Arteriovenous carbon dioxide and pH gradients during cardiac arrest

Venous Minus Arterial Carbon Dioxide Gradients in the Monitoring of Tissue Perfusion and Oxygenation: A Narrative Review

According to Fick's principle, the total uptake of (or release of) a substance by tissues is the product of blood flow and the difference between the arterial and the venous concentration of the substance. Therefore, the mixed or central venous minus arterial CO₂ content difference depends on cardiac output (CO). Assuming a linear relationship between CO₂ content and partial pressure, central or mixed venous minus arterial PCO₂ differences (P_cv-aCO₂ and P_mv-aCO₂) are directly related to CO. Nevertheless, this relationship is affected by alterations in the CO₂Hb dissociation curve induced by metabolic acidosis, hemodilution, the Haldane effect, and changes in CO₂ production (VCO₂). In addition, P_cv-aCO₂ and P_mv-aCO₂ are not interchangeable. Despite these confounders, CO is a main determinant of P_cv-aCO₂. Since in a study performed in septic shock patients, P_mv-aCO₂ was correlated with changes in sublingual microcirculation but not with those in CO, it has been proposed as a monitor for microcirculation. The respiratory quotient (RQ)-RQ = VCO₂/O₂ consumption-sharply increases in anaerobic situations induced by exercise or critical reductions in O₂ transport. This results from anaerobic VCO₂ secondary to bicarbonate buffering of anaerobically generated protons. The measurement of RQ requires expired gas analysis by a metabolic cart, which is not usually available. Thus, some studies have suggested that the ratio of P_cv-aCO₂ to arterial minus central venous O₂ content (P_cv-aCO₂/C_a-cvO₂) might be a surrogate for RQ and tissue oxygenation. In this review, we analyze the physiologic determinants of P_cv-aCO₂ and P_cv-aCO₂/C_a-cvO₂ and their potential usefulness and limitations for the monitoring of critically ill patients. We discuss compelling evidence showing that they are misleading surrogates for tissue perfusion and oxygenation, mainly because they are systemic variables that fail to track regional changes. In addition, they are strongly dependent on changes in the CO₂Hb dissociation curve, regardless of changes in systemic and microvascular perfusion and oxygenation.

Use of CO2-Derived Variables in Cardiac Intensive Care Unit: Pathophysiology and Clinical Implications

Shock is a life-threatening condition, and its timely recognition is essential for adequate management. Pediatric patients with congenital heart disease admitted to a cardiac intensive care unit (CICU) after surgical corrections are particularly at risk of low cardiac output syndrome (LCOS) and shock. Blood lactate levels and venous oxygen saturation (ScVO₂) are usually used as shock biomarkers to monitor the efficacy of resuscitation efforts, but they are plagued by some limitations. Carbon dioxide (CO₂)-derived parameters, namely veno-arterial CO₂ difference (ΔCCO₂) and the VCO₂/VO₂ ratio, may represent a potentially valuable addition as sensitive biomarkers to assess tissue perfusion and cellular oxygenation and may represent a valuable addition in shock monitoring. These variables have been mostly studied in the adult population, with a strong association between ΔCCO₂ or VCO₂/VO₂ ratio and mortality. In children, particularly in CICU, few studies looked at these parameters, while they reported promising results on the use of CO₂-derived indices for patients' management after cardiac surgeries. This review focuses on the physiological and pathophysiological determinants of ΔCCO₂ and VCO₂/VO₂ ratio while summarizing the actual state of knowledge on the use of CO₂-derived indices as hemodynamical markers in CICU.

Veno-arterial CO2 difference and respiratory quotient after cardiac arrest: An observational cohort study

PURPOSE

To characterize venous-arterial CO₂ difference (ΔpCO₂) and the respiratory quotient (RQ) in post cardiac arrest patients and evaluate the association between these parameters and patient outcome.

MATERIALS AND METHODS

Data were obtained retrospectively from post cardiac arrest patients admitted between 2007 and 2016 to a medical intensive care unit. Comatose, adult patients in whom arterial and venous blood gas analyses were concomitantly performed in the first 24 h were included. Patients were grouped according to the time-point of sampling; 0-6, 6-12 and 12-24 h after admission.

RESULTS

308 patients were included; 174 (56%) died before ICU discharge and 212 (69%) had an unfavorable neurologic outcome. RQ was associated with ICU mortality (OR:1.09 (95%CI: 1.04-1.14; p < 0.01)), although not with neurological outcome. ΔpCO₂ was negatively associated with both ICU mortality (OR: 0.92 (95%CI: 0.86-0.99; p = 0.02)) and poor neurologic outcome (adjusted OR: 0.93 (95%CI: 0.87-0.99; p = 0.02)). ΔpCO₂ predicted an elevated RQ; a ΔpCO₂ above 8.5 mmHg identified a high RQ with reasonable sensitivity and specificity.

CONCLUSIONS

RQ was associated with ICU mortality and ΔpCO₂ identified elevated RQ in the early phase after cardiac arrest. However, ΔpCO₂ were negatively associated with both ICU mortality and neurologic outcome.

How can CO2-derived indices guide resuscitation in critically ill patients?

Assessing the adequacy of oxygen delivery with oxygen requirements is one of the key-goal of haemodynamic resuscitation. Clinical examination, lactate and central or mixed venous oxygen saturation (S_vO₂ and S_cvO₂, respectively) all have their limitations. Many of them may be overcome by the use of the carbon dioxide (CO₂)-derived variables. The venoarterial difference in CO₂ tension ("ΔPCO₂" or "PCO₂ gap") is not an indicator of anaerobic metabolism since it is influenced by the oxygen consumption. By contrast, it reliably indicates whether blood flow is sufficient to carry CO₂ from the peripheral tissue to the lungs in view of its clearance: it, thus, reflects the adequacy of cardiac output with the metabolic condition. The ratio of the PCO₂ gap with the arteriovenous difference of oxygen content (PCO₂ gap/C_a-vO₂) might be a marker of anaerobiosis. Conversely to S_vO₂ and S_cvO₂, it remains interpretable if the oxygen extraction is impaired as it is in case of sepsis. Compared to lactate, it has the main advantage to change without delay and to provide a real-time monitoring of tissue hypoxia.

Point-of-care laboratory analyses of intraosseous, arterial and central venous samples during experimental cardiopulmonary resuscitation

INTRODUCTION

Screening and correcting reversible causes of cardiac arrest (CA) are an essential part of cardiopulmonary resuscitation (CPR). Point-of-care (POC) laboratory analyses are used for screening pre-arrest pathologies, such as electrolyte disorders and acid-base balance disturbances. The aims of this study were to compare the intraosseous (IO), arterial and central venous POC values during CA and CPR and to see how the CPR values reflect the pre-arrest state.

METHODS

We performed an experimental study on 23 anaesthetised pigs. After induction of ventricular fibrillation (VF), we obtained POC samples from the IO space, artery and central vein simultaneously at three consecutive time points. We observed the development of the values during CA and CPR and compared the CPR values to the pre-arrest values.

