Acid-Bases Disorders & ABGs Flashcards
Define acidemia vs acidosis
- acidemia: increase in blood H+ (pH <7.35)
- acidosis: pathophysiologic process that acidifies body fluids
Define alkalemia vs alkalosis
- alkalemia: decrease in blood H+ (pH >7.45)
- alkalosis: pathophysiologic process that alkalinizes body fluids
Define acid-base disorders
changes on CO2 partial pressure (pCO2) or serum bicarbonate (HCO3-) that produces abnormal arterial pH values
Which is the acid and which is the base: CO2, HCO3
CO2 = acid
HCO3 = base
Which organ compensates for metabolic acidosis/alkalosis
Lungs - manages CO2 levels via hypo/hyperventilation
- takes minutes to compensate
- CAN’T have respiratory acidosis & alkalosis at the same time
Which organ compensates for respiratory acidosis/alkalosis
Kidneys - manages HCO3 levels via excretion/absorption
- takes days to compensate
- CAN have metabolic acidosis/alkalosis at the same time
What is an anion gap
measure of the difference between negatively charged and positively charged electrolytes in the blood (cations = positive, anions = negative)
why does chloride loss result in metabolic alkalosis?
less chloride ions are available to exchange with bicarb so the ability to excrete excess bicarb from kidney is impaired
Describe the pathophys of respiratory acidosis
Describe the etiology of respiratory acidosis
low pH and high pCO2
What is the presentation of respiratory acidosis
somnolence, confusion, AMS, asterixis, seizures or coma if severe
What test should be done before getting an ABG from the radial artery
Allen’s test to check for good flow of the ulnar artery to continue hand perfusion
Describe the pathophys of respiratory alkalosis
Describe the etiology of respiratory alkalosis
high pH and low pCO2
Describe the presentation of respiratory alkalosis
Why is respiratory alkalosis usually self limited
because muscle fatigue/weakness will suppress ventilation
Describe the etiology of metabolic acidosis
Describe the presentation of metabolic acidosis
Describe the diagnosis of metabolic acidosis
Describe the treatment of metabolic acidosis
admit! treat underlying cause
Describe the pathophys of HAGMA and NAGMA
Describe the etiology of metabolic alkalosis
Describe the treatment of metabolic alkalosis
What are the components of an ABG measurement
- pH 7.35-7.45
- PaO2 (generally >80 mmHg)
- PaCO2 (35-45 mmHg)
- HCO3 (21-27 mEq/L)
Sometimes:
- carboxyhemoglobin (<3%)
- methemoglobin (<1%)
Describe the use of VBG over ABG
- less invasive/painful
- convenient
- not useful for oxygenation
- different values
Describe the approach to ABG analysis
- determine acidemia vs alkalemia
- determine primary disorder (respiratory - acute vs chronic, metabolic - HAGMA v NAGMA)
- is there appropriate compensation
- what is the clinical diagnosis
How do you determine if there is metabolic vs respiratory acidosis on ABG?
relationship of pH and pCO2 with HCO3*
- ROME: respiratory opposite, metabolic equal
How do you determine appropriate compensation on ABG analysis?
pCO2 and HCO3 should move in the SAME direction
compensation always moves in the SAME direction as the primary disorder
(if the compensation is higher/lower than expected pCO2 or HCO3 values using given equations - think mixed disorder like resp acidosis with metabolic alkalosis)
What element of an ABG are you looking at to determine expected compensation for respiratory vs metabolic processes
- respiratory: expected HCO3
- metabolic: expected pCO2
Define partial compensation on ABG
compensatory mechanism tried but failed to bring the pH back to normal
(pH still out of range and pCO2 & HCO3 both high or both low)
Define uncompensated on ABG
no change in compensatory mechanism
(pH still out of range and either pCO2 or HCO3 out of range while other is normal)
Define full compensation on ABG
compensatory mechanism brought pH back to normal
(pH within normal limits while pCO2 and HCO3 both high or both low)
How do you determine an acute vs chronic process on ABG analysis
look at clinical picture
