Placebo Versus Nocebo: Effects on Pain and Anxiety During Local Anaesthetic Infiltration in Parturient Undergoing Elective Caesarean Delivery

Overview

This randomized trial compared placebo and nocebo effect over anaesthetist-patient communication on pain and anxiety score during local anaesthetic (LA) skin infiltration in parturient undergoing caesarean delivery under regional anaesthesia (RA). A secondary objective was to determine if education level and previous RA experience affect pain and anxiety scores. Parturients scheduled for elective caesarean delivery were randomised into Placebo (P) or Nocebo (N) group. Baseline Amsterdam Preoperative Anxiety \& Information Scale (APAIS0) were obtained. Standardised scripts describing the LA skin infiltration for RA were used during the pre-anaesthetic review. (N) group were explained with words like "pain, prick, sharp" while words like "numb, comfort, tolerable" were used in the (P) group, avoiding "painful" expressions. The same scripts will be repeated before skin infiltration during the RA procedure. On the day of surgery, a second (APAIS1) was obtained upon arrival to the theatre. Pain score using the numerical rating scale (NRS) was assessed after LA infiltration.

We randomised participants into either the nocebo (N) or placebo (P) group. We obtained a baseline anxiety score (APAIS0) using the Amsterdam Preoperative Anxiety and Information Scale (APAIS) during the pre-anaesthesia visit. Following that, we informed subjects in the N group a negative suggestion, using the following script: "During the local anaesthetic injection, you are going to feel a sharp prick at your back; this is usually the most painful part of the procedure". On the other hand, we used a positive suggestion on the P group: "We will administer some local anaesthetic to numb your back; this will allow the procedure to be more comfortable and tolerable for you." We obtain a second anxiety score (APAIS1) in the operating theatre before the caesarean section. We carried out either spinal anaesthesia or continuous spinal epidural according to standard hospital protocol and indication. Before the LA skin infiltration, the anaesthetist repeats the same script to the subjects according to the prior randomisation. Five millilitres of lignocaine 2% is injected intradermally and subcutaneously by the anaesthetist into interspinous space in a single pass through a 22-gauge needle to create a skin wheal. During the LA infiltration, only the attending anaesthetist performing the procedure gave participants verbal instructions; other personnel remained silent throughout. We recorded the presence of vocalisation of pain, withdrawal movement or facial grimacing. Immediately after the LA infiltration, a blinded and trained general anaesthetic nurse or personnel enters the operating theatre to assess the subjects' pain score using the numerical rating scale (NRS). After collection of the pain score, the anaesthetist performed the remaining anaesthetic procedure as per clinical routine.