Gastric Carbon Dioxide Research Articles

Optical sensing in POCT: the contribution of the Institute of Applied Physics of the Italian CNR

Abstract The activity developed at the Institute of Applied Physics “Nello Carrara” in strict collaboration with physicians is described with particular attention to the measurement of bile-containing refluxes in the gastroesophageal apparatus, to the detection of gastric carbon dioxide in intensive care patients, to the measurement of sepsis biomarkers in serum samples and to the measurements of immunosuppressants in transplanted patients.

Utility of Measurements of Abdominal Perfusion Pressure as a Measure of Isovolemic Status and Intestinal Perfusion in Patients with Ruptured Aortic Aneurysm

Ruptured abdominal aorta aneurysm of ten results in intraabdominal hypertension (IAH). When IAH exceeds 20 mm Hg, intestinal ischemia can result that is a common cause of severe postoperative complications, including death. was to evaluate utility of measurement of abdominal perfusion pressure (APP) to estimate intestinal perfusion and isovolemic status in patients undergoing surgical treatment for ruptured abdominal aorta aneurysm. A group of 40 patients of either sex, aged 47-93 years (average age 70 ± 10) was treated at an Intensive Care Unit after surgical reconstruction of abdominal aorta due to ruptured aortic aneurysm. The study was prospective. The following were measured: parameters of intraabdominal pressure (intraabdominal pressure - IAP, abdominal perfusion pressure - APP); parameters of intestinal perfusion - tonometric (intramucosal gastric carbon dioxide partial pressure PgCO(2), intramucosal-arterial difference in carbon dioxide partial pressure - Pg-aCO(2)); hemodynamic parameters (mean arterial pressure - MAP, central venous pressure - CVP). A statistically significant correlation was demonstrated between parameters of visceral perfusion and abdominal perfusion pressure. Pearson correlation coefficient for APP/PgCO(2) and APP/Pg-aCO(2) was negative and was -0.4664 and -0.3498, respectively. Abdominal perfusion pressure is an useful parameter in the evaluation of intestinal perfusion in IAH patients after surgical treatment of ruptured aortic aneurysm. MAP reflects current physiological body reserves at a critical stage of the disease, informing about possibility to provide visceral perfusion and indirectly, about adequacy of fluid replacement therapy. In intraabdominal hypertension, CVP is falsely elevated, making it of low utility in the evaluation of volemic status and intestinal perfusion.

Effects of early oral fluid resuscitation on hemodynamic and tissue perfusion during shock stage in dogs with a 50% total body surface area full-thickness burn.

To investigate the effect of early oral fluid resuscitation on hemodynamic and tissue perfusion in dogs with severe burn shock. Eighteen male Beagle dogs with intubation of carotid artery, jugular vein, stomach, jejunum and bladder for 24 h were subjected to a 50%TBSA full-thickness burn, then were equally divided into non fluid resuscitation (NR), oral resuscitation (OR) and intravenous resuscitation(IR) groups, (each n = 6). Dogs in IR and OR groups were given glucose-electrolyte solution (GES) by gastric tube or intravenous infusion according to Parkland formula within 24 h after burn, while those in NR group were not given any treatment. Dogs in each group were given intravenous fluid resuscitation from 24 h after burn. The mean arterial pressure (MAP), cardiac output (CO), systemic vascular resistance (SVR), dp/dt max of left ventricular contractility (dp/dt(max)), gastric carbon dioxide pressure (PgCO2), intestinal mucosal blood flow (IMBF), and urinary output were determined before burn (0 h) and 2, 4, 8, 24, 48 and 72 h after burn at no anaesthesia state. Mortality rate of 72 h after burn was also recorded. MAP, CO, dp/dt(max), IMBF greatly decreased, and SVR and PgCO2 obviously increased from 2 h after burn in each group (P < 0.01). The measurements except IMBF of IR group returned to pre-injury levels at 72 h after burn, while CO, SVR, PgCO2 and IMBF of OR group still worse compared with 0 h (P < 0.01). All measurements of NR group kept on worsen, and died with anuria within 24 h after burn. Parameters of hemodynamic and tissue perfusion of OR group were significantly superior to those of NR group, but it inferior to those of IR group. At 72 h after burn, 6 (6/6) survived in IR group, 3 (3/6) in OR group and 0 (0/6) in NR group. Although oral resuscitation with GES is not as efficient as intravenous resuscitation in a 50%TBSA burn injury, it still can promote hemodynamic, improve the tissue perfusion and reduce the mortality comparing to no resuscitation. Oral resuscitation might be an ideal alternative way of intravenous resuscitation, especially in wars or other site of mass casualties.

