Sepsis-induced cardiomyopathy in animals: From experimental studies to echocardiography-based clinical research

Abstract

The term “sepsis-induced cardiomyopathy” (SIC) is used to describe transient cardiac dysfunction in septic patients. However, there is no universally accepted definition of SIC; a reduction in left ventricular ejection fraction (LVEF) is often used. In addition to systolic dysfunction, diastolic dysfunction is now recognized as an essential component of SIC. It can be emphasized that previous animal experiments played an essential role in revealing SIC and hemodynamic instability in sepsis and septic shock. The diagnostic and prognostic capabilities of echocardiography for the assessment of SIC have been extensively studied since its introduction into intensive care clinical practice. Recent studies in dogs, calves, and horses have shown that left and right ventricular systolic dysfunction, left ventricular diastolic dysfunction, and circulatory dysfunction can occur in sepsis, severe sepsis, and septic shock in animals. Echocardiographic variables have also shown that indices of left and right ventricular dysfunction and circulatory failure are valuable indicators of mortality in septic animals.

Introduction

It has been almost 400 y since William Harvey (1578–1657) discovered that the heart plays the most important role in the circulatory system (1). However, our knowledge of the heart and circulatory system was limited at that time; today, we have a better understanding of how this system functions, especially in health and disease. The term “sepsis-induced cardiomyopathy” (SIC), or “septic cardiomyopathy” (SC), was systematically proposed by Parker and colleagues in 1984 (2), and it can be emphasized that animal experiments played an important role in revealing the hemodynamic instability of sepsis and septic shock. Therefore, in this review, we have tried to address the significant developments in the diagnosis and evaluation of SIC and hemodynamic instability in septic animals, from experimental studies to clinical research.

Experimental studies to explore septic cardiomyopathy in animals

Prior to the introduction of pulmonary arterial catheterization (PAC) into hemodynamic studies of septic humans and animals, sepsis was described as having hyperdynamic and hypodynamic phases. Based on this, Weil et al (3) and Postel and Schloerb (4), using intravenous bolus injections of high doses of endotoxin or live organisms, showed septic shock characterized by reduced cardiac output (CO) and systemic vascular resistance (SVR) that led to animal death. Cardiovascular dysfunction in sepsis is better understood with the use of pulmonary artery thermodilution catheters, which allow measurement of both CO and pulmonary artery wedge pressure (PAWP). Animal studies in monkeys (5), rabbits (6), and dogs (7–9) have clearly shown that CO is higher and SVR is lower in cardiopulmonary-resuscitated individuals than in non-resuscitated individuals. In light of these data, it can be concluded that the description of low CO in septic shock patients was most likely due to hypovolemia. It is now generally accepted that severe sepsis and septic shock are often associated with high CO after adequate volume loading (10).

However, there is no universally accepted definition of SIC; a reduction in left ventricular ejection fraction (LVEF) is often used (11,12). The concept of SIC was first described by Parker and colleagues, using serial radionuclide cineangiography and simultaneous thermodilution CO as a reversible myocardial depression in patients with septic shock (2). They showed that 15 of 20 patients with septic shock had depression of LVEF during the first 2 d after the onset of septic shock. Interestingly, the survivors had a lower LVEF for 4 d and then recovered to typical values within 7 to 10 d. Acute left ventricular (LV) dilatation was also observed in these resuscitated patients with septic shock, and these acute changes in ventricular volume were reversible within 7 to 10 d in survivors.

Although early studies demonstrated a reduction in LV systolic function, experimental studies in canine septic shock models have shown that both left and right ventricular (RV) function can be impaired during the onset of sepsis and endotoxemia induced by Escherichia coli or Staphylococcus aureus (8,9,13,14). In the canine septic shock model, Natanson et al (8) also confirmed that LVEF was reduced in septic animals. The maximum decrease in LVEF occurred on Day 2, remained depressed for 2 to 3 d, and recovered by 7 to 10 d.

In addition to canine models of sepsis, an experimental study of acute endotoxemia in neonatal calves investigated the acute effects of endotoxemia on LV contractility, relaxation, diastolic properties, and mechanical energetics. The results after endotoxin infusion showed increased heart rate (HR), mean pulmonary artery pressure (PAP), LV contractility (end-systolic elastance), chamber stiffness, and mechanical efficiency; no change in LV relaxation; and decreased mean systemic arterial pressure, CO, and LV stroke work and pressure-volume area. The results indicated that, in neonatal calves, LV systolic performance is sufficient during 4 h of endotoxemia; and systemic hypotension, pulmonary arterial hypertension (PAH), and vascular volume depletion are the main causes of cardiovascular dysfunction during acute endotoxemia in calves (15).

