New monitors of intravascular volume: a comparison of arterial pressure waveform analysis and the intrathoracic blood volume

Objective: Two new monitoring techniques, the analysis of arterial pressure waveform during mechanical ventilation and the determination of intrathoracic blood volume, were evaluated for preload assessment in a model of graded hemorrhage. Design: 8 anesthetized dogs bled of 10, 20, and 30 % of their blood volume, then retransfused and volume loaded with plasma expander. Central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output, parameters of the arterial pressure waveform analysis [systolic pressure variation (SPV) and delta down (dDOWN)], and intrathoracic blood volume (ITBV) were measured at baseline and after each stage of hemorrhage and volume expansion. Results: The stroke volume index decreased significantly from 1.3 ± 0.4 ml/kg at baseline to 0.7 ± 0.2 ml/kg at 30 % hemorrhage and then increased after retransfusion and volume loading. The changes in the filling pressures during the various stages of hemorrhage were in the range of 1–2 mmHg. CVP decreased from 5.5 ± 0.9 to 3.1 ± 1.7 mmHg and PCWP from 8.0 ± 0.8 to 5.1 ± 1.2 mmHg at 30 % hemorrhage. Both filling pressures responded significantly to retransfusion; PCWP also changed in response to a volume load. SPV and dDOWN (expressed as percent of the systolic blood pressure during a short apnea) increased significantly from 6.7 ± 1.7 and 5.6 ± 3.2 %, respectively, at baseline, to 9.7 ± 2.6 and 8.1 ± 2.9 % after 10 % blood loss and to 13.1 ± 3.9 and 11.1 ± 3.8 % after 30 % hemorrhage. ITBV decreased significantly from 29.7 ± 4.5 to 26.8 ± 5.3 ml/kg after 10 % blood loss and to 23.1 ± 3.0 ml/kg after 30 % hemorrhage. ITBV, SPV, and dDOWN responded significantly to retransfusion and volume load. Significant correlations were found between the degree of volume change and dDOWN (r = 0.93), SPV (r = 0.96), ITBV (r = 0.95), CVP (r = 0.82), and PCWP (r = 0.90). Conclusions: The parameters of arterial pressure waveform analysis (SPV and dDOWN) and ITBV were sensitive estimates of cardiac preload during the early stages of hemorrhage. Measurement of SPV and dDOWN, being both sensitive and relatively noninvasive, has advantages over other methods of preload assessment but is limited to patients on controlled mechanical ventilation. ITBV, which supplies quantitative information about cardiac preload, is more invasive but can also be used in patients who are breathing spontaneously or who are on partial ventilatory support. Received: 6 June 1996 Accepted: 27 February 1977     

Linear Model and Algorithm to Automatically Estimate the Pressure Limit of Pressure Controlled Ventilation for Delivering a Target Tidal Volume

Objective. To theoretically assess the viability of an automatic procedure to support the anesthesiologist in properly setting mechanical ventilators when the operating conditions are switched from volume controlled to pressure controlled ventilation whilst maintaining the preset tidal volume. The procedure is based on a simple linear model of the ventilator breathing system with constant parameters and utilizes the signals gathered by the ventilator without the need to add further equipment. After a short period of stable volume controlled ventilation with the desired tidal volume, the herewith described algorithm allows the calculation of the value of pressure limit to set in pressure controlled mode which assures the previously settled tidal volume with the same breathing frequency and inspiratory-expiratory time ratio. Methods. The algorithm allows the online identification of the four parameters necessary for the mathematical model that are obtained by means of a direct comparison between the pressure, flow and volume waveforms generated by the model and the analog signals provided by the ventilator. The theoretical approach was validated by two different ventilators, various settings, two breathing circuits, endotracheal tubes of various sizes and two mechanical simulators of the respiratory system operating in various conditions. Results. Errors usually less than 5% (p < 0.05) on the target tidal volume were obtained for various settings typically used for adult ventilation in less than 10 s. The theoretical approach shows its limitations (errors of 10± 5%, p < 0.05) at high breathing frequencies (30–40 bpm) and low tidal volumes (200–300 ml). Conclusions. The proposed theoretical approach shows the viability, for adult settings, of one of the simplest mathematical model for mechanical ventilation in order to quickly and safely switch from volume controlled to pressure controlled ventilation. The algorithm could easily be in perspective implemented in the software of the ventilator providing the anesthesiologist with an indication on the value of pressure limit to set in order to safely switch ventilation mode.     

