Exam 3 lecture 9 Flashcards
Normal PH of body?
7.35-7.45
What is it called when PH <7.35? WHat about when it is greater than 7.45?
less than 7.35 is acidemia
more than 7.45 is alkalemia
Acid base imbalances can be either ______ or _____
Metabolic or respiratory
Metabolic acid base imbalances are more reflective of which organ
Kidney is metabolic
Lung is respiratory
What compounds are changed in metabolic imbalances? What about on the respiratory imbalances
metabolic imbalances- Hydrogen and HCO3 (bicarb)
respiratory imbalances- involve changes in CO2
How do compensations occur in our body? Which one is faster?
lungs compensate metabolic disorders (lung compensation is much faster)
Kidneys compensate respiratory disorders
What are normal blood gas values to remmeber? best source for these values
PaCO2- 40
HCO3- 24
PaO2- 95-100
SaO2- > or = 95%
arterial blood gases are our best sources for obtaining these values
What are adverse consequences of acidemia
- CV
-decreased CO
- impairememnt of cardiac contractility
- increased pulmonary vascular resistance
-Increased arrhythmias (due to hyperkalemia) - Metabolic
- insulin resistance
-inhibition of anaerobic glycolysis\ - hyperkalemia
How does acidemia affect the CNS? lungs?
Coma or altered mental status
hyperventilation
adverse consequences of alkalemia
- CV
- decreased coronary blood flow
- arteriolar constriction
- decreased anginal threshold
- arrhythmias - Metabolic
- decreased K+, Ca and Mg
-Stimulation of anaerobic glycolysis (increase of ATP causes metabolic remodeling, could cause HF)
How does alkalemia affect ventilation
Hypoventilation (decreased respiration)
Where is acid coming from in our body?
- Diet (1 mEq/kg/day consumed)
- Wemake some by breaking down carbohydrates (glucose)
- non volatile acids formed constantly
- Anaerobic metabolism- lactic acid, pyruvic acid
- Triglyceride oxidation- acetoaceti acid
- metabolism of cysteine/methionine- sulfuric/phosphoric acid
3 mechanisms that bpdy has to deal with acid
- buffering
- renal regulation
- ventilator regulation
What is the 1st line of defense for acidosis
Buffering system
Define buffer? What are the main buffers in body?
Buffer- ability of a solution containing a weak acid and its anion (base) to resist change in PH with addition of a strong acid or base
main buffers
- bicarb/carbonic acid
-phosphate
-protein
What is the first thing that happens when acid increases
Bicarb buffer (rapid onset with intermediate capacity)
Why is bicarb so good at being a buffer for body
HCO3 present in largest concentration extracellularly over any other buffer
- supply of CO2 is unlimited
- acidity can be controlled by HCO3 or pCO2
Our abilities to use bicarb as buffer depends on two things. What are they?
Ability of kidney and lungs to excrete and retain HCO3 and CO2 respectively
MOA of how bicarb acts as a buffer when acid is added
HCO3 becomes H2CO3 and later CO2 and H20 with carbonic anhydrase
Large quantites of CO2 can be exhaled rapidly
Body needs HCO3 added to the system in an amount equivakent to the H loas ingested every day
What is the seocnd buffer that acts after bicarb buffer?
Phosphate buffer
Onset and capacity of phospahte buffer compared to bicarb buffer
Intermediate onset and capacity (not fast at all)
What are our last buffers after bicarb and phosphate
Protein buffr
Onset and capacity of protein buffer?
rapid onset and limited capacity
Key protein buffers
albumin and hemoglobin
More effective intracellular buffers vs extracellular
After buffers what is another method of acid regulation
Renal regulation
Role of kidneys for acid base management
Reabsorb bicarb
Make new bicarb (through hydrogen excretion)
How does bicarb reabsorption occur
- filtered Bicarb in urine combines with hydrogen ion and makes H2CO3
- Carbonic anhydrase dissociates that into H20 and CO2
- Water and CO2 go into proximal tubule and get converted back into H2CO3.
- Bicarb and hydrogen form and Bicarb goes into blood stream (no net loss of hydrogen)
How does limiting H+ secretion into proximal tubule affect acid-base balance?
