Cardiac output measurement in children: comparison of Aesculon cardiac output monitor and thermodilution

Background: We compared cardiac output (CO) measurements by the non-invasiveelectrical velocimetry (Aesculon^®) monitor with the pulmonaryartery catheter (PAC) thermodilution method in children. Methods: CO values using the Aesculon^® monitor and PAC thermodilutionwere simultaneously recorded during cardiac catheterizationin children. Measurements were performed under general anaesthesia.To compare, three consecutive measurements for each patientwithin 3 min were obtained. The means of the three values werecompared using simple regression and Bland–Altman analysis.Data were presented as mean (SD). A mean percentage of <30%was defined to indicate clinical useful reliability of the Aesculon^®monitor. Results: A total of 50 patients with a median (range) age of 7.5 (0.5–16.5)yr were enrolled in the study. Mean CO values were 3.7 (1.5)litre min^–1 (PAC thermodilution) and 3.1 (1.7) litre min^–1(Aesculon^® monitor). Analysis for CO measurement showeda good correlation between the two methods (r=0.894; P<0.0001).The bias between the two methods was 0.66 litre min^–1with a precision of 1.49 litre min^–1. The mean percentageerror for CO measurements was 48.9% for the Aesculon^® monitorwhen compared with PAC thermodilution. Conclusions: Electrical velocimetry using the Aesculon^® monitor did notprovide reliable CO values when compared with PAC thermodilution.Whether the Aesculon^® monitor can be used as a CO trendmonitor has to be assessed by further investigations in patientswith changing haemodynamics.     

Evaluation of an uncalibrated arterial pulse contour cardiac output monitoring system in cirrhotic patients undergoing liver surgery

Background: The pulmonary artery catheter is invasive and may cause seriouscomplications. A safe method of cardiac output (CO) measurementis needed. We have assessed the accuracy and reliability ofa recently marketed self-calibrating arterial pulse contourCO monitoring system (FloTrac/Vigileo^TM) in end-stage liverfailure patients undergoing liver transplant. The pattern ofalterations known as cirrhotic cardiomyopathy, and the transplantprocedure itself, provided an evaluation under varying clinicalconditions. Methods: The cardiac index was measured simultaneously by thermodilution(CI_TD: mean of four readings) using a pulmonary artery catheterand pulse contour analysis (CI_V: mean value computed by theFloTrac/Vigileo^TM over the same time period). Readings weremade at 10 time-points during liver transplant surgery (T1–T5)and on the intensive care unit (T6–T10). CI_V was computedusing the latest Vigileo software version 01.10. Results: A total of 290 paired readings from 29 patients were collected.Mean (SD) CI_TD was 5.2 (1.3) and CI_V was 3.9 (0.9) litre min^–1m^–2, with a corrected for repeated measures bias betweenreadings of 1.3 (0.2) litre min^–1 m^–2 and 95% limitsof agreement of –1.5 (0.2) to 4.1 (0.3) litre min^–1m^–2. The percentage error (2SD_Bias/meanCI_TD) was 54%,which exceeded a 30% limit of acceptance. Low peripheral resistanceand increasing bias were related (r=0.69; P<0.001). The Vigileosystem failed to reliably trend CI data, with a concordancecompared with thermodilution below an acceptable level (at best68% of sequential readings). Conclusions: In cirrhotic patients with hyperdynamic circulation, the Vigileosystem showed a degree of error and unreliability higher thanthat considered acceptable for clinical purposes.     

Performance of a minimally invasive uncalibrated cardiac output monitoring system (Flotrac/Vigileo) in haemodynamically unstable patients

