Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
1995-05-05
2001-05-29
Lacyk, John P. (Department: 3311)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S504000, C600S353000
Reexamination Certificate
active
06238339
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to medical diagnostic equipment and methods and is particularly concerned with hollow viscus tonometry and remote electronic and optical sensing.
Until the advent of the tonometric method (see U.S. Pat. No. 4,643,192, issued Feb. 17, 1987) few considered any aspect of acid-base balance when attempting to monitor or maintain the adequacy of tissue oxygenation. Yet acid-base balance is primarily determined by the balance between the protons released during the release of energy by ATP hydrolysis and the resynthesis of ATP by oxidative phosphorylation. The hydrolysis of ATP generates 150,000 mmols of H+ each day in a resting 70 Kg man. All, but the 1% of this fixed acid load excreted by the kidneys each day, is presumed to be consumed in the resynthesis of ATP by oxidative phosphorylation. When the delivery of oxygen fails to satisfy the energy needs of the tissue the rate of ATP hydrolysis exceeds the rate of synthesis and the pH falls as the degree of unreversed ATP hydrolysis increases.
Information for determining global tissue oxygenation has been collected for many years. Eoda, D., “‘Gastrotonometry’ an Aid to the Control of Ventilation During Artificial Respiration,”
The Lancet
(1959). However, it is now widely accepted that global measurements of oxygen delivery, consumption and extraction do not provide reliable information about the adequacy of local or even “global” tissue oxygenation in patients. The indirect measurement of gastric intramucosal pH (pHi) as described in U.S. Pat. Nos. 4,643,192; 5,158,083; 5,186,172 provides clinicians with a minimally invasive yet sensitive means of detecting the development of a tissue acidosis, and hence inadequacy of tissue oxygenation, in a region of the body that is one of the first to exhibit an inadequacy of tissue oxygenation in shock. Use of the measurement has revealed that some 50% to 60% of patients having major surgery and 80% of ICU patients develop an intramucosal acidosis during their illness despite the conventional appearance of being adequately resuscitated.
The degree and duration oL the presence of a gastric intramucosal acidosis are highly sensitive measures of the risk of developing ischemic gut mucosal injury and its putative consequences, namely the translocation of bacteria and their toxins, cytokine release, organ dysfunctions and failures, and death from the organ failures. By providing an index of the adequacy of tissue oxygenation in one of the first parts of the body to exhibit dysoxia in shock the measurement of gastric intramucosal pH improves the opportunity to obtain advanced and accurate warning of impending complications and to intervene in time to prevent them. More importantly timely therapeutic measures that restore the intramucosal pH to normality and “gut-directed” therapies incorporating measures that reverse an intramucosal acidosis are associated with an improved outcome. “pH-directed” therapy has in addition been shown to improve outcome in a prospective randomized multicenter study of medical and surgical ICU patients.
The measurements of gastric intramucosal pH have revealed deficiencies in currently accepted practices. It has, for example, become apparent that empirical increases in global oxygen delivery may be redundant in some 40% to 50% of patients having major cardiovascular surgery who do not develop a gastric intramucosal acidosis and whose prognosis is excellent. It is further apparent that the vogue of increasing global oxygen delivery to supranormal levels cannot be relied upon to prevent or to reverse the presence of an intramucosal acidosis. Of particular concern is the intramucosal acidosis that may be induced by measures, notably the transfusion of red blood cells and dobutamine, that increase global oxygen delivery in patients who do not have an intramucosal acidosis but whose global oxygen delivery is considered too low.
THE TONOMETRIC METHOD
The measurement of pH in the most superficial layer of the mucosa is obtained indirectly by measuring the partial pressure of carbon dioxide (pCO
2
; pCO
2
) in the lumen of the gut and the bicarbonate concentration in arterial blood and substituting these two values in the Henderson-Hasselbalch equation or some modification thereof. See “Gastric Intramucosal pH as a Therapeutic Index of Tissue Oxygenation in Critically Ill Patients,”
Lancet
1992; 339; 195-99, incorporated herein by reference. The indirect measurement of the pH of the wall of the organ (pH indirect or intramucosal pH) may be employed because it is believed or assumed that the pCO
2
in the most superficial layers of the mucosa is in equilibrium with that in the lumenal contents with which it is in contact. It is further based upon the assumption that the bicarbonate concentration in the tissue is the same as that being delivered to it in arterial blood and that the pKa, 6.1, is the same as that in plasma.
At present, measurements of pCO2 in the lumen of the stomach are obtained by infusing saline into the silicone balloon of a gastrointestinal tonometer, allowing the pCO
2
in the saline to equilibrate with that in the lumen of the gut; recording the equilibration time; aspirating the saline; measuring the pCO
2
in the saline with a blood gas analyzer; using a nomogram to derive the steady-state adjusted pCO2 from the equilibration time and the measured pCO
2
; and then derive the intramucosal pH from the steady-state adjusted pCO
2
obtained and the bicarbonate concentration in a substantially contemporaneous sample of arterial blood. Again, see U.S. Pat. Nos. 4,643,192, issued Feb. 17, 1987; U.S. Pat. No. 5,174,290, issued Dec. 29, 1992; and U.S. Pat. No. 5,186,172, issued Feb. 16, 1993; as well as copending U.S. applications, Ser. No. 719,097, filed Jun. 20, 1991; Ser. No. 994,721, filed Dec. 22, 1992 and Ser. No. 014,624, filed Feb. 8, 1993; all three issued patents being completely and expressly incorporated herein by reference. The precision of the measurement of gastric intramucosal pH between healthy subjects is excellent, the gastric intramucosal pH in a healthy subject being the same as the pH in his arterial blood.
The prior art (see U.S. Pat. No. 4,643,192) has recognized that intestinal ischemia, and to a lesser degree, stress ulceration, are two problems that plague physicians involved in the management of patients in intensive care units. Intestinal ischemia, in particular, has an insidious onset and may not be detected until days after the intestine has become completely and irreversibly compromised. A delay in the diagnosis of intestinal ischemia may have devastating consequences for a patient. The availability of means for early diagnosis and management of patients with these problems would have immediate applicability in all intensive care units, especially where the procedure can be conveniently conducted with reasonable safety and reliability.
It has been established that a fall in the intramucosal pH may precede the development of intestinal ischemia and stress ulceration. As discussed in U.S. Pat. No. 4,643,192, which is expressly incorporated herein by reference, entitled “Hollow Viscus Tonometry” a fall in intramucosal pH also occurs within minutes of inducing intestinal ischemia in dogs. The fall in pH in intestinal mucosa, and hence the likelihood of lschemia or stress ulceration, can be reliably calculated from a pCO
2
(partial pressure of CO
2
) I or other indicia of pH, in lumenal fluid and the bicarbonate concentration in arterial blood. The method of calculating the pH in intestinal mucosal tissue, pursuant to principles set forth in prior related patents discussed herein, has been validated by directed measurements under a variety of conditions simulating clinical problems. A correlation coefficient on the order of 0.92 to 0.95 has been obtained in each of 16 dogs. The validity of the procedure is inherently extensible to humans, and indeed may also be useful in assessing the vitality of other hollow organs and tissue. See R. G. Fiddian-Green et al. “Splanchnic
Fiddian-Greene Richard G.
Holte Bo
Kent Joel C.
Rantala Borje Tor
Andrus Sceales Starke & Sawall LLP
Instrumentarium Corp.
Lacyk John P.
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