Fiber Optic Sensors for Biomedical Applications

Biomedicine is surely the area where the optical fibre sensors can play an important role. Thanks to their potential miniaturisation and their easy handling they are offering unique performances in invasive or minimally invasive applications. The immunity to electromagnetic interference and the absence of electrical contact make the optical fibres useful also in the case of non invasive applications for the setting of the interrogation optoelectronic unit in a safer location, keeping only the sensing element close to the patients bedside. As a matter of fact, there are many optical fibre sensors designed for biomedical applications and described in the literature, but the greater part of them stops at the prototype level, without entering the hospital. The clinical validation, which is the necessary step after the characterisation of the laboratory prototype, is often an insurmountable obstacle due to the requirements of compliance with the European Directives on Medical Devices or with the regulations of the Food and Drug Administration. The strategy followed for the clinical validation in the case of optical fibre sensors developed at the Institute of Applied Physics for the detection of bile-containing refluxes, gastric carbon dioxide and interstitial pH is described. An example for potential non-invasive applications in point of care testing is also given with a novel optical platform for the interrogation of optical biochips.

Sublingual capnometry tracks microcirculatory changes in septic patients

To test the hypothesis that microcirculatory blood flow is the main determinant of sublingual carbon dioxide pressure in patients with septic shock. Prospective, open-label study. A 31-bed medico-surgical department of intensive care. Eighteen consecutive mechanically ventilated patients with septic shock. A 5 microg/kg x min dobutamine infusion was used to increase blood flow. Sublingual carbon dioxide pressure was monitored using a microelectrode sensor, and sublingual microcirculation was assessed using orthogonal polarization spectral imaging. The sublingual carbon dioxide pressure gap was calculated as the difference between sublingual and arterial carbon dioxide pressures. In each patient, a nasogastric tonometry catheter was inserted for gastric mucosal carbon dioxide pressure measurement. The gastric carbon dioxide pressure gap was calculated as the difference between gastric mucosal and arterial carbon dioxide pressures. Dobutamine infusion was associated with increases cardiac index and mixed venous blood oxygen saturation. Dobutamine infusion resulted in decreases in sublingual carbon dioxide pressure gap from 40+/-15 to 17+/-8 mmHg (p<0.01). There was a significant correlation between sublingual and gastric mucosal carbon dioxide pressures (r 2=0.61, p<0.05). At baseline, sublingual carbon dioxide pressure gap correlated with the proportion of well-perfused capillaries (r 2=0.80). The decrease in sublingual carbon dioxide pressure gap paralleled the increase in the proportion of well-perfused capillaries in each patient. Regional microcirculatory blood flow is the main determinant of sublingual carbon dioxide pressure. Sublingual capnometry could represent a simple, non-invasive method to monitor these microcirculatory alterations in septic patients.

Effects of volume resuscitation on splanchnic perfusion in canine model of severe sepsis induced by live Escherichia coli infusion.

