Effects of Hyperchloremic Acidosis on Arterial Pressure and Circulating Inflammatory Molecules in Experimental Sepsis

[Hydroxyethyl starch]

OBJECTIVE

The purpose of this review is to draw up a statement on current knowledge available on the more recent hydroxyethyl starch (HES).

DATA SOURCES

References were obtained from computerized bibliographic research (Medline), recent review articles, the library of the service and personal files.

STUDY SELECTION

All categories of articles on this topic have been selected.

DATA EXTRACTION

Articles have been analysed for biophysics, pharmacology, toxicity, side effects, clinical effects and using prospect of HES.

DATA SYNTHESIS

The first HES was made available in the United States in 1970. The development of a new generation of HES restarted the discussion on clinical interest and the limits in the use of these macromolecules. This interest is also strengthened today by the recent data attached to plasma substitution in intensive care or perioperative resuscitation. The interest for crystalloids and colloids is still widely debated, and among the latter, the relative interest of the HES last generation compared to older ones. Recent HES development is in line with a decrease molecular weight, change rate molar substitution and to amend the glucose to hydroxyethyl report. The ultimate goal is to reduce the side effects of these molecules preventing their use. Side effects are dominated by haemostasis and renal dysfunction. The latest developments are the so-called HES "balanced" solutions.

Bench-to-bedside review: Chloride in critical illness

Chloride is the principal anion in the extracellular fluid and is the second main contributor to plasma tonicity. Its concentration is frequently abnormal in intensive care unit patients, often as a consequence of fluid therapy. Yet chloride has received less attention than any other ion in the critical care literature. New insights into its physiological roles have emerged together with progress in understanding the structures and functions of chloride channels. In clinical practice, interest in a physicochemical approach to acid-base physiology has directed renewed attention to chloride as a major determinant of acid-base status. It has also indirectly helped to generate interest in other possible effects of disorders of chloraemia. The present review summarizes key aspects of chloride physiology, including its channels, as well as the clinical relevance of disorders of chloraemia. The paper also highlights current knowledge on the impact of different types of intravenous fluids on chloride concentration and the potential effects of such changes on organ physiology. Finally, the review examines the potential intensive care unit practice implications of a better understanding of chloride.

[Hypernatremic alkalosis. Possible counterpart of hyperchloremic acidosis in intensive care patients?]

BACKGROUND

With broad acceptance of Stewart's acid-base model "hyperchloremic acidosis" is regarded as an independent form of metabolic disorder. It is unknown whether hypernatremia plays a corresponding role with respect to the development of alkalosis.

METHODS

A total of 201 artificially ventilated, critically ill patients were monitored for hypernatremic episodes. Inclusion criterion was a serum sodium concentration above 145 mmol/l.

RESULTS

In 20 patients a total of 78 periods of elevated plasma sodium levels lasting at least 24 h were observed. In 86% of these cases sodium and chloride concentrations were simultaneously increased. The development of alkalosis correlated with the strong ion difference (r=0.80, p<0.01) but not with the serum sodium concentration (r=-0.031, p=0.78). In cases without accompanying hyperchloremia (13%) metabolic alkalosis regularly occurred and a correlation between serum sodium concentration and base excess could be verified (r=0.66, p=0.03). Alkalosis occurred in 84.8% of cases where the strong on difference exceeded 39 mmol/l.

CONCLUSION

From the available data hypernatremic alkalosis could not be defined as an independent metabolic disorder. In would seem more appropriate to use the term "strong ion alkalosis" in this context.

Traditional resuscitative practices fail to resolve metabolic acidosis in morbidly obese patients after severe blunt trauma

BACKGROUND

Obesity is a risk factor for postinjury complications; in particular, obese patients develop multiple organ failure (MOF) at a greater rate than do normal weight counterparts. Evaluation of differences in resuscitative practices altered by body mass index (BMI) might provide an explanation for the increased risk of MOF seen in these high-risk patients.

METHODS

We used prospectively collected multicenter data to retrospectively compare patients grouped by BMI with regard to resuscitation volumes and traditional end points during the first 48 hours after injury. Marshall MOF score was used as the primary outcome measure.

RESULTS

One thousand sixty-six patients were analyzed, with 877 meeting inclusion and exclusion criteria. All patients received similar volumes of resuscitation per kilogram lean and ideal body weight. Morbidly obese patients attained greater central venous pressures but otherwise differed little in attainment of standard cardiovascular end points. Despite this, morbidly obese patients resolved base deficit more slowly and remained in metabolic acidosis for 48 hours postinjury. Morbidly obese patients with persistent metabolic acidosis developed MOF at a significantly greater rate than did normal weight patients with or without persistent metabolic acidosis.

CONCLUSIONS

Morbidly obese trauma patients show prolonged metabolic acidosis despite receiving similar volumes and attaining similar end points of resuscitation when compared with patients in other BMI groups. Inadequate resuscitation based on inaccurate end points and metabolic disturbances associated with increased BMI are likely responsible; identification of the etiology, sources, and consequences of this acidosis may provide further insight into the susceptibility of the morbidly obese patient to develop postinjury organ failure.