RESULTS

The IO, arterial and venous values changed differently from one another during the course of CA and CPR. Base excess and pH decreased in the venous and IO samples during untreated VF, but in the arterial samples, this only occurred after the onset of CPR. The IO, arterial and venous potassium values were higher during CPR compared to the pre-arrest arterial values (mean elevations 4.4 mmol/l (SD 0.72), 3.3 mmol/l (0.78) and 2.8 mmol/l (0.94), respectively).

CONCLUSIONS

A dynamic change occurs in the common laboratory values during CA and CPR. POC analyses of lactate, pH, sodium and calcium within IO samples are not different from analyses of arterial or venous blood. Potassium values in IO, arterial and venous samples during CPR are higher than the pre-arrest arterial values.

Monitoring of Tissue Oxygenation: an Everyday Clinical Challenge

Purpose of review

The aim of this article is to study the overview of pathophysiology and clinical application of central venous oxygen saturation monitoring in critically ill patients and during the perioperative period.

Recent findings

There are several clinical studies and animal experiments evaluating the effects of goal-directed hemodynamic stabilization on critically ill patients. Recent systematic reviews and meta-analyses found that advanced hemodynamic endpoints-targeted management has a positive effect on outcome in high-risk surgical patients. As all interventions aim to improve tissue oxygenation, it is of utmost importance to monitor the balance between oxygen delivery and consumption. For this purpose, central venous blood gas analysis provides an easily available tool in the everyday clinical practice. The adequate interpretation of central venous oxygen saturation renders the need of careful evaluation of several physiological and pathophysiological circumstances. When appropriately evaluated, central venous oxygen saturation can be a valuable component of a multimodal individualized approach, in which components of oxygen delivery are put in the context of the patients' individual oxygen consumption. In addition to guide therapy, central venous oxygen saturation may also serve as an early warning sign of inadequate oxygen delivery, which would otherwise remain hidden from the attending physician.

Summary

With the incorporation of central venous oxygen saturation in the everyday clinical routine, treatment could be better tailored for the patients' actual needs; hence, it may also improve outcome.

Correlation of Venous and Arterial Blood Gas Values Following Cardiothoracic Surgery in Infants and Children

The authors retrospectively compared the correlation of pH and pCO2 from venous and arterial blood gases following cardiothoracic surgery in neonates, infants, and children. The cohort for the study included 14 infants and children undergoing cardiovascular surgery procedures for correction of congenital heart disease. The patients ranged in age from neonates to 48 months (6.2 ± 12.3 months) and in weight from 2.9 to 16.1 kg (5.0 ± 3.2 kg). A total of 95 simultaneous samples of arterial and venous blood were obtained for blood gas analysis. The mean venous pCO2 value was 45 ± 9 mmHg, with a mean arterial pCO2 value of 37 ± 7.4 mmHg. The overall difference between the venous and arterial CO2 values was 8 ± 4 mmHg. The venous to arterial CO2 gradient was greater than 5 mmHg in 78 of 95 samples. There was a significantly greater discrepancy between the arterial and venous pCO2 values when the central venous oxygen saturation was less than 70% compared to when the central venous saturation was ≥70% (p < 0.01). Linear regression analysis of venous versus arterial pCO2 revealed a slope of 0.62, r = 0.76, and r2 = 0.58. The mean venous pH value was 7.42 ± 0.07 and the mean arterial pH value was 7.46 ± 0.07. The overall difference between the venous and arterial pH values was 0.04 ± 0.02. Chi-squared analysis showed that with a central venous oxygen saturation of ≥70%, there were a significantly greater number of values with a venous to arterial pH difference of 0.05 or less compared to samples with a central venous oxygen saturation of less than 70% (p = 0.002). Linear regression analysis of venous versus arterial pH revealed a slope of 0.84, r = 0.88, and r2 = 0.77. Venous blood gas values do not provide a clinically useful estimate of arterial blood gas values following cardiothoracic surgery in children.

Capnography in the Intensive Care Unit

Recent technical innovations have made portable cap nographic monitoring systems available for intensive care unit use. Some of these systems require little tech nical expertise to operate. Capnography has several clin ically relevant applications. It may be used as a monitor of respiration (apnea monitor), of wasted ventilation, or as a reflection of arterial carbon dioxide tension. In some clinical settings, it may provide information about changes in lung perfusion or carbon dioxide produc tion. Because this technique is noninvasive and con tinuous, it offers certain advantages over intermittent arterial blood gas monitoring. The advantages and limi tations of this technique are discussed.

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.

Can venous-to-arterial carbon dioxide differences reflect microcirculatory alterations in patients with septic shock?

Purpose

Septic shock has been associated with microvascular alterations and these in turn with the development of organ dysfunction. Despite advances in video microscopic techniques, evaluation of microcirculation at the bedside is still limited. Venous-to-arterial carbon dioxide difference (Pv-aCO₂) may be increased even when venous O₂ saturation (SvO₂) and cardiac output look normal, which could suggests microvascular derangements. We sought to evaluate whether Pv-aCO₂ can reflect the adequacy of microvascular perfusion during the early stages of resuscitation of septic shock.

Methods

Prospective observational study including 75 patients with septic shock in a 60-bed mixed ICU. Arterial and mixed-venous blood gases and hemodynamic variables were obtained at catheter insertion (T0) and 6 h after (T6). Using a sidestream dark-field device, we simultaneously acquired sublingual microcirculatory images for blinded semiquantitative analysis. Pv-aCO₂ was defined as the difference between mixed-venous and arterial CO₂ partial pressures.

Results

Progressively lower percentages of small perfused vessels (PPV), lower functional capillary density, and higher heterogeneity of microvascular blood flow were observed at higher Pv-aCO₂ values at both T0 and T6. Pv-aCO₂ was significantly correlated to PPV (T0: coefficient −5.35, 95 % CI −6.41 to −4.29, p < 0.001; T6: coefficient, −3.49, 95 % CI −4.43 to −2.55, p < 0.001) and changes in Pv-aCO₂ between T0 and T6 were significantly related to changes in PPV (R² = 0.42, p < 0.001). Absolute values and changes in Pv-aCO₂ were not related to global hemodynamic variables. Good agreement between venous-to-arterial CO₂ and PPV was maintained even after corrections for the Haldane effect.

Conclusions

During early phases of resuscitation of septic shock, Pv-aCO₂ could reflect the adequacy of microvascular blood flow.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-015-4133-2) contains supplementary material, which is available to authorized users.

Central venous-to-arterial carbon dioxide partial pressure difference in early resuscitation from septic shock: a prospective observational study

BACKGROUND

Central venous-to-arterial carbon dioxide partial pressure difference (ΔPCO2) can be used as a marker for the efficacy of venous blood in removing the total CO2 produced by the tissues. To date, this role of ΔPCO2 has been assessed only in patients after resuscitation from septic shock with already normalised central venous oxygen saturation (ScvO2 ≥70%). There are no reports on the behaviour of ΔPCO2 and its relationship to cardiac index (CI) and clinical outcome before normal ScvO2 has been achieved.

OBJECTIVES

To investigate the behaviour of ΔPCO2 and its relationship to CI, blood lactate concentration and 28-day mortality during resuscitation in the very early phase of septic shock. To examine whether patients who normalise both ΔPCO2 and ScvO2 during the first 6  h of resuscitation will have a greater percentage decrease in blood lactate concentration than those who only achieve normal ScvO2.

DESIGN

Prospective observational study.

