Hyperlactatemia, increased osmolar gap, and renal dysfunction during continuous lorazepam infusion

Nanotherapeutics for Alleviating Anesthesia-Associated Complications

Current management of anesthesia-associated complications falls short in terms of both efficacy and safety. Nanomaterials with versatile properties and unique nano-bio interactions hold substantial promise as therapeutics for addressing these complications. This review conducts a thorough examination of the existing nanotherapeutics and highlights the strategies for developing prospective nanomedicines to mitigate anesthetics-related toxicity. Initially, general, regional, and local anesthesia along with the commonly used anesthetics and related prevalent side effects are introduced. Furthermore, employing nanotechnology to prevent and alleviate the complications of anesthetics is systematically demonstrated from three aspects, that is, developing 1) safe nano-formulization for anesthetics; 2) nano-antidotes to sequester overdosed anesthetics and alter their pharmacokinetics; 3) nanomedicines with pharmacodynamic activities to treat anesthetics toxicity. Finally, the prospects and challenges facing the clinical translation of nanotherapeutics for anesthesia-related complications are discussed. This work provides a comprehensive roadmap for developing effective nanotherapeutics to prevent and mitigate anesthesia-associated toxicity, which can potentially revolutionize the management of anesthesia complications.

Considerations for deriving a safe intake of propylene glycol

The use of propylene glycol (PG) in food and other applications is widespread, and some estimates of dietary exposure to PG approach or exceed the Acceptable Daily Intake (ADI) of 25 mg/kg bw-day. The current ADI for PG applies a cumulative uncertainty factor of 100, which includes factors of 10 for both interspecies and intraspecies differences. Available toxicology studies and human data, however, indicate a plausible mode of action (MoA) that would support a chemical-specific adjustment factor (CSAF) of 1 for interspecies toxicodynamic differences, reducing the total uncertainty factor from 100 to 40. The MoA involves an increase in serum PG concentrations after metabolic saturation, leading to serum hyperosmolarity, which can ultimately cause hemolytic changes and red blood cell damage. Therefore, the species similarities in toxicodynamic response for this critical effect could support increasing the ADI from 25 to 62.5 mg/kg bw-day, applicable to both children and adults.

A Report of Two Cases: Unlearning Lactic Acidosis

Introduction

The term “lactic acidosis” reinforces the misconception that lactate contributes to acidemia. Although it is common to discover an anion gap acidosis with a concomitant elevated lactate concentration, the two are not mutually dependent.

Case Report

Here we describe two patients exhibiting high lactate concentrations in the setting of metabolic alkalemia.

Conclusion

Lactate is not necessarily the direct cause of acid-base disturbances, and there is no fixed relationship between lactate and the anion gap or between lactate and pH. The term “metabolic acidosis with hyperlactatemia” is more specific than “lactic acidosis” and thus more appropriate.

Venous Blood Analytes and Osmolality of Rehabilitated Juvenile Black-bellied Whistling Ducks (Dendrocygna autumnalis)

Venous blood samples were collected from 129 apparently healthy, rehabilitated juvenile black-bellied whistling ducks (Dendrocygna autumnalis) immediately before release from rehabilitation. Blood gas, electrolyte, and select biochemical and hematologic values were analyzed by using a point-of-care analyzer, and complete blood cell counts and osmolality were determined. Most biochemical analyte values were distributed parametrically, while most hematologic values were nonparametrically distributed. Calculated osmolality values were in poor agreement with measured osmolality values, and values of packed cell volume had poor agreement with hematocrit values determined with the i-STAT 1. The physiologic values reported provide vital information to assess individual duck health and guide fluid therapy in captivity and may prove useful to assess free-living population health of this duck species.

Sedation options for intubated intensive care unit patients

A common requirement for intubated patients in the intensive care unit (ICU) is sedation and pain management to facilitate patient safety and timely, atraumatic healing. The Society of Critical Care Medicine guidelines for management of pain, sedation, and delirium in adult ICU patients provide assessment scales for pain, sedation, and delirium; medications for sedation and pain management, and protocols for weaning sedation, are discussed. Proficient assessment skills, pharmacologic knowledge of medications administered to provide sedation, and an understanding of the importance of nonpharmacologic interventions can help the registered nurse provide patient advocacy, safety, and improved outcomes.

Update: Clinical Use of Plasma Lactate

Lactate is an essential, versatile metabolic fuel in cellular bioenergetics. In human emergency and critical care, lactate is used as a biomarker and therapeutic endpoint and evidence is growing in veterinary medicine supporting its clinical utility. Lactate production is a protective response providing ongoing cellular energy during tissue hypoperfusion or hypoxia and mitigating acidosis. Hence, hyperlactatemia is closely associated with disease severity but it is an epiphenomenon as the body attempts to protect itself. This article reviews lactate biochemistry, kinetics, pathophysiology, some practical aspects of measuring lactate, as well as its use in diagnosis, prognosis, and monitoring.

Clinical practice guidelines for the management of pain, agitation, and delirium in adult patients in the intensive care unit

OBJECTIVE

To revise the "Clinical Practice Guidelines for the Sustained Use of Sedatives and Analgesics in the Critically Ill Adult" published in Critical Care Medicine in 2002.

