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.     

Dobutamine-induced dissociation between changes in splanchnic blood flow and gastric intramucosal pH after cardiac surgery

Gastric intramucosal acidosis, a sign of splanchnic tissue hypoxia,is common after cardiac surgery. We tested the hypothesis thatan increase in splanchnic blood flow induced by dobutamine improvessplanchnic tissue oxygenation after cardiac surgery. We measuredchanges in gastric intramucosal pH, splanchnic blood flow andoxygen transport in response to increased systemic flow inducedby dobutamine (mean 4.4 (range 3.0–7.0) µg kg^–1min^–1) after coronary artery bypass. We studied 22 stablepostoperative patients who were allocated randomly to receivedobutamine (n = 11) or to serve as controls (n = 11). Dobutaminewas given also to a separate group with a low cardiac indexafter operation (n = 6). The end-point was to increase cardiacindex by at least 25% and to exceed 2 litre min^–1 m^–2.Dobutamine consistently increased mean splanchnic blood flow(control 0.6 (SD0.2) vs 0.7 (0.2) litre min^–1 m^–2(P<0.05); normal cardiac output and dobutamine 0.7 (0.2)vs 1.1 (0.4) litre min^–1 m^–2 (P<0.01); low cardiacoutput and dobutamine 0.4 (0.1) vs 0.7 (0.1) litre min^–1m^–2 (P<0.05)) and oxygen delivery (control 102 (29)vs 111 (28) ml min^–1 m^–2 (ns); normal cardiac outputand dobutamine 106 (27) vs 156 (47) ml min^–1 m^–2(P < 0.01); low cardiac output and dobutamine 75 (21) vs110 (26) ml min^–1 m^–2 (P<0.05)) but had no effecton splanchnic oxygen consumption (control 44 (10) vs 49 (10)ml min^–1 m^–2 (ns); normal cardiac output and dobutamine45(12) vs 51 (17) ml min^–1 m^–2 (ns); low cardiacoutput and dobutamine 37 (9) vs 40 (9) ml min^–1 m^–2(ns)). Despite this, dobutamine reduced gastric intramucosalpH in all patients with low cardiac output (7.33 (0.12) vs 7.25(0.06)(P<0.05)) and in 50% of patients with stable haemodynamics(7.37(0.07) vs 7.34(0.06) (ns)). In contrast, gastric intramucosalpH remained stable in the control group (7.34 (0.05) vs 7.34(0.04) (ns)).We conclude that dobutamine resulted in a dissociationbetween splanchnic oxygen delivery and gastric mucosal tissueoxygenation, suggesting inappropriate distribution of bloodflow within the splanchnic region. (Br. J. Anaesth. 1995; 74:277–282)     

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.     

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      

Comparison of the haemodynamic effects of dobutamine with enoximone after open heart surgery in small children

We have studied 28 children (mean age 13.6 months) undergoingelective cardiac surgery involving a myocardial ischaemic timegreater than 60 min. Thirteen received phenoxybenzamine 1 mgkg^–1 before cardiopulmonary bypass (CPB) and dobutamine10 µg kg^–1 min^–1 before discontinuation ofCPB; 15 received enoximone 0.5 mg kg^–1 followed by aninfusion of 10 µg kg^–1 min^–1 before discontinuationof CPB. Haemodynamic variables were measured at intervals for6 h after CPB. Two patients in each group required additionalinotropic support with adrenaline. Heart rates, right and leftatrial pressures, mean pulmonary artery pressures and systemicand pulmonary vascular resistance indices were similar in thetwo groups. Mean arterial pressure was significantly greaterin those receiving dobutamine (61.3 (SD 7.6) mm Hg) comparedwith enoximone (56.2 (5.3) mm Hg) (P < 0.05). Differencesin cardiac index (thermodilution) (dobutamine group 2.92 (0.62)litre min^–1 m^–2; enoximone group 2.55 (0.55) litremin^–1 m^–2) and left ventricular stroke work index(dobutamine group 13.1 (4.7) g m beat^–1 m^–2; enoximonegroup 10.4 (2.7) g m beat^–1 m^–2) were not statisticallysignificant. Enoximone may be used successfully in these patientsto assist discontinuation of CPB and maintain an acceptablehaemodynamic state in the early postoperative period but, whenused alone, conferred no advantage compared with the combinationof dobutamine and phenoxybenzamine. (Br. J. Anaesth. 1994; 72:77–81)     

