Effects of Propofol Sedation on the Critically Ill

Anxiety, agitation and restless movements can negatively impact the hemodynamic stability of acutely ill patients in intensive care units. Sedation is often required to reduce anxiety and agitation in ICU patients.

Propofol is a general anesthetic used to reduce anxiety, restlessness and agitation in several situations; for example, during short procedures, during the initial hours after surgery, and in agitated patients with neurological disorders or neurological injury. The sedating effects of propofol are particularly useful in critical care patients with cardiac, respiratory, or neurological disorders who are on mechanical ventilation.

The exact mechanism of action of propofol is unknown. Propofol has no analgesic (pain relieving) properties but does have amnesic (loss of memory) properties when given at a dosage of at least 5 µg/kg per minute. Propofol produces rapid sedation, usually within 40 seconds of starting the propofol drip. Awakening from sedation induced by propofol usually occurs 10 to 20 minutes after infusion of the drug is stopped.

Physiological Effects of Propofol

Propofol and the Cardiovascular System:

Propofol can cause hypotension (low blood pressure) and bradycardia (slow heart rate). However, propofol is also known to decrease myocardial oxygen consumption. This can be of some benefit, particularly in patients with adult respiratory distress syndrome, myocardial ischemic diseases, or patients in states of shock. Propofol is thought to decrease myocardial oxygen demand by decreasing cardiac contractility and, thus, decreasing myocardial workload.

Propofol must be used cautiously in shock patients due to its potential to cause hypotension. Use of alternative agents such as midazolam (versed) may be necessary when in patients with compromised blood pressure.

Propofol and the Pulmonary System:

Propofol affects several aspects of pulmonary function, possibly due to the inhibition of intracellular calcium in the bronchioles (small airways) with subsequent relaxation of bronchiolar smooth muscle and opening of the airways. Minute ventilation, tidal volume, mean inspiratory flow rate, and functional residual capacity are measures of lung function that are all decreased during use of propofol.

Propofol and the Nervous System:

Propofol easily crosses the blood-brain barrier to produce neurological effects. Propofol can decrease elevated intracranial pressure (the pressure inside the skull) without causing marked decreases in cerebral perfusion pressure (the blood pressure supplying the brain). In addition, propofol decreases cerebral blood flow, increases cerebral vascular resistance, and decreases cerebral metabolic oxygen requirements. The exact mechanism of these neurological actions of propofol is unknown.

Propofol and Metabolism:

Propofol is often prepared in a soybean oil emulsion. The use of a lipid emulsion for propofol is associated with increased fat in the bloodstream, leading to elevated triglyceride levels. Patients on long term sedation with propofol who are also receiving enteral (GI) or parenteral (IV) nutrition must, therefore, be monitored to avoid overfeeding and high triglyceride levels.

Propofol is a general anesthetic that can be used in the ICU when short-term (from several hours up to 5 days) sedation is required. Long-term sedation with propofol can result in tolerance to the medication. When tolerance occurs, increased doses of propfol are required to achieve the same level of sedation. Nurses and physicians working in the ICU should be familiar with the physiologic effects and use of propofol in acutely ill patients.

References:

Ding Y. Propofol infusion during regional anesthesia: sedative, amnesic, and anxiolytic properties. Anesth Analg. 1994;79:313-319.

Covington H. Use of Propofol for Sedation in the ICU. Critical Care Nurse, Vol 18, No. 4, pp 34-39. 1998.