Gastric and sublingual capnometry

A review of using CO2-derived variables to detect tissue hypoperfusion during cardiopulmonary bypass

Complications after cardiac surgery with cardiopulmonary bypass (CPB) are associated with increased morbidity and mortality. Early detection and prompt reversion of tissue hypoperfusion during CPB are key factors to reduce organ dysfunction after cardiac surgery. CO2 (carbon dioxide)-derived variables which are easy to assess and routinely available to evaluate the adequacy of macro- and microcirculation may offer important information on the adequacy of the perfusion during CPB. However, since some practical issues remain unsolved in providing a reliable measurement of CO2 removal from the patient, CO2-derived variables are not widely monitoring during CPB. This review aims to demonstrate the basic principles of CO2-derived variables during CPB, the available techniques to assess CO2-derived variables on CPB and the clinically relevant applications.

Regional capnometry to evaluate the adequacy of tissue perfusion

Tissue hypoperfusion is a major cause of morbidity and mortality in critically ill patients but cannot always be detected by measuring standard whole-body hemodynamic and oxygen-related parameters (e.g., blood pressure, cardiac output, and central venous oxygen saturation). Preclinical and clinical studies have demonstrated that low-flow states are consistently associated with large increases in venous and tissue PCO₂. Monitoring regional PCO₂ with gastric tonometry (PgCO₂) is known to have independent prognostic value for predicting postoperative complications and mortality. The PgCO₂ gap might also be of value as a treatment target (endpoint) in critically ill patients. However, this tool has several limitations and has not yet been developed commercially, thus restricting its use. Regional capnography with sublingual and transcutaneous sensors might be an alternative noninvasive option for evaluating the adequacy of tissue perfusion in critically ill patients. However, further studies are needed to determine whether or not this monitoring technique is of value-particularly as an endpoint for guiding resuscitation. Bladder PCO₂, has only been evaluated in animal studies, and so remains to be validated in patients.

Monitoring End Points of Burn Resuscitation

This article discusses commonly used methods of monitoring and determining the end points of resuscitation. Each end point of resuscitation is examined as it relates to use in critically ill burn patients. Published medical literature, clinical trials, consensus trials, and expert opinion regarding end points of resuscitation were gathered and reviewed. Specific goals were a detailed examination of each method in the critical care population and how this methodology can be used in the burn patient. Although burn resuscitation is monitored and administered using the methodology as seen in medical/surgical intensive care settings, special consideration for excessive edema formation, metabolic derangements, and frequent operative interventions must be considered.

Monitoring Microcirculatory Blood Flow with a New Sublingual Tonometer in a Porcine Model of Hemorrhagic Shock

Tissue capnometry may be suitable for the indirect evaluation of regional hypoperfusion. We tested the performance of a new sublingual capillary tonometer in experimental hemorrhage. Thirty-six anesthetized, ventilated mini pigs were divided into sham-operated (n = 9) and shock groups (n = 27). Hemorrhagic shock was induced by reducing mean arterial pressure (MAP) to 40 mmHg for 60 min, after which fluid resuscitation started aiming to increase MAP to 75% of the baseline value (60-180 min). Sublingual carbon-dioxide partial pressure was measured by tonometry, using a specially coiled silicone rubber tube. Mucosal red blood cell velocity (RBCV) and capillary perfusion rate (CPR) were assessed by orthogonal polarization spectral (OPS) imaging. In the 60 min shock phase a significant drop in cardiac index was accompanied by reduction in sublingual RBCV and CPR and significant increase in the sublingual mucosal-to-arterial PCO2 gap (PSLCO2 gap), which significantly improved during the 120 min resuscitation phase. There was significant correlation between PSLCO2 gap and sublingual RBCV (r = -0.65, p < 0.0001), CPR (r = -0.64, p < 0.0001), central venous oxygen saturation (r = -0.50, p < 0.0001), and central venous-to-arterial PCO2 difference (r = 0.62, p < 0.0001). This new sublingual tonometer may be an appropriate tool for the indirect evaluation of circulatory changes in shock.

Gastric feeding intolerance is not caused by mucosal ischemia measured by intragastric air tonometry in the critically ill

BACKGROUND

Gastric mucosal ischemia may be a risk factor for gastrointestinal intolerance to early feeding in the critically ill.

AIMS

To study intragastric PCO2 air tonometry and gastric residual volumes (GRV) before and after the start of gastric feeding.

