Tissue-arterial PCO2 difference is a better marker of ischemia than intramural pH (pHi) or arterial pH-pHi difference

Evaluating the Safety and Efficacy of Intraoperative Enteral Nutrition in Critically Ill Burn Patients: A Systematic Review and Meta-analysis

Major burn injuries incite a hypermetabolic response, and the initiation of early enteral nutrition is the standard of care in patients with large burns and contributes to improved outcomes. Perioperative fasting is a common cause of caloric deficits in burn patients and can be obviated with intraoperative enteral nutrition. However, the risks and benefits of this practice are unknown, and there is a concern for aspiration. We conducted a systematic review and meta-analysis to evaluate the safety and efficacy of intraoperative enteral nutrition. We performed a systematic literature search using PubMed, Scopus, and OvidSP MEDLINE databases. We identified studies that evaluated the effects of intraoperative enteral nutrition in adult burn patients compared to those undergoing routine perioperative fasting. We performed a meta-analysis on the incidence of mortality, pneumonia, wound infections, and aspiration in burn patients receiving intraoperative enteral nutrition. We identified seven articles for qualitative review and four for quantitative review (N = 83 patients). There were no statistically significant increases in the risk of mortality (odds ratio [OR] = 1.28, 95% confidence interval [CI]: 0.49, 3.31), wound infections (OR = 0.71, 95% CI: 0.16, 3.24), pneumonia (OR = 2.1, 95% CI: 0.7, 6.1), and aspiration (OR = 1.14, 95% CI: 0.07, 18.75) in patients receiving intraoperative enteral nutrition. Within individual studies, intraoperative enteral nutrition patients received significantly more calories than standard fasting patients. Intraoperative enteral nutrition may increase nutritional intake in burn patients without an increase in complications; however, this is based on limited studies. Randomized controlled trials are needed before recommendations on intraoperative enteral nutrition practice can be made.

Acute Hypervolemic Infusion Can Improve Splanchnic Perfusion in Elderly Patients During Laparoscopic Colorectal Surgery

BACKGROUND There is no adequate evidence on how the long duration of laparoscopic surgery affects splanchnic perfusion in elderly patients or the efficacy of acute hypervolemic fluid infusion (AHFI) during the induction of anesthesia. Our aim was to observe the effects of AHFI during the induction of general anesthesia on splanchnic perfusion. MATERIAL AND METHODS Seventy elderly patients receiving laparoscopic colorectal surgery were randomly divided into three groups: lactated Ringer's solution group (group R), succinylated gelatin group (group G), and hypertonic sodium chloride hydroxyethyl starch 40 injection group (group H). Thirty minutes after the induction of general anesthesia, patients received an infusion of target dose of these three solutions. Corresponding hemodynamic parameters, arterial blood gas analysis, and gastric mucosal carbon dioxide tension were monitored in sequences. RESULTS In all three groups, gastric-arterial partial CO2 pressure gaps (Pg-aCO2) were decreased at several beginning stages and then gradually increased, Pg-aCO2 also varied between groups due to certain time points. The pH values of gastric mucosa (pHi) decreased gradually after the induction of pneumoperitoneum in the three groups. CONCLUSIONS The AHFI of succinylated gelatin (12 ml/kg) during the induction of anesthesia can improve splanchnic perfusion in elderly patients undergoing laparoscopic surgery for colorectal cancer and maintain good splanchnic perfusion even after a long period of pneumoperitoneum (60 minutes). AHFI can improve splanchnic perfusion in elderly patients undergoing laparoscopic colorectal surgery.

Endpoints of Resuscitation for the Victim of Trauma

Useful resuscitation endpoints must serve both to diagnose the need for and to ensure the ongoing adequacy of resuscitation. To this end, traditional measures of organ perfusion are now widely appreciated to be grossly inadequate. Useful endpoints or milestones range from the global, to the regional, to the cellular specific. Understanding the basic principles of perfusion-related dysoxia in trauma and hemorrhage and its potential rapid transition to involve inflammatory and immune responses on cellular oxygen utilization will aid the clinician in choosing and appropriately interpreting endpoint monitoring data. There also appears to be an optimal window of opportunity for monitoring to help mitigate the development of more complicated inflammatory states. This article reviews the underlying need for endpoint selection (both global and regional, biochemical and functional) and monitoring during resuscitation of the polytrauma patient. At this juncture it appears that early use of a blend of global markers such as lactate and base deficit coupled with an available sensitive regional monitor such as gastric tonometry may offer the best combination of current technology to guard against early perfusion-related dysoxia. Future techniques involving optical spectroscopy offer the exciting potential to assess oxygenation at the cellular level. This may aid in ultra-early detection and resolution of perfusion-related dysoxia in addition to recognizing its transition to more complex inflammatory-mediated circulatory and metabolic failure.

A Comparison of Gastric and Rectal CO₂ in Cardiac Surgery Patients

Critical care nurses assess and treat clinical conditions associated with inadequate oxygenation. Changes in regional organ (gut) blood flow are believed to occur in response to a decrease in oxygenation. Although the stomach is a widely accepted monitoring site, there are multiple methodological and measurement issues associated with the gastric environment that limit the accuracy of P CO2 detection. The rectum may provide nurses with an alternative site for monitoring changes in PCO2 without the limitations associated with gastric monitoring. This pilot study used a repeated measures design to examine changes in gastric and rectal PCO2 during elective coronary artery bypass grafting with cardiopulmonary bypass (CPB) and in the immediate 4-hr postoperative period in 26 subjects. The systemic indicators explained little variation in the regional indicators during protocol. A comparison of rectal and gastric PCO2 revealed no statistically significant differences in the direction or magnitude of change over any phase of cardiac surgery (baseline, CPB, post-CPB). A reduction in both rectal and gastric PCO2 occurred during CPB, and both values trended upward during the post-CPB phase. However, poor correlation and agreement was found between the measures of PCO2 at the two sites. Although clinically important, the cause is unclear. Possible explanations include variation in CO2 production between the gastric and rectal site, differences in sensitivity of the two monitoring instruments, or the absence of hemodynamic complications, which limited the extent of change in PCO2. Further investigation using patients with more profound changes in oxygenation are needed to identify response patterns and possible mechanisms.