Xenon increases total body oxygen consumption during isoflurane anaesthesia in dogs

Background. This study was designed to examine whether the couplingbetween oxygen consumption (V^·O₂) and cardiac output(CO) is maintained during xenon anaesthesia. Methods. We studied the relationship between V^·O₂ (indirectcalorimetry) and CO (ultrasound flowmetry) by adding xenon toisoflurane anaesthesia in five chronically instrumented dogs.Different mixtures of xenon (70% and 50%) and isoflurane (0–1.4%)were compared with isoflurane alone (1.4% and 2.8%). In addition,the autonomic nervous system was blocked (using hexamethonium)to study its influence on V^·_O2 and CO during xenon anaesthesia. Results. Mean (SEM) V^·O₂ increased from 3.4 (0.1) ml kg^–1 min^–1during 1.4% isoflurane to 3.7 (0.2) and 4.0 (0.1) ml kg^–1 min^–1after addition of 70% and 50% xenon, respectively (P<0.05),whereas CO and arterial pressure remained essentially unchanged.In contrast, 2.8% isoflurane reduced both, V^·O₂ [from3.4 (0.1) to 3.1 (0.1) ml kg^–1 min^–1]and CO [from 96 (5) to 70 (3) ml kg^–1 min^–1](P<0.05). V^·O₂ and CO correlated closely during isofluraneanaesthesia alone and also in the presence of xenon (r²=0.94and 0.97, respectively), but the regression lines relating COto V^·_O2 differed significantly between conditions, withthe line in the presence of xenon showing a 0.3–0.6 ml kg^–1 min^–1greater V^·O₂ for any given CO. Following ganglionic blockade,50% and 70% xenon elicited a similar increase in V^·O₂,while CO and blood pressure were unchanged. Conclusions. Metabolic regulation of blood flow is maintainedduring xenon anaesthesia, but cardiovascular stability is accompaniedby increased V^·O₂. The increase in V^·_O2 is independentof the autonomic nervous system and is probably caused by directstimulation of the cellular metabolic rate. Br J Anaesth 2002; 88: 546–54     

Glucose,insulin and potassium for heart protection during cardiac surgery

Background. Coronary artery bypass grafting with hypothermiccardiac arrest and cardiopulmonary bypass (CPB) is associatedwith myocardial injury. Our study investigated whether an infusionof glucose, insulin and potassium (GIK) during elective coronaryartery bypass surgery decreases myocardial cell death. Methods. We measured cardiac troponin I (cTnI), a myofibrillarstructural protein, which is a sensitive and specific indicatorof myocytic injury. With ethics committee approval, 42 patientswere enrolled into a randomized, prospective, double-blindedstudy. In the GIK group, 500 ml of 50% dextrose solutioncontaining 100 IU insulin and potassium 80 mmol was infusedat the rate of 0.75 ml kg^–1 h^–1.Patients in the non-GIK group received 5% dextrose solutionat the same rate. Arterial blood samples were taken before inductionof anaesthesia, after removal of the aortic clamp and 6 and12 h after CPB. Results. In both groups there was an increase in cTnI concentration(P<0.05), which was greatest about 6 h after CPB. Atno time did the cTnI concentration differ between the two groups. Conclusion. The results suggest that GIK does not decrease theirreversible myocardial damage associated with routine coronaryartery bypass surgery. Br J Anaesth 2002; 88: 489–95     

