No abstract

We studied the effect of order in the performance of maximal respiratory pressures (PImax and PEmax). For this purpose 20 healthy subjects (male/female: 1/1) were studied. PImax and PEmax were obtained on 2 different days at the same hours (9 and 12 a.m.). The test order was random. On the first day, the entire manoeuvre was performed twice, changing the order in the second determination. On the second day, we repeated the same exercises with reversed order. There were no differences between values for PImax and PEmax when we altered the order of manoeuvres on various days.

We were delighted to read the paper by Hobbs and colleagues (Anaesthesia 1992; 47: 58-62) on the value of epidural infusion combining diamorphine and bupivacaine for postoperative analgesia, particularly in the clinical environment where pulse oximetry and capnography monitoring are not readily available. The wider availability of such quality analgesia should be encouraged with appropriate education of nursing staff and supervision by an acute pain control team, as recommended in the Joint Working Party on Post-operative Pain [I]. However, we would like to make two comments, the first regarding the incidence of respiratory depression, quoted as 6%, occurring up to 24 h after the beginning of the analgesic infusion.In our series of 800 patients receiving intermittent boluses of epidural diamorphine (2.5 mg in 10 ml saline) [2] only seven instances (0.9%) of respiratory depression occurred, defined in our study as a respiratory rate of less than 10 breath.min-'; five of these occurred in the recovery ward within an hour of the first does of epidural diamorphine. Of the remaining incidents, one, in a patient with obstructive airways disease, took place during weaning from IPPV in the intensive care unit; in the other there was a breach of protocol and 5 mg diamorphine was given. The loading dose reported in Hobbs' paper of a mean value of 2.0 mg is roughly equivalent to our first dose and this is then followed by an infusion, tailor-made to the patient and the nature of the surgery, to a mean of 9.5 mg diamorphine per 24 h in bupivacaine solution. Despite a relatively lower limit as a definition of respiratory depression, we were not suprised to see that this represented a significant side effect in their study, when the synergism of opioid and local anaesthetic has to be taken into account. We accept that respiratory depression might occur up to 6 h after an epidural top-up of diamorphine; however, our experience shows that in clinical practice this is not so, but is more likely to occur in the recovery room after the first dose has been given, and demonstrably when intravenous opioids have been used peroperatively. There was no mention in Hobbs' paper of the duration of observation of the patient in the postoperative recovery ward, which we feel should be an important aspect of epidural management.Secondly, it was of some concern to find that the ward staff were encouraged to adjust the infusion rate. If analgesia was found to be insufficient, this surely would be better corrected by the administration of a bolus dose followed by an increase in the infusion rate, thereby avoiding a prolonged latent period for analgesia to become effective? Furthermore, we feel that such a procedure would be better supervised by a member of the medical staff or one of the acute pain control team.Whilst it must be appreciated that no technique of postoperative analgesia will be 100% safe, as anaesthetists we should be striving to develop the highest efficacy/safety ratio for postoperative pain relief, and in this respect, Hobbs ...