Presentation Menu

• Sources of pre-analytical CO-Oximetry error and

strategies for reducing error

• Potential analytic error sources

• Spectrophotometry and CO-Oximetry principles

and methodology

• Measured and calculated values

• Hemoglobin and oxygenation

• CO-Oximetry case studies

2

Medicare Study on Medical Error Published in November 2011 (Dept of Health and

Human Services)

Medical Harm

• 134,000 Medicare beneficiaries experience

harm from medical error each month

• 1.6 million harmed each year

Mortality

• 15,000 or 1.5% die from causes associated

medical error each month

• 180,000 deaths each year (nearly 500/day)

3

Lab Errors

Approximately 80% of clinical

treatments are based upon lab test

results

Reduction in Lab errors will help

reduce medical treatment errors

4

How important is Pre-analytical

Error?

• Historically, most effort, regulations and

expense on related to analytical QC

• However, 75% of error in blood gases from

pre-analytical factors1

1. Bonini, et al. Errors in laboratory medicine;

Clin Chem 2002 48, 5. 691-98.

5

Blood Gas Analysis

Yields results for

• Acid-Base

• Partial Pressure

• pCO2

• pO2

• Gas exchange

• Electrolytes • Metabolites • Hematocrit

Does not result

• Hemoglobin

• Dyshemoglobins

• Oxygen Volume

• Oxygen Dissociation

• Oxygen Delivery

• a-v content

difference

6

Reducing Pre-analytical Error

• Many of the same factors that produce error in

Blood Gases contribute to CO-Oximetry errors,

making handling requirements similar.

• However, there are some special considerations

associated with handling and evaluating CO-

Oximetry samples and results

7

Potential CO-Oximetry Errors

Pre-analytic

• Inadequate mixing

• Liquid heparin dilution

• Trapped air (O2Hb & O2 content error)

• Venous admixture (O2Hb & O2 content error)

• Metabolism/icing for storage & transport

• Insufficient line waste draw

• Plastic blood collection tubes with gel separator cause + COHb bias

• Extracellular fluid contamination (capillary sampling)

Analytic

• Interfering light absorbing substances

• High lipid content in sample

• Atypical hemoglobin

• Blood Gas HCT (biased if abnormal level of serum protein )

8

Pre-analytic Error: Improper mixing

Sepsis

Multiple myleloma

Lupus erythematosus

Rheumatoid arthritis

Inflammatory bowel disease

Vasculitis

Chronic kidney disease

Chronic infections

Infective endocarditis

Tuberculosis

Kawasaki’s disease

Many other conditions

9

Whole blood samples sediment rapidly.

Sedimentation rate higher in inflammatory

conditions:

Proper mixing technique can reduce Hb

and O2 Content errors

Pre-analytic Error: Improper mixing

Proper mixing also prevents sample coagulation

and microclots, which can cause erroneous tHb

values.

Heparin can prevent clots, but cannot reverse

clotting.

10

Sample Mixing Recommendation

From: CLSI document, C46-A2 Vol 29 No 8.

Blood Gas and pH Analysis and Related Measurements, Approved

Guidelines, Second Edition.

5.3.4 Specimen Mixing Prior to Analysis

• Remove air bubbles and mix sample ASAP

• Mix for minimum of one minute prior to analysis

• Mix for longer periods if analysis is delayed

• Shorter mixing interval may be used if less than 2 minutes from sample

draw

• Gently mix sample in two axes

11

Pre-analytic Error: Liquid heparin dilution

• Liquid heparin in deadspace volume of sample

syringe (0.05ml) can dilute sample, lowering Hb

• Recommendation: Use dry heparin prepared syringes

12

Sample Size 1.0 ml 0.5 ml 0.25 ml

Heparin ml 0.05 ml 0.05 ml 0.05 ml

% Dilution 5% 10% 20%

Actual Hb 12 g/dL 12 g/dL 12 g/dL

Reported Hb 11.4 g/dL 10.8 g/dL 9.6 g/dL

Pre-analytic Error: Liquid Heparin Dilution

• Liquid heparin has a lower pH than most

samples and can reduce sample pH, which

shifts oxyhemoglobin curve to right.

