Acid-Base Balance and ABG Interpretation

Flashcards covering essential terminology, normal values, buffer systems, and clinical interpretations for Acid-Base Balance and Arterial Blood Gas (ABG) analysis.

Acute ventilatory failure

A sudden rise in $PaCO_2$ with a corresponding decrease in pH and no compensation by the kidneys.

Chronic ventilatory failure

A chronically elevated $PaCO_2$ with a normal (compensated) or near normal pH and elevated $HCO_3^-$.

Acute alveolar hyperventilation

A sudden fall in $PaCO_2$ with a corresponding increase in pH and no metabolic compensation is occurring.

Chronic alveolar hyperventilation

A chronically decreased $PaCO_2$ with a normal (compensated) or near normal pH.

Volatile acids

Acids such as carbonic acid ($H_2CO_3$) that can dissolve in gas and are excreted by the lungs through ventilation.

Fixed (non-volatile) acids

Acids including sulfuric, phosphoric, and lactic acids that cannot be excreted by the lungs and must be excreted by the kidneys.

Bicarbonate ($HCO_3^-$)

The primary buffer system for fixed acids produced by the renal system (kidneys).

Relationship between pH and $H^+$

The relationship is inverse; an increase in pH reflects a decrease in free $H^+$ ions, and a decrease in pH reflects an increase in $H^+$.

Nephron

The functional unit of the kidney where bicarbonate ($HCO_3^-$) is controlled.

Diabetic Ketoacidosis (DKA)

A condition where the body breaks down fat as fuel due to lack of insulin, producing toxic acids in the bloodstream called ketones.

Open buffer system

The bicarbonate buffer system where $H_2CO_3$ can be removed through ventilation; it handles 53% of total buffering (35% in plasma and 18% in erythrocytes).

Non-bicarbonate (closed) buffer system

A system where all reaction components remain in the system, including Hemoglobin ($Hb$), organic/non-organic phosphates, and plasma proteins; it handles 47% of total buffering.

Normal Arterial Blood Gas (ABG) pH

$7.35$ to $7.45$, with a target of $7.40$.

Normal $PaCO_2$ range

$35$ to $45\,mmHg$.

Normal $HCO_3^-$ range

$22$ to $26\,mEq/L$.

Normal $PaO_2$ range

$80$ to $100\,mmHg$.

Hypercapnia

A condition where $PaCO_2$ is greater than $45\,mmHg$ due to insufficient alveolar ventilation.

Hypocapnia

A condition where $PaCO_2$ is less than $35\,mmHg$ due to excessive alveolar ventilation.

Metabolic Alkalosis

A condition characterized by an elevated pH and an elevated $HCO_3^- > 26\,mEq/L$, often caused by gastric suctioning, vomiting, or diuretics.

Anion Gap

The difference between major serum cations and anions, calculated as $[Na^+] - ([Cl^-] + [HCO_3^-])$; the normal range is $7$ to $16\,mEq/L$.

Winter's Formula

A formula used to predict the $PaCO_2$ level needed to fully compensate for metabolic acidosis: $PaCO_2 = [(1.5 \times HCO_3^-) + 8] \pm 2$.

Total Parenteral Nutrition (TPN)

IV hyperalimentation involving acidic solutions providing nutrients to malnourished patients who cannot use enteral nutrition.

Mixed Disturbance

The simultaneous presence of both respiratory and metabolic acid-base disorders, such as in cardiac arrest where blood flow and ventilation both stop.

Moderate Hypoxemia

A concentration of oxygen in the blood ($PO_2$) between $40$ and $59\,mmHg$.

Base Excess (BE)

The amount of acid or base needed to return pH to normal at a $PaCO_2$ of $40\,mmHg$; the normal range is $-2$ to $+2\,mEq/L$.

Kussmaul Respirations

Deep, rapid breathing used by the body as compensatory hyperventilation during metabolic acidosis (e.g., in DKA).