stewart approach in acid base balance
DESCRIPTION
Diagnostic approach in metabolic acid-base disorderTRANSCRIPT
Stewart Approach
dr Iyan Darmawandr Iyan Darmawan
An Introduction
All Truth passes 3 steps
First, it is ridiculed
Second, it is violently opposed
Third, it is accepted as self-evident
Claude Pichard
Stewart Approach
Diagnosis (& prognosis) of acid-base disorders ------guide fluid therapy
Explain the role of strong ions on pH Elaborate the influences of metabolic component
of acid-base disorders (masking effect of hypoalbuminemia, phosphate in ARF)
Detect and calculate UA (unmeasured anion) Perform synergistically with ventilatory &
hemodynamic support
Vladimir Fencl (1923-2002)
Peter Stewart(1921-1993) JA Kellum
Story DA, Bellomo R. Strong ions, weak acids and base excess: a simplified Fencl–Stewart approach to clinical acid–base disorders British Journal of Anaesthesia, 2004, Vol. 92, No. 1 54-60
– BE Dihitung oleh alat (atau HCO3- - 24 + 11.6*(pH -
7.4) )
– SID effect, mEq/l = A + B• A. Free Water effect on Na+
= 0.3 x ([Na+] – 140)• B. Corrected Cl- effect
= 102 – ([Cl-] x 140/[Na+])– ATOT effect, mEq/l
= 0.123 x pH - 0.6310 x (42 - [Albumin])
UA effect = BE ef – SID ef – ATot ef
BASE EXCESS DAN STEWART
7.32 4 2.315634 2.154888
37.228.2
3.62.24.2
131
21
2.15488
2.3
86
-4.25939
55 25.45488 29.54512
29.54512 mEq/L
Background
Electrolytes & ABG should be checked
Reduced consciousness(coma) Unexplained seizures Major surgery Hemorrhagic shock Sepsis DKA Acute renal failure Complicated Stroke (SIADH,CSWS) Drug Adverse Events Drug intoxication/poisonings etc
J.A. Kellum: Most clinicians tend to
ignore the effects of exogenous Cl- on blood pH, yet many will treat even mild forms of acidemia
J.A. Kellum: Most clinicians tend to
ignore the effects of exogenous Cl- on blood pH, yet many will treat even mild forms of acidemia
::
Excessive Use of NaCl 0.9% & Meylon
Normal = 7.40 (7.35-7.45)Viable range = 6.80 - 7.80
Effects of Metabolic Acidosis
Depression of myocardial contractility
Sympathetic overactivity (incl tachycardia, vasoconstriction,decreased arrhythmia threshold)
Resistance to the effects of catecholamines
Peripheral arteriolar vasodilatation Venoconstriction of peripheral veins Vasoconstriction of pulmonary arteries Effects of hyperkalaemia on heart
Effects of Respiratory Acidosis
Depression of Intracellular Metabolism
increased cerebral blood flow, Increased intracranial pressure, & potent stimulation of ventilation. This can result in dyspnoea,
disorientation, acute confusion, headache, mental obtundation or even focal neurologic signs
Effects of Metabolic Alkalosis
decreased myocardial contractility
arrhythmias decreased cerebral blood flow confusion mental obtundation neuromuscular excitability impaired peripheral oxygen
unloading (due shift of oxygen dissociation curve to left).
Effects of Respiratory Alkalosis
Neurological effects Increased neuromuscular irritability (eg paraesthesias such as
circumoral tingling & numbness; carpopedal spasm) Decreased intracranial pressure (secondary to cerebral
vasoconstriction) Increased cerebral excitability associated with the combination of
hypocapnia & use of enflurane Inhibition of respiratory drive via the central & peripheral
chemoreceptorsCardiovascular effects Cerebral vasoconstriction (causing decreased cerebral blood flow)
[short-term only as adaptation occurs within 4 to 6 hours] Cardiac arrhythmias Decreased myocardial contractilityOther effects Shift of the haemoglobin oxygen dissociation curve to the left
(impairing peripheral oxygen unloading) Slight fall in plasma [K+]
Principles of Stewart Approach
1. Electroneutrality2 Mass conservation
Cation Anion
The amount of each component remains constant unless some of that substance is added or removed, either physically or by participating in a chemical reaction
HH Stewart
pH =CO2
HCO3
pHCO2 SID
ATOT
ATOT = Total weak acid Albumin + Pi
SID =strong ion difference= [strong cations]-[strong anions]
SID
ATOT
pCO2
Independent variables/pH determinants
• Balance of alveolar ventilation and CO2 metabolic production maintains pCO2 normal 40 mmHg.
