Monitoring the hepato-splanchnic region in the critically ill patient. Measurement techniques and clinical relevance

Monitoring peripheral perfusion and microcirculation

PURPOSE OF REVIEW

Microcirculatory alterations play a major role in the pathogenesis of shock. Monitoring tissue perfusion might be a relevant goal for shock resuscitation. The goal of this review was to revise the evidence supporting the monitoring of peripheral perfusion and microcirculation as goals of resuscitation. For this purpose, we mainly focused on skin perfusion and sublingual microcirculation.

RECENT FINDINGS

Although there are controversies about the reproducibility of capillary refill time in monitoring peripheral perfusion, it is a sound physiological variable and suitable for the ICU settings. In addition, observational studies showed its strong ability to predict outcome. Moreover, a preliminary study suggested that it might be a valuable goal for resuscitation. These results should be confirmed by the ongoing ANDROMEDA-SHOCK randomized controlled trial. On the other hand, the monitoring of sublingual microcirculation might also provide relevant physiological and prognostic information. On the contrary, methodological drawbacks mainly related to video assessment hamper its clinical implementation at the present time.

SUMMARY

Measurements of peripheral perfusion might be useful as goal of resuscitation. The results of the ANDROMEDA-SHOCK will clarify the role of skin perfusion as a guide for the treatment of shock. In contrast, the assessment of sublingual microcirculation mainly remains as a research tool.

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

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.

Instrument to detect syncope and the onset of shock

Currently the diagnosis of hemorrhagic shock is essentially clinical, relying on the expertise of nurses and doctors. One of the first measurable physiological changes that marks the onset of hemorrhagic shock is a decrease in capillary blood flow. Diffuse correlation spectroscopy (DCS) quantifies this decrease. DCS collects and analyzes multiply scattered, coherent, near infrared light to assess relative blood flow. This work presents a preliminary study using a DCS instrument with human subjects undergoing a lower body negative pressure (LBNP) protocol. This work builds on previous successful DCS instrumentation development and we believe it represents progress toward understanding how DCS can be used in a clinical setting.

Early detection of gut ischemia-reperfusion injury during aortic abdominal aneurysmectomy: a pilot, observational study

OBJECTIVE

D-lactate is the enantiomer of L-lactate, which is measured routinely in clinical practice to assess cell hypoxia. D-lactate has been proposed as a specific marker of gut ischemia-reperfusion (IR), particularly during surgery for ruptured abdominal aortic aneurysms. The aim of this study was to compare the use of D-lactate measurement and colonic tonometry (taken as a reference method) for gut IR detection during elective infrarenal aortic aneurysm (IrAA) surgery.

DESIGN

Prospective, monocenter, observational study.

SETTING

Vascular surgery unit, university hospital.

PARTICIPANTS

Candidates for elective IrAA surgery.

INTERVENTIONS

Patients without (controls) and with gut IR (defined as ΔCO2>2.6 kPa) were compared retrospectively.

MEASUREMENT AND MAIN RESULTS

D-lactate levels were compared with colonic perfusion levels (ΔCO2), as assessed by colonic tonometry, at 7 time points during surgery and until 24 hours after surgery. D-lactate also was measured in mesenteric vein blood before and after gut reperfusion. Plasma TNF-α level was measured at the same time points to assess systemic inflammatory response. Eighteen patients requiring elective IrAA surgery were included. The ΔCO2 and TNF-α level varied significantly over time. There was a significant ΔCO2 peak at the end of clamping (2.6±1.8 kPa, p = 0.006) and a significant peak in TNF-α level after 1 hour of reperfusion (183±53 ng/L, p = 0.05). D-lactate levels were undetectable in systemic and mesenteric blood in all the patients throughout the study period. Gut IR patients (n = 6) experienced a longer overall duration of intraoperative hypotensive episodes and received more catecholamines than the controls (n = 12).

CONCLUSIONS

Compared with colonic tonometry, D-lactate was not a reliable biomarker of gut IR during elective IrAA surgery.

Relationship of systemic, hepatosplanchnic, and microcirculatory perfusion parameters with 6-hour lactate clearance in hyperdynamic septic shock patients: an acute, clinical-physiological, pilot study

Background

Recent clinical studies have confirmed the strong prognostic value of persistent hyperlactatemia and delayed lactate clearance in septic shock. Several potential hypoxic and nonhypoxic mechanisms have been associated with persistent hyperlactatemia, but the relative contribution of these factors has not been specifically addressed in comprehensive clinical physiological studies. Our goal was to determine potential hemodynamic and perfusion-related parameters associated with 6-hour lactate clearance in a cohort of hyperdynamic, hyperlactatemic, septic shock patients.

Methods

We conducted an acute clinical physiological pilot study that included 15 hyperdynamic, septic shock patients undergoing aggressive early resuscitation. Several hemodynamic and perfusion-related parameters were measured immediately after preload optimization and 6 hours thereafter, with 6-hour lactate clearance as the main outcome criterion. Evaluated parameters included cardiac index, mixed venous oxygen saturation, capillary refill time and central-to-peripheral temperature difference, thenar tissue oxygen saturation (StO₂) and its recovery slope after a vascular occlusion test, sublingual microcirculatory assessment, gastric tonometry (pCO₂ gap), and plasma disappearance rate of indocyanine green (ICG-PDR). Statistical analysis included Wilcoxon and Mann–Whitney tests.

