arterial blood gases dr. abdulaziz al shaer consultant intensivist 21/2/2010

ARTERIAL BLOOD ARTERIAL BLOOD GASESGASES

DR. ABDULAZIZ AL SHAERDR. ABDULAZIZ AL SHAER

CONSULTANT INTENSIVISTCONSULTANT INTENSIVIST21/2/201021/2/2010

IndicationsIndications

OxygenationOxygenation

VentilationVentilation

Acid-base disordersAcid-base disorders

Normal Arterial Blood GasesNormal Arterial Blood Gases

pHpH 7.35 – 7.457.35 – 7.45

PaCOPaCO22 35-45 mmHg35-45 mmHg

PaOPaO22 70 – 100mmHg70 – 100mmHg

SaOSaO22 93 – 98%93 – 98%

HCOHCO33 22 – 26 mEq/L22 – 26 mEq/L

Base excessBase excess -2.0 to 2.0 mEq/L-2.0 to 2.0 mEq/L

CaOCaO22 16 – 22ml O16 – 22ml O22/dl/dl

Use of Venous VS. Arterial pHUse of Venous VS. Arterial pH

As compared with arterial blood gases:As compared with arterial blood gases:

pHpH ↓ ↓ 0.03 – 0.040.03 – 0.04

PaCOPaCO22 ↑ ↑ 7 - 8 mmHg7 - 8 mmHg

HCOHCO33 ↓ ↓ 2 mEq/L2 mEq/L

Technical ConsiderationsTechnical Considerations PaOPaO22, PaCO, PaCO22, and pH are directly measured with standard , and pH are directly measured with standard

electrodes and digital analyzers.electrodes and digital analyzers. Oxygen saturation is calculated from standard OOxygen saturation is calculated from standard O22

dissociation curves.dissociation curves. Bicarbonate concentration is calculated using the Henderson-Bicarbonate concentration is calculated using the Henderson-

Hasselbalch equation:Hasselbalch equation:

[HCO[HCO33-]-]

pH = pKa + log ----------------pH = pKa + log ----------------

0.03 [PaCO0.03 [PaCO22]]pKa is the negative logarithm of the dissociation constant of carbonic acidpKa is the negative logarithm of the dissociation constant of carbonic acid

Simplified equation:Simplified equation:

[PaCO[PaCO22]]

[H] = 24 x -----------[H] = 24 x -----------

[HCO[HCO33-]-]

Technical considerationsTechnical considerations

Leukocytosis and thrombocytosis Leukocytosis and thrombocytosis accelerate the decline of PaOaccelerate the decline of PaO22 and and pH and elevation of PaCOpH and elevation of PaCO22 within a within a stored samplestored sample

Significant increases in PaCOSignificant increases in PaCO22 and and decreases in pH occur when samples decreases in pH occur when samples are stored at room temperature for are stored at room temperature for more than 20 minutesmore than 20 minutes

Technical considerationsTechnical considerations Increased dead space in the syringe lowers Increased dead space in the syringe lowers

PaCOPaCO22.. Air bubble falsely increases PaOAir bubble falsely increases PaO22.. PaCOPaCO22 and PaO and PaO22 may diffuse out of plastic may diffuse out of plastic

syringes.syringes. Heparin and liquid solutions cause spuriously low Heparin and liquid solutions cause spuriously low

PaCOPaCO22.. Dry (sodium or lithium) heparin in ABG kits may Dry (sodium or lithium) heparin in ABG kits may

interfere with electrolyte measurement and, interfere with electrolyte measurement and, when concentrated, may lower pH.when concentrated, may lower pH.

Timing of ABG collection relative to ventilator Timing of ABG collection relative to ventilator changes should permit equilibration of alveolar changes should permit equilibration of alveolar and arterial POand arterial PO22..


PAOPAO22 = PIO = PIO22 – 1.25 (PaCO – 1.25 (PaCO22))PIOPIO22 = FIO = FIO22 (PB – 47 mmHg) (PB – 47 mmHg)

P(A-a)OP(A-a)O22 = PAO = PAO22 – PaO – PaO22

CaOCaO22 = (Hgb x 1.34 x SaO = (Hgb x 1.34 x SaO22)+(0.003 x PaO)+(0.003 x PaO22))

VVDDOO22 = CaO = CaO22 x CO x CO


PAOPAO22 remains constant with age, but PaO remains constant with age, but PaO22 decreases with age.decreases with age.

PaOPaO22 (corrected for age): (corrected for age):100 mmHg – 0.3 x age100 mmHg – 0.3 x age

Normal P(A-a)ONormal P(A-a)O22 ranges from 5 to 25 ranges from 5 to 25 mmHg breathing room air (it increases mmHg breathing room air (it increases with age).with age).

A higher than normal P(A-a)OA higher than normal P(A-a)O22 means the means the lungs are not transferring oxygen properly lungs are not transferring oxygen properly from alveoli into the pulmonary capillaries.from alveoli into the pulmonary capillaries.

Causes of HypoxemiaCauses of Hypoxemia

NON-RESPIRATORYNON-RESPIRATORY P(A-a)OP(A-a)O22

Cardiac right-to-left shuntCardiac right-to-left shunt IncreasedIncreased

Decreased PIODecreased PIO22 NormalNormal

Low mixed venous oxygen content Low mixed venous oxygen content IncreasedIncreased

RESPIRATORYRESPIRATORY P(A-a)OP(A-a)O22

Pulmonary right-to-left shuntPulmonary right-to-left shunt IncreasedIncreased

Ventilation-perfusion imbalanceVentilation-perfusion imbalance IncreasedIncreased

Diffusion barrierDiffusion barrier IncreasedIncreased

Hypoventilation (increased PaCOHypoventilation (increased PaCO22)) NormalNormal

O2 deliveryO2 delivery

VVDDOO22 = CaO = CaO22 x CO x CO

CaOCaO22 = (Hgb x 1.34 x SaO = (Hgb x 1.34 x SaO22)=(0.003 x PaO)=(0.003 x PaO22))

– OO22 saturation and not PaO saturation and not PaO22 is the parameter of is the parameter of

oxygenation that contributes most to Ooxygenation that contributes most to O22 delivery. delivery.

– The relationship between PaOThe relationship between PaO22 and SaO and SaO22 is is

demonstrated by the oxygen-hemoglobin dissociation demonstrated by the oxygen-hemoglobin dissociation curve.curve.

Oxygen-Hemoglobin dissociation curveOxygen-Hemoglobin dissociation curve

Left shiftLeft shiftDecreased tempDecreased temp

Decreased 2-3 DPGDecreased 2-3 DPGDecreased (H+) CODecreased (H+) CO

Right shiftRight shiftReduced affinity’sReduced affinity’sIncreased tempIncreased tempIncreased 2-3 DPGIncreased 2-3 DPGIncreased (H+)Increased (H+)

VentilationVentilation The only way to assess ventilation is to The only way to assess ventilation is to

check PaCO2 through ABGs.check PaCO2 through ABGs. VVAA=K x V=K x VCOCO22

/P/PAACOCO22

– VVAA is alveolar ventilation is alveolar ventilation– K is 0.863 to covert VK is 0.863 to covert VCOCO22

and V and VAA units from units from mmHgmmHg

– VVCOCO22 is CO is CO22 production production

– PPAACOCO22 is the alveolar CO is the alveolar CO22 pressure and in pressure and in general it is equal to PaCOgeneral it is equal to PaCO22..

