Gas Exchange & Acid-Base Regulation Flashcards
things that may widen the A-a gradient
- alveolar problems (ex. emphysema)
- interstitial problems (ex. pulmonary fibrosis, interstitial edema)
- capillary problems (pulmonary HTN, shunting)
factors contributing to rapid oxygen diffusion to blood from lungs
*large surface area
*small diffusion distance
*O2 has a relatively large blood/air pressure gradient
one gram of hemoglobin can bind ?mL of O2?
one gram of Hb can bind 1.34 mL of O2 (when all sites are bound to oxygen)
% Hb saturation = ?
% Hb saturation = O2 bound to Hb / O2 capacity of Hb x 100%
oxygen content of blood - formula
oxygen bound to hemoglobin + dissolved oxygen
([Hb] x 1.34 x %saturation) + 0.003(PaO2)
oxygen delivery to tissues - formula
oxygen delivery = cardiac output x oxygen content
CO x (([Hb] x 1.34 x %saturation) + 0.003(PaO2))
haldane effect
when less oxygen is bound, the affinity of hemoglobin for CO2 increases
Bohr effect
when more H+ is present (lower pH), the affinity of hemoglobin for O2 decreases (more likely to release oxygen) and H+ is able to bind to Hb
chloride shift
occurs whereby Cl- enters the red blood cell from plasma in exchange for HCO3-
cooperative binding
each molecule of O2 bound to hemoglobin increases the affinity for the next (this is why the oxyhemoglobin association curve is so steep)
factors that cause the oxyhemoglobin curve to the right (increase P50)
*decreased pH (increased H+)
*increased 2,3 DPG
*increased CO2
*increased temperature
anything that shifts the curve to the right makes hemoglobin more likely to release its oxygen molecule
partial pressures & pH in the lungs
*O2: 100 mmHg (100% saturation)
*CO2: 40 mmHg
*pH: 7.40
partial pressures & pH in the tissues
*O2: 40 mmHg (75% saturation)
*CO2: 46 mmHg
*pH: 7.35
note - Bohr effect unloads O2 in tissues; Haldane effect loads CO2 in tissues
normal physiologic pH
7.40
pH < 7.35 is acidemia
pH > 7.45 is alkalemia
carbonic acid (H2CO3) is the buffer
bicarbonate buffer system equation
normal bicarbonate concentration
24 mEq
arterial blood gas analysis (ABGs)
*used to determine a person’s acid-base status
*reports the following:
-pH
-PaCO2
-PaO2
-HCO3-
-base excess
-O2 saturation (SpO2)
RESPIRATORY alkalosis/acidosis
*disorders of PCO2
*this is because PCO2 is under control of the lung
*if PCO2 increases, it results in an acidosis
*if PCO2 decreases, it results in alkalosis
METABOLIC acidosis/alkalosis
*disorders of [HCO3-]
*this is because HCO3- is under control of the kidney
*if [HCO3-] increases, it results in alkalosis
*if [HCO3-] decreases, it results in acidosis
respiratory acidosis - simple
increased PCO2
respiratory alkalosis - simple
decreased PCO2 → high pH
metabolic acidosis - simple
decreased [HCO3-]
metabolic alkalosis - simple
increased [HCO3-]
expected acid-base changes
*if PCO2 changes, we expect a corresponding change in [HCO3-] (and vice versa)
*these corresponding changes are due to buffering
*the body will take additional action to try and return pH closer to normal (compensation)
