Acid-Base Disorders (CMPP)

What is assessed using ABG

pH

pCO2

pO2

Where are ABGs drawn

Radial Artery

Brachial Artery

If we draw an ABG from a radial artery, what must be done before we draw

Allen Test

Indications for ABG

Assessing ventilatory status

Identifying respiratory, metabolic, or mixed acid-base disorders

Identifying CO2 retainers

Assessing response to therapy

Evaluation of oxygenation with dyshemoglobinemia (CO Poisoning)

Contraindications for ABG

Abnormal Allen

Local Infection

Presence of AV fistula / vascular graft

Severe peripheral vascular disease

NOT INIDCATED

Normal Arterial pH

7.35-7.45

Normal pCO2

35-45

Normal pO2

70-100

Indication for VBG

Avoid arterial trauma

Indwelling central line

How do values need to be considered from VBG to ABG

pH is 0.05 lower

pCO2 is 5-10 higher

A low serum pH with high pCO2 indicates

Respiratory Acidosis

A high serum pH and low pCO2 indicates

Respiratory Alkalois

A low pH with low-normal pCO2 and low HCO3 indicates

Metabolic Acidosis

A high pH with normal-high pCO2 and high HCO3 indicates

Metabolic Alkalosis

How does the body compensate for metabolic acidosis

Low pH stimulates chemoreceptors and increases respiratory drive

How does the body compensate for metabolic alkalosis

Increased pH depresses respirtory drive

What limits the body’s ability to compensate for metabolic alkalosis

Hypoxia takes priotoirty over alkalosis

How does the body compensate for respiratory acidosis

Increases HCO3 reabsorption

How does the body compensate for metabolic alkalos

Decreasing acid execretion

In terms of acid-base disorders, what is the body better at dealing with

Acidosis

When is an anion gap done

Metabolic Acidosis

Anion Gap

Refers to the higher amount of cations than anions in the body

What is the forumla for AG

Na - (Cl + HCO3)

What can cause high AG metabolic acidosis

MUDPILES:

• Methanol (ETOH)

• Uremia (Kidney Fail)

• DKA (or AKA)

• Paraldehyde

• Iron / Isoniazid

• Lactic Acidosis

• Ethylene Glycol (Antifreeze)

• Salicylate (ASA)

What can cause normal AG metabolic acidosis

Diarrhea

Renal Tubular Acidosis

Carbonic Anhydrase Inhibitor

All cases of normal AG metabolic acidosis will also have

Hypercholremia

Tx for High AG Metabolic Acidosis

Treat Underlying

Osmolal Gap

The difference between predicted osmolality and measured osmolality

What is the forumla for OG

Measured Osmolality - Predicted Osmolality

What is normal vaule for OG

< 10

When do we take a OG

High AG metabolic acidosis

A patient has metabolic acidosis, high AG, and elevated OG. What is the likely causes

Methanol

Ethylene Glycol

Tx for Normal AG Metabolic Acidosis

Treat Underlying

Consider IV HCO3

Why must we be careful when giving HCO3 for metabolic acidosis

Risk for pulmonary edema and hypokalemia

What can cause metabolic alkalosis

Prolonged vomiting or diarrhea

Hypokalemia

Diuretics

CF

Hyperaldosteronism

Cushing

Contraction Metabolic Alkalosis

A state of alkalosis caused by a large fluid loss with low HCO3 loss

Tx for Contraction Metabolic Alkalosis

0.9 NS

What are the types of metabolic alkalosis

Chloride-Responsive

Chloride-Resistant

Tx for Metabolic Alkalosis

Treat Underlying

N/V = Anti-Emetic and IV hydration

Diuretic Induced = Decrease dose or change to spironolactone

Hyperaldosteronism = Spironolactone

What can cause respiratory acidosis

Severe obstructive lung disease (COPD)

Respiratory Depression (OD / Obesity)

Tx for Respiratory Acidosis

Treat the underlying

Improve ventilation

What causes respiratory alkalosis

PE (Hypoxia)

Pneumonia (Hypoxia)

Salicylate OD

Sepsis

Anxiety

Tx for Respiratory Alkalosis

Treat Underying