VVAA = 0.863 x V = 0.863 x VCOCO22/PaCO/PaCO22

PaCOPaCO22 = 0.863 x V = 0.863 x VCOCO22/V/VAA


VVAA = f x (Vt – V = f x (Vt – VDD)) The only physiologic reason for elevated The only physiologic reason for elevated

PaCOPaCO22 is inadequate alveolar ventilation is inadequate alveolar ventilation (V(VAA) for the amount of the body’s CO) for the amount of the body’s CO22 production (VCOproduction (VCO22).).

Since alveolar ventilation (VSince alveolar ventilation (VAA) equals ) equals minute ventilation (Vminute ventilation (VEE) minus dead space ) minus dead space ventilation (Vventilation (VDD), hypercapnia can arise ), hypercapnia can arise from insufficient Vfrom insufficient VEE, increased V, increased VDD, or a , or a combination of both.combination of both.


Examples of inadquate VExamples of inadquate VEE::– SedativesSedatives– Respiratory muscle paralysis, weakness, Respiratory muscle paralysis, weakness,

CIM, MS, low Mg/PhosCIM, MS, low Mg/Phos– Neuropathy: GBS, CIPNNeuropathy: GBS, CIPN– Central hypoventilationCentral hypoventilation

Examples of increased VExamples of increased VDD::– Chronic obstructive pulmonary diseaseChronic obstructive pulmonary disease– Severe restrictive lung diseaseSevere restrictive lung disease

Acid-base interpretationAcid-base interpretation

Simplified Henderson-Hasselbalch equation:Simplified Henderson-Hasselbalch equation: [PaCO[PaCO22]]

[H] = 24 x -----------[H] = 24 x -----------

[HCO[HCO33-]-]

[H] is normally is 40nEq/L which gives a pH of 7.40[H] is normally is 40nEq/L which gives a pH of 7.40 Acidemia: blood pH < 7.35Acidemia: blood pH < 7.35 Alkalemia: blood pH > 7.45Alkalemia: blood pH > 7.45

pHpH [H[H++] in nEq/L] in nEq/L7.007.00 100100

7.107.10 8080

7.307.30 5050

7.407.40 4040

7.527.52 3030

7.707.70 2020

8.008.00 1010

Approach to Acid-Base DisordersApproach to Acid-Base Disorders

Do numbers make sense?Do numbers make sense? Consider the clinical setting!Consider the clinical setting! Is the patient acidemic or alkalemic?Is the patient acidemic or alkalemic? Is the primary process metabolic or Is the primary process metabolic or

respiratory?respiratory? If metabolic acidosis, gap or non-gap?If metabolic acidosis, gap or non-gap? Is compensation appropriate?Is compensation appropriate? Is more than one disorder present?Is more than one disorder present?

Simple Acid-Base DisordersSimple Acid-Base Disorders

DisorderDisorder pHpH HH++ Primary Primary DisorderDisorder

Compensatory Compensatory ResponseResponse

Metabolic acidosisMetabolic acidosis ↓↓ ↑↑ ↓↓ HCOHCO33-- ↓↓ pCOpCO22

Metabolic alkalosisMetabolic alkalosis ↑↑ ↓↓ ↑↑ HCOHCO33-- ↑↑ pCOpCO22

Respiratory acidosisRespiratory acidosis ↓↓ ↑↑ ↑↑ pCOpCO22 ↑↑ HCOHCO33--

Respiratory alkalosisRespiratory alkalosis ↑↑ ↓↓ ↓↓ pCOpCO22 ↓↓ HCOHCO33--

Acute Respiratory Acidosis Acute Respiratory Acidosis

pH will decrease by 0.08 for each 10 pH will decrease by 0.08 for each 10 mmHg increase is PaCOmmHg increase is PaCO22..

Compensation by retaining HCOCompensation by retaining HCO33- by - by the kidney.the kidney.

HCOHCO33- will decrease by 1 for each - will decrease by 1 for each 10mmHg increase in PaCO10mmHg increase in PaCO22..

Chronic Respiratory AcidosisChronic Respiratory Acidosis

pH will decrease by 0.03 for each 10 pH will decrease by 0.03 for each 10 mmHg increase is PaCOmmHg increase is PaCO22..

Compensation by retaining HCOCompensation by retaining HCO33- by - by the kidney.the kidney.

HCOHCO33- will decrease by 4 for each 10 - will decrease by 4 for each 10 mmHg increase in PaCOmmHg increase in PaCO22..

Acute Respiratory AlkalosisAcute Respiratory Alkalosis

pH will increase by 0.08 for each 10 pH will increase by 0.08 for each 10 mmHg increase is PaCOmmHg increase is PaCO22..

Compensation by dumping HCOCompensation by dumping HCO33- by - by the kidney.the kidney.

HCOHCO33- will increase by 2 for each 10 - will increase by 2 for each 10 mmHg decrease in PaCOmmHg decrease in PaCO22..

Chronic Respiratory AlkalosisChronic Respiratory Alkalosis

pH will increase by 0.03 for each 10 pH will increase by 0.03 for each 10 mmHg fall is PaCOmmHg fall is PaCO22..

Compensation by dumping HCOCompensation by dumping HCO33- by - by the kidney.the kidney.

HCOHCO33- will rise by 5 for each 10 - will rise by 5 for each 10 mmHg fall in PaCOmmHg fall in PaCO22..

Expected changes in pH and HCOExpected changes in pH and HCO33- for - for

a 10 mmHg change in PaCOa 10 mmHg change in PaCO22

Acute Resp AcidosisAcute Resp Acidosis ChronicChronic

pH pH ↓ ↓ by 0.08 by 0.08

HCOHCO33- - ↑ ↑ by 1by 1pH pH ↓ ↓ by 0.03 by 0.03

HCOHCO33- - ↑ ↑ by 3 - 4by 3 - 4

Resp AlkalosisResp Alkalosis

pH pH ↑↑ by 0.08 by 0.08

HCOHCO33- - ↓ ↓ by 2by 2pH pH ↑↑ by 0.03 by 0.03

HCOHCO33- - ↓ ↓ by 5by 5

Metabolic AcidosisMetabolic Acidosis

Primary disorder is low HCOPrimary disorder is low HCO33--

Compensation by decreasing PaCOCompensation by decreasing PaCO22

Expected PaCOExpected PaCO22::

(1.5 x HCO(1.5 x HCO33-)+8 ± 2-)+8 ± 2 There are two typesThere are two types

– Increased anion gapIncreased anion gap– Normal anion gapNormal anion gap

Metabolic Acidosis: Elevated Anion Metabolic Acidosis: Elevated Anion GapGap

AG = NaAG = Na++ - (Cl - (Cl-- + HCO + HCO33-) = 12 ± 2-) = 12 ± 2

Anion Gap in HypoalbuminemiaAnion Gap in Hypoalbuminemia

The true anion gap is underestimated The true anion gap is underestimated in hypoalbuminemia; AG must be in hypoalbuminemia; AG must be adjusted.adjusted.

