Concepts in the pharmacologic and nonpharmacologic support of cardiovascular function in critically ill surgical patients

Hemodynamic Consequences of Heart-Lung Interactions

The management of critically ill patients requires a fundamental understanding of cardiopulmonary interactions associated with mechanical ventilation. The hemodynamic changes due to ventilation are a result of changes in lung volume and intrathoracic pressure (ITP) and can occur during spontaneous or positive pressure ventilation despite constant tidal volumes. Pulmonary vascular resistance (PVR) and mechanical heart-lung interactions play prominent roles in determining the hemodynamic response to mechanical ventilation. Lung inflation alters PVR and right ventricular wall tension and, at high lung volume, mechanically limits cardiac volumes. The authors will consider the mechanisms of the effects of ITP on the pulmonary arterial and venous branches. These effects will aid in understanding the complex interactions between ventilation and right and left ventricular pressures and volumes, as well as the influence of lung inflation pressure on ventricular interdependence.

Initial severity of metabolic acidosis predicts the development of acute lung injury in severely traumatized patients

OBJECTIVES

First, to determine whether the severity of shock, as measured by systemic hypotension and metabolic acidosis, is significantly associated with a higher risk of acute lung injury in patients with severe trauma. Second, to determine whether the volumes of blood and crystalloid solutions administered in the early posttrauma period are independent risk factors for acute lung injury in severely traumatized patients.

DESIGN

Prospective observational study.

SETTING

Level I urban trauma center in a university hospital.

PATIENTS

A total of 102 severely injured, mechanically ventilated trauma patients with an Injury Severity Score > or =16 and aged between 18 and 75 yrs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Initial clinical and laboratory data were collected in the emergency department, and on a daily basis thereafter during the patient's intensive care unit stay. Of the 102 severely injured patients enrolled, 42 developed acute lung injury (41%) and 60 did not (59%). A total of 93% of the trauma patients who developed acute lung injury during the 17-month study period were included in the study. Initial base deficit was significantly lower in patients who developed acute lung injury than in those who did not (-8.8+/-4.5 vs. -5.6+/-5.1, p<.01). The difference in systolic blood pressure between the two groups was not significant.

CONCLUSIONS

In this group of severely injured trauma patients, the degree of metabolic acidosis at the time of admission identified those patients with the highest probability of developing acute lung injury. In addition, the volume of crystalloid solution administered during the first 24 hrs was significantly greater in patients who later developed acute lung injury. Finally, there was a significantly higher morbidity in patients who developed acute lung injury, whereas mortality did not differ between the two groups.

Recent advances in cardiopulmonary resuscitation

Mechanical and pharmacologic measures intended to increase blood flow to vital organs are the mainstay of therapy for patients in cardiac arrest. Several new cardiopulmonary resuscitation (CPR) techniques as well as novel devices and pharmacologic agents have been developed and tested since the first report of manual closed chested CPR over three decades ago. These recent mechanical and pharmacologic advances in the treatment of cardiac arrest are described. Some of these new techniques, devices, and drug therapies are presently undergoing clinical evaluation in patients in cardiac arrest. While many of these new methods and techniques have shown promise in small clinical trials in humans, none have yet to be found to be conclusively superior to manual closed chested CPR and treatment with standard pharmacologic agents.

Effects of catecholamines on regional perfusion and oxygenation in critically ill patients