Results

Five patients presented a 6-hour lactate clearance <10%. Compared with 10 patients with a 6-hour lactate clearance ≥10%, they presented a worse hepatosplanchnic perfusion as represented by significantly more severe derangements of ICG-PDR (9.7 (8–19) vs. 19.6 (9–32)%/min, p < 0.05) and pCO₂ gap (33 (9.1-62) vs. 7.7 (3–58) mmHg, p < 0.05) at 6 hours. No other systemic, hemodynamic, metabolic, peripheral, or microcirculatory parameters differentiated these subgroups. We also found a significant correlation between ICG-PDR and pCO₂ gap (p = 0.02).

Conclusions

Impaired 6-hour lactate clearance could be associated with hepatosplanchnic hypoperfusion in some hyperdynamic septic shock patients. Improvement of systemic, metabolic, and peripheral perfusion parameters does not rule out the persistence of hepatosplanchnic hypoperfusion in this setting. Severe microcirculatory abnormalities can be detected in hyperdynamic septic shock patients, but their role on lactate clearance is unclear. ICG-PDR may be a useful tool to evaluate hepatosplanchnic perfusion in septic shock patients with persistent hyperlactatemia.

Trial registration

ClinicalTrials.gov Identifier: NCT01271153

Mucosal tonometry as early warning of gastrojejunal leak in laparoscopic Roux-en-y gastric bypass

The laparoscopic Roux-en-Y gastric bypass (LRYGB) is the standard surgical procedure for morbidly obese patients in many centers worldwide. The gastrojejunal anastomosis (GJA) leak has a 2 % incidence and a 10 % mortality. This prospective study aims to test gastroenteric tonometry as an early warning of GJA leak risk. A nasogastric tube with tonometric capability was used to monitor gastroenteric mucosal carbon dioxide partial pressure (PgeCO2) in 32 consecutive patients during the first 24 to 72 postoperative hours after LRYGB. Sensitivity was 100 %, specificity 96.77 %, likelihood ratio 31, and area under receiver operating characteristic curve 0.984. The only early gastrojejunal leak occurred to the patient with maximal PgeCO2 (13.9 kPa) of the cohort. The remaining patients kept a PgeCO2 below 11 kPa except one; none of these developed early GJA leak. Mucosal gastroenteric tonometry may be a useful predictor of early GJA leak of the LRYGB.

Anesthesia and the Microcirculation

There is increasing evidence that the microcirculation and its regulation are severely compromised during many pathological conditions, such as hemorrhage, sepsis, or trauma. The effects of anesthetic agents on macrohemodynamics were investigated intensively in the last several decades. Research regarding modern anesthetics and anesthesia techniques has increased knowledge regarding the nonanesthetic effects of anesthetic agents, including those on organ perfusion and the microcirculation. Alterations in microvascular reactivity, nitric oxide pathways, and cytokine release are presumably the main mechanisms of anesthetic-induced tissue perfusion changes. This review summarizes current methods of microcirculatory status assessment and current knowledge regarding the microcirculatory effects of intravenous and potent volatile anesthetics and anesthesia-related techniques under both normal and pathophysiological conditions.

Liver perfusion in sepsis, septic shock, and multiorgan failure

Sepsis causes significant alterations in the hepatic macro- and microcirculation. Diverging views exist on global hepatic blood flow during experimental sepsis because of the large variety in animal and sepsis models. Fluid-resuscitated clinical sepsis is characterized by ongoing liver ischemia due to a defective oxygen extraction despite enhanced perfusion. The effects of vasoactive agents on the hepatosplanchnic circulation are variable, mostly anecdotal, and depend on baseline perfusion, time of drug administration, and use of concomitant medication. Microvascular blood flow disturbances are thought to play a pivotal role in the development of sepsis-induced multiorgan failure. Redistribution of intrahepatic blood flow in concert with a complex interplay between sinusoidal endothelial cells, liver macrophages, and passing leukocytes lead to a decreased perfusion and blood flow velocity in the liver sinusoids. Activation and dysfunction of the endothelial cell barrier with subsequent invasion of neutrophils and formation of microthrombi further enhance liver tissue ischemia and damage. Substances that regulate (micro)vascular tone, such as nitric oxide, endothelin-1, and carbon monoxide, are highly active during sepsis. Possible interactions between these mediators are not well understood, and their therapeutic manipulation produces equivocal or disappointing results. Whether and how standard resuscitation therapy influences the hepatic microvascular response to sepsis is unknown. Indirect evidence supports the concept that improving the microcirculation may prevent or ameliorate sepsis-induced organ failure.