IntroductionWe conducted the present study to investigate whether early large-volume crystalloid infusion can restore gut mucosal blood flow and mesenteric oxygen metabolism in severe sepsis.MethodsAnesthetized and mechanically ventilated male mongrel dogs were challenged with intravenous injection of live Escherichia coli (6 × 109 colony-forming units/ml per kg over 15 min). After 90 min they were randomly assigned to one of two groups – control (no fluids; n = 13) or lactated Ringer's solution (32 ml/kg per hour; n = 14) – and followed for 60 min. Cardiac index, mesenteric blood flow, mean arterial pressure, systemic and mesenteric oxygen-derived variables, blood lactate and gastric carbon dioxide tension (PCO2; by gas tonometry) were assessed throughout the study.ResultsE. coli infusion significantly decreased arterial pressure, cardiac index, mesenteric blood flow, and systemic and mesenteric oxygen delivery, and increased arterial and portal lactate, intramucosal PCO2, PCO2 gap (the difference between gastric mucosal and arterial PCO2), and systemic and mesenteric oxygen extraction ratio in both groups. The Ringer's solution group had significantly higher cardiac index and systemic oxygen delivery, and lower oxygen extraction ratio and PCO2 gap at 165 min as compared with control animals. However, infusion of lactated Ringer's solution was unable to restore the PCO2 gap. There were no significant differences between groups in mesenteric oxygen delivery, oxygen extraction ratio, or portal lactate at the end of study.ConclusionSignificant disturbances occur in the systemic and mesenteric beds during bacteremic severe sepsis. Although large-volume infusion of lactated Ringer's solution restored systemic hemodynamic parameters, it was unable to correct gut mucosal PCO2 gap.

Continuous monitoring of gastric carbon dioxide with optical fibres

An optical fibre sensor for the continuous monitoring of gastric carbon dioxide is described, based on the utilisation of a sensing layer, in which the colour of the layer is dependent on the CO 2 concentration. The CO 2-sensitive layer consists basically of a dye/quaternary ammonium ion pair, dissolved in a thin layer of ethylcellulose. The sensor was thoroughly characterised in laboratory and its performances were compared with those of Tonocap, the instrument based on gastric tonometry, which is the present method for detecting partial pressure of gastric carbon dioxide. Its measurement range, 0–150 h Pa, its accuracy, ±2.5 h Pa, and its response time, less than 1 min, were capable of satisfying the physicians’ requirements for clinical application. The clinical tests, carried out on volunteers and on intensive care patients, showed that the developed sensor is definitely superior to the sensor that is at present available on the market: thanks to its short response time, the optical fibre sensor is able to detect rapid changes in pCO 2, currently unknown because of the lack of a tool with which to measure them.

Gastric tonometer monitoring in infants undergoing repair of coarctation of the aorta

Objective: To evaluate gastric tonometer monitoring for splanchnic hypoperfusion in infants during surgical intervention for aortic coarctation, especially within aortic cross-clamp periods. Design: A prospective study. Setting: Cardiovascular intensive care unit in a university hospital. Participants: Fourteen infant patients after elective, uncomplicated repair of coarctation of the aorta. Interventions: After the anesthesia induction, a 7F tonometry catheter was inserted into the stomach oropharyngeally. Gastric carbon dioxide, arterial blood gases, blood pressure of upper extremities, and hematocrit values were measured in 5 different time intervals. Time periods were as follows: T1 (after the anesthesia induction), T2 (before aortic cross-clamp), T3 (immediately after aortic cross-clamp removal), T4 (40 minutes after aortic cross-clamp removal), and T5 (as the patient reached the intensive care unit). Intramucosal pH was measured by means of the Henderson-Hasselbach equation. The mean values of all parameters were calculated. According to T1 time, T2, T3, T4, and T5 times were compared with Student's t-test. Measurements and Main Results: Mean aortic cross-clamp time was 19.4 ± 6.6 minutes. Intramucosal pH values of T3 (p < 0.001) and T4 (p < 0.01) were found to be lower than values of T1. The gastric carbon dioxide values of T3 were significantly higher than T1 (p < 0.01), and bicarbonate and arterial pH values of T3 were significantly lower (p < 0.01). There were no significant differences in other parameters over time intervals. Conclusion: Splanchnic hypoperfusion exists during aortic cross-clamping in infant aortic coarctation surgery, and the tonometric catheter is considered to be a safe method for monitoring this hypoperfusion. Copyright © 2000 by W.B. Saunders Company

