ABG

Prof. A. K. Sethi, UCMS, Delhi

Interpretation of Blood Gas Reports (ABG reports)d - made easy

P f A K S hiProf. A. K. SethiHead, Dept. of Anaesthesiology & Critical Care,

UCMS & GTB Hospital, Delhi, Indiap , ,

Prof. A. K. Sethi, UCMS, DelhiWhat is meant by interpreting ABG Reports ?

• ABG = Arterial Blood Gases Gases ≡ Gases in the Blood (O CO CO He Kr N )(O2,CO2, CO, He, Kr, N2)

• All BG machines G ac esMeasure pH, PaCO2, PaO2Calculate HCO3

- +………Ca cu a e CO3

• ABG 2 sets of Tests ≡ABG 2 sets of Tests ≡Acid Base Status + Gases

• Co-oximetry ≡ Hb, SaO2, Co oximetry Hb, SaO2, %COHb, %MetHb, CaO2

Prof. A. K. Sethi, UCMS, DelhiExplanation of TermsHb HCT FiO P O P CO H N + K+ S O (%)Hb, HCT, FiO2, PaO2, PaCO2 , pH, Na+ , K+ , SaO2(%)

RQ CO2 produced:O2 consumed, Set value, Can be fedHCO A Parameter for non respiratory component of acid base balanceHCO3 A (Actual)

Parameter for non-respiratory component of acid-base balance

HCO3 S Parameter for non-respiratory component of acid-base balance 3(Standard)

p y pbut reported after standardising at PCO2 at 40 mm Hg, Temperature 37°C, SO2 100%

B Diff b t l tit f T t l B ff B (BB) Base excess or deficit

Difference between normal quantity of Total Buffer Base (BB) and the BB calculated from Blood Sample. (+) or (-).Depends upon entered Hb value measured pH & PCO2 valuesDepends upon entered Hb value, measured pH & PCO2 values.

Standard Base

Difference between normal quantity of Total Buffer Base (BB) and the BB calculated from Blood Sample. (+) or (-).

excess Calculated from a standard Hb value of 6 gm%, pH of 7.4 & PCO2 of 40 mmHg.

BB (Buffer Sum of all buffer anions in blood BB (Buffer bases)

Sum of all buffer anions in blood (Hb, HCO3, Protein, Phosphate)

Prof. A. K. Sethi, UCMS, Delhi......Explanation of Terms

TCO2 Content HCO3 concentration + dissolved CO2 in plasma

O CT CaO O content Hb bound O + Plasma dissolved OO2 CT, CaO2, O2 content Hb bound O2 + Plasma dissolved O2

A-aDO2 Difference between PO2 (Alv) and PO2 (art)2 2 2

P50 Semisaturation pressure = Partial pressure of O2at which Hb is 50% saturated

LAC Lactate concentration

GLU Glucose concentration

Ca 7 4 Calcium ion concentration computed for pH 7 4Ca 7.4 Calcium ion concentration computed for pH 7.4

Li Lithium ion concentration

+ + ………. ………….


Know Normal & Reference Values for Interpretation

K+ 3.5 – 5.1Ca+ 1 12 – 1 32

Hb (gm%) Measured, Calculated or Fed Ca 1.12 1.32

Cl- 97 – 100B ( E /L) 0 2

(HCT/3)HCT (%) Measured or

Calculated (3xHb) Base excess (mEq/L) 0 ± 2

TCO2 Content (mEq/L) ≈ 27

Calculated (3xHb)FiO2 FedRQ 0 85 2 ( q )

BB (mEq/L) 48RQ 0.85PaO2 (mmHg) 80 – 100

O2 Sat (%) >95%

O2 CT (ml/dL) 16 – 22

PaCO2 (mmHg) 35 – 45

pH 7 35 – 7 45 O2 CT (ml/dL) 16 22

P50 mmHg 27

pH 7.35 7.45

HCO3 A (mEq/L) 22 – 26

A-aDO2 mmHg 5 – 25Na+ 135 – 145

Prof. A. K. Sethi, UCMS, DelhiArterial Blood Sampling

Radial

Dorsalis Paedis

Femoral

B hi lBrachial

Arterialized Tissues

Feed the Sample & Sample & Data


Acid Base HomeostasisH+ and HCO3

‐ concentration (pH) in Plasma must be regulated precisely

& constantly maintained at normal levels

Enzyme activity Tissue OxygenationEnzyme activityChemical reactions within cells

Tissue OxygenationNeurological & Muscular functioningVascular Response to CatecholaminesForce of Cardiac contraction

Hb Saturation with O2

Vascular Response to CatecholaminesResponse to effects of Medicationsand

O2 deliveryand, many more activities . . . . . .

