Lactate

Lactate

Reference ranges

Lactate <0.8: not concerning 

Lactate 0.8-2.2: normal

Lactate 3+: raised

Physiology

Lactate is a marker of anaerobic respiration.  Energy can be produced either aerobically (Kreb Cycle- apologies for bringing that up!) or anaerobically via production of lactate or ketones. Aerobic respiration is derisable- more energy, more efficient and the main waste product is C02. An athlete's VO2 max refers to the maximum amount of oxygen their heart, lungs and blood are able to deliver to their tissues, hence the maximum amount of aerobic respiration able to be done. In theory one could exercise indefinitely, in a sense we do - all of our day to day activities are aerobic respiration. 

In the wild, however, sometimes a lion appears and the body needs an emergency method for producing more energy- after the aerobic pathway is maximised. This is anaerobic respiration. It produces less energy and with biproducts that require processing- lactate and also ketones. Athletes with talk about creating a lactate or oxygen debt from heavy exercise. This refers to continuous anaerobic respiration producing lactate, which requires respiratory compensation to prevent acidosis- i.e. mild tachypnoea to blow of CO2 (acidotic) to ensure a neutral pH. 

In summary a high lactate is a indication the body has maximiesed its production of energy aerobically and requires more energy from anaerobic respiration. 

Pathology

A lactate reference range is usually 0.8-2.2 and between 2-3 of debatable significance- a lactate of 3 and above is raised.  A raised lactate is associated with increased mortality and should trigger a small alarm bell. The cause of a raised lactate is in summary any unwell patient, a few listed below. 

In sepsis and pancreatitis a raised lactate is a marker of the body requiring more energy to fight the infection and may reflect septic shock/ hypovolaemia and is a marker of poorer prognosis. A very high lactate is classically associated with ischaemia (ischaemic bowel) as the bowel is unable to receive oxygen and relies upon anaerobic energy. 

Salbutamol and adrenaline can cause a transient raised lactate through autonomic stimulation, similar to recreational stimulants- cocaine, MDMA etc. Pericarditis can cause a raised lactate from the heart working harder and requiring more energy. 

Alcoholics can have chronically fluctuating lactates as damage to their liver and a poor diet ensures the body struggles to use glucose solely for energy production. 

Causes of a raised lactate:

(Any unwell patient)

1. Ischaemia- ischaemic bowel

2. Sepsis

3. Non infective inflammatory conditions- pancreatitis

4. Drugs- sympathetic stimulation: salbutamol bursts, adrenaline; recreational stimulatants

5. Pericarditis

6. Alcoholics 

7. Hypovoloaemia or hypervolaemia

Indications

Any acutely unwell patient

Infection ?sepsis

Rule out bowel ischaemia- significant abdo pain

I am a big fan of lactates. They are commonly done with a VBG however can also be done formally with a grey tube. I like to see a normal lactate in any patient who is mildly unwell with an infection- tachycardia/ tachypnoea/ febrile, particularly if their BP is low. 

Doing a lactate on every abdominal pain is likely overkill but certainly any abdominal pain requiring morphine isn't bad practice. 

When seeing an acutely unwell patient on the ward (rapid, periarrest calls etc) I have a very low threshold for a VBG in part for the lactate. 

Management 

A raised lactate should be repeated to ensure resolution. If a cause is known and the patient looks well some would argue this is over cautious however it is to check if this is up trending. 

There is debate about whether a raised lactate indicates a septic/ pancreatitic patient is hypovolaemic. It is regardless important to ensure they are euvolaemic thererfore I would attempt to achieve this and repeat the lactate. Some lactates will resolve and this is reassuring to slow IVF down, if the lactate persists I may try more IVF but if it continues to persist then there is questionable benefit chasing the lactate with quick IVF. 

In summary a raised lactate is marker of poor prognosis and may indicate hypovolaemia. It is often worth trialing IVF and this may resolve the lactate but some lactates persists in euvolaemia states and aren't worth chasing.