12. As required for ECG
interpretation,
a systematic approach to
ABGs enhances accuracy.
There are NO short-cuts!
A Systematic Approach
13. The Anatomy
of a Blood Gas
Report
----- XXXX Diagnostics ------
Blood Gas Report
248 05:36 Jul 22 2000
Pt ID 2570 / 00
Measured37.0
o
C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Corrected38.6
o
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 %
Measured Values
Temperature Correction:
Is there any value to it?
Calculated Data:
Which are the useful ones?
Entered Data:
Derived from other sources
14. Traditional Measurements
pH electrode
pCO2 electrode (Severinghaus)
pO2 electrode (Clark)
Additional options include:
Co-oximeter; measures O2 saturation
Na
+
, K
+
, Ca
2+
, Cl
-
Haematocrit
15. ----- XXXX Diagnostics ------
Blood Gas Report
Measured37.0
o
C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Corrected38.6
o
C
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 %
t 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 %
Bicarbonate is calculated on the basis of
the
Henderson equation:
[H
+
] = 24 pCO2 / [HCO3
-
]
or
for the mathematically inclined…
Bicarbonate:
Henderson-Hasselbach equation:
pH = pKc + Log [HCO3
-
]
a pCO2
16. Steps of evaluation
• Step 1:- Check the validity of the report
• Step 2:- Identify the most obvious disorder
• Step 3:- Apply the formulae to determine
whether compensation is adequate. If not a
second disorder coexists.
• Step 4:- Calculate the anion gap
17. Checking the Reports Validity.
• Calculate H+ ion concentration from the
formula.
• H+ = 24 X pCO2/HCO3
-
• This should correspond to the H+ ion
concentration of the pH in the ABG report.
21. Appropriate compensation in simple acid
base disorders
• Metabolic acidosis-
Pco2=(1.5XHCO3)+8-/+2
• Metabolic alkalosis
Pco2= o.7x HCo3+21+_1.5
anand tiwari
22. Change in Ph
• For every increase in Paco2 of 20 mm Hg (2.6
kPa) above normal-
• mal the pH falls by 0.1
• x For every decrease of Paco2 of 10 mm Hg
(1.3 kPa) below normal
• normal the pH rises by 0.1.
• *Any change in pH outside these parameters
is therefore metabolic in origin.
23. Respiratory acidosis: < 24 hrs: D [HCO3] = 1/10 D PCO2
> 24 hrs: D [HCO3] = 3/10 D PCO2
Respiratory alkalosis: 1- 2 hrs: D [HCO3] = 2/10 D PCO2
>2 days: D [HCO3] = 6/10 D PCO2
REF-Text book of Hall criticare
anand tiwari
24. Case 1.
• 51 yr old found unresponsive at home past
history of D.M,HT.medications-
Metformin,hydrochlorothiazide,Lisinipril.
• b/p-120/70,HR-96/min.
• ABG-7.11,Paco2-28.4,pao2-86,room air
• Na 137,hco3-9,cl-90,BUN-116,CRE-
7.2mg%,Albumin-3.9gm%,bl gl-906mg%
25. ----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0
o
C
pH 7.301
pCO2 76.2 mm Hg
pO2 45.5 mm Hg
Calculated Data
HCO3 act 35.1 mmol / L
O2 Sat 78 %
pO2 (A - a) 9.5 mm Hg D
pO2 (a / A) 0.83
Entered Data
FiO2 21 %
Case 2
60 year old male smoker
with progressive
respiratory distress
and somnolence.
D CO2 =76-40=36
Expected D pH = 36/10 x0.08=0.29
Expected pH = 7.40-0.29=7.11
Chronic resp. acidosis
pH <7.35 ; acidemia
pCO2 >45; respiratory acidemia
Limits:
DHCO3 = 3/10 of D pCO2
=3/10x36=10.8
Limits of HCO3 = 24+11=35
Pure Resp Acidosis
Hypoxia
Normal A-a gradient
Due to hypoventilation
26. Case -- 1
• A middle aged female leukemia admitted to Intensive
care with respiratory failure required invasive
ventilation.
• ABG sample collected after one hour of ventilation
on Fio21 MV-8.0
lits, R.r-16/min on siemens ventilator.SpO2 on pulse
ox-96%
anand tiwari
27. Treat the patient!!!
• Ph-7.293
Pco2-39.2mm of hg
Po2-11.1mmof hg
Hco3-act-18.6mmol/l
Hco3-std-16.6mmol/l
Tco2-19.8mmol/l
BEvt=-7.4mmol/l
BE vv=-8.0
anand tiwari
Sr Electrolytes-Na+=127.3
mmol/l
K+=5.16
cl-=88mmol/l
How will you explain low po2
disparity with spo2?
