Hypoxic Brain Injury

What is Hypoxic Brain Injury?

The brain, despite its small size and weight, uses a lot of energy. It’s always busy and is very sensitive to low oxygen levels and reduced blood flow. If the brain doesn’t get enough oxygen or blood, its cells can start to get damaged within minutes. If there’s no quick action taken, long-term brain damage could happen. That’s why it’s really important to recognize the warning signs, understand how these conditions harm the brain, and know the different ways it can be treated.

What Causes Hypoxic Brain Injury?

Anoxic and hypoxic brain injuries are basically damages to the brain caused by lack of oxygen. Your brain gets its oxygen from the blood flowing to it and from the oxygen content of that blood.

So naturally, anything that affects either of these two factors can cause hypoxic brain injuries. If for some reason the blood flow to your brain gets interrupted – for instance with a heart attack or being strangled – this can lead to such injuries.

Even problems that affect the body on a larger scale, reducing the oxygen content in your blood, can cause your brain to get less oxygen than it needs. These include severe anemia (a condition where you don’t have enough red blood cells to carry oxygen), systemic hypotension (low blood pressure), and systemic hypoxia (a lack of oxygen in your body).

If these aren’t dealt with swiftly, they can lead to hypoxic brain injury too. In the United States, the most common cause of hypoxic brain injury is cardiac arrest (when the heart suddenly stops working).

Other causes can include blood vessel injuries from a trauma; near-drowning; inhaling too much smoke or being poisoned by carbon monoxide (a colorless, odorless gas that can be deadly); shock (a sudden drop in blood flow to organs and tissues), which could be from bleeding heavily or from bacterial infection in your blood; drug overdoses; and acute lung injury.

Risk Factors and Frequency for Hypoxic Brain Injury

Hypoxic brain injury can be caused by various factors, so it’s hard to tell exactly how common it is. We know from research on heart attacks and successful resuscitations that over half a million people in the U.S. have a heart attack each year. Sadly, most people who have a heart attack don’t live long enough to leave the hospital. Those who do often experience serious cognitive symptoms. In fact, 50 to 83% of survivors have clinically significant cognitive symptoms. When people don’t survive their hospital stay, it’s often because their families have chosen not to continue life-saving treatments out of concern for severe brain injury.

Survivors of hypoxic brain injury can have a range of outcomes, but many have some kind of neurological disability. Only about 10% of people who have a heart attack and can’t be treated with a defibrillator have good neurological outcomes—meaning they can carry out everyday activities—90 days after their heart attack. A recent study in Europe showed that only 5% of heart attack survivors fully recovered neurologically 30 days after their heart attack.

Research indicates over half a million people in the U.S. have a heart attack each year.
Most heart attack victims don’t survive, and those who do often have serious cognitive symptoms.
Decisions to stop life-saving treatments often lead to death during hospital stays.
Many survivors have some kind of neurological disability.
After 90 days, only about 10% of survivors who couldn’t be treated with a defibrillator can carry out everyday activities.
In a recent Europe study, only 5% of heart attack survivors fully recovered neurologically after 30 days.

Signs and Symptoms of Hypoxic Brain Injury

When a person suffers a brain injury due to a lack of oxygen, they often become unconscious and cannot follow verbal instructions. Sometimes, they may even slip into a coma. That’s why we typically get important information about what happened from emergency workers, family members, or other witnesses. It’s crucial to understand the situation that led to the injury. For instance, if someone was choked or nearly drowned after diving into shallow water, they might have also hurt their neck. The same goes for people who’ve had a heart attack; what their heart rhythm was like when it happened, whether anyone saw it, and how long they were receiving emergency medical treatment are all vital details. Doctors need to know about the patient’s medical history, what medications they take, if they have any long-term illnesses, and whether they’ve been exposed to harmful substances or illegal drugs if it’s possible to find out.

Even though we need to understand the patient’s neurological condition, the first priority is resuscitation, that is, restoring normal oxygen levels in the brain and blood flow by treating the cause of the injury. We need to fix the patient’s low blood pressure, insufficient oxygen and blood volume before proceeding with a neurological assessment.