Results in urinary bicarb loss
What do carbonase anhydrase inhibitors do?
inhibits carbonic anhydrase, leads to decreased entry of CO2 and H20 for reabsorption. This leads to metabolic acidosis (if we want to correct alkilosis this is good)
Bicarb generation is also referred to as
Enhanced H+ excretion
where does H excretion occur (exam)
distal tubule
How long does bicarb generation (h+ excretion) take? Capacity?
24 hours (delayed onset), but has large capacity
What are the two proccesses for making new bicarb (excreting H+)
- ammonium excretion
- titrateable acidity
Describe steps in ammonium excretion (how new bicarb is made)
- secreted H+ in distal tubule combines with ammonia to make ammonium (too big) and is excerted
- Bicarb generated from breakdown of carbonic acid is able to cross into capillary. (new bicarb made)
also called ammoniagenesis
describe steps in titratable acidity
- phosphoric acid combines with H+ in distal tubule and turns to dihydrogen phosphate (too big) and is excreted
- Hydrogen ion lost in process and bicarb created. New bicarb created in capillary
capacity of titrateable acidity
Capacity is small and can not be increased (because it depends on phosphates and phosphates do not have great access)
what percent of net acid excretion does distal tubule H+ secretion comprise of
50% of net acid excretion
simple way to put distal tubule actions
CO2 combines with H20 in presence of Carbonic anhydrase form H2CO3 which breaksdown into H and HCO3
The H is transported back into urine
HCO3 crosses into capillary
after buffering and renal regulation, what is the third way we control acid base in out body
Ventilatory regulation
onset and capacity of ventilatory regulation
Rapid onset and large capacity
what do chemoreceptors detect and do in ventilatory regulation
Detect an increase in PaCO2 and increase rate and depth of ventilation
When its metabolic what compound should we always check?
Always bicarb (HCO3)
In ventilatory regulation, what are peripheral chemoreceptors activated by? what about central chemoreceptors?
Peripheral chemoreceptors activated by arterial acidosis, hypercapnia (high Pco2 levels) and hypoxia
Central chemoreceptors activated by CSF acidosis
What are the 4 different acid-base imbalances and what are their compensation characteristics
Metabolic acidosis
caused by- decrease in HCO3
Compensated with- decrease in PaCO2
Metabolic alkilosis
caused by- increase in HCO3
Compensated by increase in PaCO2
Respiratory acidosis
-caused by- increase in PaCO2
compensated with increase in HCO3
Respiratory alkilosis
- caused by decrease in PaCO2
compensated with decrease in HCO3
PH and HCO3 of of metabolic acidosis? compensatory action?
low pH (<7.35), low serum HCO3 (<24) and a compensatory decrease in PaCO2
What should we always calculate for all metabolic acidosis
Anion gap
Anion gap formula? What is a normal anion gap? What does the values mean if they are high or low or normal
Na- (cl+HCO3)
Normal anion gap- 3-11
if normal or low, it is considered non anion gap metabolic acidosis
If anion gap is high, it is anion gap metabolic acidosis
non anion gap acidosis is also known as? why?
Hyperchloremic acidosis
overall there is a loss of plasma HCO3 and replaced by Cl-
common causes of non anion gap acidosis
- GI bicarb losses
- renal bicarb wasting
- exogenous acid given to patient
What are some GI bicarb losses
- diarrhea
- pancreatic fistulas/billiary drainage (these fluids are rich in HCO3)
What are some renal bicarb losses
- Type II renal tubular acidosis (RTA)
problem with proximal tubule (reabsorption site for bicarb)
What are causes of RTA (issues with proximal tubule) that cause renal bicarb losses
heavy metal toxicity
carbonic anhydrase inhibitors
topiramate
Faconis syndrome
reabsorption of bicarb is reduced. HCO3 will be lost
What is urine PH is patients that have RTA? why?
