Clinical review: splanchnic ischaemia

Kidney Doppler ultrasonography in critical care nephrology

Color pulsed-wave Doppler ultrasound (CPWD-US) emerges as a pivotal tool in intensive care units (ICUs) for diagnosing acute kidney injury (AKI) swiftly and non-invasively. Its bedside accessibility allows for rapid assessments, making it a primary imaging modality for AKI characterization. Furthermore, CPWD-US serves as a guiding instrument for key diagnostic-interventional procedures such as renal needle biopsy and percutaneous nephrostomy, while also facilitating therapy response monitoring and AKI progression tracking. This review shifts focus towards the integration of renal ultrasound into ICU workflows, offering contemporary insights into its utilization through a diagnostic standard-oriented approach. By presenting a flow chart, this review aims to provide practical guidance on the appropriate use of point-of-care ultrasound in critical care scenarios, enhancing diagnostic precision, patient management and safety, albeit amidst a backdrop of limited evidence regarding long-term outcomes.

Impairment of Mesenteric Perfusion as a Marker of Major Bleeding in Trauma Patients

The majority of potentially preventable mortality in trauma patients is related to bleeding; therefore, early recognition and effective treatment of hemorrhagic shock impose a cardinal challenge for trauma teams worldwide. The reduction in mesenteric perfusion (MP) is among the first compensatory responses to blood loss; however, there is no adequate tool for splanchnic hemodynamic monitoring in emergency patient care. In this narrative review, (i) methods based on flowmetry, CT imaging, video microscopy (VM), measurement of laboratory markers, spectroscopy, and tissue capnometry were critically analyzed with respect to their accessibility, and applicability, sensitivity, and specificity. (ii) Then, we demonstrated that derangement of MP is a promising diagnostic indicator of blood loss. (iii) Finally, we discussed a new diagnostic method for the evaluation of hemorrhage based on exhaled methane (CH₄) measurement. Conclusions: Monitoring the MP is a feasible option for the evaluation of blood loss. There are a wide range of experimentally used methodologies; however, due to their practical limitations, only a fraction of them could be integrated into routine emergency trauma care. According to our comprehensive review, breath analysis, including exhaled CH₄ measurement, would provide the possibility for continuous, non-invasive monitoring of blood loss.

Perspective: Drawing on Findings From Critical Illness to Explain Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

We propose an initial explanation for how myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS) could originate and perpetuate by drawing on findings from critical illness research. Specifically, we combine emerging findings regarding (a) hypoperfusion and endotheliopathy, and (b) intestinal injury in these illnesses with our previously published hypothesis about the role of (c) pituitary suppression, and (d) low thyroid hormone function associated with redox imbalance in ME/CFS. Moreover, we describe interlinkages between these pathophysiological mechanisms as well as “vicious cycles” involving cytokines and inflammation that may contribute to explain the chronic nature of these illnesses. This paper summarizes and expands on our previous publications about the relevance of findings from critical illness for ME/CFS. New knowledge on diagnostics, prognostics and treatment strategies could be gained through active collaboration between critical illness and ME/CFS researchers, which could lead to improved outcomes for both conditions.

Association between hepatic oxygenation on near-infrared spectroscopy and clinical factors in patients undergoing hemodialysis

The hepato-splanchnic circulation directly influences oxygenation of the abdominal organs and plays an important role in compensating for the blood volume reduction that occurs in the central circulation during hemodialysis (HD) with ultrafiltration. However, the hepato-splanchnic circulation and oxygenation cannot be easily evaluated in the clinical setting of HD therapy. We included 185 HD patients and 15 healthy volunteers as the control group in this study. Before HD, hepatic regional oxygen saturation (rSO2), a marker of hepatic oxygenation reflecting the hepato-splanchnic circulation and oxygenation, was monitored using an INVOS 5100c oxygen saturation monitor. Hepatic rSO2 was significantly lower in patients undergoing HD than in healthy controls (56.4 ± 14.9% vs. 76.2 ± 9.6%, p < 0.001). Multivariable regression analysis showed that hepatic rSO2 was independently associated with body mass index (BMI; standardized coefficient: 0.294), hemoglobin (Hb) level (standardized coefficient: 0.294), a history of cardiovascular disease (standardized coefficient: -0.157), mean blood pressure (BP; standardized coefficient: 0.154), and serum albumin concentration (standardized coefficient: 0.150) in Model 1 via a simple linear regression analysis. In Model 2 using the colloid osmotic pressure (COP) in place of serum albumin concentration, the COP (standardized coefficient: 0.134) was also identified as affecting hepatic rSO2. Basal hepatic oxygenation before HD might be affected by BMI, Hb levels, a history of cardiovascular disease, mean BP, serum albumin concentration, and the COP. Further prospective studies are needed to clarify whether changes in these parameters, including during HD, affect the hepato-splanchnic circulation and oxygenation in HD patients.

