Excessive use of normal saline in managing traumatized patients in shock: a preventable contributor to acidosis

Crystalloid Solutions in Hospital: A Review of Existing Literature

Intravenous fluids (IVF) like normal saline (NS) and Ringer's lactate (RL) are often crucial in the management of hospitalized patients. Mishandling these fluids can lead to complications in about 20% of patients receiving them. In this review, we present the current evidence through the identification of observational studies and randomized trials that observed the optimal use of IVF. We found that NS may cause hyperchloremic metabolic acidosis in surgical patients, but there is no clear difference in mortality and long-term outcomes between NS and balanced crystalloids. Critically ill patients, particularly those in sepsis, benefit from balanced crystalloids, as high chloride content fluids like NS increase the risk of complications and mortality. In pancreatitis, NS has been shown to increase the risk of ICU admission when compared to RL; however, there is no significant difference in long-term outcomes and mortality between the fluids. RL is preferred for burns due to its isotonicity and lack of protein, preventing edema formation in an already dehydrated state. Plasma-lyte may resolve diabetic ketoacidosis faster, while prolonged NS use can lead to metabolic acidosis, acute kidney injury, and cerebral edema. In conclusion, NS, RL, and plasma-lyte are the most commonly used isotonic IVF in the hospital population. Incorrect choice of fluids in a different clinical scenario can lead to worse outcomes.

Balanced Salt Solutions for Critically Ill Patients: Nonplused and Back to Basics

OBJECTIVES

The purpose of this article is to summarize the results of major randomized controlled trials (RCTs) comparing clinical outcomes of critically ill patients treated with normal saline (NS) or balanced salt solutions (BSSs), address discordant results of these studies, and provide direction for future investigations.

DATA SOURCES

PubMed (2011 to January 2022) with bibliographies of retrieved articles searched for additional articles.

STUDY SELECTION AND DATA EXTRACTION

RCTs comparing NS and BSSs in critically ill adult patients.

DATA SYNTHESIS

Recently published large RCTs comparing NS with BSSs in heterogeneous populations of intensive care unit patients did not find significant differences in mortality, despite positive findings in some end points in prior RCTs. However, there were a number of methodologic issues common to the RCTs including: varying study designs and end points, clinician discretion for the majority or all treatments other than the primary intervention fluid, heterogeneous patients with varying levels of acuity, and lack of power to investigate potential subgroup differences. In addition, there were problematic issues related to blinding and use of nonstudy fluids.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Intravenous fluids are a mainstay of supportive care for critically ill patients. Similar to the so-called crystalloid-colloid debate, there has been a long-standing debate among critical care clinicians and researchers concerning the preferred crystalloid solution, NS versus one of the available BSSs.

CONCLUSIONS

Despite the recent publication of large multicenter RCTs, the preferred resuscitation fluid, NS or a BSS, for critically ill patients is still open for debate, although the available investigations do provide some direction for clinicians and for future investigations.

Influence of acetate- vs. lactate-containing fluid bolus therapy on acid-base status, electrolytes, and plasma lactate in dogs

Objective

Acetate- and lactate-containing fluids influence the acid-base and electrolyte status. This prospective, randomized, clinical study compared two balanced crystalloid solutions regarding their influence on acid-base status, electrolytes, and lactate values, when given to dogs as a resuscitation bolus of 30 mL/kg.

Material and methods

One hundred client-owned dogs presenting to the emergency service with signs of fluid deficits were randomly assigned to receive an intravenous bolus of 30 mL/kg of either a lactate- (LAC), or an acetate-containing solution (ACET). Before and after the bolus, vital parameters were assessed, and a venous blood gas analysis was performed.

Results

Both solutions performed equally well in decreasing the heart rate (ACET: −10 ± 27 bpm, LAC: −12 ± 30 bpm; p = 0.737). The acetate-containing solution caused a significant decrease in plasma lactate levels (p = 0.016), anion gap (p < 0.001), and potassium (p < 0.001), and a significant increase in chloride (p < 0.001), and ionized calcium (p = 0.014). The lactate-containing solution caused a significant decrease in anion gap (p < 0.001), sodium (p = 0.016), and potassium (p = 0.001), and a significant increase in chloride (p < 0.001). ACET causes a stronger decrease in plasma lactate (p = 0.015), sodium (p = 0.039), potassium (p = 0.006), and an increase in chloride (p < 0.001), and ionized calcium (p = 0.016) compared to LAC.

Conclusion

Both solutions caused mild changes in electrolyte concentrations and had minor influence on acid-base status when used for bolus therapy in dogs with fluid deficits. Further studies are needed to evaluate their influence on acid-base status, lactate, and electrolytes when used in larger volumes and for a longer time span.

Mismatch between Tissue Partial Oxygen Pressure and Near-Infrared Spectroscopy Neuromonitoring of Tissue Respiration in Acute Brain Trauma: The Rationale for Implementing a Multimodal Monitoring Strategy

The brain tissue partial oxygen pressure (PbtO₂) and near-infrared spectroscopy (NIRS) neuromonitoring are frequently compared in the management of acute moderate and severe traumatic brain injury patients; however, the relationship between their respective output parameters flows from the complex pathogenesis of tissue respiration after brain trauma. NIRS neuromonitoring overcomes certain limitations related to the heterogeneity of the pathology across the brain that cannot be adequately addressed by local-sample invasive neuromonitoring (e.g., PbtO₂ neuromonitoring, microdialysis), and it allows clinicians to assess parameters that cannot otherwise be scanned. The anatomical co-registration of an NIRS signal with axial imaging (e.g., computerized tomography scan) enhances the optical signal, which can be changed by the anatomy of the lesions and the significance of the radiological assessment. These arguments led us to conclude that rather than aiming to substitute PbtO₂ with tissue saturation, multiple types of NIRS should be included via multimodal systemic- and neuro-monitoring, whose values then are incorporated into biosignatures linked to patient status and prognosis. Discussion on the abnormalities in tissue respiration due to brain trauma and how they affect the PbtO₂ and NIRS neuromonitoring is given.

Valproic acid improves survival and decreases resuscitation requirements in a swine model of prolonged damage control resuscitation

BACKGROUND

Although damage control resuscitation (DCR) is routinely performed for short durations, prolonged DCR may be required in military conflicts as a component of prolonged field care. Valproic acid (VPA) has been shown to have beneficial properties in lethal hemorrhage/trauma models. We sought to investigate whether the addition of a single dose of VPA to a 72-hour prolonged DCR protocol would improve clinical outcomes.