Influence of infusion flow rates on central venous pressure measurements through multi-lumen central venous catheters in intensive care

Objective To study the influence on central venous pressure (CVP), measured at the distal port, of crystalloid infusions administered through the proximal port(s) of a central venous multi-lumen catheter. Patients Thirty-one intensive care patients. Interventions CVP was measured at the distal port of a multi-lumen catheter inserted in the subclavian or internal jugular vein. Using the proximal port(s), saline (0.9%) was infused at rates varying from 2 ml/h to 14,340 ml/h. Results CVP measured before the infusion and during infusion (after 30 s to 1 min) were not significantly different. Positive pressure ventilation with PEEP (5.6 ± 2.5 cmH₂O) and/or norepinephrine infusion (0.25 ± 0.21 μg kg⁻¹ min⁻¹) did not produce any significant change in CVP during infusion. Conclusion The administration of crystalloids at different flow rates through the proximal port(s) of a multi-lumen catheter placed in the superior vena cava does not affect CVP measurement at the distal port, even in mechanically ventilated patients or patients receiving vasopressors.     

Morbidly Obese Patients are Hemodynamically Stable During Laparoscopic Surgery: A Thoracic Bioimpedance Study

Purpose. Morbid obesity caries an increased risk of cardiovascular morbidity and might be associated with intraoperative hemodynamic instability. Based on clinical observation, we hypothesized that during laparoscopic surgery, morbidly obese patients behave hemodynamically similar to the nonobese patients and remain hemodynamically stable. Methods. In a prospective trial, thirty nonobese and tthirty morbidly obese (BMI ≥ 35 kg/m²) patients scheduled for elective laparoscopic surgery were assigned to receive standard balanced anesthesia. We aimed at equianesthetic levels by keeping the BIS (bispectral index) value between 40–50 throughout surgery. End-tidal isoflurane was measured every 5 min. Noninvasive hemodynamic measurements included cardiac index (CI), mean arterial pressure (MAP) and heart rate (HR), recorded every 5 min and at specific predetermined times. Systemic vascular resistance (SVR) was calculated. Episodes of MAP ≤ 60 and MAP ≥ 130 mmHg or HR ≤ 50 and HR ≥ 110 bpm occurring throughout surgery and requiring pharmacological intervention were considered main end-points. Additionally, hemodynamic variables were compared at specific time points and overall throughout surgery. Secondary end-points were CI and SVRI. Results. Heart rate was higher in obese patients in head-up position (79 ± 15 mmHg vs. 65 ± 12 mmHg – P=0.011). SVR was higher in the nonobese group with head-up position (1978 ± 665 dynes s cm⁻⁵ vs. 1394 ± 496 dynes s cm⁻⁵ P=0.01). Mean overall intraoperative MAP, HR, CI and SVR were similar. There were no episodes of MAP ≤ 60 and ≥130 mmHg or HR ≤ 50 and ≥110 bpm in either of the groups. Conclusion. Our study confirmed our hypothesis that for the most periods of laparoscopic surgery, obese patients are hemodynamically as stable as their nonobese counterparts.     

Transcutaneous arterial carbon dioxide pressure monitoring in critically ill adult patients

Objective To evaluate the accuracy of transcutaneous PCO₂ (PtcCO₂) as a surrogate for arterial PCO₂ (PaCO₂) in a cohort of adult critically ill patients in a medical intensive care unit (ICU). Design Prospective observational study comparing paired measures of transcutaneous and arterial PCO₂. Setting A 26-bed medical ICU. Patients Fifty ICU patients monitored with a SenTec Digital Monitor placed at the ear lobe over prolonged periods. Results A total of 189 paired PCO₂ measures were obtained. Twenty-one were excluded from analysis, because profound skin vasoconstriction was present (PCO₂ bias = −10.8 ± 21.8  mmHg). Finally, 168 were analysed, including 137 obtained during mechanical ventilation and 82 under catecholamine treatment. Body temperature was below 36°C for 27 measurements. Mean duration of monitoring was 17 ± 17 h. The mean difference between PaCO₂ and PtcCO₂ was −0.2 ± 4.6  mmHg with a tight correlation (R ² = 0.92, p > 0.01). PCO₂ bias did not significantly change among three successive measurements. Changes in PaCO₂ and in PtcCO₂ between two blood samples were well correlated (R ² = 0.78, p > 0.01). Variations of more than 8 mmHg in PtcCO₂ had 86% sensitivity and 80% specificity to correctly predict similar changes in PaCO₂ in the same direction. Catecholamine dose or respiratory support did not affect PtcCO₂ accuracy. Hypothermia has only a small effect on accuracy. No complication related to a prolonged use of the sensor was observed Conclusion Transcutaneous PCO₂ provides a safe and reliable trend-monitoring tool, provided there is no major vasoconstriction. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

