How to Diagnose Patients with Altered Mental Status

 

 
 
 

David Ross; DO; FACEP | | Monday, October 5, 2009


Police officers were called to the home of a 73-year-old for a welfare check. Upon arrival, they found an unresponsive male lying on a bed. A neighbor had noted that the patient had not responded to the phone ringing or the doorbell. According to the neighbor, the patient had been ill for about three days. The patient had last been seen about 24 hours prior to the arrival of police.

EMS assessment revealed an estimated Glasgow Coma Scale of 6. The patient was breathing 38 times per minute, and his heart rate was 120 beats per minute. Blood pressure was 140/70 mmHg, and room air pulse oximetry was 90%. The blood sugar was 130 mg/dL. A nasal cannula end-tidal carbon dioxide (EtCO2) determination was 20 mmHg.

The man didn't feel warm to the touch. His eyes were open, but he didn't seem to be able to focus. His mucous membranes appeared moist. Pupillary size and reaction were equal but sluggish. He did, however, move all four extremities spontaneously. Breath sounds were equal and clear. The abdomen was not distended and no masses were noted. The patient's flanks and legs were mottled.

History obtained from the neighbor and by inspection of the home indicated the patient had no known medical problems. He didn't appear to be taking any medications; there was no evidence of drug overdose or alcohol consumption; and there were no known allergies.

Oxygen was administered by mask at 15 lpm. An IV was established, and the patient received a total of 100 milliliters of saline en route. The patient was transported to an emergency department (ED) without change in vital signs or overall condition.

What's Causing this Patient's Presentation?
As we've discussed in previous columns, the causes of altered mental status are varied and therefore require organized consideration. Let's start with what we know:

The patient was reported to be unresponsive, but his eyes were open. However, he did not seem to focus on the EMS crew. We can assume that he was breathing and that his airway was open.

The importance of the vital signs cannot be overstated. He was tachypneic with a respiratory rate of 38. He was also tachycardic as demonstrated by the heart rate of 120. Additionally, the pupils were sluggish, but equally reactive. No evidence of trauma was noted.

Given these findings, we need to consider causes of altered mental status that might be associated with the vital sign aberrations in this case.

Certainly pneumonia, congestive heart failure or other respiratory diseases that affect gas exchange at the alveoli could lead to tachypnea and tachycardia. However, the breath sounds were reported to be normal, and the pulse ox was 90% on room air. Although these findings suggest some hypoxia, it was likely not enough to account for the respiratory and heart rate.

Overdose of stimulant drugs, such as cocaine or methamphetamine, might explain these findings. But no obvious use of such agents was noted at the scene and, given the patient's age, this seems unlikely. Depressant drug use (such as alcohol, benzodiazepines and narcotics) would tend to depress the respiratory rate -- leading to hypoventilation and an elevated EtCO2. The EtCO2 was, in fact, low. All of these factors, in addition to the normal pupils, make a drug explanation very unlikely.

Brain tumors or hemorrhages don't tend to increase respiratory and heart rates. Additionally, the presence of equally reactive pupils makes an intracranial lesion less likely.

Metabolic acidosis is the most likely scenario. As the body tries to compensate for increasing acid loads, respiratory rate increases to produce a respiratory alkalosis. This helps to buffer the acid concentration, bringing the pH closer to normal. In response to the increased workload imposed by the acidosis, tachycardia also develops.

Clinical circumstances that produce metabolic acidosis include starvation, dehydration, diabetic ketoacidosis (DKA), liver failure, renal failure, shock and infection.

Although we don't have a specific comment about his nutritional status in the physical assessment, nothing suggests that he was not of normal weight and height. We do have a sense from the crew's report that the patient was not obviously dehydrated.

The patient's blood sugar was normal, and this suggests the patient didn't have DKA.

We shouldn't completely rule out liver failure, but the abdomen was said to be normal and there was no note of any jaundice. Additionally, the history revealed that the patient was previously healthy.

That leaves us with renal failure, shock and infection. There's no way to completely exclude new onset renal failure, but, as noted, the patient was supposedly healthy and appeared hydrated. Although normal blood pressure does not absolutely exclude shock, the fact the patient maintained a normal blood pressure during transport makes the argument for shock difficult to make.

This reasoning leaves infection as a more probable explanation. Where could the source of the infection be? Typical locations for infection include the urinary tract and the lungs -- pneumonia. Rarely, patients may harbor an infection in their spinal fluid -- meningitis. Severe infections from any source may produce bacteria in the blood.

No documented evidence in the field suggests any infection or sepsis. There was no report of rales or rhonchi to suggest pneumonia. A rash, which may be seen with some serious bacterial diseases, was not seen.

Although a body temperature thermometer wasn't available on this ambulance, the patient didn't feel febrile. It's possible, however, to have major sepsis and have a normal or low body temperature.

Outcome
Further history obtained in the ED suggested the patient had complained to the neighbor for several days about nasal congestion and a sore throat. The patient's body temperature was actually 102 degrees. Additionally, the patient appeared to have a stiff neck. Otherwise the physical examination was similar to EMS assessment.

The pH on an arterial blood gas was 6.9 (normal is 7.4). The blood gas further reflected evidence of a severe metabolic acidosis.

The patient underwent a spinal tap. The spinal fluid was yellowish in color (clear is normal) and had 500 white blood cells (less than five is normal). Additionally, the presence of bacteria was noted on initial screening tests. A culture of the fluid later confirmed infection with streptococcus pneumoniae. Cultures from the urine were negative, but blood cultures during the patient's hospital stay demonstrated the same bacteria.

The patient was started on high-dose antibiotic treatment in the ED and also received steroids, which may reduce some of the neurologic complications associated with bacterial meningitis. Fluid replacement and other interventions to treat the acidosis were started. The patient was then intubated and transferred to the ICU.

After a prolonged, complicated hospital course, which included the placement of a tracheostomy, the patient was transferred to the rehabilitation service.

The patient continued to improve. He was ultimately discharged home with improvement in cognition and overall function. An audiologist was consulted to assist with hearing impairment.

Discussion
Bacterial meningitis is a very serious disease with a potential for death or survival with significant neurologic damage. Streptococcus pneumonia and nisseria meningitidis are responsible for 90% for the bacterial cases in this country.

The mortality is estimated at between 5 10% in children beyond the neonatal period. Approximately 25 50% of survivors will have significant disabilities, including hearing loss.

Classic symptoms include malaise, decreased mental status and headache. Physical findings may include fever and a stiff neck -- known as meningismus. Meningismus is often present in otherwise healthy older children and adults. However, neonates and other patients with depressed immunity may not exhibit meningismus.

Previously healthy patients may decompensate with bacterial meningitis in less than 24 hours. As the infection (or sepsis) worsens, metabolic acidosis may develop leading to the findings noted at the scene and on the lab tests.

Viral meningitis is much more common than bacterial meningitis and generally results in less significant complications.

This case emphasizes the importance of an organized approach to the evaluation of a patient with altered mental status. It also reminds us that the presence of a stiff neck in the altered mental status patient may suggest bacterial meningitis.




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