Background: Early haemodynamic assessment is of particular importance inthe evaluation of haemodynamically compromised patients, butis often precluded by the invasiveness and complexity of theestablished cardiac output (CO) monitoring techniques. The FloTrac^TM/Vigileo^TMsystem allows minimally invasive CO determination based on thearterial pressure waveform derived from any standard arterialcatheter, and the algorithm underlying CO calculation was recentlymodified to allow a more precise estimate of aortic compliance. Methods: Using the new software, we studied 25 haemodynamically unstablepatients who had a radial artery catheter and underwent invasivehaemodynamic monitoring with the PiCCO^TM system. PiCCO^TM-derivedtranspulmonary thermodilution and pulse contour CO (reference-CO)were compared with the CO values obtained with the FloTrac^TM/Vigileo^TMsystem (AP-CO). Reported CO values are indexed to body surfacearea. Agreement between reference-CO and AP-CO recorded duringroutine clinical care was assessed using Bland–Altmanstatistics. Results: Overall bias between the reference-CO and the AP-CO (n=324)was 0.68 litre min^–1 m^–2 with a high percentageerror of ± 58.8% (95% limits of agreement ± 1.94l min^–1 m^–2). There was a significant difference(P<0.001) between the radial and the femoral mean arterialpressures, and bias was significantly larger for a mean pressuredifference of >5 mm Hg (0.93 vs 0.57 litre min^–1 m^–2,P=0.032). No connection was found between the norepinephrinedose and the CO agreement. Conclusions: Despite the updated algorithm, AP-CO still showed a limitedagreement with the reference-CO and systematically underestimatedthe CO so that the method is not suitable to replace invasiveCO monitoring at present.     

Semi-invasive monitoring of cardiac output by a new device using arterial pressure waveform analysis: a comparison with intermittent pulmonary artery thermodilution in patients undergoing cardiac surgery

BACKGROUND: Thermodilution technique using a pulmonary artery catheter (PAC)is a widely used method to determine cardiac output (CO). Itis increasingly criticized because of its invasiveness and itsunclear risk–benefit ratio. Thus, less invasive techniquesfor measuring CO are highly desirable. We compared a new, semi-invasivedevice (FloTrac/Vigileo^TM) using arterial pressure waveformanalysis for CO measurement in patients undergoing cardiac surgerywith bolus thermodilution measurements. METHODS: Forty patients undergoing coronary artery bypass grafting orvalve repair were enrolled. A PAC was inserted and routine radialarterial access was used for semi-invasive determination ofCO with the Vigileo. CO was measured simultaneously by bolusthermodilution and the Vigileo technique after induction ofanaesthesia (T1), before cardiopulmonary bypass (CPB) (T2),after CPB (T3), after sternal closure (T4), on arrival in theintensive care unit (ICU) (T5), and 4 h (T6), 8 h(T7), and 24 h after surgery (T8). CO was indexed to thebody surface area (cardiac index, CI). RESULTS: A total of 244 pairs of CI measurements were analysed. Biasand precision (1.96 SD of the bias) were 0.46 litre min^–1m^–2 and ± 1.15 litre min^–1 m^–2 (r =0.53) resulting in an overall percentage error of 46%. Subgroupanalysis revealed a percentage error of 51% for data pairs obtainedintraoperatively (T1–T4), 42% in ICU (T5–T8), and56% for values obtained during low CI (T1–T8). CONCLUSIONS: In cardiac surgery patients, CO measured by a new semi-invasivearterial pressure waveform analysis device showed only moderateagreement with intermittent pulmonary artery thermodilutionmeasurement.     

A comparison of cardiac output derived from the arterial pressure wave against thermodilution in cardiac surgery patients

In three clinical centres, we compared a new method for measuringcardiac output with conventional thermodilution. The new methodcomputes beat-to-beat cardiac output from radial artery pressureby simulating a three-element model of aortic input impedance,and includes non-linear aortic mechanical properties and a self-adaptingsystemic vascular resistance. We compared cardiac output bycontinuous model simulation (MF) with thermodilution cardiacoutput (TD) in 54 patients (18 female, 36 male) undergoing coronaryartery bypass surgery. We made three or four conventional thermodilutionestimates spread equally over the ventilatory cycle. In 490series of measurements, thermodilution cardiac output rangedfrom 2.1 to 9.3, mean 5.0 litre min^–1. MF differed +0.32(1.0) litre min^–1 on average with limits of agreementof –1.68 and +2.32 litre min^–1. Differences decreasedwhen the first series of measurements in a patient was usedto calibrate the model. In 436 remaining series, the mean differencebecame –0.13 (0.47) litre min^–1 with limits of agreementof –1.05 and +0.79 litre min^–1. When consecutivemeasurements were made, the change was greater than 0.5 litremin^–1, on 204 occasions. The direction of change was thesame with both methods in 199. The difference between the methodsremained near zero during surgery suggesting that a single calibrationper patient was adequate. Aortic model simulation with radialartery pressure as input reliably monitors changes in cardiacoutput in cardiac surgery patients. Before calibration, themodel cannot replace thermodilution, but after calibration themodel method can quantitatively replace further thermodilutionestimates. Br J Anaesth 2001; 87: 212–22     

Does the optimization of cardiac output by fluid loading increase splanchnic blood flow?

