A comprehensive ovine model of blood transfusion.

BACKGROUND: The growing awareness of transfusion-associated morbidity and mortality necessitates investigations into the underlying mechanisms. Small animals have been the dominant transfusion model but have associated limitations. This study aimed to develop a comprehensive large animal (ovine) model of transfusion encompassing: blood collection, processing and storage, compatibility testing right through to post-transfusion outcomes. MATERIALS AND METHODS: Two units of blood were collected from each of 12 adult male Merino sheep and processed into 24 ovine-packed red blood cell (PRBC) units. Baseline haematological parameters of ovine blood and PRBC cells were analysed. Biochemical changes in ovine PRBCs were characterized during the 42-day storage period. Immunological compatibility of the blood was confirmed with sera from potential recipient sheep, using a saline and albumin agglutination cross-match. Following confirmation of compatibility, each recipient sheep (n = 12) was transfused with two units of ovine PRBC. RESULTS: Procedures for collecting, processing, cross-matching and transfusing ovine blood were established. Although ovine red blood cells are smaller and higher in number, their mean cell haemoglobin concentration is similar to human red blood cells. Ovine PRBC showed improved storage properties in saline-adenine-glucose-mannitol (SAG-M) compared with previous human PRBC studies. Seventy-six compatibility tests were performed and 17·1% were incompatible. Only cross-match compatible ovine PRBC were transfused and no adverse reactions were observed. CONCLUSION: These findings demonstrate the utility of the ovine model for future blood transfusion studies and highlight the importance of compatibility testing in animal models involving homologous transfusions.

Stored blood transfusion induces transient pulmonary arterial hypertension without impairing coagulation in an ovine model of nontraumatic haemorrhage.

BACKGROUND AND OBJECTIVES: Transfusion of blood products in particular older products is associated with patient morbidity. Previously, we demonstrated a higher incidence of acute lung injury in lipopolysaccharide-treated sheep transfused with stored blood products. As transfusion following haemorrhage is more common, we aimed to determine whether a 'first hit' of isolated haemorrhage would precipitate similar detrimental effects following transfusion and also disrupt haemostasis. MATERIALS AND METHODS: Anaesthetized sheep had 33% of their total blood volume collected into Leukotrap bags (Pall Medical), which were processed into packed red blood cells and cross-matched for transfusion into other sheep. After 30 mins, the sheep were resuscitated with either: fresh (<5 days old) or stored (35-42 days old) ovine blood followed by 4% albumin to replacement volume, albumin alone or normal saline alone and monitored for 4 h. RESULTS: The first hit of haemorrhage precipitated substantial decreases in mean arterial pressure however haemostasis was preserved. Transfusion of stored ovine blood induced (1) transient pulmonary arterial hypertension but no oedema and (2) reduced fibrinogen levels more than fresh blood, but neither induced coagulopathy. Thus, transfusion of stored blood affected pulmonary function even in the absence of overt organ injury. CONCLUSION: The fact that stored blood transfusions: (1) did not induce acute lung injury in contrast to previous lipopolysaccharide-primed animal models identifies the 'first hit' as an important determinant of the severity of transfusion-mediated injury; (2) impaired pulmonary dynamics verifies the sensitivity and vulnerability of the pulmonary system to injury.

A novel in vivo ovine model of transfusion-related acute lung injury (TRALI).

BACKGROUND AND OBJECTIVES: Even with the introduction of specific risk-reduction strategies, transfusion-related acute lung injury (TRALI) continues to be a leading cause of transfusion-related morbidity and mortality. Existing small animal models have not yet investigated TRALI resulting from the infusion of heat-treated supernatant from whole blood platelet concentrates. In this study, our objective was the development of a novel in vivo two-event model of TRALI in sheep. MATERIALS AND METHODS: Lipopolysaccharide (LPS; 15 µg/kg) as a first event, modelled clinical infection. Transfusion (estimated at 10% of total blood volume) of heat-treated pooled supernatant from date-of-expire human whole blood platelet concentrates (d5-PLT-S/N) was used as a second event. TRALI was defined by both hypoxaemia that developed either during the transfusion or within two hours of its completion and post-mortem histological evidence of pulmonary oedema. RESULTS: LPS infusion did not cause lung injury itself, but did result in decreased circulating levels of lymphocytes and neutrophils with evidence of the latter becoming sequestered in the lungs. Sheep that received LPS (first event) followed by d5-PLT-S/N (second event) displayed decreased pulmonary compliance, decreased end tidal CO(2) and increased arterial partial pressure of CO(2) relative to control sheep, and 80% of these sheep developed TRALI. CONCLUSIONS: This novel ovine two-event TRALI model presents a new tool for the investigation of TRALI pathogenesis. It represents the first description of an in vivo large animal model of TRALI and the first description of TRALI caused by transfusion with heat-treated pooled supernatant from human whole blood platelet concentrates.

The practical use of methotrexate in psoriasis.

Psoriasis is an inflammatory disease of the skin associated with increased epidermal proliferation. The aetiology of the disease is unknown, but there seems to be a genetic predisposition. The goal of therapy in the treatment of psoriasis is to decrease the rate of epidermal proliferation and the underlying inflammation. Topical application of steroids and coal tar are the therapies of choice; however, for those patients with severe recalcitrant psoriasis who have failed conventional topical therapy methotrexate is an established alternative. The use of methotrexate in psoriasis is limited by its toxicity, and proper patient selection and close monitoring are essential in achieving good clinical response. The dosage used should be the lowest that will maintain the patient in comfort, not necessarily that which produces total resolution. Caution should be exercised when other agents are used concurrently with methotrexate, and possible drug interactions should be identified as these may influence the effectiveness and toxicity of methotrexate therapy. The common side effects associated with the use of methotrexate in psoriasis include bone marrow suppression, gastrointestinal symptoms and hepatotoxicity. Liver damage is a major concern in long term methotrexate therapy and thus liver biopsies are warranted to monitor any pathological changes. The drug is a known teratogen and should be avoided in pregnant patients. Women of childbearing age should use reliable contraception during therapy. Patients should be made aware of the signs and symptoms of methotrexate toxicity and inform their physicians promptly as most adverse effects can be ameliorated with appropriate dosage adjustment. Methotrexate will continue to play a major role in the treatment of psoriasis and it is thus important that it be used safely.