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

Effect of early clinical management on metabolic acidemia in neonates with hypoxic-ischemic encephalopathy

OBJECTIVE

To determine the safety and effectiveness of sodium bicarbonate administration in the management of metabolic acidemia and short-term outcomes in neonates with hypoxic-ischemic encephalopathy (HIE).

STUDY DESIGN

Retrospective cohort study of neonates born at ≥35 weeks of gestation and receiving therapeutic hypothermia. Demographics, pH, lactate, base deficit, treatment, MRI findings, seizure incidence, death prior to discharge were collected.

RESULTS

There was higher mortality (p = 0.010) and injury on MRI (p = 0.008)-primarily deep gray matter (p < 0.001) and cortical injury (p = 0.003)-in the bicarbonate group compared to controls in univariate analysis. The combined outcome of death or abnormal MRI was not significantly associated (OR 1.97, 95% CI 0.80-4.87, p = 0.141) with bicarbonate administration when adjusting for sex, 5-minute Apgar, and initial base deficit.

CONCLUSION

This study demonstrated association between bicarbonate use after HIE and negative short-term outcomes. Future prospective trials could overcome the treatment bias limitation demonstrated in this retrospective study.

Clinical Implications, Evaluation, and Management of Hyponatremia in Cirrhosis

Hyponatremia is the most common electrolyte abnormality in patients with decompensated cirrhosis on Liver Transplantation (LT) waiting list. Most of these patients have dilutional or hypervolemic hyponatremia secondary to splanchnic vasodilatation. Excessive secretion of the antidiuretic hormone also plays an important role. Hypervolemic hyponatremia is commonly associated with refractory ascites, spontaneous bacterial peritonitis, and hepatic encephalopathy. Although uncommon, the use of diuretics and laxatives can cause hypovolemic hyponatremia that is characterized by the striking absence of ascites or pedal edema. Clinical features are often nonspecific and depend on the acuity of onset rather than the absolute value of serum sodium. Symptoms may be subtle, including nausea, lethargy, weakness, or anorexia. However, rarely patients may present with confusion, seizures, psychosis, or coma. Treatment includes discontinuation of diuretics, beta-blockers, and albumin infusion. Hypertonic saline (3%) infusion may be used in patients with very low serum sodium (<110 mmol/L) or when patients present with seizures or coma. Short-term use of Vasopressin (V₂) receptor antagonists may also be used to normalize sodium levels prior to LT. However, all these measures may be futile, and LT remains the definite treatment in these patients to improve survival. In this review, we describe the classification, pathogenesis of hyponatremia, and its clinical implications in patients with cirrhosis. Approach to these patients along with management will also be discussed briefly.

Hyponatremia in Cirrhosis: An Update

Hyponatremia is frequently seen in patients with ascites secondary to advanced cirrhosis and portal hypertension. Although not apparent in the early stages of cirrhosis, the progression of cirrhosis and portal hypertension leads to splanchnic vasodilation, and this leads to the activation of compensatory mechanisms such as renin-angiotensin-aldosterone system (RAAS), sympathetic nervous system, and antidiuretic hormone (ADH) to ameliorate low circulatory volume. The net effect is the avid retention of sodium and water to compensate for the low effective circulatory volume, resulting in the development of ascites. These compensatory mechanisms lead to impairment of the kidneys to eliminate solute-free water in decompensated cirrhosis. Nonosmotic secretion of antidiuretic hormone (ADH), also known as arginine vasopressin, further worsens excess water retention and thereby hyponatremia. The management of hyponatremia in this setting is a challenge as conventional therapies for hyponatremia including fluid restriction and correction of hypokalemia are frequently inefficacious. In this review, we discuss the pathophysiology, complications, and various treatment modalities, including albumin infusion, selective vasopressin receptor antagonists, or hypertonic saline for patients with severe hyponatremia and those awaiting liver transplantation.

Update on anesthesia management for explantation of veno-arterial extracorporeal membrane oxygenation in adult patients

The utilization of temporary circulatory support in the form of extracorporeal membrane oxygenation (ECMO) has increased and its indications are expanding. Anesthesiologists may be involved in the care of these patients during the initiation of and weaning off from ECMO, surgical procedures with an ECMO in situ, and transfer of patients on ECMO between the operating theater and intensive care unit. This article addresses the anesthetic considerations and management for explant of veno-arterial ECMO in adults.

