At some point the words lactic acid or acidosis has been put forth in a firefighter class on cardiac arrest, fitness or maybe in a heat cramps lecture. You hear lactic acid and lactate used interchangeably by fire and EMS educators or those talking about acidosis as a reference to muscle breakdown.
The truth is that there is a difference between lactate and lactic acid.
Your body produces lactate in response to aerobic exercise; it serves as a fuel for the muscles, delays fatigue and prevents injury. Lactic acid contains one additional proton and is not produced during exercise, but from carbohydrate metabolism in the absence of oxygen.
Lactate does not cause muscle burning. It is actually a fuel source that keeps the muscles going until they are fatigued. Lactate also does not cause acidosis in the muscle, but helps alleviate it by transporting the hydrogen ion out of the muscle making lactic acid into lactate.
During hard exercise and exertion from firefighting efforts, breathing increases to deliver more oxygen to the working muscles. Some aspects of firefighting are so intense that your body cannot use oxygen fast enough to create fuel.
For these quick, intense bursts of activity, your body needs to move into anaerobic metabolism. During anaerobic metabolism the stored energy in your body is broken down into a compound called pyruvate.
Misconceptions about lactate
When you don’t have enough oxygen to perform activity, your body turns pyruvate into lactate to fuel the muscles. Anaerobically fit firefighters can use this form of energy production for one to three minutes. As the muscles work at intense levels, they become more acidic, which interferes with firing.
Rather than causing acidity, lactate serves as an antidote to muscle failing. As muscles lose power and energy, lactate responds to help counteract the effects.
This is the familiar fatigue in the muscles you feel when you just can’t pull another section of ceiling. Lactate production is a protective mechanism that prevents the body from hurting itself. When lactate production can’t continue to the levels needed to prevent the complete failure of the muscles, you reach your threshold.
High levels of lactate were once blamed for delayed muscle soreness. However, lactic acid or lactate are not responsible.
This soreness is due to breaks in the muscles that occur during strenuous exercise. About 75 percent of the lactate produced during exercise is used as this regulating energy source; the other 25 percent leaks into the blood.
It because of this 25 percent that field test lactate levels during rehab can be made. Fit firefighters were thought to produce less lactate, however, the science being generated indicates it is more likely that these athletes are better able to use the lactate they produce and leak less into the bloodstream, so their tests show lower amounts.
Testing in rehab
So, now we know why lactate is important as a measure of fatigue or true exhaustion. Is it feasible to measure this in the rehab unit?
The answer is yes; the economics of having a device that has multiple uses helps justify the purchase. A lactate meter is similar to a glucometer that takes a small sample of blood from a finger stick and measures the lactate level.
These meters are common among endurance athletes trying to monitor peak work out conditions. Many fire and EMS agencies purchase athletic meters verses FDA-approved meters. Frequently, they are the same meter.
There are three important uses that make these meters valuable at a fire scene rehab sector.
First and foremost, lactate is a key diagnostic tool for cyanide poisoning in the face of smoke inhalation. Elevation in the blood lactate level is a sensitive marker for cyanide toxicity.
A plasma lactate concentration of greater than 10 mmol/L in smoke inhalation or greater than 6 mmol/L after reported or strongly suspected pure cyanide poisoning suggests significant cyanide exposure. This reading in conjunction with an altered level of consciousness or hypotension is the threshold for administering hydroxocabalamin.
There could be low levels of cyanide exposure and it is difficult to actually measure cyanide in the blood. The actual measurement is a capability in only few large medical centers and is sent out to more sophisticated labs for accuracy. Almost all emergency rooms have the ability to sample for lactate.
Measuring change
Second, the use of lactate meters for sepsis patients can help identify if the patient’s infection has progressed to a potentially fatal systematic inflammatory response syndrome. The routine use of screening a suspected sepsis patient is becoming common on fire-based units.
Lactate levels greater than 4 mmol/L with a blood pressure less than 90 systolic, a temperature either above 100.4 or below 96.8 and a respiratory rate above 20 breaths per minute indicates shock. This is affiliated with a 27 percent increase in mortality.
Finally, the real benefit comes from measuring over time to look for lactate levels to drop with similar exertion levels. Over time, the lactate threshold goes down slightly as people become more fit and increase the efficiency of delivery of oxygen to the cells. The cells use lactate more efficiency to provide energy to the muscle.
The lactate threshold is 4 mmol/L in athletic conditioning for endurance; a higher reading is an indicator of severe dehydration and that the cells are not using oxygen effectively. This is the point where damage may occur.
There’s a very important number to have when evaluating if the firefighter is at a point where physical exertion has a negative return. The easy way to remember is 10-4 — 10 for cyanide exposure and four for sepsis and as a dehydration or exertion threshold on the meter.
This can influence crew rotations. A report from rehab may indicate the need for reserve companies or additional teams in the staging area. It may also give some insight into exposures and benchmark air pack use and mask confidence. It is a simple and easy way to determine what is the true state of exhaustion or dehydration of firefighters entering the rehab cycle.
