Day 2 - Kidneys, ABG Flashcards
What does the BUN stand for? The BUN test assesses the function of…
Blood urea nitrogen
How well liver and kidneys are functioning
- liver breaks down proteins and makes ammonia
- ammonia combines with other elements to form urea
- travel through blood to kidneys
- kidneys filter urea out of blood into urine
What are the 2 equations for the osmole gap?
Osmolality - [1.86(Na+) + glucose/18 + BUN/2.8 + 9]
Osmolality - [2(Na+) + glucose/20 +BUN/3]
What are the 2 equations for the anion gap?
[Na+] – ([Cl-] + [HCO3-])
[Na+] + [K+] – ([Cl-] + [HCO3-])
-K can be excluded
What are the 3 functions of the kidneys
Filtration
Reabsorption
Secretion
Blood arrives in the kidneys through the ___ arteriole and exit via the ___ arteriole
Afferent
Efferent
Approximately ___ of blood flows through kidneys every minute. Approximately ___ of water containing low MW substances pass through the glomerulus to be filtered…
1.2 liters
120 ml/min
- 10% of 1.2 liters
- most water is reabsorbed
Substances below this molecular weight can pass through the kidneys. What percentage of fluid and electrolyte get reabsorbed in the PCT?
70,000
80%
-most Na reabsorbed, most K not reabsorbed
During Na reabsorption, ___ is exchanged for Na
H+
Afferent arterioles are larger/smaller than efferent arterioles. Why?
Larger
Creates hydrostatic pressure to drive GFR
Where is carbonic anhydrase located and what is its function?
Renal tubules
Uses water and CO2 to make H+ and bicarbonate
-acid-base balance
What is the specific gravity of the glomerular filtrate?
- 01, same as plasma
- glucose and protein reabsorbed at beginning of tubules, resulting in plasma filtrate without glucose and protein
The kidneys excrete these 3 major products of protein catabolism
Creatinine - skeletal muscle dehydration product. Constant rate proportional to muscle mass
Urea (BUN) - ammonia that is converted to urea for excretion
Uric acid - from purine breakdown
Of the 3 major excretion products of protein catabolism, which one can be reabsorbed and which one is excreted?
Urea and uric acid can be reabsorbed
Creatinine excreted
Of the 3 major excretion products of protein catabolism, which one is commonly used to assess how well the kidneys are functioning? Why (2)?
Creatinine (creatinine clearance test)
Excreted into circulation at a constant rate
All creatinine excreted in urine (none reabsorbed)
-also <70,000 MW, stable, measureable within time interval
When kidneys are damaged, levels of BUN and creatinine in the blood are…
Elevated
What is uremia?
Elevated blood BUN (azotemia) with renal failure
What does a clearance test (ie creatinine clearance test) measure?
Rate at which kidneys remove a substance within a timed interval
- endogenous vs exogenous substance
- creatinine is endogenous substance (made in body)
- exogenous = injected
Clearance test - what is the gold standard for an endogenous substance? Exogenous?
Creatinine
Inulin
-IV or orally introduced
Creatinine clearance test - how long should urine be collected for?
24 hours
-greatest source of error is during collection
What is the creatinine clearance formula?
CrCl (mL/min) = [UrineCr x UrineVolume] / [PlasmaCr x time]
-time = 24 hours = 1440 mins
~80 ml/min is the creatinine “blind range”
What is the formula for the corrected creatinine clearance?
CrCl x (1.73 / A) = corrected CrCl (mL/min)
-takes into account height and weight
What are the 2 widely used creatinine clearance assays? Which one is more widely used?
Jaffe method - more widely used
-cheap, easy
Enzymatic
Jaffe method vs enzymatic method - Which one is more accurate. Why?
Enzymatic
Less interferences
-Jaffe method has a lot of interferences
Is the creatinine clearance calculation an underestimate or overestimate of the GFR? Why?
Overestimate
Extra creatinine is secreted by the distal convoluted tubule, causing overcalculation of GFR
Chronic kidney disease is a GFR less than…
60 ml/min
The MDRD GFR Study equation takes into account (3)… What is the equation?
