What are nl values for pH?
What are nl values for pCO2?
What are nl values for pO2?
What are nl values for HCO3?
What are nl values for O2 sat?
What are causes of respiratory alkalosis?
- Hypoxia, which causes hyperventilation
- Causes of hypoxia: pneumonia, pulmonary edema, pulmonary embolism, restrictive lung disease
- Causes of hyperventilation: asthma, anxiety, pain, sepsis, salicylate OD, pregnancy
What is the mechanism behind respiratory alklaosis?
The kidneys have increased renal excretion of HCO3 to create a more acidotic environment because the patient is blowing off her CO2
Describe the differences in compensation between the respiratory and renal system
- Respiratory: hours
- Renal: day or more
What are causes of respiratory acidosis?
- CNS depression: (sedatives, CNS trauma, giving too much O2 in chronic COPDers, which decreases hypoxemic drive)
- Neuromuscular disorders: myasthenia gravis, Guillan-Barre syndrome, ALS
- Upper airway obstruction
- Lower airway abnls: COPD, asthma
- Thoracic cage abnormalities: kyphoscoliosis, flail chest, pneumothorax
What is the mechanism behind compensation for respiratory acidosis?
The kidneys have increased reabsorption of HCO3 to create a more alkalotic environment because the patient is retaining CO2
What are causes of metabolic alkalosis?
- Loss of K via GI tract: vomiting, NGT
- Iatrogenic: diuretics
- Endocrine: primary hyperaldosteronism (Conn's syndrome), secondary hyperaldosteronism (renin-secreting tumor)
- Severe hypokalemia
- Chronic and high volume gastric suction
AlkaLOSis=loss of K
What is the mechanism behind metabolic alkalosis?
An increase in bicarb cauess hypoventilation to retain CO2 to balance out alkalosis. In response to metabolic alkalosis, the pt hypoventilates to retain CO2 to buffer the excess bicarb
What are causes of metabolic acidosis?
- If anion gap: MUDPILES
- >>>MUDPILES: Methanol, Uremia, Diabetic ketoacidosis, Paraldehyde, Iron, isoniazid (INH), Lactic acid, Ethanol, ethylene glycol, Salicylates
- If no anion gap: HARDUP
- >>>HARDUP: Hyperalimentation, Acetazolamide and other carbonic anhydrase inhibitors, Renal tubular acidosis, Diarrhea, Ureteroenteric fistula, Pancreaticoduodenal fistula
What is the mechanism behind metabolic acidosis and compensation?
There is a rise in H, lactate, or other ions, and this causes the pt to hyperventilate to blow off CO2 to counteract the acidosis and raise the PH.
Acidosis: bicarb is deplated, another source of H+ is present if they have a widened anion gap
How do you calculate an anion gap? What is a nl anion gap?
What are indications for ABGs?
- assess respiratory function and metabolic acid-base and electrolyte homeostasis.
- assess adequacy of oxygenation
What is pH?
When are acids normally found in the blood?
- The negative logarithm of the H+ ion concentration in the blood, which is inversely proportional to the actual H+ ion concentration
- -Carbonic acid, dietary acids, lactic acids, ketoacids
What is pCO2? How is CO2 carried in the blood?
- a measure of the partial pressure of CO2 in the blood
- CO2 is carried in the blood as follows: 10% in the plasma, 90% in RBCs. Most CO2 in the blood is HCO3
What is PCO2?
A direct measurement of the tension of CO2 in the blood, this is regulated by the lungs
What is PO2?
- An indirect measure of the O2 content of the arterial blood; measure of the pressure of O2 dissolved in the plasma.
- This pressure determines the force of O2 to diffuse across the pulmonary alveoli membrane.
When is PO2 decreased?
- Pts with O2 diffusion difficulties: (pneumonia, ARDS, congestive failure)
- Venous blood mixing with arterial blood (congenital heart disease)
- Underventilated and overperfused pulmonary alveoli (pickwick syndrome)
What is O2 saturation?
How does it relate to PO2?
How do you calculate O2 sat?
- An indication of the percentage of HGB saturated with O2
- As PO2 decreases, O2 sat decreases. Around 60, this drop stops being linear...small decreases in PO2 will cause large decreases in the percentage of HGB saturated with O2
- Volume of O2 content Hgb/Volume of O2 HGB capacity
When does carboxyHgb increase?
Why do we need to know about this clinically?
- Smoke inhalation, CO poisoning, other inhalants
- Pulse oximetry includes carboxyHgb in its measurements of O2 sats, therefore during the above conditions, the O2 sat will be inaccurately high
What is base excess/deficit?
What does a negative base deficit mean?
What does a positive base excess mean?
- It represents the amt of buffering anions in the blood by measuring pH, PCO2, and hematocrit
- Negative: metabolic acidosis
- Positive: metabolic alkalosis or compensation to prolonged respiratory acidosis
What are contraindications to performing ABGs?
- No palpable pulse
- Negative allen test
- AV fistula
- Pt has severe coagulopathy
What are complications of an ABG?
- occlusion of the artery used for access (therefore avoid use of end arteries such as brachial or femoral artery)
- Penetration of other important structures anatomically juxtaposed to the artery (such as a nerve)
What can cause abnl ABG values?
- O2 sat can be falsely increased by inhalation of carbon monoxide with increases the carboxyHgb level
- COPD pts: stimulus to breathe is not triggered by CO2 levels, but by O2 levels. If a large amt of O2 is provided to these pts, they will no longer be driven to berathe and will hypoventilate
- Respiration can be inhibited by the use of sedative hypnotics or narcotics, and OD of these drugs can cause hypoventilation in pts with nl lungs