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     

Use of cisatracurium during fast-track cardiac surgery

We prospectively studied spontaneous recovery from cisatracurium-inducedneuromuscular block in 18 patients scheduled for cardiac surgery,and its suitability for fast-track cardiac surgery. Neuromuscularblock was induced by an i.v. bolus (range 0.15–0.3 mgkg^–1) and maintained by a continuous infusion (range 1.1–3.2µg kg^–1 min^–1) of cisatracurium until sternalclosure. In the intensive care unit (ICU), spontaneous recoverywas evaluated by the train-of-four (TOF) ratio measured at theadductor pollicis muscle. The ICU medical staff were unawareof the TOF ratios until sedation was stopped. At that time,if the TOF ratio was less than 0.9, sedation was recommenced.On arrival in ICU, all patients had residual paralysis. Themean time to reaching a TOF ratio of at least 0.9 was 102 min(range 74–144 min) after discontinuation of the cisatracuriuminfusion. Fifteen patients (83%) were successfully extubatedduring the first 8 h after stopping the cisatracurium infusion.Only one patient showed residual paralysis when sedation wasdiscontinued. These results support the use of cisatracuriumas a suitable neuromuscular blocking agent for fast-track cardiacsurgery. Br J Anaesth 2001; 86: 130–2     

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.      

Enoximone pharmacokinetics in infants

Enoximone and enoximone sulphoxide concentrations were measuredin plasma of 20 infants, median age 6.0 (range 0.6–49.7) weeks,during and after prolonged continuous infusions. Patients weregiven enoximone 1 mg kg^–1 and an infusion at10 µg kg^–1 min^–1 just beforebeing weaned from cardiopulmonary bypass (CPB). The infusionwas stopped when clinically indicated, after a median 97 (range24–572) h. Arterial blood samples were taken 30 minand 12 h after CPB, every 24 h during the infusion,and then 2, 4, 8, 12 and 24 h after the infusion was stopped.Pharmacokinetic non-compartmental analysis was performed usingTOPFIT software. Fourteen patients who retained normal hepaticfunction had a median (95% confidence intervals) clearance of9.7 (6.3–14.1) ml min^–1 kg^–1,elimination half-life of 5.2 (2.4–6.8) h and a volumeof distribution of 3.6 (2.0–5.7) litre kg^–1.The six patients with significant hepatic dysfunction had alower clearance, 5.7 (2.4–14.5) ml min^–1 kg^–1,and significantly longer elimination half-life, 7.6 (6.5–10.9) h(P=0.02). Enoximone sulphoxide elimination half-life was significantlyprolonged in three patients with renal dysfunction, 16.2 (10.5–17.7) hversus 6.9 (6.1–9.4) h (P=0.03). These results confirmthat enoximone pharmacokinetics in infants is similar to thatfound in adults. The infusion rate of enoximone should be reducedif hepatic or renal dysfunction supervenes. Br J Anaesth 2000; 85: 205–10 ^* Corresponding author     

Pharmacokinetics and pulmonary extraction of clevidipine, a new vasodilating ultrashort-acting dihydropyridine, during cardiopulmonary bypass

Clevidipine is a new vascular-selective, calcium channel antagonistof the dihydropyridine type with an ester side chain susceptibleto esterase metabolism. In healthy volunteers, it has high clearance(0.069 litres min^–1 kg^–1) with a small volume ofdistribution at steady state (0.19 litres kg^–1). The half-livesof the two initial rapid phases, accounting for approximately95% of the area under the curve after an i.v. bolus, are 0.7and 2.3 min, respectively. The aims of this study were to determinethe pharmacokinetics and the pulmonary extraction ratio of clevidipinein patients undergoing cardiac surgery. Seventeen patients receivedclevidipine as an i.v. infusion before cardiopulmonary bypass(CPB), and eight of these patients were also given clevidipineduring hypothermic CPB. Mixed venous and arterial blood sampleswere taken for pharmacokinetic analysis and calculation of pulmonaryextraction ratio. A two-compartment pharmacokinetic model withzero-order input was used to describe the pharmacokinetics ofclevidipine before and during CPB. Virtually identical concentrationsin mixed venous and arterial blood suggest negligible pulmonarymetabolism of clevidipine. The total blood clearance of clevidipineis extremely high (0.055 litres min^–1 kg^–1). DuringCPB, clearance of clevidipine was significantly reduced, to0.03 litres min^–1 kg^–1 (P<0.005), probably asa consequence of reduced body temperature. Br J Anaesth 2000; 85: 683–9 ^* Corresponding author     