The echocardiography-based exploration of septic cardiomyopathy in animals

Although not perfect, PAC has long been considered the optimal form of hemodynamic monitoring because it allows almost continuous, simultaneous recording of pulmonary artery and cardiac filling pressures and CO. The diagnostic and prognostic capabilities of echocardiography for the assessment of SIC have been extensively studied since its introduction into clinical practice (16,17) (Figure 1). In addition, echocardiography is increasingly used for hemodynamic monitoring and titration of therapy in septic shock (18,19).

Figure 1.

Types of sepsis-induced cardiomyopathies and the most commonly used echocardiographic indices in animal studies.

LVEF — Left ventricular ejection fraction; LVFS — Left ventricular fractional shortening; PEP — Pre-ejection period; ET — Ejection time; CO — Cardiac output; SV — Stroke volume; LVSm — Septal mitral annulus systolic velocity; E/A — Ratio of mitral inflow peak early diastolic filling velocity (E) and mitral inflow peak late diastolic filling velocity (A); Em — Septal-mitral annulus early diastolic velocities; RVSm — Right ventricular tricuspid annulus systolic velocity.

The first clinical trials and case reports: The beginning of the journey

To the best of our knowledge, the first clinical study involving echocardiographic assessment of myocardial dysfunction in animals was conducted by Nelson and Thompson (20) in 16 critically ill dogs (Table 1). They used percent LV fractional shortening (FS), LV pre-ejection period (PEP), and PEP compared to ventricular ejection time (ET) to define LV systolic dysfunction, and the ratio of mitral valve inflow velocities (E and A) to assess LV diastolic dysfunction. They reported that 6 dogs had increased PEP/ET, 3 had diastolic dysfunction, and 3 had subnormal CO. The most common diagnoses in dogs with critical illness and LV dysfunction were bacterial sepsis (n = 5) and cancer (n = 5). Of the 16 dogs evaluated, 12 (75%) died or were euthanized within 15 d of hospitalization. The authors concluded that detection of LV dysfunction in critically ill dogs may be a poor prognostic indicator, particularly in dogs with sepsis and cancer. Early identification and treatment of ventricular dysfunction may limit morbidity and mortality in these critically ill dogs (20).

Table 1.

Key echocardiographic findings of sepsis-induced cardiomyopathy in different species, and techniques used.

Authors	Echocardiographic techniques	Species	Key findings
Nelson and Thompson, 2006 (20)	M-mode, PW-Doppler	Dog	LV systolic and diastolic dysfunction, decreased CO.
Dickinson et al, 2007 (21)	M-mode	Dog	Dilated and hypokinetic LV, dilated RV.
Nakamura et al, 2012 (22)	2D, M-mode	Dog	Decreased LVEF and LVFS.
Naseri et al, 2018 (23)	2D, M-mode	Calf	Profoundly reduced LVEF, decreased CI.
Erturk et al, 2018 (24)	2D, M-mode, CW-Doppler	Calf	Hypokinetic LV, decreased CI, dilated RV.
Borde et al, 2011 (25)	2D, M-mode, PW-Doppler	Horse	Decreased SV, ET, AoVTI. No change in LVEF and LVFS.
Kocaturk et al, 2012 (26)	PW-Doppler	Dog	High Tei index for non-survivors. Low LVFS and LVEF in non-survivors.
Borde et al, 2014 (27)	2D, M-mode, PW-Doppler, TDI	Horse	Decreased Em and PEP/ET; increased E/Em, ET, and SV in non-survivors.
Ince et al, 2019 (28)	2D, M-mode, PW-Doppler, TDI	Dog	High Sm and LVEF, low Em and E/A in non-survivors.
Akar, 2019 (29)	2D, M-mode, PW-Doppler, TDI	Dog	Decreased RVSm and LV Em in non-survivors.
de Abreu et al, 2021 (30)	2D, PW-Doppler, TDI, speckle tracking	Dog	Impaired global longitudinal St and SR. Impaired global circumferential St and SR.
Corda et al, 2019 (31)	2D, M-mode, speckle tracking	Dog	Decreased LV longitudinal endomyocardial shortening. No change in LVEF and LVFS.
Naseri et al, 2019 (32)	2D, M-mode	Calf	Slightly decreased LVEF and LVFS. Decreased CI.
Ince et al, 2021 (33)	2D, M-mode, PW-Doppler, TDI	Dog	Decreased LV E/A and Em. No change in LVEF.
Suleymanoglu et al, 2023 (35)	2D, M-mode, PW-Doppler, TDI	Dog	Isolated LV diastolic dysfunction (Em) was common.