Blood pH < 6 8 and > 7 8 Not Compatible with life Blood pH < 6.8 and > 7.8 - Not Compatible with life (Irreversible cell damage, Death)


H+ : Continuously being produced as substrates, oxidized during production of ATPduring production of ATP

Must be continuously eliminatedby Lungs and Kidneys ultimately by Lungs and Kidneys, ultimately

Normal H+ conc. (Arterial blood, ECF) = 35 – 45 nmol/L( , )≡ Arterial pH of 7.45 – 7.35 respectively (Normal Range)

Acidemia : Blood pH < 7.35Alkalemia : Blood pH > 7.45p

Life sustaining functions of Body Organs and Systems are bound to be affected adversely

D t f b t “N l H” d “N t l H”

when Acidemia or Alkalemia

Donot confuse between “Normal pH” and “Neutral pH”


What does body do when Acidemia or Alkalemia ?

1. Tries to prevent changes in pHa

2. If pHa changes, tries to bring the pH to normal

3 basic mechanisms

1. Buffer systems (HCO3-, Hb, Protein, Phosphate)

2 V til t (L )2. Ventilatory responses (Lungs)

3. Renal responses (Kidneys)p ( y )


Importance of Interpretation of ABG Report To establish diagnosisTo ascertain severityyTo decide about intensity of monitoringTo further intervene in managementg

All Clinicians, Intensivists, Physicians, Anaesthesiologists, ll l n c ans, Intens v sts, hys c ans, naesthes olog sts, should

→ Know correct techniques involved in performing an ABG analysis→ Know correct techniques involved in performing an ABG analysis

→Have an understanding of the changes in ABGs in commonly

encountered clinical conditionsencountered clinical conditions

→ Know to interpret the ABG report systematically and correctly

→Understand implications→Understand implications


When to perform ABGs ?1. Assess the adequacy of ventilation and oxygenation

(whether the patient is on a ventilator or not !)

2. Establish the diagnosis and severity of respiratory failure

3 G id h O d i i i h i l il i i3. Guide therapy ‐ O2 administration, mechanical ventilation, weaning

4. Assess changes in acid‐base homeostasis

5. Guide treatment for acid‐base abnormalities


………When to do ABGs ………6. Manage patients in ICUs for

• Respiratory dysfunction or failure

• Cardiac failure

• Renal failure• Renal failure

• Hepatic failure

• Polytrauma

• Multi‐organ failure• Multi‐organ failure

• Diabetic ketoacidosis

• Sepsis

• BurnsBurns

• Various types of poisonings etc. ………


………When to do ABGs7. Monitor patients during

C di l • Cardio-pulmonary surgery

• Cardio-pulmonary exercise testing

• Sleep studies

8. Determine prognosis in critically ill patients


Basic Precautions (Sampling)

1. Ensure a Steady State of Oxygenation & Ventilation (3,20,30 min)

2. Precautions for arterial blood sampling – Site, Puncture, Cannula, H iHeparin

3 Do not keep the sample exposed to air Any air bubble in Syringe3. Do not keep the sample exposed to air, Any air bubble in Syringe

4. Do not delay the processing. Otherwise, keep sample in Ice.

5. Analyze Step‐by‐Step and completely


Effect of keepingEffect of keeping Sample at room

temperature for 2 hours


Base Excess or Base Deficit

• Difference between normal quantity of Total Buffer Base (BB) and the BB calculated from Blood Samplep

• (+) or (-)

• 0 ± 2

Positive (+) value (Excess Base) = Alkalosis (Non respiratory or Metabolic)Positive (+) value (Excess Base) = Alkalosis (Non-respiratory or Metabolic)

Negative (-) value (Deficit Base) = Acidosis (Non-respiratory or Metabolic)Negative ( ) value (Deficit Base) Acidosis (Non respiratory or Metabolic)

Sodium Bicarbonate dosage Sodium Bicarbonate dosage

= Body weight (Kg) x Base Deficit (mmol/L) x 0.3


Base Deficit (Metabolic Acidosis)

• Compensation for Primary Respiratory Alkalosis

• Diabetic Ketoacidosis (Acidic Ketone Bodies)Diabetic Ketoacidosis (Acidic Ketone Bodies)

• Lactic Acidosis (Anaerobic metabolism - Hypoxia, Heavy exercise)

• Chronic Renal Failure (x Acid excretion, x HCO3 Resorption, Production)

• Diarrheoa (HCO3 excreted)( )

• Poisoning (Methanol, Aspirin, Ethylene glycol)

Base Excess (Metabolic Alkalosis)

• Compensation for Primary Respiratory Acidosis• Compensation for Primary Respiratory Acidosis

• Excessive Vomiting (Loss of HCl in gastric juice)

• Over production of HCO3


R di h R bReading the Report – Step-by-Step


Step 1 pCheck if the required parameters have been correctly fed ?

