Patho- Mcarthy Flashcards
ABG: normal value: pH, pCO2, pO2
pH: 7.35-7.45
pCO2: 35-35
pO2: 80-100
ABG normal value: calculated HCO3- (aka CO2 content)
24
what is the normal value for CO2 content in venous blood? what equation does the lab use to calculate this?
24-31 … represents the HCO3-
CO2 +H2O H2CO3 H+ + HCO3-
what is the partial pressure of O2 in dry air? in inspired (humidified) air?
dry: 160mmHg
inspired: 150mmHg
PAO2 (alveolar), PVO2 (venous blood), and PaO2 (arterial)
PVO2: 40
PAO2: 100 (gains from inspiration)
PaO2: 100
PCO2 in dry air, inspired air, venous blood, alveoli and arterial blood
dry air: 0 inspired air : 0 venous: 46 alveoli: 40 (loses from expiration) arterial: 40
what kind of problem is it if HCO3- values are abnormal?
chronic (aka compensatory response)
what formula do you use to calc partial pressure of O2 in alveoli?
PAO2= PIO2 - (PACO2*1.25)
and PIO2=150mmHg
FVC
forced vital capacity = amount able to fully exhale after deepest inhalation
RV
residual volume: about 1200mL : amount leftover after forced exhalation - not measurable by spirometry
FRC
functional residual capacity: amount leftover in lungs after normal tidal volume exhale
(expiratory RV + RV) –>
(1200 + 1200mL = 2400mL)
what will result from low V/Q ratio?
this means low blood O2 (hypoxemia) so youll inc. resp rate (forcibly increasing the V/Q ratio) to compensate for inc pCO2
low V/Q ratio (hypoxemia) …your resp rate increases to compensate … but what will happen if the work of breathing is too much… what pts is this common in?
work of breathing too much means you’re requiring too much O2 … you will get hypercapnia where pCO2> 45mmHg (common with COPD pts)
PCO2 < 35 is what? PCO2 >45 is what?
<35 : hypocapnia, alveolar hyperventilation : alkalosis
>45: hypercapnia, alveolar hypoventilation : acidosis
what is minute ventilation? what is the equation?
total rate of air movement into and out of the lungs
Tidal Vol * breaths/min = minute vent.
what is alveolar ventilation and its equation?
corrects for physiological dead space
(tidal vol - physiological dead space) * breaths/min = alveolar vent.
what is the relationship between PCO2 and alveolar vent (and the more useful equation for alv vent)?
inverse relationship: inc alveolar vent = dec PCO2 (blowing off more CO2)
PCO2=VCO2/VA
VCO2= rate CO2 production and VA= alveolar vent.
what is PETCO2? what is it used for?
amount of CO2 in expired air (the partial pressure of it). this gives early warning signs of respiratory compromise b/c it can be continuously monitored (“ventilation vital sign”)
what is the normal range of PETCO2?
its 1:1 with arterial ABG PCO2 so its 35-35 mmHg
increasing PCO2 = ___ H+ = ____ pH ..which means the person has…
= increasing H+ = dec. pH (acidosis)
its important to maintain normal pCO2 b/c its in equilibrium with _____ and a change in PCO2 can …
weak acid : H2CO3
disturb the acid-base balance
as lung vol increases, pressure of gas ___
decreases
increase in ____ causes ______ acidosis
decrease in _____ causes _____acidosis
inc. PCO2: respiratory
dec. HCO3- : metabolic
what is a case when there may be respiratory compensation for metabolic acidosis
if the lungs are healthy and they have diabetic ketoacidosis (serum HCO3- drops in attempt to buffer ketoacids… buffer consumes HCO3- (levels drop), pH drops… respiratory responds with hyperventilation to minimize change in pH, brain tells body to increase resp. rate.
central chemoreceptors: location, process, goal
location: brainstem
process: CO2 diffuses into CSF: inc PaCO2=inc PCO2 in CSF = dec. pH = hypervent. to dec. CO2
goal: keep arterial PCO2 in range by min-to-min control of breathing
peripheral chemoreceptors: location, process, goal
location: carotid arteries and aortic arch
process: PaO2 <60mmHg or dec. arterial pH in carotid bodies = hypervent. to dec. CO2
goal: activate and contribute to resp. rate change ONLY if PaO2<60mmHg or theres an acid-base balance alteration IN CAROTID BODIES
PO2: normal range, hypoxemia
SaO2 (saturation): normal range, hypoxemia
PO2: 80-100, hypox: <80
SaO2: >95%, hypox: <95
PO2: 60-80 , 40-60, <40 … what are the equivalent numbers in SaO2 ?