M-mode — Time motion mode; PW-Doppler — Pulsed-wave Doppler; LV — Left ventricular; CO — Cardiac output; RV — Right ventricle; 2D — Two-dimensional; LVEF — Left ventricular ejection fraction; LVFS — Left ventricular fractional shortening; CI — Cardiac index; CW — Continuous wave Doppler; SV — Stroke volume; ET — Ejection time; AoVTI — Aortic velocity time integral; TDI — Tissue Doppler imaging; Em — Septal-mitral annulus early diastolic velocities; PEP/ET — LV pre-ejection period to ejection time; E — Mitral inflow peak early diastolic filling velocity; A — Mitral inflow peak late diastolic filling velocity; Sm — Septal mitral annulus systolic velocity; RVSm — Tricuspid annulus systolic velocity; St — Strain; SR — Strain rate.

Echocardiography confirmed a clinical case of reversible SIC first described by Dickinson et al (21) in the setting of deciduous tooth eruption and development of sepsis in a 5-month-old dog. Echocardiography was done after adequate fluid therapy and indicated a dilated hypokinetic LV, increased end-systolic volume index (ESVI), dilated RV, and increased E point of septal separation (EPSS). Three months after resolution of sepsis, echocardiography revealed good LV systolic function and normal cardiac dimensions. The ESVI had decreased to the reference range. The authors concluded that the likely cause of the reversible myocardial depression was sepsis and that all abnormal findings resolved with time and correction of sepsis and SIC should be considered in dogs with sepsis (21).

Similarly, reversible myocardial depression is reported in the manuscript by Nakamura et al (22) in an 11-month-old dog referred for management after cardiopulmonary arrest (CPR). The time-motion (M-mode) echocardiographic findings revealed increased LV intraventricular systolic and diastolic dimensions (LVIDs and LVIDd, respectively) and decreased LVEF and left ventricular fractional shortening (LVFS) on admission. After hospitalization and a second echocardiographic examination on Day 4, LVIDs, LVIDd, LVEF, and LVFS were normal. However, the exact pathophysiology of myocardial dysfunction after resuscitation is unclear; the authors speculated that increased myocardial microvascular permeability and cardiac edema in CPA, mitochondrial oxidative phosphorylation deficiency, and myocardial dysfunction secondary to systemic inflammatory response syndrome (SIRS) could lead to myocardial depression in this case (22).

In addition to the use of echocardiography to identify myocardial dysfunction in small animals, the same features have been identified in large animals. The first clinical case of SIC in a calf with septic shock was described by Naseri et al (23) in a 10-day-old calf with diarrhea. M-mode echocardiographic findings at the time of admission showed increased LVIDs and LVIDd, decreased cardiac index (CI) and stroke volume (SV), and severely reduced LVEF. The second echocardiogram, done at 24 h of sepsis treatment, showed decreased LVIDs and LVIDd and increased CI, SV, and LVEF (Figure 2). Despite intensive therapy, the calf died the next morning. The authors concluded that myocardial depression may be reversible in the calf with septic shock, but traditional indices such as LVEF, CI, and SV may be inaccurate because they are influenced by changes in HR, preload, and afterload. Thus, a decreased ESVI may indicate vasodilation, and a decreased end-diastolic volume index (EDVI) may indicate hypovolemia. These were the major implications of sepsis and led to multiple organ dysfunction and death in the present case (23).

Figure 2.

Echocardiography. A — Hypokinetic left ventricle and decreased left ventricular ejection fraction, stroke volume, and cardiac index in a calf with sepsis. B — Image from the same calf at 24 h after fluid resuscitation. Improvement in systolic contractile function of the left ventricle by increasing left ventricular ejection fraction, stroke volume, and cardiac index (Naseri et al, 2018) (23).

