TECHNICAL FIELD

Embodiments of the present invention generally relate to the field of methods and devices for delivering and monitoring nitric oxide (NO). In particular, embodiments of the present invention relate to the use of NO in the contexts of extra corporeal membrane oxygenation (ECMO) systems and organ and tissue preservation.

BACKGROUND

Cells, tissues, organs, and organisms that are deprived of appropriate blood flow undergo ischemic damage. Traditional methods of reducing ischemic damage involve perfusing affected tissues with oxygen, but this procedure can cause significant tissue damage and can result in serious and/or permanent injury, such as brain damage during stroke or cardiac arrest.

Attempts have been made to reduce ischemia-reperfusion injury (IRI) by inducing tissues and organs to enter a reduced metabolic state. In the context of living tissues being preserved for transplant or grafting, one common method for reducing their metabolic activity is by immersing tissues or organs in a physiologic fluid, such as saline, and placing them in a cold environment. However, such methods cannot be relied upon for extended periods, and the success of organ and tissue transplant and limb reattachments remains inversely related to the time the organ, tissue or limb is out of contact with a living organism. Accordingly, there is a need for improved methods of preserving organs, tissues, limbs and other biological materials.

Separately, oxygen deprivation can also occur in living organisms when the lungs are improperly functioning or not functioning at all. One approach to improving oxygenation in patients is through the use of ECMO, in which venous blood is extracted from the patient, passed through a membrane oxygenator, and then returned to the patient. The ECMO system may include filters or other components which are used to remove blood clots and other biological materials that may need removal before blood is reintroduced into the patient thereby avoiding clogging of the ECMO system, in particular clogging of the membrane oxygenator. There is a need to improve existing ECMO systems and methods to avoid this clogging.

SUMMARY

Embodiments of the present invention provide methods and systems for administering NO-containing gas directly to ex vivo fluid, as well as monitoring NO and/or a NO marker and/or other relevant parameter (e.g. indicators of tissue damage) in the ex vivo fluid and/or in tissues or organs that receive the ex vivo fluid. The methods and systems described herein may be utilized for a variety of purposes, including prevention and treatment of ischemia-reperfusion injury and for preventing blood clots in an ECMO circuit. The NO may be administered to various biological materials, including cells, tissues, organs, organisms, and animals, including humans and other mammals.

Although the methods and systems described herein have many applications, in particular it is believed that the administration of NO and the monitoring thereof are beneficial in the context of ECMO circuits and/or the preservation of organs and other biological material for transplantation. With respect to ECMO, in which a patient blood's is oxygenated ex vivo, NO is added to the ECMO circuit and NO and/or a NO marker is monitored, and the NO administration is adjusted accordingly. Without wishing to be bound by any particular theory, it is expected that NO administration to blood in an ECMO circuit will reduce platelet activation in the blood, and thus help prevent clogging in the ECMO circuit. For example, a filter in the ECMO circuit may become clogged due to the aggregation of platelets, and the filter may have to be replaced, which is expensive and inconvenient. Accordingly, NO administration may be used to prevent clogs thereby extending the life of the ECMO circuit. However, excess NO may result in the formation of methemoglobin, which does not bind oxygen, and can lead to methemoglobinemia. As a result, NO administration may be monitored to ensure that the methemoglobin or other NO marker does not rise above or below a certain safety threshold.

With respect to organ and biological material transplant, an organ is removed from a donor and significant efforts are made to appropriately preserve the organ or biological material for implantation into a recipient. Biological materials, including cells, tissues and organs, that are used for transplantation require effective ex vivo preservation from the moment the organ or other biological material is retrieved to the time of transplantation. Organ transplantation includes many methods that may be used individually or in combination. In one or more methods, NO is administered to perfusion fluid, and NO and/or a NO marker and/or other relevant parameter is monitored in the perfusion fluid and the amount of NO being administered is adjusted if necessary in order to meet or maintain an appropriate amount of NO. Alternatively or in addition to monitoring the perfusion fluid, the organ or tissue may be monitored directly, such as by measuring NO and/or a NO marker and/or other parameters (such as indicators of tissue damage) in the organ or tissue. NO may also be added to gases used to persufflate an organ or to gases used to ventilate ex vivo lungs. It is expected that NO administration to perfusion fluids, persufflation gases, and ventilation gases, and the monitoring thereof, will extend organ donor pool and increase viability of donated organs. NO may be used as a preconditioning agent to limit organ damage from ischemia-reperfusion injury. NO is expected to help with organ preservation at least in part by reducing the warm ischemia “hit” which occurs when blood is re-perfused to an organ post-transplant. While not wishing to be bound by any particular theory, it is believed that this reduction in warm ischemia hit may occur by multiple mechanisms, including reduction in oxidative stress and/or preservation of key cellular function.

