M. Sydow

Comparison of cardiac output assessed by pulse-contour analysis and thermodilution in patients undergoing minimally invasive direct coronary artery bypass grafting

OBJECTIVE To investigate the precision and accuracy of continuous pulse contour cardiac output (PCCO) compared with intermittent transcardiopulmonary (TCPCO) and pulmonary artery thermodilution (TDCO) measurements in patients undergoing minimally invasive coronary bypass surgery (MIDCAB). DESIGN Prospective, controlled, clinical study. SETTING University hospital. PARTICIPANTS Twelve patients undergoing MIDCAB. INTERVENTIONS Thirty-six measurements of PCCO and thermodilution cardiac output (CO) were simultaneously performed after the start of surgery, during bypass grafting, and at the end of surgery. TCPCO and TDCO were simultaneously assessed by three injections of ice-cold saline randomly spread over the respiratory cycle. The pulse contour device was initially calibrated with an additional set of aortic thermodilution measurements. MEASUREMENTS AND MAIN RESULTS Absolute values of CO ranged between 1.6 and 9.2 L/min. A close agreement among the three techniques was observed at all measurements. Mean bias between PCCO and TDCO and TCPCO was 0.003 L/min (2 SD of differences between methods = 1.26 L/min) and 0.27 L/min (2 SD of differences between methods = 1.16 L/min), respectively. The correlation coefficients were r2 = 0.90 for TCPCO versus PCCO and r2 = 0.88 for TDCO versus PCCO. CONCLUSION The results of the present study show that compared with thermodilution CO, pulse contour analysis enables accurate measurement of continuous CO in patients undergoing MIDCAB.

Dynamic versus static respiratory mechanics in acute lung injury and acute respiratory distress syndrome.

Objectives:It is not clear whether the mechanical properties of the respiratory system assessed under the dynamic condition of mechanical ventilation are equivalent to those assessed under static conditions. We hypothesized that the analyses of dynamic and static respiratory mechanics provide different information in acute respiratory failure. Design:Prospective multiple-center study. Setting:Intensive care units of eight German university hospitals. Patients:A total of 28 patients with acute lung injury and acute respiratory distress syndrome. Interventions:None. Measurements:Dynamic respiratory mechanics were determined during ongoing mechanical ventilation with an incremental positive end-expiratory pressure (PEEP) protocol with PEEP steps of 2 cm H2O every ten breaths. Static respiratory mechanics were determined using a low-flow inflation. Main Results:The dynamic compliance was lower than the static compliance. The difference between dynamic and static compliance was dependent on alveolar pressure. At an alveolar pressure of 25 cm H2O, dynamic compliance was 29.8 (17.1) mL/cm H2O and static compliance was 59.6 (39.8) mL/cm H2O (median [interquartile range], p < .05). End-inspiratory volumes during the incremental PEEP trial coincided with the static pressure–volume curve, whereas end-expiratory volumes significantly exceeded the static pressure–volume curve. The differences could be attributed to PEEP-related recruitment, accounting for 40.8% (10.3%) of the total volume gain of 1964 (1449) mL during the incremental PEEP trial. Recruited volume per PEEP step increased from 6.4 (46) mL at zero end-expiratory pressure to 145 (91) mL at a PEEP of 20 cm H2O (p < .001). Dynamic compliance decreased at low alveolar pressure while recruitment simultaneously increased. Static mechanics did not allow this differentiation. The decrease in static compliance occurred at higher alveolar pressures compared with the dynamic analysis. Conclusions:Exploiting dynamic respiratory mechanics during incremental PEEP, both compliance and recruitment can be assessed simultaneously. Based on these findings, application of dynamic respiratory mechanics as a diagnostic tool in ventilated patients should be more appropriate than using static pressure–volume curves.