Barometric pressure

Patient’s temperature

Haemoglobin(if machine does not measure, does not calculate)

FiO2

Results in the report are bound to change get incorrect and misleadingchange, get incorrect and misleading

if the above values are not correctly fed


• A aDO value will be wrong if P & FiO (PiO ) is not fed correctly

Effects of Wrong “Feedings”• A‐aDO2 value will be wrong if PB & FiO2 (PiO2) is not fed correctlyAlveolar gas equation : PAO2 = PiO2 – 1.2(PaCO2) [PiO2 = FiO2 (PB – 47)]

• Oxygenation Impairment (Assess ) Wrong if FiO not fed correctly• Oxygenation Impairment (Assess.) ‐Wrong if FiO2 not fed correctly

Machines always analyse blood at 37 °C• Sample of Hyperthermic Patient = > 37 °C Measured value of• Sample of Hyperthermic Patient = > 37 °C ‐Measured value of

PaO2 and PaCO2 will be less than actual• Sample of Hypothermic Patient = < 37 °C ‐Measured value of p yp

PaO2 and PaCO2 will be more than actual

Temperature Change Shifting of ODC Calculated SO2 37°C (ODC)Temperature Change Shifting of ODC Calculated SO2, 37 C, (ODC)Increase Right Higher than actual

Decrease Left Lower than actualDecrease Left Lower than actual

True assessment of adequacy of O2 in arterial blood (CaO2)can only be made if Hb values are entered SaO & PaO do notonly be made if Hb values are entered. SaO2 & PaO2 do not.

Hb – affects Buffer Base values (Base excess or deficit)


Total O2 attachedto Hb Content + Total Dissolved O2

carried by Plasmato Hb Content + carried by PlasmaHb content (gm%)O carried by 1 gm Hb (ml) PaO2O2 carried by 1 gm Hb (ml)Saturation Hb (SaO2)

2Solubility Coefficient

15 x 1 34 x 100 (say) = 20 10 100 x 0 003 = 0 30+‘☺’ 15 x 1.34 x 100 (say) = 20.10 100 x 0.003 = 0.30+= 20.40 ml / dL

15 1 34 85 17 09 50 0 003 0 15+‘ ’

☺

15 x 1.34 x 85 (say) = 17.09 50 (say) x 0.003 = 0.15+= 17.24 ml / dL

8 x 1.34 x 100 (say) = 10.72 100 x 0.003 = 0.30+= 10.75 ml / dL

“ ”


FiO2

Most common mistake− FiO2 not entered while the sample

is fed in the machine− % FiO2 written on the report later

on manually− Hb also not entered at the time of

feeding sample but told later on

If FiO not fed properlyInterpretation of PO2 affected adverselyA-aDO2 values are wrongly calculated

If FiO2 not fed properly

A aDO2 values are wrongly calculated (PAO2 calculated from PiO2)

Interpretation of adequacy of Oxygenation Interpretation of adequacy of Oxygenation affected adversely if Hb not fed properly.

Prof. A. K. Sethi, UCMS, DelhiStep - 2Analyse the Adequacy of OxygenationAnalyse the Adequacy of Oxygenation

(i) Look at PaO2 and SaO2 first

PaO2 (mmHg) SaO2 (%)

N l l ( i ) 80 95

Healthy Adult ‐ Sea Level, Room Air, A‐a O2 = 4 mmHg, PAO2 = 101

Normal values (on air) > 80 > 95

Mild hypoxemia 60‐79 90‐94

Moderate hypoxemia 40‐59 75‐89

Severe hypoxemia < 40 < 75

PaO2, SaO2 - Important Low PaO2, Low SaO2 = Surely something wrong in terms of OxygenationLow PaO2 = degree of hypoxemia

→ Saturation of Hb (SaO2) is dependent upon PaO2( 2) p p 2

→ Never rely totally on PaO2 & SaO2 – Look at other parameters also (CaO2)


(ii) Relate PaO2 with FiO2 – Classify Hypoxemia

HypoxemiaRefractoryPaO2

O2 x 5 = PaO2Uncorrected < 60, on O2

Inspired O2 % PaO2 mmHg30 > 150 Corrected 60‐100, < predicted

40 > 20050 > 250 Excessively

> 100 < predicted80 > 400100 > 500

Corrected> 100, < predicted

Responsive


(iii) Find if Oxygenation is adequate or not – CaO2

PaO2 and SO2 may not give true estimate.2 2 y g

Low PaO2 but Oxygen Content still adequate . (V/Q imbalance)

Normal PaO2, still profound hypoxemia. (Anaemia, Altered affinity of Hb for O2 )

Calculated SaO2 may mislead & show false “normal” results. (CO, MHb )

(If no Co-oximeter in the machine, SaO2 is calculated from PaO2 , ODC)

Total Oxygen Content

CaO2 measured directly or calculated by O2 content equation.

