Vanessa Klee MSIV

What is an ABG?The Components

pH / PaCO2 / PaO2 / HCO3 / O2sat / BEDesired Ranges

pH - 7.35 - 7.45PaCO2 - 35-45 mmHgPaO2 - 80-100 mmHgHCO3 - 21-27O2sat - 95-100%Base Excess - +/-2 mEq/L

Why Order an ABG?Aids in establishing a diagnosis Helps guide treatment planAids in ventilator managementImprovement in acid/base management

allows for optimal function of medicationsAcid/base status may alter electrolyte

levels critical to patient status/care

LogisticsWhen to order an arterial line --

Need for continuous BP monitoringNeed for multiple ABGs

Where to place -- the optionsRadialFemoral BrachialDorsalis PedisAxillary

Acid Base BalanceThe body produces acids daily

15,000 mmol CO2

50-100 mEq Nonvolatile acids

The lungs and kidneys attempt to maintain balance

Acid Base BalanceAssessment of status via bicarbonate-carbon

dioxide buffer system

CO2 + H2O <--> H2CO3 <--> HCO3- + H+

ph = 6.10 + log ([HCO3] / [0.03 x PCO2])

The TermsACIDS

AcidemiaAcidosis

Respiratory CO2

Metabolic HCO3

BASESAlkalemiaAlkalosis

Respiratory CO2

Metabolic HCO3

Respiratory Acidosisph, CO2, VentilationCauses

CNS depressionPleural diseaseCOPD/ARDSMusculoskeletal disordersCompensation for metabolic alkalosis

Respiratory AcidosisAcute vs Chronic

Acute - little kidney involvement. Buffering via titration via Hb for example pH by 0.08 for 10mmHg in CO2

Chronic - Renal compensation via synthesis and retention of HCO3 (Cl to balance charges hypochloremia) pH by 0.03 for 10mmHg in CO2

Respiratory AlkalosispH, CO2, Ventilation CO2 HCO3 (Cl to balance charges

hyperchloremia)Causes

Intracerebral hemorrhageSalicylate and Progesterone drug usageAnxiety lung complianceCirrhosis of the liverSepsis

Respiratory AlkalosisAcute vs. Chronic

Acute - HCO3 by 2 mEq/L for every 10mmHg in PCO2

Chronic - Ratio increases to 4 mEq/L of HCO3 for every 10mmHg in PCO2

Decreased bicarb reabsorption and decreased ammonium excretion to normalize pH

Metabolic AcidosispH, HCO3

12-24 hours for complete activation of respiratory compensation

PCO2 by 1.2mmHg for every 1 mEq/L HCO3

The degree of compensation is assessed via the Winter’s Formula

PCO2 = 1.5(HCO3) +8 2

The CausesMetabolic Gap

AcidosisM - MethanolU - UremiaD - DKAP - ParaldehydeI - INHL - Lactic AcidosisE - Ehylene GlycolS - Salicylate

Non Gap Metabolic AcidosisHyperalimentationAcetazolamideRTA (Calculate urine

anion gap)DiarrheaPancreatic Fistula

Metabolic AlkalosispH, HCO3

PCO2 by 0.7 for every 1mEq/L in HCO3

CausesVomitingDiureticsChronic diarrheaHypokalemiaRenal Failure

Mixed Acid-Base DisordersPatients may have two or more acid-base

disorders at one time

Delta GapDelta HCO3 = HCO3 + Change in anion gap

>24 = metabolic alkalosis

The StepsStart with the pHNote the PCO2

Calculate anion gapDetermine compensation

Sample Problem #1An ill-appearing alcoholic male presents with

nausea and vomiting.ABG - 7.4 / 41 / 85 / 22Na- 137 / K- 3.8 / Cl- 90 / HCO3- 22

Sample Problem #1Anion Gap = 137 - (90 + 22) = 25

anion gap metabolic acidosisWinters Formula = 1.5(22) + 8 2

= 39 2 compensated

Delta Gap = 25 - 10 = 1515 + 22 = 37

metabolic alkalosis

Sample Problem #222 year old female presents for attempted

overdose. She has taken an unknown amount of Midol containing aspirin, cinnamedrine, and caffeine. On exam she is experiencing respiratory distress.

Sample Problem #2ABG - 7.47 / 19 / 123 / 14Na- 145 / K- 3.6 / Cl- 109 / HCO3- 17ASA level - 38.2 mg/dL

Sample Problem #2Anion Gap = 145 - (109 + 17) = 19

anion gap metabolic acidosisWinters Formula = 1.5 (17) + 8 2

= 34 2 uncompensated

Delta Gap = 19 - 10 = 99 + 17 = 26

no metabolic alkalosis

Sample Problem #347 year old male experienced crush injury at

construction site.ABG - 7.3 / 32 / 96 / 15Na- 135 / K-5 / Cl- 98 / HCO3- 15 / BUN- 38 /

Cr- 1.7CK- 42, 346

Sample Problem #3Anion Gap = 135 - (98 + 15) = 22

anion gap metabolic acidosisWinters Formula = 1.5 (15) + 8 2

= 30 2 compensated

Delta Gap = 22 - 10 = 1212 + 15 = 27

mild metabolic alkalosis

Sample Problem #41 month old male presents with projectile

emesis x 2 days.ABG - 7.49 / 40 / 98 / 30Na- 140 / K- 2.9 / Cl- 92 / HCO3- 32

Sample Problem #4Metabolic Alkalosis, hypochloremicWinters Formula = 1.5 (30) + 8 2

= 53 2 uncompensated