patient care - acid base labs

normal serum pH

7.35 - 7.45

normal carbon dioxide levels

35 - 45 mmHg

normal bicarbonate levels

22 - 30 mEq/L

test to find bicarbonate?

Chem 7/BMP (serum concentrations)

test to find pH and CO2?

arterial blood gas

arterial blood gas

• blood drawn from indwelling arterial catheter

• measures concentrations of compounds of acid/base status in blood

• used in

  • emergent situations when peripheral not available

  • monitoring acid/base abnormalities

  • monitor resp status

  • monitor therapy response

ABG components

• pH

• pO2

• SaO2

• PCO2

• HCO3-

• base deficit/base excess

body (kidneys)

• electrolyte control

• HCO3- control

lungs

• gas exchange

• lung acid = CO2

  • increased CO2 = more acidic —> triggers brain to breath —> hyperventilation

ABG values order

pH/CO2/HCO3/O2/BE or BD

• BE = base excess

• BD = base deficit (negative) —> acidosis

steps to interpret lab

1. obtain ABG and BMP

2. evaluate pH for acidosis/alkalosis

3. evaluate CO2 and HCO3

4. determinate if theres compensation

5. determine cause and treatment

pH

• log expression of H+ ion concentration

• pH and H+ conc are inversely related

• under 6.7 and over 7.7 arent compatible with life

evaluating CO2 and HCO3

• metabolic acid/alka - HCO3

  • HCO3 is low = metabolic acidosis

  • HCO3 is high = metabolic alklalosis

• respiratory acid/alka - CO2

  • CO2 is high = respiratory acidosis

  • CO2 is low = respiratory alkalosis

compensation

• metabolic disorder = lungs will try to compensate

• respiratory disorder = body/kidneys try to compensate

respiratory compensation

• lungs change to balance body

• occurs quickly (min to hrs)

• metabolic acidosis

  • lung wants to get rid of acid (CO2)—> hyperventilate

• metabolic alkalosis

  • lung wants to hang onto acid (CO2) —> hypoventilate

metabolic compensation

• kidneys affect bicarb

• can take days

• respiratory acidosis

  • renal absorption of HCO3

  • 12-24 hrs of aciodsis

• respiratory alkalosis

  • renal excretion of HCO3

  • 6-12 hrs of alkalosis to trigger

metabolic acidosis causes

• acid overproduction

• underexcretion of acid load (kidney failure)

• hyperchloremia (HCl)

respiratory acidosis causes

• chronic sleep apnea (not breathing out —> keeps CO2 in)

• diaphragmatic paralysis/ALS

• COPD

metabolic alkalosis

• diuretics (wastes chloride)

• gastric loss of Cl

• too much alkali admin

• hypokalemia

respiratory alkalosis

• hypxemia

• meds (salicylates, nicotine, xanthines)

• CNS disorders (meningitis, head trauma)

more causes (meds)

• loop diuretics

  • waste Cl —> alkalosis = hypochloremic metabolic alkalosis

• meds with Cl as a salt

  • increase Cl —> acidosis

• acetazolamide

  • waste bicarb —> metabolic acidosis

• meds with bicarb (acetate) as salt

  • Na HCO3

  • LR

metabolci acidosis symptoms

• hyperventilation

• Kussmaul breathing

• flushing

• fast HR

• wide pulse pressures (big diff between diastolic/systolic)

• NV

• confusion/lethargy

pH < 7.2

• life threatening

• decreased organ perfusion

• increased risk of cardiac arrhythmias

• hyperventilation —> ventilator fatigue

• insulin resistance

• hyperkalemia

• reduced ATP synthesis

• inhibition of cell metabolism

high anion gap metabolic acidosis

• CAT

  • CO, aminoglycoside, arsenic,

• MUD

• PILES

med considerations for metabolic acidosis

• give a base

  • Na HCO3

  • acetate (converted to bicarb)

  • citrate (converted to bicarb)

• dont give much chloride

metabolic alkalosis

• muscle weakness/cramping

• hypokalemia

• dizziness

• cardiac arrhythmias

• neuromuscular irritability

• mental confusion

• paresthesia

pH > 7.6

• life threatening

• cardiac arrhythmias

• respiratory depression/hypoxia

• decreased ionized calcium (tetany, hyperactive reflexes)

• mental confusion

meds for metabolic alkalosis

• chloride issue —> give more Cl

• meds that waste bicarb

  • acetazolamide

respiratory acidosis

• increased CO2 on gas

• usually life threatening

• signs/symptoms

  • AMS

  • seizures

  • stupor

  • coma

  • HA

  • papilledema

  • abnormal reflexes

med considerations for resp acidosis

• minimize chloride/acid intake

• switch to dipping meds in D5 not NS

respiratory alkalosis

• decreases in PaCO2

• signs/symptoms

  • light headedness

  • confusion/decreased cognition

  • syncope

  • seizures

  • N/V

  • cardiac arrhythmias

  • hypokalemia

med considerations for resp alkalosis

• minimize acetate/bicarb intake