Automated Air Tonometry Research Articles

Jejunal tonometry for the diagnosis of gastrointestinal ischemia. Feasibility, normal values and comparison of jejunal with gastric tonometry exercise testing

In most patients with chronic splanchnic syndrome the celiac artery is involved, enabling the use of gastric exercise tonometry as a diagnostic function test. In this study, we investigated the feasibility of combining gastric and jejunal exercise tonometry and determined the normal values. We investigated the potential diagnostic value of combining gastric with jejunal exercise tonometry. Between 1998 and 2000, combined gastric and jejunal exercise tonometry tests were performed in a healthy volunteer and in patients suspected of chronic gastrointestinal ischemia. Using automated air tonometry, gastric (PgCO2) and jejunal PCO2 (PjCO2) were measured before, during and after 10-min of exercise. Luminal-arterial PCO2 gradients (DeltagPCO2 respectively DeltajPCO2) were calculated. In the patient cohort, final diagnosis of chronic ischemia was made by our institutional multidisciplinary working group on gastrointestinal ischemia. Jejunal tonometry was possible in 25 of 27 participants. The healthy volunteer was tested twice, yielding a total of 26 combined tests. Mean normal basal PjCO2 was 0.9 kPa higher than PgCO2. The calculated upper threshold (mean+2SD) of normal DeltajPCO2 was 1.4 kPa. In five of eight patients with chronic gastrointestinal ischemia gastric exercise tonometry was abnormal, in one, both gastric and jejunal tonometry were abnormal, in two only jejunal exercise tonometry was abnormal. Combined gastric and jejunal exercise tonometry is a feasible procedure that is relatively easy to perform. On the basis of this pilot study, jejunal tonometry seems to have a small additional value in the diagnosis of chronic gastrointestinal ischemia.

Rectal luminal PrCO 2, measured by automated air tonometry, does not reflect gastric luminal PrCO 2 in children

Rectal luminal regional P(CO2) (Pr(CO2)) was compared with gastric luminal Pr(CO2) measured by automated air tonometry at intervals of 10 min in 20 children aged 6-16 years scheduled for elective surgery under general anesthesia. In 5 patients, measurement of rectal Pr(CO2) failed because of catheter-related problems. In the remaining 15 children, aged 10.6 +/- 2.5 years, 19 +/- 7 paired rectal and gastric Pr(CO2) values (n total, 241) were measured. Bias and precision for gastric compared to rectal Pr(CO2) was -1.79 kPa and 2.89 kPa. In patients with obvious feces in the rectum, bias (precision) for gastric compared to rectal Pr(CO2) was -2.7 kPa (2.6 kPa) and in those with empty rectum, -0.75 kPa (1.42 kPa; t-test; P < 0.001). Based on our in vivo data, rectal luminal Pr(CO2), measured by automated air tonometry, does not reflect gastric luminal Pr(CO2) in children. Enteral luminal gas production within feces in the rectum seems to be a major source of this disagreement.

Assessment of splanchnic perfusion by gastric tonometry in patients with acute hypovolemic burn shock

Objective To compare the changes in pHi and intramucosal–arterial CO 2-gap with invasive haemodynamic and global perfusion measurements during hypovolemic burn shock and to evaluate the sensitivity of these parameters as an early predictor of mortality in patients with extensive burns. Design Prospective, controlled, clinical study. Setting An eight-bed intensive burn care unit in a university-affiliated hospital. Patients Fifty severely burned patients with TBSA burned >25% BSA. Methods During the first 48 h after burn, gastric intramucosal CO 2 was measured every 8 h using automated air tonometry. pHi and intramucosal–arterial CO 2-gap were calculated. Simultaneously invasive haemodynamic data were registered by the transpulmonary thermodilution technique, using the mean of triplicate injections. The intramucosal–arterial CO 2-gradient and pHi were compared with haemodynamic and global perfusion data by regression analysis. Mean pHi and CO 2-gap values at 8 and 24 h after injury were compared between survivors and non-survivors to evaluate the prognostic significance of this parameter. Results Regression analyses revealed no or a negligible correlation between intramucosal and haemodynamic or perfusion data, even during the critical low flow–high resistance phase of resuscitation. Mean pHi and PCO 2-gap at 8 and 24 h did not differ significantly between survivors and non-survivors. Conclusion Gastric tonometry is a poor indicator of splanchnic perfusion in patients with burn shock, even when all precautions are taken to prevent methodological errors. The intramucosal–arterial PCO 2-gap and pHi do not distinguish survivors from non-survivors. Therefore, gastric tonometry does not seem to improve the ability to anticipate and avert regional anaerobic metabolism during burn shock and its routine use in these patients cannot be recommended.

