Propofol, pain and personality

Journal Reviewed:  Anaesthesia and Intensive Care 1999
Issues: June, July (number 3) and August, September (number 4)
Abstracted by: Dr C French  MB BCh (Registrar, University of the Witwatersrand)

Summary of abstracts

With the less expensive generic brand of Propofol becoming available a renewed interest in total intravenous anaesthesia has occurred.  Unfortunately I did not find the 3 papers on Propofol of great clinical value.  The article on Diprifusor (that is target controlled infusion) is helpful by showing no real difference with manual controlled infusion.

Postoperative pain management and the availability of an acute pain service is topical. The research will be of value to all hospitals which are trying to set up such a service.

The article on personality traits of Australian anaethetists is reviewed from absolutely impartial, totally tongue in cheek, South African point of view.

You may also wish to briefly browse our editorial comment

1.  Safety and efficacy of Target Controlled Infusion (Diprifusor TM ) versus Manually Controlled Infusion of Propofol for Anaesthesia.

A multicentre trial. The sample size (n=98) was adequate to provide statistical power (a = 0.05, b = 0.8).  Appropriate multivariate analysis of non-parametric data was done using Wilcoxon rank-sum tests.

The power of the study was hindered by the inclusion of nuisance variables, that is variables which although statistically significant do not have clinical significance. For example haemodynamic parameters such as blood pressure and heart rate.

Although induction times were found to be significantly different statistically, 67 seconds versus 54 seconds is not significant to us as anaesthetists. This is also true for induction doses of 14 ml in Target Controlled Infusion versus 16 ml in Manually Controlled Infusion.

The researchers, in their discussion, mention that Target Controlled Infusion is associated with reduced movement during surgery and with reduced awareness. Premedication with benzodiazepines is not standardised between the 2 groups.

Overall a well conducted trial. The conclusion is that Target Controlled Infusion and Manually Controlled Infusion are similar in terms of safety and efficacy.

Article 1: Safety and efficacy of Target Controlled Infusion (Diprifusor TM ) versus Manually Controlled Infusion of Propofol for Anaesthesia.
Journal:  Anaesthesia and Intensive Care 1999; 27: 260-264
Article type:  Clinical study
Authors:  Hunt-Smith, J.  Donaghy, A.   Leslie, K.  et. al.

2.  Auditory recall and response to command during recovery from Propofol anaesthesia

A pilot study with small numbers (n=10). No statistical analysis was done to show the validity of the results.

The findings do appear to be clinically significant. An awareness to motor response interval is described , ranging from 0 to 40s.  It may be more helpful to correlate the findings with plasma levels of Propofol; one could then extrapolate to intra-operative awareness under Propofol. By simply looking at the up and down slopes of the plasma concentration curves the authors are telling us very little.

Of interest is that the weight of the candidate ranged between 50 to 120 kg; was this not a full stomach scenario?

Article 2: Auditory recall and response to command during recovery from Propofol anaesthesia
Journal:  Anaesthesia and Intensive Care 1999; 27: 265-268
Article type: Laboratory study
Authors: Williams, M.  Sleigh, J.

3.  Propofol-Thiopentone admixture - Hypnotic dose, pain on injection and effect on blood pressure

The authors of this study claim a marked and prolonged hypotension following Propofol induction. Their own data of the systolic blood pressure following induction shows a moderate drop in systolic blood pressure for all three "mixtures" of Propofol but a clear trend of quick recovery for the pure Propofol group.

In the analysis of pain on injection, although the observers are blinded to which "mixture" of Propofol they are giving, their induction time is far in excess of that which is clinically used.  Normal clinical induction occurs with a bolus over 15 to 20 seconds and they used a set infusion rate of 20ml/min resulting in induction times of  40 to 60 seconds.  This increase in the time of infusion definitely diminishes the pain of injection.

They clearly show no synergistic effect with the addition of thiopentone and the only conclusion to be drawn from this study is that there is absolutely no benefit to be gained from mixing thiopentone and Propofol.

