Acid-Base Physiology Flashcards
Metabolic Alkalosis CO2 Calculation
Describe the significance of the ranges.
“0.7 plus 20”
PCO2 = 0.7 * [HCO3] + 20 (+/-) 5
1. Normal range: >40 mm Hg in order to compensate for the low H+ protons
What is the main indicator for a Respiratory Acidosis? What should we expect for acute vs. chronic?
Abnormally HIGH pCO2 > 40 mm Hg.
Acute: +1 mM HCO3 for every +10 mm Hg increase in pCO2
Chronic: +4 mM HCO3 for every +10 mm Hg pCO2 increase
What is the indicator for Metabolic Acidosis.
The amount of HCO3 present is lower than 24. Also, the AG can be within range of 7-16 mmol/L. If above, then we indicate “…with elevated AG”
What are the baseline concentrations for important blood gases?
HCO3 = 24 meq/ L PCO2 = 40 mm Hg
Acute Respiratory Acidosis
Hallmark
“Up 1 for 10”
Increase in meq/L HCO3 by 1 for every 10 mm Hg pCO2
Chronic Respiratory Acidosis
Hallmark
“Up 4 for 10”
Increase 4 meq/L HCO3 for every 10 mm Hg
Acute Respiratory Alkalosis.
Hallmark
“Down 2 for 10”
For every 2 meq/L drop in HCO3, there is a 10 mm Hg decrease in pCO2
Chronic Respiratory Alkalosis.
Hallmark
“Down 5 for 10”
For every 5 meq/L drop in HCO3-, there is a 10 mm Hg decrease in pCO2
Metabolic Acidosis.
Hallmark
“One and a half plus 8”
PCO2 = 1.5*(HCO3) + 8 (+/-) 2
Metabolic Alkalosis.
Hallmark
“Zero Point Seven plus 20”
PCO2 = 0.7*(HCO3) + 20 (+/-) 5
What is the Formula for the Plasma anion gap (AG)? Define the normal range and abnormal ranges.
AG = Na - (Cl + HCO3)
- Normal Range: 7-16 mmol/L
- Elevated AG = Metabolic Acidosis
When should we use Delta-Delta? Describe what’s being calculated.
- Delta-Delta is used when we have an ABNORMAL Anion Gap. This can indicate an underlying/co-existing ion imbalance disorder.
- DeltaAG = (AG - 12)
DeltaHCO3 = (24 - HCO3)
Describe what happens and how the body compensates for METABOLIC ACIDOSIS.
- PH decreases,
- HCO3 decreases
- pCO2 decreases to compensate
* Metabolic acidosis is associated with Ketoacidosis, Lactic Acidosis, Alcoholism and Ingestion of Strong Acids (Salicylic Acid, Methanol, Ethylene Glycol)
Describe what happens and how the body compensates for METABOLIC ALKALOSIS.
- pH Inc
- HCO3 Increases
- pCO2 increases to compensate for alkalinity
Describe what happens and how the body compensates for RESPIRATORY ACIDOSIS.
- PH decreases
- PCO2 increases
- HCO3 increases to compensate (work against the acidity of the raised CO2 levels)
Describe what happens and how the body compensates for RESPIRATORY ALKALOSIS.
- PH increases
- PCO2 decreases
- HCO3 decreases to compensate for the alkaline blood levels.
Describe the symptoms of Lactic Acidosis.
Low pH and High Lactate levels can lead to K+ channels open more often.
This can present as arrhythmias or Hypotension
Less binding of insulin and reduced catecholamines also contribute to above symptoms [Slide 59]
What is the Winter’s Formula (for acidemia) when should it be used and what are its implications?
- pCO2 = 1.5 * (HCO3) + 8 (+/-) 2
- This should be used in the scenario of “Metabolic Acidosis”, to see if it’s being compensated for. PCO2 is expected to decrease
- If calculated levels are above, Respiratory Acidosis is superimposed. If below, there is a superimposed respiratory alkalosis.
