What is Fever in the Intensive Care Patient?
Temperature is an important health indicator for all patients, including those in intensive care units (ICUs). A component of vital signs, the patient’s temperature can point out if someone has a fever or abnormally low body temperature, which typically requires further physical checks, tests, and changes in treatment in the ICU.
However, what is considered a fever in the ICU is different from the usual idea of a fever. According to both the American College of Critical Care Medicine and Infectious Disease Society of America, a fever in an ICU patient is when they have a single temperature of at least 101 degrees F or approximately 38.3 C. They also recommend further investigating only if the temperature is at least 101 degrees F. If the temperature goes above 105.8 degrees F or 41 degrees C, this situation, referred to as hyperpyrexia or hyperthermia, is unusual in intensive care settings.
In patients with weakened immune systems or low white blood cell counts (called neutropenic patients), we should consider a slightly lower temperature for identifying a fever, since these patients may not show a typical fever response. Moreover, signs of inflammation/infection, including their physical symptoms, lab test results, and imaging tests, might be sparse or not present at all, particularly in the early stages. For them, a fever is defined as a single temperature above 101 F (38.3 C) or a persistent temperature above 100.4 F (38.0 C) for more than an hour when their neutrophil count (a type of white blood cell) is under 500 cells/mm.
We should also remember that some treatments, like continuous kidney treatment or heart-lung support, can change or hide the fever response.
Fever can help the body get rid of invading germs, but it is also linked with higher death and sickness rates in ICU patients and is part of scoring systems predicting death, such as APACHE II & III. However, research on fever and death rates in ICU patients isn’t consistent. A large study in 2008 found that a temperature more than about 39.5 degrees C led to higher death rates in seriously ill patients, but merely having a temperate over 38.3 degrees C didn’t show a clear connection with the death rate. Later research in 2012 indicated that the higher death rates associated with temperatures over 39.5 degrees C were seen in non-infection patients, not those with infections. Some studies have even shown a reverse relationship between fever and death rates in ICU and emergency patients.
Fevers in the ICU can simply be a part of the ongoing illness/disorder that led to ICU admission, could be a result of unique causes in the ICU, and very rarely due to the actuation or sign of an underlying dormant disease or disorder. The fevers unique to ICU care could be due to procedures or treatments given in the ICU or the patient showing a new fever due to immune, septic, metabolic or hormonal responses. This review mainly talks about fevers in ICU patients who aren’t neutropenic or immunocompromised. However, overlaps in clinical symptoms and/or management between different patient groups are not surprising.
What Causes Fever in the Intensive Care Patient?
Fever in an Intensive Care Unit (ICU) could be either due to infections or non-infections. The majority of fevers in the ICU are caused by infections. In fact, a large-scale study found that 63% of critically ill patients with fever had a severe infection known as sepsis. Some of the most common types of infection include pneumonia caused by a ventilator, bloodstream infections linked to a catheter (a thin tube), infections from surgical sites, urinary tract infections related to catheters, and various types of bacteremia. Bacteremia is an infection that spreads through the bloodstream.
Common causes of fever are divided into two categories:
Infectious Causes:
This could range from Meningitis (infection of the fluid and membranes around the brain and spinal cord), Encephalitis (inflammation in the brain), Brain abscess (pus-filled swelling in the brain), or problems in different parts of the body like the respiratory, abdominal, cardiovascular system, skin, bone, joints etc.
Non-infectious Causes:
This could involve problems in the Central Nervous System (like Cerebral infarction, Cerebral hemorrhage, Subarachnoid hemorrhage), Respiratory issues (like ARDS, Atelectasis, Pulmonary embolism, Chemical pneumonitis), Abdominal complications (like Nosocomial diarrhea, Acalculous cholecystitis, Ischemic bowel, Gastrointestinal bleeding, Acute pancreatitis), problems in the Cardiovascular system (like myocardial infarction, Deep vein thrombosis, Pericarditis, Thrombophlebitis), and other issues in the skin, soft tissue, bone, joints, or the endocrine system.
