What’s New in Veterinary Sepsis and Septic Shock?

Overview

Veterinary sepsis and septic shock remain among the most challenging syndromes in small animal emergency and critical care. They are common, deadly, and still frustratingly underdefined in dogs and cats. What has changed in recent years is not the seriousness of sepsis, but how clinicians are being encouraged to recognize and manage it: less emphasis on SIRS alone, more attention to organ dysfunction, shock phenotype, endothelial injury, biomarkers, and measured, individualized hemodynamic support.

That shift matters. A dog with septic peritonitis and progressive vasoplegia is not clinically identical to a cat with severe pneumonia and evolving organ dysfunction, even if both meet older inflammatory criteria. Recent literature now reflects that heterogeneity more clearly and pushes small animal clinicians toward a more nuanced model of recognition, resuscitation, and prognosis.

Related reading:

• Septic peritonitis in dogs and cats
• Vasopressor use in veterinary ICU patients
• Fluid therapy in critically ill small animals

Why Veterinary Sepsis Definitions Are Changing

One of the biggest current issues in small animal sepsis diagnosis is that veterinary medicine still lacks universally accepted bedside criteria equivalent to human Sepsis-3. Cortellini and colleagues highlighted this directly in their 2024 international review, arguing that the lack of consensus definitions limits research comparability and complicates everyday recognition in dogs and cats.

The practical takeaway is straightforward: clinicians should no longer think of sepsis simply as infection plus nonspecific systemic inflammation. Older SIRS-based frameworks helped screen unstable patients, but they are too broad to distinguish infectious from noninfectious inflammatory disease reliably. Recent thinking instead centers on life-threatening organ dysfunction caused by a dysregulated host response to infection.

That conceptual shift has real bedside implications:

• documented or strongly suspected infection matters
• new or worsening organ dysfunction matters
• shock state matters
• the patient’s trajectory over the first several hours matters

At the same time, the field is not finished evolving. Veterinary ECC has embraced the idea that sepsis is more than inflammation, but there is still no universally adopted veterinary Sepsis-3 equivalent. For now, clinicians must integrate infection, physiology, organ function, and response to therapy rather than relying on any single checklist.

Current Understanding of Sepsis Pathophysiology in Dogs and Cats

Modern sepsis biology in veterinary medicine looks less like “runaway inflammation” and more like a complex failure of host regulation. Recent reviews emphasize overlapping mechanisms that help explain why some patients remain unstable even after initial macrocirculatory targets appear improved.

Dysregulated host response, not inflammation alone

The most useful current framework describes sepsis as a dysregulated host response to infection that causes organ dysfunction. That wording matters because it captures both excessive and ineffective immune responses. Some patients are hyperinflammatory. Others show immune paralysis, poor pathogen control, or mixed phenotypes.

Endothelial and glycocalyx injury

The endothelium and glycocalyx are increasingly central to how veterinary clinicians think about septic shock. Injury to this surface layer promotes capillary leak, vasoplegia, tissue edema, altered coagulation, and impaired microvascular perfusion. In practical terms, it helps explain why patients with apparently normal blood pressure or improved lactate can still be profoundly sick.

Recent canine data strengthen this concern. Rigot et al. found that serum hyaluronic acid, used as a surrogate marker of glycocalyx degradation, increased with illness severity in critically ill dogs and was associated with higher cumulative IV fluid volumes and IL-6 concentrations. That does not prove fluid therapy causes endothelial injury in every case, but it supports a growing concern that aggressive crystalloid loading is not biologically neutral.

Microcirculatory dysfunction and myocardial injury

Septic shock is also increasingly understood as a microcirculatory disease. Macro-hemodynamic improvement does not guarantee restored tissue-level perfusion. Vasoplegia, altered oxygen extraction, mitochondrial dysfunction, and sepsis-associated myocardial depression may all contribute to persistent shock or organ failure.

This is one reason simple resuscitation formulas often fail. A vasodilated dog with fluid-refractory hypotension and progressive organ dysfunction may not need more volume; it may need earlier vasoactive support, better source control, or both.

How Sepsis Is Diagnosed in Dogs and Cats Today

If there is one clinically relevant update in sepsis in dogs and cats, it is this: diagnosis now depends more on integrated assessment than on any isolated inflammatory threshold.

Infection plus clinical context

Sepsis should be suspected when infection is documented or strongly suspected and the patient shows evidence of systemic illness, hemodynamic instability, or organ dysfunction. That suspicion is then refined by serial reassessment, not by one-time categorization.

