Hyperchloraemic metabolic acidosis following open cardiac surgery

Hyperchloremia on Admission to Pediatric Intensive Care in Mechanically Ventilated Children is Associated with Impaired Renal Function

Objective  There is recent interest in the association between hyperchloremic metabolic acidosis and adverse outcomes. In vitro, hyperchloremia causes renal vasoconstriction and fall in glomerular filtration rate (GFR). The objective of this retrospective, observational study is to examine associations between chloride level at admission to pediatric intensive care (PICU) and worst GFR and requirement for renal replacement therapy. Materials and Methods  All admissions to PICU between 2009 and 2019 who received invasive mechanical ventilation and had blood gas analysis performed were included. Data analyzed included patient characteristics (age, gender, diagnosis, pediatric index of mortality [PIM]-2 score); results of initial blood gas; and maximum serum creatinine (then used to calculate minimum GFR). Primary outcome measure was worst GFR during PICU stay. Secondary outcome measures were requirement for renal replacement therapy and PICU mortality. Multivariable regression analysis was used to assess if admission chloride level was independently predictive of minimum GFR during PICU stay and to examine associations between hyperchloremia (>110 mEq/L) at admission and requirement for renal replacement therapy after adjustment for confounders. Results  Data were available for 2,217 patients. Median age was 16.4 months and 39% of patients were hyperchloremic at admission to PICU. Admission chloride level was independently predictive of worst GFR during PICU stay after adjustment for known confounders. Patients with hyperchloremia were not more likely to require renal replacement therapy or die than patients with normochloremia. Conclusion  Prospective studies are necessary to determine if high chloride, specifically chloride containing resuscitation fluids, have a causal relationship with poor outcomes.

Non-lactate strong ion difference and cardiovascular, cancer and all-cause mortality

Objectives

Non-lactate strong ion difference (SID) has been shown to be associated with predictors of mortality in intensive care unit. However, the existence of any association between non-lactate SID (nlSID) and all cause, cardiovascular and cancer mortality has not been explored before in community dwelling US adults.

Methods

In a nationally representative cross-sectional survey of the US non-institutionalized population, all adult participants (≥20 years of age) using National Health and Nutrition Examination Survey data (1999-2010) combined with National Death Index for mortality status through December 2011. Cox proportional hazard models were built to estimate the hazard ratios for cardiovascular, cancer, and all-cause mortality for each unit increase in non-lactate SID. The models were adjusted for demographic and confounder variables.

Results

In the study population the mean (SD) age was 49.6 (18.4) years. Of the study population, 31,475 (91.5%) were alive and 2,893 (8.4%) died during the mean (SD) follow-up period of 5.5 (3.5) years. In univariate regression model using nlSID as continuous variable, we found 2% (unadjusted hazard ratio, HR=1.02; 95% CI, 1.004-1.05) increase in all-cause but not in cardiovascular and cancer mortality (HR=1.03; 95% CI, 0.99-1.08, HR=1.01; 95% CI, 0.97-1.06). After adjusting for potential confounders, we found 7% (adjusted HR=1.07; 95% CI, 1.04-1.10), 5% (HR=1.05; 95% CI, 1.00-1.11) and 7% (HR=1.07; 95% CI, 1.02-1.12) increase in all-cause, cardiovascular, and cancer mortality.

Conclusions

A high nlSID is associated with an increase in cardiovascular, cancer and all-cause mortality and may be a prognostic indicator of mortality in general adult population. These findings may provide a point of reference for further studies.

Base excess is superior to lactate-levels in prediction of ICU mortality after cardiac surgery

Introduction

Cardiac surgery with the use of cardiopulmonary bypass is known to induce distinct metabolic changes. Respective changes in acid-base status including increased systemic lactate levels were previously related to clinical outcomes, but data remain controversial. Therefore, we aim to investigate the relevance of lactate and base excess (BE) levels on ICU-mortality in patients admitted to the ICU after cardiac surgery.

Materials and methods

Perioperative data of patients treated in a tertiary care academic center admitted to the ICU after on-pump surgery were analyzed in a retrospective fashion. Receiver operation characteristic (ROC) curves were constructed for admission lactate-levels and BE with calculation of optimal cut-off values to predict ICU mortality. Univariate followed by multivariate regression models were constructed to identify potential outcome-relevant indices.

