Effects of catecholamines on oxygen consumption and oxygen delivery in critically ill patients

Phenotyping and Hemodynamic Assessment in Cardiogenic Shock: From Physiology to Clinical Application

There is growing interest in invasive hemodynamic assessment in cardiogenic shock, primarily due to the widespread adoption of mechanical circulatory support (MCS). Invasive hemodynamic assessment is central to two aspects of cardiogenic shock management: (1) the phenotyping of cardiogenic shock, and (2) the assessment of response to therapy. Phenotyping of cardiogenic shock serves to guide timely therapeutic intervention, and the assessment of hemodynamic response to therapy directs the escalation or de-escalation of therapy, including MCS. This review aims to discuss these two aspects of hemodynamic assessment in cardiogenic shock. Firstly, the physiologic underpinnings of a phenotyping schema, and the implication of the cardiogenic shock phenotype on the MCS strategy in cardiogenic shock will be discussed. Secondly, the concept of cardiac power output and 'effective' oxygen delivery will be discussed in relation to hemodynamic response to therapy in cardiogenic shock.

A cell model for evaluating mitochondrial damage in cardiomyocytes

Background

Various cellular models were used for assessment of mitochondrial damage in cardiomyocyte, but most of them are based on silent cells without contractility. The mitochondria in cells at working should be more sensitive to toxic or reperfusion damage due to their high level mitochondrial respiration. Therefore, contracting cells can represent inotropic agent-mediated high-energy demand states.

Objective

To establish a cellular model to detect mitochondrial damage in cardiomyocytes at contraction.

Method

Freshly isolated Sprague–Dawley rat cardiomyocytes were incubated with or without bupivacaine, in the presence or absence of isoprenaline, and electrically stimulated to induce rhythmic contractions.

Results

Contraction under electrical field stimulation did not induce mitochondrial swelling or ROS production in DMEM; the silent cells in the presence of bupivacaine showed mild mitochondrial swelling, but contracting cells exhibited significantly higher mitochondrial swelling and increased ROS production (P < 0.05, vs. silent cells). Isoprenaline induced a further enhancement in mitochondrial swelling and ROS production in contracting cells.

Conclusions

Contracting cells are more sensitive to bupivacaine toxicity and could be more accurately represent mitochondrial damage in vivo condition.

Cardiac power output index to define hemodynamic response to Impella support in cardiogenic shock

BACKGROUND

Early assessment of response to Impella in cardiogenic shock may guide escalation of mechanical circulatory support. Therapeutic goal and response to Impella have not previously been defined. This study tested the hypothesis that targeting 3-h post- Impella cardiac power output index (CPOi)-"hemodynamic response"-in cardiogenic shock is associated with 12-h lactate clearance.

METHODS

Single-center study of 37 consecutive patients who underwent left-sided Impella support for cardiogenic shock due to either acute myocardial infarction or decompensated heart failure. Patients who achieved 3-h post-Impella CPOi ⩾ 0.30 W/m² were defined as Impella "hemodynamic responder."

RESULTS

Twelve of the thirty-seven patients achieved 3-h post-impella CPOi  ⩾ 0.30 W/m² ("hemodynamic responders"). Post-Impella CPOi correlated with 12-h lactate (r = -0.779, p < 0.001) and lactate clearance (r = 0.747, p < 0.001). "Hemodynamic responders" had lower 12-h lactate level and greater 12-h lactate clearance (52 (44-58) vs 17 (14-26)%, p < 0.001). Higher pre-Impella norepinephrine dose (-0.341, p = 0.003) and baseline lactate (-0.009, p = 0.003) were independently associated with lower 3-h post-Impella CPOi. Eighteen patients died within 30 days (2/12 "hemodynamic responders" compared to 16/25 "non-responders," p < 0.001).

CONCLUSION

Patients who achieved early 3-h post-Impella CPOi of ⩾0.30 W/m² have greater lactate clearance and better short-term survival. Early post-Impella CPOi of 0.30 W/m² may be used as a therapeutic goal and define favorable response to Impella in cardiogenic shock.

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.

Quantitative Assessment of Blood Lactate in Shock: Measure of Hypoxia or Beneficial Energy Source

Blood lactate concentration predicts mortality in critically ill patients and is clinically used in the diagnosis, grading of severity, and monitoring response to therapy of septic shock. This paper summarizes available quantitative data to provide the first comprehensive description and critique of the accepted concepts of the physiology of lactate in health and shock, with particular emphasis on the controversy of whether lactate release is simply a manifestation of tissue hypoxia versus a purposeful transfer ("shuttle") of lactate between tissues. Basic issues discussed include (1) effect of nonproductive lactate-pyruvate exchange that artifactually enhances flux measurements obtained with labeled lactate, (2) heterogeneous tissue oxygen partial pressure (Krogh model) and potential for unrecognized hypoxia that exists in all tissues, and (3) pathophysiology that distinguishes septic from other forms of shock. Our analysis suggests that due to exchange artifacts, the turnover rate of lactate and the lactate clearance are only about 60% of the values of 1.05 mmol/min/70 kg and 1.5 L/min/70 kg, respectively, determined from the standard tracer kinetics. Lactate turnover reflects lactate release primarily from muscle, gut, adipose, and erythrocytes and uptake by the liver and kidney, primarily for the purpose of energy production (TCA cycle) while the remainder is used for gluconeogenesis (Cori cycle). The well-studied physiology of exercise-induced hyperlactatemia demonstrates massive release from the contracting muscle accompanied by an increased lactate clearance that may occur in recovering nonexercising muscle as well as the liver. The very limited data on lactate kinetics in shock patients suggests that hyperlactatemia reflects both decreased clearance and increased production, possibly primarily in the gut. Our analysis of available data in health and shock suggests that the conventional concept of tissue hypoxia can account for most blood lactate findings and there is no need to implicate a purposeful production of lactate for export to other organs.