METHODS

The American College of Critical Care Medicine assembled a 20-person, multidisciplinary, multi-institutional task force with expertise in guideline development, pain, agitation and sedation, delirium management, and associated outcomes in adult critically ill patients. The task force, divided into four subcommittees, collaborated over 6 yr in person, via teleconferences, and via electronic communication. Subcommittees were responsible for developing relevant clinical questions, using the Grading of Recommendations Assessment, Development and Evaluation method (http://www.gradeworkinggroup.org) to review, evaluate, and summarize the literature, and to develop clinical statements (descriptive) and recommendations (actionable). With the help of a professional librarian and Refworks database software, they developed a Web-based electronic database of over 19,000 references extracted from eight clinical search engines, related to pain and analgesia, agitation and sedation, delirium, and related clinical outcomes in adult ICU patients. The group also used psychometric analyses to evaluate and compare pain, agitation/sedation, and delirium assessment tools. All task force members were allowed to review the literature supporting each statement and recommendation and provided feedback to the subcommittees. Group consensus was achieved for all statements and recommendations using the nominal group technique and the modified Delphi method, with anonymous voting by all task force members using E-Survey (http://www.esurvey.com). All voting was completed in December 2010. Relevant studies published after this date and prior to publication of these guidelines were referenced in the text. The quality of evidence for each statement and recommendation was ranked as high (A), moderate (B), or low/very low (C). The strength of recommendations was ranked as strong (1) or weak (2), and either in favor of (+) or against (-) an intervention. A strong recommendation (either for or against) indicated that the intervention's desirable effects either clearly outweighed its undesirable effects (risks, burdens, and costs) or it did not. For all strong recommendations, the phrase "We recommend …" is used throughout. A weak recommendation, either for or against an intervention, indicated that the trade-off between desirable and undesirable effects was less clear. For all weak recommendations, the phrase "We suggest …" is used throughout. In the absence of sufficient evidence, or when group consensus could not be achieved, no recommendation (0) was made. Consensus based on expert opinion was not used as a substitute for a lack of evidence. A consistent method for addressing potential conflict of interest was followed if task force members were coauthors of related research. The development of this guideline was independent of any industry funding.

CONCLUSION

These guidelines provide a roadmap for developing integrated, evidence-based, and patient-centered protocols for preventing and treating pain, agitation, and delirium in critically ill patients.

Altering intensive care sedation paradigms to improve patient outcomes

Providing sedation and comfort for intensive care patients has evolved in the last 30 years but remains difficult for clinicians. As research has focused on this challenging area, the authors have identified ways to improve practice, including providing analgesia before sedation, strategies to help recognize dangerous adverse effects associated with the medications that are used, and better ways to monitor pain and delirium in patients. Dexmedetomidine and propofol have become the preferred sedatives for many ICU situations, and creative ways to administer them, such as linking awakening and breathing trials, are emerging. Finally, screening survivors for cognitive impairments may allow clinicians to refer them for the focused rehabilitation they require.

Toxin-related seizures

Toxin-related seizures result from an imbalance in the brain's equilibrium of excitation-inhibition. Fortunately, most toxin-related seizures respond to standard therapy using benzodiazepines. However, a few alterations in the standard approach are recommended to ensure optimal care and expedient termination of seizure activity. If 2 doses of a benzodiazepine do not terminate the seizure activity, a therapeutic dose of pyridoxine (5 g intravenously in an adult and 70 mg/kg intravenously in a child) should be considered. Phenytoin should be avoided because it is ineffective for many toxin-induced seizures and is potentially harmful when used to treat seizures induced by theophylline or cyclic antidepressants.

Pharmacologically-induced metabolic acidosis: a review

Metabolic acidosis may occasionally develop in the course of treatment with drugs used in everyday clinical practice, as well as with the exposure to certain chemicals. Drug-induced metabolic acidosis, although usually mild, may well be life-threatening, as in cases of lactic acidosis complicating antiretroviral therapy or treatment with biguanides. Therefore, a detailed medical history, with special attention to the recent use of culprit medications, is essential in patients with acid-base derangements. Effective clinical management can be handled through awareness of the adverse effect of certain pharmaceutical compounds on the acid-base status. In this review, we evaluate relevant literature with regard to metabolic acidosis associated with specific drug treatment, and discuss the clinical setting and underlying pathophysiological mechanisms. These mechanisms involve renal inability to excrete the dietary H+ load (including types I and IV renal tubular acidoses), metabolic acidosis owing to increased H+ load (including lactic acidosis, ketoacidosis, ingestion of various substances, administration of hyperalimentation solutions and massive rhabdomyolysis) and metabolic acidosis due to HCO3- loss (including gastrointestinal loss and type II renal tubular acidosis). Determinations of arterial blood gases, the serum anion gap and, in some circumstances, the serum osmolar gap are helpful in delineating the pathogenesis of the acid-base disorder. In all cases of drug-related metabolic acidosis, discontinuation of the culprit medications and avoidance of readministration is advised.

Hunting down a double gap metabolic acidosis

Double gap metabolic acidosis occurs in the setting of unmeasured active osmoles in the serum (osmolal gap) and anion gap (AG) metabolic acidosis. We describe a 67-year-old woman with acute respiratory failure on mechanical ventilator from pneumonia and anuric acute on chronic renal failure (urea nitrogen 21.4 mmol/L, creatinine 530.4 μmol/L) requiring haemodialysis (HD). On hospital day 5, she was found to have progressive metabolic acidosis (serum pH 7.16, PCO2 4.38 kPa, HCO3− 12.1 mmol/L and AG 21 mmol/L). There was no evidence of hypoxaemia, hypoperfusion or haemodynamic instability. Normal serum ketone and l-lactate but high serum osmolal gap (89.4 mmol/kg) was detected. A search for toxic alcohols revealed a high serum propylene glycol (PG 32.9 mmol/L), a stabilizing solvent for intravenous formulations of lorazepam, which was being used as sedation for mechanical ventilation. Unexpectedly, serum l- and d-lactate as metabolites of PG were not elevated. Although extended HD for eight hours completely removed serum PG and the osmolal gap, the predialysis high AG metabolic acidosis persisted, potentially related to hypercatabolism and anuric renal failure. PG should be in the differential diagnosis of the disorders with high osmolar gap and may not always be associated with l- or d-lactic acidosis.

