Blood lactate and mixed venous-arterial PCO2 gradient as indices of poor peripheral perfusion following cardiopulmonary bypass surgery

A review of using CO2-derived variables to detect tissue hypoperfusion during cardiopulmonary bypass

Complications after cardiac surgery with cardiopulmonary bypass (CPB) are associated with increased morbidity and mortality. Early detection and prompt reversion of tissue hypoperfusion during CPB are key factors to reduce organ dysfunction after cardiac surgery. CO2 (carbon dioxide)-derived variables which are easy to assess and routinely available to evaluate the adequacy of macro- and microcirculation may offer important information on the adequacy of the perfusion during CPB. However, since some practical issues remain unsolved in providing a reliable measurement of CO2 removal from the patient, CO2-derived variables are not widely monitoring during CPB. This review aims to demonstrate the basic principles of CO2-derived variables during CPB, the available techniques to assess CO2-derived variables on CPB and the clinically relevant applications.

Physiological relationship between cardiorespiratory fitness and fitness for surgery: a narrative review

Epidemiological evidence has highlighted a strong relationship between cardiorespiratory fitness and surgical outcomes; specifically, fitter patients possess heightened resilience to withstand the surgical stress response. This narrative review draws on exercise and surgical physiology research to discuss and hypothesise the potential mechanisms by which higher fitness affords perioperative benefit. A higher fitness, as indicated by higher peak rate of oxygen consumption and ability to sustain metabolic homeostasis (i.e. higher anaerobic threshold) is beneficial postoperatively when metabolic demands are increased. However, the associated adaptations with higher fitness, and the related participation in regular exercise or physical activity, might also underpin the observed perioperative benefit through a process of hormesis, a protective adaptive response to the moderate and intermittent stress of exercise. Potential mediators discussed include greater antioxidant capacity, metabolic flexibility, glycaemic control, lean body mass, and improved mood.

Role of central venous - Arterial pCO2 difference in determining microcirculatory hypoperfusion in off-pump coronary artery bypass grafting surgery

Background:

Cardiac surgery is frequently associated with macro and microcirculatory hypoperfusion. Patients with normal central venous oxygen saturation (Scvo2) also suffer from hypoperfusion. We hypothesized that monitoring central venous-arterial pco2 difference (dCO₂) could also serve as additional marker in detecting hypoperfusion in cardiac surgery patient.

Methods:

This is a prospective observational study. Patients undergoing off-pump coronary artery bypass grafting included in this study. The dCO2 was measured postoperatively. The patients with a ScvO2 ≥70% were divided in to 2 groups, the high-dCO2 group (≥8 mmHg) and the low-dCO2 group (<8 mmHg).

Results:

The 65 patient had scvO₂ ≥70%. Out of these, 20 patients were assigned to the high dCO₂ group and 45 patients to the low dCO₂ group. Patients with high dco2 had higher lactate levels after ICU admission. They also had significantly prolonged need for mechanical ventilation (14.90 ± 10.33 vs 10 ± 9.65, P = 0.0402), ICU stay (5.05 ± 2.52 d vs 3.75 ± 2.36 d, P = 0.049) and hospital stay (12.25 ± 5.90 d vs 8.57 ± 5.55 d P = 0.018). The overall rate of post-operative complications was similar in both the group.

Conclusion:

The present study demonstrates dCO₂ as an easy to assess and routinely available tool to detect global and microcirculatory hypoperfusion in off-pump CABG patients, with assumed adequate fluid status and ScvO₂ as a hemodynamic goal. We observed that high dCO₂ (>8 mmHg) was associated with decreased DO₂I, increased oxygen extraction ratio, the longer need for mechanical ventilation and longer ICU stay.

Central venous-to-arterial CO2 difference is a poor tool to predict adverse outcomes after cardiac surgery: a retrospective study

PURPOSE

The venous-to-arterial carbon dioxide partial pressure difference (CO₂ gap) has been reported to be a sensitive indicator of cardiac output adequacy. We aimed to assess whether the CO₂ gap can predict postoperative adverse outcomes after cardiac surgery.

METHODS

A retrospective study was conducted of 5,151 patients from our departmental database who underwent cardiac surgery from 1 January 2008 to 31 December 2018. Lactate level (mmol·L^-1), central venous oxygen saturation (ScVO₂) (%), and the venous-to-arterial carbon dioxide difference (CO₂ gap) were measured at intensive care unit (ICU) admission and on days 1 and 2 after cardiac surgery. The following postoperative adverse outcomes were collected: ICU mortality, hemopericardium or tamponade, resuscitated cardiac arrest, acute kidney injury, major bleeding, acute hepatic failure, mesenteric ischemia, and pneumonia. The primary outcome was the presence of at least one postoperative adverse outcome. Logistic regression was used to assess the association between ScVO₂, lactate, and the CO₂ gap with adverse outcomes. Their diagnostic performance was compared using a receiver operating characteristic (ROC) curve.

RESULTS

There were 1,933 patients (38%) with an adverse outcome. Cardiopulmonary bypass (CPB) parameters were similar between groups. The CO₂ gap was slightly higher for the "adverse outcomes" group than for the "no adverse outcomes" group. Arterial lactate at admission, day 1, and day 2 was also slightly higher in patients with adverse outcomes. Central venous oxygen saturation was not significantly different between patients with and without adverse outcomes. The area under the ROC curve to predict outcomes after CPB for the CO₂ gap at admission, day 1, and day 2 were 0.52, 0.55, and 0.53, respectively.

CONCLUSION

After cardiac surgery with CPB, the CO₂ gap at ICU admission, day 1, and day 2 was associated with postoperative adverse outcomes but showed poor diagnostic performance.

Is Lactic Acidosis After Lung Transplantation Associated With Worse Outcomes?

BACKGROUND

Elevated lactate levels may be caused by increased production suggestive of tissue ischemia; however, they may also occur without evidence of ischemia, by catecholamine activation of beta receptors. The purpose of this study was to determine the factors associated with increased lactate levels during and after lung transplantation and to evaluate whether lactate levels were associated with increased time to extubation and postoperative complications.

METHODS

This was a retrospective study of patients who underwent lung transplantation between January 2015 and May 2017 at the University of Michigan, Ann Arbor, MI. Multivariable linear regression was used to determine the factors associated with peak lactate levels and to find the associations between lactate levels and outcomes of nitric oxide time, intubation time, length of stay, and creatinine level. Logistic regression was used to determine the associations between lactate levels and acute kidney injury and atrial fibrillation.

RESULTS

A total of 86 patients underwent single-lung transplantation (n = 17; 20%) or double-lung transplantation (n = 69; 80%). All patients initially had normal lactate levels. On univariate analysis, lactate levels at several time points were correlated with subsequent acute kidney injury, increased time to extubation, and increased nitric oxide time. After adjustment, the study found that higher peak intensive care unit lactate levels (regression coefficient B = 0.046; interquartile range, 0.006, 0.086; P = .025) were associated with longer length of stay.

CONCLUSIONS

Cardiopulmonary bypass time, total ischemic time, and catecholamine use were associated with higher lactate levels, whereas nitric oxide and higher pulmonary artery pressures were associated with lower levels. Increased lactate levels were independently associated with longer intubation times, postoperative acute kidney injury, and longer length of stay.

The relationship between inotropic support therapy and central partial pressure of venous-arterial carbon dioxide after cardiopulmonary bypass

Background

This study aims to investigate the effects of partial pressure of venous-arterial carbon dioxide changes in the early period after cardiopulmonary bypass in patients who did or did not receive inotropic support therapy and the effect of these changes on tissue perfusion.