CaO2 = Hb(gm%) x 1.34 x SaO2 + 0.003 x PaO2(mmHg).2 (g ) 2 2( g)


PaO2 = 89.2 mmHg : seems normal2 g

SaO2 = 97.3 % : seems normal

Correlate FiO2 of 60% with PaO2.

P O f 89 2 l th di t d (300) PaO2 of 89.2 - very less than predicted (300).

→ Oxygenation impaired.

PaO2 60-100 : Corrected Hypoxaemia

CaO2 = 4.2 ml/dl : Very low (16-20)

Oxygenation grossly inadequate

CaO2 = 4.2 ml/dl : Very low (16-20)

Oxygenation grossly inadequateOxygenation grossly inadequateOxygenation grossly inadequate


Terminology for Acid Base Homeostasis

Acidemia : Blood pH < 7.35Acidosis : → A primary physiologic process that,→ occurring alone, tends to cause acidemia g

(e.g., respiratory acidosis from hypoventilation or metabolic acidosis from decreased perfusion or shock)p )

Alkalemia : Blood pH > 7.45pAlkalosis : → A primary physiologic process that, y y g→ occurring alone, tends to cause alkalemia

(e.g., respiratory alkalosis from acute hyperventilation or metabolic alkalosis from excessive diuretic therapy)

Prof. A. K. Sethi, UCMS, Delhi……Terminology

Primary acid-base disordersRespiratory Acidosis, Respiratory Alkalosis, Metabolic Acidosis, Metabolic Alkalosis

manifest as initial changes in PaCO2 or HCO3ˉ

First Disorder Change Primary Effect pHFirst Change

Disorder Change Primary disorder

Effect pH

Rises Respiratory Acidemia FallsPaCO2 Respiratory

Rises Respiratory acidosis

Acidemia Falls

Falls Respiratory Alkalemia Risesp yalkalosis

Rises Metabolic Alkalemia RisesHCO3ˉ Metabolic alkalosis

Falls Metabolic Acidemia Fallsacidosis

Prof. A. K. Sethi, UCMS, Delhi……Terminology

Compensationwhen the acid-base imbalance exists over a period of time

S d h i HCO ˉ P COSecondary changes in HCO3ˉ or PaCO2

‐ occur in response to the primary event

‐ to normalize pH

Done by the organ system which is not primarily affected

Respiratory compensation for metabolic disorders‐ Respiratory compensation for metabolic disorders

‐Metabolic compensation for respiratory disorders


Step – 3 : Acid Base disturbancesAnal se pH (First Impressi n)Analyse pH (First Impression)

pH AnalysispH na ys s7.35 – 7.45 Normal No acid-base disorder

Or, Compensated disorder(7.4) (Mixed disorder)< 7.35 Acidemia Uncompensated Acidosis

Or Partially compensatedOr, Partially compensated> 7.45 Alkalemia Uncompensated Alkalosis

Or Partially compensatedOr, Partially compensated

Acidemia (pH < 7.35) Alkalemia (pH >7.45)(p ) (p )Mild 7.30 – 7.34 7.46 – 7.50

Moderate 7.20 – 7.29 7.51 – 7.54S 7 2 7 55Severe < 7.2 > 7.55

Incompatible with life < 6.8 > 7.8


Step – 4 Know the Primary disorder Respirat r r Metab lic ?- Respiratory or Metabolic ?

Respiratory

Change Disorder PaCO2 pH Primary disorder2

> 45 Respiratory acidosisPaCO2 Respiratory

< 35 Respiratory alkalosis

If pH & PaCO2 move in opposite directions– Primary defect is Respiratory– Primary defect is Respiratory.

If pH is not moving in opposite direction as PaCO2P i d f t i N t R i t (M t b li )– Primary defect is Not Respiratory (Metabolic).


