Sandhar BK, Elliot RH, Windram I, Rowbotham DJ. Peripartum changes in gastric emptying. British Journal of. Anaesthesia 1991; 67: 213P. 3. Miners JO ...
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2. Sandhar BK, Elliot RH, Windram I, Rowbotham DJ. Peripartum changes in gastric emptying. British Journal of Anaesthesia 1991; 67: 213P. 3. Miners JO, Robson RA, Birkctt DJ. Paracetamol metabolism in pregnancy. British Journal of Clinical Pharmacology 1986; 22: 359-362. 4. Gin T, Cho AMW, Lew JKL, Lau GSN, Yuen PM, Critchley JAJH, Oh TE. Gastric emptying in the postpartum period. Anaesthesia and Intensive Care 1991 (in press). 5. Simpson KH, Stakes AF, Miller M. Pregnancy delays paracetamol absorption and gastric emptying in patients undergoing surgery. British Journal of Anaesthesia 1988; 60: 24-27. 6. Wolf S. The relation of gastric function to nausea in man. Journal of Clinical Investigation 1943; 22: 877-882.
Sir,—Thank you for the opportunity to respond to the letter from Drs Gin and Lew. We agree that the use of AUC per se is a poor measure of gastric emptying, and stated in our manuscript that the change in AUC may reflect a combination of factors other than gastric emptying [1]. Drs Gin and Lew have concentrated their criticism on the change in metabolism of paracetamol that may occur during pregnancy. Paracetamol is a drug of low hepatic extraction and first pass metabolism may be as little as 10% [2]. There would have to be an enormous increase in the uptake of paracetamol by the liver, far greater than that found in the small study by Miners, Robson and Birkett [3], to explain the changes we and others have demonstrated. A change in metabolism would alter the AUC,,.^, but have a minor effect on AUC^,. The use of an AUC from 0-60 min or 0-120 min, when used in combination with the variables dependent on gastric emptying (time to maximum concentration and maximum concentration), is a valid method of comparing gastric emptying. This method was used in our study and by Simpson, Stakes and Millar [4]. The comment regarding doubts about the validity of this method should be interpreted with caution, as they reference an unsupported statement in an abstract. The point regarding differential rates of gastric emptying between solids and liquids is well known. A. G. MACFIE M. N. RICHMOND A. D. MAGIDES C. S. RELLLY
Sheffield REFERENCES 1. Macfie AG, Magides AD, Richmond MN, Reilly CS. Gastric emptying in pregnancy. British Journal of Anaesthesia 1991; 67: 54-57. 2. Rawlins MD, Henderson DB, Hijab AR. Pharmacokinetics of paracetamol after intravenous and oral administration. European Journal of Clinical Pharmacology 1977; 26: 283-286. 3. Miners JO, Robson RA, Birkett DJ. Paracetamol metabolism in pregnancy. British Journal of Clinical Pharmacology 1986; 22: 359-362. 4. Simpson KH, Stakes AF, Millar M. Pregnancy delays paracetamol absorption and gastric emptying in patients undergoing surgery. British Journal of Anaesthesia 1988; 60: 24-27.
PROPOFOL SEDATION FOR OUTPATIENT UPPER GASTROINTESTINAL ENDOSCOPY Sir,—We read with interest the study of Patterson and colleagues [1] on this important and controversial topic of sedation for outpatient procedures. Unfortunately, the study design failed to take into account the fundamental and well-known pharmacokinetics of propofol. Indeed, propofol, in contrast with midazolam, is best used as a continuous infusion because of its short 7J, high clearance rate and large volume of distribution [2]. Therefore the comparison of propofol and midazolam—each as a bolus—is illogical. In fact, it is surprising that only 24% of patients in the propofol group would have preferred another method of sedation for future endoscopy, as only 14% were amnesic to the removal of the endoscope! This shows clearly that
the sedative technique used with propofol in this clinical setting was inadequate. We would agree also that any form of adequate sedation requires supplementary oxygen, basic monitoring and the presence of a second doctor to manage sedation. A. BORGEAT O. WILDER-SMITH
Geneva REFERENCES 1. Patterson KW, Casey PB, Murray JP, O'Boyle CA, Cunningham AJ. Propofol sedation for outpatient upper gastrointestinal endoscopy: comparison with midazolam. British Journal of Anaesthesia 1991; 67: 108-111. 2. Kay NH, Sear JW, Uppington J, Cockshott ID, Douglas EJ. Disposition of propofol in patients undergoing surgery. British Journal of Anaesthesia 1986; 58: 1075-1079.
Sir,—We are grateful to Drs Borgeat and Wilder-Smith for their comments regarding our paper, and we thank the editor for this opportunity to reply. We chose to use bolus injections of both agents for several reasons. First, we wished to make a valid and realistic comparison between the two agents for sedation. Second, it may have been difficult to blind the study with regard to the endoscopist had we used an infusion of propofol. Third, diagnostic upper gastrointestinal endoscopic procedures tend to be short in duration. The mean (SEM) duration of endoscopy in this study was 9 (1) min and 8 (1) min for groups I and II, respectively. Midazolam, with a half-life of approximately 60 min, is clearly not the ideal sedative for such short procedures. We thank Drs Borgeat and Wilder-Smith for reminding us of the work of Kay and colleagues. However, it is precisely because propofol has a short distribution half-life (approximately 2-3 min) that we chose to use it in our study. Our experience has shown that endoscopic insertion is the most unpleasant part of the procedure. With good topical anaesthesia of the oropharynx (lignocaine 120 mg), the presence of the endoscope is tolerated well, and endoscope removal is not an unpleasant or painful part of the total procedure. We do agree that to obtain amnesia for the entire duration of the procedure using propofol, one would have to give another bolus or commence an infusion. However, for such a short procedure, an infusion might prove wasteful and impractical. Our aim was not to ensure amnesia for the duration of the procedure, but to compare the amnesic effects of the two drugs during a short diagnostic procedure. Lack of amnesia for the end of an endoscopy does not preclude patient acceptance of that procedure. All the patients in the propofol group who indicated a preference for another method of sedation during future endoscopy also experienced moderate to severe pain on injection. Many of those patients commented on this during the post-endoscopy interview. No patient expressed dissatisfaction regarding awareness of endoscope removal. K. W. PATTERSON A. J. CUNNINGHAM
Dublin EXTRADURAL HAEMATOMA AFTER CONTINUOUS EXTRADURAL ANAESTHESIA Sir,—Because extradural haematoma is such a rare condition, it is important that any case occurring after a central nerve block is published. Thus I read the report from Tekkok and colleagues [1] with interest, for it contains several important points. However, I would ask if they are able to provide further information on some aspects. The anaesthetic technique is described in reasonable detail, but we are given no information about how the cxtradural space was identified, or about the training and experience of the anaesthetist involved. It would also be useful to know the time interval between the last dose of heparin and removal of the extradural catheter. Other aspects seem to me to be inconsistent and I would be grateful for the authors' comments. The extradural catheter was inserted at the L2-3 interspace, yet the haematoma is shown as being at T12-L1 and the level of anaesthesia extended from T9