We studied the effects of increasing cardiac output by fluidloading on splanchnic blood flow in patients with haemodynamicallystabilized septic shock. Eight patients (five female, 39–86yr) were assessed using a transpulmonary thermo-dye-dilutiontechnique for the measurement of cardiac index (CI) intrathoracicblood volume (ITBV) as a marker of cardiac preload and totalblood volume (TBV). Splanchnic blood flow was measured by thesteady state indocyanine-green technique using a hepatic venouscatheter. Gastric mucosal blood flow was estimated by regionalcarbon dioxide tension (PR_CO2). Hydroxyethyl starch was infusedto increase cardiac output while mean arterial pressure waskept constant. In parallel, mean norepinephrine dosage couldbe reduced from 0.59 to 0.33 µg kg^–1 min^–1.Mean (SD) TBV index increased from 2549 (365) to 3125 (447)ml m^–2, as did ITBV index from 888 (167) to 1075 (266)ml m^–2 and CI from 3.6 (1.0) to 4.6 (1.0) litre min^–1m^–2. Despite marked individual differences, splanchnicblood flow did not change significantly neither absolutely (from1.09 (0.96) to 1.19 (0.91) litre min^–1 m^–2) norfractionally as part of CI (from 28.4 (19.5) to 24.9 (16.3)%).Gastric mucosal PR_CO2 increased from 7.7 (2.6) to 8.3 (3.1)kPa. The PCO₂-gap, the difference between regional and end-tidalPCO₂, increased slightly from 3.2 (2.7) to 3.4 (3.1) kPa. Thus,an increase in cardiac output as a result of fluid loading isnot necessarily associated with an increase in splanchnic bloodflow in patients with stabilized septic shock. Br J Anaesth 2001; 86: 657–62     

Simultaneous measurement of cardiac output by thermodilution, thoracic electrical bioimpedance and Doppler ultrasound

To evaluate the accuracy of two non-invasive techniques forcardiac output (CO) measurement, we have measured CO simultaneouslyby thoracic electrical bioimpedance (TEB), pulsed Doppler ultrasound(DU) and standard thermodilution methods (TD) under differentclinical conditions. Measurements were made in 10 patients:(I) during steady state anaesthesia with controlled IPPV ventilation(n = 131), spread over the entire ventilatory cycle; (II) duringapnoea (n = 56); (III) during spontaneous breathing (n = 152)in the intensive care unit. Mean (SD) cardiac output valueswere: (I) CO_TD 3.5 (1.0) litre min^–1, CO_TEB 3.4 (0.7)litre min^–1 CO_DU 2.8 (0.7) litre min^–1; (II) CO_TD3.6 (0.6) litre min^–1, CO_TEB 3.5 (0.4) litre min^–1,CO_DU 2.9 (0.7) litre min^–1; (III) CO_TD 7.7 (1.5) litremin^–1, CO_TEB 7.6 (1.9) litre min^–1, CO_DU 5.2 (1.4)litre min^–1. The mean percentage deviation of TEB fromTD ranged from –2.2% to 1.4% and that of DU from TD wasfrom –16% to –32%. There were no statistically significantdifferences between TD and TEB, but TD and DU differed significantlyduring IPPV, apnoea and spontaneous ventilation (P < 0.0001).(Br. J. Anaesth. 1994; 72:133–138) ^*Department of Anaesthesiology, Caritas Krankenhaus, Werkstr.1, 66763 Dillingen/Saar, Germany      

Effects of mid-line thoracotomy on the interaction between mechanical ventilation and cardiac filling during cardiac surgery

