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Common Illnesses of Critical Care Patients

Listed below are some of the common illnesses of patients in the intensive care unit (ICU). Although it is impossible to cover every illness and every detail here, some things occur often. This section describes some common ICU illnesses in simple language. Illnesses are grouped by the “systems” of the body.

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Cardiovascular System

The cardiovascular system includes the heart and all of the vessels that carry blood to the body. Blood carries oxygen and food that every cell in the body needs for life. If the heart or blood vessels fail to get enough blood to the body, the important organs of the body may be temporarily or permanently damaged.

Myocardial infarction – or “heart attack” – happens when the heart muscle itself doesn’t get enough blood because one or more of its blood vessels, called coronary arteries, becomes blocked (this used to be called “hardening of the arteries”). When this happens, an awake person may have chest pain or pressure, pain in the jaw, neck or shoulder, shortness of breath, sweating, nausea or vomiting. Critically ill patients are often not awake and so they may not be able to complain of these symptoms. Heart attacks are treated by measures to get blood flowing back through the blocked coronary arteries, but the longer the blockage is there, the more likely that heart cells will die leading to permanent damage.

Shock – is a term used to describe when the blood pressure drops to a dangerously low level. If the pressure falls enough, the cells in the body don’t get enough oxygen and begin to die. If enough cells die, organs of the body, like the kidneys, brain and liver, may also stop working right. Common reasons for shock are severe infections (this is called “septic shock”), heart attacks (this is called “cardiogenic shock”) or severe blood loss (called “hemorrhagic shock”). There are also other less common causes.

Arrhythmia – is a term used to describe when the heartbeat, which normally goes at a regular rate of 60 to 100 beats every minute, becomes too fast or too slow. Sometimes medicines can be given to help. But other times, abnormal heartbeats are so bad that not enough blood gets to the organs of the body or blood backs up into the lungs. If this happens an electrical shock, given by two paddles on the chest wall, may be needed to put the heart back to a more normal rate.

Congestive Heart Failure – is a term used to describe when the heart fails to pump enough blood forward to the body and as a result, fluid builds up in the lungs, called “pulmonary edema.” This can cause shortness of breath, sometimes so bad that a patient may need to go on a breathing machine until it can be treated.

Pulmonary System

The pulmonary system includes the lungs and the muscles of breathing, such as the diaphragm, which pump air into and out of the lungs. The purpose of the lungs is to get enough oxygen into the body and to get rid of carbon dioxide that is a waste product of the body.

Respiratory failure – Respiratory failure happens when a machine is needed to help with breathing.

Pneumonia – is an infection of the lungs and a very common cause of critical illness. It happens when a germ, such as a bacteria or virus, enters the body, usually through the nose or mouth, and then goes down into the lungs causing them to flood with pus and fluid. Pneumonia can be a problem that leads to the need for hospitalization or it can occur as a complication in the hospital. Pneumonia often causes fever, cough and shortness of breath.


The purpose of the kidneys is to remove waste from the blood which is carried out of the body in the urine when we pass water.

Kidney failure – A number of problems can cause the kidneys to be damaged and fail to remove waste from the body. Dehydration, low blood pressure, inflammation of the kidneys, effects of medicines or x-ray tests and blockage of the tubes that take urine out of the body are common reasons for the kidneys to fail. Patients with problems like high blood pressure or diabetes that have already damaged the kidney have a greater risk of getting kidney failure for one of the reasons listed above. When the kidneys cannot remove all of the wastes from the blood, waste builds up and can cause problems.

Gastrointestinal System

The Gastrointestinal System is the mouth, esophagus, stomach and intestines, that carry food into our body.

Bleeding – A very common reason for admission to intensive care is bleeding from the esophagus, stomach or intestines. Ulcers in the stomach or intestines may cause belly pain, nausea and vomiting of blood. Tar-black stool is another sign of bleeding from the stomach or small intestines, called “upper GI bleeding.” Tumors, outpouchings (called diverticuli), and blood vessel abnormalities in the lower intestines can cause bleeding from the colon or rectum called “lower GI bleeding.”

Malnutrition – is a common complication of critical illness. Good nutrition is very important for the body’s ability to heal and fight off infections. Food can be given by mouth, through a feeding tube or by vein.

Nervous System

The Nervous System is the brain, which is responsible for thinking and controlling other parts of the body, and spinal cord and nerves that connect the brain to the arms, legs and other organs.

Stroke – is when a blood vessel of the brain becomes blocked, so that blood cannot carry oxygen to the cells beyond the blockage. If the blockage clears before permanent damage has occurred it is sometimes called a “mini-stroke” (or transient ischemic attack; “TIA” for short). If the blockage stays for long enough, brain cells begin to die, leading to permanent damage. Depending upon which cells in the brain die, patients may have difficulty moving arms or legs, talking or may even go into a coma.

Encephalopathy – is a term used to describe when patients aren’t thinking clearly or are confused. An infection or other illness that directly involves the brain may cause encephalopathy. Many illnesses that cause critical illness can cause encephalopathy without directly involving the brain. Encephalopathy is quite common, especially in older patients who get critically ill for any reason.


Infections are caused by germs: viruses, bacteria and fungus. The most common infections that require either coming into the hospital in the first place, or that occur as a complication of being in the hospital, are caused by bacteria.

Sepsis – is the response of the body against a germ, and can occur from an infection in any part of the body. Weakness and ache are common symptoms of sepsis. Fever, a fast heart-beat and fast breathing are common signs of sepsis. The body’s immune system tries to fight the infection, but with some infections, antibiotics are needed to help the body defend itself. If the infection gets worse it can involve the kidneys, brain, lungs and other organs of the body.

Multiple System Organ Failure

Multiple System Organ Failure is when more than one organ of the body stops working normally. Since each organ of the body has its own important purpose to keep us well, the more organs that don’t work properly, the less likely it is that a patient will get better from a critical illness. Organs can stop working, or “fail,” for a number of different reasons. Some common reasons that cause more than one organ at a time to fail are serious infections, low blood pressure or serious injuries.