Does gastric tonometry-guided therapy reduce total mortality in critically ill patients?

Zhang and colleagues have recently published a systematic review and meta-analysis of six studies and conclude that ‘gastric tonometry guided therapy can reduce total mortality in critically ill patients’. So why did gastric tonometry come and go, and what can we learn from this piece of modern history?

Gastric tonometry guided therapy in critical care patients: a systematic review and meta-analysis

Introduction

The value of gastric intramucosal pH (pHi) can be calculated from the tonometrically measured partial pressure of carbon dioxide (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {P}_{C{O}_2} $$\end{document}PCO2) in the stomach and the arterial bicarbonate content. Low pHi and increase of the difference between gastric mucosal and arterial \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {P}_{C{O}_2} $$\end{document}PCO2 (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {P}_{C{O}_2} $$\end{document}PCO2 gap) reflect splanchnic hypoperfusion and are good indicators of poor prognosis. Some randomized controlled trials (RCTs) were performed based on the theory that normalizing the low pHi or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {P}_{C{O}_2} $$\end{document}PCO2 gap could improve the outcomes of critical care patients. However, the conclusions of these RCTs were divergent. Therefore, we performed a systematic review and meta-analysis to assess the effects of this goal directed therapy on patient outcome in Intensive Care Units (ICUs).

Methods

We searched PubMed, EMBASE, the Cochrane Library and ClinicalTrials.gov for randomized controlled trials comparing gastric tonometry guided therapy with control groups. Baseline characteristics of each included RCT were extracted and displayed in a table. We calculated pooled odds ratios (ORs) with 95% confidence intervals (CIs) for dichotomous outcomes. Another measure of effect (risk difference, RD) was used to reassess the effects of gastric tonometry on total mortality. We performed sensitivity analysis for total mortality. Continuous outcomes were presented as standardised mean differences (SMDs) together with 95% CIs.

Results

The gastric tonometry guided therapy significantly reduced total mortality (OR, 0.732; 95% CI, 0.536 to 0.999, P = 0.049; I² = 0%; RD, −0.056; 95% CI, −0.109 to −0.003, P = 0.038; I² = 0%) when compared with control groups. However, after excluding the patients with normal pHi on admission, the beneficial effects of this therapy did not exist (OR, 0.736; 95% CI 0.506 to 1.071, P = 0.109; I² = 0%). ICU length of stay, hospital length of stay and days intubated were not significantly improved by this therapy.

Conclusions

In critical care patients, gastric tonometry guided therapy can reduce total mortality. Patients with normal pHi on admission contributed to the ultimate result of this outcome; it may indicate that these patients may be more sensitive to this therapy.

Monitoring CO2 in shock states

The primary end point when treating acute shock is to restore blood circulation, mainly by reaching macrocirculatory parameters. However, even if global haemodynamic goals can be achieved, microcirculatory perfusion may remain impaired, leading to cellular hypoxia and organ damage. Interestingly, few methods are currently available to measure the adequacy of organ blood flow and tissue oxygenation. The rise in tissue partial pressure of carbon dioxide (CO2) has been observed when tissue perfusion is decreased. In this regard, tissue partial pressure of CO2 has been proposed as an early and reliable marker of tissue hypoxia even if the mechanisms of tissue partial pressure in CO2 rise during hypoperfusion remain unclear. Several technologies allow the estimation of CO2 content from different body sites: vascular, tissular (in hollow organs, mucosal or cutaneous), and airway. These tools remain poorly evaluated, and some are used but are not widely used in clinical practice. The present review clarifies the physiology of increasing tissue CO2 during hypoperfusion and underlines the specificities of the different technologies that allow bedside estimation of tissue CO2 content.

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.

A comparison of Ringer's lactate and acetate solutions and resuscitative effects on splanchnic dysoxia in patients with extensive burns

We compared the effects of Ringer's lactate (RL) and acetate (RA) solutions on parameters of splanchnic dysoxia such as PgCO(2) (PCO(2) of gastric mucosa) and pH(i) (pH of gastric mucosa) using a gastric tonometer, in addition to blood markers such as the serum arterial level of lactate, base excess, ketone body ratio, and antithrombin during the first 72h of the resuscitation period in patients with burns covering 30% or more of their body surface. A prospective study was conducted in the university tertiary referral centers. There were no significant differences in the average age, TBSA (total burn surface area), and resuscitative fluid volume during the first and second 24h between the two groups. In the RA group, PCO(2) gap values calculated employing the formula: PgCO(2)-PaCO(2) (arterial PCO(2)), and pH gap calculated by: pH(a) (arterial pH)-pH(i), improved to the normal ranges at 24 h postburn, which was significantly faster than in the RL group. On the other hand, there were no significant differences in blood parameters between the two groups over the course. These results suggest that fluid resuscitation with RA may more rapidly ameliorate splanchnic dysoxia, as evidenced by gastric tonometry, compared to that with RL.

