Term
| Arterial blood gas analysis - |
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Definition
| Performed on critically ill patients, main purpose is assessment of acid-base status. |
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Term
| Normal cell metabolism pH |
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Definition
| 7.35 - 7.45 (narrow range) |
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Term
| Mild pH deviations (symptoms) |
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Definition
| Can have serious effects, reduces O2 delivery, electrolyte disturbances, changes in heart muscle contractility. |
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Term
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Definition
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Term
| Normal metabolism acidic products |
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Definition
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Term
| Entities which regulate blood pH: |
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Definition
| Chemical buffers, erythrocytes, lungs, kidneys, brain |
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Term
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Definition
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Term
| Clinical alkalosis & acidosis |
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Definition
| Acidosis: Below 7.35, Alkalosis: Above 7.45 pH & hydrogen concentration equation: pH = -log10[H+] |
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Term
| What pH change from a doubling of [H+]? |
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Definition
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Term
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Definition
| Solution of a weak acid ands its conjugate base. Resists changes in solution pH. |
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Term
| Carbonic acid buffering in the body |
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Definition
| Carbonic acid is reduced via CO2 expulsion in the lungs, and kidneys continuously regenerate bicarbonate. |
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Term
| Bicarbonate chemical equation in the body: |
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Definition
| H+ & HCO3 <--> H2CO3 <--> H2O & CO2 |
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Term
| Blood CO2 levels are effected by: |
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Definition
| Cell metabolism (increases) and excretion via lungs |
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Term
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Definition
| Most diffuses into erythrocytes and fuses with water to form carbonic acid (catalyzed by carbonic anhydrase). The acid dissociates into H+ and its conjugate base (bicarbonate). H+ combine with deoxygenated hemoglobin, and bicarbonate diffuses back into the plasma. |
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Term
| Most CO2 is transported as what compound? |
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Definition
| Bicarbonate in the plasma. |
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Term
| Kidneys function in pH regulation |
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Definition
| Both eliminates H+ ions and regenerates bicarbonate. |
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Term
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Definition
| Rich with the enzyme carbonic anhydrase - facilitates the formation of carbonic acid from CO2 & H2O. The carbonic acid dissociates into H+ and HCO3- (bicarbonate), with the H+ being excreted into the lumen of the tubule to be eliminated by the body in urine. |
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Term
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Definition
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Term
| Expulsion of acid via lungs (process overview) |
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Definition
| H+ are displaces from hemoglobin as O2 is taken up. The H+ then are buffered by bicarbonate in the erythrocyte, causing a local decrease in [HCO3-], causing HCO3- to flow down its concentration gradient into erythrocytes. Carbonic acid is converted back into CO2 and H20 via carbonic anhydrase, and the CO2 diffuses from the blood into the air to be expelled by the lungs. |
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Term
| Reason for H+ excretion by the body: |
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Definition
| Buffers are only useful in the short-term, ultimately they can be used up, so H+ ions must be excreted by the body. |
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Term
| Most acid-base disturbances result from: |
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Definition
| Disease or damage to organs (kidney, lungs, brain), disease which causes increased production of acidic metabolites, medical intervention / side effects. |
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Term
| Parameters measured during blood gas analysis: |
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Definition
| pH, partial pressure of CO2 (pCO2), and [HCO3-] |
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Term
| Four categories of acid-base disturbances: |
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Definition
| Respiratory acidosis, respiratory alkalosis, metabolic acidosis, metabolic alkalosis. |
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Term
| Normal ranges for blood gas measurements: |
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Definition
pH: Adults 7.35 - 7.45, Neonates 7.30 - 7.40
pCO2 (kPa): Adults 4.7 to 6.0, Neonates 3.5 to 5.4
Bicarbonate (mmol/L): Adults 22-28, Neonates 15-25 |
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Term
| Henderson-Hasselbalch Equation: |
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Definition
| pH = pKa + log([A-]/[HA]) |
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Term
| Henderson-Hasselbalch equation from blood gas measurements: |
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Definition
| H2CO3 is not directly measured, but the relationship between pCO2(a) and H2CO3 enables us to restate the Henderson-Hasselbalch equation as: pH = 6.1 + log([HCO3-] / (pCO2(a) x 0.23)) |
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Term
| Simplified mathematical relationship of pH, bicarbonate, and pCO2(a): |
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Definition
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Term
| Crucial takeaways from blood pH / HCO3- / pCO2(a) relationship: |
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Definition
| pH remains normal as long as the ratio of bicarbonate & CO2 remains normal, alkalosis occurs if either bicarbonate increases or CO2 decreases, the reverse for acidosis. |
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Term
| Respiratory pH disturbances: |
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Definition
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Term
| Metabolic pH disturbances: |
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Definition
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Term
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Definition
| Characterized by increase pCO2(a) due to inadequate alveolar ventilation (hypoventilation) and consequent reduced elimination of CO2 from the blood. Bronchopneumonia, emphysema, asthma, chronic obstructive airways may all be associated with respiratory acidosis. |
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Term
| Drugs and respiratory acidosis: |
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Definition