Similarly, LV systolic dysfunction and right heart failure in a neonatal calf due to sepsis was reported by Erturk et al (24) in a 14-day-old calf. Echocardiographic findings included hypokinetic LV and decreased SV and CI. There was also a dilated RV and right atrium (RA). Systolic pulmonary arterial pressure, estimated by tricuspid regurgitation, showed moderate pulmonary hypertension (46 mmHg). Ultrasonographic findings included hepatomegaly and congestion, with increased echogenicity of the parenchyma, and the caudal vena cava was dilated and did not collapse during inspiration. The authors also determined high serum levels of creatine kinase-MB and cardiac troponin I. They suggested that sepsis may be the main cause of LV systolic dysfunction and pulmonary hypertension in this case.

The start of using Doppler methods

The effect of colic-induced endotoxin shock on cardiac function in horses was studied by Borde et al (25). In this study, to evaluate LV function in 50 horses, the measured and calculated echocardiographic variables were derived from 2-dimensional (2D), M-mode, and pulsed-wave Doppler (PW-Doppler) methods. All significantly lower were EDVI, ESVI, SV, stroke index (SI), ET, ejection time index corrected for heart rate (ETHR), aortic velocity time integral (AoVTI), aortic flow acceleration time, and aortic flow deceleration time. In contrast, aortic flow ejection acceleration time and HR were significantly higher in horses with endotoxic shock compared to control horses. Changes in LVEF and LVFS remained insignificant in the study groups. The authors pointed out that the results obtained should be interpreted with caution since the echocardiographic findings are related to the hemodynamic alterations and the loading state of the heart (vasodilation and hypovolemia). Also, they suggest that echocardiographic parameters derived from PW-Doppler imaging may be more accurate than 2D and M-mode indices (25).

To fill the gap in the efficacy of load-dependent parameters, Kocaturk et al (26) combined 2D, M-mode and, Doppler echocardiography imaging techniques to assess LV function in canine parvovirus enteritis (PVE) with sepsis. In addition to systolic time intervals (PEP and ET), LVEF and LVFS, they calculated the Tei index (myocardial performance index), which combines systolic and diastolic time intervals to assess global ventricular function, and mitral inflow peak early diastolic filling velocity (E) and mitral inflow peak late diastolic filling velocity (A). The authors determined that the Tei index was significantly higher in non-surviving dogs than in surviving and control dogs. Lower FS and EF were observed in non-surviving dogs compared to surviving and healthy dogs. The E/A ratio of mitral inflow was significantly lower in non-surviving dogs than in surviving and control dogs. They also determined that the Tei index had 91% sensitivity and 100% specificity for predicting mortality in dogs with PVE at an optimal cutoff of > 0.8. The slight increase in PEP/ET ratio and decrease in FS and EF in dogs with PVE may be due to a decrease in myocardial contractility. The significant increase in Tei observed in non-surviving dogs was consistent with impaired systolic and diastolic function. The findings of increased PEP/ET, prolonged isovolumetric relaxation time (IVRT) and isovolumetric contraction time (ICT), and lower mitral E/A ratio support impaired ventricular relaxation and, consequently, diastolic dysfunction. The authors also demonstrated that the use of the Tei index may be of great importance in the diagnostic workup and prognostic evaluation of dogs with PVE in practice (26).

Tissue Doppler imaging

The study by Borde et al (27) in horses admitted for colic complicated by SIRS was the next development in echocardiography in septic animals. The authors evaluated LV systolic and diastolic function in surviving and non-surviving horses with suspected sepsis using standard transthoracic echocardiography (2D and M-mode), PW-Doppler, and tissue Doppler echocardiography (TDI). They determined that TDI septal-mitral annulus early diastolic velocities (Em) were significantly lower and mitral E/Em was significantly higher in non-survivors compared to survivors. In addition, AoVTI, deceleration time, and ET, SV, SI, and ETHR were significantly lower; and PEP/ET and mean circumferential fiber shortening velocity (Vcf) were significantly higher in non-survivors compared with survivors. A cutoff value of 2.67 for E/Em predicted mortality with 100% sensitivity and 83% specificity. Other parameters related to LV systolic function, such as LVEF and LVFS, did not differ significantly between study groups. The results of this study indicated that echocardiographic markers of both systolic (SI, ET, PEP/ET) and diastolic (Em, E/Em) dysfunction predicted poor outcome in horses admitted with sepsis and suggested that echocardiography may provide useful prognostic information in these horses, as has been shown in human patients with septic shock (27).