After resuscitation, we should identify and eliminate any factors that could interfere with the evaluation of neurological function. Plenty of things can be confounding factors. For example, exposure to drugs. This involves both illegal drugs and prescription medication that were used while saving a person’s life. Some sedatives and muscle relaxants, along with high doses of certain antibiotics, anticholinergic drugs, and antiepileptic medications, can dim consciousness. Serious metabolic imbalances like severe acid-base imbalance, kidney failure, and liver damage can also interfere with a comprehensive assessment.

Once all the confounders are off the table, the initial step is to assess the patient’s level of consciousness by checking if they respond to stimuli. This includes seeing if their eyes open when you speak to them and if they can follow verbal instructions. If there’s no reaction, a gentle physical touch may be used. If that still gets no response, we may need to use painful stimuli. This could involve pressing on the forehead or jaw joint, or other methods to cause pain centrally. However, pressing on the chest or fingernails is not recommended, as it could trigger reflexes in the spine. While giving this painful stimuli, the patient’s reaction to pain and motor responses are carefully observed. Based on how the patient reacts to pain, the response can be categorized.

Testing for nerve function in the head or cranial nerve examination should also be done. This involves checking the pupils’ responses to light, corneal reflexes, and eye-head coordination. Nevertheless, if there’s any suspicion of a neck injury, testing of eye-head coordination is not appropriate. The resting position of the eyes needs to be checked as an uneven gaze or a shift in the gaze could point to localized brain injury. A full assessment of the cranial nerves may not always be possible especially if the patient is connected to a breathing tube, however, it’s important to check gag and cough reflexes. Also, regular neurological assessments can be invaluable in predicting patient’s recovery, which will be discussed later.

Testing for Hypoxic Brain Injury

If you’re admitted to the hospital due to a sudden brain injury caused by lack of oxygen, several tests and exams may be performed to figure out what caused the injury. These tests initially include straightforward blood tests checking for things like blood sugar, electrolyte balance, the health and count of your blood cells, kidney function, and liver function. The doctors may also test the gases in your blood to see how your body is managing its oxygen and carbon dioxide; this could rule out conditions like hypercarbia, where there is too much carbon dioxide in your blood. A urine drug test and/or a test to check alcohol level in your blood could be done, but it’s worth remembering that these tests don’t detect all possible medicines or substances; so a clear result doesn’t necessarily mean no drugs or medications were involved.

Generally, all patients who are unresponsive will have a head CT scan – which is a special type of X-ray to get images of the brain. This will help the doctors check for any physical reasons for the unconsciousness like bleeding, excess fluid in the brain (hydrocephalus), or injuries due to trauma like fractures in the skull. The goal will be to look for any issues that can be treated like blood collected under the protective layer (aka subdural hematoma) or acute hydrocephalus. Often, in cases of sudden brain injury due to lack of oxygen, the CT scan might not show much. However, it is possible to notice a blurring of the layer between the brain’s gray and white matter. This can be measured and the ratio of this has been found relevant in predicting how your condition might progress.

If you remain unresponsive even after attempts to resuscitate, your doctors may choose to perform additional tests. They may do a special form of CT scan to check for stroke or injuries to the blood vessels in patients who have also had trauma in the neck region. Brain wave monitoring, known as Electroencephalography, may also be done to rule out seizures that are not causing convulsions. MRI scans, which use magnetic fields and radio waves to image the brain, are better at picking up brain injuries from lack of oxygen than CT scans and can be used to help predict your condition’s likely progression, or prognosis.

Treatment Options for Hypoxic Brain Injury

When someone’s brain doesn’t receive enough oxygen due to sudden heart failure, immediate medical attention is crucial to help restore blood flow and prevent further damage to the brain. It’s important to note that treatment is focused on support and addressing the underlying cause as well as stopping more harm to the brain.