• This effect can lower reported O2Hb and O2

content.

• The smaller the sample, the greater the effect.

• Recommendation: Use dry-heparin-prepared

syringes

13

Pre-analytic Error: Trapped Air

• Trapped air primarily effects pO2, %O2Hb and

O2 Content

• Trapped air pO2 decreases with altitude

– 160 mmHg at sea level

– 130 mmHg at 1 mile elevation

• Trapped air can significantly lower or raise

sample pO2, %O2Hb and O2 Content

14

Pre-analytic Error: Trapped Air

• Volume of air/volume of blood

• Agitation (e.g. pneumatic tube transport)

• Number/size of bubbles (surface area effect)

• Time of exposure

• Initial pO2 of sample

• Hb/O2Hb%

– Oxygen buffering effect of Hb

– More pronounced at lower Hb levels

15

Pre-analytic Error: Venous Admixture

Blood

Volume (ml) pO2

SO2 Cal

@ 7.40

Arterial 4.5 86 96%

Venous 0.5 31 60%

Mixed 5.0 56 88%

Malley, WJ. Clinical Blood Gases Assessment and

Intervention, Second Ed. St. Louis, Elsevier Saunders, 2005. 16

Venous admixture occurs from

inadvertent inclusion of venous blood

with arterial draw.

Pre-analytic Error: Storage/Transportation

Iced/Non-iced

• Ice slurry (metabolic inhibition) – Helps preserve pO2 , pH, pCO2, glucose & lactate

– Can cause pO2 increase in samples collected in plastic syringes

• CLSI recommendation – Do not ice samples if analysis will occur in < 30 minutes

– Ice samples if analysis will occur > 30 minutes

17

Pre-analytic Error: pO2, %O2Hb & O2 Content (All calculations at pH 7.40 and Hb 15g/dL)

pO2

mm Hg

%O2Hb O2 Content

vol%

150 99 21.1

100 97.2 20.6

80 95.2 20.1

55 88 18.5

40 75 15.7

26.5 50 10.5

18

Practices that minimize changes to pO2 help to preserve %O2Hb

and O2 Content accuracy

Pre-analytic Error: Catheter Flush

• Arterial and venous catheters must be adequately

flushed prior to sample draw

• Inadequate flush volume will bias sample with contents

of flush solution lowering Hb/Hct and altering O2Hb

• 2 x catheter deadspace volume is recommended for

waste draw volume

19

Recommendations: Collection &

Storage of Blood Gas Samples

• Expel air immediately and completely

• Mix thoroughly in 2 axes after draw and

before analysis

– Longer mix time for delayed analysis

• Measure < 30 minutes - room temperature*

• Measure > 30 minutes - ice/water slurry*

*CLSI document H11-A4, Vol 24 No 28. Procedures for the Collection of Arterial

Blood Specimens

*

20

CO-Oximetry: Capillary Samples

• Capillary samples show more variability than

arterial or venous samples

• Variability is most often associated with

squeezing puncture site or not allowing alcohol

time to dry before puncture

• Poor peripheral circulation and edema (not

always obvious) can contribute to variability

21

CO-Oximetry: Capillary Samples

• Properly “arterialized” sample will yield pH and pCO2 that

are close to ABG and pO2 & O2Hb that are somewhat

lower than arterial

• Site should be pre-warmed up to (42C), increases flow

up to 7X

• Free-flowing sample

– “milking” introduces venous blood and interstitial fluid

• Completely filled, air free tubes, with sealed ends

• Should be analyzed within 15 minutes Adapted from:

AARC Clinical Practice Guideline: Capillary Blood Gas Sampling for

Neonatal and Pediatric Patients

22

Hemoglobin: Structure & Function

• Hemoglobin has a complex structure with 4 iron

containing heme groups (porphyrin rings) combined with

4 protein groups know as globins

• Each heme group has a central iron molecule in the

ferrous state Fe2 which can reversibly bind with an O2

molecule

• The globins are designated as alpha (141 amino acids)

and beta (146 amino acids) beta chains in HbA

• The molecular weight of Hemoglobin is 64500

• Each RBC carries approximately 280 million molecules

23

Hemoglobin Structure

24 © 1996–2012 themedicalbiochemistrypage.org, LLC

Hemoglobin: Structure & Function

• Hb structure changes in relation to physicochemical

environment as RBCs transit through body

• Structural changes are governed by reversible chemical

bonds and interactions between heme and globin groups

• These environmentally induced structural changes allow

Hb to change affinities for O2, CO2 and H+

– Releases oxygen, picks up carbon dioxide & H+ in tissues

– Buffers & carries oxygen, carbon dioxide and H+

– Picks up oxygen, releases carbon dioxide and H+ in lungs

25

Hemoglobin: Variants and Species

• Hb variants have globin chains that differ from the 2

alpha and/or 2 beta chains of HbA

• Hb variants are normal in fetal development (HbF) but

can also be present in abnormal mutant forms such as in

Sickle-cell anemia (HbS). If variant causes disease, it is

considered a hemoglobinopathy

• Adult hemoglobin (HbA) is the most common form and

typically at 95% or more

– HbA2 (2 alpha & 2 delta)also present at 1.5 to 3.5%

– HbF some presence in adults, elevated in thallasemia

26

Hemoglobin: Variants some examples

• Fetal Hemoglobin HbF (2 alpha 2 gamma) HbF has greater affinity for O2 than HbA which facilitates O2 transfer

across placenta

– At 10 weeks gestation 90% of hemoglobin is HbF

– At term 80% HbF and 20% HbA (more HbF in preemies)

– 50% HbF at 1 to 2 months

– 5% at 6 months to < 2% (adult level) after 6 months

• Due to the spectral differences, for samples containing fetal

hemoglobin, CO-Oximetry calculations based on adult hemoglobin

algorithms may result in inaccurate hemoglobin fractions. Measured

HbF eliminates this type of inaccuracy.

27

Hemoglobin: Variants some examples

• Sickle Cell HbS (2 alpha and 2 betaS) glutamate

is substituted for on beta position 6 for valine

• HbS crystallizes in hypoxia, acidosis and

hypothermia

• During sickle crisis RBCs form sickle like

structures and cause vaso-occlusion in

microvasculature

28

Hemoglobin: Variants some examples

• Over 120 variations of hemoglobin have been

identified. Some cause no discernible pathology,

while others such as HbS are considered

hemoglobinopathies.

• Some variants are designated with letters and

others are designated by region in which they

were discovered e.g. Hb St Louis, Hb Ranier

• Some variants can cause CO-Oximeter

absorbance errors

29

70*

Oxyhemoglobin Dissociation Curve

30

Hemoglobin: Species (derivatives)

Functional and dysfunctional forms of HbA

• Total Hemoglobin (tHb g/dL) – Units g/dL = grams/deciliter or grams/100 mL blood

• Hemoglobin Species (derivatives) – Units – fractions (example 0.88 O2Hb) or % (88% O2Hb)

– All Hemoglobin species should add up to approximately 100%

– Functional:

• Oxyhemoglobin (O2Hb)

• Reduced or Deoxy Hemoglobin (RHb or HHb)

– Dysfunctional (will not bind with O2)

• Carboxyhemoglobin (COHb)

• Methemoglobin (MetHb)

– Interference

• Sulfhemoglobin (SulfHb)

• Cyanmethemoglobin (CNmetHb)

31

Spectrophotometry Method

• Based upon optical absorbance of various

hemoglobin species

• Hb structure changes with chemical changes

• Hb species absorb and transmit (reflect light)

