Optimal management of the critically ill: anaesthesia, monitoring, data capture, and point-of-care technological practices in ovine models of critical care

Recovery of organ-specific tissue oxygen delivery at restrictive transfusion thresholds after fluid treatment in ovine haemorrhagic shock

Background

Fluid resuscitation is the standard treatment to restore circulating blood volume and pressure after massive haemorrhage and shock. Packed red blood cells (PRBC) are transfused to restore haemoglobin levels. Restoration of microcirculatory flow and tissue oxygen delivery is critical for organ and patient survival, but these parameters are infrequently measured. Patient Blood Management is a multidisciplinary approach to manage and conserve a patient’s own blood, directing treatment options based on broad clinical assessment beyond haemoglobin alone, for which tissue perfusion and oxygenation could be useful. Our aim was to assess utility of non-invasive tissue-specific measures to compare PRBC transfusion with novel crystalloid treatments for haemorrhagic shock.

Methods

A model of severe haemorrhagic shock was developed in an intensive care setting, with controlled haemorrhage in sheep according to pressure (mean arterial pressure 30–40 mmHg) and oxygen debt (lactate > 4 mM) targets. We compared PRBC transfusion to fluid resuscitation with either PlasmaLyte or a novel crystalloid. Efficacy was assessed according to recovery of haemodynamic parameters and non-invasive measures of sublingual microcirculatory flow, regional tissue oxygen saturation, repayment of oxygen debt (arterial lactate), and a panel of inflammatory and organ function markers. Invasive measurements of tissue perfusion, oxygen tension and lactate levels were performed in brain, kidney, liver, and skeletal muscle. Outcomes were assessed during 4 h treatment and post-mortem, and analysed by one- and two-way ANOVA.

Results

Each treatment restored haemodynamic and tissue oxygen delivery parameters equivalently (p > 0.05), despite haemodilution after crystalloid infusion to haemoglobin concentrations below 70 g/L (p < 0.001). Recovery of vital organ-specific perfusion and oxygen tension commenced shortly before non-invasive measures improved. Lactate declined in all tissues and correlated with arterial lactate levels (p < 0.0001). The novel crystalloid supported rapid peripheral vasodilation (p = 0.014) and tended to achieve tissue oxygen delivery targets earlier. PRBC supported earlier renal oxygen delivery (p = 0.012) but delayed peripheral perfusion (p = 0.034).

Conclusions

Crystalloids supported vital organ oxygen delivery after massive haemorrhage, despite haemodilution to < 70 g/L, confirming that restrictive transfusion thresholds are appropriate to support oxygen delivery. Non-invasive tissue perfusion and oximetry technologies merit further clinical appraisal to guide treatment for massive haemorrhage in the context of Patient Blood Management.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-022-00439-6.

A clinically relevant sheep model of orthotopic heart transplantation 24 h after donor brainstem death

Background

Heart transplantation (HTx) from brainstem dead (BSD) donors is the gold-standard therapy for severe/end-stage cardiac disease, but is limited by a global donor heart shortage. Consequently, innovative solutions to increase donor heart availability and utilisation are rapidly expanding. Clinically relevant preclinical models are essential for evaluating interventions for human translation, yet few exist that accurately mimic all key HTx components, incorporating injuries beginning in the donor, through to the recipient. To enable future assessment of novel perfusion technologies in our research program, we thus aimed to develop a clinically relevant sheep model of HTx following 24 h of donor BSD.

Methods

BSD donors (vs. sham neurological injury, 4/group) were hemodynamically supported and monitored for 24 h, followed by heart preservation with cold static storage. Bicaval orthotopic HTx was performed in matched recipients, who were weaned from cardiopulmonary bypass (CPB), and monitored for 6 h. Donor and recipient blood were assayed for inflammatory and cardiac injury markers, and cardiac function was assessed using echocardiography. Repeated measurements between the two different groups during the study observation period were assessed by mixed ANOVA for repeated measures.

