Daniel Steinmann

A lung area estimation method for analysis of ventilation inhomogeneity based on electrical impedance tomography.

PURPOSE To evaluate a novel method for lung area estimation (LAE method) in electrical impedance tomography (EIT) images as a prerequisite of quantitative analysis of ventilation inhomogeneity. METHODS The LAE method mirrors the lung regions in the functional EIT (fEIT) image and subsequently subtracts the cardiac related areas. In this preliminary study, 51 mechanically ventilated patients were investigated, including 39~patients scheduled for thoracic surgery (test group); 10 patients scheduled for orthopedic surgery without pulmonary disease (control group) and 2 ICU patients undergoing chest computed tomography (CT) examination. EIT data was recorded in all groups. The results of the LAE method were compared to those obtained with the fEIT method and to CT images. RESULTS The lung area size determined with fEIT in control group is S(C,fEIT) = 361 +/- 35 (mean +/- SD) and in test group S(T,fEIT) = 299 +/- 61 (p< 0.01). The sizes estimated with the LAE method in control group S(C,LAE) = 353 +/- 27 and in test group S(T,LAE) = 353 +/- 61 (p=0.41). The result demonstrates that the novel LAE method improves the identification of lung region in EIT images, from which the analysis of ventilation distribution will benefit. The preliminary comparison with CT images exemplary indicates a closer match of the lung area shapes after the LAE than after the fEIT-based analysis. CONCLUSION The LAE method is a robust lung area determination method, suitable for patients with healthy or seriously injured lungs.

Pressure-dependent stress relaxation in acute respiratory distress syndrome and healthy lungs: an investigation based on a viscoelastic model

IntroductionLimiting the energy transfer between ventilator and lung is crucial for ventilatory strategy in acute respiratory distress syndrome (ARDS). Part of the energy is transmitted to the viscoelastic tissue components where it is stored or dissipates. In mechanically ventilated patients, viscoelasticity can be investigated by analyzing pulmonary stress relaxation. While stress relaxation processes of the lung have been intensively investigated, non-linear interrelations have not been systematically analyzed, and such analyses have been limited to small volume or pressure ranges. In this study, stress relaxation of mechanically ventilated lungs was investigated, focusing on non-linear dependence on pressure. The range of inspiratory capacity was analyzed up to a plateau pressure of 45 cmH2O.MethodsTwenty ARDS patients and eleven patients with normal lungs under mechanical ventilation were included. Rapid flow interruptions were repetitively applied using an automated super-syringe maneuver. Viscoelastic resistance, compliance and time constant were determined by multiple regression analysis using a lumped parameter model. This same viscoelastic model was used to investigate the frequency dependence of the respiratory systems impedance.ResultsThe viscoelastic time constant was independent of pressure, and it did not differ between normal and ARDS lungs. In contrast, viscoelastic resistance increased non-linearly with pressure (normal: 8.4 (7.4-11.9) [median (lower - upper quartile)] to 35.2 (25.6-39.5) cmH2O·sec/L; ARDS: 11.9 (9.2-22.1) to 73.5 (56.8-98.7)cmH2O·sec/L), and viscoelastic compliance decreased non-linearly with pressure (normal: 130.1(116.9-151.3) to 37.4(34.7-46.3) mL/cmH2O; ARDS: 125.8(80.0-211.0) to 17.1(13.8-24.7)mL/cmH2O). The pulmonary impedance increased with pressure and decreased with respiratory frequency.ConclusionsViscoelastic compliance and resistance are highly non-linear with respect to pressure and differ considerably between ARDS and normal lungs. None of these characteristics can be observed for the viscoelastic time constant. From our analysis of viscoelastic properties we cautiously conclude that the energy transfer from the respirator to the lung can be reduced by application of low inspiratory plateau pressures and high respiratory frequencies. This we consider to be potentially lung protective.

Prospective model-based comparison of different laryngoscopes for difficult intubation in infants.

Background:  Difficult intubation in infants is uncommon but may be a challenge for the anesthesiologist. Many optical‐assisted techniques are available to ease endotracheal placement of tube but have not been systemically evaluated for pediatric practice.

Intraoperative pulmonary tumor embolism from renal cell carcinoma and a patent foramen ovale detected by transesophageal echocardiography.

p f a w S PULMONARY TUMOR EMBOLIZATION from renal cell carcinoma is a fatal complication during nephrectomy since it is associated with high perioperative mortality and cardiopulmonary morbidity. A persistent patent foramen ovale (PFO) is a heart defect that can be found in approximately one-fourth of the population and increases the risk for ischemic stroke and arterial embolization. A unique case of intraoperative pulmonary tumor embolism is described in a patient with a previously undiagnosed PFO, in whom intraoperative transesophageal echocardiography (TEE) led to fast diagnosis, successful surgical embolus removal and closure of the PFO.

