Systemic pressure-flow reactivity to norepinephrine in rabbits: impact of endotoxin and fluid loading

Variability in the Hemodynamic Response to Fluid Bolus in Pediatric Septic Shock

OBJECTIVES

Fluid boluses are commonly administered to improve the cardiac output and tissue oxygen delivery in pediatric septic shock. The objective of this study is to evaluate the effect of an early fluid bolus administered to children with septic shock on the cardiac index and mean arterial pressure, as well as on the hemodynamic response and its relationship with outcome.

DESIGN, SETTING, PATIENTS, AND INTERVENTIONS

We prospectively collected hemodynamic data from children with septic shock presenting to the emergency department or the PICU who received a fluid bolus (10 mL/kg of Ringers Lactate over 30 min). A clinically significant response in cardiac index-responder and mean arterial pressure-responder was both defined as an increase of greater than or equal to 10% 10 minutes after fluid bolus.

MEASUREMENTS AND MAIN RESULTS

Forty-two children with septic shock, 1 month to 16 years old, median Pediatric Risk of Mortality-III of 13 (interquartile range, 9-19), of whom 66% were hypotensive and received fluid bolus within the first hour of shock recognition. Cardiac index- and mean arterial pressure-responsiveness rates were 31% and 38%, respectively. We failed to identify any association between cardiac index and mean arterial pressure changes (r = 0.203; p = 0.196). Cardiac function was similar in mean arterial pressure- and cardiac index-responders and nonresponders. Mean arterial pressure-responders increased systolic, diastolic, and perfusion pressures (mean arterial pressure - central venous pressure) after fluid bolus due to higher indexed systemic vascular resistance and arterial elastance index. Mean arterial pressure-nonresponders required greater vasoactive-inotrope support and had higher mortality.

CONCLUSIONS

The hemodynamic response to fluid bolus in pediatric septic shock was variable and unpredictable. We failed to find a relationship between mean arterial pressure and cardiac index changes. The adverse effects of fluid bolus extended beyond fluid overload and, in some cases, was associated with reduced mean arterial pressure, perfusion pressures and higher vasoactive support. Mean arterial pressure-nonresponders had increased mortality. The response to the initial fluid bolus may be helpful to understand each patient's individualized physiologic response and guide continued hemodynamic management.

Évaluation hémodynamique précoce par échocardiographie ciblée des patients en sepsis ou choc septique (Sepsis-3) au service d’urgence

Introduction : L’identification du profil hémodynamique des patients septiques au service d’urgence (SU) pourrait permettre d’adapter individuellement les recommandations de la Surviving Sepsis Campaign (SSC). L’objectif de cette étude était de décrire le profil hémodynamique précoce par échocardiographie ciblée chez les patients en sepsis et leur impact thérapeutique.

Méthode : Étude prospective monocentrique incluant les patients septiques (score qSOFA [quick Sepsis-related Organ Failure Assessment] ≥ 2) sur une période de 30 mois. L’échocardiographie était réalisée par des médecins urgentistes de niveau échographie clinique en médecine d’urgence 1 afin de déterminer le profil hémodynamique (hypovolémie, vasoplégie avec hyperkinésie, insuffisance ventriculaire ou profil « normal ») dès le sepsis identifié au SU. L’impact thérapeutique était défini par le nombre de patients pour lesquels l’échocardiographie modifiait le traitement de la SSC.

Résultats : Quatre-vingt-un patients (44 sepsis, 37 chocs septiques) ont été étudiés (âge moyen : 70 ± 15 ans ; hommes [n = 47, 58 %] ; SOFA = 5,3 ± 2,9 ; lactates = 4,6 ± 4,2 mmol/l ; admission en réanimation [n = 30, 37 %] ; mortalité j28 [n = 28, 35 %]) après un remplissage vasculaire médian de 500 ml (écart interquartile : 250–1 500 ml). Les profils hémodynamiques dominants étaient l’hypovolémie (n = 54, 66 %), parfois associée à une vasoplégie (n = 26, 32 %) et l’insuffisance ventriculaire (n = 21, 26 %). L’impact thérapeutique concernait 21 patients (26 %), dont un arrêt précoce du remplissage vasculaire après un volume de 850 ± 740 ml chez huit patients.

Conclusion : La dysfonction ventriculaire précoce est présente chez plus de 20 % des patients septiques. L’impact pronostique d’une évaluation échocardiographique dès l’identification du sepsis au SU reste à déterminer.

Cardiovascular effects of increasing dosages of norepinephrine in healthy isoflurane-anesthetized New Zealand White rabbits

OBJECTIVE

To characterize the cardiovascular effects of increasing dosages of norepinephrine (NE) in healthy isoflurane-anesthetized rabbits.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of nine female ovariohysterectomized New Zealand White rabbits weighing 3.4 ± 0.2 kg (mean ± standard deviation).

