Hemodynamic oxygen transport and 2,3-diphosphoglycerate changes after transfusion of patients in acute respiratory failure

The goals of management of patients with respiratory failure include improving arterial oxygenation with PEEP and red cell transfusion to maintain oxygen carrying capacity, both of which contribute to improving tissue oxygen delivery. However, standard CPD-stored blood is rapidly depleted of 2,3 diphosphoglycerate (2,3 DPG) and ATP, with resultant inadequacy of the red cell oxygen transport function. In 15 patients requiring mechanical ventilation with PEEP whose initial Hct35%, we studied the effect of transfusion of 7 ml/kg of CPD-stored packed red blood cells on hemodynamic and oxygen delivery variables, pulmonary venous admixture (Q_A/Q_T), and erythrocytic P₅₀, 2,3 DPG and ATP concentrations. Hemodynamics were not significantly altered by transfusion. 2,3 DPG decreased significantly from 14.5±1.1 to 13.1±1.5 mcmol/g Hb (mean±SD, p<0.05). There was no significant change in P₅₀ or ATP. Q_A/Q_T rose significantly, from 20.1±7.8 to 28.9±12.3% (mean±SD, p<0.02). In our patients, an increase in arterial oxygen content obtained by transfusion was not followed by any associated decrease in cardiac work, as implied by solution of equations for oxygen delivery and oxygen consumption. The rise in Q_A/Q_T is undesirable in patients requiring PEEP, since it complicates management of their mechanical ventilatory support.Presented in part at the 48th Annual Scientific Assembly of the American College of Chest Physicians, 10–15 October 1982     

End-expiratory lung volume during mechanical ventilation: a comparison with reference values and the effect of positive end-expiratory pressure in intensive care unit patients with different lung conditions

Introduction

Functional residual capacity (FRC) reference values are obtained from spontaneous breathing patients, and are measured in the sitting or standing position. During mechanical ventilation FRC is determined by the level of positive end-expiratory pressure (PEEP), and it is therefore better to speak of end-expiratory lung volume. Application of higher levels of PEEP leads to increased end-expiratory lung volume as a result of recruitment or further distention of already ventilated alveoli. The aim of this study was to measure end-expiratory lung volume in mechanically ventilated intensive care unit (ICU) patients with different types of lung pathology at different PEEP levels, and to compare them with predicted sitting FRC values, arterial oxygenation, and compliance values.

Methods

End-expiratory lung volume measurements were performed at PEEP levels reduced sequentially (15, 10 and then 5 cmH₂O) in 45 mechanically ventilated patients divided into three groups according to pulmonary condition: normal lungs (group N), primary lung disorder (group P), and secondary lung disorder (group S).

Results

In all three groups, end-expiratory lung volume decreased significantly (P < 0.001) while PEEP decreased from 15 to 5 cmH₂O, whereas the ratio of arterial oxygen tension to inspired oxygen fraction did not change. At 5 cmH₂O PEEP, end-expiratory lung volume was 31, 20, and 17 ml/kg predicted body weight in groups N, P, and S, respectively. These measured values were only 66%, 42%, and 34% of the predicted sitting FRC. A correlation between change in end-expiratory lung volume and change in dynamic compliance was found in group S (P < 0.001; R ² = 0.52), but not in the other groups.

Conclusions

End-expiratory lung volume measured at 5 cmH₂O PEEP was markedly lower than predicted sitting FRC values in all groups. Only in patients with secondary lung disorders were PEEP-induced changes in end-expiratory lung volume the result of derecruitment. In combination with compliance, end-expiratory lung volume can provide additional information to optimize the ventilator settings.     