Perioperative crystalloid and colloid fluid management in children: where are we and how did we get here?

It has been more than 50 yr since the landmark article in which Holliday and Segar (Pediatrics 1957;19:823-32) proposed the rate and composition of parenteral maintenance fluids for hospitalized children. Much of our practice of fluid administration in the perioperative period is based on this article. The glucose, electrolyte, and intravascular volume requirements of the pediatric surgical patient may be quite different than the original population described, and consequently, use of traditional hypotonic fluids proposed by Holliday and Segar may cause complications, such as hyperglycemia and hyponatremia, in the postoperative surgical patient. There is significant controversy regarding the choice of isotonic versus hypotonic fluids in the postoperative period. We discuss the origins of perioperative fluid management in children, review the current options for crystalloid fluid management, and present information on colloid use in pediatric patients.

The importance of intraoperative hyperchloremia

BACKGROUND AND OBJECTIVES

Hyperchloremia associated with acidosis is associated with worse patient evolution if it is not properly diagnosed and treated. The objective of this study was to determine the intraoperative importance of hyperchloremia.

METHODS

This is a 5-month prospective study. Patients 18 years or older undergoing surgical procedures and admitted to the intensive care unit postoperatively. Terminal patients, diabetics, and with chronic renal failure were excluded. Patients were divided in two groups: CH (hyperchloremia) and SH (without hyperchloremia). Hyperchloremia was determined by analysis of the ROC (Receiver Operating Characteristic) curve, i.e., the point of greater sensitivity and specificity for death was chosen as the limit to differentiate hyperchloremia from normochloremia.

RESULTS

Three hundred and ninety-three patients participated in the study. Serum levels of chloride were 111.9 +/- 6.7 mEq.L-1, pH 7.31 +/- 0.09, and base excess -5.6 +/- 4.6 mmol.L-1. The area under the ROC curve of chloride levels was 0.76 with a cutting point of 114 mEq.L-1, sensitivity = 85.7%, and specificity = 70.1%. The CH group, with chloride levels of 114 mEq.L-1 or more was formed by 31.7% of the patients. Mortality was higher in the CH group than in SH, 19.3% versus 7.4%, p = 0.001, as well as the incidence f metabolic acidosis, pH 7.27 (0.08) versus 7.32 (0.09), p = 0.001, base excess -7.9 (3.8) mmol.L-1 versus -4.2 (4.6) mmol.L-1, p < 0.001, length of surgery 4.5 (1.8) h versus 3.6 (1.9) h, p = 0.001, and volume of intraoperative crystalloid administration, 4,250 (2,500 - 6,000) mL versus 3,000 (2,000 - 5,000) mL, p = 0.002. Other differences between both groups were not observed.

CONCLUSIONS

The incidence of hyperchloremia at the end of surgery is elevated, and it is associated with metabolic acidosis, longer surgeries, greater volumes of crystalloids, and higher postoperative mortality.

Epidemiology of infection in critically ill patients with acute renal failure

OBJECTIVES

Critically ill patients with infection are at increased risk for developing acute renal failure (ARF), and ARF is associated with an increased risk for infection. Both conditions are associated with prolonged length of stay (LOS) and worse outcome; however, little data exist on the epidemiology of infection in this specific cohort. Therefore, we investigated the occurrence of infection in a cohort of critically ill patients with ARF treated with renal replacement therapy (RRT). In addition, we assessed whether this infection worsened outcome.

DESIGN

Retrospective cohort study.

SETTING

General intensive care unit (ICU) in an academic tertiary care center comprising a 22-bed surgical ICU, eight-bed cardiac surgery ICU, 14-bed medical ICU, and six-bed burn center.

PATIENTS

Six hundred forty-seven consecutive critically ill patients with ARF treated with RRT, admitted between 2000 and 2004.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

total of 519 (80.2%), 193 (29.8%), 66 (10.2%), and ten (1.5%) patients developed one, two, three, and four episodes of infection, respectively. Of 788 episodes of infection observed, 364 (46.2%) occurred before, 318 (40.3%) during, and 106 (13.4%) after discontinuation of RRT. Pneumonia (54.3%) was most frequent, followed by intra-abdominal (11.9%) and urinary tract infections (9.7%). Infections were caused by Gram-negative organisms in 33.7%, Gram-positive organisms in 21.6%, and yeasts in 9.8%. Patients with infection had higher mortality (p = 0.04) and longer ICU and hospital LOS. They needed more vasoactive therapy and spent more time on mechanical ventilation and RRT (all p < 0.001) than patients without infection. After adjustment for potential confounders, Acute Physiology and Chronic Health Evaluation II score, age, mechanical ventilation, and vasoactive therapy were associated with worse outcome, but infection was not.

