The relation between cardiac index and oxygen extraction in acutely ill patients

Cardiovascular effects of intravenous morphine in anesthetized horse

Objectives

To investigate whether morphine causes a change in mean arterial blood pressure (MAP) heart rate (HR) and oxygen extraction (OE) rate in healthy horses anesthetized with isoflurane and a dexmedetomidine infusion.

Material and methods

The study design was prospective clinical, randomized, blinded two groups including 33 horses. All horses were sedated with romifidine IV, and anesthesia was induced with midazolam IV and ketamine IV and maintained with isoflurane in oxygen and medical air and a dexmedetomidine infusion. As a baseline venous and arterial blood, HR and MAP were sampled. Thereafter either morphine 0.1 mg kg⁻¹ IV or an equivalent volume of NaCl 0.9% IV was administered. HR and MAP were then further sampled for 5 min before venous and arterial blood was again sampled. OE was calculated based upon arterial and venous blood gas analysis. To evaluate the change in minimum MAP, mean HR, and OE, the differences between baseline and observation period values were further termed delta MAP, delta HR, and delta OE. Individual delta MAPs were normalized to the minimum baseline value and are reported as a percentage. Alpha was set to 0.05. Confidence intervals 95% (CI) were calculated for delta MAP, delta HR, and delta OE within groups, and for the difference between groups.

Results

The 95% CIs for delta MAP (%), delta HR (min⁻¹), and delta OE (mL/dL) in the morphine group were −20.5 to −9.0, 0.6 to 3.1, and −0.1 to 0.6 and in the placebo group were −17.4 to −10.1, 0.2 to 2.0, and −0.2 to 0.3, respectively. The 95% CI for the differences in delta MAP (%), delta HR (min⁻¹), and delta OE (mL/dL) were −5.5 to 7.6, −2.3 to 0.7, and −0.7 to 0.2, respectively. The minimum MAP of one horse in the morphine group decreased around 50% between baseline and observation period with almost unchanged OE and HR.

Conclusion and clinical relevance

The effects of morphine 0.1 mg kg⁻¹ IV on HR, MAP, and OE in healthy horses anesthetized with isoflurane and a CRI of dexmedetomidine are minimal.

Increased FIO2 influences SvO2 interpretation and accuracy of Fick-based cardiac output assessment in cardiac surgery patients: A prospective randomized study

INTRODUCTION

The study aimed to reveal how the fraction of inspired oxygen (FIO2) affected the value of mixed venous oxygen saturation (SvO2) and the accuracy of Fick-equation-based cardiac output (Fick-CO).

METHODS

Forty two adult patients who underwent elective cardiac surgery were enrolled and randomly divided into 2 groups: FIO2 < 0.7 or >0.85. Under stable general anesthesia, thermodilution-derived cardiac output (TD-CO), SvO2, venous partial pressure of oxygen, hemoglobin, arterial oxygen saturation, arterial partial pressure of oxygen, and blood pH levels were recorded before surgical incision.

RESULTS

Significant differences in FIO2 values were observed between the 2 groups (0.56 ± 0.08 in the <70% group and 0.92 ± 0.03 in the >0.85 group; P < .001). The increasing FIO2 values lead to increases in SvO2, venous partial pressure of oxygen, and arterial partial pressure of oxygen, with little effects on cardiac output and hemoglobin levels. When comparing to TD-CO, the calculated Fick-CO in both groups had moderate Pearson correlations and similar linear regression results. Although the FIO2 <0.7 group presented a less mean bias and a smaller limits of agreement, neither group met the percentage error criteria of <30% in Bland-Altman analysis.

CONCLUSION

Increased FIO2 may influence the interpretation of SvO2 and the exacerbation of Fick-CO estimation, which could affect clinical management.

TRIAL REGISTRATION

ClinicalTrials.gov ID number: NCT04265924, retrospectively registered (Date of registration: February 9, 2020).

Energy expenditure and oxygen uptake kinetics in critically ill elderly patients

BACKGROUND

Resting energy expenditure (REE) measurement of critically ill patients is essential for better nutrition management. Younger people increase their oxygen delivery ( D ̇ O 2 ) to meet energy demands, but few reports have investigated oxygen uptake kinetics in elderly patients, which are the main target population in today's intensive care units (ICUs). In this study, we evaluated REE, D ̇ O 2 , and oxygen extraction ratio (O₂ Ext: oxygen consumption [ V ̇ O 2 ]/ D ̇ O 2 ) to clarify appropriate energy needs and consumption in elderly ICU patients.

METHODS

This retrospective observational study included ventilated ICU patients who were divided into elderly participants (age ≥ 65 years) and nonelderly participants (age ≤64 years). V ̇ O 2 , CO₂ production, and cardiac output were measured by indirect calorimetry and noninvasive hemodynamic monitoring for up to 5 days. The initial values of REE, D ̇ O 2 , and O₂ Ext were compared between elderly and nonelderly patients.