Performance of automated air tonometry under hypothermia

Intestinal tonometry is used during hypothermic cardio-pulmonary bypass surgery to assess splanchnic perfusion. In an in vitro set-up the performance of automated air tonometry (TONOCAP) was tested for normo- and hypothermia. A 14-FG tonometry catheter was built into a testing chamber (100 cm(3)) perfused with blood from a cardio-pulmonary bypass circuit with P(a)co(2) held at 5.6-5.8 kPa (alpha-stat). P(r)co(2) from the balloon of the tonometry catheter was measured at intervals of 10 min at 37 degrees C and at 25 degrees C by the TONOCAP. Bias (precision) of P(r)co(2) - P(a)co(2 alpha-stat) and P(r)co(2) -P(a)co(2 pH-stat) at 37 degrees C blood temperature were low at 0.23 kPa (0.21) each. Tonometrically measured P(r)co(2) at 25 degrees C significantly differed from P(a)co(2 alpha-stat) bias (precision) of 2.00 kPa (0.11) but was similar to P(a)co(2 pH-stat) (0.30 kPa (0.11)). P(r)co(2) values as measured by the TONOCAP represent pH-stat approach. Identical blood gas management (pH- or alpha-stat) should be used for calculation of mucosal-arterial CO(2) difference (P(r-a)co(2) gap) or calculation of intramucosal pH.

Abnormal gastric tonometric variables and vasoconstrictor use after left ventricular assist device insertion

Background Abnormal gastric tonometric variables, a surrogate for splanchnic ischemia, occur in approximately 50% of patients at the end of routine cardiac operations and are associated with postoperative morbidity. We sought to determine whether gastric tonometric variables deteriorate after left ventricular assist device insertion and to explore the association between abnormal gastric tonometric variables and vasoconstrictor use. Methods Nineteen patients who had insertion of a left ventricular assist device were enrolled in a prospective, observational study. Automated air tonometry was used to determine the difference between gastric and arterial partial pressure of carbon dioxide (CO 2 gap) at five time points perioperatively. Results Compared with baseline, systemic blood flow was significantly increased at the end of operation (1.9 ± 0.6 versus 2.9 ± 0.7 L · min −1 · m −2, p < 0.0001). Tonometric variables, which were normal at baseline, became abnormal in 90% of patients (baseline CO 2 gap 4 ± 2 mm Hg versus end of operation CO 2 gap 24 ± 15 mm Hg, p < 0.0001). Elevated CO 2 gaps correlated with larger doses of norepinephrine ( r = 0.69, p = 0.001) and vasopressin ( r = 0.88, p < 0.0001). Abnormal gastric tonometric variables at the end of operation correlated with postoperative intensive care unit length of stay ( r = 0.70, p = 0.0009) and multiple organ dysfunction score ( r = 0.64, p = 0.0033). Conclusions Despite a significant increase in systemic blood flow after left ventricular assist device implantation, abnormal gastric tonometric variables developed and were associated with larger vasoconstrictor dose. These data provide evidence that gastric ischemia can develop independently of changes in systemic blood flow and support the potential role of vasoconstrictors as a cause of splanchnic ischemia.

Gastric hypercarbia and adverse outcome after cardiac surgery.

It has been postulated that splanchnic ischemia, as manifested by gastric hypercarbia, helps to trigger excessive systemic inflammation, which has been linked to the development of adverse postoperative outcome. This study examined whether gastric PCO(2) values are associated with adverse outcome in cardiac surgical patients. Prospective cohort study in a tertiary-care hospital. 43 patients undergoing elective cardiac surgery. Simultaneous measurements of gastric PCO(2) (using automated air tonometry) and arterial PCO(2) were obtained at the beginning and end of surgery. The difference (gap) between regional PCO(2) and arterial PCO(2) (corrected for temperature) was calculated. Adverse outcome was defined as in-hospital death or prolonged (>10 days) postoperative hospitalization. Fourteen patients fulfilled the predefined definition for adverse outcome. Postoperative ICU stay and postoperative hospital length of stay were significantly longer in these patients. At the end of surgery gastric minus arterial PCO(2) gap was significantly larger in patients with adverse outcome. Global hemodynamic and perfusion related variables were not associated with adverse outcome (cardiac index, mean arterial pressure, mixed venous oxygen saturation, arterial lactate, arterial base excess). Gastric minus arterial PCO(2) gap after surgery is larger in patients with adverse postoperative outcome, which supports the theory that gastrointestinal reduced perfusion is relevant to the pathogenesis of postoperative morbidity.

Factors affecting performance of air tonometry using the TONOCAP.