机械通气患者呼气末正压对中心静脉压的影响

【目的】评价机械通气时不同水平呼气末正压(PEEP)对中心静脉压(CVP)的影响。【方法】选择46例行机械通气并监测CVP患者,在不同水平PEEP(0、2、4、6、8、10、12、15、18cmH2O)时,分别测定CVP及心率(HR)、平均动脉压(MAP)、呼吸频率(RR)、经皮脉搏血氧饱和度(SpO2),脱机后再次测量各值并比较其差异性。【结果】PEEP对CVP有非常显著的影响(P<0.01)。PEEP≥12cmH2O患者的SpO2与PEEP≤4cmH2O时有显著性差异(P<0.01)。HR、MAP、RR与在不同PEEP相比较则差异无统计学意义。脱机与机械通气各项观察指标相比较有非常显著性差异(P<0.01)。【结论】随着PEEP水平增加,CVP逐渐增加。脱机测量CVP对患者不利,维持患者原PEEP水平测量CVP,可增加患者的安全性。     

A new automated method versus continuous positive airway pressure method for measuring pressure-volume curves in patients with acute lung injury

Objective  To compare pressure–volume (P–V) curves obtained with the Galileo ventilator with those obtained with the CPAP method in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Design  Prospective, observational study. Setting  General critical care center. Patients and participants  Patients with ALI/ARDS and receiving mechanical ventilation. Interventions  Pressure–volume curves were obtained in random order with the CPAP technique and with the software PV Tool-2 (Galileo ventilator). Measurements and results  In ten consecutive patients, airway pressure was measured by a pressure transducer and changes in lung volume were measured by respiratory inductive plethysmography. P–V curves were fitted to a sigmoidal equation with a mean R ² of 0.994 ± 0.003. Intraclass correlation coefficients were all >0.75 (P < 0.001 at all pressure levels). Lower (LIP) and upper inflection (UIP), and deflation maximum curvature (PMC) points calculated from the fitted variables showed a good correlation between methods with intraclass correlation coefficients of 0.98 (0.92, 0.99), 0.92 (0.69, 0.98), and 0.97 (0.86, 0.98), respectively (P < 0.001 in all cases). Bias and limits of agreement for LIP (0.51 ± 0.95 cmH₂O; −1.36 to 2.38 cmH₂O), UIP (0.53 ± 1.52 cmH₂O; −2.44 to 3.50 cmH₂O), and PMC (−0.62 ± 0.89 cmH₂O; −2.35 to 1.12 cmH₂O) obtained with the two methods in the same patient were clinically acceptable. No adverse effects were observed. Conclusion  The PV Tool-2 built into the Galileo ventilator is equivalent to the CPAP method for tracing static P–V curves of the respiratory system in critically ill patients receiving mechanical ventilation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A poor correlation exists between oscillometric and radial arterial blood pressure as measured by the Philips MP90 monitor

