Gabriela Simonova

Optimal Management of the Critically Ill: Anaesthesia, Monitoring, Data Capture, and Point-of-Care Technological Practices in Ovine Models of Critical Care

Animal models of critical illness are vital in biomedical research. They provide possibilities for the investigation of pathophysiological processes that may not otherwise be possible in humans. In order to be clinically applicable, the model should simulate the critical care situation realistically, including anaesthesia, monitoring, sampling, utilising appropriate personnel skill mix, and therapeutic interventions. There are limited data documenting the constitution of ideal technologically advanced large animal critical care practices and all the processes of the animal model. In this paper, we describe the procedure of animal preparation, anaesthesia induction and maintenance, physiologic monitoring, data capture, point-of-care technology, and animal aftercare that has been successfully used to study several novel ovine models of critical illness. The relevant investigations are on respiratory failure due to smoke inhalation, transfusion related acute lung injury, endotoxin-induced proteogenomic alterations, haemorrhagic shock, septic shock, brain death, cerebral microcirculation, and artificial heart studies. We have demonstrated the functionality of monitoring practices during anaesthesia required to provide a platform for undertaking systematic investigations in complex ovine models of critical illness.

ECMO – the clinician’s view

Background  Extra corporeal membrane oxygenation (ECMO) is a complex rescue therapy used to provide cardiac and/or respiratory support for critically ill patients who have failed maximal conventional medical management. ECMO is based on a modified cardiopulmonary bypass (CPB) circuit, and can provide cardiopulmonary support for up‐to several months. It can be used in a veno venous configuration for isolated respiratory failure, (VV‐ECMO), or in a veno arterial configuration (VA‐ECMO) where support is necessary for cardiac +/‐ respiratory failure. The ECMO circuit consists of five main components: large bore cannulae (access cannulae) for drainage of the venous system, and return cannulae to either the venous ( in VV‐ECMO) or arterial (in VA ECMO) system. An oxygenator, with a vast surface area of hollow filaments, allows addition of oxygen and removal of carbon dioxide; a centrifugal blood pump allows propulsion of blood through the circuit at upto 10 L/minute; a control module and a thermoregulatory unit, which allows for exact temperature control of the extra corporeal blood.

A comprehensive study of ovine haemostasis to assess suitability to model human coagulation

INTRODUCTION Similarities in size, anatomy and physiology have supported the use of sheep to model a wide range of human diseases, including coagulopathy. However, coagulation studies involving sheep are limited by the absence of high quality data defining normal ovine coagulation and fibrinolysis. MATERIALS AND METHODS Full blood examination, routine and specialised coagulation tests, rotational thromboelastometry and whole blood platelet aggregometry was performed on 50 healthy Samm & Border Leicester Cross ewes and compared to corresponding human ranges. Intraspecies breed and gender variability was investigated by comparison to a smaller population of 13 healthy Merino wethers. RESULTS Ovine coagulation was similar to human according to routine coagulation methods (PT, aPTT, TCT, Fib(C)) and some specialised coagulation tests (vWF, AT, Plasmin Inh). Despite these similarities, ovine secondary haemostasis demonstrated substantial differences to that of human. Rapid initiation of the contact activation pathway, high levels of FVIII, low Protein C, greater overall clot firmness and a reduced capacity for clot lysis was documented in sheep. In addition, ADP and collagen agonists precipitated a reduced primary haemostatic response in sheep relative to human. Intraspecies differences in whole blood platelet aggregometry between the cohorts of sheep indicate the need for breed-specific normal ranges. CONCLUSIONS The application of a board spectrum of coagulation assays has enabled elucidation of the similarities as well as differences between ovine and human coagulation. The new knowledge generated from this study will guide the design of future translational coagulation studies in ovine models.

