اشتباهات شایع در بخش آی سی یو 6
Use Cricoid Pressure when Performing Rapid Sequence Intubation or Bag-Mask Ventilation
Rahul G. Baijal MD
Cricoid pressure, first described by Sellick in 1961, is used to occlude the upper esophagus to reduce the aspiration of gastric contents during rapid-sequence intubation. Pulmonary aspiration of gastric contents occurs in three stages. First, gastric contents reflux into the esophagus when the lower esophageal sphincter relaxes. Esophageal contents then reflux into the pharynx when the upper esophageal sphincter relaxes. Finally, pulmonary aspiration of pharyngeal contents occurs after loss of laryngeal reflexes.
To briefly review, the cricoid cartilage is the only upper airway cartilaginous structure that is a complete ring. The esophagus begins at the lower border of the cricoid cartilage. Cricoid pressure replaces the function of the upper esophageal sphincter by compressing the lumen of the upper esophagus between lamina of the cricoid cartilage and the body of the sixth cervical vertebrae, preventing regurgitation of esophageal contents into the pharynx (the second phase of aspiration). The upper esophageal sphincter is formed anteriorly by the lamina of the cricoid cartilage and posteriorly by the cricopharyngeus muscle, which is attached to the lateral aspects of the cricoid cartilage. Upper esophageal sphincter tone is 40 mm Hg in awake patients and decreases to less than 10 mm Hg during induction of anesthesia. Regurgitation of esophageal contents into the pharynx occurs when the upper esophageal sphincter pressure is less than 25 mm Hg. Therefore, induction of anesthesia can decrease upper esophageal sphincter pressure sufficiently to allow regurgitation of esophageal contents into the pharynx. Cricoid pressure counteracts this reduction in upper esophageal pressure. It is important to note that other cartilaginous structures in the upper airway are u-shaped; mistakenly exerting pressure on these structures will be ineffective and possibly lead to airway damage or distortion during intubation.
To avoid this, the cricoid cartilage should first be identified and palpated before induction of anesthesia. With single-handed cricoid pressure, the thumb and middle finger can be placed on either side of the cricoid cartilage with the index finger caudal. The thumb and middle finger prevent lateral movement of the cricoid cartilage and the
index finger provides anterior-posterior pressure. The disadvantage of this technique is that the extended neck will tend to collapse the arch and reduce the glottic view. Another single-handed technique is to place the palm of the hand on the sternum and apply pressure to the cricoid cartilage with only the index and middle fingers. In the two-handed, or bimanual, technique, cricoid pressure is performed as with the single-handed technique except that the assistant's other hand provides counterpressure beneath the cervical vertebrae, supporting the neck.
Cricoid pressure can withstand esophageal pressures of 50 cm H2O (1 cm H2O = 0.73 mm Hg). Cricoid pressure can overcome gastric pressures associated with fasting (<18 cm H2O), delayed gastric emptying (<50 cm H2O), eructation (<20 cm H2O), pregnant supine patients (<35 cm H2O), or fasiculations associated with succinylcholine administration (<40 cm H2O). However, vomiting, which creates esophageal pressures >60 cm H2O, can overcome cricoid pressure, leading to regurgitation and pulmonary aspiration. Cricoid pressure should begin before the patient is fully asleep, with 10 N of pressure, increasing to 30 N of pressure when loss of consciousness is established. Recommended cricoid pressure to prevent pulmonary aspiration is between 30 and 40 N (10 N ~ 1 kg), but pressure >20 N can cause pain and retching in awake patients, and pressure >40 N can distort the trachea, making intubation difficult. Retching causes a reflex relaxation of the lower esophageal sphincter and rapid distention of the esophagus, relaxing the upper esophageal sphincter and allowing expulsion of vomit. Cricoid pressure maintained during retching allows esophageal pressure to rise, increasing the risk of esophageal rupture. Cricoid pressure is additionally contraindicated in patients with cricotracheal injury, active emesis, or unstable cervical spine injuries.
Finally, bag-mask ventilation provides positive pressure ventilation with delivery of high fraction of inspired oxygen, opening at-electatic alveoli and improving ventilation-perfusion mismatch. However, bag-mask ventilation may rapidly distend the stomach, increasing gastric pressure up to 30 cm H2O. Cricoid pressure may overcome this increased gastric pressure as noted previously but may be uncomfortable in an awake patient.
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