In anesthesia and critical care, invasive arterial blood pressure monitoring is the gold standard against which other methods of monitoring are compared. In this assessment of the Philips MP90 monitor, the objective was to determine whether or not oscillometric measurements were within the accuracy standards set by the Association for the Advancement of Medical Instrumentation (AAMI) and the British Hypertension Society (BHS). Three hundred and one invasive and noninvasive paired measurements were obtained from eleven adult patients on the neurosurgical service at Stanford University Medical Center. Bland–Altman plots were created to assess agreement between the two measurement systems. Paired correlation analysis, bias and precision calculations were performed. Oscillometric blood pressure measurements correlated with arterial measurements yielding Pearson r values of 0.68, 0.67 and 0.62 for systolic, diastolic and mean pressures, respectively (P < 0.01.) Mean differences with 95% confidence intervals were −3.8 mmHg ± 13.6, −2.4 mmHg ± 10.0, and 4.0 mmHg ± 13.1 for systolic, diastolic and mean pressures, respectively. The mean difference for these measurements was ≤5 mmHg as stipulated by the AAMI guidelines, but the standard deviation was greater than the 8 mmHg allowed by the AAMI guidelines. When the BHS guidelines were applied, the device merited a grade “D” for systolic and mean arterial pressure, and a grade “C” for diastolic pressure, with the highest possible grade level being “A.” There was a poor correlation between noninvasive and invasive measurements of arterial blood pressure as measured with a cuff and radial arterial cannula using the Philips MP90 monitor. These inaccuracies could lead to unnecessary interventions, or lack of appropriate interventions in anesthetic management. Further study is needed to specify the absolute inaccuracy of the monitor, and to determine if accuracy between the two methods varies with patient co-morbidities, surgical procedures, or anesthetic management. Mireles SA, Jaffe RA, Drover DR, Brock-Utne JG. A poor correlation exists between oscillometric and radial arterial blood pressure as measured by the Philips MP90 monitor.     

Accuracy and precision of a new, portable, handheld blood gas analyzer, the IRMA?

Objective. The accuracy and precision of the new IRMA? (Immediate Response Mobile Analysis System, Diametrics, Inc.?, St. Paul, MN) handheld blood gas analyzer was compared with that of two benchtop blood gas analyzers. The IRMA consists of a notebook-sized machine and disposable cartridges, each containing a pH, a CO₂ and an O₂ electrode, and provides bedside (point-of-care) blood gas analysis.Methods. A total of 172 samples (arterial and mined venous) were obtained from 25 informed, consenting patients undergoing cardiopulmonary bypass. The pH, PCO₂ and PO₂ of each sample was determined on four blood gas analyzers: NOVA Statlabs Profile 5 (NOVA Biomedical, Waltham, MA), the ABL-50 (Radiometer, West Lake, OH), and two IRMA machines. Linear regression and bias ± precision were determined, comparing each of the analyzers with the NOVA.Results. All three machines showed a similar, high degree of correlation with the NOVA for pH, PCO₂, and PO₂. The bias and precision of the IRMA machines compared with the NOVA was similar to that of the ABL compared with the NOVA for pH (NOVA:ABL −0.005 ± 0.011; NOVA: IRMA 1 = 0.0026 ± 0.025; NOVA: IRMA 2 = 0.0021 ± 0.025), for PCO₂ (NOVA:ABL = −1.4 ± 1.3 mmHg; NOVA: IRMA 1 = −1.3 ± 1.9 mmHg; NOVA: IRMA 2 = −1.2 ± 2.1 mmHg) and PO₂ (NOVA:ABL = 3.6 ± 21.1 mmHg; NOVA: IRMA 1 = 3.4 = 19.9 mmHg; NOVA: IRMA 2 = 6.3 ± 20.9 mmHg). The bias found for pH, PCO₂, and PO₂ was not affected by extremes of temperature (range 25.5–40°C) or hematocrit (range 11–44%) for any machine.Conclusions. The new technology incorporated in the IRMA blood gas analyzer provides results with an accuracy that is similar to that of benchtop analyzers, but with all of the advantages of point-of-care analysis.     

Hemolysis may cause false negative results and underdiagnosis of celiac disease when measuring anti-tissue transglutaminase antibodies in serum by immunoassays