PO2: 60-80 = SaO2: 90-95
40-60 = SaO2: 75-90
<40 = SaO2: <75
what are the levels of PO2 and SaO2 when it is reccomended to start O2 therapy? and the target numbers?
PO2: = or <55 TARGET: at least 60
SaO2: 88 TARGET: at least 90
A-a gradient : how do you use it? what does it mean if A-a is normal?
(age/4) + 4 … use in comparison with what is calc. from alveolar gas equation . PAO2- PaO2= calc. gradient
if A-a is normal, there is no V/Q mismatch and the hypoxia is just secondary to inc. pCO2
ANS on lung: parasympathetic effect vs sympathetic
both act on bronchial smooth muscle
PSNS –Ach–>bronchoconstriction
SNS –B2–> bronchodilation
airflow, pressure gradient and resistance equation
Q= deltaP/R
Q: airflow
delta P: pressure gradient
R: resistance
___ is the driving force of airflow (Q)
pressure difference (deltaP)
recommendations for O2 therapy: hypoxic but NOT hypercapnic?
O2 therapy!
recommendations for O2 therapy: hypoxic AND hypercapnic?
O2 therapy risks worse PCO2 retention .. monitor response to O2 w/ ABGs not with O2 Saturation (ABGs looks at pCO2)
what is O2 saturation? vs paO2
% Hgb binding sites that carrying O2
paO2: represents actual O2 content in the blood
explain the increase and rapid rise in the O2-Hgb dissosciation curve
as partial pressure inc, there are more O2 molecules available to bind. More O2 bound to Hgb, the easier it is for the next one to bind = speed inc and rapid rise in curve.. until all are filled and Hgb is saturated (getting close to saturation when O2 about 90% and paO2 60, curve begins to level off).
phenomenon: “positive cooperativity”
minimum amount of O2 conc. needed to prevent ischemia in tissues…
O2 saturation of 90% and paO2 of 60 mmHg
tissue hypoxia from inadequate tissue perfusion like HF: O2 delivery to tissues is determined by ___ and ____
blood flow (aka cardiac output) and O2 content in blood (dissolved O2 + Hgb bound O2)
most of O2 delivered to tissues is ____
attached to Hgb (99%)
when you measure PO2 from ABGs, youre measuring …
amount of O2 dissolved in blood, not what is attachd to Hgb
3 major causes of tissue hypoxia
- inadequate gas exchange in lungs (only one you can txt w/ O2 therapy)
- anemia
- inadequate tissue perfusion (HF)
Hgb affinity for fourth molecule of O2 is highest and occurs at values … what does this mean for affinity in lungs vs tissues.
PO2: 60-100mmHg , when we are closest to saturation
lungs: affinity at peak, about 100% saturated PaO2=100mmHg
tissue: affinity lower, about 75% saturated, PaO2=40mmHg
how do tissues maintain the pressure gradient of O2 so that it keeps perfusing
they use the O2, so that the PaO2 in capillaries is always higher than in tissues and therefore O2 diffuses across into tissues
cause of polycythemia:
hypoxia –> inc synthesis of erythropoietin in kidney –> acts on bone marrow –> RBC production –> inc Hgb production –> inc. O2 carrying capacity –> inc. total O2 in blood!
cor pulmonale
right sided heart failure caused by pulm. HTN (which is caused by some primary pulm disease like COPD or ILD) or pulm. vasculature (PE)
how to distinguish cor pulmonale from rightHF cause by left HF
left HF will cause inc. in PCWP (pulmonary capillary wedge pressure)
compliance explained in terms of a rubber band… disorders of high and low compliance
high compliance: thin rubber band = thin elastic “tissue”, easily stretched (i.e. emphysema)
low compliance: thick rubber band = thick elastic “tissue”, hard to stretch but stronger snapback (i.e. fibrosis)
definition of compliance
distensibility of the system: describes change in lung vol. for given change in pressure
C= deltaV * deltaP
V: lung vol.
P: transpulmonary pressure
what is transpulmonary pressure
diff between inside alveoli and pleural surface of lung
the A-a gradient is high, what are the two possible reasons for this?
- V/Q mismatch
2. shunting (essentially extreme V/Q mismatch)
The A-a gradient is low, what would this mean?
low OR normal would mean that something caused dec. CO2 (hyperventilation-panic attack or high altitude) - if alkalosis.
or other cause from inc. CO2 (if acidosis)
metabolic acidosis or alkalosis is always acute or chronic?
always acute