• We see reflected light

– Oxyhemoglobin bright red

– Deoxyhemoglobin dull red

– Carboxyhemoglobin cherry red

– Methemoglobin muddy red

32

Spectrophotometry Method

• Some pulse oximeters use 2 light wavelengths

• Blood CO-Oximeters employ multiple wavelengths

• 2000 wavelengths in GEM Premier 4000

• Light scattering can cause analytic error

– Lipids and light absorbing substances

– Cell membranes

• Potential for analytical error reduced by using multiple wave

lengths, digital detectors and by hemolyzing the sample

33

CO-Oximetry (1960s)

Spectrophotometric measurement: • tHb (total hemoglobin)

• O2Hb (oxyhemoglobin)

• COHb (carboxyhemoglobin)

• MetHb (methemoglobin)

• HbF (fetal hemoglobin)

• HHb (reduced or deoxyhemoglobin)

Calculated values: • SO2m

• cO2 (O2 Content) & a-v O2 Content difference

• O2 Capacity

34

GEM 4000 CO-Oximeter Optics

The sample spectrum between 480 to 650 nm is analyzed for CO-

Oximetry using approximately 2,000 wave lengths

35

CO-Oximeter: Interference Detection

Substance Affected Analyte (s) Interference

Concentration

cyanocobalamin CO-Oximetry 0.75 g/L

hyroxycobalamin CO-Oximetry 0.75 g/L

sulfhemoglobin CO-Oximetry 10%

turbidity (lipid) CO-Oximetry 2500 mg/dL

Specifications for GEM Premier 4000: technical capabilities vary

by manufacturer

36

CO-Oximetry: Measured & Calculated Values

Measured Values

• tHb

• %O2Hb

• %COHb

• %MetHb

• %HHb

Calculated Values

• %SO2m

• O2 Content ml O2/dL

– Arterial, venous or cap

• O2 Capacity

• a-v Content difference

37

Total Hemoglobin: tHb

• Sum of all hemoglobin derivatives in g/dL

tHb = O2Hb + COHb + MetHb + HHb

• Hemoglobin measurements are less affected by lipids or

hemolysis and provide accurate hemoglobin status as

compared to hematocrit measurements (BG analyzer)

tested during cardiac bypass surgery (CBP) with

cardioplegic solutions

• Hematocrit = tHb x 3 or Hb = Hct ÷ 3 (typical relation)

• Normal range:

11 – 17.4 g/dL (110-174 g/L)

38

Hemoglobin/hematocrit

• Hematocrit: Blood gas analyzers use

conductivity to measure hematocrit

• Electrical current passes through blood

– Electrolytes & charged proteins conduct current

– Blood cells resist current

39

Conductive hematocrit

• Conductimetry usually accurate • Sources of error:

– Protein: Conductivity method assumes normal serum protein

(low protein = under-reported Hct)

– Causes of abnormal serum protein

• Malnutrition, IBS, Celiac disease

• Liver failure, nephrotic syndrome

• Cardiopulmonary bypass (crystalloid volume expanders)

– Negative bias effect is more pronounced at Hct < 30%

– Extreme Na concentrations (effects red cell volume and

conductivity)

– Hyperlipidemia 1,000 mg/dL increase = 0.3% Hct increase

– Polycythemia

40

Conductive HCT: potential for error

Effects of protein changes: “Protein molecules, like red cells, offer mechanical interference to the

passage of an electrical current through the solution, hence, when

protein content of blood is diminished with crystalloids, conductivity

will increase. In other words, when protein concentrations are

decreased during CPB by hemodilution, conductimetric

measurements will give a value for hematocrit that is falsely lower

than the actual hematocrit of that sample”

41

Hemoglobin:

• Hemoglobin does what it needs to do, where it needs to

do it, when it needs to do it.