CONCLUSIONS

Infection occurred in four fifths of critically ill patients with ARF treated with RRT and was in an unadjusted analysis associated with longer LOS and higher mortality. After correction for other covariates, infection was no longer associated with in-hospital mortality.

High versus standard-volume haemofiltration in hyperdynamic porcine peritonitis: effects beyond haemodynamics?

OBJECTIVE

The role of haemofiltration as an adjunctive treatment of sepsis remains a contentious issue. To address the role of dose and to explore the biological effects of haemofiltration we compared the effects of standard and high-volume haemofiltration (HVHF) in a peritonitis-induced model of porcine septic shock.

DESIGN AND SETTING

Randomized, controlled experimental study.

SUBJECTS

Twenty-one anesthetized and mechanically ventilated pigs.

INTERVENTIONS

After 12 h of hyperdynamic peritonitis, animals were randomized to receive either supportive treatment (Control, n = 7) or standard haemofiltration (HF 35 ml/kg per h, n = 7) or HVHF (100 ml/kg per hour, n = 7).

MEASUREMENTS AND RESULTS

Systemic and hepatosplanchnic haemodynamics, oxygen exchange, energy metabolism (lactate/pyruvate, ketone body ratios), ileal and renal cortex microcirculation and systemic inflammation (TNF-alpha, IL-6), nitrosative/oxidative stress (TBARS, nitrates, GSH/GSSG) and endothelial/coagulation dysfunction (von Willebrand factor, asymmetric dimethylarginine, platelet count) were assessed before, 12, 18, and 22 h of peritonitis. Although fewer haemofiltration-treated animals required noradrenaline support (86, 43 and 29% animals in the control, HF and HVHF groups, respectively), neither of haemofiltration doses reversed hyperdynamic circulation, lung dysfunction and ameliorated alterations in gut and kidney microvascular perfusion. Both HF and HVHF failed to attenuate sepsis-induced alterations in surrogate markers of cellular energetics, nitrosative/oxidative stress, endothelial injury or systemic inflammation.

CONCLUSIONS

In this porcine model of septic shock early HVHF proved superior in preventing the development of septic hypotension. However, neither of haemofiltration doses was capable of reversing the progressive disturbances in microvascular, metabolic, endothelial and lung function, at least within the timeframe of the study and severity of the model.

Alteration of anion gap and strong ion difference caused by hydroxyethyl starch 6% (130/0.42) and gelatin 4% in children

BACKGROUND

Synthetic colloid administration is a common practice for preventing perioperative hypovolemia and consecutive circulatory failure in children. This prospective, randomized study was conducted to investigate the effects of two different unbalanced synthetic colloid solutions on acid-base equilibrium in children.

METHODS

Fifty pediatric patients (aged 0-12 years) scheduled for major pediatric surgery were randomized to receive either 10 ml x kg(-1) of 6% hydroxyethyl starch solution 130/0.42 (HES) or 4% modified fluid gelatin (GEL) to maintain adequate systemic hemodynamics. Before and after colloid administration, a blood sample was collected to analyze hemoglobin, hematocrit, electrolytes, and acid-base parameters. The anion gap and the strong ion difference (SID) were calculated using standard formulas.

RESULTS

Both HES and GEL administration caused a significant increase in plasma chloride concentration (P < 0.01) and an accompanying decrease in SID (P < 0.01). In the HES group, the anion gap decreased significantly (P < 0.01) whereas the anion gap remained stable in the GEL group. In both groups, initial actual base excess and pH did not change significantly after colloid administration.

CONCLUSIONS

Moderate intraoperative plasma replacement with unbalanced synthetic colloids HES and GEL leads to a decrease in SID and, in the case of HES, to a significant decrease in the anion gap in children. These alterations may result in a possible misinterpretation when the anion gap and SID are used for differential diagnosis of metabolic disturbances during major pediatric surgery.

