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

Thank Thank YOUYOU