METHODS

Fifteen Yorkshire swine (40-45 kg) were subjected to lethal (50% estimated total blood volume) hemorrhagic shock (HS) and randomized to three groups: (1) HS, (2) HS-DCR, (3) HS-DCR-VPA (150 mg/kg over 3 hours) (n = 5/cohort). In groups assigned to receive DCR, Tactical Combat Casualty Care guidelines were applied (1 hour into the shock period), targeting a systolic blood pressure of 80 mm Hg. At 72 hours, surviving animals were given transfusion of packed red blood cells, simulating evacuation to higher echelons of care. Survival rates, physiologic parameters, resuscitative fluid requirements, and laboratory profiles were used to compare the clinical outcomes.

RESULTS

This model was 100% lethal in the untreated animals. DCR improved survival to 20%, although this was not statistically significant. The addition of VPA to DCR significantly improved survival to 80% (p < 0.01). The VPA-treated animals also had significantly (p < 0.05) higher systolic blood pressures, lower fluid resuscitation requirements, higher hemoglobin levels, and lower creatinine and potassium levels.

CONCLUSION

VPA administration improves survival, decreases resuscitation requirements, and improves hemodynamic and laboratory parameters when added to prolonged DCR in a lethal hemorrhage model.

Ringer's lactate versus normal saline in acute pancreatitis: A systematic review and meta-analysis

OBJECTIVE

Aggressive i.v. hydration with crystalloids is the first step in managing acute pancreatitis (AP) and is associated with improved survival. Guidelines about the choice of crystalloids to use are unclear. This systematic review and meta-analysis was aimed to discern whether the choice of fluids in managing pancreatitis was associated with patients' outcomes.

METHODS

A comprehensive literature review was conducted by searching the Embase, MEDLINE, PubMed and Google Scholar databases to December 2017 to identify all studies that compared normal saline (NS) with Ringer's lactate (RL) for managing AP. The characteristics of the participants, outcome measurements (including mortality, the development of systemic inflammatory response syndrome [SIRS] on admission and at 24 h, and pancreatic necrosis) were analyzed.

RESULTS

Five studies (three randomized controlled trials and two retrospective cohort studies) with 428 patients were included in this analysis. Mortality trended lower in the RL group but this was not statistically significant (pooled odds ratio [OR] 0.61, 95% CI 0.28-1.29, P = 0.20). Patients in the RL group had significantly decreased odds of developing SIRS at 24 h (pooled OR 0.38, 95% CI 0.15-0.98, P = 0.05).

CONCLUSIONS

RL has anti-inflammatory effects and is associated with decreased odds of persistent SIRS at 24 h, which is a marker of severe disease in AP patients. Although mortality trended lower in the RL group this did not achieve statistical significance and hence larger randomized controlled trials are needed to evaluate this association.

Randomized Double-blind Trial of Ringer Lactate Versus Normal Saline in Pediatric Acute Severe Diarrheal Dehydration

OBJECTIVE

The aim of this study was to compare the effectiveness of Ringer lactate (RL) versus normal saline (NS) in the correction of pediatric acute severe diarrheal dehydration, as measured by improvement in clinical status and pH (≥7.35).

METHODS

A total of 68 children ages 1 month to 12 years with acute severe diarrheal dehydration (World Health Organization [WHO] classification) were randomized into RL (n = 34) and NS groups (n = 34) and received 100 mL/kg of the assigned intravenous fluid according to WHO PLAN-C for the management of diarrheal dehydration. The primary outcome was an improvement in clinical status and pH (≥7.35) at the end of 6 hours. Secondary outcomes were changes in serum electrolytes, renal and blood gas parameters, the volume of fluid required for dehydration correction excluding the first cycle, time to start oral feeding, hospital stay, and cost-effectiveness analysis.

RESULTS

Primary outcome was achieved in 38% versus 23% (relative risk = 1.63, 95% confidence interval 0.80-3.40) in RL and NS groups, respectively. No significant differences were observed in secondary outcomes in electrolytes, renal, and blood gas parameters. None required second cycle of dehydration correction. Median (interquartile range) time to start oral feeding (1.0 [0.19-2.0] vs 1.5 [0.5-2.0] hours) and hospital stay (2.0 [1.0-2.0] vs 2.0 [2.0-2.0] days) was similar. The median total cost was higher in RL than NS group ((Equation is included in full-text article.)120 [(Equation is included in full-text article.)120-(Equation is included in full-text article.)180] vs (Equation is included in full-text article.)55 [(Equation is included in full-text article.)55-(Equation is included in full-text article.)82], P ≤ 0.001).

CONCLUSION

In pediatric acute severe diarrheal dehydration, resuscitation with RL and NS was associated with similar clinical improvement and biochemical resolution. Hence, NS is to be considered as the fluid of choice because of the clinical improvement, cost, and availability.

0.9% saline is neither normal nor physiological

The purpose of this review is to objectively evaluate the biochemical and pathophysiological properties of 0.9% saline (henceforth: saline) and to discuss the impact of saline infusion, specifically on systemic acid-base balance and renal hemodynamics. Studies have shown that electrolyte balance, including effects of saline infusion on serum electrolytes, is often poorly understood among practicing physicians and inappropriate saline prescribing can cause increased morbidity and mortality. Large-volume (>2 L) saline infusion in healthy adults induces hyperchloremia which is associated with metabolic acidosis, hyperkalemia, and negative protein balance. Saline overload (80 ml/kg) in rodents can cause intestinal edema and contractile dysfunction associated with activation of sodium-proton exchanger (NHE) and decrease in myosin light chain phosphorylation. Saline infusion can also adversely affect renal hemodynamics. Microperfusion experiments and real-time imaging studies have demonstrated a reduction in renal perfusion and an expansion in kidney volume, compromising O2 delivery to the renal parenchyma following saline infusion. Clinically, saline infusion for patients post abdominal and cardiovascular surgery is associated with a greater number of adverse effects including more frequent blood product transfusion and bicarbonate therapy, reduced gastric blood flow, delayed recovery of gut function, impaired cardiac contractility in response to inotropes, prolonged hospital stay, and possibly increased mortality. In critically ill patients, saline infusion, compared to balanced fluid infusions, increases the occurrence of acute kidney injury. In summary, saline is a highly acidic fluid. With the exception of saline infusion for patients with hypochloremic metabolic alkalosis and volume depletion due to vomiting or upper gastrointestinal suction, indiscriminate use, especially for acutely ill patients, may cause unnecessary complications and should be avoided. More education regarding saline-related effects and adequate electrolyte management is needed.

