Noninvasive Measurement of Cardiac Output in Critically Ill Children

This study was performed to evaluate the hemodynamic status of children admitted to the intensive care unit, using suprasternal and transesophageal Doppler ultrasound, and to establish a suitable noninvasive technique to monitor trends in cardiac output in critically ill children. Twenty children were studied over a period of 6 months. The median age was 32.5 months and weight 14.5 kg. Minute distance (MD), which is a linear cardiac output parameter, was assessed. Seven simultaneous pairs of measurements of MD were made using transesophageal Doppler (TED) and suprasternal Doppler (SSD) by the same operator. Following a fluid challenge, seven repeat pairs of measurements were made. The mean percentage changes for MD by TED and SSD were 21.84 (SD 9.97) and 5.75 (SD 7.32). The average coefficients of variation for measurements of MD by TED and SSD were 2.34% and 15.98%, respectively. The mean difference in percentage change between MD, measured by TED and SSD, was 27.59 with a 95% confidence interval and wide limits of agreement. The repeatability of TED measurements was good, but the measurements by SSD were wide and erratic with poor reproducibility. Our study shows that TED is easy to use, reliable, and very useful for monitoring hemodynamic changes in critically ill children.     

EVALUATION OF AN AUTOMATIC OSCILLOMETRIC METHOD AND OF VARIOUS CUFFS FOR THE MEASUREMENT OF ARTERIAL PRESSURE IN THE NEONATE

ABSTRACT. We compared simultaneous measurements of aortic, direct (Dir) and of indirect (ind) systolic (S), mean (M) and diastolic (D) arterial pressure (AP) determined by an automatic oscillometric instrument (DINAMAP) in neonates with birthweight of 1000-3680 g. DINAMAP measurements were performed with cuffs of increasing width and length, recommended by the manufacturer for increasing arm circumference, and with a Standard sized cuff (2.5 × 15 cm), previously considered as suitable for neonates of any body size. In addition, we compared simultaneous measurements of Dir SAP and of Ind SAP determined by a Doppler technique and the Standard cuff. In DINAMAP SAP measurements with the Standard cuff, a statistically significant correlation between arm circumference and ΔInd-Dir SAP values (i. e. the difference between simultaneous Ind and Dir SAP measurements) was found. In DINAMAP MAP measurements with the cuff recommended for arm circumference, a statistically significant difference of the mean ΔInd-Dir MAP values was observed in infants whose arm was or was not completely encircled by the bladder of the cuff. In SAP as well as in MAP DINAMAP determinations, the overall error of measurement with the Standard cuff was smaller than with the recommended cuff. The Doppler method was found considerably more accurate than the DINAMAP method for the determination of SAP. In spite of these limitations, the DINAMAP method with the Standard cuff was considered to be reasonably accurate for the clinical determination of SAP and MAP, provided that several consecutive measurements are performed and averaged in order to minimize the error of measurement. When considering DAP measurements the error was so unacceptably high that the DINAMAP method cannot be recommended for clinical use. The need for a careful consideration of the cuff characteristics when evaluating new methods for the indirect measurement of AP in the neonate is emphasized.     

Transcranial Doppler (TCD) screening for stroke prevention in sickle cell anemia: pitfalls in technique variation

Background. The Stroke Prevention Trial in Sickle Cell Anemia (STOP) identified children as being at high stroke risk if the time-averaged maximum mean velocity (TAMMV) of the middle cerebral or intracranial internal carotid arteries measured ≥ 200 cm/s. These values were obtained utilizing a 2-mHz dedicated nonimaging pulsed Doppler technique (TCD) and manual measurements. Questions have been raised as to the comparability of results obtained with different ultrasound machines and measurement techniques.¶Objective. The purpose of this study was to compare nonimaging (TCD) and transcranial duplex imaging (TCDI) findings in children potentially at risk for stroke with sickle cell disease.¶Materials and methods. Twenty-two children with sickle cell disease and no history of stroke were evaluated by both TCD and TCDI. Examinations were performed on the same day without knowledge of the other modality results and read independently using manually obtained measurements. Mean velocities, peak systolic velocities, and end diastolic velocities obtained by the two techniques were compared. In a subgroup, manual measurements were compared to electronically obtained measurements. ¶Results. TCDI values were lower than TCD measurements for all vessels. TCDI TAMMV values were most similar to the TCD values in the middle cerebral artery (–9.0 %) and distal internal cerebral artery (–10.8 %), with greater variability in the anterior cerebral artery (–19.3 %), bifurcation (–16.3 %), and basilar arteries (–23.1 %). Risk group placement based on middle cerebral artery TAMMV values did not change when comparing the two techniques. Measurements obtained electronically were lower than those obtained manually. ¶Conclusion. Velocities obtained by TCDI may be lower than TCD measurements, and these differences should be taken into consideration when performing screening for stroke risk and selection for prophylactic transfusion based on the STOP protocol.     

