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Determination of Hb mass by CO rebreathing Christoph Siebenmann Outcome CO rebreathing Total number of hemoglobin molecules Total (g/dl) hemoglobin mass (g) Total red cell Plasma volume Total blood volume (l) (l) volume (l) Changes

SLIDE 1

Determination of Hbmass by CO rebreathing

Christoph Siebenmann

SLIDE 2

Outcome

CO rebreathing Total number of hemoglobin molecules Total hemoglobin mass (g) (g/dl) Total red cell volume (l) Plasma volume (l) Total blood volume (l)

SLIDE 3

Endurance training Anemia Heat acclimatization EPO Diuretics RCV ↓ PV → RCV → PV ↑ RCV ↑ PV ↑ RCV ↑ PV ↓ RCV → PV ↓

Changes in intravascular volumes

SLIDE 4

The dilution principle

?

1. 2. Volume of water = x Volume of sirup = n Sirup concentration = c c = n / x x = n / c x = 500 ml / 50 ml/l = 10 l Sirup 500 ml Sirupometer (ml of sirup / l) 50 ml / l 3.

SLIDE 5

For solid objects

?

Volume of water = x Volume of sirup = n Sirup concentration = c Total number of fish = x Number of tagged fish = n Fraction of tagged fish = c

1. Tag a known number of fish
2. Release fish (”mixing”)
3. Count the fraction of marked fish

c = n / x x = n / c x = 20 / 0.2 = 100 20 4/20

SLIDE 6

For hemoglobin

SLIDE 7

CO rebreathing

1. Tag
2. Mix
3. Count tagged fraction

FCOHb pre (%) FCOHb post (%) 10 min

Change

SLIDE 8

The setup

Siebenmann et al., 2017

SLIDE 9

Measurement routine

=> Standardize conditions

Place catheter
Provide 0.5 l of water
1. Subject supine

(20 min)

2. Open circuit breathing

(4 min)

3. Closed circuit rebreathing

(10 min) => Wash N2 from airways

Fill CO syringe

=> Take up/mix CO

Collect blood (Pre)
Administer CO
Collect blood (Post)

SLIDE 10

Calculations

After the rebreathing you know:

∆FCOHb (=FCOHbpost - FCOHbpre)
Volume of absorbed CO (VCO)
Hct
[Hb]
Temperature
Barometric pressure
Molar weight of Hb (6.44 × 10-4 g/mol)

SLIDE 11

Hbmass

Number of absorbed CO molecules (nCO)

= barometric pressure × VCO / (R × T)

Number of tagged Hb molecules (nHbtagged)

= nCO / 4

Total number of Hb molecules (nHbtot)

= (nHbtagged / ∆FCOHb) × 100 %

Hbmass

= nHbtot × 6.44 × 10-4 g/mol => pV = nRT

SLIDE 12

Deriving volumes

Blood volume

= Hbmass/[Hb]

Total red cell volume

= Blood volume × Hct

Plasma volume

= Blood volume – Red cell volume

Hct = RCV / BV

SLIDE 13

Circulatory CO distribution

?

Overestimation Underestimation

SLIDE 14

Distribution concerns

CO →

Mixing time ”Pockets”

SLIDE 15

Garvican et al., 2010

Mixing time

Arterial Capillary Venous

SLIDE 16

”Pockets”

Blood pooling Splenic storage

Underestimation
Variability
Underestimation (up to 10 %)
Variability

SLIDE 17

Exercise on CO distribution

p = 0.017

Keiser et al., 2013

SLIDE 18

Mixing with tilt table

SLIDE 19

Safety

➢ Subject safety ➢ Room contamination

SLIDE 20

Subject safety

Serious symptoms start at %HbCO of 20 – 25 %
%HbCO post usually < 10%

4 h %HbCO = 8% BUT:

Limited exercise capacity
Provide washout time

Heavy smokers: 10 – 15%

Washes out within 24 hours

SLIDE 21

Prevent room contamination

To the CO cylinder To the window Filling button Emptying button Stopper

SLIDE 22

Thank you

SLIDE 23

Accuracy and precision

Accuracy Precision Comparison to reference method Typical measurement error

Thomsen et al., 1991

24 h (Standard deviation of differences) / √2 Usually < 2 %

SLIDE 24

Determination of unabsorbed CO

1. Subject exhales completely
2. Subject is disconnected
3. Determine remaining volume
Pulmonary dead space (formula)
Closed circuit dead space (measured)
Volume in rebreathing bag (extract)
4. Measurement of CO concentration in

remaining volume

5. Multiply remaining volume with CO

concentration Alternatively: use 2.2 % as estimate