acid-base gas exchange - hỘi hỒi sỨc cẤp cỨu vÀ...

ABGA: bedside application

Acid-base Gas exchange

ER: GI bleeding

Patient A

• BP 95/65 mmHg

• ABGA:

7.37- 34- 73- 20

Patient B

• BP 130/50 mmHg

• ABGA:

7.28-24- 73- 13

Pneumonia

Patient A

Ceftriaxone + Azythromycin

• D1:

7.32- 30- 60- 16

• D2:

7.38- 34- 73- 20

Patient B

Ceftriaxone + Azythromycin

• D1:

7.32- 30- 60- 16

• D2:

7.26- 24- 73- 12

• Vital signs

BP RR PR BT

• Vital signs

BP RR PR BT [ ? ]

pH

1909, SPL Sorensen, Carlsberg Lab, Denmark

Ion concentration & protein function

[H+] in the blood: 0.00000004 mEq/L

pH (pH) : pouissance hydrogen

(power of H+)

Clinical symptoms of abnormal pH

pH manifestations

7.80 Death

Convulsion

Arrhythmia Increased excitability

Irritability

7.40 Normal

Drowsiness

Lethargy Depressive effect

Coma

6.80 Death

pH homeostasis

• Metabolism: acids

• Homeostatic organ-systems

Lung Blood

buffer Kidney

Acids production

13,000 mEq/day

• Volatile acid:

98 % of daily acids

• Non-volatile acid:

1-2% of normal acid

pathologic acids

40-80 mEq/day

Volatile acids (carbonic acid, H2CO3)

CO2

Lung: moment-to-moment regulation

Fixed (Non-volatile) acids

1) Source: metabolism non-metabolic: NH4Cl

2) Via kidney, blood buffers

Blood buffers

• H+(liquid) + A- (sponge) HA (wet sponge)

• First line of defense against abrupt pH change

Bicarbonate buffer system - more than 50 % of total blood buffering

HCO3: Open system Hb: Closed system

Units Mean Normal Acidotic Alkalotic

2 SD

1 SD

pH - 7.40 7.35 - 7.45 <7.35 >7.45

7.38 - 7.42

PCO2 mmHg 40 35 - 45 <45 >35

38 - 42

HCO3- mEq/L 25 22 - 28 <22 >28

24 – 26

ABG: normal values

Don’t discard VBGA

• 7.26- 43- 48- 12.8- 64 %

Arterial blood Venous blood

pH 7.40 7.36

PCO2 40 46

PO2 90 40

HCO3- 24 26

Pre-analytical errors of ABGA

– Anticoagulant

Dilution effect: liquid heparin

Liquid heparin

Lyophilized heparin

– Air contamination

• PaO2 < 158 mmHg (room air PO2): inc

• PaCO2: dec (less marked than PaO2)

• Air bubbles should be expelled within 2 min

cf. PaO2 > 158 mmHg

(MV, Anesthesia): dec

Calaf et al. Tech Note 2004

D: air bubble at the cone E: air bubble at the plunger

– Analysis timing

Calaf et al. Tech Note 2004

ABGA results: immediate, and 30, 60 min at 4 °C

ABGA: glass syringe vs. plastic syringe

• Paradoxical change:

inc PaO2, dec PaCO2

• microbubble due to friction

iced sample: diffusion of ambient air thru plastic

• Best to analyse within 30 min

66/M. CLL. WBC 282,000/mm3

ABGA: 7.38- 47- 31- 29- 54% (O2 2 L/min)

