Measuring blood lactate
Dec 29, 2015
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