Measuring blood lactate

Lactate Lactate production is a

normal physiologic process and occurs in all animals its presence does not indicate

disease

A key indicator of hypoxia Correlates with mortality Lactate can also be used to

characterize fitness levels

SUGAR

OXYGENENERGY

CO2 and WATER

SUGAR

OXYGENENERGY

CO2 and WATER

LACTATE

Anaerobic conditions: without oxygen

Why do cells make lactate? Cells consume oxygen in a process that

produces energy When the oxygen supply is insufficient

(anaerobic conditions) cells produce energy by another pathway that results in the production of lactate

Lactate accumulation is the price to be paid for maintaining energy production under anaerobic conditions

A clinical example

Dog with gastric dilatation-volvulus (GDV)

A relatively common abdominal catastrophe requiring aggressive stabilisation and surgery

A vet’s nightmare

Gastric dilatation-volvulus

Rapid onset, profound vomiting Stomach twists about its axis

and ‘bloats up’ Respiratory difficulty Cardiovascular collapse

Gastric dilatation-volvulus

Lactic acidosis from hypoperfusion

Initial rise after restoring circulation

If it fails to fall rapidly, then you have not fully restored oxygen delivery

With GDVs, it is a strong indicator of likely outcome

+1 hour

+2 hours

+4 hours

+3 hours

Do not over interpret the result Vets (and owners) want

tests that tell them the likely outcome

Magnitude of elevation corresponds to the severity of the underlying problem

Generally, severe disease is associated with poor prognosis (likely outcome)

However, some severe diseases are easily treatable

Lactate trends

High lactate levels: the patient’s condition warrants aggressive treatment

Serial evaluation is a must A decreasing trend towards normal is a

good sign A rising trend in the face of aggressive

treatment is a very poor sign +1 hour

+2 hours+4 hours

+3 hours

BLOOD LACTATE

BLOOD GLUCOSE

LIVERMUSCLES

Blood lactate terminology

Blood lactate Lactic acid Lactate anion

Lactic acidosis - a common type of metabolic acidosis

Lactate-H+ ↔ Lactate- + H+

Lactic acid Lactic anion

Blood sampling

Arterial blood is best Venous blood drawn from

a central venous catheter is essentially equivalent

Restraint and prolonged venous occlusion can cause mild increases

Venous blood drawn from a peripheral site should be interpreted with caution

Handling blood samples

Do NOT use serum Separate plasma within 5

minutes lactate values can

increase if sample stay in contact with RBCs

Only useful if fast turn around

Avoiding confused vets

Does not replace acid-base analysis there are other types of metabolic acidosis does not look at respiratory component poor correlation between blood lactate

concentration and magnitude of metabolic acidosis

Avoiding confused vets

Hartmann’s fluid a.k.a. Lactated Ringer’s

Solution or Compound Sodium Lactate

a treatment for mild metabolic acidosis

lactate converted by the liver to bicarbonate

Respiratory/blood gases cassette

Respiratory/blood gases cassette Na+, K+, Cl-, HCO3

-, anion gap, pH, pCO2, TCO2, pO2

Use this cassette for patients with respiratory and cardiovascular disorders, advanced anesthetic cases and all patients on ventilators to improve their chances of success in critical situations.

Assess respiratory and breathing abnormalities Monitor cardiovascular and respiratory functions Assess a critical patient’s need for supplemental oxygen

immediately Monitor oxygen and respiratory function

Respiratory/blood gases cassette

Na+, K+, Cl-, HCO3-, anion gap, pH, pCO2,

TCO2, pO2

Electrolytes and acid-base (like the fluid therapy/acid-base cassette) but also gives pO2

Use this one whenever you are questioning the content of oxygen in the patient’s arterial blood

Why do we need to do blood gases?

An arterial blood sample is useful for assessment of:

1. alveolar ventilation

2. oxygenation

3. acid-base balance

Eight-year-old Labrador

Increased respiratory rate

Chest x-ray: no abnormality detected

Previously treated with oxygen

Our first example…

FiO2 Room air (21%)

pH 7.55

PaO2 112mmHg

PaCO2 25mmHg

HCO3- 20mmol/L

PCV 41%

Eight-year-old Labrador

Increased respiratory rate

Chest x-ray: no abnormality detected

Previously treated with oxygen

FiO2: fraction (%) of inspired

oxygen

Partial pressure of

oxygen

‘a’ indicates an arterial

sample

Partial pressure of

carbon dioxide

Percentage of haemoglobin molecules

carrying oxygen

Partial pressure of oxygen dissolved in the arterial

blood

Oxygen-haemoglobin dissociation curve

FiO2 Room air (21%)

pH 7.55

PaO2 112mmHg

PaCO2 25mmHg

HCO3- 20mmol/L

PCV 41%

How did the blood gas help?

High pH and low PaCO2 are consistent

with respiratory alkalosis

?pain ?fear Changed direction of

the treatment

Understanding oxygen content

PaO2 determines what percentage of the haemoglobin molecules carry oxygen

Think of oxygen as being in two “states”:

1) dissolved in the plasma2) in association with

haemoglobin Anaemia does not affect PaO2

PLASMA PLASMA+ RBCS

Oxygen dissolved in liquid

Small amounts Small amounts

Oxygen with haemoglobin

None Lots and lots

Total oxygen content

Small amounts Lots and lots

How much oxygen is in the blood?

Patient A Patient B

PaO2 mmHg 50 100

[Hb] g/DL

O2 content ml/DL

Patient A Patient B

PaO2 mmHg 50 100

[Hb] g/DL 15 10

O2 content ml/DL

How much oxygen is in the blood?

Patient A Patient B

PaO2 mmHg 50 100

[Hb] g/DL 15 10

O2 content ml/DL

17 13

How much oxygen is in the blood?

Adequate oxygenation

If the PaO2 is less than 70mmHg (further) oxygen therapy is required

Alternative methods of assessment are of limited use

Pulse oximetry Non-invasive, easy to attach Movement artifacts Few vets attempt to use this on

conscious patients

Mucous membranes

Pink is desirable!

A pale colour could be due to: drug induced vasoconstriction

poor peripheral perfusion

Cyanosis: takes 5g/dL of

unoxygenated haemoglobin

to generate the blue colour

Our second example

One-year-old Newfie

Very flat one day following surgery for a fractured femur

FiO2 21% (room air)

SpO2 Failed

pH 7.43

PaO2 92mmHg

PaCO2 22mmHg

PCV 21%

One-year-old Newfie

Very flat one day following surgery for a fractured femur

Using a pulse oximeter to estimate the % of

haemoglobin molecules in association with oxygen

FiO2 21% (room air)

SpO2 Did not attempt

pH 7.43

PaO2 92mmHg

PaCO2 22mmHg

PCV 21%

PAO2 calculated by

VetSTAT as 124mmHG

PAO2 - PaO2 =

32mmHg 10 to 20mmHg

considered normal

Assessing alveolar ventilation

High PaCO2 = hypoventilation

Low PaCO2 = hyperventilation

Capnography can provide a non-invasive estimate of PaCO2

only intubated patients

Our third example

Two-year-old spaniel

Rescued from the

river yesterday

Near-drowning

episode

Give oxygen via a

face-mask

FiO2 Face-mask (40%)

pH 7.22

PaO2 92mmHg

PaCO2 38mmHg

HCO3- 15mmol/L

Two-year-old spaniel

Rescued from the

river yesterday

Near-drowning

episode

Give oxygen via a

face-mask

As a rule-of-thumb, the PaO2 should be 4 to 5 times the percentage

inspired oxygen

Acidaemia if blood pH <7.3

Metabolic acidosis