Article 3: Propofol-Thiopentone admixture - Hypnotic dose, pain on injection and effect on blood pressure
Journal: Anaesthesia and Intensive Care 1999; 27: 346-356
Article type: Clinical study
Authors: Jones, D.  Prankerd, R.  Lange, C. et al.

4.  The impact of an acute pain service on postoperative pain management

This is a longitudinal audit of patient management.  The "control" group was captured prior to the implementation of the acute pain service.  The "study" group collected after the implementation shows a higher incidence of major surgery, as this would tend towards a negative impact on the audit, the final result of improved pain management must be seen in an even more positive light.

The researches found a verbal response score (VRS) superior to a numerical response score (NRS) in their population group. The verbal response score (" no pain, a little, more, a lot, very bad ") is dependant on the observer understanding the language.  A visual analogue score (VAS), pictorially depicted , may in my opinion be less open to observer bias.

The authors main conclusion is that, when the anaesthesiology team is involved in the acute pain service, that is translated into better intraoperative care.   They found a marked increase in the amount of morphine given intraoperatively and in the recovery room.  And an increased trend towards using epidurals, with better insight into the futility of placing the epidural remote from the operative dermatome.

Although the researchers claimed a better cost benefit ratio to the hospital, there were no figures to prove this. It should not be taken for granted that less pain implies less morbidity or shorter hospital stay. The authors themselves illustrate that patient satisfaction is not related to pain experience.

A well designed study which shows very real benefits in reducing pain for patients at institutions which have an acute pain service.

Article 4: The impact of an acute pain service on postoperative pain management
Journal:  Anaesthesia and Intensive Care 1999; 27: 375-380
Article type:  Clinical audit
Authors: Sartain, J.  Barry, J.

5.  Personality profiles of Australian Anaesthetists.

A group level study which lays open the personality traits of Australian anaethetists. The authors propose that certain personality traits are more easily "stressed " and more likely to fail in a " stressful" situation. Unfortunately the study does not extend to the real life situation in theatre.

There are 143 male and 23 female respondents (representing a 33% response rate). Female anaethetists self report themselves as more calm, patient and tolerant compared with the male of species. Given the small numbers, however, the significance of this finding is unclear.

Australian anaesthetists rated themselves as being more sensitive, more careful and shrewder (as compared to Canadian anaesthetists).  In an American study of pilots, shrewdness is found to correlate with increased incidence of accidents; whether this could apply to anaesthetists is unclear.

The study uses a 28 year old self assessment questionnaire. An observer based questionnaire would be less biased.

This is a fun study which casts Australian anaesthetists in a good light. It Fails to show any significant difference to the patient as to whom or what performs the anaesthesia, be it a happy wallaby or a sad wallaby.

Article 5: Personality profiles of Australian Anaesthetists.
Journal:  Anaesthesia and Intensive Care 1999; 27: 282-286
Article type:  Questionnaire based survey
Authors: Kluger, M.  Laidlaw, T.  Khursandi, D.


Editorial pointers

True .Target Controlled Infusion of Propofol is an anaesthetist's dream.  It will revolutionize the practice of giving total intravenous anaesthesia, in the same way that the vaporiser revolutionized inhalational anaesthesia. The conclusion after reading the first study is that due to exposure and need we are very adept at manually controlling Propofol infusions, but that this is only as good as a poor targeted controlled infusion.  There were a number of methodological points that worried me in this article
  • Despite very clear inclusion and exclusion criteria, 9 patients, who should have been excluded on the basis of a lean body mass >120%, were included in the TCI group. What is then interesting to note is that the mean weight for the TCI group (72Kg) is smaller than for the MCI group (78Kg)
  • The authors found the induction dose, TCI = 14 (5)mls versus MCI = 16 (4)mls, to be statistically different between the two groups, but when looked at in terms of mls/kg it works out to TCI = 0.19mls/kg and MCI = 0.2mls/kg
  • No attempt was made at standardising potentially confounding variables.  The premedication, amount of nitrous oxide, amount and type of analgesics and the usage of muscle relaxation was left to each individual's discretion.


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