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Background It has been suggested that blood loss during liver resection may be reduced if central venous pressure (CVP) is kept at a low level. This can be achieved by changing patient position but it is not known how position changes affect portal (PVP) and hepatic (HVP) venous pressures. The aim of the study was to assess if changes in body position result in clinically significant changes in these pressures. Methods We studied 10 patients undergoing liver resection. Mean arterial pressure (MAP) and CVP were measured using fluid-filled catheters, PVP and HVP with tip manometers. Measurements were performed in the horizontal, head up and head down tilt position with two positive end expiratory pressure (PEEP) levels. Results A 10° head down tilt at PEEP 5 cm H2O significantly increased CVP (11 ± 3 to 15 ± 3 mmHg) and MAP (72 ± 8 to 76 ± 8 mmHg) while head up tilt at PEEP 5 cm H2O decreased CVP (11 ± 3 to 6 ± 4 mmHg) and MAP (72 ± 8 to 63 ± 7 mmHg) with minimal changes in transhepatic venous pressures. Increasing PEEP from 5 to 10 resulted in small increases, around 1 mmHg in CVP, PVP and HVP. There was no significant correlation between changes in CVP vs. PVP and HVP during head up tilt and only a weak correlation between CVP and HVP by head down tilt. Conclusions Changes of body position resulted in marked changes in CVP but not in HVPs. Head down or head up tilt to reduce venous pressures in the liver may therefore not be effective measures to reduce blood loss during liver surgery.

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. Patients and methods: We performed a prospective randomised cross-over study where 16 ventilated patients with early ALI/ARDS each were subjected to the two RMs, followed by decremental PEEP titration. Volume-dependent initial, middle and final compliance (Cini, Cmid and Cfin) were determined. Electric impedance tomography and end-expiratory lung volume measurements were used to follow lung volume changes. Results: The maximum response in compliance, PaO2/FIO2, venous admixture and Cini/Cfin after recruitment, during decremental PEEP, was at significantly lower PEEP and plateau pressure after SLRM than VICM. Fewer patients responded in gas exchange after the SLRM, which was not the case for lung mechanics. The response in Cini was more pronounced than in conventional compliance. Conclusions: The same compliance increase is achieved with SLRM as with VICM, and lower PEEP can be used, with correspondingly lower plateau pressures. VDC seems promising to identify successful recruitment and optimal PEEP.

Background: Continuous positive airway pressure (CPAP) has been shown to improve oxygenation and a number of different CPAP systems are available. The aim of this study was to assess lung volume and ventilation distribution using three different CPAP techniques. Methods: A high-flow CPAP system (HF-CPAP), an ejector-driven system (E-CPAP) and CPAP using a Servo 300 ventilator (V-CPAP) were randomly applied at 0, 5 and 10 cmH2O in 14 volunteers. End-expiratory lung volume (EELV) was measured by N2 dilution at baseline; changes in EELV and tidal volume distribution were assessed by electric impedance tomography. Results: Higher end-expiratory and mean airway pressures were found using the E-CPAP vs. the HF-CPAP and the V-CPAP system (P

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. Methods: Sixteen mechanically ventilated patients with early ALI/ARDS were subjected to a recruitment manoeuvre and decremental PEEP titration. Electric impedance tomography, together with measurements of end-expiratory lung volume (EELV) and tracheal pressure, were used to determine PRLV. The method defines fully recruited open lung volume (OLV) as the volume reached at the end of two consecutive vital capacity manoeuvres to 40 cmH2O. It also uses extrapolation of the baseline alveolar pressure/volume curve up to 40 cmH2O, the volume reached being the non-recruited lung volume. The difference between the fully recruited and the non-recruited volume was defined as PRLV. Results: We observed a considerable heterogeneity among the patients in lung recruitability, PRLV range 11–47%. In a post hoc analysis, dividing the patients into two groups, a high and a low PRLV group, we found at baseline before the recruitment manoeuvre that the high PRLV group had lower compliance and a lower fraction of EELV/OLV. Conclusions: Using non-invasive radiation-free bedside methods, it may be possible to measure PRLV in ALI/ARDS patients. It is possible that this technique could be used to determine the need for recruitment manoeuvres and to select PEEP level on the basis of lung recruitability.