Important bedside components include:

• likely infectious source
• perfusion status
• mentation
• renal parameters and urine output
• coagulation changes
• acid-base status
• illness progression over the first hours of care

Organ dysfunction is prognostically useful, but not a standalone sepsis test

Ciuffoli et al. evaluated 275 dogs with systemic inflammation and found that new-onset organ dysfunction did not reliably distinguish septic from noninfectious inflammatory disease overall. That is an important caution against overinterpreting organ dysfunction as a cause-specific diagnostic marker.

However, the same study showed something equally important: the burden of organ dysfunction was strongly associated with outcome. Dogs with two or more organ dysfunctions had significantly higher mortality, and several specific abnormalities were linked to worse prognosis, including:

• acute kidney injury
• stupor or coma
• prolonged prothrombin time
• decreased base excess

In other words, organ dysfunction may be a poor discriminator of cause in some patients, but it remains a powerful indicator of severity.

Fluid-refractory hypotension deserves special attention

One of the most clinically useful findings from recent literature is that fluid-refractory hypotension was strongly associated with sepsis in dogs with systemic inflammation, with an odds ratio of 10.51 in the Ciuffoli study.

That does not make hypotension pathognomonic for infection. It does mean that persistent hypotension after reasonable initial resuscitation should heighten suspicion for septic shock and prompt aggressive reassessment of both perfusion strategy and source control.

Source-specific assessment still matters

A large proportion of veterinary sepsis is still encountered through source-defined diseases, including:

• septic peritonitis
• pyometra-associated sepsis
• severe pneumonia
• pyothorax
• biliary sepsis
• wound and soft tissue infection
• urosepsis

That matters because source affects diagnostics, timing, procedures, microbial risk, and prognosis. In septic peritonitis, for example, recent reviews emphasize prompt cytologic evaluation, awareness of blood-effusion glucose confounding with point-of-care glucometers, improving roles for ultrasound and CT, and rapid source control when indicated.

Biomarkers in Veterinary Sepsis: What Is Actually Useful?

Sepsis biomarkers in dogs and cats are gaining attention, but the literature still supports their use as adjuncts, not replacements for judgment.

Acute-phase proteins and inflammatory markers

C-reactive protein (CRP) in dogs and serum amyloid A (SAA) in cats remain clinically useful inflammatory markers, especially for trending response over time. They support recognition of systemic inflammation, but they are not specific enough to define sepsis on their own.

Other candidate markers include:

• procalcitonin
• inflammatory cytokines
• cell-free DNA
• nucleosomes
• NETosis-related markers
• endothelial injury markers such as hyaluronan

These tools may improve biologic characterization of critical illness, but none currently outperform integrated bedside assessment enough to replace it.

Neutrophil cell population data are promising

One interesting newer development is hematology analyzer-derived neutrophil cell population data (CPD). O’Toole et al. reported that NE-SFL outperformed total white blood cell count and band neutrophil count for identifying systemic inflammation in both dogs and cats, with AUCs of 0.82 in dogs and 0.77 in cats.

That does not make NE-SFL a sepsis test. It does suggest that analyzer-derived neutrophil signals may become useful adjunctive markers, particularly in settings where acute-phase proteins or expert smear review are not rapidly available.

Lactate still matters, but derivative ratios are less convincing

Lactate remains relevant because it reflects a mix of hypoperfusion, adrenergic stress, altered clearance, and overall illness severity. It is still worth following, especially serially. But recent veterinary evidence does not support overconfidence in derivative ratios.

Hunka et al. found that the lactate:albumin ratio was not predictive of mortality in septic dogs. That is a good reminder that derived biomarker formulas can look attractive conceptually but fail to deliver consistent clinical prognostic value.

The better approach is to use lactate as one part of a broader reassessment strategy rather than a stand-alone predictor.

Hemodynamic Support in Veterinary Septic Shock

Management of veterinary septic shock is changing most visibly in the area of hemodynamic support. The trend is clear: resuscitate early, but more carefully.

Early priorities in the first hours

The most defensible early priorities remain:

1. recognize infection and shock early
2. obtain cultures when feasible without dangerous delay
3. start appropriate antimicrobials promptly
4. achieve source control
5. restore perfusion while minimizing fluid excess
6. escalate to vasopressors when shock proves fluid-refractory or fluid overload risk is high

This is a meaningful departure from older large-volume fluids first habits.

Balanced crystalloids remain first-line, but fluid therapy is more conservative

Balanced crystalloids are still the default first-line resuscitation fluid in septic dogs and cats. What has changed is how they are given. Recent reviews increasingly favor fluid-responsiveness-guided resuscitation rather than large empiric volumes delivered by protocol alone.

