Acid-Base Disturbances Flashcards
Respiratory Acidosis is a result of what?
Can be caused by what?
Hypoventilation
Anything that interrupts ventilation form brainstem to alveolus
Examples of problems that lead to respiratory acidosis are?
Airway obstruction
Obesity
Sedatives
Oxygen therapy
COPD
Muscle Weakness
How long after the onset of respiratory acidosis does it take for the kidneys to begin contributing to the compensation?
How do they help to compensate?
48hrs
excreting more acid and generating more HCO3-
PaCO2 levels > 60 result in what type of symptoms?
HA
confusion
somnolence
Knowing if a respiratory acidosis helps to determine whether or not there is a what?
In acute respiratory acidosis bicarbonate rises approximately how much compared to PaCO2?
In chronic respiratory acidosis bicarbonate rises approximately how much compared to PaCO2?
superimposed metabolic disturbance
1mEq/L of HCO3- for every 10 mmHg PaCO2
3.5mEq/L of HCO3- for every 10 mmHg PaCO2
Treatment of Respiratory acidosis should be focused on what?
Sedating medications should be what?
Bronchodilators and steroids can be helpful in what conditions?
What may be required?
ensuring airway patency and getting good air in and bad air out
stopped
COPD and asthma
Intubation and mechanical ventilation
Respiratory Alkalosis is the result of what?
Hyperventilation
What can contribute to respiratory alkalosis?
Anxiety
Pain
Hypoxia from PE, Pneumonia, Pulmonary Edema
Chemical stimulators such as progesterone and ASA overdose
Most commonly in the ICU, respiratory alkalosis is stimulated not by ____ and not by ____
But by inadvertent over-breathing on the ventilator either by ____ or ____
low Oxygenation; an increased central drive
over-aggressive settings; insufficient sedation
Respiratory Alkalosis symptoms include?
light-headedness, altered consciousness, and tingling around the mouth and the extremities
How do the kidneys compensate for respiratory alkalosis?
dumping large amounts of HCO3- into the urine
In Acute Respiratory Alkalosis from conditions such as hypoxia and a blood clot in the lungs, the bicarbonate drops only how much compared to the drop in PaCO2?
When Chronic Respiratory Acidosis from being pregnant (why?) the bicarbonate leves drop for how much compared to the drop in PaCO2?
2 mEq/L of HCO3- for every 10 mmHg of PaCO2
Elevated Progesterone Levels; 4-5 mEq/L of HCO3- for every 10 mmHg of PaCO2
Treatment for Respiratory Alkalosis should be focused on what?
Ventilator settings may need to be adjusted for the patient who is doing what?
treating the underlying condition
inadvertently being artificially over-ventilated
Metabolic Alkalosis is a result of what?
Either acid lost or bicarb added
What can cause the kidneys to become overwhelmed leading to a metabolic alkalosis?
Giving the patient too much bicarb or to much of something that can be converted to bicarbonate such as citrate
What can cause the kidneys to become tricked leading to a metabolic alkalosis?
Volume depletion leads to obligate NaHCO3 retention and H+ secretion
A contraction alkalosis is the result of what?
What is stimulated from these leading to more acid lost in the urine?
- Loss of gastric secretions
- Diuretic use and abuse
Aldosterone
Treatment of metabolic alkalosis is what?
Correct the volume deficit with Normal saline
Sit back and let the kidneys work their magic
Less commonly a saline-resistant form of metabolic alkalosis occurs. These patients DO NOT have volume contraction, but more likely, what?
To much of what is being made in the adrenal glands?
Treatment of this involves what?
volume excess
aldosterone
surgical removal of the adenoma, or utilize medications that block aldosterones effect (spironolactone, eplerenone, amiloride, triametrene)
Compensation for metabolic alkalosis does occur, but why is this not usually very successful?
Hypoventilation leads to a rise of how much PaCO2 compared to the rise in HCO3-?
Because it doesn’t take long for the hypoventilation to lead to hypoxia
0.7 mmHg of PaCO2 for every 1 mEq/L of HCO3-
Why is Metabolic Acidosis the most difficult acid-base disorder? (4 reasons)
- There are two kinds (anion gap & non-anion gap)
- Anion gap acidoses can have an osmolar gap
- Non-gap acidoses can be renal or extra-renal
- Can be simultaneous with a metabolic alkalosis
What constitutes an anion gap acidosis?
gain, retention, or production of an organic anion
To detect if anion gap is present, calculate the anion gap, how?
[Na+] - [Cl-] - [HCO3-]
Normal anion gap is ~ what?
However if albumin is low, then your normal range should change, how?
