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Description / Table of Contents: Abstract During pressure support ventilation (PSV), the timing of the breathing cycle is mainly controlled by the patient. Therefore, the delivered flow pattern during PSV might be better synchronised with the patient's demands than during volume-assisted ventilation. In several modern ventilators, inspiration is terminated when the inspiratory flow decreases to 25% of the initial peak value. However, this timing algorithm might cause premature inspiration termination if the initial peak flow is high. This could result not only in an increased risk of dyssynchronization between the patient and the ventilator, but also in reduced ventilatory support. On the other hand, a decreased peak flow might inappropriately increase the patient's inspiratory effort. The aim of our study was to evaluate the influence of the variation of the initial peak-flow rate during PSV on respiratory pattern and mechanical work of breathing. Patients. Six patients with chronic obstructive pulmonary disease (COPD) and six patients with no or minor nonobstructive lung pathology (control) were studied during PSV with different inspiratory flow rates by variations of the pressurisation time (Evita I, Drägerwerke, Lübeck, Germany). During the study period all patients were in stable circulatory conditions and in the weaning phase. Method. Patients were studied in a 45° semirecumbent position. Using the medium pressurization time (1 s) during PSV the inspiratory pressure was individually adjusted to obtain a tidal volume of about 8 ml/kg body weight. Thereafter, measurements were performed during five pressurization times (〈0.1, 0.5, 1, 1.5, 2 s defined as T 0.1, T 0.5, T 1, T 1.5 and T 2) in random order, while maintaining the pressure support setting at the ventilator. Between each measurement steady-state was attained. Positive end-exspiratory pressure (PEEP) and FIO2 were maintained at prestudy levels and remained constant during the study period. Informed consent was obtained from each patient or his next of kin. The study protocol was approved by the ethics committee of our medical faculty. Gas flow was measured at the proximal end of the endotracheal tube with a pneumotachometer (Fleisch no. 2, Fleisch, Lausanne, Switzerland) and a differential pressure transducer. Tracheal pressure (Paw) was determined in the same position with a second differential pressure transducer (Dr. Fenyves & Gut, Basel, Switzerland). Esophageal pressure (Pes) was obtained by a nasogastric balloon-catheter (Mallinckrodt, Argyle, NY, USA) connected to a further differential pressure transducer of the same type as described above. The balloon was positioned 2–3 cm above the dome of the diaphragm. The correct balloon position was verified by an occlusion test as described elsewhere. The data were sampled after A/D conversion with a frequency of 20 Hz and processed on an IBM-compatible PC. Software for data collection and processing was self-programmed using a commercially available software program (Asyst 4.0, Asyst Software Technologies, Rochester, NY, USA). Patient's inspiratory work of breathing Wpi (mJ/l) was calculated from Pes/volume plots according to the modified Campbell's diagram. Dynamic intrinsic PEEP (PEEPidyn) was obtained from esophageal pressure tracings relative to airway pressure as the deflection in Pes before the initiation of inspiratory flow Patient's additive work of breathing (Wadd) against ventilator system resistance was calculated directly from Paw/V tracings when Paw was lower than the pressure on the compliance curve. Two-way analysis of variance (ANOVA) was used for statistical analysis, followed by post hoc testing of the least significant difference between means for multiple comparisons. Probability values less than 0.05 were considered as significant. Results. COPD patients had significantly higher pressure support than control patients. With decreasing inspiratory flow, Wpi increased significantly in COPD patients. Additionally, the duct cycle (Ti/Ttot) significantly increased with decreased flow rates which resulted in a higher PEEPidyn compared to the baseline. At T 1.5 and T 2 with lower flow rates, the pre-set pressure support level was not achieved within inspiration in the COPD patients. Wadd increased significantly at T 1, T 1.5 and T 2 in COPD patients and at T 1.5 and T 2 in the control group. In one patient, premature termination of inspiration owing to high initial peak flow was corrected by adjustment of the inspiratory flow. Conclusion. Our results demonstrate that a decreased peak flow during PSV resulted in increased patient's work of breathing in COPD patients. During lower flow, the pre-set pressure support level was not attained and additional work had to be done on the ventilator system. Furthermore, the higher PEEPidyn during lower flow rates indicates a higher risk of dynamic pulmonary hyperinflation in patients with COPD. We conclude that the use of pressurization times ≥1 s to decrease inspiratory peak flow during PSV is of no benefit and should be avoided, particularly in COPD patients. However, in selected cases, slight decrease of inappropriately high peak flows might be useful for optimization of PSV setting to avoid premature termination of inspiration.

Description / Table of Contents: Abstract. Variations in anatomy of the bony and soft-tissue structures of the neck and facial cranium due to trauma, disease, or dysmorphic syndromes may lead to severe intubation problems. These patients are admitted for mandibulofacial and otolaryngologic surgery. It is important to inspect the patient's outer and inner pharyngeal structures carefully during preoperative assessment, as suggested by Mallampati [5]. The observer estimates the facility of intubation by inspection of the faucial pillars, soft palate, and uvula. Unfortunately, even careful examination does not predict every case of difficult intubation, so that unexpected problems may occur. There may also be difficulties in ventilating these patients with a face mask. Safe intubation is possible in these cases using the laryngeal mask airway (LMA) [1, 6, 7], laryngoscopy with a rigid optical aid [2], and the fibreoptic bronchoscope. Case report. We report a 14-month-old girl with Goldenhar's syndrome (oculo-auricular dysplasia) [3] who presented for soft-palate surgery. This syndrome belongs to the group of cranio-mandibular-facial malformations; the main symptoms are congenital unilateral malformations in the area of the 1st and 2nd branchial arches. The patient's jaw was hypoplastic with aplasia of the temporo-mandibular joint, which led to asymmetry of the lower face and an extremely short mandible. Additionally, we observed a large tongue in relation to the small jaw. Macrostomia is part of the syndrome, and may lead to underestimation of intubation problems. As the faucial pillars were visible but the uvula was masked by the base of the tongue, we assigned our patient to Mallampati class 2 [5]. Other findings in the syndrome can be malformations of the eyes, ears, heart, and spinal column. Our patient had complete atresia of the right outer ear and a subconjunctival lipoma. Due to these conditions, we expected a difficult intubation. Anaesthesia was induced with 250 mg methohexitone rectally and continued with halothane via a Rendell-Baker mask. After relaxation with vercuronium, laryngoscopy was performed. Due to the extremely short chin and relatively large tongue, it was impossible to visualise the vocal cords or epiglottis. Safe face-mask ventilation was also difficult. Therefore, we decided to introduce a LMA, which was easily done. Since reconstruction of the soft palate was not possible with a LMA, we used a fibreoptic bronchoscope to intubate the patient with a Vygon tube via the lumen of the LMA. Fixing the endotracheal tube with a long forceps, the LMA was easily removed. The LMA was successfully applied at a second procedure for a change of dressing. Discussion. In cases of difficult mask ventilation and intubation problems, the LMA improves the safety of both patient and the anaesthetist. Airway management with the LMA is easy and safe and without the risk of trauma caused by violent attempts to position an endotracheal tube by normal laryngoscopy when abnormal anatomy is present or unexpected problems occur. When a difficult intubation can be expected (e.g., in facial dysmorphic syndromes such as Goldenhar's syndrome, Pierre-Robin syndrome, or Franceschetti's syndrome) we recommend considering the LMA as a safe additional tool for airway management.