SETTING

Intensive Care Unit (ICU) in a university hospital.

PATIENTS

Eighty patients with septic shock were consecutively recruited.

INTERVENTIONS

Patients were resuscitated in accordance with the recommendations of the Surviving Sepsis Campaign.

MAIN OUTCOME MEASURES

Blood lactate concentrations, and haemodynamic and oxygen-derived variables were obtained at ICU admission (T0) and 6  h after admission (T6). Lactate decrease was defined as the percentage decrease in lactate concentration from T0 to T6. All cause 28-day mortality was also recorded.

RESULTS

Data are presented as median (interquartile range). At T0, there were significant differences (P < 0.0001) between normal (ΔPCO2 ≤0.8 kPa) and high ΔPCO2 groups for CI (3.9 [3.3 to 4.7] vs. 2.9 [2.3 to 3.1] l min m) and ScvO2 (73 [65 to 80] vs. 61 [53 to 63]%). The correlation between changes in CI and ΔPCO2 was r  =  -0.62, P < 0.0001. Patients who reached a normal ΔPCO2 at T6 had larger decreases in blood lactate concentration and Sequential Organ Failure Assessment scores on day 1. The lactate decrease was greatest in the subgroup achieving both normal ScvO2 and ΔPCO2 at T6. Lactate decrease, unlike ΔPCO2 and ScvO2, was an independent predictor of 28-day mortality.

CONCLUSION

Monitoring ΔPCO2 may be a useful tool to assess the adequacy of tissue perfusion during resuscitation. The normalisation of both ΔPCO2 and ScvO2 is associated with a greater decrease in blood lactate concentration than ScvO2 alone. The lactate decrease is an independent predictor of 28-day mortality. Further research is needed to confirm this hypothesis.

SCMHBP: prediction and analysis of heme binding proteins using propensity scores of dipeptides

Background

Heme binding proteins (HBPs) are metalloproteins that contain a heme ligand (an iron-porphyrin complex) as the prosthetic group. Several computational methods have been proposed to predict heme binding residues and thereby to understand the interactions between heme and its host proteins. However, few in silico methods for identifying HBPs have been proposed.

Results

This work proposes a scoring card method (SCM) based method (named SCMHBP) for predicting and analyzing HBPs from sequences. A balanced dataset of 747 HBPs (selected using a Gene Ontology term GO:0020037) and 747 non-HBPs (selected from 91,414 putative non-HBPs) with an identity of 25% was firstly established. Consequently, a set of scores that quantified the propensity of amino acids and dipeptides to be HBPs is estimated using SCM to maximize the predictive accuracy of SCMHBP. Finally, the informative physicochemical properties of 20 amino acids are identified by utilizing the estimated propensity scores to be used to categorize HBPs. The training and mean test accuracies of SCMHBP applied to three independent test datasets are 85.90% and 71.57%, respectively. SCMHBP performs well relative to comparison with such methods as support vector machine (SVM), decision tree J48, and Bayes classifiers. The putative non-HBPs with high sequence propensity scores are potential HBPs, which can be further validated by experimental confirmation. The propensity scores of individual amino acids and dipeptides are examined to elucidate the interactions between heme and its host proteins. The following characteristics of HBPs are derived from the propensity scores: 1) aromatic side chains are important to the effectiveness of specific HBP functions; 2) a hydrophobic environment is important in the interaction between heme and binding sites; and 3) the whole HBP has low flexibility whereas the heme binding residues are relatively flexible.

Conclusions

SCMHBP yields knowledge that improves our understanding of HBPs rather than merely improves the prediction accuracy in predicting HBPs.

Metabolic engineering of lactate dehydrogenase rescues mice from acidosis

Acidosis causes millions of deaths each year and strategies for normalizing the blood pH in acidosis patients are greatly needed. The lactate dehydrogenase (LDH) pathway has great potential for treating acidosis due to its ability to convert protons and pyruvate into lactate and thereby raise blood pH, but has been challenging to develop into a therapy because there are no pharmaceutical-based approaches for engineering metabolic pathways in vivo. In this report we demonstrate that the metabolic flux of the LDH pathway can be engineered with the compound 5-amino-2-hydroxymethylphenyl boronic acid (ABA), which binds lactate and accelerates the consumption of protons by converting pyruvate to lactate and increasing the NAD⁺/NADH ratio. We demonstrate here that ABA can rescue mice from metformin induced acidosis, by binding lactate, and increasing the blood pH from 6.7 to 7.2 and the blood NAD⁺/NADH ratio by 5 fold. ABA is the first class of molecule that can metabolically engineer the LDH pathway and has the potential to have a significant impact on medicine, given the large number of patients that suffer from acidosis.

The multimodal concept of hemodynamic stabilization

Hemodynamic instability often leads to hypoperfusion, which has a significant impact on outcome in both medical and surgical patients. Measures to detect and treat tissue hypoperfusion early by correcting the imbalance between oxygen delivery and consumption is of particular importance. There are several studies targeting different hemodynamic endpoints in order to investigate the effects of goal-directed therapy on outcome. A so-called multimodal concept putting several variables in context follows simple logic and may provide a broader picture. Furthermore, rather than treating population based "normal" values of certain indices, this concept can be translated into the individualized patient care to reach adequate oxygen supply and tissue oxygenation in order to avoid under, or over resuscitation, which are equally harmful. The purpose of this review is to give an overview of current data providing the basis of this a multimodal, individualized approach of hemodynamic monitoring and treatment.

Persistently high venous-to-arterial carbon dioxide differences during early resuscitation are associated with poor outcomes in septic shock

Introduction

Venous-to-arterial carbon dioxide difference (Pv-aCO₂) may reflect the adequacy of blood flow during shock states. We sought to test whether the development of Pv-aCO₂ during the very early phases of resuscitation is related to multi-organ dysfunction and outcomes in a population of septic shock patients resuscitated targeting the usual oxygen-derived and hemodynamic parameters.

Methods

We conducted a prospective observational study in a 60-bed mixed ICU in a University affiliated Hospital. 85 patients with a new septic shock episode were included. A Pv-aCO2 value ≥ 6 mmHg was considered to be high. Patients were classified in four predefined groups according to the Pv-aCO2 evolution during the first 6 hours of resuscitation: (1) persistently high Pv-aCO2 (high at T0 and T6); (2) increasing Pv-aCO2 (normal at T0, high at T6); (3) decreasing Pv-aCO2 (high at T0, normal at T6); and (4) persistently normal Pv-aCO2 (normal at T0 and T6). Multiorgan dysfunction at day-3 was compared for predefined groups and a Kaplan Meier curve was constructed to show the survival probabilities at day-28 using a log-rank test to evaluate differences between groups. A Spearman-Rho was used to test the agreement between cardiac output and Pv-aCO2. Finally, we calculated the mortality risk ratios at day-28 among patients attaining normal oxygen parameters but with a concomitantly increased Pv-aCO2.

