Haem questions Flashcards
What does blood typing involve?
forward grouping - patient’s RBC vs. standard sera
reverse grouping for confirmation - patient’s sera vs. standard RBCs
What is antibody screening?
Patient’s serum + control RBC in saline
Screening for clinically relevant antibodies
What are the additives for PRBCs?
SAGM sodium chloride adenine dextrose mannitol
What are the anticoagulant additive to blood at collection?
CPD
citrate
phosphate
dextrose
Define a circle system
Circle breathing system is a closed or semi-closed system used to deliver oxygen and anaesthetic gases, while eliminating CO2 and recirculates patient’s respiratory gases.
Advantages of circle system?
provides constant inspired concentration
conserve heat and humidity
reduced anaesthetic gas waste
efficient CO2 removal
Disadvantage of circle system?
slow equilibration of anaesthetic gas
soda lime degradation products
complex system prone to error
high resistance within circuit
how much O2 is dissolved in blood at room air?
PaO2 (RA) = 100mmHg
0.03 x 100 = 3ml/L of blood
How is intrapleural pressure different between the base vs. apex of lung?
Base - gravity, weight of lung onto tissue.
High intrapleural pressure, less negative.
How is FRC measured by gas dilution?
Helium dilution method
Known volume and concentration of helium.
Helium minimally uptaken
V1 x [He] = (V1 + FRC) x [He]
Define FRC
Lung volume at end-expiration of normal tidal breathing
RV + ERV
Volume at lung inward recoil and chest wall outward recoil are in equilibrium
What is the correction factor F in the alveolar gas equation
F = ~2mmHg on RA
How much does MV increase with every mmHg of CO2?
2-3L/min
What are the effectors of ventilatory response?
Phrenic nerve - diaphragm
intercostal nerves - external intercostal
C-spine nerves - scalenes
CNIX/X - pharyngeal dilators
What hormones are regulated by the liver?
EPO, 10% - hepatic synthesis of RBC particularly in neonatal period
Conversion of cholecalciferol to 25 hydroxy-D3
Angiotensinogen
Androgens/oestrogen
Effect of sevo on cardiac muscle?
dose dependent reduction in HR/contractility anaesthetic preconditioning (activation of ATP-sensitive K channels) -> reduce risk of iscahemia Increase QT interval ?MOA Coronary steal syndrome - rarely significant
How does hypokalaemia affect NMB?
HypoK -> increase K efflux gradient -> intracellularly become more negative -> hyperpolarisation of membrane -> potentiates effect of NMB
How does amino glycoside affect NMB?
competes with Ca for binding site -> reduce Act release and potentiate NMB effect.
Also reduces post-synaptic nACHr sensitivity rot Ach
What are the factors that affect venous return?
Flow = pressure change / resistance
RA flow = (MSFP - RAP) / RVR (resistance to venous return)
What are the factors that affect MSFP?
Total blood volume
Venous tone
Posture
Skeletal muscle pump
What factors affect RAP?
IPPV
PVR
Congestive heart failure
What factors affect RVR?
arteriolar resistance - vasodilators -> move more blood for artery -> veins -> increase venous return
External compression - pneumoperitoneum
Metabolic alkalosis
How does one gain alkali in ECF?
endogenous - recovery from lactic / kept acidosis, as acids are cleared by liver
exogenous - IV fluid, IV NaHCO3
Endo causes of metabolic alkalosis?
Hyperaldosterone - Conn’s, Cushing’s, high dose steroids
Hypokalaemia
