Interpreting Arterial Blood Gases: Simplistic Methods and Comprehensive Approaches, Lecture notes of Physiology

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Doug Pursley, M.Ed., RRT-ACCS, FAARC

 1. Discuss various simplistic, stepwise methods for interpreting the acid-base status of a patient  2. Describe the primary components of a comprehensive approach to assessing acid-base balance

 Uses systematic

arrangement of values

according to established

criteria in order to arrive at a

diagnosis

 Arrow Method (high-low)  Variations of the arrow method  Tic-Tac-Toe method  Romanski method  “H” method

http://nurseslabs.com/8-step-guide-abg-analysis-tic-tac-toe-method/

 Step 1: Evaluate pH

 Step 2: Evaluate respiratory and metabolic

components

 Step 3: Determine consistent value

 Step 4: Determine compensation

Larkin, B. G., MS, RN, ACNS-BC, CNS-CP, CNOR, & Zimmanck, E. J., MD. (2015, October). Interpreting Arterial Blood Gases Successfully. Retrieved June 13, 2016, from https://www.aorn.org/websitedata/cearticle/pdf_file/CEA 2 - 0001.pdf

 Uses physiologic rules

and mathematical

equations in order to

apply a proper

interpretation to the

results

 1. Basic instruction about the four parts of

acid-base physiology (pH, PaCO2, HCO3, Base)

and how to check consistency/inconsistency

via H-H equation

 2. Then we teach one acid-base disorder at a

time (including causes) followed by mixed

disorders and case studies to put it all together.

Always use patient history, electrolytes, and

previous ABGs when available.

 All acid-base data should calculate out according to the Henderson-Hasselbalch equation  [HCO3 ÷ (PaCO2 x 0.03)] log + 6.1 = pH

http://www-users.med.cornell.edu/~spon/picu/calc/basecalc.htm Or just Google: “Cornell base excess”

 AG = (Na + K

) - (Cl +HCO3) or clinical equation…  AG = Na – (Cl + HCO3)  12 is normal  > 20 suggests metabolic acidosis  >30 is 100% chance of metabolic acidosis

 BG = Δ AG – Δ HCO3 or clinical shortcut…  BG = Na – Cl – 36  > +6 suggests metabolic alkalosis or compensation for respiratory acidosis  < - 6 suggests hyperchloremic metabolic acidosis or compensation for respiratory alkalosis

Condition Acute Chronic Respiratory acidosis pH by 0. HCO3 by 1 (hydrolysis) pH by 0. HCO3 by 4 Respiratory alkalosis pH by 0. HCO3 by 2 (hydrolysis) pH by 0. HCO3 by 5

 pH 7.  PaCO2 19  Expected PaCO2 = 27  HCO3 13  Na 146  Cl 106  AG = 27  BG = +  Arrow method: partially compensated respiratory alkalosis.  Actual interpretation is metabolic acidosis with respiratory OVER compensation (respiratory alkalosis)