12
add 2.5 to your measured gap for each point the albumin is < 4.0 mEq/L
To determine what is causing a Metabolic Acidosis use the acronym GOLDMARK which represents
G - glycols (propylene, ethylene)
O - 5’–Oxoproline (acetaminophen)
L - Lactate
D - D-lactate
M - Methanol
A - Acetylsalicylic acid (ASA)
R - Renal Failure
K - Ketoacidosis (diabetic, alcoholic)
From the GOLDMARK acronym, which components have measurable levels?
L - Lactate
D - D-lactate
A - Acetylsalicylic acid (ASA)
K - Ketoacidosis
From the GOLDMARK acronym, which components cause an elevated osmolar gap?
G - glycols (propylene, ethylene)
M - Methanol
How to measure the osmolar gap?
2[Na+] + [glucose]/18 + [BUN]/2.8
The proper setting of methanol and ethylene glycol levels causing metabolic acidosis? (4 items)
compare the “calculated value” to the actual measured value of serum osmolality, if the difference is > ___ suspect ethylene glycol or methanol intoxication.
- Patient with an unknown ingestion
- Metabolic acidosis present
- Anion gap acidosis present
- Osmolar gap is elevated
20
Ingestion of what can cause an elevated osmolar gap, but does not cause an anion gap acidosis?
rubbing alcohol (isopropyl alcohol)
What is a metabolic acidosis with a normal anion gap caused from and called?
hyperchloremic metabolic acidosis, because the retained acid is essentially the equivalent of HCl
Non-gap metabolic acidosis are caused by what?
the kidneys
or not the kidneys
How do you tell if the kidneys are the culprit of the non-gap acidosis?
How do you measure this?
the normal response of the kidneys in a prevailing acidosis is to dump acid, measuring this response is how
A urine anion gap will tell you if there is room for ammonium
How do you measure the urine anion gap?
What does it mean if the number is negative?
What does it mean if the number is positive?
Urine [Na+] + Urine [K+] - Urine [Cl-]
Lots of room for NH4+; the kidneys are doing their job (extra renal cause)
Less room for NH4+; good kidneys gone bad (renal cause)
What are the extra-renal causes of non-anion gap acidosis?
bicarb-rich diarrhea, pancreatic losses
What are the renal causes of non-anion gap acidosis?
Renal tubular necrosis
Type 1: problem with acidification
Type 2: problem with bicarbonate reclamation
Type 4: problem with aldosterone axis
A fall in serum pH to < 7.2 can predispose what?
a reduction in cardiac contractility and blunted response to catecholamines
There are several ways to calculate the expected compensation you might find on a blood gas, what are they?
The Winter Equation
The “Plus 15” rule
The “Rule of Thumb”
What is the Winter Equation
An example, if the bicarbonate is 16 mEq/L, the expected PaCO2 should be what?
1.5(HCO3-) + 8(+/-2)
24 + 8 +/-2 = between 30 and 34 mmHg
What is the “Plus 15” rule?
For example if the bicarbonate level is 16 mEq/L, the expected PaCO2 should be what?
Add 15 to bicarbonate
16 + 15 or 31 mmHg
What is the “Rule of Thumb”
For example, if the pH is 7.32, the PaCO2 should be what?
Cover the “7” on the pH with you thumb
32 mmHg
The importance for calculating the expected compensation for metabolic acidosis (as well as the others) the need to determine what?
If the compensation is > would be expected, then what may be present?
second acid-base problem is present
a super imposed respiratory alkalosis
Treatment of metabolic acidoses depend primarily on what?
Examples may be?
treating the underlying cause
Correct the insulin deficiency
Correct the underlying cause of shock
Dialyze off exogenous toxins
When is it advisable to administer sodium bicarbonate?
When pH falls to an acutely life threating level (< 7.2)
What could happen if sodium bicarbonate is administered above acute life threatening pH levels?
an “overshoot” alkalosis once the ketoacids are excreted or the lactate is is metabolized in the liver to bicarb
For severe metabolic acidosis cases what is a temporizing measure to correct the acidemia?
goal of this therapy?
Patient over-breathing the ventilator
PaCO2 levels can be blown down to minimal levels (~10-15 mmHg)
What is the systematic approach to Acid Base Imbalances?
- Calculate the anion gap always
- Is the final pH Acidic or Alkaline?
3 Who is to blame? Respiratory check the PaCO2, Metabolic Check the HCO3-, could it be both? - Is the disturbance mixed? Compensation? Overcompensation?
What acid-base problem has a nasty habit of hiding amongst mixed disturbances?
If the gap is high, but the bicarbonate level is normal what is it? This suggests what?
Anion gap metabolic acidosis
metabolic acidosis; combined metabolic acidosis & alkalosis (each pushing bicarbonate in opposite levels.)
