The issues involved in the anesthetic management of patients with KOS are respiratory distress due to thoracic abnormalities and difficult endotracheal intubation due to craniofacial dysmorphism.
Respiratory distress in patients with KOS develops immediately after birth, requiring intubation and mechanical ventilation in most cases. The duration of mechanical ventilation is variable, with a median period of 1 month, and is apparently unrelated to gestational age [2]. The mechanism of this respiratory distress has not yet been clarified, although there are several possible explanations. Structural thoracic abnormalities are presumed to be part of the cause, leading to reduced lung volume, functional residual capacity (FRC), and low thoracic compliance, generally resulting in restrictive respiratory disease. The small thorax is also seen in patients with Jeune syndrome, campomelic dysplasia, thanatophoric dysplasia, and achondrogenesis [5]. Jeune syndrome is a rare condition [6] that primarily affects the bones. Common signs and symptoms include a small thorax and short ribs which restrict the growth and expansion of the lungs, often causing life-threatening breathing difficulties [7]. In many cases, the cause of Jeune syndrome is unknown. Changes in several different genes have been identified in some families with the condition. However, the small bell-shaped thorax and coat-hanger appearance of the ribs are specific to patients with KOS [2]. A previous report evaluated the ratio of the mid to widest thoracic diameter (M/W ratio) in patients with small bell-shaped thoraxes, and the angle between the sixth posterior rib and the horizontal axis (coat hanger angle, CHA) for the coat-hanger appearance [8]. According to the literature, the CHA in patients with KOS remains above the normal range for age-matched control children, while the M/W ratio, although below the normal range in infancy, becomes within the normal range after infancy. Furthermore, as the M/W ratio improves with growth, respiratory distress becomes less severe [2]. Our patient developed severe respiratory distress immediately after birth, which required mechanical ventilation with tracheal intubation. However, his preoperative respiratory condition was stable and he did not require a high driving pressure during the operation. This is because the M/W ratio of his small bell-shaped thorax tended to improve with growth, from 67% at birth to 79% before surgery (Fig. 2). This indicates that the M/W ratio could aid effective evaluation of the preoperative respiratory condition in patients with KOS.
Tracheal intubation in patients with KOS is predicted to be difficult because of the presence of certain craniofacial anomalies, such as micrognathia and a short-webbed neck. Additionally, our case was complicated by marked tracheal deviation. His trachea was extremely deviated at an angle of 90 ° from the ventral to dorsal side. Since this tracheal deviation was not recognized on his chest X-ray at birth, it was thought to have probably developed during the growth process. However, it is unclear whether this tracheal deviation is specific to patients with KOS, because there are no previous reports of tracheal deviation in patients with KOS. The tracheal deviation could be caused by various factors, including a thyroid goiter, a tumor in the neck and thorax, trauma, lung collapse, or spinal deformities [9]. Whatever the cause may be, in most previous reports, the authors tried to advance the tracheal tube below the deviated area and were usually successful [9]. However, there are a few reports of failure to intubate below the deviated area. Davies reported that it was impossible to intubate a patient with a combination of tracheal deviation and tracheal diverticulum [10]. In that case, an LMA was used to secure the airway. Kim et al. reported that the tracheal tube could not be advanced more than 3 cm beyond the vocal cords in a patient with tracheal deviation due to kyphoscoliosis [7].
In our case, we decided to use LMA as the airway device under consideration of his preoperative respiratory condition, tracheal deviation, and planned surgical procedure. Subsequent anesthetic management was performed successfully.