One promising technique doctors use to prevent brain cells from dying in this situation is a process called ‘therapeutic hypothermia’ or ‘targeted temperature management.’ This means deliberately reducing the patient’s body temperature. It’s become a common method of care for patients who remain in a coma after sudden heart failure. Research has shown that this method can lower death rates and help improve brain function outcomes.

These findings suggest that for every seven patients treated under therapeutic hypothermia, one life can be saved, and for every five patients, one can expect improved brain function. There is currently no evidence of any side effects from this treatment that could limit its use. Therefore, the American Heart Association recommends that all adult patients who remain in a coma after cardiac arrest receive this treatment. The ideal body temperature during this treatment should fall between 32 and 36 degrees Celsius and should be maintained for 24 hours following the cardiac arrest.

However, a recent study contradicts these findings, suggesting that this temperature range offers no benefit over normal body temperature in terms of survival rates or functional outcomes for adult patients experiencing cardiac arrest outside of a hospital due to heart-related causes. As a result, these findings should be considered when forming future guidelines, and recommendations should be made regarding fever prevention instead.

In layman’s terms, therapeutic hypothermia works by putting the brakes on several damaging effects of lack of oxygen to the brain, such as cell death and mitochondrial dysfunction. It helps to lower the body’s oxygen demand and stabilize the protective barrier around the brain, reducing the chance of brain swelling. To get the best results, doctors need to start treatment as soon as possible after the brain injury preferably within six hours. Still, doctors also need to manage the various effects of this treatment, including its influences on heart function, insulin levels, kidney function, and how patients metabolize drugs.

Patients undergoing this treatment can often experience slow heart rhythms and sometimes low blood pressure. Although a slow heart rate is generally not a concern, some patients may need medications to support organ performance. If slow heart rhythms become a problem, warming the body by just 1 to 2 degrees Celsius can help.

A side effect of this treatment is high blood sugar levels caused by lower insulin levels and the body’s resistance to insulin. The body can also experience low potassium levels. In addition, this treatment can lead to increased urine production, affecting the body’s electrolyte balance and fluid levels. As the body warms up after treatment, this can lead to high potassium levels, especially if low potassium levels were treated aggressively during treatment. Therefore, close monitoring of blood sugar levels and electrolyte levels is required during treatment and rewarming phases.

Pain relief and sedation are very important during targeted temperature management treatment. Some medications such as propofol or midazolam are often used along with pain medication. However, these medications can sometimes obscure neurologic assessments. It’s also worth noting that seizures are a common side effect of oxygen-starved brain injuries. So, brainwave monitoring (known as Electroencephalography) can be very useful.

A common issue with induced hypothermia or targeted temperature management is shivering. Shivering can increase the metabolic rate in the body, slow the rate of cooling, and even raise the pressure inside the skull. This can essentially negate the benefits of the treatment. There are many ways doctors can manage shivering, such as providing adequate pain relief and sedation. Heating the hands, face, and upper chest, and using specific medications have all been shown to help. It is advised that patients undergoing therapeutic hypothermia be monitored for shivering continuously and treated accordingly.

Conditions that may have similar symptoms include:

Bleeding between the brain and the skull (Epidural hemorrhage)
Stroke due to insufficient blood supply to the brain (Ischemic stroke)
Seizure or condition after a seizure (post-ictal state)
Bleeding in the area surrounding the brain (Subarachnoid hemorrhage)
Bleeding between the brain and its outer covering (Subdural hemorrhage)
Injury to the brain due to trauma (Traumatic brain injury)

What to expect with Hypoxic Brain Injury

Anoxic brain injuries, which are injuries due to a lack of oxygen to the brain, can result in serious damage and are often hard to predict in terms of recovery. It’s important to note that establishing a prognosis, or a likely outcome, can be especially tricky due to certain treatment methods. For instance, therapeutic hypothermia – a method where a patient’s body temperature is deliberately reduced – and targeted temperature management can interfere with the body’s absorption and use of common pain-relieving and sedative medications, like propofol and fentanyl.