Formulas for adjusted AG:Formulas for adjusted AG:– For every 1.0 fall in albumin, increased For every 1.0 fall in albumin, increased

AG by 2.5AG by 2.5– Consider the patient’s “normal” AG to Consider the patient’s “normal” AG to

be (2 x alb) + (0.5 x phosphate)be (2 x alb) + (0.5 x phosphate)– Adjusted AG = Observed AG + (2.5 x Adjusted AG = Observed AG + (2.5 x

[normal alb – adjusted alb][normal alb – adjusted alb]

Causes AG Acidosis Causes AG Acidosis

KetoacidosisKetoacidosis Lactic acidosisLactic acidosis IntoxicationsIntoxications Renal failureRenal failure RhabdomyolysisRhabdomyolysis

KetosisKetosis

DiabetesDiabetes StarvationStarvation AlcoholicAlcoholic Isopropyl alcohol *Isopropyl alcohol *

*Ketosis with normal AG and HCO*Ketosis with normal AG and HCO33

Lactic AcidosisLactic Acidosis

Type A:Type A: Hypoxic Hypoxic

Lactate: pyruvate > Lactate: pyruvate > 10:110:1

Type B:Type B: GlycolyticGlycolytic

Lactate: pyruvate = Lactate: pyruvate = 10:110:1

Intoxications Causing High AG Intoxications Causing High AG AcidosisAcidosis

AspirinAspirin MethanolMethanol Ethylene GlycolEthylene Glycol ParaldehydeParaldehyde

The Delta/Delta: The Delta/Delta: ΔΔ AG/ AG/Δ Δ HCOHCO33

Rationale:Rationale:For each unit INCREASE in AG (For each unit INCREASE in AG (

““Normal” values:Normal” values:– AG = 12AG = 12

– HCOHCO3 3 = 24= 24

Use of the Delta/Delta: ExamplesUse of the Delta/Delta: Examples

AG (12)AG (12) HCOHCO33 DiagnosisDiagnosis18 18 ↑↑(6)(6) 18 18 ↓↓(6)(6) Appropriate: pure AG Appropriate: pure AG

acidosisacidosis18 18 ↑↑(6)(6) 22 22 ↓↓(2)(2) HCOHCO33 has has ↓ ↓ less than less than

predicted, so HCOpredicted, so HCO33 is is too high; mixed AG too high; mixed AG acidosis AND met alkacidosis AND met alk

18 18 ↑↑(6)(6) 12 12 ↓↓(12)(12) HCOHCO33 has has ↓ ↓ more than more than predicted, so HCOpredicted, so HCO33 is is too low; mixed AG too low; mixed AG AND non-AG acidosisAND non-AG acidosis

Osmolar GapOsmolar Gap

Measured serum osmolality > Measured serum osmolality > Calculated serum osmolality by > 10 Calculated serum osmolality by > 10 mOsmmOsm

Calculated osmolality:Calculated osmolality:– 2[Na] + BUN/2.8 + glucose/18 ethanol/4.62[Na] + BUN/2.8 + glucose/18 ethanol/4.6– BUN, glucose and ethanol are converted from mg/dl to mmol/LBUN, glucose and ethanol are converted from mg/dl to mmol/L– If using mmol/L:If using mmol/L:

2[Na] + BUN + glucose + ethanol2[Na] + BUN + glucose + ethanol

Causes of High Osmolar GapCauses of High Osmolar Gap Isotonic hyponatremiaIsotonic hyponatremia

HyperlipidemiaHyperlipidemiaHyperproteinemiaHyperproteinemiaMannitolMannitol

Glycine infusionGlycine infusion Chronic renal failureChronic renal failure Ingestions:Ingestions:

Ethanol, isopropyl alcohol, ethylene glycol, Ethanol, isopropyl alcohol, ethylene glycol, mannitolmannitol

Contrast mediaContrast media

Relationship between AG and Relationship between AG and Osmolar GapOsmolar Gap

AGAG Osm gapOsm gap

Ethylene glycolEthylene glycol ++ ++

MethanolMethanol ++ ++

Renal failureRenal failure ++ ++

Isopropyl alcoholIsopropyl alcohol -- ++

EthanolEthanol -- ++

Lipids, proteinsLipids, proteins -- ++

Approach to Metabolic Acidosis

Osmolar GapAnion Gap GI Fluid Loss?

Normal Increased

Yes No

High Normal

Uremia Lactate Ketoacids Salicylate

Ethylene glycolMethanolol

DiarrheaIlleostomyEnteric fistula

Urine pH

Distal RTA (Type 1) Serum K

Proximal RTA (Type 2)

Type 4 RTA

>5.5 <5.5

Low High

Metabolic AlkalosisMetabolic Alkalosis EtiologyEtiology: Requires both generation of : Requires both generation of

metabolic alkalosis (loss of Hmetabolic alkalosis (loss of H++ through GI through GI tract or kidneys) and maintenance of tract or kidneys) and maintenance of alkalosis (impairment in renal alkalosis (impairment in renal HCOHCO33 excretion)excretion)

Causes of metabolic alkalosisCauses of metabolic alkalosis– Loss of HydrogenLoss of Hydrogen– Retention of bivarbonateRetention of bivarbonate– Contraction alkalosisContraction alkalosis

Maintenance factorsMaintenance factors: Decrease in GFR, : Decrease in GFR, increase in increase in HCOHCO33 reabsorptionreabsorption

Use of Spot Urine Cl and KUse of Spot Urine Cl and K

Urine Chloride Very Low(< 10mEq/L)

Vomiting, NG suctionPostdiuretic, posthypercapneicVillous adenoma, congenital chloridorrhea, post- alkali

> 20 mEq/L

Urine Potassium Low (< 20mEq/L)

Laxative abuseOther profound K depletion30 mEq/L

Diuretic phase of diuretic Rx, Barter’s, Gitelman’s, primary aldo, Cushings, Liddle’s, secondary aldosteronism

Treatment of Metabolic AlkalosisTreatment of Metabolic Alkalosis

Remove offending culprits.Remove offending culprits. Chloride (saline) responsive alkalosis: Chloride (saline) responsive alkalosis:

Replete volume with NaCl.Replete volume with NaCl. Chloride non-responsive (saline Chloride non-responsive (saline

resistant) alkalosisresistant) alkalosisAcetazolamide (CA inhibitor)Acetazolamide (CA inhibitor)

Hydrochloric acid infusionHydrochloric acid infusion

Correct hypokalemia if presentCorrect hypokalemia if present

Case studiesCase studies

Q.1 Q.1 22 male known D.M. developed 22 male known D.M. developed sever upper respiratory infectionsever upper respiratory infection

Na 128 K 5.9 Cl 94 Na 128 K 5.9 Cl 94

Hco3 6 Pco2 = 15 Po2=102 Hco3 6 Pco2 = 15 Po2=102

PH =7.19 PH =7.19

Glucose = 324 Glucose = 324

1A1A R the data internally consistent?R the data internally consistent?

yes it is internally consistentyes it is internally consistent

Pco2= [H]* [HCO3] /24Pco2= [H]* [HCO3] /24

Pco2=61*6/24Pco2=61*6/24

Pco2=15Pco2=15 1B1B Is the patient acidemic or alkalemic?Is the patient acidemic or alkalemic?