Gastrointestinal perfusion in septic shock

Septic shock is characterised by vasodilation, myocardial depression and impaired microcirculatory blood flow, resulting in redistribution of regional blood flow. Animal and human studies have shown that gastrointestinal mucosal blood flow is impaired in septic shock. This is consistent with abnormalities found in many other microcirculatory vascular beds. Gastrointestinal mucosal microcirculatory perfusion deficits have been associated with gut injury and a decrease in gut barrier function, possibly causing augmentation of systemic inflammation and distant organ dysfunction. A range of techniques have been developed and used to quantify these gastrointestinal perfusion abnormalities. The following techniques have been used to study gastrointestinal perfusion in humans: tonometry, laser Doppler flowmetry, reflectance spectrophotometry, near-infrared spectroscopy, orthogonal polarisation spectral imaging, indocyanine green clearance, hepatic vein catheterisation and measurements of plasma D-lactate. Although these methods share the ability to predict outcome in septic shock patients, it is important to emphasise that the measurement results are not interchangeable. Different techniques measure different elements of gastrointestinal perfusion. Gastric tonometry is currently the most widely used technique because of its non-invasiveness and ease of use. Despite all the recent advances, the usefulness of gastrointestinal perfusion parameters in clinical decision-making is still limited. Treatment strategies specifically aimed at improving gastrointestinal perfuision have failed to actually correct mucosal perfusion abnormalities and hence not shown to improve important clinical endpoints. Current and future treatment strategies for septic shock should be tested for their effects on gastrointestinal perfusion; to further clarify its exact role in patient management, and to prevent therapies detrimental to gastrointestinal perfusion being implemented.

Catecholamines and vasopressin during critical illness

This article summarizes the effects of catecholamines and vasopressin on the cardiovascular system, focusing on their metabolic and immunologic properties. Particular attention is dedicated to the septic shock condition.

Jaundice in critical illness: promoting factors of a concealed reality

OBJECTIVE

In critical illness, liver dysfunction (LD) is associated with a poor outcome independently of other organ dysfunctions. Since strategies to support liver function are not available, a timely and accurate identification of factors promoting LD may lead to prevention or attenuation of its consequences. The aim of this study was to assess risk factors for LD in critically ill patients.

DESIGN

Prospective, observational study.

SETTING

A multidisciplinary intensive care unit (ICU) of a university hospital.

PATIENTS

All patients consecutively admitted over a 6-month period.

INTERVENTION

None.

MEASUREMENTS AND RESULTS

LD was defined as serum bilirubin levels >or=2 mg/dl and lasting for at least 48 h. Out of 283 patients, 141 matched inclusion criteria. Forty-four patients (31.2%) showed LD (LD group), while 97 (68.8%) were included in control group (C group). A binomial analysis showed that LD occurrence was associated with moderate (odds ratio [OR] 3.11; p=0.04) and severe shock (OR 3.46; p= 0.05), sepsis (OR 3.03; p=0.04), PEEP ventilation (OR 4.25; p=0.006), major surgery (OR 4.03; p=0.03), and gram-negative infections (OR 3.94; p=0.002). In stepwise multivariate analysis, the single independent predictive factors of LD resulted in severe shock (p=0.002), sepsis (p=0.03), PEEP ventilation (p=0.04), and major surgery (p=0.05).

CONCLUSIONS

In critically ill patients jaundice is common, and severe shock states, sepsis, mechanical ventilation with PEEP and major surgery are critical risk factors for its onset. Since there is no specific treatment, prompt resuscitation, treatment of sepsis and meticulous supportive care will likely reduce its incidence and severity.

Monitoring global volume-related hemodynamic or regional variables after initial resuscitation: What is a better predictor of outcome in critically ill septic patients?

OBJECTIVE

Regional variables of organ dysfunction are thought to be better monitoring variables than global pressure-related hemodynamic variables. Whether a difference exists between regional and global volume-related variables in critically ill patients after resuscitation is unknown.

DESIGN

Prospective diagnostic test evaluation.

SETTING

University-affiliated mixed intensive care unit.

PATIENTS

Twenty-eight critically ill patients.

INTERVENTIONS

Using standardized resuscitation, hemodynamic optimization was targeted at mean arterial pressure, heart rate, occlusion pressure, cardiac output, systemic vascular resistance, and urine output. Primary outcome variable was in-hospital mortality.

MEASUREMENTS AND MAIN RESULTS

During resuscitation, global volume-related hemodynamic variables were measured simultaneously and compared with regional variables. At admission no variable was superior as a predictor of outcome. During resuscitation, significant changes were seen in mean arterial pressure, central venous pressure, oxygen delivery, systemic vascular resistance, total blood volume, right heart and ventricle end-diastolic volume, right ventricle ejection fraction, right and left stroke work index, intramucosal carbon dioxide pressure, gastric mucosal pH, mucosal-end tidal Pco2 gap, indocyanine green blood clearance, indocyanine green plasma clearance, and plasma disappearance rate. Multivariate analysis identified lactate, gastric mucosal pH, mucosal-end tidal Pco2 gap, mucosal-arterial Pco2 gap, indocyanine green plasma clearance, and plasma disappearance rate of dye as nondependent predictors of outcome. Patients who subsequently died had a significantly lower gastric mucosal pH, higher intramucosal carbon dioxide pressure and mucosal-end tidal Pco2 gap, and lower indocyanine green blood clearance, indocyanine green plasma clearance, plasma disappearance rate, and right ventricular end-diastolic volume index, of which gastric mucosal pH, mucosal-end tidal Pco2 gap, and indocyanine green blood clearance were the most important predictors of outcome.

CONCLUSIONS

Initial resuscitation of critically ill patients with shock does not require monitoring of regional variables. After stabilization, however, regional variables are the best predictors of outcome.

Cytochrome P-450 activity is differentially altered in severely injured patients

OBJECTIVE

To assess whether changes in cytochrome P-450 (CYP) activity of specific CYP enzymes occur in severely injured patients and to assess changes in CYP activity during recovery.

DESIGN

Prospective clinical study.

