Intensive Care Unit

The high dependency unit (HDU) and intensive care unit (ICU) are specialised hospital wards that manage severely unwell patients. Generally, level 1 patients can be managed on a general acute ward, level 2 patients can be managed on the high dependency unit and level 3 patients can be managed on the intensive care unit (the highest level of support). 

ICUs are run by intensive care specialists and specialist intensive care nurses. Each nurse only cares for one or two patients at a time. Patients admitted to the unit usually have some form of organ failure, requiring organ support and intensive monitoring.


Common reasons patients are admitted to intensive care are:

  • Following major surgery (e.g., aortic aneurysm repair)
  • Severe sepsis
  • Major trauma
  • Following cardiopulmonary resuscitation
  • Organ failure (acute respiratory, renal or liver failure)


In the intensive care unit, patients can have advanced organ support. This includes:

  • Respiratory support
  • Cardiovascular support
  • Renal support
  • Nutritional support
  • Neurological support
  • Dermatological support
  • Liver support



Whether to admit someone to the intensive care unit is the decision of the intensive care specialists. The capacity of intensive care units is often low, and the impact of intensive therapy on patients is very high, meaning that careful thought and consideration need to be put into deciding whether a patient will benefit from admission. The two main factors that are considered are the potential to reverse the acute condition and the baseline physiological reserve (their baseline health).

For example, in patients with a 90% probability of dying from their current illness and an underlying terminal condition, it does not make sense to admit them for extensive invasive interventions. A palliative care approach on a general ward or at home would be much more appropriate. 

There are scoring systems that can help predict mortality at the time of admission to ICU:

  • APACHE (Acute Physiology and Chronic Health Evaluation)
  • SAPS (Simplified Acute Physiology Score)
  • MPM (Mortality Prediction Model)


Nutritional Support

Nutrition is really important in critically ill patients. They are in a hypermetabolic state and have increased nutritional requirements. There is a high risk of malnutrition, which can contribute to worse outcomes. Dieticians are involved in helping ensure patients meet their nutritional requirements.

Where possible, patients should get their nutrition via their gastrointestinal tract. Having nutrition via the gastrointestinal tract is called enteral nutrition. This could be by:

  • Mouth
  • NG tube
  • Percutaneous endoscopic gastrostomy (PEG) – a tube from the surface of the abdomen to the stomach


Total parenteral nutrition (TPN) involves meeting the complete nutritional requirements of the patient using an intravenous infusion of a solution of carbohydrates, fats, proteins, vitamins and minerals. This is used where it is not possible to use the gastrointestinal tract for nutrition. It is prescribed under the guidance of a dietician. TPN is very irritant to veins and can cause thrombophlebitis, so it is normally given through a central line rather than a peripheral cannula.



There are various complications associated with admission and treatment on ICU. These include:

  • Ventilator-associated lung injury
  • Ventilator-associated pneumonia
  • Catheter-related bloodstream infections (e.g., from central venous catheters)
  • Catheter-associated urinary tract infections
  • Stress-related mucosal disease (erosion of the upper gastrointestinal tract)
  • Delirium
  • Venous thromboembolism
  • Critical illness myopathy
  • Critical illness neuropathy


Ventilator-associated lung injury is a common complication of mechanical ventilation. Forcefully blowing air into the lungs can cause volutrauma (damage from over-inflating the alveoli), barotrauma (damage from pressure changes) and inflammation. It can lead to short term pulmonary oedema and hypoxia. Long-term, it can lead to fibrosis of lung tissue, reduced lung function, recurrent infections and cor-pulmonale. Using optimal settings and pressures during mechanical ventilation helps reduce the risk of lung injury. 

Ventilator-associated pneumonia is a common complication of mechanical ventilation (up to 25%) and carries a high risk of death (up to 25%). Being ventilated increases the risk of bacteria being aspirated into the lungs. Positioning the bed at a 30-degree angle with the patient’s head elevated reduces the risk of aspirating secretions from the stomach. Good oral care with regular mouth cleaning is also important to reduce the risk of ventilator-associated pneumonia.

Catheter-related bloodstream infections describe infections introduced by invasive lines, such as central venous catheters. These are also common (up to 25%) and carry a high risk of death (up to 25%). The risk may be reduced by using antibiotic-impregnated or silver-impregnated catheters and keeping them in for the shortest time possible.

Catheter-associated urinary tract infections are common. The risk can be reduced by only using urinary catheters when necessary and keeping them in for the shortest time possible.

Stress-related mucosal disease is common in critically unwell patients. Damage to the stomach mucosa occurs mainly due to impaired blood flow. It increases the risk of upper gastrointestinal bleeding, which can be life-threatening. The risk may be reduced by suppressing acid secretion in the stomach using proton pump inhibitors (e.g., omeprazole) or H2 receptor antagonists (e.g., ranitidine). Starting NG feeding early in patients that cannot eat normally also has a protective effect, even if only small volumes are used (trophic feeds are small volumes used for gastrointestinal benefits but are insufficient to meet nutritional requirements).

Delirium (impaired mental state) is a very common complication of both critical illness and intensive care. A long list of things can cause acute confusion, including pain, infection, hypoxia, electrolyte disturbances, renal failure, and medications. Usually, patients in ICU will have many of these occurring at the same time. The Confusion Assessment Method (CAM) can be used as a scoring system for identifying delirium. Dexmedetomidine is a medication used in the intensive care unit to sedate agitated patients.

Venous thromboembolism (VTE) includes deep vein thrombosis and pulmonary embolism. Critically ill patients are at higher risk of VTE. Every patient will have a risk assessment to determine whether they require prophylaxis. The main preventative measures are low molecular weight heparin (e.g., enoxaparin) and intermittent pneumatic compression devices (e.g., Flowtrons) that regularly inflate to squeeze the legs and promote blood flow. 

Critical illness myopathy refers to muscle wasting and weakness during critical illness and treatment in the ICU. The weakness mostly affects the limbs and respiratory muscles. The use of corticosteroids or muscle relaxants is an important cause. Short-term, it can lead to difficulty weaning the patient off mechanical ventilation. Long-term, it can result in reduced exercise capacity and quality of life. It can take years to recover.  

Critical illness polyneuropathy refers to degeneration of the sensory and motor nerve axons during critical illness and treatment in the ICU. It often occurs alongside critical illness myopathy. There is a wide range of pathological processes that result in degeneration of the nerves. Having optimal control of blood sugar levels (glycaemic control) is important in reducing the risk. It causes symmetrical weakness, decreased muscle tone and reduced reflexes. It often makes it difficult to wean patients off mechanical ventilation.


Last updated August 2021
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