Abstract

Aims. Patients with type 2 diabetes have increased arterial stiffness and a high incidence of cardiovascular disease compared with non-diabetics. Arterial stiffness and central waveforms can be assessed by carotid-femoral pulse wave velocity (PWV) and pulse wave analysis (PWA) using the SphygmoCor device. These methods can potentially improve cardiovascular risk stratification in the future. However, a prerequisite is acceptable reproducibility. The objective of this study was to assess the intra- and inter-observer reproducibility of PWV and PWA indices in patients with type 2 diabetes using the SphygmoCor device. Methods. Two trained observers (A and B) each undertook two PWA and two carotid-femoral PWV recordings in random order in 20 patients with type 2 diabetes under standardized conditions on the right side of the patients. Observer A also made double recordings on the left side. The mean of the two recordings was used for inter-observer comparison. Data were analyzed by Bland-Altman plots. Results. The mean intra-observer differences (± 2SD) on the right side for observer A and B, respectively, were 0.0 ± 2.8 mmHg and 0.3 ± 3.2 mmHg (aortic systolic blood pressue (BP)), 0.0 ± 1.2 mmHg and 0.1 ± 1.0 mmHg (aortic diastolic BP), ? 1.1 ± 3.2% and 1.1 ± 9.6% (central augmentation index (Aix)), ? 1.6 ± 6.6% and 0.1 ± 9.0% (Aix normalized to heart rate 75 beats/min (Aix@HR75)) and 0.1 ± 1.8 m/s and 0.0 ± 1.6 m/s (PWV). The mean inter-observer differences (± 2SD) were ? 2.6 ± 13.0 mmHg (aortic systolic BP), ? 2.1 ± 7.4 mmHg (aortic diastolic BP), ? 0.8 ± 8.4% (Aix), ? 1.5 ± 7.4% (Aix@HR75) and ? 0.3 ± 1.6 m/s (PWV). Left-vs-right comparison showed comparable results (observer A). Conclusions. PWA and PWV assessed with the SphygmoCor device are characterized by good reproducibility in patients with type 2 diabetes.     

The Initial Tangent of the Aortic Pressure Increase is an Estimate of Left Ventricular Contractility in Pigs

The aim was, to identify an estimate of left ventricular contractility derived from the aortic pressure wave without load changing manoeuvres. For this purpose, left ventricular contractility was assessed with several aortic pressure wave form derived parameters and was compared to standard parameters of left ventricular contractility (conductance technique) in an experimental study. Measurements were taken during baseline, after β-stimulation and after injection of a β-antagonist. The initial and the secondary tangent, the area under the aortic pressure, and the stroke volume were correlated with the endsystolic elastance, a mainly load independent measure of left ventricular contractility: The initial tangent of the aortic pressure increase correlated significantly with the endsystolic elastance (r = 0.54, P < 0.05). The initial tangent of the aortic pressure increase was significantly increased from baseline at β-stimulation (from 20.2 ± 4.7 to 36.4 ± 6.8 mmHg  s⁻¹, P < 0.05) and decreased after injection of a β-antagonist (from 20.2 ± 4.7 to 12.3 ± 2.0, P < 0.05). Thus, we conclude that the initial tangent of the aortic pressure increase is a valid estimate of left ventricular contractility in piglets. Kisch-Wedel H, Kemming G, Meisner F, Flondor M, Bruhn S, Koehler C, Zwissler B. The initial tangent of the aortic pressure increase is an estimate of left ventricular contractility in pigs.     

Peripherally inserted central catheters are equivalent to centrally inserted catheters in intensive care unit patients for central venous pressure monitoring

To determine the equivalency of pressure measurements from peripherally inserted central catheters (PICCs) versus centrally inserted central venous catheters (CVCs) in vitro as well as in vivo. The in vitro study was performed in a clinical laboratory. Static pressure measurements from PICCs and CVCs were obtained in vitro over a physiologic range of 5–25 mmHg. Triple and dual lumen PICCs were directly compared to CVC controls. Dynamic pressure waveforms were recorded to simulate physiologic intravascular pressure variation. The in vivo study was executed in the medical intensive care unit (MICU) of a tertiary-level academic medical center. Data was collected from ten adult patients with both a PICC and a CVC in place for on-going clinical care. Measurements of central venous pressure (CVP) were recorded simultaneously from PICCs and CVCs. Duplicate measurements were taken after a stable waveform was recorded. For the in vitro study, a total of 540 pressure measurements were recorded. The average bias determined by Bland–Altman plot was 0 mmHg for the 5Fr PICC and 0.071 mmHg for the 6Fr PICC. The correlation coefficient for both catheters was 1.0 (P < 0.001). Dynamic pressure waveforms revealed equivalent amplitude. During the in vivo trial, 70 CVP measurements were collected. The paired CVP measurements were found to be highly reliable across subjects (r = 0.99, P < 0.0001). No significance in the average difference in CVP measurement (PICC–CVC) was determined by the Wilcoxon Signed Rank test (S = 1, P = 0.93). In conclusion, PICCs are equivalent to CVCs when measuring static and dynamic pressure in vitro and CVP in ICU patients.     