Name at least 3 lung pathologies that can lead to respiratory acidosis.
- COPD
- Severe Asthma
- Pneumonia
* Any disorder that affects gas exchange and increases resistance of the diffusion barrier.
Name 5 pathologies that can be associated with AG-Elevated Metabolic Acidosis.
- Diabetes (Ketoacidosis), Alcoholism
- Lactic acidosis
- Renal Failure
- GI excretion of HCO3-
- Ingestion of strong metabolized acids (salicylic acid, glycolic acid, formic acid, ketoacids, lactic acid)
What is the equation for Urine Anion Gap (UAG) and what are the indications?
AG = UNa + UK - UCl
- ”U” is concentration in urine
1. Urine AG should = 0 normally
2. If UAG <0, then Metabolic Acidosis occurs with intact Kidneys- Cl- is excreted
3. If UAG >0, then Impaired Distal (Urine) Acidication
- Cl- is excreted
- NH4-Cl is excreted; kidneys can’t acidify urine
Name at least 3 common causes of Metabolic Alkalosis.
- Diarrhea
- Vomiting
- Hypovolemia
What 2 channels are activated in the kidneys due to metabolic alkalosis (linked to water loss).
- Na/H exchanger
- Na is reabsorbed at the expense of H+ (acidify urine in the process) - Na/HCO3 symporter
- HCO3 is reabsorbed with Na and can compensate for metabolic alkalosis.
What is the Delta-Delta difference and how is it calculated?
- D-D difference indicates the one:one relationship of unmeasured anions and HCO3. Abnormal is when D-D is not =0
- D-D = (delta-AG) - (delta-HCO3)
* Delta-AG = AG -12
* Delta-HCO3 = 24 - HCO3
What are the ranges of Delta-Delta values and what do they indicate?
- Normal range: (-5 to +5) indicates metabolic acidosis alone
- If Large +: (>+5) then AG Metabolic Acidosis and Metabolic Alkalosis co-exist.
- If Large - : (
Name 2 types of ionic imbalances that can be associated with Metabolic Acidosis.
- Hyperkalemia: to maintain electroneutrality, most cells dump out intracellular K+ in exchange for picking up extracellular H+
- Hyperchloremia: too much chloride in the kidneys is being reabsorbed back into blood plasma along with HCO3 to offset acidosis AND add more negative charge to plasma [maintain electroneutrality]
Describe associated acid-base disorders of the following clinical symptoms:
- Vomiting
- Diarrhea
- Tachypnea
- Metabolic Alkalosis - vomiting
- Non-AG Metabolic Acidosis- diarrhea
- Respiratory Alkalosis - hyperventilation
Describe the important buffers for regulating blood pH (in RBCs and kidneys, respectively).
- HCO3-: made in RBCs from CO2 and H2O. This offsets H+ in the blood plasma to control impending acidosis.
- HPO4 - excreted as H2PO4
What is the Henderson-Hasselbach equation for calculating pH from HCO3 and CO2?
pH = 6.1 * log [(HCO3-)/(0.03*pCO2)]
What are some symptoms associated with a metabolic acidosis/alkalosis without AG elevation (non-AG)
Chronic Diarrhea or Chronic Vomiting DO NOT raise the Anion Gap!
Ex:) We would expect a non-AG metabolic acidosis for diarrhea
Describe how these ionic imbalances are associated with Metabolic Acidosis.
- Hyperkalemia
- Hyperchloremia
- K+/H+ swap occurs after several hours of metabolic acidosis. Many cells release intracellular K+ and buffers into the blood while removing H+, hence high K+ levels in the blood.
- Cl- replaces lost HCO3- to maintain Electroneutrality in the blood. HCl is buffered by HCO3- and fluid loss altogether has the kidneys retain more NaCl > Non-AG Metabolic Acidosis.