Effects of PEEP on pulmonary mechanics and oxygen transport in the late stages of acute pulmonary failure

In 23 patients with advanced stages of acute respiratory failure, the value of various parameters for estimating the efficiency of ventilation with PEEP were analysed. PEEP increments of 1 cm of water corresponded to an increase of PaO₂ of 2 mmHg. The cardiac output decreased from 8.3±0.3 l/min mean value at ZEEP to 7.3±0.3 l/min at a PEEP of +15 cm H₂O. Corresponding to this, the oxygen transport showed a decrease from 1042±62 ml/min to 894±115 ml/min. The total compliance of 34 ml/cm H₂O at ZEEP is already significantly reduced (a sign of the severe respiratory failure) and falls still further at a PEEP of 15 cm H₂O to 22 ml/cm H₂O. No notable recruitment of non ventilated alveolar spaces can be expected, in spite of the slight increase in the arterial oxygen tension. Taking the best PEEP (PEEP with maximum oxygen transport) as a reference point, arterial and mixed venous oxygen tension increase, the cardiac output decreases above this point and the total respiratory compliance shows no obvious changes. In the advanced stage of severe respiratory failure one cannot use the mixed venous oxygen tension or the compliance to find the best PEEP. The danger of barotrauma by PEEP ventilation in cases of significantly reduced compliance has to be considered in the choice of the ventilation pattern. The arterial oxygen tension may lead to a wrong estimation of the total efficiency of PEEP.Excerpts presented at the Central European Congress of Anesthesia; Geneva, September 1977     

Time to reach a new steady state after changes of positive end expiratory pressure

Purpose

To assess the time interval required to reach a new steady state of oxygenation-, ventilation-, respiratory mechanics- and hemodynamics-related variables after decreasing/increasing positive end expiratory pressure (PEEP).

Methods

In 23 patients (group 1) with acute respiratory distress syndrome (ARDS), PEEP was decreased from 10 to 5 cmH₂O and, after 60′, it was increased from 5 to 15 cmH₂O. In 21 other ARDS patients (group 2), PEEP was increased from 10 to 15 cmH₂O and, after 60′, decreased from 15 to 5 cmH₂O. Oxygenation, ventilation, respiratory mechanics and hemodynamic variables were recorded at time 5′, 15′, 30′ and 60′ after each PEEP change.

Results

When PEEP was decreased, PaO₂, PaO₂/FiO₂, venous admixture and arterial oxygen saturation reached their equilibrium after 5′. In contrast, when PEEP was increased, the equilibrium was not reached even after 60′. The ventilation-related variables did not change significantly with PEEP. The respiratory system compliance, when PEEP was decreased, significantly worsened only after 60′. Hemodynamics did not change significantly with PEEP. In the individual patients the change of oxygenation-related variables and of respiratory system compliance observed after 5′ could predict the changes recorded after 60′. This was not possible for PaCO₂.

Conclusions

We could not find a unique equilibration time for all the considered variables. However, in general, a decremental PEEP test requires far lower equilibrium time than an incremental PEEP test, suggesting a different time course for derecruitment and recruitment patterns.     

Cerebro-pulmonary interactions during the application of low levels of positive end-expiratory pressure

Objective In patients with severe brain injury and acute lung injury the use of positive end-expiratory pressure (PEEP) is limited by conflicting results on its effect on intracranial pressure. We hypothesised that the occurrence of alveolar hyperinflation during the application of PEEP would lead to an increase in PaCO₂ responsible for a rise in intracranial pressure.Design Prospective interventional study.Setting Intensive Care Unit of University Hospitals.Patients and participants Twelve severely brain-injured patients with acute lung injury and intracranial pressure higher than applied PEEP.Interventions 5 and 10 cmH₂O of PEEP was randomly applied.Measurements and results In all patients intracranial pressure, flow velocity by transcranial Doppler of middle cerebral artery, and jugular oxygen saturation were recorded. Static volume-pressure curves of the respiratory system were obtained, recruited volume and elastance calculated to classify patients as recruiters and non-recruiters. In recruiters (= 6 patients), elastance decreased (P<0.01) and PaO₂ increased (P<0.005), while in non-recruiters (= 6 patients) elastance and PaCO₂ significantly increased (P<0.001). Intracranial pressure, Doppler flow velocity, and jugular saturation remained constant in recruiters but significantly increased (P<0.0001) in non-recruiters. A significant correlation was found between changes in intracranial pressure and elastance (r² = 0.8 P<0.0001) and between changes in PaCO₂ and intracranial pressure (P<0.001, r² = 0.4) and elastance (P<0.001, r² = 0.4), respectively.Conclusions When PEEP induced alveolar hyperinflation leading to a significant increase in PaCO₂, intracranial pressure significantly increased, whereas when PEEP caused alveolar recruitment intracranial pressure did not change.Supported by Ministero dellUniversità e della Ricerca Scientifica e Tecnologica     