......Step – 4A l th P i di dAnalyse the Primary disorder- Respiratory or Metabolic ?

h i d i di d

Metabolic

Change Disorder HCO3ˉ pH Primary disorder

HCO3ˉ Metabolic> 26 Metabolic alkalosis

HCO3(base)

Metabolic< 22 Metabolic acidosis

¯If pH moves in same direction as HCO3– Primary defect is Metabolic

If pH moves in opposite direction as HCO3¯– Primary defect is not Metabolic (Respiratory)


Step – 5 : Analyse if Compensation ?p y p

• Compensation - Body tries to bring pH towards normal, with time

• Lungs and kidneys are primary buffer response systems

• pH outside normal range – Uncompensated or Partially compensated

• pH in normal range – Fully compensated, or Mixed disorder, (or no acid base disturbance)

Prof. A. K. Sethi, UCMS, DelhiStep – 6 : Calculate the Expected Compensation- Match it with actual reportMatch it with actual report

Compensations – Base for Acid(Formula for every 10 mmHg change in PaCO2)(Formula for every 10 mmHg change in PaCO2)

Change in PaCO2 Disorder Compensation (Kidney)10 mmHg Acute rise Respiratory acidosis 1 mEq/L rise in HCO3Respiratory acidosis10 mmHg Chronic rise 4 mEq/L rise in HCO310 mmHg Acute fall Respiratory alkalosis 2 mEq/L fall in HCO310 mmHg Chronic fall 4 mEq/L fall in HCO10 mmHg Chronic fall 4 mEq/L fall in HCO3

Compensations –Acid for Basep(Formula for every 1 mEq/L change in HCO3)

Change in HCO3 Disorder Compensation (Lungs)1 E /L f ll M b li id i 1 25 H f ll i P CO1 mEq/L fall Metabolic acidosis 1.25 mmHg fall in PaCO21 mEq/L rise Metabolic alkalosis 0.75 mmHg rise in PaCO2

Match the Calculated Compensation with the Actual (Report)


Step – 7 : pFind out if the Disorder is “Mixed” ?

(1) Check relative movement of both pairs

pH ≈ PaCO and pH ≈ HCOpH ≈ PaCO2 and pH ≈ HCO3

If both pairs are moving & in correct directions

– Mixed disorder

(2) Presume the Primary disorder to be Respiratory or

Metabolic Then analyse compensation Metabolic. Then analyse compensation

If analysis supports no compensation – Mixed disorder


Step – 8 : Unmask Hidden Metabolic DisordersUse concept of Serum Electrolytes

Do not interpret any ABG data without Serum ElectrolytesDo not interpret any ABG data without Serum Electrolytes(Na+, K+, Cl-, CO2)

3 Parameters need to be determined

1. Anion Gap and its change from normal (∆ AG)

2. Venous CO2 and its change from normal (∆ CO2)

3. Bicarbonate Gap (BG)


Anion Gap and its change from normal

……Hidden Metabolic Disorders

Anion Gap and its change from normalAG = (Routinely measured Cations – Routinely measured Anions)

AG = (Na+ + K+) (Cl- + HCO )AG = (Na + K ) – (Cl + HCO3)AG = (Na+) – (Cl- + CO2)

Normal AG = 16 ± 4 mEq/L (12 ± 4 )Normal AG = 16 ± 4 mEq/L (12 ± 4 )

Change in AG from normal (Δ AG) = Measured AG – 12

Positive (+) or Elevated AG (> 16)• Metabolic Acidosis• Metabolic AcidosisNegative (-) or Low AG• Reduction in unmeasured Anions (Hypoprotienemia)Reduction in unmeasured Anions (Hypoprotienemia)• Excess unmeasured Cations (Lithium Toxicity)• Excess abnormal ‘+’vely charged proteins (Multiple Myeloma)• Halide ion measured as Chloride (Bromism, Cough syrups)

Prof. A. K. Sethi, UCMS, Delhi……Hidden Metabolic Disorders

Venous CO2 and its change from normal

Index of Plasma HCO3

Total CO2 = Plasma HCO3 + Dissolved CO2 in PlasmaTotal CO2 = Plasma HCO3 + Dissolved CO2 in Plasma

Normal = 24 – 30 mEq/L (27 mEq/L)

Change in Venous CO2 from normal

(Δ CO2 ) = 27 – measured CO2


……Hidden Metabolic Disorders

Bicarbonate Gap Unmasks the co-existence of 2 metabolic disorders

BG = ∆ AG - ∆ CO2

BG = (Measured AG – 12) – (27 – Measured CO2)

Positive (+) or Elevated BG = > + 6 mEq/LM t b li Alk l i• Metabolic Alkalosis

• Bicarbonate retention as compensation for Respiratory Acidosis

Negative (-) or Low BG = < – 6 mEq/L• Metabolic Acidosis• Bicarbonate excretion as compensation for Respiratory Alkalosis


Steps (Summary)p y

Step – 1 : Check if the required parameters have been correctly fed?

