Stroke output variations calculated by esophageal Doppler is a reliable predictor of fluid response

Objective Esophageal Doppler allows continuous monitoring of stroke volume index (SVI) and corrected flow time (FTc). We hypothesized that variations in stroke output index SOI (SVI/FTc) during volume expansion can predict the hemodynamic response to subsequent fluid loading better than the static values.Design and setting Prospective study in the intensive care unit of a university hospital.Patients Fifty-one patients with circulatory failure were monitored by esophageal Doppler.Interventions Patients who responded to a first fluid challenge received a second one. Patients who responded to both were classified as responders-responders, and those who did not respond to the second as responders-nonresponders. In these two groups we compared SVI, FTc, and SOI during each fluid challenge and also static values at the end of each fluid challenge.Measurements and results After the first fluid challenge SOI and SVI were significantly higher in patients who responded to subsequent volume expansion than in patients who no longer responded. ROC curves showed that SOI was a better predictor of fluid responsiveness than SVI. During volume expansion a SOI value of 11% discriminated between responders and nonresponders to subsequent volume expansion with a sensitivity of 91% and a specificity of 97%. There was no significant difference between the two groups for FTc value at the end of first fluid challenge.Conclusions Analysis of SOI during fluid challenge predicts response to subsequent fluid challenge and FTc is not a reliable indicator of cardiac preload.     

Positive end-expiratory pressure: Implications for tidal volume changes in anesthesia machine ventilation

In clinical practice, the addition of positive end-expiratory pressure (PEEP) into a standard anesthesia circle circuit decreases the delivered tidal volume (DTV) to a patient. We studied the magnitude of the DTV/PEEP relationship in two commonly used anesthesia systems. In addition, the magnitude of the DTV/PEEP relationship varies with both pulmonary compliance and volume of gas contained in the patient's breathing system between the ventilator and PEEP valve site, and this was also evaluated. Routine monitoring of expired tidal volume should be used whenever PEEP is added to an anesthesia circuit.     

The respiratory variation in inferior vena cava diameter as a guide to fluid therapy

Objective To investigate whether the respiratory variation in inferior vena cava diameter (D_IVC) could be related to fluid responsiveness in mechanically ventilated patients.Design Prospective clinical study.Setting Medical ICU of a non-university hospital.Patients Mechanically ventilated patients with septic shock (n=39).Interventions Volume loading with 8 mL/kg of 6% hydroxyethylstarch over 20 min.Measurements and results Cardiac output and D_IVC were assessed by echography before and immediately after the standardized volume load. Volume loading induced an increase in cardiac output from 5.7±2.0 to 6.4±1.9 L/min (P<0.001) and a decrease in D_IVC from 13.8±13.6 vs 5.2±5.8% (P<0.001). Sixteen patients responded to volume loading by an increase in cardiac output 15% (responders). Before volume loading, the D_IVC was greater in responders than in non-responders (25±15 vs 6±4%, P<0.001), closely correlated with the increase in cardiac output (r=0.82, P<0.001), and a 12% D_IVC cut-off value allowed identification of responders with positive and negative predictive values of 93% and 92%, respectively.Conclusion Analysis of D_IVC is a simple and non-invasive method to detect fluid responsiveness in mechanically ventilated patients with septic shock.     

Monitoring of respiratory variations of aortic blood flow velocity using esophageal Doppler

Objective The purpose of this study was to determine whether monitoring of respiratory changes in aortic blood flow velocity, recorded by esophageal Doppler, could be used to detect changes in volume depletion.Design Animal study.Animals and interventions After general anesthesia and tracheotomy, ten New Zealand female rabbits, weighing 4–4.5 kg were studied under mechanical ventilation at a fixed tidal volume; during this time 5-ml blood samples were withdrawn (in increments up to a total of 30 ml) and then retransfused.Measurements and results At each step, systolic (SBP), diastolic (DBP), pulse (PP) pressures and maximum descending aortic blood flow (V) were recorded. Respiratory changes of V (V), SBP (SBP) and PP (PP) were calculated as the difference of maximal and minimal values divided by their respective means and expressed as a percentage. The amount of blood withdrawn correlated negatively with SBP, DBP, PP and V and positively with SBP, PP and V. Among these parameters, V correlated best with the amount of blood withdrawn (r=0.89, p<0.001) and it was the most accurate index of volume depletion.Conclusion Monitoring of the respiratory variation in V, calculated by esophageal Doppler technique, seems to be a highly accurate index of blood volume depletion and restitution.Supported by Philips Medical System and Arrow.     