Comparison of acid-base models for prediction of hospital mortality after trauma

This study determines whether mortality after major trauma is predicted by the strong ion gap (SIG) and whether recent refinements in the calculation of SIG improve its predictive value. The design was an observational, retrospective review of trauma patients admitted on a single service at a level 1 facility. The setting was an urban level 1 trauma facility. An unselected cohort of patients sustaining blunt and/or penetrating injury requiring intensive care unit care was chosen. There were no interventions. Age, injury mechanism, survival, arterial blood gases, hemoglobin, albumin, electrolytes, lactate, standard base deficit, strong ion difference (SID), buffer base, and SIG were analyzed. Patients were grouped into survivors and nonsurvivors according to in-hospital survival truncated to 28 days. Multivariate logistic regression was used for further analysis of univariate predictors of mortality, and receiver-operator characteristic curves were generated for mortality. Both nonsurvivors (n = 26) and survivors (n = 52) were similar with respect to age (31.9 +/- 11.5 vs. 33.5 +/- 11.6 years) and injury mechanism (blunt 61% vs. 58%) Nonsurvivors were more likely to have multicavity injury (54% vs. 26%; P < 0.01) than survivors. Nonsurvivor and survivor pH (7.36 +/- 0.15 vs. 7.38 +/- 0.09), HCO3(-) (20.4 +/- 3.9 vs. 21.7 +/- 2.5 mEq/L; P = 0.11), albumin (3.6 +/- 0.7 vs. 3.5 +/- 0.5 gm/dL), lactate (2.9 +/- 2.5 vs. 2.3 +/- 1.3 mmol/L; P = 0.24), and phosphate (3.1 +/- 0.9 vs. 3.4 +/- 0.8 mEq/L; P = 0.26) were similar. Forty-two percent of nonsurvivors had normal lactate levels, whereas 33% of survivors had lactic acidosis. However, the apparent SID (41.0 +/- 4.2 vs. 36.7 +/- 5.5 mEq/L; P < 0.001), effective SID (32.7 +/- 4.2 vs. 35.4 +/- 4.9 mEq/L; P = 0.019), and SIG (8.3 +/- 4.4 vs. 1.3 +/- 3.6 mEq/L; P < 0.001) were all significantly different between nonsurvivors and survivors. Only one (2%) survivor had an SIG greater than 5 mEq/L, and only two (7%) nonsurvivors had an SIG less than 5 mEq/L. Admission pH, HCO3-, and lactate were poor predictors of hospital mortality after trauma. An elevated SIG presaged mortality after injury and should be assessed on admission.

Buffer capacity of 4% succinylated gelatin does not provide any advantages over acidic 6% hydroxyethyl starch 130/0.4 for acid-base balance during experimental mixed acidaemia in a porcine model

BACKGROUND AND OBJECTIVE

Four percent gelatine is an alkaline compound due to NH2 groups, whereas 6% hydroxyethyl starch 130/0.4 (HES130) has acidic features. We investigated whether these solutions lead to differences in acid-base balance in pigs during acidaemia and correction of pH.

METHODS

Anaesthetized pigs were randomized to HES130 or gelatine infusion (n = 5 per group). Animals received acid infusion (0.4 M solution of lactic acid and HCl diluted in normal saline) and low tidal volume ventilation (6-7 mL kg(-1), PaCO2 of 80-85 mmHg, pH 7.19-7.24). Measurements were made before and after induction of acidaemia, before and after correction of pH with haemofiltration (continuous venovenous haemofiltration) and tris-hydroxymethylaminomethane infusion. We measured parameters describing acid-base balance according to Stewart's approach, ketone body formation, oxygen delivery, haemodynamics, diuresis and urinary pH.

RESULTS

Acid-base balance did not differ significantly between the groups. In HES130-treated pigs, the haemodilution-based drop of haemoglobin (1.4 +/- 1.0 g dL(-1), median +/- SD) was paralleled by an increase in the cardiac output (0.5 +/- 0.4 L min(-1). Lacking increases in cardiac output, gelatine-treated pigs demonstrated a reduction in oxygen delivery (149.4 +/- 106.0 mL min(-1)). Tris-hydroxymethylaminomethane volumes required for pH titration to desired values were significantly higher in the gelatine group (0.7 +/- 0.1 mL kg(-1) h(-1) vs. HES130: 0.5 +/- 0.2 mL kg(-1) h(-1)).

CONCLUSION

The buffer capacity of gelatine did not lead to favourable differences in acid-base balance in comparison to HES130.

Disorders of acid-base balance

BACKGROUND

Intensivists spend much of their time managing problems related to fluids, electrolytes, and blood pH. Recent advances in the understanding of acid-base physiology have resulted from the application of basic physical-chemical principles of aqueous solutions to blood plasma. All changes in blood pH, in health and in disease, occur through changes in three variables: carbon dioxide, relative electrolyte concentrations, and total weak acid concentrations. However, while this quantitative approach has enjoyed widespread use among researchers, clinicians are reluctant to employ it. Recent advances have brought a measure of parity between the newer and the older, descriptive approach to acid-base physiology.

DATA SYNTHESIS

Case-based review of the literature.

CONCLUSION

Both quantitative and traditional approaches can be easily combined to result in a powerful tool for bedside acid-base analysis.

Effects of hypercapnia on BP in hypoalbuminemic and Nagase analbuminemic rats

STUDY OBJECTIVE

To determine if animals with abnormally low albumin levels are more susceptible to the effects of hypercapnia on BP compared to normal animals.

DESIGN

Prospective, controlled laboratory experiment.

SETTING

University research laboratory.

ANIMALS

Eighteen male Sprague-Dawley rats: 6 rats 10 to 12 weeks old (young Sprague-Dawley [YSD]), 6 rats 6 to 9 months old (old Sprague-Dawley [OSD]), and 6 rats 10 to 12 weeks old (Nagase analbuminemic mutant Sprague-Dawley [NAR]).

METHODS

Under general anesthesia and paralysis, we varied the Paco(2) by changing the respiratory rate on mechanical ventilation. Mean arterial pressure (MAP) was monitored in a continuous fashion. We obtained arterial blood for blood gas and electrolyte analysis, and nitric oxide (NO) production.