Tonometry revisited: perfusion-related, metabolic, and respiratory components of gastric mucosal acidosis in acute cardiorespiratory failure

Mucosal pH (pHi) is influenced by local perfusion and metabolism (mucosal-arterial pCO2 gradient, DeltapCO2), systemic metabolic acidosis (arterial bicarbonate), and respiration (arterial pCO2). We determined these components of pHi and their relation to outcome during the first 24 h of intensive care. We studied 103 patients with acute respiratory or circulatory failure (age, 63+/-2 [mean+/-SEM]; Acute Physiology and Chronic Health Evaluation II score, 20+/-1; Sequential Organ Failure Assessment score, 8+/-0). pHi, and the effects of bicarbonate and arterial and mucosal pCO2 on pHi, were assessed at admission, 6, and 24 h. pHi was reduced (at admission, 7.27+/-0.01) due to low arterial bicarbonate and increased DeltapCO2. Low pHi (<7.32) at admission (n=58; mortality, 29% vs. 13% in those with pHi>or=7.32 at admission; P=0.061) was associated with an increased DeltapCO2 in 59% of patients (mortality, 47% vs. 4% for patients with low pHi and normal DeltapCO2; P=0.0003). An increased versus normal DeltapCO2, regardless of pHi, was associated with increased mortality at admission (51% vs. 5%; P<0.0001; n=39) and at 6 h (34% vs. 13%; P=0.016; n=45). A delayed normalization or persistently low pHi (n=47) or high DeltapCO2 (n=25) was associated with high mortality (low pHi [34%] vs. high DeltapCO2 [60%]; P=0.046). In nonsurvivors, hypocapnia increased pHi at baseline, 6, and 24 h (all P<or=0.001). In patients with initially normal pHi or DeltapCO2, outcome was not related to subsequent changes in pHi or DeltapCO2. Increased DeltapCO2 during early resuscitation suggests poor tissue perfusion and is associated with high mortality. Arterial bicarbonate contributes more to pHi than the DeltapCO2 but is not associated with mortality. Hyperventilation partly masks mucosal acidosis. Inadequate tissue perfusion may persist despite stable hemodynamics and contributes to poor outcome.

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.

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.

Acid-base and bio-energetics during balanced versus unbalanced normovolaemic haemodilution

Fluids balanced to avoid acid-base disturbances may be preferable to saline, which causes metabolic acidosis in high volume. We evaluated acid-base and bio-energetic effects of haemodilution with a crystalloid balanced on physical chemical principles, versus crystalloids causing metabolic acidosis or metabolic alkalosis. Anaesthetised, mechanically ventilated Sprague-Dawley rats (n=32, allocated to four groups) underwent six exchanges of 9 ml crystalloid for 3 ml blood. Exchange was with one of three crystalloids with strong ion difference (SID) values of 0, 24 (balanced) and 40 mEq/l. Controls did not undergo haemodilution. Mean haemoglobin concentration fell to approximately 50 g/l after haemodilution. With SID 24 mEq/l fluid, metabolic acid-base remained unchanged. Dilution with SID 0 mEq/l and 40 mEq/l fluids caused a progressive metabolic acidosis and alkalosis respectively. Standard base excess (SBE) and haemoglobin concentration were directly correlated in the SID 0 mEq/l group (R2 = 0.61), indirectly correlated in the SBE 40 mEq/l group (R2 = 0.48) and showed no correlation in the SID 24 mEq/l group (R2 = 0.003). There were no significant differences between final ileal values of CO2 gap, nucleotides concentration, energy charge, or luminal lactate concentration. SID 40 mEq/l crystalloid dilution caused a significant rise in subcutaneous lactate. In this group mean kidney ATP concentration was significantly less than controls and renal energy charge significantly lower than SID 0 mEq/l and control groups. We conclude that a crystalloid SID of 24 mEq/l provides balanced haemodilution. Bio-energetic perturbations with higher SID haemodilution may be more severe and need further investigation.

Effects of intra-aortic balloon counterpulsation on parameters of tissue oxygenation

BACKGROUND AND OBJECTIVE

To investigate the effects of intra-aortic balloon pump therapy on parameters of global and regional oxygenation in patients undergoing cardiac surgery.

METHODS

As part of a large surveillance study in cardiac surgery patients (n=266) we retrospectively analyzed the course of 28 patients requiring intra-aortic balloon pump therapy. Patients were grouped according to the time point of pump insertion (during weaning from cardiopulmonary bypass: group early intra-aortic balloon pumping (n=17); after admission to the intensive care unit: group late intra-aortic balloon pumping (n=9). Haemodynamic and tonometric variables, arterial lactate, and use of catecholamines were measured hourly.

MEASUREMENTS AND RESULTS

Cardiac index increased in both groups after intra-aortic balloon pump insertion (2.2+/-0.5 baseline; 3.4+/-0.8 L min-1 m-2 4 h later (group early intra-aortic balloon pumping); 2.8+/-0.5 baseline, 3.6+/-L min-1 m-2 4 h later (group later intra-aortic balloon pumping), each P<0.05), there were no differences between groups. Arterial lactate values increased in group later intra-aortic balloon pumping after pump insertion to a maximum 2 h later (8.4+/-6.1 mmol L-1 baseline; 12.7+/-7.4 mmol L-1, P<0.05), and decreased continuously afterwards. The difference of arterial and gastric CO2 showed a sharp decrease after pump insertion in group later intra-aortic balloon pumping (26.4+/-9.8 baseline; 7.0+/-11.1 mmHg, P<0.05). There were no differences between groups. Epinephrine doses were higher in group later intra-aortic balloon pumping (P<0.05).

CONCLUSIONS

Intra-aortic balloon pump therapy improved global and regional splanchnic oxygenation in cardiac surgery patients with low-cardiac-output syndrome. Gastro-intestinal tonometry could provide additional information concerning tissue oxygenation. Patients with later intra-aortic balloon pump insertion needed more catecholamine therapy to achieve similar haemodynamic values.

Sublingual capnometry: a non-invasive measure of microcirculatory dysfunction and tissue hypoxia

With improvement in supportive care patients rarely die from their presenting illness but rather from its sequela, namely sequential multi-organ failure. Tissue hypoxia is believed to be the causation of multi-organ dysfunction syndrome (MODS). The expedient detection and correction of tissue hypoxia may therefore limit the development of MODS. The standard oxygenation and hemodynamic variables (blood pressure, arterial oxygenation, cardiac output) which are monitored in critically ill patients are 'upstream' markers and provide little information as to the adequacy of tissue oxygenation. Global 'downstream' markers such as mixed venous oxygen saturation and blood lactate are insensitive indicators of tissue hypoxia. Sublingual PCO(2) is a regional marker of microvascular perfusion and tissue hypoxia that holds great promise for the risk stratification and end-point of goal directed resuscitation in critically ill patients. This paper reviews the technology and application of sublingual PCO(2) monitoring.