RESULTS

This study included 102 patients, of whom 52% (n = 53) were elderly. The absolute deviation of measured REE per ideal body weight (IBW) was significantly higher in elderly than in nonelderly patients (9.3 ± 6.9 vs 6.3 ± 6.6 kcal/kg; P < .01). D ̇ O 2 had a strong negative correlation with age (P < .01). The O₂ Ext value was significantly higher in elderly than in nonelderly patients (37 ± 19% vs 29 ± 13%; P = .03).

CONCLUSIONS

Elderly critically ill patients were characterized by higher deviations in REE, lower D ̇ O 2 , and higher O₂ Ext. In elderly patients, O₂ Ext rather than D ̇ O 2 could be increased to meet energy consumption demands.

Effects of red blood cell transfusion on global oxygenation in anemic critically ill patients

BACKGROUND

Consensus for transfusion in intensive care unit (ICU) patients recommends a restrictive strategy, based on a hemoglobin (Hb) concentration of 7 g/dL. Red blood cell (RBC) transfusion is used to prevent tissue hypoxia by improving oxygen transport (DO₂ ) and therefore oxygen consumption (VO₂ ). We studied the effects of RBC transfusion on systemic oxygenation parameters reflecting systemic oxygen extraction (EO₂ = DO₂ /VO₂ ): S(c)vO₂ , lactate level, venous-to-arterial carbon dioxide difference (Pv-aCO₂ ), and cardiac index/EO₂ (CI/EO₂ ) and evaluated their usefulness in guiding transfusion decisions in ICU patients.

STUDY DESIGN AND METHODS

Prospectively, all adult patients transfused were included except those with active bleeding or without a jugular or subclavian catheter. We measured O₂ parameters before and after transfusion. Patients were a priori grouped according to their initial S(c)vO₂ (< or ≥70%), treatment with vasopressors, cardiac function, and septic status.

RESULTS

A total of 62 patients received 105 RBC transfusions. For all, mean arterial pressure (77 [69-88] to 81 [73-91] mm Hg), Hb concentration (7.4 [7.0-7.8] to 8.4 [7.7-8.9] g/dL) and S(c)vO₂ (65% [59%-73%] to 69% [62%-75%]) increased after transfusion (all P < .001). S(c)vO₂ improved after transfusion only when initial S(c)vO₂ was less than 70% (62% [56%-65%] to 66% [61%-71%]; P < .001). In this group, Pv-aCO₂ , lactate concentrations, and CI/EO₂ did not change after transfusion. Cardiac function, sepsis, or vasopressor therapy did not affect these results.

CONCLUSIONS

Among systemic O₂ parameters, only a S(c)vO₂ < 70% in anemic ICU patients improves after transfusion. As S(c)vO₂ can reflect a DO₂ /VO₂ imbalance, it could be helpful when combined with the Hb concentration to decide whether to transfuse. However, the benefit on outcome should be further studied.

Central Venous Oxygen Saturation as a Predictor of a Successful Spontaneous Breathing Trial from Mechanical Ventilation: A Prospective, Nested Case-Control Study

Background:

Weaning from mechanical ventilation is a key element in the care of critically ill patients, and Spontaneous Breathing Trial (SBT) is a crucial step in this procedure. This nested case-control study aimed to evaluate whether central oxygen saturation (ScvO₂) values and their changes could independently predict the SBT outcome among mechanically ventilated patients.

Methods:

A prospective cohort of patients who were mechanically ventilated for at least 48hours and fulfilled the criteria of readiness to wean constituted the study population. All patients attempted a SBT and were then categorized in SBT success group and SBT failure group, based on a combination of criteria which indicated whether SBT was successful or not. Multivariate binary logistic regression analysis was utilized to indicate the independent predictors of SBT success, while the Receiver Operating Characteristic (ROC) curves were used to demonstrate the diagnostic accuracy of these independent predictors.

Results:

Seventy-seven patients 69(18-86) years old; 62.3% male) constituted the study population. SBT was successful among 63.6% of them. A decrease in ScvO₂ values (ΔScvO₂) < 4% between the beginning and the end of the trial independently predicted the successful outcome (OR=18.278; 95% CI=4.017-83.163), along with age, Hemoglobin concentration (Hb) and arterial oxygen saturation (SaO₂). Diagnostic accuracy for ΔScvO₂ alone (ROC area=0.715) was slightly superior to that of either SaO₂ (0.625) or Hb (0.685) to predict SBT success.

Conclusion:

ScvO₂ is an independent predictor of the weaning outcome and its evaluation may further facilitate the accurate categorization among those patients who pass or fail the SBT.