Results

Brainstem death caused an immediate catecholaminergic hemodynamic response (mean arterial pressure, p = 0.09), systemic inflammation (IL-6 - p = 0.025, IL-8 - p = 0.002) and cardiac injury (cardiac troponin I, p = 0.048), requiring vasopressor support (vasopressor dependency index, VDI, p = 0.023), with normalisation of biomarkers and physiology over 24 h. All hearts were weaned from CPB and monitored for 6 h post-HTx, except one (sham) recipient that died 2 h post-HTx. Hemodynamic (VDI - p = 0.592, heart rate - p = 0.747) and metabolic (blood lactate, p = 0.546) parameters post-HTx were comparable between groups, despite the observed physiological perturbations that occurred during donor BSD. All p values denote interaction among groups and time in the ANOVA for repeated measures.

Conclusions

We have successfully developed an ovine HTx model following 24 h of donor BSD. After 6 h of critical care management post-HTx, there were no differences between groups, despite evident hemodynamic perturbations, systemic inflammation, and cardiac injury observed during donor BSD. This preclinical model provides a platform for critical assessment of injury development pre- and post-HTx, and novel therapeutic evaluation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-021-00425-4.

An Ovine Model of Hemorrhagic Shock and Resuscitation, to Assess Recovery of Tissue Oxygen Delivery and Oxygen Debt, and Inform Patient Blood Management

BACKGROUND

Aggressive fluid or blood component transfusion for severe hemorrhagic shock may restore macrocirculatory parameters, but not always improve microcirculatory perfusion and tissue oxygen delivery. We established an ovine model of hemorrhagic shock to systematically assess tissue oxygen delivery and repayment of oxygen debt; appropriate outcomes to guide Patient Blood Management.

METHODS

Female Dorset-cross sheep were anesthetized, intubated, and subjected to comprehensive macrohemodynamic, regional tissue oxygen saturation (StO2), sublingual capillary imaging, and arterial lactate monitoring confirmed by invasive organ-specific microvascular perfusion, oxygen pressure, and lactate/pyruvate levels in brain, kidney, liver, and skeletal muscle. Shock was induced by stepwise withdrawal of venous blood until MAP was 30 mm Hg, mixed venous oxygen saturation (SvO2) < 60%, and arterial lactate >4 mM. Resuscitation with PlasmaLyte® was dosed to achieve MAP > 65 mm Hg.

RESULTS

Hemorrhage impacted primary outcomes between baseline and development of shock: MAP 89 ± 5 to 31 ± 5 mm Hg (P < 0.01), SvO2 70 ± 7 to 23 ± 8% (P < 0.05), cerebral regional tissue StO2 77 ± 11 to 65 ± 9% (P < 0.01), peripheral muscle StO2 66 ± 8 to 16 ± 9% (P < 0.01), arterial lactate 1.5 ± 1.0 to 5.1 ± 0.8 mM (P < 0.01), and base excess 1.1 ± 2.2 to -3.6 ± 1.7 mM (P < 0.05). Invasive organ-specific monitoring confirmed reduced tissue oxygen delivery; oxygen tension decreased and lactate increased in all tissues, but moderately in brain. Blood volume replacement with PlasmaLyte® improved primary outcome measures toward baseline, confirmed by organ-specific measures, despite hemoglobin reduced from baseline 10.8 ± 1.2 to 5.9 ± 1.1 g/dL post-resuscitation (P < 0.01).

CONCLUSION

Non-invasive measures of tissue oxygen delivery and oxygen debt repayment are suitable outcomes to inform Patient Blood Management of hemorrhagic shock, translatable for pre-clinical assessment of novel resuscitation strategies.

Brain stem death induces pro-inflammatory cytokine production and cardiac dysfunction in sheep model

Introduction

Organs procured following brain stem death (BSD) are the main source of organ grafts for transplantation. However, BSD is associated with inflammatory responses that may damage the organ and affect both the quantity and quality of organs available for transplant. Therefore, we aimed to investigate plasma and bronchoalveolar lavage (BAL) pro-inflammatory cytokine profiles and cardiovascular physiology in a clinically relevant 6-h ovine model of BSD.