Results

Patients with persistently high and increasing Pv-aCO₂ at T6 had significant higher SOFA scores at day-3 (p < 0.001) and higher mortality rates at day-28 (log rank test: 19.21, p < 0.001) compared with patients who evolved with normal Pv-aCO₂ at T6. Interestingly, a poor agreement between cardiac output and Pv-aCO₂ was observed (r² = 0.025, p < 0.01) at different points of resuscitation. Patients who reached a central venous saturation (ScvO)₂ ≥ 70% or mixed venous oxygen saturation (SvO₂) ≥ 65% but with concomitantly high Pv-aCO₂ at different developmental points (i.e., T0, T6 and T12) had a significant mortality risk ratio at day-28.

Conclusion

The persistence of high Pv-aCO₂ during the early resuscitation of septic shock was associated with more severe multi-organ dysfunction and worse outcomes at day-28. Although mechanisms conducting to increase Pv-aCO2 during septic shock are insufficiently understood, Pv-aCO₂ could identify a high risk of death in apparently resuscitated patients.

Hemodynamic management of cardiovascular failure by using PCO(2) venous-arterial difference

The difference between mixed venous blood carbon dioxide tension (PvCO(2)) and arterial carbon dioxide tension (PaCO(2)), called ∆PCO(2) has been proposed to better characterize the hemodynamic status. It depends on the global carbon dioxide (CO(2)) production, on cardiac output and on the complex relation between CO(2) tension and CO(2) content. The aim of this review is to detail the physiological background allowing adequate interpretation of ∆PCO(2) at the bedside. Clinical and experimental data support the use of ∆PCO(2) as a valuable help in the decision-making process in patients with hemodynamic instability. The difference between central venous CO(2) tension and arterial CO(2) tension, which is easy to obtain can substitute for ∆PCO(2) to assess the adequacy of cardiac output. Differences between local tissue CO(2) tension and arterial CO(2) tension can also be obtained and provide data on the adequacy of local blood flow to the local metabolic conditions.

Prognostic value of venoarterial carbon dioxide gradient in patients with severe sepsis and septic shock

AIM

To investigate the changes in the venoarterial carbon-dioxide gradient (V-a Pco(2)) and its prognostic value for survival of patients with severe sepsis and septic shock.

METHODS

The study was conducted in General Hospital Holy Spirit from January 2004 to December 2007 and included 71 conveniently sampled adult patients (25 women and 46 men), who fulfilled the severe sepsis and septic shock criteria and were followed for a median of 8 days (interquartile range, 12 days). The patients were divided in two groups depending on whether or not they had been mechanically ventilated. Both groups of patients underwent interventions with an aim to achieve hemodynamic stability. Mechanical ventilation was applied in respiratory failure. Venoarterial carbon dioxide gradient was calculated from the difference between the partial pressure of arterial CO(2) and the partial pressure of mixed venous CO(2), which was measured with a pulmonary arterial Swan-Ganz catheter. The data were analyzed using Kaplan-Meier survival analysis, along with a calculation of the hazard ratios.

RESULTS

There was a significant difference between non-ventilated and ventilated patients, with almost 4-fold greater hazard ratio for lethal outcome in ventilated patients (3.85; 95% confidence interval, 1.64-9.03). Furthermore, the pattern of changes of many other variables was also different in these two groups (carbon dioxide-related variables, variables related to acid-base status, mean arterial pressure, systemic vascular resistance, lactate, body mass index, Acute Physiology and Chronic Health Evaluation II, Simplified Acute Physiology II Score, and Sepsis-related Organ Failure Assessment score). Pco(2) values (with a cut-off of 0.8 kPa) were a significant predictor of lethal outcome in non-ventilated patients (P=0.015) but not in ventilated ones (P=0.270).

CONCLUSION

V-a Pco(2) was a significant predictor of fatal outcome only in the non-ventilated group of patients. Ventilated patients are more likely to be admitted with a less favorable clinical status, and other variables seem to have a more important role in their outcome.

Potassium in hemorrhagic shock: a potential marker of tissue hypoxia

BACKGROUND

This study was designed to evaluate serum potassium level variation in a porcine model of hemorrhagic shock (HS).

METHODS

Eight pigs were studied in a controlled hemorrhage model of HS. Blood withdrawal began at a 50 mL/min to 70 mL/min rate, adjusted to reach a mean arterial pressure (MAP) level of 60 mm Hg in 10 minutes. When MAP reached 60 mm Hg, the blood withdrawal rate was adjusted to maintain a MAP decrease rate of 10 mm Hg every 2 minutes to 4 minutes. Arterial and mixed venous blood samples were collected at MAP levels of 60 mm Hg, 50 mm Hg, 40 mm Hg, 30 mm Hg, 20 mm Hg, and 10 mm Hg and analyzed for oxygen saturation, Po2, Pco2, potassium, lactate, bicarbonate, hemoglobin, pH, and standard base excess.

RESULTS

Significant increase in serum potassium occurred early in all animals. The rate of rise in serum potassium and its levels accompanied the hemodynamic deterioration. Hyperkalemia (K >5 mmol/L) incidence was 12.5% at 60 mm Hg and 50 mm Hg, 62.5% at 40 mm Hg, 87.5% at 30 mm Hg, and 100% at 20 mm Hg. Strong correlations were found between potassium levels and lactate (R = 0.82), SvO2 (R = 0.87), DeltapH (R = 0.83), and DeltaPco2 (R = 0.82).

CONCLUSIONS

Serum potassium increase accompanies the onset of HS. The rise in serum potassium was directly related to the hemodynamic deterioration of HS and strongly correlated with markers of tissue hypoxia.

Monitoring the quality of cardiopulmonary resuscitation

PURPOSE OF REVIEW

Numerous recent reports have described limitations in the quality of cardiopulmonary resuscitation. Thus, there has been increasing interest in the techniques available to monitor quality. This review focuses on the major publications since the review published by the International Liaison Committee on Resuscitation in 2005. Some key articles published prior to this time period have also been included.

RECENT FINDINGS

A number of devices can monitor various components of the quality of cardiopulmonary resuscitation. End-tidal CO2 measurement assists in confirming placement of endotracheal tubes, correlates with cardiac output and detects the return of spontaneous circulation. Turbine flow-meters monitor respiratory rate and tidal volume. Transthoracic impedance monitoring measures respiratory rate, and may assist in confirmation of endotracheal tube placement. A new mechanical device (CPREzy) and a new defibrillator/monitor allow estimation of depth (and rate) of compressions. Ventricular-fibrillation waveform analysis may facilitate better timing of defibrillation. Echocardiography detects conditions that may impair the quality of cardiopulmonary resuscitation.

SUMMARY

Many options are available to monitor the quality of cardiopulmonary resuscitation. Some have significant limitations, and others are only readily available in hospital. The use of the information from this more intensive monitoring promises to improve outcomes of cardiopulmonary resuscitation.

A comparison of central venous and arterial base deficit as a predictor of survival in acute trauma

BACKGROUND

The arterial base deficit has been demonstrated to be a marker of shock and predictive of survival in injured patients. The venous blood, however, may better reflect tissue perfusion. Its usefulness in trauma is unknown. We compared central venous with arterial blood gas analysis to determine which was a better predictor of survival in injured patients.

METHODS

A prospective, nonrandomized series of acutely injured patients was investigated. Patients who had an arterial blood gas analysis for acid-base determination had a simultaneous central venous blood gas analysis and routine blood tests. Patient demographics, Injury Severity Score, and survival past 24 hours were recorded. Arterial and venous blood samples were analyzed for pH, PCO2, PO2, HCO3, hemoglobin-oxygen saturation, base deficit, and lactate.

