Influence of an acute increase in systemic vascular resistance on transpulmonary thermodilution-derived parameters in critically ill patients

Vasopressor Responsiveness Beyond Arterial Pressure: A Conceptual Systematic Review Using Venous Return Physiology

ABSTRACT

We performed a systematic review to investigate the effects of vasopressor-induced hemodynamic changes in adults with shock. We applied a physiological approach using the interacting domains of intravascular volume, heart pump performance, and vascular resistance to structure the interpretation of responses to vasopressors. We hypothesized that incorporating changes in determinants of cardiac output and vascular resistance better reflect the vasopressor responsiveness beyond mean arterial pressure alone.We identified 28 studies including 678 subjects in Pubmed, EMBASE, and CENTRAL databases.All studies demonstrated significant increases in mean arterial pressure (MAP) and systemic vascular resistance during vasopressor infusion. The calculated mean systemic filling pressure analogue increased (16 ± 3.3 mmHg to 18 ± 3.4 mmHg; P = 0.02) by vasopressors with variable effects on central venous pressure and the pump efficiency of the heart leading to heterogenous changes in cardiac output. Changes in the pressure gradient for venous return and cardiac output, scaled by the change in MAP, were positively correlated (r2 = 0.88, P < 0.001). Changes in the mean systemic filling pressure analogue and heart pump efficiency were negatively correlated (r2 = 0.57, P < 0.001) while no correlation was found between changes in MAP and heart pump efficiency.We conclude that hemodynamic changes induced by vasopressor therapy are inadequately represented by the change in MAP alone despite its common use as a clinical endpoint. The more comprehensive analysis applied in this review illustrates how vasopressor administration may be optimized.

Application strategy of PiCCO in septic shock patients

Septic shock, also known as infectious or toxic shock, is a medical condition caused by severe infection and sepsis. Early identification, timely diagnosis and effective treatments are imperative to prevent this medical condition. The aim of the present study was to examine the application of pulse index continuous cardiac output (PiCCO) technique in the treatment of septic shock patients. Fifty septic shock patients were randomly divided into the conventional detection group (group C, n=25) and the PiCCO detection group (group P, n=25). A central venous catheter and radial artery catheter were placed into the patients of group C and a central venous catheter and PiCCO catheter (through femoral artery) were placed in the patients of group P to detect haemodynamics, which was managed and treated according to early goal-directed therapy (EGDT). PiCCO was applied to monitor and guide the application of fluid resuscitation, vasoconstriction drugs (dopamine) and positive inotropic drugs (dobutamine). The EGDT qualified rate of patients from the two groups at the 6th h of treatment, changes of post-resuscitation relevant parameters [blood lactate level, central venous oxygen saturation (ScvO₂), central venous pressure (CVP), mean arterial pressure (MAP) and urine volume], positive fluid balance quantity and the dosage of dopamine and dobutamine at the 6th, 24th and 48th h were observed. In comparison to group C, group P showed an increase in the EGDT qualified rate and ScvO₂ at the 6th h of treatment while the blood lactate level was decreased. The positive fluid balance quantity at the 6th and 24th h and the dosage of dobutamine were increased while the dosage of dopamine was reduced (P<0.05). There was no statistical significance in terms of the differences of positive fluid balance quantity and the dosage of dopamine and dobutamine in the two groups at the 48th h of treatment (P>0.05). There was also no statistical significance in terms of the differences of CVP, MAP and urine volume in the two groups (P>0.05). In conclusion, under the monitoring and guidance of the PiCCO technique, EGDT treatment should be applied to septic shock patients together with early fluid resuscitation and positive inotropic drugs instead of using only vasoconstriction drug, which cause elevation of blood pressure.