Central venous saturation is a predictor of reintubation in difficult-to-wean patients

OBJECTIVE

To evaluate the predictive value of central venous saturation to detect extubation failure in difficult-to-wean patients.

DESIGN

Cohort, multicentric, clinical study.

SETTING

Three medical-surgical intensive care units.

PATIENTS

All difficult-to-wean patients (defined as failure to tolerate the first 2-hr T-tube trial), mechanically ventilated for >48 hrs, were extubated after undergoing a two-step weaning protocol (measurements of predictors followed by a T-tube trial). Extubation failure was defined as the need of reintubation within 48 hrs.

INTERVENTIONS

The weaning protocol evaluated hemodynamic and ventilation parameters, and arterial and venous gases during mechanical ventilation (immediately before T-tube trial), and at the 30th min of spontaneous breathing trial.

MEASUREMENTS AND MAIN RESULTS

Seventy-three patients were enrolled in the study over a 6-mo period. Reintubation rate was 42.5%. Analysis by logistic regression revealed that central venous saturation was the only variable able to discriminate outcome of extubation. Reduction of central venous saturation by >4.5% was an independent predictor of reintubation, with odds ratio of 49.4 (95% confidence interval 12.1-201.5), a sensitivity of 88%, and a specificity of 95%. Reduction of central venous saturation during spontaneous breathing trial was associated with extubation failure and could reflect the increase of respiratory muscles oxygen consumption.

CONCLUSIONS

Central venous saturation was an early and independent predictor of extubation failure and may be a valuable accurate parameter to be included in weaning protocols of difficult-to-wean patients.

Downregulation of diaphragm electron transport chain and glycolytic enzyme gene expression in sepsis

Cellular energy metabolism is altered in sepsis as a consequence of dysfunction of mitochondrial electron transport and glycolytic pathways. The purpose of the present study was to determine whether sepsis is associated with compensatory increases in gene expression of electron transport chain and glycolytic pathway proteins or, alternatively, whether gene expression decreases in sepsis, contributing to abnormalities in energy metabolism. Studies were performed using diaphragms from control and endotoxin-treated (8 mg x kg(-1) x day(-1)) rats; at 48 h after endotoxin administration, animals were killed. Microarrays and RNAse protection assays were used to assess the expression of several electron transport chain components (cytochrome-c oxidase subunits Cox 5A, Cox 5B, and Cox 6A, ATP synthase, and ATP synthase subunit 5B) and of the rate-limiting enzyme for glycolysis, phosphofructokinase (PFK). Western blotting was used to assess protein levels for these electron transport chain subunits and PFK. Activity assays were used to assess electron transport chain and phosphofructokinase function. We found that sepsis evoked 1) a downregulation of genes encoding all examined electron transport chain components (e.g., cytochrome-c oxidase 5A decreased 45 + 7%, P < 0.01) and PFK (P < 0.001), 2) reductions in protein levels for these electron transport chain subunits and PFK (P < 0.05 for each), and 3) decreases in mitochondrial state 3 respiration rates and phosphofructokinase enzyme activity (P < 0.01 for each comparison). We speculate that these sepsis-induced reductions in the expression of genes encoding critical electron transport and glycolytic proteins contribute to the development and persistence of sepsis-induced abnormalities in cellular energy metabolism.

Differential cardiovascular responses during weaning failure: effects on tissue oxygenation and lactate

OBJECTIVE

To test the following two hypotheses during weaning failure: (a) mixed venous oxygen saturation (SvO2) does not decrease in patients whose oxygen consumption does not increase, and (b) blood lactate may increase in patients who demonstrate substantial decreases in SvO2.

DESIGN AND SETTING

A prospective observational and physiological study in a 30-bed university intensive care unit.

PATIENTS AND PARTICIPANTS

18 patients who failed weaning and 12 patients who succeeded weaning (controls).

MEASUREMENTS AND RESULTS

Hemodynamics, global tissue oxygenation, cardiovascular response (cardiac index/oxygen extraction diagram), and blood lactate were measured in ventilator-supported patients undergoing a spontaneous breathing trial. In patients who failed without having increased their oxygen consumption (n=9) the increase in oxygen delivery was accompanied by a decrease in oxygen extraction (by 15+/-4%). In patients who failed (n=9) having increased their oxygen consumption (by>10%) this increase was met mainly by an increase in oxygen extraction (by 30+/-7%). SvO2 increased by 2+/-1% in the former patients, whereas it decreased by 20+/-5% in the latter. Arterial lactate increased (range 2.3-3.1 mM/l) in only three patients who failed to have increased oxygen consumption and exhibited heart failure and the highest decreases in SvO2 (by 12-39%).

CONCLUSIONS

Patients whose SvO2 does not decrease during weaning failure do not have increased oxygen consumption probably due to respiratory center depression in some of them. Patients whose SvO2 decreases have increased oxygen consumption.