RESULTS

One hundred patients were enrolled. There were 76 survivors and 24 nonsurvivors. Wilcoxon rank sum test and multivariate logistic regression were used for each recorded variable; only central venous base deficit was predictive of survival past 24 hours (P = .0081). Specifically, arterial base deficit was not predictive of survival past 24 hours.

CONCLUSION

In a prospective series of acutely injured patients, central venous base deficit, not arterial base deficit, was predictive of survival past 24 hours.

Nitric oxide-releasing xerogel-based fiber-optic pH sensors

A xerogel-based optical pH sensor capable of releasing low levels of nitric oxide (NO) and measuring changes in solution pH is reported. Through simple dip-coating procedures, aminoalkoxysilane-based xerogel films modified with N-diazeniumdiolate NO donor precursors and the fluorescent pH indicator seminaphthorhodamine-1 carboxylate (SNARF-1) were sequentially deposited onto optical fibers. The resulting sensors were characterized by fast and linear response to pH throughout the physiological range (pH 7.0-7.8). Real-time chemiluminescence measurements confirmed that the presence of the overlying SNARF-1-containing TMOS layer did not have an inhibitory effect on N-diazeniumdiolate formation or NO release, and the NO-releasing coatings were capable of maintaining NO fluxes >0.4 pmol/cm(2) s up to 16 h. In vitro blood compatibility studies using porcine platelets confirmed the expected thromboresistivity of the NO-releasing xerogel coatings.

Arterio-venous gradients of free energy change for assessment of systemic and splanchnic perfusion in cardiac surgery patients

Objective: Adequacy of organ perfusion depends on sufficient oxygen supply in relation to the metabolic needs. The aim of this study was to evaluate the relationship between gradients of free energy change, and the more commonly used parameter for the evaluation of the adequacy of organ perfusion, such as oxygen-extraction in patients undergoing valve replacement surgery using normothermic cardiopulmonary bypass (CPB).

Methods: In 43 cardiac patients, arterial, mixed venous, and hepato-venous blood samples were taken synchronously after induction of anaesthesia (preCPB), during CPB, and 2 and 7 h after admission to the intensive care unit (ICU+2, ICU+7). Blood gas analysis, cardiac output, and hepato-splanchnic blood flow were measured. Free energy change gradients between mixed venous and arterial (-ΔΔG(v-a)) and hepato-venous and arterial (-ΔΔG(hv-a)) compartments were calculated.

Measurements and results: Cardiac index (CI) increased from 1.9 (0.7) to 2.8 (1.3) L/min/m (median, inter-quartile range) (p =0.001), and hepato-splanchnic blood flow index (HBFI) from 0.6 (0.22) to 0.8 (0.53) L/min/m (p =0.001). Despite increasing flow, systemic oxygen extraction increased after CPB from 24 (10)% to 35 (10)% at ICU+2 (p =0.002), and splanchnic oxygen extraction increased during CPB from 37 (19)% to 52 (14)% (p =0.001), and remained high thereafter. After CPB, high splanchnic and systemic gradients of free energy change gradients were associated with high splanchnic and systemic oxygen extraction, respectively (p =0.001, 0.033, respectively).

Conclusion: Gradients of free energy change may be helpful in characterising adequacy of perfusion in cardiac surgery patients independently from measurements or calculations of data from oxygen transport.

Gas concentrations in expired air during basic life support using different ratios of compression to ventilation

AIM

In cardiopulmonary resuscitation, different ratios of compression to ventilation with regard to optimal oxygen transport are considered. We hypothesised that the end tidal fraction of oxygen might increase from levels found in the conventional compression-ventilation ratio of 15:2 if more consecutive ventilations are given because the rescuer would hyperventilate. The second hypothesis was that the air blown into an infant with mouth to mouth ventilation consists of rescuer's dead space air only, meaning that the fraction of oxygen should increase.

METHODS

In a basic life support simulation, we measured the expired air of rescuers using a VmaxST (Sensormedics, USA) respiratory gas analyser connected to an adult and to an infant resuscitation manikin. Fourteen participants performed five different compression-ventilation ratios (30:2, 30:5, 50:5, 100:10 and 5:1). These were compared to a ratio of 15:2 (control group).

RESULTS

We found a significant increase in end tidal oxygen in 30:2 (16.3%), 30:5 (16.8%), 50:5 (16.8%), 100:10 (17.0%) compared to 15:2 (15.9%), p< or =0.004 for all groups versus control; p for trend: 0.014. In the infant CPR observation (ratio 5:1), the difference with the adult control group (15:2) also reached statistical significance (17.9% versus 15.9%, p=0.0005).

CONCLUSION

Increasing consecutive compressions and ventilations above 15:2 leads to a statistically significant increase in expired fraction of oxygen. In infant ventilation, the air exhaled into a victim contains some dead space air with a higher end tidal oxygen fraction than in adults.

Prehospital and emergency department care to preserve neurologic function during and following cardiopulmonary resuscitation

Considerable progress has been made in providing high-quality prehospital and emergency cardiac care for OHCA victims. The use of early CPR, early defibrillation, early ACLS, and state-of-the-art postresuscitation care offers the best promise for improved community survival and neurologic outcome statistics in the future. The NIH-sponsored Resuscitation Outcomes Consortium represents the largest governmentally sponsored effort of its kind that that will test the value of promising pharmacologic and device interventions on improving survival and neurologic outcome in OHCA patients.

Sublingual capnometry: a non-invasive measure of microcirculatory dysfunction and tissue hypoxia

With improvement in supportive care patients rarely die from their presenting illness but rather from its sequela, namely sequential multi-organ failure. Tissue hypoxia is believed to be the causation of multi-organ dysfunction syndrome (MODS). The expedient detection and correction of tissue hypoxia may therefore limit the development of MODS. The standard oxygenation and hemodynamic variables (blood pressure, arterial oxygenation, cardiac output) which are monitored in critically ill patients are 'upstream' markers and provide little information as to the adequacy of tissue oxygenation. Global 'downstream' markers such as mixed venous oxygen saturation and blood lactate are insensitive indicators of tissue hypoxia. Sublingual PCO(2) is a regional marker of microvascular perfusion and tissue hypoxia that holds great promise for the risk stratification and end-point of goal directed resuscitation in critically ill patients. This paper reviews the technology and application of sublingual PCO(2) monitoring.

Use of high-dose epinephrine and sodium bicarbonate during neonatal resuscitation: is there proven benefit?

For adults and pediatric age patients, high-dose intravenous epinephrine was recommended if standard-dose epinephrine failed to achieve return of spontaneous circulation. More recent trials suggest that high-dose epinephrine is not beneficial and may result in increased harm. There are no randomized clinical studies of high-dose versus standard-dose intravenous epinephrine in neonates. Routine use of high-dose epinephrine during neonatal resuscitation cannot be recommended. Although sodium bicarbonate has been used during neonatal resuscitation, the only randomized controlled trial of its use during brief neonatal resuscitation showed no benefit. Sodium bicarbonate infusion during neonatal cardiopulmonary resuscitation (CPR) has several known and potential side effects. The use of sodium bicarbonate infusion should be discouraged during brief CPR. Whether sodium bicarbonate is beneficial for infants who require prolonged CPR despite adequate ventilation is unknown.

