113. Acid Base Flashcards by Tegan Turner

How is a normal pH in the body maintained?

kidneys regulation of plasma bicarb (hco3) and lungs regulation of pp of arterial co

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What is the Henderson Hasselbach equation?

pH = pK +log10 [hco3]/[0.03xpaco2]

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What does the HH equation describe? Relationship…

between hco3 and paco2 to ph

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Acidemia and alkalemia describe what? vs acidosis and alkalosis

summary acid-base state or pH of flood (ie blood pH <7.35 vs pH >7.45)

acidosis and alkalosis are discrete conditions (ie acidosis is an A-B disturbance that incr H and lowers pH)

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What does the “metabolic system” in broad strokes include?

cellular production
renal excretion of acid and bases

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What (in general) causes metabolic acid-base disorders? Dysregulation in which 3 components…

abnormal cellular function
altered renal excretion of acid and bases
exogenous gain or loss of acids and gases through GI

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How long does a paco2 take to compensate in a metabolic process?

12-24h for metabolic acidosis vs 24-36 in metabolic alkalosis

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How long does a hco3 take to compensate in a respiratory process?

compensatory incr hco3 for resp acidosis 2-5d
compensatory decr hco3 after 2-5d

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Basic 5 step approach for A-B problems with a VBG/ABG:
1.

Check the pH (N 7.35-7.45)
and hco3 (24) and pco2 (40)

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Basic 5 step approach for A-B problems with a VBG/ABG:
2.

Check AG
Na - Cl + Hco3
Wide AG >12 ish

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What is an elevated anion gap?

accumulation of unmeasured anions

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Basic 5 step approach for A-B problems with a VBG/ABG:
If a metabolic acidosis is present:
3.

Check to see if concomittent resp-acid base disorder or if compensated:
Expected PCO2 = (1.5 x serum HCO3) + 8 ± 2

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If PCO2 is lower than predicted by Winter’s formula, what is present?

resp alkalosis ie they are blowing off more acid than is required to combat the acidosis from the metabolic cause and therefore, are losing more acid than would be expected from this process alone

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If PCO2 is higher than expected in Winter’s formula for a compensatory resp in metabolic acidosis, what does this mean?

concomittent resp acidosis
ie they are not blowing off co2 as expected to compensate for rise in acid from metabolic acidosis and therefore have more acid in body than expected

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Basic 5 step approach for A-B problems with a VBG/ABG:
If a wide AG metabolic acidosis is present….
4.

check the delta gap
to see if there is additional metabolic acid base disturbances

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How to check the delta gap

know that a hco3 is 24
note the current bicarb
calculate the change from normal to current
for every 1mmol increase in the AG above 15, expected drop hco3 should be one below 24

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If the measured bicarb concentration is higher than predicted by the delta gap, this indicates a concomittent metabolic ___

alkalosis (ie bicarb should have dropped more so there is still more base in solution than should be)

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If the measured bicarb concentration is lower than predicted by the delta gap, this indicates a concomittent metabolic ___

NAGMA

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Basic 5 step approach for A-B problems with a VBG/ABG:
5. if the wide anion gap metabolic acidosis is present, but the cause isn’t clear, what equation should you check?

osmolar gap

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How to calculate the osmolar gap?

find the serum one in the labs
calculate: 2xNa + glucose + bun
**+ (Ethanol (mmol/L) x 1.25) if present

measured - serum = osmolar
Normal is 10 or less

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For every increase in pco2 (resp acidosis): expected hco3 in ACUTE

incr 1

For every increase in pco2 (resp acidosis) *10mmhg above 40: expected hco3 in CHRONIC

incr 4

For every decr in pco2 (resp alkalosis: expected hco3 in ACUTE

decr 2

For every decr in pco2 (resp alkalosis: expected hco3 in CHRONIC

decr 5

When applying bicarb compensation rule to a respiratory/pco2, what is the general rule in terms of how much it needsto be above 40/normal?

for every increase in 10 above or below 40 you get the change of 1/4/2/5 respectively depending on resp acido ac/chronic vs resp alkalosis ac chronic

DDX of metabolic acidosis - AGMA

Methanol Uremia Diabetic ketoacidosis/alcoholic ketoacidosis Paraldehyde/Polyethylene glycol/Paracetamol (acetaminophen) Iron Lactic acidosis Ethylene glycol Salicylates

DDX of NAGMA

Hyperalimentation/Hospital-acquired administration of saline Acid infusion/Addison disease / Carbonic Anhydrase Inhibitors Renal tubular acidosis (RTA) Diarrhea Ureterosigmoidostomy (and ileal diversion) Pancreatic drainage/fistula

Metabolic alkalosis- what is important to determine in terms of ___ responsive vs not

chloride!