SETTING

University-affiliated, level I trauma center and trauma critical care unit.

PATIENTS

Twenty-three multiply injured patients admitted to a trauma critical care unit were compared with healthy volunteers.

INTERVENTIONS

CYP metabolizing activity was assessed using the probe drugs mephenytoin (CYP-2C19), chlorzoxazone (CYP-2E1), dapsone (multiple CYP enzymes), and flurbiprofen (CYP-2C9).

MEASUREMENTS AND MAIN RESULTS

Mephenytoin metabolism was profoundly suppressed after injury and increased during postinjury recovery, whereas chlorzoxazone metabolism was suppressed to a lesser degree. Measures of dapsone and flurbiprofen metabolism were elevated throughout the study. Chlorzoxazone and mephenytoin metabolism correlated with the multiple organ dysfunction score and with the multiple organ failure score.

CONCLUSIONS

CYP isoform activity is differentially altered by shock and trauma in injured patients. The metabolic activity of selected CYP isoforms may have potential for evaluating acute hepatic dysfunction in critically ill trauma patients.

EFFECTS OF DOPAMINE AND NOREPINEPHRINE ON SYSTEMIC AND HEPATOSPLANCHNIC HEMODYNAMICS, OXYGEN EXCHANGE, AND ENERGY BALANCE IN VASOPLEGIC SEPTIC PATIENTS

Dopamine is widely used to improve systemic and hepatosplanchnic hemodynamics and oxygenation during sepsis. However, some studies have suggest that norepinephrine may have beneficial effects on regional blood flow and metabolism, whereas dopamine might have deleterious effects related to redistribution of blood flow away from the intestinal mucosa or by decreasing directly the cell redox state. In 12 vasoplegic septic patients, we compared the effects of norepinephrine and dopamine on systemic and hepatosplanchnic hemodynamics, oxygenation, and energy metabolism. Catecholamines were administered in a crossover randomized order to maintain mean arterial pressure (MAP) at 80 mmHg. Hepatosplanchnic blood flow (Qspl) was determined using a continuous infusion of indocyanine green dye. Despite a similar MAP, the cardiac index was higher with dopamine than with norepinephrine (6.3 [5.3-7.3] vs. 4.3 [3.8-4.9] L.min.m) (P <0.001). Qspl was similar with both catecholamines, but the ratio of Qspl to cardiac output was significantly lower with dopamine (23.9% [17.5-33.5]) than with norepinephrine (33.5% [25.8-37]) (P <0.05). Although global O2 delivery and O2 consumption were higher with dopamine (782 [707-859] vs. 553 [512-629] mL.min.m, P <0.001 and 164 [134-192] vs. 128 [111-149] mL.min.m, P <0.001, respectively), hepatosplanchnic O2 delivery and consumption were not different. Hepatic lactate uptake was lower (0.47 [0.3-0.89] vs. 1.01 [0.69-1.34] mmol.min) (P <0.01), and hepatic venous lactate-to-pyruvate ratio was higher (15.3 [7.6-21.1] vs. 11.2 [6.6-15.1], P <0.05) with dopamine than with norepinephrine. In vasoplegic septic patients, maintaining mean arterial pressure, hepatosplanchnic hemodynamics, and oxygen exchange with dopamine requires a consequent increased cardiac output, which is responsible for an increased global oxygen demand when compared with norepinephrine. In addition, dopamine impairs the hepatic energy balance. Its position as a preferential treatment compared with norepinephrine in this context may therefore be questionable.

A comparison among portal lactate, intramucosal sigmoid Ph, and deltaCO2 (PaCO2 - regional Pco2) as indices of complications in patients undergoing abdominal aortic aneurysm surgery

Our aim in this observational, prospective, noncontrolled study was to detect, in 29 patients who underwent abdominal aortic aneurysm (AAA) surgery, correlations between the incidence of postoperative organ failure and intraoperative changes in arterial and portal blood lactate; changes in intramucosal sigmoid pH (pHi); differences between sigmoid Pco(2) and arterial Pco(2) (DeltaCO(2)); and hemoglobin (Hb). Hb, arterial blood lactate concentrations, pHi, and DeltaCO(2) (air tonometry) were recorded at the start of anesthesia (T0), before aorta clamping (T1), 30 minutes after clamping (T2), and at the end of surgery (T3). Portal venous lactate concentrations were recorded at T1 and T2. Patients were stratified into two groups: group A patients had no postoperative organ failure, and group B patients had one or more organ failures. As compared with group A (n = 16), group B patients (n = 13) had a lower pHi value at T2 and T3 and a higher DeltaCO(2) at T3. A pHi value of <7.15 was a predictor of organ failure, with a sensitivity of 92.3%, a specificity of 68.8%, and positive and negative predictive values of 70.6% and 91.7%, respectively, whereas a DeltaCO(2) value of >28 mm Hg predicted later organ failure with a sensitivity of 92.3%, a specificity of 62.5%, and positive and negative predictive values of 66.6% and 90.9%, respectively. Portal venous lactate concentrations were larger in group B at T2 (P < 0.001), and an increase >or=5 g/dL predicted later postoperative organ failure with a sensitivity of 92.3%, a specificity of 100%, and positive and negative predictive values of 100% and 94.1%, respectively. The comparison of the receiving operator characteristic curves to test the discrimination of each variable and the logistic regression analysis revealed that the increase in portal lactate was the best predictor for the development of postoperative organ failure. Hb concentration was significantly smaller in group B at T0 (13.8 +/- 1.0 g/dL versus 12.2 +/- 2.2 g/dL) and T2 (10.9 +/- 1.2 g/dL versus 9.1 +/- 1.9 g/dL). In conclusion, both pHi and DeltaCO(2) are reasonably sensitive prognostic indices of organ failures after AAA surgery, but they are less specific and accurate than portal venous lactate.