Volume/pressure curve of total respiratory system in paralysed patients: artefacts and correction factors

The volume/pressure (V/P) curve of the total respiratory system in paralysed patients is drawn assuming that volume changes of the respiratory system (V resp) equals volume displacement of the measuring apparatus (V syr), usually a supersyringe. However, in 93 VP curves we found that O₂ removed from the lung-syringe system during the procedure (proportional to the time) largely exceedes the CO₂ added to the lung-syringe system (V gas). This results in a net loss of volume from the system (V resp相似文献   

Intrathoracic blood volume accurately reflects circulatory volume status in critically ill patients with mechanical ventilation

Positive pressure ventilation in patients with acute respiratory failure (ARF) may render the interpretation of central venous pressure (CVP) or pulmonary wedge pressure (PCWP) difficult as indicators of circulating volume. The preload component of cardiac (CI) and stroke index (SI) is also influenced by the increased intrathoracic pressures of positive pressure ventilation. Moreover CI and SI do not indicate volume status exclusively but also contractility and afterload. We investigated whether intrathoracic blood volume (ITBV) more accurately reflects blood volume status and the resulting oxygen transport (DO₂). CVP, PCWP, cardiac (CI) and stroke index (SI) were measured, oxygen transport index (DO₂I) and oxygen consumption index (VO₂I) were calculated in 21 ARF-patients. Ventilatory patterns were adjusted as necessary. CI, SI and intrathoracic blood volume index (ITBVI) were derived from thermal dye dilution curves which were detected with a 5 F fiberoptic thermistor femoral artery catheter and fed into a thermaldye-computer. All data were collected in intervals of 6h. There were 224 data sets obtained. Linear regression analysis was performed between absolute values as well as between the 6 h changes (prefix ). The following correlation coefficients were determined: CVP/CI and PCWP/CI 0.01 and –0.142 (p<0.05); CVP/SI and PCWP/SI –0.108 and –0.228 (p<0.01); ITBVI/CI and ITBV/SI 0.488 (p<0.01) and 0.480 (p<0.01); ITBVI and DO₂I 0.460 (p<0.01); CVP/CI and PCWP/CI –0.069 and–0.018; CVP/SI and PCWP/SI –0.083 and –0.009; ITBVI/CI and ITBVI/SI 0.715 (p<0.01) and 0.646 (p<0.01); ITBVI and DO₂I 0.707 (p<0.01). We conclude that in mechanically ventilated patients ITBV is a suitable indicator of circulating blood volume.     

Alveolar pressure during high-frequency jet ventilation

We studied the influence of ventilatory frequency (1–5 Hz), tidal volume, lung volume and body position on the end-expiratory alveolar-to-tracheal pressure difference during high-frequency jet ventilation (HFJV) in Yorkshire piglets. The animals were anesthetized and paralysed. Alveolar pressure was estimated with the clamp off method, which was performed by a computer controlled ventilator and which had been extensively tested on its feasibility. The alveolar-to-tracheal pressure difference increased with increasing frequency and with increasing tidal volume, the common determinant appearing to be the mean expiratory flow. The effects in prone and in supine position were similar. Increasing thoracic volume decreased the alveolar-to-tracheal pressure difference indicating a dependence of this pressure difference on airway resistance. We concluded that the main factors determining the alveolar-to-tracheal pressure difference (P) during HFJV are expiratory flow (V_E) and airway resistance (R), PV_E×R.     