Shock complicating severe falciparum malaria in European adults

Objective: To study adult patients with severe falciparum malaria who developed shock. Design: Retrospective study from 1987 to 1993. Setting: Medical intensive care unit in a university hospital. Patients: 14 patients admitted with severe falciparum malaria who developed shock. All received intravenous quinine. Measurements and results: The mean Simplified Acute Physiology Score II was 59.5 ± 7.1; 2.6 ± 0.4 criteria defining severe disease were present on admission in 12 patients; and initial parasitemia was 21 ± 6 %. Twelve patients received inotropic drugs. Pulmonary artery catheterization showed the following results in 7 patients: mean arterial pressure 57 ± 4 mmHg; pulmonary artery occlusion pressure 11 ± 1 mmHg; cardiac index 5.5 ± 0.9 l · min⁻¹· m⁻²; and systemic vascular resistance index 783 ± 122 dyne · s · cm⁻⁵· m⁻². Seven patients had evidence of bacterial infection at the time of shock. Of the 7 deaths (50 %), 5 were due to shock, with documented bacterial infection in all patients and persistent parasitemia in 4. Conclusions: Shock complicating severe falciparum malaria in adults is associated with peripheral vasodilation and carries a poor prognosis. In falciparum malaria with shock, bacterial coinfection should be suspected immediately and treated empirically with broad-spectrum antibiotics. Nevertheless, Plasmodium falciparum may contribute directly or indirectly to the onset of shock. Received: 26 May 1996 Accepted: 1 April 1997     

A comparison between continuous central venous pressure measurement from right atrium and abdominal vena cava or common iliac vein

Objective To determine the accuracy of meancontinuous central venous pressure (CVP) measurements in the abdominal vena cava.Design We simultaneously measured the CVP at the superior vena cava or right atrium and at the abdominal vena cava or common iliac vein. The study was conducted at the pediatric intensive care unit of a major university-affiliated medical center.Patients Nine patients, aged 6 months to 14 years, were included in our study.Measurements and results Elevencontinuous recordings of 12 to 68 min were taken, eight of them while the children were mechanically ventilated. Mean overall CVP ranged from 3 to 30 mmHg. A total of 519 simultaneous recordings were made, of which 515 (99.2%) were within the accepted limits of agreement of ±2 mmHg: 301 (58%) with CVP of ±mmHg, 189 (36,4%) with CVP of ±1 mmHg, and 25 (4.8%) with CVP of ±2 mmHg. The mean pressure difference was –0.22±1.52 mmHg. Accuracy was maintained within all ranges of CVP (3–10, 11–20, and 21–30 mmHg) and was not influenced by mechanical ventilation or abdominal fluid colection.Conclusion In children with no obstruction of blood flow from the abdominal vena cava to the right atrium, the pressure in the abdominal vena cava or common iliac vein accurately reflects the pressure in the right atrium.     

Early SjvO2 monitoring in patients with severe brain trauma

Objective: To investigate early cerebral variables after minimal resuscitation and to compare the adequacy of a cerebral perfusion pressure (CPP) guideline above 70 mmHg, with jugular bulb venous oxygen saturation (SjvO₂) monitoring in a patient with traumatic brain injury (TBI). Design: Prospective, observational study. Setting: Anesthesiological intensive care unit. Patients: 27 TBI patients with a postresuscitation Glasgow Coma Scale score less than 8. Intervention: After initial resuscitation, cerebral monitoring was performed and CPP increased to 70 mmHg by an increase in mean arterial pressure (MAP) with volume expansion and vasopressors as needed. Measurements and results: MAP, intracranial pressure (ICP), CPP, and simultaneous arterial and venous blood gases were measured at baseline and after treatment. Before treatment, 37 % of patients had an SjvO₂ below 55 %, and SjvO₂ was significantly correlated with CPP (r = 0.73, p < 0.0001). After treatment, we observed a significant increase (p < 0,0001) in CPP (78 ± 10 vs 53 ± 15 mmHg), MAP (103 ± 10 vs 79 ± 9 mmHg) and SvjO₂ (72 ± 7 vs 56 ± 12), without a significant change in ICP (25 ± 14 vs 25 ± 11 mmHg). Conclusion: The present study shows that early cerebral monitoring with SjvO₂ is critical to assess cerebral ischemic risk and that MAP monitoring alone is not sensitive enough to determine the state of oxygenation of the brain. SjvO₂ monitoring permits the early identification of patients with low CPP and high risk of cerebral ischemia. In emergency situations it can be used alone when ICP monitoring is contraindicated or not readily available. However, ICP monitoring gives complementary information necessary to adapt treatment. Received: 10 July 1998 Final revision received: 5 January 1999 Accepted: 20 January 1999     

