ABCs of ABGs - Notes on understanding and interpreting arterial blood gases. Lecture by Dr. PDF

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Summary

Notes on understanding and interpreting arterial blood gases. Lecture by Dr. Sauls when she instructed this course....

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HCO3 (bicarbonate) and BE (base excess) mean the same thing

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Hydrogen ions create acidity in the ion! • More hydrogen, the more acidic

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Partial pressure of arterial oxygen! Measured in mmHg! ! Tells us how well we're diffusing oxygen across the alveolar capillary membrane! ! Most oxygen carried on hemoglobin! ! Hypoxemia is defined as anything less than 60!! • If you see a trending down of the PaO2 you should be concerned!

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! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! Very small percentage carried in the blood.. A lot is carried in protein or disguised as bicarbonate! ! CO2 is a measure of carbonic acid! • MEASURE OF ACID! • Too much CO2 = acid problem! • Too little CO2 = base problem! ! CO2 is a gas! • Lungs handle gasses! • Lungs buffer acid base balance by holding onto or getting rid of CO2! • Reflection of alveolar ventilation! ◦ Has nothing to do with oxygenation! ◦ Too low- hyperventilating! ‣ CO2 being let off! ◦ Too high- hypoventilating! ‣ CO2 building up ! ! ! ! ! ! ! ! ! ! ! ! !

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CO2 too high = acidosis (too much acid!)! ! CNS depression! • Stroke?! Impaired nm function! • Multiple sclerosis! • ALS! Chest wall trauma! • Fractured ribs! ◦ Patient doesn't want to take deep breath! Pneumothorax! Airway disease or obstruction! • COPD- CO2 retainers

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Overdose! • Anti-anxiety medication, narcotics, opioids, anesthesia! ! Electrolyte imbalance

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! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! Think of acid as a depressant!! ! Increased RR! • Lungs attempt to compensate by blowing off CO2! • If cause is something like an OD probably not going to see that! • If patient is alert and lungs are healthy we will probably see this! ! Oxyhemoglobin dissociation curve! • Too much acid in the body decreases hemoglobin's love of oxygen! • So that when the hemoglobin passes the alveoli it normally fills up to 95%-98% capacity! • In a state of acidosis it's like hemoglobin is miffed with oxygen.. decreased affinity for oxygen! • When hemoglobin gets to the cellular level cells don't get enough oxygen ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

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Primary treatment: try to correct the cause and fix the ventilation problem! ! Cause: Hypoventilation! • Increase ventilation! • Sit up in the bed and take slow deep breaths! • Treat pain if it hurts to breathe (post-op)! • Cough to loosen pus in alveoli! • Suction secretions to promote ventilation! • Intubate if it's really bad

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Respiratory alkalosis! ! Hyperventilation! ! Hypoxemia! • Hyperventilation is the response to hypoxemia! ! Artificial ventilation! • Get carried away with ventilator settings or the ambu bag! • About 15 minutes after changing ventilation settings can you draw an ABG! ! Stress! • Anything that causes a stress response causes some kind of hyperventilation! !

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Alkalosis = stimulant! ! In a state of alkalosis hemoglobin loves oxygen so much it takes ALL OF IT!! • Hemoglobin doesn't want to give up the oxygen once it gets to the cellular level

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However we have to do that! • Give person a bag to breathe in! ◦ Re-inhaling CO2! • May have to call doctor or respiratory therapist to change the vent settings! ◦ Change the vent settings!! ◦ Decrease the respiratory rate and/or tidal volume (depth)! ‣ Rate and depth

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Not enough bicarbonate = acidosis! ! Causes:! • Increased production of acids! ◦ DKA! ‣ Causes body to produce too much acid! • Problems that cause increased excretion of acids! ◦ Acute kidney injury, kidney failure, renal failure, etc.! ‣ Prevents the body from excreting acid! • Problems that cause excess loss of base! ◦ Upper GI = acid! ‣ Acid in abundance in the stomach! ◦ Lower GI = alkaline! ‣ Pancreases squirts bicarbonate into the duodenum to prevent duodenal ulcers! ◦ Intestinal flu! ‣ Copious diarrhea for several days! • Getting rid of a lot of bicarbonate (or base!)! • Acid is left in the body with no where to go and no one to be with :(

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headache

Acid is still a depressant!

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Will fix it most of the time

Don't typically do this unless it's pretty severe! • pH less than 7! • bicarbonate less than 5

DKA! • hyperglycemia = main problem! • hyperglycemia cascade caused acidosis! • correcting the blood sugar is solution!! ◦ give insulin! ! Renal failure! • Dialysis

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Too much bicarb = ALKALOSIS! ! Causes! • Loss of chloride! ◦ Probs most common cause! • Chronic respiratory acidosis! • Base administration! ◦ NS, PPI, malox, NG suction

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Stopped listening

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Still not listening

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BE is just another measure of bicarbonate! !

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arterial blood sample

Saturation of the hemoglobin molecule with oxygen! ! SaO2 and SpO2 are not the same!! Can vary by 3%! ! Cyanosis occurs when SaO2 (SpO2) is below 60

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Healthy lungs are quick!! • Can work in just a few minutes to adjust pH! • How do they do this?! ◦ Adjusting respiratory rate and depth to adjust CO2

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Kidneys are slow, but steady (win the race!)! • Powerful buffers! • May take several days! • Work well if they're healthy!! ◦ Person in renal failure can't buffer! • For every hydrogen ion that is secreted and excreted (peed out) a sodium and a bicarbonate are reabsorbed

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• Absent! ◦ Means none! • Partial! ◦ Goal of compensation: normalize the pH! • Complete! ◦ Normal pH!! ◦ May still have respiratory alkalosis or acidosis or whatever but the systems have worked together to normalize the pH

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pH- acidic! CO2- acidic (respiratory)! HCO3- normal! ! respiratory acidosis that is uncompensated! ! Increase ventilation! • Tripod position! • Pursed lip breathing! Supplemental oxygen

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pH- acid! CO2- base! CO3- acid! ! Metabolic acidosis with partial compensation ! ! • Kidneys haven't been able to excrete hydrogen and absorb bicarbonate! • Lungs are trying to blow off CO2! • Dialysis

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