0.9% saline induced hyperchloremic acidosis

In the acute care setting, the type and amount of fluid administered has a significant impact on patient outcomes. In particular, 0.9% saline infusions are known to cause or exacerbate hyperchloremia. The studies presented evaluate possible complications from 0.9% saline infusions. These studies compared administration of 0.9% saline with lactated ringer or plasmalyte in the acute care setting. In each trial, the patients who were randomized to receive 0.9% saline infusions had a more severe acidosis from increased serum chloride levels. From the available data, chloride-restrictive intravenous fluid such as plasmalyte appears to reduce acid-base disturbances and improve patient outcomes.

Acid-base and hemodynamic status of patients with intraoperative hemorrhage using two solution types: Crystalloid Ringer lactate and 1.3% sodium bicarbonate in half-normal saline solution

Background:

Intraoperative hemorrhage is one of the problems during surgery and, if it happens in a high volume without an immediate action to control, it can be fatal. Nowadays, various injectable solutions are used. The aim of this study was to compare the acid–base and hemodynamic status of the patient using two solutions, Ringer lactate and 1.3% sodium bicarbonate, in half saline solution.

Materials and Methods:

This clinical trial was performed at the Al-Zahra Hospital in 2013 on 66 patients who were randomly selected and put in two studied groups at the onset of hemorrhage. For the first group, crystalloid Ringer lactate solution and for the second group, 1.3% sodium bicarbonate in half-normal saline solution was used. Electrocardiogram, heart rate, O2 saturation non-invasive blood pressure and end-tidal CO2 were monitored. The arterial blood gas, blood electrolytes, glucose and blood urea nitrogen were measured before serum and blood injection. After the infusion of solutions and before blood transfusions, another sample was sent for measurement of blood parameters. Data were analyzed using SPSS software.

Results:

The mean arterial pressure was significantly higher in the second group than in the first group at some times after the infusion of solutions. pHh levels, base excess, bicarbonate, sodium, strong ion differences and osmolarity were significantly greater and potassium and chloride were significantly lower in the second group than in the first group after the infusion of solutions.

Conclusion:

1.3% sodium bicarbonate in half-normal saline solution can lead to a proper correction of hemodynamic instability. By maintaining hemodynamic status, osmolarity and electrolytes as well as better balance of acid–base, 1.3% sodium bicarbonate solution in half-normal saline solution can be more effective than Ringer lactate solution during intraoperative bleeding.

Pharmacokinetics of centhaquin citrate in a rat model

OBJECTIVE

Centhaquin citrate is a novel agent being developed for use in the treatment of haemorrhagic shock. It has decreased mortality in rat, rabbit and pig models of hypovolaemic shock compared to hypertonic saline and lactated Ringer's resuscitation. The pharmacokinetics of centhaquin citrate have not been described to date.

METHODS

Sixteen male Sprague Dawley rats were given an intravenous bolus of 0.45 mg/kg centhaquin citrate. Rats were divided into two groups; plasma concentrations were measured at five time points for each group within 24 h after administration. Competing compartmental pharmacokinetic models were assessed. The nonparametric adaptive grid function within the Pmetrics package for R was used for parameter estimation. Predicted concentrations were calculated using population median and individual Bayesian posterior parameters.

KEY FINDINGS

A two-compartment model of centhaquin citrate best fit the data. Median (IQR) values for elimination coefficient (Ke), volume of distribution (V) and intercompartmental transfer rates (Kcp, Kpc) were 8.8 (5.2-12.8) h(-1), 6.4 (2.8-10.4) l, 11.9 (4.6-15.0) h(-1) and 3.7 (2.3-9.1) h(-1), respectively.

CONCLUSION

This is the first report of the pharmacokinetic parameters of centhaquin citrate in a rat model. Centhaquin citrate was found to have a short half-life with a large volume of distribution.

Impact of intravenous fluid composition on outcomes in patients with systemic inflammatory response syndrome

Introduction

Intravenous (IV) fluids may be associated with complications not often attributed to fluid type. Fluids with high chloride concentrations such as 0.9 % saline have been associated with adverse outcomes in surgery and critical care. Understanding the association between fluid type and outcomes in general hospitalized patients may inform selection of fluid type in clinical practice. We sought to determine if the type of IV fluid administered to patients with systemic inflammatory response syndrome (SIRS) is associated with outcome.

Methods

This was a propensity-matched cohort study in hospitalized patients receiving at least 500 mL IV crystalloid within 48 hours of SIRS. Patient data was extracted from a large multi-hospital electronic health record database between January 1, 2009, and March 31, 2013. The primary outcome was in-hospital mortality. Secondary outcomes included length of stay, readmission, and complications measured by ICD-9 coding and clinical definitions. Outcomes were adjusted for illness severity using the Acute Physiology Score. Of the 91,069 patients meeting inclusion criteria, 89,363 (98 %) received 0.9 % saline whereas 1706 (2 %) received a calcium-free balanced solution as the primary fluid.

Results

There were 3116 well-matched patients, 1558 in each cohort. In comparison with the calcium-free balanced cohort, the saline cohort experienced greater in-hospital mortality (3.27 % vs. 1.03 %, P <0.001), length of stay (4.87 vs. 4.38 days, P = 0.016), frequency of readmission at 60 (13.54 vs. 10.91, P = 0.025) and 90 days (16.56 vs. 12.58, P = 0.002) and frequency of cardiac, infectious, and coagulopathy complications (all P <0.002). Outcomes were defined by administrative coding and clinically were internally consistent. Patients in the saline cohort received more chloride and had electrolyte abnormalities requiring replacement more frequently (P <0.001). No differences were found in acute renal failure.

Conclusions

In this large electronic health record, the predominant use of 0.9 % saline in patients with SIRS was associated with significantly greater morbidity and mortality compared with predominant use of balanced fluids. The signal is consistent with that reported previously in perioperative and critical care patients. Given the large population of hospitalized patients receiving IV fluids, these differences may confer treatment implications and warrant corroboration via large clinical trials.