< 7.4 so acidemic< 7.4 so acidemic

1C1C Is the primary disorder respiratory?Is the primary disorder respiratory?

Pco2 is not elevated so this metabolicPco2 is not elevated so this metabolic

Q 1 cont.Q 1 cont.

1D 1D The patient has MA ,is this The patient has MA ,is this hyperchloremic or high anion gap MA ?hyperchloremic or high anion gap MA ?

AG = Na-Cl-HCO3 = 28 ( normal 10-12)AG = Na-Cl-HCO3 = 28 ( normal 10-12)

so high AG MAso high AG MA 1F1F Is the compensation for the MA is Is the compensation for the MA is

appropriate?appropriate?

Expected Pco2 =1.5*HCO3 +8 -+ 2Expected Pco2 =1.5*HCO3 +8 -+ 2

so expected 17 -+ 2 so expected 17 -+ 2

so simple compensated MAso simple compensated MA

1E 1E Is there another ( M alk) acid base Is there another ( M alk) acid base disturbance present ? What is the delta anion gap disturbance present ? What is the delta anion gap

Delta AG=measured AG-normal AG=28-10=18Delta AG=measured AG-normal AG=28-10=18

Adding the delta gap to the measured HCO3 give Adding the delta gap to the measured HCO3 give the predicted starting HCO3 ( before the anion the predicted starting HCO3 ( before the anion gap acidosis).gap acidosis).

Here, Here, 18+6=2418+6=24,normal preacidosis level of HCO3. ,normal preacidosis level of HCO3. so NO underlying met alkalosisso NO underlying met alkalosis

Q 1 cont.Q 1 cont.

1G1G what a re the causes of an increase AG what a re the causes of an increase AG

DKA ,DKA ,

alcoholic ketoacidosis,alcoholic ketoacidosis,

and lactic acidosis and lactic acidosis

Drugs and toxin methanol and ethylene glycolDrugs and toxin methanol and ethylene glycol

Most likely her is DKAMost likely her is DKA

Q.2 Q.2 47 female CRF admitted with sever alcoholic 47 female CRF admitted with sever alcoholic intoxication, she is somnolent and febrile, RR 10 /minintoxication, she is somnolent and febrile, RR 10 /min

Na = 134 K=6.1 Cl= 112Na = 134 K=6.1 Cl= 112 HCO3=10 Pco2 =30 Po2=52HCO3=10 Pco2 =30 Po2=52

PH=7.10 Creatnine =3.7 BUN=62PH=7.10 Creatnine =3.7 BUN=62

2A2A R the data internally consistent?R the data internally consistent?

the data are internally consistentthe data are internally consistent

Pco2=[H]*[HCO3]/24Pco2=[H]*[HCO3]/24

Pco2=70*10/24Pco2=70*10/24

Pco2=29Pco2=29

2B2BIs the patient acidemic or Is the patient acidemic or alkalemic?alkalemic?

PH< 7.4 ,so the patient is acidemicPH< 7.4 ,so the patient is acidemic

2C2C Is the primary disorder Is the primary disorder respiratory?respiratory?

This MA as the Pco2 is not elevatedThis MA as the Pco2 is not elevated

2D2D the pt has MA is this the pt has MA is this hyperchlormic or a high anion gap hyperchlormic or a high anion gap type MA ?type MA ?

AG 134-112-10=12 so the patient AG 134-112-10=12 so the patient has normal AG or hyperchlormic MAhas normal AG or hyperchlormic MA

2E2E Is the compensation for the MA appropriate?Is the compensation for the MA appropriate?

Expected Pco2=1.5*HCO3+8 +- 2 for this degree Expected Pco2=1.5*HCO3+8 +- 2 for this degree of acidemiaof acidemia

Expected Pco2Expected Pco2= 1.5*10+8+- 2= 23 +- 2= 1.5*10+8+- 2= 23 +- 2

The measured Pco2 is The measured Pco2 is 30 which is higher than what 30 which is higher than what is expected with adequate compensation. is expected with adequate compensation. therefore, this is mixed acid base disturbance , therefore, this is mixed acid base disturbance , that is that is combined metabolic and respiratory combined metabolic and respiratory acidosis. acidosis.

Even though the Pco2 is low it is not low enoughEven though the Pco2 is low it is not low enough

2F2F What could it cause this acid-base What could it cause this acid-base disorder ?disorder ?

This MA is may be related to the patient underlying This MA is may be related to the patient underlying CRF .The respiratory acidosis may be related to the CRF .The respiratory acidosis may be related to the alcoholic intoxication with reduction in respiratory drive alcoholic intoxication with reduction in respiratory drive ( R.R. is only 10 b/min). Alternatively, and less likely, the ( R.R. is only 10 b/min). Alternatively, and less likely, the patient may have respiratory failure for another reason patient may have respiratory failure for another reason ( e.g. acute lung injury)( e.g. acute lung injury)

Double acid-base disorder: Metabolic and respiratory Double acid-base disorder: Metabolic and respiratory acidosisacidosis

Q.3Q.3 A 32 man with history of chronic alcohol use is brought to the A 32 man with history of chronic alcohol use is brought to the emergency center after 3 days of nausea, vomiting and abdominal emergency center after 3 days of nausea, vomiting and abdominal

pain.4 hrs ago he took, something to help with pain. He is awake and pain.4 hrs ago he took, something to help with pain. He is awake and alert, and PE is unremarkable:alert, and PE is unremarkable:

Na=132 K=3.9 Cl=82Na=132 K=3.9 Cl=82 HCO3= 4 Pco2= 10 Po2 110HCO3= 4 Pco2= 10 Po2 110

PH=7.25 Glucose = 68 BUN = 14PH=7.25 Glucose = 68 BUN = 14

Blood alcohol=106Blood alcohol=106

UrinanalysisUrinanalysis: no protein or ketones,: no protein or ketones,

positive for Crystalspositive for Crystals

3A3A Are the data internally consistent ?Are the data internally consistent ?

