Haemodynamic studies in shock associated with infection

Blood pressure targets for vasopressor therapy: a systematic review

Physicians often prescribe vasopressors to correct pathological vasodilation and improve tissue perfusion in patients with septic shock, but the evidence to inform practice on vasopressor dosing is weak. We undertook a systematic review of clinical studies evaluating different blood pressure targets for the dosing of vasopressors in septic shock. We searched MEDLINE, EMBASE, CENTRAL (to November 2013), reference lists from included articles, and trial registries for randomized controlled trials (RCTs) and observational and crossover intervention studies comparing different blood pressure targets for vasopressor therapy in septic shock. Two reviewers independently selected eligible studies and extracted data on standardized forms. We identified 2 RCTs and 10 crossover trials but no observational studies meeting our criteria. Only one RCT measured clinical outcomes after comparing mean arterial pressure targets of 80 to 85 mmHg versus 65 to 70 mmHg. There was no effect on 28-day mortality, but confidence intervals were wide (hazard ratio, 95% confidence interval [95% CI] 0.84 - 1.38). In contrast, this intervention was associated with a greater risk of atrial fibrillation (relative risk, 2.36; 95% CI, 1.18 - 4.72) and a lower risk of renal replacement therapy in hypertensive patients (relative risk, 0.75; 95% CI, 0.57 - 1.0). Crossover trials suggest that achieving higher blood pressure targets by increasing vasopressor doses increases heart rate and cardiac index with no effect on serum lactate. Our findings underscore the paucity of clinical evidence to guide the administration of vasopressors in critically ill patients with septic shock. Further rigorous research is needed to establish an evidence base for vasopressor administration in this population.

The haemodynamics of human septic shock

In the time it has taken medicine to develop the techniques to describe the circulatory changes of severe infections, both pattern and process have been profoundly influenced by the use of intravenous fluids, vasopressors, antibiotics, steroids, mechanical ventilation and haemoflltration. Constant features of severe sepsis include a reduction in peripheral vascular tone on both the arterial and venous sides of the circulation, a defect in oxygen utilisation resulting in lactic acidosis, and varying degrees of myocardial dysfunction. These events have a temporal progression, the precise pattern observed depending on the tempo of the infection, the influence of therapeutic manoeuvres, the age and comorbidities of the patient, and the time the observations are made in the course of events. Early sepsis is accompanied by a decrease in systemic vascular resistance and a metabolic acidosis. The clinical picture includes fever, tachycardia, tachypnoea, respiratory alkalosis and an increased cardiac output with warm, dry peripheries and a bounding pulse. Advanced sepsis involves varying degrees of venous and myocardial contractile failure, and is characterised by progressive acidaemia, respiratory failure and marked sympathetic adrenergic activation. In the absence of vigorous fluid resuscitation, the cardiac output is decreased and the patients are cold, clammy peripherally shut down, and frequently confused, obtunded or comatose. In infections with a silent primary focus (predominantly involving Gram-negative organisms), this stage is frequently the first to attract the attention of attending staff. Late sepsis is characterised by profound acidaemia, vascular hypo-responsiveness, multiple organ failure and death.

Has the mortality of septic shock changed with time

OBJECTIVES

To determine whether a systematic review of the literature could identify changes in the mortality of septic shock over time.

DATA SOURCES

A review of all relevant papers from 1958 to August 1997, identified through a MEDLINE search and from the bibliographies of articles identified.

DATA SYNTHESIS

The search identified 131 studies (99 prospective and 32 retrospective) involving a total of 10,694 patients. The patients' mean age was 57 yrs with no change over time. The overall mortality rate in the 131 studies was 49.7%. There was an overall significant trend of decreased mortality over the period studied (r=.49, p < .05). The mortality rate in those patients with bacteremia as an entry criterion was greater than that rate in patients whose entry criterion was sepsis without definite bacteremia (52.1% vs. 49.1%; chi2=6.1 and p< .05). The site of infection altered noticeably over the years. Chest-related infections increased over time, with Gram-negative infections becoming proportionately less common. If all other organisms and mixed infections are included with the Gram-positives, the result is more dramatic, with these organisms being causative in just 10% of infections between 1958 and 1979 but in 31% of infections between 1980 and 1997.

CONCLUSIONS

The present review showed a slight reduction in mortality from septic shock over the years, although this result should be approached with caution. The heterogeneity of the articles and absence of a severity score for most of the studies limited our analysis. Furthermore, there was an increasing prevalence of Gram-positive causative organisms, and a change of the predominant origin of sepsis from the abdomen to the chest.

Management of septic shock

There have been important advances in the resuscitation of patients in septic shock in recent years. Survival can be improved by earlier recognition and therefore eradication of the sepsis combined with logical supportive measures. As with any acutely ill patient consultation with intensive care unit staff may be useful. Consultation with the intensive care unit does not necessarily imply the need for admission and mechanical ventilation; helpful advice may be forthcoming. Equally, referral to the intensive care unit does not mean an admission of failure but merely a recognition that additional skills and technical facilities are necessary for the patient's survival.

