Jan Karsten

Protective ventilation using electrical impedance tomography

Dynamic thoracic EIT is capable of detecting changes of the ventilation distribution in the lung. Nevertheless, it has yet to become an established clinical tool. Therefore, it is necessary to consider application scenarios wherein fast and distinct changes of the tissue conductivities are to be found and also have a clear diagnostic significance. One such a scenario is the artificial ventilation of patients suffering from the acute respiratory distress syndrome (ARDS). New protective ventilation strategies involving recruitment manoeuvres are associated with noticeable shifts of body fluids and regional ventilation, which can quite easily be detected by EIT. The bedside assessment of these recruitment manoeuvres will help the attending physician to optimize treatment. Hence, we performed an animal study of lavage-induced lung failure and investigated if EIT is capable of qualitatively as well as quantitatively monitoring lung recruitment during a stepwise PEEP trial. Additionally, we integrated EIT into a fuzzy controller-based ventilation system which allows one to perform automated recruitment manoeuvres (open lung concept) based on online PaO2 measurements. We found that EIT is a useful tool to titrate the proper PEEP level after fully recruiting the lung. Furthermore, EIT seems to be able to determine the status of recruitment when combining it with other physiological parameters. These results suggest that EIT may play an important role in the individualization of protective ventilation strategies.

Effect of PEEP on regional ventilation during laparoscopic surgery monitored by electrical impedance tomography

Background: Anesthesia per se and pneumoperitoneum during laparoscopic surgery lead to atelectasis and impairment of oxygenation. We hypothesized that a ventilation with positive end‐expiratory pressure (PEEP) during general anesthesia and laparoscopic surgery leads to a more homogeneous ventilation distribution as determined by electrical impedance tomography (EIT). Furthermore, we supposed that PEEP ventilation in lung‐healthy patients would improve the parameters of oxygenation and respiratory compliance.

Functional residual capacity-guided alveolar recruitment strategy after endotracheal suctioning in cardiac surgery patients.

Objective:To determine whether the results of functional residual capacity measurements after endotracheal suctioning could guide the decision to perform an alveolar recruitment maneuver and thus improve lung function. Design:Prospective, randomized, controlled interventional study. Setting:Intensive care unit of a university hospital. Patients:Fifty-nine mechanically ventilated patients within 2 hrs after elective cardiac surgery without preexisting lung diseases. Interventions:Patients received a standard suctioning procedure with disconnection of the ventilator (20 secs, 14 F catheter, 200 cm H2O negative pressure). Prospectively, patients were stratified into two groups by the postsuctioning functional residual capacity value (group A: functional residual capacity >94% of baseline; group B: functional residual capacity <94% of baseline). Both groups were randomized into either a recruitment maneuver (RM) group (positive end-expiratory pressure 15 cm H2O, peak inspiratory pressure 35–40 cm H2O for 30 secs, group RM) or a non-RM group, in which ventilation was resumed without an RM (group NRM), resulting in four groups. Measurements and Main Results:Functional residual capacity and arterial blood gases were recorded for up to 1 hr. In addition, distribution of ventilation was measured by means of electrical impedance tomography. The RM had an impact on distribution of ventilation, functional residual capacity, and oxygenation in patients with a decrease of functional residual capacity after suctioning. In contrast, the RM showed no impact on these parameters in patients with no decrease of functional residual capacity after suctioning. Conclusions:By measurements of functional residual capacity after endotracheal suctioning, patients profiting from a consecutive recruitment maneuver could be identified. Guiding the recruitment strategy on changes of functional residual capacity may improve patient care.

The suitability of EIT to estimate EELV in a clinical trial compared to oxygen wash-in/wash-out technique.

Abstract Introduction: Open endotracheal suctioning procedure (OSP) and recruitment manoeuvre (RM) are known to induce severe alterations of end-expiratory lung volume (EELV). We hypothesised that EIT lung volumes lack clinical validity. We studied the suitability of EIT to estimate EELV compared to oxygen wash-in/wash-out technique. Methods: Fifty-four postoperative cardiac surgery patients were enrolled and received standardized ventilation and OSP. Patients were randomized into two groups receiving either RM after suctioning (group RM) or no RM (group NRM). Measurements were conducted at the following time points: Baseline (T1), after suctioning (T2), after RM or NRM (T3), and 15 and 30 min after T3 (T4 and T5). We measured EELV using the oxygen wash-in/wash-out technique (EELVO2) and computed EELV from EIT (EELVEIT) by the following formula: EELVEITTx,y…=EELVO2+ΔEELI×VT/ΔZ. EELVEIT values were compared with EELVO2 using Bland-Altman analysis and Pearson correlation. Results: Limits of agreement ranged from -0.83 to 1.31 l. Pearson correlation revealed significant results. There was no significant impact of RM or NRM on EELVO2-EELVEIT relationship (p=0.21; p=0.23). Discussion: During typical routine respiratory manoeuvres like endotracheal suctioning or alveolar recruitment, EELV cannot be estimated by EIT with reasonable accuracy.