Furthermore, NO administration may also reduce microcirculation alterations that can occur after removing an organ for transplant and/or during/following ECMO. For example, after an organ is removed, the microcirculation of the organ can undergo restructuring, which can greatly affect perfusion through the organ. The more restructuring that occurs, the poorer the prognosis for the organ transplant. NO may be used to treat and/or prevent such microcirculation alteration, such as by administering NO, monitoring microcirculation and adjusting the NO administration in response to microcirculation alterations.

Accordingly, one aspect of the present invention is directed to a method of monitoring NO administration. In one or more embodiments, this method comprises administering NO to an ex vivo fluid, monitoring NO and/or a NO marker and/or other relevant parameter in the ex vivo fluid and adjusting the NO administration based on the monitoring of the NO and/or NO marker and/or other relevant parameter. The ex vivo fluid may contain components such as red blood cells, etc. Administrating NO to the ex vivo fluid may comprise contacting the ex vivo fluid with a gas comprising a NO concentration in the range from 0.1 ppm to 300 ppm. The ex vivo fluid can be contacted with cells after administrating NO to the fluid or during administration of NO to the ex vivo fluid. As set forth above, NO and/or a NO marker and/or other relevant parameter may also be measured in an organ or tissue, in addition to or as an alternative to measuring NO and/or a NO marker and/or other relevant parameter in the ex vivo fluid.

In one or more embodiments, the ex vivo fluid comprises one or more of blood or perfusion fluid. The ex vivo fluid may comprise blood that is recirculated in an extracorporeal membrane oxygenation (ECMO) circuit and, the ex vivo blood may be introduced into a living organism (such as a human) so that the blood may contact cells in the living organism. As an alternative example, the ex vivo fluid may comprise perfusion fluid and the cells that are contacted with the ex vivo fluid may comprise ex vivo organ cells.

The ex vivo fluid may also be oxygenated before administrating NO to the ex vivo fluid and/or after administrating NO to the ex vivo fluid. The NO and/or NO marker and/or other parameter may be monitored before oxygenating the ex vivo fluid, after oxygenating the ex vivo fluid and before administering NO to the ex vivo fluid, after administering NO to the ex vivo fluid and before contacting the cells with the ex vivo fluid, and/or after contacting the cells with the ex vivo fluid.

The NO monitoring may be performed continuously or intermittently and the nitric oxide administration may be adjusted continuously or intermittently. In one or more embodiments, monitoring the NO marker comprises one or more of monitoring methemoglobin in the ex vivo fluid or monitoring NOx in the ex vivo fluid. In one or more embodiments, adjusting the NO administration comprises adjusting one or more of the NO concentration or the flow rate of the gas comprising NO that is delivered to the ex vivo fluid.

Another aspect of the present invention relates to a method of monitoring NO administration during extracorporeal membrane oxygenation (ECMO). In one or more embodiments, this method comprises administering NO to ex vivo blood in an ECMO circuit by contacting the ex vivo blood with a gas comprising a NO concentration in the range from 1 ppm to 50 ppm, monitoring one or more of (1) a pressure drop in the ECMO circuit to determine if the pressure drop is above a pressure drop threshold or (2) NO and/or a NO marker in the ex vivo blood to determine if the NO and/or NO marker is below or above a NO threshold, and adjusting the NO administration based on one or more of the monitoring of the pressure drop or the monitoring of the NO and/or NO marker. The NO administration may be increased if the pressure drop is above the pressure drop threshold and the NO administration may be decreased if the NO and/or NO marker is above the NO threshold.

In one or more embodiments, the pressure drop threshold is in the range from 1% to 30% of the maximum pressure in the ex vivo circuit.