The use of echocardiography to predict mortality

Accordingly, the work of Ince et al (28) in dogs with severe sepsis and septic shock established the prognostic value of LV systolic and diastolic dysfunction. Two-dimensional, M-mode, and transthoracic Doppler echocardiography was done in dogs with sepsis. The septic dogs were followed for 28-day mortality and divided into survivors and non-survivors. The authors determined that 75% of the dogs had at least one type of myocardial dysfunction. Systolic and diastolic dysfunction were present in 15% and 70% of dogs, respectively, and both types of dysfunction were present in 10% of dogs. They determined that impaired relaxation (grade 1) and pseudonormal dysfunction (grade 2) were the most common types of LV diastolic dysfunction in dogs with severe sepsis and septic shock. The authors also showed that septalmitral annulus systolic velocity (LVSm), Em, LVEF, and mitral annulus E/A ratio were independent predictors of mortality. At admission, LVEF and Sm were significantly higher in non-surviving dogs than in surviving dogs, and mitral annulus E/A and Em were lower in non-surviving dogs than in surviving dogs. They also reported that Sm, an index of systolic dysfunction, had high sensitivity and specificity (83% and 83%, respectively) and an optimal cutoff of ≥ 9.90 to differentiate survivors from non-survivors. For diastolic dysfunction, Em was the most sensitive and specific (both 100%) index, with an optimal cutoff of ≤ 6.50 to differentiate survivors from non-survivors (28).

Right ventricle should not be neglected

The hypothesis of pulmonary hypertension and RV dysfunction in dogs with sepsis and septic shock was confirmed in a pilot study by Akar (29). Two-dimensional, M-mode, and transthoracic Doppler echocardiography were done in dogs with sepsis. To detect RV systolic dysfunction, tricuspid annulus systolic velocity (RVSm) was performed using TDI. The primary results showed that LV systolic dysfunction, LV diastolic dysfunction, and RV systolic dysfunction were present in 16%, 64%, and 60% of the dogs, respectively. Both types of dysfunction (LV diastolic dysfunction and RV systolic dysfunction) were present in 28% of the septic dogs. In addition, the prognostic value of Em and RVSm for 28-day mortality was evaluated. The RVSm, an index of RV systolic dysfunction, showed good sensitivity and specificity (87% and 82%, respectively) with a cutoff value of ≤ 8.88 to discriminate survivors from non-survivors. The Em, an index of diastolic dysfunction, was also the most sensitive and specific variable (100% and 94%, respectively) with a cutoff of ≤ 5.06 to estimate outcome in septic dogs. The author suggested that endothelial dysfunction in sepsis and increased pulmonary vascular resistance (PVR), suspected acute respiratory distress syndrome, and pulmonary embolism may lead to RV systolic dysfunction in dogs with sepsis and is associated with poor outcomes (29).

Advanced techniques: Speckle-tracking echocardiography

Recently, 2-dimensional speckle-tracking echocardiographic (2D-STE) variables have been used to assess myocardial function in dogs with canine parvovirus infection and dogs with SIRS. The previous study by de Abreu et al (30) was the first to use strain (St) and strain rate (SR) by 2D-STE to assess global and regional myocardial function in dogs with PVE during inflammation. The authors determined that global longitudinal St and SR were impaired at the endocardial and epicardial levels in all dogs with PVE. Global circumferential St and SR were impaired only at the endocardial level in all groups of dogs with PVE. Global epicardial circumferential St was impaired only in the PVE-dead group, whereas global epicardial circumferential SR remained normal in all groups. However, the results of standard echocardiographic variables showed that all variables were within reference ranges, and the impaired St and SR values in dogs with PVE indicated the presence of systolic myocardial dysfunction in infected animals. This dysfunction may have been caused by direct viral action and/or the effects of SIRS on the myocardium.

