The pulmonary aspiration of gastric contents can cause a pneumonitis with bronchospasm and pulmonary oedema if acidic liquid is inhaled, or less often airway obstruction or massive atelectasis if particulate matter is inhaled. Cricoid pressure can cause problems with the airway. It is important that cricoid pressure is released or adjusted to become Optimal External Laryngeal Pressure (OELP) if intubation is difficult as this may improve the view at laryngoscopy. The three-finger technique to apply cricoid pressure described by Sellick is actually almost impossible to apply when the patient's head is resting on a pillow. The incidence of regurgitation is not known following intravenous induction of anaesthesia with muscle relaxants, without cricoid pressure applied in patients at high risk. During a rapid sequence induction, intubation has failed after two unsuccessful attempts at laryngoscopy both using the gum elastic bougie.