Gastric tonometry and monitoring gastrointestinal perfusion: using research to support nursing practice

The principles and physiological underpinnings of gastric tonometry are reviewed. Tonometric variables, including the PtCO2, pHi and CO2 gap, are described and critiqued as measurements of gastrointestinal perfusion. Increases in gastrointestinal CO2 unrelated to gastrointestinal hypoperfusion are discussed within different clinical contexts. The technical limitations of gastric tonometry, including procedural errors and PtCO2 measurement are discussed in relation to the accuracy of tonometric measurements. Tonometric measurement using semi-continuous air tonometry is introduced as a strategy to minimize technical limitations.

Intramucosal pH monitoring during liver transplantation

PURPOSE

To apply tonometry as a quick estimation of the early liver graft function.

PATIENTS AND METHODS

Forty-five liver-transplanted patients were examined. Data were collected prospectively and analysed retrospectively. According to the early graft function, patients were classified into two groups: in group 1 (n = 28) adequate graft function, in group 2 (n = 17) deteriorated graft function was detected in the early post-operative period. Complete conventional and volumetric haemodynamic monitoring and intramucosal pH (pHi), regional CO2 tension (PrCO2) measurements were performed during surgery and until the 36 hours post-operatively.

RESULTS

In group 2 the packed blood cell, fresh frozen plasma consumption intraoperatively, and the time of hepatectomy were significantly higher; ICU treatment days, respiration time was longer and mortality rate was higher. Almost the whole examination period pHi was mostly below 7.3 and PrCO2 above 50 mmHg in group 2. There were significant differences in pHi between the groups from the preparation phase until the 24th post-operative hour. In group 2, there were significantly lower values in cardiac output in the whole examination period and in the mean arterial pressure values in the revascularization phase. In group 1, the oxygen delivery values were significantly higher in the preparation phase and oxygen consumption values after revascularization phase. With regression analysis there were no significant correlations between pHi, PrCO2 and global haemodynamic parameters.

CONCLUSION

Regional parameters were completely different from global haemodynamic parameters, therefore pHi and PrCO2 can be a good indicator of the early liver graft dysfunction.

Gastric Tonometry and Enteral Nutrition: a Possible Conflict in Critical Care Nursing Practice

• Background Gastric tonometry is used to assess gastrointestinal mucosal perfusion in critically ill patients. However, enteral feeding is withheld during monitoring with gastric tonometry because enteral feeding is thought to influence tonometric measurements.

• Objectives To examine the effect of enteral feeding on the tonometric measurement of gastric mucosal carbon dioxide.

• Methods Gastric tonometers were placed in 20 critically ill patients, and the Pco2 of the gastric mucosa was measured in both the full and the empty stomach during a 48-hour period.

• Results The Pco2 measured by the tonometer increased after enteral feeding, and a significant difference in the Pco2 of the full versus the empty stomach was evident at 24 and 48 hours. Pco2 at 4, 24, and 48 hours differed significantly in the full stomach and in the empty stomach. However, the data did not reveal a significant difference in either the full stomach or the empty stomach between Pco2 at 24 hours and Pco2 at 48 hours.

• Conclusion After 24 hours of feeding, the initial increase in Pco2 observed at 4 hours was not evident, suggesting stabilization of the intragastric environment. However, a higher Pco2 was evident in the empty stomach, indicating that the presence of the feeding solution may reduce the diffusion of carbon dioxide into the tonometer balloon. Consequently, measurements of intragastric Pco2 obtained after 24 hours of feeding may be reliable if the stomach is emptied by aspiration via the tonometer immediately before measurement.

In vivo monitoring of the gastrooesophageal system using optical fibre sensors

In the present paper optical fibre sensors for the detection of foregut diseases are described, in particular, sensors for the detection of bile, carbon dioxide and pH. Bile-containing refluxes are measured by means of a sensor which uses bilirubin as natural marker. The sensor, which is already present on the market, has been clinically validated by various hospitals. The clinically relevant parameter is the exposure time of the stomach/oesophagus mucosa to the bile. When measured in the oesophagus, it has been shown to be closely correlated with the onset of Barrett's oesophagus or general oesophagitis. Recently, optical fibres have been proposed for the continuous monitoring of carbon dioxide in the stomach: an important parameter in critically ill patients. A clinically validated prototype has shown its superiority in comparison with the traditional method, that is based on gastric tonometry. For the sake of completeness, also gastric pH sensors are considered, although at the moment their development is stationary at the laboratory stage.