The contribution of Swiss scientists to the assessment of energy metabolism

Although Switzerland is considered a small country, it has its share in discoveries, inventions and developments for the assessment of energy metabolism. This includes seminal contributions to respiratory and metabolic physiology and to devices for measuring energy expenditure by direct and indirect calorimetry in vivo in humans and small animals (as well as in vitro in organs/tissues), for the purpose of evaluating the basic nutritional requirements. A strong momentum came during World War II when it was necessary to evaluate the energy requirements of soldiers protecting the country by assessing their energy expenditure, as well as to determine the nutritional needs of the Swiss civil population in time of war when food rationing was necessary to ensure national neutrality and independence. A further impetus came in the 1970s at the start of the obesity epidemics, toward a better understanding of the metabolic basis of obesity, ranging from the development of whole-body concepts to molecular mechanisms. In a trip down memory lane, this review focuses on some of the earlier leading Swiss scientists who have contributed to a better understanding of the field.

Optimization of Positive End-Expiratory Pressure Targeting the Best Arterial Oxygen Transport in the Acute Respiratory Distress Syndrome: The OPTIPEP Study

The optimal setting for positive end-expiratory pressure (PEEP) in mechanical ventilation remains controversial in the treatment of acute respiratory distress syndrome (ARDS). The aim of this study was to determine the optimum PEEP level in ARDS, which we defined as the level that allowed the best arterial oxygen delivery (DO2). We conducted a physiologic multicenter prospective study on patients who suffering from ARDS according to standard definition and persistent after 6 hours of ventilation. The PEEP was set to 6 cm H2O at the beginning of the test and then was increased by 2 cm H2O after at least 15 minutes of being stabilized until the plateau pressure achieved 30 cm H2O. At each step, the cardiac output was measured by transesophageal echocardiography and gas blood was sampled. We were able to determine the optimal PEEP for 12 patients. The ratio of PaO2/FiO2 at inclusion was 131 ± 40 with a mean FiO2 of 71 ± 3%. The optimal PEEP level was lower than the higher PEEP despite a constant increase in SaO2. The optimal PEEP levels varied between 8 and 18 cm H2O. Our results show that in patients with ARDS the optimal PEEP differs between each patient and require being determined with monitoring.

Hemodynamic effects of Ivabradine in addition to dobutamine in patients with severe systolic dysfunction

BACKGROUND

Dobutamine induced tachycardia increases myocardial oxygen consumption and impairs ventricular filling. We hypothesized that Ivabradine may be efficient to control dobutamine induced tachycardia.

METHODS

We assessed the effects of Ivabradine in addition to dobutamine in stable heart failure (HF) patients (LVEF < 35%, n = 22, test population) and validated its effects in refractory cardiogenic shock patients (n = 9, validation population) with contraindication to cardiac assistance or transplant. In the test population (62 ± 17 years, LVEF = 24 ± 8%), systolic and diastolic function were assessed at rest and under dobutamine [10 γ/min], before and after Ivabradine [5mg per os]. In the validation population (54 ± 11 years, LVEF = 22 ± 7%), Ivabradine [5mg twice a day] was added to the dobutamine infusion.

RESULTS

In the test population, Ivabradine decreased heart rate [HR] at rest and during dobutamine echocardiography (-9 ± 8 bpm, P = 0.0004). The decrease in HR was associated with a decrease in cardiac power output and an increase in diastolic duration at rest (+ 74 ± 67 ms, P = 0.0002), and during dobutamine infusion (+ 75 ± 67 ms, P < 0.0001). Change in LVEF during dobutamine was greater after Ivabradine treatment than before (+ 7.2 ± 4.7% vs. + 3.6 ± 4.2%, P = 0.002). In the validation population, Ivabradine decreased HR (-18 ± 11 bpm, P = 0.008) and improved diastolic filling time (+ 67 ± 42 ms, P = 0.012) without decreasing cardiac output. At 24h, Ivabradine improved systolic blood pressure (+ 9 ± 5 mmHg, P = 0.007), daily urine output (+ 0.7 ± 0.5L, P = 0.008), oxygen balance (ΔScv02 = + 13 ± 15%, P = 0.010), and NT-pro BNP (-2270 ± 1912 pg/mL, P = 0.017). Finally, only 2/9 (22%) patients died whereas expected mortality determined from a historical cohort was 78% (P = 0.017).

CONCLUSION

This pilot study demonstrates the safety and potential benefit of a HR lowering agent in cardiogenic shock.

Time course of central venous-to-arterial carbon dioxide tension difference in septic shock patients receiving incremental doses of dobutamine

PURPOSE

To assess the time course of the central venous-arterial carbon dioxide tension difference (∆PCO2)-as an index of the carbon dioxide production (VCO2)/cardiac index (CI) ratio-in stable septic shock patients receiving incremental doses of dobutamine.

METHODS

Twenty-two hemodynamically stable septic shock patients with no signs of global tissue hypoxia, as testified by normal blood lactate levels, were prospectively included. A dobutamine infusion was administered at a dose of up to 15 μg/kg/min in increments of 5 μg/kg/min every 30 min. Complete hemodynamic and gas measurements were obtained at baseline, and at each dose of dobutamine.

RESULTS

Dobutamine induced a significant dose-dependent increase of CI from 0 to 15 μg/kg/min (P < 0.001). Oxygen consumption (VO2) and VCO2 were progressively increased by dobutamine. These increases were more marked between 10 and 15 μg/kg/min (8.3 and 8.6 %, respectively) than between the lower doses. ∆PCO2 and oxygen extraction (EO2) significantly decreased between 0 (8.0 ± 2.0 mmHg and 43.8 ± 13.4 %, respectively) and 10 μg/kg/min of dobutamine (4.2 ± 1.6 mmHg and 28.9 ± 7.9 %, respectively), but remained unchanged from 10 to 15 μg/kg/min (5.4 ± 2.4 mmHg and 29.5 ± 8.2 %, respectively). The central venous oxygen saturation significantly (ScvO2) increased from 0 to 10 μg/kg/min and remained unchanged from 10 to 15 μg/kg/min. Time courses of ∆PCO2, ScvO2, and EO2 were linked therefore to the biphasic changes of VO2 and VCO2.