In one or more embodiments, adjusting the NO administration comprises adjusting one or more of the NO concentration or the flow of the gas comprising NO.

In one or more embodiments, monitoring the NO marker comprises one or more of monitoring methemoglobin in the ex vivo blood or monitoring NOx in the ex vivo blood. Monitoring the NO marker may comprise monitoring methemoglobin and the NO threshold may be in the range from 1% to 15% methemoglobin. In some embodiments, the NO marker is monitored via one or more of pulse oximetry, optical measurement or any other means for measuring or co-relating NO and/or NO markers either directly or indirectly.

Another aspect of the present invention pertains to a method of monitoring NO administration to an ex vivo fluid for biological material preservation. In one or more embodiments, this method comprises administering NO to an ex vivo fluid by contacting the ex vivo fluid with a gas comprising a NO concentration in the range from 0.1 ppm to 300 ppm, monitoring NO and/or a NO marker and/or other parameter in the ex vivo fluid, and adjusting the NO administration based on the monitoring of the NO and/or NO marker and/or other parameter. The biological material may comprise one or more of isolated cells, tissue, a partial organ or a complete organ. In one or more embodiments, the organ comprises one or more of a heart, lung, kidney, liver, pancreas, eye, bone, skin, heart valve, bowel, tendon, ligament or vein. In particular embodiments, the organ may be a liver. In other particular embodiments, the organ may be one or more lungs. In other particular embodiments, the organ may be a heart.

In one or more embodiments, monitoring the NO marker comprises one or more of monitoring methemoglobin in the ex vivo fluid or monitoring NOx in the ex vivo fluid. Monitoring the NO marker may comprise monitoring methemoglobin and the NO threshold may be in the range from 1 to 50% methemoglobin.

In one or more embodiments, adjusting the NO administration comprises adjusting one or more of the NO concentration or the flow rate of the gas comprising NO.

Another aspect of the present invention relates to a method of preserving an ex vivo liver for transplant. In various embodiments of this aspect, the method comprises persufflating the liver with a persufflation gas comprising NO, monitoring one or more persufflation parameters in (i) the liver and/or (ii) a preservation fluid used to store the liver during persufflation, and adjusting the amount of NO provided to the liver by the persufflation gas based on the monitoring of the one or more persufflation parameters. In one or more embodiments, the one or more persufflation parameters is selected from the group consisting of NO, a NO marker, an indicator of tissue damage, and combinations thereof. Examples of indicators of tissue damage include, but are not limited to, aspartate aminotransferase (AST) and alanine aminotransferase (ALT).

In one or more embodiments, the concentration of NO in the persufflation gas is in the range from 0.1 ppm to 300 ppm. The persufflation gas may contain other gases in addition to NO, such oxygen and/or air and/or carrier gases such as nitrogen and helium.

Monitoring may be performed continuously or intermittently and adjusting the amount of NO and/or the NO donor may be performed continuously or intermittently.

In various embodiments of this aspect, the method further comprises perfusing the liver with a perfusion fluid comprising NO and/or a NO donor. The liver may be perfused with the perfusion fluid before the liver is persufflated with the persufflation gas. In one or more embodiments, one or more perfusion parameters (such as NO and/or a NO marker and/or an indicator of tissue damage) is monitored in the perfusion fluid and/or in the liver itself, and the amount of NO and/or NO donor provided to the liver by the perfusion fluid is adjusted based on the monitoring of the one or more perfusion parameters.

According to one or more embodiments, adjusting one or more of (i) the amount of NO provided to the liver by the persufflation gas or (ii) the amount of NO provided to the liver by the perfusion fluid comprises adjusting the NO concentration in a flow of gas delivered to the persufflation gas and/or perfusion fluid, and/or adjusting the flow rate of the gas delivered to the persufflation gas and/or perfusion fluid.

The perfusion fluid may comprise red blood cells, and the method may further comprise oxygenating the perfusion fluid before perfusing the liver. In some embodiments, monitoring the NO marker in the perfusion fluid comprises monitoring methemoglobin.

In some embodiments, the viability of the liver is increased by the persufflation and/or perfusion with NO and/or NO donor, particularly when the NO administration is adjusted based on the monitoring as described herein.