Methods

A total of 100 consecutive patients (70 males, 30 females; mean age 61.8±2.3 years; range, 20 to 75 years) who underwent open heart surgery were divided into two groups as those who did not receive any inotropic agent (group 1, n=50) and those who received at least one inotropic agent (group 2, n=50) during the early postoperative period. Heart rate, blood oxygen saturation level, mean arterial pressure, central venous pressure and urine volume, lactate and base excess levels were recorded during the postoperative first 24 hours. At the same timeframe, partial pressure of venous-arterial carbon dioxide level was calculated from central venous and peripheral blood samples.

Results

In both groups, partial pressure of venous-arterial carbon dioxide were significantly higher in the postoperative fourth hour compared with basal values. This significant difference continued for the postoperative first 24 hours. Partial pressure of venous-arterial carbon dioxide in group 2 was significantly higher at the 12^th-hour measurement (p=0.002). Lactate levels at zeroth and eighth hours were significantly higher in group 2 (p=0.012 and p=0.017, respectively). Fourthhour urine excretion volumes were significantly lower in group 1 (p=0.010). Mean arterial pressure at zeroth, 12th and 20th hours was significantly higher in group 2 (p=0.001, p=0.016, and p=0.027, respectively). At the eighth-hour measurement, a positive weak relationship was detected between partial pressure of venousarterial carbon dioxide and lactate levels (r=0.253 and p=0.033).

Conclusion

This study demonstrated that partial pressure of venous-arterial carbon dioxide increased in the first few hours and remained to be high for 24 hours after cardiopulmonary bypass independently of the use of inotropic support. However, in the postoperative period, even after lactate and base excess levels return to baseline values, partial pressure of venous-arterial carbon dioxide may continue to remain at high values, which may indicate impaired perfusion in some tissues.

Central venous-to-arterial PCO2 difference, arteriovenous oxygen content and outcome after adult cardiac surgery with cardiopulmonary bypass: A prospective observational study

BACKGROUND

Rapid identification and treatment of tissue hypoxia reaching anaerobiosis (dysoxia) may reduce organ failure and the occurrence of major postoperative complications (MPC) after cardiac surgery. The predictive ability of PCO2-based dysoxia biomarkers, central venous-to-arterial PCO2 difference (ΔPCO2) and ΔPCO2 to arteriovenous oxygen content difference ratio, is poorly studied in this setting.

OBJECTIVES

We evaluated the ability of PCO2-based tissue dysoxia biomarkers, blood lactate concentration and central venous oxygen saturation measured 2 h after admission to the ICU as predictors of MPC.

DESIGN

A prospective, observational cohort study.

SETTING

Single-centre, academic hospital cardiovascular ICU.

PATIENTS

We included adult patients undergoing cardiac surgery with cardiopulmonary bypass and measured dysoxia biomarkers at ICU admission, and after 2, 6 and 24 h.

MAIN OUTCOME MEASURES

The primary endpoint was MPC, a composite of cardiac and noncardiac MPC evaluated in the 48 h following surgery. After univariate analysis of MPC covariates including dysoxia biomarkers measured at 2 h, multivariate logistic regression analyses were performed to identify the association of these biomarkers with MPC for confounders. Areas under the receiver operating characteristic curves were determined for biomarkers which remained independently associated with MPC.

RESULTS

MPC occurred in 56.5% of the 308 patients analysed. ΔPCO2, blood lactate concentration and central venous oxygen saturation measured at 2 h, but not ΔPCO2 to arteriovenous oxygen content difference ratio, were significantly associated with MPC. However, only ΔPCO2 was independently associated with MPC after multivariate analysis. The areas under the receiver operating characteristic curves of ΔPCO2 measured at 2 h for MPC prediction was 0.64 (95% CI 0.57 to 0.70, P < 0.001).

CONCLUSION

After cardiac surgery with cardiopulmonary bypass, ΔPCO2 measured 2 h after ICU admission was the only dysoxia biomarker independently associated with MPC, but with limited performance.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03107572.

Improving the prognostic value of ∆PCO2 following cardiac surgery: a prospective pilot study

Conflicting results have been published on prognostic significance of central venous to arterial PCO₂ difference (∆PCO₂) after cardiac surgery. We compared the prognostic value of ∆PCO₂ on intensive care unit (ICU) admission to an original algorithm combining ∆PCO₂, ERO₂ and lactate to identify different risk profiles. Additionally, we described the evolution of ∆PCO₂ and its correlations with ERO₂ and lactate during the first postoperative day (POD1). In this monocentre, prospective, and pilot study, 25 patients undergoing conventional cardiac surgery were included. Central venous and arterial blood gases were collected on ICU admission and at 6, 12 and 24 h postoperatively. High ∆PCO₂ (≥ 6 mmHg) on ICU admission was found to be very frequent (64% of patients). Correlations between ∆PCO₂ and ERO₂ or lactate for POD1 values and variations were weak or non-existent. On ICU admission, a high ∆PCO₂ did not predict a prolonged ICU length of stay (LOS). Conversely, a significant increase in both ICU and hospital LOS was observed in high-risk patients identified by the algorithm: 3.5 (3.0–6.3) days versus 7.0 (6.0–8.0) days (p = 0.01) and 12.0 (8.0–15.0) versus 8.0 (8.0–9.0) days (p < 0.01), respectively. An algorithm incorporating ICU admission values of ∆PCO₂, ERO₂ and lactate defined a high-risk profile that predicted prolonged ICU and hospital stays better than ∆PCO₂ alone.

Venous-to-arterial pCO2 difference in high-risk surgical patients

Alteration of tissue perfusion is a main contributor to organ dysfunction in high-risk surgical patients. The difference between venous carbon dioxide and arterial carbon dioxide pressure (pCO₂ gap) has been described as a parameter reflecting tissue hypoperfusion in critically ill patients who are insufficiently resuscitated. The pCO₂ gap/CavO₂ ratio has also been described as an indicator of the respiratory quotient, thus the relationship between DO₂ and VO₂. Most of the knowledge about the pCO₂ gap and the pCO₂ gap/CavO₂ ratio has come from studies in the literature on animal models or intensive care unit (ICU) patients. To date, publications pertaining to the operative setting are sparse. In the present review, we will first discuss the physiological background of the pCO₂ gap and CO₂-O₂ derived parameters used in the operating room. Few studies have focused on the clinical relevance of the pCO₂ gap in high-risk non-cardiac surgical patients. Prospective observational studies with a small sample size and retrospective studies have shown that the pCO₂ gap may be a useful complementary tool to identify patients who remain insufficiently optimized hemodynamically. In a few studies, a high pCO₂ gap was associated with postoperative complications following non-cardiac high-risk surgery. Results of observational studies conducted in patients undergoing cardiac surgery are contradictory. We focused on the divergence between non-cardiac surgery, cardiac surgery, and septic critically ill patients. When analyzing the literature, we can find some explanations for the discrepancies in the published results between cardiac and non-cardiac surgery. Finally, we will discuss the clinical utility of the pCO₂ gap in high-risk surgical patients.

Increased admission central venous-arterial CO2 difference predicts ICU-mortality in adult cardiac surgery patients

BACKGROUND

Invasive procedures such as cardiac surgery are associated with perioperative dysfunction of macrocirculation and/or microcirculation and organ failures. Maintenance or resuscitation of an adequate macrocirculation and/or microcirculation is thus crucial in patients after cardiac surgery. We investigated the prognostic power of early central venous-arterial carbon dioxide pressure difference (delta-pCO2) after cardiac surgery.

