1Department of Anaesthesiology, 2Department of Gastroenterology and 3Department of Nuclear Medicine, Hôpital Henri Mondor, AP-HP, Université Paris XII, 51 avenue du Maréchal de Lattre de Tassigny, F-94010 Créteil, France*Corresponding author
Presented in part at the 39th Meeting of the French Society of Anaesthesia and Intensive Care, Paris, France, September 27, 1997.
Accepted for publication: February 26, 2001;
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Abstract |
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Br J Anaesth 2001; 87: 2046
Keywords: lung, pulmonary aspiration; surgery, colonoscopy; anaesthetics i.v., propofol; measurement techniques, scintigraphy
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Introduction |
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Colonoscopy is a routine day-case procedure commonly carried out under i.v. sedation. In France, the 800 000 procedures performed each year account for 10% of all anaesthetics.4 Various sedative regimen, including neuroleptics and benzodiazepines, may cause the loss of protective airway reflexes57 and therefore potentially induce pulmonary aspiration of gastric contents. Patients undergoing colonoscopy often complain of gastrointestinal disorders or have other medical conditions associated with swallowing dysfunction, a large gastric fluid volume, or regurgitation. Moreover, increased intra-abdominal pressure as a result of colonic air insufflation, external abdominal compression or a change of body position are widely used to facilitate progression of the endoscope,8 and may favour gastric regurgitation.
This study aimed to assess silent pulmonary aspiration by a specific scintigraphic method in patients undergoing elective colonoscopy under i.v. propofol.
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Methods |
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Procedure
Patients were not pre-medicated. Two hours before the administration of propofol, patients swallowed in the upright position 0.5 mCi of technetium 99m sulphur colloid mixed in 10 ml of water, as a radioactive tracer. During the procedure, patients were placed in the supine position and turned to left lateral if necessary. Propofol 1.01.5 mg kg1 was given as an i.v. bolus followed by a continuous infusion of 3 mg kg1 h1. The infusion of propofol was switched off after forward movement of the colonoscope. All patients received supplemental oxygen via a face mask, started at least 5 min before the propofol infusion. The level of unconsciousness was defined as a loss of response to verbal commands. The heart rate was monitored continuously and the arterial pressure at 3 min intervals. Pulse oximetry and end-tidal carbon dioxide were recorded continuously during the procedure (Viridia, Hewlett-Packard) and pharyngeal obstruction was avoided by insertion of a Guedel airway when necessary. Patients were monitored in a recovery room for a minimum of 1 h after completion of the procedure. Perioperative side effects such as cough or decrease in oxygen saturation (SpO2) below 90% for more than 30 s were noted for each patient.
The control group consisted of 10 healthy men aged 2545 yr. None had any health problems or took any medication. All were asked to refrain from food and water for 12 h before the start of the study. After ingestion of the labelled suspension in the upright position, they remained supine for 2 h.
Diagnosis of pulmonary aspiration
As technetium 99m has a half-life of 6 h, patient and control scans were performed 36 h after administration of the radiotracer. Once patients had fully recovered consciousness, they were transferred to the nuclear medicine department for lung scanning (anterior and posterior view) using a Gamma camera (Elscint). Scans were interpreted independently by a nuclear medicine physician. Scan results were considered positive when the tracer was detected within the thorax and lateral to the midline. A scan that showed the tracer only in the midline of the thorax was considered negative, because this localization could correspond to the oesophagus. A scan was also considered negative if it showed tracer in the pharynx or the stomach. A chest x-ray was performed in each patient with a positive scinti-scan.
Statistical analysis
Age, weight, and duration of colonoscopy were expressed as mean (SD), and categorical variables (sex ratio, ASA physical status) as percentage.
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Results |
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Discussion |
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Several techniques have been developed in the past to assess the incidence of pulmonary aspiration or regurgitation of gastric contents, such as examination of pharyngeal or tracheal aspirates for acidity1 or ingested dyes.2 Dye indicators such as methylene blue,2 contained in a capsule, were swallowed before induction of anaesthesia and their presence in the pharynx or the trachea was assessed at the end of the surgery, before recovery from anaesthesia. As half of all pulmonary aspirations occur in the early postoperative period,9 the incidence of pulmonary aspiration may be underestimated by this approach. In the current study, patients swallowed technetium 99m sulphur colloid before the propofol infusion and pulmonary aspiration was defined as detection of the labelled tracer in the pulmonary field. This method allowed us to study all the perioperative period until complete recovery from anaesthesia. This diagnostic approach has previously been used in awake patients with gastro-oesophageal reflux3 and in intensive care patients undergoing controlled ventilation and treated with enteral nutrition.10 Technetium 99m sulphur colloid is insoluble in water and not absorbed through mucous membranes or the gastrointestinal tract, so that any labelled tracer found in the lung parenchyma must have been aspirated.
The 3% incidence of pulmonary aspiration during i.v. propofol for elective colonoscopy found in this study may be considered high. Such pulmonary aspiration includes silent aspiration and thus comparison with other studies can be misleading. Studies based on examination of pharyngeal or tracheal aspirates for acidity or ingested dyes have also indicated a high incidence of regurgitation during anaesthesia (426%); detectable aspiration occurred in as many as 1320% of cases.1114 In contrast, life-threatening pulmonary aspiration in the perioperative period is uncommon: the incidence derived from large anaesthesia surveys varies from 1 in 1560 to 1 in 7140 anaesthetics.9 15 16
In summary, a radioisotope scinti-scanning technique to diagnose pulmonary aspiration was used in 96 patients undergoing elective colonoscopy. We found the incidence of detectable pulmonary aspiration to be 3%, without serious morbidity.
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References |
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