Association Between the Use of Sodium Bicarbonate and Mortality in Acute Kidney Injury Using Marginal Structural Cox Model

OBJECTIVE

Acute kidney injury with metabolic acidosis is common in critically ill patients. This study assessed the associations between the use of IV sodium bicarbonate and mortality of patients with acute kidney injury and acidosis.

DESIGN

The study was conducted by using data from Beth Israel Deaconess Medical Center, which included several ICUs such as coronary care unit, cardiac surgery recovery unit, medical ICU, surgical ICU, and trauma-neuro ICU. Marginal structural Cox model was used to assess the relationship between receipt of sodium bicarbonate and hospital mortality, allowing pH, PaCO2, creatinine, and bicarbonate concentration as time-varying predictors of sodium bicarbonate exposure while adjusting for baseline characteristics of age, gender, Sequential Organ Failure Assessment score, acute kidney injury stage, Elixhauser score, quick Sequential Organ Failure Assessment, and Simplified Acute Physiology Score II.

SETTING

A large U.S.-based critical care database named Medical Information Mart for Intensive Care.

PATIENTS

Patients with Kidney Disease: Improving Global Outcomes acute kidney injury stage greater than or equal to 1 (> 1.5 (Equation is included in full-text article.)baseline creatinine) and one measurement of acidosis (pH ≤ 7.2). Baseline creatinine was estimated using the Chronic Kidney Disease Epidemiology Collaboration equation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of the 3,406 eligible patients, 836 (24.5%) had received sodium bicarbonate treatment. Patients who received sodium bicarbonate treatment had a higher Sequential Organ Failure Assessment (9 vs 7; p < 0.001), lower pH (7.16 vs 7.18; p < 0.001), and bicarbonate concentration (16.51 ± 7.04 vs 20.57 ± 6.29 mmol/L; p < 0.001) compared with those who did not receive sodium bicarbonate. In the marginal structural Cox model by weighing observations with inverse probability of receiving sodium bicarbonate, sodium bicarbonate treatment was not associated with mortality in the overall population (hazard ratio, 1.16; 95% CI, 0.98-1.42; p = 0.132), but it appeared to be beneficial in subgroups of pancreatitis (hazard ratio, 0.53; 95% CI, 0.28-0.98; p = 0.044) and severe acidosis (pH < 7.15; hazard ratio, 0.75; 95% CI, 0.58-0.96; p = 0.024). Furthermore, sodium bicarbonate appeared to be beneficial in patients with severe bicarbonate deficit (< -50 kg·mmol/L).

CONCLUSIONS

In the analysis by adjusting for potential confounders, there is no evidence that IV sodium bicarbonate is beneficial for patients with acute kidney injury and acidosis. Although the study suggested potential beneficial effects in some highly selected subgroups, the results need to be validated in experimental trials.

Bicarbonate Therapy for Critically Ill Patients with Metabolic Acidosis: A Systematic Review

The management of acid-base disorders always calls for precise diagnosis and treatment of the underlying disease. Sometimes additional means are necessary to combat systemic acidity itself. In this systematic review, we discuss the concept and some specific aspects of bicarbonate therapy for critically ill patients with metabolic acidosis (i.e., patients with blood pH < 7.35). We conducted a systematic literature review of three online databases (PubMed, Google Scholar, and Cochrane) in November 2018 to validate usage of bicarbonate therapy for critically ill patients with metabolic acidosis. Twelve trials and case series were included in the final analysis, from which we assessed population, intervention, comparison, and outcome data. The current literature suggests limited benefit from bicarbonate therapy for patients with severe metabolic acidosis (pH < 7.1 and bicarbonate < 6 mEq/L). However, bicarbonate therapy does yield improvement in survival for patients with accompanying acute kidney injury.

Effectiveness of sodium bicarbonate infusion on mortality in septic patients with metabolic acidosis

OBJECTIVE

Although sodium bicarbonate (SB) solution has been widely used in clinical practice, its effect on mortality when administered to a large population of patients with acidosis is not known. The study aimed to investigate the effectiveness of SB infusion in septic patients with metabolic acidosis.