Age
Gender
African-American
GFR (mg/dL) = 175 x PCr^(-1.154) x age^(-0.203) x [0.742 if female] x [1.210 if black]
-equation less reliable above 60 ml/min
Creatinine clearance calculation takes into account creatinine found in… GFR calculation takes into account creatinine found in…
Both plasma and urine creatinine
Just serum creatininediff
A new protein being proposed to use instead of creatinine is… What’s the advantage of using this protein over creatinine (2)?
Cystatin C
Larger than creatinine, so not removed by traditional dialysis
-assess if kidneys are functioning again
-made by all nucleated cells, not just muscles (creatinine)
-metabolized by nephrons, not secreted
No ethnicity involved in GFR calc, less adjustment for females
If we measure the specific gravity (concentration) of urine throughout the day, we can detect renal failure by this condition… What does it mean?
Isothenuria
Kidneys lack ability to concentrate or dilute urine so that blood filtrate remains unchanged and respond to the body’s hydration status
-specific gravity of urine is neither greater (more concentrated) nor less than (more dilute) that of protein-free plasma
Renal blood flow test (PAH; para-aminohippurate) is an example or endogenous or exogenous for tubular secretions?
Exogenous
-old method
Urine protein electrophoresis looks for this protein if the patient is suspected of having multiple myeloma…
Bence Jones protein
Should protein ever show up in the urine? Why or why not?
No
Large proteins cannot pass glomerulus, small proteins that slip through get metabolized by nephrons
-proteins in the urine indicate a problem
An acid is a substance that can give up ___. A base is a substance that can give up ___.
H+
OH-
What does the K value mean?
Ability of an acid or base to dissociate in water
- determines the strength of the acid or base
- strong acids/bases completely dissociate in water
What does the pK value mean?
Negative log of K
- strong acid = pK < 3.0
- strong base = pK > 9.0
What is a buffer? Name the main buffer in the blood
Combination of a weak acid or weak base and its salt, resisting pH changes
Bicarbonate (HCO3-)
What are the 3 blood “gases”?
pH
Carbon dioxide
Oxygen
What is pH a measure of? How does low and high pH relate to the number of hydrogen ions?
Hydrogen ions (H+) in solution -logarithmic scale (pH 5 is 10x more acidic than pH 6)
Lower pH = higher hydrogen ion concentration
Higher pH = lower hydrogen ion concentration
Most blood gases are collected from arteries or veins?
Arteries (ABG)
What do the following blood gas terms stand for: t, a, v, c, B, P
t = total a = arterial v = venous c = capillary B = blood P = plasma
Why is dried heparin the preferred anticoagulant over liquid heparin?
Liquid heparin may dilute sample
-also acidic
Why is a glass or plastic syringe preferred over a vacuum tube?
Vacuum tubes don’t fill correctly all the way up. Vacuum leftover above blood level can cause loss of blood gas
-underestimate values
How does the pCO2 in blood compare with pCO2 in air? What does this mean if there’s an air bubble in the ABG syringe? What happens to the pH?
pCO2 blood > pCO2 air
Exposure to air bubble causes both total CO2 and pCO2 to decrease in blood
Less CO2 = increase in pH
How does the pO2 in blood compare with pO2 in air? What does this mean if there’s an air bubble in the ABG syringe?
pO2 blood < pO2 air
pO2 in blood will increase
ABG samples are usually taken from the ___ artery. Good collateral flow through the ulnar artery can be performed using the ___ test
Radial
Allen test
3 classes of patients likely to require blood gas analysis
Critical care: trauma, surgery, intensive care
COPD
Newborns
pH balance/buffering is maintain by these two organs in the body. Which one is fast and which is slow?
Lungs = rapid, minutes
Kidneys = slow, days
“Respiratory” and “metabolic” are terms used to refer to which organs?
Respiratory = lungs
Metabolic = kidneys
Breathing (esp hyperventilation) can quickly remove these two things from the body
CO2
Hydrogen ion
Carbon dioxide is transported in the body as…
Bicarbonate (HCO3-)
-carbonic acid (H2CO3) is intermediate molecule between CO2 and HCO3-
What is the normal ratio of bicarbonate to carbonic acid in a healthy person?
20:1 (bicarbonate:carbonic acid)
Total CO2 in the blood is composed of (4)
CO2 in solution
CO2 bound to proteins
CO2 as bicarbonate (HCO3-)
CO2 as carbonic acid (H2CO3)
What does pCO2 measure?
