Haem Flashcards
What is the triad of HUS
Thrombocytopenia
Renal failure
Microangiopathich haemolytic anaemia (MAHA)
Types of HUS
Typical (epidemic) or atypical
Causes of Typical HUS
Infection with verotoxin producing enterococci e.g
E.coli 0157
Shigella
Causes of atypical HUS
Rarer - poor diagnosis
Strep pneumoniae, CMV, HIV Bone marrow transplant Solid organ transplant Qunine, heroin, ciclosporin Malignancy Pregnancy
Pathophys of HUS
Toxin causes haemorragic colitis–> bloody diarrhoea and prodomal illness
AKI develops within a week –> direct injury to renal vascular epithelium
Platelet aggregatraion, micro thrombi
Hypertension and fluid overload commonly follow
Atypical - complement dysreguation
Ix for HUS
FBC
Film –> reticulocytes, haemolysis, thrombocytopenia
Direct Coombs test - immune and non immune mediated
LDH - raised in haemolysis
HIV,
Renal screen
Managig HUS
Supportive
Treat infectious cause - cipro for ecoli and shigella
Plasma exchange as difficult to tell from TTP
Recommended in atypical
In epidemia HUS - PEx, IVIg, steroids, antiplatelts have no role
Which has worse prognosis, typical or atypical
atypical -25% (50% is ESRD)
How does HUS differ from TTP,
spectrum of same disease process
Featrues of TTP
Thrombocytopenia MAHA Fluctuating neurology Renal impairment Fever
Clotting now, DIC is late
Pathology of TTP
deficiency of vWF cleaving protease (vWF-CP) or ADAMTS 13.
Can be genetic, lack of enzyme or acquired, presence of antibody
vWF activates and binds platelets in repsonse to injury
Inactivated when cleaved by vWF-CP.
With TTP , lack of vWF-CP means no cleavage.
Fibrin is deposited and thrombus propogated creating ischaemia. Red cells shred as they pass the fibrin/platelet mesh (MAHA)
TTP management
PEx wth octaplas (FFP with ultrao large vWF)
Keep going for two daya after platelemt recovery
Removes antibodies
High dose pulsed methylpred
Rituximab in acute life threatening refractory disease
Low dose aspirin once plts>50
Red cell transfusion and folate.
Threshold for neutropenia
0.5-1.0
NICE say 0.5 neutrophil count
Neutropenic sepsis definition
neutropenia plus temp greater than 38
Abx for neutropenic sepsis
Commonly tazocin with gent
If CVP add vanc
What is TLS
Tumour lysis syndrome Breakdown of malignant cells with High K High PO3 Low Ca
Pathophys of TLS
Cell lysis:
Release of K and PO
Binds Ca by PO, CaPO crystlises n tissue and renal tubules
Release of nucleic acids, metabolism –> rise in uric acid
AKI, arrhytmias, seizures, death
Risk factors for TLS
High tumour load High turnover of tumour cells High LDH High sensitivity to chemo Pre-existing renal dysfunction +/- low urine output
Associated with acute leukaemias and high grade lymphoma e.g Burkitts
Prevent TLS
Hydrate 3 litres per day
Avoid other uric acid forming agent - dieuretics, coffee, alcohol
Allopurinol - xanthine oxidase inhibitory
Rasburicase - urate oxidase preparation iv
Management TLS
High hydration and urine output
100mls/hr/m2 BSA
Avoid furosemide
Rasburicase has a role in treating as well as preventing
Allopurinol does not
Electrolyte abnormalities corrected
RRT
Is there a role for urine alkalinisation in TLS
No
What are the causes of methaemoglobinaemia? How would it represent on an A-A gradient and what would the patients sats be?
It can be congenital (cytochrome b5 reductase deficiency) or acquired.
Acquired causes include exposure to drugs including:
Nitrates
Certain local anaesthetics – e.g. prilocaine, benzocaine
Certain antibiotics – e.g. dapsone
Analine dyes
Normal A-a gradient
Pa02 would be normal/high and O2 sats would be low as a result of the absorption spectrum of methaemoglobin
detected on pulse oximetry
Why does methaemoglobinaemia cause hypoxia?
The ferrous ion Fe+2 in haem is oxidized to the ferric state Fe+3. Fe+3 ions have poor oxygen affinity. The remaining ferrous ions have increased oxygen affinity causing a left shift of the oxygen disassociation curve and reduced oxygen delivery to tissue.
What is the treatment for methaemoglobinaemia?
Administer supplemental oxygen.
Intravenous methylene blue is a specific antidote, facilitating the reduction of methaemoglobin.
The role for hyperbaric oxygen and exchange transfusion remains anecdotal.