Combination of Magnesium and Lidocaine for the Pretreatment of Pain That is Caused by the Injection of Propofol

Since the introduction of propofol into routine anesthesia practice, the phenomena of pain on injection has plagued anesthesia providers. Propofol, an unstable phenol, triggers the release of bradykinin on injection. This release causes a painful burning sensation in the patient at the site of injection. Anesthesia providers have attempted a large number of remedies to prevent this pain on injection. Previously explored ideas include injecting propofol into larger veins, warming of the hand with hot packs, and intravenous pretreatment with numerous other medications. Currently, pretreatment with lidocaine is commonly administered to prevent propofol injection pain. No studies to date have looked at the combination of lidocaine and magnesium in a single syringe for the pretreatment of pain on injection caused by propofol. In addition, the administration protocols that have been studied thus far do not mirror clinical practice at the University of Wisconsin. The investigators propose studying the use of magnesium and lidocaine in a single syringe for pretreatment of propofol related pain on injection.

This study will involve little if any change from the typical induction of general anesthesia. Considering that lidocaine is routinely used for the induction of anesthesia, and that some anesthesia staff also inject magnesium prior to propofol, there will be little variation in the induction of anesthesia. Patients will be randomly assigned (by microsoft excel program providing a random number 1-4) to one of four groups:

1. Lidocaine 50 mg in a 10 cc syringe
2. Magnesium sulfate 0.25 g (2 mOsmol) in a 10 cc syringe
3. 0.9% saline in a 10 cc syringe
4. Lidocaine 50 mg and 0.25 g (2 mOsmol) magnesium sulfate in a 10 cc syringe

Study drugs will be prepared in identical syringes by the Pharmaceutical Research Center (PRC). Study personnel will receive a syringe labeled with the study number as well as a data collection sheet labeled with the study number. A 20 gauge angiocatheter will be inserted into the dorsum of the hand for IV fluids and medication administration. Subjects will be given preoperative 1-2 mg intravenous midazolam for sedation when the subject is en route to the operating room as is typically done at the discretion of the anesthesia provider caring for the patient. After instituting standard monitors and providing preoxygenation, the study drug will be injected. Twenty seconds later, 50 mg of propofol will be injected. Ten seconds after infusion of propofol, the subjects will then be asked a standard question about pain on injection "Are you having pain at your IV site?". Any behavioral signs such as facial grimacing, arm withdrawal, or tears will be noted. Pain will be assessed using a four point scale: 0=no pain, 1=mild pain (pain reported only in response to questioning and without behavioral signs), 2=moderate pain (pain reported in response to questioning and accompanied by a behavioral sign, or pain reported spontaneously without questioning), 3=severe pain (strong vocal response or response accompanied by facial grimacing, arm withdrawal, or tears). Study key personnel will do these pain assessments; the behavioral signs and self-reporting of pain will be recorded separate from one another. The induction of anesthesia will then by completed with the appropriate amount of propofol. Formally assessing pain following injection is not something that is standard care but all patients are currently warned prior to injection that they may experience some warmth or burning at the site of their intravenous line.

Eligibility Criteria:
Inclusion Criteria:

* All adults American Society of Anesthesiologists (ASA) physical status 1 and 2 patients selected for general anesthesia.

Exclusion Criteria:

* age \< 18 years
* allergy to local anesthetics
* end stage renal disease
* pregnancy
* prisoners
* patients requiring a rapid sequence induction
* refusal to participate and patients already participating in another study