Comparison of functional residual capacity and static compliance of the respiratory system during a positive end-expiratory pressure (PEEP) ramp procedure in an experimental model of acute respiratory distress syndrome

Introduction

Functional residual capacity (FRC) measurement is now available on new ventilators as an automated procedure. We compared FRC, static thoracopulmonary compliance (Crs) and PaO₂ evolution in an experimental model of acute respiratory distress syndrome (ARDS) during a reversed, sequential ramp procedure of positive end-expiratory pressure (PEEP) changes to investigate the potential interest of combined FRC and Crs measurement in such a pathologic state.

Methods

ARDS was induced by oleic acid injection in six anesthetised pigs. FRC and Crs were measured, and arterial blood samples were taken after induction of ARDS during a sequential ramp change of PEEP from 20 cm H₂O to 0 cm H₂O by steps of 5 cm H₂O.

Results

ARDS was responsible for significant decreases in FRC, Crs and PaO₂ values. During ARDS, 20 cm H₂O of PEEP was associated with FRC values that increased from 6.2 ± 1.3 to 19.7 ± 2.9 ml/kg and a significant improvement in PaO₂. The maximal value of Crs was reached at a PEEP of 15 cm H₂O, and the maximal value of FRC at a PEEP of 20 cm H₂O. From a PEEP value of 15 to 0 cm H₂O, FRC and Crs decreased progressively.

Conclusion

Our results indicate that combined FRC and Crs measurements may help to identify the optimal level of PEEP. Indeed, by taking into account the value of both parameters during a sequential ramp change of PEEP from 20 cm H₂O to 0 cm H₂O by steps of 5 cm H₂O, the end of overdistension may be identified by an increase in Crs and the start of derecruitment by an abrupt decrease in FRC.     

Review: Artifical ventilation with positive end-expiratory pressure (PEEP)

CPPV (continuous positive pressure ventilation) is obviously superior to IPPV (intermittent positive pressure ventilation) for the treatment of patients with acute respiratory insufficiency (ARI) and results within a few minutes in a considerable increase in the oxygen transport.The principle is to add a positive end-expiratory plateau (PEEP) to IPPV, with a subsequent increase in FRC (functional residual capacity) resulting in re-opening in first and foremost,the declive alveolae, which can then once again take part in the gas exchange and possibly re-commence the disrupted surfactant production. In this manner the ventilation/perfusion ratio in the diseased lungs is normalized and the intrapulmonary shunting of venous blood will decrease. At the same time the dead space ventilation fraction (V_D/V_T) normalizes and the compliance of the lungs (C_L) increases.The PEEP value, which results in a maximum oxygen transport, and the lowest dead space fraction, also appears to result in the greatest total static compliance (CT) and the greatest increase in mixed venous oxygen tension ; this value can be termed optimal PEEP.The greater the FRC is, with an airway pressure = atmospheric pressure, the lower the PEEP value required in order to obtain maximum oxygen transport.If the optimal PEEP value is exceeded the oxygen transport will fall because of a falling (cardiac output) due to a reduction in venous return. CT and will fall and V_D/V_T will increase. Increasing hyperinflation of the alveolae will result in a rising danger of alveolar rupture.The critical use of CPPV treatment means that the lungs may be safeguarded against high oxygen percents.The mortality of newborn infants with RDS (respiratory distress syndrome) has fallen considerably after the general introduction of CPPV and CPAP (continuous positive airway pressures). The same appears to be the case with adults suffering from ARI (acute respiratory insufficiency).Abbreviations and explanations (A-a)DO₂ Alveolo - arterial - O₂ - difference - ARI Acute respiratory insufficiency - CaO₂ Arterial O₂-content - O₂-extraction ratio - O₂-uptake, consumption - CC Closing capacity - CV Closing volume - CPAP Continuous positive airway pressure - CPPV (IPPV + PEEP) Continuous positive pressure ventilation - C_L Lung compliance - C_T Total static compliance - Mixed venous O₂-content (O₂-reserve) - ETP End Tidal point - ERV Expiratory reserve volume - FRC Functional residual capacity - IC Inspiratory capacity - IPPV Intermittent positive pressure ventilation - IRV Inspiratory reserve volume     