Transthoracic electrical impedance during extracorporeal hemodialysis in acute respiratory failure (“Shocked lung syndrome”)

The alteration (Z ₀ ) of transthoracic electrical impedance (TEI) during extracorporeal hemodialysis (EHD) was investigated in two Groups of patients with acute renal and acute respiratory failure, that differed with respect to the severity of respiratory insufficiency. Group I had moderate respiratory failure (Fi _{O 2} 0.31±0.10, Pa _{0 2} 84±14 mmHg), and Group II had severe respiratory failure (Fi _{0 2} 0.75±0.17, Pa _{O O} 77±14 mmHg). There was a significant correlation between increase in TEI (Z₀) and decrease in body weight (BW) in each individual patient, but the slope of regression lines was remarkably flattened in Group II. In Group I, TEI was 1.9±0.9 , the calculated TEI for 500 gr decrease in BW (Z_{0–500 gr}) was 0.59±0.21 , and a significant correlation existed between pooled data of Z₀ and BW. In Group II TEI increased less significantly, TEI was 0.6±0.3 (P<0.001), Z_{0–500 gr} was 0.26±0.27 (P<0.01), and there was no correlation between pooled data of Z₀ and BW. Increase of TEI in Group II could be completely attributed to increase in hematocrit. It is concluded that patients of Group I with acute renal failure and moderate respiratory failure lost intrathoracic fluid during EHD, whereas patients of Group II with severe respiratory failure did not. TEI during EHD may serve as a test for detection of fixed fluid within the pulmonary interstitium indicating a poor prognosis of the acute respiratory failure.     

Left ventricular function after acute myocardial infarction

10 patients with their first AMI were studied within the first 48 hours and again after 3 weeks. Central and peripheral haemodynamics (CI, SV, SW, TPR) were examined, including indices of contractility (dp/dlmax) and wall stiffness (P/V, relation P/V to P) of the left ventricle.In the early phase CI and SW, as well as LV dp/dt_max were depressed in accordance with symptoms of LV failure. P/V was increased. Elevation of LVEDP correlated well with ventricular gallop rhythm, but less consistently with LV functional disturbance.During convalescence CI increased uniformly, both in digitalized and non-digitalized individuals. In contrast heart rate, aortic pressure, LVEDP and dp/dt_max remained unchanged. The increase of CI, SV and SW was accompanied by a fall of TPR and P/V. LV wall stiffness was still elevatedabove normal after 3 weeks. The improvement of cardiac pumping during infarct convalescence may have been effected through a fall of TPR and LV wall stiffness. Recovery of depressed contractile performance was generally not observed, and does therefore not seem to contribute to recuperation.Herrn Prof. Dr. med. P. Schölmerich zum 60. Geburtstag.     

New aspects of pulmonary mechanics: ‘slowly” distensible compartments of the respiratory system,identified by a PEEP step maneuver

Objective The aims of the present study were 1) to evaluate a method for identification of slowly distensible compartments of the respiratory system (rs), which are characterized by long mechanical time constants (RC) and 2) to identify slowly distensible rs-compartments in mechanically ventilated patients.Design Prospective studyon a physical lung model.Setting Intensive Care Unit, University Hospital, Tübingen.Patients and participants 19 patients with severe lung injury (acute respiratory distress syndrome, ARDS) and on 10 patients with mild lung injury.Measurements and results Positive end-expiratory pressure (PEEP)-increasing and-decreasing steps of about 5 cmH₂O were applied and the breath-by-breath differences of inspiratory and expiratory volumes (V) were measured. The sequence of Vs were analyzed in terms of volume change in the fast compartment (V_fast), the slow compartment (V_slow), total change in lung volume (VL) and mechanical time constant of the slow compartment (RC_slow). Thirty-eight measurements in a lung model revealed a good correlation between the preset V_slow/VL and V_slow/VL measured: r²=0.91 The V_slow/VL measured amounted to 0.94±0.15 of V_slow/VL in the lung model. RC_slow measured was 0.92±0.43 of the RC_slow reference. Starting from a PEEP level of 11 cmH₂O PEEP-increasing and PEEP-decreasing steps were applied to the mechanically ventilated patients. Three out of ten patients with mild lung injury (30%) and 7/19 patients with ARDS (36.8%) revealed slowly distensible rscompartments in a PEEP-increasing step, whereas 15/19 ARDS patients and 1/10 patients with mild lung injury showed slowly distensible rs-compartments in a PEEP-decreasing step (78.9% vs 10%,P<0.002, chi-square test).Conclusions The gas distribution properties of the respiratory system can be easily studied by a PEEP-step maneuver. The relative contribution of the slow units to the total increase of lung volume following a PEEP step could be adequately assessed. Slowly distensible rs-compartments could be detected in patients with severe and mild lung injury, however significantly more ARDS patients revealed slow rs-compartments in PEEP-decreasing steps. The influence of slowly distensible rs-compartments on pulmonary gas exchange is unknown and has yet to be studied.The work was performed at the Klinik für Anaesthesiologie und Transfusionsmedizin der Universität Tübingen     