Methods

Twelve healthy female sheep (37–42 Kg) were anaesthetized and mechanically ventilated prior to undergoing BSD induction and then monitored for 6 h. Plasma and BAL endothelin-1 and cytokines (IL-1β, 6, 8 and tumour necrosis factor alpha (TNF-α)) were assessed by ELISA. Differential white blood cell counts were performed. Cardiac function during BSD was also examined using echocardiography, and cardiac biomarkers (A-type natriuretic peptide and troponin I were measured in plasma.

Results

Plasma concentrations big ET-1, IL-6, IL-8, TNF-α and BAL IL-8 were significantly (p < 0.01) increased over baseline at 6 h post-BSD. Increased numbers of neutrophils were observed in the whole blood (3.1 × 10⁹ cells/L [95% confidence interval (CI) 2.06–4.14] vs. 6 × 10⁹ cells/L [95%CI 3.92–7.97]; p < 0.01) and BAL (4.5 × 10⁹ cells/L [95%CI 0.41–9.41] vs. 26 [95%CI 12.29–39.80]; p = 0.03) after 6 h of BSD induction vs baseline. A significant increase in ANP production (20.28 pM [95%CI 16.18–24.37] vs. 78.68 pM [95%CI 53.16–104.21]; p < 0.0001) and cTnI release (0.039 ng/mL vs. 4.26 [95%CI 2.69–5.83] ng/mL; p < 0.0001), associated with a significant reduction in heart contractile function, were observed between baseline and 6 h.

Conclusions

BSD induced systemic pro-inflammatory responses, characterized by increased neutrophil infiltration and cytokine production in the circulation and BAL fluid, and associated with reduced heart contractile function in ovine model of BSD.

Endothelin receptor antagonist improves donor lung function in an ex vivo perfusion system

BACKGROUND

A lung transplant is the last resort treatment for many patients with advanced lung disease. The majority of donated lungs come from donors following brain death (BD). The endothelin axis is upregulated in the blood and lung of the donor after BD resulting in systemic inflammation, lung damage and poor lung graft outcomes in the recipient. Tezosentan (endothelin receptor blocker) improves the pulmonary haemodynamic profile; however, it induces adverse effects on other organs at high doses. Application of ex vivo lung perfusion (EVLP) allows the development of organ-specific hormone resuscitation, to maximise and optimise the donor pool. Therefore, we investigate whether the combination of EVLP and tezosentan administration could improve the quality of donor lungs in a clinically relevant 6-h ovine model of brain stem death (BSD).

METHODS

After 6 h of BSD, lungs obtained from 12 sheep were divided into two groups, control and tezosentan-treated group, and cannulated for EVLP. The lungs were monitored for 6 h and lung perfusate and tissue samples were processed and analysed. Blood gas variables were measured in perfusate samples as well as total proteins and pro-inflammatory biomarkers, IL-6 and IL-8. Lung tissues were collected at the end of EVLP experiments for histology analysis and wet-dry weight ratio (a measure of oedema).

RESULTS

Our results showed a significant improvement in gas exchange [elevated partial pressure of oxygen (P = 0.02) and reduced partial pressure of carbon dioxide (P = 0.03)] in tezosentan-treated lungs compared to controls. However, the lungs hematoxylin-eosin staining histology results showed minimum lung injuries and there was no difference between both control and tezosentan-treated lungs. Similarly, IL-6 and IL-8 levels in lung perfusate showed no difference between control and tezosentan-treated lungs throughout the EVLP. Histological and tissue analysis showed a non-significant reduction in wet/dry weight ratio in tezosentan-treated lung tissues (P = 0.09) when compared to control.

