Surgery – Diagnostic testing – Respiratory
Reexamination Certificate
2000-05-22
2002-03-12
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Respiratory
C600S532000, C128S204230, C128S204180, C128S204210
Reexamination Certificate
active
06355002
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a lung inflection point monitor and method, and more particularly to a monitoring device and method for finding the critical opening pressure, the critical closing pressure and the over distention pressure of the lungs.
BACKGROUND OF THE INVENTION
When a patient is ill and requires help breathing, a mechanical ventilator is used. The ventilator typically assists in the breathing process by first delivering a volume of air to the lungs during the inspiratory phase of the breath, and then allowing gas to passively evacuate during the expiratory phase of the breath. During this process gas is exchanged in small air sacks called alveoli. It is in the alveoli that blood becomes oxygenated and expels carbon dioxide, which is, in turn, removed during exhalation.
If a patient is sick enough to require mechanical assistance to breathe, often times a number of alveoli will collapse preventing gas from being exchanged. A goal of the clinician is to re-open these alveoli and keep them open during the ventilation process. The pressure point at which these alveoli open during the inspiratory phase of the breath is called “critical opening pressure.” If the critical opening pressure is known, the clinician can program the ventilator so that there is sufficient pressure in the lungs at the end of the expiratory phase of the breath to keep the alveoli from collapsing. This pressure is called “positive end expiratory pressure” or “PEEP.”
It is important to know the pressure point at which the lungs again collapse during exhalation. This pressure is referred to as “critical closing pressure.” If the critical closing pressure can be ascertained, this pressure point can be correlated to the critical opening pressure allowing the clinician to fine tune the PEEP setting.
As gas is introduced into the lungs during the inspiratory phase of the breath, the lungs continue to expand. If more gas is delivered than the lungs can comfortably accommodate the lungs are stressed and over distend. This “over distention” damages the lungs beginning on a cellular level and may escalate to the point of ripping holes in the lungs. The pressure at which the lungs begin to overfill is referred to as the “over distention pressure.” If the over distention pressure is known, the ventilator may be programmed to limit the amount of gas given during the inspiratory phase of the breath by setting a “peak inspiratory pressure” or “PIP” at just below the over distention pressure.
The critical opening pressure, the critical closing pressure and the over distention pressure points are known as “inflections points.” By knowing the inflections points, the clinician can program the ventilator to keep the pressures during inspiration and expiration at levels that keep the airways open and prevent over distention. This reduces the risk of injury to the lungs and allows the ventilator to more efficiently ventilate the patient.
The importance of preventing both the collapse and over distention of the lung is well documented. In an article entitled “Open up the lung and keep the lung open” by B. Lachmann, Intensive Care Medicine (1992) 18:319-321, a rationale for preventing airway collapse during ventilation is set forth in order to avoid the dangers concomitant with the pressures required to re-open the airways. The pressure necessary to open collapsed or partially collapsed airways creates dangerous shear forces which can deplete the alveoli of natural surfactant, damage capillaries, decrease compliance, and render gas exchange dysfunctional.
An article entitled “International Consensus Conferences in Intensive Care Medicine: Ventilator-associated Lung Injury in ARDS”, which represents a consensus report sponsored by The American Thoracic Society, the European Society of Intensive Care Medicine, the Societe de Reanimation de Langue Francaise utilizing consensus methods established by the National Institutes of Health, asserts that over inflation of the lung induces severe alveolar damage such as alveolar hemorrhage and hyaline membrane disease. The article suggests that ventilator modes associated with properly set PEEP, and delivered tidal volumes which result in a PIP below the over distention point, achieve significant reductions in mortality.
In U.S. Pat. No. 5,937,854, a ventilator pressure optimization method and device is described which attempts to optimize mechanical ventilation by finding the lung inflection points and transmitting this information to the ventilator. The method used involves delivering a known pressure to the patient and measuring the approximate resulting lung volumes. The volumes are then correlated to the delivered pressures and the inflection points are extrapolated. Although this method may provide information helpful in approximating the inflection points, the procedure necessitates measuring lung volume, a costly and difficult maneuver at best. Subsequently, the “approximate” lung volume is used to calculate the “approximate” volume differences as the pressure increases and decreases. These approximate volume differences are used to calculate the inflection points.
U.S. Pat. No. 5,575,283 describes a device for determining the opening pressure of the lungs by trying to measure the delivered lung volumes and trying to establish a relationship between those volumes and delivered pressures. Although different methods are used for trying to establish the lung volumes, the clinician still faces the same difficulties as enumerated in the methodology mentioned above.
U.S. Pat. No. 5,738,090 describes a system for determining the opening pressure of the lung by using a blood gas analyzer to measure partial pressures of oxygen in the blood. When the partial pressure reaches a “predetermined thresholds,” the threshold is correlated to a pressure that is designated as the opening pressure. However, the partial pressures may or may not be indicative of open airways. The airways may be open, yet still not able to exchange gases due to an underlying pathology of the pulmonary, cardiac, or circulatory system. In addition, the partial pressures may be considered optimal at the very time irreparable, long-term damage is being done to the lungs.
SUMMARY OF THE INVENTION
The present invention is a method and apparatus for determining lung inflection points in order to optimally ventilate a patient on a mechanical ventilator. The method for determining lung inflection points includes the basic steps of: immobilizing the lungs; closing an exhalation valve; introducing gas into the lungs in pulsatile increments; measuring the resulting pressures; and determining the inflection points by analyzing a pressure-time line graph while observing overall pressure changes and incremental pressure changes.
The apparatus consists of a gas-controlling device, a device for measuring and displaying pressures and a monitor-patient interface. A microprocessor within the device is used for purposes of measuring, analyzing, displaying and transmitting data resultant from the maneuvers described herein.
REFERENCES:
patent: 5575283 (1996-11-01), Sjoestrand
patent: 5660170 (1997-08-01), Rajan et al.
patent: 5738090 (1998-04-01), Lachmann et al.
patent: 5752509 (1998-05-01), Lachmann et al.
patent: 5937854 (1999-08-01), Stenzler
patent: 6116241 (2000-09-01), Huygen et al.
Faram Joseph Dee
Fish Philip E.
Comedica Technologies Incorporated
Natnithithadha Navin
Vandigriff John E.
Winakur Eric F.
LandOfFree
Lung inflection point monitor apparatus and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lung inflection point monitor apparatus and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lung inflection point monitor apparatus and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2881261