2nd ABGA, < 1 min: PaO2 41 mmHg

3rd ABGA, centrifuged: PaO2 68 mmHg

ABGA: whole blood vs. plasma

44/F. AML

8. 24

WBC 172,000

PaO2-Whole blood 51 mmHg

SpO2 82 %

PaO2-Plasma

8. 24 8. 25

8. 25

43,500

81 mmHg

95 %

118 mmHg

O2 CO2 H+

Clark Electrode

Serveringhaus Electrode

Sanz Electrode

Arterial blood

Buffer pH = 6.840

----- XXXX Diagnostics ------

Blood Gas Report 248 5:36 Jul 22 2000t ID

2570 / 00

Measured 37.0o C

pH 7.463

pCO2 44.4 mm Hg pO2 113.2 mm Hg

Corrected 38.6o C pH 7.439

pCO2 47.6 mm Hg pO2 123.5 mm Hg

Calculated Data

HCO3 act 31.1 mmol / L HCO3 std 30.5 mmol / L BE 6.6 mmol / L

O2 CT 14.7 mL / dl O2 Sat 98.3 % ct CO2 32.4 mmol / L

pO2 (A - a) 32.2 mm Hg pO2 (a / A) 0.79

Entered Data Temp 38.6 oC

ct Hb 10.5 g/dl

FiO2 30.0 %

Internal consistency

• Indirect metabolic

assessment

• Rule of eights

• Modified Henderson

equation

• Acid-base map

External congruity

• Lab-lab congruity

• Pt-lab congruity

• FIO2-PaO2 congruity

• SaO2-SPO2 congruity

Modified Henderson Equation

• H = 24 x PaCO2/HCO3

• Linear relationship between H+ and pH in 7.20-7.50

Ex) 7.30-28-86-18

H: 50

24 x 28/18 = 37.3

HCO3

• calculated value

• arterial blood

• anaerobic

• immediate

handling/ice-stored

Total CO2

• measured value

• venous blood

• air-contaminated

• lag in

measurement/room

temperature exposure

Difference 2 mEq/L: Good congruity

> 5 mEq/L: Incongruous !

Q: Metabolic acidosis, alkalosis에는 왜 acute, chronic 분류가 없나?

acidosis

alkalosis

respiratory

metabolic

acute ? chronic

acute ? chronic

metabolic

respiratory

Acute changes in PaCO2

Immediate changes in pH

Approximate PaCO2-pH Relationship

PaCO2 [HCO3-]P*

(mm Hg) pH (mmol3/L)

80 7.20 28

60 7.30 26

40 7.40 24

30 7.50 22

20 7.60 20 [HCO3

-]p = plasma bicarbonate concentration

Causes of Respiratory Acidosis

• Central: drugs (anesthetics, morphine, sedatives, antihistamine), stroke, infection, central hypoventilation syndrome

• Airway: asthma, COPD, airway obstruction

• Neuromuscular: poliomyelitis, kyphoscoliosis, myasthenia, muscular dystrophies

• Miscellaneous: obesity, permissive

Respiratory Acidosis

Drowsy

Confusion

Headache

Flapping tremor

Renal compensation in RAc

Acute: HCO3- ↑ = 0.1 × PCO2 ↑

Chronic: HCO3- ↑ = 0.35 × PCO2 ↑

Causes of Respiratory Alkalosis

1. Hypoxia

2. Pulmonary disease: pulmonary edema, pneumonia, pulmonary embolism, ILD

3. CNS-mediated

- hyperventilation syndrome

- CNS infection, hemorrhage, tumor

- medical conditions: sepsis, liver failure, pregnancy

- trauma, heat exposure

- medicine: salicylate, nicotine, xanthine, progesterone

4. Mechanical ventilation

Renal compensation in RAk

Acute: HCO3- ↓ = 0.2 × PCO2 ↓

Chronic: HCO3- ↓ = 0.5 × PCO2 ↓

Respiratory alkalosis

(Hypocapnia)

Cerebral vasospasm

Confusion headache

Paresthesia

tetany

Brain in respiratory acid-base disturbance

• More vulnerable to acid-base change than anticipated

by blood pH: faster movement of CO2 than HCO3-.

• Brain is significantly affected by

(1) acute changes in pH

(2) rapid correction of acidosis or alkalosis

pH = Acidemia

PaCO2 = Normal or low metabolic acidosis (MAc)

HCO3- = Low

pH = Alkalemia

PaCO2 = Normal or high metabolic alkalosis (MAk)

HCO3- = High

Metabolic acid-base disorders

Anion Gap?

ECF

state?

Anion Gap (AG)

• AG = Na – (Cl- + HCO3-) = 12 2

– 1 g/dL albumin = 2.5 mEq/L anion

– corrected AG = AG - 2.5 x (4.5-alb)

MAc- high AG

• Lactic acidosis

• Ketoacidosis

• Renal failure: acute, chronic

• Toxins: ethylene glycol, methanol, salicylate,

propylene glycol, pyrolglutamic acid

80/M. Distal CB stone

Liver abscess with septic shock

High lactate does not always mean

lactic acidosis

62/F

• 8년전 Coronary Artery Bypass Graft 받음

• Effort-related dyspnea AR/MR 진단

• AVR/MVR

• 의식상태 양호

인공호흡기 없이 호흡

WBC: 17500 12500

CRP: 7.1 5.8

• 임상 으로 호전되고 있으나 lactic acid가 증가되어 있슴

• 약물: lactic acidosis 유발 가능한 약물 없슴

• RAk 및 glucose 정상화 후

• Resp alkalosis에 의한 hyperlactemia

알칼리증과 당대사: 3번 과정을 촉진

6번 과정의 NADH+H+생성↑

pyruvate 생성 증가

lactate로의 전환 증가

신부전의 경우 gluconeogenesis 및 glycogenolysis 과정의 효소 장애

lactate level 증가

• 혈당에 의한 hyperlactemia

High AG is significant

• Even when HCO3- appears normal.