RESULTS

OSD rats had reduced serum albumin, while NAR rats were analbuminemic. Although NAR animals had a decreased buffer capacity compared to age-matched control animals (0.010 vs 0.013, p < 0.05), the MAP decreased in an identical fashion in all three groups. NO production increased with hypercapnia but was similar in all three groups. However, NAR rats had consistently higher plasma strong ion gap (2.8 to 4.1 mEq/L greater) compared to either YSD or OSD rats (p < 0.01), and baseline strong ion difference (mean +/- SD) was significantly lower in NAR rats (28.7 +/- 2.1 mEq/L) compared to either YSD rats (33.0 +/- 5.1 mEq/L) or OSD rats (31.2 +/- 5.1 mEq/L) [p < 0.05].

CONCLUSIONS

These findings suggest that analbuminemic or hypoalbuminemic rats are not more susceptible to hypercapnia-induced hemodynamic instability. Baseline values for apparent strong ion difference are lower in NA rats consistent with a reduced buffer base resulting from analbuminemia.

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.

Qu'apporte le modèle de Stewart à l'interprétation des troubles de l'équilibre acide–base?

OBJECTIVES

To explain the different approaches for interpreting acid-base disorders; to develop the Stewart model which offers some advantages for the pathophysiological understanding and the clinical interpretation of acid-base imbalances.

DATA SOURCE

Record of french and english references from Medline data base. The keywords were: acid-base balance, hyperchloremic acidosis, metabolic acidosis, strong ion difference, strong ion gap.

DATA EXTRACTION

Data were selected including prospective and retrospective studies, reviews, and case reports.

DATA SYNTHESIS

Acid-base disorders are commonly analysed by using the traditional Henderson-Hasselbalch approach which attributes the variations in plasma pH to the modifications in plasma bicarbonates or PaCO2. However, this approach seems to be inadequate because bicarbonates and PaCO2 are completely dependent. Moreover, it does not consider the role of weak acids such as albuminate, in the determination of plasma pH value. According to the Stewart concept, plasma pH results from the degree of plasma water dissociation which is determined by 3 independent variables: 1) strong ion difference (SID) which is the difference between all the strong plasma cations and anions; 2) quantity of plasma weak acids; 3) PaCO2. Thus, metabolic acid-base disorders are always induced by a variation in SID (decreased in acidosis) or in weak acids (increased in acidosis), whereas respiratory disorders remains the consequence of a change in PaCO2. These pathophysiological considerations are important to analyse complex acid-base imbalances in critically ill patients. For example, due to a decrease in weak acids, hypoalbuminemia increases SID which may counter-balance a decrease in pH and an elevated anion gap. Thus if using only traditional tools, hypoalbuminemia may mask a metabolic acidosis, because of a normal pH and a normal anion gap. In this case, the association of metabolic acidosis and alkalosis is only expressed by respectively a decreased SID and a decreased weak acids concentration. This concept allows to establish the relationship between hyperchloremic acidosis and infusion of solutes which contain large concentration of chloride such as NaCl 0.9%. Finally, the Stewart concept permits to understand that sodium bicarbonate as well as sodium lactate induces plasma alkalinization. In fact, sodium remains in plasma, whereas anion (lactate or bicarbonate) are metabolized leading to an increase in plasma SID.

CONCLUSION

Due to its simplicity, the traditional Henderson-Hasselbalch approach of acid-base disorders, remains commonly used. However, it gives an inadequate pathophysiological analysis which may conduct to a false diagnosis, especially with complex acid-base imbalances. Despite its apparent complexity, the Stewart concept permits to understand precisely the mechanisms of acid-base disorders. It has to become the most appropriate approach to analyse complex acid-base abnormalities.

A total balanced volume replacement strategy using a new balanced hydoxyethyl starch preparation (6% HES 130/0.42) in patients undergoing major abdominal surgery

BACKGROUND AND OBJECTIVE

The kind of fluid for correcting hypovolaemia is still a focus of debate. In a prospective, randomized, controlled and double-blind study in patients undergoing major abdominal surgery, a total balanced volume replacement strategy including a new balanced hydroxyethyl starch (HES) solution was compared with a conventional, non-balanced fluid regimen.

METHODS

In Group A (n = 15), a new balanced 6% HES 130/0.42 was given along with a balanced crystalloid solution; in Group B (n = 15), an unbalanced conventional HES 130/0.42 plus an unbalanced crystalloid (saline solution) were administered. Volume was given when mean arterial pressure (MAP) was <65 mmHg and central venous pressure (CVP) minus positive end-expiratoric pressure (PEEP) level was <10 mmHg. Haemodynamics, acid-base status, coagulation (thrombelastography (TEG)) and kidney function (including kidney-specific proteins, N-acetyl-beta-d-glucosaminidase (beta-NAG) and alpha-1-microglobulin) were measured after induction of anaesthesia, at the end of surgery, 5 and 24 h after surgery.