IMPROVED DETERMINATION OF STATIC COMPLIANCE BY AUTOMATED SINGLE VOLUME STEPS IN VENTILATED PATIENTS

A new method for determination the static compliance of the respiratory system is described (“static compliance by automated single steps”-SCASS). In 12 ventilated patients pressure/volume (P/V) curves were determined by automated repetitive occlusion (6 s) at single volume steps and compared to the conventional syringe method (SM). All measurements were corrected for effects of temperature, humidity and pressure (THP). SM was found to be significantly influenced by intrapulmonary gas exchange causing an effective mean volume deficit of 217.4±65.7 ml (BTPS) at the end of the deflation. In contrast to that, the short duration of occlusion in SCASS minimize the gas exchange effects. The methodical differences between both methods result in overestimation of the inflation compliance in the uncorrected SM (SMuncorr: 83.4±12.6; SCASS: 76.0±11.9 ml/cmH2O.p<0.01) and underestimation of the deflation compliance resp. (SMuncorr: 58.3±7.5; SCASS: 79.1±15.0 ml/cmH2O.p<0.005). In contrast to the P/V curves by SM no significant hysteresis was found by SCASS. Gas exchange seems to be the main reason for the hysteresis. Even after correcting gas exchange and THP effects a significant hyseresis remained. The SCASS method avoids these problems and allows furthermore an accurate checking of leaks.

High-dose intravenous magnesium sulfate in the management of life-threatening status asthmaticus

In severe status asthmaticus basic medical treatment often fails to improve the patients condition. Mechanical ventilation in this situation is associated with a high incidence of serious complications. After the bronchodilating effect of moderate-dose magnesium sulfate in asthmatic patients had been demonstrated in previous studies we treated five mechanically ventilated patients with refractory status asthmaticus successfully with high dosages of MgSO4 IV (10–20 g within 1 h depending on the bronchodilating effect). MgSO4 resulted in a significant decrease of peak airway pressure (43.0±6.8 to 32.0±8.0 cmH2O) and inspiratory flow resistance (22.7±7.0 to 11.9±6.0 cmH2O·l−1·s−1) within 1 h. The resulting serum magnesium levels after one hour were up to threefold of the normal serum levels. Although a main-tainance dose of 0.4 g/h had been administered continuously during the following 24 h serum magnesium decreased towards normal values within this time. The only relevant side-effect was a mild to moderate arterial hypotension in two of the five patients during the high dose administration period of MgSO4 which responded readily to dopamine treatment.

Determination of functional residual capacity (FRC) by multibreath nitrogen washout in a lung model and in mechanically ventilated patients

Objective: Validation of an open-circuit multibreath nitrogen washout technique (MBNW) for measurement of functional residual capacity (FRC). The accuracy of FRC measurement with and without continuous viscosity correction of mass spectrometer delay time (TD) relative to gas flow signal and the influence of baseline FIO2 was investigated. Design: Laboratory study and measurements in mechanically ventilated patients. Setting: Experimental laboratory and anesthesiological intensive care unit of a university hospital. Patients: 16 postoperative patients with normal pulmonary function (NORM), 8 patients with acute lung injury (ALI) and 6 patients with chronic obstructive pulmonary disease (COPD) were included. Interventions: Change of FIO2 from baseline to 1.0. Measurements and main results: FRC was determined by MBNW using continuous viscosity correction of TD (TDdyn), a constant TD based on the viscosity of a calibration gas mixture (TD0) and a constant TD referring to the mean viscosity between onset and end of MBNW (TDmean). Using TDdyn, the mean deviation between 15 measurements of three different lung model FRCs (FRCmeasured) and absolute volumes (FRCmodel) was 0.2 %. For baseline FIO2 ranging from 0.21 to 0.8, the mean deviation between FRCmeasured and FRCmodel was −0.8 %. However, depending on baseline FIO2, the calculation of FRC using TDmean and TD0 increased the mean deviation between FRCmeasured and FRCmodel to 2–4 % and 8–12 %, respectively. In patients (n = 30) the average repeatability coefficient was 6.0 %. FRC determinations with TDmean and TD0 were 0.8–13.3 % and 4.2–23.9 % (median 2.7 % and 8.7 %) smaller than those calculated with TDdyn.Conclusion: A dynamic viscosity correction of TD improves the accuracy of FRC determinations by MBNW considerably, when gas concentrations are measured in a sidestream. If dynamic TD correction cannot be performed, the use of constant TDmean might be suitable. However, in patient measurements this can cause an FRC underestimation of up to 13 %.