Clinical review: hemodynamic monitoring in the intensive care unit

Since the beginning of modern anesthesia, in 1846, the anesthetist has relied on his natural senses to monitor the patient, aided more recently by simple technical devices such as the stethoscope. There has been a tremendous increase in the availability of monitoring devices in the past 30 years. Modern technology has provided a large number of sophisticated monitors and therapeutic instruments, particularly in the past decade. Most of these techniques have enhanced our understanding of the mechanism of the patients' decompensation and have helped to guide appropriate therapeutic interventions. As surgery and critical care medicine have developed rapidly, patient monitoring capability has become increasingly complex. The most important aspect in monitoring the critically ill patient is the detection of life-threatening derangements of vital functions. Aggressive marketing strategies have been promoted to monitor almost every aspect of the patient's status. However, these strategies are only telling us what is possible; they do not tell us whether they enhance patient safety, improve our therapy, or even improve patient outcome.

ARDS. Monitoring tissue perfusion

A clinically feasible method for assessing regional splanchnic perfusion is still lacking. Methods used for research purposes demonstrate that the effects of current therapies on splanchnic perfusion are not predictable in intensive care patients with and without ARDS. Tonometry, laser Doppler flowmetry, and spectrophotometry have been used to assess splanchnic perfusion. Combining the available methods in different parts of the gastrointestinal tract may help assess splanchnic perfusion more accurately in the near future.

Enoximone in contrast to dobutamine improves hepatosplanchnic function in fluid-optimized septic shock patients

OBJECTIVE

To investigate the impact of dobutamine and enoximone on hepatosplanchnic perfusion and function in fluid-optimized septic patients.

DESIGN

Prospective, randomized, double-blinded interventional study.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Forty-eight septic shock patients were examined within 12 hrs after onset of septic shock. Patients were conventionally resuscitated, achieving an optimal pulmonary artery occlusion pressure at which the left ventricular stroke work was on the maximal plateau. Liver blood flow was estimated by venous suprahepatic catheterization using the continuous indocyanine green infusion technique. Microsomal liver function was assessed by the plasma appearance of monoethylglycinexylidide, and release of hepatic tumor necrosis factor-alpha (TNF-alpha) was measured to estimate the severity of hepatic ischemia-reperfusion syndrome.

INTERVENTIONS

Patients were randomly treated with dobutamine or enoximone. Within the first 10 hrs after baseline measurements, the dosage was increased until no further increase in the left ventricular stroke work index occurred. Then, positive inotropes were kept constant throughout the study.

MEASUREMENTS AND MAIN RESULTS

Measurements were performed at baseline and after 12 and 48 hrs after baseline measurements. Cardiac index, systemic oxygen delivery, systemic oxygen consumption, and liver blood flow increased significantly in both groups during treatment (p <.01) without a significant difference between groups. Fractional liver blood flow (liver blood flow/cardiac index) did not change in the enoximone group and showed a significant but only minor (median, 10%) decrease in the dobutamine group (p <.05 after 12 hrs and p <.01 after 48 hrs vs. baseline). After 12 hrs of enoximone treatment, monoethylglycinexylidide kinetics and hepatosplanchnic oxygen consumption demonstrated a significant increase (p <.05). The release of hepatic TNF-alpha after 12 hrs of dobutamine treatment was twice as high (p <.05) as during enoximone.

CONCLUSION

The increase in hepatosplanchnic oxygen consumption, together with an increased lignocaine metabolism and decreased release of hepatic TNF-alpha, indicates improved hepatosplanchnic function and antiinflammatory properties after 12 hrs of enoximone treatment. Therefore, if the inflammatory response should be attenuated in high-risk patients, administration of enoximone in fluid-optimized septic shock patients may be favorable compared with dobutamine.

Impact of enteral feeding on gastric tonometry in healthy volunteers and critically ill patients

BACKGROUND

Enteral feeding may interfere with gastric tonometry measurement. The effect of enteral nutrition on gastric tonometry has not been fully documented.

METHODS

Seven healthy volunteers and nine stable intensive care unit (ICU) patients with poor tolerance of gastric feeding were investigated. Consecutive continuous postpyloric and gastric feeding, both at two different rates (40 and 100 ml. h-1, respectively), and an intragastric 200 ml nutrition bolus were studied. Gastric intramucosal PCO2 (PiCO2) was measured by air tonometry and in patients a gastric intramucosal-arterial PCO2 difference (PCO2 gap) was calculated. Hemodynamics and blood gases were also measured.

RESULTS

In volunteers, PiCO2 remained stable during the postpyloric phase. During continuous gastric feeding PiCO2 did not change significantly, although in 4 volunteers PiCO2 increased >0.5 kPa. PiCO2 decreased significantly after gastric bolus from 6.9+/-0.4 to 6.1+/-0.5 kPa (P<0.05). Eight patients had an increased PCO2 gap (>1 kPa) at baseline (1.8+/-0.6 kPa). PCO2 gap changes during the whole study were not statistically significant. However, during the postpyloric phase (or immediately afterwards), the PCO2 gap increased by more than 0.5 kPa in 5 patients. After gastric bolus, a decrease in PCO2 gap >0.5 kPa was seen in 5 patients.

CONCLUSION

In volunteers, postpyloric feeding does not interfere with gastric tonometry measurement and gastric bolus leads to a PiCO2 decrease. The impact of postpyloric and gastric feeding on gastric tonometry in ICU patients with compromised gut is variable.

Does gastric juice pH influence tonometric PCO2 measured by automated air tonometry?

