13 - Acid Base Emergencies Flashcards Preview

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Flashcards in 13 - Acid Base Emergencies Deck (46):

Case study

o 16-year-old with recent ankle break, found unarousable and nausea
o History of weight loss, depression, increased food intake, thirst



o Thyroid (high pulse, anxiety)
o Pregnancy
o Infection
o Anxiety



o Pregnancy test
o CMP (sodium normal, potassium high, bicarb low, creatinine high means mild renal failure, acidotic)
o CBC (+/- cultures, +/- lactic acid)
o Urine drug screen
o Blood drug screen (salicylate, alcohol, acetaminophen)
o Arterial blood gas
o Serum ketones
o Urinalysis (ketones, UTI)
o HbA1c, TSH



o Classic presentation of DKA
o Need to give fluids, insulin bolus then drip, etc.


Arterial blood gas (ABGs)

A very fast lab (minutes for results) that reads blood directly from artery sample.
o pH
o Oxygenation
o Ventilation
o Bicarb


You can get blood gasses other ways

o pH accurate
o PCO2 close
o PO2 unreliable

CBG (used in kids)
o pH accurate
o PCO2 add 5
o PO2 unreliable


Basic abnormalities in ABGs

- Metabolic Acidosis
- Metabolic Alkalosis
- Respiratory Acidosis
- Respiratory Alkalosis
- Mixed
- Compensated


Acidosis and alkalosis

- Acidosis – the gain of too many acids OR loss of too many bases
- Alkalosis – the gain of too many bases OR the loss of too many acids


When to order ABGs

- Vent management
- Unknown disorder
- Unknown OD or known OD that causes acid base issues
- When on fence about admission status
- Suspected DKA
- Code decisions
- Will it change the plan????


Buffer system

- The renal system compensates for respiratory and the respiratory for the renal.
- Although many other systems, primarily done through bicarb and CO2
- Respiratory system is fast to kick in but the renal system is not


pH imbalances

- PH imbalances occur when a disturbance overwhelms the buffering systems


Clinical manifestations

- Hypercapnea (Respiratory Acidosis) – altered mental status, delirium, HA, dyspnea
- Hypocapnea (Respiratory Alkalosis) – lightheaded, nausea, tachycardia, carpel spasm/tingling
- Acidemia (Metabolic Acidosis) – deep/fast breathing, pale/clammy, often combative then delirious
- Alkalemia (Metabolic Alkalosis) – tingling, tetany, seizures, delirium


Respiratory acidosis – VERY COMMON ***

- Acute – due to decreased respiratory rate or function, so CO2 builds. Causes – head trauma, med OD, vent settings, pulmonary issues (PE, pneumonia)
- *****Chronically – due to lung/body issue so cannot get rid of CO2 (dead space) – VERY common COPD, pregnancy, obesity*****


Buffering respiratory acidosis

- As CO2 increases, kidneys reabsorb bicarb in an attempt to compensate. See big swing in ph initially
- Eventually more secondary buffering systems engage, and the ph becomes more normal.

o Change in pH = 0.8 X change in paCO2 (Acute respiratory acidosis)
o Change in pH = 0.3 X change in paCO2 (Chronic respiratory acidosis)



- PaCO2 of 60 – what ph changes would you expect?
- 60 – 40 (normal CO2) = 20 (change in CO2)
o 20 X .8 = 16 gives ph of 7.19 (acute)
o 20 X .3 = 6 gives ph of 7.29 (chronic)


Respiratory acidosis treatment = Correct underlying cause…

- Narcan (narcotic OD)
- Chest tube (pneumothorax)
- Vent (increase respiratory rate)
- Careful with O2 and CO2 retainers
- BiPAP and CPAP
- Nebulizers, steroids, diuretics
- Even intubation seems to help when things are severe


Respiratory alkalosis

- Due to hyperventilation (getting rid of too much CO2)


*** Causes of respiratory alkalosis *** KNOW THIS

- *** Anxiety/pain = MOST COMMON ***
- Vent settings (rate too high)
- Fever
- *****Sepsis (gram negatives)***** KNOW THIS
- OD (aspirin especially)
- Head trauma
- Lung issues (PE, pneumothorax)


Acute vs chronic

- In acute situations, the low PaCO2 will cause a big shift in pH, while in chronic situations the pH becomes more normal because the buffering systems have time to kick in.


Acute alkalosis

- In acute respiratory alkalosis, the bicarbonate concentration level decreases by 2 mEq/L for each decrease of 10 mm Hg in the PaCO2 level


Chronic alkalosis

- In chronic respiratory alkalosis, the bicarbonate concentration level decreases by 5 mEq/L for each decrease of 10 mm Hg in the PaCO2 level
- Plasma bicarbonate levels rarely drop below 12 mm Hg


Respiratory alkalosis treatment

- Treat underlying cause
- Adjust ventilation rate


Metabolic alkalosis

- Metabolic loss of hydrogen or gain in bicarb
- Can have high mortality if pH >7.65
- Goes along with low Ca, low K


Rise in bicarb

- If see a rise in bicarb, could be respiratory acidosis or metabolic alkalosis…rarely see bicarb >35 in respiratory acidosis because the compensation mechanisms have limits