Transbronchial regional electroplethysmography of the lungs

Objective. The objective of this study was to describe a method of transbronchial regional electroplethysmography of the lungs.Methods. The electrical resistance of a division of a lung, such as a segment or subsegment, as well as its pulsatile oscillation, were measured using a two-part process: A catheter-transducer was wedged into a small bronchus and the electrical resistance of a blood sample obtained from the same patient was measured. The electroplethysmograph (EPG) was developed for this purpose. The theory behind our method is based on a model of the lung as a three-component structure (blood-tissue-air). We performed experiments on isolated lung lobes of animals, using simultaneous electrometric and direct determination of physiologic indices for regional lung function.Results. Equations have been proposed to calculate blood volume, V_b (±10%); air volume, V_a (±11%); pulsatile increment of the blood volume, V (±10%); and regional stroke volume, RSV (±20%) per 100 cm³ of the lung. The proposed formulas yield an accuracy that is adequate for the clinical range of variations in V_b and V_a, as well as V and RSV. Experiments on lung lobes indicate that the conductivity of lung tissue (_t) is not large. This allows one to calculate the above indices without our having obtained accurate values for conductivity.Conclusions. The method of Transbronchial regional electroplethysmography of the lungs is described and cases in which this method was used for clinical investigation are presented.Glossary Resistivity of suspension - ₁ Resistivity of conducting medium - ₂ Resistivity of conducting spheres - Electroconductivity of the lung at diastole - ₁ Electroconductivity of the lung at systole - _b Electroconductivity of blood - _t Electroconductivity of tissue - _bt Electroconductivity of conducting medium (blood+tissue) - Pulsatile electroconductivity increment in the lung - _e Electrical equivalent of regional stroke volume - V Volume of lung - V_B Blood volume of lung - V_T Tissue volume of lung - V_A Air volume of lung - V_b Regional blood volume per lung volume unit - V_a Regional air volume per lung volume unit - V Regional pulsatile blood increment in the lungs - Ratio of the conducting medium (blood+tissue) volume to the lung volume unit - Ratio of the blood volume to the volume unit of the conducting medium - R Electrical resistance - R Electrical resistance increment - RSV Regional stroke volume per the organ volume unit - F Form-factor - l Cell length - S Cell cross-section area - K Empirical correction coefficient - K₁ Coefficient of electrode installation     

Oxygenation remains unaffected by increased inspiration-to-expiration ratio but impairs hemodynamics in surfactant-depleted piglets