High Transaminases Following Cardiac Surgery: A Narrative Review

Elevation of liver enzymes after cardiac surgery is encountered infrequently. Acute heart failure during and after surgery may be the culprit responsible for liver dysfunction. However, it may create clinical confusion whether acute liver dysfunction could induce some sort of cardiac dysfunction through mechanisms similar to those encountered in chronic liver disease. We searched through the Medline, Cochrane, and Embase databases up to January 2018. We included review articles, meta-analyses, and original trials on the elevation of liver enzymes after cardiac surgery, and combined the following MESH terms: “intensive care, “cardiac surgery,” “high liver enzymes,” “ischemia,” “left ventricular dysfunction,” and “critical illness.” Case reports were excluded. Language restrictions were not applied. References were examined for other potentially useful articles. We did not find any articles that supported the cardiac decompensation phenomenon after acute liver injury. In contrast, low-hepatic flow, hypoxemia, or pump-induced inflammation could induce hepatic dysfunction in acute settings after cardiac surgery. In conclusion, a rise in the transaminases following cardiac surgery would favor an ischemic etiology for the condition.

Refractory septic shock: our pragmatic approach

Despite timely intervention, there exists a small subgroup of patients with septic shock who develop progressive multi-organ failure. Seemingly refractory to conventional therapy, they exhibit a very high mortality. Such patients are often poorly represented in large clinical trials. Consequently, good evidence for effective treatment strategies is lacking. In this article, we describe a pragmatic, multi-faceted approach to managing patients with refractory septic shock based on our experience of toxin-mediated sepsis in a specialist referral centre. Many components of this strategy are inexpensive and widely accessible, and so may offer an opportunity to improve outcomes in these critically ill patients.

Fiber-optic fluorescence-quenching oxygen partial pressure sensor using platinum octaethylporphyrin

The development and bench testing of a fiber-optic oxygen sensor is described. The sensor is designed for measurement of tissue oxygen levels in the mucosa of the digestive tract. The materials and construction are optimized for insertion through the mouth for measurement in the lower esophagus. An oxygen-sensitive fluorescence-quenching film was applied as a solution of platinum octaethylporphyrin (PtOEP) poly(ethyl methacrylate) (PEMA) and dichloromethane and dip coated onto the distal tip of the fiber. The sensor was tested by comparing relative fluorescence when immersed in liquid water at 37°C, at a range of partial pressures (0-101 kPa). Maximum relative fluorescence at most oxygen concentrations was seen when the PtOEP concentration was 0.1  g.L^-1, four layers of coating solution were applied, and a fiber core radius of 600 μm was selected, giving a Stern-Volmer constant of 0.129  kPa^-1. The performance of the sensor is suitable for many in vivo applications, particularly mucosal measurements. It has sufficient sensitivity, is sterilizable, and is sufficiently flexible and robust for insertion via the mouth without damage to the probe or risk of harm to the patient.

A new device for continuous assessment of gut perfusion: proof of concept on a porcine model of septic shock

INTRODUCTION

We evaluate an innovative device consisting of an enteral feeding tube equipped with a photoplethysmography (PPG) sensor in contact with the duodenal mucosa. This study aims to determine if the PPG signal, composed of a continuous (PDC) and a pulsatile part (PAC), is a reliable method to assess gut perfusion in a porcine model of septic shock.

METHOD

Fourteen piglets were anesthetized and mechanically ventilated. They were randomly assigned to two groups: the nonseptic (NS) group received an infusion of Ringer's lactate solution (RL) alone, the septic (S) group received in addition a suspension of live Pseudomonas aeruginosa. Heart rate (HR), pulse oximetry (SpO2), mean arterial pressure (MAP), cardiac index (CI) and serum lactates were recorded and gut microcirculation (GM) was monitored with a laser Doppler probe applied on the duodenal serosa. PDC and PAC were given by the PPG probe inserted in the duodenum. Data was collected every 15 minutes (t0, t15…) during 150 minutes (t150). After administration of the bacteria suspension (t0), resuscitation maneuvers were performed following a defined algorithm. GM PAC, and PDC were expressed as variation from baseline (GMvar, PACvar, PDCvar). Analysis of variance (ANOVA) with repeated measures was performed to compare hemodynamic variables, with Bonferroni correction as post hoc analysis on t0, t60 and t150.

