Stefan Maisch

Compliance and dead space fraction indicate an optimal level of positive end-expiratory pressure after recruitment in anesthetized patients.

BACKGROUND:“Optimal” positive end-expiratory pressure (PEEP) can be defined as the PEEP that prevents recollapse after a recruitment maneuver, avoids over-distension, and, consequently, leads to optimal lung mechanics at minimal dead space ventilation. In this study, we analyzed the effects of PEEP and recruitment on functional residual capacity (FRC), compliance, arterial oxygen partial pressure (Pao2) and dead space fraction, and we determined the most suitable variables indicating optimal PEEP. METHODS:We studied 20 anesthetized patients with healthy lungs undergoing faciomaxillary surgery. After a stepwise increase of PEEP/inspiratory pressures (0/10, 5/15, 10/20, 15/25 cm H2O, each level lasting for 20 min) using a pressure-controlled ventilation mode, a recruitment maneuver (at 20/45 cm H2O for a maximum of 20 min) was performed, followed by a stepwise pressure reduction (15/25, 10/20, 5/15, 0/10 cm H2O, with 20 min at each level). At each pressure level, FRC, compliance, Pao2, and dead space fraction were measured. RESULTS:When comparing the values before and after recruitment at identical PEEP levels, all variables showed significant changes at 10/20 cm H2O; compliance was also significantly higher at the pressure step 15/25 cm H2O. In addition, FRC values showed significant differences at 5/15 cm H2O and 15/25 cm H2O. CONCLUSIONS:All variables showed the positive effects of PEEP in conjunction with a recruitment maneuver. Optimal PEEP was 10 cm H2O because at this pressure level the highest compliance value in conjunction with the lowest dead space fraction indicated a maximum amount of effectively expanded alveoli. FRC and Pao2 were insensitive to alveolar over-distension.

The effect of a checklist on the quality of post-anaesthesia patient handover: a randomized controlled trial

OBJECTIVE Patient handover is an important element of continuity, quality and safety in patient care. Handover without standardized protocols is prone to information loss and might be a possible danger to patient safety. Checklists are established methods that help to structure complex processes in other high-risk fields such as aviation. In the past few years, their implementation has attracted research interest in medicine. We hypothesize that a checklist for handover between anaesthesiologist and post-anaesthesia care unit nurse will increase the amount of information transfer during patient handover after anaesthesia. DESIGN AND SETTING A total of 120 post-anaesthesia patient handovers were recorded on video and analyzed. Forty handovers before the implementation of the checklist and 80 after the implementation of the checklist, randomized into two groups: with and without the use of the checklist. MAIN OUTCOME MEASURES An overall number of items handed over, handover of specific items and duration of the handover were analyzed. RESULTS With the use of the written checklist, the overall items handed over increased significantly from a median of 32.4-48.7%. The duration of handover increased from a median of 86-121 s. Instructions about items that should be included in handovers, but without the use of a written checklist, was not associated with an increase in the number of items handed over or duration of the interview. CONCLUSIONS This study suggests that the use of a checklist for post-anaesthesia handover might improve the quality of patient handover by increasing the information handed over.

The effects of lung recruitment on the Phase III slope of volumetric capnography in morbidly obese patients.

BACKGROUND: In this study, we analyzed the effect of the alveolar recruitment strategy (ARS) and positive end-expiratory pressure (PEEP) titration on Phase III slope (SIII) of volumetric capnography (VC) in morbidly obese patients. METHODS: Eleven anesthetized morbidly obese patients were studied. Lungs were ventilated with tidal volumes of 10 mL · kg−1, respiratory rates of 12–14 bpm, inspiration:expiration ratio of 1:2, and Fio2 of 0.4. ARS was performed by increasing PEEP in steps of five from 0 end-expiratory pressure to 15 cm H2O. During lung recruitment, plateau pressure was limited to 50 cm H2O, whereas tidal volume was increased to the ventilator’s maximum value of 1400 mL, and PEEP was increased to 20 cm H2O for 2 min. Thereafter, PEEP was reduced in steps of 5 cm H2O, from 15 to 0. VC, arterial blood gases, and lung mechanics data were determined for each PEEP step. RESULTS: SIII decreased from 0.014 ± 0.006 to 0.005 ± 0.005 mm Hg/mL when 0 end-expiratory pressure was compared against 15 cm H2O of PEEP after ARS (15ARS, P < 0.05). This decrement in SIII was accompanied by increases in Pao2 (27%, P < 0.002) and compliance (32%, P < 0.001), whereas Paco2 decreased by 8% (P < 0.038) when comparing values before and after ARS. A good prediction of the lung recruitment effect by SIII was derived from the receiver operating characteristic curve analysis (area under the curve of 0.81, sensitivity of 0.75, and specificity of 0.74; P < 0.001). CONCLUSION: The SIII in VC was useful to detect the optimal level of PEEP after lung recruitment in anesthetized morbidly obese patients.

