W. Golisch

Monitoring perioperative changes in distribution of pulmonary ventilation by functional electrical impedance tomography

Background: Electrical impedance tomography (EIT) is a noninvasive technique providing cross‐sectional images of the thorax. We have tested an extended evaluation procedure, the functional EIT (f‐EIT), to identify the local shifts of ventilation known to occur during the transition between spontaneous, controlled and assisted ventilation modes.

Effect of low-level PEEP on inspiratory work of breathing in intubated patients, both with healthy lungs and with COPD

ObjectiveEvaluation of low-level PEEP (5 cm H2O) and the two different CPAP trigger modes in the Bennett 7200a ventilator (demand-valve and flow-by trigger modes) on inspiratory work of breathing (Wi) during the weaning phase.DesignProspective controlled study.SettingThe intensive care unit of a university hospital.PatientsSix intubated patients with normal lung function (NL), ventilated because of non-pulmonary trauma or post-operative stay in the ICU, and six patients recovering from acute respiratory failure due to exacerbation of chronic obstructive pulmonary disease (COPD), breathing either FB-CPAP or DV-CPAP with the Bennett 7200a ventilator.InterventionsThe patients studied were breathing with zero end-expiratory pressure (ZEEP), as well as CPAP of 5 cm H2O (PEEP), with the following respiratory modes: the demand-valve trigger mode, pressure support of 5 cm H2O, and the flow-by trigger mode (base flow of 20 l/min and flow trigger of 2 l/min). Furthermore, Wi during T-piece breathing was evaluated.Measurements and resultsWi was determined using a modified Campbells diagram. Total inspiratory work (Wi), work against flow-resistive resistance (Wires), work against elastic resistance (Wiel), work imposed by the ventilator system (Wimp), dynamic intrinsic positive end-expiratory pressure (PEEPidyn), airway pressure decrease during beginning inspiration (Paw) and spirometric parameters were measured. In the NL group, only minor, clinically irrelevant changes in the measured variables were detected. In the COPD group, in contrast, PEEP reduced Wi and its components Wires and Wiel significantly compared to the corresponding ZEEP settings. This was due mainly to a significant decrease in PEEPidyn when external PEEP was applied. Flow-by imposed less Wi on the COPD patients during PEEP than did demand-valve CPAP. Differences in Wimp between the flow-by and demand-valve trigger models were significant for both groups. However, in relation to Wi these differences were small.ConclusionWe conclude that the application of low-level external PEEP benefits COPD patients because it reduces inspiratory work, mainly by lowering the inspiratory threshold represented by PEEPidyn. Differences between the trigger modes of the ventilator used in this study were small and can be compensated for by the application of a small amount of pressure support.

Heterogeneous Distribution of Pulmonary Ventilation in Intensive Care Patients Detected by Functional Electrical Impedance Tomography

Electrical impedance tomography (EIT) is a new noninvasive imaging technique which utilizes the different electrical properties of biological tissues to produce cross-sectional images of selected parts of the body. When applied on the thorax, the cyclic fluctuations of electrical impedance of the lung tissue, associated with different air contents of the lungs in the course of the respiratory cycle, can be used to generate derived EIT tomograms which represent the spatial distribution of ventilation in the chosen transverse plane. The corresponding evaluation technique, the functional EIT, was used for the first time to follow the regional ventilation in three intensive care patients. The method was shown (1) to identify the redistribution of inspired air in the lungs associated with controlled ventilation in a patient undergoing elective laparotomy, (2) to follow the improvement of locally impaired lung ventilation in the course of severe pneumonia, and (3) to detect regional reduction of ventilation due to lobar atelectasis with stasis pneumonia in a patient with bronchial carcinoma.

