Effect of prone positioning and PEEP on respiratory mechanics in children undergoing scoliosis surgery.

BACKGROUND: Surgery for severe scoliosis (SS) is usually performed in the prone position. Changes in respiratory mechanics related to position and positive end expiratory pressure (PEEP) titration during anesthesia of SS are understudied. We aimed to investigate the effect of prone position and PEEP on the respiratory mechanics of scoliotic children undergoing spine surgery. METHODS: Prospective, crossover study performed in two pediatric hospitals (Montevideo, Uruguay-Centro Hospitalario Pereira Rossell- and Milano, Italy-Vittore Buzzi Children's Hospital). Shortly after intubation, pulmonary mechanics measurements were performed using inspiratory and expiratory breath holds during volume-controlled ventilation with a set tidal volume (TV) of 8 ml/kg and a respiratory rate adjusted to maintain normocapnia. Measurements of peak (PIP), plateau (PPLAT) and total PEEP (tPEEP) were obtained at three levels of applied PEEP: 0 (ZEEP), 5, and 10 cmH2O both in supine (baseline) and prone positions. Driving pressure (∆P: PPLAT-tPEEP) was calculated to obtain static respiratory system compliance (Crs: TV/∆P). Crs and pressures were analyzed using a mixed linear regression model with a random subject effect in their relationship with position and PEEP. RESULTS: Sixty-nine patients were enrolled. Crs was negatively associated with Cobb angle in all the cohorts. Only in secondary scoliosis, it was positively associated with body mass index. Crs was also negatively correlated with the prone position and positively correlated with increasing PEEP levels. The interaction between PEEP and position was studied and showed no significance. CONCLUSIONS: Crs is influenced by the severity of scoliosis and the nutritional status during spine surgery. The addition of PEEP improves Crs and reduces ∆P in the supine position, but both worsen in the prone position. These changes can be related to the effects of position on chest wall compliance.