RESULTS

One piglet was withdrawn from analysis due to a defective probe. S group (six piglets) received resuscitation therapy while NS group (seven piglets) did not. A significant group effect was found for the all parameters except HR. Post hoc analysis found a significant decrease for GM and PAC at t60. The correlation between PAC, PDC and microcirculatory parameters were as follows: rPACvar-GMvar = 0.496, P <0.001, rPDCvar-GMvar = 0.244; P = 0.002. In the septic group, correlations were as follows: rPAC-lactate = -0.772, P <0.001; rPDC-lactate = -0.681, P <0.01). At the onset of shock, a decrease of PAC, PDC and GM occurred before the alteration of MAP.

CONCLUSIONS

PAC and PDC decreased at the onset of shock and were correlated with GM and lactate. These results confirm that PPG signal reliably reflects the early perfusion alteration of the gut. Further studies should assess the clinical use of this device.

Beneficial effects of theophylline infusions in surgical patients with intra-abdominal hypertension

BACKGROUND

Intra-abdominal hypertension (IAH) can cause high mortality. Recently, we found that IAH was associated with increased serum levels of adenosine and interleukin 10. Our present "hypothesis-generated study" was based on the above mentioned results.

MATERIALS AND METHODS

In this uncontrolled clinical trial, a total of 78 patients with IAH were enrolled representing a 13-20 mmHg range of intra-abdominal pressure (IAP). Patients requiring surgical abdominal decompression were excluded. Patients were treated with the following protocols: standard supportive therapy (ST, n = 38) or ST plus infusion with the adenosine receptor antagonist theophylline (T, n = 40). Over the 5-day measurement period, IAP was monitored continuously and serum adenosine concentration and other clinical and laboratory measurements were monitored daily. Mortality was followed for the first 30 days following the diagnosis of IAH.

RESULTS

Mortality of ST patients was 55%, which is compatible to other studies. Serum adenosine concentration was found to be directly proportional to IAP. Of the 40 patients receiving T treatment, survival was 100%. An increased survival related to theophylline infusion correlated with improving serum concentrations of IL-10, urea, and creatinine, as well as 24-h urine output, fluid balance, mean arterial pressure, and O(2)Sat.

CONCLUSIONS

Adenosine receptor antagonism with T following IAH diagnosis resulted in markedly reduced mortality in patients with moderated IAH (<20 mmHg). Theophylline-associated mortality reduction may be related to improved renal perfusion and improved MAP, presumably caused by adenosine receptor blockade. Because this study was not a randomized controlled study, these compelling observations require further multicentric clinical confirmation.

[Intraabdominal hypertension and abdominal compartment syndrome]

Although intraabdominal pressure (IAP) has been studied for more than 100 years, the concepts of intraabdominal hypertension (IAH) and abdominal compartmental syndrome (ACS) have only been developed as clinical entities of interest in intensive care in the last 5 years. At the first Congress on Abdominal Compartment Syndrome in December 2004, a series of definitions were established, which were published in 2006. IAH is defined as IAP ≥ 12 mmHg and is classified in four severity grades, the maximum grade being ACS, with the development of multiorgan failure. The incidence of IAH in patients in intensive care units is high, around 30% at admission and 64% in those with a length of stay of 7 days. The increase in IAP leads to reduced vascular flow to the splenic organs, increased intrathoracic pressure and decreased venous return, with a substantial reduction in cardiac output. If IAH persists, these physiopathologic episodes are followed by the development of multiorgan failure with renal, cardiocirculatory and respiratory failure and intestinal ischemia. Mortality from untreated ACS is higher than 60%. The only treatment for ACS is surgical decompression. In patients with moderate IAH, medical treatment should be optimized, based on the following measures: a) serial IAP monitoring; b) optimization of systemic perfusion and the function of the distinct systems in patients with high IAP; c) instauration of specific measures to decrease IAP; and d) early surgical decompression for refractory IAH. The application of the medical measures that can reduce IAP and early abdominal decompression in ACS improve survival in critically ill patients with IAH.