METHODS

Retrospective analysis of data from 1,019 cardiac surgery patients treated in the ICU of a tertiary medical care academic center. Clinical outcomes and laboratory measures including metabolic indices and calculated delta-pCO₂ were assessed. Receiver operating characteristic (ROC) curves were generated and sensitivity / specificity analysis was performed. Univariate and multivariate regression models were analyzed.

RESULTS

The area under the ROC curve for delta-pCO₂ to predict ICU mortality was 0.72 (sensitivity 65% / specificity 76%) with an optimal delta-pCO₂ cut-off value of 8.6 mmHg. In multivariate regression, delta-pCO₂ was associated with increased ICU mortality (HR 3.72, 95%-CI 1.3-10.66, p = 0.02). After adjustment for typical confounders, delta-pCO₂ remained as independent predictor of ICU mortality after cardiac surgery.

CONCLUSIONS

In a retrospective data analysis in a large sample of adult post cardiac surgery patients treated in the ICU, we observed that admission central venous-arterial delta-pCO₂ independently predicts ICU mortality. Delta-pCO₂ might thus contribute risk stratification in ICU patients after cardiac surgery.

Lactate Elevation During and After Major Cardiac Surgery in Adults: A Review of Etiology, Prognostic Value, and Management

Elevated lactate is a common occurrence after cardiac surgery. This review summarizes the literature on the complex etiology of lactate elevation during and after cardiac surgery, including considerations of oxygen delivery, oxygen utilization, increased metabolism, lactate clearance, medications and fluids, and postoperative complications. Second, the association between lactate and a variety of outcomes are described, and the prognostic role of lactate is critically assessed. Despite the fact that elevated lactate is strongly associated with many important outcomes, including postoperative complications, length of stay, and mortality, little is known about the optimal management of postoperative patients with lactate elevations. This review ends with an assessment of the limited literature on this subject.

Mixed Venous-Arterial CO2 Tension Gradient after Cardiopulmonary Bypass

Significant venous hypercarbia has been reported in septic shock and circulatory failure. Cardiopulmonary bypass also impairs systemic and pulmonary blood perfusion. The objective of this study was to determine the clinical significance of the increased venous-arterial CO2 tension gradient resulting from venous hypercarbia after cardiopulmonary bypass. On arrival in the intensive care unit, venous and arterial CO2 tensions were measured in the radial and pulmonary arteries in 140 consecutive patients who had undergone coronary ( n = 79), valve ( n = 34), aortic ( n = 20), and other ( n = 7) surgery under cardiopulmonary bypass. The mean venous-arterial CO2 tension gradient was 5.0 ± 3.3 mm Hg (range, 7.7 to 15.7 mm Hg). By linear regression analysis, the factors that significantly correlated with venous-arterial CO2 tension gradient were bypass duration, aortic crossclamp time, initial arterial lactate level, transpulmonary arteriovenous lactate difference, arterial bicarbonate level, base excess, cardiac index, mixed venous O2 saturation, O2 delivery, O2 consumption, and the peak value of creatine kinase. The venous-arterial CO2 tension gradient may reflect impaired perfusion and anaerobic metabolism induced by cardiopulmonary bypass and could be a simple and useful indicator for patient management after surgery under cardiopulmonary bypass.

High veno-arterial carbon dioxide gradient is not predictive of worst outcome after an elective cardiac surgery: a retrospective cohort study

Alteration of tissue perfusion is a main contributor of organ dysfunction. In cardiac surgery, the importance of organ dysfunction is associated with worse outcome. Central venous-arterial difference in CO₂ tension (ΔCO₂) has been proposed as a global marker of the adequacy of tissue perfusion in shock states. We hypothesized that ΔCO₂ could be increased in case of postoperative organ failure or worse outcome. In this monocentric retrospective cohort study, we retrieved, from our database, 220 consecutive patients admitted in intensive care after an elective cardiac surgery. Four time points were formed: ICU admission, and 6, 24 and 48 h after. A ΔCO₂ below 6 mmHg defined the normal range values. The SOFA score, intensive care unit and hospital length of stay, hospital and 6-month mortality rate were recorded. We compared patient with low ΔCO₂ (<6 mmHg) and high ΔCO₂ (≥6 mmHg). We included 55 (25 %) and 165 patients in low and high ΔCO₂ groups, respectively. The SOFA score, the hospital and 6 months mortality rate were higher in patients with low ΔCO₂. Surprisingly, we did not find results previously published in other surgical settings. In cardiac surgery, ΔCO₂ has a low predictive value of outcome.

Splanchnic oxygen transport, hepatic function and gastrointestinal barrier after normothermic cardiopulmonary bypass

BACKGROUND

The effect of non-pulsatile, normothermic cardiopulmonary-bypass (CPB) on the splanchnic blood-flow and oxygen-transport, the hepatic function and the gastrointestinal barrier were observed in a prospective observational study in 31 adults undergoing cardiac valve replacement surgery.

METHODS

The splanchnic (i.e. hepatic) blood-flow (HBF) was measured by the constant infusion of indocyanine-green (ICG) using a hepatic-venous catheter. Liver function was examined by calculation of lactate uptake, ICG extraction and the monoethylglycinexylidide (MEGX) test. A day before and after surgery the gastrioduodenal and intestinal permeability was measured by determination of sucrose and lactulose/mannitol excretion.

RESULTS

Splanchnic blood flow and oxygen delivery did not decrease during and after surgery while splanchnic oxygen consumption (P < 0.0125) and arterial lactate concentrations increased. The splanchnic lactate uptake paralleled the lactate concentration. After but not during CPB an increase of systemic oxygen consumption was observed. The MEGX test values decreased on the first day after surgery. The ICG extraction was attenuated during the operation. The gastroduodenal and the intestinal permeability increased significantly postoperatively (P < 0.002, respectively, P < 0.001). There was no correlation between these findings and the duration of CPB. There was a significant correlation of the intestinal permeability but not of the gastroduodenal permeability between the prior and after surgery values (P < 0.001).

CONCLUSION

Increased oxygen consumption during CPB may indicate an inflammatory reaction due to the pump beginning in the splanchnic area or a redistribution of the splanchinc blood flow during the CPB. Normothermic CPB does not lead to a significant or prolonged reduction of liver function. Normothermic CPB causes an increase of gastrointestinal permeability. The intestinal barrier function prior to surgery was accountable for the degree of loss of intestinal barrier function following surgery.

Efficacy of a criterion-driven transfusion protocol in patients having pediatric cardiac surgery

OBJECTIVES

Low-hematocrit bypass is one technique used to prevent allogeneic transfusion during cardiopulmonary bypass. The purpose of this study is to determine the efficacy of a criterion-driven transfusion protocol and the effect of low-hematocrit bypass with moderate hypothermia in pediatric cardiac surgery.

METHODS

Seventy-five children who underwent cardiopulmonary bypass with low-hematocrit bypass for repair of congenital heart disease were studied. Criteria for red blood cell transfusion included anemia with a hematocrit level of less than 15% during bypass and 20% after bypass. During cardiopulmonary bypass, venous oxygen saturation, hematocrit values, and regional cerebral oxygenation were continuously monitored. Arterial lactate levels were measured postoperatively.