Objective: To assess lung volume changes during and after bronchoscopic suctioning during volume or pressure-controlled ventilation (VCV or PCV). Design: Bench test and patient study. Participants: Ventilator-treated acute lung injury (ALI) patients. Setting: University research laboratory and general adult intensive care unit of a university hospital. Interventions: Bronchoscopic suctioning with a 12 or 16 Fr bronchoscope during VCV or PCV. Measurements and results: Suction flow at vacuum levels of −20 to −80 kPa was measured with a Timeter™ instrument. In a water-filled lung model, airway pressure, functional residual capacity (FRC) and tidal volume were measured during bronchoscopic suctioning. In 13 ICU patients, a 16 Fr bronchoscope was inserted into the left or the right main bronchus during VCV or PCV and suctioning was performed. Ventilation was monitored with electric impedance tomography (EIT) and FRC with a modified N2 washout/in technique. Airway pressure was measured via a pressure line in the endotracheal tube. Suction flow through the 16 Fr bronchoscope was 5 l/min at a vacuum level of −20 kPa and 17 l/min at −80 kPa. Derecruitment was pronounced during suctioning and FRC decreased with −479±472 ml, P

To evaluate the efficacy of different lung recruitment maneuvers using electric impedance tomography.Experimental study in animal model of acute lung injury in an animal research laboratory.Fourteen pigs with saline lavage induced lung injury.Lung volume, regional ventilation distribution, gas exchange, and hemodynamics were monitored during three different recruitment procedures: (a) vital capacity maneuver to an inspiratory pressure of 40 cmH2O (ViCM), (b) pressure-controlled recruitment maneuver with peak pressure 40 and PEEP 20 cmH2O, both maneuvers repeated three times for 30 s (PCRM), and (c) a slow recruitment with PEEP elevation to 15 cmH2O with end inspiratory pauses for 7 s twice per minute over 15 min (SLRM).Improvement in lung volume, compliance, and gas exchange were similar in all three procedures 15 min after recruitment. Ventilation in dorsal regions of the lungs increased by 60% as a result of increased regional compliance. During PCRM compliance decreased by 50% in the ventral region. Cardiac output decreased by 63+/-4% during ViCM, 44+/-2% during PCRM, and 21+/-3% during SLRM.In a lavage model of acute lung injury alveolar recruitment can be achieved with a slow lower pressure recruitment maneuver with less circulatory depression and negative lung mechanic side effects than with higher pressure recruitment maneuvers. With electric impedance tomography it was possible to monitor lung volume changes continuously.

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. Methods: Base line exchange of oxygen and carbon dioxide was measured with indirect calorimetry. End-tidal (∼alveolar) O2 and CO2 concentrations were measured before and after a short apnea, 8–12 s, and FRC was calculated according to standard washin/washout formulas taking into account the increased solubility of CO2 in blood when the tension is increased during the apnea. The method was tested in a lung model with CO2 excretion and O2 consumption achieved by combustion of hydrogen and implemented in six ventilator-treated patients with acute respiratory failure (ARF). Results: In the lung model the method showed excellent correlation (r = 0.98) with minimal bias (34 ml) and a good precision, limits of agreement being 160 and -230 ml, respectively, compared to the reference method. In six ARF patients changes in FRC induced by increase or decrease in PEEP and measured with the O2/CO2 flux FRC method corresponded well with changes in reference values of FRC (r = 0.76–0.94). Conclusions: A new method has been proposed in which FRC could be monitored from measurements of physiological fluxes of gases during a short apnea with the use of standard ICU equipment and some calculations. We anticipate that with further development, this technique could provide a new tool for monitoring respiratory changes and ventilator management in the ICU.

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. Methods Eight landrace pigs were studied during experimental repeated cardiac tamponade and 14 patients during liver transplantation. Aortic blood flow was measured by using transoesophageal echo-Doppler technique. A total of 91 paired measurements of aortic blood flow and cardiac output with different techniques were performed in the pigs and 124 paired measurements in the patients. Results Transoesophageal echo-Doppler did provide continuous real-time monitoring of the rapid and dramatic haemodynamic changes occurring during cardiac tamponade and during liver transplantation, while only intermittent information was obtained from the bolus thermodilution technique. Changes in haemodynamics were more difficult to detect with the "continual" cardiac output thermodilution technique. Changes in aortic blood flow closely followed changes in cardiac output determined by the bolus thermodilution technique both in pigs (r= 0.89) and in patients (r=0.80). In patients, aortic blood flow constituted about 70% of cardiac output determined by the bolus thermodilution technique. Conclusions A combined echo-Doppler technique can be valuable for continuous monitoring of haemodynamic changes in the perioperative setting, and changes in aortic blood flow agree well with corresponding changes in cardiac output intermittently obtained by thermodilution cardiac output measurements. With the combined echo-Doppler technique a proper position of the Doppler beam is greatly facilitated by the M-mode echo visualisation of the aortic wall and aortic cross-sectional area is continuously measured.