Results

Data from 1,058 patients were included in the analysis. Area under the curves for prediction of ICU mortality were 0.79 for lactate levels at ICU admission (sensitivity 61.9%/ specificity 87.5%; optimal cut-off level 3.9mmol/l), and 0.7 for BE (sensitivity 52.4%/ specificity 93.8%, optimal cut-off level -6.7), respectively. Multivariate regression identified BE < -6.7 as the single metabolic predictor of ICU-mortality (HR 4.78, 95%-CI 1.4–16.33, p = 0.01). Explorative subgroup analyses revealed that the combination of lactate ≤3.9mmol/l and BE ≤ -6.7 has stronger impact on mortality than a combination of lactate of >3.9mmol/l and BE > -6.7 (HR 2.56, 95%-CI 0.18–37.17).

Conclusions

At ICU-admission, severely reduced BE appears superior to hyperlactatemia with regard to prediction of ICU-mortality in patients after cardiac surgery.

Postoperative Compensatory Ammonium Excretion Subsequent to Systemic Acidosis in Cardiac Patients

Background

Postoperative acid-base imbalances, usually acidosis, frequently occur after cardiac surgery. In most cases, the human body, not suffering from any severe preexisting illnesses regarding lung, liver, and kidney, is capable of transient compensation and final correction. The aim of this study was to correlate the appearance of postoperatively occurring acidosis with renal ammonium excretion.

Materials and Methods

Between 07/2014 and 10/2014, a total of 25 consecutive patients scheduled for elective isolated coronary artery bypass grafting with cardiopulmonary bypass were enrolled in this prospective observational study. During the operative procedure and the first two postoperative days, blood gas analyses were carried out and urine samples collected. Urine samples were analyzed for the absolute amount of ammonium.

Results

Of all patients, thirteen patients developed acidosis as an initial disturbance in the postoperative period: five of respiratory and eight of metabolic origin. Four patients with respiratory acidosis but none of those with metabolic acidosis subsequently developed a base excess > +2 mEq/L.

Conclusion

Ammonium excretion correlated with the increase in base excess. The acidosis origin seems to have a large influence on renal compensation in terms of ammonium excretion and the possibility of an overcorrection.

Non-lactate strong ion difference: a clearer picture

PURPOSE

The recommended method for elucidating the effects of strong ions other than lactate on acid-base balance is to calculate the non-lactate strong ion difference (SIDnl). A relationship between HCO3 (-) and SIDnl in hyperchloremic patients has already been demonstrated; in the present study, the relationships between SIDnl, the apparent strong ion difference (SIDa), and mortality at intensive care unit (ICU) admission were investigated.

METHODS

In our two-center study, 2691 patients admitted to the ICU were retrospectively evaluated, including 1069 critically ill patients. These patients were divided into three subgroups according to their SIDnl levels at admission to the ICU: low (<38 mmol L(-1)), normal (38-40 mmol L(-1)), and high (>40 mmol L(-1)). Patient age, gender, diagnosis, blood gas values, length of ICU stay, and mortality were recorded.

RESULTS

The low-SIDnl group included 768 patients (71.8 %), the normal-SIDnl group consisted of 127 patients (11.9 %), and the high-SIDnl group contained 174 patients (16.3 %). There was no significant difference in lactate levels among the SIDnl groups (p = 0.635). In a multivariate logistic regression model, likelihood of mortality was increased 1.24-fold (1.20-1.28), 2.56-fold (1.61-4.08) and 2.55-fold (1.003-6.47) by APACHE II, lactate level ≥2mmol L(-) and low SIDnl (p < 0.001, p < 0.001, and p = 0.049, respectively).

CONCLUSIONS

SIDnl can be used to determine the effects of strong ions other than lactate on SIDa values and acid-base balance. Furthermore, a low SIDnl at ICU admission can be a prognostic indicator of mortality.

