Controversies in lactic acidosis. Implications in critically ill patients

Clinical presentations and prognosis of metformin-associated lactic acidosis patients in the intensive care unit: A 20-year survey

METHODS

We retrospectively analyzed 82 adult patients with MALA admitted to the ICU over 20 years. The association between the clinical parameters and mortality post-MALA was estimated using logistic regression analysis.

RESULTS

Patients with MALA admitted to the ICU presented with clinical symptoms mainly associated with the head (40.24%), chest (41.46%), and abdomen (35.37%). Additionally, the PLL distribution significantly varied with age, APACHE II = Acute Physiology and Chronic Health Evaluation II (APACHE II) score, various laboratory parameters like nadir arterial bicarbonate level, multiple treatment modalities such as renal replacement therapy, and mortality. The overall mortality rate was 17.07%. After adjustment of age and gender, the significant predictors of mortality were APACHE II score, PLL, vasoactive support, ventilator support, and cardiopulmonary resuscitation.

CONCLUSIONS

Despite MALA being a rare event, it is necessary to evaluate its clinical characteristics, especially the associated PLL and mortality. In the current study, higher levels of APACHE II score and PLL show a greater likelihood of mortality in MALA patients.

Acid-base abnormalities and liver dysfunction

In addition to the kidneys and lungs, the liver also plays an important role in the regulation of the Acid-Base Equilibrium (ABE). The involvement of the liver in the regulation of ABE is crucial because of its role in lactic acid metabolism, urea production and in protein homeostasis. The main acid-base imbalance that occurs in patients with liver cirrhosis is Respiratory Alkalosis (RAlk). Due to the fact that in these patients additional pathophysiological mechanisms that affect the ABE are present, other disorders may appear which compensate or enhance the primary disorder. Conventional ABE reading models fail to identify and assess the underlying disorders in patients with liver cirrhosis. This weakness of the classical models led to the creation of new physicochemical mathematical models that take into account all the known parameters that develop and affect the ABE. In addition to the RAlk, in patients with liver cirrhosis, metabolic alkalosis (due to hypoalbuminemia), hyponatremic metabolic acidosis, hyperchloremic metabolic acidosis, lactic acidosis and metabolic alkalosis due to urea metabolism are some of the pathophysiological mechanisms that affect the ABE.

Euglycemic Diabetic Ketoacidosis in a Sedated Patient after Coronary Artery Bypass Grafting: A Case Report and Literature Review

Euglycemic diabetic ketoacidosis (EDKA) is a rare and serious adverse effect of sodium-glucose cotransporter 2 inhibitors (SGLT-2i). The diagnosis is challenging due to the rarity, nonspecific symptoms, and absence of the alarmingly high blood glucose levels, and thus, it could be initially missed resulting in delayed treatment. This is particularly important for sedated patients, as the absence of typical clinical signs and symptoms can obscure the diagnosis. We present the case of a patient with type 2 diabetes mellitus on empagliflozin who developed EDKA while sedated after coronary artery bypass grafting (CABG) despite stopping the medication 24 hours prior to surgery. We also summarize the current literature on EDKA after CABG. Physicians must be aware and maintain a high index of suspicion for the illness, especially in patients with T2DM taking SGLT-2i and undergoing a major operation such as CABG. Emergent treatment and multidisciplinary follow-up are needed to improve patient outcomes and mitigate complications. Physicians should also consider identifying the optimal time to discontinue SGLT-2i before major surgeries and possible ketone studies in such patients, especially those sedated following the surgery.

Compensatory Reserve Index: Performance of A Novel Monitoring Technology to Identify the Bleeding Trauma Patient

INTRODUCTION

Hemorrhage is one of the most substantial causes of death after traumatic injury. Standard measures, including systolic blood pressure (SBP), are poor surrogate indicators of physiologic compromise until compensatory mechanisms have been overwhelmed. Compensatory Reserve Index (CRI) is a novel monitoring technology with the ability to assess physiologic reserve. We hypothesized CRI would be a better predictor of physiologic compromise secondary to hemorrhage than traditional vital signs.

METHODS

A prospective observational study of 89 subjects meeting trauma center activation criteria at a single level I trauma center was conducted from October 2015 to February 2016. Data collected included demographics, SBP, heart rate, and requirement for hemorrhage-associated, life-saving intervention (LSI) (i.e., operation or angiography for hemorrhage, local or tourniquet control of external bleeding, and transfusion >2 units PRBC). Receiver-operator characteristic (ROC) curves were formulated and appropriate thresholds were calculated to compare relative value of the metrics for predictive modeling.

RESULTS

For predicting hemorrhage-related LSI, CRI demonstrated a sensitivity of 83% and a negative predictive value (NPV) of 91% as compared with SBP with a sensitivity to detect hemorrhage of 26% (P < 0.05) and an NPV of 78%. ROC curves generated from admission CRI and SBP measures demonstrated values of 0.83 and 0.62, respectively. CRI identified significant hemorrhage requiring potentially life-saving therapy more reliably than SBP (P < 0.05).

CONCLUSION

The CRI device demonstrated superior capacity over systolic blood pressure in predicting the need for posttraumatic hemorrhage intervention in the acute resuscitation phase after injury.

Acid-base status and its clinical implications in critically ill patients with cirrhosis, acute-on-chronic liver failure and without liver disease

Background

Acid–base disturbances are frequently observed in critically ill patients at the intensive care unit. To our knowledge, the acid–base profile of patients with acute-on-chronic liver failure (ACLF) has not been evaluated and compared to critically ill patients without acute or chronic liver disease.

Results

One hundred and seventy-eight critically ill patients with liver cirrhosis were compared to 178 matched controls in this post hoc analysis of prospectively collected data. Patients with and without liver cirrhosis showed hyperchloremic acidosis and coexisting hypoalbuminemic alkalosis. Cirrhotic patients, especially those with ACLF, showed a marked net metabolic acidosis owing to increased lactate and unmeasured anions. This metabolic acidosis was partly antagonized by associated respiratory alkalosis, yet with progression to ACLF resulted in acidemia, which was present in 62% of patients with ACLF grade III compared to 19% in cirrhosis patients without ACLF. Acidemia and metabolic acidosis were associated with 28-day mortality in cirrhosis. Patients with pH values < 7.1 showed a 100% mortality rate. Acidosis attributable to lactate and unmeasured anions was independently associated with mortality in liver cirrhosis.

Conclusions

Cirrhosis and especially ACLF are associated with metabolic acidosis and acidemia owing to lactate and unmeasured anions. Acidosis and acidemia, respectively, are associated with increased 28-day mortality in liver cirrhosis. Lactate and unmeasured anions are main contributors to metabolic imbalance in cirrhosis and ACLF.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0391-9) contains supplementary material, which is available to authorized users.