Invertography versus ultrasonography and distal colostography for the determination of bowel-skin distance in children with anorectal malformations.

PURPOSE: To evaluate the usefulness, reliability and sensitivity of invertography, perineal ultrasonography (US) and augmented-pressure distal colostography (APDC) in the diagnostic assessment of children with anorectal malformations (ARM). MATERIAL AND METHODS: Author retrospectively analysed the results of bowel-skin distance measured by means of three different imaging techniques in 39 children with ARM. The obtained results were verified by intraoperative measurements. RESULTS: Sensitivity of invertography performed in 22 patients was 27 % with a mean error of measurement of 0.84 cm, and the difference between measurements and real distance was statistically significant. Sensitivity of perineal US (22 children) was 86 % (mean error 0.12 cm) and of APDC (26 patients) was 100 % (0.05 cm) with no significant difference between measurements and intraoperative findings (p > 0.001). CONCLUSIONS: The study revealed a limited usefulness of invertography in the diagnostic evaluation of ARM. Perineal US was extremely useful in the newborn period and provided reliable information on which to base a decision for either preliminary colostomy or definitive operation. With a colostomy in place APDC, the most sensitive of the three methods, allowed for later precise definition of the defect and visualization of fistulas between bowel and urogenital tract.     

Three-Dimensional Echocardiographic Measurement of Left Ventricular Stroke Volume in Children: Comparison with Doppler Method

Three-dimensional echocardiography (3DE) allows calculation of ventricular volumes without geometric assumption on the ventricular shape. Our aim was to apply 3DE in a normal pediatric population and to compare the left ventricular stroke volume measurements to the Doppler method. Twenty-four normal patients (median age 7 years) underwent Doppler echocardiography and 3DE for left ventricular stroke volume calculation. The left ventricular stroke volume by Doppler method was calculated as the product of the aortic Doppler flow mean velocity and the area of the aortic annulus. The 3DE method was performed using a transthoracic rotational probe (TomTec) and left ventricular volumes were calculated using the Simpson's rule. The mean time for 3DE acquisition was 90 seconds without any sedation. 3DE correlated well with the Doppler method for left ventricular stroke volume measurements (y= 0.8x− 0.2, r= 0.94). The mean difference between the average values of left ventricular stroke volume obtained by Doppler method and 3DE was 5 ± 4 ml. Intraobserver and interobserver variabilities in the left ventricular stroke volume measurement by 3DE were 2.6% and 4.4%. In conclusion, 3DE compared to the Doppler method is an accurate, noninvasive, and reproducible method to measure the left ventricular stroke volume in normal children.     

Continuous wave doppler cardiac output: Use in pediatric patients receiving inotropic support

Summary Doppler estimates of cardiac output have been shown to correlate closely with invasive measurement of cardiac output in hemodynamically stable adults and children. However, this method has not been validated in hemodynamically unstable pediatric patients. To assess the accuracy of continuous wave Doppler echocardiography in pediatric patients with unstable hemodynamics, we performed 27 simultaneous Doppler and thermodilution comparisons in 12 pediatric patients receiving inotropic support and afterload-reducing agents. Doppler cardiac output was calculated using aortic diameter measured from long-axis two-dimensional echocardiograms at three different sites: the aortic valve anulus, the aortic root at the sinuses of Valsalva, and the ascending aorta. For all measurements, there was a close correlation between Doppler and thermodilution techniques. However the site of measurement of aortic diameter had a significant impact on the strength on the correlation and the variability between Doppler and thermodilution. The best correlation and least variability were obtained using the aortic valve anulus diameter (r=0.94). On serial determinations, percent change in Doppler stroke volume correlated well with thermodilution stroke volume (r=0.87) and was useful in detecting both direction and magnitude of change in thermodilution stroke volume. Despite the administration of positive inotropic and afterload-reducing agents, Doppler cardiac output is a useful method for estimating cardiac output in hemodynamically unstable pediatric patients.     

