Update in Anaesthesia 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 1 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 1234567890123456789012345678901212345678901234567890123456789012123456789012345678UPDATE IN 9 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 WA 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 UPDATE IN 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 ANAESTHESIA 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789 12345678901234567890123456789012123456789012345678901234567890121234567890123456789ANAESTHESIA A journal for anaesthetists in developing countries WORLD ANAESTHESIA No. 12 2000 ISSN 1353-4882 Editorial The World Congress of Anaesthesiology was held in Contents: No. 12 Montreal, Canada in June of this year. The event, staged by the Canadian Society of Anaesthetists, was a fantastic Editorial 1 success with over 6000 delegates from more than 90 Pre-operative Fasting Guidelines 2 countries attending. It was fascinating to hear and see Acute Oxygen Treatment 6 presentations from many parts of the world, from vaious Regional Blocks at the Wrist 12 grades of anaesthetist concerning all aspects of anaesthesia. Topical Anaesthesia for Eye Surgery 15 Thanks to generous donations, over 50 delegates from developing countries were able to attend and were warmly Self Assessment 17 applauded at the opening ceremony. Spinal Anaesthesia - a Practical Guide 21 Dr Kester Brown from Melbourne, Australia was elected Post-operative Analgesia in Paediatric Day as President of the World Federation of Societies of Case Surgery 34 Anaesthesiologists. We congratulate Kester on his Intraosseous Infusion 38 appointment and also thank him for his continuing support Answers to Self Assessment 40 of Update in Anaesthesia. Respiratory Physiology 42 We are delighted that the W.F.S.A. has decided to continue Anaesthesia for the Patient with to fund Update in Anaesthesia, making it available free of Respiratory Disease 51 charge to those working in developing countries who are unable to afford the subscription. Please note that we are Central Venous Access and Monitoring 59 revising our distribution list for Update in Anaesthesia and Anaphylaxis 71 if you wish to continue to receive Update please register Distribution 72 with us by following the instructions on the back cover of this edition. Alternatively contact the editor by email [email protected]. Contacts: Update is now produced in Russian, French, Spanish and Russian Edition:- Andrei Varvinski, Dept. of Mandarin as well as English. Contact details to receive these Anaesthesia, University of Wales School of Medicine, are printed below. Heath Park, Cardiff, U.K. The English version is produced in a paper format, CD Rom Email: [email protected] (email [email protected]) and on the web Spanish Edition:- Oscar Gonzales, Rio Parana 445, Bo www.nda.ox.ac.uk/wfsa. The demand for Update has Felicidad - Lambare, Paraquay increased dramatically and we hope it will continue to meet Email: [email protected] the needs of our readers. French Edition:- Michel Pinaud, Service d’anaesthesia, We are always pleased to receive letters about any material Hotel Dieu, 44093 Nantes Cedex 1, France in Update and would be grateful for ideas for future articles. Email:[email protected] If you wish to contribute to Update please contact the Editor Mandarin Edition:- Jing Zhao, Dep. of Anaesthesia, for further information. Peking Union Medical College Hospital, No. 1 Shuai Fu Dr Roger Eltringham Chairman - Publications Yuan, Beijing 100730, Peoples Rep. of China Committee WFSA Dr Iain Wilson Editor - Update in Anaesthesia 2 Update in Anaesthesia PREOPERATIVE FASTING GUIDELINES J. Roger Maltby, MB, BChir, FRCA, FRCPC, Professor of Anesthesia, University of Calgary, Alberta, Canada Clinically significant pulmonary aspiration during The myth of 25ml in the stomach being a surrogate general anaesthesia is rare in healthy patients having marker for high risk of aspiration is now discredited. elective surgery. The largest study reports an incidence [6] Clinical studies show that 40-80% of fasting patients of 1 in approximately 10,000 patients, with no deaths fall into that category, [7] yet the incidence of pulmonary in more than 200,000.[1] The majority of serious cases aspiration is 1 in 10,000. Raidoo et al[8] have of pulmonary aspiration occur in emergency cases, demonstrated that 0.8ml/kg in the trachea of monkeys particularly trauma, obstetrics and abdominal surgery (equivalent to >50ml in adult humans) is required to in which delayed gastric emptying may be further produce pneumonitis. For this volume to reach the prolonged by administration of opioid narcotic lungs, the volume in the stomach must be greater, even analgesics. If, in addition, tracheal intubation is if the lower and upper oesophageal sphincters are difficult, anaesthesia is allowed to lighten and incompetent. suxamethonium (succinylcholine) to wear off, repeated Gastric pressure attempts at laryngoscopy may precipitate gagging, vomiting and aspiration. [1] The human stomach is a very dispensable organ and can accommodate up to 1000ml before intragastric pressure Fasting guidelines increases.[9] In cats, whose lower oesophageal sphincter The purpose of fasting guidelines for healthy patients mechanism is similar to that in humans, the minimum volume undergoing elective surgery is to minimize the volume of of gastric fluid required to overcome the sphincter varies gastric contents while avoiding unnecessary thirst and from 8ml/kg to >20ml/kg.[10] In humans, the lower figure dehydration. Dehydration is particularly important in hot is equivalent to approximately 500ml and the higher one countries. Guidelines should be based on clinical studies 1200ml. The volume of gastric contents after an overnight in surgical patients or, when this evidence is not available, (> 8 hours) fast averages 20 to 30ml, and varies from 0 to on the physiology of digestion and gastric emptying. >100ml (Table 1). Therefore, unless the patient has an Although the earliest books on anaesthesia did not mention incompetent sphincter, reflux of gastric contents does not fasting, in 1883 the famous surgeon Lister [2] recommended occur with the normal range of fasting gastric volumes. If that there should be no solid matter in the stomach, but we know how long the stomach takes to return to the that patients should drink clear liquid about 2 hours before fasting state, we can formulate appropriate fasting surgery. For the next 80 years until the 1960s most guidelines for elective surgery. textbooks recommended a 6-hour fast for solids and 2-3 Gastric emptying hours for clear liquids. Modern physiological studies use a dual isotope technique During the 1960s in North America the preoperative order in which solids and liquids are tagged with different ‘nothing by mouth after midnight’ was applied to solids as radioactive isotopes.[11] Clear liquids empty exponentially, well as liquids. The change was widely accepted although 90% within 1 hour and virtually all within 2 hours. They the reasons for it have been lost in the mists of time. do not contain particles >2mm and therefore pass Pulmonary aspiration was known to be one of the leading immediately through the pylorus. The pylorus prevents causes of anaesthetic related mortality. Concern about the passage of particles >2mm, so digestible solids (bread, risk of pulmonary aspiration was fuelled by Roberts and lean meat, boiled potatoes) must be broken down to [3] Shirley’s 1974 statement that patients with 0.4ml/kg particles <2mm before they can pass into the small bowel. (25ml in adults) of gastric contents, with pH <2.5 are at Total emptying of a meal normally takes 3-5 hours. Large high risk of pulmonary aspiration. However, Roberts and particles of indigestible food, especially cellulose-