Acid/Base Disorders Flashcards
Describe normal arterial blood gases (ABG’s)
PH: 7.35-7.45 (7.4) PaCO2: 35-45 (40) PaO2: 80-100 (90) HCO3: 22-26 (24) O2 Sat: 92-100%
What should you get to completely evaluate acid base states?
Basic metabolic panel
What is important about hypoxemia?
Subnormal oxygenation in blood
Normal O2 = 104-.27 x age = 100-1/3 x age = decreases with age
What are cause of hypoxia?
Hypoventilation
Ventilation/Perfusion mismatch as seen in pulmonary embolus
Shunting, eg cardiac abnormalities
Low inspired fraction of O2 (FiO2)
High altitude
Diffusion abnormalities, eg alveolar hemorrhage, connective tissue disorder
Describe ABG terms
Acidosis pH7.45
Hypoxia pO245
Hypocapnia pCO2
When does kidney start to retain HCO3?
In 12-16 hrs
Max conc in 1 week
What is the 3 step approach to ABG analysis?
- Does patient have acidosis or alkalosis? pH high or low?
- Is acidosis/alkalosis a respiratory or metabolic process?
- If it is a respiratory acidosis/alkalosis, is it a pure respiratory process, or is there a metabolic component?
How do you determine respiratory vs metabolic acidosis/alkalosis?
If pH and pCO2 are both increased or decreased in same direction, then the process is metabolic
If one is increased, while the other is decreased (opposite), the process is respiratory
-as pCO2 increases, then pH decreases
Describe the change in a pure respiratory process of acidoss/alkalosis
For each 10 mmHg change in PaCo2, the pH should move in opposite direction by 0.08 (+/- 0.02)
If PaCO2 is 30, what should the pH be?
If PaCo2 is 60, what should the pH be?
A decrease of 10 mmHg from 40 will lead to pH of 7.48 (7.4+0.08)
An increase of 20 mmHg from 40 will lead to pH of 7.24 (7.4-(2x0.08)), a decrease of 0.16, or 0.08 for each 10 mmHg rise in pCO2
Describe the mixed process of acidosis/alkalosis
Step 3 of ABG analysis compares the “should be” (expected/calculated) pH to actual measured pH
If actual pH is not what it should be, is it higher or lower?
If higher, there must be a concomitant metabolic alkalosis
If lower, there must be a concomitant metabolic acidosis
70 y/o M presents to ED with increasing dyspnea (RR 25 breaths/min)
PE: JVD at 45 degrees, estimated CVP 11mm H2O
Lungs: b/l crackles in bases and scattered wheezes
Heart: grade 3/6 systolic murmur at apex with radiation into left axilla, S3 gallop heard, no S4
B/l peripheral edema of legs. Cool extremities
BP 100/68, P 115/min, afebrile, O2 sat 78%
Venous lab: Na 128 K 5.8 Cl 92 HCO3 12 BUN 42 Cr 2.1 BNP 500
- What is his anion gap?
- What is his diagnosis?
- What other tests would you use?
- How would you treat this pt?
- Na - (Cl + HCO3)
128 - (92+12)
24 - Metabolic acidosis with high anion gap
Acute HF
Atrial fibrillation with rapid ventricular response
Hyponatremia
Azotemia
Mitral regurgitation - Echocardiogram, lactic acid level, cardiac enzymes (troponin I, CK MB)
4. Oxygen 2-4 L/min N/C IV - loop diuretic Fluid restriction 1-1.5 L/day Na HCO3 - cautiously ACEI - cautiosly
What are normal electrolytes values?
Na 135-145 (140)
K 3.5-5 (4)
Cl 98-106 (103)
CO2 21-28 (24)
What is the anion gap?
Na-(Cl + HCO3)
12+/-2
Reflects concentration of anions that are not routinely measured (sulfates, phosphates, acetoacetic acid, beta hydroxybutyric acid)
Describe metabolic acidosis
Decrease in extracellular pH caused by a decrease in HCO3
- Loss of HCO3: GI tract, renal
- Increase hydrogen load: DKA or lactic
- Decrease hydrogen excretion by kidney: uremic acidosis or RTA
2 types:
Elevated anion gap
Normal anion gap with hyperchloremia
What are causes of high anion gap?
High anion gap, metabolic acidosis: MUDPILES
Methanol: formic A
Uremia (renal failure)
- increased BUN, Cr
- increased sulfates, phosphates as unmeasured anions
Diabetic ketosis
- increased glucose. Starvation, alcohol abuse
- acetoacetic acid, B-hydroxybutyric acid
Paraladehyde
INH, iron
Lactic acid
-shock, sepsis, low perfusion, marathon runners
Ethylene glycol, glycolic
Salicylates
CCAT
-CO, cyanide, alcohol, toluene
Describe lactic acidosis
Type A (tissue hypoxia) -shock, severe anemia, heart failure, CO poisoning
Type B1 (associated with systemic disorders) -DM, liver failure, sepsis, seizures
Type B2 (associated with drugs/toxins) -ethanol, methanol, ethylene glycol, ASA
Type B3 (associated with inborn errors of metabolism) -G6PD deficiency
68 y/o F presents to ED in lethargic state. Past 3-4 weeks, anorexia, confusion, edema, and weight gain.
