How To Systematically Interpret a Head CT: Blood Can Be Bad

Head CTs are a common, inexpensive, and fast way of evaluating intracranial pathology. Although they do not give the anatomical detail of an MRI, they are still extremely important in diagnosing “gross” pathology that needs emergent intervention.

CT scans are based on the Hounsfield unit (HU), which is an indirect way to measure density. Interestingly, Sir Godfrey Newbold Hounsfield won a Nobel prize for his work on developing the CT scanner, but I digress…

The importance of the Hounsfield unit is that things that are hyper-dense (very dense) appear bright; those things that are hypo-dense (not very dense) appear dark. The different tissues and fluids within the confines of the skull have varying densities. The most dense materials, like bone, have very high Hounsfield units; less dense materials such as air and cerebrospinal fluid have very low Hounsfield units.

It is important to approach head CTs in a systematic fashion so that subtle (and not so subtle) pathology is not missed. The easiest way I have found to read a head CT is to remember the following mnemonic:

Blood Can Be Very Bad

The first “B” in the mnemonic stands for, you guessed it, blood. There are five different pathological locations that blood can be located: epidural, subdural, subarachnoid, intraventricular, and intraparenchymal. Depending on the age of the blood, it may be hyper-dense (acute/active bleeding), isodense (roughly 3 to 7 days old), or hypo-dense (older than 7 days).

CT scans of Intracerebral Hemorrhages
The "C" in the mnemonic stands for "cisterns". Cisterns are enlarged subarachnoid spaces where cerebrospinal fluid pools. The most important cisterns are around the brainstem. They include the interpeduncular, suprasellar, ambient, quadrigeminal and pre-pontine cisterns. A healthy amount of cerebrospinal fluid should “bathe” the brainstem; if there is increased intracranial pressure cerebrospinal fluid will get pushed out of these cisterns as brain tissue starts to herniate into them. And that as they say is “no bueno”.

The second "B" stands for "brain". Although blatant pathology such as blood clots are usually readily apparent, more subtle pathology can also be obtained from a CT. For example, blurring of the gray-white junction may indicate evolving stroke. Any areas of hypodensity (ie: dark areas) within the brain may indicate edema associated with a tumor.

The "V" represents the ventricular system. The ventricular system consists of a pair of lateral ventricles, a third ventricle, and a fourth ventricle (don’t ask me what happened to the first and second ventricle!). The ventricles are in communication with one another via holes known as foramen. The paired foramen of Monroe connect the lateral ventricles to the third ventricle; the cerebral aqueduct of Sylvius connects the third ventricle to the fourth ventricle. The fourth ventricle drains into the subarachnoid space surrounding the spinal cord via the foramen of Magendie and Lushka.

The ventricular system is quite symmetric. Any obvious asymmetries may indicate a pathologic process "pushing" on a ventricle causing it to become distorted. In addition, if the ventricles are larger than normal it may indicate the presence of hydrocephalus, a condition in which cerebrospinal fluid is not reabsorbed appropriately.

The final "B" in the mnemonic stands for "bone". The skull should be assessed for fractures, especially in trauma patients. A common place for fractures is at the skull base. Time should be spent assessing this area to rule out fractures that extend across the canals and foramen that house the carotid arteries, jugular veins, and cranial nerves.

Reading a head CT is the first step in determining what additional imaging studies are necessary, or what treatment should be given. By using the above mnemonic it allows the interpreter of the scan to quickly and effectively assess if there is underlying pathology that needs further evaluation.


The mnemonic – blood can be very bad – can be used to systematically interpret a head CT. The first "B" stands for blood. The "C" stands for cisterns. The second "B" stands for brain. The "V" represents the ventricular system. And the last "B" stands for bone. By looking at these five components it is possible to assess all the important pathology that may require further imaging and/or treatment.

References and Resources

SOCRATES: Thinking About Pain

When I was in medical school one of the most useful mnemonics I came across was "SOCRATES". The mnemonic is designed to figure out the characteristics of someone’s pain. The characteristics of pain help the clinician develop a differential diagnosis from which testing can be ordered, and then hopefully, treatment can be given.