Step – 2 : Analyse the Adequacy of Oxygenation.

St 3 A l s H A id i Alk l i ?Step – 3 : Analyse pH – Acidemia or Alkalemia?

Step – 4 : Analyse the Primary disorder - Respiratory or Metabolic ?

Step – 5 : Find if Compensation ?

Step – 6 : Calculate the Expected Compensation. Match it with actual.

Step – 7 : Find out if the Disorder is “Mixed” ?Step 7 Find out if the Disorder is Mixed ?

Step – 8 : Unmask Hidden Metabolic Disorders.


Examples


Example 1

pH PaCO2 HCO3¯N

ReportpH 7.22 NpH 7.22PaCO2 55HCO3¯ 25

Respiratory Acidosis, U t dHCO3 25 Uncompensated

1 pH = Low (7 35 7 45 7 4) = Acidosis1. pH = Low (7.35 - 7.45, 7.4) = Acidosis

2. PaCO2 = High (35 - 45, 40), Opposite direction than pH = Respiratory

3. HCO3¯ = Within Normal range (22 - 26, 24) = Not Metabolic

4 No secondary change (rise) in HCO ¯ = No compensation4. No secondary change (rise) in HCO3 = No compensation


Example 2

pH PaCO2 HCO3¯N

ReportpH 7.50 NpH 7.50PaCO2 42HCO3¯ 33 Metabolic Alkalosis, HCO3 33 Uncompensated

1 pH = High (7 35 7 45 7 4) = Alkalosis1. pH = High (7.35 - 7.45, 7.4) = Alkalosis

2. PaCO2 = Normal (35 - 45, 40), = Not Respiratory

3. HCO3¯ = High (22 - 26, 24), Moving in same direction = Metabolic

4 No secondary change (rise) in PaCO = No compensation4. No secondary change (rise) in PaCO2 = No compensation


pH PaCO HCO ¯

Example 3

Report Change from N pH PaCO2 HCO3Report Change from NpH 7.32 - 0.08PaCO 32 8PaCO2 32 - 8HCO3¯ 18 - 6

Metabolic Acidosis,Partially compensatedy p

1. pH = Low (7.35 - 7.45, 7.4) = Acidosis

2. PaCO2 = Low (35 – 45, 40), Moving in same direction as pH 2. PaCO2 Low (35 45, 40), Moving in same direction as pH - Not Respiratory = Metabolic ?

3 HCO ¯ = Low (22 – 26 24) = Moving in same direction as pH = Metabolic3. HCO3 = Low (22 – 26, 24) = Moving in same direction as pH = Metabolic

4. Secondary changes (Fall) in PaCO2 = Compensation by Lungs is on

5. Metabolic Acidosis – 1 mEq/L fall in HCO3 ≈ 1.25 mmHg fall in PaCO2

6. Estimated compensation (PaCO2) = - 6 x 1.25 = - 7.50 (Actual = - 8 mmHg)6. Estimated compensation (PaCO2) 6 x 1.25 7.50 (Actual 8 mmHg)

7. pH - Not in normal range = Partial compensation


H P CO HCO ¯R t Ch f N

Example 4

pH PaCO2 HCO3

N RangeReport Change from NpH 7.35 0.05PaCO2 48 + 8HCO3¯ 27 + 3

Respiratory Acidosis, Fully compensated

1. pH = Normal but lower side of range (7.35 - 7.45) = Acidosis2 PaCO2 = Raised (35 - 45) Moving in the opposite direction to pH 2. PaCO2 Raised (35 45), Moving in the opposite direction to pH

= Respiratory3 HCO ¯ = Raised (22 26) = Should move in same direction as pH 3. HCO3 = Raised (22 – 26) = Should move in same direction as pH,

Here, moving in opposite direction to pH = Not Metabolic, Respiratory4. Secondary change (Rise) in HCO3 = Compensation by Kidneys5. pH near neutral, in the normal range (7.35) = Fully compensated Acidosis

Calculate Compensation now


pH PaCO2 HCO3¯N

Report Change from NH 7 35 0 05 NpH 7.35 0.05

PaCO2 48 + 8 Respiratory Acidosis, F ll t d

Respiratory Acidosis, Ch i F ll t dHCO3¯ 27 + 3

Estimate CompensationFully compensatedChronic, Fully compensated

For every 10 mmHg change in PaCO2Disorder Change in PaCO2 Compensation (Kidney)

m mp

Respiratory acidosis 10 mmHg Acute rise 1 mEq/L rise in HCO310 mmHg Chronic rise 4 mEq/L rise in HCO3

