (PFCs). PFC compounds contain elements other than fluorine and carbon, with fluorine or other halogens comprising the majority of peripheral moieties. within the molecule. As a class, PFC compounds comprise molecules that are relatively insoluble in either water or lipid, and are more-or-less chemically and pharmacologically inert. PFCs do not dissolve native lung surfactants, and are far less injurious to the lungs than any known silicone or water-based solution.
Total Liquid Ventilation
Historically, the first mode of liquid ventilation studied was total liquid ventilation (TLV). In TLV all of the gas within an animal's lungs is replaced with li
Federowicz Michael
Harris Steven B.
Russell Sandra R.
Critical Care Research, Inc.
Erezo Darwin P.
Lo Weilun
LandOfFree
Mixed-mode liquid ventilation gas and heat exchange does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mixed-mode liquid ventilation gas and heat exchange, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mixed-mode liquid ventilation gas and heat exchange will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3315038