The base excess gap is not a valid tool for the quantification of unmeasured ions in cardiac surgical patients: a retrospective observational study

BACKGROUND

The base excess gap (BE(gap)) method is commonly used for the quantification of unmeasured ions in critically ill patients. However, it has never been validated against the standard quantitative acid-base approach.

OBJECTIVE

To compare the BE(gap) as a tool for the prediction of the excess of unmeasured ions with the offset of strong ion gap (SIG) from its reference value.

DESIGN

A retrospective observational study.

SETTING

Adult ICU in a tertiary hospital.

PATIENTS

One hundred and thirty-five cardiac surgical patients admitted for postoperative care.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

BE(gap) was calculated as BE(gap) = SBE - BE(si) - BE(wa), where SBE is the standard base excess, BE(si) is the partition due to strong ions ([Na+]-[Cl-]-[lactate-] - 30.5) and BE(wa) is the partition due to weak acids [0.25×{42 - (albumin)}]. The deviation of the observed SIG (SIG(ob)) from its reference value was calculated as deltaSIG = 2.85 - SIG(ob). We used Bland-Altman and concordance correlation analysis to compare BE(gap) with deltaSIG. A bias of ±1 meq l(-1) with limits of agreement of ±2 meq l(-1) and a concordant correlation coefficient of more than 0.9 were considered to indicate a strong agreement.

RESULTS

The concordant correlation coefficient between BE(gap) and deltaSIG was 0.702. The mean bias between the two variables was 1.8 meq l(-1), with a lower limit of agreement of -0.9 meq l(-1) and an upper limit of agreement of 4.4 meq l(-1).

CONCLUSION

The BE gap method cannot reliably quantify the unmeasured ion excess in cardiac surgical patients. Clinicians should use the full Stewart-Figge model for quantitative acid-base assessments.

Hydrogen ion concentration and coronary artery bypass graft surgery with and without cardiopulmonary bypass

Background

Acidosis during cardiopulmonary bypass (CPB) has been related to the strong ion difference (SID) and the composition of intravascular fluids that are administered. Less intravascular fluids tend to be administered during off- than on-pump CABG and should influence the degree of acidosis that develops. This study aimed to explore the role of CPB in the development of acidosis by comparing changes in hydrogen ion concentration ([H⁺]) and electrolytes in patients undergoing on- and off-pump coronary artery bypass graft (CABG) surgery.

Methods

Eighty two patients had arterial blood gas measurements pre-operatively, following CABG and at approximately 0600 h the morning after surgery. Carbon dioxide tension (PaCO₂) and concentrations of sodium, potassium, chloride, [H⁺], bicarbonate and haemoglobin were measured and strong ion difference calculated. Data was analysed using mixed repeated-measures analysis of variance.

Results

Intra-operatively, mean SID decreased more in the on- compared to the off-pump group (4.0 mmol/L, 95% confidence interval 2.8-5.3 mmol/L, p < 0.001). Neither [H⁺] or PaCO₂ changed significantly and there were no significant difference between the groups. By the morning following surgery, [H⁺] and PaCO₂ had both increased (p < 0.001) and difference in SID had disappeared (p = 0.17).

Conclusion

Despite significant differences in changes in SID, there were no differences in [H⁺] between patients during or after CABG surgery whether performed on- or off-pump. This may be have been the result of greater haemodilution in the on- compared to the off-pump group, compensating for change in SID by reducing the concentration of weak acids. Although it was associated with significantly greater decrease in SID, CPB was not associated with any significant increased risk of acidosis.

Factors related to post-operative metabolic acidosis following major abdominal surgery

BACKGROUND

Metabolic acidosis is frequently observed in perioperative patients, especially those who undergo major surgery. The aim of this study was to evaluate the factors related to post-operative metabolic acidosis and to attempt to identify the clinical effect of metabolic acidosis following major abdominal surgery.

METHODS

We included 172 patients admitted to a surgical intensive care unit (ICU) following major abdominal surgery. All cases were divided into either the acidosis or the normal group using immediate post-operative standard base excess (SBE). The following clinical data were retrospectively obtained from the chart and ICU database: basic clinical characteristics, operative data, type and volume of fluid infused during the operation, post-operative arterial blood gas analysis, lactate, and central venous oxygen saturation.