To determine the influence of changes in gastric juice pH due to intravenous administration of pentagastrin and omeprazole on intramucosal regional PCO2 (Pr(CO2)), we investigated 17 healthy human volunteers. Gastric juice pH was obtained from a glass pH electrode for continuous gastric juice pH measurement and Pr(CO2))was measured by using automated air tonometry. After baseline (8:00 A.M.-9:00 A.M.) the subjects received 0.6 microg/kg/h pentagastrin intravenously for 1 h (9:00 A.M.-10:00 A.M., after stimulation 10:00 A.M.-11:00 A.M.) and 40 mg omeprazole intravenously (after omeprazole 11:00 A.M.-3:00 P.M.). Following pentagastrin administration gastric juice pH significantly decreased from 1.2 +/- 0.4 to 0.6 +/- 0.4 (mean +/- SD, p < 0.007, versus baseline), whereas omeprazole transiently increased luminal pH up to 4.4 +/- 1.7 (p < 0.007 versus baseline). These subsequent changes in gastric juice pH were accompanied by a significant increase in Pr(CO2) from 48 +/- 12 to 61 +/- 17 mm Hg (p < 0.007 versus baseline) and a decrease to 44 +/- 5 mm Hg (p < 0.002 versus pentagastrin), respectively. A gastric juice pH > 4 considerably reduces mean gastric Pr(CO2) and interindividual variability. Thus omeprazole may improve the validity of gastric tonometry data.

Inter-organ substrate exchanges in the critically ill

Metabolic inter-organ exchange is a major field of research for improving the treatment of the critically ill. Adapting regional blood flows is the first regulatory step, although the relationships between hypoperfusion and metabolic disorders are matter of controversy. Metabolic steady state results from a vast inter-organ interplay and several nutrients or metabolites are signalling molecules in the regulation of gene transcription. Inter- or intra-organ substrate recycling shares or delays the mandatory need for aerobic ATP synthesis in some conditions. Nitrogen metabolism is highly compartmentalised in an inter-organ co-operation and liver, muscle, kidney and gut are the most important organs. By remodelling the amino acid mixture delivered to peripheral cells after intestinal absorption, the liver plays a determinant role in whole body protein synthesis. Albumin turnover increases after brain injury. Since the location of synthesis is different to that of breakdown this turnover can be viewed as an inter-organ exchange. The metabolic side of pH homeostasis is also an inter-organ exchange mainly shared by liver, kidney and muscle.

N-acetylcysteine increases liver blood flow and improves liver function in septic shock patients: results of a prospective, randomized, double-blind study

OBJECTIVE

In septic shock, decreased splanchnic blood flow is reported, despite adequate systemic hemodynamics. Aacetylcysteine (NAC) was found to increase hepatosplanchnic blood flow in experimental settings. In septic shock patients, NAC improved the clearance of indocyanine green and the relationship of systemic oxygen consumption to oxygen demand. We investigated the influence of NAC on liver blood flow, hepatosplanchnic oxygen transport-related variables, and liver function during early septic shock.

DESIGN

Prospective, randomized, double-blind study.

SETTING

Septic shock patients admitted to an interdisciplinary surgical intensive care unit.

PATIENTS

We examined 60 septic shock patients within 24 hrs after onset of sepsis. They were conventionally resuscitated with volume and inotropes and were in stable condition. A gastric tonometer was inserted into the stomach and a catheter into the hepatic vein. Microsomal liver function was assessed by using the plasma appearance of monoethylglycinexylidide (MEGX).

INTERVENTIONS

Subjects randomly received either a bolus of 150 mg/kg iv NAC over 15 mins and a subsequent continuous infusion of 12.5 mg/kg/hr NAC over 90 mins (n = 30) or placebo (n = 30).

MEASUREMENTS AND MAIN RESULTS

Measurements were performed before (baseline) and 60 mins after beginning the infusion (infusion). After NAC, a significant increase in absolute liver blood flow index (2.7 vs. 3.3 L/min/m2; p = .01) and cardiac index (5.0 vs. 5.7 L/min/m2; p = .02) was observed. Fractional liver blood flow index (cardiac index-related liver blood flow index) did not change. The difference between arterial and gastric mucosal carbon dioxide tension decreased (p = .05) and MEGX increased (p = .04). Liver blood flow index and MEGX correlated significantly (r(s) = .57; p < or = .01).

CONCLUSIONS

After NAC treatment, hepatosplanchnic flow and function improved and may, therefore, suggest enhanced nutritive blood flow. The increase of liver blood flow index was not caused by redistribution to the hepatosplanchnic area, but by an increase of cardiac index. Because of its correlation with liver blood flow index, MEGX may be helpful in identifying patients who benefit from NAC treatment in early septic shock.

Gastric tonometry in patients with cardiogenic shock and intra-aortic balloon counterpulsation

OBJECTIVE

To study the course of gastric regional PCO2 (PrCO2) in patients with cardiogenic shock requiring intra-aortic balloon (IAB) counterpulsation and the prognostic value of PrCO2 in this patient population.

DESIGN

A prospective, observational clinical study.

SETTING

Medical intensive care unit in a university hospital.