Monitoring of central venous oxygen saturation versus mixed venous oxygen saturation in critically ill patients

Continous monitoring of mixed venous (SvO₂) and central venous (ScO₂) oxygen saturation was compared in 7 critically-ill patients (Apache II score: 19±2.1) to determine whether or not information derived from ScO₂ were reliable in clinical practice. Patients were catheterized with both a pulmonary artery (PA) and a central venous (CV) catheter, each of them mounted with fiberoptic sensors (Opticath PA Catheter P7110 and Opticath CV Catheter U440, Abbott). A total of 580 comparative measurements were obtained during periods without and with therapeutic interventions (drug-titration, bronchial suction, use of PEEP, changes in FiO₂...). The systematic error between the 2 measurement techniques was 0.6% and 0.3% in periods with and without therapeutic interventions, respectively. The variability between the 2 techniques was 10% for both periods. Differences between the values were 5% in 49% of values during periods of stability and in 50% of values during periods with therapeutic interventions. There were poor correlations between the values during periods without (r=0.48) and with therapeutic interventions (r=0.62). Better, but still less than ideal, correlations were obtained with changes in SvO₂ and ScO₂ during periods without (r=0.70) and with therapeutic interventions (r=0.77). Although there is a need to develop a simple technique to monitor mixed venous oxygen saturation, the present study indicates that ScO₂ monitoring was not reliable in the study patients.     

Postoperative spontaneous breathing with CPAP to normalize late postoperative oxygenation

After intubation for elective upper abdominal surgery 30 patients were randomized in group A or B. Both groups had the same anaesthetics and were ventilated with a tidal volume of 12 ml/kg the rate keeping P_aCO₂ near 40 mm Hg. Group A was ventilated with ZEEP and group B with PEEP 10 cm H₂O. Group A was extubated when VC reached 15 ml/kg and P_aCO₂ did not exceed 50 mm Hg breathing spontaneously. Group B was allowed to breathe spontaneously with CPAP and PEEP 5 cm H₂O (Basel PEEP-Weaner^R) for 3 hours before extubation. Measurements: BP, PAP, RAP, HR, Hb, arterial and mixed-venous blood gases with F_IO₂=0,21. Both groups were similar in age, sex, cigarette consumption, preoperative pulmonary pathology, surgical procedure pathology, surgical procedure and time of operation.Results: RAP, PAP, BP, HR, P_aCO₂, P_aH, P_v–O₂ did not show important differences. Mean P_aO₂ changed as follows: Postoperative chest X-rays showed in Group A a total of 56 negative scores, in Group B 25.Conclusion: After upper abdominal surgery the well known decrease of FRC with its increased venous admixture can be prevented if the patient is ventilated with PEEP during operation and is breathing spontaneously with CPAP and PEEP for 3 postoperative hours before extubation.Deceased 1976     

Automated measurement of functional residual capacity by sulfur hexafluoride washout

