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Graphical Analysis
Charles L. Webber, Jr., Ph.D.

Loyola University Medical Center

 

Learning Objectives: You should be able to:

Rhoades & Tanner Text Readings: Chapter 25, Pages 481-483

Arterial PCO2 Isobars     Davenport's Diagram     Compensatory Processes     Base Excesses and Deficits     MainMenu

 

 

Arterial PC02 Isobars and the Normal Buffer Line

  1. CO2 Hydration Reaction (Fig. 24)

     

  2. PaCO2 Isobars and Metabolic Disturbances (Fig. 25)

     

  3. Normal Blood Buffer Line and Respiratory Disturbances (Fig. 13)

Arterial PCO2 Isobars     Davenport's Diagram     Compensatory Processes     Base Excesses and Deficits     MainMenu

 

Davenport's Diagram

  1. Introduction

     

  2. Quadrants of the pH-HCO3- Diagram (Fig. 25)

     

  3. Sextants of the pH-HCO3- Diagram (Fig. 26)

Arterial PCO2 Isobars     Davenport's Diagram     Compensatory Processes     Base Excesses and Deficits     MainMenu

 

Compensatory Processes

  1. Rules for Moving on the Davenport Diagram (Fig. 27)

Arterial PCO2 Isobars     Davenport's Diagram     Compensatory Processes     Base Excesses and Deficits     MainMenu

 

Base Excesses and Base Deficits

  1. Importance of HCO3- Values

     

  2. Determination of Abnormal Base Concentrations (Fig. 28)

     

  3. Specific Examples Using Davenport's Analysis
    Data
    Point
    pH
    (unit)
    PaCO2
    (mm Hg)
    [HCO3]
    (mM)
    Compen-
    sation
    Base Excess
    (mM)
    A 7.17 80 28 none 28 - 28 = +0
    B 7.32 60 30 partial 30 - 26 = +4
    C 7.39 55 32 full 32 - 24 = +8
    D 7.60 20 25 --- incompatible data ---

     

  4. Time Course of Acid-Base Status (Fig. 29)
    • points A, B and C from Table above are plotted on a Davenport Diagram
    • the points are connected with a line to show time course changes in acid-base status
    • following the time course of corrective therapy cannot be stressed enough

        ■ maintenance of pH in chronic patients is very touchy (an art)
        ■ a one time administration of some agent will seldom correct the problem
        ■ time-course plots enable the physician to continuously evaluate success of treatment program
        ■ beware that 2° compensation can become 1° problem if treatment is too aggressive

Arterial PCO2 Isobars     Davenport's Diagram     Compensatory Processes     Base Excesses and Deficits     MainMenu