Why the caution? Because indiscriminate volume loading can worsen:

• interstitial edema
• pulmonary dysfunction
• abdominal compartment effects
• dilutional coagulopathy
• endothelial glycocalyx injury

A practical modern approach is to give smaller boluses with repeated reassessment instead of committing early to large cumulative crystalloid volumes.

What to reassess after each fluid intervention

Useful reassessment domains include:

• mentation
• pulse quality
• mean arterial pressure
• lactate trend
• urine output
• venous or arterial blood gas trends
• focused ultrasound, where available

Clinicians should stop escalating crystalloids when:

• perfusion no longer improves
• hypotension appears predominantly vasoplegic
• edema or effusions worsen
• respiratory signs increase

That shift toward restraint is supported indirectly by glycocalyx-focused data in critically ill dogs, where larger cumulative fluid exposure was associated with higher hyaluronic acid concentrations.

Earlier norepinephrine use is increasingly supported

For septic shock with persistent hypotension after limited, reasonable fluid resuscitation, norepinephrine is increasingly viewed as the preferred first-line vasopressor. In small animals, this recommendation is based largely on expert consensus and human critical care extrapolation, but it aligns with contemporary veterinary review literature.

Clinically, earlier vasopressor use should be considered when:

• MAP remains inadequate after initial resuscitation
• the patient has a high risk of fluid overload
• ultrasound or clinical assessment suggests poor fluid responsiveness
• vasoplegia appears to dominate the shock picture

Evidence in cats is thinner than in dogs, so treatment remains more individualized.

Corticosteroids remain controversial

The role of corticosteroids in septic shock is still unsettled. Current veterinary reviews generally support considering them in fluid- and vasopressor-refractory shock, but this position relies primarily on human literature and expert opinion rather than robust small animal trials.

That means corticosteroids should be framed as a selective adjunct, not standard therapy for every septic patient.

Why Source Control Still Determines Survival

Even with better biomarkers and more nuanced hemodynamics, source control remains one of the strongest determinants of outcome.

This is especially true in septic peritonitis. Recent 2026 reviews in Veterinary Surgery reinforce that source control is often more decisive for survival than any isolated resuscitation maneuver. The message is familiar but important: no vasopressor, fluid plan, or biomarker trend can rescue a patient whose underlying source is still leaking, devitalized, or untreated.

Useful source-control principles include:

• do not delay definitive intervention unnecessarily
• use imaging strategically to define anatomy and complications
• interpret cytology quickly and in context
• remain alert to recurrent leakage, dehiscence, or missed infectious foci
• reassess antimicrobial appropriateness once cultures and clinical course evolve

For abdominal sepsis in particular, perioperative monitoring also includes attention to electrolytes. Debie et al. found that ionized calcium and magnesium disturbances were common in dogs and cats with septic peritonitis, though survival associations were inconsistent. These findings support monitoring rather than indiscriminate correction of every abnormality.

Outcome Prediction in Dogs and Cats With Sepsis

Outcome prediction in canine and feline sepsis remains imperfect. No single biomarker, ratio, or score reliably captures the complexity of disease trajectory.

Organ dysfunction burden is one of the strongest current signals

Among newer veterinary data, the clearest prognostic signal is the cumulative burden of organ dysfunction. In dogs with systemic inflammation, two or more organ dysfunctions were associated with mortality, and AKI, neurologic depression, prolonged PT, and decreased base excess were linked with poorer outcome.

This is clinically more useful than asking whether the patient meets sepsis in a binary sense. Severity appears to matter more than labeling.

Single biomarkers remain weak as standalone prognostic tools

Several promising markers have been explored, but recent data remain inconsistent:

• lactate:albumin ratio did not predict mortality in septic dogs
• hyaluronic acid tracked severity but not outcome directly in critically ill dogs
• electrolyte disturbances in septic peritonitis were common, but mortality associations were inconsistent

That does not make these tests useless. It means they are best interpreted as supporting data rather than final answers.

Serial reassessment beats one-time prognostication

The most defensible prognostic approach remains multivariable and serial. Clinicians should integrate:

• infectious source
• timing of antimicrobials
• adequacy of source control
• trend in perfusion markers
• progression or resolution of organ dysfunction
• ICU nursing intensity and monitoring capability

This is especially important because outcome data in conditions like septic peritonitis remain heterogeneous across institutions due to case mix, referral bias, and variation in available resources.

Emerging Research and Unresolved Controversies

Several themes are shaping where veterinary sepsis and septic shock management is heading next.