Einsatz von Vasopressin und Terlipressin bei Sepsis und systemischen Entzündungsreaktionen

Vasopressin and terlipressin are increasingly used as alternative non-adrenergic vasopressors for hemodynamic support of septic patients with arterial hypotension. Despite excellent vasopressive effects, vasopressin analogues may potentially impair macro-hemodynamics, oxygen transport and microvascular blood flow. Due to those unwanted side-effects, vasopressin and terlipressin may potentially compromise organ function and possibly foster the development of multiple organ failure. This review article discusses the results of clinical and experimental studies to judge the effects of vasopressin and terlipressin on microcirculation, oxygen supply, metabolism and organ function in patients with sepsis or systemic inflammatory response syndrome (SIRS). Although vasopressin analogues are emerging as promising alternatives to treat catecholamine-refractory hypotension, there is no evidence that vasopressin receptor agonists improve outcome. To date, vasopressin and terlipressin can, therefore, not be recommended for routine clinical use.

The effect of physiotherapy treatment on oxygen consumption and haemodynamics in patients who are critically ill

The purpose of this study was to determine metabolic and haemodynamic changes with and without physiotherapy treatment in haemodynamically stable, intubated and ventilated patients. This was a prospective, randomised cross-over study. Ten intubated, ventilated and haemodynamically stable patients underwent a 20 min physiotherapy treatment and a 20 min period of undisturbed side lying. Mean oxygen consumption (VO2mean) was measured on a minute-to-minute basis by indirect calorimetry. Mean arterial pressure (MAP) was recorded minutely from the indwelling arterial line and cardiac index (CI) was calculated from the indwelling pulmonary artery catheter. Time to recovery to within 5% of resting VO2 was also recorded. The results showed no significant increase in VO2mean with either positioning the patient in side lying or physiotherapy treatment (p = 0.17). Time to recovery to within 5% of baseline VO2 occurred within seven minutes for all patients and there was no significant difference between either physiotherapy treatment or positioning in side lying (p = 0.63). There were no significant differences in CI (p = 0.44) or MAP (p = 0.95) during physiotherapy treatment compared with undisturbed side lying. It is concluded that physiotherapy treatment does not significantly alter VO2mean or MAP and CI in stable intubated and ventilated patients.

Reliability of mixed venous oxygen saturation as an indicator of the oxygen extraction ratio demonstrated by a large patient data set

BACKGROUND Mixed venous saturation (SVO2) represents the oxygen extraction ratio (O2ER) through the following relationship: SVO2 approximately equal 1 - O2ER, assuming a negligible contribution of dissolved oxygen to blood oxygen content. We sought to determine whether altered FiO2 levels would affect the correlation between SVO2 and O2ER.

METHODS

A theoretical analysis was performed to determine the extent to which SVO2 should be affected by different Fio2 levels at various ranges of O2ER using several linked spreadsheets. The relationships obtained were compared with actual patient data stored in a large patient data set. RESULTS Theoretical analysis indicated that increases in Fio2 should produce a small stepwise increase in the observed SVO2 that is independent of O2ER. However, analysis of 8,324 simultaneous data points for SVO2 and O2ER failed to demonstrate this pattern, primarily because patients with higher Fio2 concentrations tend to have higher O2ERs, and hence lower SVO2. CONCLUSION SVO2 measurements are not significantly affected by Fio2 levels in critically ill patients.

The International Sepsis Forum's frontiers in sepsis: High cardiac output should be maintained in severe sepsis

Despite a usually normal or high cardiac output, severe sepsis is associated with inadequate tissue oxygenation, leading to organ failure and death. Some authors have suggested that raising cardiac output and oxygen delivery to predetermined supranormal values may be associated with improved survival. While this may be of benefit in certain patients, bringing all patients to similar, supranormal values, is simplistic. It is much preferable to titrate therapy according to the needs of each individual patient. A combination of variables should be used for this purpose, in addition to a careful clinical evaluation, including not only cardiac output but also the mixed venous oxygen saturation and the blood lactate concentrations. The concept is to assess the adequacy of the cardiac output in patients with severe sepsis, enabling management strategies aimed at optimizing cardiac output to be tailored to the individual patient.

Gastric tonometer monitoring in infants undergoing repair of coarctation of the aorta

OBJECTIVE

To evaluate gastric tonometer monitoring for splanchnic hypoperfusion in infants during surgical intervention for aortic coarctation, especially within aortic cross-clamp periods.

DESIGN

A prospective study.

SETTING

Cardiovascular intensive care unit in a university hospital.

PARTICIPANTS

Fourteen infant patients after elective, uncomplicated repair of coarctation of the aorta.