METHODS

This is a two-center study in intensive care units of a university and teaching hospital. Twenty-nine critically ill, consecutive and consenting patients scheduled to start gastric feeding were studied after insertion of a gastric tonometry catheter and prior to and after start of gastric feeding (500 ml over 1 h), when clinically indicated.

RESULTS

Blood gasometry and intragastric tonometry were performed prior to and 2 h after gastric feeding. The intragastric to arterial PCO2 gap (normal <8 mm Hg) was elevated in 41% of patients prior to feeding and measured (mean ± standard deviation) 13 ± 20 and 16 ± 23 mm Hg in patients with normal (<100 ml, 42 ± 34 ml, n = 19) and elevated GRV (250 ± 141 ml, n = 10, P = 0.75), respectively. After feeding, the gradient did not increase and measured 27 ± 25 and 23 ± 34 mm Hg, respectively (P = 0.80).

CONCLUSION

Gastric mucosal ischemia is not a major risk factor for intolerance to early gastric feeding in the critically ill.

A Newly Developed Sublingual Tonometric Method for the Evaluation of Tissue Perfusion and Its Validation In Vitro and in Healthy Persons In Vivo and the Results of the Measurements in COPD Patients

Introduction. Since its first publication in the medical literature, an extremely large number of references have demonstrated that the tonometric measurement of tissue perfusion is a reliable indicator of the actual condition of critically ill patients. Later a new method was developed by the introduction of sublingual tonometry for the determination of tissue perfusion. In comparison with gastric tonometry, the new method was simpler and could even be used in awake patients. Unfortunately, at present, because of severe failures of manufacturing, the device is withdrawn from commerce. Materials and Methods. In this study, we present a new method using a newly developed tool for the P_slCO₂ measurement in sublingual tonometry as well as the data for its validation in vitro and in vivo and the results of 25 volunteers and 54 COPD patients belonging to different GOLD groups at their hospitalization due to the acute exacerbation of the disease but already in a stable condition at the time of the examination. Results and Conclusion. The results of the performed examinations showed that the method is suitable for monitoring the actual condition of the patients by mucosal perfusion tonometry in the sublingual region.

Endpoints of resuscitation

Despite the multiple causes of the shock state, all causes possess the common abnormality of oxygen supply not meeting tissue metabolic demands. Compensatory mechanisms may mask the severity of hypoxemia and hypoperfusion, since catecholamines and extracellular fluid shifts initially compensate for the physiologic derangements associated with patients in shock. Despite the achievement of normal physiologic parameters after resuscitation, significant metabolic acidosis may continue to be present in the tissues, as evidenced by increased lactate levels and metabolic acidosis. This review discusses the major endpoints of resuscitation in clinical use.

Bladder mucosal CO2 compared with gastric mucosal CO2 as a marker for low perfusion states in septic shock

Recent reports indicate the possible role of bladder CO(2) as a marker of low perfusion states. To test this hypothesis, shock was induced in six beagle dogs with 1 mg/kg of E. coli lipopolysaccharide, gastric CO(2) (CO(2)-G) was measured with a continuous monitor, and a pulmonary catheter was inserted in the bladder to measure CO(2) (CO(2)-B). Levels of CO(2)-B were found to be lower than those of CO(2)-G, with a mean difference of 36.8 mmHg (P < 0.001), and correlation between both measurements was poor (r(2) = 0.16). Even when the correlation between CO(2)-G and ΔCO(2)-G was narrow (r(2) = 0.86), this was not the case for the relationship between CO(2)-B and ΔCO(2)-B (r(2) = 0.29). Finally, the correlation between CO(2)-G and base deficit was good (r(2) = 0.45), which was not the case with the CO(2)-B correlation (r(2) = 0.03). In our experience, bladder CO(2) does not correlate to hemodynamic parameters and does not substitute gastric CO(2) for detection of low perfusion states.

Tissue gas tensions and tissue metabolites for detection of organ hypoperfusion and ischemia

BACKGROUND

The aim of this study was to evaluate how tissue gas tensions and tissue metabolites measured in situ can detect hypoperfusion and differentiate between aerobic and anaerobic conditions during hemorrhagic shock. We hypothesized that tissue PCO(2) (PtCO(2)) would detect hypoperfusion also under aerobic conditions and detect anaerobic metabolism concomitantly with or earlier than other markers.