CONCLUSIONS

These data indicate that administration of tezosentan could improve pulmonary gas exchange during EVLP.

Development and validation of ELISAs for the quantitation of interleukin (IL)-1β, IL-6, IL-8 and IL-10 in ovine plasma

There is growing evidence that inflammation underpins many common diseases. Inflammatory/immunomodulatory/immune mediators, such as cytokines, are key modulators of inflammation and mediate both immune cell recruitment and complex intracellular signalling pathways. Ovine models of disease are increasingly utilized in pre-clinical research, however existing methods for measuring cytokine levels are limited. We established and validated enzyme-linked immunosorbent assays (ELISAs) targeting interleukin (IL)-1β, IL-6, IL-8 and IL-10 in sheep plasma. These ELISAs showed high sensitivity and specificity with intra- and inter-assay CV's below 10%, and recovery rates between 82 and 123%. Sensitivity for IL-1β, IL-6, IL-8 and IL-10 were 117.6 pg/mL, 443.1 pg/mL, 30.9 pg/mL, and 64.3 pg/mL, respectively. ELISA test result reproducibility decreased significantly after 12 weeks of plasma storage at -80 °C. Therefore, for accurate cytokine measurements, plasma samples need to be tested within three months of sample collection to account for cytokine protein degradation. These ELISAs offer a reliable and convenient method to identify inflammatory cytokine changes in sheep, allowing key insights into the disease pathogenesis of these ruminants.

Cardiorespiratory physiological perturbations after acute smoke-induced lung injury and during extracorporeal membrane oxygenation support in sheep

Background: Numerous successful therapies developed for human medicine involve animal experimentation. Animal studies that are focused solely on translational potential, may not sufficiently document unexpected outcomes. Considerable amounts of data from such studies could be used to advance veterinary science. For example, sheep are increasingly being used as models of intensive care and therefore, data arising from such models must be published. In this study, the hypothesis is that there is little information describing cardiorespiratory physiological data from sheep models of intensive care and the author aimed to analyse such data to provide biological information that is currently not available for sheep that received extracorporeal life support (ECLS) following acute smoke-induced lung injury. Methods: Nineteen mechanically ventilated adult ewes undergoing intensive care during evaluation of a form of ECLS (treatment) for acute lung injury were used to collate clinical observations. Eight sheep were injured by acute smoke inhalation prior to treatment (injured/treated), while another eight were not injured but treated (uninjured/treated). Two sheep were injured but not treated (injured/untreated), while one received room air instead of smoke as the injury and was not treated (placebo/untreated). The data were then analysed for 11 physiological categories and compared between the two treated groups. Results: Compared with the baseline, treatment contributed to and exacerbated the deterioration of pulmonary pathology by reducing lung compliance and the arterial oxygen partial pressure to fractional inspired oxygen (PaO 2/FiO 2) ratio. The oxygen extraction index changes mirrored those of the PaO 2/FiO 2 ratio. Decreasing coronary perfusion pressure predicted the severity of cardiopulmonary injury. Conclusions: These novel observations could help in understanding similar pathology such as that which occurs in animal victims of smoke inhalation from house or bush fires, aspiration pneumonia secondary to tick paralysis and in the management of the severe coronavirus disease 2019 (COVID-19) in humans.

Preclinical septic shock research: why we need an animal ICU

Animal experiments are widely used in preclinical medical research with the goal of disease modeling and exploration of novel therapeutic approaches. In the context of sepsis and septic shock, the translation into clinical practice has been disappointing. Classical animal models of septic shock usually involve one-sex-one-age animal models, mostly in mice or rats, contrasting with the heterogeneous population of septic shock patients. Many other factors limit the reliability of preclinical models and may contribute to preclinical research failure in critical care, including the host specificity of several pathogens, the fact that laboratory animals are raised in pathogen-free facilities and that organ support techniques are either absent or minimal. Advanced animal models have been developed with the aim of improving the clinical translatability of experimental findings. So-called animal ICUs refer to the preclinical investigation of adult or even aged animals of either sex, using—in case of rats and mice—miniaturized equipment allowing for reproducing an ICU environment at a small animal scale and integrating chronic comorbidities to more closely reflect the clinical conditions studied. Strength and limitations of preclinical animal models designed to decipher the mechanisms involved in septic cardiomyopathy are discussed. This article reviews the current status and the challenges of setting up an animal ICU.