CONCLUSION

∆PCO2 is a good indicator of the change of VCO2 induced by dobutamine. Measurement of ∆PCO2, along with ScvO2 and EO2, may be presented as a useful tool to assess the adequacy of oxygen supply versus metabolic and oxygen demand.

Challenges in understanding the impact of blood pressure management on cerebral oxygenation in the preterm brain

Systemic hypotension in preterm infants has been related to increased mortality, cerebrovascular lesions, and neurodevelopmental morbidity. Treatment of hypotension with inotropic medications aims at preservation of end organ perfusion and oxygen delivery, especially the brain. The common inotropic medications in preterm infants include dopamine, dobutamine, adrenaline, with adjunctive use of corticosteroids in cases of refractory hypotension. Whether maintenance of mean arterial blood pressure (MAP) by use of inotropic medication is neuroprotective or not remains unclear. This review explores the different inotropic agents and their effects on perfusion and oxygenation in the preterm brain, in clinical studies as well as in animal models. Dopamine and adrenalin, because of their α-adrenergic vasoconstrictor actions, have raised concerns of reduction in cerebral blood flow (CBF). Several studies in hypotensive preterm infants have shown that dopamine elevates CBF together with increased MAP, in keeping with limited cerebro-autoregulation. Adrenaline is also effective in raising cerebral perfusion together with MAP in preterm infants. Experimental studies in immature animals show no cerebro-vasoconstrictive effects of dopamine or adrenaline, but demonstrate the consistent findings of increased cerebral perfusion and oxygenation with the use of dopamine, dobutamine, and adrenaline, alongside with raised MAP. Both clinical and animal studies report the transitory effects of adrenaline in increasing plasma lactate, and blood glucose, which might render its use as a 2nd line therapy. To investigate the cerebral effects of inotropic agents in long-term outcome in hypotensive preterm infants, carefully designed prospective research possibly including preterm infants with permissive hypotension is required. Preterm animal models would be useful in investigating the relationship between the physiological effects of inotropes and histopathology outcomes in the developing brain.

[Evaluation of energy expenditure in children. Physiological and clinical implications and measurement methods]

The present article reviews the importance of the study of energy metabolism and its methods of assessment in children. Classically, energy requirements have been assessed by predictive equations based on anthropometric data. However, there are several physiologic and pathogenic states that may cause discrepancies between estimated and real values and consequently direct measurements of energy expenditure should be used. The gold standard to assess total energy expenditure during prolonged periods is the doubly labeled water method, which is mainly used for research studies. The best approach for resting energy expenditure determination in the clinical setting is indirect calorimetry. However, this method does not provide data on energy consumption under free-living conditions and its use in some critical care patients is restricted by technical limitations. Several other approaches to assess activity have been developed, based on heart rate, body temperature measurements, motion sensors and combined methods.

Increasing mean arterial pressure in patients with septic shock: effects on oxygen variables and renal function

OBJECTIVE

To measure the effects of increasing mean arterial pressure on oxygen variables and renal function in septic shock.

DESIGN

Prospective, open-label, randomized, controlled study.

SETTING

Medical-surgical intensive care unit of a tertiary care teaching hospital.

PATIENTS

Twenty-eight patients with a diagnosis of septic shock who required fluid resuscitation and pressor agents to increase and maintain mean arterial pressure > or =60 mm Hg.

INTERVENTIONS

Patients were treated with fluid and norepinephrine to achieve and maintain a mean arterial pressure of 65 mm Hg. Then they were randomized in two groups: In the first group (control group, n = 14), mean arterial pressure was maintained at 65 mm Hg, and in the second group (n = 14), mean arterial pressure was increased to 85 mm Hg by increasing the dose of norepinephrine.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables (mean arterial pressure, heart rate, mean pulmonary artery pressure, pulmonary artery occlusion pressure, cardiac index, systemic vascular resistance index, pulmonary vascular resistance index, left and right ventricular stroke indexes), metabolic variables (oxygen delivery, oxygen consumption-calorimetric method, arterial lactate), and renal function variables (urine flow, serum creatinine, creatinine clearance) were measured. After introduction of norepinephrine, similar values of hemodynamic, metabolic, and renal function variables were obtained in both groups. No changes were observed in group 1 during the study period. Increasing mean arterial pressure from 65 to 85 mm Hg with norepinephrine in group 2 resulted in a significant increase in cardiac index from 4.8 (3.8-6.0) to 5.8 (4.3-6.9) L.min.m. Arterial lactate and oxygen consumption did not change. No changes were observed in renal function variables: urine flow, 63 (14-127) and 70 (15-121) mL; serum creatinine, 170 (117-333) and 153 (112-310) mumol.L; and creatinine clearance, 50 (12-77) and 67 (13-89) mL.min.1.73 m.

CONCLUSIONS

Increasing mean arterial pressure from 65 to 85 mm Hg with norepinephrine neither affects metabolic variables nor improves renal function.

Effects of perfusion pressure on tissue perfusion in septic shock

OBJECTIVE

To measure the effects of increasing mean arterial pressure (MAP) on systemic oxygen metabolism and regional tissue perfusion in septic shock.

DESIGN

Prospective study.

SETTING

Medical and surgical intensive care units of a tertiary care teaching hospital.

PATIENTS

Ten patients with the diagnosis of septic shock who required pressor agents to maintain a MAP > or = 60 mm Hg after fluid resuscitation to a pulmonary artery occlusion pressure (PAOP) > or = 12 mm Hg.

INTERVENTIONS

Norepinephrine was titrated to MAPs of 65, 75, and 85 mm Hg in 10 patients with septic shock.