Multiple organ failure is the major cause of death in patients with sepsis. Bacterial translocation from the gut is considered to induce and maintain sepsis. Therefore, the splanchnic region plays an important role in the pathogenesis and treatment of sepsis. There is evidence for a very high risk of imbalance between oxygen delivery and oxygen consumption especially in the splanchnic region. Consequently, there is a crucial interest whether it is possible to influence the splanchnic perfusion by specific catecholamines. Unfortunately, only a few, conflicting studies have looked at the effects of the various catecholamines on regional blood flow. Therefore, a clear recommendation for a specific catecholamine regimen in septic shock is impossible. Furthermore, it is unknown whether the choice of a specific catecholamine in the treatment of septic shock affects the patient's outcome. In most patients, the use of vasopressors is indispensable because adequate haemodynamic perfusion pressure is not achieved with fluid therapy alone. The negative effects of vasopressors on splanchnic perfusion are known from studies carried out under non septic conditions. Norepinephrine and dopamine in doses of 10 micrograms/kg/min in septic animals are without negative effects on splanchnic perfusion. Preliminary results show Preliminary results show a decrease in splanchnic oxygenation in patients with septic shock treated with epinephrine. Catecholamines with beta mimetic effects are often used to increase DO2. The question as to whether dobutamine or dopamine should be used first in treatment of septic shock cannot be answered yet. Whether treatment with low dose dopamine or dopexamine actually improves renal function and splanchnic oxygenation is the purpose of ongoing studies.

Right ventricular end-diastolic volume as a measure of preload

Right ventricular (RV) end-diastolic volume index (RVEDVI) measured by a modified thermodilution pulmonary artery catheter has been proposed as an improved measure of cardiac preload, compared with pulmonary capillary wedge pressure (PCWP). This study compared the correlation of RVEDVI and PCWP with cardiac index (CI) to determine which parameter better reflected ventricular preload. Modified thermodilution catheters were placed in 38 critically ill patients. Hemodynamic parameters were recorded in these patients at 2- to 4-hour intervals for 1 to 7 days. Complete data sets (1,008) were obtained. Regression analysis was performed comparing PCWP, RVEDVI, RV ejection fraction (RVEF) to CI in the entire group and in individual patients. Because mathematical coupling may exist between RVEDVI and CI, the correlation between these variables was corrected for mathematical coupling using the method described by Stratton. Simple regression analysis of data from all patients, uncorrected for mathematical coupling, yielded a significant correlation between CI and RVEDVI (r = 0.60, p < 0.0001), RVEF (r = 0.37, p < 0.0001), and PCWP (r = 0.01, p < 0.001). Correction for mathematical coupling between RVEDVI and CI resulted in a minor changes of the correlation coefficient to 0.56. In individual patients, a significant, uncorrected correlation (p < 0.05) was found between RVEDVI and CI in 27 of the 38 patients, whereas 11 patients had a significant correlation between PCWP and CI. RVEDVI correlated more closely with CI than did PCWP, even after correlation for mathematical coupling. In both the group as a whole and in individual patients, RVEDVI was a better indicator of cardiac preload.

Metabolic and haemodynamic effects of dopamine plus domperidone in volunteers

There are no studies of the relationship between infusion rate of dopamine and the arterial and venous dopamine plasma concentration and the resulting haemodynamic and metabolic effects. Dopamine was administered to seven volunteers using five infusion rates (1, 3, 6, 9, 13 micrograms/kg per minute) in an escalating sequence lasting for 30 min for each step. Since dopamine can cause nausea and vomiting, this relationship was investigated after administration of domperidone for infusion rates above 3 micrograms/kg per minute. Haemodynamic effects were assessed using 2-dimensional echocardiography. During the highest infusion rate the arterial plasma dopamine concentration reached 1,379 +/- 181 nmol/l. There was a linear correlation between the dopamine infusion rate and both the arterial and the venous plasma concentration. There was no significant change in heart rate or diastolic blood pressure. Systolic blood pressure, ejection fraction and cardiac index increased in a dose-dependent manner. Systemic vascular resistance decreased during the two low doses of dopamine and was not different from baseline values during the three high infusion rates. The plasma concentrations of glucose and non-esterified fatty acids increased from 5.3 +/- 0.4 to 0.68 +/- 0.9 nmol/l, and from 360 +/- 119 to 971 +/- 307 mumol/l, respectively, during the 13 micrograms/kg per minute infusion rate. As the plasma noradrenaline concentration increased up to 7.84 +/- 2.46 nmol/l in correlation to the dopamine plasma concentration, an indirect sympathomimetic effect may contribute to the actions of dopamine plasma concentration.