Significant Lactic Acidosis from Albuterol

Lactic acidosis is a clinical entity that demands rapid assessment and treatment to prevent significant morbidity and mortality. With increased lactate use across many clinical scenarios, lactate values themselves cannot be interpreted apart from their appropriate clinical picture. The significance of Type B lactic acidosis is likely understated in the emergency department (ED). Given the mortality that sepsis confers, a serum lactate is an important screening study. That said, it is with extreme caution that we should interpret and react to the resultant elevated value. We report a patient with a significant lactic acidosis. Though he had a high lactate value, he did not require aggressive resuscitation. A different classification scheme for lactic acidosis that focuses on the bifurcation of the “dangerous” and “not dangerous” causes of lactic acidosis may be of benefit. In addition, this case is demonstrative of the potential overuse of lactates in the ED.

Comparison of compensatory reserve and arterial lactate as markers of shock and resuscitation

BACKGROUND

During traumatic hemorrhage, the ability to identify shock and intervene before decompensation is paramount to survival. Lactate is extremely sensitive to shock, and its clearance has been demonstrated a useful gauge of shock and resuscitation status. Though lactate can be measured in the field, logistical constraints render it impractical in certain environments. The compensatory reserve represents a new clinical measurement reflecting the remaining capacity to compensate for hypoperfusion. We hypothesized the compensatory reserve index (CRI) would be an effective surrogate marker of shock and resuscitation compared to lactate.

METHODS

The CRI device was placed on consecutive patients meeting trauma center activation criteria and remained on the patient until discharge, admission, or transport to operating suite. All subjects had a lactate level measured as part of their routine admission metabolic analysis. Time-corresponding CRI and lactate values were matched in regards to initial and subsequent lactate levels. Mean time from lactate sample collection to data availability in the electronic medical record was calculated. Predictive capacity of CRI and lactate in predicting hemorrhage was determined by receiver-operator characteristic curve analysis. Correlation analysis was performed to determine if any association existed between changing CRI and lactate values.

RESULTS

Receiver-operator characteristic (ROC) curves were generated and area under the curve was 0.8052 and 0.8246 for CRI and lactate, respectively. There was no significant difference in each parameter's ability to predict hemorrhage (p = 0.8015). The mean duration from lactate sample collection to clinical availability was 44 minutes whereas CRI values were available immediately. Analysis of the concomitant change in serial CRI and lactate levels revealed a Spearman's correlation coefficient of -0.73 (p < 0.01).

CONCLUSION

CRI performed with equivalent predictive capacity to lactate with respect to identifying initial perfusion status associated with hemorrhage and subsequent resuscitation.

LEVEL OF EVIDENCE

Diagnostic, Level II.

Relationship Between Peak Lactate and Patient Outcome Following High-Risk Gastrointestinal Surgery: Influence of the Nature of Their Surgery: Elective Versus Emergency

OBJECTIVES

The association between hyperlactatemia and adverse outcome in patients admitted to ICUs following gastrointestinal surgery has not been reported. To explore the hypothesis that in a large cohort of gastrointestinal surgical patients, the peak serum lactate (in the first 24 hr) observed in patients admitted to ICU following surgery is associated with unadjusted and severity-adjusted acute hospital mortality and that the strength of association is greater in patients admitted following "emergency" surgery than in patients admitted following "elective" surgery.

DESIGN

A retrospective cohort study of all patients who had gastrointestinal surgery and were admitted directly to the ICU between 2008 and 2012.

SETTING

Two hundred forty-nine hospitals in the United Kingdom.

PATIENTS

One hundred twenty-one thousand nine hundred ninety patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Peak blood lactate in the first 24 hours of admission to critical care, acute hospital mortality, length of stay, and other variables routinely collected within the U.K. Intensive Care National Audit and Research Centre Case Mix Programme database. Elevated blood lactate was associated with increased risk of death and prolonged duration of stay, and the relationship was maintained once adjusted for confounding variables. The positive association between mortality and levels of blood lactate continued down into the "normal range," without evidence of a plateau. There was no difference in the extent to which hyperlactatemia was related to mortality between patients admitted following elective and emergency surgery.

CONCLUSIONS

These findings have implications for our understanding of the role of lactate in critically ill patients.

Can we predict arterial lactate from venous lactate in the ED?

OBJECTIVE

We aimed to generate equation to predict arterial lactate (a-Lac) using venous lactate (v-Lac) and other lab data.

METHODS

A prospective cross-sectional study was conducted on emergency patients in the emergency department for 6 months at a general hospital in Tokyo, Japan. We collected arterial and venous gas analysis data. Patients were eligible for entry into the study if an arterial blood gas analysis was required for appropriate diagnostic care by the treating physician. Univariate linear regression analysis was conducted to generate an equation to calculate a-Lac incorporating only v-Lac. A multivariate forward stepwise logistic regression model (p-value of 0.05 for entry, 0.1 for removal) was used to generate an equation including v-Lac and other potentially relevant variables. Bland-Altman plot was drawn and the two equations were compared for model fitting using R-squares.

RESULTS

Seventy-two arterial samples from 72 participants (61% male; mean age, 58.2 years) were included in the study. An initial regression equation was derived from univariate linear regression analysis:"(a-Lac) = -0.259 + (v-Lac) × 0.996". Subsequent multivariate forward stepwise logistic regression analysis, incorporating v-Lac and Po2, generated the following equation:"(a-Lac) = -0.469+(venous Po2) × 0.005 + (v-Lac) × 0.997". Calculated R-squares by single and multiple regression were 0.94 and 0.96, respectively.

CONCLUSION

v-Lac estimates showed a high correlation with arterial values and our data provide two clinically useful equations to calculate a-Lac from v-Lac data. Considering clinical flexibility, "Lac = -0.259 + v-Lac × 0.996" might be more useful while avoiding a time-consuming and invasive procedure.

Prehospital lactated ringer's solution treatment and survival in out-of-hospital cardiac arrest: a prospective cohort analysis

BACKGROUND

No studies have evaluated whether administering intravenous lactated Ringer's (LR) solution to patients with out-of-hospital cardiac arrest (OHCA) improves their outcomes, to our knowledge. Therefore, we examined the association between prehospital use of LR solution and patients' return of spontaneous circulation (ROSC), 1-month survival, and neurological or physical outcomes at 1 month after the event.

