Block 4: Acid-Base Disorders Flashcards
What is the underlying cause of acid-base disorders?
Don’t just treat pH, you treat homeostatic imbalances
What is purpose of respiration?
Provide O2 for ATP
What is the equation for cellular respiration?
Glucose + 6 O2 → 6 CO2 + 6 H2O + 38 ATP (energy)
What is the equation for bicarb buffer system?
What are the variables that affect H+?
CO2: lungs
Bicarb: Kidneys
What what are ABGs? Normal values?
pH
PaCO2
PaO2
HCO3
What is the difference between alkalemia and academia?
Alkalosis → Alkalemia >7.45
Acidosis → Acidemia <7.35
What is a primary disorder?
Process that causes a pH shift in the direction that the pH actually shifted
What is compensatory response?
A change in either bicarb or CO2 that is in the opposite direction expected for the change in pH
Describe the time it takes for respiratory vs metabolic compensation?
Respiratory: Minutes and max comp within 24 hrs
Metabolic: 3-5 days
How are CO2 and HCO3 affected by acidosis?
↑ CO2
↓ HCO3-
How are CO2 and HCO3 affected by alkalosis?
↑ HCO3-
↓ CO2
In which direction would a simple respiratory acidosis move CO2?
UP
If the disorder is respiratory acidosis in which direction would metabolic compensation (after 3-5 days) move the bicarb?
UP
In which direction would a simple respiratory alkalosis move CO2?
Down
In which direction would a simple metabolic acidosis move bicarb.?
Down
If the disorder is metabolic acidosis in which direction would respiratory compensation move the CO2?
Down
In which direction would metabolic compensation for a simple respiratory alkalosis move bicarb?
Down
In which direction would respiratory compensation for a simple metabolic alkalosis move CO2?
Up
Describe the compensation and primary disturbances of acid base disorders?
How do you calculate an anion gap?
[Na+] – ([Cl-] + [HCO3-])
sum all negative charges = sum all positive charges
[Na+] + All unmeasured cations = [Cl-] + [HCO3-] + all unmeasured anions
What is the normal anion gap?
11-12 mol/L
What are the steps of acid-base disorder diagnosis?
- Identify abnormalities in pH, PaCO2, and bicarbonate (ABG + electrolytes).
- Which abnormalities are primary and which compensatory
- Estimate the compensatory response.
Describe the respiratory a-b disorder w or w/o composition? Labs?
What is the general rule of a-b compensation?1
Compensation can not fully bring the back to normal state
What are the rules of identifying primary abnormalities and which compensatory?
- The process consistent with the pH shift is primary
- Calculate anion gap: Gap > 20mmol/L - primary metabolic acidosis, regardless of pH or bicarb
- Calculate excess anion gap (total – normal) add that to measured bicarb. If sum > normal bicarb there is underlying metabolic alkalosis. Sum < normal bicarb there is an underlying non-anion gap metabolic acidosis.
What are the causes of metabolic acidosis and an ↑ in anion gap?
- Lactic acidosis
- Kidney disease
- Methanol ingestion
- Ethylene glycol ingestion
- Salicylate overdose
- Starvation
What are the causes of metabolic acidosis and a normal anion gap?
- GI bicarbonate loss
- Drugs: cholestyramine, magnesium
- Renal tubular acidosis
What are the causes of metabolic alkalosis?
- Volume depletion - vomiting, nasogastric suctioning
- Diuretic use
- Hypokalemia
- Increased aldosterone
- Increased mineralocorticoids
What would an electrolyte fishbone panel look like?
What are the causes of anion gap of metabolic acidosis?
What is the gold mark?
G – Glycols (ethylene and propylene)
O – Oxoproline
L – L-lactate
D – D-lactate
M – Methanol
A – Aspirin (salicylates)
R – Renal failure
K - Ketoacidosis
What is acute acidosis caused by? Tx?
medications/ADRs, tissue hypoxia (lactic acidosis), DKA
More severe/symptomatic
Corect underlying Pathophysiology and consider dialysis or IV bicarb
What are the causes of chronic acidosis? Treatment?
RTA or GI bicarb wasting
Mild/asymptomatic but bone/growth disorders
Tx: oral alkali replacement (Na vs K, Bicarb vs citrate)
What are the complications of using just HCO3?
Administering exogenous HCO3 for chronic respiratory acidosis with relatively normal kidney function results in urinary excretion of the administered HCO3 without any further increase in serum HCO3 concentration
What do the guidelines say about using HCO3 for acidosis?
Bicarbonate administration is **NOT ** recommended except for treatment of life-threatening hyperkalemia or for severe acidosis (pH<6.9) with evidence of compromised cardiac contractility
How is HCO3 only recommended for cardiac arrest?
Related to hyperkalemia (to cause K shift) or overdose of tricyclic antidepressants
What is the common cause of metabolic alkalosis?
Either Vomiting or Loop Diuretics + AKI
1. loss of H+ and Cl-
2. Injured kidneys cannot excrete enough HCO3- and Na+ to compensate
3. Vague S/Sx: patient history very important
How do you treat metabolic alkalosis?
- NaCl fluids (increased renal perfusion and replaces lost Cl-)
- Acetazolamide (inhibits renal HCO3 absorption) - first line
- HCl or HD (severe only)
What are some of the cause of respiratory acidosis?
- CNS depression – opiates, CNS event
- Neuromuscular disorders – myopathies, neuropathies
- Acute airway obstruction
- Severe pneumonia
- Pulmonary edema
- Impaired lung motion – hemothorax, pneumothorax
- Thoracic cage injury – flail chest
- Ventilator dysfunction
What are the common causes of respiratory alkalosis?
- Progesterone
- Theophylline
- Nicotine
- Hypoxia
- Lung disease with or without hypoxia
- CNS disease
- Sepsis
- Hepatic encephalopathy
- Mechanical ventilation
How do you use a mechanical ventilation for respiratory acid base disorders?
Give analgesics and sedatives, then you can control rate and depths of breaths to correct
But first you treat the underlying cause