INTERVENTIONS

After the anesthesia induction, a 7F tonometry catheter was inserted into the stomach oropharyngeally. Gastric carbon dioxide, arterial blood gases, blood pressure of upper extremities, and hematocrit values were measured in 5 different time intervals. Time periods were as follows: T1 (after the anesthesia induction), T2 (before aortic cross-clamp), T3 (immediately after aortic cross-clamp removal), T4 (40 minutes after aortic cross-clamp removal), and T5 (as the patient reached the intensive care unit). Intramucosal pH was measured by means of the Henderson-Hasselbach equation. The mean values of all parameters were calculated. According to T1 time, T2, T3, T4, and T5 times were compared with Student's t-test.

MEASUREMENTS AND MAIN RESULTS

Mean aortic cross-clamp time was 19.4 +/- 6.6 minutes. Intramucosal pH values of T3 (p < 0.001) and T4 (p < 0.01) were found to be lower than values of T1. The gastric carbon dioxide values of T3 were significantly higher than T1 (p < 0.01), and bicarbonate and arterial pH values of T3 were significantly lower (p < 0.01). There were no significant differences in other parameters over time intervals.

CONCLUSION

Splanchnic hypoperfusion exists during aortic cross-clamping in infant aortic coarctation surgery, and the tonometric catheter is considered to be a safe method for monitoring this hypoperfusion.

Assessment of cardiac index in anemic patients

STUDY OBJECTIVES

During isovolemic hemodilution, healthy individuals maintain oxygen consumption VO2 by identical increases in cardiac index (CI) and oxygen extraction ratio (O(2)ER). In critically ill patients, the relationship between CI and O(2)ER may be different. Patients with an altered cardiac function may have a decreased CI/O(2)ER ratio, whereas patients with sepsis may have an increased CI/O(2)ER ratio. We hypothesized that the analysis of the CI-O(2)ER relationship could help us to assess the adequacy of cardiac function in critically ill patients with anemia.

DESIGN

Prospective, observational study.

SETTING

Thirty-one-bed medicosurgical ICU of a university hospital.

PATIENTS

Sixty patients equipped with arterial and Swan-Ganz catheters presenting with anemia, which was defined as a hemoglobin level < or = 10 g/dL in the absence of active bleeding. Patients were classified into those with compromised cardiac function (group 1; n = 40), and those with normal cardiac function (group 2; n = 20).

MEASUREMENTS AND RESULTS

In addition to the pertinent clinical data, initial hemodynamic measurements, including pulmonary artery occlusion pressure (PAOP), CI, and O(2)ER, were collected in all patients at the onset of anemia. As anticipated, group 1 patients (n = 40) had lower CIs, higher O(2)ER levels, and lower CI/O(2)ER ratios than group 2 patients. However, there was no significant difference in PAOP values between the groups. The CI/O(2)ER ratio was < 10 in 27 of 40 group 1 patients but only in 4 of 20 group 2 patients. Of these latter four patients, three were found to be hypovolemic, and one patient with sepsis had severe myocardial depression. There was no statistically significant difference in PAOP in group 2 patients with or without hypovolemia ([mean +/- SD] 12.3+/-2.1 mm Hg) vs 13.7+/-4.3 mm Hg; p = 0.21). In group 1, survivors had a higher CI and CI/O(2)ER ratio than nonsurvivors. In group 2, however, such a relationship did not reach statistical significance.

CONCLUSIONS

The relationship between CI and O(2)ER level can help interpret the CI in anemic patients. In anemic patients with no cardiac history, a low CI/O(2)ER ratio (< 10) suggests hypovolemia even when CI is not depressed.

Effects of dopexamine and volume loading on hemodynamics and oxygenation parameters in patients undergoing pulmonary resection

BACKGROUND

Pulmonary resection may result in a reduction in arterial oxygen pressure as well as in cardiac output. Since cardiac index, oxygen delivery, and oxygen consumption are considered as important determinants of patients' outcome, we evaluated the effects of dopexamine and volume loading on cardiopulmonary variables in patients undergoing pulmonary resection.

METHODS

Forty adult patients undergoing pulmonary resection for lung or bronchial tumors were included in an open placebo-controlled study. The patients were selected according to a randomized sequence to group A (n=20) or group B (n=20). Dopexamine (2 microg x kg(-1) x min(-1)) was started when steady state conditions were achieved after induction of anesthesia in group A. Saline 0.9% was given as control (group B). Hemodynamic monitoring was performed using a pulmonary artery catheter.

RESULTS

Dopexamine increased heart rate, cardiac output and oxygen delivery compared with control without increasing oxygen consumption during anesthesia and surgery. Furthermore, dopexamine was found not to alter the course of PaO2/FiO2 values.

CONCLUSION

In patients undergoing pulmonary resection, dopexamine can be used perioperatively to increase cardiac index without decreasing the PaO2/FiO2 ratio.