RESULTS

Group A received 3533 +/- 1302 mL of HES and 5333 +/- 1063 mL of crystalloids, in Group B, 3866 +/- 1674 mL of HES and 5966 +/- 1202 mL of crystalloids were given. Haemodynamics, laboratory data, TEG data and kidney function were without significant differences between the groups. Cl- concentration and base excess (-5 +/- 2.4 mmol L-1 vs. 0.4 +/- 2.4 mmol L-1) were significantly higher in patients of Group B than of Group A.

CONCLUSIONS

A complete balanced volume replacement strategy including a new balanced HES preparation resulted in significantly less derangement in acid-base status compared with a non-balanced volume replacement regimen. The new HES preparation showed no negative effects on coagulation and kidney function.

Lactate versus non-lactate metabolic acidosis: a retrospective outcome evaluation of critically ill patients

Introduction

Acid–base abnormalities are common in the intensive care unit (ICU). Differences in outcome exist between respiratory and metabolic acidosis in similar pH ranges. Some forms of metabolic acidosis (for example, lactate) seem to have worse outcomes than others (for example, chloride). The relative incidence of each type of disorder is unknown. We therefore designed this study to determine the nature and clinical significance of metabolic acidosis in critically ill patients.

Methods

An observational, cohort study of critically ill patients was performed in a tertiary care hospital. Critically ill patients were selected on the clinical suspicion of the presence of lactic acidosis. The inpatient mortality of the entire group was 14%, with a length of stay in hospital of 12 days and a length of stay in the ICU of 5.8 days.

Results

We reviewed records of 9,799 patients admitted to the ICUs at our institution between 1 January 2001 and 30 June 2002. We selected a cohort in which clinicians caring for patients ordered a measurement of arterial lactate level. We excluded patients in which any necessary variable required to characterize an acid–base disorder was absent. A total of 851 patients (9% of ICU admissions) met our criteria. Of these, 548 patients (64%) had a metabolic acidosis (standard base excess < -2 mEq/l) and these patients had a 45% mortality, compared with 25% for those with no metabolic acidosis (p < 0.001). We then subclassified metabolic acidosis cases on the basis of the predominant anion present (lactate, chloride, or all other anions). The mortality rate was highest for lactic acidosis (56%); for strong ion gap (SIG) acidosis it was 39% and for hyperchloremic acidosis 29% (p < 0.001). A stepwise logistic regression model identified serum lactate, SIG, phosphate, and age as independent predictors of mortality.

Conclusion

In critically ill patients in which a measurement of lactate level was ordered, lactate and SIG were strong independent predictors of mortality when they were the major source of metabolic acidosis. Overall, patients with metabolic acidosis were nearly twice as likely to die as patients without metabolic acidosis.

Hyperchloremic Acidosis Increases Circulating Inflammatory Molecules in Experimental Sepsis

RATIONALE

Hyperchloremic acidosis is common in the critically ill and is often iatrogenic. We have previously shown that hyperchloremic acidosis increases nuclear factor-kappaB DNA binding in lipopolysaccharide-stimulated RAW 264.7 cells. However, evidence that hyperchloremic acidosis leads to increased inflammation in vivo has been limited to nitric oxide.

OBJECTIVES

To determine if acidosis, induced by dilute hydrochloric acid (HCl) infusion, will increase circulating inflammatory mediator levels in an experimental model of severe sepsis in rats.

METHODS

Eighteen hours after inducing lethal sepsis by cecal ligation and puncture in 20 adult, male, Sprague-Dawley rats, we randomized animals into three groups. In groups 2 and 3, we began an IV infusion of 0.1 N HCl to reduce the standard base excess (SBE) by 5 to 10 mEq/L and 10 to 15 mEq/L, respectively. In group 1, we infused a similar volume of lactated Ringer solution. In all groups infusion continued 8 h or until the animal died.

MEASUREMENTS AND MAIN RESULTS

We measured arterial blood gases, whole-blood lactate, and chloride, tumor necrosis factor (TNF), interleukin (IL)-6, and IL-10 levels at 0 h, 4 h, and 8 h. All measured cytokines increased over time. Compared to group 1, animals in groups 2 and 3 exhibited greater increase in all three cytokines, with the greatest increases seen with severe acidosis.

CONCLUSION

Moderate (SBE, - 5 to - 10) and severe (SBE, - 10 to - 15) acidosis, induced by HCl infusion, increases circulating levels of IL-6, IL-10, and TNF in normotensive septic rats.

Year in review 2005: Critical Care - resource management

During 2005 Critical Care published several original papers dealing with resource management. Emphasis was placed on sepsis, especially the coagulation cascade, prognosis and resuscitation. The papers highlighted important aspects of the pathophysiology of coagulation and inflammation in sepsis, as well as dealing with the proper use of newly developed compounds. Several aspects of prognosis in critically ill patients were investigated, focusing on biological markers and clinical indexes. Resuscitation received great attention, dealing with the effects of fluid infusion in hemodynamics and the lung. The information obtained can be used to address unknown effects of established therapies, to enlighten current clinical discussion on controversial topics, and to introduce novel medical resources and strategies. Future clinical work will rely heavily on these preclinical and laboratory data.