METHODS AND FINDINGS

We conducted a prospective, non-randomized, observational study using national data of all patients with OHCA from 2005 through 2009 in Japan. We performed a propensity analysis and examined the association between prehospital use of LR solution and short- and long-term survival. The study patients were ≥18 years of age, had an OHCA before arrival of EMS personnel, were treated by EMS personnel, and were then transported to hospitals. A total of 531,854 patients with OHCA met the inclusion criteria. Among propensity-matched patients, compared with those who did not receive pre-hospital intravenous fluids, prehospital use of LR solution was associated with an increased likelihood of ROSC before hospital arrival (odds ratio [OR] adjusted for all covariates [95% CI] = 1.239 [1.146-1.339] [p<0.001], but with a reduced likelihood of 1-month survival with minimal neurological or physical impairment (cerebral performance category 1 or 2, OR adjusted for all covariates [95% CI] = 0.764 [0.589-0.992] [p = 0.04]; and overall performance category 1 or 2, OR adjusted for all covariates [95% CI] = 0.746 [0.573-0.971] [p = 0.03]). There was no association between prehospital use of LR solution and 1-month survival (OR adjusted for all covariates [95% CI] = 0.960 [0.854-1.078]).

CONCLUSION

In Japanese patients experiencing OHCA, the prehospital use of LR solution was independently associated with a decreased likelihood of a good functional outcome 1 month after the event, but with an increased likelihood of ROSC before hospital arrival. Prehospital use of LR solution was not associated with 1-month survival. Further study is necessary to verify these findings. Please see later in the article for the Editors' Summary.

The association of blood lactate concentration with outcome in dogs with idiopathic immune-mediated hemolytic anemia: 173 cases (2003-2006)

OBJECTIVE

To determine the association of blood lactate with outcome and response to transfusion therapy in dogs with idiopathic immune-mediated hemolytic anemia (IMHA).

DESIGN

Retrospective study.

SETTING

Urban veterinary small animal emergency hospital.

ANIMALS

One hundred and seventy-three client-owned dogs with IMHA.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Serial blood lactate concentration, therapeutic interventions, and outcome were recorded. Nonsurvivors were defined as those that died or were euthanized. One hundred and thirty-three dogs (77%) survived, 35 (20%) were euthanized, and 5 (3%) died. One hundred forty-five dogs (84%; 145/173) had a lactate concentration above the laboratory reference interval [0.46-2.31 mmol/L] on presentation. Blood lactate at presentation was higher in the nonsurvivors (median 4.8 mmol/L; 0.5-13.6) compared with survivors (median 2.9 mmol/L; 0.3-13.2) (P<0.01). All dogs presenting with hyperlactatemia that normalized (<2.0 mmol/L) within 6 hours of admission survived, whereas, 71% of dogs that had a persistent hyperlactatemia at 6 hours survived (P=0.034). Lactate was positively correlated with age, BUN, and alkaline phosphatase, and inversely correlated with PCV. Receiver operating curve analysis for lactate concentration at admission as a test for outcome had an area under the curve of 0.69 with an optimal lactate cutoff concentration of 4.4 mmol/L correctly predicting outcome 73% of the time (sensitivity 60%, specificity 77%).

CONCLUSIONS

Lactate concentration at presentation was significantly higher in nonsurvivors than survivors. Lactate was significantly correlated with previously reported outcome variables but lactate concentration at admission, as a predictor for outcome was less than optimal. However, serial lactate concentration measurements may be more predictive as patients with persistent hyperlactatemia 6 hours after admission were less likely to survive. Prospective studies evaluating serial lactate concentration while controlling for other variables may provide further insight into lactate measurement as a prognostic indicator in animals with IMHA.

Arterial lactate concentration, hospital survival, sepsis and SIRS in critically ill neonatal foals

REASONS FOR PERFORMING STUDY

Blood lactate concentration has been shown to be a useful clinical indicator in human patients, but has not been formally investigated in critically ill foals.

OBJECTIVE

To investigate the association of blood lactate with hospital survival, markers of cardiovascular status, metabolic acid base status, sepsis and systemic inflammatory response syndrome (SIRS).

METHODS

A database containing clinical, haematological, plasma biochemical and hospital outcome data on neonatal foals referred to an intensive care unit in 2000-2001 was analysed. Seventy-two foals for which arterial lactate was measured at admission were included in the study.

RESULTS

Sixty-one foals had an admission lactate concentration > 2.5 mmol/l. Admission lactate was statistically associated with hospital survival, mean arterial pressure, blood creatinine concentration, bacteraemia, anion gap, lactate concentration at 18-36 h after admission and evidence of SIRS, but not with packed cell volume or heart rate. Lactate at 18-36 h was also associated with survival and evidence of SIRS. Anion gap, base excess, base excess due to unidentified anions (BEua), simplified strong ion gap or bicarbonate correctly classified foals for presence of hyperlactaemia (> 5 mmol/l) in < or = 80% of animals.

CONCLUSIONS

Admission blood lactate gives important prognostic information. Lactate should be measured rather than assumed from the anion gap, base excess, BEua, simplified strong ion gap or bicarbonate.

POTENTIAL RELEVANCE

Blood lactate concentrations at admission are clinically relevant in neonatal foals and warrant further investigation. This should include the clinical value of measuring changes in lactate in response to treatment.

Differentiating the causes of metabolic acidosis in the poisoned patient

Numerous drugs and toxins may induce the development of a metabolic acidosis. The treating physician should be cognizant of the many compounds that can produce metabolic acidosis following an overdose or an accidental exposure, or with therapeutic use. Knowledge and comprehension of the substances associated with metabolic acidosis will facilitate the diagnosis and treatment of poisoned patients.

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.

Metabolic acidosis: differentiating the causes in the poisoned patient

Metabolic acidosis may arise from several drugs and toxins through a variety of mechanisms. Differentiating the causes of metabolic acidosis in the poisoned patient is an indispensable skill in clinical practice. Comprehension of toxin-induced metabolic acidosis, combined with a thorough history, physical examination, appropriate use of laboratory tests, and a stepwise approach, should aid the clinician in determining the cause of metabolic acidosis in the poisoned patient. When confronted with such a patient, it is imperative that one administer appropriate antidotal therapy, when necessary, and provide the patient with exceptional supportive care.

Cyanides

Cyanide is a likely weapon for terrorists due to its notoriety, lethality, and availability. Poisoning results in central nervous system and cardiovascular dysfunction due to inhibition of oxidative phosphorylation. Laboratory findings of anion gap metabolic acidosis and hyperlactemia aid in confirming the diagnosis. Treatment for significant poisonings includes aggressive supportive care and administration of antidotes such as sodium nitrite, sodium thiosulfate, and hydroxocobalamin. Survivors of significant poisonings can have long-term neurologic dysfunction.