METHODS

Septic patients with metabolic acidosis were identified from the Medical Information Mart for Intensive Care (MIMIC)-III database. Propensity score (PS) was used to account for the baseline differences in the probability to receive SB or not. The marginal structural Cox model (MSCM) was employed to adjust for both baseline and time-varying confounding factors.

MAIN RESULTS

A total of 1718 septic patients with metabolic acidosis were enrolled in the study, including 500 in the SB group and 1218 in the non-SB group. Both pH [7.16 (standard deviation (SD): 0.10) vs. 7.22 (SD: 0.07); p < 0.001] and bicarbonate concentration (BC) [11.84 (SD: 3.63) vs. 14.88 (SD: 3.36) mmol/l; p < 0.001] were significantly lower in the SB than that in the non-SB group. While there was no significant mortality effect in the overall population [hazard ratio (HR): 1.04; 95% CI 0.86-1.26; p = 0.67], SB was observed to be beneficial in patients with acute kidney injury (AKI) stage 2 or 3 and pH < 7.2 (HR 0.74; 95% CI 0.51-0.86; p = 0.021). Similar results were replicated with the MSCM.

CONCLUSION

Our study observed that SB infusion was not associated with improved outcome in septic patients with metabolic acidosis, but it was associated with improved survival in septic patients with AKI stage 2 or 3 and severe acidosis. The results need to be verified in randomized controlled trials.

Treatment options for lactic acidosis and metabolic crisis in children with mitochondrial disease

The mitochondrial pyruvate oxidation route is a tightly regulated process, which is essential for aerobic cellular energy production. Disruption of this pathway may lead to severe neurometabolic disorders with onset in early childhood. A frequent finding in these patients is acute and chronic lactic acidemia, which is caused by increased conversion of pyruvate via the enzyme lactate dehydrogenase. Under stable clinical conditions, this process may remain well compensated and does not require specific therapy. However, especially in situations with altered energy demands, such as febrile infections or longer periods of fasting, children with mitochondrial disorders have a high risk of metabolic decompensation with exacerbation of hyperlactatemia and severe metabolic acidosis. Unfortunately, no controlled studies regarding therapy of this critical condition are available and clinical outcome is often unfavorable. Therefore, the aim of this review was to formulate expert-based suggestions for treatment of these patients, including dietary recommendations, buffering strategies and specific drug therapy. However, it is important to keep in mind that a specific therapy for the underlying metabolic cause in children with mitochondrial diseases is usually not available and symptomatic therapy especially of severe lactic acidosis has its ethical limitations.

Sodium bicarbonate therapy in patients with metabolic acidosis

Metabolic acidosis occurs when a relative accumulation of plasma anions in excess of cations reduces plasma pH. Replacement of sodium bicarbonate to patients with sodium bicarbonate loss due to diarrhea or renal proximal tubular acidosis is useful, but there is no definite evidence that sodium bicarbonate administration to patients with acute metabolic acidosis, including diabetic ketoacidosis, lactic acidosis, septic shock, intraoperative metabolic acidosis, or cardiac arrest, is beneficial regarding clinical outcomes or mortality rate. Patients with advanced chronic kidney disease usually show metabolic acidosis due to increased unmeasured anions and hyperchloremia. It has been suggested that metabolic acidosis might have a negative impact on progression of kidney dysfunction and that sodium bicarbonate administration might attenuate this effect, but further evaluation is required to validate such a renoprotective strategy. Sodium bicarbonate is the predominant buffer used in dialysis fluids and patients on maintenance dialysis are subjected to a load of sodium bicarbonate during the sessions, suffering a transient metabolic alkalosis of variable severity. Side effects associated with sodium bicarbonate therapy include hypercapnia, hypokalemia, ionized hypocalcemia, and QTc interval prolongation. The potential impact of regular sodium bicarbonate therapy on worsening vascular calcifications in patients with chronic kidney disease has been insufficiently investigated.

Lactic acidosis secondary to metformin overdose: a case report

INTRODUCTION

Metformin is a commonly used treatment modality in type 2 diabetes mellitus, with a well documented side effect of lactic acidosis. In the intensive care setting lactate and pH levels are regularly used as a useful predictor of poor prognosis. In this article we highlight how high lactate levels are not an accurate predictor of mortality in deliberate metformin overdose.

