The page describes the logic utilized to generate the text reports. as well as the development of the necessary equations and iterative subroutines required to convert the raw data into the diagrams on the screen.
Technique for the text Interpretations
1. Mathematics. See the Equations below. The pH and PCO2 are used to calculate:
Standard Base Excess (SBE)
2. Radial Search. See the Computing Strategy below. The Acid-Base diagram is searched to find:
This diagram shows the radial zones employed to generate the sentence fragments. Each zone is numbered. The numbers correspond to the radial search used to choose a code which generate the Sentence Fragments.
Acute Respiratory Acidosis (7 & 8)
Chronic Respiratory Acidosis (5)
Metabolic Alkalosis (3)
Acute Respiratory Alkalosis (18 & 19)
Chronic Respiratory Alkalosis (16)
Metabolic Acidosis (14)
In a Classical Zone a phrase or sentence is added describing the zone.
Rectangles Determine the Adjectives
The expanding family of rectangles determine the choice of adjectives used to describe the degree of acidosis and alkalosis. Normal; Minimal; Mild; Moderate; Marked; Severe. The corners of these rectangles corresponds to the slope for pH = 7.4.
To Simulate Human Report
Objective of the Algorithm.
The algorithm produces reports with a style and a range of distinctions which a human being might compose. Each report, or even a small series of reports, should appear to be "human". However, because no random variation is included, there is no pretense that a longer series of reports might be mistaken as actually coming from a human hand.
Radial Search & Characterize Magnitude
The computer program conducts a radial search of the diagram to determine which sector (1 - 29) contains the result. The sector corresponds to a stored numerical sequence, each number in which corresponds to a sentence fragment in the final report. Two additional numbers govern the adjectives which describe the magnitude of the respiratory and metabolic components; these numbers are derived from the location either inside or outside the central rectangles ( A - E) and are inserted at the appropriate point in the numerical sequence. A final descriptive phrase is included when the location is characteristic of a chronic or an acute disturbance.
[H+] (30.17 + BE) = 22.63 (PCO2 + 13.33)
A position on the diagram generates X and Y coordinates (PCO2 and SBE). An initial approximation is essential. Without it, the iterative process diverges instead of converging. These equations provide a first approximation, e.g., to obtain bic from BE and PCO2.
The program gives precedence to the dominant component: respiratory or metabolic. Whether the two components are in opposition or supplement each other - the dominant one is described first in the report. Dominance is determined utilizing the slope of the pH = 7.4 line to compare the metabolic and respiratory components.
When the components are additive, the wording changes from, e.g., " . . . is a marked metabolic acidosis with a moderate respiratory compensation" to a more appropriate: " . . . has both a marked metabolic acidosis and a moderate respiratory acidosis."
When choosing adjectives to rank and compare the metabolic and respiratory components we indicate that, e.g., the respiratory component is dominant with a phrase like :....marked respiratory acidosis compensated by a moderate metabolic ....." The adjectives "marked" or "moderate" do not consistently indicate magnitude; a small number of adjectives are used as it suits us. Such fluidity is harder to program. To allow the computer to have a sufficient "hierarchy" of adjectives, the following adjective sequence was employed:
To demonstrate the discrepancy between bicarbonate and Base Excess, both isopleths and numerical values are displayed. Particularly at low PCO2 levels the change in the bicarbonate value can be seen to deviate from Base Excess.