We have constructed a computerized, totally automated system for measuring functional residual capacity (FRC) during mechanical ventilation, at any positive end-expiratory pressure (PEEP) and fraction of inspired oxygen. This system uses washout of a small amount (0.5 to 1.0%) of an insoluble, nontoxic tracer gas, sulfur hexafluoride, to measure FRC. It requires no modification of the ventilator and only minimal changes in the breathing circuit; it can be programmed to make measurements routinely without manual intervention.The system was evaluated with three tests. (1) The prototype sulfur hexafluoride analyzer characteristic curve was determined, and the analyzer was evaluated to determine carbon dioxide interference. (2) A comparison with nitrogen washout FRC measurements was made in an extensive bench test with a Plexiglas lung model. The bench test was designed to determine the effects of changing gas composition and minute volume. (3) A study was done in six healthy dogs to determine reproducibility of the FRC measurements at four PEEP levels (0, 5, 10, and 15 cm H₂O: two repetitions in each animal).The sulfur hexafluoride analyzer was well characterized by an exponential equation with a multiple r² = 0.996. The analyzer was not affected by the presence of carbon dioxide (pairedt test,t ₁₉ = 1.23,P > 0.10). The bench test indicated that FRC (measured) = 0.969 × FRC (true) – 5.3 ml. (Multiple r² = 0.979.) This was significantly better than the nitrogen washout system, whose regression equation was also a function of minute volume. In the six animals studied, increasing PEEP always increased FRC and did not significantly alter reproducibility of the FRC measurement (P > 0.1).This automated sulfur hexafluoride washout system should make routine FRC measurements both relatively simple and possible without altering normal ventilatory therapy.     

Errors in 14 pulse oximeters during profound hypoxia

The accuracy of pulse oximeters from fourteen manufacturers was tested during profound brief hypoxic plateaus in 125 subject sets using 50 normal adult volunteers, of whom 29 were studied two to nine times. A data set usually consisted of 10 subjects, and 13 sets were collected between August 1987 and July 1988. In the first 6 sets, six 30-second hypoxic plateaus were obtained per subject at 55±6% oxyhemoglobin (O₂Hb) (range, 40 to 70%). In the last 7 sets, three hypoxic plateaus were obtained at each of four levels, approximately 86, 74, 62, and 50% O₂Hb, for the purpose of linear regression analysis. Inspired oxygen was adjusted manually breath by breath in response to arterial oxygen saturation computed on-line from end-tidal oxygen and carbon dioxide tensions. End-plateau arterial blood O₂Hb was analyzed by a Radiometer OSM-3 oximeter, and plateau pulse oximeter saturation (SpO₂) was read by cursor from a computer record of the analog output. Three to 13 instruments were tested simultaneously by using 1 to 3 duplicate instruments from each of one to seven manufacturers. Variations introduced by manufacturers were tested on subsequent sets in several instruments. An index of error, ambiguity () of oxygen saturation, was defined as the absolute sum of bias and precision (mean and SD of SpO₂–O₂Hb) at O₂Hb=55.8±4.5%, preserving the sign when bias was significant atP<0.05. Ambiguity values for finger probes (unless specified) with latest data were: Physio-Control, 3.9 (ear, 3.3); Puritan-Bennett, –4.4; Criticare, 5.8 (forehead, 4.7); Kontron, 5.9 (infant probe) and 6.1 (ear, 5.8; forehead, 7.1); Biochem, –6.0; Datex 6.4 (ear, 6.9; forehead, 6.8); Critikon, 8.4; SiMed, 8.6; Marquest, 9.0; Novametrix, 10.2; Invivo, –12.2 (ear, –14.3); Nellcor, –15.1; Ohmeda, –21.2; and Radiometer, –21.2 (ear, –9.6). Linear regression slopes of 36 instruments from twelve manufacturers generally deviated from 1 in proportion to . The data showed substantial differences in bias and precision between pulse oximeters at low saturations, the most common problems being underestimation of saturation and failing precision.     

Optimal endexpiratory airway pressure for ventilated patients

In patients ventilated for acute respiratory failure PEEP was changed either by gradual increase and decrease (5 cm H₂O/min) or in steps of 5 cm H₂O. The effects on gas exchange, pulmonary mechanics and pulmonary and systemic circulation were studied. Total compliance did not change uniformly and cardiac index decreased so much due to PEEP that the increase in P_aO₂ could not prevent the decrease of arterial oxygen transport. No variable was found helpful to predict the best PEEP in a clinical situation.With the support of the Swiss National Fund for the advancement of Scientific Research, Berne. Application No. 3.831-0.79     

Effect of positive end‐expiratory pressure on acoustic wave propagation in experimental porcine lung injury