Objectives Prolongation of inspiratory time is used to reduce lung injury in mechanical ventilation. The aim of this study was to isolate the effects of inspiratory time on airway pressure, gas exchange, and hemodynamics, while ventilatory frequency, tidal volume, and mean airway pressure were kept constant.Design Randomized experimental trial.Setting Experimental laboratory of a University Department of Anesthesiology and Intensive Care.Animals Twelve anesthetised piglets.Interventions After lavage the reference setting was pressure-controlled ventilation with a decelerating flow; IE was 11, and PEEP was set to 75% of the inflection point pressure level. The IE ratios of 1.51, 2.31, and 41 were applied randomly. Under open lung conditions, mean airway pressure was kept constant by reduction of external PEEP.Measurement and results Gas exchange, airway pressures, hemodynamics, functional residual capacity (SF₆ tracer), and intrathoracic fluid volumes (double indicator dilution) were measured. Compared to the IE of 11, PaCO₂ was 8% lower, with IE 2.31 and 41 (p0.01) while PaO₂ remained unchanged. The decrease in inspiratory airway pressure with increased inspiratory time was due to the response of the pressure-regulated volume-controlled mode to an increased IE ratio. Stroke index and right ventricular ejection fraction were depressed at higher IE ratios (SI by 18% at 2.31, 20% at 41; RVEF by 10% at 2.31, 13% at 41;p0.05).Conclusion Under open lung conditions with an increased IE ratio, oxygenation remained unaffected while hemodynamics were impaired.This study was supported by the Swedish Medical Research Council (project 4252), the Swedish Heart-Lung Foundation, Stockholm, Sweden, and the Laerdal Foundation for Acute Medicine, Stavanger, Norway     

Increased oxygen consumption after cardiac surgery is associated with the inflammatory response to endotoxemia

Objective The aim of this study was to determine whether the increase in post-operative oxygen consumption (VO₂) in cardiac surgery patients in related to endotoxemia and subsequent cytokine release and whether VO₂ can be used as a parameter of post-perfusion syndrome.Design Prospective study.Setting Operating room and intensive care unit of a university hospital.Patients Twenty-one consecutive male patients undergoing elective coronary artery bypass surgery without major organ dysfunction and not receiving corticosteroids.Measurements and results Plasma levels of endotoxin, tumor necrosis factor (TNF) and interleukin-6 (IL-6) were measured before, during and for 18 h after cardiac surgery. Oxygen consumption, haemodynamics, the use of IV fluids and dopamine, body temperature and the time of extubation were also measured. Measurements from patients with high VO₂ (median value of the entire group) were compared with measurements from patients with low VO₂ (2 had higher levels of circulating endotoxin (P=0.004), TNF (P=0.04) and IL-6 (P=0.009) received more IV fluids and dopamine while in the ICU, and were extubated later than patients with low VO₂. Several hours after VO₂ the patient's body temperature rose, Forward stepwise regression analysis showed that circulating endotoxin and TNF explained 50% of the variability of VO₂.Conclusions This study demonstrates that patients with high post operative oxygen comsumption after elective cardiac surgery have higher circulating levels of endotoxin, TNF and IL-6 and also have more symptoms of post-perfusion syndrome. Early detection of high VO₂ might be used as a clinical signal to improve circulation in order to meet the high oxygen demand of inflammation. In addition, continuous measurement of VO₂ provides us with a clinical parameter of inflammation in interventional studies aiming at a reduction of endotoxemia or circulating cytokines.Part of this study was supported financially by Jaussen Pharmaceutica B.V. (Tilburg, The Netherlands)     

On-line computer estimation of carbon dioxide response curves

Anesthesiologists are concerned with the effect of various anesthetics on a patient's central nervous ventilatory control. The most widely accepted method of determining the effect of a drug is to compare carbon dioxide response curves ( e/PetCO₂, where e = minute ventilation [in L/min] andPetCO₂ = end-tidal carbon dioxide [in mm Hg]) measured before and after administration of the drug. Additional information concerning neuromechanical control can be obtained by also including a measure of the airway occlusion pressure (generally measured 100 ms after occlusion, i.e., P₁₀₀).To facilitate these measurements we have developed a portable, computer-controlled data acquisition system. It includes an Apple II+ computer and measures e,PetCO₂, and P₁₀₀. Each subject rebreathes exhaled carbon dioxide through a two-way breathing valve attached to a 9-liter reservoir, which is initially filled with 5% carbon dioxide and balance oxygen. Exhaled carbon dioxide concentrations are measured with an infrared medical gas analyzer on samples taken through a catheter connected at the mouthpiece. The exhaled flow is measured with a pneumotachograph in conjunction with a differential pressure transducer, and P₁₀₀ is determined with a Validyne MP45 pressure transducer.     