Altering intensive care sedation paradigms to improve patient outcomes

Providing sedation and comfort for intensive care patients has evolved in the last few years. New approaches to improving outcomes for intensive care unit (ICU) patients include providing analgesia before adding sedation and recognizing dangerous adverse effects associated with sedative medications, such as prolonged effects of midazolam, propylene glycol toxicity with lorazepam, propofol infusion syndrome, the deliriogenic effects of benzodiazepines and propofol, and bradycardia with dexmedetomidine. There are now reliable and valid ways to monitor pain and delirium in ICU patients. Dexmedetomidine reduces the incidence of delirium, reduces the duration of mechanical ventilation, and appears to be cost effective.

Sedation management in the mechanically ventilated critically ill patient

Sedation management in the mechanically ventilated critically ill patient is a topic of continuing interest in the critical care literature. The wide variety of clinical practices described in the literature with regard to sedation management has limited the implementation of evidence-based practice guidelines. Common themes for a coherent sedation management strategy include articulation of indications for sedation, initial and daily evaluation of sedation goals, sedation-level assessment, appropriate sedative selection, effective sedation management strategy, and efficient sedation weaning strategy. We provide a summary of the literature on key aspects of sedation in clinical practice. Evidence-based recommendations are provided for clinicians involved in the management of sedation in mechanically ventilated patients.

A prospective evaluation of propylene glycol clearance and accumulation during continuous-infusion lorazepam in critically ill patients

Propylene glycol is a commonly used diluent in several pharmaceutical preparations, including the sedative lorazepam. Fifty critically ill patients receiving continuous-infusion lorazepam for a minimum of 36 hours were prospectively evaluated to determine the extent of propylene glycol accumulation over time, characterize propylene glycol clearance in the presence of critical illness, and develop a pharmacokinetic model that would predict clearance based on patient-specific clinical, laboratory, and demographic factors. In this cohort, the median lorazepam infusion rate was 2.1 mg/h (0.5-18). Propylene glycol concentration correlated poorly with osmolality, osmol gap, and lactate. In all, 8 patients (16%) had significant propylene glycol accumulation (>25mg/dL). When propylene glycol concentrations were >25 mg/dL, the median lorazepam infusion rate before sample collection was higher, 6.4 (1.9-11.3) versus 2.0 (0.5-7.4) mg/h (P =.0003). A linear first-order model with interoccasion variability on clearance adjusted for total body weight and Acute Physiology and Chronic Health Evaluation II score predicted propylene glycol concentration.

Clinical uses of dexmedetomidine in pediatric patients

Dexmedetomidine is being used off-label as an adjunctive agent for sedation and analgesia in pediatric patients in the critical care unit and for sedation during non-invasive procedures in radiology. It also has a potential role as part of anesthesia care to prevent emergence delirium and postanesthesia shivering. Dexmedetomidine is currently approved by the US FDA for sedation only in adults undergoing mechanical ventilation for <24 hours. Pediatric experiences in the literature are in the form of small studies and case reports. In patients sedated for mechanical ventilation and/or opioid/benzodiazepine withdrawal, the loading dose ranged from 0.5 to 1 microg/kg and was usually administered over 10 minutes, although not all patients received loading doses. This patient group also received a continuous infusion at rates ranging from 0.2 to 2 microg/kg/h, with higher rates used in burn patients and those with withdrawal following > or =24 hours of opioid/benzodiazepine infusion. The dexmedetomidine dosage used for anesthesia and sedation during non-invasive procedures, such as radiologic studies, ranged from a loading dose of 1-2 microg/kg followed by a continuous infusion at 0.5-1.14 microg/kg/h, with most patients spontaneously breathing. For invasive procedures, such as awake craniotomy or cardiac catheterization, dosage ranged from a loading dose of 0.15 to 1 microg/kg followed by a continuous infusion at 0.1-2 microg/kg/h. Adverse hemodynamic and respiratory effects were minimal; the agent was well tolerated in most patients. The efficacy of dexmedetomidine varied depending on the clinical situation: efficacy was greatest during non-invasive procedures, such as magnetic resonance imaging (MRI), and lowest during invasive procedures, such as cardiac catheterization. Dexmedetomidine may be useful in pediatric patients for sedation in a variety of clinical situations. The literature suggests potential use of dexmedetomidine as an adjunctive agent to other sedatives during mechanical ventilation and opioid/benzodiazepine withdrawal. In addition, because of its minimal respiratory effects, dexmedetomidine has also been used as a single agent for sedation during non-invasive procedures such as MRI. However, additional studies in pediatric patients are warranted to further evaluate its safety and efficacy in all age ranges.