Prior to assessing a patient’s neurological health after an anoxic brain injury (for prognosis), medical professionals need to ensure the patient’s body temperature is back to normal, and they are no longer under the influence of sedative medications. It’s also crucial to appreciate that brain function can change over time following an injury. For instance, soon after a cardiac arrest, the initial absence of some brain responses may actually improve later on. This is why doctors often delay making a prognosis for 72 hours after an incident. If certain reflexes related to the eyes and the motor functions are absent after this period, it may be indicative of a severe neurological outcome.

In addition to examining a patient physically, doctors also utilize electrophysiological studies, which are tests that evaluate the electrical activity within our body, aiding in predicting recovery outcomes. These include techniques like somatosensory evoked potentials (SSEPs), which measure the brain’s electrical activity in response to touch and sensation. An absent response in SSEPs can predict a poor outcome but isn’t always reliable unless certain other responses are also present. Conversely, Electroencephalography (EEG), another method of measuring brain activity, can be used to identify patients who may recover. Changes in EEG patterns could be the signs of a poor or a favorable outcome.

Magnetic Resonance Imaging (MRI), a common imaging technique, is also beneficial in assessing brain injury due to lack of oxygen after a cardiac arrest. MRIs show different features in several phases post injury: an acute phase (24 hours after loss of oxygen), early subacute phase (1 to 13 days), late subacute phase (14 to 20 days), and chronic phase (from the 21st day onwards). An MRI taken 2 to 7 days after the incident can provide the most useful results. Certain findings in the MRI results, like swelling and signals in the deeper regions of brain, have been associated with poor prognosis.

Although blood markers for predicting the result of brain injury are of interest, they are not commonly used in practice. Neuron-specific enolase (NSE), a specific protein in the nerve cells, is a blood marker that has been significantly studied. High levels of NSE have been associated with a poor outcome. However, therapeutic hypothermia, or temperature reduction treatment, can affect NSE levels, leading to potentially misleading results. Therefore, it’s important not to rely solely on NSE levels and interpret them carefully, especially in patients treated with therapeutic hypothermia.

Possible Complications When Diagnosed with Hypoxic Brain Injury

Anoxic brain injury, or damage due to lack of oxygen, can result in various outcomes ranging from a lengthy coma to minimal thinking problems, and in some instances, may even result in death. Research shows that out of all patients who experienced a coma because of lack of oxygen, 27% regained consciousness within a month, while nearly 9% stayed in a coma or vegetative state. Sadly, the largest group, making up 64%, did not survive.

After facing an anoxic brain injury, people can exhibit a number of long-term effects, which can vary from person to person:

Persistent vegetative states
Seizures
Myoclonus (sudden, involuntary jerking of a muscle or group of muscles)
Movement disorders
Cognitive dysfunction (issues with memory, attention, and problem-solving)
Other neurological abnormalities

Preventing Hypoxic Brain Injury

Patients and their families need to be educated and counseled on the possible outcomes and long-term effects of an injury that limits oxygen flow to the brain. If the brain injury was due to a drug overdose, the patient may also need extensive counseling to help manage any substance use disorders. In cases where the brain injury was due to cardiac arrest, patients need to be informed about adjusting their lifestyle, including changes to their diet, exercise, and consistency with taking medication.

Frequently asked questions

Hypoxic brain injury is a condition where the brain does not receive enough oxygen, which can lead to damage to its cells and potentially result in long-term brain damage if not treated promptly.

Hypoxic brain injury can be caused by various factors, so it's hard to tell exactly how common it is.