Improved resuscitation outcome in emergency medical systems with increased usage of sodium bicarbonate during cardiopulmonary resuscitation

BACKGROUND

The use of sodium bicarbonate (SB) in cardiopulmonary resuscitation (CPR) is controversial. This study analyzes the effects of SB use on CPR outcome in the Brain Resuscitation Clinical Trial III (BRCT III), which was a multicenter randomized trial comparing high-dose to standard-dose epinephrine during CPR. Sodium bicarbonate use in BRCT III was optional.

METHODS

The entire BRCT III database was reviewed. Analysis included only patients who arrested out of the hospital and whose time from collapse to initiation of ACLS was no longer than 30 min (total n = 2122 patients). Sodium bicarbonate use by the 16 participating study sites was analyzed. The study sites were divided according to their SB usage profile: 'low SB user' sites administered SB in less than 50% of CPRs and their first epinephrine to SB time exceeded 10 min; and 'high SB user' sites used SB in over 50% of CPRs and their first epinephrine to SB time was <10 min.

RESULTS

Sites' SB usage rates ranged between 3.1% and 98.2% of CPRs. Sodium bicarbonate usage rates correlated inversely with the sites' intervals from collapse (r = - 0.579 P = 0.018) from initiation of ACLS (r = - 0.685 P = 0.003) and from first epinephrine (r = - 0.611 P = 0.012) to SB administration. Mean ROSC rate in the 'high SB user' sites was 33.5% (CI = 30.0-37.0) compared to 25.7% (CI = 23.1-28.4) in the 'low SB user' sites. In the 'high SB user' sites, hospital discharge rate was 5.3% (CI = 3.6-7.0) compared to 3% (CI = 2.0-4.0) in the 'low SB user' sites, and 5.3% (CI = 3.6-7.0) had a favorable neurological outcome compared to 2.1% (CI = 1.2-3.0) in the 'low SB user' sites. Collapse to ACLS interval was 8.5 min (CI = 8.1-9.0) in the 'high SB user' sites compared to 10.2 min (CI = 9.8-10.6) in the 'low SB user' sites, and their ACLS to first epinephrine interval was 7.0 min (CI = 6.5-7.5) compared to 9.7 min (CI = 9.3-10.2). Multivariate regression analysis found that belonging to 'high SB user' sites independently increased the chances for ROSC (OR 1.36, CI 1.08-1.7) and for achieving a good neurological outcome (OR 2.18, CI 1.23-3.86).

CONCLUSIONS

Earlier and more frequent use of SB was associated with higher early resuscitability rates and with better long-term outcome. Sodium bicarbonate may be beneficial during CPR, and it should be subjected to a randomized clinical trial.

Intramucosal-Arterial Pco2 Gradient Does Not Reflect Intestinal Dysoxia in Anemic Hypoxia

BACKGROUND

An increase in intramucosal-arterial Pco2 gradient (DeltaPco2) might be caused by tissue hypoxia or by diminished blood flow. Our hypothesis was that DeltaPco2 should not be altered in anemic hypoxia with preserved blood flow.

METHODS

In 18 anesthetized, mechanically ventilated sheep, oxygen transport was stepwise reduced by hemorrhage (hypovolemia, n = 9) or by hemorrhage and simultaneous dextran infusion (hemodilution, n = 9).

RESULTS

Hypovolemia and hemodilution produced comparable decreases in systemic and intestinal oxygen transport and uptake. However, mixed venoarterial and mesenteric venoarterial Pco2 gradients and DeltaPco2 were significantly higher in hypovolemia than in hemodilution (25 +/- 5 vs. 10 +/- 2 mm Hg; 21 +/- 6 vs. 10 +/- 5 mm Hg; and 41 +/- 18 vs. 14 +/- 9 mm Hg, respectively; p < 0.01).

CONCLUSION

DeltaPco2 did not reflect intestinal dysoxia during Vo2/Do2 dependency attributable to hemodilution. Blood flow seems to be the main determinant of DeltaPco2.

Treatment of hypotension in pigs with an inspiratory impedance threshold device: a feasibility study

OBJECTIVE

An inspiratory impedance threshold device was evaluated in spontaneously breathing animals with hypotension to determine whether it could help improve systemic arterial pressures when fluid replacement was not immediately available.

DESIGN

Prospective, randomized.

SETTING

Animal laboratory.

SUBJECTS

Thirty-nine female farm pigs (weight, 28-33 kg).

INTERVENTIONS

A total of 39 anesthetized spontaneously breathing pigs were treated with an impedance threshold device, with cracking pressures from 0 to -20 cm H2O. Four separate experimental protocols were performed: protocol A, in which the hemodynamics of seven pigs were examined during application of an impedance threshold device at various levels of inspiratory impedance (-5, -10, -15, and -20 cm H(2)O), both before and after a severe, controlled hemorrhage to a systolic blood pressure of 50 - 55 mm Hg; protocol B, in which nine pigs bled to systolic blood pressure of 50 -55 mm Hg were treated with an impedance threshold device set at -12 cm H2O and were compared with nine others treated with a sham device; protocol C, in which the effects of the impedance threshold device on mixed venous gases were measured in seven hemorrhaged pigs; and protocol D, in which the effects of the impedance threshold device on cardiac output in seven hemorrhaged pigs were measured.

METHODS AND MAIN RESULTS

During initial studies with both normovolemic and hypovolemic pigs, sequential increases in inspiratory impedance resulted in a significant increase in systolic blood pressure, whereas diastolic left ventricular and right atrial pressures decreased significantly and proportionally to the level of impedance. When comparing the sham vs. active impedance threshold device (-12 cm H(2)O) in hypotensive pigs, systolic blood pressure (mean +/- sem) with active impedance threshold device treatment increased from 70 +/- 2 mm Hg to 105 +/- 4 mm Hg (p <.01). Pressures in the control group remained at 70 +/- 4 mm Hg (p <.01). Cardiac output increased by nearly 25% (p <.01) with the active impedance threshold device when calculated using the mixed gas equation and when determined by thermodilution.

CONCLUSIONS

These studies demonstrate that it is feasible to use a device that creates inspiratory impedance in spontaneously breathing normotensive and hypotensive pigs to increase blood pressure and enhance cardiopulmonary circulation in the absence of immediate fluid resuscitation. Further studies are needed to evaluate the potential long-term effects and limitations of this new approach to treat hypovolemic hypotension.

A Mathematical Model of Tissue–Blood Carbon Dioxide Exchange during Hypoxia

A two-compartment mass transport model of tissue CO(2) exchange is developed to examine the relative contributions of blood flow and cellular hypoxia (dysoxia) to increases in tissue and venous blood CO(2) concentration. The model assumes perfectly mixed homogeneous conditions, steady-state equilibrium, and CO(2) production occurring exclusively at the tissues. The behavior of the model is compared with published data derived from an isolated dog hindlimb preparation subjected to either reductions in blood flow (ischemic hypoxia) or decreases in arterial PO(2) (hypoxic hypoxia). The results of the model corroborate the experimental finding of greater venous and tissue CO(2) concentrations with ischemic hypoxia than with hypoxic hypoxia. The model also predicts increases in tissue CO(2) concentration under conditions of adequate O(2) supply if CO(2) transfer from tissue to blood becomes impaired. Consequently, from a theoretical perspective, it appears that increases in the tissue or venous blood CO(2) concentration are neither sensitive nor specific markers of tissue dysoxia. The results of the model support the notion that changes in tissue and venous blood CO(2) concentration during dysoxia reflect primarily alterations in vascular perfusion and not scarcity in cellular energy supply.