Perspectives on adjunctive use of ketamine for analgosedation during extracorporeal membrane oxygenation

Analgosedation on ECMO is more than the choice of any drug, it has to be context specific. Ketamine may be considered as an adjunctive therapy in patients requiring high-dose opioids and sedatives during ECMO support with difficulty to achieve a target RASS. Considering ketamine provides analgesia while maintaining airway reflexes, it could be useful for early ECMO weaning and use of ECMO in awake, non-intubated, spontaneously breathing patients with respiratory failure ('awake' ECMO), especially for patients having considerable waiting periods while being bridged to transplant. The hemodynamic effects of ketamine may provide the benefit of decreasing vasopressor requirements, thereby potentially improving microcirculation. In this context, the effects on end-organ function and the need for renal replacement therapy should be investigated. Pharmacokinetic and pharmacodynamic studies on ketamine ex- and in vivo are of utmost importance to delineate its pharmacological profile and effectiveness during ECMO therapy and to create admissible future study hypothesis.

Improving pregnancy outcomes in humans through studies in sheep

Experimental studies that are relevant to human pregnancy rely on the selection of appropriate animal models as an important element in experimental design. Consideration of the strengths and weaknesses of any animal model of human disease is fundamental to effective and meaningful translation of preclinical research. Studies in sheep have made significant contributions to our understanding of the normal and abnormal development of the fetus. As a model of human pregnancy, studies in sheep have enabled scientists and clinicians to answer questions about the etiology and treatment of poor maternal, placental, and fetal health and to provide an evidence base for translation of interventions to the clinic. The aim of this review is to highlight the advances in perinatal human medicine that have been achieved following translation of research using the pregnant sheep and fetus.

Lymphatic cannulation models in sheep: Recent advances for immunological and biomedical research

Lymphatic cannulation models are useful tools for studying the immunobiology of the lymphatic system and the immunopathology of specific tissues in diseases. Sheep cannulations have been used extensively, as models for human physiology, fetal and neonatal development, human diseases, and for studies of ruminant pathobiology. The development of new and improved cannulation techniques in recent years has meant that difficult to access sites, such as mucosal associated tissues, are now more readily available to researchers. This review highlights the new approaches to cannulation and how these, in combination with advanced omics technologies, will direct future research using the sheep model.

An Ovine Model of Hyperdynamic Endotoxemia and Vital Organ Metabolism

BACKGROUND

Animal models of endotoxemia are frequently used to understand the pathophysiology of sepsis and test new therapies. However, important differences exist between commonly used experimental models of endotoxemia and clinical sepsis. Animal models of endotoxemia frequently produce hypodynamic shock in contrast to clinical hyperdynamic shock. This difference may exaggerate the importance of hypoperfusion as a causative factor in organ dysfunction. This study sought to develop an ovine model of hyperdynamic endotoxemia and assess if there is evidence of impaired oxidative metabolism in the vital organs.

METHODS

Eight sheep had microdialysis catheters implanted into the brain, heart, liver, kidney, and arterial circulation. Shock was induced with a 4 h escalating dose infusion of endotoxin. After 3 h vasopressor support was initiated with noradrenaline and vasopressin. Animals were monitored for 12 h after endotoxemia. Blood samples were recovered for hemoglobin, white blood cell count, creatinine, and proinflammatory cytokines (IL-1Beta, IL-6, and IL-8).

