Nasogastric tubes and cricoid pressure.
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Cricoid Cartilage↗
Biomedical subjects
R G Vanner
Publications and source records attributed to R G Vanner.
Tolerance of cricoid pressure by conscious volunteers.
It is recommended that a cricoid pressure (force) of 40 N should be applied to prevent regurgitation. The tolerance of incremental levels of cricoid pressure was assessed in 22 conscious volunteers. Each level of cricoid pressure was applied for 20 s using a cricoid yoke. Only 14 volunteers could tolerate 40 N of cricoid forte for 20 s; all 22 volunteers could tolerate 25 N for that time but 19 of them found it uncomfortable and 1 wanted to retch. Nine subjects complained of breathing difficulties at cricoid forces of 35 N or above; 2 had complete airway obstruction. A, cricoid force of over 20 N is likely to be poorly tolerated by the awake patient. It is recommended that a force of 20 N should be maintained before loss of consciousness and the full force of 40 N be reserved for the onset of general anaesthesia; the assistant can practise these levels on a set of weighing scales.
Journal Article↗
Gastro-oesophageal reflux and regurgitation during general anaesthesia for termination of pregnancy.
Gastro-oesophageal reflux (GOR) and regurgitation were investigated with an oesophageal pH electrode, inserted after the induction of general anaesthesia with methohexitone, in 100 patients undergoing termination of pregnancy, 50 in the first trimester and 50 in the second. GOR occurred in 17 patients, 8 in the first trimester and 9 in the second trimester. On withdrawal of the pH electrode into the pharynx it was found that only 2 of these patients had regurgitated, 1 from each trimester. Regurgitation was not clinically detectable and there was no pulmonary aspiration. Twenty three patients had hiccup of whom 10 refluxed, 9 of them immediately after starting to hiccup. Those patients with hiccup were more likely to reflux than the remainder (P<0.001). Patients with preoperative symptoms of GOR had no greater incidence of reflux during anaesthesia than those without symptoms. The function of the upper oesophageal sphincter appears to be preserved in the majority of these patients with the general anaesthetic technique used. This work therefore suggests that the need for rapid sequence induction is no greater in the second trimester than the first.
Journal Article↗
Upper oesophageal sphincter pressure and the effect of cricoid pressure.
Upper oesophageal sphincter pressure has been measured in 24 patients with a sleeve device. The median sphincter pressure when awake was 38 mmHg, and when anaesthetized and paralysed was 6 mmHg. After tracheal intubation, cricoid pressure was applied at measured values between 5 and 50 N using a hand-held cricoid yoke while the sphincter pressure was recorded in two head and neck positions: with and without a standard intubating pillow with neck support. A cricoid force of 40 N increased sphincter pressure to above 38 mmHg in all the patients and the use of the pillow did not alter this effect. With the application of cricoid pressure, operating department assistants raised sphincter pressure to above 38 mmHg in only 50% of patients. Laryngoscopy made little difference to the effect of cricoid pressure except in one patient in whom it reduced the sphincter pressure by 27 mmHg.
Adult↗
Upper oesophageal sphincter pressure and the intravenous induction of anaesthesia.
The upper oesophageal sphincter can prevent regurgitation of oesophageal contents into the pharynx following gastrooesophageal reflux in the awake patient. Upper oesophageal sphincter pressure was recorded with a Dent sleeve after hypnosis with midazolam (n = 7) and also during the rapid intravenous induction of anaesthesia with thiopentone (n = 16) or ketamine (n = 7). Thiopentone decreased mean (SD) sphincter pressure from an awake value of 43 (19) to 9 (7) mmHg (p less than 0.001) and midazolam from 38 (25) to 7 (3) mmHg (p less than 0.02). Mean (SD) sphincter pressures before and after ketamine were not significantly different at 29 (15) and 32 (21) mmHg respectively. After suxamethonium mean (SD) sphincter pressure in all patients (n = 30) was 7 (4) mmHg. Laryngoscopy (n = 30) caused a small increase in mean (SD) sphincter pressure to 13 (10) mmHg (p less than 0.001). Thiopentone caused a rapid fall in upper oesophageal sphincter pressure which usually started before loss of consciousness. These findings have implications for the timing of cricoid pressure application.
Adult↗
Upper oesophageal sphincter pressure during inhalational anaesthesia.