A rational approach to fluid therapy in sepsis

Aggressive fluid resuscitation to achieve a central venous pressure (CVP) greater than 8 mm Hg has been promoted as the standard of care, in the management of patients with severe sepsis and septic shock. However recent clinical trials have demonstrated that this approach does not improve the outcome of patients with severe sepsis and septic shock. Pathophysiologically, sepsis is characterized by vasoplegia with loss of arterial tone, venodilation with sequestration of blood in the unstressed blood compartment and changes in ventricular function with reduced compliance and reduced preload responsiveness. These data suggest that sepsis is primarily not a volume-depleted state and recent evidence demonstrates that most septic patients are poorly responsive to fluids. Furthermore, almost all of the administered fluid is sequestered in the tissues, resulting in severe oedema in vital organs and, thereby, increasing the risk of organ dysfunction. These data suggest that a physiologic, haemodynamically guided conservative approach to fluid therapy in patients with sepsis would be prudent and would likely reduce the morbidity and improve the outcome of this disease.

Early administration of norepinephrine increases cardiac preload and cardiac output in septic patients with life-threatening hypotension

Introduction

We sought to examine the cardiac consequences of early administration of norepinephrine in severely hypotensive sepsis patients hospitalized in a medical intensive care unit of a university hospital.

Methods

We included 105 septic-shock patients who already had received volume resuscitation. All received norepinephrine early because of life-threatening hypotension and the need to achieve a sufficient perfusion pressure rapidly and to maintain adequate flow. We analyzed the changes in transpulmonary thermodilution variables associated with the increase in mean arterial pressure (MAP) induced by norepinephrine when the achieved MAP was ≥65 mm Hg.

Results

Norepinephrine significantly increased MAP from 54 ± 8 to 76 ± 9 mm Hg, cardiac index (CI) from 3.2 ± 1.0 to 3.6 ± 1.1 L/min/m², stroke volume index (SVI) from 34 ± 12 to 39 ± 13 ml/m², global end-diastolic volume index (GEDVI) from 694 ± 148 to 742 ± 168 ml/m², and cardiac function index (CFI) from 4.7 ± 1.5 to 5.0 ± 1.6 per min. Beneficial hemodynamic effects on CI, SVI, GEDVI, and CFI were observed in the group of 71 patients with a baseline echocardiographic left ventricular ejection fraction (LVEF) >45%, as well as in the group of 34 patients with a baseline LVEF ≤45%. No change in CI, SVI, GEDVI, or CFI was observed in the 17 patients with baseline LVEF ≤45% for whom values of MAP ≥75 mm Hg were achieved with norepinephrine.

Conclusions

Early administration of norepinephrine aimed at rapidly achieving a sufficient perfusion pressure in severely hypotensive septic-shock patients is able to increase cardiac output through an increase in cardiac preload and cardiac contractility. This effect remained in patients with poor cardiac contractility except when values of MAP ≥75 mm Hg were achieved.

Effects of norepinephrine on dynamic variables of fluid responsiveness during hemorrhage and after resuscitation in a pediatric porcine model

BACKGROUND

The effect of vasopressors on pulse pressure variation (PPV), stroke volume variation (SVV) and on the volumetric variable global end-diastolic volume (GEDV) during changing loading conditions is currently under debate. The aim of our study was to investigate the effect of norepinephrine (NE) on PPV, SVV and GEDV in a pediatric animal model of hemorrhage and resuscitation.

METHODS

Eight anesthetized piglets were studied at normovolemia, after stepwise blood withdrawal (25 ml x kg(-1)), after infusion of NE to restore mean arterial pressure (MAP), after NE titration was stopped and shed blood was retransfused and finally again after NE titration. Stroke volume (SV) was measured using a thermodilution pulmonary artery catheter. GEDV was measured by transpulmonary thermodilution. PPV and SVV were monitored continuously by pulse contour analysis. In response to NE administration during hemorrhage, MAP significantly increased (P < 0.01), PPV significantly decreased (P = 0.02), whereas SVV, SV and GEDV remained unchanged. After retransfusion, SVV and GEDV significantly correlated with volume induced percentage change in SV. This significant correlation was reversed after NE administration for SVV and persisted for GEDV. In conclusion, NE administration significantly affected PPV and SVV, whereas the volumetric variable GEDV remained unchanged.