Effects of dopexamine in a rat model of supracoeliac aortic cross-clamping and declamping

This experimental study in rats was designed to demonstrate effects of dopexamine (3 microg kg(-1) min(-1), n = 6) or physiologic saline solution (n = 6) on systemic as well as regional perfusion during 30 min of supracoeliac aortic cross-clamping and during 180 min of reperfusion following declamping. Rats were surgically instrumented with arterial, right atrial and portal venous catheters, ultrasonic flow probes around the abdominal aorta, superior mesenteric and carotid artery, and a paediatric tonometer for intestinal mucosal PCO(2) measurement. During 120 min of reperfusion, fluid resuscitation was titrated to keep abdominal aortic blood flow above 80% of baseline values. We found that during cross-clamping, values of arterial lactate (p = 0.002) and intestinal tonometric PCO(2) (p = 0.018) were higher in the dopexamine group than in the control group.

Monitoring therapeutic interventions in critically ill septic patients

Sepsis is the leading cause of admission to intensive care units in the United States. Although the treatment of sepsis is complex and multimodal, nutrition support plays an important role in the management of these patients. The diagnosis of sepsis, disease category, and severity of illness and the change in sepsis severity and organ function over time affect the delivery of nutrition support. This paper reviews the diagnostic criteria of sepsis, the use of "sepsis biomarkers," and regional and global markers of organ function in sepsis and quantitative measures of illness severity and organ dysfunction.

Regional carbon dioxide monitoring to assess the adequacy of tissue perfusion

PURPOSE OF REVIEW

Tissue dysoxia is now widely regarded as the major factor leading to organ dysfunction in critically ill patients. Recent data suggests that early aggressive resuscitation of critically ill patients, which limits and/or reverses tissue dysoxia may prevent progression to organ dysfunction and improve outcome. The traditional clinical and laboratory markers used to assess tissue dysoxia are, however, insensitive and have numerous limitations. Regional carbon dioxide monitoring appears to be ideally suited to monitoring the adequacy of resuscitation. This review provides an update on this evolving technology.

RECENT FINDINGS

Gastric intramucosal carbon dioxide as measured by gastric tonometry has proven to be useful as a prognostic marker, in evaluating the response to specific therapeutic interventions and as an end point of resuscitation. Gastric tonometry is, however, cumbersome and has a number of limitations that may have prevented its widespread adoption. The measurement of carbon dioxide in the sublingual mucosa by sublingual capnometry is technically simple, noninvasive, and provides near instantaneous information. Clinical studies have demonstrated a good correlation between gastric intramucosal carbon dioxide and sublingual mucosa carbon dioxide. Sublingual mucosa carbon dioxide responds more rapidly to therapeutic interventions than does gastric intramucosal carbon dioxide and may be a better prognostic marker.

SUMMARY

Sublingual capnometry may be the ideal technology for guiding early goal directed therapy. This technology may be useful for monitoring tissue oxygenation, titrating therapeutic interventions, and as an end point for resuscitation in critically ill and injured patients.

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.

Inducible nitric oxide synthase inhibition improves intestinal microcirculatory oxygenation and CO2 balance during endotoxemia in pigs

OBJECTIVE

We examined whether selective inhibition of inducible nitric oxide synthase (iNOS) promotes intestinal microvascular oxygenation (microPO2) and CO2 off-load after endotoxic shock.

DESIGN AND SETTING

Prospective, controlled experimental study in a university animal research laboratory.

SUBJECTS

13 domestic pigs.

INTERVENTIONS

After baseline measurements shock was induced by 1 microg kg-1 h-1 endotoxin until mean arterial pressure fell below 60 mmHg. After 30 min in shock the animals were resuscitated with either fluid alone (control, n=6) or fluid and the iNOS inhibitor N-[3-(aminomethyl)benzyl]acetamidine hydrochloride (1400W, n=7). As final experimental intervention all animals received the nonselective NOS inhibitor L-NAME.

MEASUREMENTS AND RESULTS

Systemic and regional hemodynamic and oxygenation parameters were measured at baseline, during endotoxemia and shock, hourly for 3 h of 1400W therapy, and 30 min after the final L-NAME administration. microPO2 was assessed by the Pd-porphyrin phosphorescence technique, and the arterial to intestinal PCO2 gap was determined by air tonometry. Endotoxemia and shock resulted in a decrease in ileal mucosal and serosal microPO2 and a rise in PCO2 gap. The combination of 1400W and fluid resuscitation, but not fluid alone, normalized both the serosal microPO2 and the intestinal PCO2 gap. Administration of L-NAME decreased cardiac output and oxygen delivery and intestinal microPO2 and blood flow in both groups.

CONCLUSIONS

Partial blockade of NO production by 1400W increased serosal microvascular oxygenation and decreased the intestinal CO2 gap. This findings are consistent with the idea that 1400W corrects pathological flow distribution and regional dysoxia within the intestinal wall following endotoxic shock.

Equipment review: the success of early goal-directed therapy for septic shock prompts evaluation of current approaches for monitoring the adequacy of resuscitation

A recent trial utilizing central venous oxygen saturation (SCVO₂) as a resuscitation marker in patients with sepsis has resulted in its inclusion in the Surviving Sepsis Campaign guidelines. We review the evidence behind SCVO₂ and its relationship to previous trials of goal-directed therapy. We compare SCVO₂ to other tools for assessing the adequacy of resuscitation including physical examination, biochemical markers, pulmonary artery catheterization, esophageal Doppler, pulse contour analysis, echocardiography, pulse pressure variation, and tissue capnometry. It is unlikely that any single technology can improve outcome if isolated from an organized pattern of early recognition, algorithmic resuscitation, and frequent reassessment. This article includes a response to the journal's Health Technology Assessment questionnaire by the manufacturer of the SCVO₂ catheter.

