Blood transfusions, fluid therapy, SIRS. Ch 2-4

Question 1

Clinical indications for blood transfusion (4)

Answer 1

PCV <20% (remembering PCV may not fall until at least 12hrs)

Estimated 30% or more blood loss

Oxygen extraction ratio >50%

Lactate >4mmol/L

Question 2

Equine blood volume

Answer 2

8% bodyweight ie 40L in a 500kg horse

Question 3

Blood donation volume

Answer 3

Maximum 20% of blood volume (ie 8L in 500kg horse)

Replacement IVFT is recommended if >15% blood volume taken

Question 4

Blood transfusion equation based on PVC

Answer 4

Transfusion volume (L) = bodywt x 0.08 x (desired PCV-actual PVC)

donor PCV

Question 5

Equation to calculate amount of plasma to be transfused

Answer 5

Bwt x 0.045 x (desired TP - actual TP)

donor TP

Same as for blood transfusion except times by 0.045 vs 0.08 (blood volume vs plasma volume)

Question 6

Oxygen extraction ratio

Answer 6

O2 ER = PaO2 - PVO2

PaO2

Transfusion required at >50% - ie if venous blood is very deoxygenated

Question 7

Ideal blood donor

Answer 7

Large gelding with no previous blood transfusion

Negative for Aa and Qa alloantigens - these are the two most likely associated with transfusion reactions

Question 8

Red blood cell half life of allogenic and autogenous red cells collected 24hr previously

Answer 8

20 days allogenic

45 days autogenous

Question 9

Major crossmatch

Answer 9

Detects agglutination between donor red cells and recipient serum

Question 10

Minor crossmatch

Answer 10

Detects agglutination between donor serum and recipients red cells

Question 11

Blood storage times

Answer 11

Can store whole blood in CPDA-1 for 28days (says upto 21d in a fridge at 1-6’C in Slatter)

Packed red cells for 35d (not recommended in humans - higher mortality vs whole blood)

(Says 21d in Slatter with CPDA-1 and longer if red cell additive used)

FFP - upto 1 year at -18’C. Upto 3 months in normal household freezer

FP - 4 years

Question 12

Distribution of total body water

Answer 12

60% of body weight

66% intracellular

33% extracellular

ECF divided into interstitial (75%) and intravascular (25%)

IV fluid compartment is the smallest

Question 13

Difference between fresh frozen plasma and frozen plasma

Answer 13

FFP is plasma separated and frozen at -18’C within 8 hours of collection

FP is either FFP after 1 year of frozen storage (it is then useable as FP for 4 years at -18) or blood that has been separated and stored >8hours after collection

Frozen plasma products maintain factors II, VII, IX and X (also the vit K dependent factors) and albumin and Igs. BUT LACK factors V, VIII and von Willebrand factor

Question 14

Administration of packed red cells

Answer 14

Last refrigerated at least 21 days with CPDA-1

Ideally leave with some plasma such that PCV <80%. Agitate daily

To administer, resuspend with 0.9%NaCl. Calcium containing fluids incl Hartmanns should NOT be used - can cause coagulation

(says 10ml saline per 30-40ml red cells in slatter)

Question 15

Components of primary haemostasis

Answer 15

Local vasoconstricton

vWF factor release from endothelial cells (Weibel-Pallade bodies)

Platelet attraction, activation and adhesion (the 3 a’s)

The interaction of activated platelets with the exposed subendothelium of blood vessels is the basis of primary hemostasis

Question 16

Role of platelets in secondary haemostasis

Answer 16

Once activated, they undergo conformational change exposing binding sites for specific coagulation factors

Question 17

How is platelet adhesion mediated

Answer 17

Through expression of P-selectin on activated (damaged) vascular endothelium and through the platelet receptor GPIbα, which attaches to vWF

Question 18

Definition of SIRS

Answer 18

Inappropriate generalised inflammatory response to tissue damage/infection w mechanisms intended to defend & repair; but exaggerated systemic reaction rx in clinical state of SIRS - can be more detrimental than the initial insut itself