Difficult intubation due to facial malformations in children: use of the laryngeal mask airway

Zusammenfassung. Anatomische Veränderungen, Verletzungen und Fehlbildungen im Hals- und Kopfbereich sind Gründe erschwerter bis unmöglicher konventioneller Intubation. Auch eine präoperative Einschätzung anhand der Einsehbarkeit von Tonsillen, Uvula und weichem Gaumensegel korreliert nicht immer mit dem späteren Intubationssitus. Wir berichten im folgenden über eine 14 Monate alte Patientin mit Goldenharsyndrom (Dysplasia oculo-auricularis), bei der ein Weichgaumenverschluß durchgeführt werden sollte. Das Syndrom gehört zum Formenkreis der kranio-mandibulo-fazialen Dysmorphien. Typisch sind Entwicklungsstörungen im Bereich des 1. und 2. Kiemenbogens mit Fehlbildung von Augen-, Ohren- und Kieferanlage. Die resultierende Hypoplasie des aufsteigenden Unterkieferastes mit Mikro-, Retrogenie kann zu erheblichen Intubationsproblemen führen. Nach Narkoseeinleitung mit Brevimethal rektal, Halothan und Vecuronium wurde eine Einstellung mit dem Laryngoskop vorgenommen. Im relativ zu kleinen Hypopharynx ließ sich die Glottis nicht einsehen. Wir entschieden uns eine Kehlkopfmaske einzulegen, was problemlos gelang. Da diese für die geplante Operation nicht belassen werden konnte, plazierten wir mit Hilfe einer Fiberoptik einen Vygon-Tubus durch den Ansatzschlauch der Kehlkopfmaske. Durch die Kombination von Kehlkopfmaske und fiberoptischem Endoskop als Intubationshilfsmittel waren die Atemwege der kleinen Patientin zu jeder Zeit gesichert. Wir empfehlen daher, bei zu erwartender schwieriger Intubation auch die Kehlkopfmaske grundsätzlich mit in Betracht zu ziehen.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 patients 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 Goldenhars 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 patients 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 Goldenhars syndrome, Pierre-Robin syndrome, or Franceschettis syndrome) we recommend considering the LMA as a safe additional tool for airway management.

Variation des inspiratorischen Gasflusses unter druckunterstützter Spontanatmung

ZusammenfassungBei einigen Respiratoren kann unter Pressure Support Ventilation (PSV) der Inspirationsfluß (V˙i) durch Veränderung der Druckanstiegszeit variiert werden. Über den Einfluß des Inspirationsflußprofils unter PSV auf die Atemarbeit ist besonders bei Patienten mit chronischer Atemwegsobstruktion (COPD) kaum etwas bekannt. Wir untersuchten an 6 COPD-Patienten und 6 Patienten ohne Lungenerkrankung (Kontrollgruppe) die Effekte einer Variation von V˙i unter PSV auf atemmechanische Variablen und die mechanische Atemarbeit. Unter individuell eingestellter Druckunterstützung wurde die Druckanstiegszeit in 5 Stufen verändert. Die Verlängerung der Druckanstiegszeit verminderte den initialen V˙i in beiden Patientengruppen. Gleichzeitig stieg die Atemarbeit in der COPD-Gruppe bei verringertem V˙i signifikant an. Eine Ursache hierfür war, daß bei den COPD-Patienten bei langsamen Druckanstiegszeiten die eingestellte Druckunterstützung nicht mehr erreicht wurde. Der langsamere V˙i führte zu einer Verlängerung der Inspiration auf Kosten der Exspirationszeit. Dies verursachte bei COPD-Patienten eine unerwünschte Erhöhung des intrinsischen PEEP. Die Auswirkungen eines niedrigeren V˙i unter PSV in der Kontrollgruppe waren klinisch nur wenig relevant. Unsere Ergebnisse zeigen, daß besonders bei Patienten mit COPD unter PSV hohe initiale Inspirationsflüsse zu bevorzugen sind, da ein niedriger Fluß die Patientenatemarbeit erhöht und eine dynamische Lungenüberblähung verstärkt. Allerdings konnte bei einem Patienten ein vorzeitiger Inspirationsabbruch aufgrund eines hohen Initialflusses durch Anpassung des Flußprofils korrigiert werden. In Einzelfällen kann daher eine Verlängerung der Druckanstiegszeit bis auf maximal 1 s sinnvoll sein.AbstractDuring 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 patients 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 patients 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). Patients inspiratory work of breathing Wpi (mJ/l) was calculated from Pes/volume plots according to the modified Campbells 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 Patients 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 patients 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.