• When alveolar ventilation increases or decreases not proportionally with CO2
production, respiratory acid-base disorder occurs.
.
Strong Ions
CATIONS
Na+
K+
Mg++
Ca++
ANIONS
Cl-
Sulfate=
Latate- & Urate-
?
STRONG ION DIFFERENCESID = [Strong cations]-[strong anions]
Strong cations
Strong anions( Cl-,sulphate, urate)
SIDe
STRONG ION DIFFERENCE
SIDe =[HCO3- + A-]
SIDe= effective SID
Na+
Cl-
A-
HCO3-
Mg++
Ca++
K+
Kation kuat
Anionkuat
SID = [strong cations]-[strong anions] SIDa = [Na+ + K+ + Ca++ + Mg++] – [Cl - + laktat- + Urat- ]
SIDe = [HCO3- + Alb- + P-]
SIDe
Strong ion Gap (SIG) = SIDa – SIDe
Theoretically normal =0. Positive values reflect the presence of
unmeasured anion(s)
Gamblegram
Na+
137
K+ 4Ca++ 2.2Mg++ 1
Cl-
107
HCO3-
26
CATIONS ANIONS
SIDe
Weak acid(Alb- 46,P- 1)
TOTAL WEAK ACIDor ATOT
SIDa = (137 + 4 + 2.2 +1) – 107 = 37 SIDe= 26 + 0.2x[alb] + 1.5 x [phosphate]SIDe= 26 + 0.2x[46] + 1.5 x [1]
Why strong ions influence pH
Effect on water dissociation
Water is polar
Oxygen is negatively charged
Hydrogen is positively charged
O
HO
H HH
Proton Jumping
Water does not spontaneously Disassociate……………strong ions must be present!
Cl-
Na+
O
H
HO
H
H
Cl-
Na+
OH
H
O
HH
Cl-
Na+
OH-
H3O+
Cl-
Na+
OH-
H3O+
Cl
Na
If Na+ >> SID will increase
Cl-
Na+
OH-
H3O+Na
If Cl- >> SID will decrease
Cl
Relation between SID, H+ & OH-
SID(–) (+)
[H+] [OH-]
At 370C, SID ranges from 30-40 mEq/L(dependent on albumin conc)
Acidosis Alkalosis
[H+]
Na+ Cl-
ATOT
SIDa SIDe
Urate,Lactate,sulphate
K+
Mg ++Ca++
HCO3-
If SIDa - SIDe or SIG = >0 , it means there are unmeasured anions (UA)
Normal
Na+ Cl-
ATOT
SIDa SIDe
Urate,lactate,sulphate
K+
Mg ++Ca++
HCO3-
Alkalizing effect of increased Na+
Na+ Cl-
ATOT
SIDa SIDe
Urat,laktat,sulfat
K+
Mg ++Ca++
HCO3-
Alkalizing effect hypoalbuminemia
Na+ Cl-
ATOT
SIDa SIDe
Urate,lactate,sulfate
K+
Mg ++Ca++
HCO3-
Alkalizing effect of hypochloremia
Cl-
Na+ Cl-
ATOT
SIDa SIDe
Urat,laktat,sulfat
K+
Mg ++Ca++
HCO3-
Hyperchloremic acidosis
Na+ Cl-
ATOT
SIDa SIDe
laktat,
K+
Mg ++Ca++
HCO3-
Lactic Acidosis
Na+ Cl-
ATOT
SIDa SIDe
Urate,lactate,sulphate
K+
Mg ++Ca++
HCO3-
Acidosis with Increased Anion gap due to UA (keton bodies,ethyleneGlycol,methanol etc). The presence of UA can be detected by FencleStewart approach or more corerectly by SIG calkulator of Kellum
UA
Note that when SIDa > SIDe , SIG is positive
Na+ Cl-
ATOT
SIDa SIDe
Urate,lactate,sulfate
K+
Mg ++Ca++
HCO3-
UA
Examples in DKA (diabetic ketoacidosis) and ARF
Acidosis with Increased Anion gap due to UA (keton bodies,ethyleneGlycol,methanol etc). The presence of UA can be detected by FencleStewart approach or more corerectly by SIG calkulator of Kellum
Acid-Base Pattern in ARF
ARF Group Match Controls ICU Controls
Story DA, Bellomo R. Strong ions, weak acids and base excess: a simplified Fencl–Stewart approach to clinical acid–base disorders British Journal of Anaesthesia, 2004, Vol. 92, No. 1 54-60
BE measured by machine(or HCO3- - 24 +
11.6*(pH - 7.4) )SID effect, mEq/l = A + B
A. Free Water effect on Na+
= 0.3 x ([Na+] – 140)B. Corrected Cl- effect
= 102 – ([Cl-] x 140/[Na+])ATOT effect, mEq/l
= 0.123 x pH - 0.6310 x (42 - [Albumin])
UA effect = BE ef – SID ef – ATot ef
HOW TO DETECT THE PRESENCE OF UA?