Purpose of review Classic 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 findings Compliance 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. Summary Functional lung mechanics obtained during ongoing ventilator treatment have the potential to provide information for optimizing ventilator management in critically ill patients.

The static pressure volume (P/V) curve has been regarded as the gold standard tool for assessment of the mechanical properties of the lung. On this curve, a lower inflection point (LIP) can be detected in some patients and in most patients an upper inflection point (UIP) can be seen. The most common interpretation of the LIP and the UIP is that LIP represents the point where alveoli collapse at the end of expiration and reopen at the start of inspiration and that the UIP represents the pressure above which alveoli become overdistended. It has been proposed that in order to avoid cyclic closing and opening and overdistension of alveoli, ventilation should be performed with pressures between the LIP and UIP, where the compliance of the lungs is highest.

OBJECTIVE: To assess lung volume and compliance changes during open- and closed-system suctioning using electric impedance tomography (EIT) during volume- or pressure-controlled ventilation.DESIGN AND SETTING: Experimental study in a university research laboratory.SUBJECTS: Nine bronchoalveolar saline-lavaged pigs.INTERVENTIONS: Open and closed suctioning using a 14-F catheter in volume- or pressure-controlled ventilation at tidal volume 10 ml/kg, respiratory rate 20 breaths/min, and positive end-expiratory pressure 10 cmH2O.MEASUREMENTS AND RESULTS: Lung volume was monitored by EIT and a modified N2 washout/-in technique. Airway pressure was measured via a pressure line in the endotracheal tube. In four ventral-to-dorsal regions of interest regional ventilation and compliance were calculated at baseline and 30 s and 1, 2, and 10 min after suctioning. Blood gases were followed. At disconnection functional residual capacity (FRC) decreased by 58+/-24% of baseline and by a further 22+/-10% during open suctioning. Arterial oxygen tension decreased to 59+/-14% of baseline value 1 min after open suctioning. Regional compliance deteriorated most in the dorsal parts of the lung. Restitution of lung volume and compliance was significantly slower during pressure-controlled than volume-controlled ventilation.CONCLUSIONS: EIT can be used to monitor rapid lung volume changes. The two dorsal regions of the lavaged lungs are most affected by disconnection and suctioning with marked decreases in compliance. Volume-controlled ventilation can be used to rapidly restitute lung aeration and oxygenation after lung collapse induced by open suctioning.

To assess acute cardiorespiratory effects of recruitment manoeuvres in experimental acute lung injury.Experimental study in animal models of acute lung injury.Experimental laboratory at a University Medical Centre.Ten pigs with bronchoalveolar lavage and eight pigs with endotoxin-induced ALI.Two kinds of recruitment manoeuvres during 1 min; a) vital capacity manoeuvres (ViCM) consisting in a sustained inflation at 30 cmH(2)O and 40 cmH(2)O; b) manoeuvres obtained during ongoing pressure-controlled ventilation (PCRM) with peak airway pressure 30 cmH(2)O, positive end-expiratory pressure (PEEP) 15 and peak airway pressure 40, PEEP 20. Recruitment manoeuvres were repeated after volume expansion (dextran 8 ml/kg). Oxygenation, mean arterial, and pulmonary artery pressures, aortic, mesenteric, and renal blood flow were monitored.Lower pressure recruitment manoeuvres (ViCM30 and PCRM30/15) did not significantly improve oxygenation. With ViCM and PCRM at peak airway pressure 40 cmH(2)O, PaO(2) increased to similar levels in both lavage and endotoxin groups. Aortic blood flow was reduced from baseline during PCRM40/20 and ViCM40 by 57+/-3% and 61+/-6% in the lavage group and by 57+/-8% and 82+/-7% (P0.05 vs PCRM40/20) in endotoxin group. The decrease in blood pressure was less pronounced. Prior volume expansion attenuated circulatory impairment. After cessation of recruitment hemodynamic parameters were restored within 3 min.Effective recruitment resulted in systemic hypotension, pulmonary hypertension, and decrease in aortic blood flow especially in endotoxinemic animals. Circulatory depression may be attenuated using recruitment manoeuvres during ongoing pressure-controlled ventilation and by prior volume expansion.