Plasma endothelin-1 during central hypovolaemia in man

Summary. Endothelin-1 (ET-1) is a potent vasoconstricting peptide with effect on resistance as well as capacitance vessels. We followed ET-1 in arterial plasma together with heart rate (HR), central venous pressure (CVP), mean arterial pressure (MAP), and thoracic electrical impedance (TI) in seven men during central hypovolaemia induced by 50± head-up tilt. During tilting plasma ET-1 increased from 1.1 ±0.2 to 1.4 ± 0.3 pmol 1^-1 (mean ± SE) concomitant with an increase in total peripheral resistance (TPR) (from 15 ± 2 to 25 ± 3 mmHg min 1^-1) (P< 001), and HR (from 67 ± 2 to 94 ± 5 beats min^-1) (P<0.01) while MAP remained unchanged. CVP decreased (from 1.8±0.9 to -1.6±1.0 mmHg) (P<0.01) during tilting and remained unchanged during sustained tilt despite further reduction of central blood volume as recorded by TI. Presyncopal symptoms occurred after 28 ± 6 min associated with decreases in HR (to 70 ± 6 beats min^-1), MAP (from 90 ± 3 to 52 ± 4 mmHg) and TPR (to 11 ± 2 mmHg min l^-1) (P<0.01). At this time plasma ET-1 reached its highest level of 1.6±0.3 pmol l^-1 (P<0.01). Data show that head-up tilt is associated with increased plasma concentrations of ET-1 which may play a role in maintaining vascular tone in situations with a reduced central blood volume.     

The impact of perioperative atelectasis on antibiotic penetration into lung tissue: an in vivo microdialysis study

Objective  Postoperative pneumonia is a potentially devastating complication associated with high mortality in intensive care unit (ICU)-patients. One of the major predisposing factors is the perioperative occurrence of atelectatic formations in non-dependent lung areas. Perioperative ventilation/perfusion mismatch due to atelectasis may influence antibiotic distribution to lung tissue, hence increasing the risk of postoperative pneumonia. We evaluated whether differences in ventilation/perfusion mismatch can influence antibiotic distribution into lung tissue by means of in vivo microdialysis, comparing patients undergoing coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) (atelectasis model), with patients operated with the off-pump coronary artery bypass grafting (OPCAB)-technique. Patients and methods  We compared five patients operated with CPB (CPB-group) and five patients undergoing CABG with OPCAB-technique (OPCAB-group). Levofloxacin (500 mg) was administered intravenously, after surgery, in the ICU. Time versus concentration profiles of levofloxacin in lung tissue and plasma were measured at regular time-intervals. Results  In the OPCAB-group, the median of the maximum concentration of levofloxacin in lung tissue (4.1 μg ml⁻¹ ± 7, range 3.7–11.8 μg ml⁻¹) was significantly higher compared with the CPB-group (2.5 μg ml⁻¹ ± 0.3, range 2.0–2.9 μg ml⁻¹) (P = 0.046). Median levofloxacin tissue/plasma area under the concentration curve (AUC) ratio in lung tissue was 0.3 ± 0.2 (range 0.1–0.7) in the CPB-group versus 0.7 ± 1.6 (range 0.4–0.8) in the OPCAB-group (P = 0.015). Conclusions  Data indicate that postoperative interstitial antibiotic concentration is influenced by perioperative atelectasis formation. Our findings suggest the re-evaluation of clinical dosing schemas of antibiotic therapy in a variety of diseases associated with atelectasis formation.     

