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• W1755822349 abstract "Cricoid pressure is a technique used to prevent regurgitation of gastric and oesophageal contents into the pharynx and their subsequent pulmonary aspiration during the induction of general anaesthesia. It was originally described for this purpose by Sellick in 1961 [1] and since then, in combination with pre-oxygenation, an intravenous induction and tracheal intubation, it has become a routine part of anaesthetic practice for those patients at risk of aspiration [2]. We believe that cricoid pressure could be applied in a safer manner which could reduce complications such as difficult tracheal intubation, airway obstruction, pulmonary aspiration and rarely oesophageal rupture. Most problems with cricoid pressure occur when too much force is applied. More than 20 N of force applied to an awake subject is uncomfortable and can cause retching [3] which can lead to pulmonary aspiration [4] or oesophageal rupture [5, 6]. Therefore, cricoid pressure cannot be expected to prevent regurgitation during coughing, straining or retching during induction of anaesthesia as the excessive force that would be necessary could itself cause these problems. More than 40 N of force applied to the cricoid cartilage after loss of consciousness can obstruct the airway [3, 7] and possibly cause difficulty with tracheal intubation [8]. Sellick originally suggested that cricoid pressure should be applied lightly initially and then with ‘firm pressure’ as soon as consciousness is lost [1]. Traditional teaching of the required force has been 44 N and often the applied force is even more than this [9]. This force was recommended by Wraight et al. as a cricoid force that would prevent regurgitation with a theoretical maximum gastric pressure of 59 mmHg in 50% of patients [10]. Can we apply less force and still prevent regurgitation? Gastric pressures are generally less than 25 mmHg in the supine position under general anaesthesia [11, 12] even during emergency Caesarean section with a full stomach [13]. Although suxamethonium fasciculations can increase gastric pressure, the peak pressure is still rarely more than 25 mmHg [11, 12, 14]. If we accept that gastric and therefore oesophageal pressures are unlikely to be above 25 mmHg, what cricoid force would be adequate? Wraight et al. have shown that 34 N occluded a manometry catheter behind the cricoid cartilage at a pressure greater than 30 mmHg in all patients [10]. In another study of anaesthetised patients, a cricoid force of 30 N occluded a manometry catheter with a pressure greater than 25 mmHg in all patients [15]. A study of 10 cadavers showed that 20 N of cricoid force prevented the regurgitation of oesophageal fluid at a pressure of 25 mmHg in all cases and 30 N prevented regurgitation at a pressure of 40 mmHg in all cases [6]. Therefore, 20 N of cricoid pressure is probably enough and 30 N is more than enough to prevent regurgitation into the pharynx. A reasonable recommendation is to apply 10 N (1 kg) to the cricoid cartilage when the patient is awake and to increase the force to 30 N (3 kg) once the patient has lost consciousness. Anaesthetic assistants can be trained to apply the correct force by practising on weighing scales [16]. By doing this, the range of forces can become within 5 N above or below the target force [16, 17]. The so-called cricoid yoke [15, 18], a force transducer applied to the neck, is not necessarily ideal, since it may not be applied accurately to the cricoid cartilage and may cause tracheal compression or extreme lateral displacement of the larynx, resulting in difficulty with tracheal intubation [18]. Manually applied cricoid pressure may also cause difficulty with tracheal intubation by distorting the larynx, particularly if the pressure is applied too far from the midline with excessive force or incorrectly to the thyroid cartilage [8]. Although Sellick's original description of cricoid pressure was with the head and neck in the extended position (tonsillectomy position) [1], intubation is easier when a pillow is placed beneath the occiput to adopt the ideal intubating position − the Magill position. Although some considered that cricoid pressure might be less effective in the Magill position than in the tonsillectomy position, pressure above 15 N of force is similarly effective for the two positions [15]. Some also consider that support of the neck by a hand or some sort of neck support is required when the patient's head and neck are placed in the Magill position, as cricoid pressure may flex the head on the neck, making it more difficult to see the glottis at laryngoscopy [19]. Three recent studies have formally assessed this hypothesis [17, 20, 21] but their results are apparently contradictory. In one study [20], the view of the glottis at laryngoscopy during cricoid pressure was slightly better when the neck was supported by a hand than when it was not supported, concurring with the hypothesis. In contrast, in the other two studies [17, 21], there was no marked difference in the view at laryngoscopy, with or without support of the neck. Although the reason for the discrepancy between studies is not clear, one likely reason is the difference in the pressure applied to the cricoid cartilage. In the former study [20], a strong force (50–55 N) was applied to the cricoid cartilage, whereas in the latter two studies, either ≈ 40 N [21] or 30 N [17] was used. Therefore, it appears that when cricoid pressure is applied using an adequate force, it does not worsen, but even improves [17], the view of the glottis at laryngoscopy, whereas if too strong a force is used, cricoid pressure is more likely to flex the head and to make laryngoscopy more difficult, requiring neck support to counteract it. Ventilation of the lungs is imperative following failure to intubate the trachea. Cricoid pressure may prevent ventilation [3, 7, 22]. In a recent report of 23 failed intubations over a 17-year period in one maternity unit, all mothers survived; cricoid pressure was maintained during their failed intubation drill [23]. In 14 patients (60%), ventilation via a facemask was not difficult, indicating that cricoid pressure