Question 19

List 5 pro-inflammatoy cytokines

Answer 19

IL-1

IL-6

IL-8

TNF-∝

IFN-𝛾

Question 20

List 5 (predominantly) anti-inflammatory cytokines (NB some X-over in pro/anti-inflammatory function)

Answer 20

IL-4

IL-10

IL-11

IL-13

TGF-β

Question 21

Briefly describe the arachadonic acid cascade

Answer 21

• AA rx from membrane phosopholipid through the action of PLA2
• AA is metabolised via COX and LOX pathways to generate eicosanoids
• Eicosanoids comprise leucotrines (LOX) and prostanoids (COX) = prostaglangins and thromboxane A2

Question 22

What are the 2 main acute phase proteins in horses?

Answer 22

SAA

C-reactive protein (role in complement activation)

Colletively responsible for many of the effects incl pyrexia, anorexia and depression

Synthesised in the liver; ↑in response to IL-1,6 & TNF

Question 23

Briefly describe the complement system

Answer 23

Functions to enhance immune defense (phagocytosis and antibody function) against pathogens. Part of the innate immune system but can be stimulated by the adaptve (AG-AB complexes)

Several inactive protein precursors (synthesised in the liver); when activated they induce bacteriolysis, ↑vascular permeability, ↑neut chemotaxis & ↑opsonisation (susceptibility to phagocytosis) of microbes and damaged cells

Question 24

List the diagnostic criteria for SIRS in adults (3)

Answer 24

1. Rectal temp: >38.5°C of <37°C
2. HR >52bpm
3. WBC count: >12.5 or <5x10⁹/L, or >10% bands

Addition of lactate >2.06mmol/L and abnormal mm colour may be useful

Can make a dx when 2 or more are satisfied

Question 25

Key considerations in sepsis scoring for neonates

Answer 25

Scoring of 0-4 for 14 parameters

HISTORY - 1. placentitis? Y=3/N=0

2. Gestation length - <300=3, 300-310=2, 311-330=1 >330=0

PE: 3. Petechiae/scleral injection

4. Fever -
5. Hypotonia, coma, seizure - Marked=2, mild=1
6. Anterior uv, d+, ARDS, joint effusions - Y=3, N=0

LAB: 7. Neuts - <2=3, 2-4 or >12=2, 8-12=1

8. Band neuts/µL - >200=3, 50-200=2
9. Toxic neuts - Marked=4, mod=3, mild=2, none=0
10. Fib - >600=2, 4-600 =1, <400=0
11. Glucose - <50=2, 50-80=1, >80=0
12. IgG - <200=4, 2-400 =3, 4-800=3, >800=0
13. PaO2 - <40=3, 40-50=2, 50-70=1, >70=0
14. Metabolic acidosis - Y=1, N=0

TOTAL SCORE ≥11 IS PREDICTIVE OF SEPSIS (or use cutoff of 12 if PaO2 and metabolic acidosis are included)

Question 26

Definition of MODS

Answer 26

Altered organ function in acutely ill patient such that homeostasis cannot be maintained

Question 27

Diagnostic criteria for MODS

Answer 27

No equine consensus. Various human scoring systems, none really validated in EQ other than 1 in surgical colics only (JVIM 2016) - score >8 on d1 and >6 on d2 assoc w nonsurvival

Looks at lab parameters from 8 organ/systems

Question 28

Obel laminitis grading

Answer 28

Graded 0-4 (0=normal)

1 - Normal walk, stilted trot but no obv head not

2 - Stilted walk, obv lameness at trot but can easily lift limbs

3 - Lameness obvious at walk, reluctant to lift limb(s)