– Releases oxygen, picks up carbon dioxide & H+ in tissues

– Buffers and transports oxygen, carbon dioxide and H+

– Picks up oxygen, releases carbon dioxide in lungs

42

Hemoglobin and oxygenation

HEMOGLOBIN

Picks up O2 in lungs

Carries O2 in vascular system

Releases O2 in tissues

43

Oxygenation

pO2 important in Hb oxygen loading/unloading

pO relatively minor contribution to volume of

oxygen, as measured by oxygen content

Oxygen Content (volume) primarily determined by

Hb and O2Hb%

44

Oxygenation Assessment

pO2 mmHg (O2 diffusion pressure or loading

pressure)

Oxygen Content (Oxygen volume carried in blood

tHb and O2Hb)

Cardiovascular (Cardiac output and perfusion)

45

Oxygen Content

O2 content =

(Hb g x 1.39ml O2/g) x O2Hb% + (pO2 x 0.003)

Example:

Hb=15 g/dL O2Hb%=98 pO2=100 mmHg

15 x 1.39 x 0.98 = 20.4 ml O2 combined with Hb

100 x 0.003 = 0.3 ml O2 dissolved in plasma

O2 content: 20.4 + 0.3 = 20.7 ml O2/dL

46

Oxygen Content

O2 Content 20.7 ml O2/dL

Contribution from O2Hb 20.4 ml (98.5% of total)

Contribution from pO2 0.3 ml (1.5% of total)

Normal Arterial O2 Content

15-24 ml/dL (vol%)

Normal Mixed Venous O2 Content

15-19 ml/dL (vol%)

47

Oxyhemoglobin (O2Hb%)

• 94 - 97% arterial

• 40 - 70% venous

• Hb = O2 sponge

• O2Hb% is normally < SpO2 pulse oximetry or

SO2 (calculated sat) from blood gas analyzer

• Measured to assess oxygen saturation (sO2)

and oxygen content (ctO2) & a-v cont. difference

48

Hb loading and unloading O2

O2 reversibly bound to Hb - influenced by:

• pH

• pCO2

• pO2

• temperature

• 2-3 BPG

49

Hb and O2 Relationship is Unpredictable

• Normally occurring factors

pH, pCO2, temperature, 2-3 BPG

• Pathological problems

• Presence of dyshemoglobins (COHb, MetHb)

• Phosphate metabolism, anemia

• Presence of variant hemoglobins

50

O2Hb Dissociation Curve

Left Shift

O2 uptake

O2 release

= Lungs

pH pCO2

temp

2-3 BPG

= P50

Right shift

O2 uptake

O2 release

= Tissues

pH pCO2

temp

2-3 BPG

= P50

51

Altered oxygen affinity

Cause left shift in O2Hb

• Carboxyhemoglobin

COHb

• Methemoglobin

MetHb

• Sulfhemoglobin

Sulf Hb

• Hb Rainier (L shift)

• Hb Seattle (R shift)

• Hb Kansas (R shift)

• Hb St. Louis (L shift)

• Hb Sickle (hypoxic

crystallization)

Other:

• HbFetal (L shift)

• Myoglobin (L shift in tissues)

52

Dyshemoglobins

Variant Hemoglobins

53

Deoxyhemoglobin, HHb

• Also known as Reduced Hemoglobin (RHb)

• HHb does not carry O2

• Able to pick up and carry oxygen when it is available

(functional Hb)

• Due to various factors, not all hemoglobin is oxygenated

in the lungs leaving a small amount of HHb in arterial

blood

54

CO-Oximeter: Calculated Value %SO2m

• %SO2m 100 x [O2Hb/(O2Hb+HHb)], where HHb = 100-(O2Hb+COHb+Met Hb)

• %SO2m expresses O2Hb as a ratio of Hb that is

available to carry oxygen

• %SO2m will be higher than %O2Hb and

%SO2cal (calculated from pH and pO2)

55

CO-Oximeter: Calculated Values

• O2 Content (arterial, or mixed venous) CaCt or CvCt

(Hb g x 1.39ml O2/g) x O2Hb% + (pO2 x 0.003)

• O2 Capacity

(Hb g x 1.39ml O2/g) + (pO2 x 0.003)

• a-v Content difference

CaCt – CvCt

Normally around 5 vol% (ml O2/dL)

56

Dyshemoglobins

Dyshemoglobins

Carboyxyhemoglobin (< 3.0% urban environment)

Methemoglobin (<2.0%)

