The purpose of this study is to determine if propofol could protect erythrocytes by directly scavenging free radicals from the blood current and increasing resistance of their cell membranes in patients submitted to gastroplasty.

Inclusion Criteria:

• patients between BMI 40-50 kg/m2

Exclusion Criteria:

• patients with BMI under 40 kg/m2 and over 50 kg/m2
• alcohol users
• illicit-drug users
• patients in regular use of anti-depressants, proton bomb inhibitors or calcium canal blockers
• patients transfused either recently, during the intra-operative period or within 10 hours post-operative
• patients previously known to be hypersensitive to any drug that is used during the study
• patients with any psychiatric disorder or dementia