Toxic alcohol ingestions: clinical features, diagnosis, and management

Alcohol-related intoxications, including methanol, ethylene glycol, diethylene glycol, and propylene glycol, and alcoholic ketoacidosis can present with a high anion gap metabolic acidosis and increased serum osmolal gap, whereas isopropanol intoxication presents with hyperosmolality alone. The effects of these substances, except for isopropanol and possibly alcoholic ketoacidosis, are due to their metabolites, which can cause metabolic acidosis and cellular dysfunction. Accumulation of the alcohols in the blood can cause an increment in the osmolality, and accumulation of their metabolites can cause an increase in the anion gap and a decrease in serum bicarbonate concentration. The presence of both laboratory abnormalities concurrently is an important diagnostic clue, although either can be absent, depending on the time after exposure when blood is sampled. In addition to metabolic acidosis, acute renal failure and neurologic disease can occur in some of the intoxications. Dialysis to remove the unmetabolized alcohol and possibly the organic acid anion can be helpful in treatment of several of the alcohol-related intoxications. Administration of fomepizole or ethanol to inhibit alcohol dehydrogenase, a critical enzyme in metabolism of the alcohols, is beneficial in treatment of ethylene glycol and methanol intoxication and possibly diethylene glycol and propylene glycol intoxication. Given the potentially high morbidity and mortality of these intoxications, it is important for the clinician to have a high degree of suspicion for these disorders in cases of high anion gap metabolic acidosis, acute renal failure, or unexplained neurologic disease so that treatment can be initiated early.

Acute kidney injury, hyperosmolality and metabolic acidosis associated with lorazepam

BACKGROUND

A 54-year-old male with a history of multiple admissions for alcohol intoxication was admitted to hospital with right flank pain. He received a high-dose lorazepam infusion for alcohol withdrawal during hospitalization and developed severe hyperosmolality, high anion gap metabolic acidosis, and acute kidney injury on his eighth day of hospitalization.

INVESTIGATIONS

Serum chemistries, arterial blood gas analysis, and measurement of serum propylene glycol, ethylene glycol and methanol levels.

DIAGNOSIS

Propylene glycol toxicity.

MANAGEMENT

Discontinuation of lorazepam infusion, administration of fomepizole, hemodialysis for five consecutive days, hemodynamic support, and follow-up of serum osmolality as a measure of propylene glycol decay.

Symptom-driven lorazepam protocol for treatment of severe alcohol withdrawal delirium in the intensive care unit

STUDY OBJECTIVE

To compare outcomes of treating alcohol withdrawal delirium (AWD) with a symptom-driven benzodiazepine protocol versus nonprotocol benzodiazepine infusions in the intensive care unit (ICU).

DESIGN

Retrospective observational study of a quality improvement project.

SETTING

Medical intensive care unit at a Veterans Affairs medical center.

PATIENTS

Thirty-six patients who had 40 ICU admissions for AWD between January 1, 1994, and May 31, 2003. Sixteen episodes (15 patients [historical controls]) occurred before implementation of the symptom-driven protocol in 1998, and 24 episodes (21 patients) occurred after implementation.

MEASUREMENTS AND MAIN RESULTS

Outcomes evaluated were time to reach symptom control, total dose of benzodiazepine, amount of time receiving continuous benzodiazepine infusion, length of ICU and hospital stay, polypharmacy (use of multiple benzodiazepines), and complications of treatment. The historical control group was treated according to physician preference, which consisted of continuous-infusion midazolam without a protocol. The symptom-driven protocol used lorazepam administered initially as intermittent intravenous doses, progressing to a continuous intravenous infusion according to a locally developed symptom scale. The mean +/- SD values for the outcomes in the historical control group versus the protocol group were as follows: time to control symptoms 19.4 +/- 9.7 versus 7.7 +/- 4.9 hours (p=0.002), cumulative benzodiazepine dose in lorazepam equivalents 1677 +/- 937 versus 1044 +/- 534 mg (p=0.014), time receiving benzodiazepine continuous infusion 122.1 +/- 64.4 versus 52.0 +/- 35.1 hours (p=0.001), length of stay in the ICU 7.7 +/- 6.3 versus 5.6 +/- 1.7 days (p=0.21), and length of hospital stay 15.3 +/- 8.9 versus 11.2 +/- 3.4 days (p=0.43).

CONCLUSIONS

Use of a symptom-driven protocol was associated with significantly decreased time to symptom control, amount of sedative required, and time spent receiving benzodiazepine infusion compared with historical controls. The use of the protocol is effective but requires close monitoring to ensure protocol compliance and to avoid potential propylene glycol toxicity.

Osmol Gap as a Surrogate Marker for Serum Propylene Glycol Concentrations in Patients Receiving Lorazepam for Sedation

STUDY OBJECTIVES

To correlate serum propylene glycol concentration with osmol gap, serum lactate concentration, and amount of propylene glycol administered to mechanically ventilated patients receiving continuous infusions of lorazepam (80% propylene glycol by weight), and to characterize the prevalence of hyperosmolality and range of serum propylene glycol concentrations in this patient population.

DESIGN

Prospective, controlled, observational study.

SETTING

Adult surgical and cardiothoracic intensive care units (ICUs) of a 1200-bed, urban, tertiary care, teaching hospital.

PATIENTS

Sixty-four consecutively enrolled intensive care patients requiring mechanical ventilation and pharmacologic sedation.

INTERVENTION

Thirteen patients received continuous infusions of high-dose lorazepam (> or = 6 mg/hr) for a minimum of 36 hours, and 26 received continuous infusions of low-dose lorazepam (2-5.99 mg/hr) for 36 hours. Twenty-five control patients received sedatives that did not contain propylene glycol.

MEASUREMENTS AND MAIN RESULTS

Serum propylene glycol and lactate concentrations, osmolality, and basic metabolic profiles were obtained 72-108 hours after ICU admission. Clinical data, drug administration, and severity of illness scores were recorded. Osmol gap and the amount of propylene glycol administered before serum sampling predicted propylene glycol concentrations (r(2)=0.692, p<0.05). Osmol gap alone also predicted serum propylene glycol concentrations (r(2)=0.532, p<0.05). Serum lactate concentrations did not correlate with serum propylene glycol concentrations. Unlike the low-dose and control patients, eight (62%) of 13 high-dose patients had osmol gaps above 10. All 13 high-dose patients had serum propylene glycol concentrations previously associated with toxicity.