Causes of metabolic alkalosis

- GI losses of acids
- Loss of Chloride (CF)
- Endocrine issues like Cushing's
- Drugs (diuretics, non-absorbable antacids)
- Renal issues


Treatment of metabolic alkalosis

- Treat underlying cause
- May have to replace K, Ca, Cl
- Maybe dialysis
- Maybe HCL, potassium sparing diuretics, ACE


Metabolic acidosis (“bread and butter of acid base emergencies” – this is important)

- Caused by increase of acids or loss of bases
- Unlike respiratory acidosis, in metabolic acidosis there are a number of different acids that maybe increased


We divide metabolic acidosis into 2 types

- High Anion Gap
- Normal Anion Gap


What’s an anion gap??

- Some anions and cations we can measure…others we can’t
- We have a formula that will show an increase when there is an excess of unmeasured acids
- Normal anion gap is 8 to 12******
- Na – (Cl + bicarb)******


Anion gap example

- Na = 135
- Bicarb = 10
- Cl = 98
- Anion gap: 135 – 108 = 27 = high


What causes normal gap metabolic acidosis? (not many – this is not common)

- GI loss of bicarb (diarrhea)
- Kidneys are not making or not reabsorbing bicarb





***High anion gap causes *** KNOW THIS

- M = methanol
- U = uremia
- L = lactic Acidosis
- E = ethylene glycol, EtOH
- P = paraldehyde
- A = ASA
- K = ketoacidosis


High anion gap

- Either kidneys can’t get rid of acids (like phosphate)
- Or body over producing acids
- Almost all Metabolic Acidosis is High Anion Gap types
- Usually the cause is pretty obvious


Obvious examples

- 85 y/o female confused, high WBC, fever 101 and UTI
- 56 y/o male with BS of 980, breathing hard, pale, sweaty, irritable
- 90 y/o with diagnosis of acute bowel ischemia


Understanding ABGs

- Is pH high or low?
- Do CO2 and bicarb go in same direction (both high or both low)?
o In a normal situation, they should either both be high or both be low
- If pH is normal is it compensated or mixed?
- If CO2 and bicarb in opposite directions, mixed (one high one low)


Step by step

- Look at pH – is it acidic or basic?
- Look at CO2 and bicarb – are they both high or both low
o If acidic, is it caused from too many acids or not enough bases?
o Is the cause respiratory (CO2) or metabolic (bicarb)?


Someone else’s way

- Follow the CO2
- When the CO2 and the pH move in the same direction (both low or both high) it is metabolic
- When the CO2 and the pH move in opposite directions (one high and one low) it is respiratory


Let’s try an easy one

- 55 y/o with pneumonia, sleepy – thinking respiratory acidosis
- pH 7.15 (acidosis)
- pCO2 70 (35-45) – high
- HCO3 30 (21-28) – high
- pH is low – so acidodic
- Bicarb and CO2 both high (normal response)
- There is too much acid AND too much base
- Only one that could cause acidosis is too much acid which is CO2 which is respiratory
- OR CO2 and pH in opposite direction so respiratory


Acute or chronic?

- 70 (Co2) -40 = 30
- 30 x 0.8= 24 (7.40 - .24)
- 30 x 0.3 = 9 (7.40 - .09)
- Is pH closer to 7.16 or 7.31?
- Lower pH, bigger swing so acute
- Acute problem because it is closer to 7.16


Another example… 75-year-old female with COPD

- pH 7.37 (normal)
- PCO2 55
- HCO3 35
- PO2 58
- CO2 and bicarb both high = Compensated respiratory acidosis


Overdose on a vent

- pH 7.54
- PCO2 19
- HCO3 16
- Alkalosis
- Low acid from respiratory (blowing off too much CO2)
- What should they do to vent setting? Turn it down


Healthy teen vomiting for 4 days

- pH 7.50
- PCO2 50
- HCO3 50
- pH HIGH; CO2 high so is bicarb…which will cause alkalosis?
- What does she need for treatment??
- High bicarb is causing the alkalosis, so she needs fluids


16-year-old new diagnosis DM with vomiting and confusion

- pH 7.20
- PCO2 20
- HCO3 12
- Expected BS? High
- K+?? High
- Expected anion gap? Yes
- Treatment? First fluids, then supplement potassium because after you give fluids it will start to correct itself



- pH will be normal – look at ph and which direction it “leans”
- Again, look at CO2 and bicarb for cause
- Basically if they are compensated leave them alone
- ***NOTE: if the pH is in the normal range on the exam, say COMPENSATED***


***Salicylate OD***

- Shows up on Board questions
- ***Respiratory Alkalosis and Metabolic Acidosis***
- Initially the respiratory center is stimulated causing rapid RR giving respiratory alkalosis
- Then inhibition of citric acid cycle so accumulation on acids leads to metabolic acidosis
- Aspirin, Ben Gay
- Nausea, ***tinnitus*** initially
- Then can get changes in vitals (***tachypnea, tachycardia, hyperthermia***)
- MS changes (agitation to lethargy)