In addition to these, some causes of fever are unique to the ICU environment:
1. Ventilator-associated pneumonia: A type of lung infection that occurs in people who are on breathing machines in hospitals.
2. Catheter-related bloodstream infection: Infection that happens when bacteria enter the bloodstream through a catheter.
3. Catheter-associated urinary tract infection: Infection in the urinary system caused by a catheter.
4. Clostridioides difficile colitis: A type of infection in the colon that can happen after antibiotic use.
5. Pressure ulcer: Bed sores that usually develop in people who can’t move around much.
6. Surgical wound-related infection: Infections that develop in the area of a recent surgical wound.
Risk Factors and Frequency for Fever in the Intensive Care Patient
The likelihood of developing a fever while in an Intensive Care Unit (ICU) can vary quite a bit. It can range between 26 to 88%. This percentage largely depends on the type of ICU, the group of patients being treated, and the specific definition of a fever that’s being used. One large study found that 44% of patients in medical and surgical ICUs developed a fever, with 8% experiencing a high fever. Another study found that the rate of fever occurrence in surgical ICUs was 26%. Interestingly, the percentage of fevers that stemmed from infectious and non-infectious sources was roughly the same.
A different study observed over 24,000 adults in ICUs. It found that in cases where a patient had a fever equal to or higher than 39.5 C (103 F), the death rate jumped from 12% to 20%. Aside from the increase in death rate, high fevers can also lead to longer hospital stays and higher healthcare costs. Additionally, patients with pancreatitis, traumatic head injuries, or subarachnoid hemorrhages can have worse health outcomes when they experience a fever.
Signs and Symptoms of Fever in the Intensive Care Patient
When a person in intensive care has a fever, it’s crucial for healthcare professionals to take a comprehensive medical history and conduct a detailed physical examination. This helps differentiate between infectious and non-infectious causes of fever, aiding in adjusting the ongoing treatment plan. Certain areas of the patient’s body, such as areas with a vascular access point, urinary catheters, drains, and surgical cuts, need careful examination.
Signs of possible infections need to be checked for, including changes in heart sounds which might suggest a heart infection, and the color, smell, thickness, and amount of secretions from the trachea. Also, evaluating the condition of the skin and soft tissue is essential, as conditions like cellulitis (a skin infection), furunculosis (boil infection), and paronychia (nail bed infection) are frequently observed. Other inconspicuous or undiagnosed sources of infection can include sinusitis, pressure sores, dental or throat infections, beneath the skin infections or abscesses, and wounds in the genital area. It’s important to be alert to drug-related fever as well, although such a diagnosis is usually a last resort.
In patients with weakened immune systems or those with a reduced count of certain white blood cells (neutropenic), the usual symptoms of infection might be lacking or very mild. In these cases, only a keen clinical eye can identify the origin of the fever-causing infection. Skin signs, such as sores, lumps, blisters, sinus infections around the tailbone area, and different skin conditions may be the hidden cause of an infection and need to be specifically checked in patients with a weakened immune system or those neutropenic. Infections around the anus can often be overlooked in neutropenic patients.
The body temperature’s accurate measurement is vital when a patient is in the ICU. The preferred way is to use a probe of a pulmonary artery catheter, but it’s rarely used because it’s invasive. Therefore, healthcare providers lean toward using sensors in the nose, throat, or bladder, followed by rectal and ear temperature measurements. Measurements taken from the armpit, mouth, or forehead are discouraged in the ICU. The severity of the fever might give clues about the potential cause.
Fevers with body temperature between 38.3 to 38.8 degrees Celsius can result from both infectious and non-infectious causes, leading to a broad list of possible diagnoses. Fevers above 38.9 and below 41 degrees are mostly linked to infections, whereas a fever of 41.1 degrees or higher is generally considered non-infectious.