Another aspect of the present invention pertains to a method of preserving an ex vivo lung for transplant. In various embodiments of this aspect, the method comprises perfusing the lung with a perfusion fluid comprising NO and/or a NO donor, and/or ventilating the lung with a ventilation gas comprising NO. The method may also comprise monitoring one or more parameters of the perfusion fluid and/or monitoring one or more parameters of the ventilation gas and/or monitoring one or more parameters of the lung, and adjusting one or more of (i) the amount of NO and/or NO donor provided to the lung by the perfusion fluid based on the monitoring of the one or more parameters of the perfusion fluid and/or the monitoring of the one or more parameters of the lung, or (ii) the amount of NO provided to the lung by the ventilation gas based on the monitoring of the one or more parameters of the ventilation gas and/or the monitoring of the one or more parameters of the lung. In one or more embodiments, the one or more parameters of the perfusion fluid is selected from the group consisting of NO, a NO marker, an indicator of tissue damage, and combinations thereof. In one or more embodiments, the one or more parameters of the ventilation gas is selected from the group consisting of NO, NO2, and combinations thereof. In one or more embodiments, the one or more parameters of the lung is selected from the group consisting of NO, a NO marker, an indicator of tissue damage, a pulmonary parameter, and combinations thereof.

In exemplary embodiments, pulmonary vascular resistance is monitored and the amount of NO provided to the lung by the ventilation gas is adjusted based on the monitoring of pulmonary vascular resistance.

In one or more embodiments, the concentration of NO in the ventilation gas is in the range from 0.1 ppm to 300 ppm. The ventilation gas may contain other gases in addition to NO, such oxygen and/or air and/or carrier gases such as nitrogen and helium. For example, the ventilation gas can have at least 20% oxygen.

The lung may be perfused and ventilated simultaneously, or the perfusion and ventilation may be sequential. The perfusion and ventilation may also occur for different lengths of time.

In some embodiments, the perfusion fluid comprises red blood cells. Monitoring the NO marker in the perfusion fluid may comprise monitoring methemoglobin.

As described above, monitoring may be performed continuously or intermittently and adjusting the amount of NO and/or the NO donor may be performed continuously or intermittently.

In one or more embodiments, adjusting one or more of (i) the amount of NO provided to the lung by the perfusion fluid or (ii) the amount of NO provided to the lung by the ventilation gas adjusting the NO concentration in a flow of gas delivered to the ventilation gas and/or perfusion fluid, and/or adjusting the flow rate of the gas delivered to the ventilation gas and/or perfusion fluid.

In some embodiments, the viability of the lung is increased by the ventilation and/or perfusion with NO and/or NO donor, particularly when the NO administration is adjusted based on the monitoring as described herein.

Also provided is a system for delivering and monitoring NO. In one or more embodiments, the system comprises a NO delivery device for administering NO to an ex vivo fluid such as perfusion fluid, persufflation gas and/or ventilation gas. The system may also comprise a monitoring device for monitoring NO and/or a NO marker and/or other relevant parameter in the ex vivo fluid, in an organ, or in the environment of the organ. The monitoring device may be in communication with the NO delivery device, and the NO delivery device may adjust the NO administration based on the monitoring of the NO and/or NO marker and/or other parameter. The monitoring device may be part of or integrated with the NO delivery device, or it may be a separate component from the NO delivery device.

In one or more embodiments, administrating NO comprises contacting the ex vivo fluid with a gas comprising a NO delivery concentration in the range from 0.1 ppm to 300 ppm. Such NO concentrations can also be used in a persufflation gas and/or ventilation gas.

The monitoring device may comprise any appropriate measurement device, including one or more of a pulse oximeter or an optical measurement device.

In one or more embodiments, the NO delivery device is in communication with a first pressure sensor and a second pressure sensor in an extracorporeal oxygenation (ECMO) circuit that provide a first pressure reading and a second pressure reading, respectively, and the NO delivery device adjusts the NO administration based on a differential between the first pressure reading and the second pressure reading. In some embodiments, the NO delivery device increases the NO administration if the differential between the first pressure reading and the second pressure reading is above 1% to 30% of the first pressure reading.

In one or more embodiments, the NO delivery device adjusts one or more of the NO concentration or the flow of gas comprising NO.