MEASUREMENTS AND MAIN RESULTS

At each level of MAP, hemodynamic parameters (heart rate, PAOP, cardiac index, left ventricular stroke work index, and systemic vascular resistance index), metabolic parameters (oxygen delivery, oxygen consumption, arterial lactate), and regional perfusion parameters (gastric mucosal Pco2, skin capillary blood flow and red blood cell velocity, urine output) were measured. Increasing the MAP from 65 to 85 mm Hg with norepinephrine resulted in increases in cardiac index from 4.7+/-0.5 L/min/m2 to 5.5+/-0.6 L/min/m2 (p < 0.03). Arterial lactate was 3.1+/-0.9 mEq/L at a MAP of 65 mm Hg and 3.0+/-0.9 mEq/L at 85 mm Hg (NS). The gradient between arterial P(CO2) and gastric intramucosal Pco2 was 13+/-3 mm Hg (1.7+/-0.4 kPa) at a MAP of 65 mm Hg and 16+/-3 at 85 mm Hg (2.1+/-0.4 kPa) (NS). Urine output at 65 mm Hg was 49+/-18 mL/hr and was 43+/-13 mL/hr at 85 mm Hg (NS). As the MAP was raised, there were no significant changes in skin capillary blood flow or red blood cell velocity.

CONCLUSIONS

Increasing the MAP from 65 mm Hg to 85 mm Hg with norepinephrine does not significantly affect systemic oxygen metabolism, skin microcirculatory blood flow, urine output, or splanchnic perfusion.

Energy expenditure and severity of injury and illness indices in multiple trauma patients

OBJECTIVE

To determine whether the energy expenditure of mechanically ventilated multiple trauma patients correlates with the severity of injury and illness indices before important systemic infection has complicated the clinical course, and to compare the energy expenditure with the energy expenditure expected from the Harris-Benedict equation adjusted with correction factors for trauma.

DESIGN

Prospective, clinical study.

SETTING

General intensive care unit of a university teaching hospital.

PATIENTS

Immediate multiple trauma adult patients who required mechanical ventilation.

INTERVENTIONS

Metabolic cart connected to the ventilator.

MEASUREMENTS AND MAIN RESULTS

Data on admission to the emergency department and during the first 24 hrs of intensive care unit admission were collected for computation of severity of injury and illness indices, respectively. Resting and total energy expenditures were derived at least 48 hrs after intensive care unit admission by continuous indirect calorimetry. Predicted basal energy expenditure was obtained using the Harris-Benedict equation and predicted total energy expenditure was calculated using the Harris-Benedict value adjusted with correction factors for trauma. Twenty-six multiple trauma adult patients completed the study. No statistically significant correlations were observed between both the resting energy expenditure and the total energy expenditure and the Injury Severity Score, Revised Trauma Score, Simplified Acute Physiologic Score II, Acute Physiology and Chronic Health Evaluation II score, and Glasgow Coma Scale score. A regression model of total energy expenditure was developed with the following variables: Harris-Benedict equation, heart rate, and minute ventilation (p = .01; r2 = .74). The resting energy expenditure/predicted basal energy expenditure ratio was 1.17+/-0.2 and the total energy expenditure/predicted total energy expenditure ratio was 0.76+/-0.1.

CONCLUSIONS

In mechanically ventilated multiple trauma patients the energy expenditure is not correlated to the severity of injury and illness indices but is dependent on the Harris-Benedict equation in addition to heart rate and minute ventilation. Furthermore, this patient population is characterized by a moderate state of hypermetabolism, and the Harris-Benedict prediction modified with correction factors for trauma systematically overestimates the total energy expenditure.

Relationship of mortality to increasing oxygen delivery in patients > or = 50 years of age: a prospective, randomized trial

OBJECTIVE

To investigate the relationship of mortality to early resuscitation using two levels of oxygen delivery (DO2) in critically ill surgical patients > or =50 yrs of age who were stratified into groups: age < or =75 yrs (age 50 to 75 yrs group); and age >75 yrs (age >75 yrs group).

DESIGN

A prospective, randomized trial, continued from a previous project.

SETTING

Surgical intensive care unit, university affiliated.

PATIENTS

Consecutive patients, >50 yrs of age, unable to generate a DO2 of > or =600 mL/min/m2 with fluid resuscitation alone, with a diagnosis of systemic inflammatory response syndrome, sepsis, severe sepsis, septic shock, and/or acute respiratory distress syndrome.

INTERVENTIONS

During the first 24 hrs of resuscitation, patients were randomized to receive fluids, blood transfusions, and vasoactive agents in order to achieve DO2 treatment goals of > or =600 mL/ min/m2 in the protocol group and 450 to 550 mL/min/m2 in the control group.

MEASUREMENTS AND MAIN RESULTS

One hundred five patients completed the study. In patients aged 50 to 75 yrs, the mortality rate was 21% (9/43) in the protocol group and 52% (12/23) in the control group (p=.01, 95% confidence interval of -58% to -4%). In patients >75 yrs of age, the mortality rate was 57% (12/21) in the protocol group and 61% (11/18) in the control group. Oxygen extraction ratios (O2ER) and oxygen consumption values were significantly (p=.02) lower in the age >75 yrs group compared with the age 50 to 75 yrs group.

CONCLUSIONS

Patients 50 to 75 yrs of age receiving a DO2 of > or =600 mL/min/m2 demonstrated a statistically significant (p=.01) improved survival rate over patients in the control group. Patients >75 yrs of age demonstrated no benefit from attempts to increase DO2 to >600 mL/min/m2, and they may have been overtreated as reflected by the lower O2ER values in this age group. Treating to an O2ER that reflects a balance between oxygen consumption and DO2 may be an alternative goal that allows individual titration.

Value of the venous-arterial PCO2 gradient to reflect the oxygen supply to demand in humans: effects of dobutamine

OBJECTIVE

To test the value of venous-arterial PCO2 gradient (deltaPCO2) measurements to reflect the adequacy of cardiac index (CI) to oxygen demand in patients submitted to rapid changes of CI and oxygen demand.

