These wide range differences and confidence limits would lead to large errors if superior vena cava or right atrial oxyhemoglobin saturations were substituted for true mixed venous blood in oxygen transport or pulmonary venous admixture calculations, or if clinical decision making was based on individual results. In patients in shock in whom clinical decisions may be based on the value of mixed venous oxyhemoglobin, oxyhemoglobin saturation is only reliably measured in samples taken from the pulmonary artery.
-ntanil IS the most potent opioid available l'or iisc in m a n . It has been ahown to be ~iseful a s the analgesic compcincnt of general anaesIhcsi;i. nit11 a similar effect, speed o f onsct and dur-ation o f action after ii single intravcnous injection to ten times the dosc of fentanyl.' Howevcr. sufcntanll has ~1 Shorter elimination h;iILlife t h a n fcntanyl a n d is probably lcss cuinulativc. This results in u potency ratio of approxiinatcly 1 : 7 when the drugs are given by repeated in.jections. I Sufcntanil is the least toxic opioid in dogs whose lungs are mechanically ventilated and allohs better cardiovascular control t h a n fentanyl during neurosurgical a n a~s t h e s i a .~ Laryngoscopy and tracheal intubation after thc use of a n intravenous anacsthetic and suxilmethonium. local anaesthesia o r light gcneral ariaestlicsia have frequently been s h o w n to cause cardiac dysrhythmias.s-7 Such cardiovascular ~~ ~~
SummaryThis study investigated whether pretreatment with glycopyrronium can attenuate the hypotension caused by anaesthesia of the elderly with propofol. Twenty elderly patients (77.1 k2.44 years, mean SEM) of ASA physical status 2 or 3 scheduled for elective urological procedures were given glycopyrronium 0 ( n = 10) or 5 pg.kg-' ( n = 10) in a randomised, double-blind manner, 5 rnin before induction of anaesthesia with propofol infused at 600 ml.h-' (average induction dose 1.7f0.06 mg.kg-', mean f SEM) followed by maintenance with a propofol infusion at 10 mg.kg-'.h-'. Although glycopyrronium significantly increased heart rate ( p < 0.01, A NO V A ) , the decrease in blood pressure 2 and 5 min after induction was similar in both groups.The study had a power of 80% to detect a 20 mmHg diference in systolic arterial pressure between treatment groups with p < 0.05.
Key wordsAnaesthetics, intravenous; propofol. Parasympathetic nervous system, glycopyrronium. Complications; hypotension.Propofol anaesthesia often causes hypotension and this may be particularly severe in the elderly [I]. When glycopyrronium 5 pg.kg-l, atropine 10 pg.kg-' and placebo were compared as pretreatments given 5 min before total intravenous anaesthesia with propofol and alfentanil, the two anticholinergic agents caused equivalent increases in heart rate but those patients who received glycopyrronium suffered less hypotension than those receiving atropine or saline [2]. This apparent antihypotensive effect was attributed to differences in affinity of atropine and glycopyrronium for the MI and M, muscarinic receptor subtypes. Subsequently, a larger study compared placebo, 2.5, 5 and 7.5 pg.kg-l of glycopyrronium as pretreatments before anaesthesia with propofol and a small dose of fentanyl [3]. The average ages of the patients in these two studies were 42.5 years [2] and 39 years [3] respectively.We have compared the effects of glycopyrronium 5 pg.kg-' and placebo on the haemodynamic consequences of induction and early maintenance anaesthesia with propofol in elderly patients.
MethodsThe study was approved by the South Manchester District Ethics Committee and all patients gave informed consent in writing. Twenty patients of ASA physical status 2-3 weighing 35-80 kg and aged 65-85 years who were scheduled for urological procedures (usually check cystoscopy) were recruited into the study. Day surgery patients received no premedication; patients expected to stay overnight received oral temazepam 10-20 mg 100 min pre-operatively .An anaesthetist who was not otherwise involved in the study mixed glycopyrronium injection and 0.9% saline solution to give a solution containing glycopyrronium 0 or 400pg in 8 ml, and 0.1 ml.kg-' of this solution was administered intravenously in a randomised, double-blind manner 5 min before the start of induction giving a glyco-
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