Increased serum adenosine and interleukin 10 levels as new laboratory markers of increased intra-abdominal pressure

BACKGROUND

Increased intra-abdominal pressure (IAP), intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are severe complications of surgical interventions with a high rate of mortality. The technique of IAP measurement is accurate, precise, reproducible and cost-effective. However, laboratory measures for monitoring of IAH have not been defined. We investigated the linkage between the serum levels of adenosine and interleukin 10 (IL-10) with IAP.

METHODS

The sera of 25 surgical patients with IAP <12 mmHg and of 45 surgical patients with IAP >12 mmHg were tested. Serum adenosine concentration was measured by HPLC. Serum IL-1β, IL-2, IL-4, IL-10, TNFα, IFNγ and IL-10 were determined by enzyme linked immunosorbent assay (ELISA). CRP was measured by nephelometry.

RESULTS

Significant correlations of IAP were found only with serum levels of adenosine and IL-10. In the sera of patients with IAP >12 mmHg, the levels of both adenosine (1.61 versus 0.06 µM, p < 0.01) and IL-10 (63.23 versus 27.27 pg/ml, p < 0.01) were significantly higher than those in patients with IAP <12 mmHg. Moreover, significant correlations were found between individual patient IAP-adenosine values (r = 0.766, p < 0.001), IAP-IL-10 values (r = 0.792, p < 0.001) and adenosine-IL-10 values (r = 0.888, p < 0.001). A direct linear correlation between IAP-adenosine and IAP-10 values was only observed with IAP >15 (Grade II-IV).

CONCLUSION

We report associations between IAP and the serum adenosine and IL-10 levels providing new tools for the laboratory monitoring of IAH as well as further understanding of the pathomechanisms contributing to ACS.

Fetal superior mesenteric artery: longitudinal reference ranges and evidence of regulatory link to portal liver circulation

OBJECTIVE

To establish longitudinal reference ranges for the fetal superior mesenteric artery (SMA) flow velocity and pulsatility index (PI(SMA)). Also to examine the hemodynamic relationship to venous liver perfusion and umbilical flow distribution in the liver, to other splanchnic arteries, and more generally to the middle cerebral and umbilical artery.

METHODS

Prospective longitudinal study of 161 low-risk pregnancies using Doppler recordings including the SMA, repeated on 3-5 occasions at 3-5 weekly intervals. Umbilical venous flow was estimated, blood velocity in the shunt ductus venosus represented umbilico-caval (i.e. porto-caval) pressure gradient, and left portal vein blood velocity represented umbilical distribution within the liver. The correlation between PI(SMA) and the splenic and hepatic artery PI were analysed (PI(SA) and PI(HA)), and the association to middle cerebral and umbilical artery PI (PI(MCA) and PI(UA)) assessed.

RESULTS

Reference ranges for the SMA for gestational weeks 21-39 were based on 589 observations. Low impedance in the SMA (i.e. low PI(SMA)) was associated with low umbilical flow and porto-caval pressure gradient (i.e. <10th centile), and high distribution of umbilical flow to the right lobe (i.e. left portal vein blood velocity >90th centile). PI(SMA) correlated weakly with PI(SA) and PI(HA) (r=0.30, 95%CI 0.22-0.37, and r=0.39, 95%CI 0.27-0.51, respectively). PI(SMA) was positively associated with PI(MCA) and PI(UA).

CONCLUSION

We have provided longitudinal reference ranges for fetal SMA flow velocity and PI, and shown that the SMA, which perfuses the fetal gut, is also involved in the regulation of the liver perfusion.

Management of sepsis: early resuscitation

Key links in the chain of survival for the management of severe sepsis and septic shock are early identification and comprehensive resuscitation of high-risk patients. Multiple studies have shown that the first 6 hours of early sepsis management are especially important from a diagnostic, pathogenic, and therapeutic perspective, and that steps taken during this period can have a significant impact on outcome. The recognition of this critical time period and the robust outcome benefit realized in previous studies provides the rationale for adopting early resuscitation as a distinct intervention. Sepsis joins trauma, stroke, and acute myocardial infarction in having "golden hours," representing a critical opportunity early on in the course of disease for actions that offer the most benefit.