Nonocclusive bowel necrosis occurring in critically ill trauma patients receiving enteral nutrition manifests no reliable clinical signs for early detection

Background: Nonocclusive bowel necrosis (NOBN) has been associated with early enteral nutrition (EN). The purpose of this study was to determine the incidence of this complication in our trauma intensive care unit population and to define a typical patient profile vulnerable to NOBN.Methods: Thirteen cases of NOBN were identified among 4,311 patients (0.3%) over a 64-month period ending October 1998. Their charts were analyzed for a variety of clinical data, including prospective EN tolerance data in 4.Results: Twelve (92%) patients were enterally fed prior to diagnosis for 10 ± 8 days (range 3 to 21). Tachycardia (n = 12, 92%); fever/hypothermia, (n = 12, 92%), and an abnormal white blood cell count (n = 11, 85%) were consistently present. Abdominal distention was common but tended to be a late sign (n = 12). Seven (56%) survived. In 4 patients with tolerance data, 3 reached the goal rate of feeds prior to diagnosis. Two became distended at >12 hours from diagnosis. Gastric tonometry demonstrated a decreased NgpHi (<7.30) after starting EN in all 3 in whom it was monitored.Conclusions: NOBN developed in 0.3% of our trauma patients. Onset occurs in the second week in high-acuity patients who have had a period of EN tolerance. Clinical findings resemble bacterial sepsis with tachycardia, fever, and leukocytosis. Gastrointestinal specific signs are not consistent or occur late. Thus, we could not identify an early, useful clinical indicator. Gastric carbon dioxide tonometry may detect a vulnerable subgroup of patients.

Continuous monitoring of gastric carbon dioxide with optical fibers: European project COMOCADOF, in vitro evaluation

Continuous monitoring of gastric carbon dioxide with optical fibers: European project COMOCADOF, in vitro evaluation

A simple method for frequent monitoring of gastric carbon dioxide.

Intragastric PCO2 has been recognized to rise in states of gastric hypoperfusion. A device including a gas-permeable balloon on a conventional sump nasogastric tube (TRIP catheter, Tonometrics) has permitted simple measurement of the intragastric PCO2 following equilibration of intragastric PCO2 with saline in the balloon. This method is slow to equilibrate and time-consuming. We describe an automated method using air instead of saline in the balloon with measurement using capnography. Equilibration is much faster using air and the automated system permits measurements to be taken at regular intervals (10 minutes) without additional workload.

Exercise-induced gastric mucosal acidosis

Gastric acidosis as assessed by tonometry was applied to evaluate changes in splanchnic blood flow during exercise. In six healthy male oarsmen, we determined gastric acidosis in response to 30 min of maximal ergometer rowing. The gastric mucosa carbon dioxide tension was determined by equilibration of isotonic saline to the tonometer. Arterial bicarbonate (HCO3-), pH, arterial oxygen tension (PaO2), and saturation (SaO2) were obtained simultaneously, while pH (pHi) of the gastric mucosa was calculated using the Henderson-Hasselbach equation. During rowing PaO2 and SaO2 decreased to values of 73.7 mm Hg and 95.5%, respectively (P < 0.05). However, during the last minute of rowing the values were normalized with a hyperventilation reducing PaCO2 to 27.1 mm Hg (P < 0.05). Rowing decreased HCO3- from 25.8 (21.4-28.5) to 14.1 (11.6-17.4) mmol l-1, while the gastric carbon dioxide tension increased from 36.8 (24.1-63.9) to 61.7 (48.9-82.0) mm Hg (P < 0.05). Accordingly, pHi decreased from 7.25 (7.04-7.48) to 6.79 (6.67-6.85) (P < 0.05). Arterial pH also decreased (from 7.42 (7.41-7.44) to 7.29 (7.26-7.33) (P < 0.05)), with the enlarged difference between pH and pHi suggesting marked splanchnic hypoperfusion during rowing.