End-Tidal CO2-Arterial CO2 Differences: A Useful Intraoperative Mortality Marker in Trauma Surgery

OBJECTIVE

The gradient of end-tidal CO2 to arterial CO2 (Pa-ET)CO2 has been identified as a predictor of mortality in patients undergoing emergency trauma surgery. In an effort to further elucidate this phenomena, we accumulated additional data on trauma patients undergoing emergency surgery.

METHODS

Five-hundred and one patients undergoing emergent trauma surgery at an Urban Level I Trauma Center were used as a database. Data were obtained both prospectively and retrospectively. End-tidal and CO2 measurements were serially obtained during surgery. Data were arbitrarily placed in three categories: initial OR, post-resuscitation, and final OR. (Post-resuscitation was identified after bleeding controlled and vital signs normalizing). Correlation of the end-tidal CO2 with the PACO2 difference were correlated with various factors including survival.

RESULTS

Overall mortality was 29%. Mean ISS was 22 +/- 9.8. Mean emergency department systolic blood pressure was 81 mm Hg. Sixty-three people died in the operating room, 54 died within 24 hours post-op, and 30 patients died greater than 24 hours post-op. The average (Pa-ET)CO2 difference was <10 mm Hg in all survivors at all measurement times. The average (Pa-ET)CO2 was >10 mm Hg in non-survivors in patients that died at all time intervals.

CONCLUSION

(Pa-ET)CO2 can be used as a predictor of mortality and may be useful as an intraoperative tool for assessing the physiologic conditions of the patient. This predictor of mortality was valid even in patients that died greater than 24 hours after surgery. This information is almost always already available and may be used to further guide the decisions regarding patient care, particularly in decisions regarding damage control surgery.

Stroke volumes and end-tidal carbon dioxide generated by precordial compression during ventricular fibrillation

OBJECTIVE

The objective of this study was to measure stroke volumes produced by precordial compression during cardiopulmonary resuscitation and to quantitate relationships of stroke volume to measurements of end-tidal carbon dioxide.

DESIGN

A prospective, observational animal study.

SETTING

Medical research laboratory in a university-affiliated research and educational foundation.

SUBJECTS

Domestic pigs.

INTERVENTIONS

Eighteen anesthetized male, domestic pigs weighing between 40 and 45 kg were investigated. Ventricular fibrillation was electrically induced and continued for intervals ranging from 4 to 10 mins. Precordial compression was maintained at 80 per minute together with mechanical ventilation after endotracheal intubation.

MEASUREMENTS AND MAIN RESULTS

Stroke volumes were measured with the aid of transesophageal echocardiographic imaging. End-tidal carbon dioxide was quantitated with conventional capnography. Baseline values of thermodilution cardiac output were highly correlated with echocardiographic measurements (r =.92). The stroke volume index produced by precordial compression averaged 0.45 mL/kg or approximately 37% of the average prearrest value of 1.22 mL/kg. The end-tidal carbon dioxide was highly predictive of stroke volume index (r =.88, p <.001) with a mean bias of 0.003 mL/kg.

CONCLUSIONS

We confirmed that precordial compression produces approximately one third of prearrest stroke volumes during cardiopulmonary resuscitation and demonstrated that end-tidal carbon dioxide was quantitatively predictive of stroke volume index estimated by transesophageal echocardiographic imaging.

Sublingual capnometry: an alternative to gastric tonometry for the management of shock resuscitation

Normal vital signs do not reflect the physiologic aberrations after blood loss. Recognition of hypoperfusion during resuscitation can avoid the development of multiple organ failure. Advances in technology enable the clinician to monitor changes, potentially identifying tissue hypoxia much earlier than previously was possible. Gastric tonometry can be quite helpful in the intensive care unit in identifying gastric hypoperfusion, but has considerable drawbacks. The ability to monitor P(SI)CO(2) via sublingual capnometers overcomes some limitations of gastric tonometry and may be a valuable aid in the prehospital phase, the emergency department, and the intensive care unit in identifying end points of resuscitation.

End-tidal CO2-derived values during emergency trauma surgery correlated with outcome: a prospective study

BACKGROUND

The purpose of this study was to determine whether end-tidal carbon dioxide (PETCO) derived variables assist in evaluating the adequacy of resuscitation during emergency surgery for trauma.

METHODS

This was a prospective study of end-tidal derived variables and outcome in 106 trauma patients in an urban Level I trauma center.

RESULTS

The patients who lived (compared with those who died) had higher final end-tidal Pco levels, lower arterial-end tidal CO differences (Pa-ET)CO, and a decreased alveolar dead space ratio (p < 0.001). The best survival rates were with a PETCO > 27 mm Hg, a (Pa-ET)CO < or = 9 mm Hg, and 96% (56 of 58) for an alveolar dead space ratio < or = 0.20 (p < 0.001). An inappropriately high or "excess Paco also correlated with a decreased (Pa-ET)CO and poorer prognosis. If, after the initial resuscitation, the PETCO -derived values did not achieve these "optimal" levels, survival was significantly reduced.

CONCLUSION

During emergency trauma surgery, the PETCO and its derived values help to predict outcome and may be used to identify patients needing more aggressive resuscitation.

Clinical use of sodium bicarbonate during cardiopulmonary resuscitation--is it used sensibly?

This study retrospectively analyzed the pattern of sodium bicarbonate (SB) use during cardiopulmonary resuscitation (CPR) in the Brain Resuscitation Clinical Trial III (BRCT III). BRCT III was a prospective clinical trial, which compared high-dose to standard-dose epinephrine during CPR. SB use was left optional in the study protocol. Records of 2915 patients were reviewed. Percentage, timing and dosage of SB administration were correlated with demographic and cardiac arrest variables and with times from collapse to Basic Life Support, to Advanced Cardiac Life Support (ACLS) and to the major interventions performed during CPR. SB was administered in 54.5% of the resuscitations. The rate of SB use decreased with increasing patient age-primarily reflecting shorter CPR attempts. Mean time intervals from arrest, from start of ACLS and from first epinephrine to administration of the first SB were 29+/-16, 19+/-13, and 10.8+/-11.1 min, respectively. No correlation was found between the rate of SB use and the pre-ACLS hypoxia times. On the other hand, a direct linear correlation was found between the rate of SB use and the duration of ACLS. We conclude that when SB was used, the time from initiation of ACLS to administration of its first dose was long and severe metabolic acidosis probably already existed at this point. Therefore, if SB is used, earlier administration may be considered. Contrary to physiological rationale, clinical decisions regarding SB use did not seem to take into consideration the duration of pre-ACLS hypoxia times. We suggest that guidelines for SB use during CPR should emphasize the importance of pre-ACLS hypoxia time in contributing to metabolic acidosis and should be more specific in defining the duration of "protracted CPR or long resuscitative efforts", the most frequent indication for SB administration.