Regional blood flow distribution and oxygen metabolism during mesenteric ischemia and congestion

BACKGROUND

Acute mesenteric ischemia is a potentially fatal vascular emergency with mortality rates ranging between 60% and 80%. Several studies have extensively examined the hemodynamic and metabolic effects of superior mesenteric artery occlusion. On the other hand, the cardiocirculatory derangement and the tissue damage induced by intestinal outflow obstruction have not been investigated systematically. For these reasons we decided to assess the initial impact of venous mesenteric occlusion on intestinal blood flow distribution, and correlate these findings with other systemic and regional perfusion markers.

METHODS

Fourteen mongrel dogs were subjected to 45 min of superior mesenteric artery (SMAO) or vein occlusion (SMVO), and observed for 120 min after reperfusion. Systemic hemodynamics were evaluated using Swan-Ganz and arterial catheters. Regional blood flow (ultrasonic flow probes), intestinal O(2)-derived variables, and mesenteric-arterial and tonometric-arterial pCO(2) gradients (D(mv-a)pCO(2) and D(t-a)pCO(2)) were also calculated.

RESULTS

SMVO was associated with hypotension and low cardiac output. A significant increase in the regional pCO(2) gradients was also observed in both groups during the ischemic period. After reperfusion, a progressive reduction in D(mv-a)pCO(2) occurred in the SMVO group; however, no improvement in D(t-a)pCO(2) was observed. The histopathologic injury scores were 2.7 +/- 0.5 and 4.8 +/- 0.2 for SMAO and SMVO, respectively.

CONCLUSIONS

SMV occlusion promoted early and significant hemodynamic and metabolic derangement at systemic and regional levels. Additionally, systemic pCO(2) gradient is not a reliable parameter to evaluate the local intestinal oxygenation. Finally, the D(t-a)pCO(2) correlates with histologic changes during intestinal congestion or ischemia. However, minor histologic changes cannot be detected using this methodology.

Abdominal compartment syndrome in patients with severe acute pancreatitis in early stage

AIM: To study retrospectively the influence of intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) in patients with early acute pancreatitis (AP) (during the first week after admission) on physiological functions, and the association of the presence of IAH/ACS and outcome.

METHODS: Patients (n = 74) with AP recruited in this study were divided into two groups according to intra-abdominal pressure (IAP) determined by indirect measurement using the transvesical route via Foley bladder catheter during the first week after admission. Patients (n = 44) with IAP ≥ 12 mmHg were assigned in IAH group, and the remaining patients (n = 30) with IAP < 12 mmHg in normal IAP group. For analysis of the influence of IAH/ACS on organ function and outcome, the physiological parameters and the occurrence of organ dysfunction during intensive care unit (ICU) stay were recorded, as were the incidences of pancreatic infection and in-hospital mortality.

RESULTS: IAH within the first week after admission was found in 44 patients (59.46%). Although the APACHE II scores on admission and the Ranson scores within 48 h after hospitalization were elevated in IAH patients in early stage, they did not show the statistically significant differences from patients with normal IAP within a week after admission (16.18 ± 3.90 vs 15.70 ± 4.25, P = 0.616; 3.70 ± 0.93 vs 3.47 ± 0.94, P = 0.285, respectively). ACS in early AP was recorded in 20 patients (27.03%). During any 24-h period of the first week after admission, the recorded mean IAP correlated significantly with the Marshall score calculated at the same time interval in IAH group (r = 0.635, P < 0.001). Although ACS patients had obvious amelioration in physiological variables within 24 h after decompression, the incidences of pancreatitic infection, septic shock, multiple organ dysfunction syndrome (MODS) and death in the patients with ACS were significantly higher than that in other patients without ACS (pancreatitic infection: 60.0% vs 7.4%, P < 0.001; septic shock: 70.0% vs 11.1%, P < 0.001; MODS: 90.0% vs 31.5%, P < 0.001; mortality: 75.0% vs 3.7%, P < 0.001).

CONCLUSION: IAH/ACS is a frequent finding in patients admitted to the ICU because of AP. Patients with IAP at approximately 10-12 mmHg and early signs of changes in physiologic variables should be seriously considered for urgent decompression to improve survival.

Vasopressin in septic shock: effects on pancreatic, renal, and hepatic blood flow

Introduction

Vasopressin has been shown to increase blood pressure in catecholamine-resistant septic shock. The aim of this study was to measure the effects of low-dose vasopressin on regional (hepato-splanchnic and renal) and microcirculatory (liver, pancreas, and kidney) blood flow in septic shock.

