The perfusion index (PI) is the ratio of the pulsatile to the non-pulsatile blood flow in peripheral tissue. It represents a non-invasive measure of peripheral perfusion that can be continuously obtained from a pulse oximeter. This property explains the fact that it decreases with vasoconstriction and increases with vasodilatation.

An increase in PI was proved to be an early indicator for the success of general and regional anaesthesia, which cause initial peripheral vasodilatation before the onset of anaesthetic effect. Whereas a failed increase in PI would suggest failure of anaesthesia.

The PI has been reported to decrease when noxious stimulus was applied to anaesthetized volunteers. A recent study on critically ill non-intubated patients has demonstrated a good correlation between changes in PI and changes in Behavioral Pain Scale-non intubated values after a painful stimulus was applied.

Despite the rising use of perfusion index in anaesthesia and intensive care, few studies have investigated its capability as a pain assessment tool, and to our knowledge, it has not been investigated in intubated critically ill patients yet.

All patients after admission will be monitored with the use of routine monitoring tools: Electrocardiogram, pulse oximetry, and automated noninvasive blood pressure (NIBP). Day-to-day investigations will be carried out to monitor and individualize treatment. Medical (and/or) surgical treatment will be performed, supervised by the attending intensivist and surgeon.

Sedation and analgesia protocol will be prescribed by the patient's primary intensivist. Another pulse oximeter probe (Masimo Radical 7; Masimo Corp., Irvine, CA, USA) will be attached to the patient's index finger during changing the patient's position (head of bed elevation) after abdominal surgery. This pulse oximeter will be connected to the Masimo monitor and shielded to prevent outside light from interfering with the signal.

Sedation will be assessed by using the Richmond Agitation- Sedation scale (RASS). Pain assessment will be achieved by using the behavioural pain scale intubated (BPS-IN).

Sedation and analgesia will be guided by the BPS and RASS. For analgesia the patients will receive a loading dose (0.05-0.2 mg/kg) morphine sulphate I.V., followed by (2-10 mg/h) infusion to keep the BPS between 3 and 6. If the pain score is more than 6, a rescue dose of 3 mg will be given, and then the pain will be reassessed after 5 min. If the patient received more than 2 boluses/h, the infusion dose will be increased by 2 mg/h.

For sedation, the patients will receive a loading dose of propofol 0.005 mg/kg/min IV for at least 5 min., followed by (0.005-0.05 mg/kg/min) IV infusion to achieve a RASS score of 0 to -1. A rescue dose of 5-10 mcg/kg/min over 5-10 min intervals if the RASS score is more than 0; allow a minimum of 5 min between adjustments for onset of peak effect.

Inclusion Criteria:

• Sedated intubated surgical ICU patients during the first two postoperative days following abdominal surgery.

Exclusion Criteria:

• Patients with a history of neurologic disorder (hemiparesis, quadriparesis, and neuropathy).
• Patients with an epidural catheter with local anaesthetic injection for the purpose of analgesia.
• Patients receiving neuromuscular blockade.
• Patients with peripheral vascular disease.
• Patients suffering from fever.
• Hypothermia.
• Use of vasopressors.
• Patients with altered level of consciousness (GCS <4).

Sedated intubated surgical ICU patients aged 18 to 60 years old