PH often <5.3
When HCO3 is lost in RTA, this also results in Na and fluid loss, which will then activate the renin angiotensin system
Aldosterone increases Na/H20 reabsorption and augments K+ excretion
Other than type II RTA, what causes impaired renal acid excretion?
reduced renal H+ excretion
What are some causes for impaired renal H+ excretion? Which one is most common
Distal tubule RTA (most common)
Type 1 RTA (hypokalemia RTA)
Type IV RTA
chronic renal failure
what causes type I RTA
distal tubule might have defect
Lupus , myeloma, sickle cell can cause damage to distal tubule
H+ can not be pumped into urine , urine can not be maximally acidified. Since H+ can not be secreted in response to Na+ reabsorption, there is an increase in K+ excretion
causes of type IV RTA
Low aldosterone (hypo aldosterone state)
Aldosterone stimulates H+ excretion
How does chronic renal failure lead to impaired renal acid excretion
H secretion is decreases. also less ammonia production (decreases ability to make new CO3 )
When does exogenous acid gain occur
Administering TPN (just fix TPN)
HCl given for treatment of a condition may cause acidosis
ammonium chloride given for treatment may cause acidosis
What are potential causes of anion gap acidosis
Calculate anion gap, if high these things could be the cause
(MUDPILES mnemonic)
Methanol intoxication
Uremia
Diabetic ketoacidosis
Poisoning/propylene glycol
intoxication/infection
lactic acidosis
ethylene glycol
salicylates/sepsis
difference between anion gap acidosis and non anion gap acidosis
Overall HCO3, losses are replaced with another anion besides Cl-
when we suspect anion gap metabolic acidosis what do we do
we calculate delta gap
what is the use of delta gap
Used in assessment of anion gap metabolic acidosis to determine if a mixed disorder is present. (only used in anion gap metabolic acidosis)
How to calculate delta gap?
Difference between patients anion gap and normal value (use 10)
We take the value we get from the above and add it onto the HCO3 (bicarb). It should be normal.
What does it mean if we take the delta gap and add it to patients HCO3 and results are elevated?
It means there is a mixed disorder (metabolic alkilosis on top of metabolic acidosis)
most common cause of anion gap acidosis
lactic acidosis
What is the normal level of lactic acid in circulation? What is levels are diagnostic for lactic acidosis? What levels have higher than 75% mortality?
1 meq/l= normal
> 5 is diagnostic
75% with levels 5-9
Are increased levels of lactic acidosis caused by decreased clearence or over production? What is the principal route of conversion of lactic acid? What is it disposed by?
- increased levels are mainly due to decreased clearence
Principal route of elimination is reconversion to pyruvate
Disposal via liver (50%), kidney, muscle and CNS
causes of lactic acidosis
- shock
- drugs/toxins (ethanol- decreased blood sugar, ketosis and lactic acidosis)
metformin
NRTIs
linezolid, propofol, isoniazid
Propylene glycol - seizures (resolves within 2 hrs)
- leukemia
- hepatic/renal failure
- diabetes
- malnutrition
- rhabdomylosis
What are other things besides lactic accidosis that can cause anion gap metabolic acidosis (EXAM)
Ketoacidosis
Drug intoxication (salicylate toxicity) (EXAM)
how does salicylate toxicity lead to anion gap metabolic acidosis (EXAM)
respiratory alkilosis from stimulation of respiratory drive
also metabolic acidosis from accumulatio of acid (Has BOTH Acidosis and alkilosis) PH WILL LOOK NORMAL
Drug intoxications other than salicylates that cause acidosis
Methanol
Ethylene glycol
symptoms of acidosis
- Kussmaul respiration (deep and fast) (compensation to get rid of all that CO2)
- peripheral vasodilation (tachycardia/ arrhythmia)
- hyperkalemia
- bone demineralization
When do we consider acute bicarb therapy (giving patient bicarb) in hospital
-Hyperkalemia
-PH<7.1 (common in cardiac arrest)
- to reverse overdose
How do we dose bicarb? (EXAM) WHat to monitor?
(0.5 x IBW) x (12 - bicarb number of patient)
then give 1/3 or 1/2 of what we calculated, monitor ABG (blood gas) and K+ supplement if needed
how much bicarb to give during cardiac arrest?
1 mEq/kg
What are the hazards of bicarb therapy?
Overalkylazation can reduce cerebral flow and impair oxygen release from Hgb to tissues
hypernatremia/hyperosmolarity
CSF acidosis (YES ACIDOSIS)
hypokalemia
hypocalcemia
electrolyte shift