Impact of intraoperative duodenal feeding on the oxygen balance of the splanchnic region in severely burned patients

Enteral feeding causes an increase of intestinal oxygen demand depending on the amount administered. The aim of this study presented was to evaluate, whether intraoperative duodenal feeding might put patients at risk developing splanchnic O(2)-imbalance due to an intraoperatively compromised intestinal perfusion based on stress and unrecognized hypovolemia. In 18 severely burned patients, the CO(2)-gap between the arterial and gastric CO(2), as a parameter for the intestinal O(2)-balance, was measured during the first operation. All operations were performed on day 3-5 after admission and lasted for 4-5h. Half of the patients (nine patients) were fed intraoperatively, whereas in the other nine patients feeding was suspended beginning 1h prior to surgery until 6h after surgery. CO(2)-gap measurements were carried out prior to surgery, hourly during the operation and 5h postoperatively. Measurements 3 and 4h after beginning of the operation revealed significantly higher CO(2)-gap values in the fasting group. All other measurements showed no significant difference between both groups. Therefore, intraoperative enteral nutrition, at least in the early postburn phase, is not only necessary for reducing caloric deficits, but also seems to have a protective effect on gut oxygen balance.

Bladder Mucosa pH and Pco2 as a Minimally Invasive Monitor of Hemorrhagic Shock and Resuscitation

BACKGROUND

Continuous monitoring of pH, Pco2, and Po2 using fiberoptic sensor technology has been proposed recently as a clinical monitor of the severity of shock and impaired tissue perfusion. Surrogates of gut tissue perfusion such as gastric tonometry, although cumbersome, have been used to indirectly quantify the degree of gut ischemia. The purpose of this study was to demonstrate the feasibility of monitoring bladder mucosa (BM) and to compare urinary bladder mucosa and proximal jejunum mucosa interstitial pH and Pco2 during hemorrhagic shock and resuscitation.

METHODS

Eleven male miniature swine (25-35 kg) (control, n = 4; shock, n = 7) underwent jejunal tonometry and cystostomy. A multisensor probe was placed adjacent to the BM. Urine was diverted. Normocarbia was maintained. Animals were hemorrhaged and kept at a mean arterial pressure of 40 mm Hg. When a constant infusion was required to maintain the mean arterial pressure at 40 mm Hg (decompensation), animals were resuscitated with shed blood plus two times the shed volume in lactated Ringer's solution (20 minutes) and observed for 2 hours.

RESULTS

During decompensation, BM pH values decreased significantly from 7.33 +/- 0.08 to 7.01 +/- 0.2 (p < 0.01) and recovered to 7.11 +/- 0.19 at 120 minutes after completion of resuscitation. During decompensation, BM Pco2 values increased significantly compared with baseline (from 49 +/- 6 mm Hg to 71 +/- 19 mm Hg, p < 0.05) and returned to baseline with resuscitation. Jejunum mucosa and BM interstitial Pco2 correlated throughout shock and resuscitation (r = 0.49). Bland-Altman analysis demonstrated significant differences between jejunum mucosa (intramucosal pH) and BM interstitial pH.

CONCLUSION

Shock-induced changes in the Pco2 of the BM are comparable to tonometric changes in the gut. These data suggest that continuous fiberoptic multisensor probe monitoring of the BM could potentially provide a minimally invasive method for the assessment of impaired tissue perfusion of the splanchnic circulation during shock and resuscitation.

Intramucosal-Arterial Pco2 Gradient Does Not Reflect Intestinal Dysoxia in Anemic Hypoxia

BACKGROUND

An increase in intramucosal-arterial Pco2 gradient (DeltaPco2) might be caused by tissue hypoxia or by diminished blood flow. Our hypothesis was that DeltaPco2 should not be altered in anemic hypoxia with preserved blood flow.

METHODS

In 18 anesthetized, mechanically ventilated sheep, oxygen transport was stepwise reduced by hemorrhage (hypovolemia, n = 9) or by hemorrhage and simultaneous dextran infusion (hemodilution, n = 9).

RESULTS

Hypovolemia and hemodilution produced comparable decreases in systemic and intestinal oxygen transport and uptake. However, mixed venoarterial and mesenteric venoarterial Pco2 gradients and DeltaPco2 were significantly higher in hypovolemia than in hemodilution (25 +/- 5 vs. 10 +/- 2 mm Hg; 21 +/- 6 vs. 10 +/- 5 mm Hg; and 41 +/- 18 vs. 14 +/- 9 mm Hg, respectively; p < 0.01).

CONCLUSION

DeltaPco2 did not reflect intestinal dysoxia during Vo2/Do2 dependency attributable to hemodilution. Blood flow seems to be the main determinant of DeltaPco2.

Tissue capnometry: does the answer lie under the tongue?

Increases in tissue partial pressure of carbon dioxide (PCO(2)) can reflect an abnormal oxygen supply to the cells, so that monitoring tissue PCO(2) may help identify circulatory abnormalities and guide their correction. Gastric tonometry aims at monitoring regional PCO(2) in the stomach, an easily accessible organ that becomes ischemic quite early when the circulatory status is jeopardized. Despite substantial initial enthusiasm, this technique has never been widely implemented due to various technical problems and artifacts during measurement. Experimental studies have suggested that sublingual PCO(2 )(P(sl)CO(2)) is a reliable marker of tissue perfusion. Clinical studies have demonstrated that high P(sl)CO(2) values and, especially, high gradients between P(sl)CO(2) and arterial PCO(2) (DeltaP(sl-a)CO(2)) are associated with impaired microcirculatory blood flow and a worse prognosis in critically ill patients. Although some questions remain to be answered about sublingual capnometry and its utility, this technique could offer new hope for tissue PCO(2) monitoring in clinical practice.

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.