PMH positive for poorly controlled HTN and diabetes mellitus, DJD, and hypothyroidis
Meds: HCTZ 50 mg daily, Lantus insulin 20 units hs, NSAID for arthritis, and synthyroid 0.05 mg orally daily
Arousable but lethargic
BP 158/88, P 90/min, R 10 breaths/min, temp 98F, O2 sat 88%
Neck veins mildly distended at 45
Heart: 2/6 systolic murmur 2nd ICS, RSB with slight radiation into R carotid
Lungs: basilar crackles, R>L
Abdomen: tenderness RUQ, edge of liver is 3 fingers below costal margin. Percussion span of liver is 8 cm (normal)
Extremities: marked pitting edema of feet, calves, and thighs
- What is your diagnosis?
- Differential diagnosis?
- What tests do you order?
- PH 7.1, pCO2 45, pO2 68, HCO3 8. Analysis?
- Na 150, K 7, Cl 115, HCO3 10. Anion gap?
- Interpretation?
- How would you treat the pt?
- Metabolic encephalopathy: R/O hypothyroid (myxedema)
Likely ischemic cerebral vascular disease due to poorly controlled hypertension
Electrolyte/acid-base disorder
Fluid overload
2. Myxedema Ischemic cerebral vascular disease Valvular heart disease Heart failure Hypertension
- CBC: Hgb 9 g, Hct 27%
CMP
TSH: 10
HbA1C - Metabolic and respiratory acidosis
- 150 - (115+10) = 25
- High anion gap metabolic acidosis because of renal failure (retention of hydrogen ions) in uremic acidosis
And respiratory acidosis: lungs haven’t compensated as you’d expect for metabolic acidosis by decreasing pCO2 - Dialysis: hemodialysis
Na HCO3
Synthyroid
Aerosol treatments with nebulizers
37 y/o F presents to ED with 6 day history of diarrhea. Approximately 7 stools/day and up 3-4 times through night with watery, non-bloody stools. Able to drink fluids, soups, jello. Hasn’t traveled out of country, camped outdoors, or ingested spring/river water. Aunt has Crohn’s disease. No antibiotics over past 4 months.
BP 80/50, P 110/min, R 18/min, Temp 100F, O2 Sat 94
General: pale, poor skin turgor, dry mucous membranes
Neck veins flat
Heart: no murmur, S3 or S4.Tachycardia 110 p/min
Lungs: clear
Abdomen: hyperactive bowel sounds, mildly tender diffusely, no organomegaly
Extremities: coo to touch. Tattoo R ankle
Neurologic: normal
- Diagnosis/differential diagnosis?
- CBC Hb16, Hct 50%, WBC 14,000
CMP: Na 148, K 2.6, Cl 114, HCO3 20
Stools: culture for enteric pathogens, ova parasites, WBC’s/hemoccult of stool
ABG: pH 7.1, pCO2 34, pO2 92, HCO3 20
Anion gap? - ABG analysis?
- Treatment?
- Diarrhea: secretory, infectious, consider inflammatory bowel disease
Hypovolemia: volume contracted, possible electrolyte/acid base disturbance
Hypotension - 148 - (114+20) = 14 (normal)
- Metabolic acidosis (normal anion gap, low HCO3, elevated Cl)
- IV fluids for volume restoration (careful not to give too much NaCl or N/S)
Could give fluids of 1/2 strength N/S with Na HCO3 and K
What are causes of normal anion gap metabolic acidosis (HCO3 falls and Cl rises. hyperchloremic met acid)?
HARDUPS
Hyperalimentation
Acid infusion, acetazolamide
Renal tubular acidosis
-Renal loss of HCO3 or decreased H sec
Diarrhea
-losing HCO3, decreases K
Ureteral sigmoid or ileal diversion
-losing HCO3/increasing Cl and H resorption
Pancreatic fistula
-losing HCO3, decreased K
Describe distal renal tubular acidosis
Type I
Decreased secretion of H, so not getting rid of acid, ie failure to acidify urine
Possible causes: SLE, Sjogren’s, toluene
Describe proximal renal tubular acidosis
Type II
Decreased absorption of HCO3, so not absorbing buffer
Possible causes: multiple myeloma, heavy metal poisoning, Wilson’s disease, amyloidosis
Describe hyperkalemic renal tubular acidosis
Type IV
Hyporenin and hypoaldosterone
Decreased NH4 excretion and decreased HCO3 production
Possible causes: analgesic nephropathy, sickle cell disease, and SLE
Describe treatment of metabolic acidosis
Rx underlying cause
Rx of CV compromise; pH