Low preoperative cerebral oxygen saturation is associated with longer time to extubation during fast-track cardiac anaesthesia

OBJECTIVES Fast-track cardiac anaesthesia programs aiming at early tracheal extubation have not only been linked to a decrease in intensive care unit and hospital length of stay but also to a decrease in morbidity and mortality as well as a containment of rising medical costs. General recommendations for the inclusion criteria concerning fast-track programs are not available. METHODS The present study determined the factors influencing the time to extubation in patients undergoing a newly implemented fast-track protocol. Seventy-nine patients were retrospectively studied. Successful fast track was defined as time to extubation within 75 min after admission to ICU. RESULTS Sixty patients fulfilled the successful fast-track criteria with a mean time to extubation of 43.9 min (range 15-75 min). Nineteen patients needed more than 75 min to be weaned from the respirator with a mean time to extubation of 135 min (range 90-320 min). Analysis of pre- and intraoperative factors revealed that these groups differed only with respect to preoperative cerebral oxygen saturation levels: 67.7 ± 5.2 versus 60.8 ± 7.4%. CONCLUSIONS Cerebral oxygen saturation assessment prior to cardiac surgery is significantly related to time to extubation and may thus be used to stratify candidates in fast-track programs.

Determination of optimal positive end-expiratory pressure based on respiratory compliance and electrical impedance tomography: a pilot clinical comparative trial

Abstract There is no agreement on gold standard method for positive end-expiratory pressure (PEEP) titration. Electrical impedance tomography (EIT) may aid in finding the optimal PEEP level. In this pilot trial, we investigated potential differences in the suggested optimal PEEP (BestPEEP) as derived by respiratory compliance and EIT-derived parameters. We examined if compliance-derived PEEP differs with regard to the regional ventilation distribution in relation to atelectasis and hyperinflation. Measurements were performed during an incremental/decremental PEEP trial in 15 ventilated intensive care patients suffering from mild-to-moderate impairment of oxygenation due to sepsis, pneumonia, trauma and metabolic and ischemic disorders. Measurement agreement was analyzed using Bland-Altman plots. We observed a diversity of EIT-derived and compliance-based optimal PEEP in the evaluated patients. BestPEEPCompliance did not necessarily correspond to the BestPEEPODCL with the least regional overdistension and collapse. The collapsed area was significantly smaller when the overdistension/collapse index was used for PEEP definition (p=0.022). Our results showed a clinically relevant difference in the suggested optimal PEEP levels when using different parameters for PEEP titration. The compliance-derived PEEP level revealed a higher proportion of residual regional atelectasis as compared to EIT-based PEEP.

Can today's house officers teach effectively? An assessment in undergraduate emergency training.

Background Previous publications describe house officers (HOs) as unaware of their ineffective teaching skills. Objective The aim of this study was to evaluate the role of teaching seniority in the comparison of teaching skills between HOs and faculty. Materials and methods Ten HOs (F: n=4, M: n=6, age: 35.1±6.8 years) and nine faculty (F: n=3, M: n=6, age: 41.4±4.9 years) who actively teach undergraduate emergency medicine were immediately evaluated at the end of the course by their students using the questionnaire SFDP26. The questionnaire consists of one item on ‘overall teaching effectiveness’ (OTE) (1=very poor to 5=excellent) and 25 items measured on a five-point Likert scale (1–5=strongly disagree to strongly agree) divided into seven subscales: 1, ‘establishing the learning climate’ (LC); 2, ‘control of session’ (CS); 3, ‘communication of goals’ (CG); 4, ‘facilitating understanding and retention’ (UR); 5, ‘evaluation’ (E); 6, ‘feedback’ (FB) and 7, ‘promoting self-directed learning’ (SL). The sample included 173 medical students in their third year of training who were randomly assigned to the instructors. A Mann–Whitney U-test was used to calculate group-related differences (resident vs. teaching faculty). For significant differences, effect size was calculated (r=Z/√N). Results No sex-related differences were found. Significantly better ratings for HOs were found in subscales: 1, ‘LC’ (P=0.001; r=0.20); 2, ‘CS’ (P=0.037; r=0.15); 5, ‘E’ (P=0.007; r=0.20); 6, ‘FB’ (P=0.001; r=0.23); 7, ‘SL’ (P=0.004; r=0.24) and ‘OTE’ (P=0.027; r=0.26). Conclusion From a learner’s perspective, the quality of teaching provided by HOs was rated at least similar and mostly better overall than that provided by faculty. These findings contradict results from previous studies on the quality of HO teaching and therefore warrant further assessment.