Ethanol intoxication and lactated Ringer's resuscitation prolong hemorrhage-induced lactic acidosis

Ethanol (EtOH) blunts the respiratory and metabolic compensation during hemorrhage, resulting in a more severe lactic acidemia. We hypothesized that lactated Ringer's (LR) resuscitation may exacerbate this lactic acidemia. Male guinea pigs were implanted with arterial and venous catheters. Two days after catheter placement, conscious animals were injected intraperitoneally with 1 g/kg EtOH, 0.3 g/kg EtOH, or an equal volume of water 30 min before hemorrhage (60% of estimated blood volume). After 30 min of hemorrhagic shock, animals were resuscitated with isotonic saline (S) or LR at 1 mL/min (three times shed blood volume). Mean arterial blood pressure (MABP) was not affected by pretreatment with either dose of EtOH, but was significantly decreased by hemorrhage in all groups. Both S and LR resuscitation slightly increased MABP, but neither restored it to prehemorrhage values. Blood lactate levels increased in all groups during hemorrhage and remained elevated for 3 h in animals pretreated with 1 g/kg EtOH. In the group pretreated with 0.3 g/kg EtOH, pH decreased during shock but returned to prehemorrhage levels during the resuscitation period. Resuscitation with S returned pH to prehemorrhage values in animals pretreated with 1.0 g/kg EtOH. Resuscitation with LR did not exacerbate, but did prolong, the lactic acidemia after shock in animals pretreated with 1.0 g/kg EtOH. Administration of additional lactate during intoxication and hypovolemia for hemodynamic stabilization before blood transfusion may exacerbate a metabolic stress.

Tissue oxygenation and perfusion in patients with systemic sepsis

OBJECTIVE

Multiple organ dysfunction is associated with systemic sepsis. To investigate whether this is attributable to peripheral tissue hypoperfusion and/or cellular hypoxia, simultaneous measurements of tissue perfusion and oxygenation were made in patients with severe sepsis and in controls.

DESIGN

Prospective, observational study.

SETTING

Adult intensive care unit, tertiary referral center.

PATIENTS

Volunteers (group C, n = 7), patients undergoing cardiopulmonary bypass (group B, n = 6), and patients with severe sepsis (group S, n = 6).

INTERVENTIONS

Limb ischemia and reperfusion.

MEASUREMENTS AND MAIN RESULTS

Tissue oxygenation and microvascular flow were measured by using microelectrodes inserted into brachoradialis muscle and overlying subcutaneous tissue. Forearm cutaneous red cell flux and regional blood flow were measured simultaneously. Responses to 20 mins of limb ischemia and subsequent reperfusion were observed. Baseline muscle tissue oxygenation was greater in sepsis (1.7 +/- 0.2, 1.5 +/- 0.7, and 4.4 +/- 0.6 kPa for groups C, B, and S, respectively, mean +/- sem, p <.05), although baseline subcutaneous tissue oxygenation did not vary between groups. During ischemia tissue oxygenation, values decreased in muscle (to 1.3 +/- 0.2, 1.0 +/- 0.4, and 1.5 +/- 0.4 kPa for groups C, B, and S, respectively) and subcutaneous tissue (to 2.0 +/- 0.3, 1.7 +/- 0.5, and 2.3 +/- 0.2 kPa for groups C, B, and S, respectively). Decline in tissue oxygen tension was initially more rapid in septic muscle compared with controls (25% decrease, 68 +/- 23 vs. 176 +/- 38 for group S vs. group C, p <.05, and 50% decrease, 126 +/- 34 vs. 398 +/- 72 secs for group S vs. group C, p <.01). However, overall rate of tissue decline was similar (95% decrease, 444 +/- 122 vs. 614 +/- 96 for group S vs. group C, p >.05). After reperfusion, significant differences in muscle tissue oxygenation reappeared between groups (2.0 +/- 0.3, 1.5 +/- 0.7, and 4.0 +/- 0.4 kPa for groups C, B, and S, respectively, p <.05). There were no differences in time to 25%, 50%, or 95% tissue oxygen recovery. Whole limb reperfusion was significantly less in patient groups compared with controls (10.6 +/- 0.9, 4.5 +/- 1.2, and 4.3 +/- 1.6 mL x 100 mL(-1) x min(-1) for groups C, B, and S, respectively, p <.05).

CONCLUSIONS

Significant differences in tissue oxygenation distribution between muscle and subcutaneous tissues occur in patients with severe sepsis. High baseline muscle tissue oxygen levels are accompanied by rapid extraction of oxygen during stagnant ischemia.

Serial blood lactate measurements predict early outcome after neonatal repair or palliation for complex congenital heart disease

OBJECTIVES

Neonates with congenital heart disease may appear hemodynamically stable after operation and then suddenly experience catastrophic decompensation. An improved means of predicting which infants will suddenly die in the early postoperative period may lead to lifesaving interventions. Studies indicate that blood lactate level is proportional to tissue oxygen debt, but information linking lactate levels with outcome in infants after operation is limited. We sought to determine whether a change in lactate level over time was predictive of a poor outcome defined as death within the first 72 hours or the need for extracorporeal membrane oxygenation.

METHODS

To test this hypothesis, we studied prospectively 46 infants who were less than 1 month old and were undergoing complex cardiac surgical palliation or repair. Postoperative arterial oxygen saturation, bicarbonate, and lactate levels were recorded on admission to the intensive care unit and every 3 to 12 hours for the first 3 days.

RESULTS

Thirty-seven patients had a good outcome, and 9 patients had a poor outcome. Mean initial lactate level was significantly greater in patients with a poor outcome (9.4 +/- 3.8 mmol/L) than in patients with a good outcome (5.6 +/- 2.1 mmol/L; P =.03). However, an elevated initial lactate level of more than 6 mmol/L had a low positive predictive value (38%) for poor outcome. In contrast, a change in lactate level of 0.75 mmol/L per hour or more was associated with a poor outcome (P <.0001) and predicted a poor outcome with an 89% sensitivity value, a 100% specificity value, and a 100% positive predictive value.

CONCLUSIONS

Serial blood lactate level measurements may be an accurate predictor of death or the requirement for extracorporeal membrane oxygenator support for patients who undergo complex neonatal cardiac surgery.