RESULTS

The endotoxin infusion was successful in producing distributive shock with the mean arterial pressure decreasing from 84.5 ± 12.8 mm Hg to 49 ± 8.03 mm Hg (P < 0.001). Cardiac index remained within the normal range decreasing from 3.33 ± 0.56 L/min/m to 2.89l ± 0.36 L/min/m (P = 0.0845). Lactate/pyruvate ratios were not significantly abnormal in the heart, brain, kidney, or arterial circulation. Liver microdialysis samples demonstrated persistently high lactate/pyruvate ratios (mean 37.9 ± 3.3).

CONCLUSIONS

An escalating dose endotoxin infusion was successful in producing hyperdynamic shock. There was evidence of impaired oxidative metabolism in the liver suggesting impaired splanchnic perfusion. This may be a modifiable factor in the progression to multiple organ dysfunction and death.

Characterisation of the circulating acellular proteome of healthy sheep using LC-MS/MS-based proteomics analysis of serum

BACKGROUND

Unlike humans, there is currently no publicly available reference mass spectrometry-based circulating acellular proteome data for sheep, limiting the analysis and interpretation of a range of physiological changes and disease states. The objective of this study was to develop a robust and comprehensive method to characterise the circulating acellular proteome in ovine serum.

METHODS

Serum samples from healthy sheep were subjected to shotgun proteomic analysis using nano liquid chromatography nano electrospray ionisation tandem mass spectrometry (nanoLC-nanoESI-MS/MS) on a quadrupole time-of-flight instrument (TripleTOF® 5600+, SCIEX). Proteins were identified using ProteinPilot™ (SCIEX) and Mascot (Matrix Science) software based on a minimum of two unmodified highly scoring unique peptides per protein at a false discovery rate (FDR) of 1% software by searching a subset of the Universal Protein Resource Knowledgebase (UniProtKB) database (http://www.uniprot.org). PeptideShaker (CompOmics, VIB-UGent) searches were used to validate protein identifications from ProteinPilot™ and Mascot.

RESULTS

ProteinPilot™ and Mascot identified 245 and 379 protein groups (IDs), respectively, and PeptideShaker validated 133 protein IDs from the entire dataset. Since Mascot software is considered the industry standard and identified the most proteins, these were analysed using the Protein ANalysis THrough Evolutionary Relationships (PANTHER) classification tool revealing the association of 349 genes with 127 protein pathway hits. These data are available via ProteomeXchange with identifier PXD004989.

CONCLUSIONS

These results demonstrated for the first time the feasibility of characterising the ovine circulating acellular proteome using nanoLC-nanoESI-MS/MS. This peptide spectral data contributes to a protein library that can be used to identify a wide range of proteins in ovine serum.

Porcine pulmonary auto-transplantation for ex vivo therapy as a model for new treatment strategies

OBJECTIVES

Lung auto-transplantation is the surgical key step in experiments involving ex vivo therapy of severe or end-stage lung diseases. Ex vivo therapy has become a clinical reality because of systems such as the Organ Care System (OCS) Lung, which is the only commercially available portable lung perfusion system. However, survival experiments involving porcine lung auto-transplantation pose special surgical and anaesthesiological challenges. This current study was designed to describe the development of surgical techniques and aneasthesiological management strategies that facilitate lung auto-transplantation survival surgery including a follow-up period of 4 days.

METHODS

Left pneumonectomy was performed in 12 Mini-Lewe miniature pigs. After ex vivo treatment of the harvested lungs within the OCS Lung for 2 h, the lungs were retransplanted into the same animal (auto-transplantation). Four animals were used to develop the optimal techniques and establish an experimental protocol. According to the final protocol, eight additional animals were operated. The follow-up period was 4 days.

RESULTS

There were four severe intraoperative surgical complications [anatomical variant of the superior vena cava (two times), a complication related to the bronchial anastomosis and a complication related to the pulmonary arterial anastomosis]. The major postoperative problems were hyperkalaemia, prolonged recovery from anaesthesia and pulmonary oedema after reperfusion. Establishment of the surgical technique showed that using a pericardial tube to facilitate the anastomosis of the thin left superior pulmonary vein should be considered to prevent thrombosis. However, routine use of the patch technique to construct venous and arterial anastomoses is not necessary. Furthermore, traction on the venous anastomoses can be avoided by performing the bronchial anastomosis first.

