To provide adequate sedation and analgesia is integral to the care and management of the patient in critical care.
The postoperative patient
In contrast to most other types of surgery, patients after cardiac surgery are usually sedated and ventilated in the immediate postoperative period, until normothermia and haemodynamic stability are achieved and lack of bleeding is confirmed.
Sedation allows a reduction of oxygen consumption during rewarming; it inhibits shivering. Shivering is associated with a three- to four-fold increase in O2 consumption and leads to an increase in CO2 production with respiratory acidosis. Intraoperative hypothermia should be avoided where possible and active warming employed. Increasing sedation or adding clonidine may be beneficial if shivering persists.
Early postoperative haemodynamic instability can have many causes, and might necessitate reexploration or further investigation. Deep levels of sedation were advocated in the past to reduce the stress response of cardiac surgery and the incidence of myocardial ischemia, but this is no longer thought to be beneficial. Moreover, heavy sedation has itself been associated with increased myocardial ischemia.
The non-postoperative patient
The most common reason for sedation in critical care is to permit mechanical ventilation and tolerance of the artificial airway (endotracheal tube). Low levels of sedation should be used and patients should ideally be easy to rouse and remain calm and cooperative.