Total dissolved CO2
Acute bicarbonate compensation calculation… Give two scenarios when acute kidney compensation will happen…
Change HCO3 (mM) = 0.2 x change pCO2 (mmHg)
Hyperventilation
Suffocation
Long term kidney compensation calculation… Give two scenarios when long term kidney compensation will happen…
Change HCO3 (mM) = 0.35 x change pCO2 (mmHg)
Long-term COPD
Living at high altitudes
If imbalance is metabolic, compensation is by… If imbalance is respiratory, compensation is by…
Ventilation
Kidneys
- kidneys slower (2-4 days) but better long term
- lungs faster (minutes) but better acute
Respiratory status (lungs) can be determined by this compound… Metabolic status (kidney) can be determined by this compound…
pCO2
HCO3-
Respiratory acidosis: levels of blood pCO2, HCO3, pH
Increase
Increase
Decrease
- release of carbon dioxide from blood into lungs decreased
- lungs can’t expel CO2
- COPD, pulmonary edema, bradycardia, drugs
- asthma, respiratory distress syndrome in newborn
- smoking long-term
Respiratory alkalosis: levels of blood pCO2, HCO3, pH
Decrease
Decrease
Increase
- hyperventilation
- excessive crying
- pregnancy
- CNS respiratory center damage
- fever
- pulmonary embolism
- living at high altitude
Metabolic acidosis: levels of blood pCO2, HCO3, pH
Decrease
Decrease
Decrease
- keto diet (ketosis)
- kidney disorder
- excessive diarrhea - loss of bicarbonate
Metabolic alkalosis: levels of blood pCO2, HCO3, pH
Increase
Increase
Increase
- eat a lot of bicarbonate, alkali antacids
- severe loss of chloride (vomiting - lose gastric HCl)
- corticosteroids, Cushing’s disease
How do lungs compensate for metabolic acidosis?
Hyperventilation
- releases CO2
- kidney retains bicarbonate
How do kidneys compensate for respiratory acidosis (2)?
Increased H+ excretion
Increase bicarbonate reabsorption and production
How do lungs compensate for metabolic alkalosis?
Slow breathing (hypoventilation) -retains CO2
How do kidneys compensate for respiratory alkalosis (2)?
Reabsorb H+ to blood
Increase bicarbonate excretion/reabsorb less bicarbonate
Proper ABG sample collection requires sample stored at this temp… Tested within…
Ice
15 mins
Which two other forms of hemoglobin can interfere with oxygen binding?
Carboxyhemoglobin (COHb)
Methemoglobin (MetHb)
What are the units for the following: GFR, anion gap, creatinine clearance, serum osmolality
mL/min
mM or mEq/L
mL/min
mOsm/kg
What is the Henderson-Hasselbalch equation to calculate pH? To calculate bicarbonate?
pH = 6.1 +log (HCO3-/ (0.03 x PCO2))
HCO3 = 0.03 * pCO2 * 10^(pH - 6.1)
What do the following terms mean for oxygen gas in the blood: P or p, S or s, c, d
P or p = partial pressure (pO2)
S or s = saturation fraction (sO2)
c = concentration (cO2)
d = dissolved (cdO2)
Factors that contribute to the oxygen dissociation curve (5)
Temperature
pH
pCO2 and 2,3-DPG levels
Interfering substances (ie carbon monoxide)
Presence of dysfunctional hemoglobin types
If PO2 and oxygen saturation are high, this indicates a ___ shift of the oxygen dissociation curve. If PO2 and oxygen saturation are low, this indicates a ___ shift of the oxygen dissociation curve
Left
Right
Increased 2,3-DPG or CO2 shifts the oxygen dissociation curve to the… Does hemoglobin affinity for oxygen increase or decrease?
Right
Decrease
-enhances release of oxygen
As 2,3-DPG or CO2 increase, pH…
Decreases
- increased CO2 = decreased pH
- right shift
How many oxygen molecules can one hemoglobin molecule carry?
4
Methemoglobin - which form is iron in? Can this form bind oxygen?
Ferric (Fe 3+), cannot bind oxygen
What is P50?
Partial pressure of oxygen at which hemoglobin is 50% saturated with oxygen