PATIENTS

Twenty-six consecutive patients with cardiogenic shock requiring mechanical support with an IAB counterpulsation undergoing mechanical ventilation

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULT

Hemodynamic variables, tonometric variables, arterial blood gases, and arterial lactate were assessed before insertion of IAB (baseline), and 1, 2, 3, 8, 16, 24, and 48 hrs thereafter. A subset of these patients (n = 14) were studied just before and 1, 8, 24, and 32 hrs after IAB removal; 12/26 patients (46.2%) died. Cardiac index increased from baseline to 1 hr after insertion of IAB (1.7 +/- 0.3 to 2.6 +/- 0.8 L/min/m2, p < .05). PrCO2 did not change between admission (47 +/- 13 torr [6.3 +/- 1.7 kPa]) and 8 hrs after placement of IAB but increased to 63 +/- 22 torr (8.4 +/- 2.9 kPa) at 16 hrs (p < .05) without any further alteration until 48 hrs. CO2 gap showed a similar pattern with 15 +/- 11 torr (2.0 +/- 1.5 kPa) at baseline and an increase to 28 +/- 22 torr (3.7 +/- 2.9 kPa) 16 hrs later. PrCO2 and CO2 gap remained at high levels (59 +/- 11 torr [7.7 +/- 1.5 kPa] and 22 +/- 10 torr [2.9 +/- 1.3 kPa], respectively), before IAB removal without further improvement or deterioration thereafter. PrCO2 values showed no difference between survivors and nonsurvivors at any time point.

CONCLUSION

Patients with cardiogenic shock developed high PrCO2 within the first 24 hrs, which reflects gastric mucosal ischemia. Persistently high levels of PrCO2 were indicative for prolonged hypoperfusion of the gut. Gastric tonometry failed to discriminate between survivors and nonsurvivors.

Norepinephrine and N(G)-monomethyl-L-arginine in hyperdynamic septic shock in pigs: effects on intestinal oxygen exchange and energy balance

OBJECTIVES

To compare the effects of norepinephrine (NOR) and the nonselective nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), on intestinal blood flow, oxygen exchange, and energy metabolism over 24 hrs of hyperdynamic, normotensive porcine endotoxic shock.

DESIGN

Prospective, randomized, experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Twenty-seven pigs were divided into three groups: seven animals received no vasopressor therapy (ETX) during endotoxic shock; ten animals were treated with NOR; and ten animals were treated with L-NMMA.

INTERVENTIONS

Pigs were anesthetized, mechanically ventilated, and instrumented. Eight hours later, endotoxic shock was initiated by an infusion of Escherichia coli lipopolysaccharide. Animals were resuscitated by hetastarch directed to maintain the intrathoracic blood volume and a mean arterial pressure (MAP) of >60 mm Hg. Twelve hours after the start of the endotoxin infusion, NOR or L-NMMA was administered for 12 hrs in the treatment groups to maintain a MAP at preshock levels.

MEASUREMENTS AND MAIN RESULTS

ETX caused a continuous fall in MAP, despite a sustained increase in the cardiac output achieved by fluid resuscitation. NOR maintained MAP at preshock levels because of a further rise in cardiac output, whereas hemodynamic stabilization during L-NMMA resulted from systemic vasoconstriction. NOR increased portal venous blood flow concomitant with decreased intestinal oxygen extraction, whereas L-NMMA influenced neither portal venous blood flow nor intestinal oxygen extraction. Mean capillary hemoglobin oxygen saturation of the ileal mucosa as well as the frequency distributions reflecting microcirculatory oxygen availability remained unchanged as well. Nevertheless, portal venous pH similarly decreased and portal venous lactate/pyruvate ratios increased in all three groups. The arterial-ileal mucosal PCO2 gap progressively increased in the ETX and L-NMMA groups, whereas NOR blunted this response.

CONCLUSIONS

Neither treatment could reverse the ETX-induced derangements of cellular energy metabolism as reflected by the increased portal venous lactate/pyruvate ratios. The NOR-induced attenuation of ileal mucosal acidosis was possibly caused by a different pattern of blood flow redistribution compared with L-NMMA.

Effect of a dopexamine-induced increase in cardiac index on splanchnic hemodynamics in septic shock

In 12 patients with hyperdynamic septic shock we studied the effect of dopexamine, a combined dopamine and beta-adrenergic agonist, on hepatosplanchnic hemodynamics and O(2) exchange. All patients required noradrenaline to maintain mean arterial pressure > 60 mm Hg (noradrenaline >/= 0.04 microg x kg(-1) x min(-1)) with a cardiac index >/= 3.0 L/min/m(2). Splanchnic blood flow (Qspl) was measured using primed continuous infusion of indocyanine green dye with hepatic venous sampling. In addition tonometric gastric mucosal-arterial and gastric mucosal-hepatic venous P CO(2) gradients were assessed as indicators of regional energy balance. After 90 min of stable hemodynamics a first measurement was obtained. Then dopexamine infusion was titrated (1-4 microg x kg(-1) x min(-1)) to increase cardiac output by approximately 25% (20-30%). After 90 min all measurements were repeated, and dopexamine was withdrawn followed by a third measurement. Median Qspl (0.86/1.23-0. 66 versus 0.96/1.42-0.85 L/min/m (2) [median value/25th-75th percentiles], p < 0.05) increased whereas the fractional contribution of Qspl to total blood flow decreased (21/28-13 versus 19/28-12%, p < 0.05). Although both global and regional oxygen delivery (DO(2)) consistently increased, neither global or regional V O(2) nor PCO(2) gradients were significantly affected. In patients with septic shock and ongoing noradrenaline treatment dopexamine seems to have no preferential effects on hepatosplanchnic hemodynamics, O(2) exchange, or energy balance.