CONCLUSIONS

Lung auto-transplantation is a feasible experimental model for ex vivo therapy of lung diseases and is applicable for experimental questions concerning human lung transplantation.

The Complex Relationship of Extracorporeal Membrane Oxygenation and Acute Kidney Injury: Causation or Association?

Extracorporeal membrane oxygenation (ECMO) is a modified cardiopulmonary bypass (CPB) circuit capable of providing prolonged cardiorespiratory support. Recent advancement in ECMO technology has resulted in increased utilisation and clinical application. It can be used as a bridge-to-recovery, bridge-to-bridge, bridge-to-transplant, or bridge-to-decision. ECMO can restitute physiology in critically ill patients, which may minimise the risk of progressive multiorgan dysfunction. Alternatively, iatrogenic complications of ECMO clearly contribute to worse outcomes. These factors affect the risk : benefit ratio of ECMO which ultimately influence commencement/timing of ECMO. The complex interplay of pre-ECMO, ECMO, and post-ECMO pathophysiological processes are responsible for the substantial increased incidence of ECMO-associated acute kidney injury (EAKI). The development of EAKI significantly contributes to morbidity and mortality; however, there is a lack of evidence defining a potential benefit or causative link between ECMO and AKI. This area warrants investigation as further research will delineate the mechanisms involved and subsequent strategies to minimise the risk of EAKI. This review summarizes the current literature of ECMO and AKI, considers the possible benefits and risks of ECMO on renal function, outlines the related pathophysiology, highlights relevant investigative tools, and ultimately suggests an approach for future research into this under investigated area of critical care.

Proteogenomics of selective susceptibility to endotoxin using circulating acute phase biomarkers and bioassay development in sheep: a review

Scientists have injected endotoxin into animals to investigate and understand various pathologies and novel therapies for several decades. Recent observations have shown that there is selective susceptibility to Escherichia coli lipopolysaccharide (LPS) endotoxin in sheep, despite having similar breed characteristics. The reason behind this difference is unknown, and has prompted studies aiming to explain the variation by proteogenomic characterisation of circulating acute phase biomarkers. It is hypothesised that genetic trait, biochemical, immunological and inflammation marker patterns contribute in defining and predicting mammalian response to LPS. This review discusses the effects of endotoxin and host responses, genetic basis of innate defences, activation of the acute phase response (APR) following experimental LPS challenge, and the current approaches employed in detecting novel biomarkers including acute phase proteins (APP) and micro-ribonucleic acids (miRNAs) in serum or plasma. miRNAs are novel targets for elucidating molecular mechanisms of disease because of their differential expression during pathological, and in healthy states. Changes in miRNA profiles during a disease challenge may be reflected in plasma. Studies show that gel-based two-dimensional electrophoresis (2-DE) coupled with either matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) or liquid chromatography–mass spectrometry (LC-MS/MS) are currently the most used methods for proteome characterisation. Further evidence suggests that proteomic investigations are preferentially shifting from 2-DE to non-gel based LC-MS/MS coupled with data extraction by sequential window acquisition of all theoretical fragment-ion spectra (SWATH) approaches that are able to identify a wider range of proteins. Enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qRT-PCR), and most recently proteomic methods have been used to quantify low abundance proteins such as cytokines. qRT-PCR and next generation sequencing (NGS) are used for the characterisation of miRNA. Proteogenomic approaches for detecting APP and novel miRNA profiling are essential in understanding the selective resistance to endotoxin in sheep. The results of these methods could help in understanding similar pathology in humans. It might also be helpful in the development of physiological and diagnostic screening assays for determining experimental inclusion and endpoints, and in clinical trials in future.