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Abstract
Propofol has been accepted in recent years as an alternative to the time tested thiopentone for intravenous induction. Induction with propofol is smooth, rapid, has more rapid awakening and orientation times, less hangover, better intubating conditions and upper airway integrity compared with thiopentone .(1)
The high lipid solubility of propofol results in an onset of action that is almost as rapid as that of thiopentone. Awakening from a single bolus dose is also rapid due to a very short initial distribution half-life (2-8 minutes) .This makes it a good agent for outpatient anaesthesia. (2) However, major disadvantage of induction with propofol is the considerable decrease in the systemic arterial blood pressure and its high cost . (2)
Changes in heart rate and cardiac output are usually transient and insignificant in healthy patients but may be rarely severe enough to lead to asystole , particularly in patients in extremes of age, on negative chronotropic medications, or undergoing surgical procedures associated with the oculocardiac reflex.
A search through the literature reveals that various methods are available to reduce the induction dose requirements of propofol and thus reduce the associated haemodynamic changes. These methods include concurrent use of nitrous oxide,(5) opioids,(6) barbiturates,(7) benzodiazepines, (8,9) augmentation with local anaesthetics,(10) or magnesium sulfate (11) and the use of priming principle.(12,13)
This study was carried out to evaluate whether the priming principle applied for the induction dose of propofol would affect the total induction dose requirements of propofol and thereby reduce the associated haemodynamic changes.
The present study was carried out on 60 patients aged 18-40years old of both sexes, with American Society of Anaesthesiologists (ASA) І and II health status, admitted to general surgery department in the Alexandria Main University Hospitals and scheduled for elective surgery under general anaesthesia.
Exclusion criteria included pregnant and lactating females, patients allergic to studied medications, cardiac patients and hypertensive patients.
All patients were pre-medicated on the previous night with oral alprazolam 0.25 mg tablet and ranitidine 150 mg tablet. On the morning of surgery, midazolam 0.03mg/kg was given IV 15 minutes prior to induction. Pre-operative baseline values of heart rate, blood pressure and oxygen saturation were recorded .
Patients in group I were given fentanyl 1ug/kg IV followed by 30 mg xylocaine before giving propofol until loss of verbal response. whereas, patients in group II were given the same dose of fentanyl and xylocaine then primed with 20% of the calculated dose of propofol 30 seconds prior to induction and were later given propofol until loss of verbal response .
In both groups, speed of injecting propofol was at a rate of 30 mg per 10 seconds. Subsequent relaxation and intubation was accomplished with IV cisatracurium 0.15 mg/kg.
The following parameters were recorded and statistically analysed:
(i) Total dose of propofol (including the priming dose in group II),
(ii) Heart rate, arterial blood pressure (systolic, diastolic and mean blood pressure in mmHg) and oxygen saturation just before induction, one minute after induction, immediately after intubation then five and ten minutes later .
(iii) Any complications after injection of propofol like involuntary movements, laryngeal spasm, coughing and pain on injection were noted .
Significant reduction in the induction dose requirements of propofol when using the priming principle was observed, without any effect on the heart rate and oxygen saturation values at the peri-induction and post-intubation times.
Also the systolic, diastolic and mean blood pressure values were significantly higher at all measured times when using the priming principle.