To evaluate the effect of positive end‐expiratory pressure (PEEP) on sound propagation through injured lungs, we injected a multifrequency broad‐band sound signal into the airway of eight anesthetized, intubated and mechanically ventilated pigs, while recording transmitted sound at three locations bilaterally on the chest wall. Oleic acid injections effected a severe pulmonary oedema predominately in the dependent lung regions, with an average increase in venous admixture from 19 ± 15 to 59 ± 14% (P<0·001), and a reduction in dynamic respiratory system compliance from 34 ± 7 to 14 ± 4 ml cmH₂O^?1 (P<0·001). A concomitant decrease in sound transit time was seen in the dependent lung regions (P<0·05); no statistically significant change occurred in the lateral or non‐dependent areas. The application of PEEP resulted in a decrease in venous admixture, increase in respiratory system compliance and return of the sound transit time to pre‐injury levels in the dependent lung regions. Our results indicate that sound transmission velocity increases in lung tissue affected by permeability‐type pulmonary oedema in a manner reversible during alveolar recruitment with PEEP.     

Impact of positive end-expiratory pressure on cerebral injury patients with hypoxemia

Background

Traumatic brain injury or intracranial hemorrhage patients with acute lung injury/acute respiratory distress syndrome need mechanical ventilation. The use of positive end-expiratory pressure (PEEP) in this situation remains controversial. This study explored the impact of PEEP on intracranial pressure (ICP), cerebral perfusion pressure (CPP), central venous pressure (CVP), and mean arterial pressure (MAP) in cerebral injury patients.

Methods

Nine cerebral injury patients with lung injury who needed mechanical ventilation and met the criteria for ICP monitoring were included in this study. Intraventricular catheters were positioned in 1 of the bilateral ventricles and connected to pressure transducers. Invasive arterial pressure and CVP were monitored continuously. Pressure control ventilation was applied during this clinical trial in a stepwise recruitment maneuver (RM) with 3 cm H₂O intermittent increments and decrements of PEEP.

Results

A total of 28 RMs were completed in 9 patients. Mean values of MAP, CVP, ICP, and CPP 5 minutes after RMs showed no significant differences compared with baseline (P > 0.05). Correlation analysis of all the mean values of MAP, CVP, ICP, and CPP showed significant correlation between MAP and CPP, PEEP and CVP, PEEP and ICP, and PEEP and CPP with all P values less than 0.05.

Conclusion

The impact of PEEP on blood pressure, ICP, and CPP varies greatly in cerebral injury patients. Mean arterial pressure and ICP monitoring is of benefit when using PEEP in cerebral injury patients with hypoxemia.     

Association between systemic hemodynamics and septic acute kidney injury in critically ill patients: a retrospective observational study

Introduction

The role of systemic hemodynamics in the pathogenesis of septic acute kidney injury (AKI) has received little attention. The purpose of this study was to investigate the association between systemic hemodynamics and new or persistent of AKI in severe sepsis.

Methods

A retrospective study between 2006 and 2010 was performed in a surgical ICU in a teaching hospital. AKI was defined as development (new AKI) or persistent AKI during the five days following admission based on the Acute Kidney Injury Network (AKIN) criteria. We studied the association between the following hemodynamic targets within 24 hours of admission and AKI: central venous pressure (CVP), cardiac output (CO), mean arterial pressure (MAP), diastolic arterial pressure (DAP), central venous oxygen saturation (ScvO₂) or mixed venous oxygen saturation (SvO₂).

Results

This study included 137 ICU septic patients. Of these, 69 had new or persistent AKI. AKI patients had a higher Simplified Acute Physiology Score (SAPS II) (57 (46 to 67) vs. 45 (33 to 52), P < 0.001) and higher mortality (38% vs. 15%, P = 0.003) than those with no AKI or improving AKI. MAP, ScvO₂ and CO were not significantly different between groups. Patients with AKI had lower DAP and higher CVP (P = 0.0003). The CVP value was associated with the risk of developing new or persistent AKI even after adjustment for fluid balance and positive end-expiratory pressure (PEEP) level (OR = 1.22 (1.08 to 1.39), P = 0.002). A linear relationship between CVP and the risk of new or persistent AKI was observed.