METHODS

Prospective experimental animal study with eight anesthetized pigs subjected to a continuous blood loss ∼8% of total blood volume per hour until death. We measured cardiac index, organ blood flows, and tissue levels of PO(2), PCO(2), glucose, pyruvate, lactate, and glycerol in intestine, liver, kidney, and skeletal muscle.

RESULTS

With reduction in blood flow to the organs under aerobic conditions, PtCO(2) increased ∼1-4 kPa from baseline. With the onset of tissue hypoxia there was a pronounced increase of PtCO(2), lactate, lactate-pyruvate (LP) ratio, and glycerol. Tissue pH and bicarbonate decreased significantly, indicating that metabolic acid was buffered by bicarbonate to generate CO(2).

CONCLUSION

Moderate tissue hypoperfusion under aerobic conditions is associated with increased PtCO(2), in contrast to metabolic parameters of ischemia (lactate, LP ratio, and glycerol) which remain low. From the onset of ischemia there is a much more rapid and pronounced increase in PtCO(2), lactate, and LP ratio. PtCO(2) can be used as a marker of hypoperfusion under both aerobic and anaerobic conditions; it gives an earlier warning of hypoperfusion than metabolic markers and increases concomitantly with or earlier than other markers at the onset of tissue anaerobiosis.

Review article: Part two: Goal-directed resuscitation--which goals? Perfusion targets

Haemodynamic targets, such as cardiac output, mean arterial blood pressure and central venous oxygen saturations, remain crude predictors of tissue perfusion and oxygen supply at a cellular level. Shocked patients may appear adequately resuscitated based on normalization of global vital signs, yet they are still experiencing occult hypoperfusion. If targeted resuscitation is employed, appropriate use of end-points is critical. In this review, we consider the value of directing resuscitation at the microcirculation or cellular level. Current technologies available include sublingual capnometry, video microscopy of the microcirculation and near-infrared spectroscopy providing a measure of tissue oxygenation, whereas base deficit and lactate potentially provide a surrogate measure of the adequacy of global perfusion. The methodology and evidence for these technologies guiding resuscitation are considered in this narrative review.

Consecutive Daily Measurements of Luminal Concentrations of Lactate in the Rectum in Septic Shock Patients

In a recent study we found no difference in the concentrations of luminal lactate in the rectum between nonsurvivors and survivors in early septic shock (<24 h). This study was initiated to investigate if there are any changes in the concentrations of luminal lactate in the rectum during the first 3 days of septic shock and possible differences between nonsurvivors and survivors. Methods. We studied 22 patients with septic shock in this observational study. Six to 24 h after the onset of septic shock the concentration of lactate in the rectal lumen was estimated by 4 h equilibrium dialysis (day 1). The rectal dialysis was repeated on day 2 and day 3. Results. The concentration of lactate in the rectal lumen did not change over the 3 days in neither nonsurvivors nor survivors. Rectal luminal and arterial lactate concentrations were not different. Conclusion. There was no change in the concentration of lactate in the rectal lumen over time in patients with septic shock. Also, there was no difference between nonsurvivors and survivors.

Mitochondrial function and tissue vitality: bench-to-bedside real-time optical monitoring system

BACKGROUND

The involvement of mitochondria in pathological states, such as neurodegenerative diseases, sepsis, stroke, and cancer, are well documented. Monitoring of nicotinamide adenine dinucleotide (NADH) fluorescence in vivo as an intracellular oxygen indicator was established in 1950 to 1970 by Britton Chance and collaborators. We use a multiparametric monitoring system enabling assessment of tissue vitality. In order to use this technology in clinical practice, the commercial developed device, the CritiView (CRV), is tested in animal models as well as in patients.

METHODS AND RESULTS

The new CRV enables the optical monitoring of four different parameters, representing the energy balance of various tissues in vivo. Mitochondrial NADH is measured by surface fluorometry/reflectometry. In addition, tissue microcirculatory blood flow, tissue reflectance and oxygenation are measured as well. The device is tested both in vitro and in vivo in a small animal model and in preliminary clinical trials in patients undergoing vascular or open heart surgery. In patients, the monitoring is started immediately after the insertion of a three-way Foley catheter (urine collection) to the patient and is stopped when the patient is discharged from the operating room. The results show that monitoring the urethral wall vitality provides information in correlation to the surgical procedure performed.

[What non invasive haemodynamic assessment in paediatric intensive care unit in 2009?]