Correlating the severity of paraquat poisoning with specific hemodynamic and oxygen metabolism variables

OBJECTIVE

To investigate the hemodynamics and oxygen metabolism of patients with varying degrees of severity of paraquat poisoning.

DESIGN

Prospective, observational, clinical study.

SETTING

Intensive care unit in a university hospital.

PATIENTS

Forty-three consecutive patients with paraquat and/or diquat poisoning were classified into three groups by the severity index of paraquat poisoning (SIPP; hr/mg/L).

INTERVENTIONS

Standard treatments included specific respiratory management, fluid resuscitation, and aggressive circulatory support.

MEASUREMENTS AND MAIN RESULTS

Serum paraquat and diquat levels were measured at arrival, and SIPP was calculated. The cardiac index (CI), left ventricular stroke work index (LVSWI), systemic vascular resistance index (SVRI), oxygen delivery index (DO2I), oxygen consumption index (VO2I), and oxygen extraction ratio (O2ER) were measured at 6, 12, 24, 36, 48, 72, and 96 hrs postadmission. A significant inverse correlation between SIPP and survival time was found in 31 fatal cases (r = .85; p < .001). In the SIPP 10-50 group, CI, DO2I, VO2I, and O2ER were maintained at higher levels than in the SIPP group of <10 (p < .05), whereas SVRI decreased significantly (p < .05). In the SIPP group of >50, CI, LVSWI, SVRI, DO2I, and VO2I decreased, whereas O2ER had a tendency to increase progressively. There was a significant correlation between SVRI and SIPP, O2ER and SIPP, and O2ER and SVRI 24 hrs after admission, respectively (p < .001).

CONCLUSIONS

Paraquat poisoning is characterized by high oxygen consumption with high oxygen extraction, with the degree of derangement based on the severity index. The development of a marked imbalance between increased oxygen demand and decreased oxygen supply because of myocardial depression might be a possible cause of death in circulatory failure.

Differential alterations in systemic and regional oxygen delivery and consumption during the early and late stages of sepsis

BACKGROUND

Studies have indicated that regional changes in oxygen utilization during sepsis cannot be predicted from the changes in the whole body oxygen delivery (DO2) and consumption (VO2). The aim of this study, therefore, was to determine whether differential alterations in systemic and regional DO2 and VO2 occur during the early and late stages of sepsis.

METHODS

Adult male Sprague-Dawley rats were subjected to sepsis by cecal ligation and puncture (CLP). At 5 hours (i.e., the early, hyperdynamic phase of sepsis) or 20 hours (i.e., the late, hypodynamic phase) after CLP, cardiac output, and organ blood flow were measured by radioactive microspheres. Systemic and regional DO2 and VO2 were determined and plasma levels of lactate were measured.

RESULTS

Cardiac output and blood flow to the liver, small intestine, and kidneys increased at 5 hours and decreased at 20 hours after CLP. Although both systemic DO2 and VO2 increased at 5 hours after CLP, systemic DO2 but not VO2 decreased at 20 hours. At 5 hours after CLP, intestinal and renal DO2 increased. However, DO2 in all the tested organs decreased at 20 hours after CLP. VO2 increased in the liver, small intestine, and kidneys at 5 hours after CLP but decreased only in the liver and small intestine at 20 hours after the onset of sepsis. Moreover, plasma lactate levels increased at the late stage of sepsis.

CONCLUSION

Because hepatic and intestinal VO2 but not systemic and renal VO2 decreased at 20 hours after CLP, the liver and small intestine seem to be more vulnerable to the hypoxic insult during the hypodynamic stage of polymicrobial sepsis.

Importance of the sampling site for measurement of mixed venous oxygen saturation in shock

OBJECTIVES

To determine if oxyhemoglobin saturation in blood samples taken from the superior vena cava or right atrium can be substituted for oxyhemoglobin saturation in blood taken from the proximal pulmonary artery (SVO2) in patients in shock.

DESIGN

Prospective clinical investigation.

SETTING

Mixed surgical/medical intensive care unit in a university hospital.

PATIENTS

Thirty consecutive patients in severe circulatory shock who required insertion of a pulmonary artery flotation catheter (PAFC) immediately on intensive care unit admission. All patients fulfilled the criteria described below which were established in advance.

MEASUREMENTS AND MAIN RESULTS

Oxyhemoglobin saturation in the superior vena cava, right atrium, and pulmonary artery (SVO2) was measured by cooximetry in consecutive blood samples from each site during initial insertion of the PAFC. The mean standard deviation of values from these sites was similar: 74 +/- 12.5%, 70.+/- 13%, and 71.3 +/- 12.7%, respectively. However, when superior vena cava and right atrial oxyhemoglobin saturations and SvO2 were compared, the ranges and 95% confidence limits were found to be clinically unacceptable. The ranges were -19.3 to 23.1% and -19.7 to 16.7%, respectively, and the 95% confidence limits were -18.4 to 24.2% and -18.6 to +17.3%, respectively.