RESULTS

The predominant intraoperative fluid was either 0.9% saline or lactated Ringer's solution. The operation length, estimated blood loss, total fluid infused, total saline infused, lactate and corrected chloride were significantly higher in the acidosis group; however, central venous oxygen saturation was lower in the normal group. Among these factors, total infused saline and lactate level were independent factors related to metabolic acidosis. The comparison between the types of fluid revealed that the saline group had a significantly lower SBE, strong ion difference and higher corrected chloride. SBE was significantly correlated with lactate and total infused saline. ICU and hospital length of stay were significantly longer in the acidosis group.

CONCLUSIONS

Post-operative metabolic acidosis following major abdominal surgery was closely related to both hyperchloremic acidosis associated with large saline infusion and lactic acidosis caused by lactataemia.

Management of the postoperative pediatric cardiac surgical patient

OBJECTIVE

To review the salient aspects and latest advances in the management of the postoperative pediatric cardiac patient.

DATA SOURCE

A Medline-based literature source.

CONCLUSION

The practice of pediatric cardiac intensive care has evolved considerably over the last several years. These efforts are the result of a collaborative effort from all subspecialties involved in the care of pediatric patients with congenital heart disease. Discoveries and innovations that are representative of this effort include the extension of cerebral oximetry from the operating room into the critical care setting; mechanical circulatory devices designed for pediatric patients; and surgery in very low birth weight neonates. Advances such as these impact postoperative management and make the field of pediatric cardiac intensive care an exciting, demanding, and evolving discipline, necessitating the ongoing commitment of various disciplines to pursue a greater understanding of disease processes and how to best go about treating them.

A balanced view of balanced solutions

The present review of fluid therapy studies using balanced solutions versus isotonic saline fluids (both crystalloids and colloids) aims to address recent controversy in this topic. The change to the acid-base equilibrium based on fluid selection is described. Key terms such as dilutional-hyperchloraemic acidosis (correctly used instead of dilutional acidosis or hyperchloraemic metabolic acidosis to account for both the Henderson-Hasselbalch and Stewart equations), isotonic saline and balanced solutions are defined. The review concludes that dilutional-hyperchloraemic acidosis is a side effect, mainly observed after the administration of large volumes of isotonic saline as a crystalloid. Its effect is moderate and relatively transient, and is minimised by limiting crystalloid administration through the use of colloids (in any carrier). Convincing evidence for clinically relevant adverse effects of dilutional-hyperchloraemic acidosis on renal function, coagulation, blood loss, the need for transfusion, gastrointestinal function or mortality cannot be found. In view of the long-term use of isotonic saline either as a crystalloid or as a colloid carrier, the paucity of data documenting detrimental effects of dilutional-hyperchloraemic acidosis and the limited published information on the effects of balanced solutions on outcome, we cannot currently recommend changing fluid therapy to the use of a balanced colloid preparation.

Impact of normal saline infusion on postoperative metabolic acidosis

BACKGROUND

Standard base excess (SBE) is an important parameter for guiding fluid management in postoperative metabolic acidosis. However, individual SBE components, notably the chloride effect (Cl(eff)), provide valuable additional information. Cl(eff) is the deviation of the strong ion difference (SID) from normal caused by chloride loss or increase and represents the effect on SBE of an abnormal chloride-sodium ratio. Many centers use normal saline (NS) for intravascular volume therapy. In this study, we examined the impact of NS infusion on SBE and its chloride-driven component (Cl(eff)) in postoperative children.

METHODS

The study was conducted in 119 children who underwent post-heart surgery in a Swiss pediatric intensive care unit. The 72-h postoperative course was divided into six observation periods, during which NS input and its impact on SBE and Cl(eff) were measured per period in each patient, and the results compared between patients infused and not infused with NS during each period.

RESULTS

Normal saline was infused in 168/625 observation periods if indicated by volume deficit. Postoperative metabolic acidosis and the acidifying Cl(eff) were aggravated in the first 12 postoperative hours. Over the 72 h, NS infusion simultaneously lowered SBE by -0.06 mm x ml(-1) x kg(-1) body weight infused and Cl(eff) by -0.07 mm.