Indicates a mixed acid-base disorder

• If pH is alkalotic:

MAc + Alkalosis (metabolic/respiratory)

62/M. Alcoholic LC

• AGBA: 7.40- 40 -85- 25- 96

• Na 135, Cl 80, K 2.8

• AG= 135- (80+25)= 30 [High AG!]

AG = 30 - 12= 18

HCO3-= 25 - 24= 1

PI) vomiting for the last few days

Dx) metabolic acidosis + metabolic alkalosis

Non-AG acidosis

• Gastrointestinal bicarbonate loss: diarrhea, external

pancreatic/small bowel drainage [GI acidosis]

• Renal disease: proximal RTA, distal RTA, generalized

distal nephron dysfunction [Renal acidosis]

• Drug-induced hyperkalemia (with renal insufficiency):

K-sparing diuretics, trimethoprim, pentamidine, ACEI, ARB, NSAID, cyclosporin/tacrolimus [Medication acidosis]

• Others: rapid saline infusion

Non-AG acidosis

Urinary Anion Gap = Urine [Na++ K+- Cl- ]

Positive Negative

Renal cause Extra-renal cause

Urine pH

> 6 < 5.5

(Type I, RTA)

Hypokalemia

Hyperkalemia (Type IV RTA) (Type II RTA)

Low or negative AG

• Severe hypoalbuminemia: nephrotic

syndrome

• Multiple myeloma, paraproteinemias

(cationic proteins)

• Bromism (dextromethorphan bromide)

• Lithium (cation)

Useful parameters for assessment of MAc/MAk

• Anion gap (AG)

• Total CO2 (TCO2)

• Base excess (BE)

Total CO2= [HCO3- ] + [dissolved CO2 ]+ [H2CO3]

= [HCO3

- ] + 0.03 x PCO2

Total CO2

“You are seeing [HCO3- ] without arterial puncture.”

COPD A

7.35-60-54-33

2 mo ago

Na 138

K 4.1

Cl 102

TCO2 31

COPD B

7.35-60-54-33

2 mo ago

Na 138

K 4.1

Cl 102

TCO2 24

Azotemia A

Cr 3.0

2 mo ago

Na 138

K 5.4

Cl 102

TCO2 23

Azotemia B

Cr 3.0

2 mo ago

Na 138

K 5.4

Cl 102

TCO2 17

73/M. DM, CKD, HTN, s/p CABG

CC. Sore throat

Previous admission

TCO2 22.4

BUN/Cr 19/1.5

Day 1

TCO2 17.1

BUN/Cr 107/6.3

Base excess (BE)

Change in [strong acid] or [strong base] required to restore pH to 7.4 at 40 mm Hg of PaCO2 on 37℃

• BE = 0 +/- 3 mmol/L: WNL BE > +10, < -10 mmol/L: metabolic component in acid-base imbalance • Trend of BE

73/M. DM, CKD, HTN, s/p CABG

CC. Sore throat

CPCR D4

D2

D1

85/F. COPD, thyroid cancer with lung metastasis

Lasix

Acetazolamide

Causes of Metabolic Alkalosis

• ECF contraction

– GI: vomiting, gastric aspiration, villous adenoma

– Renal: diuretics, posthypercapnic state, hypercalcemia/hypoparathyroidism

– Recovery form lactic acidosis/ketoacidosis

– Nonabsorbable anions (penicillin, carbenicillin)

– Magnesium deficiency

– K depletion

– Bartter’s syndrome, Gitelman’s syndrome

High renin

renal artery stenosis

accelerated HTN

renin-secreting tumor

estrogen therapy

• ECF expansion MAk

Low renin

primary aldosteronism

adrenal enzyme defects

Cushing’s syndrome

licorice

Metabolic alkalosis & CO2 retention

• If PaCO2 > 55- 60

mmHg in MAk, suspect

primary respiratory

insufficiency.

Mixed acid-base disorder

When pH of a sick patient is around 7.40

suspect a mixed acid-base disorder

pH = 7.390

PaCO2 = 64 mmHg

PaO2 = 76 mmHg

HCO3- = 39 mEq/L

BE = 12

pH = 7.427

PaCO2 = 16 mmHg

PaO2 = 123.9 mmHg

HCO3- = 7 mEq/L

BE = -20.5

F/57. Cx ca with rectovaginal

fistula, hydronephrosis

67/M. COPD, Cor pulmomale

Lasix

Mixed acid-base disorder

• Compare AG and HCO3- :

AG > HCO3

- : coexisting MAk, RAc

AG < HCO3- : coexisting non-AG acidosis, RAk

70/M. DM, HTN

◈C.C vomiting (onset: 5 DA)

◈P.I

5년전부터 DM, HTN 으로 medication 하면서 지냄

(최근까지 insulin 은 사용하지 않고 OHA 복용함)