Effect of low-level PEEP on inspiratory work of breathing in intubated patients, both with healthy lungs and with COPD

ObjectiveEvaluation of low-level PEEP (5 cm H2O) and the two different CPAP trigger modes in the Bennett 7200a ventilator (demand-valve and flow-by trigger modes) on inspiratory work of breathing (Wi) during the weaning phase.DesignProspective controlled study.SettingThe intensive care unit of a university hospital.PatientsSix intubated patients with normal lung function (NL), ventilated because of non-pulmonary trauma or post-operative stay in the ICU, and six patients recovering from acute respiratory failure due to exacerbation of chronic obstructive pulmonary disease (COPD), breathing either FB-CPAP or DV-CPAP with the Bennett 7200a ventilator.InterventionsThe patients studied were breathing with zero end-expiratory pressure (ZEEP), as well as CPAP of 5 cm H2O (PEEP), with the following respiratory modes: the demand-valve trigger mode, pressure support of 5 cm H2O, and the flow-by trigger mode (base flow of 20 l/min and flow trigger of 2 l/min). Furthermore, Wi during T-piece breathing was evaluated.Measurements and resultsWi was determined using a modified Campbells diagram. Total inspiratory work (Wi), work against flow-resistive resistance (Wires), work against elastic resistance (Wiel), work imposed by the ventilator system (Wimp), dynamic intrinsic positive end-expiratory pressure (PEEPidyn), airway pressure decrease during beginning inspiration (Paw) and spirometric parameters were measured. In the NL group, only minor, clinically irrelevant changes in the measured variables were detected. In the COPD group, in contrast, PEEP reduced Wi and its components Wires and Wiel significantly compared to the corresponding ZEEP settings. This was due mainly to a significant decrease in PEEPidyn when external PEEP was applied. Flow-by imposed less Wi on the COPD patients during PEEP than did demand-valve CPAP. Differences in Wimp between the flow-by and demand-valve trigger models were significant for both groups. However, in relation to Wi these differences were small.ConclusionWe conclude that the application of low-level external PEEP benefits COPD patients because it reduces inspiratory work, mainly by lowering the inspiratory threshold represented by PEEPidyn. Differences between the trigger modes of the ventilator used in this study were small and can be compensated for by the application of a small amount of pressure support.

A RATIONAL BASIS FOR THE MEASUREMENT OF FREE PHENYTOIN CONCENTRATION IN CRITICALLY ILL TRAUMA PATIENTS

Phenytoin binding to serum proteins and factors influencing protein binding were investigated in 38 critically ill trauma patients. In 24% of these patients, the free fraction of phenytoin was ≤10%, whereas in 76%, the free phenytoin fraction was increased >10%—up to 24%. Nonantiepileptic co-medication, sex, or age had no influence on phenytoin binding in any of the 38 patients. Elevated free phenytoin fraction was found in those with hypoalbuminemia and hepatic and renal impairments. In these patients, the free phenytoin fraction should be measured routinely.

Postoperative pulmonary complication rate and long‐term changes in respiratory function following esophagectomy with esophagogastrostomy

Upper abdominal surgery has a high incidence of postoperative respiratory complications. Although operations involving a thoracic as well as an upper abdominal incision as encountered in esophageal surgery are likely to be associated with an even higher complication rate and perhaps permanent alterations of respiratory function, only a few studies have addressed this problem. We evaluated the postoperative course of patients undergoing thoracoabdominal esophagectomy with esophagogastrostomy. Twenty patients were evaluated, of whom 10 (50%) developed respiratory complications as defined by our criteria, which were the simultaneous occurrence of rectal temperature over 38°C on the first postoperative day and radiographic evidence of pulmonary infiltration. Although there is no general consensus regarding the diagnostic criteria of a postoperative pulmonary complication, we were able to validate the clinical relevance of our definition by showing that these patients suffered from a more severe and more prolonged impairment of global oxygen exchange than those who did not fulfill the criteria. They also required a longer period of respiratory support (median duration of intubation 12 vs. 3 days, P<0.005). A comparison of the preoperative pulmonary function with that determined at least 6 months after the operation showed that only vital capacity (VC) and total lung capacity (TLC) were significantly (P<0.05) reduced following the operation, but not to a clinically relevant degree (VC ‐6%, TLC ‐7%).

Variation of nitric oxide concentration during inspiration.

