Acid-Base Disorders & ABG's (Exam II) Flashcards
What is the excessive production of H⁺ in relation to hydroxyl ions?
Acidemia (Acidosis)
Excessive production of OH- in relation to H⁺ is known as ________.
Alkalemia (alkalosis)
What ion is used to measure pH?
H⁺
Where does HCO₃⁻ enter and leave the body?
Proximal tubule of the kidneys
Where are H⁺ reabsorbed in the kidney?
Distal tubule and collecting duct
What is the name of the acid-base balance equation?
Henderson-Hasselbalch Equation
If both PaCO₂ and HCO₃⁻ increase at the same time, then you have what?
Primary disorder with secondary compensation.
If PaCO₂ decreases and HCO₃⁻ increases at the same time, then you have what?
A mixed acid/base disorder
If the PaO₂ is is 60 at room air, what would the PaO₂ be with an FiO₂ of 80%?
PaO₂ ≈ 240 mmHg at an FiO₂ of 80%
A patients ABG is drawn and shows the PaO₂ to be 120 mmHg on an FiO₂ of 60%. What would the CRNA anticipate the patient’s PaO₂ to be on room air?
PaO₂ ≈ 40 mmHg on room air
What are the cardiovascular consequences of acidosis?
- ↓ contractility
- ↓ arterial BP
- Re-entry dysrhythmias
- Lower threshold for v-fib
- Less responsive to catecholamines.
What cardiovascular consequence occurs at a pH of 7.2?
Impaired contractility
What cardiovascular consequence occurs at a pH of 7.2?
Impaired contractility
What cardiovascular consequence occurs at a pH of 7.1?
Decreased responsiveness to catecholamines
What are the consequences of acidosis on the nervous system?
Obtundation & Coma
What are the consequences of acidosis on the pulmonary system?
- Hyperventilation
- Dyspnea
- Respiratory muscle fatigue
What are the consequences of acidosis on body metabolism?
- Hyperkalemia
- Insulin resistance
- Anaerobic glycolysis inhibition
How is respiratory acidosis defined?
- An acute decrease in alveolar ventilation results in increased PaCO₂.
- pH < 7.35
- Essentially respiratory failure
What are the three umbrella causes of respiratory acidosis?
- Central ventilation control
- Peripheral ventilation control
- VQ mismatch
What are the more granular causes of respiratory acidosis?
- Drug-induced resp depression
- Permissive hypercapnia
- Upper airway obstruction
- Status asthmaticus
- Restriction of ventilation (flail chest, rib fracture)
- Neuromuscular dysfunction
- MH
- Pneumonia/ edema / pleural effusion
In acute hypercarbia, how much will plasma HCO₃⁻ increase for every 10 mmHg increase in PaCO₂ ?
↑ HCO₃⁻ by 1 mmol/L (1mEq/L) for every 10 mmHg of PaCO₂
An acutely hypercarbic patients PaCO₂ is noted to be 70 mmHg. What would the CRNA anticipate the HCO₃⁻ to be?
3 mmol/L ( or 3 mEq/L) higher than normal
How much will plasma HCO₃⁻ compensate in the chronically hypercarbic patient?
3 mEq/L for every 10 mmHg in the PaCO₂
A chronically hypercarbic patient has a PaCO₂ of 60mmHg. What would the CRNA anticipate the HCO₃⁻ to be?
6 mEq/L higher than normal ( normal range is 22 - 26 so 28 - 32 expected)
What is the treatment for a hypercarbic, respiratory acidotic patient?
Mechanical Ventilation
If hypercarbia is excessive and CO₂ narcosis is present.
What can occur if a COPD patient’s chronic hypercarbia is corrected?
Seizures
Excessive HCO₃⁻ in chronically hypercarbic patients causes CNS irritability.
What is the response of the ventilatory center to metabolic acidosis?
Hyperventilation (blow off CO₂ and thus acid)
Can metabolic acidosis be corrected through mechanical ventilation?
Nope
What shift in the oxyhemoglobin dissociation curve occurs with metabolic acidosis?
Right shift
What cellular alterations occur with metabolic acidosis?
- ↑ ionized Ca⁺⁺
- Dysfunctional transcellular ion pumps
How can expected PaCO₂ be calculated in an acute metabolic acidosis patient?
PaCO₂ ≈ (1.5 x HCO₃⁻ ) + 8
What would the expected PaCO₂ be an acute metabolic acidosis patient with an HCO₃⁻ of 14?
PaCO₂ ≈ (1.5 x 14) + 8
PaCO₂ ≈ 29 mmHg
If PaCO₂ is greater than 29 then compensation is inadequate.