So what does each letter in the mnemonic SOCRATES stand for??? Let’s go letter by letter…

S   O   C   R   A   T   E   S

The first “S” stands for “site”. What body part or parts are involved? Is the pain in the leg? Is it in the abdomen? Is it a general sense of overall discomfort? The site of pain helps you fine tune your subsequent physical exam and diagnostic decision making.

The next letter is “O”, which stands for “onset”. When did the pain start? Asking about the onset of the pain is extremely important! For example, if someone has had chronic low back pain for 10 years that invokes a much lower sense of urgency than someone complaining of the sudden onset of severe belly pain or headache.

S O C R A T E S 

S – Site
O – Onset
C – Characteristics
R – Radiation
A – Associated
T – Timing
E – Exacerbating/
S – Severity

“C” stands for “characteristics”. What are the characteristics of the pain? You want the patient to describe the pain in their own terms without influencing them too much. The pain may be sharp, dull, heavy, burning, etc, or a combination of descriptors.

The next letter is “R”, which represents “radiation”. I typically ask if the pain stays at the site or if it travels somewhere else in the body. For example, someone with chest pain radiating to the left arm might be experiencing a heart attack. Back pain that is associated with radiation down the leg might indicate a herniated lumbar disc that may require surgery. Back pain radiating to the abdomen could be intraabdominal pathology. Radiation of the pain is an important component to help guide your decision making.

“A” stands for associated symptoms. What other symptoms are present with the pain? For example, if the patient is complaining of belly pain do they also have nausea or vomiting? If they have a headache do they also complain of double vision or photophobia? Associated symptoms can provide a wealth of information to help you hone your differential diagnosis even more.

“T” stands for timing. When does the pain occur? Does it happen at specific times of the day, or is it constant? Does it happen during a certain movement? All of these can give you an idea of the origin for the pain.

The letter “E” represents “exacerbating” factors; grouped within this is also alleviating factors. The patient should be probed as to what makes their pain better or worse. Certain physical positions, medications, etc. may make the pain better or more unbearable. These factors can all provide historical clues about the root cause.

The final “S” stands for “severity”. In most hospitals this is formulated on a 1 to 10 scale with 10 being the most severe pain they’ve ever experienced. This can be a tricky one to gauge because many patients will describe 10 out of 10 pain when they are lying comfortably in bed; therefore, it is often necessary to ask more pointed questions and place pain in a context.

Overall, the answers obtained when using the mnemonic SOCRATES can provide a solid framework from which to order new testing and treatments.

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ICU Notes: The Devil is in the Details

Patients in the intensive care unit (ICU) are usually the sickest in the hospital and require a ton of care. Unlike a normal patient note, which is generally brief and written in the SOAP format, the ICU note is more thorough and exhaustive. Below is a discussion of how an ICU note can be organized so that important information is not missed. Please note that this is not the only way to organize an ICU note, but it is a way that many units use because it is extremely thorough and organized.

Organize by Systems

The beginning of any ICU note should always have the patient’s name, date, time, hospital day, post operative day (if in the surgical ICU), lines (ie: any tubes going into or out of the patient), and drips.

  • Patient’s name
  • Hospital day
  • Post operative day (if applicable)
  • Lines
  • Drips (often abbreviated as “gtts”)

Unlike normal floor notes, which are typically organized by problem, ICU notes are more commonly organized by body system. The systems are usually written in the following order:

So what information should we include in each section?


At the bare minimum the neurological part of the note should include the patient’s alertness and orientation (ie: “AAOx3, confused, intubated but following commands, etc.”), and their Glasgow coma scale (GCS) score. If the patient is in the neuro-ICU the exam should be more thorough and include the GCS score by component, as well as a neurological exam. A common question asked by neuro-intensivists is “what can the patient do?” Do they follow all commands? Do they withdraw to pain? Are they decorticate? Decerebrate? Give a description of what the patient can “do” or “not do”.

Less commonly some ICU patients may have an external ventricular drain or lumbar drain used to remove cerebrospinal fluid. If this is the case the output of the EVD or lumbar drain should be recorded. EVDs are set to a specific height above the tragus of the ear; this number is important to record as well.