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     

Effect of two anaesthetic regimens on airway nitric oxide production in horses

There is evidence that halothane inhibits nitric oxide synthasein vitro, but the effect of intravenous anaesthetic agents isless clear. This study was undertaken to compare the rate ofexhaled nitric oxide production (V_NO) in spontaneously breathinghorses anaesthetized with halothane or an intravenous regimen.Seven adult horses were studied twice in random order. Afterpremedication with romifidine 100 µg kg^–1,anaesthesia was induced with ketamine 2.2 mg kg^–1and maintained with halothane in oxygen (HA) or by an intravenousinfusion of ketamine, guaiphenesin and romifidine (IV). Inhaledand exhaled nitric oxide (NO) concentrations, respiratory minuteventilation (V_E), pulmonary artery pressure (P_PA), fractionalinspired oxygen concentration (FI_O2), end-tidal carbon dioxideconcentration (E'_CO2), cardiac output (Q) and partial pressuresof oxygen and carbon dioxide in arterial blood (Pa_O2, Pa_CO2)were measured. Exhaled nitric oxide production rate was significantlylower (40 min, P<0.01; 60 min, P<0.02) duringHA [40 min, 1.4 (SD 1.4) pmol l^–1 kg^–1 min^–1;60 min, 0.7 (0.7) pmol l^–1 kg^–1 min^–1]than during IV [40 min, 9.3 (9.9) pmol l^–1 kg^–1min^–1; 60 min, 12.5 (13.3) pmol l^–1 kg^–1min^–1). Mean pulmonary artery pressure was significantlyhigher (40 min, P<0.01; 60 min, P<0.001) during HA[40 min, 5.9 (1.1) kPa; 60 min, 5.9 (0.9) kPa] comparedwith IV (40 min, 4.4 (0.4) kPa; 60 min, 4.4 (0.5) kPa].NO is reduced in the exhalate of horses anaesthetized with halothanecompared with an intravenous regimen. It is suggested that increasedmean pulmonary artery pressure during halothane anaesthesiamay be linked to the differences in NO production. Br J Anaesth 2001; 86: 127–30     

Inhalation anaesthetics increase heart rate by decreasing cardiac vagal activity in dogs

Inhalation anaesthetics decrease heart rate in isolated heartsbut mostly increase heart rate in the intact organism, althoughmost inhibit sympathetic drive. Differences in the degree ofincrease in heart rate between agents may be related to differencesin their vagolytic action. To test this hypothesis, we studied theeffects of halothane (H), isoflurane (I), enflurane (E), sevoflurane (S)and desflurane (D) [1–3 MAC (minimum alveolar concentration)]on heart rate and heart rate variability (HRV) as a measureof cardiac vagal activity in seven dogs. HRV was analysed inthe time domain as the standard deviation of the RR interval(SDNN) and in the frequency domain as power in the high-frequency(HF, 0.15–0.5 Hz) and low-frequency (LF, 0.04–0.15 Hz)ranges. Heart rate increased with anaesthetic concentrationand there were corresponding decreases in SDNN, HF power and LFpower. Heart rate increased most with D (+40 beats min^–1),least with H (+8 beats min^–1) and to an intermediate extentwith S, I and E. SDNN and HF power, as measures of vagal activity, changedin the opposite direction and decreased in the same order asheart rate increased. However, SDNN and HF power correlatedsignificantly with heart rate [r=–0.81 (0.04) and –0.81 (0.03)respectively] and were independent of the anaesthetic and its concentration(P<0.05). Consistent with our hypothesis, these results suggestthat differences between agents in the degree of increase inheart rate are explained by differences in their vagolytic action. Br J Anaesth 2001; 87: 748–54     

