[Hyperchloremic acidosis druing plasma volume replacement]

Balanced versus chloride-rich solutions for fluid resuscitation in brain-injured patients: a randomised double-blind pilot study

INTRODUCTION

We sought to investigate whether the use of balanced solutions reduces the incidence of hyperchloraemic acidosis without increasing the risk for intracranial hypertension in patients with severe brain injury.

METHODS

We conducted a single-centre, two-arm, randomised, double-blind, pilot controlled trial in Nantes, France. Patients with severe traumatic brain injury (Glasgow Coma Scale score ≤8) or subarachnoid haemorrhage (World Federation of Neurosurgical Society grade III or higher) who were mechanically ventilated were randomised within the first 12 hours after brain injury to receive either isotonic balanced solutions (crystalloid and hydroxyethyl starch; balanced group) or isotonic sodium chloride solutions (crystalloid and hydroxyethyl starch; saline group) for 48 hours. The primary endpoint was the occurrence of hyperchloraemic metabolic acidosis within 48 hours.

RESULTS

Forty-two patients were included, of whom one patient in each group was excluded (one consent withdrawn and one use of forbidden therapy). Nineteen patients (95%) in the saline group and thirteen (65%) in the balanced group presented with hyperchloraemic acidosis within the first 48 hours (hazard ratio = 0.28, 95% confidence interval [CI] = 0.11 to 0.70; P = 0.006). In the saline group, pH (P = .004) and strong ion deficit (P = 0.047) were lower and chloraemia was higher (P = 0.002) than in the balanced group. Intracranial pressure was not different between the study groups (mean difference 4 mmHg [-1;8]; P = 0.088). Seven patients (35%) in the saline group and eight (40%) in the balanced group developed intracranial hypertension (P = 0.744). Three patients (14%) in the saline group and five (25%) in the balanced group died (P = 0.387).

CONCLUSIONS

This study provides evidence that balanced solutions reduce the incidence of hyperchloraemic acidosis in brain-injured patients compared to saline solutions. Even if the study was not powered sufficiently for this endpoint, intracranial pressure did not appear different between groups.

TRIAL REGISTRATION

EudraCT 2008-004153-15 and NCT00847977.

[The damage control resuscitation concept]

OBJECTIVE

Damage control is a strategy of care for bleeding trauma patients, involving minimal rescue surgery associated to perioperative resuscitation. The purpose of this review is to draw up a statement on current knowledge available on damage control.

DATA SOURCES

References were obtained from recent review articles, personal files, and Medline database research of English and French publications. All categories of articles on this topic have been selected.

DATA SYNTHESIS

Historical damage control surgery, that consist of abbreviated laparotomy with second-look after resuscitation, is now included in a wider concept called "damage control resuscitation", addressing the lethal triad (coagulopathy, hypothermia and acidosis) at an early phase. Care is focused on coagulopathy prevention. Early resuscitation, or damage control ground zero, has been improved: aggressive management of hypothermia, bleeding control techniques, permissive hypotension concept and early use of vasopressors. Transfusion practices also have evolved: early platelets and coagulation factors administration, use of hemostatic agents like recombinant FVIIa, whole blood transfusion, denote the damage control hematology. Progress in surgical practices and development of arteriographic techniques lead to wider indications of damage control strategy.

Concentration-Dependent Effect of Hypocalcaemia on Mortality of Patients with Critical Bleeding Requiring Massive Transfusion: A Cohort Study

Mortality of patients with critical bleeding requiring massive transfusion is high. Although hypothermia, acidosis and coagulopathy have been well described as important determinants of mortality in patients with critical bleeding requiring massive transfusion, the risk factors and outcome associated with hypocalcaemia in these patients remain uncertain. This cohort study assessed the relationship between the lowest ionised calcium concentration during the 24-hour period of critical bleeding and the hospital mortality of 352 consecutive patients, while adjusting for diagnosis, acidosis, coagulation results, transfusion requirements and use of recombinant factor VIIa. Hypocalcaemia was common (mean concentrations 0.77 mmol/l, SD 0.19) and had a linear, concentration-dependent relationship with mortality (odds ratio [OR] 1.25 per 0.1 mmol/l decrement, 95% confidence interval [CI]: 1.04 to 1.52; P=0.02). Hypocalcaemia accounted for 12.5% of the variability and was more important than the lowest fibrinogen concentrations (10.8%), acidosis (7.9%) and lowest platelet counts (7.7%) in predicting hospital mortality. The amount of fresh frozen plasma transfused (OR 1.09 per unit, 95% CI: 1.02 to 1.17; P=0.02) and acidosis (OR 1.45 per 0.1 decrement, 95% CI: 1.19 to 1.72; P=0.01) were associated with the occurrence of severe hypocalcaemia (<0.8 mmol/l). In conclusion, ionised calcium concentrations had an inverse concentration-dependent relationship with mortality of patients with critical bleeding requiring massive transfusion. Both acidosis and the amount of fresh frozen plasma transfused were the main risk factors for severe hypocalcaemia. Further research is needed to determine whether preventing ionised hypocalcaemia can reduce mortality of patients with critical bleeding requiring massive transfusion.

[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.

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.

Comparison of lactated Ringer's solution and a physiologically balanced 6% hetastarch plasma expander for the treatment of hypotension induced via blood withdrawal in isoflurane-anesthetized dogs

OBJECTIVE

To compare the effects of lactated Ringer's solution (LRS) with those of a physiologically balanced 6% hetastarch plasma expander administered to isoflurane-anesthetized dogs with hypotension induced by blood withdrawal.

ANIMALS

12 healthy Beagles.

PROCEDURE

Blood was withdrawn from isoflurane-anesthetized dogs (volume withdrawn measured) to a systolic arterial blood pressure (SAP) of 80 mm Hg. Six dogs each received either LRS or hetastarch solution (90 mL/kg/h, i.v.). Hemodynamic variables, pH, blood gas concentrations, PCV, serum electrolyte and total protein concentrations, and colloid osmotic pressure (COP) were determined at baseline, while SAP was 80 mm Hg, and after fluid treatment. The volume of fluid administered and rate of return of SAP to within 10% of baseline values were recorded.

RESULTS

Mean +/- SD volume of blood withdrawn to decrease SAP to 80 mm Hg was 173 +/- 38 mL. Hemodynamic variables decreased after blood withdrawal but returned to baseline values more rapidly after infusion of a smaller volume of hetastarch solution, compared with the response to LRS infusion. Whereas PCV and serum total protein concentration decreased after administration of either solution, COP decreased only after administration of LRS. The total volume of hetastarch solution and LRS required to restore and maintain SAP to within 10% of baseline values was 1.1 +/- 0.9 and 4.4 +/- 1.7 times greater than the volume of blood removed, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with LRS infusion, smaller volumes of hetastarch solution normalized and maintained SAP without lowering COP in isoflurane-anesthetized dogs after blood withdrawal.