Resp. Acid-Base Disorders Flashcards by Jacob Thorn

What are the normal arterial blood gas (ABG) values?

pH: 7.35 - 7.45 (normal: 7.40

PaCO₂: 35 - 45 mmHg (normal: 40 mmHg)

PaO₂: 80 - 100 mmHg

HCO₃⁻: 22 - 28 mEq/L (normal: 24 mEq/L)

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How do you differentiate between metabolic and respiratory acidosis/alkalosis?

Metabolic disorders: Primary change is in HCO₃⁻
Acidosis: HCO₃⁻ < 22 mEq/L
Alkalosis: HCO₃⁻ > 28 mEq/L

Respiratory disorders: Primary change is in PaCO₂
Acidosis: PaCO₂ > 45 mmHg
Alkalosis: PaCO₂ < 35 mmHg

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What are the key buffering systems in the body that help regulate pH?

Bicarbonate (HCO₃⁻) buffer system (Most important in ECF)

Phosphate buffer system (Important in ICF and renal system)

Protein buffer system (Hemoglobin in RBCs, Albumin in plasma)

Respiratory compensation (Alters CO₂ levels to affect pH)

Renal compensation (Alters H⁺ secretion and HCO₃⁻ reabsorption)

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What is the difference between simple and mixed acid-base disorders?

Simple disorder: Only one primary acid-base disturbance with appropriate compensation.

Mixed disorder: More than one acid-base disorder is present, compensation is inappropriate.

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How does the body compensate for metabolic and respiratory acid-base disorders?

Metabolic acidosis → Respiratory compensation (Hyperventilation to ↓ CO₂)

Metabolic alkalosis → Respiratory compensation (Hypoventilation to ↑ CO₂)

Respiratory acidosis → Renal compensation (↑ HCO₃⁻ reabsorption, ↑ H⁺ excretion)

Respiratory alkalosis → Renal compensation (↓ HCO₃⁻ reabsorption, ↓ H⁺ excretion)

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How do you determine if respiratory acidosis is acute or chronic?

Acute: For every 10 mmHg ↑ in PaCO₂, HCO₃⁻ ↑ by 1 mEq/L

Chronic: For every 10 mmHg ↑ in PaCO₂, HCO₃⁻ ↑ by 3.5 mEq/L

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What are the major causes of respiratory acidosis?

Hypoventilation, leading to CO₂ retention

Airway obstruction (COPD, sleep apnea)
Respiratory muscle weakness (Myasthenia gravis, Guillain-Barré)
CNS depression (Opioids, sedatives)
Obesity hypoventilation syndrome

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What are the major causes of respiratory alkalosis?

Hyperventilation, leading to CO₂ loss

Anxiety or panic attacks
Hypoxemia (high altitude, pulmonary embolism)
Salicylate poisoning
Sepsis or fever
Excessive mechanical ventilation

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What is Winter’s formula, and when is it used?

Used to determine expected PaCO₂ in metabolic acidosis to check for appropriate compensation.

PaCO₂ = 1.5[HCO₃⁻] + 8 ± 2
If actual PaCO₂ is higher than expected → Mixed metabolic and respiratory acidosis
If actual PaCO₂ is lower than expected → Superimposed respiratory alkalosis

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What is the stepwise approach to analyzing an ABG?

Look at pH (Acidosis or Alkalosis?)
Check PaCO₂ and HCO₃⁻ (Respiratory or Metabolic cause?)
Determine compensation (Appropriate or mixed disorder?)
Use Winter’s formula (if metabolic acidosis)
Assess for mixed disorders

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A patient presents with pH 7.29, PaCO₂ 54 mmHg, HCO₃⁻ 26 mEq/L. What is the diagnosis?

Respiratory Acidosis (pH <7.35, CO₂ elevated, normal HCO₃⁻)

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A patient with sepsis has pH 7.28, HCO₃⁻ 16 mEq/L. Using Winter’s formula, what is an appropriate PaCO₂ compensation?

32 mmHg (1.5 × 16 + 8 ± 2 = 30-34 mmHg)

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A patient with obesity (BMI 61) is found lethargic with ABG: pH 7.21, PaCO₂ 70 mmHg, HCO₃⁻ 28 mEq/L. What is the cause?