Trial registration

NCT02083198 clinicaltrials.gov; March 5, 2014

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1045-z) contains supplementary material, which is available to authorized users.

Meta-analysis of high- versus low-chloride content in perioperative and critical care fluid resuscitation

Background

The objective of this systematic review and meta-analysis was to assess the relationship between the chloride content of intravenous resuscitation fluids and patient outcomes in the perioperative or intensive care setting.

Methods

Systematic searches were performed of PubMed/MEDLINE, Embase and Cochrane Library (CENTRAL) databases in accordance with PRISMA guidelines. Randomized clinical trials, controlled clinical trials and observational studies were included if they compared outcomes in acutely ill or surgical patients receiving either high-chloride (ion concentration greater than 111 mmol/l up to and including 154 mmol/l) or lower-chloride (concentration 111 mmol/l or less) crystalloids for resuscitation. Endpoints examined were mortality, measures of kidney function, serum chloride, hyperchloraemia/metabolic acidosis, blood transfusion volume, mechanical ventilation time, and length of hospital and intensive care unit stay. Risk ratios (RRs), mean differences (MDs) or standardized mean differences (SMDs) and confidence intervals were calculated using fixed-effect modelling.

Results

The search identified 21 studies involving 6253 patients. High-chloride fluids did not affect mortality but were associated with a significantly higher risk of acute kidney injury (RR 1·64, 95 per cent c.i. 1·27 to 2·13; P < 0·001) and hyperchloraemia/metabolic acidosis (RR 2·87, 1·95 to 4·21; P < 0·001). High-chloride fluids were also associated with greater serum chloride (MD 3·70 (95 per cent c.i. 3·36 to 4·04) mmol/l; P < 0·001), blood transfusion volume (SMD 0·35, 0·07 to 0·63; P = 0·014) and mechanical ventilation time (SMD 0·15, 0·08 to 0·23; P < 0·001). Sensitivity analyses excluding heavily weighted studies resulted in non-statistically significant effects for acute kidney injury and mechanical ventilation time.

Conclusion

A weak but significant association between higher chloride content fluids and unfavourable outcomes was found, but mortality was unaffected by chloride content.

Should chloride-rich crystalloids remain the mainstay of fluid resuscitation to prevent 'pre-renal' acute kidney injury?: con

The high chloride content of 0.9% saline leads to adverse pathophysiological effects in both animals and healthy human volunteers, changes not seen after balanced crystalloids. Small randomized trials confirm that the hyperchloremic acidosis induced by saline also occurs in patients, but no clinical outcome benefit was demonstrable when compared with balanced crystalloids, perhaps due to a type II error. A strong signal is emerging from recent large propensity-matched and cohort studies for the adverse effects that 0.9% saline has on the clinical outcome in surgical and critically ill patients when compared with balanced crystalloids. Major complications are the increased incidence of acute kidney injury and the need for renal replacement therapy, and that pathological hyperchloremia may increase postoperative mortality. However, there are no large-scale randomized trials comparing 0.9% saline with balanced crystalloids. Some balanced crystalloids are hypo-osmolar and may not be suitable for neurosurgical patients because of their propensity to cause brain edema. Saline may be the solution of choice used for the resuscitation of patients with alkalosis and hypochloremia. Nevertheless, there is evidence to suggest that balanced crystalloids cause less detriment to renal function than 0.9% saline, with perhaps better clinical outcome. Hence, we argue that chloride-rich crystalloids such as 0.9% saline should be replaced with balanced crystalloids as the mainstay of fluid resuscitation to prevent ‘pre-renal' acute kidney injury.

Dose and type of crystalloid fluid therapy in adult hospitalized patients

OBJECTIVE

In this narrative review, an overview is given of the pros and cons of various crystalloid fluids used for infusion during initial resuscitation or maintenance phases in adult hospitalized patients. Special emphasis is given on dose, composition of fluids, presence of buffers (in balanced solutions) and electrolytes, according to recent literature. We also review the use of hypertonic solutions.

METHODS

We extracted relevant clinical literature in English specifically examining patient-oriented outcomes related to fluid volume and type.

RESULTS

A restrictive fluid therapy prevents complications seen with liberal, large-volume therapy, even though restrictive fluid loading with crystalloids may not demonstrate large hemodynamic effects in surgical or septic patients. Hypertonic solutions may serve the purpose of small volume resuscitation but carry the disadvantage of hypernatremia. Hypotonic solutions are contraindicated in (impending) cerebral edema, whereas hypertonic solutions are probably more helpful in ameliorating than in preventing this condition and improving outcome. Balanced solutions offer a better approach for plasma composition than unbalanced ones, and the evidence for benefits in patient morbidity and mortality is increasing, particularly by helping to prevent acute kidney injury.

CONCLUSIONS

Isotonic and hypertonic crystalloid fluids are the fluids of choice for resuscitation from hypovolemia and shock. The evidence that balanced solutions are superior to unbalanced ones is increasing. Hypertonic saline is effective in mannitol-refractory intracranial hypertension, whereas hypotonic solutions are contraindicated in this condition.

A physicochemical model of crystalloid infusion on acid-base status

The objective of this study is to develop a physicochemical model of the projected change in standard base excess (SBE) consequent to the infused volume of crystalloid solutions in common use. A clinical simulation of modeled acid-base and fluid compartment parameters was conducted in a 70-kg test participant at standard physiologic state: pH =7.40, partial pressure of carbon dioxide (PCO2) = 40 mm Hg, Henderson-Hasselbalch actual bicarbonate ([HCO3]HH) = 24.5 mEq/L, strong ion difference (SID) = 38.9 mEq/L, albumin = 4.40 g/dL, inorganic phosphate = 1.16 mmol/L, citrate total = 0.135 mmol/L, and SBE =0.1 mEq/L. Simulations of multiple, sequential crystalloid infusions up to 10 L were conducted of normal saline (SID = 0), lactated Ringer's (SID = 28), plasmalyte 148 (SID = 50), one-half normal saline þ 75 mEq/L sodium bicarbonate (NaHCO3; SID = 75), 0.15 mol/L NaHCO3 (SID = 150), and a hypothetical crystalloid solution whose SID = 24.5 mEq/L, respectively. Simulations were based on theoretical completion of steady-state equilibrium and PCO2 was fixed at 40 mm Hg to assess nonrespiratory acid-base effects. A crystalloid SID equivalent to standard state actual bicarbonate (24.5 mEq/L) results in a neutral metabolic acid-base status for infusions up to 10 L. The 5 study solutions exhibited curvilinear relationships between SBE and crystalloid infusion volume in liters. Solutions whose SID was greater than 24.5 mEq/L demonstrated a progressive metabolic alkalosis and less, a progressive metabolic acidosis. In a human model system, the effects of crystalloid infusion on SBE are a function of the crystalloid and plasma SID, volume infused, and nonvolatile plasma weak acid changes. A projection of the impact of a unit volume of various isotonic crystalloid solutions on SBE is presented. The model's validation, applications, and limitations are examined.