The haemodynamic assessment of the patients is a daily activity in paediatric intensive care unit. It completes and is guided by the clinical examination. The will to develop the least invasive possible coverage of the patients is a constant concern. The haemodynamic monitoring, all the more if it is invasive, ceaselessly has to put in balance the profit and the risk of beginning this technique at a fragile patient. In the last three decades, numerous non-invasive haemodynamic tools were developed. The ideal one must be reliable, reproducible, with a time of fast, easily useful answer, with a total harmlessness, cheap and allowing a monitoring continues. Among all the existing tools (oesophageal Doppler ultrasound method, transthoracic echocardiography, NICO, thoracic impedancemetry, plethysmography, sublingual capnography), no one allies all these qualities. We can consider that the transthoracic echocardiography gets closer to most of these objectives. We shall blame it for its cost and for the fact that it is an intermittent monitoring but both in the diagnosis and in the survey, it has no equal among the non-invasive tools of haemodynamic assessment from part the quality and the quantity of the obtained information. The learning of the basic functions (contractility evaluation, cardiac output, cardiac and the vascular filling) useful for the start of a treatment is relatively well-to-do. We shall miss the absence of training in this tool in France in its paediatric and neonatal specificity within the university or interuniversity framework.

Intestinal and gastric tonometry during experimental burn shock

INTRODUCTION

The occurrence of organ failure following thermal injury, despite restoration of hemodynamic parameters and urine output during resuscitation, has led to efforts to measure end-organ perfusion. The purpose of this 24-h study was to evaluate the utility of gastrointestinal (GI) tonometry during burn shock and resuscitation.

METHODS

Male swine (n=11, 23.3+/-0.9 kg) were anesthetized with ketamine and propofol. A 70% full thickness burn was caused by immersion in 97 degrees C water for 30 s. Resuscitation with lactated Ringer's, 4 ml/kg/% burn, was begun at hour 6 and titrated to urine output (UO). Arterial blood gases and pulmonary artery catheter data were measured every 6 h. Gastric and ileal regional PCO(2) (PrCO(2)) were measured continuously by air tonometry, and the gastric and ileal intramucosal pH (pHi) and PCO(2) gap (PrCO(2)-PaCO(2)) were calculated every 6 h.

RESULTS

Gastric pHi, ileal PrCO(2), ileal pHi, and ileal PCO(2) gap (but not gastric PrCO(2) or PCO(2) gap) all decreased with shock and were restored to baseline levels by resuscitation. Changes in ileal PrCO(2) were of greater magnitude and demonstrated decreased variability than those in gastric PrCO(2).

CONCLUSIONS

In this model, ileal tonometry outperformed gastric tonometry during burn shock and resuscitation.

Capnometry in the prehospital setting: are we using its potential?

Capnometry is a non-invasive monitoring technique which allows fast and reliable insight into ventilation, circulation, and metabolism. In the prehospital setting it is mainly used to confirm correct tracheal tube placement. In addition it is a useful indicator of efficient ongoing cardiopulmonary resuscitation due to its correlation with cardiac output, and successful resuscitation. It helps to confirm the diagnosis of pulmonary thromboembolism and to sustain adequate ventilation in mechanically ventilated patients. In patients with haemorrhage, capnometry provides improved continuous haemodynamic monitoring, insight into adequacy of tissue perfusion, optimisation within current hypotensive fluid resuscitation strategy, and prevention of shock progression through controlled fluid administration.

Role of buccal PCO2 in the management of fluid resuscitation during hemorrhagic shock

Arterial pressure is a widely used measurement for estimating the severity of hemorrhagic shock and to guide its management. However, this capability is reduced when very low arterial pressure values cannot be reliably measured by noninvasive methods. Moreover, hypoperfusion may be masked by compensatory hemodynamic changes, and therefore, in the presence of near normal blood pressure, tissue hypoperfusion may progress undetected. Accordingly, hypercarbia is a general phenomenon of perfusion failure, which occurs in coincidence of the onset of hypotension and is promptly reversed with restoration of normal blood flows. Increases in buccal mucosa PCO2 are highly correlated with increases in gastric wall and sublingual mucosa PCO2 and decreases in tissue blood flows during hemorrhagic shock. In both clinical and experimental settings, tissue PCO2 measured in the oral mucosa proved to be a practical and reliable measurement for the diagnosis of circulatory failure states and an indicator of its severity. In contrast to intraarterial pressure, buccal PCO2 discriminated between short- and long-term survival after large-volume blood loss. Buccal PCO2 measurement therefore emerges as a useful predictor for survival and outcome and a useful guide to manage fluid resuscitation during hemorrhagic shock.