The impact of acute lung injury, ECMO and transfusion on oxidative stress and plasma selenium levels in an ovine model

The purpose of this study was to determine the effects of smoke induced acute lung injury (S-ALI), extracorporeal membrane oxygenation (ECMO) and transfusion on oxidative stress and plasma selenium levels. Forty ewes were divided into (i) healthy control (n=4), (ii) S-ALI control (n=7), (iii) ECMO control (n=7), (iv) S-ALI+ECMO (n=8) and (v) S-ALI+ECMO+packed red blood cell (PRBC) transfusion (n=14). Plasma thiobarbituric acid reactive substances (TBARS), selenium and glutathione peroxidase (GPx) activity were analysed at baseline, after smoke injury (or sham) and 0.25, 1, 2, 6, 7, 12 and 24h after initiation of ECMO. Peak TBARS levels were similar across all groups. Plasma selenium decreased by 54% in S-ALI sheep (1.36±0.20 to 0.63±0.27μmol/L, p<0.0001), and 72% in sheep with S-ALI+ECMO at 24h (1.36±0.20 to 0.38±0.19, p<0.0001). PRBC transfusion had no effect on TBARS, selenium levels or glutathione peroxidase activity in plasma. While ECMO independently increased TBARS in healthy sheep to levels which were similar to the S-ALI control, the addition of ECMO after S-ALI caused a negligible increase in TBARS. This suggests that the initial lung injury was the predominant feature in the TBARS response. In contrast, the addition of ECMO in S-ALI sheep exacerbated reductions in plasma selenium beyond that of S-ALI or ECMO alone. Clinical studies are needed to confirm the extent and duration of selenium loss associated with ECMO.

Lessons from sheep models of transfusion

Animal models have been a valuable tool for research into blood products and outcomes of blood transfusions. Small animal models have been applied extensively and large animal models less frequently. This review describes the experience and details the findings from a recent series of in vivo sheep transfusion models.

Extracoproreal membrane oxygenation (ECMO) has more profound influence on ciprofloxacin pharmacokinetics in critically ill sheep when compared with healthy sheep

Background / Purpose: Extracoproreal membrane oxygenation (ECMO) is a life saving supportive tool for patients with severe cardiorespiratory failure. However ECMO has a significant impact on pharamcokinetics(PK) of vital drugs that are intended to reverse the pathology which will then result in liberation from ECMO. This mechanistic study aimed to relatively quantify the independent effects of the ECMO device on ciporfloxacin PK.Main conclusion: Critical illness has a major influence on ciprofloxacin PK during ECMO support and the independent effects of ECMO device may not be significant.; ;

Red cell and albumin resuscitation following acute massive haemorrhage alters haemostasis

Background: Dengue is not endemic in Australia; rather in North Queensland, outbreaks occur seasonally. One of the largest epidemics in the last 50 years took place in 2008/2009, affecting a significant geographical area of North Queensland, with separate outbreaks in Cairns (and surrounding regions; DENV-2,3,4 08–09) and Townsville (DENV-1,3 09). Collectively, in these outbreaks there were more than 1000 confirmed clinical cases, with the majority of cases occurring in the Cairns region. Given the absence of an approved screening test, the strategy utilised by the Australian Red Cross Blood Service (Blood Service) for managing the risk of transfusion-transmitted dengue was exclusion of at risk donors. During this epidemic, supplementary questioning for all donors was implemented to determine exposure risk, and fresh components were not manufactured from at risk donors. Aims: This study aimed to estimate dengue fever viral exposure rates among Australian blood donors during this large epidemic. Methods: Samples were collected from blood donors during the 2008/2009 epidemic and 3 months after the last confirmed cased. Selected samples were tested for the presence of the dengue NS1 antigen with commercially available ELISA-based assay kits from PanBio. Results: Nineteen of 1020 donations collected in Cairns during the epidemic and selected for testing showed repeat reactivity towards the NS1 antigen, and one of 67 donations collected in Townsville during the epidemic and selected for testing showed repeat reactivity towards the NS1 antigen. Viral RNA was not detected in any of these NS1 reactive donations. Summary/conclusions: This study suggests recent dengue exposure in a self-declared asymptomatic population, and provides an understanding of the rate and dynamics of asymptomatic dengue infection in North Queensland during these recent outbreaks. Discordant results between NS1 and viral RNA detection needs further evaluation. Collectively, this study justifies the use of DENV management strategy during a DENV outbreak in north Queensland.