Early chloride intake does not parallel that of sodium in extremely-low-birth-weight infants and may impair neonatal outcomes

BACKGROUND AND OBJECTIVE

Accurate data on the optimal chloride (Cl) intake in premature infants are scarce. The aim of the present study was to describe Cl intakes in the first 10 days of life and to assess the relations between high Cl intakes and corrected serum Cl level or markers of severe acidosis in infants <28 weeks' gestation.

METHODS

Retrospective cohort study including all of the infants <28 weeks admitted to the neonatal intensive care unit during a 3-year period and cared for from birth until day 10 or more.

RESULTS

Fifty-six infants were included. Cumulative total Cl intakes reached 9.6 ± 3.7 mmol/kg at day 3 and 49.2 ± 13.5 mmol/kg at day 10. Inadvertent intakes (from intravenous fluids other than parenteral nutrition) represented on average 70% of total Cl intakes in the first 3 days. Difference between Cl and sodium intakes reached 7.8 ± 4.8 mmol/kg at day 10 and mainly originated from parenteral nutrition. By multivariate analysis, cumulative Cl intake >10 mmol/kg during the first 3 days was an independent risk factor of base excess <-10 mmol/L. Cumulative Cl intake >45 mmol/kg during the first 10 days was an independent risk factor of corrected chloremia >115 mmol/L and of base excess <-10 mmol/L.

CONCLUSIONS

Cumulative Cl intake >10 mmol/kg during the first 3 days (ie, 3.3 mmol · kg (-1) · day(-1) on average) and >45 mmol/kg during the first 10 days (ie, 4.5 mmol · kg (-1) · day(-1) on average) may have unwanted metabolic consequences and should be avoided. Imbalance between electrolytes provided by the parenteral nutrition solution need to be detected and corrected.

Impact of Plasma-Lyte pH 7.4 on acid-base status and hemodynamics in a model of controlled hemorrhagic shock

OBJECTIVE

Intravenous infusion of crystalloid solutions is a cornerstone of the treatment of hemorrhagic shock. However, crystalloid solutions can have variable metabolic acid-base effects, perpetuating or even aggravating shock-induced metabolic acidosis. The aim of this study was to compare, in a controlled volume-driven porcine model of hemorrhagic shock, the effects of three different crystalloid solutions on the hemodynamics and acid-base balance.

METHODS

Controlled hemorrhagic shock (40% of the total blood volume was removed) was induced in 18 animals, which were then treated with normal saline (0.9% NaCl), Lactated Ringer's Solution or Plasma-Lyte pH 7.4, in a blinded fashion (n = 6 for each group). Using a predefined protocol, the animals received three times the volume of blood removed.

RESULTS

The three different crystalloid infusions were equally capable of reversing the hemorrhage-induced low cardiac output and anuria. The Lactated Ringer's Solution and Plasma-Lyte pH 7.4 infusions resulted in an increased standard base excess and a decreased serum chloride level, whereas treatment with normal saline resulted in a decreased standard base excess and an increased serum chloride level. The Plasma-Lyte pH 7.4 infusions did not change the level of the unmeasured anions.

CONCLUSION

Although the three tested crystalloid solutions were equally able to attenuate the hemodynamic and tissue perfusion disturbances, only the normal saline induced hyperchloremia and metabolic acidosis.

Damage control in trauma and abdominal sepsis

Damage control surgery, initially formalized <20 yrs ago, was developed to overcome the poor outcomes in exsanguinating abdominal trauma with traditional surgical approaches. The core concepts for damage control of hemorrhage and contamination control with abbreviated laparotomy followed by resuscitation before definitive repair, although simple in nature, have led to an alteration in which emergent surgery is handled among a multitude of problems, including abdominal sepsis and battlefield surgery. With the aggressive resuscitation associated with damage control surgery, understanding of abdominal compartment syndrome has expanded. It is probably through avoiding this clinical entity that the greatest improvement in surgical outcomes for various emergent surgical problems has occurred in the past two decades. However, with its success, new problems have emerged, including increases in enterocutaneous fistulas and open abdomens. But as with any crisis, innovative strategies are being developed. New approaches to control of the open abdomen and reconstruction of the abdominal wall are being developed from negative pressure dressing therapies to acellular allograft meshes. With further understanding of new resuscitative strategies, the need for damage control surgery may decline, along with its concomitant complications, at the same time retaining the success that damage control surgery has brought to the critically ill trauma and general surgery patient in the past few years.

Renal and cardiorespiratory effects of treatment with lactated Ringer's solution or physiologic saline (0.9% NaCl) solution in cats with experimentally induced urethral obstruction

OBJECTIVE

To compare the renal and cardiorespiratory effects of IV treatment with lactated Ringer's solution (LRS) or physiologic saline (0.9% NaCl) solution (PSS) in severely decompensated cats with urethral obstruction (UO).

ANIMALS

14 cats (4 cats were used only to establish infusion rates).

PROCEDURES

An occluded urethral catheter was used to induce UO in each cat. After development of severe metabolic acidosis, hyperkalemia, and postrenal azotemia, the obstruction was relieved (0 hours); LRS or PSS (5 cats/group) was administered IV (gradually decreasing rate) beginning 15 minutes before and continuing for 48 hours after UO relief. Ten minutes before urethral catheter placement (baseline), at start of fluid therapy (SFT), and at intervals during fluid administration, various physical and clinicopathologic evaluations were performed.

