Respiratory Quiz #5 Flashcards
Describe how a weak acid behaves in a solution such as blood.
• Weak acids (HA-carbonic acid), such as H2CO3 reversibly donate H+ • When HA is in solution, it can ACT AS AN ACID by donating an H+ • All body fluids have acid-base buffer systems that instantly combine with any acid or alkali to prevent changes in [H+]
Describe how a weak base behaves in solution such as blood.
• Its conjugate base, (A-), can ACT AS A BASE by rapidly and reversibly taking up H+ • Weak bases (A-), such as HCO3 - REVERSIBLY BIND H+ • All body fluids have acid-base buffer systems that instantly combine with any acid or alkali to prevent changes in [H+]
Compare the three mechanisms responsible for H+ regulation.
• Buffer systems (rapid but incomplete) • Ventilatory responses (less rapid) • Renal responses (slow, but produces almost nearly complete correction of pH)
Identify four buffering systems the body incorporates in regulating acid-base balance
HHb H+ + Hb- Hprot H+ + Prot- H2PO4- H+ + HPO42 H2CO3 H+ + HCO3 -
Describe the effect of oxygen saturation on hemoglobin’s buffering capacity.
Hemoglobin Buffering Systems • Effective because of its high concentration • Buffering capacity varies with oxygenation (reduced hemoglobin is a weaker acid) • In its reduced form (carrying less oxygen), more base is available to combine with H+ produced by the dissociation of carbonic acid in the tissues
Discuss rationale for why the bicarbonate system is the most important buffering system in the body
Bicarbonate Buffering System • HCO3 - accounts for > 50% of total buffering capacity of the blood (extracellular) • HCO3 - DIFFUSES EASILY INTO RBC’S SO THAT 1/3 OF ALL BICARBONATE BUFFERING OCCURS HERE • pKa is 6.1 (blood pH 7.4), so that it is a weak buffer (20:1 ratio HCO3 - to CO2 )
Describe the role of ventilation in regulating H+ concentration
Role of Ventilation in Bicarbonate Buffering System • The main importance of this buffering system is that its element can be regulated by both the kidneys and the lungs • The CO2 produced by the reaction of H+ and HCO3- is easily removed by the body • Ability to maintain pH 7.4 depends on the free movement of CO2 out of the body (need ventilation and renal function) • H2O + CO2 H2CO3 H+ + HCO3 • Ventilatory responses occur within 1-5 minutes of a change in hydrogen ion concentration • Doubling alveolar ventilation eliminates sufficient CO2 to increase pH to 7.6 • Decreasing alveolar ventilation to one-fourth of normal decreases pH to 7.0 -
Describe renal regulation of H+ concentration
Renal Responses • Renal responses that regulate [H+] do so by acidification or alkalinization of urine • Incomplete titration of H+ and HCO3-occurs, allowing either to enter urine and be excreted • IN THE PRESENCE OF ACIDOSIS H+ IS EXCRETED AND HCO3- IS EXCRETED IN ALKALOSIS
Describe how pH may be calculated by the Henderson-Hasselbach equation using bicarbonate and CO2 concentrations in the blood
Acid-Base Status of the Blood • In the blood, the three components of the Henderson-Hasselbach equation are pH, HCO3, and CO2 (0.03 mmol H2CO3 for each mmHg PCO2) • pH results from [HCO3] and CO2 in blood: • pH=pKA + log (HCO3)/0.03 (PaCO2) • pH=6.1 + log (24)/0.03 (40) • pH=6.1 + log 20 • pH=6.1 + 1.3, or pH =7.4 • Therefore, as long as the ratio of HCO3 to (PaCO2 x 0.03) remains 20, pH will remain 7.4 • FROM THIS EQUATION IT IS APPARENT THAT THE PH IS RELATED TO THE RATIO OF CONJUGATE BASE TO THE UNDISSOCIATED ACID IMPLICATIONS OF THE HENDERSON-HASSELBACH EQUATION • PH IS A FUNCTION OF THE RATIO OF BICARBONATE AND CO2 CONCENTRATIONS IN THE BLOOD • IF RATIO IS GREATER THAN 20, RELATIVE DEGREES OF ALKALOSIS RESULT • IF RATIO IS LESS THAN 20, RELATIVE DEGREES OF ACIDOSIS RESULT • CALCULATION IS MADE USING PKA OF CARBONIC ACID, SERUM BICARBONATE AND ARTERIAL PCO2
Compare and contrast ventilatory and renal response to acidosis in regard to efficacy and speed
VENTILATORY RESPONSE TO ACID-BASE STATUS • Lungs have a profound effect on acid-base status of blood • Lungs excrete over 10,000 mEq of carbonic acid/day as compared with 50-500 mEq by the kidneys • By altering alveolar ventilation and elimination of CO2, the body compensates for pH change within 1-5 minutes • Able to buffer up to twice the amount of acid or base as all other buffers combined RENAL RESPONSE TO ACID-BASE STATUS • Regulation of acid-base occurs by allowing either H+ or HCO3 - to be removed from extracellular fluid (slow, but completely neutralizes) • Ordinarily the kidneys can excrete up to 500 mEq of acid or alkali each day (urine pH 6.4) • Higher concentrations of CO2 cause excretion of H+ while hyperventilation causes retention
List five anesthetic considerations with acidosis
• Potentiation of depressant effects of sedatives and anesthetic agents on CNS and circulatory system (increased nonionized fraction and increased penetration into brain) • Decreased sympathetic tone • Increased arryhthmogenicity of volatile agents • Increased K+ with succinylcholine • Augmentation of neuromuscular blockade
Categorize a provided arterial blood gas as either compensated/uncompensated and either primarily metabolic or respiratory
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Identify the role of the medulla in regulating respiration
Medullary respiratory centers • Regulate initiation of inspiration (dorsal) • Regulate forced expiration (ventral)
pH PaCO2 [HCO3-] 1. 7.56 28 mmHg 24mM 2. 7.58 20 mmHg 18 mM 3. 7.43 22 mmHg 14 mM 4. 7.34 50 mmHg 26 mM 5. 7.29 65 mmHg 30 mM 6. 7.36 55 mmHg 30 mM 7. 7.56 38 mmHg 33 mM 8. 7.69 50 mmHg 35 mM 9. 7.24 43 mmHg 18 mM 10.7.30 25 mmHg 12 mM
- Uncompensated respiratory alkalosis 2. Partially compensated respiratory alkalosis 3. Completely compensated respiratory alkalosis 4. Uncompensated respiratory acidosis 5. Partially compensated respiratory acidosis 6. Completely compensated respiratory acidosis 7. Uncompensated metabolic alkalosis 8. Partially compensated metabolic alkalosis 9. Uncompensated metabolic acidosis 10. Partially compensated metabolic acidosis
Identify the role of the pons in regulating respiration
Pons respiratory centers • Apneustic center prolongs respiration • Pneumotaxic center regulates respiratory rate