DESIGN

Prospective, comparative study.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

Ten patients with congestive heart failure exhibiting low baseline CI (< or =2.5 L/min/m2) but no evidence of global tissue hypoxia, as attested by the absence of clinical signs of shock and by normal blood lactate concentrations.

INTERVENTIONS

Infusion of incremental doses of dobutamine: 0 (D0), 5 (D5), 10 (D10), and 15 (D15) microg/kg/min.

MEASUREMENTS AND MAIN RESULTS

The CI increased by a linear fashion from D0 (1.6+/-0.1 L/min/m2) to D15 (2.4+/-0.2 L/min/m2) (p< .05). The mixed venous oxygen saturation (SVO2) increased from D0 (49+/-2%) to D10 (61+/-2%) (p < .05) and remained unchanged from D10 to D15 (60+/-2%). The oxygen extraction ratio (O2 ER) and the deltaPCO2 decreased from D0 (48+/-2% and 9+/-1 torr [1.2+/-0.3 kPa], respectively) to D10 (36+/-2% and 5+/-1 torr [0.7+/-0.1 kPa], respectively) (p < .05 for both comparisons) and remained unchanged from D10 to D15 (36+/-2% and 6+/-1 torr [0.8+/-0.1 kPa], respectively). The biphasic courses of SVO2, O2 ER, and deltaPCO2 were related to the course of oxygen consumption that remained constant from D0 (113+/-9 mL/min/m2) to D10 (112+/-8 mL/min/m2) and significantly increased from D10 to D15 (127+/-10 mL/min/m2) (p <.05).

CONCLUSIONS

deltaPCO2 can be reliably used at the bedside for informing on the adequacy of CI with respect to a given metabolic condition, and particularly for detecting changes in oxygen demand (e.g., the changes accompanying drug-induced changes in CI). In this regard, deltaPCO2, together with O2 ER and SVO2, can help to assess the adequacy of CI to global oxygen demand.

The American-European Consensus Conference on ARDS, part 2: Ventilatory, pharmacologic, supportive therapy, study design strategies, and issues related to recovery and remodeling. Acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) continues as a contributor to the morbidity and mortality of patients in intensive care units throughout the world, imparting tremendous human and financial costs. During the last 10 years there has been a decline in ARDS mortality without a clear explanation. The American-European Consensus Committee on ARDS was formed to re-evaluate the standards for the ICU care of patients with acute lung injury (ALI), with regard to ventilatory strategies, the more promising pharmacologic agents, and the definition and quantification of pathologic features of ALI that require resolution. It was felt that the definition of strategies for the clinical design and coordination of studies between centers and continents was becoming increasingly important to facilitate the study of various new therapies for ARDS.

The American-European Consensus Conference on ARDS, part 2. Ventilatory, pharmacologic, supportive therapy, study design strategies and issues related to recovery and remodeling

The acute respiratory distress syndrome (ARDS) continues as a contributor to the morbidity and mortality of patients in intensive care units throughout the world, imparting tremendous human and financial costs. During the last ten years there has been a decline in ARDS mortality without a clear explanation. The American-European Consensus Committee on ARDS was formed to re-evaluate the standards for the ICU care of patients with acute lung injury (ALI), with regard to ventilatory strategies, the more promising pharmacologic agents, and the definition and quantification of pathological features of ALI that require resolution. It was felt that the definition of strategies for the clinical design and coordination of studies between centers and continents was becoming increasingly important to facilitate the study of various new therapies for ARDS.

A profile of amino acid and catecholamine levels during endotoxin-induced acute lung injury in sheep: searching for potential markers of the acute respiratory distress syndrome

The identification of plasma markers of the course of the acute respiratory distress syndrome (ARDS) is needed to improve its treatment and to further advance the development of new therapeutic agents. The status of markers of lung injury in ARDS is reviewed and some new potential markers are proposed. This study focused on plasma amino acids, related amino compounds, and catecholamine levels during the acute phase of endotoxin-induced lung injury in 8 sheep characterized by the onset of pulmonary edema caused by increased microvascular permeability. A number of significant changes from baseline values were found. During the sixth hour of a 12-hour period of endotoxin infusion, norepinephrine, epinephrine, and alanine levels increased whereas the isoleucine level decreased. During the sixth hour of the immediate postendotoxin period, the taurine level increased while the levels of arginine, citrulline, glycine, isoleucine, methionine, ornithine, serine, threonine, and tryptophan decreased. These findings are compared with prior studies in human subjects detailing the amino acid profile characteristic of advanced sepsis. We conclude that the present profile of catecholamine and amino acid changes during endotoxemia in sheep deserves further study in human subjects to determine its significance as a marker of the early stage of ARDS.

The relationship of oxygen consumption measured by indirect calorimetry to oxygen delivery in critically ill patients

OBJECTIVE

The existence of oxygen supply dependency, defined as oxygen consumption (VO2) limited by oxygen delivery (DO2), is still questioned. This study examined the relationship between VO2 and DO2 in two groups of critically ill surgical patients 50 years and older in the first 24 hours of resuscitation after pulmonary artery catheter insertion. Group 1 patients had systemic inflammatory response syndrome (SIRS), sepsis, severe sepsis, septic shock, and adult respiratory distress syndrome (ARDS). Group 2 patients had hemorrhagic shock.

METHODOLOGY

Study methodology included (1) augmenting DO2 with fluids, blood, and vasopressors, (2) measuring VO2 by indirect calorimetry to avoid the problem of mathematical coupling with DO2 calculation, and (3) analyzing data during steady states of temperature, sedation, paralyzing agents, and vasopressors.