The data are internally consistentThe data are internally consistent

Pco2=55*4/24Pco2=55*4/24

Pco2=29Pco2=29 3B3B Is the patient acidmic or alkalemic?Is the patient acidmic or alkalemic?

AcidmicAcidmic

3C3C Is the primary disorder respiratory?Is the primary disorder respiratory?

This is MA as the Pco2 is not elevatedThis is MA as the Pco2 is not elevated

3D3D The patient has MA is this hyperchlormic or The patient has MA is this hyperchlormic or high AG type MA ?high AG type MA ?

AG= 132-82-4= 46AG= 132-82-4= 46

so high AG metabolic acidosisso high AG metabolic acidosis

3E3E Is there another ( metabolic alkalosis) acid Is there another ( metabolic alkalosis) acid base disturbance present? What is the delta gap?base disturbance present? What is the delta gap?

Delta AG 46-10=36 the potential fate of this anion Delta AG 46-10=36 the potential fate of this anion is to become bicarbonate. HCO3 level before acid is to become bicarbonate. HCO3 level before acid base disturbance was 36+4=40 .therfore, there is base disturbance was 36+4=40 .therfore, there is an underling metabolic alkalosis as wellan underling metabolic alkalosis as well

3F3F Is the compensation for the metabolic acidosis Is the compensation for the metabolic acidosis appropriate?appropriate?

Expected Pco2 1.5*4+8+-2=14+-2Expected Pco2 1.5*4+8+-2=14+-2

As the measured Pco2 is 10 the compensation is As the measured Pco2 is 10 the compensation is close enough to say that it is close enough to say that it is appropriate.appropriate.

3.G What are the potential causes of the increase 3.G What are the potential causes of the increase in AG ?in AG ?

In the absence of ketones ,the diagnosis of In the absence of ketones ,the diagnosis of diabetic ketoacidosis or alcoholic diabetic ketoacidosis or alcoholic ketoacidosis is not likely.IN the other hand ketoacidosis is not likely.IN the other hand the patient has taken something's in the patient has taken something's in association with an anion gap MA and association with an anion gap MA and crystals in the urine. whereas methanol crystals in the urine. whereas methanol ingestion give metabolic acidosis, they do ingestion give metabolic acidosis, they do not yield crystaluria.On the other hand, not yield crystaluria.On the other hand, this is consistent with ethylene glycol this is consistent with ethylene glycol ingestion.ingestion.

3.H3.H How one make the diagnosis of the How one make the diagnosis of the ethylene glycol ingestion ?ethylene glycol ingestion ?

the presence of an osmolal gap would the presence of an osmolal gap would suggest that the patient ingested a suggest that the patient ingested a compound with a small molecular weight. compound with a small molecular weight. Ethylene glycol level are essential, but will Ethylene glycol level are essential, but will take time to obtain. The demonstration of take time to obtain. The demonstration of crystals in the urine,especialy calcium crystals in the urine,especialy calcium oxalate crystals ,would be highly oxalate crystals ,would be highly suggestive of ethylene glycol.suggestive of ethylene glycol.

What are the possible causes of the What are the possible causes of the metabolic alkalosis ?metabolic alkalosis ?

The vomiting, presumably due to ulcer, gastritis, or The vomiting, presumably due to ulcer, gastritis, or pancreatic diseases, lead to alkalosis.pancreatic diseases, lead to alkalosis.

So this double acid-base disorder: MA secondary to So this double acid-base disorder: MA secondary to ethylene glycol ingestion and Metabolic Alkalosis ethylene glycol ingestion and Metabolic Alkalosis due to vomiting.due to vomiting.

Q.4Q.4 male with mild CHF and COPD is admitted to hospital male with mild CHF and COPD is admitted to hospital with recurrent pneumonia. required intubation for 2 with recurrent pneumonia. required intubation for 2

days .after extubation he been treated with ceftrixone and days .after extubation he been treated with ceftrixone and enalopril. 5 days later,when he is awake,alert and enalopril. 5 days later,when he is awake,alert and ambulating, the following lab abnormalities were ambulating, the following lab abnormalities were

observed :observed :

Na=129 K=3.2 Cl=81Na=129 K=3.2 Cl=81 HCO3=38 Pco2 =48 Po2 =68 on 1 l/minHCO3=38 Pco2 =48 Po2 =68 on 1 l/min PH=7.51 Glucose= 108 BUN=21 Creatnine=1.8PH=7.51 Glucose= 108 BUN=21 Creatnine=1.8

4.A4.A Are the data internally consistent ?Are the data internally consistent ?

Internally consistentInternally consistent

Paco2=29*38/24=46 ( pretty close)Paco2=29*38/24=46 ( pretty close) 4.B4.B Is the patient acdmic or alkalemic?Is the patient acdmic or alkalemic?

PH > 7.4 so alkalemic.PH > 7.4 so alkalemic. 4.C4.C Is the primary disorder respiratory? Is the primary disorder respiratory?

Metabolic alkalosis since the Pco2 is not Metabolic alkalosis since the Pco2 is not lowlow

4.D4.D Is the compensation appropriate ?Is the compensation appropriate ?

Expected Pco2=0.7*HCO3+ 21+-1.5Expected Pco2=0.7*HCO3+ 21+-1.5

= 0.7*38+21+-1.5= 48+-1.5= 0.7*38+21+-1.5= 48+-1.5

Pco2 is 48 so change in Pco2 is appropriate, and the Pco2 is 48 so change in Pco2 is appropriate, and the hypoventilation due to Metabolic alkalosis so this is simple hypoventilation due to Metabolic alkalosis so this is simple compensated metabolic alkalosis.compensated metabolic alkalosis.

4.E4.E What are the various type of metabolic alkalosis ?What are the various type of metabolic alkalosis ?

Metabolic alkalosis is divided to chloride responsive and Metabolic alkalosis is divided to chloride responsive and resistantresistant

Urine CL=46,Urine Na 51, and Urinary K =75 so as the urinary Urine CL=46,Urine Na 51, and Urinary K =75 so as the urinary Cl is high, this is indicative of a chloride resistant metabolic Cl is high, this is indicative of a chloride resistant metabolic alkalosisalkalosis

4.F4.F What are the causes of a chloride resistant What are the causes of a chloride resistant metabolic alkalosis ?metabolic alkalosis ?

This not common chloride responsive M Alkalosis are This not common chloride responsive M Alkalosis are generally caused by gastric or renal loss of chloride. C generally caused by gastric or renal loss of chloride. C resistant met alkalosis occur in the presence of mineral resistant met alkalosis occur in the presence of mineral corticoid or glucocortcoid excess stats. These include corticoid or glucocortcoid excess stats. These include primary aldosteronism or Cushing's syndrome. CS is primary aldosteronism or Cushing's syndrome. CS is caused by either increase in ACTH from central or caused by either increase in ACTH from central or peripheral source or an adrenal glucocorticoid-peripheral source or an adrenal glucocorticoid-producing adenoma. Measuring the ACTH level would producing adenoma. Measuring the ACTH level would distinguish ACTH-dependent versus ACTH- independent distinguish ACTH-dependent versus ACTH- independent Cushing's SyndromeCushing's Syndrome

..