The difference between intramural and arterial partial pressure of carbon dioxide increases significantly during laparoscopic cholecystectomy: the effect of thoracic epidural anesthesia

We studied the effects of pneumoperitoneum on gastric submucosal perfusion metabolism during elective laparoscopic cholecystectomy (LASC) by measuring the PCO(2) gap, defined as the difference between intramucosal PCO(2) and arterial PCO(2), using gas tonometry in 20 patients. Furthermore, we examined whether thoracic epidural anesthesia (TEA) affects gastric submucosal perfusion metabolism during LASC. Patients were randomly allocated to receive general anesthesia (group G, n = 10) or general anesthesia combined with TEA (group E, n = 10). In both groups, the PCO(2) gap increased significantly during pneumoperitoneum and remained at this level until the end of surgery compared with the baseline value. There were no significant differences in PCO(2) gap values between the two groups at any time sampled. These results suggested that pneumoperitoneum significantly impaired gastric submucosal perfusion and metabolism and that TEA did not attenuate the impairment of gastric submucosal perfusion during or after pneumoperitoneum.

IMPLICATIONS

We investigated the effect of pneumoperitoneum on gastric submucosal perfusion by measuring PCO(2) gap with the use of gas tonometry. PCO(2) gap significantly increased during and after the pneumoperitoneum compared with the control level. Thoracic epidural anesthesia did not attenuate this inhibition.

Gastric mucosal acidosis and cytokine release in patients with septic shock

OBJECTIVE

It has been postulated that in critically ill patients, splanchnic hypoperfusion may lead to cytokine release into the systemic circulation. The presence of cytokines could trigger an inflammatory response and cause multiple organ dysfunction syndrome. Although experimental studies support this hypothesis, humans studies remain controversial. The aim of the study was to determine the relationship between splanchnic hypoperfusion and cytokine release during septic shock.

DESIGN

Human prospective study.

SETTING

Medical intensive care unit at a university hospital.

PATIENTS

A total of 30 patients with mean arterial pressure of <60 mm Hg after volume loading with either oliguria or hyperlactatemia.

MEASUREMENTS

Gastric intramucosal measurements as an indicator of splanchnic hypoperfusion and blood samples were obtained at admission to the medical intensive care unit and repeated during 48 hrs. Cytokine (tumor necrosis factor-alpha and interleukin-6) values were evaluated by enzyme-linked immunoassays at the following periods: at the time of admission and 2, 4, 8, 12, 24, 36, and 48 hrs later.

MAIN RESULTS

High levels of interleukin-6 and tumor necrosis factor-alpha were observed at admission in survivors and nonsurvivors, without significant difference. At 48 hrs, cytokine levels were significantly higher in patients who died compared with the survivors (tumor necrosis factor: 163 +/- 16 for nonsurvivors vs. 34 +/- 9 ng/mL for survivors; interleukin-6: 2814 +/- 485 for nonsurvivors vs. 469 +/- 107 ng/mL for survivors). At 48 hrs, the PCO2 gap was significantly higher in the nonsurvivors compared with survivors (25.87 +/- 2.73 vs. 11.35 +/- 2.25 mm Hg), despite systemic hemodynamic variables in the normal range. A positive relationship was demonstrated between plasma levels of tumor necrosis factor-alpha and interleukin-6 and the PCO2 gap throughout the study. The PCO2 gap was not correlated with hemodynamic variables.

CONCLUSIONS

Our data suggest a relationship between gastric mucosal acidosis, as assessed by PCO2 gap, and cytokine levels in critically ill patients with septic shock. Gut injury may be a contributor of the inflammatory response in patients with septic shock.

'On-line' alterations of contralateral jugular blood gas profile during carotid clamping

The aim of this work was to record the metabolic status of the brain (pH, PCO(2) and PO(2)) during carotid endarterectomy (CEA), with the use of an intravascular multiparameter sensor (Paratrend 7) via retrograde catheterization of the contralateral jugular vein. Twenty-four patients with ASA grades II and III scheduled for CEA were included in the study. After induction of anesthesia, the contralateral internal jugular vein was punctured retrogradely and the sensor was introduced. During clamping, pH became persistently more acidotic (7.34-7.31; p < 0.05), PCO(2) was elevated (43.2-46.8 mm Hg; p < 0.05) while most of the patients showed a non-significant decrease in PjvO(2)/SjvO(2) (jv = jugular venous). Correlation with clamping time or stump pressure was not significant. Unclamping was followed by a short period (5- 9 min) of decrease in pH and elevation of PCO(2) (7.30-7.22; p < 0.05, and 48.0-52.5 mm Hg; p < 0.05, respectively). PjvO(2) was significantly elevated (51.8-58.0 mm Hg; p < 0.001) after the restoration of flow. The study suggests that local CO(2) creates conditions for compensation of flow after the application of a carotid clamp. We consider that this monitoring technique, after further validation, may provide useful information.

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.

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 (CO2 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 x min(-1) x m(-2), p < 0.0001). Tonometric variables, which were normal at baseline, became abnormal in 90% of patients (baseline CO2 gap 4 +/- 2 mm Hg versus end of operation CO2 gap 24 +/- 15 mm Hg, p < 0.0001). Elevated CO2 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 tonometry: the hemodynamic monitor of choice (Pro)

Controversy exists as to the best means to monitor the critically ill patient and the appropriate end points of therapy. Use of global hemodynamic or metabolic parameters may be normal in the patient who has not been completely or adequately resuscitated. Decreased perfusion to the gut is not well tolerated and may contribute to the development of the multiple organ dysfunction syndrome. Gastric tonometry is a minimally invasive way to monitor splanchnic perfusion in the critically ill patient. Data suggest that tonometry is useful for outcome prognostication and for detection of early hypovolemia. In addition, use of gastric intramucosal pH or mucosal-arterial CO(2) gap as end points of resuscitation may be superior to other conventional whole-body parameters. For these reasons, gastric tonometry must be considered the hemodynamic monitor of choice.

