MAPD: Modifiable Factors Affecting Propofol Dosing

The investigators hypothesise that modifiable environmental factors may cause reversible changes in a patients neurobiology which affect their responsiveness to anaesthetic drugs. Such factors may include chronic caffeine intake, chronic sleep deprivation, acute anxiety about surgery, alcohol intake and smoking. Investigation of the relationship between such factors and the dose of anaesthetic required for loss of consciousness may not only allow for better prediction of dose requirements but may also allow for optimisation of patients prior to undergoing general anaesthesia with a view to decreasing anaesthetic dose requirements and the complications associated with this.

To address this questions, the investigators will be asking patients admitted for any day case surgery at Chelsea & Westminster hospital to complete five short questionnaires and a demographic sheet addressing 1) Caffeine intake 2) Sleep habits 3) Anxiety about the operation 4) Alcohol intake 5) Smoking status.

This will then be compared to the amount of the anaesthetic drug Propofol required and the time taken to induce loss of consciousness prior to surgery. Loss of consciousness will be measured subjectively by loss of eye opening response and loss of verbal response when a patient is asked to count upwards from 1.

The investigators also wish to investigate whether these same 5 factors affect patient reported postoperative pain and analgesia requirements. As such the investigators will also ask participants to rate their level of pain whilst at rest and whilst coughing at 1 hour after the operation. We will also record how much analgesia is requested and received in the postoperative period.

Inclusion criteria

ASA I or II patients scheduled for elective day case general anaesthesia with Laryngeal Mask Airway (LMA) airway insertion and a standard propofol-fentanyl induction, aged between 18-65 years at Chelsea & Westminster Hospital.

Exclusion criteria

• Pregnancy
• Neurological disease
• Substance abuse
• Cardiac disease
• Renal disease
• Obesity

Additional exclusion criteria include:

• Any patient requiring adjunctive analgesia including local/epidural/spinal anaesthesia.
• Any patient requiring an anesthetic induction regime other than propofol-fentanyl (inc. administration of benzodiazepines or other strong opioids).
• Any patient who does not receive a standard anaesthetic induction regime due to clinical need