Saline tonometry has been replaced by automated air tonometry (TONOCAP). As with saline tonometry there are some pitfalls to consider. We investigated the influence of different filling handicaps to the tonometry catheter sampling balloon on measurement of regional PCO2 (PrCO2). In an in vitro set-up, PrCO2 was measured using the TONOCAP at intervals of 10 minutes from a 8F tonometry catheter sampling balloon placed in a container with constant PCO2 (PcCO2). Catheter alarms displayed by the TONOCAP device were noted. The following experiments were performed: A) control measurement without modifications; B) adding deadspace of 7 ml into the sampling line; C) placing the sampling balloon in a 3 ml syringe; D) cross-clamping of the sampling balloon. Each experiment was performed four times using two catheters on two TONOCAP devices. Differences between PcCO2 and PrCO2 were calculated as Pc-rCO2. Results are presented as mean +/- SD and were compared using ANOVA with Scheffe's correction. Pc-rCO2 in the control set-up (A) amounted to 0.16 +/- 0.22%. Increasing catheter deadspace (B) resulted in a higher Pc-rCO2 of 3.2 +/- 0.57% (P < 0.0001). Restriction of balloon expansion (C) caused an Pc-rCO2 gap of 1.17 +/- 0.36% (P < 0.0001). With filling restriction (D) the Pc-rCO2 gap increased to 3.87 +/- 0.29% (P < 0.0001). The catheter alarms provided were not able to indicate all catheter problems and initial alarms disappeared although the problems continued. We conclude that impaired catheter deadspace to balloon volume relation can negatively influence accuracy of PrCO2 measurement by the TONOCAP.

Effect of prone position on hepato-splanchnic hemodynamics in acute lung injury.

To evaluate the effects of prone position on hepato-splanchnic hemodynamics, metabolism and gut mucosal energy balance. Prospective clinical study. Medical intensive care unit in a university hospital. Eleven hemodynamically stable patients with acute lung injury (ALI) requiring mechanical ventilation. Patients were studied in the supine position, after 90 min in the prone position and after 90 min of supine repositioning. In addition to global hemodynamics we measured intra-abdominal pressure (IAP, bladder), hepato-splanchnic blood flow (HSBF, steady state indocyanine green technique using a hepatic vein catheter) and gastric mucosal-arterial PCO(2) gap (PCO(2) gap, automated air tonometry). Systemic hemodynamics did not change during the whole study. Prone positioning did not significantly affect IAP. HSBF as well as splanchnic oxygen consumption remained unaltered, too. Similarly, neither liver lactate uptake nor indocyanine green extraction were influenced by positional changes. Finally, stable regional hemodynamics were accompanied by an unchanged PCO(2) gap. We conclude that if IAP and systemic hemodynamics remain unaffected, the prone position in ALI patients compromises neither hepato-splanchnic perfusion nor gastric mucosal energy balance.

The effect of hypothermia on calculated values using saline and automated air tonometry

Objective: To quantify in vitro the effect of hypothermia on results obtained when performing automated air tonometry (Tonocap, Datex-Ohmeda, Instrumentarium Corp, Helsinki, Finland) and saline tonometry. Design:In vitro validation study. Setting: University hospital research laboratory. Interventions: Two TRIP sigmoid catheters, one connected to the Tonocap device and the other instilled with 2.5 mL of 0.9% saline, were placed in a saline bath at 30.3°C (mean) through which 5% carbon dioxide (CO2) was bubbled. Measurements and Main Results: A total of 50 paired measurements were taken at 30-minute equilibration times of saline bath CO2 tension and saline tonometry and air tonometry readings. Saline samples were analyzed at 37°C and corrected for temperature. Bias and precision of each technique as a percentage of predicted CO2 values were calculated. The Tonocap device had bias and precision values of −2.6% and ±1.4%. Measurement of CO2 is in the gaseous phase so that temperature correction is not required. Saline tonometry readings processed at 37°C exhibited a large positive bias of 23.06% (precision ± 7.02%). Correction for temperature improved bias to −10.98 % with a similar precision profile of ±5.78%. Conclusion: When using gastrointestinal tonometry during hypothermic cardiopulmonary bypass, saline tonometry samples should be temperature corrected. The Tonocap device proved the most accurate and precise measurement technique independent of the need for temperature correction. Copyright 2002, Elsevier Science (USA). All rights reserved.

