Nasrullah Khan, Tariq Masood Tipu, Saadia Tariq, Muhammad Rashid Khan.
Efficacy of Lignocaine / Propofol Vs Ketamine/Propofol Mixtures in reducing pain on Injection of Propofol 1% at the time of induction.
Pak J Med Health Sci Jan ;7(1):236-8.

Propofol is a commonly used induction agent in day to day anesthesia practice especially after unavailability of thiopentone sodium. The disadvantage of this agent is pain at the site of injection, which at times is very severe in nature. A higher concentration of propofol in the aqueous phase of the preparation causes a higher incidence of pain on injection while addition of 1% lidocaine or 1% ketamine in saline to propofol reduces pain. The low concentration of these agents and rapid pain relief observed indicates that some mechanism other than local anesthetizing effect is also involved, and that possibly could be change in pH as well. We carried out a clinical study to investigate the effects of change in pH by adding lidocaine or ketamine in saline solution with propofol at time of injection to see pain response of patient.18 parts of 1% propofol were mixed either with 2ml of 1% ketamine or 1% lidocaine. The pH of both solutions was measured. The lowering of pH due to addition of these solutions to propofol is considered the reason for pain relief because when same agents were given prior to propofol without mixing with it, the pain was not completely relieved. Thus pH changes may modify propofol-induced pain on injection by a mechanism different from the effect of the local anesthetic on the vascular endothelium.

PakMediNet -Pakistan's largest Database of Pakistani Medical Journals - http://www.pakmedinet.com