4 - Marked lameness, difficulty weight bearing and reluctant to move

Question 29

What is the main mechanism of innate immunity

Answer 29

• Via pattern recognition receptors (PRRs) which detect pathogen associated molecular patterns (PAMPs); evolutionary conserved molecules unique to microbes, usually essential for their survival/virulence
• 3 main types of mammalian PRRs incl 1) secreted PRRs, incl defensins; (2) cell membrane PRRs involved in phagocytosis; and (3) cell membrane PRRs involved in signal transduction
• PAMPs incl bacterial cell wall extracts (LPS), peptidoglycan, prokaryotic DNA

Question 30

Structure of endotoxin

Answer 30

3 main domains

1. Lipid A
2. Core polysaccharide
3. O antigen

Variation in no/length of FAs on glucosamine disaccharide backbone of lipid A confers degree of toxicity

Question 31

What is the main source of endotoxin

Answer 31

Large pool of GRAM NEGATIVE gut bacteria - LPS is major component of their outer membrane.

Endotoxin must gain access to circulation to exert toxic effect

Question 32

Cellular steps in pathophysiology of endotoxaemia

Answer 32

• Lipopolysaccharide binding protein (LBP) (acute phase protein) binds LPS & extracts it from aggregated micelles in the blood - transport to various sites which determines host response in large part - [LBP] can ↑>100fold in 24hr
• Can be transported to the cell surface of host inflammatory cells to evoke inflamm response or can be transferred to other neutralising lipoproteins, such as high-density lipoprotein, for eventual removal from the blood
• Once at the cell surface, LPS is transferred to CD14, expressed by monocytes/macrophages - membrane and soluble CD14 -can bind/neutralise LPS
• Conversely CD14 can also potentiate toxic effects of endotoxins, by transferring it to membrane CD14 or to cells that do not express it.
• CD14 does not structurally cross the cell membrane; has to associate w 2ary protein, toll-like receptor (TLR), that contains a transmembrane portion capable of comms w intracellular domain.
• TLR-4 is mandatory for responsiveness to endotoxin
• Once the CD14-TLR4-endotoxin complex is compiled at the cell surface, TLR-4 req help of a 160–amino acid molecule, MD2, to transmit a signal to the cytosol → intracellular signalling pathways incl NF𝞳B ⇒ stimulates inflamm response
• Most of the deleterious effects of endotoxin rx from overzealous endogenous synthesis of pro-inflammatory mediators and initiation of SIRS - AA metabolites most widely studied

Question 33

Management of endotoxaemia

Answer 33

2 therapeutic options

• Polymixin B - a cationic antibiotic that has bacteriocidal properties & binds/neutralises endotoxin through direct interaction with lipid A (highly conserved so PB theoretically has broader endotoxin-binding capabilities than anticore-endotoxin antibodies)
• Can be stored at room temp. Does have inherent nephrotoxic and neurotoxic side effects when used IV at bactericidal doses, but for neutralisation, sub-bactericidal doses are efficacious without toxicity; recommended dose is 1000-6000IU/kg q 8-12hrs, care w azotaemic patients nonetheless. Effect is dose dependent, use higher end of dose range if ↑endotoxin anticipated
• 2) Anti-endotoxin antibodies - anticore antibodies have conflictin rx. Endoserum = hyperimmune serum from horses vacc w Salmonella typhimurium, Re mutant. Disadv of requiring refrigeration. Dilutied w sterile isotonic saline or LRS (1:10 to 1:20) and administered IV over 1-2 hr to reduce risk hypersensitivity reactions.
• Hyperimmune anticore plasma to Escherichia coli J5 (Equiplas) can be used in foals for concurrent tx of endotoxemia, septicemia, & FPT, given at 20-40 ml/kg, or in adults.
• Plasma products are expensive, req freezer storage, ∴ need thawed
• Others incl flunixin - 0.25 mg/kg IV q 8 hr is commonplace; benefit of this low-dose incl reduced risk of potential toxic side effects (not cited elsewhere)

Question 34

Approximate % blood volume in adults and neonates

Answer 34

8% adults, upto 14% in fit horses

15% in neonates