4.G4.G What is the most likely cause of the What is the most likely cause of the chloride resistant metabolic alkalosis at this chloride resistant metabolic alkalosis at this patient?patient?

Chloride-resistant metabolic alkalosis in the Chloride-resistant metabolic alkalosis in the setting of recurrent pneumonia is likely setting of recurrent pneumonia is likely mediated by lung cancer with post mediated by lung cancer with post obstructive pneumonia. Lung cancers are not obstructive pneumonia. Lung cancers are not infrequent producers of ACTH and ectopic infrequent producers of ACTH and ectopic ACTH syndrome.ACTH syndrome.

SO Compensated, Chloride-resistant metabolic SO Compensated, Chloride-resistant metabolic alkalosisalkalosis

Q.5Q.5 46 male with COPD came to ER with 46 male with COPD came to ER with increasing SOB ,CXR reveals RLL infiltrate.increasing SOB ,CXR reveals RLL infiltrate.

Na =140 K=4.1 Cl=98Na =140 K=4.1 Cl=98 HCO3= 30 Pco2 66 Po2 38HCO3= 30 Pco2 66 Po2 38 PH= 7.28 PH= 7.28

5.A5.A Is the data internally consistent ?Is the data internally consistent ?

The data are internally consistentThe data are internally consistent

Pco2=52*30/24=65Pco2=52*30/24=65

5.B5.B Is the patient acdmic or alkalemic ?Is the patient acdmic or alkalemic ? PH < 7.4 so the patient is acidemicPH < 7.4 so the patient is acidemic

5.C5.C Is the primary disorder respiratory ?Is the primary disorder respiratory ?

This is respiratory acidosis as the Pco2 is highThis is respiratory acidosis as the Pco2 is high

5.D5.D What type of respiratory acidosis is this ??What type of respiratory acidosis is this ??

RA cab be acute or chronic. There are nomograms for changes in PH RA cab be acute or chronic. There are nomograms for changes in PH in acute versus chronic respiratory acidosis. In acute RA ,the in acute versus chronic respiratory acidosis. In acute RA ,the [HCO3]=[(Pco2-40)/10]+24,or 27.In chronic RA [HCO3]=[Pco2-[HCO3]=[(Pco2-40)/10]+24,or 27.In chronic RA [HCO3]=[Pco2-40)/3]+24 so [(66-40)/3]+24 or 33 .in this case ,the 40)/3]+24 so [(66-40)/3]+24 or 33 .in this case ,the HCO3=30,midway suggesting an acute and chronic process.HCO3=30,midway suggesting an acute and chronic process.

5.E 5.E What are the causes of the acute and chronic What are the causes of the acute and chronic respiratory acidosis ?respiratory acidosis ?

Most likely is COPD with acute pneumonia.Most likely is COPD with acute pneumonia.

so this Respiratory acidosis, acute on chronicso this Respiratory acidosis, acute on chronic

Q.6Q.6 47 years women with history of being 47 years women with history of being drinking with nausea ,vomiting and fever drinking with nausea ,vomiting and fever ..

Na=140 K=2.9 Cl = 96Na=140 K=2.9 Cl = 96 HCO3 = 19 Pco2 = 49 Po2 =45HCO3 = 19 Pco2 = 49 Po2 =45

PH= 7.15 Glucose= 96 PH= 7.15 Glucose= 96 Urinalysis: 4 + ketonesUrinalysis: 4 + ketones

CXR… LUL,RML,RLL infiltratesCXR… LUL,RML,RLL infiltrates

6.A6.A Is the data internally consistent .Is the data internally consistent .The data is internally consistentThe data is internally consistentPco2=65*18/24=49Pco2=65*18/24=49

6.B6.B Is the patient acidmic or alkalemic?Is the patient acidmic or alkalemic?

The patient is acidemicThe patient is acidemic

6.C6.C Is the primary disorder respiratory?Is the primary disorder respiratory?

There is primary respiratory acidosis, but it There is primary respiratory acidosis, but it magnitude is insufficient to cause this degree of magnitude is insufficient to cause this degree of acidemia( all else being equal, raising the Pco2 to acidemia( all else being equal, raising the Pco2 to 49 should lower the PH to 7.33). Thus, there must 49 should lower the PH to 7.33). Thus, there must be another basis for part of the be another basis for part of the acidosis(ie,metabolic acidosis). This must be acidosis(ie,metabolic acidosis). This must be double acid-base disturbance, in other words, a double acid-base disturbance, in other words, a metabolic and a respiratory acidosismetabolic and a respiratory acidosis

6.D6.D Patient has MA so is it Patient has MA so is it hyperchloremic or high AG MA?hyperchloremic or high AG MA?

AG 140-96-18=26 High anion gap type acidosisAG 140-96-18=26 High anion gap type acidosis

6.E6.E What are the causes of high AG What are the causes of high AG MA??MA??

Most likely diagnosis in this patient is alcoholic Most likely diagnosis in this patient is alcoholic ketoacidosi as the patient has 4+ ketones in her ketoacidosi as the patient has 4+ ketones in her urine.An alternative possibility would be diabetic urine.An alternative possibility would be diabetic ketoacidosis, but this unlikely in view of the normal ketoacidosis, but this unlikely in view of the normal blood glucose level of 96.blood glucose level of 96.

6.F6.F What about the compensation ?What about the compensation ?In MA ,the Pco2 should decrease . Because the Pco2 is In MA ,the Pco2 should decrease . Because the Pco2 is

increased, there is no compensation. As Discussed above, increased, there is no compensation. As Discussed above, this a double acidosis.this a double acidosis.

6.G6.G What is the most likely explanation What is the most likely explanation for the patients clinical syndrome ?for the patients clinical syndrome ?

Most likely this patient is chronic alcoholic with nausea and Most likely this patient is chronic alcoholic with nausea and vomiting( resulting in a metabolic alkalosis: did you notice vomiting( resulting in a metabolic alkalosis: did you notice the delta gap [14]+the [HCO3]= 32 ?) who discontinued her the delta gap [14]+the [HCO3]= 32 ?) who discontinued her alcohol intake and developed alcoholic ketoacidosis ( MA) alcohol intake and developed alcoholic ketoacidosis ( MA) and also developed pneumonia resulting in respiratory and also developed pneumonia resulting in respiratory acidosisacidosis..

Q.7Q.7 62 male admitted to ICU with SOB. Number of empty 62 male admitted to ICU with SOB. Number of empty bottles had been found in his apartment, including bottles had been found in his apartment, including

furosemid,enalapril,potassium chloride,asprin. XCR reveals furosemid,enalapril,potassium chloride,asprin. XCR reveals pulmonary edema ?pulmonary edema ?