Dyshemoglobins interfere with O2 delivery

1. Diminish the amount of Hb for carrying O2

2. Interfere with O2Hb ability to release oxygen

(left shift)

3. Carboxyhemoglobin reduces myoglobin affinity for oxygen

4. Severe tissue hypoxia can occur with normal or supernormal pO2

and/or Normal SpO2 (pulse oximetry) & SO2 cal

57

Carboxyhemoglobin

CO 200-250x affinity for Hb compared to O2

COHb blood has cherry red appearance

Cigarette and crack cocaine smoking (3-12% COHb)

Exposure to hydrocarbon combustion

TREATMENT

Tremendous variability in individual susceptibility

Half life: 2-5 Hrs on RA

1 Hr 20 min on 100% O2

23 min Hyperbaric O2 58

Carboxyhemoglobinemia

• Most common poisoning

• 15,000 ED visits in US

• 3,800 US deaths per year

• pO2 N-, pCO2 - N

• SpO2 N

• Headache common

• Syncope/coma at 40% COHb

• Treat with high % or hyperbaric O2

59

Carboxyhemoglobin: %COHb

Less common causes

• Exposure to Methylene Chloride

• Intrinsic CO production

– Abnormal rate of Hb breakdown

• AIHA (autoimmune hemolytic anemia)

60

Methemoglobin : %MetHb

Hb Ferrous iron (Fe2) oxidized to Ferric (Fe3)

HbMet blood has muddy red appearance

• Normal < 2.0%

• Hereditary

• Drug & chemical

Causes hypoxia by:

• Chemical anemia

• O2Hb left shift

61

Methemoglobinemia

• Hereditary - Type 1 & 2

• Liver failure

• Tylenol overdose

• Nitric Oxide (NO) therapy, toxicity marker

• Nitrate poisoning

• Sepsis

• Sulfonamide antibiotics

• Aniline dyes

• Toluidene (prilocaine breakdown)

• Benzenes

62

Methemoglobinemia

• Cyanosis: Non-responsive to O2

• SpO2 (varies)

• Fatigue, lethargy

• Headache, dizziness

• Dyspnea

• Coma (>50% MetHb)

• Treatment - Methylene Blue infusion (1-2 mg/Kg body weight)

63

COHb and MetHb

COHb% Clinical Manifestations

<5% None

5-10% Mild headache, tire easily

11-20% Moderate headache, exertional SOB

21-30% Throbbing headache, mild nausea, dizziness, fatigue, slightly impaired judgment

31-40% Severe headache, vomiting, vertigo, altered judgment

41-50% Confusion, syncope, tachycardia

51-60% Seizures, unconsciousness

MetHb% Clinical Manifestation

0-3% Normal concentration, no symptoms

3-15% Slight skin discoloration (palor, gray, or blue) may be present

15-20% Patient may be relatively asymptomatic, cyanosis likely

25-50% Headache, dyspnea, lightheadedness, weakness, confusion, palpitations, chest pain

50-70% Altered mental status, delirium

64

Sulfhemoglobin: SulfHb

• Sulfur bound hemoglobin; sulfur replaces the oxygen binding site

• SHb is incapable of binding oxygen (dysfunctional Hb)

• Caused by a number of drugs (sulfonamides, phenacetin, dapsone),

or industrial and environmental pollutants (sulfur dioxide, hydrogen

sulfide)

• Rarely reaches levels that are fatal

• There is no effective therapy and is reduced only by red cell

recycling (natural or by transfusion)

• SHb Detection and correction (varies with manufacturerer)

– SHb < 10%, CO-Oximetry results are corrected for SHb

– SHb > 10%, Flagged by iQM as SHb interference

–

65

Case Study 1

A 37 YO M was admitted to ED, with dizziness,

SOB, diaphoretic, severe headache and nausea.

BP and HR were moderately elevated.

No Hx of migraine, Normal HEENT, no neck or

back pain

pH 7.48, pCO2 32, pO2 96, HCO3 24, SO2c 98,

SpO2 99

After 2 hours, symptoms subsided and he was

discharged after 3+ hours in ED.