Finally, specific medicines related to neurological disease should be added. Any medications used to sedate or paralyze the patient should also be included as they may confound the physical exam findings. For example, are they on propofol or fentanyl drips? How much of this medicine is “dripping” into them per hour? Someone on a large amount of fentanyl may not respond much to painful stimuli so it is important to give a description of what may be confounding your examination.

To recap, the neurological section should include the following elements:

  • Physical exam findings
    • Level of alertness and orientation
    • GCS broken down by components
    • Neurological exam (ie: cranial nerves, strength, reflexes, sensation, etc.)
  • Vital signs and tubes
    • EVD and/or lumbar drain output
      • Output over last shift
      • Output over last 24 hours
      • Height of the EVD
  • Neurological medicines
    • Sedatives (ie: propofol, midazolam, etc.)
    • Pain medications
    • Treatment specific medications (anti-seizure meds)


In addition to physical exam findings, the cardiovascular section should start off with the heart rate, rhythm, blood pressure, and central venous pressure (if a central line is present). Patients with significant cardiovascular disease may have a pulmonary artery catheter (aka: Swan-Ganz catheter). The data obtained from it should also be included: pulmonary artery pressure, pulmonary artery wedge pressure, cardiac output, cardiac index, central venous pressure, and stroke volume.

The cardiovascular section of the note should also include what drips the patient is on to control blood pressure. Are they on anti-hypertensive medications or pressors?

To recap, the cardiovascular section should include:

  • Physical exam findings
  • Vital signs and tubes
    • Heart rate
    • Heart rhythm (from telemetry)
    • Blood pressure
    • Central venous pressure (from central line or Swan Ganz catheter)
    • Pulmonary artery pressure (from Swan Ganz catheter)
    • Pulmonary artery wedge pressure (from Swan Ganz catheter)
    • Cardiac output and index (from Swan Ganz catheter)
    • Chest tube output (if present)
      • Output over last shift
      • Output over last 24 hours
  • Cardiac specific medications
    • Intravenous drips used to control blood pressure
    • Other cardiac medications (β-blocker, ACEI, etc.)

Respiratory (Pulmonary)

In addition to physical exam findings, the most important thing to include in this section are the ventilator settings. It should be organized in the following way: mode, FiO2, tidal volume, patient’s respiratory rate, ventilator’s rate, peak end expiratory pressure (PEEP), pressure support, peak airway pressure.

After the ventilator settings, the patient’s oxygen saturation should also be stated.

Any laboratory data specific to the pulmonary system is given next. This commonly includes arterial blood gas values written in the following order: pH, PaO2, PaCO2, and HCO3. Chest x-ray results should also be written here.

To recap, the respiratory portion of the note should include:

  • Physical exam findings
  • Ventilator settings
    • Mode
    • FiO2
    • Tidal volume
    • Patient’s respiratory rate
    • Ventilator’s respiratory rate
    • Peak end expiratory pressure (PEEP)
    • Pressure support
    • Peak airway resistance
  • Vital signs
    • Oxygen saturation
  • Laboratory data
    • Arterial blood gas results
    • Chest x-ray results
  • Pulmonary medications
    • Nebulizers, etc.


The renal section includes an evaluation of the patient’s kidney function. The first piece of data that should be recorded are the "in and outs". The "ins" include the total amount of fluid the patient has received intravenously and orally. The "outs" include the total amount of urine the patient has made. The urine output should be recorded in mL/kg of body weight per hour, shift, and over the last 24 hours.

Laboratory data that should be recorded in the renal section includes the creatinine, blood urea nitrogen (BUN), urinalysis, urine microscopy, and any imaging studies specific to the urinary tract. You may also need to calculate and include the fractional excretion of sodium.

To recap, the renal section of the note should include:

  • Vital signs
    • Ins and outs
      • Output over last shift
      • Output over last 24 hours
  • Laboratory data
    • Creatinine
    • Blood urea nitrogen (BUN)
    • Urinalysis
    • Urine microscopy

Fluids, Electrolytes, and Nutrition (FEN)

The fluids, electrolytes, and nutrition section should have what fluids, both intravenously and orally, the patient is receiving. The patient’s electrolytes should also be recorded in this section. The most common electrolytes that are measured are sodium, potassium, chloride, bicarbonate, phosphorus, calcium, and magnesium. In addition, the patients diet, either orally or intravenously should be discussed along with their nutritional status (usually measured by albumin or prealbumin levels).