Hypothermia, coagulopathy, and acidosis

The management of patients requiring a damage control approach taxes the abilities of the best equipped trauma center. These patients present with severe metabolic abnormalities, most notably characterized by a deadly triad of hypothermia, coagulopathy, and acidosis. Using volumetric, oxymetric pulmonary artery catheters, hypothermia and any ongoing cardiovascular abnormalities can be identified quickly and treatment can be monitored. External, forced air rewarming is a valuable technique in treating the patient with hypothermia, as are more invasive modalities, including body cavity lavage. Although there is no shotgun approach to blood component transfusion therapy, the coagulopathy shown by these patients has a time course that is more rapid than stat laboratories can presently keep up with. Given the fulminant nature of this coagulopathy, the authors feel justified in empirically initiating platelet and plasma or cryoprecipitate transfusion on identification of visible coagulopathy. The willingness of trauma surgeons to push the envelope in treating these most severely afflicted patients has allowed patients who once would have certainly died to lead meaningful lives.

A model analysis of lactate accumulation during muscle ischemia

PURPOSE

The mechanistic basis of the relationship between tissue [O2] and tissue or blood lactate (LA) concentration during tissue hypoxia are not fully understood. However, blood and tissue lactate accumulation are still used as indicators of tissue hypoxia in critically ill patients. To investigate this relationship, we applied a previously developed mathematical model of human bioenergetics to simulate the integrated responses (cellular, tissue, and whole body) to moderate (10% to 45%) and severe (50% to 80%) reductions in muscle blood flow.

MATERIALS AND METHODS

Model simulations of muscle ischemia predicted metabolite concentration changes in muscle, splanchnic bed, and other tissues, and were compared with experimental data in humans for model validation.

RESULTS

In general, simulations closely predicted the pattern of change in substrates and control metabolites to that observed experimentally. Specifically, simulations showed that most of the increase in muscle LA production during moderate ischemia was due to an increase in pyruvate (PY) and notto the change in redox state induced by a small decrease in O2 consumption. However, during severe ischemia, changes in [LA]/[PY] ratio in venous blood corresponded very closely to changes in tissue redox state. Because both blood [LA] and [LA]/[PY] tracked changes in tissue redox state very well, these can be used reliably as indices of tissue hypoxia during severe muscle ischemia.

CONCLUSIONS

Based on the simulations, the commonly used threshold value for venous [LA]/[PY] = 14 as evidence of tissue hypoxia seems appropriate during severe ischemia.

Use of different anticoagulants in test tubes for analysis of blood lactate concentrations: Part 2. Implications for the proper handling of blood specimens obtained from critically ill patients

OBJECTIVES

a) To test the hypothesis that the measurement of the circulating lactate concentration is influenced by the anticoagulant in the test tube that contains the blood sample; b) to test the hypothesis that the measurement of the circulating lactate concentration is influenced by the tissue used for analysis.

DESIGN

A prospective, controlled study.

SETTING

A critical care research laboratory, a 20-bed intensive care unit (ICU), and the general wards.

SUBJECTS

Twenty-three ICU and ward patients with hyperlactatemia and 19 healthy volunteers.

INTERVENTIONS

Blood samples were collected for determination of blood lactate concentration.

MEASUREMENTS AND MAIN RESULTS

Venous blood samples (12 mL) were obtained from each of the 19 normal subjects and each 12-mL specimen was evenly divided into six aliquot portions (six test tubes). Experiment 1: Of the six tubes, two tubes were set aside for experiment 2. The other four tubes were used to test four anticoagulants (one anticoagulant per tube). The anticoagulants tested were: sodium heparin; EDTA; lithium heparin; and sodium citrate. Lactate concentrations were analyzed using an ion-selective, amperometric electrode that we have previously validated. There were no statistically significant differences between the lactate concentrations derived from blood samples stored in sodium heparin, EDTA, or lithium heparin (p > .05; n = 19; Student-Newman-Keuls' multiple comparisons test). The lactate concentration of blood stored in sodium citrate, however, was lower than all other anticoagulants (p < .001; n = 19; Student-Newman-Keuls' multiple comparisons). Experiment 2: Of the remaining two test tube samples from each subject, one tube contained sodium heparin and the other tube did not contain an anticoagulant. Each of these two tubes was centrifuged at 50 degrees F (10 degrees C) for 15 mins to obtain plasma and serum samples. Lactate concentrations were measured in the serum and plasma and compared with those concentrations found in whole blood samples from the tube containing sodium heparin from experiment 1. The plasma and serum lactate concentrations were consistently higher than the whole blood lactate values from the same specimen (p < .05; n = 42; Student-Newman-Keuls' multiple comparisons test). Since experiment 1 involved the collection of blood from healthy volunteers with normal lactate concentrations, we chose to investigate whether this discordance between plasma or serum and whole blood was dependent on the lactate concentration. To answer this question, we studied 23 patients with known hyperlactatemia and found that in subjects with a lactate concentration of < 2.2 mmol/L, there was a difference of 0.11 mmol/L in the mean values between plasma and whole blood concentrations (p < .0004; n = 19; paired t-test). In subjects with a lactate concentration of > 2.2 mmol/L, there was a difference of 0.14 mmol/L (p < .0001; n = 23; paired t-test) in the mean values between plasma and whole blood. In all samples at all concentrations, there was no significant difference between serum vs. plasma samples (p > .05; Student-Newman-Keuls' test).

CONCLUSIONS

a) Sodium citrate, as an anticoagulant, caused lower lactate concentrations to be measured as compared with heparin or EDTA; b) the measurement of lactate concentrations in plasma or serum samples yields a higher value than the concentration found in the original whole blood specimen.

Effect of intravenous lactated Ringer's solution infusion on the circulating lactate concentration: Part 3. Results of a prospective, randomized, double-blind, placebo-controlled trial

OBJECTIVES

We previously discovered that small amounts of lactated Ringer's solution, which are inadequately cleared from an intravenous catheter, falsely increase the circulating lactate concentration in blood samples collected from that catheter. That finding prompted us to test the hypothesis that intravenous lactated Ringer's solution, infused at a rate used in resuscitation, would increase the circulating lactate concentration.

DESIGN

A prospective, randomized, double-blinded, placebo-controlled study.

SETTING

A critical care research laboratory.

SUBJECTS

Twenty-four normal, healthy, adult volunteer subjects.

INTERVENTIONS

Two intravenous catheters were placed. One was used for the infusion of the test solution and the other catheter was used for blood sampling. Blood samples were serially collected for the determination of blood lactate concentrations.