Conclusions

We observed no association between most systemic hemodynamic parameters and AKI in septic patients. Association between elevated CVP and AKI suggests a role of venous congestion in the development of AKI. The paradigm that targeting high CVP may reduce occurrence of AKI should probably be revised. Furthermore, DAP should be considered as a potential important hemodynamic target for the kidney.     

Estimation of cardiac index by means of the arterial and the mixed venous oxygen content and pulmonary oxygen uptake determination in the early post-operative period following surgery of congenital heart disease

Objective To assess the reliability of estimation of cardiac index based on the mixed venous oxygen saturation and methods of improving the estimation of cardiac index.Setting PICU in an university hospital.Design In the post-operative period following complete repair of congenital heart disease we carried out 55 measurements of blood gases in 25 infants and children (mean age 16.1 months, mean body surface 0.43 m²) from a systemic artery (arterial) and the pulmonary artery (mixed venous). We also determined the pulmonary oxygen uptake and calculated the cardiac index (CI) using Fick's principle. In the analysis we compared the CI with the mixed venous oxygen saturation and with the quotient of the arterial oxygen content (C_aO₂) and the oxygen extraction . This quotient is equal to arterial oxygen delivery (DO₂) divided by the oxygen consumption (VO₂).Results Pearson's correlation coefficient was 0.77 when was compared to CI in a linear regression model. Assuming an inverse relationship between and CI the correlation was much better (r=0.90). However, the best estimation of CI provides the quotient .Conclusions correlates much better with CI than the , therefore CI could be better estimated based on . Furthermore provides good information about the oxygen supply situation of the body.     

Tracing best PEEP by applying PEEP as a RAMP

Objective: The aim of this study was to show the feasibility of a slow, continuously increasing level of positive end-expiratory pressure (PEEP) (ramp manoeuvre) in selecting best PEEP and to evaluate whether best PEEP, as definded by maximal oxygen transport, coincides with best systemic arterial oxygenation or best compliance. Design: In 11 anaesthetized piglets, PEEP was increased between 0 cmH₂O (zero end-expiratory pressure; ZEEP) and 15 cmH₂O (PEEP₁₅) with a constant rate of 0.67 cmH₂O · min⁻¹. This ramp manoeuvre was performed both under normal conditions and after induction of an experimental lung oedema. During the ramp manoeuvre, haemodynamic and pulmonary variables were monitored almost continuously. Results: During the rise in PEEP, cardiac output declined in a non-linear way. In the series with normal conditions, best PEEP was always found at ZEEP. In the series with experimental lung oedema, best PEEP, as defined by maximum oxygen transport, was found at PEEP_1–6, as defined by maximal compliance, at PEEP_7.5 and by maximal arterial oxygen tension (PaO₂) at PEEP_10–14. Conclusions: Best PEEP according to oxygen transport is lower than best PEEP according to compliance and PaO₂; the use of PEEP as a ramp might prevent unnecessarily high levels of PEEP. Received: 16 June 1997 Accepted: 24 April 1998     

Critical evaluation of the ‘heated-hand-technique’ for obtaining ‘arterialized’ venous blood: incomplete arterialization and alterations in glucagon responses