CASE PRESENTATION

We present the case of a 70-year-old Caucasian man who took a deliberate metformin overdose of unknown quantity. He had a profound lactic acidosis at presentation with a pH of 6.93 and a lactate level of more than 20mmol/L. These figures would normally correspond with a mortality of more than 80%; however, with appropriate management this patient's condition improved.

CONCLUSION

We provide evidence that the decision to treat severe lactic acidosis in deliberate metformin overdose should not be based on arterial lactate and pH levels, as would be the case in other overdoses. We also demonstrate that appropriate treatment with hemodiafiltration and 8.4% sodium bicarbonate, even in patients with a very high lactate and low pH, can be successful.

A severe case of iatrogenic lactation ketoacidosis

Lactation ketosis is a recognised disorder in postpartum lactating cows where a negative energy balance develops because the energy demands of milk production exceed the energy capacity of the animal. Rarely, nursing women can develop problems with lactation ketosis when their glycogen stores are depleted, causing the body to turn to gluconeogenesis as an energy substrate for galactopoiesis. The authors describe the case of a breastfeeding woman admitted to hospital and made nil per os (NPO) to treat a bowel obstruction. She did not receive intravenous glucose and 3 days postadmission developed a dangerous starvation ketosis (venous pH of 6.64). She was treated with intravenous dextrose, bicarbonate as well as cessation of breastfeeding and recovered quickly. Only four previous reports describe human lactation ketosis and this is the first iatrogenic case reported to our knowledge. It highlights the importance of addressing the unique caloric requirements of nursing women, especially when they are kept NPO.

Acute renal response to rapid onset respiratory acidosis

Renal strong ion compensation to chronic respiratory acidosis has been established, but the nature of the response to acute respiratory acidosis is not well defined. We hypothesized that the response to acute respiratory acidosis in sheep is a rapid increase in the difference in renal fractional excretions of chloride and sodium (Fe(Cl) - Fe(Na)). Inspired CO(2) concentrations were increased for 1 h to significantly alter P(a)CO(2) and pH(a) from 32 ± 1 mm Hg and 7.52 ± 0.02 to 74 ± 2 mm Hg and 7.22 ± 0.02, respectively. Fe(Cl) - Fe(Na) increased significantly from 0.372 ± 0.206 to 1.240 ± 0.217% and returned to baseline at 2 h when P(a)CO(2) and pH(a) were 37 ± 0.6 mm Hg and 7.49 ± 0.01, respectively. Arterial pH and Fe(Cl) - Fe(Na) were significantly correlated. We conclude that the kidney responds rapidly to acute respiratory acidosis, within 30 min of onset, by differential reabsorption of sodium and chloride.

Understanding lactic acidosis in paracetamol (acetaminophen) poisoning

Paracetamol (acetaminophen) is one of the most commonly taken drugs in overdose in many areas of the world, and the most common cause of acute liver failure in both the UK and USA. Paracetamol poisoning can result in lactic acidosis in two different scenarios. First, early in the course of poisoning and before the onset of hepatotoxicity in patients with massive ingestion; a lactic acidosis is usually associated with coma. Experimental evidence from studies in whole animals, perfused liver slices and cell cultures has shown that the toxic metabolite of paracetamol, N-acetyl-p-benzo-quinone imine, inhibits electron transfer in the mitochondrial respiratory chain and thus inhibits aerobic respiration. This occurs only at very high concentrations of paracetamol, and precedes cellular injury by several hours. The second scenario in which lactic acidosis can occur is later in the course of paracetamol poisoning as a consequence of established liver failure. In these patients lactate is elevated primarily because of reduced hepatic clearance, but in shocked patients there may also be a contribution of peripheral anaerobic respiration because of tissue hypoperfusion. In patients admitted to a liver unit with paracetamol hepatotoxicity, the post-resuscitation arterial lactate concentration has been shown to be a strong predictor of mortality, and is included in the modified King's College criteria for consideration of liver transplantation. We would therefore recommend that post-resuscitation lactate is measured in all patients with a severe paracetamol overdose resulting in either reduced conscious level or hepatic failure.

[Acid-base disturbances in intensive-care patients]

BACKGROUND

Acid-base disturbances may cause a variety of symptoms, multi-organ failure and compromised immune defense. The aim of this paper is to provide an overview of acid-base disturbances in intensive-care patients.