Intracavitary therapy of neoplastic effusions with cytokines: comparison among interferon α, β and interleukin-2

Preliminary studies have suggested that the intracavitary administration of cytokines may represent a new effective palliative therapy of malignant effusions. To define further the therapeutic role of cytokines in the treatment of neoplastic fluid accumulation, 70 cancer patients with pleural, pericardial or peritoneal cytologically proven neoplastic effusions were randomized to receive intracavitary cycles with interleukin-2 (IL-2; 6x10⁶ IU), interferon (IFN; 2x10⁷ U) or IFN (6x10⁶ U) every week for 2 or 3 weeks. A clinical control of fluid accumulation was obtained in 39/70 (56%) patients. In patients with mesothelioma, the response rate was significantly higher with IL-2 than with IFN or-, while there was no difference in patients with tumors other than mesothelioma. Moreover, the duration of the period during which drainage was not required was significantly longer in patients treated with Il-2 than in the other groups. Toxicity was low in all patients. According to preliminary data, this study demonstrates that intracavitary administration of cytokines, including IL-2, IFN and-, is a new well-tolerated palliative therapy for malignant effusions, with an efficacy substantially comparable to that described with the most commonly used treatments with tetracyclines or cytostatic agents.     

Endotracheal suctioning: from principles to practice

Objective This paper aims to highlight the physical principles of pressure and flow dynamics underlying endotracheal suctioning, to demonstrate these on a simple illustrative model and to discuss the clinical implications of these principles for paediatric practice.Design Prospective in vitro study.Setting Paediatric intensive care unit of a tertiary, academic hospital.Measurements and main results The peak pressure change (P) obtained in a bag-in-box model was recorded during suctioning, using different combinations of endotracheal tube (ETT) and catheter sizes, different suction pressures and techniques. Suction was also performed on three different consistencies of gelatine, using a range of suction catheter sizes and vacuum pressures. The mass of gelatine suctioned per second was calculated. A large P was measured when using neonatal-sized ETTs. There was a linear relationship (r=0,8, p<0.05) between P and the ratio of external catheter area to area difference (internal ETT area–external catheter area). Significantly greater P was measured when using a short versus long suction catheter (p<0.001) and when applying suction for longer duration (p<0,001) and with higher vacuum pressures (p<0.05). The amount of mucus suctioned in a given time was related to catheter size, suction pressure and mucus density.Conclusion Applied clinically, these results indicate that intrapulmonary pressure changes generated by the endotracheal suctioning of intubated neonates are likely to be considerable, possibly translating into loss of lung volume.This work was supported by research grants from Institute of Child Health (University of Cape Town) and South African Physiotherapy Research Foundation. Consumables were funded by EMS – VEN Medical (RSA).     

Assessment of left ventricular diastolic function with Doppler tissue imaging: effects of preload and place of measurements

Mitral inflow velocities are widely used for the evaluation of left ventricular (LV) diastolic function. However, they are closely affected by other factors such as preload. The purpose of this study was to evaluate the usefulness of tissue Doppler velocities obtained from the mitral annulus for the evaluation of ventricular relaxation in patients under different loading conditions. We also evaluated the effect of preload at different sides on the mitral annulus. The study population consisted of 62 consecutive patients (38 male, 24 female with a mean age of 42 ± 13 years) who have undergone hemodialysis. Both mitral inflow velocities (E wave, A wave, E wave deceleration time and isovolumetric relaxation time) and mitral annulus tissue Doppler velocities (E, A) from the septal, lateral, anterior, posterolateral and inferior sides of the mitral annulus were measured immediately before and after hemodialysis. Mitral inflow E and A wave velocities and E/A ratio decreased significantly (p < 0.001, p = 0.007, p < 0.001, respectively) after hemodialysis. Mitral annulus E wave velocities and E/A ratios obtained from five different sides of the annulus also changed significantly (p < 0.001 for all); however, there was no change in the A wave velocity (p > 0.05 for all) after hemodialysis. The decrease in E wave and E/A ratio in mitral inflow measurements and E velocities and E/A ratios in tissue Doppler measurements were correlated with the amount of fluid extracted (for mitral inflow E wave, r = 0.392, p = 0.002 and E/A ratio, r = 0.280 and p = 0.027; for lateral side E, r = 0.329, p = 0.009 and E/A ratio, r = 0.286, p = 0.04; for septal side E, r = 0.376, p = 0.003 and E/A ratio, r = 0.297, p = 0.019; for anterior side E, r = 0.342, p = 0.007 and E/A ratio, r = 0.268, p = 0.035; for posterolateral side E, r = 0.423, p = 0.001 and E/A ratio, r = 0.343, p = 0.007; and for inferior side E, r = 0.326, p = 0.01 and E/A ratio, r = 0.278, p = 0.029). We conclude that mitral annular velocities obtained by tissue Doppler are preload dependent parameters for the evaluation of LV diastolic function.     

