Gastric tonometry

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Gastric tonometry

Gastric tonometry describes the measurement of the carbon dioxide level inside the stomach in order to assess the degree of blood flow to the stomach and bowel. [1]

Gastric tonometry has been introduced as a novel method of monitoring tissue perfusion in critically ill patients. Tonometry is based on the principle that at equilibrium the partial pressure of a diffusible gas such as CO2 is the same in both the wall and lumen of a viscus. The technique therefore can estimate gut mucosal PCO2 by measuring gut luminal PCO2 at equilibrium. A saline-filled balloon made of CO2 permeable silicone attached to a sampling tube is introduced into the gastric lumen as a nasogastric tube would be. After an equilibration period the fluid is sampled to measure PCO2. Because the mucosal and systemic bicarbonate concentrations are equal, a modified Henderson-Hasselbalch equation may be used to calculate the intramucosal pH: pHi = 6.1 + log [HCO3−/0.03 x PCO2]. Thus, only gastric luminal PCO2 is directly measured. Mucosal PCO2 is presumed to be proportional at equilibrium and mucosal pH is calculated. PO2 and luminal pH play no role in these calculations. Proponents of this technique maintain that it is a relatively inexpensive noninvasive, tissue-specific method to evaluate the adequacy of tissue perfusion. It is of special value when used in the gastric lumen because splanchnic circulation is one of the vascular beds that is subject to early blood flow redistribution in shock states. Critics of the technique caution that while directly measured factors are usually accurate and calculated factors correspondingly reliable, the assumption that gut mucosal pH alterations are uniquely a function of mucosal hypoxia is not. Tonometry may adequately reflect the degree of tissue perfusion, but its accuracy as an index of tissue oxygenation is less reliable.

The measurement of gut mucosal carbon dioxide has been used to detect decreased blood flow. Accumulation of carbon dioxide is predominantly a result of hypoperfusion and not hypoxia. Because the introduction of a nasogastric tube is almost routine in critically ill patients, the measurement of gastric carbon dioxide can be an easy method to monitor tissue perfusion. The gastric mucosal pH is measured according to an equation that assumes that arterial bicarbonate is equal to intramucosal bicarbonate, an argument that is not always valid. Given that the gastric mucosal carbon dioxide is the directly measured value, whereas the gastric mucosal pH is the derived and possibly inaccurate value, studies that used gastric pH to monitor perfusion may be inherently flawed. Most studies have failed to effectively affect gastric pH and for this reason failed to produce improvements in outcome. One study,[ when? ] by Gutierrez and colleagues, has shown that therapeutic interventions guided by gastric tonometry improved survival in critically ill patients. In a direct comparison of splanchnic-oriented therapy as guided by gastric tonometry with conventional shock management of trauma patients, there was no difference in mortality rates, organ dysfunction rates, or length of stay. [2]

After a surge in popularity,[ when? ] the use of gastric tonometry waned and it is currently found with less frequency in surgical ICUs. [2]

See also

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3.

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Arterial blood gas test A test of blood taken from an artery that measures the amounts of certain dissolved gases

An arterial-blood gas (ABG) test measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe and a thin needle, but sometimes the femoral artery in the groin or another site is used. The blood can also be drawn from an arterial catheter.

Nasogastric intubation

Nasogastric intubation is a medical process involving the insertion of a plastic tube through the nose, past the throat, and down into the stomach. Orogastric intubation is a similar process involving the insertion of a plastic tube through the mouth. Abraham Louis Levin invented the NG tube.

Acidosis is a process causing increased acidity in the blood and other body tissues. If not further qualified, it usually refers to acidity of the blood plasma.

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2) in the respiratory gases. Its main development has been as a monitoring tool for use during anesthesia and intensive care. It is usually presented as a graph of expiratory CO
2 (measured in millimeters of mercury, "mmHg") plotted against time, or, less commonly, but more usefully, expired volume. The plot may also show the inspired CO
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2 (ETCO2).

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3), and carbon dioxide (CO2) in order to maintain pH in the blood and duodenum, among other tissues, to support proper metabolic function. Catalyzed by carbonic anhydrase, carbon dioxide (CO2) reacts with water (H2O) to form carbonic acid (H2CO3), which in turn rapidly dissociates to form a bicarbonate ion (HCO−
3 ) and a hydrogen ion (H+) as shown in the following reaction:

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Portal hypertensive gastropathy

Portal hypertensive gastropathy refers to changes in the mucosa of the stomach in patients with portal hypertension; by far the most common cause of this is cirrhosis of the liver. These changes in the mucosa include friability of the mucosa and the presence of ectatic blood vessels at the surface. Patients with portal hypertensive gastropathy may experience bleeding from the stomach, which may uncommonly manifest itself in vomiting blood or melena; however, portal hypertension may cause several other more common sources of upper gastrointestinal bleeding, such as esophageal varices and gastric varices. On endoscopic evaluation of the stomach, this condition shows a characteristic mosaic or "snake-skin" appearance to the mucosa of the stomach.

Chloride shift (also known as the Hamburger phenomenon or lineas phenomenon, named after Hartog Jakob Hamburger) is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO3−) and chloride (Cl−) across the membrane of red blood cells (RBCs).

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In some individuals, the effect of oxygen on chronic obstructive pulmonary disease is to cause increased carbon dioxide retention, which may cause drowsiness, headaches, and in severe cases lack of respiration, which may lead to death. People with lung ailments or with central respiratory depression, who receive supplemental oxygen, require careful monitoring.

Blood gas tension refers to the partial pressure of gases in blood. There are several significant purposes for measuring gas tension; the most common gas tensions measured are oxygen tension (PxO2), the carbon dioxide tension (PxCO2) and carbon monoxide tension (PxCO). The subscript x in each symbol represents the source of the gas being measured; "a" meaning arterial, "A" being alveolar, "v" being venous, "c" being capillary. Blood gas tests (such as arterial blood gas tests) measure these partial pressures.

Intestinal mucosal barrier

The intestinal mucosal barrier, also referred to as intestinal barrier, refers to the property of the intestinal mucosa that ensures adequate containment of undesirable luminal contents within the intestine while preserving the ability to absorb nutrients. The separation it provides between the body and the gut prevents the uncontrolled translocation of luminal contents into the body proper. Its role in protecting the mucosal tissues and circulatory system from exposure to pro-inflammatory molecules, such as microorganisms, toxins, and antigens is vital for the maintenance of health and well-being. Intestinal mucosal barrier dysfunction has been implicated in numerous health conditions such as: food allergies, microbial infections, irritable bowel syndrome, inflammatory bowel disease, celiac disease, metabolic syndrome, non-alcoholic fatty liver disease, diabetes, and septic shock.

References

  1. ↑ Carlesso E, Taccone P, Gattinoni L (June 2006). "Gastric tonometry". Minerva Anestesiol. 72 (6): 529–32. ISSN   0375-9393. PMID   16682926.
  2. 1 2 George C. Velmahos MD, MSE and Hasan B. Alam MD (July 2008). "Advances in Surgical Critical Care". Current Problems in Surgery. 45 (7): 453–516. doi:10.1067/j.cpsurg.2008.03.003. PMID   18503823.
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