Fencle-Stewart Approach is good for screening because it measures the effect of UA on base excess.
Kellum SIG calculator directly measures the amount of UA (UA = SIDa-SIDe)
Practical ApplicationFor NON-ICU personnel
Na+ = 140 mEq/LCl- = 102 mEq/LSID = 38 mEq/L
140/1/2 = 280 mEq/L102/1/2 = 204 mEq/L SID = 76 mEq/L1 liter ½ liter
WATER DEFICITDiuretic
Diabetes Insipidus
Evaporation
SID : 38 76 = alkalosis
Contraction alkalosis
Plasma Plasma
Na+ = 140 mEq/LCl- = 102 mEq/L SID = 38 mEq/L
140/2 = 70 mEq/L102/2 = 51 mEq/L SID = 19 mEq/L
1 liter 2 liter
WATER EXCESS
1 Liter H2O
SID : 38 19 = Acidosis
DILUTIONAL ACIDOSIS
Plasma
Na+ = 140 mEq/LCl- = 102 mEq/LSID = 38 mEq/L
Na+ = 154 mEq/LCl- = 154 mEq/LSID = 0 mEq/L1 liter 1 liter
PLASMA + NaCl 0.9%
SID : 38
Plasma NaCl 0.9%
2 liter
Hypechloremic acidosis due to NaCl 0.9%
=
SID : 19 Acidosis
Na+ = (140+154)/2 mEq/L= 147 mEq/L
Cl- = (102+ 154)/2 mEq/L= 128 mEq/L
SID = 19 mEq/L
Plasma
In DSS or DKA resuscitation with NaCl 0.9% may lead to hyperchloremic acidosis
Many protocols advocate the use in shock of 0.9 percent sodium chloride,which has been shown to be as effective as 4.5 percent human albumin in adults admitted to intensive care units.However, large volumes of normal saline may cause hyperchloremic acidosis, and with no glucose or potassium, its use in some cases of shock, acidosis, or electrolyte imbalance could make matters worse.
Molyneux ElM. , Maitland K, Intravenous Fluids — Getting the Balance Right. N Engl J Med 2005 353:941-944
Na+ = 140 mEq/L Cl- = 102 mEq/L SID= 38 mEq/L
Cation+ = 137 mEq/L Cl- = 109 mEq/LAcetate- = 28 mEq/L SID = 0 mEq/L
1 liter
1 liter
PLASMA + Ringer’s acetate
SID : 38
Plasma RA Acetate rapidly
metabolized
2 liter
=
Normal pH after RINGER’s Acetate
SID : 34 more alkalotic than NaCl 0.9%
Na+ = (140+137)/2 mEq/L= 139 mEq/L
Cl- = (102+ 109)/2 mEq/L = 105 mEq/L Acetate- (metabolized) = 0 mEq/L SID = 34 mEq/L
Plasma
RINGER’S ACETATE FIRST-LINE resuscitation fluid for patients with shock and dehydration (eg diarrhea, DSS & DKA
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