Strain and strain rate echocardiography for evaluation of right ventricular dysfunction in patients with idiopathic pulmonary arterial hypertension

Optimizing the non-invasive imaging of right ventricular (RV) function is of increasing interest for therapy monitoring and risk stratification in patients with idiopathic pulmonary hypertension (IPAH). Therefore, this study evaluated strain and strain rate echocardiography as a tool for comprehensive assessment of RV function and disease severity in IPAH patients. In 30 IPAH patients [WHO functional classes II–IV; mean pulmonary artery pressure (mPAP) 48.8 ± 12.5 mmHg; pulmonary vascular resistance (PVR) 7.9 ± 5.3 Wood units] and in 10 matched healthy control subjects’ two-dimensional echocardiography, 6-MWD and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels were obtained. In IPAH patients when compared with controls, RV systolic strain (−18.8 ± 4.3 vs. −34.5 ± 3.8%, p = 0.0016) and strain rate (−1.6 ± 0.6 vs. −2.7 ± 0.5 s⁻¹, p = 0.018) were significantly altered and correlated significantly with elevated NT-proBNP levels (r = 0.73 and r = 0.62; p < 0.001, respectively) and reduced 6-MWD (r = −0.76 and r = −0.81; p < 0.001). In IPAH patients, reduced strain correlated with both mPAP (r = 0.61, p = 0.01 for strain; and r = 0.55, p = 0.04 for strain rate, respectively), and PVR (r = 0.84, p < 0.001 for strain; and r = 0.67, p < 0.001 for strain rate, respectively). This study gives first comprehensive evidence that strain echocardiography allows accurate non-invasive assessment of RV function and disease severity in patients with IPAH.     

Use of bladder pressure to correct for the effect of expiratory muscle activity on central venous pressure

Objective To assess whether subtracting the expiratory change in intra-abdominal (bladder) pressure (ΔIAP) from central venous pressure (CVP) provides a reliable estimate of transmural CVP in spontaneously breathing patients with expiratory muscle activity. Design and setting Prospective observational study in a medical ICU. Patients Twenty-four spontaneously breathing patients with central venous and bladder catheters: 18 with no clinical evidence of active expiration (group 1) and 6 with active expiration (group 2). Interventions Patients in group 1 were coached to change their breathing pattern to one of active expiration for several breaths; those in group 2 were asked to sip water through a straw to briefly interrupt active expiration. Measurements and results During active expiration end-expiratory CVP (uncorrected CVP) and ΔIAP were measured; ΔIAP was subtracted from uncorrected CVP to obtain corrected CVP. End-expiratory CVP during relaxed breathing (best CVP) was assumed to represent the best estimate of transmural CVP. The absolute difference between corrected CVP and best CVP was much less than the difference between uncorrected CVP and best CVP (2.3 ± 2.0 vs. 12.5 ± 4.7 mmHg). Conclusions In patients with active expiration, subtracting ΔIAP from end-expiratory CVP yields a more reliable (and lower) estimate of transmural CVP than does the uncorrected CVP value. This article is discussed in the editorial available at: .     

Relation between invasive hemodynamics and measured glomerular filtration rate by 51Cr-EDTA clearance in advanced heart failure

The interaction between hemodynamics and kidney function in heart failure (HF) is incompletely understood. We investigated the association between invasive hemodynamic parameters and measured glomerular filtration rate (mGFR) by plasma clearance of 51-chromium-labeled ethylenediamine tetra-acetic acid (⁵¹Cr-EDTA) in patients with advanced HF and tested the hypothesis that patients with reduced mGFR have lower cardiac index (CI) and mean arterial pressure (MAP) as well as higher central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP). We retrospectively studied 242 patients (mean age 50?±?13?years) referred for evaluation for heart transplantation or implantation of a left ventricular assist device with a left ventricular ejection fraction < 45% on optimal medical therapy, who underwent right heart catheterization (RHC) and measurement of ⁵¹Cr-EDTA clearance. Mean mGFR was 63?±?21?mL/min/1.73 m², CI was 2.3?±?0.7?L/min/m², PCWP was 21?±?9?mmHg, and CVP was 10.3?±?5.2?mmHg. Univariate analysis demonstrated a significant correlation between mGFR and CI (r² = 0.030, p?=?.007) and CVP (r² = 0.017, p?=?.049) but not between mGFR and MAP or PCWP. In multivariate analyses, none of the hemodynamic variables remained significantly associated with mGFR. While CVP and CI were correlated with mGFR in univariate analysis the results of analyses adjusted for multiple covariates suggest that hemodynamics are only correlated to renal function in advanced HF to a modest degree challenging the hypothesis that renal dysfunction in HF mainly is a consequence of renal congestion.