RESULTS

All patients had an uncomplicated perioperative course, and no perioperative death occurred. Twenty-two patients (29.3%) received a transfusion, and 53 (70.7%) patients did not. The hematocrit levels before and after modified ultrafiltration in the transfused group (21.6 +/- 5.5%, 26.6 +/- 6.5%) were significantly higher than those in the nontransfused group (18.9 +/- 3.7%, 23.1 +/- 4.1%) (P <.05). There was no significant difference between the group's arterial lactate levels immediately after admission to the intensive care unit and 1 day after the operation. The arterial lactate levels 6 hours after the admission to the intensive care unit for the nontransfused patients were higher than with the transfused patients (4.3 +/- 3.0 versus 2.5 +/- 1.5 mmol/L, (P <.05). For arterial lactate level, the relation with patients' weight had the highest correlation (R = 0.678, P <.0001).

CONCLUSIONS

A criterion-driven transfusion program can be effective, and low-hematocrit bypass with a hematocrit value below 20% may affect lactate production or clearance from the body.

Oxygen metabolism during and after cardiac surgery: role of CPB

BACKGROUND

Cardiopulmonary bypass (CPB) has been reported to increase oxygen metabolism and to influence the relation between oxygen consumption (VO(2)) and delivery (DO(2)) in the early hours after cardiac surgery. To investigate the role of CPB, we studied oxygen metabolism in coronary artery bypass procedures performed on-pump (CABG) and off-pump (OPCAB).

METHODS

Twenty-five patients were randomized to undergo CABG (n = 14) or OPCAB (n = 11). All patients received the same anesthetic management. Oxygen metabolism variables were assessed before induction of anesthesia and up to 18-hours after surgery.

RESULTS

At baseline, before induction of anesthesia, there were no differences between CABG and OPCAB in oxygen consumption (VO(2)), delivery (DO(2)), or extraction (ExO(2)). After surgery VO(2) and ExO(2) increased in both groups, while DO(2) decreased. No significant differences between CABG and OPCAB were detected in postoperative VO(2), DO(2), and ExO(2) levels. The relation between VO(2) and DO(2) was very similar in CABG and OPCAB patients throughout the study, and no significant differences were detected in slopes and intercepts of the regression lines between CABG and OPCAB at all time points. There was, however, a significant effect of time on the relation between VO(2) and DO(2): this relation was stronger in the postoperative period, and the slope of this relation increased over time as well.

CONCLUSIONS

A hypermetabolic state and progressive and significant increases in the strength of the relationship between VO(2) and DO(2) and in the slope of this relationship occur after both CABG and OPCAB. Cardiopulmonary bypass is not responsible for these changes in oxygen metabolism.

Lactic acidosis following heart transplantation: a common phenomenon?

BACKGROUND

Lactic acidosis (LAc) is a common form of metabolic acidosis early after heart transplantation (HTX). The mechanism remains unclear. This study analyzed 13 patients who developed severe LAc after HTX.

METHODS

From a series of 60 consecutive heart transplant patients, we identified 13 patients with LAc in the first hours following HTX. Nine patients with normal or mildly elevated lactate levels (<5.0 mmol/l) were investigated as controls.

RESULTS

Thirteen patients developed a moderate or severe LAc (up to 14.6 mmol/l) after HTX. Serum lactate levels increased immediately following surgery with a peak after 6.3+/-1.4 h, spontaneously returning to normal values within 24 h. In contrast to the control group, a significant correlation was found between the maximal serum lactate level and the maximal dosage of inotropic drugs (r=0.93, P<0.02), administered during the reperfusion phase and continued for 12-24 h postoperatively. No correlation was found between LAc and blood gas analysis during extracorporeal perfusion period.

CONCLUSION

LAc can occur after HTX and seems to be related to the inotropic support of the graft. In contrast to other forms, LAc after HTX has an excellent prognosis and resolves rapidly and spontaneously without treatment. The fact that inotropic support during and immediately after cardiac transplantation can enhance preexisting severe peripheral metabolic cellular dysfunction remains hypothetical.

Difficult separation from cardiopulmonary bypass and deltaPCO2

PURPOSE

Veno-arterial and regional differences of the partial pressure in CO2 (deltaPCO2), may be used as index to evaluate the adequacy of the cardiac output to the oxygen consumption. To determine the incidence of elevated deltaPCO2 and its relationship with difficult separation from bypass (DSB) in patients undergoing cardiac surgery, we conducted a prospective observational cohort study.

METHODS

Data were collected from 58 consecutive patients undergoing various cardiac operations requiring cardiopulmonary bypass (CPB). During the procedure, arterial and venous blood gases and lactate were sampled. Blood was drawn after induction of anesthesia, during bypass and at the closure of the chest wall. Difficult separation from bypass was defined as a systolic arterial pressure < 80 mmHg, and diastolic pulmonary artery pressure > 15 mmHg during progressive separation from CPB with inotropic or mechanical support of cardiac function, or hemodynamic instability resulting in reintroduction of extra-corporeal circulation or insertion of an intra-aortic balloon pump.

RESULTS

In our study, 65% of the samples were associated with elevated deltaPCO2 (> 6 mmHg). Variables associated with difficult weaning were LVEF; duration of bypass and aortic cross-clamping, pre-bypass deltaPCO2 and in-bypass lactate values (P < 0.05). Multivariable analysis identified the pre-bypass deltaPCO2 and the duration of bypass as predictors of DSB.

CONCLUSION

Elevated deltaPCO2 is frequently observed during cardiac surgery and values obtained before bypass were associated with DSB. The deltaPCO2 gradients could be used as marker of the adequacy of tissue perfusion during cardiac surgery.

Effects of cardiogenic shock on lactate and glucose metabolism after heart surgery

BACKGROUND

Hyperlactatemia is a prominent feature of cardiogenic shock. It can be attributed to increased tissue production of lactate related to dysoxia and to impaired utilization of lactate caused by liver and tissue underperfusion. The aim of this prospective observational study was to determine the relative importance of these mechanisms during cardiogenic shock.

PATIENTS

Two groups of subjects were compared: seven cardiac surgery patients with postoperative cardiogenic shock and seven healthy volunteers.

METHODS

Lactate metabolism was assessed by using two independent methods: a) a pharmacokinetic approach based on lactate plasma level decay after the infusion of 2.5 mmol x kg(-1) of sodium lactate; and b) an isotope dilution technique for which the transformation of [13C]lactate into [13C]glucose and 13CO2 was measured. Glucose turnover was determined using 6,62H2-glucose.

RESULTS

All patients suffered from profound shock requiring high doses of inotropes and vasopressors. Mean arterial lactate amounted to 7.8 +/- 3.4 mmol x L(-1) and mean pH to 7.25 +/- 0.07. Lactate clearance was not different in the patients and controls (7.8 +/- 3.4 vs. 10.3 +/- 2.1 mL x kg(-1) x min(-1)). By contrast, lactate production was markedly enhanced in the patients (33.6 +/- 16.4 vs. 9.6 +/- 2.2 micromol x kg(-1) x min(-1); p < .01). Exogenous [13C]lactate oxidation was not different (107 +/- 37 vs. 103 +/- 4 mmol), and transformation of [13C]lactate into [13C]glucose was not different (20.0 +/- 13.7 vs. 15.2% +/- 6.0% of exogenous lactate). Endogenous glucose production was markedly increased in the patients (1.95 +/- 0.26 vs. 5.3 +/- 3.0 mg x kg(-1) x min(-1); p < .05 [10.8 +/- 1.4 vs. 29.4 +/- 16.7 micromol x kg(-1) x min(-1)]), whereas net carbohydrate oxidation was not different (1.7 +/- 0.5 vs. 1.3 +/- 0.3 mg x kg(-1) x min(-1) [9.4 +/- 2.8 vs. 7.2 +/- 1.7 micromol x kg(-1) x min(-1)]).