Effects of epinephrine and norepinephrine on hemodynamic parameters and arrhythmias during a continuous infusion of amitriptyline in rats

Epinephrine and norepinephrine were evaluated in treatment of hemodynamic compromise in amitriptyline intoxication. One hundred and one male Wistar rats were monitored hemodynamically during amitriptyline intoxication and given one of three infusion rates (0.1, 0.5 or 5.0 mg/kg/min) of either epinephrine or norepinephrine. Sixteen rats served as controls and received only glucose after intoxication. Amitriptyline intoxication lowered mean arterial pressure, heart rate, left ventricular max dP/dt, and increased left ventricular end-diastolic pressure. All doses of norepinephrine and the two higher doses of epinephrine increased mean arterial blood pressure and left ventricular max dP/dt. Heart rate increased with both drugs, more with epinephrine, but not beyond pre-intoxicated levels at any dose. Left ventricular end-diastolic pressure was unaltered by both drugs. Malignant arrhythmias appeared in 7% of all animals, whereas a progressive decline of cardiac contractility caused cardiac arrest in 36% of all animals. This suggests that myocardial depression is the aspect most likely to cause death. At intermediate doses epinephrine resulted in significantly fewer arrhythmias and lower mortality compared to norepinephrine. We conclude that epinephrine and norepinephrine each appeared effective in reversing amitriptyline-induced hemodynamic alterations. Epinephrine had fewer arrhythmogenic properties than norepinephrine and may be preferable to norepinephrine.

Acute pancreatitis at its centenary. The contribution of Reginald Fitz

1989 represents the 100th anniversary of Reginald Fitz's initial characterization of acute pancreatitis. Our current understanding of this disease has advanced little beyond Fitz's early description. While survival from pancreatitis has improved largely through advancements in critical care techniques, no medical or surgical therapy exists that can limit pancreatic autodigestion and inflammation. Recent investigations have suggested that pancreatitis may result from a disruption of normal stimulus-secretion coupling within the acinar cell. Future research based on these observations may ultimately result in successful therapy for this disease.

Clinical issues regarding the use of total nutrient admixtures

The introduction of total nutrient admixtures (TNAs) has offered several clinical advantages. Substituting a portion of the daily dextrose calories with lipids may reduce the incidence of carbohydrate-associated complications (e.g., disturbances in glucose control and immune function). In addition, providing intravenous lipids continuously over 24 hours as a TNA appears to be better utilized by the liver and less likely to interfere with reticuloendothelial system function when compared with conventionally administered, discontinuous lipid infusions. If the peripheral vein is used as a route for parenteral nutrition, the addition of fat to the admixture provides the advantage of enhancing caloric density, while contributing significantly less tonicity than dextrose. Certain pharmaceutical and microbiological issues need to be considered to ensure the intravenous administration of a safe and homogenous dispersion. Attention to established guidelines provided by the lipid manufacturers, as well as careful extrapolation of TNA stability data, will avert the dangers associated with infusion of coalesced lipid particles. This article reviews the evidence supporting the use of lipids as daily caloric sources, with particular emphasis on the role of the total nutrient admixtures as the primary vehicle for administration.

Lactic acidosis

An understanding of the pathophysiology of lactic acidosis is crucial in facilitating the optimal care of critically ill patients. The relevant biochemistry of lactic acidosis is reviewed, and the more controversial aspects relating to the genesis of the acidosis are highlighted. The current system of classification of lactic acidosis divides etiologies on the basis of the presence or absence of clinical signs of tissue hypoperfusion. Several types of lactic acidosis in which clinical evidence of tissue hypoperfusion is lacking demonstrate hemodynamic evidence of occult hypoperfusion. The diagnostic and therapeutic implications of this observation are discussed. Current diagnostic criteria for lactic acidosis include a pH less than 7.35 and blood lactate concentration greater than 5 to 6 mM/L. An important issue relates to the implications of lactate values that are greater than normal but below this diagnostic range. The use of the oxygen flux test may be valuable in the diagnosis of occult tissue hypoperfusion in patients with low-grade elevations in lactate levels. The current therapy for lactic acidosis involves addressing the primary cause and supportive management. The use of bicarbonate in the therapy for lactic acidosis is controversial due to potential adverse effects on cardiac function. The specifics of this controversy are outlined, and newer therapeutic alternatives are reviewed. The use of blood lactate concentration as a prognostic index may be more useful in patients with shock than without shock.