Background. Mid-line thoracotomy is a standard approach forcardiac surgery. However, little is known how this surgicalapproach affects the interaction between the circulation andmechanical ventilation. We studied how mid-line thoracotomyaffects cardiac filling volumes and cardiovascular haemodynamics,particularly variations in stroke volume and pulse pressurecaused by mechanical ventilation. Methods. We studied 19 patients during elective coronary arterybypass surgery. Before and after mid-line thoracotomy, we measuredarterial pressure, cardiac index (CI) and global end-diastolicvolume index (GEDVI) by thermodilution, left ventricular end-diastolicarea index (LVEDAI) by transoesophageal echocardiography andthe variations in left ventricular stroke volume and pulse pressureduring ventilation by arterial pulse contour analysis. Results. After thoracotomy, CI increased from 2.3 (0.4) to 2.9(0.6) litre min^–1 m^–2, GEDVI increased from 605(110) to 640 (94) litre min^–1 m^–2, and LVEDAI increasedfrom 9.2 (3.7) to 11.2 (4.1) cm² m^–2. All these changeswere significant. In contrast, stroke volume variation (SVV)decreased from 10 (3) to 6 (2)% and pulse pressure variation(PPV) decreased from 11 (3) to 5 (3)%. Before thoracotomy, SVVand PPV significantly correlated with GEDVI (both P<0.01).When the chest was open, similar significant correlations ofSVV (P<0.001) and PPV (P<0.01) were found with GEDVI. Conclusion. Thoracotomy increases cardiac filling and preload.Further, thoracotomy reduces the effect of mechanical ventilationon left ventricular stroke volume. However, also under openchest conditions, SVV and PPV are preload-dependent. Br J Anaesth 2004; 92: 808–13     

Pharmacodynamic modelling of the bispectral index response to propofol-based anaesthesia during general surgery in children

Background: This study describes a pharmacodynamic model during generalanaesthesia in children relating the bispectral index (BIS)response to the anaesthetic dosing of propofol, fentanyl, andremifentanil. Methods: BIS, heart rate, mean arterial pressure, sedation scores, andanaesthetic protocols from 59 children aged 1–16 yr undergoinggeneral surgery were considered for the study. Anaesthesia wasperformed with propofol, fentanyl, and remifentanil. A sigmoidmodel assuming additive interaction of propofol, fentanyl, andremifentanil was fitted to individual BIS as effect variable.The pharmacodynamic parameters were estimated by non-linearregression analysis. The ability of BIS to predict anaestheticdrug effect was quantified by the prediction probability Pk. Results: BIS started at a baseline of 90 (9), decreased during inductionto 30 (14) and remained at 57 (10) during anaesthesia. BIS predictedthe anaesthetic drug effect with a Pk of 0.79 (0.08). The EC_50Propofol and the k_{e0 Propofol} were 5.2 (2.7) µg ml^–1and 0.60 (0.45) min^–1, respectively. The k_{e0 Propofol}decreased from approximately 0.91 min^–1 at 1 yr to 0.15min^–1 at 16 yr. The EC_{50 Remifentanil}, k_{e0 Remifentanil},EC_{50 Fentanyl}, and the k_{e0 Fentanyl} were 24.1 (13.0) ng ml^–1,0.71 (0.32) min^–1, 8.6 (7.4) ng ml^–1, and 0.28 (0.46)min^–1, respectively. Conclusions: The effect equilibration half-time of propofol in children wasage dependent. The pharmacodynamics of fentanyl and remifentanilin children were similar to those reported in adults. The BISshowed a close relationship to the modelled effect-site concentration,and therefore, it may serve as a measure of anaesthetic drugeffect in children older than 1 yr.     