Methods

Thirty-two pigs were anesthetized, mechanically ventilated, and randomly assigned to one of four groups (n = 8 in each). Group S (sepsis) and group SV (sepsis/vasopressin) were exposed to fecal peritonitis. Group C and group V were non-septic controls. After 240 minutes, both septic groups were resuscitated with intravenous fluids. After 300 minutes, groups V and SV received intravenous vasopressin 0.06 IU/kg per hour. Regional blood flow was measured in the hepatic and renal arteries, the portal vein, and the celiac trunk by means of ultrasonic transit time flowmetry. Microcirculatory blood flow was measured in the liver, kidney, and pancreas by means of laser Doppler flowmetry.

Results

In septic shock, vasopressin markedly decreased blood flow in the portal vein, by 58% after 1 hour and by 45% after 3 hours (p < 0.01), whereas flow remained virtually unchanged in the hepatic artery and increased in the celiac trunk. Microcirculatory blood flow decreased in the pancreas by 45% (p < 0.01) and in the kidney by 16% (p < 0.01) but remained unchanged in the liver.

Conclusion

Vasopressin caused marked redistribution of splanchnic regional and microcirculatory blood flow, including a significant decrease in portal, pancreatic, and renal blood flows, whereas hepatic artery flow remained virtually unchanged. This study also showed that increased urine output does not necessarily reflect increased renal blood flow.

Effects of ventilation with 100% oxygen during early hyperdynamic porcine fecal peritonitis

OBJECTIVE

Early goal-directed therapy aims at balancing tissue oxygen delivery and demand. Hyperoxia (i.e., pure oxygen breathing) has not been studied in this context, since sepsis increases oxygen radical production, which is believed to be directly related to the oxygen tension. On the other hand, oxygen breathing improved survival in various shock models. Therefore, we hypothesized that hyperoxia may be beneficial during early septic shock.

DESIGN

Laboratory animal experiments.

SETTING

Animal research laboratory at university medical school.

SUBJECTS

Twenty domestic pigs of either gender.

INTERVENTIONS

After induction of fecal peritonitis, anesthetized and instrumented pigs were ventilated with either 100% oxygen or supplemental oxygen as needed to maintain arterial hemoglobin oxygen saturation > or = 90%. Normotensive and hyperdynamic hemodynamics were achieved using hydroxyethyl starch and norepinephrine infusion.

MEASUREMENTS AND MAIN RESULTS

Before and at 12, 18, and 24 hrs of peritonitis, we measured lung compliance; systemic, pulmonary, and hepatosplanchnic hemodynamics; gas exchange; acid-base status; blood isoprostanes; nitrates; DNA strand breaks; and organ function. Gluconeogenesis and glucose oxidation were calculated from blood isotope and expiratory 13CO2 enrichments during continuous intravenous 1,2,3,4,5,6-(13)C6-glucose. Apoptosis in lung and liver was assessed postmortem (TUNEL staining). Hyperoxia did not affect lung mechanics or gas exchange but redistributed cardiac output to the hepatosplanchnic region, attenuated regional venous metabolic acidosis, increased glucose oxidation, improved renal function, and markedly reduced the apoptotic death rate in liver and lung.

CONCLUSIONS

During early hyperdynamic porcine septic shock, 100% oxygen improved organ function and attenuated tissue apoptosis without affecting lung function and oxidative or nitrosative stress. Therefore, it might be considered as an additional measure in the first phase of early goal-directed therapy.

Drug Absorption in the Management of Congestive Heart Failure: Loop Diuretics

Congestive heart failure is a disease state distinguished by the regular presence of both renal and hepatic abnormalities in drug handling. One such abnormality involves flaws in the process of drug absorption. In most instances, congestive heart failure-related abnormalities in drug absorption are of inconsequential significance. However, this is not the case with loop diuretics. Loop diuretic action ordinarily tracks the rate and extent of absorption if a sufficient amount of diuretic has been given to exceed the threshold for diuretic effect. In congestive heart failure, both the rate and absolute amount of loop diuretic absorbed can be reduced as a function of the heart failure state itself. In this setting, drug dissolution characteristics can assume added significance. Furosemide is the loop diuretic with the widest intra- and interpatient variability of absorption. Alternatively, the loop diuretic torsemide is rapidly and fairly completely absorbed independent of the heart failure state. This pattern of absorption establishes it as the preferred loop diuretic in the otherwise diuretic-resistant heart failure patient. However, the exact role of torsemide in the outpatient management of congestive heart failure remains to be determined.