Signs and symptoms of Hypoxic Brain Injury include: - Unconsciousness: A person who has suffered a brain injury due to a lack of oxygen may become unconscious and unable to follow verbal instructions. - Coma: In some cases, the person may slip into a coma. - Lack of response to stimuli: The person may not react to verbal instructions or gentle physical touch. - Need for painful stimuli: If there is no response to gentle touch, painful stimuli may be necessary to elicit a reaction. - Impaired neurological function: Hypoxic brain injury can result in impaired neurological function, including changes in consciousness, motor responses, and nerve function. - Confounding factors: Factors such as exposure to drugs, metabolic imbalances, and other medical conditions can interfere with the evaluation of neurological function. - Neck injury: If the person was choked or nearly drowned, they may have also hurt their neck, which can be a sign of hypoxic brain injury. - Abnormal eye movements: Uneven gaze or a shift in the gaze can indicate localized brain injury. - Altered pupil responses: Changes in the pupils' responses to light can be a sign of hypoxic brain injury. - Impaired corneal reflexes: The corneal reflexes may be affected in cases of hypoxic brain injury. - Disrupted eye-head coordination: Testing eye-head coordination can help identify any abnormalities that may be indicative of hypoxic brain injury. - Gag and cough reflexes: Checking the gag and cough reflexes can provide important information about the patient's neurological function. - Limited cranial nerve examination: In some cases, a full assessment of the cranial nerves may not be possible, especially if the patient is connected to a breathing tube. However, checking certain reflexes is still important. - Predictive value for recovery: Regular neurological assessments can be invaluable in predicting the patient's recovery from hypoxic brain injury.

Hypoxic brain injury can be caused by various factors, including interrupted blood flow to the brain, reduced oxygen content in the blood, severe anemia, low blood pressure, a lack of oxygen in the body, cardiac arrest, blood vessel injuries, near-drowning, inhaling too much smoke or carbon monoxide, shock, drug overdoses, and acute lung injury.

The doctor needs to rule out the following conditions when diagnosing Hypoxic Brain Injury: - Bleeding between the brain and the skull (Epidural hemorrhage) - Stroke due to insufficient blood supply to the brain (Ischemic stroke) - Seizure or condition after a seizure (post-ictal state) - Bleeding in the area surrounding the brain (Subarachnoid hemorrhage) - Bleeding between the brain and its outer covering (Subdural hemorrhage) - Injury to the brain due to trauma (Traumatic brain injury)

The types of tests that may be needed for Hypoxic Brain Injury include: - Blood tests to check blood sugar, electrolyte balance, blood cell health and count, kidney function, liver function, and gases in the blood - Urine drug test and/or alcohol level test - Head CT scan to check for physical reasons for unconsciousness, such as bleeding, excess fluid in the brain, or skull fractures - Special form of CT scan to check for stroke or injuries to blood vessels in the neck region - Electroencephalography (EEG) to rule out seizures - MRI scan to better pick up brain injuries from lack of oxygen and help predict prognosis

Hypoxic brain injury is treated through a process called therapeutic hypothermia or targeted temperature management. This involves deliberately reducing the patient's body temperature to prevent brain cell death and improve brain function outcomes. The ideal body temperature during this treatment should fall between 32 and 36 degrees Celsius and should be maintained for 24 hours following the cardiac arrest. However, recent studies have suggested that this temperature range may not offer any benefit over normal body temperature in terms of survival rates or functional outcomes for adult patients experiencing cardiac arrest outside of a hospital due to heart-related causes. Therefore, future guidelines may focus on fever prevention instead.

When treating Hypoxic Brain Injury, there are several side effects that can occur. These include: - Slow heart rhythms and low blood pressure, which may require medication to support organ performance. - High blood sugar levels caused by lower insulin levels and the body's resistance to insulin. - Low potassium levels, which can be exacerbated by increased urine production during treatment. - Imbalances in electrolyte levels and fluid levels. - Pain relief and sedation can obscure neurologic assessments. - Seizures, which are a common side effect of oxygen-starved brain injuries. - Shivering, which can increase metabolic rate, slow cooling, and raise pressure inside the skull. Shivering should be continuously monitored and managed with pain relief, sedation, and other interventions.

- Survivors of hypoxic brain injury often have some kind of neurological disability. - Only about 10% of people who have a heart attack and can't be treated with a defibrillator have good neurological outcomes after 90 days. - In a recent study in Europe, only 5% of heart attack survivors fully recovered neurologically after 30 days.

A neurologist.