–
LAB
WBC—297000/ul
Hgb-10 gm/dl
Hct-23.4%
Plt--108
29. Learning point---
• Be aware of “leukocyte larcency” (aka
pseudohypoxemia)—phenomenon of
artificially
• low pO2 on ABG due to markedly increased
O2 consumption by malignant leukocytes
• -in these instances, pulse oximetry often a
better measure of oxygenation
Majhail NS, Lichtin AE. Acute leukemia with a very high leukocyte count: confronting a medical
emergency. Cleve Clin J Med. 2004 Aug;71(8):633-7.anand tiwari
30. Case 2
18yr old asthmatic 3 days of
cough,dyspnea,orthopnea,not
responding to bronchodilators.
ABG-Ph-7.24
PCO2-49.1
PO2-66
HCO3---18 sat 92%
Calculate A-a Gradient
32. Case 3
• A 29-year-old previously healthy female, is
admitted in semiconcious state. She has c/o
fever,sweating and vomitting for last one day.
Following is her ABG (Fio2-.21) and biochemical
report.
anand tiwari
PH - 7.38
> PCO2- 24
> PO2 - 96
> HCO3- 16
> Sr.Sodium - 138 meq/l
> Sr.Potassium - 3.7 meq/l
> Sr.Chloride - 102 meq/l
> Blood Sugar - 48 mg%
> BUN -32 meq/l
> Sr.Creatinine - 1.5 meq
33. • Causes of metabolic acidosis with
hypoglycemia are:
Alcohol intoxication, seizures, Advanced liver
failure, acute adrenal insufficiency, myxedema coma,
severe malaria, starvation ketoacidosis and drug
intoxication such as metformin, salicylates,
anand tiwari
34. Learning point
• the abnormalities here are: High AG Metabolic
acidosis with respiratory alkalosis with
Hypoglycemia In given scenario the likely causes are:
1. severe malaria/cerebral malaria.
2. Quininie toxicity.
3. Salicylate toxicity
anand tiwari
35. Case 4
• ABG was taken from patient who presented
with abdominal pain and vomiting.
• Ph-7.31
• Pco2-45.7 Na-142,k-3.7,cl-91
• Po2-98.1
• Hco3-22.3
• Base excess=3
36. Case 5
• Young male patient of recurrent seizures was
on regular intravenous doses of
benzodiazepine lorazepam for control of
convulsion dose was reduced on day 7 as
spasm came under control
anand tiwari
37. • Biochemical profile of above patient
anand tiwari
Measured
serum
osmolarit
Day1
290
Day4
300
Day7
315
Day10
298
calculated 285 281 284 286
Plasma
lactate
2.1 4.9 2.9
“
Likely explanation for change in osmolar gap
39. Case -- 5
• 63 year old female with history of CHF presented to
ER with c/o
• shortness of breath over preceding 2 days
• Fever
• Cough with thick yellow sputum
• Past history hypertension and chf treated with furosemide
20mg/day digoxin 0.25mg/day
anand tiwari
40. • Lung right sided basilar crackles
B.P 140/80
HR-100/MIN
R;R-30/MIN
TEMP 39*
Lab-TLC 14000
HGB 13
NA 139
K-3.4
CI-98
ABG
PH-7.59
PCO2-30
PO2-58
HCO3-29
Chest x ray –lobar infiltrate in right lobe
Sputum exam stain – gpc diplococci and
anand tiwari
41. • Initial presentation is alkalemia pc02 decreased but
bicarbonate is at upper end of normal so combined metabolic
alkalosis +respiratory alkalosis
• History gives a clue that chronic metabolic
alkolosis due to diuretics and acute respiratory
alkalosis is due to pneumonia
anand tiwari
42. • She is started on antibiotic therapy with o2 supplementation
• 12 hours later she complains of increased shortness of breath
ABG
Ph-7.40
Pco2 48
P02 44
Intubate and ventilated tidal vol 600 R.r 16
Fio2 1
Peep-5
ABGg
Ph-7.24
Pco2 38
Po2-86 hco3 16
Anion gap 23
Sr lactate 8 mmol/lit
anand tiwari
43. • As patient developed ventilatory failure ABG showed
normal Ph and respiratory acidosis ie balanced by
chronic increase in bicarbonate level.
• As sepsis developed acidemia with decreased
bicarbonate level and increased anion gap
anand tiwari
44. • Over a period clinical condition improved a she was started on
TPN,dobutamine dicontinued and furosemide 40mg/day
• Her oxygenation continued to improve but
ABG
PH-7.55
PCO2-44
HCO38
Furisemide dicontinued
Acetozolamide begun
ABG
PH-7.6
PCO2 46
HCO3 44
anand tiwari
45. • Her final acid base disorder is severe alkalemia
of metabolic origin
• Was initially thought to be due to diuretic but
found after searching all medication and
substances administrated that patient
parental nutrition contained 70 meq of
acetate /litre
• Acetate –biacarb load –na avidity –
hypochloremia –vol deficit
anand tiwari
46. Final word
Effects of preexisting disease state may exacerbate
or mitigate degree of Ph change
Acid base equilbrium in ICU is dynamic system and
multiple disorders may occur simultaneously.
Look for the underlying cause
Unexplained disorder should prompt through search
of all administrated substances
anand tiwari