was at least not harmful in these patients. In the remaining nine patients, ventilation was difficult in seven patients (30%) and impossible in two (9%). Although some patients had laryngeal oedema, it is possible that cricoid pressure contributed to the difficult ventilation in these patients [7]. The ‘cannot intubate, cannot ventilate’ scenario is a life-threatening emergency and if there are difficulties with ventilation sufficient to cause hypoxaemia, cricoid pressure should be released. Ventilation may then be possible via a facemask but if not there are three choices of airway that could help: the laryngeal mask, the Combitube or the cricothyrotomy cannula. However, these are all better inserted without application of cricoid pressure. Although the laryngeal mask does not protect against aspiration of gastric contents and despite several case reports of successful insertion of the laryngeal mask in this situation with cricoid pressure applied, correct insertion is more likely without cricoid pressure [24]. Cricoid pressure is effective if reapplied after insertion of the laryngeal mask [25], although it may cause a partial airway obstruction [26]. Releasing cricoid pressure could cause regurgitation not only because these patients are at risk but as cricoid pressure itself has been shown to reduce lower oesophageal sphincter pressure in awake volunteers [27] (although it has not been shown to cause gastro-oesophageal reflux in similar subjects [28]). So how should cricoid pressure be applied and released? When a nasogastric tube is already in place before induction of anaesthesia, gastric contents should be removed by suction. The tube should be left in place, since its presence does not reduce the efficacy of cricoid pressure and may actually improve it [6]. By leaving the gastric tube open to atmospheric pressure, it is possible to vent liquid and gas remaining in the stomach, minimising the increase in the intragastric pressure. The patient's head and neck are placed in the Magill position and the patient is pre-oxygenated. Immediately before intravenous induction of anaesthesia, while the patient is still awake, cricoid pressure is applied lightly (10 N or 1 kg) by a trained assistant who has recently practised the correct forces. The anaesthetist should confirm that the assistant's fingers are correctly placed on the cricoid cartilage and that it is tolerable to the patient. Although intravenous agents start to decrease the tone of the upper oesophageal sphincter before loss of consciousness, the sphincter is not full relaxed until 30 s later [29]. Once the patient has lost consciousness, the force on the cricoid cartilage is increased to 30 N (3 kg). To avoid coughing, straining or retching, anaesthesia must be deep enough and ideally full muscle relaxation quickly follows loss of consciousness. Therefore, both the intravenous anaesthetic and the neuromuscular blocking agent must be of rapid onset and of sufficient dose. The term ‘rapid sequence induction’ probably originated from this principle. Cricoid pressure is released after tracheal intubation is confirmed. If tracheal intubation is difficult, cricoid pressure should not be released at once; changing the direction of cricoid pressure, upward and backward, may improve the view at laryngoscopy [17]. It has been suggested that cricoid pressure is released to have another attempt at intubation, but if cricoid pressure was applied at a force of about 30 N, releasing it would be unlikely to improve the view at laryngoscopy [17]. If the anaesthetist considers that cricoid pressure is distorting the larynx because of incorrect application it can be adjusted. If tracheal intubation is judged to be not possible, manual ventilation is attempted without delay using 100% oxygen via a facemask and oral airway; the patient is left supine and cricoid pressure is continued, although the majority of people can maintain sufficient force (30 N) only for a few minutes [30]. When breathing, the patient is turned onto their left side with a head down position and cricoid pressure can then be released. However, if it is difficult to ventilate via a facemask, the amount of cricoid pressure should be reduced; if difficulty persists it should be completely released. This should be done in the supine position with a laryngoscope inserted and suction in hand. Ventilation may then be possible, but if not, either the laryngeal mask, Combitube or a cricothyrotomy cannula is inserted, depending on the familiarity and availability of each device and on the local failed intubation drill. Pulmonary aspiration is not confined to the induction of general anaesthesia, but it also occurs after tracheal extubation [31]. In fact, since the routine use of cricoid pressure [2], mortality from aspiration in women undergoing Caesarean section is more frequent after tracheal extubation than during induction of anaesthesia [32]. Therefore, patients at risk of aspiration should also have antacid prophylaxis and their stomachs emptied with an orogastric tube before extubation [32]. Although cricoid pressure is apparently a simple technique, there is growing evidence that incorrect application can produce several serious problems during induction of anaesthesia. Therefore, anaesthetic assistants must be properly trained in the technique and regularly practice the correct forces on weighing scales. Some anaesthetists have wanted to abandon cricoid pressure on the ground that it may make tracheal intubation more difficult and prevent ventilation via a facemask. However, to abandon cricoid pressure and to continue intravenous induction of anaesthesia in patients at increased risk of pulmonary aspiration may well return us to the high mortality rates of the past when patients frequently regurgitated during induction of anaesthesia. The time has come to make cricoid pressure a safer technique. Teaching the correct application of cricoid pressure will further reduce both the incidence of pulmonary aspiration and difficulty with tracheal intubation." @default.
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• W1755822349 title "Safe use of cricoid pressure" @default.
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