Effect of prone position on hepato-splanchnic hemodynamics in acute lung injury

Abstract Objective. To evaluate the effects of prone position on hepato-splanchnic hemodynamics, metabolism and gut mucosal energy balance. Design. Prospective clinical study. Setting. Medical intensive care unit in a university hospital. Patients. Eleven hemodynamically stable patients with acute lung injury (ALI) requiring mechanical ventilation. Intervention. Patients were studied in the supine position, after 90 min in the prone position and after 90 min of supine repositioning. Measurements and results. In addition to global hemodynamics we measured intra-abdominal pressure (IAP, bladder), hepato-splanchnic blood flow (HSBF, steady state indocyanine green technique using a hepatic vein catheter) and gastric mucosal-arterial PCO2 gap (PCO2 gap, automated air tonometry). Systemic hemodynamics did not change during the whole study. Prone positioning did not significantly affect IAP. HSBF as well as splanchnic oxygen consumption remained unaltered, too. Similarly, neither liver lactate uptake nor indocyanine green extraction were influenced by positional changes. Finally, stable regional hemodynamics were accompanied by an unchanged PCO2 gap. Conclusion. We conclude that if IAP and systemic hemodynamics remain unaffected, the prone position in ALI patients compromises neither hepato-splanchnic perfusion nor gastric mucosal energy balance.

Report from the meeting: Gastrointestinal Tonometry: State of the Art. 22nd-23rd May 1998, London, UK.

Gastrointestinal (GI) tonometry, the only clinically available method for the accurate diagnosis of compromised GI blood flow, has been shown to be a sensitive predictor of increased morbidity, mortality and prolonged hospitalization. The recent introduction of the Tonocap, as a means of performing automated air tonometry, has simplified the application of GI tonometry in the clinical setting. Despite this the utility of GI tonometry remains controversial. The GI Tonometry: State of the Art meeting brought together a group of clinicians with a proven track record of research, clinical interest and expertise in this field. The aim of the meeting was to come to a consensus regarding certain issues such as the past and future roles of GI tonometry and standards for its correct usage and interpretation. Finally suggestions as to further research and clinical evaluation were made within a broader discussion regarding the complexities of applying the principles of evidence-based medicine to the introduction of a new piece of medical technology.

Current status of gastrointestinal tonometry

The use of gastric tonometry for the measurement of splanchnic perfusion as a surrogate of tissue oxygen delivery is a well-established technique, but one that has not enjoyed widespread clinical usage. Automated air tonometry, together with the measurement of gastric to arterial or end-tidal alveolar differences in carbon dioxide tension, is starting to replace the use of saline tonometry and the measurement of intramucosal pH. Although this technique is in the early stages of validation, it is thought that it will be a more clinically useful tool.

Regional Capnometry with Air-Automated Tonometry Detects Circulatory Failure Earlier Than Conventional Hemodynamics After Cardiac Surgery

Gastrointestinal automated online air tonometry has been proposed for monitoring gastric perfusion in patients at risk of circulatory failure (CF) after cardiopulmonary bypass. In this study, CF was prospectively defined as the requirement for vasoactive support to maintain mean arterial pressure > or = 70 mm Hg after optimization of preload. Hemodynamic variables--oxygen (O2) delivery (DO2), O2 uptake (Vo2), venous-to-arterial [P(v-a)CO2], gastric-to-arterial [P(r-a)CO2], and gastric-to-end-tidal [P(r-et)CO2]Pco2 gap-were retrospectively compared in 14 patients with or without CF during a 12-hr postbypass period (HO-H12). In contrast to patients without CF (n = 7), in patients with CF (n = 7) increased VO2 was not associated with an increase in DO2. P(r-a)CO2 was larger at H0 in CF patients and was the only variable that differed between the two groups. P(v-a)CO2 did not vary significantly in both groups, whereas P(r-a)CO2 increased to a larger extent from H0 to H12 in patients with CF, suggesting selective gastrointestinal hypoperfusion in this group. P(r-et)CO2 provided comparable information to P(r-a)CO2. Hospital length of stay was 4 days longer (P < 0.05) in patients with CF. Increased P(r-a)CO2 and P(r-et)CO2, as monitored with automated air tonometry, were associated with rapid occurrence of CF and prolonged hospital stay after cardiac surgery. Regional and automated capnometry may be used noninvasively to identify patients at risk of circulatory failure after cardiopulmonary bypass earlier than with conventional variables.

Gastrointestinal PCO2 tonometry in 1998

Gastrointestinal luminal tonometry is a minimally invasive monitoring technique for critically ill patients. It is not widely accepted yet, possibly because of uncertainties with respect to physiologic background, methodology, and clinical usefulness. This review discusses recent developments, including automated air tonometry, that might render tonometry easier to apply by replacing the laborious and error-prone manual saline technique, the value of the blood-intragastric PCO2 gap versus the intramucosal pH, the need for gastric acid suppression during tonometry in the stomach, the sources of error for fluid PCO2 tonometry, and the luminal PCO2 in parts of the gastrointestinal tract other than the stomach. Finally, new clinical investigations are reviewed.