Testing for Fever in the Intensive Care Patient
If you’re taken into hospital with concerns of sepsis, one of the first things they’ll test for is your lactate levels. High lactate levels are usually an indicator of sepsis because they show that the body is working harder than normal to produce fuel for your cells. In addition, your doctor might also want to conduct a complete blood count, as well as kidney and liver function tests to get a better understanding of your overall health.
If you have abdominal pain, certain tests like serum amylase and lipase might be conducted to rule out pancreatitis, which is a severe inflammation of the pancreas. In certain scenarios, tests like direct antiglobulin test, haptoglobin, free hemoglobin in the plasma, and repeat blood grouping and cross-matching might be necessary to detect transfusion reactions, which occur when your body reacts negatively to receiving a blood transfusion.
Your doctor might also want to check your thyroid profile if they suspect a thyroid storm, which is a severe and life-threatening complication of hyperthyroidism. An ACTH test or free cortisol measurement might be required for examining adrenal insufficiency, a condition where your adrenal glands don’t make enough hormones.
Before starting antibiotics, they will take fresh cultures. Blood cultures should be taken from all patients with fever, and additional cultures might be taken depending on the suspected source of infection. For example, tracheal secretions might be taken if pneumonia is suspected, urine cultures for suspected urinary tract infections, and cerebrospinal fluid (CSF) for suspected meningitis.
Doctors often look at C-reactive protein (CRP) and procalcitonin levels. CRP is a substance produced by the liver in response to inflammation and is often used to assess sepsis, although its specificity is low. Procalcitonin, another sepsis biomarker, aligns more with bacterial infections and can indicate disease severity better than CRP. However, bear in mind that increased procalcitonin levels can also appear in patients with non-infective conditions like trauma, major surgery, organ failure, and heart attack.
Imaging studies such as chest X-rays can help identify respiratory causes of fever and differentiate between pneumonia and tracheobronchitis. Ultrasound scans of the lung, abdomen, and pelvis can also help rule out sources of infection. For suspected deep vein thrombosis, a compression ultrasound & Doppler study of deep veins may be performed. In some complicated cases, a CT scan may be required to diagnose early and subtle limb ischemia, which can cause fever.
At times, a Contrast-Enhanced Abdominal CT is needed to detect an unknown source of fever in the abdomen. In certain cases when infection source is not detected, sinusitis is evaluated especially in neutropenic patients – a CT scan of the paranasal sinuses is performed. In rare occasions, a whole-body positron emission tomography (PET) scan may be required to diagnose the fever source in an ICU patient.
Endoscopic procedures might be required to diagnose uncommon causes of fever. These procedures involve inserting a thin tube with a camera on the end into the body to visualise organs. In cases where certain infectious gastrointestinal conditions are suspected, colonoscopy might be required.
If you’re about to undergo treatment with antimicrobials, blood cultures from two different sites should be drawn. Also, if you have a central intravascular catheter inserted, blood from the catheter should be obtained. For probable fungal infection, blood would be used to additionally inoculate fungal culture vessels.
In cases where respiratory tract infection is suspected, endotracheal aspirate (fluid from your windpipe) or sputum (mucus from your respiratory tract) might be collected and analysed under a microscope for any signs of infection.
Treatment Options for Fever in the Intensive Care Patient
If a patient is suspected of having an infection, it’s important to start them on antibiotic treatments as soon as possible – this is especially key in serious infection cases like sepsis and septic shock. The choice of antibiotics depends on various factors such as the type of infection, the body part affected, local antibiotic resistance patterns, and the patient’s specific risk for drug resistance. To provide effective treatment, the antibiotics need to be given in the right amount and for the right length of time.
Where possible, doctors will try to ‘deescalate’ the treatment – that means, they will aim to switch the patient from a broad-spectrum to a narrower-spectrum antibiotic (based on culture tests), switch from intravenous to oral antibiotics if possible, and stop the treatment once the infection is under control. This approach is key to preventing more widespread antibiotic resistance.