Monitoring of Functional Residual Capacity by an Oxygen Washin/Washout; Technical Description and Evaluation

Objective. It was the goal of this study to develop and test an automated method for measuring functional residual capacity (FRC) by an oxygen washin/washout in intensive care settings. Such a method is required to work with conventional ventilator breathing systems and to use only medical grade sensors. Methods. The oxygen setting on a standard intensive care ventilator is changed by at least 10percnt;. Ventilatory pressure and flow are measured by the built-in sensors of the intensive care ventilator. Oxygen concentration is measured by a diverting medical oxygen analyzer. In order to overcome the known problem that synchrony between flow and concentration measurement is corrupted by the change of gas viscosity and by the cyclic change of airway pressure, a physical/mathematical model of the pneumatic circuit of the analyzer was developed. With this model, the change of sample flow is calculated continuously. Thus, synchrony between flow and gas concentration measurement is restored. This allows the determination of volumetric gas fluxes as needed for the FRC measurement. The setup was tested in the laboratory with a lung simulator. Simulated lung compliance, breathing frequency and tidal volume were varied. Results. The mean difference between measured and simulated FRC (range 1.7 to 5 L) was less than 1percnt; at tidal volumes greater than 400 mL. This difference ranged from −5percnt; to 8percnt;, depending on simulated lung compliance and ventilator setting. The variability of consecutive measurements was about 2.5percnt;. Conclusions. A method has been developed for reliable measurement of the FRC with an oxygen washin/washout technique. This method is sufficiently easy to use to suit for application in intensive care units. It does not require any action by the operator except a manual change of inspired oxygen concentration. Accuracy and sensitivity of the method have been proven sufficient to meet clinical and scientific requirements. Future clinical studies will reveal the applicability of the chosen procedure under clinical conditions.

Heart-lung interactions measured by electrical impedance tomography

Objective:The clinical value of stroke volume variations to assess intravascular fluid status in critically ill patients is well known. Electrical impedance tomography is a noninvasive monitoring technology that has been primarily used to assess ventilation. We investigated the potential of electrical impedance tomography to measure left ventricular stroke volume variation as an expression of heart-lung interactions. The objective of this study was thus to determine in a set of different hemodynamic conditions whether stroke volume variation measured by electrical impedance tomography correlates with those derived from an aortic ultrasonic flow probe and arterial pulse contour analysis. Design:Prospective animal study. Setting:University animal research laboratory. Subjects:Domestic pigs, 29–50 kg. Interventions:A wide range of hemodynamic conditions were induced by mechanical ventilation at different levels of positive end-expiratory pressure (0–15 cm H2O) and with tidal volumes of 8 and 16 mL/kg of body weight and by hypovolemia due to blood withdrawal with subsequent retransfusion followed by infusions of hydroxyethyl starch. Measurements and Main Results:In eight pigs, aortic stroke volume variations measured by electrical impedance tomography were measured and compared to those derived from an aortic ultrasonic flow probe and from arterial pulse contour analysis. Data for four animals were used to develop and train a novel frequency-domain electrical impedance tomography analysis algorithm, while data for the remaining four were used to test the performance of the novel methodology. Correlation of stroke volume variation measured by electrical impedance tomography and that derived from an aortic ultrasonic flow probe was significant (r2 = 0.69; p < .001), as was the correlation between stroke volume variation measured by electrical impedance tomography and that derived from arterial pulse contour analysis (r2 = 0.73; p < .001). Correlation of stroke volume variation derived from an aortic ultrasonic flow probe and that derived from arterial pulse contour analysis was significant too (r2 = 0.82; p < .001). Bland-Altman analysis comparing stroke volume variation measured by electrical impedance tomography and that derived from an aortic ultrasonic flow probe revealed an overall bias of 1.87% and limits of agreement of ±7.02%; when comparing stroke volume variation measured by electrical impedance tomography and that derived from arterial pulse contour analysis, the overall bias was 0.49% and the limits of agreement were ±5.85%. Conclusion:Stroke volume variation measured by electrical impedance tomography correlated with both the gold standard of direct aortic blood flow measurements of stroke volume variation and pulse contour analysis, marking an important step toward a completely noninvasive monitoring of heart-lung interactions.

Comparison of the over-the-head, lateral and alternating positions during cardiopulmonary resuscitation performed by a single rescuer with a bag--valve--mask device.