OBJECTIVE To evaluate the pattern of inspiratory nitric oxide concentration in a simple, constant flow delivery system during the use of two phasic-flow ventilatory modes. DESIGN Laboratory study in a lung model. SETTING University experimental laboratory. SUBJECT Nitric oxide (800 ppm in nitrogen) was administered continuously into the inspiratory circuit to deliver a nitric oxide concentration of 10 and 40 ppm to a test lung during volume-controlled (constant flow) and pressure-controlled (decelerating flow) ventilation, with an FIO2 of 1.0. INTERVENTIONS In each mode, minute ventilation of 7, 14, and 21 L/min and installation of mixing chambers (none, 1-L, 2-L, and 3.2-L turbulence boxes) were studied, respectively. Nitric oxide and nitric dioxide were monitored by chemiluminescence. Since the nitric oxide/nitrogen gas is the only nitrogen source in the system during ventilation with an FIO2 of 1.0, we evaluated the fluctuation in the inspiratory nitric oxide (NOx) concentration by measuring nitrogen with a fast-response analyzer. To test the effect of the measurement site, we measured nitric oxide concentrations using chemiluminescence at different positions in the inspiratory and expiratory limbs, with and without the mixing chambers, with a minute ventilation of 14 L/min and a nitric oxide concentration of 40 ppm. MEASUREMENTS AND MAIN RESULTS Nitrogen dioxide production was not influenced by the flow pattern. During a nitric oxide concentration of 10 ppm, nitrogen dioxide was always < 0.6 ppm. During a nitric oxide concentration of 40 ppm, the highest nitrogen dioxide (4.47 ppm) concentration was found at the lowest minute ventilation and the largest inspiratory circuit volume. Nitric oxide values displayed by chemiluminescence indicated stable concentrations at all settings. However, without mixing chambers, NOx concentration calculated from nitrogen measurements demonstrated marked inspiratory fluctuations and was highest with a minute ventilation of 21 L/min and higher during pressure-controlled ventilation compared with volume-controlled ventilation (nitric oxide concentration of 40 ppm, pressure-controlled ventilation: 14.5 to 130.5 ppm; volume-controlled ventilation: 21.6 to 104.7 ppm; nitric oxide concentration of 10 ppm, pressure-controlled ventilation: 3.2 to 30.9 ppm; volume-controlled ventilation: 4.5 to 27.1 ppm). NOx concentration fluctuation decreased with an increasing mixing chamber, and was negligible at all settings with the 3.2-L turbulence box. Nitric oxide concentration fluctuation influenced chemiluminescence measurements. The displayed nitric oxide values varied, depending on the sampling site, and did not accurately reflect mean inspiratory nitric oxide concentration. Incorporation of a mixing chamber eradicated this sampling site influence. CONCLUSIONS Continuous flow delivery of nitric oxide into the circuit of a phasic-flow ventilator results in marked inspiratory nitric oxide concentration fluctuation that is not detected by a slow-response chemiluminescence analyzer. Moreover, nitric oxide concentration fluctuation can influence the accuracy of the chemiluminescence measurements. These effects can be diminished by using additional mixing chambers to facilitate a stable gas concentration. As these mixing volumes increase the contact time of nitric oxide with oxygen, an increase of nitrogen dioxide has to be taken into account.

Total intravenous anaesthesia with methohexitone-alfentanil or propofol-alfentanil. Clinical aspects and hemodynamic, endocrine, and metabolic effects