Changes of FRC during noninvasive ventilation in spontaneous breathing subjects can be determined by the oxygen washin/washout method

Recently, the feasibility of the oxygen washin/washout method for determination of functional residual capacity (FRC) in intubated, spontaneously breathing patients has been shown. During noninvasive ventilation using a face-mask the technique has not been validated so far. The aim of this study was to determine if the technique is able to follow FRC changes caused by change of body positions and application of continuous positive airway pressure in spontaneously breathing subjects wearing a face mask.

Automation of Protective Ventilation in Acute Lung Injury

Mechanical ventilation with positive pressure is the supportive therapy for patients with acute lung failure. To minimize pulmonary stress by prevention of end-expiratory alveolar collapse and over-distension of pulmonary areas, lung protective ventilation strategy has become standard therapy. Low tidal volume ventilation (VT ≤ 6ml, per kg predicated body weight) proved to reduce mortality rates in patients with lung failure notably. Recent surveys on intensive care units showed that the transfer of this evidence-based knowledge to ventilation therapy has not been realized in the current care of ventilated patients. Automated execution of protective ventilation protocols would help to optimize the individual setting in mechanical ventilated patients. To test the ability to automate protective ventilation protocols, the adjustment of positive pressure ventilation was realized in a saline lavage induced lung injury study in pigs. The implemented controllers were programmed to meet the therapeutic goals (tidal volume, oxygenation, plateau pressure, pH, inspiratory to expiratory ratio) of the ARDSnet-protocol. During the trial, all measurements were made using an online blood gas monitor (TrendCare Satellite, Diametrics Medical Inc., England), a monitor for hemodynamic parameters (Sirecust 1281, Siemens, Germany), a capnograph (CO2SMO+, Respironics, Inc., USA), and an electrical impedance tomography (EIT) prototype system (EIT evaluation Kit, Draeger Medical, Germany). After successful automated therapy, PaCO2 and FiO2 levels could be significantly reduced. Thus, the execution of automated protective ventilation protocols with an electronically controlled ventilator was possible and led to pulmonary stabilization in saline lavage induced acute lung injury.

Monitoring of Perioperative Ventilation Therapy by Electrical Impedance Tomography (EIT) in Clinical Practice

Mechanical ventilation ensures adequate oxygenation if ventilation is distributed in proportion to regional lung blood flow. General anesthesia, supine position, tracheal suctioning and intraoperative pulmonary complications lead to atelectasis and an impairment of oxygenation. Unfortunately, in standard clinical routine there is no bedside technique available to monitor regional ventilation in order to determine perioperative respiratory function. The EIT allows a bedside assessment of regional lung ventilation and dynamic evaluation of lung status within each breath. In terms of “proof-of-principle” we used EIT in relevant clinical settings, e.g. spontaneous breathing in different body positions in the recovery room, general anesthesia and mechanical ventilation with and without PEEP during surgery, and ventilation therapy while recovering from anesthesia at the ICU. We investigate the ability of EIT detecting the changes in regional pulmonary ventilation known to occur during perioperative ventilation therapy. EIT confirmed the differences in the distribution of regional ventilation associated with spontaneous breathing and mechanical ventilation together with PEEP or alveolar recruitment during the perioperative period. Accentuated impedance change of dependent lung regions was examined during spontaneous breathing, while there was a shift of ventilation to the non-dependent lung regions after the induction of anesthesia. The effect of PEEP as part of the perioperative ventilation therapy or alveolar recruitment after tracheal suctioning during mechanical ventilation at the ICU can be detected at bedside. In conclusion, the effect of perioperative ventilation therapy can be evaluated by dynamic real-time EIT monitoring. The EIT has the potential to be used as a simple bedside technique for the measurement of pulmonary aeration and ventilation distribution.