Summary. In order to test the degree of ‘arterialization’ and the occurrence of arterio-(or capillary-) venous differences in glucose concentrations for commonly used blood sampling sites (including the retrogradely cannulated dorsal hand vein with application of dry heat to this hand/arm – the ‘heated-hand-technique’), oxygen partial pressure (oxygen saturation) and plasma glucose was determined in blood drawn from different venous sites before and after an oral glucose load (75 g). Experiments with and without heating (hot air 68°C) were compared in nine healthy volunteers. Basal pO₂ (and oxygen saturation) increased in the order cubital fossa vein < superficial forearm vein < dorsal hand vein. Heating raised pO₂ by ?20 mmHg; P=0.008) and oxygen saturation (P= 0.008–0.02) at all sites, including those on the contralateral arm. Capillary-venous glucose differences after the glucose challenge were significantly related to the sampling site (P< 0.0001). They were reduced by ?50% in response to heat exposure (P=0.008–0.011) and could be correlated to pO₂-values (r=0.92; P= 0.01). The lowest capillary-venous glucose concentration difference was measured with the ‘heated-hand-technique’ (0.4 ± 0.1 mmol l^-1). Heating did not alter integrated incremental glucose (capillary values), insulin, and C-peptide-responses and late, counter-regulatory responses (120–240 min after glucose) of Cortisol, growth hormone, and adrenalin. However, the late glucagon response was enhanced (P=0.011) by heating, concomitant with a significantly reduced ‘reactive’ decrement in glucose concentrations. In conclusion, the ‘heated-hand-technique’ provides blood more similar to arterial blood that can be obtained from other venous sampling sites. However, significant residual differences in pO₂ and glucose concentrations remain. In addition, altered counter-regulatory hormone responses may occur with heating.     

Thoracic duct lymph and PEEP studies in anaesthetized dogs

The effect of positive end-expiratory pressure ventilation (PEEP, 11–12 mmHg, 60–90 min without, 19 h with circulatory support) on fractional escape rate of plasma proteins (FER), and on thoracic duct lymph flow draining against jugular venous (LF_JVP) or atmospheric pressure (LF_AP) was studied in anaesthetized dogs. RER was 10.8%/h, 15.3%/h, and 8.5%/h before, during, and after PEEP, respectively, indicating augmented lymph formation probably due to the increase in venous pressure from 4.8 to 10.8 mmHg during PEEP. LF_JVP was 39 l/min per kg before PEEP, decreased transiently during PEEP but the steady state value (up to 19 h) was not different from control, and increased transiently after PEEP. LF_AP was 37, 80, and 38 l/min per kg before, during, and after PEEP, respectively. Long-term PEEP increased LF_AP fourfold. Changing the drainage mode during PEEP yielded and immediate increase from LF_JVP=34 to LF_AP=79 l/min per kg and an instantaneous reduction from LF_AP=95 to LF_JVP=35 l/min per kg. Lymph protein concentration and protein lymph/plasma ratio increased concomitantly with LF_AP during PEEP suggesting augmented hepatic contribution to LF_AP, augmented intestinal contribution was revealed by labelling intestinal lymph using olive oil orally, muscular lymph flow was not increased as shown by i.m. Evans blue. In conclusion, the augmentation of venous pressure by PEEP promotes capillary filtration but obstructs lymph drainage from the thoracic duct into the jugular vein. PEEP imbalances formation and return of lymph and affects the development and removal of oedema.     

Resuscitation of canine hemorrhagic hypotension with large-volume isotonic crystalloid: Impact on lung water,venous admixture,and systemic arterial oxygen saturation

The objective of this study was to test the hypothesis that after hemorrhagic hypotension, reinfusion of the shed blood with threefold that volume of lactated Ringer's (LR) solution will significantly increase lung water and venous admixture and hence decrease systemic arterial oxygen saturation. A prospective, randomized, fixed-volume hemorrhage laboratory study was performed at the Oklahoma University Health Sciences Center on 18 anesthetized mongrel dogs. After 40 mL/kg of blood were withdrawn through a femoral artery catheter, the dogs were randomized either to the control group (n = 9) that received a reinfusion of the shed blood, or to the LR treatment group (n = 9) that received an intravenous mixture of the shed blood with 120 mL/kg of LR. After fluid resuscitation, pulmonary artery occlusion pressure (PAOP) and cardiac output (CO) were significantly increased in the LR group compared with control animals (PAOP, 18.7 ± 1.1 vs 13.4 ± 2.9 mm Hg; CO, 8.14 ± 1.08 vs 4.59 ± 0.47 L/min; P < .05 each). However, lung water, venous admixture, and systemic arterial Po₂ were similar between groups. In this fixed-volume hemorrhage model, hemodiluting the reinfused shed blood with threefold the volume of LR did not significantly influence lung water, venous admixture, or systemic arterial oxygen saturation.