CONCLUSION

Osmol gap can be used as a surrogate marker for serum propylene glycol concentration. In critically ill patients receiving lorazepam for sedation, an osmol gap above 10 was associated with concentrations previously reported to cause toxicity.

Lactic acidosis: from sour milk to septic shock

Lactic acidosis is frequently encountered in the intensive care unit. It occurs when there is an imbalance between production and clearance of lactate. Although lactic acidosis is often associated with a high anion gap and is generally defined as a lactate level >5 mmol/L and a serum pH <7.35, the presence of hypoalbuminemia may mask the anion gap and concomitant alkalosis may raise the pH. The causes of lactic acidosis are traditionally divided into impaired tissue oxygenation (Type A) and disorders in which tissue oxygenation is maintained (Type B). Lactate level is often used as a prognostic indicator and may be predictive of a favorable outcome if it normalizes within 48 hours. The routine measurement of serum lactate, however, should not determine therapeutic interventions. Unfortunately, treatment options remain limited and should be aimed at discontinuation of any offending drugs, treatment of the underlying pathology, and maintenance of organ perfusion. The mainstay of therapy of lactic acidosis remains prevention.

Propylene Glycol–Induced Lactic Acidosis in a Patient with Normal Renal Function: A Proposed Mechanism and Monitoring Recommendations

OBJECTIVE:

To report a case of severe propylene glycol–induced lactic acidosis not attributable to renal dysfunction that was secondary to administration of high-dose intravenous lorazepam.

CASE SUMMARY:

A 24-year-old female with community-acquired pneumonia presented with severe acute respiratory distress syndrome. To maintain adequate sedation and ventilation and reduce airway pressure, several relaxation strategies were used including high-dose intravenous lorazepam, fentanyl, and cisatracurium. After 18 days of high-dose continuous infusion of lorazepam (maximum dose 50 mg/h), the patient developed severe lactic acidosis secondary to propylene glycol toxicity, the main diluent of lorazepam. The acidosis temporarily resolved with bicarbonate administration and discontinuation of lorazepam. Her renal function remained stable for a time (serum creatinine 0.5 mg/dL, blood urea nitrogen 10 mg/dL, urine output 100–200 mL/h). However, after several more days, the patient's condition deteriorated, and she ultimately died.

DISCUSSION:

Previous cases of propylene glycol toxicity secondary to high-dose lorazepam infusion have occurred in patients with compromised renal function. Our patient's renal function remained stable throughout the hospital course, which caused us to look further for an explanation for the propylene glycol–induced lactic acidosis. Based on the Naranjo probability scale, propylene glycol was determined to be the probable cause of lactic acidosis. Since this case occurred, our intensive care unit has instituted recommendations for the prevention of lorazepam-associated propylene glycol toxicity.

CONCLUSIONS:

Our case highlights the development of propylene glycol–induced lactic acidosis secondary to high-dose lorazepam infusion not associated with renal dysfunction.

The use of the osmole gap as a screening test for the presence of exogenous substances

The rapid and accurate diagnosis of toxic alcohol poisoning due to methanol (methyl alcohol) [MeOH] and ethylene glycol (EG), is paramount in preventing serious adverse outcomes. The quantitative measurement of specific serum levels of these substances using gas chromatography is expensive, time consuming and generally only available at major tertiary-care facilities. Therefore, because these toxic substances are osmotically active and the measurement of serum osmolality is easily performed and more readily available, the presence of an osmole gap (OG) has been adopted as an alternative screening test. By definition, the OG is the difference between the measured serum osmolality determined using the freezing point depression (Osm(m)) and the calculated serum molarity (Mc), which is estimated from the known and readily measurable osmotically active substances in the serum, in particular sodium, urea, glucose, and potassium and ethanol (alcohol). Thus, the OG=Osm(m)-Mc, and an OG above a specific threshold (the threshold of positivity) suggests the presence of unmeasured osmotically active substances, which could be indicative of a toxic exposure. The objectives of this study were to review the principles of evaluating screening tests, the theory behind the OG as a screening test and the literature upon which the adoption of the OG as a screening test has been based. This review revealed that there have been numerous equations derived and proposed for the estimation of the Mc, with the objective of developing empirical evidence of the best equation for the determination of the OG and ultimately the utility of OG as a screening test. However, the methods and statistical analysis employed have generally been inconsistent with recommended guidelines for screening test evaluation and although many equations have been derived, they have not been appropriately validated. Specific evidence of the clinical utility of the OG requires that a threshold of positivity be definitively established, and the sensitivity and specificity of the OG in patients exposed to either EG or MeOH be measured. However, the majority of studies to date have only evaluated the relationship between the Osm(m) (mmol/kg H2O) and the Mc (mmol/L) in patients that have not been exposed to either MeOH or EG. While some studies have evaluated the relationship between the OG and serum ethanol concentration, these findings cannot be extrapolated to the use of the OG to screen for toxic alcohol exposure. This review shows that there has not been an appropriately designed empirical evaluation of the diagnostic utility of the OG and that its clinical utility remains hypothetical, having been theoretically extrapolated from the non-poisoned population.

Relationship of continuous infusion lorazepam to serum propylene glycol concentration in critically ill adults*

OBJECTIVES

The primary objective was to evaluate the relationship between high-dose lorazepam and serum propylene glycol concentrations. Secondary objectives were a) to document the occurrence of propylene glycol accumulation associated with continuous high-dose lorazepam infusion; b) to assess the relationship between lorazepam dose, serum propylene glycol concentrations, and propylene glycol accumulation; and c) to assess the relationship between the osmol gap and serum propylene glycol concentrations.