CONCLUSIONS

These wide range differences and confidence limits would lead to large errors if superior vena cava or right atrial oxyhemoglobin saturations were substituted for true mixed venous blood in oxygen transport or pulmonary venous admixture calculations, or if clinical decision making was based on individual results. In patients in shock in whom clinical decisions may be based on the value of mixed venous oxyhemoglobin, oxyhemoglobin saturation is only reliably measured in samples taken from the pulmonary artery.

Oxygen supply dependency can characterize septic shock

OBJECTIVE

To demonstrate that oxygen consumption (VO2) can be dependent on oxygen delivery (DO2) during hemodynamic instability and independent of DO2 following stabilization.

DESIGN

We retrospectively reviewed hemodynamic and blood gas data collected from ten patients in whom DO2 was acutely altered during an episode of septic shock (phase A) and after recovery from this episode (phase B).

SETTING

General intensive care unit of a university hospital.

PATIENTS

10 critically ill adult patients (aged 55 +/- 19 years).

INTERVENTIONS

DO2 was altered by fluid challenge, administration of vasoactive agents, or application of positive end-expiratory pressure.

RESULTS

In phase A, changes in VO2 (121 +/- 32 vs 165 +/- 36 ml/min.m2; p < 0.001) paralleled changes in DO2 (415 +/- 153 vs 607 +/- 217 ml/min.m2; p < 0.001), but oxygen extraction (O2ER) remained stable (31.9 +/- 11.2 vs. 30.2 +/- 8.9%; NS). In phase B, changes in DO2 (412 +/- 118 vs 526 +/- 152 ml/min.m2; p < 0.001) were associated with opposite changes in O2ER (36.1 +/- 4.2 vs 28.9 +/- 4.9%; p < 0.001), and VO2 was unchanged (147 +/- 35 vs 149 +/- 33 ml/min.m2; NS). The mean VO2/DO2 slope was greater in phase A than in phase B (0.26 +/- 0.09 vs. 0.08 +/- 0.08; p < 0.004). Blood lactate levels were higher in phase A than in phase B (3.3 +/- 1.8 vs 1.6 +/- 0.6 mEq/l; p < 0.05).

CONCLUSIONS

Oxygen supply independency and dependency can be found at different times in the same critically ill patient. Our findings are consistent with the concept that VO2/DO2 dependency is a marker of septic shock. Interventions to increase DO2 are probably justified when this phenomenon is present.

A nomogram to evaluate the arterial mixed venous oxygen saturation difference during cardiopulmonary bypass

A nomogram providing the arterial mixed venous haemoglobin saturation difference (S(a-v)O2) corresponding to normal oxygen consumption (VO2) during cardiopulmonary bypass (CPB) was produced. Normal VO2 during CPB (95.8 +/- 20.1 ml/min/m2 at 37 degrees C) was obtained from the literature. The nomogram computes the S(a-v)O2 from the body surface, pump flow, blood haemoglobin and patient temperature; a table is also presented which supplies the S(a-v)O2 ranges corresponding to VO2 mean +/-1 and +/-2SD. The nomogram was tested on 10 subjects undergoing CPB for myocardial revascularization. S(a-v)O2 was determined by arterial and mixed venous blood oximetry 5, 20, and 35 min after the start of CPB. The measured S(a-v)O2 was 27.1 +/- 7.2% while S(a-v)O2 obtained from the nomogram was 24.9 +/- 4.0%, the difference was not statistically significant. Eighteen values (60%) were within the range corresponding to VO2 mean +/-1SD. One value was lower than the S(a-v)O2 value corresponding to VO2 mean - 2SD and was associated with the lowest value of blood haemoglobin. Two values were higher than the S(a-v)O2 value corresponding to VO2 mean + 2SD and were associated with inadequate muscle relaxation. By comparing measured S(a-v)O2 values with those obtained by the nomogram and the table, anaesthesiologists and perfusionists can easily detect patients presenting abnormally low or high VO2 values.

Early markers of major adverse events in children after cardiac operations

OBJECTIVES

The purpose of this study was to determine the physiologic variables that predict major adverse events in children in the intensive care unit after cardiac operations.

METHODS

A cohort observational study was conducted. At the time of admission to the intensive care unit and 4, 8, 12, and 24 hours later the following variables were recorded: mean arterial pressure, heart rate, cardiac index, oxygen delivery, mixed venous oxygen saturation, base deficit, blood lactate, gastric intramucosal pH, carbon dioxide difference (the difference between arterial carbon dioxide tension and gastric intraluminal carbon dioxide tension), and toe-core temperature gradient. Major adverse events were prospectively identified as cardiac arrest, need for emergency chest opening, development of multiple organ failure, and death.