Zusammenfassung. Die totale intravenöse Anästhesie (TIVA) gewinnt zunehmend an Popularität als Narkoseverfahren auch für abdominalchirurgische Eingriffe. Bei weniger traumatisierenden Eingriffen, bei denen eine absichtlich verzögerte Aufwachphase nicht erforderlich ist, bieten sich Methohexital und Propofol aufgrund ihrer Pharmakokinetik als hypnotischer Bestandteil eines solchen Anästhesieverfahrens an. In der vorliegenden randomisierten und kontrollierten Studie an 27 gesunden Frauen, bei denen eine Hysterektomie durchgeführt wurde, wurden beide Hypnotika in Kombination mit Alfentanil als Analgetikum miteinander und mit einer balanzierten Anästhesie (Isofluran-Lachgas, Fentanyl) verglichen. Als Zielparameter dienten Hämodynamik (arterieller Blutdruck, Herzfrequenz), postoperative Befindlichkeit (Übelkeit-Erbrechen, Zittern, Schmerzmittelbedarf) sowie endokrine und metabolische Streßreaktionen (Katecholamine, Kortisol, Prolaktin, Glukose, freie Fettsäuren, Laktat). Es fanden sich kaum nennenswerte Unterschiede zwischen den beiden TIVA-Verfahren, wohl aber zwischen den TIVA-Verfahren und der balanzierten Anästhesie. Der hämodynamische Verlauf war in allen Gruppen im wesentlichen gleich, aber die intraoperativen Streßreaktionen wurden durch die TIVA effektiver gedämpft. Die Aufwachzeit war nach der balanzierten Anästhesie, die Inzidenz des postoperativen Zitterns nach der Propofol-Alfentanil TIVA am geringsten. Die Häufigkeit postoperativen Erbrechens war in allen Gruppen gleich. Die Ergebnisse der Studie belegen einige Vorteile der TIVA gegenüber der balanzierten Anästhesie. Sie geben jedoch keine eindeutige Entscheidungsgrundlage für oder gegen eines der untersuchten Hypnotika.Abstract. Total intravenous anaesthesia (TIVA) using a combination of a hypnotic and an analgesic agent is gaining increasing popularity as an alternative to balanced anaesthesia with volatile anaesthetics for abdominal surgery. Among the required characteristics of the drugs used in this technique are a good correlation between dose, plasma concentrations, and effect as well as rapid elimination from the circulation, allowing close control of anaesthetic depth. Two hypnotic drugs with similar pharmacokinetic and pharmacodynamic profiles are propofol and methohexitone, both of which can be employed as a component of a TIVA technique. Two TIVA combinations utilising either of these drugs with alfentanil were tested against isoflurane-nitrous oxide in a balanced regimen. Methods. Twenty-seven healthy women undergoing hysterectomy for non-malignant diseases participated in the study after having given written consent. They were randomly allocated to receive either isoflurane (Iso), methohexital-alfentanil (M-A), or propofol-alfentanil (P-A). Blood samples for determination of cortisol, prolactin, catecholamines, glucose, lactate, non-esterified fatty acids, and pharmacon concentrations were drawn repeatedly from before induction until 360 min after surgery. Anaesthesia was induced in group Iso with fentanyl 0.1 mg and M 1.5 mg⋅kg−1 and maintained with Iso-N2O. In the TIVA groups M or P was given in a two-step infusion to load peripheral compartments and then maintain plasma concentrations within the hypnotic range. A was given as a continuous infusion in an identical dose (0.1 mg⋅kg−1 initial, 0.125 mg⋅kg−1⋅h−1 maintenance) in both groups. If signs of insufficient depth of anaesthesia occurred (heart rate or systolic blood pressure >25% above baseline), then first A (0.5 – 1 mg), and if that was ineffective, then 50 mg hypnotic was administered. The A infusion was stopped 30 min before the end of surgery, and Iso or the hypnotic was stopped at skin closure. Recovery time was the time until the patients were able to give their birth date after stopping the Iso or hypnotic. Results. The three groups were comparable with regard to age, weight, and duration of surgery. The total doses of M and P were 1,357±125 mg (mean±SEM) and 1,315±121 mg, respectively, and the total A doses were 20.7±2.5 mg (M-A) and 23.4±3.5 (P-A). The peak plasma concentrations were P 10.6±1.5 µg⋅ml−1 and M 12.4±2.6 µg⋅ml−1. At the end of surgery the P concentrations were in the projected range while those of M were somewhat lower than expected (P3.7±0.4 µg⋅ml−1; M 3.5±0.6 µg⋅ml−1). Three patients each in the P-A and M-A groups required supplementary A injections. Five patients in the P-A group required additional bolus injections of the hypnotic as compared to 2 in the M-A group. The median recovery times were Iso 15 min, M-A 50 min, and P-A 25 min (P<0.05). The incidence of shivering was Iso 3/9, M-A 5/9, and P-A 0/9 (P<0.05); vomiting occurred with equal frequency in all groups (Iso 33%, M-A 33%, P-A 22%). The patients were somewhat more restless in group M-A. Systolic blood pressure dropped in a similar manner in all groups after induction of anaesthesia (Iso −31%, M-A −37%, P-A −36%) but recovered during surgery. The intraoperative response of cortisol (Iso +216%, M-A +92%, P-A +43%) and catecholamines (noradrenaline Iso +56%, M-A +30%, P-A −21%) was lower in the TIVA groups, whereas prolactin increased after induction in all groups. Plasma concentrations of glucose, lactate, and fatty acids were lower in the TIVA groups than in the Iso group intraoperatively, but increased to comparable postoperative levels. Conclusions. Both TIVA regimens are acceptable alternatives to balanced anaesthesia with Iso N2O. Both are similar with regard to haemodynamic, endocrine, and metabolic changes and are able to reduce the stress response more effectively than Iso N2O. Of the two, P seems to offer the advantage of a somewhat shorter recovery time, less shivering, and calmer patients in the immediate postoperative period, although M might be preferred if economic considerations are important.