Background The 2005 guidelines for cardiopulmonary resuscitation (CPR) do not include a statement on performance of basic life support by a single healthcare professional using a bag–valve–mask device. Three positions are possible: chest compressions and ventilations from over the head of the casualty (over-the-head CPR), from the side of the casualty (lateral CPR), and chest compressions from the side and ventilations from over the head of the casualty (alternating CPR). The aim of this study was to compare CPR quality of these three positions. Methods 102 healthcare professionals were randomised to a crossover design and performed a 2-min CPR test on a manikin for each position. Results The hands-off time over a 2-min interval was not significantly different between over-the-head (median 31 s) and lateral (31 s) CPR, but these compared favourably with alternating CPR (36 s). Over-the-head CPR resulted in significantly more chest compressions (155) compared with lateral (152) and alternating CPR (149); the number of correct chest compressions did not differ significantly (119 vs 122 vs 109). Alternating CPR resulted in significantly less inflations (eight) compared with over-the-head (ten) and lateral CPR (ten). Lateral CPR led to significantly less correct inflations (three) compared with over-the-head (five) and alternating CPR (four). Conclusions In the case of a single healthcare professional using a bag–valve–mask device, the quality of over-the-head CPR is at least equivalent to lateral, and superior to alternating CPR. Because of the potential difficulties in bag–valve–mask ventilation in the lateral position, the authors recommend over-the-head CPR.

Single-channel electroencephalography of epileptic seizures in the out-of-hospital setting: an observational study

Objectives To evaluate whether single-channel electroencephalography (EEG) recording can be conducted in the out-of-hospital setting and whether it can be used to record electrographic signs of convulsive epileptic seizures. Methods This prospective observational feasibility study included patients who presented with a recent or ongoing epileptic seizure during out-of-hospital emergency treatment. Bifrontal single-channel EEG recordings were conducted by ambulance physicians throughout the initial treatment. The data recorded were analysed for the quality of recording and the occurrence of ictal EEG patterns. Results There were 45 adult patients who had a recent or an ongoing epileptic seizure in the study group and 15 patients with no neurological disorders in the control group. The median percentage of time during which no artefacts were detected by the device was 88.0% in the study group and 96.0% in the control group. EEG recordings for 3 out of 45 (6.6%) patients were of poor quality and not evaluable. Spike/wave or polyspike patterns were found in 98% and 100% of patients in the study and control groups, respectively, whereas the occurrence of periodic epileptiform discharges and delta waves with spikes showed a sensitivity and specificity of 100% (10/10) for the presence of an ongoing epileptic seizure. Conclusions Single-channel EEG can be performed outside the hospital and yields useful recordings in most patients with acceptable rates of artefact. The diagnosis of generalised convulsive epileptic seizures by offline analysis of out-of-hospital EEG showed a high sensitivity and specificity when compared with the clinical diagnosis.

Reliability of transcardiopulmonary thermodilution cardiac output measurement in experimental aortic valve insufficiency

Background Monitoring cardiac output (CO) is important to optimize hemodynamic function in critically ill patients. The prevalence of aortic valve insufficiency (AI) is rising in the aging population. However, reliability of CO monitoring techniques in AI is unknown. The aim of this study was to investigate the impact of AI on accuracy, precision, and trending ability of transcardiopulmonary thermodilution-derived COTCPTD in comparison with pulmonary artery catheter thermodilution COPAC. Methods Sixteen anesthetized domestic pigs were subjected to serial simultaneous measurements of COPAC and COTCPTD. In a novel experimental model, AI was induced by retraction of an expanded Dormia basket in the aortic valve annulus. The Dormia basket was delivered via a Judkins catheter guided by substernal epicardial echocardiography. High (HPC), moderate (MPC) and low cardiac preload conditions (LPC) were induced by fluid unloading (20 ml kg-1 blood withdrawal) and loading (subsequent retransfusion of the shed blood and additional infusion of 20 ml kg-1 hydroxyethyl starch). Within each preload condition CO was measured before and after the onset of AI. For statistical analysis, we used a mixed model analysis of variance, Bland-Altman analysis, the percentage error and concordance analysis. Results Experimental AI had a mean regurgitant volume of 33.6 ± 12.0 ml and regurgitant fraction of 42.9 ± 12.6%. The percentage error between COTCPTD and COPAC during competent valve function and after induction of substantial AI was: HPC 17.7% vs. 20.0%, MPC 20.5% vs. 26.1%, LPC 26.5% vs. 28.1% (pooled data: 22.5% vs. 24.1%). The ability to trend CO-changes induced by fluid loading and unloading did not differ between baseline and AI (concordance rate 95.8% during both conditions). Conclusion Despite substantial AI, transcardiopulmonary thermodilution reliably measured CO under various cardiac preload conditions with a good ability to trend CO changes in a porcine model. COTCPTD and COPAC were interchangeable in substantial AI.