RESULTS

Six to 18 measurements collected on all study patients during a period within the first 24 hours were analyzed using a linear regression analysis. Statistical significance was set at p < or = 0.05. Seven of nine patients in group 1 demonstrated positive, statistically significant relationships between VO2 and DO2. Of six patients in group 2, one patient demonstrated a positive, significant relationship of VO2 and DO2, three demonstrated inverse relationships, and two patients did not show a DO2/VO2 relationship. Supply dependency did not exist in all patients but was present in seven out of nine patients with systemic inflammatory response syndrome, sepsis, severe sepsis, septic shock, and adult respiratory distress syndrome in the first 24 hours of treatment.

The use of oxygen consumption and delivery as endpoints for resuscitation in critically ill patients

OBJECTIVE

Oxygen consumption (VO2I) and delivery (DO2I) indices have been stated to be superior to conventional parameters as endpoints for resuscitation. However, another interpretation of published data is that inability to increase VO2I/DO2I given adequate volume resuscitation reflects inadequate physiologic reserve and poor outcome.

DESIGN

Fifty-eight critically ill patients were randomized to two groups. In group 1 (27 patients) attempts were made to maintain VO2I > or = 150 or DO2I > or = 600 mL/min/m2. If DO2I was > 600, no attempt was made to increase VO2I even if it was < 150. Group 2 (31 patients) was resuscitated based on conventional parameters. Volume resuscitation protocols and goals for pulmonary capillary wedge pressure were the same in both groups. VO2I/DO2I were recorded in group 2, but physicians were blinded to this data. Age, Injury Severity Score, and Acute Physiology and Chronic Health Evaluation (APACHE II) score were not different between groups.

MAIN RESULTS

Three patients in group 1 and two patients in group 2 died of organ failure (OF). One additional patient in group 2 died of refractory shock within 24 hours. Two of the patients in group 1 who died failed to meet VO2I/DO2I goals within 24 hours despite maximal resuscitation. Mortality was not different between the groups even with exclusion of the group 1 patients who failed to meet VO2I/DO2I goals (p = 0.66). After exclusion of the patient in group 2 who died of refractory shock, OF occurred in 18 of 27 (67%) in group 1 and in 22 of 30 (73%) in group 2 (p = 0.58). Length of ventilator support, intensive care unit stay, and hospital stay were not different between groups. When all patients were assessed, no difference was found in the incidence of OF between patients who attained the VO2I goal and those who did not. OF occurred in 20 of 34 (59%) patients who maintained a mean DO2I > or = 600 during the first 24 hours of the study and in 21 of 24 (88%) of those who did not (p < 0.02).

CONCLUSIONS

No difference was found in the incidence of OF or death in patients resuscitated based on oxygen transport parameters compared to conventional parameters. These data suggest that given adequate volume resuscitation, oxygen-based parameters are more useful as predictors of outcome than as endpoints for resuscitation.

Oxygen delivery and consumption during sepsis

This article discusses the oxygen consumption (VO2) and delivery (DO2) relationship as it pertains to animal models of sepsis and human sepsis syndrome and septic shock. Pathologic dependence of VO2 on DO2 is not present in resuscitated patients who have sepsis syndrome and septic shock. Defects in oxygen extraction and use at the individual organ level with maldistribution of blood flow probably do occur in sepsis; however, there is no clinical evidence that augmenting DO2 to supernormal levels decreases organ dysfunction or mortality in sepsis. We need improved techniques to assess tissue hypoxia at the organ level, and we need to test therapies directed at correcting the maldistribution of blood flow and O2 use defects of sepsis.

Pharmacodynamics and pharmacokinetics of milrinone administration to increase oxygen delivery in critically ill patients

OBJECTIVES

The positive inotropic and vasodilator actions of phosphodiesterase (PDE) inhibitor drugs may offer therapeutic alternatives to beta-agonists in critically ill patients. We hypothesized that milrinone administration would increase cardiac index (CI) and oxygen delivery (Do2) in ICU patients, and that a pharmacokinetic model previously developed in cardiac surgery patients may be used to predict milrinone plasma concentrations in a medical-surgical ICU population.

SETTING

ICU in two tertiary-care, university medical centers.

DESIGN AND INTERVENTIONS

A prospective, open-label, multicenter, dose-escalating study in three successive groups of eight ICU patients who received a 10-min loading dose of milrinone (25 micrograms/kg [LOW], 50 micrograms/kg [MED], and 75 micrograms/kg [HIGH]). In addition, all patients then received a milrinone infusion of 0.5 microgram/kg/min for 1 h.

MEASUREMENTS

Hemodynamic measurements included heart rate (HR); mean arterial, pulmonary artery, central venous, and pulmonary artery occlusion pressures; and thermodilution cardiac output. Oxygen transport indexes included arterial and venous blood oxygen tensions to determine Do2 and oxygen consumption (Vo2). Data were analyzed by univariate repeated measures analysis of covariance, with baseline values utilized as covariate regressors.

RESULTS

Twenty-four adult ICU patients 20 to 84 years of age completed the study. The three groups did not differ, except that the patients in the MED group were significantly older (67 +/- 4 years, mean +/- SEM) compared with either the patients in the LOW (48 +/- 7 years) or HIGH (47 +/- 6 years) group. While HR did not change in the LOW group (90 +/- 4 to 93 +/- 3 beats/min), HR increased significantly in the HIGH group (94 +/- 5 to 112 +/- 8 beats/min) (baseline to 60 min infusion time points). All milrinone doses increased both CI and Do2. At the end of the 10-min loading dose, CI increased 0.3 L/min/m2 in the LOW group, 1.1 L/min/m2 in the MED group, and 0.9 L/min/m2 in the HIGH group. Do2 increased 8% in the LOW group, 33% in the MED group, and 23% in the HIGH group, similar to the changes in CI. Mixed venous oxygen saturation increased 3 to 5% during the 10-min loading dose of milrinone. During this same time period, mean arterial pressure decreased 6 to 16% and pulmonary artery pressures decreased 9 to 15%. Peak plasma milrinone concentrations increased as a function of the loading dose (159 +/- 9 ng/mL in the LOW group, 302 +/- 33 ng/ml in the MED group, and 411 +/- 45 ng/mL in the HIGH group). However, milrinone concentrations were similar in all three groups after the 1-h infusion; 113 +/- 14 ng/ml (LOW), 147 +/- 22 ng/mL (MED), and 119 +/- 14 ng/ml (HIGH). In all patients with final plasma milrinone concentrations greater than 100 ng/mL (15/23), the CI increased by at least 0.4 L/min/m2 (range, 0.4 to 1.8 L/min/m2).

