Term
| Define: respiratory acidosis |
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Definition
| 1) acid-base disturbance initiated by an increase in PaCO2 (primary hypercapnia) |
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Term
| Equation: Henderson Equation |
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Definition
| 1) [H+], nEq/L = 24*PaCO2/[HCO3-] |
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Term
| What two factors determine the level of PaCO2? |
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Definition
1) VCO2
2) V_A =~= V_E*(1-V_d/V_t) |
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Term
| What is the cause of respiratory acidosis in most cases? Why? |
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Definition
| 1) decrease in alveolar ventilation; overproduction of CO2 is usually matched with increase excretion via increased alveolar ventilation |
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Term
| What are examples of clinical circumstances of overproduction of carbon dioxide? |
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Definition
- increase physical activity
- augmented work of breathing by the respiratory muscles
- shivering
- seizures
- fever
- hyperthyroidism
- admin of large loads of bicarb |
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Term
| With respiratory acidosis, what is the major threat to life (use alveolar gas equation, write alveolar gas equation) |
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Definition
| 1) obligatory hypoxemia: PaCO2 = FiO2*(Patm - P_h2o) - PaCO2/R; therefore, increased PaCO2 will lead to decreased O2, eventually to dangerous levels |
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Term
| What is the secondary physiologic response to respiratory acidosis? |
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Definition
| - acidification of body fluids leads to adaptive increments in plasma bicarbonate concentration to attenuate the impact of hypercapnia on systemic acidity |
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Term
| Describe the acute adaptation to respiratory acidosis |
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Definition
- 5-10min of onset
- exclusively from acidic titration of body's nonbicarbonate buffers
- plasma bicarb: +0.1mEq/L/mmHgPaCO2
- plasma H+: +0.75mEq/L/mmHgPaCO2 |
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Term
| Describe chronic adaptation for respiratory acidosis |
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Definition
- 3-5 days of onset w/ sustained hypercapnia
- upregulation of renal acidification mechanisms (inc. in urinary net acid excretion (ammonium); persistent inc. in rate of renal bicarb reabsorption)
- plasma bicarb: +0.3mEq/L/mmHgPaCO2
- plasma H+: +0.3nEq/L/mmHgPaCO2
- unchanged plasma anion gap due to increased chloride excretion |
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Term
| What are the most common cause of chronic hypercapnia? |
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Definition
| - chronic lower airway obstruction from bronchitis and emphysema |
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Term
| Describe "hypercapnic encephalopathy" |
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Definition
- irritability
- inability to concentrate
- headache
- anorexia
- apathy
- confusion
- combativeness
- hallucinations
- delirium
- progressive narcosis and coma
*depends on magnitude, rapidity, severity of acidemia, degree of hypoxemia |
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Term
| What are characteristics used to identify respiratory acidosis |
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Definition
1) hypercapnia
2) acidemia
3) secondary increase in plasma bicarbonaate concentration |
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Term
| What are the therapeutic principles for acute respiratory acidosis? |
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Definition
1) prompt removal of the underlying cause
2) securing airway and adequate oxygenation |
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Term
| What are the therapeutic principles for chronic respiratory acidosis? |
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Definition
1) improve alveolar ventilation (antibiotics, bronchodilators, diuretics)
2) avoidance of irritants
3) elimination of retained secretions
4) gradual reduction of supp O2 aimed for PaO2 =~= 60mmHg
5) adequate quantities of Cl |
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Term
| Define: respiratory alkalosis |
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Definition
| - acid-base d/o characterized by an initial disturbance of decreased PaCO2 (primary hypocapnia) |
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Term
| What is the primary cause of respiratory alkalosis? Why? |
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Definition
| 1) increased in alveolar ventilation; decreased CO2 production generally is paralleled by decreased alveolar ventilation |
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Term
| What is the secondary response physiologically to respiratory alkalsosis? |
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Definition
- alkalinize body fluids
- adaptive decrements in plasma bicarb concentration that attenuate the impact of hypocapnia on systemic acididty |
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Term
| Describe acute adaptation of respiratory alkalosis |
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Definition
- 5-10 minutes of onset
- alkaline titration of body's nonbicarbonate buffers
- plasma bicarb: -0.2mEq/L/mmHgPaCO2
- plasma H+: -0.75nEq/L/mmHgPaCO2 |
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Term
| Describe chronic adapation to respiratory alkalosis |
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Definition
- 2-3 days of sustained hypocapnia
- downregulation of renal acidification mechanisms (dec in ammonium excretion; persistent dec in rate of renal bicarb reabsorption)
- plasma bicarb: -0.4mEq/L/mmHgPaCO2
- plasma H+: -0.4nEq/L/mmHgPaCO2
- small increase in plasma anion gap (inc. plasma chloride) |
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Term
| What are the neurological clinical manifestations of respiratory alkalosis? |
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Definition
- paresthesias of extremities
- chest discomfort
- circumoral numbness
- lightheadedness
- confusion
- tetany
- seizures (infrequent) |
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Term
| What are the features for a diagnosis of respiratory alkalosis? |
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Definition
1) hypocapnia
2) alkalemia
3) secondary decrease in plasma bicarbonate concentration |
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Term
| What are the therapeutic principles used to manage respiratory alkalosis? |
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Definition
1) correct underlying cause
2) alkalosis does not require tx usually; minimal/no sx and little risk to health
3) acetazolamide for high altitude sickness |
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