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.

Potential therapeutic efficacy of inhibitors of human phospholipase A2 in septic shock

Soluble phospholipase A2 has been implicated in the pathogenesis of local and systemic inflammatory reactions. Elevated levels of circulating phospholipase A2 (PLA2) correlate with the severity of circulatory collapse and pulmonary dysfunction in gram-negative septic shock. Characterization of septic shock serum PLA2 revealed a calcium-dependent enzyme with absolute 2-acyl specificity with a pH optimum of 7.5. We tested a number of therapeutic agents for their ability to inhibit PLA2 from human septic shock serum. Chloroquine, chlorpromazine, dexamethasone base, dexamethasone sodium phosphate, indomethacin, lidocaine, oleic acid, palmitic acid, promethazine, trans-retinoic acid, rutin and dl-alpha-tocopherol were all studied over the range of 10(-2) to 10(-7) M. All agents, with the sole exception of dexamethasone base, inhibited PLA2 activity at concentrations greater than 10(-3) M. PLA2 inhibition by dexamethasone sodium phosphate was factitious, due to the formation of calcium-phosphate complexes. Of the 11 agents studied, chlorpromazine was the most effective, with an IC50 of 7.5 X 10(-5) M, a membrane concentration achievable within its therapeutic range. Inhibition was non-competitive with an apparent Ki of 5 nM. Since serum PLA2 levels correlate with mortality in both experimental endotoxemia and clinical gram-negative septic shock, and chlorpromazine was previously shown to improve survival in these conditions, we postulate that its therapeutic efficacy resides at least in part in its PLA2-inhibitory activity.

The relationship between oxygen delivery and consumption during fluid resuscitation of hypovolemic and septic shock

The effects of increasing oxygen delivery (DO2) on oxygen consumption (VO2) in eight patients with septic shock and five patients with hypovolemic shock were studied during fluid resuscitation. In the septic shock group, DO2 increased from 315 +/- 29 to 424 +/- 25 ml/min/m2 (p less than 0.01) and VO2 increased from 134 +/- 8 to 151 +/- 7 ml/min/m2 (p less than 0.01). In the hypovolemic shock group, DO2 increased from 239 +/- 26 to 386 +/- 48 ml/min/m2 (p less than 0.01) and VO2 increased from 96 +/- 9 to 135 +/- 6 ml/min/m2 (p less than 0.01). There was no significant difference in either the increase in DO2 or VO2 between the septic shock and hypovolemic shock patients. We conclude that increasing DO2 by fluid resuscitation increases VO2 during both hypovolemic and septic shock.

Cardiovascular response to severe head injury

The cardiovascular, pulmonary, and metabolic responses to severe head injury were studied clinically in the acute phase after severe head injury with the object of determining if a common response was present and, if so, its significance in the management of the patients' intracranial and systemic physiological states. Cardiac output, pulmonary capillary wedge pressure, arterial blood pressure, arterial and mixed venous blood gases, and arterial and mixed venous epinephrine (E) and norepinephrine (NE) levels were measured serially in 15 patients during the first 3 days after injury. A hyperdynamic state was found, characterized by increased cardiac output, cardiac work, moderate hypertension, tachycardia, decreased or normal systemic and pulmonary vascular resistance, increased pulmonary shunting, and increased oxygen delivery and utilization. Arterial E and NE levels correlated well with the cardiac output, cardiac work, blood pressure, heart rate, oxygen delivery, and oxygen utilization but not with vascular resistance or pulmonary shunt. The magnitude of the hyperdynamic state did not correlate with intracranial pressure, Glasgow Coma Scale score, or computerized tomography findings. It is concluded that a hyperdynamic cardiovascular state occurs after severe head injury, and that it is mediated in part by sympathetic nervous activity. The significance of this state for systemic management of patients with head injury is discussed.

Hemodynamic and cardiometabolic effects of prenalterol in patients with gram negative septic shock

The hemodynamic effects of prenalterol, a new inotropic agent, were investigated in 10 patients with gram negative septic shock. In four of the patients, coronary sinus blood flow (CSF) and myocardial oxygen and lactate extraction were also determined. After baseline hemodynamic measurements, prenalterol was infused intravenously over a 10-min period to a total dose of 150 micrograms/kg. All patients responded within 15 min after completion of prenalterol infusion by increasing mean arterial pressure from 57 +/- 11 to 75 +/- 20 mmHg (7.58 +/- 46 to 9.97 +/- 2.66 kPa), (+32%), (P less than 0.01) and cardiac index from 2.65 +/- 0.40 to 3.80 +/- 0.47 1.min-1.m-2, (+44%) (P less than 0.001). There was no change in heart rate or systemic vascular resistance, nor were any arrhythmias recorded. The urinary output increased significantly. After prenalterol, CSF increased from 185 +/- 14 to 246 +/- 14 ml.min-1, (+33%), (P less than 0.001) and myocardial oxygen and lactate extraction rose from 19.8 +/- 2.1 to 26.6 +/- 2.1 ml O2.min-1, (+34%) (P less than 0.001) and from 33.2 +/- 2.3 to 44.7 +/- 2.1 mumol.min-1, (+35%), (P less than 0.001), respectively. The total body oxygen consumption increased from 287 +/- 13 to 348 +/- 23 ml O2.min-1, (+21%), (P less than 0.01) and the arterial lactate concentration decreased from 5.61+/- 0.55 to 3.94 +/- 0.16 mmol.l-1, (-30%), (P less than 0.01), suggesting improved tissue perfusion. The results demonstrate that prenalterol is a potent, highly selective inotropic agent inducing the same magnitude of increase in blood pressure and cardiac output as reported for dopamine in septic shock.