MEASUREMENTS AND MAIN RESULTS

Twenty-four healthy adult volunteers were randomized to receive a 1-hr infusion of either lactated Ringer's solution (n = 6), 0.9% saline (n = 6), 5% dextrose in lactated Ringer's solution (D5RL) (n = 6), or 5% dextrose in water (D5W) (n = 6). Each subject received nothing by mouth after midnight. At 0800 hrs, catheters were inserted and each subject received 1 L of the assigned solution over 1 hr. Throughout the study, the subjects were at rest. Three-milliliter samples of venous blood were collected before, during (at 15, 30, 45, and 60 mins), and after (at 90, 120, and 240 mins) the infusion. Blood samples were placed on ice immediately after collection and analyzed within 5 mins of collection. Lactate concentrations were determined using an ion-selective, amperometric electrode, which we have previously validated. Lactate concentrations were compared between subjects receiving lactated Ringer's solution vs. subjects receiving normal saline. A similar comparison was made between subjects receiving D5RL vs. D5W at similar time points during the study. There were no clinically or statistically significant differences in lactate values at the time points studied in those subjects receiving lactated Ringer's solution vs. those persons receiving normal saline (p > .05; n = 12; Student-Newman-Keuls' multiple comparison test) or those subjects receiving D5W vs. those subjects infused with D5RL (p > .05; n = 12; Student-Newman-Keuls' multiple comparison test). In no case did the circulating lactate values exceed 2 mmol/L (the upper limit of normal).

CONCLUSIONS

The short-term infusion of lactated Ringer's solution in normal adults (hemodynamically stable) does not falsely increase circulating lactate concentrations when 1 L is given over 1 hr. Therefore, clinicians should not disregard increased lactate concentrations in patients receiving a rapid infusion of lactated Ringer's solution.

ED use of rapid lactate to evaluate patients with acute chest pain

STUDY OBJECTIVE

To test the hypothesis that ED arrival venous lactate levels can be used to diagnose acute myocardial infarction (AMI) and to identify patients with critical illness in the triage of ED patients presenting with chest pain.

METHODS

This was a prospective, double-blind, clinical study in an urban, academic ED. We enrolled a convenience sample of adult patients who had chest pain or cardiac symptoms suggesting AMI that began within 24 hours of presentation. Patients underwent standard medical management for their chest pain. Venous lactate samples were analyzed in the ED on whole blood. An abnormal lactate level of 1.5 mmol/L or higher at the time of arrival was prospectively defined as indicating the presence of acute cardiac disease. ECG findings, levels of creatine phosphokinase (CK) and CK-MB, hospital stay data, and diagnosis of AMI by the cardiology admitting team were recorded.

RESULTS

Of the 129 patients included in the study, 73 had an initial lactate level of 1.5 mmol/L or higher. The mean lactate level (+/- SD) for all patients was 1.8 +/- 1.2 mmol/L. A total of 28 patients (21%) were diagnosed with AMI and had a mean lactate level of 2.2 +/- .7 mmol/L, compared with 1.7 +/- 1.3 mmol/L in those patients who were not diagnosed with AMI (P < .03). The sensitivity of this lactate level in diagnosing AMI was 96% (95% confidence interval [CI], 89% to 100%), and the specificity was 55% (95% CI, 45% to 64%). The negative predictive value of blood lactate was 98% (95% CI, 95% to 100%). Lactate was elevated independent of the duration of chest pain symptoms, with a median time from onset to sampling of 3 hours. Lactate was elevated in patients who either died or required longer than 48 hours of ICU care, compared with survivors not requiring ICU care (4.5 +/- 4.3 mmol/L versus 1.4 +/- .6 mmol/L, respectively; P < .01).

CONCLUSION

The blood lactate concentration obtained on ED arrival identifies those chest pain patients with critical cardiac illness (eg, AMI, severe congestive heart failure [CHF], decompensated arrhythmias). A normal blood lactate result has a high negative predictive value for AMI. An elevated lactate level used in conjunction with ECG and history distinguishes patients with significant myocardium at risk who are likely to benefit from more urgent attention and interventions by the attending physician. Additionally, hyperlactatemia clearly correlates with mortality and the need for ICU management in the acute cardiac patient presenting to the ED.

The association between blood lactate concentration on admission, duration of cardiac arrest, and functional neurological recovery in patients resuscitated from ventricular fibrillation

OBJECTIVE

To assess the association between arterial lactate concentration on admission and the duration of human ventricular fibrillation cardiac arrest, and to what degree the arterial lactate concentration on admission is an early predictor of functional neurological recovery in human cardiac arrest survivors.

DESIGN

Cohort study. Arterial lactate concentrations and out-of-hospital data concerning cardiac arrest and cardiopulmonary resuscitation were collected retrospectively according to a standardized protocol. Functional neurological recovery was assessed prospectively at regular intervals for 6 months.

SETTING

Emergency department of an urban tertiary care hospital.

PATIENTS

A total of 167 primary survivors of witnessed out-of-hospital ventricular fibrillation cardiac arrest.

MEASUREMENTS

The association between arterial lactate concentration on admission, the duration of cardiac arrest, and functional neurological recovery was assessed. Further, we assessed whether admission concentrations of arterial lactate and duration of cardiac arrest can predict unfavorable functional neurological recovery. Functional neurological recovery was measured in cerebral performance categories (CPC). No or minimal functional impairment (CPC 1 and 2) was defined as favorable outcome; the remaining categories (CPC 3, 4 and 5) were defined as unfavorable functional neurological recovery.

RESULTS

In 167 patients, a weak association between total duration of cardiac arrest and admission levels of lactate (r = 0.49, P < 0.001) could be shown. With increasing admission concentrations of arterial lactate functional neurological recovery was more likely to be unfavorable (OR 1.15 per mmol/l increase, 95% CI 1.04-1.27). Nevertheless, only at very high levels of lactate (16.3 mmol/l) could unfavorable neurological recovery be detected with 100% specificity, yielding a very low sensitivity of 16%.

CONCLUSIONS

The arterial admission lactate concentration after out-of-hospital ventricular fibrillation cardiac arrest is a weak measure of the duration of ischemia. High admission lactate levels are associated with severe neurological impairment. However, this parameter has poor prognostic value for individual estimation of the severity of subsequent functional neurological impairment.

Epinephrine-induced lactic acidosis following cardiopulmonary bypass

OBJECTIVE

To determine if lactic acidosis occurring after cardiopulmonary bypass could be attributed to the metabolic or other effects of epinephrine administration.

DESIGN

Prospective, randomized study.

SETTING

Postsurgical cardiothoracic intensive therapy unit.

PATIENTS

Thirty-six adult patients, without acidosis, requiring vasoconstrictors for the management of hypotension after cardiopulmonary bypass.