Redefining veterinary sepsis

The field is actively trying to move toward more modern definitions, but no consensus bedside standard has replaced older frameworks yet. This remains the foundational challenge for both clinical care and research design.

Glycocalyx injury and de-resuscitation thinking

The glycocalyx literature is pushing critical care away from reflexive volume expansion and toward cumulative fluid awareness, earlier vasopressors, and eventual de-resuscitation thinking once immediate shock goals are met.

Biomarker expansion without biomarker overreach

Neutrophil CPD, endothelial markers, procalcitonin, and NETosis-related markers are all promising. Still, current evidence does not justify replacing clinical synthesis with biomarker-led decision-making.

Microcirculation-guided care is appealing but immature

Microcirculatory dysfunction is clearly important biologically, but bedside strategies that reliably improve decisions in veterinary practice remain early-stage. Steblaj et al. showed in a canine endotoxemia model that dexmedetomidine did not improve microcirculation or reduce norepinephrine needs, underscoring how difficult it is to translate physiology into therapeutic wins.

Precision phenotypes and extracorporeal therapies are not ready for routine use

Human sepsis literature is moving toward subphenotypes, precision vasopressor strategies, and extracorporeal adjuncts. Veterinary medicine is not there yet. Reviews discussing phenotypes and blood purification are useful conceptually, but most practical application in dogs and cats remains extrapolated and investigational.

Disclosure: Portions of current veterinary septic shock practice, especially around vasopressor sequencing, corticosteroid use in refractory shock, phenotype-based care, and extracorporeal adjuncts, remain informed partly by human critical care literature because direct veterinary evidence is limited.

Key Clinical Takeaways for Practice

Recent evidence supports a more modern, practical approach to veterinary sepsis and septic shock:

• Do not rely on SIRS alone for recognition.
• Prioritize infection, organ dysfunction, shock phenotype, and illness trajectory.
• Treat organ dysfunction as an important severity and prognostic marker, even when it does not prove infection.
• Recognize fluid-refractory hypotension as an especially meaningful clue in suspected sepsis.
• Use biomarkers as adjuncts, not replacements for bedside judgment.
• Favor measured, response-guided crystalloid resuscitation over indiscriminate volume loading.
• Consider norepinephrine earlier in vasoplegic or fluid-intolerant shock states.
• Keep source control central, especially in septic abdomen cases.
• Avoid single-marker prognostic shortcuts; serial, multivariable assessment remains best.

For clinicians managing unstable dogs and cats, the biggest update is not one new test or one new drug. It is a change in mindset: sepsis is heterogeneous, dynamic, and best managed with individualized reassessment rather than formula-driven care alone.

FAQ

How is sepsis diagnosed in dogs and cats?

Sepsis in dogs and cats is diagnosed by integrating suspected or confirmed infection with evidence of systemic illness, organ dysfunction, shock, and clinical progression over time. Current literature supports moving beyond SIRS-only screening and toward whole-patient assessment, because no universally accepted veterinary Sepsis-3 equivalent yet exists.

What is the difference between sepsis and septic shock in veterinary patients?

Sepsis refers to life-threatening organ dysfunction caused by a dysregulated response to infection. Septic shock is a more severe subset in which circulatory failure persists despite initial resuscitation, often with hypotension, vasoplegia, abnormal perfusion, and a need for vasopressor support.

Are biomarkers reliable for diagnosing veterinary sepsis?

Biomarkers can support diagnosis and monitoring, but they are not definitive on their own. CRP, SAA, procalcitonin, neutrophil cell population data, lactate, and endothelial injury markers may add useful context, yet none should override clinical examination, source assessment, and serial reassessment.

What is new about fluid therapy in veterinary septic shock?

The major change is a move toward smaller, reassessed boluses and fluid-responsiveness-guided therapy rather than large empiric crystalloid loads. This reflects growing concern about edema, impaired gas exchange, dilutional effects, and possible endothelial glycocalyx injury from excessive cumulative fluids.

Is norepinephrine now first-line for septic shock in dogs and cats?

Norepinephrine is increasingly considered the preferred first-line vasopressor for fluid-refractory vasoplegic septic shock, especially in dogs. This practice is supported mainly by expert consensus and human extrapolation, but it aligns with current veterinary critical care review literature.

Which findings are most helpful for predicting outcome in veterinary sepsis?

Current evidence suggests that the burden of organ dysfunction is more useful than any single biomarker. Acute kidney injury, neurologic depression, prolonged PT, and worsened base excess have been associated with poorer outcomes, while isolated markers like lactate:albumin ratio have shown inconsistent prognostic value.