H. Odenstedt

Positive end-expiratory pressure optimization using electric impedance tomography in morbidly obese patients during laparoscopic gastric bypass surgery.

Background:  Morbidly obese patients have an increased risk for peri‐operative lung complications and develop a decrease in functional residual capacity (FRC). Electric impedance tomography (EIT) can be used for continuous, fast‐response measurement of lung volume changes. This method was used to optimize positive end‐expiratory pressure (PEEP) to maintain FRC.

Clinical evaluation of a partial CO2 rebreathing technique for cardiac output monitoring in critically ill patients

Background: Monitoring central hemodynamics is essential in critically ill patients and less invasive techniques are needed. In this study, the clinical and technical performance of a new non‐invasive cardiac output monitor (NICO) based on partial CO2 rebreathing technique and a modified Fick equation were evaluated. The various sources of possible errors in measurement of cardiac output (CO), carbon dioxide production (V˙CO2) and pulmonary shunt were also assessed.

Descending aortic blood flow and cardiac output : A clinical and experimental study of continuous oesophageal echo-Doppler flowmetry

Background: Several studies have demonstrated that perioperative optimisation of oxygen delivery and haemodynamics can reduce mortality and morbidity for high‐risk surgical patients. To optimise cardiac output, reliable, continuous and “less invasive” methods for measuring cardiac output are urgently needed.

A new non‐radiological method to assess potential lung recruitability: a pilot study in ALI patients

Introduction: Potentially recruitable lung has been assessed previously in patients with acute lung injury (ALI) by computed tomography. A large variability in lung recruitability was observed between patients. In this study, we assess whether a new non‐radiological bedside technique could determine potentially recruitable lung volume (PRLV) in ALI patients.

Dynamic respiratory mechanics in acute lung injury/acute respiratory distress syndrome: research or clinical tool?

Purpose of reviewClassic static measurements of lung mechanics have been used mainly for research purposes, but have not gained widespread clinical acceptance. Instead, dynamic measurements have been used, but interpretation of results has been hampered by lack of clear definitions. The review provides an overview of possible definitions and a description of methods for evaluating lung mechanics in acute lung injury/acute respiratory distress syndrome patients. Recent findingsCompliance measured using static techniques is significantly higher compared to measurements during ongoing ventilation. This indicates that lung mechanic properties depend on flow velocity during inflation and the time allowed for equilibration of viscoelastic forces. Thus, methods for evaluating lung mechanics should be clearly defined in terms of whether they are classically static, i.e. excluding resistance to flow and equilibration of viscoelastic forces, or truly dynamic, i.e. including flow resistance and unequilibrated viscoelastic forces. New techniques have emerged which make it possible to monitor lung mechanics during ongoing, therapeutic ventilation, ‘functional lung mechanics’, where the impact of flow resistance on tube and airway resistance has been eliminated, providing alveolar pressure/volume curves. SummaryFunctional lung mechanics obtained during ongoing ventilator treatment have the potential to provide information for optimizing ventilator management in critically ill patients.

Bronchoscopic suctioning may cause lung collapse: a lung model and clinical evaluation

Objective: To assess lung volume changes during and after bronchoscopic suctioning during volume or pressure‐controlled ventilation (VCV or PCV).

Prolonged moderate pressure recruitment manoeuvre results in lower optimal positive end-expiratory pressure and plateau pressure

Background: In acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), recruitment manoeuvres (RMs) are used frequently. In pigs with induced ALI, superior effects have been found using a slow moderate‐pressure recruitment manoeuvre (SLRM) compared with a vital capacity recruitment manoeuvre (VICM). We hypothesized that the positive recruitment effects of SLRM could also be achieved in ALI/ARDS patients. Our primary research question was whether the same compliance could be obtained using lower RM pressure and subsequent positive end‐expiratory pressure (PEEP). Secondly, optimal PEEP levels following the RMs were compared, and the use of volume‐dependent compliance (VDC) to identify successful lung recruitment and optimal PEEP was evaluated.

Monitoring functional residual capacity (FRC) by quantifying oxygen/carbon dioxide fluxes during a short apnea

Background: Clinically applicable methods for measuring FRC are currently lacking. This study presents a new method for FRC monitoring based on quantification of metabolic gas fluxes of O2 and CO2 during a short apnea.

Fast and Slow Compliance: Time, in Addition to Pressure and Volume, is a Key Factor for Lung Mechanics

Static lung mechanics are considered state of the art in spite of the fact that they only provide a narrow view and do not represent the mechanical behavior of the lung during on-going tidal ventilation. Static measurements are usually cumbersome to perform and are uncommon in clinical practice. There is now ample proof of the importance of choosing a protective ventilatory strategy, which has been defined as ventilating with pressures between the lower and upper inflection point (LIP, UIP) [1, 2]. Determination of these two inflection points demands static or at least quasi static measurements. The definition of true static conditions is that a sufficiently long end-inspiratory and end-expiratory pause is used to not only stop gas flow in the airways, but also equilibrate visco-elastic forces of the lung tissue. It has been shown that this equilibration time is short and the tracheal pressure decreased as little as ∼ 2 cmH2O during the five seconds after instigation of an end-inspiratory pause [3]. This pressure fall is small compared to the pressure fall that occurs within milliseconds immediately after closing the inspiratory valve of the ventilator. The initial pressure drop is a result of obtaining no-flow conditions in the patient’s airways and the time is correlated to the endotracheal tube and patient airway resistance (R in cmH2O/L/s), the breathing circuit compliance (C in l/cmH2O) and the flow immediately before closing the valve: t = time constant = R × C In a typical case, the breathing circuit has a compliance of 0.5 × 10−3 l/cmH2O and a tube resistance of 6 cmH2O/l/s which gives a time constant of 3 ms. In this case the flow will decrease by 95% in three time constants, i.e., ∼ 10 ms.