In another study, Corda et al (31) attempted to compare 2D-STE with 2D and M-mode echocardiography to assess systolic function in dogs with SIRS. They determined that mild-to-moderate stages of SIRS in dogs were associated with LV systolic impairment identified by 2D-STE, but not by 2D- and M-mode-derived EF and FS. The results of their investigation suggest that mild and moderate stages of SIRS in dogs affect LV longitudinal endomyocardial shortening without altering longitudinal epimyocardial or radial contraction. Ischemia, sepsis-induced microcirculatory changes, and inflammatory mediators may affect longitudinally oriented subendocardial myocytes, resulting in a decrease in endomyocardial longitudinal systolic shortening.

The emergence of the longitudinal studies

The first longitudinal evaluation of LV systolic dysfunction in animals was completed by Naseri et al (32) in neonatal calves with naturally occurring sepsis or septic shock due to diarrhea. Two-dimensional, M-mode, and systolic time intervals were evaluated in septic calves for 3 d after admission to the intensive care unit. They determined significant decreases in left ventricular EDVI, ESVI, stroke volume index (SVI), and CI on admission. The HR and other parameters of LV systolic function (ET, ETHR, PEP:ET, Vcf ) were not significantly different between septic and healthy calves. The LVEF and LVFS were slightly increased in septic calves. After treatment initiation, the results showed that left ventricular EDVI, ESVI, SVI, CI and blood pressure (BP) significantly increased in septic calves within the first 6 h of treatment initiation. However, EDVI, SVI, and CI remained low and failed to reach the mean value for healthy calves despite ongoing fluid therapy. Ninety percent of the calves died during the hospitalization period. Although one of the major limitations of the study was the lack of load-independent parameters of myocardial function, such as Doppler, the echocardiographic findings obtained suggest that circulatory dysfunction (decreased preload as manifested by low EDVI; decreased afterload as manifested by low ESVI), rather than systolic dysfunction, was the most clinically important cardiovascular abnormality in septic calves (32).

Recently, another longitudinal study of LV systolic and diastolic functions in dogs with severe sepsis and septic shock was completed by Ince et al (33) in dogs with PVE. Two-dimensional, M-mode, and Doppler echocardiographic indices of LV systolic and diastolic function were evaluated in this study. The authors did not find a significant difference in LVEF between the septic and healthy dogs. Mitral annulus E/A and Em in the dogs with sepsis decreased on admission compared to healthy dogs. The authors determined that LV systolic dysfunction, LV diastolic dysfunction, and both types of dysfunction were present in 13%, 70%, and 9% of dogs with sepsis, respectively. They concluded that dogs with LV diastolic dysfunction had worse outcomes and short-term mortality (1.3 ± 1.4 d).

Provide guidance on the treatment protocol

Early goal-directed therapy protocols have been developed to normalize irregular measurable indices of tissue perfusion and oxygenation (34). The first attempt to assess hemodynamic instability in dogs with severe sepsis and septic shock using a combination of macrovascular parameters, such as blood pressure, and echocardiographic indices of LV systolic and diastolic function was made by Suleymanoglu and colleagues (35). They used serial blood pressure measurements and transthoracic echocardiographic parameters in surviving and non-surviving septic dogs in response to targeted hemodynamic optimization and to evaluate the use of norepinephrine and dobutamine and their effectiveness in predicting death. The authors determined that, at the time of admission, 74% of septic dogs had at least one type of myocardial dysfunction, and 60% of septic dogs had both types. Isolated LV diastolic dysfunction was a more common type of dysfunction (46%). A total of 8 dogs with LV diastolic dysfunction and 1 dog with LV systolic dysfunction died. They also determined that the surviving and non-surviving dogs had no significant differences in macrovascular and microvascular characteristics; the only difference was in the amount of norepinephrine administered. The non-surviving dogs were given a greater amount of norepinephrine and the surviving dogs were given a lesser amount of norepinephrine. In contrast, survivors received more dobutamine.

Conclusion

Although our view of cardiovascular dysfunction and hemodynamic instability in animals is now more advanced and evolved, we should not forget that animal-based studies have undoubtedly made important contributions to the development of our knowledge in this area over the past decades. With the introduction of echocardiography in the intensive care unit and real-time monitoring of critically ill patients, especially those with sepsis, veterinarians gained more realistic information about the functioning of the cardiovascular system during sepsis and septic shock. The improvements in veterinary intensive care units also highlighted the idea that echocardiography could provide more advantages, helping to guide treatment characteristics (e.g., fluid therapy, vasopressors, positive inotropes) and determine prognoses in septic animals. CVJ