METHODS

Rabbits were premedicated intramuscularly with buprenorphine (0.05 mg kg^-1) and midazolam (0.5 mg kg^-1). Anesthesia was induced with intravenous propofol and maintained with a 1.1 × minimum alveolar concentration of isoflurane for this species to induce hypotension. Rabbits were administered NE infusions at three doses: low, 0.1 μg kg^-1 minute^-1; medium, 0.5 μg kg^-1 minute^-1; and high doses, 1 μg kg^-1 minute^-1 for 10 minutes each in that order. Cardiovascular variables including heart rate (HR), cardiac output (CO) by lithium dilution technique and systolic (SAP), mean (MAP) and diastolic (DAP) invasive arterial blood pressures measured in the auricular artery were recorded at baseline, 10 minutes after the start of the infusion of each NE treatment and 10 minutes after NE was discontinued. A linear mixed model and a type III anova with Tukey's post hoc comparison was performed (p < 0.05).

RESULTS

Significant increases in SAP (28% and 90%), MAP (27% and 90%) and DAP (33% and 97%) were measured with medium and high dose treatments, respectively (p < 0.001), with no changes in CO. HR decreased and stroke volume increased significantly with high dose treatment (by 17% and 15%, respectively; p < 0.05). No arrhythmias were noticed with NE treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

The infusion of NE at 0.5-1.0 μg kg^-1 minute^-1 is a potentially effective treatment for hypotension in healthy isoflurane-anesthetized New Zealand White rabbits.

Fluid resuscitation in sepsis: the great 30 mL per kg hoax

Large volume fluid resuscitation is currently viewed as the cornerstone of the treatment of septic shock. The surviving sepsis campaign (SSC) guidelines provide a strong recommendation to rapidly administer a minimum of 30 mL/kg crystalloid solution intravenously in all patients with septic shock and those with elevated blood lactate levels. However, there is no credible evidence to support this recommendation. In fact, recent findings from experimental, observational and randomized clinical trials demonstrate improved outcomes with a more restrictive approach to fluid resuscitation. Accumulating evidence suggests that aggressive fluid resuscitation is harmful. Paradoxically, excess fluid administration may worsen shock. In this review, we critically evaluate the scientific evidence for a weight-based fluid resuscitation approach. Furthermore, the potential mechanisms and consequences of harm associated with fluid resuscitation are discussed. Finally, we recommend an individualized, conservative and physiologic guided approach to fluid resuscitation.

Prognostic impact of left ventricular diastolic function in patients with septic shock

Background

Left ventricular (LV) diastolic dysfunction is highly prevalent in the general population and associated with a significant morbidity and mortality. Its prognostic role in patients sustaining septic shock in the intensive care unit (ICU) remains controversial. Accordingly, we investigated whether LV diastolic function was independently associated with ICU mortality in a cohort of septic shock patients assessed using critical care echocardiography.

Methods

Over a 5-year period, patients hospitalized in a Medical–Surgical ICU who underwent an echocardiographic assessment with digitally stored images during the initial management of a septic shock were included in this retrospective single-center study. Off-line echocardiographic measurements were independently performed by an expert in critical care echocardiography who was unaware of patients’ outcome. LV diastolic dysfunction was defined by the presence of a lateral E′ maximal velocity <10 cm/s. A multivariate analysis was performed to determine independent risk factors associated with ICU mortality.

Results

Among the 540 patients hospitalized in the ICU with septic shock during the study period, 223 were studied (140 men [63 %]; age 64 ± 13 years; SAPS II 55 ± 18; SOFA 10 ± 3; Charlson 3.5 ± 2.5) and 204 of them (91 %) were mechanically ventilated. ICU mortality was 35 %. LV diastolic dysfunction was observed in 31 % of patients. The proportion of LV diastolic dysfunction tended to be higher in non-survivors than in their counterparts (28/78 [36 %] vs. 41/145 [28 %]: p = 0.15). Inappropriate initial antibiotic therapy (OR 4.17 [CI 95 % 1.33–12.5]: p = 0.03), maximal dose of vasopressors (OR 1.38 [CI 95 % 1.16–1.63]: p = 0.01), SOFA score (OR 1.16 [CI 95 % 1.02–1.32]: p = 0.02) and lateral E′ maximal velocity (OR 1.12 [CI 95 % 1.01–1.24]: p = 0.02) were independently associated with ICU mortality. After adjusting for the SAPS II score, inappropriate initial antibiotic therapy and maximal dose of vasopressors remained independent factors for ICU mortality, whereas a trend was only observed for lateral E′ maximal velocity (OR 1.11 [CI 95 % 0.99–1.23]: p = 0.07).

Conclusion

The present study suggests that LV diastolic function might be associated with ICU mortality in patients with septic shock. A multicenter prospective study assessing a large cohort of patients using serial echocardiographic examinations remains required to confirm the prognostic value of LV diastolic dysfunction in septic shock.

