Effects of the depth of anesthesia on distortion product otoacoustic emissions.

To analyze the effects of the depth of anesthesia on inner ear function measured with distortion product otoacoustic emissions (DPOAEs) at 2f 1 - f 2. Thirty patients who underwent tonsillectomy under general anesthesia (GA) were included. Patients were assigned randomly to one of two groups: group 1 (n = 15) received propofol, group 2 (n = 15) sevoflurane as anesthetic agent. The sedation level was assessed by the bispectral index system. DPOAE measurements were performed before premedication (T 1), 5 min after premedication (T 2), 3 min after induction of general anesthesia (T 3) and every 10 min (T 4, T 5) thereafter until the end of surgery at about 23 min post-anesthetic induction, while sedation levels were obtained starting at the beginning until the end of anesthesia. After premedication, both blood oxygen saturation and heart rate decreased. Following induction of anesthesia systolic and diastolic blood pressure decreased, while, as expected, the level of sedation increased. Analyzing the propofol and sevoflurane group separately, both groups showed comparable overall courses of DPOAE levels at higher frequencies (2.8 kHz p = 0.310, 4 kHz p = 0.193, 6 kHz p = 0.269, 8 kHz p = 0.223) and no changes of DPOAE levels compared with baseline values were observed. At T5 the 1 kHz DPOAE level increased in the propofol group and slightly decreased in the sevoflurane group (p < 0.001). While the 1.4 kHz DPOAE level in the propofol group did not change over time the 1.4 kHz DPOAE level decreased in the sevoflurane group (baseline to T 4 p = 0.045; Baseline to T 5 p = 0.004). While overall there were different courses between these two groups in the 2 kHz DPOAE level, in the post hoc analysis only a tendency in the change from baseline to T 4 could be observed (p = 0.082). These results indicate that while the amplitudes of certain DPOAEs were influenced by GA, the depth of anesthesia had no effect on this measure of cochlear function in clinical routine. Therefore, DPOAE measurements in sedation and during GA are useful but the effect of anesthetic agents on DPOAE levels needs to be taken into account when analyzing the test.

Experimental model of laryngotracheal stenosis in infants: effects of different high-frequency jet ventilation patterns on pulmonary parameters.

BACKGROUND: Supraglottic high-frequency jet ventilation (HFJV) in laryngotracheal surgery in infants with modified jet laryngoscopes offers the surgeon an unimpaired operating field. However, supraglottic HFJV is associated with the development of high airway pressures, inadvertent positive end-expiratory pressure (PEEP) levels, and barotrauma. METHODS: We investigated the total lung volumes (TLV) and tidal volume variations at peak inspiratory pressure levels (PIP) and at PEEP levels along with the pulmonary pressures (PIP and PEEP) during two conventional methods of supraglottic HFJV in an infant trachea-lung model without stenosis and with different degrees of stenosis. RESULTS: With augmentation of the driving pressure in the experiment without stenosis, the TLV plus the pulmonary pressures increased. With narrowing of the stenosis, TLV reduced at PIP level and increased at PEEP level. Volume shifts were significantly higher during superimposed HFJV compared with monofrequent HFJV at equivalent stenosis diameter (P < 0.05) except for the setting with 0.3 bar driving pressure (P > 0.05). The pulmonary PIP was in none of the test series higher than 20 mbar, and the pulmonary PEEP did not exceed 14 mbar. CONCLUSIONS: The results from our experimental model support the safe and effective clinical use of supraglottic HFJV in infants with tracheal stenosis. Moderate driving pressures provide acceptable pulmonary pressures in normal compliant lungs.

Airway management and anesthesia in neonates, infants and children during endolaryngotracheal surgery.

BACKGROUND: Endolaryngotracheal surgery in neonates, infants and children poses a big challenge for both anesthesiologist and surgeon. The narrowness of the airways and the great variability of the pathological lesions necessitate close collaboration between the surgical and the anesthesia team to provide optimal operating conditions and ensure adequate ventilation and oxygenation. METHODS: Sixty-two anesthetic records of endolaryngotracheal surgical procedures in neonates, infants and children with ASA physical status 1-3 were analyzed retrospectively. Anesthesia was administered as total intravenous anesthesia; propofol supplemented with remifentanil. Ventilation was performed as supraglottic, superimposed high-frequency jet ventilation via jet laryngoscope with integrated jet nozzles. RESULTS: Age was 58.93 (SD 35.40) months, range 3 weeks to 14 years; body weight 17.83 (SD 8.79) kg, range 2.4-50 kg. The capillary pCO(2) 5 min after the start of the surgical procedure (n = 62) was 40.01 (SD 7.71) mmHg and after 20 min (n = 24) 41.77 (SD 7.12) mmHg. No hypoxemia (oxygen saturation <90%) developed. All patients were hemodynamically stable during jet ventilation. Barotrauma or gas insufflation in the stomach did not occur. No perioperative tracheostomy was necessary. Laryngospasm occurred in one child during emergence from anesthesia. Four infants received postoperative conventional respirator therapy in the ICU overnight. CONCLUSIONS: Supraglottic superimposed high-/low-frequency jet ventilation via jet laryngoscopes with integrated jet nozzles is a minimally invasive ventilation technique for neonates, infants and children in endolaryngotracheal surgery, which allows an unimpaired operating field for the surgeon especially in LASER surgery.