Determination of ‘recruited volume’ following a PEEP step is not a measure of lung recruitability

It has been proposed that the analysis of positive end‐expiratory pressure (PEEP)‐induced volume changes can quantify alveolar recruitment. The potential of a lung to be recruited is expected to be high in acute respiratory distress syndrome (ARDS), where collapsed lung tissue is very common. The volume change that is beyond the delta volume because of the patients compliance has been termed ‘recruited volume’ (RecV). However, data of patients with low and high RecV showed less severe lung disease in high ‘recruiters’, indicating that RecV may not equal the ‘potentially recruitable lung tissue’ seen in computed tomography scans. We hypothesized that RecV is higher in lung‐healthy (LH) patients with little collapsed lung compared with ARDS patients.

Comparison of Bullard and Airtraq laryngoscopes with conventional laryngoscopy in a manikin study of simulated difficult intubation.

Background When airway management is difficult, various measures can be taken to facilitate tracheal intubation. The Bullard and Airtraq laryngoscopes were developed for this purpose. We hypothesised that the Bullard and Airtraq laryngoscopes would perform better than a conventional laryngoscope in the management of a simulated difficult airway. We also hypothesised that the indirect laryngoscopes would perform comparably. Methods In a randomised controlled study, 60 anaesthetists (30 with no or little experience and 30 with broader experience in the use of the Bullard laryngoscope, referred to as beginners and experts, respectively) performed three successive intubation attempts using conventional, Bullard and Airtraq laryngoscopes in two simulated difficult airway scenarios: neck immobilisation (scenario A) and neck immobilisation with additional tongue oedema (scenario B). The primary endpoint was overall intubation success rate. Secondary endpoints were time required for successful intubation, the amount of dental stress exerted during laryngoscopy and satisfaction with each airway device. Results In scenario A, intubation success rates were 97–100% with all devices. In scenario B, all participants failed to intubate the trachea using the conventional laryngoscope. When using the Bullard laryngoscope, intubation success rates of 87–97% did not differ significantly (P > 0.05) from those during scenario A and between groups (beginners vs. experts). In contrast, when using the Airtraq laryngoscope, the overall intubation success rate was significantly lower (P < 0.05) compared with scenario A and compared with use of the Bullard laryngoscope, and differed between beginners and experts (20 and 50%, respectively). In cases of successful intubation, intubation times were comparable between devices and groups. Intubation times were longer during scenario B. Dental stress was always lower (P < 0.05) during use of the Bullard and Airtraq laryngoscopes compared with the conventional laryngoscope, lowest (P < 0.05) during use of the Bullard laryngoscope and (with the exception of use of the conventional laryngoscope by the experts) higher during scenario B than during scenario A. In scenario A, participants preferred both video laryngoscopes to the conventional laryngoscope. Conclusion In a moderately difficult airway scenario, all laryngoscopes performed equally well. However, in a more difficult airway scenario, the Bullard and Airtraq laryngoscopes performed better than the conventional laryngoscope, with the Bullard device performing better than the Airtraq. This may be in part related to differing prior experiences of operators with the respective airway devices.

Determination of Lung Area in EIT Images

Electrical impedance tomography (EIT), as a noninvasive, radiation-free imaging technique, has the potential for bedside monitoring of regional lung function. Evaluation of EIT imaging requires the identification of the lung area in the images. By Hahn and Frerichs et al. a functional EIT based method (fEIT) was proposed to identify the lung area in EIT images for patients with healthy lungs. However, a method for patients with serious lung disease is missing. The aim of this study was to develop an improved method for lung area estimation in EIT images (LAE), which is also suitable for patients with serious pulmonary diseases. In LAE the lung area as determined by fEIT is mirrored and the cardiac related area is subtracted. 49 mechanically ventilated patients were investigated, including 39 patients waiting for thoracic surgery (test group) and 10 patients for orthopedic surgery without pulmonary disease (control group). The sizes of the lung area determined with fEIT are in control group S C,fEIT =361plusmn35.1 (meanplusmnSD) and in test group S T,fEIT =299plusmn60.8 (p<0.01). The sizes estimated with the LAE method in control group S C,LAE = 353plusmn27.2 and in test group S T,LAE =353plusmn61.1 (p=0.41). It is assumed that the fraction of the lung in the thorax for different people should be more or less in the same range, in spite of the state of the lung. The result demonstrates that the novel LAE method can better access the lung region in EIT images, from which the analysis of regional lung ventilation will benefit.