DESIGN

Prospective, observational study.

SETTING

Tertiary care, medical intensive care unit.

PATIENTS

Nine critically ill adults receiving high-dose lorazepam (> or =10 mg/hr) infusion.

INTERVENTIONS

Cumulative lorazepam dose (mg/kg) and the rate of infusion (mg.kg(-1).hr(-1)) were monitored from initiation of lorazepam infusion until 24 hrs after discontinuation of the high-dose lorazepam infusion. Serum osmolarity was collected at 48 hrs into the high-dose lorazepam infusion and daily thereafter. Serum propylene glycol concentrations were drawn at 48 hrs into the high-dose lorazepam infusion, and the presence of propylene glycol accumulation, as evidenced by a high anion gap (> or =15 mmol/L) metabolic acidosis with elevated osmol gap (> or =10 mOsm/L), was assessed at that time.

MEASUREMENTS AND MAIN RESULTS

The mean cumulative high-dose lorazepam received and mean high-dose lorazepam infusion rate were 8.1 mg/kg (range, 5.1-11.7) and 0.16 mg.kg(-1).hr (-1)(range, 0.11-0.22), respectively. A significant correlation between high-dose lorazepam infusion rate and serum propylene glycol concentrations was observed (r =.557, p =.021). Osmol gap was the strongest predictor of serum propylene glycol concentrations (r =.804, p =.001). Propylene glycol accumulation was observed in six of nine patients at 48 hrs. No significant correlation between duration of lorazepam infusion and serum propylene glycol concentrations was observed (p =.637).

CONCLUSION

Propylene glycol accumulation, as reflected by a hyperosmolar anion gap metabolic acidosis, was observed in critically ill adults receiving continuous high-dose lorazepam infusion for > or =48 hrs. Study findings suggest that in critically ill adults with normal renal function, serum propylene glycol concentrations may be predicted by the high-dose lorazepam infusion rate and osmol gap.

Management of agitation in the intensive care unit

Although the effective evaluation and management of agitated patients often receives less attention than other aspects of critical illness, it is among the most important and rewarding challenges that face critical care physicians. Key features of effective management include a thorough, organized search for potentially dangerous and correctable causes; a sound understanding of the pharmacology of analgesics and sedatives; and keeping a steady eye on appropriate management goals. In turn, the reward for excellent care will be shorter lengths of stay, more rapid liberation from mechanical ventilation, improved cognition, cost savings, and, perhaps, improved survival.

Propylene Glycol–Associated Renal Toxicity from Lorazepam Infusion

OBJECTIVES

Using data from patients who developed elevations in serum creatinine concentrations while receiving continuous-infusion lorazepam, we sought to determine the correlations between the magnitude of serum creatinine concentration rise and each of the following variables: serum propylene glycol level, cumulative lorazepam dose, and duration of lorazepam administration. An additional objective was to identify clinical markers for propylene glycol toxicity.

DESIGN

Retrospective chart review.

SETTING

Medical-surgical intensive care unit and burn unit at a university hospital.

PATIENTS

Eight patients who developed elevations in serum creatinine concentrations while receiving continuous-infusion lorazepam (range 2-28 mg/hr).

MEASUREMENTS AND MAIN RESULTS

The mean cumulative dose of lorazepam was 4305 mg (range 1200-10,920 mg), and the mean propylene glycol level determined at the time of peak serum creatinine concentration was 1103 microg/ml (range 186-3450 microg/ml). Serum creatinine concentrations increased in all eight patients during lorazepam infusion and decreased in seven within 3 days after stopping infusion. A weak-to-moderate correlation existed between the magnitude of the rise in serum creatinine concentration and propylene glycol level (r=0.53). A weak-to-moderate correlation also was identified between cumulative lorazepam dose and magnitude of serum creatinine concentration rise (r=0.43), and a strong-to-moderate correlation was found between duration of lorazepam infusion and magnitude of serum creatinine concentration rise (r=0.60). Propylene glycol levels were strongly correlated with both serum osmolality and osmol gap.

CONCLUSION

The patients' increased serum creatinine concentrations are likely to have resulted from exposure to propylene glycol as a result of lorazepam infusion. Serum osmolality and osmol gap may be useful markers for propylene glycol toxicity.

Acute Tubular Necrosis Associated with Propylene Glycol from Concomitant Administration of Intravenous Lorazepam and Trimethoprim-Sulfamethoxazole

A 46-year-old morbidly obese man was admitted to the medical intensive care unit with respiratory failure. He required pressure-control ventilation and high levels of sedation with continuous-infusion lorazepam. He developed Stenotrophomonas maltophilia pneumonia; treatment included scheduled intravenous trimethoprim-sulfamethoxazole. Each of these drugs contain several hundred milligrams/milliliter of propylene glycol. On day 17 of his hospital course, 3 days after starting the trimethoprim-sulfamethoxazole, the patient developed acute renal failure consistent with acute tubular necrosis. Propylene glycol toxicity was suspected; therefore, all drugs containing propylene glycol were discontinued, and laboratory data were collected. A marked osmol gap, metabolic acidosis, and renal toxicity were attributed to both continuous and large intermittent doses of intravenous propylene glycol. Particular attention should be paid to the total amount of propylene glycol provided to patients from administered drugs. Patients in the intensive care setting who require high doses of intravenous lorazepam for sedation, as well as antimicrobial therapy with trimethoprim-sulfamethoxazole for treatment of either Stenotrophomonas maltophilia or Pneumocystis carinii pneumonia, may be at increased risk for propylene glycol toxicity and should be monitored closely.