Metabolic acidosis in the intensive care unit

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

Effects of active compression-decompression cardiopulmonary resuscitation with the inspiratory threshold valve in a young porcine model of cardiac arrest

Active compression-decompression (ACD) cardiopulmonary resuscitation (CPR) with the inspiratory threshold valve (ITV) has been recently recommended by the American Heart Association for treatment of adults in cardiac arrest (class IIb: alternative, useful intervention), but this new technique has never been used in a pediatric population. Thus, this study was designed to evaluate ACD + ITV CPR in a young porcine model of cardiac arrest. After 10 min of ventricular fibrillation, and 8 min of standard CPR, ACD + ITV CPR was performed in seven 4- to 6-wk-old pigs (8-12 kg); defibrillation was attempted 8 min later. Within 2 min after initiation of ACD + ITV CPR, mean (+/- SEM) coronary perfusion pressure increased from 18 +/- 2 to 24 +/- 3 mm Hg (p = 0.018). During standard versus ACD + ITV CPR, mean left ventricular myocardial and total cerebral blood flow was 59 +/- 21 versus 126 +/- 32 mL.min(-1).100 g(-1), and 36 +/- 7 versus 60 +/- 15 mL.min(-1).100 g(-1), respectively (p = 0.028). Six of seven animals were successfully defibrillated, and survived >15 min. In conclusion, the combination of ACD + ITV CPR significantly increased both coronary perfusion pressure and vital organ blood flow after prolonged standard CPR in this young porcine model of ventricular fibrillation.

Low-dose Carbicarb improves cerebral outcome after asphyxial cardiac arrest in rats

STUDY OBJECTIVE

Controversy surrounds the use of buffers during cardiac arrest to correct acidosis. The objective of this study was to determine whether attenuation or neutralization of cerebral acidosis by Carbicarb alters hippocampal glutamate levels, neuronal cell death, and neurologic deficits after reperfusion from asphyxial cardiac arrest in rats.

METHODS

Rats were prospectively randomized to either a control (n=45), low-dose Carbicarb (LDC; 3 mL/kg, n=45), or high-dose Carbicarb (HDC; 6 mL/kg, n=45) group in a blinded fashion during resuscitation after 8 minutes of asphyxial cardiac arrest. Microdialysis was used to assess brain pH and glutamate. A neurologic deficit score and neuronal cell death in the hippocampus were determined at day 7.

RESULTS

Resuscitation was greatest in LDC rats (42/45) and least in HDC rats (28/45) versus that in control rats (34/45). Brain pH was higher in the LDC and HDC rats 10 minutes after resuscitation and remained higher than that of control rats for 120 minutes after resuscitation. Glutamate levels at 10 to 120 minutes after reperfusion were lowest in the LDC rats. LDC rats had the lowest neurologic deficit score (1+/-2) versus that of control rats (13+/-8) and HDC rats (19+/-6). Hippocampal neuronal cell death was lowest in LDC rats (30+/-20) versus that in control rats (86+/-47) and HDC rats (233+/-85).

CONCLUSION

LDC administered during resuscitation from asphyxial cardiac arrest attenuated acidosis, improved resuscitation, and reduced neurologic deficits and the number of dead hippocampal neurons. Neutralization of cerebral acidosis with HDC increased the number of dead hippocampal neurons and neurologic deficits after resuscitation from cardiac arrest in rats.

Intramucosal-arterial PCO2 gap fails to reflect intestinal dysoxia in hypoxic hypoxia

INTRODUCTION

An elevation in intramucosal-arterial PCO2 gradient (DeltaPCO2) could be determined either by tissue hypoxia or by reduced blood flow. Our hypothesis was that in hypoxic hypoxia with preserved blood flow, DeltaPCO2 should not be altered.

METHODS

In 17 anesthetized and mechanically ventilated sheep, oxygen delivery was reduced by decreasing flow (ischemic hypoxia, IH) or arterial oxygen saturation (hypoxic hypoxia, HH), or no intervention was made (sham). In the IH group (n = 6), blood flow was lowered by stepwise hemorrhage; in the HH group (n = 6), hydrochloric acid was instilled intratracheally. We measured cardiac output, superior mesenteric blood flow, gases, hemoglobin, and oxygen saturations in arterial blood, mixed venous blood, and mesenteric venous blood, and ileal intramucosal PCO2 by tonometry. Systemic and intestinal oxygen transport and consumption were calculated, as was DeltaPCO2. After basal measurements, measurements were repeated at 30, 60, and 90 minutes.

RESULTS

Both progressive bleeding and hydrochloric acid aspiration provoked critical reductions in systemic and intestinal oxygen delivery and consumption. No changes occurred in the sham group. DeltaPCO2 increased in the IH group (12 +/- 10 [mean +/- SD] versus 40 +/- 13 mmHg; P < 0.001), but remained unchanged in HH and in the sham group (13 +/- 6 versus 10 +/- 13 mmHg and 8 +/- 5 versus 9 +/- 6 mmHg; not significant).

DISCUSSION

In this experimental model of hypoxic hypoxia with preserved blood flow, DeltaPCO2 was not modified during dependence of oxygen uptake on oxygen transport. These results suggest that DeltaPCO2 might be determined primarily by blood flow.

Optimizing timing of ventricular defibrillation

OBJECTIVE

Our intent was to evolve a prognosticator that would predict the likelihood that an electrical shock would restore a perfusing rhythm. Such a prognosticator was to be based on conventional electrocardiographic signals but without constraints caused by artifacts resulting from precordial compression. The adverse effects of "hands off" intervals for rhythm analyses would therefore be minimized. Such a prognosticator was further intended to reduce the number of electrical shocks and the total energy delivered and thereby minimize postresuscitation myocardial dysfunction.

DESIGN

Observational study.

SUBJECTS

Medical research laboratory of a university-affiliated research and educational institute.

SUBJECTS

Domestic pigs.

INTERVENTIONS

Ventricular fibrillation was induced in an established porcine model of cardiac arrest. Recordings of scalar lead 2 over the frequency range of 4-48 Hz were utilized. The area under the curve representing the amplitude and frequency was defined as the amplitude spectrum area (AMSA).

MEASUREMENTS AND MAIN RESULTS

A derivation group of 55 animals yielded a threshold value of AMSA that uniformly predicted successful resuscitation. A separate group of 10 animals, a validation group, confirmed that an AMSA value of 21 mV.Hz predicted restoration of perfusing rhythm after 7 of 8 electrical shocks and failure of electrical conversion in 21 of 23 electrical shocks, yielding sensitivity and specificity of about 90%. The negative predictive value of AMSA was 95% and statistically equivalent to that of coronary perfusion pressure, mean amplitude, and median frequency. The positive predictive value that would prompt continuation of cardiopulmonary resuscitation without interruption for an unsuccessful defibrillation attempt was greatly improved with AMSA (78%) as compared with coronary perfusion pressure (42%), mean amplitude (32%), and median frequency (29%).

CONCLUSION

AMSA has the potential for guiding more optimal timing of defibrillation without adverse interruption of cardiopulmonary resuscitation or the delivery of unsuccessful high energy electrical shocks that contribute to postresuscitation myocardial injury.