The distal tip of a properly positioned tracheal tube will be located in the mid-trachea, roughly 2 cm (1 in) above the bifurcation of the carina; this can be confirmed by chest x-ray. If it is inserted too far into the trachea (beyond the carina), the tip of the tracheal tube is likely to be within the right main bronchus—a situation often referred to as a "right mainstem intubation". In this situation, the left lung may be unable to participate in ventilation, which can lead to decreased oxygen content due to ventilation/perfusion mismatch. Special situations
Emergencies
Tracheal intubation in the emergency setting can be difficult with the fiberoptic bronchoscope due to blood, vomit, or secretions in the airway and poor patient cooperation. Because of this, patients with massive facial injury, complete upper airway obstruction, severely diminished ventilation, or profuse upper airway bleeding are poor candidates for fiberoptic intubation. Fiberoptic intubation under general anesthesia typically requires two skilled individuals. Success rates of only 83–87% have been reported using fiberoptic techniques in the emergency department, with significant nasal bleeding occurring in up to 22% of patients. These drawbacks limit the use of fiberoptic bronchoscopy somewhat in urgent and emergency situations.Personnel experienced in direct laryngoscopy are not always immediately available in certain settings that require emergency tracheal intubation. For this reason, specialized devices have been designed to act as bridges to a definitive airway. Such devices include the laryngeal mask airway, cuffed oropharyngeal airway and the esophageal-tracheal combitube (Combitube).
Dissociated vertical deviation (DVD) is an eye condition which occurs in association with a squint, typically infantile esotropia. The exact cause is unknown, although it is logical to assume it is from faulty innervation of eye muscles. Presentation
The eye drifts upward spontaneously or after being covered. The condition usually affects both eyes, but can occur unilaterally or asymmetrically. It is often associated with latent or manifest-latent nystagmus and, as well as occurring with infantile esotropia, can also be found associated with exotropias and vertical deviations. DVDs are usually controlled from occurring with both eyes open, but may become manifest with inattention. Usually some level of dissociative occlusion is required - to trigger the brain to suppress vision in that eye and then not control a DVD from occurring. The level of dissociative occlusion required may involve using a red filter, a darker filter or complete occlusion (e.g. with a hand). Onset
DVD typically becomes apparent between 18 months and three years of age, however, the difficulties of achieving the prolonged occlusion required for accurate detection in the very young make it possible that onset is generally earlier than these figures suggest. Mechanism
Dissociation refers to the situation where the innervation of one eye causes it to move involuntarily and independently of the other eye. Usually both eyes work together as described by Herings and Sherringtons laws of innervation. A DVD is a slow upward and sometimes temporal movement of one eye, with cortical suppression of the vision in that eye while it is deviated.