MATERIAL AND METHOD

The article is based on a non-systematic search in Pub Med, a textbook on intensive care and the authors' clinical experience.

RESULTS

The Henderson-Hasselbalch equation describes acid-base status by changes in pCO2 and bicarbonate. Changes in pCO2 reflect the respiratory and bicarbonate the metabolic status. Standard base excess describes the metabolic part more exactly. Anion gap is calculated as a supplement. The Stewart method, describes acid-base status through three independent variables (pCO2, weak acids and strong ion difference [SID]) that regulate the dependent variables pH and bicarbonate concentration.

INTERPRETATION

The Henderson-Hasselbalch equation and standard base excess do not consider which acids or bases that are involved, The anion gap may disclose unmeasured anions and distinguish hyperchloremic acidosis from other types of metabolic acidosis, but the calculation is associated with uncertainty. The Stewart method describes the involved ions, but complicated equations makes it unsuitable in clinical practice. A combination of standard base excess and anion gap corrected for albumin levels provide a good description of acid-base status.

Treatment of lactic acidosis: appropriate confusion

BACKGROUND

Lactic acidosis (LA) is common in hospitalized patients and is associated with poor clinical outcomes. There have been major recent advances in our understanding of lactate generation and physiology. However, treatment of LA is an area of controversy and uncertainty, and the use of agents to raise pH is not clearly beneficial.

AIM AND METHODS

We reviewed animal and human studies on the pathogenesis, impact, and treatment of LA, published in the English language and available through the PubMed/MEDLINE database. Our aim was to clarify the physiology of the generation of LA, its impact on outcomes, and the different treatment modalities available. We also examined relevant data regarding LA induced by medications commonly prescribed by hospitalists: biguanides, nucleoside analog reverse-transcriptase inhibitors (NRTIs), linezolid, and lorazepam.

RESULTS/CONCLUSIONS

Lactic acid is a marker of tissue ischemia but it also may accumulate without tissue hypoperfusion. In the latter circumstance, lactic acid accumulation may be an adaptive mechanism-a novel possibility quite in contrast to the traditional view of lactic acid as only a marker of tissue ischemia. Studies on the treatment of LA with sodium bicarbonate or other buffers fail to show consistent clinical benefit. Severe acidemia in the setting of LA is a particularly poorly studied area. In the settings of medication-induced LA, optimal treatment, apart from prompt cessation of the offending agent, is still unclear.

Is there a role for sodium bicarbonate in treating lactic acidosis from shock?

PURPOSE OF REVIEW

Bicarbonate therapy for severe lactic acidosis remains a controversial therapy.

RECENT FINDINGS

The most recent 2008 Surviving Sepsis guidelines strongly recommend against the use of bicarbonate in patients with pH at least 7.15, while deferring judgment in more severe acidemia. We review the mechanisms causing lactic acidosis in the critically ill and the scientific rationale behind treatment with bicarbonate.

SUMMARY

There is little rationale or evidence for the use of bicarbonate therapy for lactic acidosis due to shock. We agree with the Surviving Sepsis guidelines recommendation against the use of bicarbonate for lactic acidosis for pH at least 7.15 and we further recommend a lower target pH of 7.00 or less. If bicarbonate is used, consideration must be given to slow infusion and a plan for clearing the CO2 that is produced and measuring and correcting ionized calcium as the resultant 10% drop may decrease cardiac and vascular contractility and responsiveness to catecholamines. When continuous renal replacement therapy is used during severe acidosis, we recommend bicarbonate-based replacement fluid over citrate as citrate may increase the strong ion gap. Effective therapy of lactic acidosis due to shock is to reverse the cause.

Metabolic acid-base disorders in the critical care unit

The recognition and management of acid-base disorders is a commonplace activity in the critical care unit, and the role of weak and strong acids in the genesis of metabolic acid-base disorders is reviewed. The clinical approach to patients with metabolic alkalosis and metabolic acidosis is discussed in this article.