Endotoxin, prekallikrein, complement and systemic vascular resistance. Sequential measurements in man

Eighteen patients were studied prior to and again within 6 hours after transurethral resection or cystoscopy. In addition to hemodynamic measurements, detection of endotoxin by limulus assay and bacteriologic sampling; prekallikrein, C3, C3 proactivator and lysosomal enzyme levels were measured. In five patients limulus assays were positive, and in one, gram-positive bacteremia developed but limulus assay remained negative. All six had significant decreases in prekallikrein, C3 or C3 proactivator. Systemic vascular resistance fell in all six. Four additional patients who had a decrease in systemic vascular resistance were not endotoxemic or bacteremic; one of these had a decrease in prekallikrein only. In the remaining eight patients with neither bacteremia nor endotoxemia, systemic vascular resistance did not change or increase after instrumentation. One had a decrease in C3 proactivator, another in prekallikrein. There was no significant difference in age, disease, antibiotic therapy or bactermia in the two groups of patients. Four of the five resectional procedures were performed in the group that showed decreases in systemic vascular resistance. The data suggest that acute endotoxemia or gram-positive bacteremia in man is associated with depletion of prekallikrein, decreased peripheral resistance and, in some instances, activation of the complement system.

Acute hemodynamic effects of dopamine in patients with shock

The hemodynamic effects of dopamine were studied in 62 patients with clinical shock. In 36 patients with infection dopamine increased mean arterial pressure (MAP) 30%, and cardiac output (CO) 37%. Urine flow (UF) increased from 0.5 ml/min to 1.6 ml/min. Norepinephrine (NE) in 26 patients resulted in a higher MAP, lower CO, and similar UF. Isoproterenol (Isp) in 19 patients resulted in a lower MAP, higher CO, and a significantly lower UF. In 13 patients with cardiogenic shock dopamine increased MAP 6%, and CO 40%. UF increased from 0.6 ml/min to 1.1 ml/min. NE in eight patients resulted in a lower CO than during dopamine infusion, and Isp in five patients resulted in a higher CO. Dopamine improves MAP pressure, CO, and UF when shock is due to infection and is superior to Isp which does not increase perfusion pressure to adequate levels and does not improve UF. In patients with cardiogenic shock who have reduced CO and increased systemic vascular resistance, perfusion pressure tended to be adequate, and improved CO occurred with dopamine and Isp but not with NE. Although Isp increased CO more than dopamine, differences in regional perfusion are important in selection of the best inotropic agent and in most patients make dopamine the preferred agent.

Hypovolemia in shock due to acute myocardial infarction

Twelve patients with the clinical features of shock following acute myocardial infarction were treated with low molecular weight dextran (LMWD) as a plasma volume expander. Two of the patients had elevated central venous pressures (CVP), and neither responded favorably to plasma volume expansion. The remaining 10 patients had CVPs under 7 mm Hg prior to dextran infusion; five survived. Each survivor responded favorably to dextran infusion manifested by an increase in arterial pressure and cardiac index. The average increase in CVP in these patients was 1.0 mm Hg per 100 ml of dextran infused. The other five patients died either without recovering from shock or in chronic cardiac failure. These patients failed to show a significant increase in arterial pressure or cardiac index after dextran infusion; CVP increased by an average of 1.9 mm Hg per 100 ml infused. Hypovolemia must be considered in all patients in whom clinical evidence of shock develops as a complication of acute myocardial infarction, and if the CVP is normal or low, plasma volume expansion should be undertaken with caution. Increase in arterial pressure and evidence of improved cardiac index with little rise in CVP indicate a good response to the infusion and excellent prognosis for survival.

Volume expansion and flow promotion in shock

Volume replacement is the most important step in treating hypovolaemic shock.

Blood is needed when the oxygen carrying capacity threatens to fall below a critical level, but has the disadvantage of transmitting virus hepatitis. Anicteric hepatitis is about four times more frequent than the icteric form. Pasteurized plasma protein solution and albumin are free from the risk of transmitting hepatitis virus, and are good volume restorers.

Dextran 70 represents the best artificial colloid with additional anti-thrombotic properties. Dextran 40 is indicated in special situations to promote flow.

There is no proof that large amounts of Ringer solution are superior for treating hypovolaemic shock in man compared with colloids and electrolytes.