Differential effects of lower body negative pressure and upright tilt on splanchnic blood volume

Upright posture and lower body negative pressure (LBNP) both induce reductions in central blood volume. However, regional circulatory responses to postural changes and LBNP may differ. Therefore, we studied regional blood flow and blood volume changes in 10 healthy subjects undergoing graded lower-body negative pressure (-10 to -50 mmHg) and 8 subjects undergoing incremental head-up tilt (HUT; 20 degrees , 40 degrees , and 70 degrees ) on separate days. We continuously measured blood pressure (BP), heart rate, and regional blood volumes and blood flows in the thoracic, splanchnic, pelvic, and leg segments by impedance plethysmography and calculated regional arterial resistances. Neither LBNP nor HUT altered systolic BP, whereas pulse pressure decreased significantly. Blood flow decreased in all segments, whereas peripheral resistances uniformly and significantly increased with both HUT and LBNP. Thoracic volume decreased while pelvic and leg volumes increased with HUT and LBNP. However, splanchnic volume changes were directionally opposite with stepwise decreases in splanchnic volume with LBNP and stepwise increases in splanchnic volume during HUT. Splanchnic emptying in LBNP models regional vascular changes during hemorrhage. Splanchnic filling may limit the ability of the splanchnic bed to respond to thoracic hypovolemia during upright posture.

Different patterns of pulse spectrum between survivors and non-survivors during progressive hemorrhage in rats

Previous work from our laboratory has demonstrated that the percentage differences of 2nd (C2) and 3rd (C3) pulse harmonics related to Kidney and Spleen were both increased toward another steady state in rats after acute hemorrhage. Therefore, it is suggested that changes in pulse spectra might represent the ability of animals to survive a model of progressive hemorrhage. In this study, the difference of the pulse spectra patterns between survivors and non-survivors after progressive hemorrhage (by loss of 5%, 10% or 20% of the estimated blood volume) in anesthetized rats is determined. Seven rats, dead within 2 hours after a loss of 20% of the estimated blood volume hemorrhage, were defined as 'non-survivors'. The other eleven rats, more than 2 hours after hemorrhage, were defined as 'survivors'. Pulse waves of arterial blood pressure before and after the hemorrhage were measured in parallel to the pulse spectrum analysis. Data among different phases were analyzed using one-way analysis of variance (ANOVA) with Duncan's test for pairwise comparisons. Differences between survivor and non-survivor groups at each phase were analyzed using Student's t-test. A mixed-effects linear regression model was applied to evaluate the relationship in harmonics, which significantly differed between the two groups. The study results showed that in rats, during progressive hemorrhage, the percentage differences of 2nd harmonic proportion increased significantly; however, the result failed to show any significant difference between survivors and non-survivors. After the third blood withdrawal process, the percentage differences of 3rd harmonic proportion increased more significantly in the survivors. In addition, the percentage differences of 1st harmonic proportion related to the Liver for the survivor group was significantly lower than that of the non-survivors. After analysis with the mixed linear regression model, C3 and C1 demonstrated a linear regression relationship, and there existed significant differences between survivors and non-survivors. These results suggest that C3 might play an important role in physiology regarding surviving capability after progressive hemorrhage.

Vasoconstriction and blood flow responses in visceral arteries to mental task in humans

The vascular responses to mental task in visceral arteries in humans have not been elucidated. We observed the responses in the renal (RA) and superior mesenteric (SMA) arteries to mental stress, using simultaneous pulsed and echo Doppler ultrasound flowmetry. Nine healthy females performed a computerized colour word conflict test (CWT) for 3 min. The mean blood velocity (MBV) in the right RA and SMA, heart rate (HR) and blood pressure were measured. The mean arterial pressure (MAP) was divided by the flow velocity to assess the vascular resistance (VR). The CWT significantly increased the MAP, HR and VR in both arteries from the first minute. During the CWT, flow in the RA decreased significantly at the third minute relative to baseline, while flow in the SMA showed no significant change from the first to the third minute. The degree of vasoconstriction in the RA bed was greater than that in the SMA bed. These results suggest that the mental task causes vasoconstriction in visceral arteries, and imply that it induces differential blood flow and vascular responses in visceral arteries.