Oesophageal Doppler monitoring overestimates cardiac output during lumbar epidural anaesthesia

Oesophageal Doppler monitoring (ODM) has been advocated as anon-invasive means of measuring cardiac output (CO). However,its reliance upon blood flow measurement in the descending aortato estimate CO is susceptible to error if blood flow is redistributedbetween the upper and lower body. We hypothesize that lumbarepidural anesthesia (LEA), which causes blood flow redistribution,causes errors in CO estimates. We compared ODM with thermodilution(TD) measurements in fourteen patients under general anaesthesiafor radical prostatectomy, who had received an epidural catheterat the intervertebral level L2–L3. Coupled measurementsof CO by means of the TD and ODM techniques were performed atbaseline (general anaesthetic only) and after epidural administrationof 10 ml of 0.25% bupivacaine. The two methods were comparedusing Bland-Altman analysis: before LEA there was a bias of–0.89 litre min^–1 with limits of agreement rangingbetween –2.67 and +0.88 litre min^–1. Following lumbarsympathetic block, bias became positive (+0.55 litre min^–1)and limits of agreement increased to –3.21 and +4.30 litremin^–1. ODM measured a greater increase in CO after LEA(     

Less invasive determination of cardiac output from the arterial pressure by aortic diameter-calibrated pulse contour

Background. Cardiac output by modelflow pulse contour methodcan be monitored quantitatively and continuously only afteran initial calibration, to adapt the model to an individualpatient. The modelflow method computes beat-to-beat cardiacoutput (COmf) from the radial artery pressure, by simulatinga three-element model of aortic impedance with post-mortem datafrom human aortas. Methods. In our improved version of modelflow (COmfc) we adaptedthis model to a real time measure of the aortic cross-sectionalarea (CSA) of the descending aorta just above the diaphragm,measured by a new transoesophageal echo device (HemoSonic 100).COmf and COmfc were compared with thermodilution cardiac output(COtd) in 24 patients in the intensive care unit. Each thermodilutionvalue was the mean of four measurements equally spread overthe ventilatory cycle. Results. Least squares regression of COtd vs COmf gave y=1.09x[95%confidence interval (CI) 0.96–1.22], R²=0.15, and of COtdvs COmfc resulted in y=1.02x(95% CI 0.96–1.08), R²=0.69.The limits of agreement of the un-calibrated COmf were –3.53to 2.79, bias=0.37 litre min^–1 and of the diameter-calibratedmethod COmfc, –1.48 to 1.32, bias=–0.08 litre min^–1.The coefficient of variation for the difference between methodsdecreased from 28 (un-calibrated) to 12% after diameter-calibration. Conclusions. After diameter-calibration, the improved modelflowpulse contour method reliably estimates cardiac output withoutthe need of a calibration with thermodilution, leading to aless invasive cardiac output monitoring method.      

Continuous and intermittent cardiac output measurement: pulmonary artery catheter versus aortic transpulmonary technique

Background. Cardiac output (CO) can be measured intermittentlyby bolus thermodilution methods in the pulmonary artery (COpa)or in the aorta (COart). A continuous thermodilution method(CCO) and a method for continuous estimation using the arterialpulse wave (PCCO) are also available. Methods. We compared two methods of intermittent CO measurementsin patients during liver transplantation: COpa, regarded asthe current clinical standard, and an aortic transpulmonarythermodilution technique (COart) performed with the PiCCO system.We also compared CCO and PCCO. Measurements were made in 62patients at three stages: after the induction of anaesthesia,after caval clamping phase, and at the end of surgery. We usedBland–Altman and correlation analysis. Results. We found close agreement between the techniques. Meanbias between COart and COpa and PCCO and CCO was 0.15 (2SDof differences between methods=1.74) litre min^–1and –0.03 (1.75) litre min^–1, respectively.Mean bias between CCO and COpa and PCCO and COpa was 0.02 (1.48)litre min^–1 and 0.04 (1.69) litre min^–1,respectively. Conclusions. Measurement with the aortic transpulmonary thermodilutiontechnique gives continuous and intermittent values that agreewith the pulmonary thermodilution method. Br J Anaesth 2002; 88: 350–6     

Clinical evaluation of the FloTrac/Vigileo system and two established continuous cardiac output monitoring devices in patients undergoing cardiac surgery