Na=140 K= 2.8 Cl=108Na=140 K= 2.8 Cl=108 HCO3 =10 HCO3 =10 Pco2 =16 Pco2 =16 Po2 = 106Po2 = 106 PH= 7.42PH= 7.42

7.A Is the data internally consistent ?7.A Is the data internally consistent ?The data are internally consistent The data are internally consistent

Pco2=38*10/24=16Pco2=38*10/24=16


Neither. The PH is normal, but this dose not exclude Neither. The PH is normal, but this dose not exclude underlying acid-base disorderunderlying acid-base disorder

7.C7.C Is the primary disorder respiratory?Is the primary disorder respiratory?

For any primary acid base disorder, one cannot fully For any primary acid base disorder, one cannot fully return PH to normal. The finding of normal PH return PH to normal. The finding of normal PH implies 2 primary disorders. There must be a implies 2 primary disorders. There must be a primary respiratory alkalosis( Pco2=16) but also a primary respiratory alkalosis( Pco2=16) but also a primary metabolic acidosis ( because the PH is primary metabolic acidosis ( because the PH is normal)normal)

7.D7.D The patient has MA so is it hyperchlormic or The patient has MA so is it hyperchlormic or high AG MA ?high AG MA ?

AG = 22 so this high AG MAAG = 22 so this high AG MA

7.E7.E Is there metabolic alkalosis present as well ? Is there metabolic alkalosis present as well ? What is the delta gap?What is the delta gap?

The delta AG 22-10=12. when one adds 12 to the The delta AG 22-10=12. when one adds 12 to the measured bicarbonate of 10 to equal 22,this measured bicarbonate of 10 to equal 22,this indicates that there is no underlying metabolic indicates that there is no underlying metabolic acidosis.acidosis.

7. F 7. F What is the most likely cause of What is the most likely cause of this acid-base disturbance ?this acid-base disturbance ?

This patient appears to have ingested salicylates. This patient appears to have ingested salicylates. The finding of The finding of mixed acid –base mixed acid –base disturbance of a disturbance of a respiratory alkalosis and metabolic acidosis is respiratory alkalosis and metabolic acidosis is very suggestive of this disturbance. very suggestive of this disturbance.

In particular, this acid-base disturbance in the In particular, this acid-base disturbance in the setting of pulmonary edema is highly suggestive setting of pulmonary edema is highly suggestive of of salicylate intoxication.salicylate intoxication.

Q.8Q.8 28 women is admitted with unexplained delirium and 28 women is admitted with unexplained delirium and acidosis s after cleaning her motorcycle with solvents .acidosis s after cleaning her motorcycle with solvents .

Na= 139 K=1.7 Cl= 115Na= 139 K=1.7 Cl= 115 HCO3 = 12 Pco2= 28 Po2= 92HCO3 = 12 Pco2= 28 Po2= 92 PH=7.24 BUN= 7 Creatnine=1.3PH=7.24 BUN= 7 Creatnine=1.3

Urinalysis PH=6.5Urinalysis PH=6.5 SG = 1.020SG = 1.020

No cells or castsNo cells or casts

8.A8.A Is the data internally consistent ?Is the data internally consistent ?

The data internally consistent, The data internally consistent, Pco2=56*12/24=28Pco2=56*12/24=28


AcidemicAcidemic 8.C8.C Is the primary disorder Is the primary disorder

respiratory ?respiratory ?

This is MA as the Pco2 is not elevatedThis is MA as the Pco2 is not elevated

8.D8.D The patient has MA so is it The patient has MA so is it hyperchlormic or high AG MA?hyperchlormic or high AG MA?

As AG is 12 this hyperchloremic MA. This is an As AG is 12 this hyperchloremic MA. This is an important finding because one of the possible important finding because one of the possible causes of the acidosis would be methanol causes of the acidosis would be methanol ingestion. Methanol is a solvent often used to ingestion. Methanol is a solvent often used to clean machine engines. In contrast to the finding clean machine engines. In contrast to the finding of this patient, however, methanol ingestion of this patient, however, methanol ingestion would be expected to cause a high AG MA..So would be expected to cause a high AG MA..So Methanol can be excluded based on this acid Methanol can be excluded based on this acid base abnormality.base abnormality.

8.E 8.E what are the causes of the what are the causes of the hyperchlormic MA ?hyperchlormic MA ?

GastrointestinalGastrointestinal loss of Na in excess loss of Na in excess of chloride, as is typical in diarrheaof chloride, as is typical in diarrhea

Inorganic acid Inorganic acid ingestion such as ingestion such as ammonium chlorideammonium chloride

Renal tubular Renal tubular acidosis ( RTAs)acidosis ( RTAs)

88.F How one distinguish between these .F How one distinguish between these possibilities ?possibilities ?

The The urine PH urine PH is the most helpful test to distinguish is the most helpful test to distinguish various causes of hyperchlormic metabolic various causes of hyperchlormic metabolic acidosis. In the setting of systemic acidosis, a acidosis. In the setting of systemic acidosis, a healthy kidney is able to acidify the urine so the healthy kidney is able to acidify the urine so the urine PH is low ( <5.5).urine PH is low ( <5.5).

Ingestion of inorganic acid Ingestion of inorganic acid or or diarrhea-induced diarrhea-induced acidosis dose not interfere with kidney function acidosis dose not interfere with kidney function and is associated with urine PH < 5.5.and is associated with urine PH < 5.5.

In contrast, in some types of RTA ( egg, distal RTA In contrast, in some types of RTA ( egg, distal RTA or type 1 RTA) the urine cannot be acidified or type 1 RTA) the urine cannot be acidified normally. This result in an inappropriately high normally. This result in an inappropriately high ( > 5.5) urinary PH despite systemic acidosis.( > 5.5) urinary PH despite systemic acidosis.

This patient has a urine This patient has a urine PH of 6.5PH of 6.5, a , a value clearly inappropriately high for value clearly inappropriately high for the degree of systemic acidosis. the degree of systemic acidosis. Therefore, Therefore,

the patient has distal RTAthe patient has distal RTA

8.G8.G What are the potential causes of the distal What are the potential causes of the distal renal tubular acidosis in this women ??renal tubular acidosis in this women ??

Other than Methanol ,Other than Methanol ,toluenetoluene is often used as is often used as solvent in cleaning solutions.solvent in cleaning solutions.

This patient inadvertently absorbed ( through the This patient inadvertently absorbed ( through the skin) toluene from the solvent and developed a skin) toluene from the solvent and developed a distal RTA.distal RTA.

So Hyperchlormic metabolic acidosis So Hyperchlormic metabolic acidosis secondary to toluene intoxication.secondary to toluene intoxication.

Case 1Case 1

A 30 y/o man with DM presents with A 30 y/o man with DM presents with a week of polyuria, polydipsia, fever a week of polyuria, polydipsia, fever to 102, nausea, and abdominal pain. to 102, nausea, and abdominal pain. He is orthostatic on admission.He is orthostatic on admission.