RESULTS

Metabolic acidosis was detected in the PSS-treated group at SFT and 2 hours after relief of UO and in the LRS-treated group only at SFT The PSS-treated group had significantly lower blood pH and bicarbonate concentrations at 8 through 48 hours and lower base excess values at 2 through 48 hours, compared with the LRS-treated group. Hypocalcemia and hypernatremia were detected in the PSS-treated group at 2 and 12 hours, respectively. Absolute serum potassium and chloride concentrations did not differ significantly between groups at any time point.

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment with LRS or PSS appeared to be safe and effective in cats with experimentally induced UO; however, LRS was more efficient in restoring the acid-base and electrolyte balance in severely decompensated cats with UO.

Recognition and management of major vessel injury during laparoscopy

Laparoscopy is one of the most commonly performed procedures in the United States. Injury to a major retroperitoneal vessel occurs in 0.3% to 1.0% of procedures, most commonly during laparoscopic entry while placing the Veress needle or primary trocar. Fatal outcome can be related to massive gas embolism or exsanguination. Recommended treatment for gas embolism can range from supportive measures to external chest compression and insertion of a central line to withdraw gas from the right side of the heart. Recommended treatment of major vessel injury with massive hemorrhage consists of rapid laparotomy and control of hemorrhage using direct pressure until a surgeon experienced in vascular procedures arrives. When a major vessel injury occurs in a surgical facility distant from a medical center and without an available surgeon with vascular experience, based on the trauma literature, we recommend temporary control of blood loss using abdominal packing and closure (i.e., "damage control surgery") and judicious resuscitation (i.e., "damage control resuscitation") before transportation to a medical center.

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.

Reproducibility of an animal model simulating complex combat-related injury in a multiple-institution format

We developed a complex combat-relevant model of abdominal and extremity trauma, hemorrhagic shock, hypothermia, and acidosis. We then simulated injury, preoperative, and operative phases. We hypothesized that this model is reproducible and useful for randomized multicenter preclinical trials. Yorkshire swine were anesthetized, intubated, and instrumented. They then underwent femur fracture, 60% total blood volume hemorrhage, a 30-min shock period, induced hypothermia to 33 degrees C, and hemorrhage volume replacement with 3:1 isotonic sodium chloride solution (NS) at each of three centers. Hemodynamic parameters were measured continuously. Thromboelastography, arterial blood gas, and laboratory values were collected at baseline, after the shock period, and after NS replacement. Thirty-seven animals were used for model development. Eight (21%) died before completion of the study period. Twenty-nine survivors were included in the analysis. MAP (+/-SEM) after the shock period was 32 +/- 2 mmHg and was similar between centers (P = 0.4). Mean pH, base deficit, and lactate levels were 7.29 +/- 0.02, 8.20 +/- 0.65 mmol/L, and 5.29 +/- 0.44 mmol/L, respectively, after NS replacement. These were similar between centers (P > 0.05). Prothrombin time values increased significantly over time at all centers, reflecting a progressive coagulopathy (P < 0.02). Thromboelastography maximum amplitude values were similar among centers (P > 0.05) and demonstrated progressively weakened platelet interaction over time (P < 0.03). Hematocrit was similar after controlled hemorrhage (P = 0.15) and dilution (P = 0.9). The pH, lactate, base deficit, and coagulation tests reflect a severely injured state. A complex porcine model of polytrauma and shock can be used for multi-institutional study with excellent reproducibility. A consistent severe injury profile was achieved, after which experimental interventions can be applied. This is the first report of a reproducible multicenter trauma and resuscitation-related animal model.

Comparison of lactated Ringer's solution and 0.9% saline in the treatment of rhabdomyolysis induced by doxylamine intoxication

OBJECTIVE

To compare the effectiveness and side effects of lactated Ringer's solution (LR) and 0.9% saline (NS) in the treatment of rhabdomyolysis induced by doxylamine intoxication.

METHODS

In this 15-month-long prospective randomised single-blind study, after excluding 8 patients among 97 doxylamine-intoxicated patients, 28 (31%) patients were found to have developed rhabdomyolysis and were randomly allocated to NS group (n = 15) or LR group (n = 13).

RESULTS

After 12 h of aggressive hydration (400 ml/h), urine/serum pH was found to be significantly higher in the LR group, and serum Na+/Cl- levels to be significantly higher in the NS group. There were no significant differences in serum K+ level and in the time taken for creatine kinase normalisation. The amount of sodium bicarbonate administered and the frequency administration of diuretics was significantly higher in the NS group. Unlike the NS group, the LR group needed little supplemental sodium bicarbonate and did not develop metabolic acidosis.

CONCLUSION

LR is more useful than NS in the treatment of rhabdomyolysis induced by doxylamine intoxication.

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.

Fluid, electrolytes and nutrition: physiological and clinical aspects

Fluid and electrolyte balance is often poorly understood and inappropriate prescribing can cause increased post-operative morbidity and mortality. The efficiency of the physiological response to a salt or water deficit, developed through evolution, contrasts with the relatively inefficient mechanism for dealing with salt excess. Saline has a Na+:Cl-of 1:1 and can produce hyperchloraemic acidosis, renal vasoconstriction and reduced glomerular filtration rate. In contrast, the more physiological Hartmann's solution with a Na+:Cl-of 1·18:1 does not cause hyperchloraemia and Na excretion following infusion is more rapid. Salt and water overload causes not only peripheral and pulmonary oedema, but may also produce splanchnic oedema, resulting in ileus or acute intestinal failure. This overload may sometimes be an inevitable consequence of resuscitation, yet it may take 3 weeks to excrete this excess. It is important to avoid unnecessary additional overload by not prescribing excessive maintenance fluids after the need for resuscitation has passed. Most patients require 2–2·5 litres water and 60–100?mmol?Na\d for maintenance in order to prevent a positive fluid balance. This requirement must not be confused with those for resuscitation of the hypovolaemic patient in whom the main aim of fluid therapy is repletion of the intravascular volume. Fluid and electrolyte balance is a vital component of the metabolic care of surgical and critically-ill patients, with important consequences for gastrointestinal function and hence nutrition. It is also of importance when prescribing artificial nutrition and should be given the same careful consideration as other nutritional and pharmacological needs.