Hyponatremia after hip arthroplasty may be related to a translocational rather than to a dilutional mechanism

OBJECTIVE

Postoperative hyponatremia is a frequent metabolic disturbance that may cause life-threatening complications. It results from both a positive electrolyte-free water (EFW) balance and an antidiuretic hormone release. During surgery, intracellular solutes may leak out of cells because of an increased membrane permeability leading to increased osmolality, cellular water shift, and redistribution hyponatremia, a concept coined the sick cell syndrome. Because of release of osmotically active solutes, plasma or urinary osmolar gap should increase. Therefore, we tested the hypothesis that postoperative hyponatremia may be related to a translocational mechanism evidenced by a postoperative increase of the osmolar gap rather than to a positive EFW balance.

SETTING

An anesthesiology department in a 1,200-bed university hospital.

DESIGN

A 5-month prospective observational study.

SUBJECTS

Thirty-three consecutive patients undergoing elective hip arthroplasty under general anesthesia. They were divided into two groups whether the postoperative plasma sodium concentration decrease was > or = 2 mmol/L (group 1) or <2 mmol/L (group 2).

MEASUREMENTS

Plasma sodium concentration ([Na+]p) and plasma osmolality were measured before induction of anesthesia and at skin closure. Osmolality was calculated at the same times. Plasma osmolar gap (OG(p)) was calculated as the difference between measured and calculated osmolality. Postoperative urinary osmolar gap (OG(u)) was calculated in the same way. EFW balance was calculated as the ratio of (infused EFW - excreted urinary EFW) to total body water.

RESULTS

In 33 patients, a significant [Na+]p decrease of -2.0 was observed. No relationship was demonstrated between EFW balance and perioperative [Na+]p variation (r =.28; p=.12). A relationship was observed between perioperative OG(p) variation and perioperative [Na+]p variation (r =.74; p<.0001). In the 19 group 1 patients, [Na+]p decreased by -3.0 mmol/L. EFW balance did not differ between group 1 and group 2 patients. No statistical relationship was observed between EFW balance and perioperative [Na+]p variation in group 1 (r =.20; p=.40) and in group 2 (r =.43; p=.14). OG(p) increased only in group 1 but not in group 2 patients, and postoperative OG(u) was greater in group 1 than in group 2 patients. A relationship was observed between perioperative OG(p) variation and perioperative [Na+]p variation in group 1 (r =.53; p=.02) but not in group 2 (r =.32; p=.26).

CONCLUSION

Hyponatremia after hip arthroplasty may not be related to a positive EFW balance. The postoperative increase of the OG(p) and the greater postoperative OG(u) in patients developing postoperative hyponatremia suggest the release of osmotically active solutes leading to cellular water shift from intracellular to extracellular spaces. These data may support the clinical relevance of the sick cell syndrome in the postoperative context.

Propylene glycol accumulation associated with continuous infusion of lorazepam in pediatric intensive care patients

OBJECTIVE

To determine if propylene glycol accumulates in children receiving continuous lorazepam infusion and, if accumulation occurs, to determine if it is associated with significant laboratory abnormalities.

DESIGN

Prospective study.

SETTING

A tertiary care pediatric intensive care unit.

PATIENTS

Eleven intubated pediatric intensive care patients receiving continuous lorazepam infusion for sedation.

INTERVENTIONS

Propylene glycol accumulation was determined by comparing concentrations at baseline, after 48 hrs, and at end of therapy. Laboratory abnormalities were determined by comparing serum lactate and osmolar gap at baseline, after 48 hrs, and at end of therapy. Correlation between the cumulative dose of lorazepam received and the propylene glycol concentration measured at the end of therapy was determined.

MEASUREMENTS AND MAIN RESULTS

Patients aged 1-15 months were studied. Lorazepam infusion rates ranged from 0.1 to 0.33 mg.kg.hr and lasted 3-14 days. Propylene glycol accumulated significantly in patients receiving continuous infusion of lorazepam. The propylene glycol concentration increased during the study from 86 +/- 93 microg/mL at baseline to 763 +/- 660 microg/mL at the end of the study ( p=.038). A statistically significant correlation between the cumulative dose of lorazepam received and propylene glycol concentration at the end of therapy was demonstrated ( r(2)=.65, p<.005). However, the propylene glycol accumulation was not associated with significant laboratory abnormalities. Neither serum lactate concentrations nor osmolar gap were significantly elevated over baseline.

CONCLUSION

Propylene glycol accumulated significantly in pediatric intensive care patients receiving continuous lorazepam infusion, and propylene glycol concentration correlated with the cumulative lorazepam dose the patient received. However, significant laboratory abnormalities due to propylene glycol accumulation were not observed.

Propylene glycol toxicity associated with lorazepam infusion in a patient receiving continuous veno-venous hemofiltration with dialysis

IMPLICATIONS

We report a case of toxicity from the drug solvent propylene glycol resulting from prolonged, large-dose lorazepam infusion. The case is unusual in that toxicity developed during continuous veno-venous hemofiltration with dialysis, a renal replacement therapy that should been have been effective at eliminating the chemical and its metabolites.

Osmolar gap hyponatremia in critically ill patients: evidence for the sick cell syndrome?

OBJECTIVE

Accumulation of nondiffusible solutes in plasma leads to redistribution hyponatremia with an increased osmolar gap (i.e., the difference between measured and calculated osmolality). In critically ill patients, intracellular solutes may leak out of the cell because of an increased membrane permeability and may lead to redistribution hyponatremia with increased osmolar gap, a concept called the "sick cell syndrome." The aims of this prospective study were to determine whether an increased osmolar gap related to endogenous solutes accumulation was present in intensive care patients with true hyponatremia and to identify the solutes accounting for this increased osmolar gap.