66

Case Study 1 (two weeks later)

Patient returned to ED with similar symptoms and

physical findings.

pH 7.49, pCO2 33, pO2 94, HCO3 23, SO2c 98,

SpO2 99

Hb 13.5, %O2Hb 73, %COHb 22, %MetHb 1%,

O2 Cont 14.0 vol%

Is this patient hypoxic?

67

Case Study 1

Blood Gas and Pulse Oximetry indicate normal

blood oxygenation

pO2 94, SpO2 99 & SO2c 98

CO-Oximetry reveals significant hypoxia

%O2Hb 73, %COHb 22

Carbon Monoxide Poisoning

68

Case Study 2

• 26 YO M hospitalized 3 for days with significant

SOB

• CXR- mild pulmonary vascular congestion

LLL infiltrate

mild cardiomegaly

• Nonsmoker

69

Case Study 2

• Chest CT scan revealed

– no mediastinal mass

– bilateral, multiple small scattered nodules

– small diffuse areas of hemorrhage

• Abdominal CT scan

– presence of splenomegaly

70

Case Study 2

– pH 7.23

– pCO2 48

– pO2 65

– HCO3 19.4

– Room Air

– Hb 6.0

– O2Hb% 89.3

– COHb% 9.2

– MetHb% 1.4

– O2 cont 7.5

71

Case Study 2

• COHb elevated

– Hemoglobin breakdown in liver

– Intrinsic CO production

72

Case Study 2

• AIHA

– Autoimmune Hemolytic Anemia

• Treatment

– Steroids

– O2 administration

– Splenectomy in severe cases

73

Case Study 2

• Hemolytic Anemia

– CO production from accelerated Hb breakdown

• Causes of Hemolytic Anemia

– Autoimmune hemolytic anemias (AIHA)

– Hereditary

• Hereditary spherocytosis

• Glucose-6-phosphate dehydrogenase deficiency G6PD

74

Case Study 3

• 81 YO M

• Repeat CAB x 5 vessels

• Five hours in surgery

• Received four units packed cells in surgery

• Platelets administered post-op

75

Case Study 3

• Post - Operative

– Ventilator support

– Balloon pump

– Four units packed cells

– Antiarrythmics required

– Critically low blood pressure

with max vasopressors and fluids

76

– pH - 7.20

– pCO2 - 46

– pO2 - 61

– Hb - 14.1

– %O2Hb- 92.3

– %SO2c - 84.9

– K+ - 3.3

– Na+ - 143

– Ca++ - 1.39

– Lac - 5.5

Case Study 3 Ventilator: 100% O2, f 14, VT 900

77

Case Study 3

• CO-Oximetry indicated - Left Shift HbO2 as

indicated by 92.3 %O2Hb > 84.9% SO2 cal

• Left O2Hb shift secondary to hypophosphatemia

(reduced level of 2-3 BPG) from stored blood

78

Case Study 3

• iv potassium phosphate administered

– Improved BP

– Improved oxygenation

• Hypophosphatemia

– Common in COPD

– Common in critically ill

– Can cause left O2Hb shift if severe, compromising

tissue oxygenation

79

Case Study 3

• Decreased phosphate in stored blood (decreased 2-3 BPG)

• Phosphate - 0.9 mg/dL (normal 2.5 - 4.5)

• Phosphorus needed for ATP production

– Cardiac Output

– Unstable Hemodynamics

• Hypoxia (from left shift) detected by comparing O2Hb% to %SO2Cal

80

Case Study 3

• Balloon Pump off in 4 hrs

• Weaned from vasopressors

• Weaned from ventilator in 48 hrs

• Discharged to home in 6 days

81

Summary

• Pre-analytical error for CO-Oximetry can be

reduced with knowledge, training and monitoring

staff practices.

• Adequate heparinization, good mixing

techniques and proper storage and handling

practices can be very effective in reducing error.

• CO-Oximetry can offer a more complete picture

in the evaluation of oxygenation status.

82