How perioperative fluid balance influences postoperative outcomes

Fasting, anaesthesia and surgery affect the body's physiological capacity not only to control its external fluid and electrolyte balance but also the internal balance between the various body fluid compartments. Conversely, abnormalities of fluid and electrolyte balance may adversely affect organ function and surgical outcome. Perioperative fluid therapy has a direct bearing on outcome, and prescriptions should be tailored to the needs of the patient. The goal of fluid therapy in the elective setting is to maintain the effective circulatory volume while avoiding interstitial fluid overload whenever possible. Weight gain in elective surgical patients should be minimized in an attempt to achieve a 'zero fluid balance status'. On the other hand, these patients should arrive in the anaesthetic room in a state of normal fluid and electrolyte balance so as to avoid the need to resuscitate fluid-depleted patients in the anaesthetic room or after the induction of anaesthesia. Optimal fluid delivery should be part of an overall care package that involves minimization of the period of preoperative fasting, preoperative carbohydrate loading, thoracic epidural analgesia, avoidance of nasogastric tubes, early mobilization, and early return to oral feeding, as exemplified by the enhanced recovery after surgery programme.

The cellular, metabolic, and systemic consequences of aggressive fluid resuscitation strategies

Increasing evidence has demonstrated that aggressive crystalloid-based resuscitation strategies are associated with cardiac and pulmonary complications, gastrointestinal dysmotility, coagulation disturbances, and immunological and inflammatory mediator dysfunction. As large volumes of fluids are administered, imbalances in intracellular and extracellular osmolarity occur. Disturbances in cell volume disrupt numerous regulatory mechanisms responsible for keeping the inflammatory cascade under control. Several authors have demonstrated the detrimental effects of large, crystalloid-based resuscitation strategies on pulmonary complications in specific surgical populations. Additionally, fluid-restrictive strategies have been associated with a decreased frequency of and shorter time to recovery from acute respiratory distress syndrome and trends toward shorter lengths of stay and lower mortality. Early resuscitation of hemorrhagic shock with predominately saline-based regimens has been associated with cardiac dysfunction and lower cardiac output, as well as higher mortality. Numerous investigators have evaluated potential risk factors for developing abdominal compartment syndrome and have universally noted the excessive use of crystalloids as the primary determinant. Resuscitation regimens that cause early increases in blood flow and pressure may result in greater hemorrhage and mortality than those regimens that yield comparable flow and pressure increases late in resuscitation. Future resuscitation research is likely to focus on improvements in fluid composition and adjuncts to administration of large volume of fluid.

A review of emergency equipment carried and procedures performed by UK front line paramedics on paediatric patients

OBJECTIVES

In 1997 a review of paramedic practice upon adult patients in the UK found many inconsistencies and deficiencies in basic care. A follow up review in 2002 identified widespread improvement in provision of equipment and skills to provide basic and advanced life support.Paediatric care was not assessed in either review. The authors conducted this study to identify current standards of care in paediatric paramedic practice and areas of potential improvement.

METHOD

A questionnaire designed to determine what equipment and skills were available to paramedics for the management of common or serious paediatric emergencies was sent to chief executives of the 32 NHS Ambulance Trusts in England and Wales.

RESULTS

The trend of expanding and standardising practice among adult patients has not extended to paediatric practice despite national guidelines from the Joint Royal Colleges Ambulance Liaison Committee (JRCALC). Furthermore there are some serious failings in the provision of care and skills. Many Trusts have not adopted JRCALC guidelines for the management of life threatening paediatric emergencies such as asthma, meningitis, and fluid replacement in hypovolaemia.

CONCLUSIONS

Ambulance Trusts not meeting standards set out in the JRCALC guidelines must address their areas of deficiency. Failure to do so endangers children's lives and leaves Trusts open to criticism.

Serum lactate and base deficit as predictors of mortality after ruptured abdominal aortic aneurysm repair

OBJECTIVE

Whole body hypoperfusion and lower torso ischaemia-reperfusion contribute to post-operative organ dysfunction in patients undergoing repair of ruptured abdominal aortic aneurysm (AAA). Serum lactate and base deficit are markers of tissue ischaemia and are used to assess the adequacy of resuscitation. This study examines the prognostic value of immediate post-operative levels of serum lactate and base deficit in ruptured AAA.

METHODS

Thirty patients (24 men and 6 women of median age 74, range 51-85, years) who survived to at least 12h after ruptured AAA repair were studied retrospectively. The relationship between immediate post-operative lactate, base deficit and mortality was determined.

RESULTS

Fifteen patients (50%) died, all from organ failure. An elevated lactate (>2.1 mmol/l) and base deficit (<-2 mmol/l) were present in 20 (67%) and 27 (90%) patients, respectively. Lactate (p<0.001) and base deficit (p=0.003) were significantly higher in non-survivors compared with survivors. Lactate (p=0.021) and base deficit levels (p=0.028) were independently significant for predicting mortality and a significant interaction existed between lactate and base deficit levels for predicting mortality (p=0.027). The sensitivity and specificity of lactate > or =4.0 mmol/l was 13 of 15 (87%) and 12 of 15 (80%), respectively, and base deficit < or =-7 mmol/l was 12 of 15 (80%) and 12 of 15 (80%), respectively. The likelihood ratios for a positive result with the defined cut-off values for lactate and base deficit were 4.3 and 4.0, respectively. Lactate > or =4.0 mmol/l and base deficit <or =-7 mmol/l were associated with a 94.5% probability of death while lactate < or =4.0 mmol/l and base deficit > or =-7 mmol/l were associated with a 4% probability of death.

CONCLUSION

These data demonstrate that an immediate post-operative serum lactate > or =4.0 mmol/l and base deficit < or =-7 mmol/l are good predictors of outcome after ruptured AAA repair. The prognostic value of these simple and inexpensive tests require corroboration in a larger prospective study.

Are we giving enough coagulation factors during major trauma resuscitation?

Hemorrhage is a major cause of trauma deaths. Coagulopathy exacerbates hemorrhage and is commonly seen during major trauma resuscitation, suggesting that current practice of coagulation factor transfusion is inadequate. Reversal of coagulopathy involves normalization of body temperature, elimination of the causes of disseminated intravascular coagulation (DIC), and transfusion with fresh-frozen plasma (FFP), platelets, and cryoprecipitate. Transfusion should be guided by clinical factors and laboratory results. However, in major trauma, clinical signs may be obscured and various factors conspire to make it difficult to provide the best transfusion therapy. Existing empiric transfusion strategies for, and prevailing teachings on, FFP transfusion appear to be based on old studies involving elective patients transfused with whole blood and may not be applicable to trauma patients in the era of transfusion with packed red blood cells (PRBCs). Perpetuation of such concepts is in part responsible for the common finding of refractory coagulopathy in major trauma patients today. In this review, we argue that coagulopathy can best be avoided or reversed when severe trauma victims are transfused with at least the equivalent of whole blood in a timely fashion.