To recap the fluids and electrolytes section should include:

  • Intravenous fluids (ie: normal saline, hyper or hypotonic saline, colloids, etc.)
  • Diet
  • Laboratory data
    • Chemistry panel
    • Calcium, magnesium, phosphorus
    • Albumin
    • Prealbumin

Infectious Diseases

The infectious diseases section should always begin with the maximum temperature over the last 24 hours followed by the current temperature.

After that the patient’s white blood cell count should be mentioned. If there are any pending or final culture results they should be included in sequential order. Common data recorded include blood, urine, and sputum cultures. Sometimes cerebrospinal fluid cultures will also be available.

Finally, all antibiotics the patient is receiving should be listed along with how many days they’ve been on each one.

To recap, the infectious disease section should include:

  • Vital signs
    • Maximum temperature
    • Current temperature
  • Laboratory data
    • White blood cell count
    • Culture results
  • Antibiotics


Physical exam findings such as bruising, petechiae, oozing from surgical incisions should be mentioned.

The hematology section should have the hemoglobin, hematocrit, platelet count, prothrombin time, INR, and partial thromboplastin time. Other values that are less common, but may be present include iron studies, d-dimer results, fibrinogen levels, and mixing studies.

Since blood clot formation is a huge concern in hospitalized patients, any results related to this should be included. Studies such as lower extremity dopplers, chest CT or ventilation perfusion scans should be included in this section.

To recap, the hematology section should include:

  • Physical exam findings (ie: bruising, oozing, petechiae, etc.)
  • Laboratory data
    • Hemoglobin and hematocrit
    • Platelet count
    • PT, INR, PTT
    • Lower extremity doppler results
    • Chest CT or ventilation/perfusion scan


The gastrointestinal section is devoted to the patient’s bowel function. A discussion of how the patient is being fed and what is being fed to the patient is written in this section. For example, oral versus intravenous feedings. Is a nasogastric tube present?

Laboratory data that should be included here are the patient’s albumin level (measured every few weeks) and the patient’s prealbumin level (usually measured every 48 hours).

Physical examination findings of the gastrointestinal tract should be written as well. They may include abnormal bowel sounds, enlarged liver or spleen, ascites, or blood in the stool.

To recap, the gastrointestinal section should include:

  • Physical exam findings (ie: distended, peritoneal signs, etc.)
  • Laboratory data
    • Liver function tests
    • Amylase and lipase


The most important thing for the endocrine section is the blood sugar results. Other common values that are often ordered for ICU patients include serum osmolality. Any medications used to control glucose levels such as insulin drips or hypoglycemic agents should be recorded.

  • Laboratory data
    • Blood glucose levels (fingerstick, metabolic panel)
  • Medications
    • Insulin drip and rate (if any)
    • Sliding scale insulin
    • Subcutaneous insulin
    • Oral hypoglycemics (ie: metformin, glyburide, etc.)


The psychiatric portion of the note is often neglected or omitted, but is an important component to at least think about. Many psychiatric issues will be dealt with once the patient is out of the ICU.


The prophylaxis section is very important! Most patients in the ICU will be on a medicine to decrease the risk of developing gastric ulcers, as well as several methods to prevent deep venous thrombosis and pulmonary embolism. Any prophylactic measures should be listed and addressed during rounds.

The prophylaxis section includes:

  • Ulcer prophylaxis
    • H2 or proton pump inhibitor
  • Deep venous thrombosis prophylaxis
    • Subcutaneous heparin
    • Compression boots (venodynes)
    • Graduated/compression stalkings

To Sum It All Up…

There are different ways to organize an ICU note. By far the most common way is to organize it by systems. However, various services (ie: neurosurgery, cardiothoracic, etc) will have very specific ways they want data presented depending on what information is most important to them.

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