Monitoring skeletal muscle and subcutaneous tissue acid-base status and oxygenation during hemorrhagic shock and resuscitation

Gastric tonometry correlates with the severity of blood loss during shock. However, tonometry is cumbersome, has a slow response time, and is not practical to apply in the acute resuscitation setting. We hypothesized that subcutaneous tissue (SC) and skeletal muscle (SM) pH, pCO2, and pO2 changes are comparable with changes seen in bowel tonometry during shock and resuscitation. Thirteen male mini-swine (25-35 kg; n = 4 control, n = 9 shock) underwent laparotomy and jejunal tonometry. A multisensor probe (Diametrics Medical, Roseville, MN) was placed in the carotid artery, the chest SC, and the adductor muscle of the leg (SM). PaCO2 was maintained between 40 and 45 mmHg. Shocked animals were hemorrhaged and kept at mean arterial pressure of 40 mmHg. Animals were bled until a reinfusion of >10% of the total shed blood was needed to maintain the mean arterial pressure at 40 mmHg. Animals were resuscitated with shed blood plus 2x shed volume in lactated Ringer's solution (20 min) and were observed for 3 h. The average blood loss was 47.2% +/- 8.7% of calculated blood volume. During the hemorrhagic phase, SM and SC displayed tissue acidosis (r2 = 0.951), tissue hypercapnea (r2 = 0.931), and tissue hypoxia (r2 = 0.748). Overall, pH displayed the best correlation between SM and SC during shock and resuscitation. PCO2 in the jejunum (tonometry), SM, and SC increased during decompensation. However, during resuscitation as tonometric pCO2 normalized, only SC pCO2 decreased to its baseline value, whereas the SM pCO2 decrease tended to lag behind. Bland-Altman analyses demonstrated that the variability of the tissue pH changes in SM and SC are predictable according to the phases of hemorrhage and resuscitation. Changes in tissue pH correlated during bleeding and during resuscitation among SC and SM, and these changes followed the trends in gut tonometry as well. Continuous pCO2 and pO2 monitoring in the SM and SC tissues had significant correlations during the induction of shock only. SM and SC continuous pH and pCO2 monitoring reflect bowel pCO2 values during hemorrhagic shock. The response of these indicators as potential surrogates of impaired tissue metabolism varies among tissues and according to the phases of hemorrhage or resuscitation.

Cardiovascular dysfunction caused by cecal ligation and puncture is attenuated in CD8 knockout mice treated with anti-asialoGM1

The present study was designed to assess hemodynamics and myocardial function at 18 h after injury caused by cecal ligation and puncture (CLP) in CD8-knockout mice treated with anti-asialoGM1 (CD8KO/alphaAsGM1 mice). Arterial pressure was measured by carotid artery cannulation, and left ventricular pressure-volume measurements were obtained by use of a 1.4-Fr conductance catheter. Blood acid-base balance and indexes of hepatic, renal, and pulmonary injury were also measured. CD8KO/alphaAsGM1 mice exhibited higher mean arterial pressure and increased systemic vascular resistance compared with wild-type mice. Cardiac output was significantly decreased in wild-type, but not CD8KO/alphaAsGM1, mice compared with sham controls. Myocardial function was better preserved in CD8KO/alphaAsGM1 mice as indicated by less impairment of left ventricular pressure development over time, time varying maximum elastance, end-systolic pressure-volume relationship, and preload recruitable stroke work. The impairment in myocardial function was associated with induction of proinflammatory cytokine mRNAs in the hearts of wild-type mice. The hemodynamic derangements in wild-type mice were coupled with significant metabolic acidosis and elevated serum creatinine levels. Overall, this study shows that cardiovascular collapse and shock characterized by hypotension, myocardial depression, low systemic vascular resistance, and metabolic acidosis occurs after CLP in wild-type mice but is attenuated in CD8KO/alphaAsGM1 mice. These observations likely explain, in part, the previously observed survival advantage of CD8KO/alphaAsGM1 mice following CLP.

Physiologic Consequences of Acute Renal Failure on the Critically Ill

Acute renal failure (ACF) causes increased levels of uremic retention products, acidosis, and volume overload. These factors contribute to a dysregulated inflammatory response and decreased immunity, and interfere with normal function of many organs. ACF may play an important role in the etiology of multiple organ dysfunction.

Determinants of Plasma Acid-Base Balance

An advanced understanding of acid-base physiology is central to the practice of critical care medicine. Intensivists spend much of their time managing problems that are related to fluids, electrolytes, and blood pH. Recent advances in the understanding of acid-base physiology occurred as the result of the application of basic physical-chemical principles of aqueous solutions to blood plasma. This analysis revealed three independent variables that regulate pH in blood plasma: carbon dioxide, relative electrolyte concentrations, and total weak acid concentrations. All changes in blood pH, in health and in disease, occur through changes in these three variables. This article reviews the physical-chemical approach to acid-base balance and considers clinical implications for these findings.