A review of emergency equipment carried and procedures performed by UK front line paramedics

OBJECTIVES

To assess which items of resuscitation equipment are carried on United Kingdom (UK) front line ambulances and what procedures paramedics are able to perform. To compare these findings with those of a previous survey in 1997.

METHOD

Postal survey to the chief executives of all the UK ambulance services and direct comparison with the data from 1997.

RESULTS

Nasopharyngeal airway usage (NPA) has increased (21-55%) and the laryngeal mask airway (LMA) (from 10 to 26%). No services employ the Combitube. 94% of services use a Hudson type trauma mask (increase of 17%). One service no longer allows its paramedics to deliver 12-15 l of oxygen. 68% of trust paramedics can perform needle thoracocentesis (increase of 35%). No paramedics perform chest drain insertion. All services have 14G intravenous cannulae available and 45% carry the intraosseous needle (increase of 30%). No services employ the MAST suit. There is an increase by 29% in the use of crystalloids and a decrease in the use of colloids of 22%. 23% of fluid resuscitation protocols are based upon the principles of hypotensive resuscitation. Spinal boards and extrication devices are used by 97% of services. The use of inflatable splints has decreased (38-23%). There has been a minor increase in the use of traction splints to 74% of services. The use of Entonox is universal. Nalbuphine (Nubain) is the most widely used opioid. The use of morphine/diamorphine has doubled to 10% with a further 26% to introduce their use. 29% of services have equipped some vehicles with automatic external defibrillators.

CONCLUSIONS

The equipment available to UK paramedics and procedures that they may perform continues to expand. There are still variations in the basic management of airway, breathing and circulation care and only some services are keeping up to date with current medical thinking, for example the increasing use of crystalloids and hypotensive resuscitation. It remains to be seen whether the widespread use of Nalbuphine as a first line analgesic may decrease as the use of natural strong opiates becomes more widespread.

Systemic inflammatory response secondary to abdominal compartment syndrome: stage for multiple organ failure

BACKGROUND

The abdominal compartment syndrome (ACS) has been implicated in the pathogenesis of postinjury multiple organ failure. The ACS is defined as intra-abdominal hypertension causing adverse physiologic response. This study was designed to determine the effects of IAH on the production of interleukin-1b (IL-1beta), interleukin-6 (IL-6), tumor necrosis factor (TNF-alpha), and the effects on remote organ injury.

METHODS

IAH was induced in Sprague-Dawley rats which were divided into 5 groups, 10 animals each. Intra-abdominal pressure (IAP) was increased to 20 mm Hg for 60 and 90 minutes in two different groups. In a third group following IAP of 20 mm Hg the abdomen was decompressed for 30 minutes before samples were collected. The other animals were used as controls. Hemodynamic response was monitored throughout the procedure. Cytokine levels were assessed in the plasma. Remote organ injury was assessed by histopathology and myeloperoxidase activity.

RESULTS

IAH caused a significant decrease in MAP. After abdominal decompression MAP returned to baseline levels. A significant decrease in arterial pH was also noted. Increase in the levels of TNF-alpha and IL-6 was noted 30 minutes after abdominal decompression. Plasma concentration of IL-1b was elevated after 60 minutes of IAH. Abdominal decompression, however, did not cause a significant increase in the levels of this cytokine. Lung neutrophil accumulation was significantly elevated only after abdominal decompression. Histopathological findings showed intense pulmonary inflammatory infiltration including atelectasis and alveolar edema.

CONCLUSIONS

IAH provokes the release of pro-inflammatory cytokines which may serve as a second insult for the induction of MOF.

Acute Respiratory Distress Syndrome in Blunt Trauma: Identification of Independent Risk Factors

Acute respiratory distress syndrome (ARDS) is a major contributor to morbidity and mortality in trauma patients. Although many injuries and conditions are believed to be associated with ARDS independent risk factors in trauma patients and their relative importance in development of the syndrome are undefined. The aim of this project is to identify independent risk factors for the development of ARDS in blunt trauma patients and to examine the contributions of each factor to ARDS development. Patients with ARDS were identified from the registry of a Level I trauma center over a 4.5-year period. Records were reviewed for demographics, injury characteristics, transfusion requirements, and hospital course. Variables examined included age >65 years, Injury Severity Score (ISS) >25, hypotension on admission (systolic blood pressure <90), significant metabolic acidosis (base deficit <-5.0), severe brain injury as shown by a Glasgow Coma Scale score (GCS) <8 on admission, 24-hour transfusion requirement >10 units packed red blood cells, pulmonary contusion (PC), femur fracture, and major infection (pneumonia, empyema, or intraabdominal abscess). Both univariate and stepwise logistic regression were used to identify independent risk factors, and receiver operating characteristic curve (ROC) analysis was used to determine the relative contribution of each risk factor. A total of 4397 patients having sustained blunt trauma were admitted to the intensive care unit and survived >24 hours between October 1995 and May 2000. Of these patients 200 (4.5%) developed ARDS. All studied variables were significantly associated with ARDS in univariate analyses. Stepwise logistic regression, however, demonstrated age >65 years, ISS >25, hypotension on admission, 24-hour transfusion requirement >10 units, and pulmonary contusion as independent risk factors, whereas admission metabolic acidosis, femur fracture, infection, and severe brain injury were not. Using a model based on the logistic regression equation derived yields better than 80 per cent discrimination in ARDS patients. The risk factors providing the greatest contribution to ARDS development were ISS >25 (ROC area 0.72) and PC (ROC area 0.68) followed by large transfusion requirement (ROC area 0.56), admission hypotension (ROC area 0.57), and age >65 (ROC area 0.54). Independent risk factors for ARDS in blunt trauma include ISS >25, PC, age >65 years, hypotension on admission, and 24-hour transfusion requirement >10 units but not admission metabolic acidosis, femur fracture, infection, or severe brain injury. Assessment of these variables allows accurate estimate of risk in the majority of cases, and the most potent contributors to the predictive value of the model are ISS >25 and PC. Improvement in understanding of which patients are actually at risk may allow for advances in treatment as well as prevention in the future.