For every 1 mEq/L drop in Base Excess, PaCO₂ should fall by _______.
1.2 mmHg
If Base Deficit is -2 then the PaCO₂ should be….
38 mmHg
If the PaCO₂ is higher than this, then compensation is inadequate.
A patient’s base deficit is -11, what would on expect the compensatory PaCO₂ to be?
11 x 1.2 = 13.2
PaCO₂ ≈ 26.8
If higher then compensation is inadequate.
What are the causes of hyperchloremic metabolic acidosis?
- Saline
- Diarrhea
- Early Renal Failure
What type of anion gap is produced in hyperchloremic metabolic acidosis?
Normal Anion Gap
HCO₃⁻ loss is countered by net gain of Cl⁻
What are some causes of a high anion gap?
- Lactic acidosis
- Ketoacidosis
- Renal failure
- Poisonings
More HCO₃⁻ is available with high anion gap disorders. T/F?
False.
Excessive acid combines with HCO₃⁻ → carbonic acid → less available HCO₃⁻
How is a simple anion gap calculated?
Na⁺ - ( Cl⁻ + HCO₃⁻ )
What should a normal anion gap be?
Na⁺ - ( Cl⁻ + HCO₃⁻ )
140 - (102 - 24)
≈ 12 - 14 mEq/L
How is a conventional anion gap calculated?
(Na⁺ + K⁺) - (Cl⁻ + HCO₃⁻)
What should a conventional anion gap be?
(Na⁺ + K⁺) - (Cl⁻ + HCO₃⁻)
140 + 4 - (106 - 24)
≈ 14 - 18 mEq/L
What two conditions will cause an underestimation of the extent of the anion gap?
- Hypoalbuminemia
- Hypophosphatemia
What is the treatment for a discordant anion gap?
Treat the underlying cause!
- Ketoacidosis = insulin & fluids
- Lactic acidosis = improve tissue perfusion
- Renal failure = dialysis
When is Na⁺HCO₃⁻ (Sodium Bicarbonate injection) indicated?
- pH < 7.1
- HCO₃⁻ < 10 mEq/L
What are the two reasons for Na⁺HCO₃⁻ treatment controversiality?
- HCO₃⁻ + H⁺ → CO₂ = more acidosis
- With chronic acidosis, acute pH changes negates curve shift to the right and results in tissue hypoxia
How is a correction dose of Na⁺HCO₃⁻ calculated?
Dose (mmol) = 0.3 x base deficit x kg
The CRNA wishes to calculate a correction dose of Na⁺HCO₃⁻ for an 82 kg patient with a base deficit of -4. What would the dose of Na⁺HCO₃⁻ be?
Dose = 0.3 (-4) x 82kg
Dose = 98.4 mmol of Na⁺HCO₃⁻
When giving a correction dose of Na⁺HCO₃⁻, how much should be given initially?
½ the correction dose.
What is respiratory alkalosis?
- Acute increase in alveolar ventilation
- ↓ PaCO₂
- pH > 7.45
What are four common causes of respiratory alkalosis?
- Pregnancy
- High altitude
- Iatrogenic Hyperventilation
- Salicylate overdose
What are common symptoms of respiratory alkalosis?
- Lightheadedness
- Visual disturbances
- Dizziness
all of these from vasoconstriction.
What occurs with calcium levels during respiratory alkalosis?
Ca⁺⁺ binds to albumin more easily → hypocalcemia
What are the signs/symptoms of hypocalcemia?
- Paresthesias
- Muscle spasms
- Cramps
- Tetany
- Mouth numbness
- Seizures
- Trousseau’s Sign
- Chvostek’s Sign
What is Trousseau’s sign?
Wrist flexion that occurs with BP cuff inflated.
What is Chvostek’s sign?
Tapping of Facial Nerve (CN VII) resulting in involuntary facial contraction.
What are the branches of the facial nerve?
To Zanzibar By Motor Car.
- Temporal
- Zygomatic
- Buccal
- Marginal mandibular
- Cervical
How is metabolic alkalosis defined?
- Marked increase in HCO₃⁻ usually with compensatory increase in CO₂
- Loss of H⁺ or gain of HCO₃⁻
- Renal or extrarenal
Is metabolic alkalosis a disorder of volume overload or volume depletion?
Can be either!
What are common causes of metabolic alkalosis?
- Hypovolemia
- Vomiting
- NG suction
- Diuretic therapy
- HCO₃⁻ administration
- Hyperaldosteronism
What are the treatments for metabolic alkalosis?
Treat underlying cause
- Volume depletion? saline resuscitation
- Gastric H⁺ loss? PPI’s
- Loop diuretics? add K⁺ sparing diuretics