Identifying and treating the source of the infection is also a key step – that might involve removing devices such as catheters or IV lines that might have become contaminated, or draining infected fluid collections such as abscesses or empyemas.
Managing fever in patients with infections is another important aspect of care. Fever can be a body’s natural response to fight off infections – it can inhibit bacterial growth, stimulate immune responses, and activate infection-fighting white blood cells. However, fever can also increase the body’s metabolism and oxygen needs, and can have negative effects in patients with nerve or brain injuries.
Whether to treat a fever in a patient is something doctors must weigh carefully. High fevers above 40 degrees Celsius (104 degrees Fahrenheit) in patients without infections need to be controlled aggressively. In some cases, mild to moderate fevers (37.5 to 38.4 degrees Celsius, or 99.5 to 101.1 degrees Fahrenheit) in patients with sepsis were found to be associated with a decrease in mortality rates. A review study showed that fever-reducing drugs didn’t lower mortality rates or prevent hospital-acquired infections in critically ill patients with sepsis.
For fever control in the Intensive Care Unit (ICU), experts often prefer acetaminophen (or paracetamol) over aspirin. Acetaminophen is usually delivered via the mouth or feeding tubes and is well absorbed by the body. Intravenous administration of acetaminophen may be needed when a patient cannot take medications by mouth, but it has been associated with a decrease in blood pressure, which doctors need to monitor carefully.
What else can Fever in the Intensive Care Patient be?
In medical settings like the ICU, most fevers are caused by infections. However, sometimes they can be caused by non-infectious conditions. It’s always important to explore all possibilities to avoid unnecessarily using antibiotics.
For example, fever is commonly observed in the first two days after surgery. This early post-surgery fever doesn’t usually mean there’s an infection, but rather, it’s a response to the inflammation caused by the surgery. This type of fever doesn’t usually require more investigation. However, if a fever shows up between 72-96 hours after surgery, it might be caused by an infection and further tests will be necessary. Potential causes include infections of the surgical wound, a collapsed lung, urinary tract infections, deep vein thrombosis, inflamed veins, and blood clots in the lung.
In ICU settings, there are other scenarios to consider:
- Ventilator-associated Pneumonia (VAP): This is a form of pneumonia that happens 48 hours or more after intubation. The diagnosis is typically based on clinical signs, chest x-rays, and lab cultures from the lower respiratory tract. It can often be prevented by following stringent infection control practices and specific prevention measures. Treatment usually involves intravenous antibiotics.
- Catheter-related Bloodstream Infection (CRBSI): These infections can happen due to intravenous catheters and are a common cause of hospital-acquired bloodstream infections. A confirmed diagnosis typically requires finding the same bacteria both in blood samples and on the catheter tip. Treatment includes removal of the catheter and antibiotics.
- Urinary Tract Infections from Catheters (CAUTI): These infections can occur in patients who have a urinary catheter currently or who had one within the last 48 hours. Diagnosing this condition requires testing urine samples obtained directly from the sampling port of the catheter. If the catheter has been in for more than 2 weeks, it should be replaced before testing.
- Pressure Ulcers: These wounds are a non-infectious cause of fever. However, they can often lead to infection and sepsis. Care can be costly, and they’re often uncomfortable for the patient.
- Acalculous Cholecystitis: This gallbladder inflammation typically happens without the presence of gallstones and is due to the dysfunction of gallbladder emptying. Symptoms include fever, jaundice, and right upper abdominal pain. Diagnosis requires abdominal ultrasound, and sometimes, a CT scan may be required. Treatment includes drainage or stent placement in unstable patients, while removal of the gallbladder is a definitive treatment.