Obesity Hypoventilation Syndrome → Chronic Respiratory Acidosis

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PCO₂ > 45 mmHg

Respiratory acidosis

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PCO₂ < 35 mmHg

Respiratory alkalosis

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HCO₃^- < 22 mmol/L

Metabolic acidosis

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HCO₃^- > 28 mmol/L

Metabolic alkalosis

pH < 7.35

Acidemia

pH > 7.45

Alkalemia

Compensation of metabolic acidosis

Metabolic acidosis → Respiratory compensation (Hyperventilation to ↓ CO₂)

Compensation of respiratory acidosis

Respiratory acidosis → Renal compensation (↑ HCO₃⁻ reabsorption, ↑ H⁺ excretion)

[H⁺], [HCO₃^-], and PCO₂ deviations in metabolic acidosis

[H⁺] = Increased

[HCO₃^-] = Decreased

PCO₂ = Decreased (secondary respiratory alkalosis)

[H⁺], [HCO₃^-], and PCO₂ deviations in metabolic alkalosis

[H⁺] = Decreased

[HCO₃^-] = Increased

PCO₂ = Increased (secondary respiratory acidosis)

[H⁺], [HCO₃^-], and PCO₂ deviations in respiratory acidosis

[H⁺] = increased

[HCO₃^-] = increased (secondary metabolic alkalosis)

PCO₂ = increased

[H⁺], [HCO₃^-], and PCO₂ deviations in respiratory alkalosis

[H⁺] = decreased [HCO₃^-] = decreased (secondary metabolic acidosis) PCO₂ = decreased

Term that describes a low arterial partial pressure of oxygen

Hypoxemia

Term that describes poor oxygen delivery to tissues

Hypoxia

HH equation used to calculate pH of arterial blood

ICF Buffers

*Organic phosphates and proteins *Deoxyhemoglobin (given venous system has significantly higher partial pressure of CO₂ to maintain venous pH of 7.37)

How long does complete renal compensation for acute changes in acid-base status take?

Typically days to achieve

Respiratory compensation in acid-base disorders occurs through regulation of what process?

Ventilation

Given an ABG with a pH of 7.50, a pCO2 of 48 mm Hg, and a bicarbonate of 36 mEq/L, what acid-base disorder is present?

Metabolic alkalosis

Given an ABG with a pH of 7.26, a pCO2 of 32 mm Hg, and a bicarbonate of 14 mEq/L, what acid-base disorder is present?

Metabolic acidosis

Given an ABG with a pH of 7.52, a pCO2 of 24 mm Hg, and a bicarbonate of 19 mEq/L, what acid-base disorder is present?

Respiratory alkalosis

Given an ABG with a pH of 7.22, a pCO2 of 80 mm Hg, and a bicarbonate of 32 mEq/L, what acid-base disorder is present?

Respiratory acidosis

Winter's formula can be used to assess the appropriateness of compensation in what primary acid-base disorder?

**Metabolic acidosis** In metabolic acidosis, appropriate respiratory compensation is determined using Winter’s formula: pCO2 = (1.5 [HCO3-] +8) ± 2

Which of the following conditions would be most likely to cause a respiratory acidosis? A. Anxiety B. Salicylate poisoning C. Overstimulation of respiratory centers due to sepsis D. Use of opioid pain medication E. Over-ventilation on a mechanical ventilator

D. Use of opioid pain medication

Which of the following conditions would be most likely to cause a respiratory alkalosis? A. COPD exacerbation B. Respiratory muscle weakness C. Hypoxemia D. Obstructive sleep apnea E. Obesity hypoventilation syndrome

C. Hypoxemia

Which of the following is not directly measured on an arterial blood gas? A. pH B. PaO₂ C. Bicarbonate D. Volatile acid E. Non-volatile acid

non-volatile acid

What medication overdose first presents as respiratory alkolosis and then progresses to metabolic acidosis?

Salicylate toxicity initially presents with respiratory alkalosis through direct respiratory stimulation, but then progresses to metabolic acidosis from carbohydrate metabolism disruption and resulting buildup of lactic acid. ## Footnote o Excessive stimulation of the medullary respiratory centers can cause respiratory alkalosis:  Sepsis  Salicylate poisoning  Neurologic disorders  Hysterical hyperventilation (anxiety)

Acute on chronic respiratory acidosis ## Footnote For every 10 mmHg PCO₂ there is a 1.5 mmol/L [HCO₃^-] = acute respiratory acidosis (change of 3.5 mmol/L = chronic) or pH drops 0.8 units for every 10 mmHg rise of PCO_{2_{= acute

or 0.03 pH units for every 10 mmHg PCO_{2_{= chronic resp acidosis}}}}