Effect of hypertonic saline dextran on acid-base balance in patients undergoing surgery of abdominal aortic aneurysm*

OBJECTIVE

To evaluate the magnitude and cause of metabolic acidosis after infusion of 7.5% sodium chloride 6% dextran 70.

DESIGN

Randomized, prospective clinical study.

SETTING

University hospital.

PATIENTS

Two groups of 14 patients each, undergoing repair of abdominal aortic aneurysm.

INTERVENTIONS

Patients were randomly assigned to receive either 250 mL of hypertonic saline dextran (HSD) or a conventional fluid regimen with 250 mL of hydroxyethyl starch in normal saline solution (H-NS) during the period of aortic clamping. Additionally, normal saline was used in both groups to reach a target pulmonary artery occlusion pressure of 15-18 mmHg. pH, Paco2, and serum concentrations of sodium, potassium, magnesium, calcium, chloride, lactate, albumin, and phosphate were measured. Strong ion difference was calculated as (sodium + potassium + magnesium + calcium) - (chloride + lactate). The amount of weak plasma acid was calculated.

MEASUREMENTS AND MAIN RESULTS

The infusion of HSD resulted in an immediate large increase in serum sodium (19 mmol/L) and chloride (22 mmol/L), whereas the infusion of H-NS led only to mild increases in serum sodium (3 mmol/L) and chloride (6 mmol/L). Both HSD and H-NS caused concomitant and equal decreases in the amount of weak plasma acid, strong ion difference, and pH (7.28-7.30). The reduction of bicarbonate was also identical and proportional to the extent of dilution due to infusion of HSD and H-NS. This induced metabolic acidosis was corrected spontaneously in both groups 24 hrs after surgery.

CONCLUSION

Both the intravenous administration of 7.5% sodium chloride and the conventional fluid regimen with saline-based 6% hydroxyethyl starch solution resulted in a metabolic acidosis of equal extent. This suggests dilution of plasma buffers or a decrease in strong ion difference to be the primary cause of metabolic acidosis.

Regulatory and functional interaction of vasoactive factors in the kidney and extracellular pH

A growing body of evidence suggests that vasoactive factors produced in the kidney such as nitric oxide, endothelins, angiotensin, and prostaglandins participate actively in the regulation of acid-base homeostasis under physiologic conditions. In addition, recent reports indicate that alterations in the systemic acid-base status may also influence the generation of vasoactive cytokines in the kidney, which in turn may mediate the renal effector processes that tend to restore normality under such conditions. Metabolic acidosis, which so frequently accompanies many forms of chronic renal failure (CRF), may contribute to down-regulation of intrarenal nitric oxide production that characterizes CRF. Reduced extracellular pH inhibits inducible nitric oxide production in mesangial cells by altering the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) oxidation, an important posttranslational mechanism in the inducible nitric oxide synthase (iNOS) activation. The underlying defects resulting in the uncoupling of NADPH oxidation in acidemic microenvironment are discussed. Acidosis stimulates renal production of endothelins, which mediate proximal tubular acidification by enhancing sodium-hydrogen exchanger-3 (NHE-3) activity. Renal endothelins mediate enhanced urinary acid excretion following dietary acid ingestion, an effect that is effectively blocked by endothelin receptor blockers. Reduced extracellular pH stimulates endothelin secretion from renal microvascular endothelial cells, which may promote enhanced acid excretion from the distal tubule under conditions of acidosis. These phenomena as well as the role of angiotensin and renal prostaglandins in mediating renal acidification in normal and acidotic conditions are discussed in this review, which describe the regulatory interaction between extracellular pH and renal vasoactive factors.

Science review: extracellular acidosis and the immune response: clinical and physiologic implications

Metabolic acidosis is among the most common abnormalities seen in patients suffering from critical illness. Its etiologies are multiple and treatment of the underlying condition is the mainstay of therapy. However, growing evidence suggests that acidosis itself has profound effects on the host, particularly in the area of immune function. Given the central importance of immune function to the outcome of critical illness, there is renewed interest in elucidating the effects of this all too common condition on the immune response. In this review we concentrate on the effects of extracellular acids on production and release of inflammatory mediators, and we demonstrate that different acids produce different effects despite similar extracellular pH. Finally, we discuss potential clinical implications.

Bench-to-bedside review: treating acid-base abnormalities in the intensive care unit - the role of buffers

The recognition and management of acid-base disorders is a commonplace activity for intensivists. Despite the frequency with which non-bicarbonate-losing forms of metabolic acidosis such as lactic acidosis occurs in critically ill patients, treatment is controversial. This article describes the properties of several buffering agents and reviews the evidence for their clinical efficacy. The evidence supporting and refuting attempts to correct arterial pH through the administration of currently available buffers is presented.