CONCLUSIONS

Hyperlactatemia in early postoperative cardiogenic shock was mainly related to increased tissue lactate production, whereas alterations of lactate utilization played only a minor role. Patients had hyperglycemia and increased nonoxidative glucose disposal, suggesting that glucose-induced stimulation of tissue glucose uptake and glycolysis may contribute significantly to hyperlactatemia.

Outcome with high blood lactate levels during cardiopulmonary bypass in adult cardiac operation

BACKGROUND

High blood lactate levels during cardiopulmonary bypass (CPB) are associated with tissue hypoperfusion and may contribute to postoperative complications or death. The objective of this study was to determine an association between blood lactate levels during CPB and perioperative morbidity and mortality.

METHODS

We reviewed 1,376 patients who underwent cardiac operation with CPB. Patients with abnormal preoperative blood lactate levels were excluded (n = 101). Blood lactate concentration during CPB, clinical data, and perioperative events were recorded.

RESULTS

Peak blood lactate levels of 4.0 mmol/L or higher during CPB were present in 227 patients (18.0%). Postoperative mortality was higher in this group than in the patients who had peak blood lactate levels of less than 4.0 mmol/L during CPB (11.0% versus 1.4%; p < 0.001, relative risk [RR] = 9.0). Postoperative hemodynamic instability occurred in 29.5% of patients with elevated levels of lactate during CPB compared with 10.9% of patients with lower lactate levels (p < 0.001, RR = 3.4). Overall, major postoperative complications occurred in 43.2% and 21.8% of patients in each group, respectively (p < 0.001, RR = 2.7). Logistic regression analysis revealed that peak blood lactate levels of 4.0 mmol/L or higher during CPB were strongly associated with postoperative mortality (p = 0.0001) and morbidity (p = 0.013).

CONCLUSIONS

Blood lactate concentration of 4.0 mmol/L or higher during CPB identifies a subgroup of patients with increased risk of postoperative morbidity and mortality.

Venous saturation and the anaerobic threshold in neonates after the Norwood procedure for hypoplastic left heart syndrome

BACKGROUND

Reduction in oxygen delivery can lead to organ dysfunction and death by cellular hypoxia, detectable by progressive (mixed) venous oxyhemoglobin desaturation until extraction is limited at the anaerobic threshold. We sought to determine the critical level of venous oxygen saturation to maintain aerobic metabolism in neonates after the Norwood procedure (NP) for the hypoplastic left heart syndrome (HLHS).

METHODS

A prospective perioperative database was maintained for demographic, hemodynamic, and laboratory data. Invasive arterial and atrial pressures, arterial saturation, oximetric superior vena cava (SVC) saturation, and end-tidal CO2 were continuously recorded and logged hourly for the first 48 postoperative hours. Arterial and venous blood gases and cooximetry were obtained at clinically appropriate intervals. SVC saturation was used as an approximation of mixed venous saturation (SvO2). A standard base excess (BE) less than -4 mEq/L (BElo), or a change exceeding -2 mEq/L/h (deltaBElo), were used as indicators of anaerobic metabolism. The relationship between SvO2 and BE was tested by analysis of variance and covariance for repeated measures; the binomial risk of BElo or deltaBElo at SvO2 strata was tested by the likelihood ratio test and logistic regression, with cutoff at p < 0.05.

RESULTS

Complete data were available in 48 of 51 consecutive patients undergoing NP yielding 2,074 valid separate determinations. BE was strongly related to SvO2 (model R2 = 0.40, p < 0.0001) with minimal change after adjustment for physiologic covariates. The risk of anaerobic metabolism was 4.8% overall, but rose to 29% when SvO2 was 30% or below (p < 0.0001). Survival was 100% at 1 week and 94% at hospital discharge.

CONCLUSIONS

Analysis of acid-base changes revealed an apparent anaerobic threshold when SvO2 fell below 30%. Clinical management to maintain SvO2 above this threshold yielded low mortality.

Oxygen consumption, carbon dioxide production and lactic acid during normothermic cardiopulmonary bypass

The objective of this study was to measure oxygen consumption, carbon dioxide production and lactic acid levels during normothermic cardiopulmonary bypass. A prospective study was undertaken in a tertiary care community hospital, involving 20 adults undergoing cardiopulmonary bypass with prolonged (>65 min) crossclamping of the aorta. O2 consumption, CO2 production, hemoglobin and lactic acid levels were measured 5, 35 and 65 min after crossclamping of the aorta. O2 consumption was 79.7 +/- 14.5, 78.8 +/- 15.4 and 81.5 +/- 14.1 ml/min/m2 at 5, 35 and 65 min after crossclamping the aorta. CO2 production was 61.8 +/- 42.9, 60.6 +/- 26.3 and 62.2 +/- 35.9 ml/min/m2 at the same times. Lactic acid levels were 1.6 +/- 0.5 mM/dl at all three times and did not correlate with O2 consumption or CO2 production. In conclusion, although oxygen consumption was low, there was no evidence of abnormal lactate or anaerobic metabolism to suggest tissue ischemia.

Oxygen consumption after cardiopulmonary bypass surgery in children: determinants and implications

OBJECTIVE

We sought to assess oxygen consumption and its determinants in children shortly after undergoing cardiopulmonary bypass operations.

METHODS

Twenty children, aged 2 months to 15 years (median, 3.75 years), undergoing hypothermic cardiopulmonary bypass operations were studied during the first 4 hours after arrival in the intensive care unit. Central and peripheral temperatures were monitored. Oxygen consumption was continuously measured by using respiratory mass spectrometry. Oxygen delivery was calculated from oxygen consumption and arterial and mixed venous oxygen contents, which were sampled every 30 minutes. Oxygen extraction was derived by the ratio of oxygen consumption and oxygen delivery. Arterial blood lactate levels were measured every 30 minutes.

RESULTS

There was a correlation between oxygen consumption and age in patients older than 3 months (r = -0.76). Mean oxygen consumption increased by 14.7% during the study. The increase in oxygen consumption was correlated with the increase in central temperature (r = 0.73). Nine patients had an arterial lactate level above 2 mmol/L on arrival. There were no significant differences in oxygen consumption, oxygen delivery, and oxygen extraction between the group with lactate levels between 2 and 3 mmol/L and the groups with normal lactate levels both on arrival and at 2 hours. One patient with a peak lactate level of 6.8 mmol/L had initially low oxygen delivery (241.3 mL. min(-1). m(-2)).

CONCLUSIONS

During the early hours after a pediatric cardiac operation, the increase in oxygen consumption is mainly attributed to the increase in central temperature. Oxygen consumption is negatively related to age. Mild lactatemia is common and does not appear to reflect oxygen delivery or oxygen consumption or a more complicated recovery.

Changes in circulating blood volume after cardiac surgery measured by a novel method using hydroxyethyl starch

OBJECTIVE

To determine the incidence and extent of postoperative blood volume (BV) changes in patients after elective cardiac surgery using a new method based on dilution of hydroxyethyl-starch.

DESIGN

Prospective, clinical, and laboratory investigation.

SETTING

University hospital intensive care unit.

PATIENTS

A total of thirty-five patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB).

INTERVENTIONS

Perioperative measurements of circulating BV, systemic hemodynamics, lactate, and collection of clinical data.