Comparison of electrical velocimetry and transoesophageal Doppler echocardiography for measuring stroke volume and cardiac output

Background. Impedance cardiography (ICG) has been used extensivelyto estimate stroke volume (SV) and cardiac output (CO) fromchanges of thoracic electrical bioimpedance (TEB). However,studies comparing ICG with reference methods have questionedthe reliability of this approach. Electrical velocimetry (EV)provides a new algorithm to calculate CO from variations inTEB. As the transoesophageal Doppler echocardiographic quantificationof CO (TOE–CO) has emerged as a reliable method, the purposeof this study was to determine the limits of agreement betweenCO estimations using EV (EV–CO) and TOE–CO. Methods. Standard ECG electrodes were used for non-invasiveEV–CO measurements. These were placed on 37 patients scheduledfor coronary artery surgery necessitating transoesophageal echocardiographymonitoring. Simultaneous EV–CO and TOE–CO measurementswere recorded after induction of anaesthesia. EV–CO wascalculated using the Bernstein–Osypka equation. TOE–COwas measured across the aortic valve using continuous-wave Dopplerechocardiography and a triangular orifice model. Results. A significant high correlation was found between theTOE–CO and the EV–CO measurements (r²=0.86). Datawere related linearly. The slope of the line (1.10 (SE 0.07))was not significantly different from unity, and the point atwhich it intersected the ordinate (–0.46 (0.32) litremin^–1) was not significantly different from zero. Bland–Altmananalysis revealed a bias of 0.18 litre min^–1 with narrowlimits of agreement (–0.99 to 1.36 litre min^–1). Conclusions. The agreement between EV–CO and TOE–COis clinically acceptable, and these two techniques can be usedinterchangeably.      

Role of propofol and its solvent,intralipid, in nitric oxide-induced peripheral vasodilatation in dogs

Background. The commercial propofol preparation in an intralipidsolution causes marked vasodilatation. Both propofol and itssolvent seem to stimulate the nitric oxide (NO) pathway. Therole of intralipid in cardiac and regional haemodynamic changesinduced by propofol and their respective interactions with theNO pathway was assessed. Methods. Dogs were instrumented to record arterial pressure,heart rate, cardiac output, dP/dt (the first derivative of leftventricular pressure) and vertebral, carotid, coronary, mesenteric,hepatic, portal and renal blood flows. Experimental groups wereas follows. Group 1 (control; n=11): N-methyl-L-arginine (L-NMA)20 mg kg^–1 i.v.; Group 2 (n=8): propofol (10mg ml^–1) 4 mg kg^–1 i.v. bolus followedby 0.6 mg kg^–1 min^–1; Group 3 (n=6):intralipid 0.25 ml kg^–1 bolus followed by 0.06ml kg^–1 min^–1. After 60 min, L-NMAwas injected in Groups 2 and 3. Results. Propofol induced increases in heart rate, coronaryand carotid blood flows, and decreases in systemic vascularresistance and dP/dt. Intralipid increased renal blood flow,carotid vascular resistance and mesenteric vascular resistance.In the presence of intralipid, L-NMA-induced pressor responseand systemic, carotid and renal vasoconstriction were more pronouncedthan in control dogs. Conclusions. Except for the coronary and carotid circulations,intralipid modulates the NO pathway in cardiac and regionalblood flow. Br J Anaesth 2002; 89: 492–8     

Rate of injection through whitacre needles affects distribution of spinal anaesthesia