Gastric tonometry: the role of mucosal pH measurement in the management of trauma

Effective management of hemorrhagic shock depends on titration of therapies against reliable resuscitation end points. Conventional clinical and laboratory indexes of shock are often slow to respond to progressive circulatory compromise. GI mucosal ischemia resulting from redistribution of blood flow may, however, precede uncompensated shock and may compound the initial hemorrhagic insult by touching off cascades of inflammatory responses. Trauma patients with evidence of subclinical GI ischemia have been shown to have poor outcomes. Gastric tonometry, by detecting the presence of gastric intramucosal acidosis as a proxy of splanchnic hypoperfusion, may facilitate more timely and rational shock resuscitation. This article reviews the development and validation of gastric tonometry and summarizes the clinical studies that have used this modality to guide the management of shock in trauma patients.

Gastric hypercarbia and adverse outcome after cardiac surgery

OBJECTIVE

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.

DESIGN AND SETTING

Prospective cohort study in a tertiary-care hospital.

PATIENTS

43 patients undergoing elective cardiac surgery.

INTERVENTIONS

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.

MEASUREMENTS AND RESULTS

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).

CONCLUSIONS

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.

Esophageal capnometry during hemorrhagic shock and after resuscitation in rats

BACKGROUND

Splanchnic perfusion following hypovolemic shock is an important marker of adequate resuscitation. We tested whether the gap between esophageal partial carbon dioxide tension (PeCO2) and arterial partial carbon dioxide tension (PaCO2) is increased during graded hemorrhagic hypotension and reversed after blood reinfusion, using a fiberoptic carbon dioxide sensor.

MATERIALS AND METHOD

Ten Sprague-Dawley rats were anesthetized, tracheotomized, and cannulated in one femoral artery and vein. A calibrated fiberoptic PCO2 probe was inserted into the distal third of the esophagus for determination of luminal PeCO2 during maintained anesthesia (pentobarbital 15 mg/kg per hour), normothermia (38 +/- 0.5 degrees C), and fluid balance (saline 5 ml/kg per hour). Three out of 10 rats were used to determine the limits of hemodynamic stability during gradual hemorrhage. Seven of the 10 rats were then subjected to mild and severe hemorrhage (15 and 20-25 ml/kg, respectively). Thirty minutes after severe hemorrhage, these rats were resuscitated by reinfusion of the shed blood. Arterial gas exchange, hemodynamic variables, and PeCO2 were recorded at each steady-state level of hemorrhage (at 30 and 60 min) and after resuscitation.

RESULTS

The PeCO2-PaCO2 gap was significantly increased after mild and severe hemorrhage and returned to baseline (prehemorrhagic) values following blood reinfusion. Base deficit increased significantly following severe hemorrhage and remained significantly elevated after blood reinfusion. Significant correlations were found between base deficit and PeCO2-PaCO2 (P < 0.002) and PeCO2 (P < 0.022). Blood bicarbonate concentration decreased significantly following mild and severe hemorrhage, but its recovery was not complete at 60 min after blood reinfusion.

CONCLUSION

Esophageal-arterial PCO2 gap increases during graded hemorrhagic hypotension and returns to baseline value after resuscitation without complete reversal of the base deficit. These data suggest that esophageal capnometry could be used as an alternative for gastric tonometry during management of hypovolemic shock.

Gastric intramucosal pH is stable during titration of positive end-expiratory pressure to improve oxygenation in acute respiratory distress syndrome

BACKGROUND

Optimal positive end-expiratory pressure (PEEP) is an important component of adequate mechanical ventilation in acute lung injury and acute respiratory distress syndrome (ARDS). In the present study we tested the effect on gastric intramucosal pH of incremental increases in PEEP level (i.e. PEEP titration) to improve oxygenation in ARDS. Seventeen consecutive patients with ARDS, as defined by consensus criteria, were included in this clinical, prospective study. All patients were haemodynamically stable, and were not receiving vasopressors. From an initial level of 5 cmH2O, PEEP was titrated at 2 cmH2O increments until the partial arterial oxygen tension was 300 mmHg or greater, peak airway pressure was 45 cmH2O or greater, or mean arterial blood pressure decreased by 20% or more of the baseline value. Optimal PEEP was defined as the level of PEEP that achieved the best oxygenation. The maximum PEEP was the highest PEEP level reached during titration in each patient.

RESULTS

Gastric mucosal pH was measured using gastric tonometry at all levels of PEEP. The thermodilution technique was used for measurement of cardiac index. Gastric mucosal pH was similar at baseline and at optimal PEEP levels, but it was slightly reduced at maximum PEEP. Cardiac index and oxygen delivery remained stable at all PEEP levels.

CONCLUSION

Incremental titration of PEEP based on improvement in oxygenation does not decrease gastric intramucosal perfusion when cardiac output is preserved in patients with ARDS.

Gas tonometry for evaluation of gastrointestinal mucosal perfusion: experimental models of trauma, shock and complex surgical maneuvers - Part 1

Substantial clinical and animal evidences indicate that the mesenteric circulatory bed, particularly the gut mucosa, is highly vulnerable to reductions in oxygen supply and prone to early injury in the course of hemodynamic changes induced by trauma, shock, sepsis and several complex surgical maneuvers. Gut hypoxia or ischemia is one possible contributing factor to gastrointestinal tract barrier dysfunction that may be associated with the development of systemic inflammatory response and multiple organ dysfunction syndrome, a common cause of death after trauma, sepsis or major surgeries. Monitoring gut perfusion during experiments may provide valuable insights over new interventions and therapies highly needed to reduce trauma and sepsis-related morbidity and mortality. We present our experience with gas tonometry as a monitor of the adequacy of gastrointestinal mucosal perfusion in clinical and experimental models of trauma, shock and surgical maneuvers associated with abrupt hemodynamic changes, such as aortic occlusion and hepatic vascular exclusion. Next issue we will be presenting our experience with gas tonometry in experimental and clinical sepsis.

Evaluation of intestinal intramucosal pH, arterial and portal venous blood gas values, and intestinal blood flow during small intestinal ischemia and reperfusion in dogs

OBJECTIVES

To determine whether small intestinal ischemia and reperfusion affects intestinal intramucosal pH (pHi), arterial and portal venous blood gas values, and intestinal blood flow (IBF) and to investigate relationships between regional intestinal tissue oxygenation and systemic variables in dogs.