Perioperative management of a child with long‐chain 3‐hydroxyacyl‐CoA dehydrogenase (LCHAD) deficiency

paracetamol, diclofenac and morphine, she received local anesthetic infiltration with bupivicaine 0.25% with epinephrine to each tonsil bed before proceeding to emergence. She was extubated in the left lateral position, 15 degrees head down, breathing sevoflurane in 100% oxygen with an end-tidal concentration of sevoflurane of 3.2%. She had an uneventful recovery period. Malpuech syndrome is a rare multiple congenital anomaly syndrome. The incidence is unknown, but at least 12 patients worldwide are reported to have this condition (2). There is often difficulty regarding a definite clinical diagnosis. The condition is believed to be inherited in an autosomal recessive pattern, but this has not as yet been confirmed because of the small numbers affected. A genetic locus has not been determined, but abnormalities in the PAX2gene, the ROR2 gene, and the P63 gene are believed to be involved in the generation of this syndrome (3). The facial features of this disorder are typically cleft lip and palate, hypertelorism, ptosis and malar hypoplasia, micrognathia and prominent dentition (2). Affected children may also present with omphalocele, umbilical hernia, renal aplasia, undescended testis, micropenis, caudal appendage and a sacral dimple suggestive of spina bifida occulta (2). As patients get older hearing defects become obvious, possibly related to an increased frequency of upper respiratory tract infections. There can be a sensorineural component to the hearing deficit. A mild to moderate intellectual disability is present in all patients, with a global developmental delay. Weight and height usually remain below the 50th centile. There has been a reported association with fetal hydrops and cardiac defects such as hypoplastic left heart syndrome, patent ductus arteriosus and ventricular septal defect (4). Teeth eruption may be present at birth, but any teeth present will be lost soon after birth. This could potentially cause problems during intubation in the neonate. As children get older they have prominent teeth. This, together with micrognathia and malar hypoplasia results in a high risk of a potentially difficult airway. Thoracolumbar scoliosis is a common feature which may compound difficulty in airway management. Early identification of this rare condition is important to assess the full extent of the anomalies before proceeding with anesthesia. These children frequently require surgery in childhood, predominantly for genitourinary abnormalities, omphalocele and umbilical hernia. The presence of the characteristic facial abnormalities will require the anesthetist to be prepared for a potentially difficult airway. Spinal malformations may make the placement of caudal or spinal blocks challenging. However, despite the presence of these anomalies, we can report the safe use of an endotracheal tube in our patient during the conduct of anesthesia using sevoflurane in oxygen and nitrous oxide. Key learning points

Anesthesia for orthopedic surgery in Pallister-Killian syndrome

dexmedetomidine in humans. II: Hemodynamic changes. Anesthesiology 1992; 77: 1134–1142. 3 Hall JE, Uhrich TD, Barney JA et al. Sedative, amnestic, and analgesic properties of small-dose dexmedetomidine infusions. Anesth Analg 2000; 90: 699–705. 4 Xu H, Aibiki M, Seki K et al. Effects of dexmedetomidine, an alpha 2-adrenoceptor agonist, on renal sympathetic nerve activity, blood pressure, heart rate and central venous pressure in urethane-anesthetized rabbits. J Auton Nerv Syst 1998; 71: 48– 54. 5 Transverse Myelitis Consortium Working Group. Proposed diagnostic criteria and nosology of acute transverse myelitis. Neurology 2002; 59: 499–505. 6 Ingersoll-Weng E, Manecke GR, Thistlethwaite PA. Dexmedetomidine and cardiac arrest. Anesthesiology 2004; 100: 738–739. 7 Berkenbosch JW, Tobias JD. Development of bradycardia during sedation with dexmedetomidine in an infant concurrently receiving digoxin. Pediatr Crit Care Med 2003; 4: 203–205.

The pressure drop across the endotracheal tube in mechanically ventilated pediatric patients.

During mechanical ventilation, the airway pressure (Paw) is usually monitored. However, Paw comprises the endotracheal tube (ETT)‐related pressure drop (∆PETT) and thus does not reflect the pressure in the patients’ lungs. Therefore, monitoring of mechanical ventilation should be based on the tracheal pressure (Ptrach). We systematically investigated potential factors influencing ∆PETT in pediatric ETTs.