Lactic Acid and Base Deficit in Trauma Patients

Lactic acid is a byproduct of anaerobic metabolism (Metabolism without oxygen). Normally, the cells use anaerobic metabolism and it breaks down the glucose to form energy. Normally, the cells use oxygen available to breakdown the glucose and produce ATP. This occurs when you have oxygen. If the body does not have the oxygen, it then converts the metabolism to an anaerobic metabolism. The end product is lactic acid. If the body is acidic, and the pH drops, this means that there is a tissue ischemia. If we take the glucose (CCCCCC), and break it down, you will have two pyruvates—each attached to a CCC. That’s not a lot of energy and the pyruvate is a mild acid.

There are different ways to get more energy, such as going to the mitochondria to use the oxygen and produce more ATP. When we break down the glucose to produce energy in the presence of oxygen, so the glucose will split into two separate three carbon molecules called the pyruvate and produces ATP. If you don’t have oxygen, then the pyruvate will be attached to hydrogen atoms, which is H+ (proton that is an acid). If you are acidotic and a sick patient, you will have a lot of floating hydrogen atoms and a lot of floating protons.

The pyruvate will attach to the free hydrogen protons. The H+ pyruvate is called lactic acid. It is a pyruvate that is holding onto hydrogen. The lactic acid is the end product of anaerobic metabolism.

Now, with a base deficit, as the number of protons goes up, which is hydrogen, then the pH will go down and the patient will become acidotic. The body uses bicarbonate as a buffer if the pH goes down. There are a lot of protons within the body and the bicarbonate will be exhausted in this situation. The bicarbonate goes down because we are combining it with the protons. When the bicarbonate goes down, this becomes metabolic acidosis.

When you combine the bicarbonate with the protons, this will make carbonic acid (H₂CO₃), rather than HCO₃^-, which is bicarbonate. The carbonic acid can give water (H₂O), and CO₂. The lactic acid will give out the protons and be buffered by the bicarbonate, leaving lactic acid. When this occurs, the bicarbonate will go down, and this will be the base deficit.

When checking if a patient has been resuscitated, you can check in several ways

The two ways this is asked on exams:

1. Base deficit from -2 to +2
2. Serum lactate level (normal is less than 2.5, some sources use normal less than 2)

Orthopaedic Emergencies Part IV

In our final blog post regarding Orthopaedic Emergencies, we will review:

1. Transverse Atlantal Ligament Rupture
2. Bilateral Cervical Facet Dislocation
3. Spinal Cord Compression
4. Cauda Equina Syndrome

Transverse Atlantal Ligament Rupture

The normal Atlanto-Dental Interval is less than 3mm. An A.D.I measuring greater than 3mm will be translationally unstable in the sagittal plane due to transverse atlantal ligament rupture. This is usually apparent on x-rays or CT scan. If the condition is not diagnosed, it can result in spinal cord compression, respiratory arrest, and a catastrophic outcome. Treatment typically requires a posterior atlanto-axial arthrodesis.

Bilateral Cervical Facet Dislocation

Facet dislocations of the cervical spine:

1. Unilateral Facet Dislocation
   1. Displacement is less than 50% of the vertebral body width
   2. May need surgery
2. Bilateral Facet Dislocation
   1. Displacement greater than 50% of the vertebral body width
   2. Usually needs surgery
   3. Exclude disc herniation

Obtain a preoperative MRI to rule our disc herniation associated with facet dislocations.

 

Spinal Cord Compression

Spinal cord compression is more common with cervical spine injuries and thoracic spine injuries. Neurogenic shock resulting from spinal cord injury may complicate resuscitation of the patient and should be differentiated from hypovolemic shock. It is important to look for hypotension and bradycardia as well as thoracolumbar fractures which could be missed. Treatment consists of emergency management involving resuscitation and hemodynamic stabilization with concurrent neurologic examination. Protocol requires steroids given early. Definitive treatment consists of stabilization of unstable spinal injuries.

Cauda Equina Syndrome

Central disc herniation compressing the cauda equine. It results from injury to the lumbosacral nerve roots within the spinal canal. This syndrome presents with involvement of the bladder, bowel, and lower limbs and usually results from central disc herniation or fractures. Central disc herniation or bony fragments results in the compression of the nerve roots. Early diagnosis is imperative to find the cause of the compression on the nerve roots. Urgent decompression by the removal of the central disc herniation or stabilization of the fracture is necessary for treatment.