5일전 oral sore 발생. 물을 포함하여 거의 사하지 못함

이후 vomiting, weight loss 발생하여 응급실 통해 입원함

ABGA: 7.16-26-96-(-17.7)-9.0

Ca 8.7

Glucose 931

Cr 3.7

Protein 6.2

Albumin 3.6

Na 139, K 6.2, Cl 101, TCO2 6.5

AG = Na – ( Cl + HCO3) = 139 - (101 + 9) = 29 corrected AG = 12 - 2.5 x (4.5 – 3.6) = 10

AG acidosis (DKA) + MAk (vomiting)

AG = 29 - 10 = 19

HCO3 = 24 – 9 = 15

접수일자 접수 간 BE pH lactic acid Chloride Cr

810 17:14 -12 9.2 108 2.46

18:49 -14.1 7.2 6.5

20:12 -13 7.2 4.5

21:48 -13.1 7.25 3.3 1.85

811 0:01 -12.4 7.28 2.2

6:04 -11.3 7.33 3.6 113 2.03

12:04 -11.6 7.33 4.5

18:52 -13.1 7.31 3.8

19:47 -12.8 7.3 3.4

20:53 -11.6 7.32 2.2

22:26 -13 7.28 2.8

23:35 -11.9 7.27 1.8

812 5:29 -14.5 7.22 2.3 112 2.57

9:00 -13.4 7.26 3.1

11:13 -12.7 7.26 2.7

98/M, aspiration pneumonia

호

전

8/12

Na 139, Cl 112, TCO2 11.8 HCO3 12.0 mmEq/L Cr 2.57 mg/dL AG 15.0 mEq/L Albumin 2.0 (corrected AG: ca 7) AG = 15 - 7= 8 HCO3 = 12 AG acidosis + Non-AG acidosis (due N/S infusion)

접수일자 접수 간 BE pH lactic acid Chloride Cr NS total NS

20140810 17:14 -12 9.2 108 2.46 300

18:49 -14.1 7.2 6.5 700 1000

20:12 -13 7.2 4.5 1000 2000

21:48 -13.1 7.25 3.3 1.85 2000 4000

20140811 0:01 -12.4 7.28 2.2

6:04 -11.3 7.33 3.6 113 2.03

12:04 -11.6 7.33 4.5

18:52 -13.1 7.31 3.8 500

19:47 -12.8 7.3 3.4 500 1000

20:53 -11.6 7.32 2.2 1000 2000

22:26 -13 7.28 2.8 30 2030

23:35 -11.9 7.27 1.8 30 2060

20140812 5:29 -14.5 7.22 2.3 112 2.57 180 2240

9:00 -13.4 7.26 3.1 120 2360

11:13 -12.7 7.26 2.7

pH

0

2

4

6

8

10

lactic acid

100

105

110

115

120

125

Chloride

-16

-14

-12

-10

-8

-6

-4

-2

0

BE

0

0,5

1

1,5

2

2,5

3

Cr

Common settings associated with mixed disorder

ABG Analysis

Pre-existing disease

Acute disease

Drugs

Hb

WBC

BUN/Cr

Electrolytes

(past TCO2)

Albumin

CXR

PFT

ECG

Hb

WBC

BUN/Cr

Electrolytes

(past TCO2)

Albumin

CXR

PFT

ECG

Supplemental Info:

Vital signs

Hb

WBC

BUN/Cr

Electrolytes

(past TCO2)

Albumin

CXR

ABGA

pH

PaCO2

PaO2

BE

HCO3

ABGA

pH

PaCO2

PaO2

BE

HCO3

ABGA

pH

PaCO2

PaO2

BE

HCO3

ABGA

pH

PaCO2

PaO2

BE

HCO3

ABG

REPORT

pH

PaCO2

HCO3-

Acid Base

+ History

+ Previous ABGA/lab

pH = 7.25, PaCO2 = 70 mmHg

HCO3- = 31 mEq/L

Previous healthy, basal PaCO2 40 mm Hg

expected HCO3- = 24 + 0.1 x (70 - 40) = 27 mEq/L

Ans) Acute RAc + MAk superimposed

pH = 7.25, PaCO2 = 70 mmHg

HCO3- = 31 mEq/L

COPD, basal PaCO2 70 mm Hg

expected HCO3- = 24 + 0.35 x (70- 40)= 34.5 mEq/L

Ans) Chronic RAc + MAc superimposed

pH = 7.25, PaCO2 = 70 mmHg

HCO3- = 31 mEq/L

COPD, basal PaCO2 55 mm Hg

expected HCO3- = 24 + 0.35 x (55 - 40) + 0.1 x (70

- 55) = 29 + 1.5= 31.5 mEq/L

Ans) Acute on chronic RAc. No metabolic

component present