CONCLUSIONS

Our study confirms that a milrinone loading dose of 50 micrograms/kg/min followed by an infusion of 0.5 microgram/kg/min achieves adequate plasma concentrations of 100 ng/mL or greater, which significantly increases both CI and Do2. In addition, a previously established pharmacokinetic model of milrinone disposition is confirmed in this mixed ICU population.

Effect of epinephrine on oxygen consumption and delivery during progressive hemorrhage

OBJECTIVE

To determine whether, during hemorrhagic shock, the effect of epinephrine on energy metabolism could be deleterious, by enhancing the oxygen requirement at a given level of oxygen delivery (DO2).

DESIGN

Prospective, randomized, control trial.

SETTING

Experimental laboratory.

SUBJECTS

Two groups of seven mongrel dogs were studied. The epinephrine group received a continuous infusion of epinephrine (1 microgram/min/kg) while the control group received saline.

INTERVENTION

Dogs were anesthetized with pentobarbital, and shock was produced by stepwise hemorrhage.

MEASUREMENTS AND MAIN RESULTS

Oxygen consumption (VO2) was continuously measured by the gas exchange technique, while DO2 was independently calculated from cardiac output (measured by thermodilution) and blood oxygen content. A dual-lines regression fit was applied to the DO2 vs. VO2 plot. The intersection of the two regression lines defined the critical value of DO2. Values above critical DO2 belonged to phase 1, while phase 2 occurred below critical DO2. In the control group, VO2 was independent of DO2 during phase 1; VO2 was dependent on DO2 during phase 2. In the epinephrine group, the expected increase in VO2 (+19%) and DO2 (+50%) occurred under normovolemic conditions. During hemorrhage, VO2 immediately decreased, and the slope of phase 1 was significantly (p < .01) different from zero, and was significantly (p < .05) steeper than in the control group (0.025 +/- 0.005 vs. 0.005 +/- 0.010). However, the critical DO2 (8.7 +/- 1.7 vs. 9.7 +/- 2.4 mL/min/kg), the critical VO2 (5.6 +/- 0.5 vs. 5.5 +/- 0.9 mL/min/kg), and the slope of phase 2 (0.487 +/- 0.080 vs. 0.441 +/- 0.130) were not different from control values.

CONCLUSIONS

The administration of pharmacologic doses of epinephrine significantly increased VO2 under normovolemic conditions due to the epinephrine-induced thermogenic effect. This effect progressively decreased during hemorrhage. The critical DO2 and the relationship between DO2 and VO2 in the supply-dependent phase of shock were unaffected by epinephrine infusion. These results suggest that during hemorrhagic shock, epinephrine administration did not exert a detrimental effect on the relationship between DO2 and VO2.

Patterns of systemic oxygen utilization in cardiac ischemic syndromes: oxygen utilization in cardiac ischemia

Cardiac ischemia can present as distinctive clinical syndromes such as acute myocardial infarction, cardiogenic shock, sudden cardiac arrest or chronic congestive heart failure. All of the clinical syndromes share common pathophysiological events including reduction of cardiac output and systemic oxygen delivery (DO2) and activation of neurohumoral stress response. The balance between systemic DO2 and oxygen consumption (VO2) is maintained by modification of systemic oxygen utilization and demands which are essential for tissue viability and survival in cardiac ischemic syndromes. Low blood flow and the neurohumoral response may influence cellular metabolism (e.g., acute ischemia preconditioning and chronic downregulation of aerobic metabolism) and microcirculatory perfusion patterns to decrease systemic oxygen demands and VO2 in harmony with low cardiac output and systemic DO2. The clinical relevance of these metabolic adaptations and their influence on the outcome in cardiac ischemic syndromes remains unknown.

An argument for colloid resuscitation for shock

A focused review of the physiologic mechanisms of colloid and crystalloid fluid resuscitations for acute critical illness is presented. This review suggests that postresuscitation plasma volume, cardiac output, left ventricular mechanical performance, and global and microcirculatory O2 supplies are more favorable with colloid therapy. Conversely, crystalloid may adversely affect microcirculatory blood flow and resultant O2 supply and use by ischemic tissues in shock. Poor relief of global and regional hypoxia may persist in critically ill patients after resuscitation with crystalloid.

Prostacyclin improves glucose utilization in patients with sepsis

PURPOSE

In patients with sepsis, impaired glucose metabolism and altered microcirculatory blood flow are common findings. Prostacyclin (PGI2) improves tissue oxygenation, indicated by enhanced oxygen delivery (DO2) and oxygen uptake (VO2). The purpose of this study was to explore whether these effects are associated with improved glucose utilization.

METHODS

In 7 patients with sepsis, glucose metabolism was analyzed using dideuterated and 13C-labeled glucose and isotope dilution mass spectrometry. All patients received total parenteral nutrition with glucose covering 60% to 70% of the predicted energy expenditure and needed continuous intravenous insulin (40 microU.kg-1.min-1) to keep blood glucose concentrations below 10 mmol.l-1.VO2 and carbon dioxide production (VCO2) were continuously measured directly from the respiratory gases via indirect calorimetry. After equilibration of the infused labeled glucose with body glucose pool, baseline variables of glucose metabolism were assessed: glucose oxidation rate was determined from the enrichment of 13CO2 in the expired gas during primed constant infusion of [U-13C]glucose, glucose turnover rate (Ra) from the plasma enrichment of simultaneously infused [6,6-2H2]glucose. Endogenous glucose production rate was calculated as the difference between Ra and glucose infusion rate. Then, we examined the effect of PGI2 infusion (5 to 12.5 ng.kg-1.min-1) on glucose metabolism and gaseous exchange.