Endotoxin impairs cardiac hemodynamics by affecting loading conditions but not by reducing cardiac inotropism

Acute myocardial dysfunction is a typical manifestation of septic shock. Experimentally, the administration of endotoxin [lipopolysacharride (LPS)] to laboratory animals is frequently used to study such dysfunction. However, a majority of studies used load-dependent indexes of cardiac function [including ejection fraction (EF) and maximal systolic pressure increment (dP/dt(max))], which do not directly explore cardiac inotropism. Therefore, we evaluated the direct effects of LPS on myocardial contractility, using left ventricular (LV) pressure-volume catheters in mice. Male BALB/c mice received an intraperitoneal injection of E. coli LPS (1, 5, 10, or 20 mg/kg). After 2, 6, or 20 h, cardiac function was analyzed in anesthetized, mechanically ventilated mice. All doses of LPS induced a significant drop in LV stroke volume and a trend toward reduced cardiac output after 6 h. Concomitantly, there was a significant decrease of LV preload (LV end-diastolic volume), with no apparent change in LV afterload (evaluated by effective arterial elastance and systemic vascular resistance). Load-dependent indexes of LV function were markedly reduced at 6 h, including EF, stroke work, and dP/dt(max). In contrast, there was no reduction of load-independent indexes of LV contractility, including end-systolic elastance (ejection phase measure of contractility) and the ratio dP/dt(max)/end-diastolic volume (isovolumic phase measure of contractility), the latter showing instead a significant increase after 6 h. All changes were transient, returning to baseline values after 20 h. Therefore, the alterations of cardiac function induced by LPS are entirely due to altered loading conditions, but not to reduced contractility, which may instead be slightly increased.

The effects of milrinone on hemodynamics in an experimental septic shock model

OBJECTIVE

To investigate the specific hemodynamic effects of the phosphodiesterase inhibitor milrinone in a rabbit model of septic shock in the absence of any other treatment.

DESIGN

A prospective, controlled, interventional study. Animal Model: Fourteen sedated New Zealand rabbits.

SETTING

Research laboratory of a health sciences university.

INTERVENTIONS

Rabbits were anesthetized and vascular catheters inserted in femoral artery and jugular vein. After a stabilization period and the recording of baseline measurements (H0), all animals received a 10-mL infusion of Pseudomonas aeruginosa. Two hours later (H2rabbits were randomly assigned to receive 5% dextrose (control group) or milrinone (milrinone group).

MEASUREMENTS AND MAIN RESULTS

Mean arterial blood pressure (MAP) was monitored continuously, and a cardiac index (CI) was determined every 30 mins by a transpulmonary thermodilution technique using an integrated monitoring device (PICCO). No differences were detected between the two groups after stabilization (H0) or before the treatment (H2) for either CI (mL/min(-1)/kg(-1)) or MAP (mm Hg). CI decreased progressively in the control group during the following 4 hrs, but not in the treated group (at H6: 122 +/- 4 vs. 207 +/- 16 mL/min(-1)/kg(-1); p < .05). No drop of MAP occurred after milrinone infusion. A comparison of the treated and control group reveals that milrinone improved tissue perfusion as evidenced by measurements of central venous saturation (at H4: 0.59 +/- 0.05 vs. 0.71 +/- 0.03, p = .04), lactacidemia (at H6: 10.3 +/- 2.4 vs. 3.9 +/- 0.9 mmol/L, p = .03), creatinemia (at H6: 95 +/- 11 vs. 60 +/- 5 micromol/L, p = .02) and survival (at H6: 5 vs. 7, not significant).

CONCLUSION

Milrinone improves cardiac output and tissue perfusion in a rabbit model involving severe septic shock.

Systemic and renal macro- and microcirculatory responses to arginine vasopressin in endotoxic rabbits

OBJECTIVE

Arginine vasopressin is being used increasingly to treat vasodilatory hypotension, although little is known of its effects on regional perfusion. Arginine vasopressin hemodynamic effects in physiology are mainly mediated through the V1a receptor on blood vessels. To investigate this further, we studied the effect of arginine vasopressin on systemic and renal blood flow in anesthetized, ventilated rabbits given either intravenous saline or endotoxin, and the impact of blocking V1a receptors.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal research laboratory.

SUBJECTS

Male White New Zealand rabbits.

INTERVENTIONS

Measurement was made of mean arterial blood pressure, aortic and renal blood flow velocities (pulsed Doppler), and renal cortical and medullary flow (laser Doppler).

MEASUREMENTS AND MAIN RESULTS

In a first series of animals, incremental intravenous boluses of arginine vasopressin ranging from 1 to 1000 ng were administered 90 mins postendotoxin or saline. In control rabbits (n = 9), increasing doses of arginine vasopressin elevated mean arterial blood pressure but reduced both aortic and renal blood flow velocity and renal cortical flow (p <.05). In endotoxic animals (n = 6), arginine vasopressin produced a similar increase in mean arterial blood pressure although aortic flow was maintained while renal blood flow velocity increased, mostly in its diastolic component (p <.05). Pretreatment with the V1a receptor antagonist in a second series of animals blunted all the effects observed in both control (n = 5) and endotoxic (n = 6) animals, suggesting that arginine vasopressin acted mainly through V1a subtype in this early phase of sepsis.

CONCLUSIONS

Preservation of renal blood flow with arginine vasopressin during endotoxemia, in particular to the cortex, suggests it could be a promising agent for hemodynamic support during septic shock.