INTERVENTIONS

Randomized administration of either epinephrine or norepinephrine by infusion.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic and metabolic data were collected before commencement of vasoconstrictor therapy (time 0) and then 1 hr (time 1), 6 to 10 hrs (time 2), and 22 to 30 hrs (time 3) later. Six of the 19 patients who received epinephrine developed lactic acidosis. None of the 17 patients receiving norepinephrine developed lactic acidosis. In the epinephrine group, but not in the norepinephrine group, lactate concentration increased significantly at times 1 and 2 (p = .01), while pH and base excess decreased (p < or = .01). Blood glucose concentration was higher in the epinephrine group at time 2 (p = .02), while the cardiac index (p < .03) and the mixed venous Po2 (p = .04) were higher at time 1. compared with the norepinephrine group, the patients receiving epinephrine had higher femoral venous lactate concentrations (p = .03), increased lower limb blood flow (p = .05), and increased femoral venous oxygen saturations (p = .04).

CONCLUSIONS

The use of epinephrine after cardiopulmonary bypass precipitates the development of lactic acidosis in some patients. This phenomenon is presumably a beta-mediated effect, and is associated with an increase in whole-body and lower limb blood flow and a decrease in whole-body and transfemoral oxygen extraction. The phenomenon does not appear to be related to reduced tissue perfusion and does not have the poor outlook of lactic acidosis associated with shock.

Determinants and utility of the anion gap in predicting hyperlactatemia in cattle

The objectives of this study were to investigate the determinants of the anion gap (AG) in cattle and to evaluate the utility of AG in detecting hyperlactatemia in sick neonatal calves and adult cattle. The AG was calculated as AG = ([Na+] + [K+])-([Cl-] + [HCO-3]), with all values in mEq/L. The AG of healthy neonatal calves (n = 16) was 29.6 +/- 6.2 mEq/L (mean +/- SD), and the blood L-lactate concentration ranged from 0.5 to 1.2 mM/L. The AG was significantly (P < .05) correlated with serum phosphate (r = .66) and creatinine (r = .51) concentrations. The AG of neonatal calves with experimentally induced diarrhea (n = 16) was 28.6 +/- 5.6 mEq/L, and the blood L-lactate concentration ranged from 1.1 to 2.9 mM/L. The AG was significantly correlated with blood L-lactate concentration (r = .67), serum phosphate concentration (r = .63), creatinine concentration (r = .76), and blood pH (r = -.61). The AG of adult cattle with abomasal volvulus (n = 41) was 20.5 +/- 7.8 mEq/L, and the blood L-lactate concentration ranged from 0.6 to 15.6 mM/L. The AG was significantly correlated with blood L-lactate concentration (r = .60), serum phosphate concentration (r = .71), creatinine concentration (r = .65), albumin concentration (r = .47), total protein concentration (r = .54), blood pyruvate concentration (r = .67), and blood pH (r = -.41) but not plasma beta-OH butyrate concentration. The results indicate that the AG in cattle is only moderately correlated with blood L-lactate concentration and is similarly correlated with serum phosphate and creatinine concentrations in neonatal calves and adult cattle, as well as with serum albumin and total protein concentrations in adult cattle. Anion gap determination is of limited usefulness in predicting blood L-lactate concentration in sick cattle, whereas the correlation between AG and serum creatinine concentration in sick cattle suggests that an increased AG should alert the clinician to the potential presence of uremic anions.

Effects of increased red cell mass on subclinical tissue acidosis in hyaline membrane disease

AIM

To determine whether there are subclinical deficits in oxygen delivery in ventilated premature neonates.

METHOD

Ventilated premature neonates weighing less than 1500 g, who were transfused for anaemia or who were given colloids for clotting abnormalities (or oedema), were haemodynamically monitored during the first week of life. Calf muscle surface pH (pH) was measured in conjunction with peripheral limb blood flow by occlusion plethysmography.

RESULTS

Packed red blood cell transfusions corrected a subclinical regional tissue acidosis (low tpH) without affecting arterial pH or limb blood flow. This observation also correlated with an increase in regional oxygen delivery. The data were also suggestive of a pattern of pathological, supply dependent, oxygen delivery and are similar to other observations made in adults with adult respiratory distress syndrome.

CONCLUSIONS

Packed red blood cells increase regional oxygen delivery and tissue surface pH. In contrast, colloid infusion provided no substantial cardiovascular or metabolic benefit to these patients and should be avoided when oxygen delivery is at issue and when there may be leaky pulmonary capillaries.

Transvisceral lactate fluxes during early endotoxemia

The pathogenesis of hyperlacticemia during sepsis is poorly understood. We investigated the role of lung, kidney, gut, liver, and muscle in endogenous lactate uptake and release during early endotoxemia in an intact, pentobarbital-anesthetized dog model (n = 14). Ultrasonic flow probes were placed around the portal vein and hepatic, renal, and femoral arteries. After splenectomy, catheters were inserted into the pulmonary artery, aorta, and hepatic, left renal, and femoral veins. Whole blood lactate and blood gases from all catheters, organ flows, and cardiac output were measured before and 30 to 45 min after a bolus infusion of Eacherichia coli endotoxin (1 mg/kg). After endotoxin infusion, mean arterial blood lactate level increased from 0.92 +/- 0.11 to 1.60 +/- 0.15 mmol/L (p < 0.0001). Lung lactate flux changed from uptake to release of lactate adding a mean of 9.97 +/- 16.23 mmol/h (p < 0.05) to the systemic circulation. Liver and muscle lactate fluxes remained neutral at all times, while kidney and gut took up lactate from the circulation both before and after endotoxin infusion (mean renal uptake, 2.73 +/- 3.85 mmol/L; p < 0.001; mean gut uptake, 2.46 +/- 2.31 mmol/h; p < 0.002). Except for the kidney, where a decrease in blood flow correlated with diminished uptake, there was no correlation between changes in transvisceral lactate fluxes and organ or systemic oxygen delivery during endotoxemia. A positive correlation between lactate uptake and oxygen consumption during endotoxemia was seen for both gut (p < 0.0001) and kidney (p < 0.002). We conclude that, in the dog, the pathogenesis of endotoxin-induced hyperlacticemia is complex. The lung may be responsible for significant lactate release, and other viscera that normally take up lactate are unable to adequately clear this increased lactate.

Relationship between blood lactate concentrations and ionized calcium, glucose, and acid-base status in critically ill and noncritically ill patients

OBJECTIVE

To determine the relationships between circulating blood lactate concentrations and several biochemical variables including ionized calcium, glucose, pH, and acid-base status in critically ill and noncritically ill patients.