- Nosocomial Sinusitis: This term refers to sinusitis, or inflammation of the sinuses, that develops during a hospital stay. Nasogastric or nasotracheal tubes, facial fractures, nasal packing, and steroids are risk factors. Diagnosing this condition can be challenging in ICU patients and may require a CT scan. Treatment usually involves removing any foreign bodies like a nasogastric tube, using nasal vasoconstrictors, and administering antibiotics.
- Diarrhea from Hospital-acquired Infections: The organism Clostridioides difficile, often referred to as C. diff, frequently causes diarrhea in hospital environments – mostly impacting patients who have been treated with antibiotics. The key signs of infection are loose and frequent stools and the presence of toxins created by the bacterium in the stools. Treatment involves adjusting the patient’s current antibiotic regimen, supportive remedies and specific antibiotics to clear the C. diff infection, such as metronidazole, vancomycin or fidaxomicin.
- Drug Fever: Around 3-5% of fevers in the ICU are caused by medication reactions. This type of fever is diagnosed based on the timing of the fever in relation to when the drug was taken. Some common medications associated with drug fever include antibiotic beta-lactams, anti-epileptics such as phenytoin, antiarrhythmic drugs, diuretics, allopurinol, and heparin. The fever typically starts 7-10 days after starting the medication and disappears within 72 hours after stopping the medication.
- Hyperthermia Syndromes: These include conditions with extremely high body temperatures (above 41 degrees C, or about 106 degrees F). Various conditions can cause hyperthermia, such as heat stroke, malignant hyperthermia, neuroleptic malignant syndrome, serotonin syndrome, and other endocrine conditions like thyrotoxicosis and adrenal crises.
What to expect with Fever in the Intensive Care Patient
For patients who have had a stroke or other neurological injuries, having a fever, regardless of the reason, has demonstrated worse outcomes. This can lead to a more challenging recovery and a longer stay in the hospital. On the other hand, there is no clear evidence that a fever increases the risk of death in patients without neurological conditions. The outcomes can differ, depending on the cause of the fever.
Possible Complications When Diagnosed with Fever in the Intensive Care Patient
Fever can have some harmful effects on the body. It can make your heart work harder, cause you to use up more oxygen, and produce more carbon dioxide. It’s important to be aware that fever can trigger seizures in children between the ages of 3 months and six years, especially if there’s a family history of this happening.
Fever can also make the outcomes worse for people who’ve had a brain injury or stroke. When people with these conditions develop a new fever, they may often show a drop in their GCS score, which is a measurement of consciousness level.
Another important aspect is that fever during pregnancy can be linked with birth defects and miscarriage.
- Increased heart workload
- Raised oxygen consumption
- Increased carbon dioxide production
- Seizures in children
- Lower GCS scores in patients with brain injury or stroke
- Birth defects and miscarriage linked to pregnancy fevers
If a high fever keeps going for a long time, it can even cause a condition called rhabdomyolysis, which can, in turn, cause acute kidney injury and the need for kidney dialysis.
There could be significant indirect effects of fever as well. The cost of diagnosing and treating fevers can build up. Also, unexplained fevers can often result in misuse or overuse of antibiotics, leading to financial strain and the possibility of bacteria becoming resistant to multiple drugs.
- Possible development of rhabdomyolysis
- Acute kidney injury
- Need for kidney dialysis
- Higher costs for diagnosing and treating fevers
- Misuse or overuse of antibiotics
- Risk of bacteria becoming drug-resistant
Preventing Fever in the Intensive Care Patient
If a patient who is already in the intensive care unit (ICU) starts having a fever, he or she or their family should be properly informed about the number of tests and check-ups that may be needed. This situation becomes more critical if a new fever appears out of the blue, especially if it shows signs of a serious condition called sepsis or septic shock. Sepsis happens when an infection spreads throughout the body, which can cause organs to stop working properly.
The patient’s family should also be made aware of the possible complications, including an extended stay in the ICU. It’s important they understand the serious nature of these types of illnesses (secondary sepsis) and the associated health risks, including a potentially fatal outcome.