Intra-abdominal hypertension in the critically ill: it is time to pay attention

PURPOSE OF THE REVIEW

There has been an exponentially increasing interest in intra-abdominal hypertension (IAH). Comparison of the published data however is difficult due to the lack of consensus definitions. This review will focus on the available literature from the last 2 years. A Medline and PubMed search was performed using 'intra-abdominal pressure' (IAP), 'intra-abdominal hypertension' (IAH), and 'abdominal compartment syndrome' (ACS) as search items. The aim was to find an answer to the question 'Isn't it time to pay attention to intra-abdominal pressure in the critically ill?'

RECENT FINDINGS

Although the number of studies published on this topic is steadily increasing and confirms the pathophysiologic implications of IAH on end-organ function within and outside the abdominal cavity it remains difficult to compare the literature data because the measurement methods and definitions used are not uniform. Provocative data have been published regarding the interactions between the abdominal and thoracic compartments especially in patients with capillary leak and fluid overload; most of this data raises even more questions than it gives answers and may therefore strengthen the nonbelievers who consider IAP, IAH and ACS as epiphenomena in critically ill patients. Unless the international scientific community does not come forward with clear-cut definitions we will keep comparing 'apples with oranges.'

SUMMARY

It is time to pay attention to intra-abdominal pressure in the critically ill. It is also time for standardized IAP measurement methods, good consensus definitions and randomized interventional studies.

Increased blood flow prevents intramucosal acidosis in sheep endotoxemia: a controlled study

Introduction

Increased intramucosal–arterial carbon dioxide tension (PCO₂) difference (ΔPCO₂) is common in experimental endotoxemia. However, its meaning remains controversial because it has been ascribed to hypoperfusion of intestinal villi or to cytopathic hypoxia. Our hypothesis was that increased blood flow could prevent the increase in ΔPCO₂.

Methods

In 19 anesthetized and mechanically ventilated sheep, we measured cardiac output, superior mesenteric blood flow, lactate, gases, hemoglobin and oxygen saturations in arterial, mixed venous and mesenteric venous blood, and ileal intramucosal PCO₂ by saline tonometry. Intestinal oxygen transport and consumption were calculated. After basal measurements, sheep were assigned to the following groups, for 120 min: (1) sham (n = 6), (2) normal blood flow (n = 7) and (3) increased blood flow (n = 6). Escherichia coli lipopolysaccharide (5 μg/kg) was injected in the last two groups. Saline solution was used to maintain blood flood at basal levels in the sham and normal blood flow groups, or to increase it to about 50% of basal in the increased blood flow group.

Results

In the normal blood flow group, systemic and intestinal oxygen transport and consumption were preserved, but ΔPCO₂ increased (basal versus 120 min endotoxemia, 7 ± 4 versus 19 ± 4 mmHg; P < 0.001) and metabolic acidosis with a high anion gap ensued (arterial pH 7.39 versus 7.35; anion gap 15 ± 3 versus 18 ± 2 mmol/l; P < 0.001 for both). Increased blood flow prevented the elevation in ΔPCO₂ (5 ± 7 versus 9 ± 6 mmHg; P = not significant). However, anion-gap metabolic acidosis was deeper (7.42 versus 7.25; 16 ± 3 versus 22 ± 3 mmol/l; P < 0.001 for both).

Conclusions

In this model of endotoxemia, intramucosal acidosis was corrected by increased blood flow and so might follow tissue hypoperfusion. In contrast, anion-gap metabolic acidosis was left uncorrected and even worsened with aggressive volume expansion. These results point to different mechanisms generating both alterations.

Gut oxygenation in sepsis: still a matter of controversy?

Part of Stephan Jakob's exhaustive review paper in the present issue of Critical Care deals with the notion that intestinal cellular energetics are deranged in sepsis, in terms not only of inadequate tissue perfusion but also of impaired mitochondrial respiration and/or coupling (i.e. organ dysfunction in sepsis may occur as a result of 'cytopathic hypoxia'). This suggests that efforts to improve outcome in septic patients by manipulating systemic oxygen delivery and regional blood flow are doomed to failure. That suggestion remains largely speculative, and experimental and clinical results presented here consistently demonstrate that there is still a place for treatment of abnormal perfusion in the context of early severe sepsis and septic shock.