DESIGN

A prospective, cohort study.

SETTING

The critical care research laboratory, intensive care unit (ICU), emergency room (ER), and general ward of a 466 bed university-affiliated hospital.

PATIENTS

Three-hundred thirty-four critically ill and noncritically ill patients.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

Circulating blood lactate concentrations, ionized calcium concentrations, blood glucose, pH, and base deficit values were simultaneously determined in blood samples from various patient populations. Descriptive data and physiologic parameters were also recorded. Circulating lactate and ionized calcium determinations were performed simultaneously in 334 whole blood samples from 334 subjects. There was neither a statistically significant nor clinically relevant correlation between circulating lactate concentrations and ionized calcium concentrations when lactate values were < or = 2 mmol/L (p = 0.8962, r2 = .01) or when lactate values were > 2 mmol/L (p = .3697, r2 = .09) in a heterogeneous patient population. Our study populations included five subject groups: a) nonhypotensive ICU patients (n = 93), b) nonhypotensive ER patients (n = 85), c) nonhypotensive general ward patients (n = 44), d) hypotensive patients from the ICU, ER, and general wards (n = 39), and e) normal controls (n = 73). There was neither a statistically significant nor clinically relevant correlation between circulating lactate concentrations and ionized calcium concentrations in each of the five populations studied for lactate values either < or = 2 mmol/L or > 2 mmol/L. We studied the relationship between circulating lactate concentrations and blood glucose concentrations (n = 334 patients), arterial pH and base deficit (n = 163 patients), and venous pH and base deficit (n = 171 patients). Statistically significant, but perhaps not clinically relevant correlations were observed when comparing circulating lactate values with blood glucose values (p = .0330, r2 = .12), arterial pH (p = .0007, r2 = .26) and base deficit from arterial specimens (p = .0014, r2 = .25). There were neither statistically significant nor clinically relevant correlations when comparing circulating lactate concentrations with venous pH (p = .9098, r2 = .01) or base deficit determined from venous blood specimens (p = .1365, r2 = .11).

CONCLUSIONS

a) There is neither a statistically significant nor clinically relevant relationship between whole blood lactate concentrations and ionized calcium concentrations when studying patients with or without hyperlactatemia. b) Although there is a statistically significant correlation between circulating lactate concentrations and blood glucose concentrations, arterial pH or arterial base deficit, such associations do not appear to be clinically important.

The effect of prostaglandin E1 on the increase of serum lactate and plasma granulocyte elastase activity during radical surgery for esophageal cancer

Serum lactate concentrations and the lactate/pyruvate (L/P) ratio were measured in two groups of patients undergoing radical esophagectomy, as an indicator of tissue hypoxia, and β-glucuronidase and granulocyte elastase as indicators of tissue damage. One group received prostaglandin E1 (PGE1) and the other group received nothing. Serum lactate concentrations and the L/P ratio increased significantly 30 min after starting thoracotomy in the patients who were not treated with PGE1. On the contrary, intravenous drip infusion of PGE1 (0.04 μg·kg(-1)·min(-1)) suppressed the increases in serum lactate concentratons and L/P ratios. Plasma granulocyte elastase activity increased significantly at the end of surgery in both groups. There was no change in serum β-glucuronidase activity in both groups. This study suggests that low doses of PGE1 maintain organ blood flow without affecting blood pressure. However, these low doses of PGE1 could not suppress granulocyte elastase release.

Alterations in hepatic fructose metabolism in cirrhotic patients demonstrated by dynamic 31phosphorus spectroscopy

Quantitative liver function tests are based on the clearance concept and measure the plasma disappearance of a test compound such as galactose. Metabolism is inferred to be predominantly hepatic, and usually no knowledge is obtained of the true time course of metabolite formation. Dynamic 31phosphorus magnetic resonance spectroscopy after intravenous administration of fructose directly measures hepatic sugar metabolism. To determine the feasibility and the utility of 31P magnetic resonance spectroscopy, we studied the responses of six healthy subjects and nine patients with nonalcoholic cirrhosis to a fructose load. Results were related to the impairment of hepatic function assessed by the galactose-elimination capacity test. Liver spectra were acquired in a 1.5 T whole-body nuclear magnetic resonance unit with a surface coil (9-cm diameter) placed ventrally on the liver; the one-dimensional chemical-shift imaging technique was used to obtain spectra from tissue slices parallel to the surface coil. After a basal spectrum had been obtained, fructose (250 mg/kg) was injected intravenously, and further spectra were collected sequentially every 6 min for 1 hr. Formation of monophosphate esters (9% +/- 5% vs. 20% +/- 8% of total area; p less than 0.01) and utilization of inorganic phosphate (5% +/- 4% vs. 11% +/- 3% of total area; p less than 0.005) were markedly decreased in cirrhotic patients. These measures correlated with the severity of the impairment of liver function measured by the galactose-elimination capacity (r = 0.53 to 0.69; p less than 0.05). We conclude that dynamic 31P magnetic resonance spectroscopy is a safe, clinically feasible test that allows detailed insights into biochemical events in liver disease.

Comparison of systemic oxygen delivery and uptake with NIR spectroscopy of brain during normovolemic hemodilution in the rabbit

Incremental hyperoxic normovolemic hemodilution was utilized to progressively decrease oxygen delivery (DO2) in anesthetized rabbits. At decreasing DO2, we compared systemic responses related to the adequacy of DO2, i.e. mixed venous oxygen saturation (SvO2), oxygen consumption (VO2), and arterial lactate concentrations, to near infrared spectroscopy (NIRS) of the brain, a regional measure of intracellular oxygen availability. We sought concomitantly to define critical SvO2 and DO2, beyond which whole body VO2 begins to decline and arterial lactate concentrations increase. NIR Spectroscopy provided the means to test the hypothesis that systemic indicators of inadequate DO2 would not accurately reflect the oxygenation of a critical organ such as the brain. In thirteen rabbits anesthetized with fentanyl, paralyzed and artificially ventilated at an FIO2 of 0.60, hemodilution produced an early decrease in mixed venous oxygen saturation. When mixed venous oxygen saturation decreased below approximately 50%, arterial lactate concentrations began to increase significantly. Further decreases in oxygen delivery precipitated a decline in systemic VO2. Finally, NIRS revealed an increase in the reduction level of brain cytochrome a,a3 after systemic parameters of oxygen delivery had been altered. Analysis of the data indicated that falling SvO2 predicted inadequate DO2 to tissue during early hemodilution under narcotic/relaxant anesthesia and that the brain showed evidence of intracellular hypoxia only after systemic parameters such as SvO2 were affected markedly.