Chap. 55 Non-trad Flashcards
nontraditional approaches to acid-base analysis may provide greater insight into:
Stewart approach identifies three independent determinants of acid-base balance:
Strong ion gap (SIG) is Stewart measure of:
underlying mechanisms of metabolic acid-base abn.
PCO2
strong ion difference (SID)
total weak acids (ATOT)
unmeasured anions or cations
and is not affected by changes in albumin
semi-quantitative approach to acid-base analysis calculates the effects of five parameters on base excess:
parameter XA is the semi-quantitative evaluation of:
- free water (marked by sodium concentration)
- changes in chloride
- albumin
- phosphate
- lactate
unmeasured anions or cations
Evaluation of respiratory acid-base balance is similar across all diagnostic approaches
traditional HH
Steward
semi-quant
Stewart approach three independent determinants of acid-base balance:
quantity of hydrogen (or bicarbonate) ions added to, or removed from, the system is not considered relevant bc:
SID and ATOT are proposed to affect hydrogen ion concentration:
Stewart approach is able to identify ____, ___ acid-base abnormalities
PCO2
SID cation - anion diff
total weak acids ATOT
not an “independent” variable
directly by altering the dissociation of water via electrochemical forces
five metabolic acid-base abnormalities (not resp.)
5 Metabolic Acid-Base Abnormalities Identified by the Stewart Approach
Increased SID metabolic alkalosis (increased HCO3)
Decreased SID metabolic acidosis (hyperCl)
Increased ATOT metabolic acidosis (increased alb.phos)
Decreased ATOT metabolic alkalosis (decreased alb.phos)
Increased SIG metabolic acidosis (increasedG)
Strong ions are ions that are:
major strong ions include:
formula SID full:
formula SID partial:
important to note that changes in SID will reflect changes in bicarbonate concentration if ____
fully dissociated at physiologic pH
sodium, potassium, calcium, magnesium
chloride +/- lactate and ketoacids
ATOT remains constant (phostate and albumin)
A decreased SID =
can be due to (2):
increased SID = due to (2) hypernatremia, hypochloremia, or both
metabolic acidosis
hyponatremia, hyperchloremia, or combination
metabolic alkalosis
hypernatremia, hypochloremia, or both
Treatment of abnormalities in SID generally focuses on:
SID of intravenous fluids can be determined as it is for plasma. This value can help guide fluid selection
increased SID alkalosis may benefit from:
decreased SID acidosis may be best treated with:
Sodium bicarbonate is a fluid with ____ SID because ________:
fluid therapy to restore SID to normal
low SID such as 0.9% saline (SID = 0)
lactated Ringer’s with an effective SID of approximately 28 mmol/L (after the lactate is metabolized)
very high SID because bicarbonate is not counted as having any effect
sodium bicarbonate with a concentration of 2000 mmol/L has a SID of approximately 2000 mmol/L (na)
=effective treatment of patients with a low-SID metabolic acidosis
Total Weak Acids (ATOT)
What are weak acids:
major contributors to ATOT:
dissociation of these substances varies with pH, there are complex formulas to calculate ATOT & simplified equations to estimate the plasma protein contribution to ATOT using a species-specific dissociation constant (Ka)
b/c ATOT represents a value for weak acids, increases in ATOT indicate ____ and decreases in ATOT _____.
Treatment of abnormalities of ATOT aim to normalize:
Total Weak Acids (ATOT)
only partially dissociated at physiologic pH
albumin and phosphate
metabolic acidosis (primarily from decreased albumin) metabolic alkalosis
albumin and phosphate
Strong Ion Gap
Stewart evaluation of ____:
calculation:
if there are no unmeasured anions (SIG = 0) SID should equal the sum _____:
a simplified formula for the calculation of SIG has been developed by Constable for dogs as:
for cats:
does not account for changes in phosphate
Strong Ion Gap
unmeasured anions similar to AG
SIG = SID - ATOT
HCO3 and ATOT
SIGsimplified = ([alb] × 4.9) − AG SIGsimplified = ([alb] × 7.4) − AG
Semi-Quantitative Approach
uses equations to estimate the magnitude of effect of:
Differences between the sum total of all these calculated and BE are attributed to the presence of unmeasured (unknown) acids or bases
simplified or shorthand version of these formulas used to make a rough estimate and allow clinical application of this approach without use of a computer spreadsheet
requires measurement of:
from these measured parameters, ____ metabolic acid-base influences can be identified and the magnitude of their contribution to the overall BE estimated
Negative contributions indicate an ______on BE
Positive calculated effect indicates an ______on BE
individual acid-base processes on base excess BE
(1) a free water effect (marked by sodium concentration)
(2) changes in chloride concentration
(3) an albumin effect
(4) a phosphate effect
(5) a lactate effect
pH, PCO2, BE, measurement: sodium, chloride, albumin, lactate, and phosphate
10 metabolic acid-base
acidotic influence on BE
alkalotic influence
Free water effect Corrected chloride Chloride effect Albumin effect Phosphate effect Lactate effect Sum XA
(Measured sodium − Normal sodium) / 4
Measured chloride × (Normal sodium / Measured sodium)
Normal chloride − Corrected chloride
(Normal albumin − Measured albumin) × 4
(Normal phosphate − Measured phosphate) / 2
Lactate effect Measured lactate × −1
Free water effect + Chloride effect + Albumin effect + Phosphate effect + Lactate effect
XA (Unmeasured) = Base Excess − Sum
excess of free water - hyponatremia:
free water deficit - hypernatremia:
acidotic effect—a dilutional acidosis
alkalotic effect—a contraction alkalosis
processes within the body, chloride and bicarbonate are _____ linked
i.e.:
chloride concentration will also be altered by changes in free water concentration, it needs to be:
formula:
difference between ___ estimates the contribution to BE
increased (positive) chloride
decreased chloride effect (negative)
reciprocally
chloride ion is excreted, a bicarbonate ion is retained
gastric acid secretion, intestinal bicarbonate secretion, renal acid-base handling, and transcellular ion exchange
corrected before calculation of the chloride effect
corrCl- = patients Cl x (normal Na/ patients Cl)
Mid-normal [Cl−] − corrected [Cl−]
increases bicarbonate - alkalotic process
acidotic process
Albumin Effect
Albumin acts as a:
bc it has many:
hypoalbuminemia is equivalent to the removal of a weak acid from the system;
hyperalbuminemia will be evident as a negative effect,
weak acid
H+ binding sites associated with the imidazole group of the amino acid histidine
positive effect and indicates an alkalotic effect
hyperalbuminemia - negative effect -indicating acidotic influence