RESULTS

The PGI2-induced increase in DO2 (from 15.8 to 17.7 ml.kg-1.min-1; P < .05) resulted in an increase in directly measured VO2 from 5.0 to 5.3 ml.kg-1.min-1 (P < .01) whereas VCO2 remained unchanged. Although glucose turnover and production rates remained constant, glucose oxidation rate increased significantly from 1.21 to 1.38 mg.kg-1.min-1 (P < .02).

CONCLUSIONS

Improving tissue perfusion and oxygenation with PGI2 may also modify the impaired glucose metabolism by increasing glucose oxidation rate in patients with sepsis, suggesting enhanced adenosine triphosphate production.

The effects of dopamine infusion on the postoperative energy expenditure, metabolism, and catecholamine levels of patients after esophagectomy

Although dopamine is one of the most widely used vasoactive agents, its postoperative thermogenic and metabolic effects have not been studied. In this study, the effects of low-dose dopamine, given at 5 microgram/kg/min, on resting energy expenditure (REE), metabolism, and plasma catecholamine levels were examined in eight postsurgical patients. Dopamine infusion increased REE from 1,839 +/- 171 kcal/day to 2,071 +/- 170 kcal/day, and it decreased to 1,867 +/- 141 kcal/day after cessation of the infusion. Dopamine also increased the plasma levels of glucagon from 109.4 +/- 8.7 pg/ml to 132.5 +/- 8.0 pg/ml, and it decreased to 102.9 +/- 11.1 pg/ml after cessation of the infusion. The plasma levels of dopamine before, during, and after the infusion were 116.1 +/- 18.3, 161.1 +/- 25.6 and 121.4 +/- 17.2 ng/ml, respectively. Insulin and glucose were affected by dopamine, but changes in their plasma levels did not parallel the dopamine levels. Epinephrine and norepinephrine were increased by the infusion of dopamine and continued to increase even after its cessation. The results of this study revealed that low-dose dopamine increased REE in postsurgical patients and that this might be associated with the concomitant increase in plasma glucagon.

Measurement of oxygen consumption after uncomplicated acute myocardial infarction

BACKGROUND

Oxygen consumption (VO2) has been shown to be decreased after acute myocardial infarction (AMI) complicated by cardiogenic shock.

STUDY OBJECTIVE

To evaluate early measurement of VO2 by indirect calorimetry after an uncomplicated AMI (UAMI).

STUDY DESIGN

Prospective nonrandomized case study.

SETTING

Emergency department of a large urban hospital.

PARTICIPANTS AND INTERVENTIONS

Twenty-six consecutive patients presenting with confirmed UAMI. VO2 was measured by indirect calorimetry (Deletrac, Datex Ins,) which is noninvasive. All patients received buccal or intravenous nitroglycerin and thrombolytic therapy, and none received opiates before VO2 measurement.

RESULTS

Two groups of patients were identified by subsequent development of cardiogenic shock. Group 1 did not develop cardiogenic shock, and group 2 developed shock within 24 h of admission. Group 1 (n = 22) had a significantly higher VO2 compared to group 2 (n = 4), mean 154(SD 25) vs mean 100(SD 13) ml/min.m2, p < 0.002. Group 1 had a significantly higher increase in basal metabolic rate than group 2, mean 30 percent (SD 11) vs mean 10(SD 15) percent, p < 0.007. There was no significant difference in age, heart rate (HR), shock index (SI), or rate-pressure product (RPP) between groups 1 and 2. All patients in group 2 developed cardiogenic shock despite thrombolytic therapy, and two died within 24 h of admission.

CONCLUSION

VO2 is increased in UAMI and represents increased metabolic demands of peripheral tissues and not cardiac oxygen uptake. A reduction in VO2 (< 100 ml/min.m2) after AMI may be an early predictor of subsequent development of cardiogenic shock. Measurement of VO2 in UAMI by indirect calorimetry in the emergency department may be of value to identify patients at high risk and could influence their management.

Cardiac index vs oxygen-derived parameters for rational use of dobutamine in patients with congestive heart failure

In patients with congestive heart failure (CHF), catecholaminergic agents may exert thermogenic effects that limit their beneficial effects in terms of global tissue oxygenation. Oxygen extraction ratio (O2ER) or mixed venous blood saturation (SvO2) might take into account better than cardiac index (CI) the resultant effect of such agents on peripheral oxygenation. We tested this hypothesis in a series of 20 patients with severe CHF and normal blood lactate levels undergoing pulmonary artery catheterization and receiving incremental doses of dobutamine: 0 (Do), 5 (D5), 10 (D10), and 15 micrograms/kg/min (D15). A significant dose-effect relationship (p < 0.01) was found between dose of dobutamine and CI (CI = 0.06 dose + 1.82). By contrast, no dose-effect relationship was observed between dobutamine dose and either O2ER or SvO2. Indeed, a biphasic profile was observed for O2ER and SvO2. From D0 to D10, O2ER decreased (from 45 +/- 6 to 35 +/- 7 percent) and SvO2 increased (from 52 +/- 7 to 62 +/- 7 percent). From D10 to D15, no further change was observed for both parameters. This latter finding was related to a significant increase in VO2 at D15 (p < 0.01). In these normolactatemic patients with unchanged VO2 from D0 to D10 while DO2 linearly increased (from D0 to D15), the increase in VO2 at D15 was probably due to an increase in oxygen demand induced by the drug. Our results suggest that dobutamine at a dose of 15 micrograms/kg/min can induce an increase in O2 demand that might offset the improvement in CI. Thus, in patients with CHF, oxygen-derived parameters such as O2ER and SvO2 should be more appropriate than CI to assess the efficacy of dobutamine.