Pain is an unpleasant and important stress factor, and a potentially harmful experience for critically ill patients. Pain is harder to evaluate in non-communicative patients, who can´t report their own pain. Behavioral indicators have been proved as useful and reliable for detecting and measuring pain in these patients, and have been the basis for constructing scales for measuring pain, such as the Behavioural Pain Scale (BPS), the Critical Care Observation Tool (CPOT) and the Scale of Behaviors Indicating Pain (ESCID) .

The BPS and ESCID were tested in a study with a sample of 42 critically ill patients in Spain, showing good validity and reliability.

The objective of this Spanish multicentre study is to test the validity and reliability of the ESCID scale in a large sample of critically ill patients with medical and postsurgical pathology for the detection and measurement of pain.

The specific Aims for the study are :

To determine the validity and reliability of the ESCID scale to assess pain in non-communicative critically ill patients on mechanical ventilation, in a large sample of critically ill medical and surgical patients.

To assess the relationship between the application of a common and painful procedure, usual in daily practice, and its associated changes in physiological indicators of pain: variation of heart rate, blood pressure, respiratory rate, sweating.

To assess the degree of pain when applying two painful procedures documented as common in the usual care of critically ill patients, and one non-painful procedure, using two pain scales: ESCID and BPS.

To assess the differences in the employment of the pain scales in patients with medical and surgical pathology.

Inclusion Criteria:

• Patient must be 18 years of age or older
• Patient's primary language spanish where the evaluation is performed
• Patient meets IRB/Central EC requirements of the institution/ country where the evaluation is performed
• Patient is receiving the study's procedures as part of standard care, excepting the non painful procedure

Exclusion Criteria:

• Patient's condition is very unstable at the time of measurement of pain
• Patient is receiving neuromuscular blocking medications at the time of measurement of pain
• Patient´s probable or diagnosed delirium

ICU patients who are uncommunictive, receiving mechanical ventilation and undergoing any of the study procedures. Consent to participate will be requested to the family of the patient. Adults age 18 and over will be eligible for the study if they meet study inclusion criteria and don't meet any exclusion criteria.