MEASUREMENTS AND MAIN RESULTS

Measurements were made before and 1 to 72 hrs after CPB. The majority of patients undergoing cardiac surgery showed postoperative BV deficits compared with preoperative BV despite marked positive fluid balances after CPB. At 1 hr and 5 hrs after CPB, 18% and 33% of the patients, respectively, had BV deficits in the range of 0.5 L and 1.5 L, and in 3% to 10% of the cases, postoperative BV deficits exceeded 1.5 L. Concomitantly, at 5 hrs after CPB, mean arterial pressure was maximally reduced, and heart rate and lactate levels were maximally elevated. Thereafter, BV began to normalize, and at 24 hrs after CPB, pre- and postoperative mean BV were no longer significantly different. At 48 hrs and 72 hrs, even a BV surplus of more than 1 L could be observed in 6% and 14% of the patients, respectively.

CONCLUSIONS

During the first hours after CPB, a high percentage of patients had significantly reduced BV and, concomitantly, showed cardiovascular dysfunction and hyperlactemia. Because hypovolemia is associated with increases of perioperative morbidity and mortality, rapid determination of BV is warranted to guide fluid therapy and optimize treatment in patients undergoing cardiac surgery.

Proposed entry criteria for postoperative cardiac extracorporeal membrane oxygenation after pediatric open heart surgery

While extracorporeal membrane oxygenation (ECMO) is being used increasingly after pediatric cardiac surgery, criteria are lacking for initiating ECMO after bypass weaning. To develop clinically useful ECMO entry criteria based on parameters readily available, children were examined at postoperative pediatric intensive care unit (PICU) admission. Using hospital mortality as the primary outcome, univariate and multiple logistic regressions were performed to estimate the predictive value of clinical (age, weight, and diagnosis) and laboratory (arterial blood pressure, pH, lactate, creatine kinase, and arterial and central venous oxygen saturation [ScvO2]) variables. Data from 218 children over a 2 year period were analyzed retrospectively. Univariate regression demonstrated that age, weight, diagnosis, blood pressure, venous and arterial saturation, and lactate were significantly associated with postoperative mortality (p < 0.05). In multiple regression, ScvO2 and lactate level were found to be independent predictors and were used in a predictive model (ScvO2 odds ratio: 2.03-828.6, p = 0.016) (lactate odds ratio: 1.58 -4.20, p = 0.0002) (R2 = 0.70). Applying an 80% risk of mortality to establish entry criteria as in neonatal ECMO, PICU admission values of lactate > 70 mg/dl if ScvO2 < 60% or lactate >163 mg/dl if ScvO2 > 60% are proposed to serve as postoperative ECMO entry criteria if bypass weaning has been possible but is followed by low cardiac output.

High oxygen delivery and extraction by perfluorocarbon-primed extracorporeal membrane oxygenation do not prevent anaerobic metabolism in rabbits

PURPOSE

This study was designed to evaluate the advantage of perfluorocarbon (PFC) emulsion priming for venoarterial extracorporeal membrane oxygenation (ECMO) by comparison with hydroxyethyl starch (HES) solution in rabbits (2.8 to 3.9 kg).

RESULTS

ECMO initiation was accompanied by a profound decrease in hematocrit (from 40.1% to 14.9%) in both groups. The arterial and the right atrial oxygen contents in the PFC group (n = 4; 38.5 and 11.5 mL/dL) were greater than in the HES group (n = 5; 7.0 and 5.1 mL/dL). Right atrial oxygen tension in the PFC group increased at the beginning of ECMO (from 38.4 to 51.2 mm Hg; P = .031) and remained higher than in the HES group for 60 minutes. These results indicate that oxygen supply and extraction in the PFC group were much greater than in the HES group. However, plasma lactate increased progressively during the 120-minute ECMO procedure in both groups (from 1.8 to 14.5 in the HES group, and from 2.3 to 12.2 in the PFC group).

CONCLUSION

Perfluorocarbon priming for ECMO, although providing high oxygen delivery and extraction, does not prevent anaerobic metabolism.

Early bloodstream infection after cardiopulmonary bypass: frequency rate, risk factors, and implications

OBJECTIVE

To determine the incidence, predisposing factors, and outcome of early bloodstream infection after cardiopulmonary bypass.

DESIGN

A case control study.

SETTING

A 54-bed cardiac surgical intensive care in a tertiary referral center.

PATIENTS

Patients from a 30-month period with preoperative hospital stay of <48 hrs and subsequent bloodstream infection within 96 hrs of cardiopulmonary bypass were included in a case group. The control group consisted of patients who had cardiac surgery on the same day as the case group.

MEASUREMENTS AND MAIN RESULTS

Patient demographics, history of comorbidity, preoperative laboratory testing, details of surgery, transfusion requirement, inotropic infusions, hemodynamics, and arterial blood gases on admission to intensive care were compared in the two groups. Measures of outcome were duration of mechanical ventilation and intensive care stay, serum creatinine on the first postoperative day, highest creatinine and bilirubin concentrations, and hospital mortality. During the study period, 7,928 patients had cardiac surgery. Sixteen (0.2%) patients had early bloodstream infection; the control group consisted of 95 patients. Thirteen of the patients with bloodstream infection had Gram-negative bacilli on blood culture, two had Candida species, and two had Gram-positive bacteria. On multivariate logistic regression analysis, greater prevalence of preoperative pulmonary hypertension (odds ratio 9; 95% confidence interval 2 to 41.8; p = .004), diabetes (odds ratio 4.6; 95% confidence interval 1.4 to 15.8; p = .01), number of blood products transfused (odds ratio 1.09; 95% confidence interval 1.04 to 1.17; p = .005), and infusion of inotropes (odds ratio 4.7; 95% confidence interval 1.3 to 16.4; p = .02) or vasopressors (odds ratio 4.1; 95% confidence interval 1.3 to 15.6; p = .02) were associated with postoperative bloodstream infection. Early bloodstream infection was associated with significantly prolonged duration of mechanical ventilation (117.2 +/- 21.5 vs. 18 +/- 8.8 hrs; p = .0001), intensive care stay (213 +/- 27.5 vs. 53 +/- 11.3 hrs; p < .0001), greater creatinine concentrations on the first postoperative day (1.6 +/- 0.1 vs. 1.2 +/- 0.04 mg/dL; p = .0002), greater maximum creatinine concentration (2.4 +/- 0.2 vs. 1.3 +/- 0.1 mg/dL; p < .0001), and greater maximum bilirubin concentration (4.7 +/- 0.6 vs. 1.3 +/- 0.2 mg/dL; p < .0001) when compared with the control group. Five (32%) of 16 bacteremic patients died vs. none of the 95 control patients (p < .0001).

CONCLUSIONS

Early bloodstream infection after cardiac surgery is uncommon and involves predominantly Gram-negative bacteria. The risk factors associated with bloodstream infection were preoperative morbidity and more complex surgery. Bloodstream infection was associated with a significantly adverse impact on outcome after cardiac surgery.

Effects of crystalloid solutions on circulating lactate concentrations: Part 1. Implications for the proper handling of blood specimens obtained from critically ill patients

OBJECTIVES

a) To test the hypothesis that circulating lactate concentrations are the same in simultaneously collected arterial and central venous blood specimens; b) to test the hypothesis that even small amounts of crystalloid solutions, which are inadequately "cleared" from these indwelling arterial and venous catheters, can lead to clinically important and misleading changes in the measured lactate values.

DESIGN

A prospective, multiexperiment study.

SETTING

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

PATIENTS

Three hundred fifty-five patients.

INTERVENTIONS

Blood samples were collected.