ANIMALS

15 healthy adult Beagles.

PROCEDURE

Occlusion of superior mesenteric artery (SMA) for 0, 30, or 60 minutes, followed by reperfusion for 180 minutes, was performed; IBF, pHi, arterial and portal venous blood gas values, arterial pressure, and heart rate were measured at various time points; and intestinal mucosal injury was histologically graded.

RESULTS

Occlusion of the SMA induced significant decreases in pHi and IBF. After the release of the occlusion, IBF returned rapidly to baseline values, but improvement in pHi was slow. Arterial and portal venous blood gas analyses were less sensitive than tonometric measurements of pHi, and there was no correlation between results of blood gas analyses and tonometric measurements. Histologic score for intestinal mucosal injury increased significantly, depending on duration of ischemia, and there was a correlation between tonometric results and the histologic score.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that it is difficult to accurately evaluate local oxygenation disorders by monitoring at the systemic level, whereas clinically pHi is the only reliable indicator of inadequate regional intestinal tissue oxygenation in dogs.

Impact of duodenal feeding on the oxygen balance of the splanchnic region during different phases of severe burn injury

Enteral nutrition is recommended in burned patients. Depending on the amount administered, enteral feeding causes an increase of intestinal oxygen-demand. Since intestinal perfusion is decreased after major burns the aim of this study was to evaluate, whether duodenal feeding might be a cofactor for the development of a splanchnic O(2)-imbalance. In 15 severely burned patients during duodenal feeding starting within 6 h after injury the assessment of the CO(2)-gap between arterial and gastric CO(2), as a parameter for the measurement of intestinal O(2)-balance was performed. Beginning prior to enteral nutrition CO(2)-gap measurements were carried out to show when the CO(2)-gap increased above 30 mmHg during the whole critical illness phase of the patients. When the CO(2)-gap increased above 30 mmHg enteral nutrition was reduced by 50% and the CO(2)-gap was measured 1 h later. In none of the patients the CO(2)-gap increased during increase of enteral nutrition. In seven patients, the CO(2)-gap increased between the 6th and 13th day above 30 mmHg and fell significantly 1 h after reduction of enteral nutrition. Contrary to the early postburn phase, enteral feeding might have adverse effects on the oxygen balance of the intestine in the later stages of the critical illness phase.

Intramucosal-arterial PCO2 gap fails to reflect intestinal dysoxia in hypoxic hypoxia

INTRODUCTION

An elevation in intramucosal-arterial PCO2 gradient (DeltaPCO2) could be determined either by tissue hypoxia or by reduced blood flow. Our hypothesis was that in hypoxic hypoxia with preserved blood flow, DeltaPCO2 should not be altered.

METHODS

In 17 anesthetized and mechanically ventilated sheep, oxygen delivery was reduced by decreasing flow (ischemic hypoxia, IH) or arterial oxygen saturation (hypoxic hypoxia, HH), or no intervention was made (sham). In the IH group (n = 6), blood flow was lowered by stepwise hemorrhage; in the HH group (n = 6), hydrochloric acid was instilled intratracheally. We measured cardiac output, superior mesenteric blood flow, gases, hemoglobin, and oxygen saturations in arterial blood, mixed venous blood, and mesenteric venous blood, and ileal intramucosal PCO2 by tonometry. Systemic and intestinal oxygen transport and consumption were calculated, as was DeltaPCO2. After basal measurements, measurements were repeated at 30, 60, and 90 minutes.

RESULTS

Both progressive bleeding and hydrochloric acid aspiration provoked critical reductions in systemic and intestinal oxygen delivery and consumption. No changes occurred in the sham group. DeltaPCO2 increased in the IH group (12 +/- 10 [mean +/- SD] versus 40 +/- 13 mmHg; P < 0.001), but remained unchanged in HH and in the sham group (13 +/- 6 versus 10 +/- 13 mmHg and 8 +/- 5 versus 9 +/- 6 mmHg; not significant).

DISCUSSION

In this experimental model of hypoxic hypoxia with preserved blood flow, DeltaPCO2 was not modified during dependence of oxygen uptake on oxygen transport. These results suggest that DeltaPCO2 might be determined primarily by blood flow.

The influence of deliberate hypotension on splanchnic perfusion balance with use of either isoflurane or esmolol and nitroglycerin

Various techniques to induce deliberate hypotension (DH) have different influences on splanchnic perfusion. The aim of our study was to determine whether splanchnic perfusion is clinically impaired during DH by using either isoflurane (ISO) or a combination of esmolol and nitroglycerin (E/N). We randomized 16 patients undergoing elective maxillofacial surgery to receive either ISO (0.7%-1.8%) or E (105 g x kg(-1) x min(-1)) and N (1-6 mg/h) to induce DH. General anesthesia was performed in both groups by IV midazolam 0.07 mg/kg, fentanyl 0.003 mg/kg, propofol 1.5 mg/kg, and vecuronium 0.1 mg/kg followed by a propofol infusion with 6 mg x kg(-1) x h(-1). After the induction of anesthesia, a gastric tonometer (TRIP NGS Catheter) and a radial artery catheter were inserted. Baseline values of gastric intramucosal pH (pHi) were determined 60 min after placement of the catheter and before the induction of DH. The pHi values were calculated every 60 min until DH was discontinued. In both groups, DH was satisfactorily established. None of the pHi values calculated was less than 7.37 in the E/N or 7.41 in the ISO group. Arterial blood lactate levels did not increase in any of the patients. We conclude that neither method of producing DH compromises splanchnic tissue oxygen balance in healthy patients. Furthermore, overall organ perfusion was sufficient in both groups, because none of the patients showed an increase in blood lactate.

IMPLICATIONS

Neither the isoflurane nor the esmolol/nitroglycerin method of producing deliberate hypotension compromises splanchnic tissue oxygen balance in healthy patients. Furthermore, overall organ perfusion was sufficient in both groups, because none of the patients showed an increase in blood lactate.