RESULTS

Ninety children were included in the study; 12 had major adverse events and there were 4 deaths. Blood lactate level, mean arterial pressure, and duration of cardiopulmonary bypass were the only significant, independent predictors of major adverse events when measured at the time of admission to the intensive care unit. The odds ratio (95% confidence intervals) for major adverse events if a lactate level was greater than 4.5 mmol/L was 5.1 (1.2 to 21.1), for admission hypotension 2.3 (0.5 to 9.8), and for a cardiopulmonary bypass time greater than 150 minutes 13.7 (3.3 to 57.2). Four hours after admission lactate and carbon dioxide difference, and 8 hours after admission lactate and base deficit, were independently significant predictors. The odds ratios for major adverse events if the blood lactate level was greater than 4 mmol/L at 4 and 8 hours were 8.3 (1.8 to 38.4) and 9.3 (1.9 to 44.3), respectively. At no time in the first 24 hours were cardiac output, oxygen delivery, mixed venous oxygen saturation, toe-core temperature gradient, or heart rate significant predictors of major adverse events.

CONCLUSIONS

In the context of our current treatment strategies, the duration of cardiopulmonary bypass and blood lactate level, measured in the early postoperative period, were the best predictors of impending major adverse events.

Determination of oxygen delivery and consumption versus cardiac index and oxygen extraction ratio

Measuring cardiac output without knowledge of the oxygen extraction by the tissues is of limited value. Instead of calculating oxygen consumption and oxygen delivery, a diagram relating cardiac index to the oxygen extraction ratio is proposed to interpret hemodynamic data at the bedside. This diagram is particularly helpful in interpreting cardiac index in the presence of changes in hemoglobin or oxygen demands and in evaluating the effects of therapy.

Transient fall in oxygen intake during exercise in congestive heart failure

We report four cases in which oxygen intake abruptly decreased during a graded exercise test. In all these cases, there was an acute event (arrhythmia, mitral regurgitation) that had very likely resulted in a decrease in cardiac output. These studies provide new evidence of oxygen intake dependence on oxygen transport, even in nonsteady-state situations.

Early hemodynamic course of septic shock

OBJECTIVE

To assess the relative contributions of changes in vascular tone and changes in cardiac function to hemodynamic recovery from septic shock.

DESIGN

Case series, observational study.

SETTING

Multidisciplinary department of intensive care in an academic hospital.

PATIENTS

Sixty-seven patients with septic shock (prolonged hypotension, signs of tissue hypoperfusion, signs of sepsis, suspected source of infection, or documented bacteremia). In addition to the antibiotic therapy and the removal of the source of sepsis whenever possible, each patient received intravenous fluids and vasoactive agents (dopamine, norepinephrine, and dobutamine). Each patient was also treated with mechanical ventilation. Twenty-four (36%) patients survived their intensive care unit course.

INTERVENTIONS

Hemodynamic measurements were obtained at baseline, after initial resuscitation (as soon as apparent hemodynamic stability was achieved), after 12 hrs, and after 24 hrs.

MEASUREMENTS AND MAIN RESULTS

There were no significant differences in hemodynamic or oxygen-derived variables at baseline between the survivors and the nonsurvivors. During the initial resuscitation period, only the survivors demonstrated a significant increase in mean arterial pressure (from 69 +/- 17 to 82 +/- 18 mm Hg; p < .02) and left ventricular stroke work index (from 25.2 +/- 11.0 to 35.5 +/- 19.4 g.m/m2; p < .05). The increases in cardiac index and systemic vascular resistance were greater in the survivors than in the non-survivors, but the differences did not reach statistical significance. Study of the left ventricular function curves indicated an improvement of left ventricular function in the survivors but not in the nonsurvivors.

CONCLUSION

An early improvement in left ventricular function is a hallmark of the survivors from septic shock.

Oxygen uptake/oxygen supply dependency: fact or fiction?

More than a decade ago, observations of co-variance between VO2 and DO2 led to the identification of a condition known as pathological O2 supply dependency. This condition was subsequently observed in critically ill patients with sepsis and acute circulatory failure. More recently, other authors have challenged the existence of this condition, often citing methodologic problems or mathematical coupling to account for spurious observations in the earlier studies. Here, we review the evidence for and against pathological O2 supply dependency. We find that many of the arguments have some validity but only in specific circumstances. We conclude, therefore, that pathological O2 supply dependency is a hallmark of acute circulatory failure and that an effective therapeutic approach should be based on an evaluation of organ system function in each individual case. Parameters such as blood lactate, pHi and veno-arterial PCO2 may be useful in this respect.