Inotropic response to digoxin and dopamine in patients with severe sepsis, cardiac failure, and systemic hypoperfusion

We studied the inotropic response to dopamine and digoxin in 20 patients with severe sepsis and left ventricular failure. Left ventricular failure was defined as a left ventricular stroke work index less than or equal to 40 g.m/m2 at a pulmonary artery wedge pressure greater than or equal to 15 mm Hg. Hemodynamic assessment was obtained before and following administration of digoxin 10 micrograms/kg IV or dopamine, 5 to 12 micrograms/kg/min IV. Patients treated with digoxin demonstrated a significant increase in LVSWI. The LVSWI increased 13 +/- 10 percent in the dopamine-treated patients compared with 74 +/- 16 percent in the digoxin patients (p less than 0.02). We conclude that digoxin exhibited significant inotropic activity in patients with sepsis.

Outcome prediction in critically ill patients by means of oxygen consumption index and simplified acute physiology score

Both oxygen consumption index (VO2-index) and simplified acute physiology score (SAPS) are reported to be reliable predictors of the ultimate outcome in critically ill patients. The purpose of this study was to verify whether survivors and nonsurvivors have different VO2-indices and whether the prognostic potency of SAPS can be improved by addition of VO2-index as a supplemental physiological variable. In 50 mechanically ventilated surgical ICU patients with heterogeneous underlying diseases, SAPS was calculated and VO2-index was determined by continuous 24-h measurement of oxygen consumption. The VO2-indices of survivors and nonsurvivors were not significantly different (p greater than 0.05), which is in contrast to the results of earlier studies. This contrast may be explained by a difference both in methods of VO2-measurement and in study populations. SAPS was significantly lower in survivors than in nonsurvivors (p less than 0.005) and was able to classify the patients correctly into groups of increasing probability of death. However, SAPS failed to be a helpful prognosticator in the individual patient. The addition of VO2-index to SAPS as a supplemental physiological variable did not substantially improve the prognostic potency. Because a higher VO2-index did not necessarily indicate a better survival chance, there is no argument for therapeutic interventions aimed exclusively at increasing VO2-index, as suggested previously.

Hemodynamic adaptation to acute myocardial contusion complicating blunt chest injury

The immediate hemodynamic sequelae of blunt chest injury complicated by acute myocardial contusion were examined in multiply traumatized patients. Focal defects of ventricular wall motion defined by gated cardiac scintigraphy identified acute myocardial contusion in 28 of 43 patients, involving the right ventricle alone in 18 (group 1A), the left ventricle in 4 (group 1B) and both ventricles in 6 (group 1C). Qualitatively normal ventricular wall motion was found in the 15 patients (group 2). Although there was no difference between groups 1A and 2 in mean systemic oxygen transport (620 +/- 189 vs 627 +/- 105 ml/min/m2), left ventricular ejection fraction (52 +/- 14% vs 60 +/- 9%) or calculated left ventricular end-diastolic and end-diastolic and end-systolic volumes, mean right ventricular (RV) ejection fraction was significantly lower in group 1A (29 +/- 9%) than in group 2 (47 +/- 7%, p less than 0.01). Concomitantly, evidence of RV systolic dysfunction was ml/m2) but not in group 2 (RV end-systolic volume, 50 +/- 21 ml/m2, p less than 0.05). RV stroke work was similar between the groups, and RV pump function was identical by virtue of a larger RV preload in group 1A (RV end-diastolic volume 143 +/- 63 ml/m2) than in group 2 (RV end-diastolic volume 93 +/- 26 ml/m2, p less than 0.05). Thus, use of the RV Frank-Starling mechanism in patients with traumatic RV contusion maintains RV pump function at a level similar to that in traumatized patients without acute myocardial contusion.