130 130 ll 94 94 ll 75 75 ll 906 906 pH 7.14pH 7.14

6.1 6.1 ll 6 6 ll 2.3 2.3 pCOpCO22 18 18

pOpO22 102 102

Case 1 contCase 1 cont Anticipate the disorder Anticipate the disorder

DKA (with anion gap acidosis)DKA (with anion gap acidosis) Acidemic or alkalemic?Acidemic or alkalemic? Metabolic or respiratory?Metabolic or respiratory?

pH = acidemic; must be metabolic low HCOpH = acidemic; must be metabolic low HCO33, low pCO, low pCO22)) If metabolic acidosis: gap or non-gap?If metabolic acidosis: gap or non-gap?

AG = 30; + anion gap metabolic acidosisAG = 30; + anion gap metabolic acidosis Is compensation appropriate?Is compensation appropriate?

PaCOPaCO22 should = last 2 digits of pH [18] or (1.5 x HCO should = last 2 digits of pH [18] or (1.5 x HCO33) + 8 [17]) + 8 [17] Mixed disorder?Mixed disorder?

AG = 30 (-18); HCOAG = 30 (-18); HCO33 = 6 (-18); thus simple AG met acidosis = 6 (-18); thus simple AG met acidosis

130 130 ll 94 94 ll 75 75 ll 906 906 7.14/18/1027.14/18/1026.1 6.1 ll 6 6 ll 2.3 2.3

Case 2Case 2

A 30 y/o man with DM presents with A 30 y/o man with DM presents with a week of polyuria, polydipsia, fever a week of polyuria, polydipsia, fever to 102 and vomiting for four days.to 102 and vomiting for four days.

135 135 ll 89 89 ll 50 50 ll 1181 1181 pH 7.26pH 7.26

6.1 6.1 ll 10 10 ll 2.3 2.3 pCOpCO22 23 23

pOpO22 88 88


DKA (AG acidosis); met alk from vomitingDKA (AG acidosis); met alk from vomiting Acidemic or alkalemic?Acidemic or alkalemic? Metabolic or respiratory? Metabolic or respiratory?

pH = acidemic; must be metabolic low HCOpH = acidemic; must be metabolic low HCO33, low pCO, low pCO22)) If metabolic acidosis: gap or non-gap?If metabolic acidosis: gap or non-gap?

AG = 36; + anion gap metabolic acidosisAG = 36; + anion gap metabolic acidosis Is compensation appropriate?Is compensation appropriate?

pCOpCO22 should = last 2 digits of pH [26] or (1.5 x HCO should = last 2 digits of pH [26] or (1.5 x HCO33) + 8 [23]) + 8 [23] Mixed disorder?Mixed disorder?

AG = 36 (-24); HCOAG = 36 (-24); HCO33 = 10 (-14); HCO = 10 (-14); HCO33 is too high; mixed AG is too high; mixed AG metabolic acidosis metabolic acidosis andand metabolic alkalosis metabolic alkalosis

135 135 ll 89 89 ll 50 50 ll 1181 1181 7.26/23/887.26/23/886.1 6.1 ll 10 10 ll 2.3 2.3

Case 7Case 7

A 55 y/o woman with a history of a A 55 y/o woman with a history of a CVA presents to clinic complaining of CVA presents to clinic complaining of shortness of breathshortness of breath

140 140 ll 100 100 ll 30 30 ll 115 115 pH 7.36pH 7.36

3.9 3.9 ll 30 30 ll 1.5 1.5 pCOpCO22 38 38

pOpO22 91 91

Case 7 contCase 7 cont

Anticipate the disorder Anticipate the disorder Resp alk due to CNS disorder or acute pulmonary processResp alk due to CNS disorder or acute pulmonary process

Acidemic or alkalemic?Acidemic or alkalemic?pH = acidemicpH = acidemic

Metabolic or respiratory? Metabolic or respiratory? If metabolic acidosis: AG?If metabolic acidosis: AG?

HCOHCO33 is high (not metabolic acidosis); pCO is high (not metabolic acidosis); pCO22 is < 40 (not is < 40 (not respiratory acidosis); AG is normal (10), so what’s going respiratory acidosis); AG is normal (10), so what’s going on?on?

140 140 ll 100 100 ll 30 30 ll 115 115 7.36/38/917.36/38/913.9 3.9 ll 30 30 ll 1.5 1.5

Case 7 contCase 7 cont

LAB ERROR!LAB ERROR!By Henderson-HasselbachBy Henderson-Hasselbach

HH++ = 24 x pCO = 24 x pCO22/HCO/HCO33 = 24 x (38/30) = 30 = 24 x (38/30) = 30

pH should be 7.50pH should be 7.50

140 140 ll 100 100 ll 30 30 ll 115 115 7.36/38/917.36/38/913.9 3.9 ll 30 30 ll 1.5 1.5

Case 8Case 8 You are in the ER, and are aware that the lab has You are in the ER, and are aware that the lab has

been having intermittent problems with the been having intermittent problems with the chemistry auto analyzer. A 30 y/o diabetic man, chemistry auto analyzer. A 30 y/o diabetic man, well known to you from pervious visits, comes in well known to you from pervious visits, comes in with severe nausea and vomiting. His blood with severe nausea and vomiting. His blood alcohol level is very high. The ER attending alcohol level is very high. The ER attending advises you to check his labs and send him home advises you to check his labs and send him home if they are OKif they are OK

140 140 ll 84 84 ll 28 28 ll 160 160 pH 7.40pH 7.40

3.0 3.0 ll 24 24 ll 1.3 1.3 pCOpCO22 40 40

pOpO22 88 88


Vomiting - > met alk; if unconscious, resp acidosisVomiting - > met alk; if unconscious, resp acidosis Acidemic or alkalemic?Acidemic or alkalemic? Metabolic or respiratory? Metabolic or respiratory?

pH, PCO2 and HCO2 are all normal pH, PCO2 and HCO2 are all normal no apparent disorder no apparent disorder Lab error? Check H-H equations.Lab error? Check H-H equations.

HH++ = 24 x pCO = 24 x pCO22/HCO/HCO33 = 24 x (40/24) = 40 = 24 x (40/24) = 40pH should be 7.40pH should be 7.40

Do you send him home?Do you send him home?AG = 32; + anion gap acidosisAG = 32; + anion gap acidosisAG = 32 (-20); HCOAG = 32 (-20); HCO33 = 24 ( = 24 (--0); so HCO0); so HCO33 is too high; must is too high; must have a superimposed metabolic alkalosis. Thus, mixed AG have a superimposed metabolic alkalosis. Thus, mixed AG acidosis and metabolic alkalosis acidosis and metabolic alkalosis

140 140 ll 84 84 ll 28 28 ll 160 160 7.40/40/887.40/40/883.0 3.0 ll 24 24 ll 1.3 1.3

THANK YOUTHANK YOU

arterial blood gases dr. abdulaziz al shaer consultant intensivist 21/2/2010

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