Presume Acute Rise and Calculate compensationEstimated HCO3 compensation for an acute 8 mmHg rise of PaCO2= 1 x (+8)/10 = + 0 8 = 1 x (+8)/10 = + 0.8

Presume Chronic Rise and Calculate compensationE ti t d HCO ti f h i 8 H i f P COEstimated HCO3 compensation for a chronic 8 mmHg rise of PaCO2= 4 x (+8)/10 = + 3.2


pH PaCO2 HCO3¯Example 5

Report Change from NN Range

Report Change from NpH 7.43 + 0.03PaCO 48 + 8 Metabolic Alkalosis PaCO2 48 + 8HCO3¯ 36 + 12

Metabolic Alkalosis, Fully Compensated

1. pH = Normal, higher side of range (7.35 - 7.45) = Alkalosis2. PaCO2 = Raised (35 – 45) = Should move in opposite direction to pH –2

Moving in the same direction = Not Respiratory, Metabolic3. HCO3¯ = Raised (22 – 26) = Should move in same direction as pH.3 ( ) p

Here, moving in same direction to pH = Metabolic4. Secondary changes (Rise) in PaCO2 = Compensation by Lungs (Hypo)Seco da y c a ges ( se) aCO2 Co pe sat o by u gs ( ypo)5. pH = In the range of normal = Fully Compensated Alkalosis

Estimate Compensation now


pH PaCO2 HCO3¯Example 5

Report Change from NN

Report Change from NpH 7.43 + 0.03PaCO 48 + 8 Metabolic Alkalosis Metabolic Alkalosis PaCO2 48 + 8HCO3¯ 36 + 10

Metabolic Alkalosis, Fully Compensated

Metabolic Alkalosis, ≈ Fully compensated

- ReconfirmedEstimate Compensation

Formula for every 1 mEq/L change in HCO3Formula for every 1 mEq/L change in HCO3Disorder Change in HCO3 Compensation (Lungs)Metabolic acidosis 1 mEq/L fall 1.25 mmHg fall in PaCO2q g 2Metabolic alkalosis 1 mEq/L rise 0.75 mmHg rise in PaCO2

Estimated PaCO2 compensation for a 10 mEq/L rise of HCO3= 10 x 0.75 = + 7.5 mmHg


pH PaCO2 HCO3¯Example 6 (Mixed disorders)

Report Change from NReport Change from NpH 7.6 + 0.2PaCO 30 10 d R lk l h PaCO2 30 – 10HCO3¯ 30 + 6

Mixed Respiratory Alkalosis with Metabolic Alkalosis

1. pH = High, (7.35 – 7.45) = Alkalosis2. PaCO2 = Low (35 – 45) = Moving in opposite direction to pH = Respiratory2 ( ) g pp p p y

(Respiratory Alkalosis)3. HCO3¯ = High (22–26) = Moves in same direction as pH if Metabolic.3 g ( ) p

Moving in same direction = Metabolic (Metabolic Alkalosis)

Mixed Disorder ≈ Correct movement of both pairsMixed Disorder ≈ Correct movement of both pairs


Diagnosing Hidden Mixed Metabolic DisturbancesC t f U i S El t l t (N + K+ Cl¯ CO ¯)Concept of Using Serum Electrolytes (Na+, K+, Cl , CO2 )

Example 7 (Mixed disorders)

pH PaCO2 HCO3¯Report Change from NpH 7 46 + 0 06pH 7.46 + 0.06PaCO2 30 – 10HCO ¯ 20 4

Partially compensated R s i t Alk l sisHCO3 20 – 4 Respiratory Alkalosis

1. pH = Raised, (7.35 – 7.45) = Alkalosis2. PaCO2 = Low, Should move opposite to pH – Moving = Respiratory3. HCO3¯ = Low, Should move in same direction as pH – Not moving in 3 , p g

same direction = Not Metabolic, Respiratory4 Secondary changes (Fall) in HCO = Compensation by Kidney4. Secondary changes (Fall) in HCO3 = Compensation by Kidney5. pH not normalized, Still > Normal Range, > 7.45 = Partially compensated


pH PaCO2 HCO3¯Report Change from NpH 7.46 + 0.06PaCO2 30 – 10 Partially compensated