CONCLUSIONS

Implementing serial Cl(eff) assessment could improve postoperative management by disclosing or excluding hyperchloremia as a cause of acidosis undetectable from SBE alone. Calculating the chloride-driven acidifying side effect of NS infusion using Cl(eff) improves the interpretation of SBE values and can optimize fluid management in postoperative metabolic acidosis.

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.

Hyperchloremia is the dominant cause of metabolic acidosis in the postresuscitation phase of pediatric meningococcal sepsis

OBJECTIVE

Metabolic acidosis is common in septic shock, yet few data exist on its etiological temporal profile during resuscitation; this is partly due to limitations in bedside monitoring tools (base excess, anion gap). Accurate identification of the type of acidosis is vital, as many therapies used in resuscitation can themselves produce metabolic acidosis.

DESIGN

Retrospective, cohort study.

SETTING

Multidisciplinary pediatric intensive care unit with 20 beds.

PATIENTS

A total of 81 children with meningococcal septic shock.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Acid-base data were collected retrospectively on 81 children with meningococcal septic shock (mortality, 7.4%) for the 48 hrs after presentation to the hospital. Base excess was partitioned using abridged Stewart equations, thereby quantifying the three predominant influences on acid-base balance: sodium chloride, albumin, and unmeasured anions (including lactate). Metabolic acidosis was common at presentation (mean base excess, -9.7 mmol/L) and persisted for 48 hrs. However, the pathophysiology changed dramatically from one of unmeasured anions at admission (mean unmeasured anion base excess, -9.2 mmol/L) to predominant hyperchloremia by 8-12 hrs (mean sodium-chloride base excess, -10.0 mmol/L). Development of hyperchloremic acidosis was associated with the amount of chloride received during intravenous fluid resuscitation (r = .44), with the base excess changing, on average, by -0.4 mmol/L for each millimole per kilogram of chloride administered. Hyperchloremic acidosis resolved faster in patients who 1) manifested larger (more negative) sodium chloride-partitioned base excess, 2) maintained a greater urine output, and 3) received furosemide; and slower in those with high blood concentrations of unmeasured anions (all, p < .05).

CONCLUSIONS

Hyperchloremic acidosis is common and substantial after resuscitation for meningococcal septic shock. Recognition of this entity may prevent unnecessary and potentially harmful prolonged resuscitation.

The lactate:pyruvate ratio following open cardiac surgery in children

OBJECTIVE

To explore the relationship between lactate:pyruvate ratio, hyperlactataemia, metabolic acidosis, and morbidity.

DESIGN AND SETTING

Prospective observational study in the paediatric intensive care unit (PICU) of a university hospital.

PATIENTS

Ninety-seven children after open cardiac surgery. Most children (94%) fell into low-moderate operative risk categories; observed PICU mortality was 1%.

INTERVENTIONS

Blood was sampled on admission for acid-base analysis, lactate, and pyruvate. Metabolic acidosis was defined as standard bicarbonate lower than 22 mmol/l, raised lactate as higher than 2 mmol/l, and raised lactate:pyruvate ratio as higher than 20.

MEASUREMENTS AND RESULTS

Median cardiopulmonary bypass and aortic cross-clamp times were 80 and 46 min. Metabolic acidosis occurred in 74%, hyperlactataemia in 42%, and raised lactate:pyruvate ratio in 45% of children. In multivariate analysis lactate:pyruvate ratio increased by 6.4 in children receiving epinephrine infusion and by 0.4 per 10 min of aortic cross-clamp. Duration of inotropic support increased by 0.29 days, ventilatory support by 0.27 days, and PICU stay by 0.42 days, for each 1 mmol/l increase in lactate. Neither standard bicarbonate nor lactate:pyruvate ratio were independently associated with prolongation of PICU support.

CONCLUSIONS

Elevated lactate:pyruvate ratio was common in children with mild metabolic acidosis and low PICU mortality. Hyperlactataemia, but not elevated lactate:pyruvate ratio or metabolic acidosis, was associated with prolongation of PICU support. Routine measurement of lactate:pyruvate ratio is not warranted for children in low-moderate operative risk categories.