Acid base balance Flashcards
What information is included in arterial blood gas?
pH pCO2 pO2 HCO3- BE
normal pH
7.35-7.45
normal pCO2
5.1-5.5KPa
normal PO2
11.5-14.5kpa
HCO3-
24-28mmol/L
Base excess
0 (-1 to +1)
in A&E
use venous blood gas as less invasive, but less accurate.
why is acid-base important?
enzyme function electrolyte regulation drug ionisation good diagnostic guide monitoring therapy
acid-base
acid production and acid elimination balance
acid production
respiratory
metabolic
respiratory production of acid
carbonic acid from CO2
0.5kg/day
metabolic production. of acid
organic - lactic, amino, hydroxybutyric acids
inorganic - suplfuric and phosphoric
80mmol/day = inorganic
acidic/ alkaline secretions
In gastric and pancreatic physiology
if either is lost in substantial quantities acid/base disturbance can result
gastric
high H+
pancreatic
high HCO3-
acid elimination
respiratory
metabolic
respiratory acid elimination
ventilation removes CO2
metabolic acid elimination
inorganic acids - excreted by kidneys unchanged
organic acids - generally undergo liver metabolism
lactate metabolism
to CO2 and water or back to glucose in cori cycle
pH
-log[H+]
pH scale
logarithmic scale
wide range encountered so easier scale to use
a small change in pH is a big change in H+
pH of plasma
7.4
pH of stomach
2
how to keep pH constant?
buffers
respiratory
renal/ metabolic
what is the point of acid-base homeostasis?
to keep pH constant
time of buffers
immediate - seconds/ minutes
time of respiratory
rapid - minutes/ hours
time of renal
slow - hours/ days
small contribution by liver
what are the different types of buffers?
proteins
phosphate
carbonic acid/ bicarbonate
protein buffers
albumin in ECF
haemoglobin in ICF
via histidine residues
how do protein buffers work?
negatively charged when in contact with ammonium salt
hydrogen ions attracted to protein
phosphate buffer
HPO42- + H+ –> H2PO4-
interacts with free H+ ions
intracellular
carbonic acid/ bicarbonate
main extracellular buffer
involved in metabolic and respiratory regulations