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When do you use arterial versus venous blood for blood gas analysis?
- assessment of oxy/vent required arterial
- assessment of acid/base balance can use either, usually use venous b/c easier
anything less than pH 7.4
anything over pH 7.4
What are the physiologic effects of acid base imbalance? (4)
- proteins denature, enzymes deactivate
- catecholamines lose function (myocardial function impaired, loss of vascular tone)
- CNS disturbance (loss of osmotic gradients, impaired depolarization)
- muscle weakness
Any gain of acid or loss of base, leading to a net effect of decreased HCO3.
Any reduction in alveolar ventilation relative to CO2 production, resulting in high PCO2.
Any loss of acid or increase in base, leading to a net effect of increased HCO3.
Any increase in alveolar ventilation relative to CO2 production, resulting in low PCO2.
What are the body buffering systems? (3)
- chemical buffers (seconds to hours)- phosphates, proteins, hemoglobin
- respiratory buffers (minutes to hours)- change ventilation to alter CO2
- renal buffering (hours to days)- change H+ or HCO3- excretion
What equation describes the body's buffering systems?
H+ + HCO3- <--> H2CO3 <--> H2O + CO2
Describe respiratory compensation.
changes in CO2 in response to a primary metabolic disturbance
Primary metabolic acidosis leads to ______________.
Primary metabolic alkalosis leads to ______________.
- compensatory resp alkalosis (hyperventilation)
- compensatory resp acidosis (hypoventilation)
Describe metabolic compensation.
changes in HCO3- in response to a primary respiratory disturbance, which has acute (chemical) and chronic (renal) components
How do you know which is the primary disturbance on a blood gas?
look at the pH; the compensation will almost never return the pH to normal
Amount of acid or base required to return the blood pH to the reference interval with CO2 held at a standard value.
Base Excess/ Deficit
Base excess is the amount of acid or base that must be added to ____________ at __________.
return pH to 7.4; pCO2 of 40mmHg
Describe interpretation of base excess.
- normally 0
- positive BE= metabolic alkalosis
- negative BE (deficit)= metabolic acidosis
Na+ + K+ - (Cl- + HCO3-)
Increased in _________ will widen the anion gap.
unmeasured anions (adding acid to the system)
Relative difference between Na+ and Cl-, which can have an impact on acid-base balance.
strong ion difference (SID= Na+ - Cl-)
In order to develop a change in SID,...
Na+ or Cl- must change independently or disproportionately.
Decreased SID means...
decreased Na+ or increased Cl---> acidosis b/c HCO3- decreases to maintain electroneut
Increased SID means...
increased Na+ or decreased Cl- --> alkalosis b/c HCO3- increased to maintain electroneut
What is the effect of albumin on acid base?
albumin has a significant negative charge' decreased albumin effectively means less acid --> alkalosis
- metabolic alkalosis
- no true cause/ relative to dehydration--> no effect on acid base
With respiratory acidosis, the primary change is ___________; the compensatory response is ___________.
increased PCO2; increased HCO3-
With respiratory alkalosis, the primary change is ___________; the compensatory response is ___________.
decreased PCO2; decrease HCO3-
With metabolic acidosis, the primary change is ___________; the compensatory response is ___________.
decreased HCO3-; decreased PCO2
With metabolic alkalosis, the primary change is ___________; the compensatory response is ___________.
increased HCO3-; increased PCO2