Background: Assessment of cardiac output (CO) by the FloTrac/Vigileo^TM systemmay offer a less invasive means of determining the CO than eitherthe pulmonary artery catheter (PAC) or the PiCCOplus^TM system.The aim of this study was to compare CO measurements made usingthe FloTrac/Vigileo^TM system with upgraded software (FCO, EdwardsLifesciences, Irvine CA, USA), the PiCCOplus^TM system (PCO,Pulsion Medical Systems, Munich, Germany) and continuous COmonitoring using a PAC (CCO; Vigilance^TM monitoring, EdwardsLifesciences, Irvine CA, USA) with intermittent pulmonary arterythermodilution (ICO). The study was conducted in patients undergoingelective cardiac surgery. Methods: Thirty-one patients with preserved left ventricular functionwere enrolled. CCO, FCO, and PCO were recorded in the perioperativeperiod at six predefined time points after achieving stablehaemodynamic conditions; ICO was determined from the mean ofthree bolus injections. Bland–Altman analysis was usedto compare CCO, FCO, and PCO with ICO. Results: Bland–Altman analysis revealed a comparable mean biasand limits of agreement for all tested continuous CO monitoringdevices using ICO as reference method. Agreement for all devicesdecreased in the postoperative period. Conclusion: The performance of the FloTrac/Vigileo^TM system, the PiCCOplus^TM,and the Vigilance^TM CCO monitoring for CO measurement were comparablewhen tested against intermittent thermodilution in patientsundergoing elective cardiac surgery.     

Effects of short-term simultaneous infusion of dobutamine and terlipressin in patients with septic shock: the DOBUPRESS study

Background: Terlipressin bolus infusion may reduce cardiac output and globaloxygen supply. The present study was designed to determine whetherdobutamine may counterbalance the terlipressin-induced depressionin mixed-venous oxygen saturation (Sv_O2) in patients with catecholamine-dependentseptic shock. Methods: Prospective, randomized, controlled study performed in a universityhospital intensive care unit. Septic shock patients requiringa continuous infusion of norepinephrine (0.9 µg kg^–1min^–1) to maintain mean arterial pressure (MAP) at 70(SD 5) mm Hg were randomly allocated to be treated either with(i) sole norepinephrine infusion (control, n=20), (ii) a singledose of terlipressin 1 mg (n=19), or (iii) a single dose ofterlipressin 1 mg followed by dobutamine infusion titrated toreverse the anticipated reduction in Sv_O2 (n=20). Systemic,pulmonary, and regional haemodynamic variables were obtainedat baseline and after 2 and 4 h. Laboratory surrogate markersof organ (dys)function were tested at baseline and after 12and 24 h. Results: Terlipressin (with and without dobutamine) infusion preservedMAP at 70 (5) mm Hg, while allowing to reduce norepinephrinerequirements to 0.17 (0.2) and 0.2 (0.2) µg kg^–1min^–1, respectively [vs1.4 (0.3) µg kg^–1 min^–1in controls at 4 h; each P<0.001]. The terlipressin-linkeddecrease in Sv_O2 was reversed by dobutamine at a mean dose of20 (8) µg kg^–1 min^–1 [Sv_O2 at 4 h: 59 (11)%vs 69 (12)%, P=0.028]. Conclusions: In human catecholamine-dependent septic shock, terlipressin(with and without concomitant dobutamine infusion) increasesMAP and markedly reduces norepinephrine requirements. Althoughno adverse events were noticed in the present study, potentialbenefits of increasing Sv_O2 after terlipressin bolus infusionneed to be weighted against the risk of cardiovascular complicationsresulting from high-dose dobutamine.     

Norepinephrine kinetics and dynamics in septic shock and trauma patients

Background. There is considerable variability in the inter-patientresponse to norepinephrine. Pharmacokinetic studies of dopamineinfusion in volunteers and in patients have also shown largevariability. The purpose of this study was to define the pharmacokineticsof norepinephrine in septic shock and trauma patients. Methods. After Ethical Committee approval and written informedfamily consent, 12 patients with septic shock and 11 traumapatients requiring norepinephrine infusion were studied. Norepinephrinedose was increased in three successive steps of 0.1 mg kg^–1min^–1 at 15-min intervals (20% maximum allowed increasein arterial pressure). Arterial blood was sampled before andat 0.5, 13, and 15 min after each infusion rate change and 30s, 1, 2, 5, 10, and 15 min after return to baseline dosing.Norepinephrine was assayed by HPLC. The pharmacokinetics weremodelled using NONMEM (one-compartment model). The effects ofgroup, body weight (BW), gender and SAPS II (Simplified AcutePhysiology Score II) [Le Gall JR, Lemeshow S, Saulnier F. Anew Simplified Acute Physiology Score (SAPS II) based on a European/NorthAmerican multicenter study. J Am Med Assoc 1993; 270: 2957–63]patients score on clearance (CL) and volume of distribution(V) were tested. Results. Group, gender, and BW did not influence CL or V. CLwas negatively related to SAPS II. CL and T_1/2 varied from 3litre min^–1 and 2 min, respectively, when SAPS II=20 to0.9 litre min^–1 and 6.8 min when SAPS II=60. Conclusion. In trauma patients and in septic shock patients,norepinephrine clearance is negatively related to SAPS II.     