Metabolic acidosis in the critically ill: part 2. Causes and treatment

The correct identification of the cause, and ideally the individual acid, responsible for metabolic acidosis in the critically ill ensures rational management. In Part 2 of this review, we examine the elevated (corrected) anion gap acidoses (lactic, ketones, uraemic and toxin ingestion) and contrast them with nonelevated conditions (bicarbonate wasting, renal tubular acidoses and iatrogenic hyperchloraemia) using readily available base excess and anion gap techniques. The potentially erroneous interpretation of elevated lactate signifying cell ischaemia is highlighted. We provide diagnostic and therapeutic guidance when faced with a high anion gap acidosis, for example pyroglutamate, in the common clinical scenario 'I can't identify the acid--but I know it's there'. The evidence that metabolic acidosis affects outcomes and thus warrants correction is considered and we provide management guidance including extracorporeal removal and fomepizole therapy.

Scientific justification of cryonics practice

Very low temperatures create conditions that can preserve tissue for centuries, possibly including the neurological basis of the human mind. Through a process called vitrification, brain tissue can be cooled to cryogenic temperatures without ice formation. Damage associated with this process is theoretically reversible in the same sense that rejuvenation is theoretically possible by specific foreseeable technology. Injury to the brain due to stopped blood flow is now known to result from a complex series of processes that take much longer to run to completion than the 6 min limit of ordinary resuscitation technology. Reperfusion beyond the 6 min limit primarily damages blood vessels rather than brain tissue. Apoptosis of neurons takes many hours. This creates a window of opportunity between legal death and irretrievable loss of life for human and animal subjects for cryopreservation with possibility of future resuscitation. Under ideal conditions, the time interval between onset of clinical death and beginning of cryonics procedures can be reduced to less than 1 min, but much longer delays could also be compatible with ultimate survival. Although the evidence that cryonics may work is indirect, the application of indirect evidence is essential in many areas of science. If complex changes due to aging are reversible at some future date, then similarly complex changes due to stopped blood flow and cryopreservation may also be reversible, with life-saving results for anyone with medical needs that exceed current capabilities.

Bicarbonate therapy in severe metabolic acidosis

The utility of bicarbonate administration to patients with severe metabolic acidosis remains controversial. Chronic bicarbonate replacement is obviously indicated for patients who continue to lose bicarbonate in the ambulatory setting, particularly patients with renal tubular acidosis syndromes or diarrhea. In patients with acute lactic acidosis and ketoacidosis, lactate and ketone bodies can be converted back to bicarbonate if the clinical situation improves. For these patients, therapy must be individualized. In general, bicarbonate should be given at an arterial blood pH of < or =7.0. The amount given should be what is calculated to bring the pH up to 7.2. The urge to give bicarbonate to a patient with severe acidemia is apt to be all but irresistible. Intervention should be restrained, however, unless the clinical situation clearly suggests benefit. Here we discuss the pros and cons of bicarbonate therapy for patients with severe metabolic acidosis.

Advances in critical care for the nephrologist: acute lung injury/ARDS

Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are a major cause of acute respiratory failure in the critically ill patient. ALI and ARDS are characterized by the acute onset of severe hypoxemia and bilateral pulmonary infiltrates in the absence of clinical evidence for left atrial hypertension. These conditions are differentiated from one another by the ratio of the partial pressure of oxygen in the arterial blood to the inspired fraction of oxygen; ARDS requires a more severe oxygenation defect. ALI and ARDS may occur in association with a number of clinical disorders, including sepsis, pneumonia, aspiration, trauma including inhalational injury, and blood transfusions. The mortality rate remains high, in the range of 25% to 40%. The pathophysiology of ALI/ARDS involves resident lung cells, including endothelial and epithelial cells, as well as neutrophils, monocytes/macrophages, and platelets. When ALI/ARDS is complicated by acute kidney injury, mortality increases substantially. Several supportive and pharmacologic therapies have been tested in clinical trials. Of these, a low tidal volume, lung protective ventilation strategy is the only strategy that has been demonstrated in a large, multicenter randomized clinical trial to reduce mortality for patients with ALI/ARDS. Based on a recent randomized trial, a conservative fluid management strategy reduces the duration of mechanical ventilation without increasing the incidence of renal failure. Pharmacologic strategies and other ventilator management strategies have not been successful to date; however, several randomized, placebo controlled treatment trials are ongoing.