What is meant by a chloride responsive metabolic alkalosis

ciruclating vol is decreases RAAS activated kidneys reabsorb filtered na, hco3 and cl, leading to a decr [] of urine chloride thus if you gave chloride via solution, would get a correction in metabolic alkalosis (ur cl <40)

What is meant by a chloride UN-responsive metabolic alkalosis

Not correctable by fluids typically by mechanism of hyperaldosteronism causing inapproppriate renal excretion of H and Cl (spot urine cl >40)

Causes of chloride responsive metabolic alkalosis

Nasogastric suction Vomiting Chloride-wasting diarrhea Villous adenoma Persistent diuretic use

Chlroide unresponsive metabolic alkalosis causes

Primary hyperaldosteronism Secondary hyperaldosteronism (Bartter syndrome, Gitelman syndrome, con- gestive heart failure, liver failure, chronic renal failure) Steroids Cushing disease Severe hypercalcemia Severe hypomagnesemia Bicarbonate ingestion Licorice overdose (glycyrrhizic acid)

What are four categories of respiratory acidosis?

resp disease from lungs and airways chest wall disease resp m weakness decreased resp drive

Causes of resp disease/lung and airways causing resp acidosis

Airway obstruction Obstructive pulmonary diseases (e.g., chronic obstructive pulmonary disease) Pneumothorax Pulmonary effusion Pulmonary edema Pneumonia Mechanical ventilation (iatrogenic hypoventilation)

Causes of chest wall disease causing resp acidosis

Chest wall trauma (e.g., flail chest) Obesity hypoventilation syndrome

Causes of resp m weakness disease causing resp acidosis

Myopathies (e.g., muscular dystrophy) Neuropathies (e.g., Guillain-Barré) Electrolyte abnormalities (e.g., hypokalemia, hypophosphatemia)

Causes of decreased resp drive disease causing resp acidosis

Brain space-occupying lesion (e.g., intracranial mass, intracranial hemorrhage) Drugs/toxins (e.g., sedative-hypnotics, narcotics)

Hypoventilation causes resp ___

acidosis

Hyperventilation caues resp ___

alkalosis

DDX cateogries of resp alkalosis based on pathophysioologic mechanism: 7

resp GI GU psych toxic metabolic fever sepsis pain

Name 8 causes of resp alkalosis

Respiratory: Conditions that cause hypoxemia (e.g., pulmonary embolus) Mechanical ventilation (iatrogenic hyperventilation) Gastrointestinal: Hepatic encephalopathy Neurologic Brain lesion Genitourinary: Pregnancy Psychiatric: Anxiety Toxic-Metabolic: Drugs (e.g., salicylates, catecholamines, progesterone) Hyperthyroidism Infectious: Fever Sepsis Miscellaneous: Pain

How much sodium is in 1L of saline?

9g/1000ml

what are the mmol/L concentrations of na and cl for NaCl

154 154

What are the mmol/L [] of na, k, cl, ca lactate in LR?

130 4 109 2.7 28

What can you get from too much NCl?

nagma hyperchloremic metabolic acidosis

A patient presents to the emergency department with severe meta- bolic acidosis. In addition to initial stabilization, what should be a priority for the clinician? a. Infuse sodium bicarbonate to normalize pH to approximately 7.40. b. Induce a respiratory alkalosis to normalize pH to approximately 7.40. c. Identify the cause of metabolic acidosis and target therapy at that cause. d. Infuse saline with the goal of decreasing the strong ion differ- ence.

2. What causes an increase in the anion gap? a. A decrease in plasma bicarbonate concentration accompanied by an increase in plasma chloride concentration of the same magnitude b. An increase in the concentration of unmeasured anions in the plasma c. Saline infusion d. Hypoventilation

A patient in the emergency department has the following labo- ratory values. Select the term that best characterizes this patient’s acid-base status. pH = 7.36; Paco2 = 36 mm Hg; Pao2 = 135 mm Hg; Na = 142 mmol/L; Cl = 100 mmol/L; HCO3 = 21 mmol/L. a. Acidemia b. alkalemia c. Respiratory alkalosis with metabolic compensation d. Metabolic acidosis with respiratory compensation

. How can calculation of an osmolar gap be used clinically? a. To rule out toxic alcohol ingestion b. To assist with understanding potential causes of a wide anion gap metabolic acidosis c. To differentiate primary lung pathology from respiratory muscle weakness in a patient with respiratory acidosis d. To understand if metabolic compensation has occurred after respiratory alkalosis

A patient presents to the emergency department with short- ness of breath. Plasma bicarbonate concentration is 44 mmol/L. What is a potential explanation for this laboratory value? a. Administration of a large volume of saline b. Acute respiratory failure from a spontaneous pneumothorax sustained 2 hours prior to presentation c. Chronic respiratory failure from chronic obstructive pulmonary disease d. Diabetic ketoacidosis