Respiratory and haemodynamic effects of volume-controlled vs pressure-controlled ventilation during laparoscopy: a cross-over study with echocardiographic assessment

Background: The effects of pressure-controlled (PC) ventilation on the ventilatoryand haemodynamic parameters during laparoscopy procedures hadnot been carefully assessed. This prospective cross-over studywas undertaken to compare how volume-controlled (VC) and PCmodes could affect pulmonary mechanics, gas exchange, and cardiacfunction in patients undergoing laparoscopy. Methods: Twenty-one patients undergoing laparoscopic urological procedureshad their lungs ventilated at the beginning with VC ventilation.PC ventilation was instituted at the end of the VC sequence.Ventilator settings were adjusted to keep tidal volume, respiratoryrate, and FI_O2 constant in every mode. A complete set of ventilatory,haemodynamic, and gas exchange parameters was obtained underVC after 40 min of pneumoperitoneum and 20 min after switchingfor PC. Transoesophageal echocardiography was performed in orderto evaluate systolic and diastolic function of the heart. Results: When VC was switched to PC, peak airway pressure decreased [mean(SD) 32 (6) vs 27 (6) cm H₂O; P < 0.0001], peak inspiratoryflow increased [17 (3) vs 48 (8) litre min^–1; P < 0.0001),and dynamic compliance improved [+15 (8)%]. No difference wasnoted for static airway pressure, static compliance, and arterialoxygenation. No significant change could be demonstrated inthe systolic [left ventricular end-systolic wall stress 66 (16)vs 63 (14)·10³ dyn cm^–2 m^–2] or diastolicfunction [early diastolic velocity 10.3 (2.5) vs 10.5 (2.7)cm s^–1]. Conclusions: In this study, no short-term beneficial effect of PC ventilationcould be demonstrated over conventional VC ventilation in patientswith pneumoperitoneum.     

TRANSOESOPHAGEAL PULSED WAVE DOPPLER MEASUREMENT OF CARDIAC OUTPUT DURING MAJOR VASCULAR SURGERY: COMPARISON WITH THE THERMODILUTION TECHNIQUE

We measured cardiac output in 12 patients undergoing electiveabdominal vascular surgery at specific times during the procedurewith simultaneous thermodilution and transoesophageal pulsedDoppler echocardiographic techniques. No patient had clinicalevidence of valvular heart disease before surgery. Five patientshad echocardiographic evidence of mitral regurgitation on colour-codedDoppler. Using Bland and Altman analysis to compare the cardiacoutput measurement by the two techniques, the Doppler methodoverestimated the cardiac output (bias = 0.86 litre min^–1)compared with the thermodilution technique and there were widelimits of agreement between the two techniques (+2.4 to –4.1 litre min^–1). However, in the seven patients withno evidence of mitral regurgitation, closer agreement (bias0.14 litre min^–1) and narrower limits (+1.6 to –1.3litre min^–1) were observed. We conclude that, in patientswith competent mitral valves, transoesophageal echocardiographmay provide accurate determination of cardiac output. ^*Present address, for correspondence: Department of Anesthesia,University of Washington, Seattle 98195, U.S.A.     