Upper oesophageal sphincter pressure was recorded with a Dent sleeve in 30 patients breathing nitrous oxide, oxygen and halothane. Twenty-three patients, after thiopentone induction, received suxamethonium and had their trachea intubated either before (group A, n = 11), or after (group B, n = 11), a study period of inhalational anaesthesia. Group C (n = 8) received an inhalational induction. Mean (SD) sphincter pressure after loss of consciousness was 8 (7) mmHg (group A), 6 (5) mmHg (group B) and 24 (13) mmHg (group C) increasing to 19 (7) mmHg in group A immediately after intubation. With an end-tidal halothane concentration of 1.5%, mean sphincter pressure in group B, 16 (7) mmHg, was significantly lower than in group A, 45 (21) mmHg (p < 0.001) and group C, 27 (14) mmHg (p < 0.05). Halothane had no dose-related effect on sphincter pressure. Insertion of a laryngeal mask in group C (n = 7) had no significant effect on sphincter pressure. Induction and maintenance of anaesthesia with halothane, unlike thiopentone or suxamethonium, maintained a degree of upper oesophageal sphincter tone, although three patients in this study had sphincter pressures of less than 10 mmHg and would therefore have been at risk of regurgitation in the presence of gastro-oesophageal reflux.
Adult↗
Regurgitation and oesophageal rupture with cricoid pressure: a cadaver study.
The efficacy of cricoid pressure was studied in 10 adult cadavers. The oesophageal pressure that would result in regurgitation during measured values of cricoid pressure was determined. Oesophageal pressure, recorded by a 2 mm diameter oesophageal tube, was increased by oesophageal distension with saline, and incremental levels of cricoid force, 20, 30 and 40 Newtons, were applied with a cricoid yoke. With each 10 Newton increment of cricoid force there was a significant rise in the oesophageal pressure required to provoke regurgitation (p < 0.01). Thirty Newtons of cricoid force prevented regurgitation of saline in all cadavers with oesophageal pressures of up to 40 mmHg. Rupture of the oesophagus occurred in three cadavers: one at 30 and two at 40 Newtons of cricoid force, but there was no rupture at 20 Newtons of cricoid force. In the other seven cadavers oesophageal pressures were also studied with a 4.6 mm diameter (14 FG) oesophageal tube, which did not reduce the efficacy of cricoid pressure in preventing regurgitation.
Aged↗
'Overdose' of vecuronium.
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Drug Overdose↗
Provoked gastro-oesophageal reflux?
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Esophagogastric Junction↗
Effects of incremental doses of alfentanil and propofol on the breathing of anaesthetized patients.
Incremental doses of alfentanil and propofol were given to anaesthetized healthy patients undergoing routine orthopaedic surgery. Ventilation was recorded by respiratory inductance plethysmography and analysed by microcomputer. Alfentanil affected primarily expiratory time. The onset of effect lasted 82 s (range 25-173 s); offset was exponential, with a half-life of 146 s (range 62-260 s). Alfentanil also reduced tidal volume, but the effect was less obvious and less consistent. Propofol affected primarily tidal volume. The onset of effect lasted 34 s (range 17-69 s); offset was linear, with a time to 50% recovery of 92 s (range 47-161 s). Propofol had little effect on expiratory time. The drugs had little effect on inspiratory time. Three patients showed periods when the distribution of expiratory times was bimodal; the mechanism for this is unknown.
Adult↗
Gastro-oesophageal reflux in pregnancy at term and after delivery.
Gastro-oesophageal reflux during a 40-minute reflux provocation test was assessed by lower oesophageal pH monitoring in 25 pregnant women at term, and again on about the second day after delivery. At term 17 women refluxed a total of 29 times; after delivery five women refluxed once each. There was a significant decrease in gastro-oesophageal reflux by the second day after delivery (p less than 0.05). Gastro-oesophageal reflux is, however, only one of the factors that predisposes to acid aspiration pneumonitis.
Esophagus↗
Acetylcholinesterase--a specific marker for cerebrospinal fluid.
An oedematous pre-eclamptic patient received lumbar epidural analgesia during labour. Clear fluid leaked from the skin puncture site for 4 days. The fluid was analysed using protein electrophoresis for cholinesterase enzymes and was found not to contain the cerebrospinal fluid specific form of the enzyme, acetylcholinesterase. The sensitivity of this test was explored using serial dilutions of cerebrospinal fluid. It is now possible to say that the leaking fluid did not contain cerebrospinal fluid.
Acetylcholinesterase↗