Low tidal volume ventilation induces proinflammatory and profibrogenic response in lungs of rats

Objective We examined whether mechanical ventilation with low tidal volume induces polymorphonuclear infiltration and proinflammatory and profibrogenic responses in rat lungs compared dependent and nondependent lung region to expression of interleukin-1 (IL-1) and -1 procollagen III (PC III) mRNA.Design An experimental, randomized and controlled protocol with previously normal rats.Interventions Three groups of ten animals were studied. Two groups were ventilated (FIO₂=0.3) in supine position for 1 h without positive end expiratory pressure, one group with a low tidal volume (6 ml/kg), and the other with a high tidal volume (24 ml/kg). In the third group animals were kept in spontaneous ventilation for 1 h.Measurements and results After ventilation the right lung was used to quantify polymorphonuclear infiltration. The left lung was divided into dependent and nondependent regions, and expression of IL-1 and PC III mRNA was quantified by northern blot analysis. The group ventilated with low tidal volume had greater polymorphonuclear infiltration IL-1 and PC III mRNA expression than the nonventilated group. Similar results were observed with high tidal volumes. There was no difference between low and high tidal volume ventilation. Expression levels of IL-1 and PC III mRNA were higher in the nondependent region of ventilated groups and equal in the nonventilated group.Conclusions Even a low tidal volume mode of mechanical ventilation induces proinflammatory and profibrogenic response, with a nondependent predominance for IL-1 and PC III mRNA expression in supine, ventilated, previously normal rats.     

Plasma catecholamines and oxygen consumption during weaning from mechanical ventilation

Previous studies on oxygen consumption ( ) during weaning from mechanical ventilation assumed that an increase in ( ) reflected oxygen consumption by respiratory muscles ( ), and proposed as a weaning predictor. We measured CO₂ production ( ) and plasma catecholamines in 20 short-term ventilated patients during weaning by SIMV and CPAP. as a percentage of during spontaneous ventilation ( %) ranged from 4.8% to 41.5%. also increased and correlated with . Plasma adrenaline and noradrenaline increased significantly to levels known to produce considerable increases in metabolic rate. Mean arterial pressure and heart rate concomitantly increased, but spontaneous minute ventilation decreased. Thus, since the increased plasma catecholamines are calorigenic, the assumption that represents is incorrect. Although mean % of successfully weaned patients was significantly less than that of failure-to-wean patients, the wide scatter of individual values in the latter group excludes % as an accurate weaning predictor.     

Effects of the heat-moisture exchangers on dynamic hyperinflation of mechanically ventilated COPD patients

In recent years the use of devices called Heat and Moisture Exchangers (HME) has become widespread as gas conditioners for ICU patients requiring mechanical ventilation. As an important variation of the resistive properties of the HME, related to flow and duration of use, has recently been pointed out during in vitro studies, the use of these devices in COPD patients could increase the levels of auto PEEP and dynamic hyperinflation. In this study we have compared the levels of auto PEEP and difference in functional residual capacity ( FRC) in a group of COPD patients, requiring controlled mechanical ventilation (CMV), at basal conditions and after the insertion into the circuit of three HMEs (Dar Hygrobac, Pall Ultipor, Engstrom Edith) at random: the results obtained excluded a significant increase of auto PEEP and (FRC) both with new HMEs and after 12 h of continuous use.