Diabetic ketoacidosis and hyperglycaemic hyperosmolar syndrome - clinical guidelines

BACKGROUND

The aim of this study was to establish a standardized approach to the initial care of patients with diabetic ketoacidosis (DKA) and hyperglycaemic hyperosmolar syndrome (HHS). DKA and HHS are metabolic emergencies. Effective and efficient management is the responsibility of the multidisciplinary team. The admission of patients to the intensive care unit (ICU) with DKA and HHS is rare, and management of patients' diverse problems is prone to error because of a lack of familiarity.

AIM

The paper's aim is to set the developmental process of a clinical guideline following a review of the literature.

DISCUSSION

This clinical guideline is based on a review of the evidence available within the literature in the early phase of resuscitation. Collaborative working among the multidisciplinary team through clinical practice group was the method adopted. Management of DKA and HHS is divided into three main areas: intravenous fluid replacement, insulin therapy and electrolyte management. The controversy associated with the administration of sodium bicarbonate is discussed.

CONCLUSION

Effective treatment requires a rapid initial assessment of the patient based on current medical history and clinical presentation. To this end, a quick reference algorithm and guide to management were also developed. Key criteria for evaluating the effectiveness of treatment are provided and complications of treatment are addressed. The formation of the practice development group that led to this innovation is outlined, and in conclusion, the success of the group is reflected upon.

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.

Year in review: Critical Care 2004 - nephrology

We summarize all original research in the field of critical care nephrology published in 2004 or accepted for publication in Critical Care and, when considered relevant or directly linked to this research, in other journals. Articles were grouped into four categories to facilitate a rapid overview. First, regarding the definition of acute renal failure (ARF), the RIFLE criteria (risk, injury, failure, loss, ESKD [end-stage kidney disease]) for diagnosis of ARF were defined by the Acute Dialysis Quality Initiative workgroup and applied in clinical practice by some authors. The second category is acid-base disorders in ARF; the Stewart-Figge quantitative approach to acidosis in critically ill patients has been utilized by two groups of researchers, with similar results but different conclusions. In the third category - blood markers during ARF - cystatin C as an early marker of ARF and procalcitonin as a sepsis marker during continuous venovenous haemofiltration were examined. Finally, in the extracorporeal treatment of ARF, the ability of two types of high cutoff haemofilters to influence blood levels of middle- and high-molecular-weight toxins showed promise.

The meaning of acid-base abnormalities in the intensive care unit: part III -- effects of fluid administration

Stewart's quantitative physical chemical approach enables us to understand the acid–base properties of intravenous fluids. In Stewart's analysis, the three independent acid–base variables are partial CO₂ tension, the total concentration of nonvolatile weak acid (A_TOT), and the strong ion difference (SID). Raising and lowering A_TOT while holding SID constant cause metabolic acidosis and alkalosis, respectively. Lowering and raising plasma SID while clamping A_TOT cause metabolic acidosis and alkalosis, respectively. Fluid infusion causes acid–base effects by forcing extracellular SID and A_TOT toward the SID and A_TOT of the administered fluid. Thus, fluids with vastly differing pH can have the same acid–base effects. The stimulus is strongest when large volumes are administered, as in correction of hypovolaemia, acute normovolaemic haemodilution, and cardiopulmonary bypass. Zero SID crystalloids such as saline cause a 'dilutional' acidosis by lowering extracellular SID enough to overwhelm the metabolic alkalosis of A_TOT dilution. A balanced crystalloid must reduce extracellular SID at a rate that precisely counteracts the A_TOT dilutional alkalosis. Experimentally, the crystalloid SID required is 24 mEq/l. When organic anions such as L-lactate are added to fluids they can be regarded as weak ions that do not contribute to fluid SID, provided they are metabolized on infusion. With colloids the presence of A_TOT is an additional consideration. Albumin and gelatin preparations contain A_TOT, whereas starch preparations do not. Hextend is a hetastarch preparation balanced with L-lactate. It reduces or eliminates infusion related metabolic acidosis, may improve gastric mucosal blood flow, and increases survival in experimental endotoxaemia. Stored whole blood has a very high effective SID because of the added preservative. Large volume transfusion thus causes metabolic alkalosis after metabolism of contained citrate, a tendency that is reduced but not eliminated with packed red cells. Thus, Stewart's approach not only explains fluid induced acid–base phenomena but also provides a framework for the design of fluids for specific acid–base effects.