R i t Alk l i Ch iHCO3¯ 20 – 4 Respiratory Alkalosis

Estimate Compensation

Chronic

Disorder Change in PaCO2 Compensation (Kidney)Acute fall by 10 mmHg 2 mEq/L fall in HCO


Respiratory Alkalosis

Acute fall by 10 mmHg 2 mEq/L fall in HCO3Chronic fall by 10 mmHg 4 mEq/L fall in HCO3

P i A t Presuming Acute Estimated HCO3 compensation for an acute 10 mmHg fall of PaCO2= 2 x (–10)/10 = –2 0

Presuming Chronic Estimated HCO compensation for a chronic 10 mmHg fall of PaCO

2 x ( 10)/10 2.0

Estimated HCO3 compensation for a chronic 10 mmHg fall of PaCO2= 4 x (–10)/10 = – 4.0


Is there any thing else to be done ?

3 more Parameters need to be determined

1. Anion Gap and its change from normal (∆ AG)

2. Venous CO2 and its change from normal (∆ CO2)

3. Bicarbonate Gap (BG)


Equations neededEquations needed

• AG = (Na+) – (Cl- + CO2)AG (Na ) (Cl CO2)

• Normal AG = 12 ± 4 mEq/L

• ∆ AG = Measured AG – 12

• Normal CO2 = 24 – 30 mEq/L (27 mEq/L)

• ∆ CO = 27 – measured CO• ∆ CO2 = 27 – measured CO2

BG ∆ AG ∆ CO• BG = ∆ AG - ∆ CO2

• BG = (Measured AG – 12) – (27 – measured CO2)


pH PaCO2 HCO3¯Report Change from NpH 7.46 + 0.06PaCO2 30 – 10 Partially compensated

R i t Alk l i Ch iHCO3¯ 20 – 4 Respiratory Alkalosis


Chronic

Disorder Change in PaCO2 Compensation (Kidney)Acute fall by 10 mmHg 2 mEq/L fall in HCO


Respiratory Alkalosis

Acute fall by 10 mmHg 2 mEq/L fall in HCO3Chronic fall by 10 mmHg 4 mEq/L fall in HCO3

P i A t Presuming Acute Estimated HCO3 compensation for an acute 10 mmHg fall of PaCO2= 2 x (–10)/10 = –2 0

Presuming Chronic Estimated HCO compensation for a chronic 10 mmHg fall of PaCO

2 x ( 10)/10 2.0

Estimated HCO3 compensation for a chronic 10 mmHg fall of PaCO2= 4 x (–10)/10 = – 4.0

Prof. A. K. Sethi, UCMS, DelhiSame Example 7

ReportpH 7.46

• AG = (Na+) – (Cl- + CO2)= (150) – (102 + 20) = 150 – 122

28 ( 16 M t b li A id i ith AG)PaCO2 30HCO3¯ 20

= + 28 ( > 16 = Metabolic Acidosis, with AG)• ∆ AG = 28 – 12 = +16

3

Na+ 150K+ 3 5

• ∆ CO2 = 27 – measured CO2∆ CO2 = 27 – 20 = +7

K+ 3.5Cl¯ 102CO 20

• BG = ∆ AG – ∆ CO2= (+16) – (+7)

+9 (> +6 Metabolic Alkalosis)CO2 20

Partially compensated

= +9 (> +6 = Metabolic Alkalosis)Respiratory AlkalosisMetabolic AcidosisPartially compensated

Chronic Respiratory AlkalosisMetabolic AcidosisMetabolic Alkalosis

Vomiting for several days Developed Hypotension Hyperventilated CompensationVomiting for several days Developed Hypotension Hyperventilated, CompensationMetabolic Alkalosis Lactic Acidosis Respiratory Alkalosis

Prof. A. K. Sethi, UCMS, DelhiExample 8

ReportpH 7.40 N • AG = (149) – (100 + 24) = 149 – 124 = +25pPaCO2 38 NHCO ¯ 24 N

( ) ( )• ∆ AG = 25 – 12 = +13 ( Metabolic Acidosis)

∆ CO 27 24 3HCO3 24 NNa+ 149 N

• ∆ CO2 = 27 – 24 = +3

• BG = ∆ AG – ∆ CO2K+ 3.8 NCl¯ 100 N

2

= (+13) – (+3)= +10 (> +6 = Metabolic Alkalosis)

CO2 24 N( )

pH (N), PaCO2 (N), HCO3 (N)M b li id i (U i )Metabolic Acidosis (Uremia)

Metabolic Alkalosis (Diuretic)BUN 110Creatinine 8 7Creatinine 8.7


Best of Luck

ABG

Documents

Transcript of ABG