MEASUREMENTS AND MAIN RESULTS

Experiment 1: Simultaneously collected arterial and central venous blood specimens were obtained on 148 occasions from 48 medical ICU patients receiving no lactated Ringer's solution (RL). Arterial and central venous lactate values were nearly identical in these patients. The correlation between the arterial and central venous lactate concentrations was excellent (r2 = .85; p < .0001) and the agreement between the arterial and central venous lactate concentrations was also excellent (bias and precision = 0.04 mmol/L and +/- 0.38 mmol/L, respectively). Experiment 2: Arterial and mixed venous blood samples were obtained from 100 percutaneous transluminal coronary angioplasty (PTCA) and 75 cardiac surgical patients immediately before the performance of these cardiac procedures. We found the central venous lactate concentrations to be higher than arterial lactate values in the cardiac surgical group, and there was a very poor correlation (r2 = .07) between arterial and central venous lactate values in the cardiac surgical group. The correlation between central venous and arterial lactate concentrations in the PTCA patients was excellent (r2 = .84) and similar to the findings of experiment 1. Since the cardiac surgical patients received RL and the PTCA patients received no RL, we speculated that the intravenous infusion of RL in the cardiac surgical group accounted for these discordant findings. To test this speculation, we performed experiments 3 and 4. Experiment 3: In a large bench study, blood specimens were divided into multiple 1-mL aliquot portions, to which 0.01, 0.05, 0.10, 0.50, or 1.0 mL of various crystalloid solutions, containing or not containing RL, were added. In a volume-dependent and linear manner, solutions containing RL increased the circulating lactate concentration from 10% to > 400% of the baseline lactate value. In a volume-dependent and linear fashion, the non-RL crystalloid solutions decreased the lactate concentration by 0 to 66% of the baseline nondiluted lactate concentration. Experiment 4: In 30 different cardiac surgical patients, we simultaneously obtained central venous and arterial blood specimens. Patients this time received no RL, and catheter lines were adequately cleared (removal > 5 mL) of crystalloid solutions. We found a correlation (r2 = .82; p < .0001) that was virtually identical to the findings of experiment 1 and to the findings in the PTCA group of experiment 2.

CONCLUSIONS

a) Arterial and central venous lactate concentrations are similar in hemodynamically stable critically ill patients, b) Even small amounts of RL-containing solutions in catheters used for blood sampling may cause false increases in the circulating lactate concentration. c) Even small amounts of non-RL crystalloid solutions in catheters used for blood sampling may falsely decrease circulating lactate values. d) When blood specimens are drawn from indwelling catheters, all crystalloid solutions must be cleared from the line.

Early onset of acute pulmonary dysfunction after cardiovascular surgery: risk factors and clinical outcome

OBJECTIVE

To define the incidence, risk factors, and clinical outcome of early pulmonary dysfunction after cardiovascular surgery for adults.

STUDY

Inception cohort.

SETTING

Adult cardiovascular intensive care unit (ICU).

PATIENTS

All adult admissions after cardiovascular surgery without preoperative pulmonary parenchyma or vascular disease over a period of 12 consecutive months.

INTERVENTION

Collection of data on demographics, preoperative organ insufficiency, emergency surgery, type of surgical procedure, cardiopulmonary bypass time, transfusion of blood products, postoperative arterial blood gases, and systemic hemodynamics on admission to the cardiovascular ICU.

MEASUREMENTS AND MAIN RESULTS

Early postoperative pulmonary dysfunction was defined by mechanical ventilation with a PaO2/FIO2 ratio of < or = 150 torr (< or = 20 kPa) and chest radiography on admission to the cardiovascular ICU. Secondary outcome included postoperative renal and neurologic dysfunction, nosocomial infections, length of mechanical ventilation, hospitalization, and death. A total of 3,122 patients were evaluated and 1,461 patients satisfied the entry criteria of the study. Early postoperative pulmonary dysfunction was present in 180 (12%) patients on admission to the cardiovascular ICU. Preoperative variables: age of > or = 75 yrs (odds ratio 1.69, 95% confidence interval [CI] 1.06 to 2.65), body mass index of > or = 30 kg/m2 (odds ratio 1.60, 95% CI 1.09 to 2.32), mean pulmonary arterial pressure of > or = 20 mm Hg (odds ratio 1.60, 95% CI 1.13 to 2.28), stroke volume index of < or = 30 mL/m2 (odds ratio 1.57, 95% CI 1.08 to 2.26), serum albumin (odds ratio 0.71, 95% CI 0.49 to 0.97), history of cerebral vascular disease (odds ratio 1.81; 95% CI 1.08 to 2.96); operative variables: emergency surgery (odds ratio 2.12, 95% CI 1.01 to 4.51), total cardiopulmonary bypass time of > or = 140 mins (odds ratio 1.54, 95% CI 1.0 to 2.34); and postoperative variables (on admission to cardiovascular ICU): hematocrit of > or = 30% (odds ratio 2.46, 95% CI 1.71 to 3.56), systemic mean arterial pressure of > or = 90 mm Hg (odds ratio 1.67, 95% CI 1.13 to 2.42), and cardiac index of > or = 3.0 L/min/m2 (odds ratio 2.09, 95% CI 1.44 to 3.01) were predictors of early postoperative pulmonary dysfunction. Pulmonary dysfunction was associated with a postoperative increase of serum creatinine (1.36 +/- 0.4 vs. 1.24 +/- 0.4 mg/dL, p < .02), neurologic complications (3% vs. 1.6%, p < .001), nosocomial infections (3% vs. 1.6%, p < .001), prolonged mechanical ventilation (2.2 +/- 5.9 vs. 1.7 +/- 5.6 days, p < .001), length of stay in the cardiovascular ICU (4.4 +/- 12.2 vs. 2.6 +/- 6.2 days, p < .001) and hospital (14.8 +/- 13.1 vs. 10.5 +/- 8.0 days, p < .001), and death (4.4% vs. 1.6%, p < .001).

CONCLUSIONS

The incidence of early postoperative pulmonary dysfunction is uncommon; however, once developed, it is associated with increased morbidity and mortality after cardiovascular surgery. Advanced age, large body mass index, preoperative increased pulmonary arterial pressure, low stroke volume index, hypoalbuminemia, history of cerebral vascular disease, emergency surgery, and prolonged cardiopulmonary bypass time are risk factors for early onset of severe pulmonary dysfunction after surgery. Postoperative hematocrit and systemic hemodynamics suggest that early postoperative pulmonary dysfunction can be a component of a generalized inflammatory reaction to cardiovascular surgery.

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.

Type B lactic acidosis following cardiopulmonary bypass

OBJECTIVE

To describe, characterize, and identify the associations of postcardiac surgical lactic acidosis occurring in the absence of clinical evidence of tissue hypoperfusion.

DESIGN

The preliminary study is a report of a series of observations in 12 patients. The prospective study is also observational, involving the structured collection of hemodynamic and metabolic variables in a prescribed series of patients.

SETTING

Cardiac surgical intensive care unit of a university teaching hospital.

PATIENTS

Twelve patients who developed an unexplained lactic acidosis after cardiac surgery are reported in the preliminary study. The prospective study involved observations in 112 consecutive patients undergoing cardiopulmonary bypass for cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Preliminary study: Cardiac index was increased before, during and after recovery from lactic acidosis. Recovery from lactic acidosis was associated with a decrease in oxygen transport index and significant increases in oxygen consumption index and oxygen extraction ratio.