A prospective, randomized, double-blind study was performedto investigate whether altering the rate of injection of localanaesthetic through a Whitacre needle had any effect on thespinal block achieved. Twenty patients scheduled for electiveurological surgery under spinal anaesthesia received an injectionof 3 ml of 0.5% plain bupivacaine either by hand (fast)over 10 s (18 ml min^–1) or by infusionpump (slow) over 3 min (1 ml min^–1). Allpatients were in the sitting position both during insertionof the spinal needle and for 3 min after the start of spinalinjection, and they then changed to the supine position. Theslow injection group achieved peak sensory block earlier, aftera median interval of 20 (95% confidence interval 12.5–30) minvs 30 (22.5–45) min (P<0.05) for the fast group. Thelevel of peak sensory block was similar: T3.5 (T2–T4.5)vs T4 (T1.5–T6.5). The time to lowest mean arterial pressureoccurred earlier in the slow group, at 10 (8 to 18) vs 20 (15–31) min(P<0.05). Duration of the motor block was shorter in theslow group: 180 (152–242) vs 270 (225–300). We concludethat a slow spinal injection of plain bupivacaine results ina block of more rapid onset and recovery. Br J Anaesth 2001; 86: 245–8     

Endothelial-related coagulation in cardiac surgery

The endothelium appears to play an important degrees in theregulation of intravascular coagulation. Thrombomodulin is oneof the anticoagulant substances that is expressed by endothelialcells. The influence of age and illness on the thrombomodulin-proteinC system was studied prospectively in 80 cardiac surgery patients.Patients > 70 yr old (n = 20) were compared with patients< 50 yr (n = 20) (group I), and patients undergoing a simplecardiac procedure (n = 20) were compared with patients scheduledfor complex surgery (n = 20) (group II). Thrombomodulin (normal<40 ng ml^–1 protein C and (free) protein S plasma concentrationswere measured by enzyme-linked immunosorbent assays (ELISA)after induction of anaesthesia (baseline values), during andafter cardiopulmonary bypass (CPB), at the end of surgery, 5h after CPB and on the first day after operation. Blood lossand use of homologous blood and blood products were significantlygreater in patients > 70 yr and in those undergoing complexsurgery. At baseline, thrombomodulin concentration was increasedin patients undergoing complex surgery (mean 52 (SD 9) ng ml^–1After bypass and after operation, thrombomodulin increased mostin patients > 70 yr (from 40 (8) to 78 (10) ng ml^–1and in those patients who underwent complex cardiac operations(from 52 (8) to 79 (10) ng ml^–1 (P < 0.05). Changesin protein C and protein S concentrations were similar in allgroups. On the first day after operation only, protein C concentrationswere reduced in patients > 70 yr and in patients who underwentcomplex cardiac surgery. Older patients and those who underwentcomplex cardiac surgery had greater changes in the thrombomodulin-proteinC system which may contribute to increased postoperative bloodloss.     

Influence of tramadol on the ventilatory response to hypoxia in humans

We studied the effect of tramadol on the ventilatory responseto 7 min acute isocapnic hypoxia (Sp_O2 85.1 (SD 0.4)%)during steady mild hypercapnia (PE'_co2 0.7 kPa above normoxicbaseline) in 14 healthy volunteers (seven male). The acute hypoxicresponse was measured before and 1 h after oral placeboor tramadol (100 mg). After tramadol, ventilation duringmild hypercapnia (mean 11.28 litres min^–1) wassignificantly less (P<0.05) than during placebo baseline(13.93 litres min^–1), tramadol baseline (14.63 litres min^–1),or after placebo (14.95 litres min^–1), confirmingthat tramadol has a small depressive effect on the hypercapnicventilatory response. There was no significant difference inthe hypoxic ventilation/Sp_O2 response (l min^–1 %^–1)measured during the placebo baseline (0.99), placebo (1.18),tramadol baseline (0.78) or tramadol (0.68) runs. These datasuggest that tramadol does not depress the hypoxic ventilatoryresponse. Br J Anaesth 2000; 85: 211–6 ^* Correspondingauthor