Applying a physiological model to quantify the delay between changes in end-expired concentrations of sevoflurane and bispectral index

Background: The delay between changes in end-expired sevoflurane concentrationsand bispectral index (BIS) may be characterized by a ‘rateconstant’ (k_e0). A smaller k_e0 reflects a longer delay.Values for k_e0 vary substantially among studies. The questionarises how k_e0 depends on experimental conditions, includingventilation and apparatus. Methods: Increasing and decreasing sevoflurane concentrations were cyclicallydelivered to our validated model. First, we quantified theoreticalk_e0 values for distinct alveolar ventilations, estimating k_e0from sevoflurane tensions in alveolar space and grey matter.Secondly, we investigated the impact of experimental conditions.To predict BIS, the model was extended with a pharmacodynamicsection, including k_e0. Known values, matching theoretical values,were assigned to this k_e0. These were recovered from end-expiredconcentrations and BIS. Possible determinants of error (differencebetween assigned and recovered k_e0) were varied, that is fractionof dead space gas in end-expired gas (d), and time delays inmeasuring BIS (t_BIS) and end-expired concentrations (t_EE). Results: Theoretical k_e0s were 0.7, 0.53, 0.35, and 0.2 min^–1 foran arterial PCO₂ of 8, 6.67, 5.33 (normocapnia), and 4 kPa,respectively. For spontaneous ventilation, k_e0 = 0.53 min^–1.Recovered k_e0s depended on d and t (= t_BIS – t_EE) andwere smaller than assigned values (if t > 0). Errors increasedwith increasing d and t. For normocapnia, k_e0 was between 0.32and 0.23 min^–1 (d = 0.1; any t = 0–60 s). For spontaneousventilation, k_e0 was between 0.51 and 0.40 min^–1 (d =0–0.1; t = 5–20 s). Conclusions: Published k_e0s (0.22–0.53 min^–1), including ourown for sevoflurane-depressed spontaneous ventilation (0.48min^–1), are in the ranges dictated by investigation-specificconditions.     

Comparison of three devices for oxygen administration in the late postoperative period

We have evaluated three different devices for oxygen administrationin the surgical ward, the Hudson face mask (oxygen 3 litre min^–1air 12 litre min^–1) the nasal prong (oxygen 3 litre min^–1)and the binasal catheter (oxygen 3 litre min^–1) We evaluatedthe three devices in random order for periods of 30 mm eachin 25 patients with postoperative hypoxaemia (Sp^o2 94%). Arterialoxygen saturation was measured by continuous pulse oximetryand comfort was evaluated with a questionnaire after each treatmentperiod. The three systems increased arterial oxygen saturationto similar levels, but the highest degree of comfort was foundwith the binasal catheter. Use of the binasal catheter is recommendedfor oxygen administration in the late postoperative period.(Br. J. Anaesth. 1995; 74: 607–609)     

Prediction of fluid responsiveness in patients during cardiac surgery

Background. Left ventricular stroke volume variation (SVV) hasbeen shown to be a predictor of fluid responsiveness in varioussubsets of patients. However, the accuracy and reliability ofSVV are unproven in patients ventilated with low tidal volumes. Methods. Fourteen patients were studied immediately after coronaryartery bypass grafting (CABG). All patients were mechanicallyventilated in pressure-controlled mode [tidal volume 7.5 (1.2)ml kg^–1]. In addition to standard haemodynamic monitoring,SVV was assessed by arterial pulse contour analysis. Left ventricularend-diastolic area index (LVEDAI) was determined by transoesophagealechocardiography. A transpulmonary thermodilution techniquewas used for measurement of cardiac index (CI), stroke volumeindex (SVI) and intrathoracic blood volume index (ITBI). Allvariables were assessed before and after a volume shift inducedby tilting the patients from the anti-Trendelenburg (30°head up) to the Trendelenburg position (30° head down). Results. After the change in the Trendelenburg position, SVVdecreased significantly, while CI, SVI, ITBI, LVEDAI, centralvenous pressure (CVP) and pulmonary artery occlusion pressure(PAOP) increased significantly. Changes in SVI were significantlycorrelated to changes in SVV (r=0.70; P<0.0001) and to changesin LVEDAI, ITBI, CVP and PAOP. Only prechallenge values of SVVwere predictive of changes in SVI after change from the anti-Trendelenburgto the Trendelenburg position. Conclusions. In patients after CABG surgery who were ventilatedwith low tidal volumes, SVV enabled prediction of fluid responsivenessand assessment of the haemodynamic effects of volume loading.