PROSPECTIVE STUDY

Hemodynamic, oxygen transport, and oxygen consumption variables, together with arterial blood gas and lactate concentrations, were assessed every 6 hrs for 24 hrs after surgery. Sixteen patients developed lactic acidosis (peak lactate concentration > 5.0 mmol/L). Compared with the remainder of the patients, this subgroup had longer duration of cardiopulmonary bypass (116 +/- 31 vs. 76 +/- 31 mins, p < .01), greater intraoperative hypothermia (24.9 +/- 2.0 degrees vs. 26.6 +/- 2.3 degrees C, p < .01), more frequent requirement for vasopressor agents (14/16 vs. 35/96, p < .05) and a higher frequency of hyperglycemia (15/16 vs. 28/96, p < .01). Hemodynamic variables, including cardiac index, were remarkably similar in the acidotic and nonacidotic groups. All of the acidotic patients, in both parts of this study, recovered from their acidosis. Eleven of the patients in the preliminary study and all of the 16 acidotic patients in the prospective study were ultimately discharged from the hospital.

CONCLUSIONS

This report documents the occurrence of lactic acidosis in a subgroup of patients undergoing cardiopulmonary bypass. The pathogenesis of this disorder is uncertain, but it appears to not relate to inadequate oxygen delivery. Systemic vasodilation and reduced oxygen extraction appear to be features of this disorder, which has an excellent prognosis.

Initial postoperative serum lactate levels predict survival in children after open heart surgery

OBJECTIVE

To evaluate the relationship between postoperative serum lactate levels and outcome in children undergoing open heart surgery.

DESIGN

Prospective, noninterventional study.

SETTING

Pediatric intensive care unit (PICU) of a university hospital.

PATIENTS

41 nonconsecutive children who had had cardiopulmonary bypass for repair of congenital heart disease.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Serum lactate levels were measured on admission to the PICU immediately after open heart surgery. Lactate levels were correlated with bypass and cross clamp times, estimated intraoperative blood loss, lowest temperature on bypass, admission Pediatric Risk of Mortality score, anion gap, and measures of postoperative morbidity. Mean lactate levels on admission to the PICU were 6.86 +/- 0.79 mmol/l for nonsurvivors (n = 7) and 2.38 +/- 0.13 mmol/l for survivors (n = 34) (p < 0.0001), and 4.87 +/- 0.7 mmol/l and 2.35 +/- 0.19 mmol/l, for patients with (n = 11) and without (n = 30) multiple organ system failure, respectively (p < 0.0001). Admission lactate levels correlated with all measurements of postoperative morbidity. A serum lactate level of greater than 4.2 mmol/l had a positive predictive value of 100% and a negative predictive value of 97% for postoperative death.

CONCLUSIONS

Initial postoperative serum lactate levels after pediatric open heart surgery may be predictive of outcome. Lactate levels are also higher in patients who go on to develop multiple organ system failure. Elevated postoperative lactate levels may reflect intraoperative tissue hypoperfusion, and measures aimed at increasing oxygen delivery, with normalization of lactate, may improve patient outcome.

Does gastric tonometry work? No

Gastrointestinal tonometry is supposed to diagnose gut mucosal hypoxia using gastric luminal PCO2 and arterial bicarbonatemia, which are substituted in a modified Henderson-Hasselbach equation. This article reviews some of the problems inherent to the multiple assumptions underlying this technique. Tonometry is influenced by several local factors and by systemic acid-base imbalances that are unrelated to oxygenation. Tonometry is a rather crude and cumbersome method of gut capnometry, a technology that may provide valuable information regarding visceral perfusion, but not necessarily oxygenation.

Splanchnic tonometry: a review of physiology, methodology, and clinical applications

The objective of this article is to review splanchnic tonometry. The English literature, involving both animal and human studies, was used for review, with emphasis on papers on physiological and methodological principles and clinical applications. Tonometry involves the measurement of intraluminal PCO2 as a measure of mucosal PCO2 in the gastrointestinal tract via a catheter in, for instance, stomach or sigmoid colon, and the calculation, with help of the blood bicarbonate content and the Henderson-Hasselbalch equation, of the mucosal pH (pHi). The latter is considered as a relatively simple index of the adequacy of mucosal blood flow. Concerning methodology, it is still unclear whether acid secretion should be inhibited for proper assessment of PCO2 in the stomach. Buffering of bicarbonate by gastric acid may elevate the intraluminal PCO2 independently from mucosal PCO2, thereby confounding pHi as a measure of perfusion adequacy. This can be prevented by inhibition of acid secretion. Authors have raised doubts whether the composite variable pHi is of additive value to the acid-base status of arterial blood, so that it is unclear whether a subnormal pHi is a specific and sensitive indicator of mucosal ischemia, as suggested by others on the basis of a decline in the pHi along the gastrointestinal tract in animals subjected to vascular occlusion or circulatory shock. Moreover, tissue PCO2 depends on the PCO2 of supplying blood. Conversely, the bicarbonate concentration in ischemic mucosa may not equal that in arterial blood. Taken together, an elevated tonometer fluid arterial blood PCO2-gradient might be a more sensitive and specific indicator of mucosal ischemia than a decrease in the pHi, analogous to an increase in tissue PCO2 and widening of the venoarterial PCO2 gradient during various types of hypoperfusion, in animals and humans. Although splanchnic ischemia is an early event in shock, the sensitivity and specificity of this index for mucosal ischemia and its clinical value, relative to that of the pHi, have not been formally evaluated yet. Nevertheless, the pHi has been suggested to be of predictive value for gastrointestinal complications, multiple organ failure, success or failure of weaning from mechanical ventilation, and outcome in critically ill patients. Tonometry may be a useful monitoring technique to guide treatment and to improve survival. Splanchnic tonometry is a relatively simple, noninvasive, and thereby promising technique to monitor the critically ill. However, some aspects need further evaluation before the technique can be advocated for routine use.

Biphasic extrathoracic pressure CPR. A human pilot study

HYPOTHESIS

Alternating intrathoracic pressure by means of a chest cuirass can cause perfusion and ventilation equal to or better than standard cardiopulmonary resuscitation (CPR) for humans in cardiac arrest.

DESIGN

Nonrandomized, nonblinded, crossover pilot study.

SETTING

Large urban emergency department.

SUBJECTS

Five adult normothermic, nontraumatic, out-of-hospital cardiac arrest patients unresponsive to standard advanced cardiac life support.

METHOD

Right atrial and aortic catheters were inserted for pressure measurement and blood gas analysis while the patient was receiving standard CPR by a pneumatic compression device (Thumper). The Thumper was then replaced by a chest cuirass (Hayek Oscillator). Pressure and blood gas measurements were then repeated.

RESULTS

The coronary perfusion pressure increased from -1.2 +/- 8.6 mm Hg to 6.2 +/- 6.9 mm Hg for a mean change of 7.4 +/- 3.1 mm Hg (p = 0.006). The compression phase gradient increased 10.0 +/- 21.9 mm Hg (p = 0.364). The venous to arterial PCO2 gradient decreased 44.5 +/- 32.3 mm Hg (p = 0.070). The oxygen extraction ratio increased 1.6 +/- 9.4 percent (p = 0.761). The mean arterial PO2 and PCO2 changed from 252 to 240 mm Hg (p = 0.836) and from 53 to 66 (p = 0.172) mm Hg, respectively.

CONCLUSION

The Hayek Oscillator chest cuirass produced a significant improvement in the coronary perfusion pressure. There was a trend for improved systemic perfusion as indicated by an improved compression phase gradient and venous to arterial PCO2 gradient, although this was not supported by the lack of improvement in the oxygen extraction ratio. The cuirass also adequately oxygenates and ventilates unassisted by positive pressure ventilation.