SETTING

A 14-bed medical intensive care unit in an 821-bed university hospital.

DESIGN

A 20-wk prospective observational study.

PATIENTS

Fifty-five consecutive patients with a measured plasma sodium concentration <or=130 mmol/L (mean +/- sd, 126 +/- 6 mmol/L) were automatically identified by the Biochemistry Department. Patients were excluded in the case of reduced plasma water content resulting from hyperlipidemia or hyperproteinemia, in the case of hyperglycemia, or if exogenous compounds known to increase the osmolar gap were present.

INTERVENTIONS

Plasma osmolar gap was calculated.

MEASUREMENTS AND MAIN RESULTS

Plasma osmolar gap was considered significant if >10 mosm/kg. Total plasma amino acid concentration also was measured. Organ dysfunctions were assessed with the Sequential Organ Failure Assessment. Thirty of the 55 patients (54%) had an osmolar gap >10 mosm/kg (17.2 +/- 7.1 mosm/kg). Sequential Organ Failure Assessment score was significantly higher in the osmolar gap patients (6.4 +/- 3.2 vs. 4.5 +/- 2.0; p =.015). No difference of amino acids concentration was observed between osmolar gap and non-osmolar gap patients, and no correlation was observed between osmolar gap and amino acid concentration. Accumulation of ketone bodies and lactic acid was also unlikely. During correction of hyponatremia in osmolar gap patients, a significant decrease of plasma osmolar gap was observed and a statistically significant inverse relationship was demonstrated between osmolar gap decrease and plasma sodium concentration increase.

CONCLUSION

Hyponatremia with increased osmolar gap related to endogenous solutes accumulation is observed frequently in hyponatremic intensive care patients, especially in patients with the most severe organ dysfunctions. The nature of the endogenous solutes accounting for the increased osmolar gap remains to be determined. Simultaneous correction of sodium and osmolar gap suggests a causal link between increased osmolar gap and hyponatremia and may support the concept of sick cell syndrome.

Metabolic acidosis in the intensive care unit

Metabolic acidosis is a common occurrence in critically ill patients. Understanding the pathological mechanisms underlying the generation of protons will enable the clinician to quickly recognize these disorders and establish an acceptable treatment strategy. This article presents a logical approach to metabolic acidosis.

Advances and Controversies in Adult ICU Sedation, Part 3: Evolving Pharmacological Treatment Issues

This feature examines the impact of pharmacologic interventions on the treatment of the critically ill patient—an area of health care that has become increasingly complex. It will review recent advances (including evolving and controversial data) in drug therapy for adult ICU patients and assess these new modalities in terms of clinical, humanistic, and economic outcomes.

Benzodiazepines in the intensive care unit

The effects of BZ drugs result from interaction at the GABAA receptor within the CNS, producing anxiolysis, hypnosis, and amnesia in a dose-dependent fashion. These sedative effects are best titrated to reproducible clinical endpoints, using scoring systems such as the Ramsay scale. All BZs exhibit similar pharmacologic effects, but the important differences in pharmacokinetics and pharmacodynamics should be recognized to use these drugs safely and effectively within the ICU. Diazepam is the classic anxiolytic, amnestic, and sedative agent, but the presence of long-acting active metabolites that depend on the kidneys for elimination limits its use in many ICU patients. Lorazepam is the most potent BZ used in the ICU; it has stable pharmacokinetics and relatively low cost. This drug is best reserved for situations in which rapid onset is not essential and long-term sedation is anticipated. Midazolam has the shortest t1/2 of the commonly used BZs, generates few active metabolites, and is water soluble at physiologic pH. Thus, it is well suited for continuous infusion in the ICU, and the recent introduction of generic formulations of midazolam has decreased the drug-acquisition cost for many hospitals. Optimal sedation for ICU patients often requires BZ and concomitant therapy with drugs such as haloperidol, dexmedetomidine, opioids, and so forth, to reduce untoward side effects and, perhaps, overall drug costs. Flumazenil, a specific BZ antagonist, can be used for diagnostic or therapeutic reversal of BZ agonists when appropriate. Most experienced intensivists recommend an individualized approach to sedation and titration of anxiolysis to maximize efficacy, minimize side effects, and optimize cost effectiveness in the ICU. New CNS monitors of the EEG, such as the BIS or entropy EEG monitors, may refine titration algorithms further in the near future.

Short-term lorazepam infusion and concern for propylene glycol toxicity: case report and review

A 34-year-old woman with a history of renal insufficiency induced by long-term cocaine use was admitted with acute shortness of breath remarkable for submandibular and anterior throat swelling. She required intubation, mechanical ventilation, and sedation. Sedation was administered with daily infusions of intravenous lorazepam 65, 313, and 305 mg for 3 days, respectively. Forty-eight hours into the infusion the patient experienced anion gap metabolic acidosis with hyperlactatemia, hyperosmolality, and increased osmolal gap. Propylene glycol (PG), a component of lorazepam intravenous formulation, was considered the potential source of the metabolic abnormality. The patient received greater than 40 times the acceptable recommended amount of PG over 72 hours. Cessation of lorazepam produced major improvements in lactic acid, serum osmolality, and anion and osmolal gaps. The large PG exposure associated with long-term cocaine-induced renal insufficiency produced a toxic metabolic state. Agents containing PG should be avoided in patients with compromised renal function (creatinine clearance < or = 30 ml/min) induced by cocaine use.