| Some drugs (morphine & barbiturates) can cause respiratory acidosis by depressing the respiratory center in the brain. |
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Term
| Trauma & respiratory acidosis: |
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Definition
| Damage to the chest wall & musculature can lead to a reduction in ventilation rate. Explains respiratory acidosis in poliomyelitis, Guillain-Barre syndrome, and recovery from chest trauma. |
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Term
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Definition
| Characterized by decreases pCO2(a) due to excessive alveolar ventilation, resulting in excessive elimination of CO2 from blood. Due to reduced O2 in the blood (hypoxemia), the respiratory center is stimulated (hyperventilation). |
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Term
| Diseases associated with respiratory alkalosis: |
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Definition
| Severe anemia, pulmonary embolism, adult respiratory syndrome, anxiety attacks, response to severe pain. |
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Term
| Drug effects - respiratory alkalosis: |
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Definition
| Salicylate (aspirin) can stimulate the respiratory center. A salicylate overdose can cause respiratory alkalosis. |
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Term
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Definition
| Characterized by a deceased [HCO3-], decreased pH |
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Term
| Why is reduced HCO3- always a feature of metabolic acidosis? |
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Definition
| Increased use of bicarbonate occurs when buffering an increased acid load, increased removal of bicarbonate from the body. |
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Term
| Diseases affecting metabolic acidosis: |
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Definition
| Diabetic ketoacidosis and lactic acidosis are two conditions characterized by overproduction of metabolic acids - consequently exhausting the bicarbonate supply. |
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Term
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Definition
| Abnormally high blood concentrations of keto-acids (b-hydroxybutyric acid and acetoacetic acid) reflect the severe metabolic derangements which result from insulin deficiency. |
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Term
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Definition
| All cells produce lactic acid if they are deficient of O2, so lactic acidosis may result from any condition in which tissue oxygen delivery is severely compromised. |
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Term
| Conditions displaying lactic acidosis: |
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Definition
| Cardiac arrest, any condition associated with hypovolemic shock (massive fluid loss), liver failure (given that liver metabolizes lactic acid). |
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Term
| Other conditions associated with metabolic acidosis: |
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Definition
| Severe diarrhea can result in excessive loss of bicarbonate from the body. Renal failure can lead to decreased regeneration of bicarbonate. |
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Term
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Definition
| Characterized by increased bicarbonate and pH |
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Term
| Causes of metabolic alkalosis: |
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Definition
| Rarely, excessive administration / ingestion of bicarbonate (antacids) - though typically transient. Abnormal loss of H+ (loss of gastric juices), severe K+ depletion can cause acidosis due to a reciprocal relationship between K+ and H+ ions. |
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Term
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Definition
| A consequence of acid-base disturbance. The body will attempt to return a normal pH when the acid-base balance is disturbed. A patient with low [HCO3-] must lower his pCO2(a) to return pH to normal. To achieve this, the respiratory center will increase ventilation (hyperventilation) - thereby increasing elimination of CO2. |
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Term
| Compensation for respiratory acidosis & alkalosis: |
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Definition
| Renal adjustments of H+ excretion result in changes in [HCO3-] that compensate for changes in pCO2(a). For acidosis, the kidneys increase bicarbonate reabsorption, for alkalosis - reduced bicarbonate reabsorption. |
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Term
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Definition
| Respiratory compensation for a primary metabolic disturbance occurs much more quickly than a metabolic compensation for a primary respiratory disturbance. |
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Term
| Fully compensated vs. partially compensated: |
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Definition
| If normal pH is achieved, a patient is fully compensated...but in many cases, pH is returned towards normal without actually achieving a normal pH completely (partially compensated). |
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Term
| Partially compensated example: |
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Definition
| A patient with a chronic lung disease (such as emphysema) who has long-standing partially compensated respiratory acidoses. If this patient were also diabetic in a state of diabetic ketoacidosis, blood gas results would reflect the combined effect of respiratory acidosis and metabolic acidosis. Such mixed acid-base disturbances are not infrequent and may be difficult to unravel on the basis of arterial blood gas results alone. |
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Term
| Respiratory acidosis (review): |
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Definition
Common causes - emphysema, COPD, pneumonia, depression of respiratory center.
Compensatory mechanism - renal increase in bicarbonate.
Initial blood gas - pH decreased, pCO2 increased, HCO3- normal.
Blood gas after compensation - pH normal, pCO2 increased, bicarbonate increased. |
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Term
| Respiratory alkalosis (review): |
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Definition
Common causes - hyperventilation, anxiety attacks, stimulation of respiratory center.
Compensatory mechanism - renal disease in bicarbonate.
Initial blood gas - pH increased, pCO2 decreased, bicarbonate normal.
Blood gas after compensation - pH normal, pCO2 decreased, bicarbonate decreased. |
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Term
| Metabolic acidosis (review): |
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Definition
Common causes - Renal failure, diabetic ketoacidosis, circulatory failure, clinical shock (lactic acidosis).
Compensatory mechanism - respiratory decrease in pCO2.
Initial blood gas - pH decreased, pCO2 normal, bicarbonate decreased.
Blood gas after compensation - pH normal, pCO2 decreased, bicarbonate decreased. |
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Term
| Metabolic alkalosis (review): |
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Definition
Common causes - bicarbonate administration, potassium depletion.
Compensatory mechanism - respiratory increase in pCO2 (but limited).
Initial blood gas - pH increased, pCO2 normal, bicarbonate increased.
Blood gas after compensation - limited compensation in metabolic alkalosis. |
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