Cerebral blood flow in the newborn infant: comparison of Doppler ultrasound and 133xenon clearance

Two techniques of Doppler ultrasound examination, continuous-wave and range-gated, applied to the anterior cerebral artery and to the internal carotid artery, were compared with 133xenon clearance after intravenous injection. Thirty-two sets of measurements were obtained in 16 newborn infants. The pulsatility index, the mean flow velocity, and the end-diastolic flow velocity were read from the Doppler recordings. Mean cerebral blood flow was estimated from the 133Xe clearance curves. The correlation coefficients between the Doppler and the 133Xe measurements ranged from 0.41 to 0.82. In the subset of 16 first measurements in each infant, there were no statistically significant differences between the correlation coefficients of the various Doppler ultrasound variables, but the correlation coefficients were consistently lower for the pulsatility index than for mean flow velocity or end-diastolic flow velocity, and they were consistently higher for the range-gated than for the continuous-wave Doppler technique.     

Evaluation of a noninvasive cardiac output monitor in mechanically ventilated children.

OBJECTIVE: To compare measurements of cardiac output (CO) and cardiac index (CI) obtained by a recently developed noninvasive continuous cardiac output system, NICO (CONICO), and transthoracic Doppler echocardiography (COTTE) in mechanically ventilated children. DESIGN AND SETTING: Prospective study in a university-affiliated tertiary pediatric intensive care unit. PATIENTS: A total of 21 mechanically ventilated children, weighing >15 kg, in stable respiratory and hemodynamic condition. MEASUREMENTS: Sets of three successive measurements of CO with the NICO system and transthoracic Doppler echocardiography were obtained. Bland-Altman analysis was used to compare the agreement between the two methods. RESULTS: The mean +/- sd CO values were 4.06 +/- 1.43 L/min for CONICO and 4.67 +/- 1.78 L/min for COTTE. Bias +/- sd between the two methods was -0.61 +/- 0.94 L/min. The variability of the difference between the two methods increased as the magnitude of the CO measurement increased. Similar results were obtained for cardiac index: 4.01 +/- 1.40 L.min.m for CINICO and 4.59 +/- 1.48 L.min.m for CITTE. Bland-Altman analysis revealed a nonuniform relationship between CI difference and the magnitude (y = -0.299 - 0.0655 x mean). The variability of the differences did not increase as the magnitude of the CO measurement increased (sd of estimate was 0.827 L.min.m). With both CONICO and CINICO, each measurement was highly repeatable, with coefficient of variation of only 2.88% +/- 2.31%. Repeatability with Doppler echocardiography was 7.02% +/- 4.33%. CONCLUSIONS: The NICO system is a new device that measures CO easily and automatically in mechanically ventilated children weighing >15 kg. CO values obtained with this technique were in agreement with those obtained with Doppler echocardiography in children in respiratory and hemodynamic stable condition. The NICO system needs further investigation in children in unstable respiratory and hemodynamic condition.     

The reliability of 2D and colour Doppler ultrasound in localising longline position

Background:   The position of percutaneously inserted central venous catheters (longlines) in neonates is critical, as malpositioned longlines are associated with potentially fatal complications.
Aim:   To determine if cardiac ultrasound (two-dimensional (2D) and colour Doppler) is useful in evaluating longline position, when compared with the position identified by contrast radiography.
Setting:   Single level 3 neonatal unit.
Participants:   Forty-four neonates undergoing insertion of 24-gauge silastic longlines between July 2004 and September 2005.
Methods:   Infants who had a longline inserted underwent echocardiography by a novice and an experienced operator. Operators identified longline position using a 2D then colour Doppler echocardiography during a rapid bolus infusion of saline. The position was identified from contrast radiography by two independent observers.
Results:   Using 2D echocardiography, the novice and experienced operators could identify 41 and 59% of longlines, respectively. However, only 34% of longlines were identified by both operators. In 15 infants whose longline positions were identified by both operators, there was agreement in only eight infants (53%). Colour Doppler improved the experienced operator's success but did not assist the novice operator. For radiographs, there was 68% agreement on longline position between observers. The experienced echocardiographer located three (7%) longlines within the heart that from radiographs were thought to be in a proximal central vessel.
Conclusions:   This technique is experience-dependent and complements rather than replaces the use of contrast radiography. However, some infants with an apparently acceptable longline position on contrast radiography have longlines located within the heart on echocardiography.     

Cardiac function in healthy infants and children: Doppler echocardiographic evaluation

Summary To establish normal values for Doppler-derived parameters of cardiac function, pulsed-wave Doppler recordings from the ascending aorta were obtained in 80 healthy infants and children. Stroke and minute distance, peak velocity, mean acceleration, acceleration and ejection time intervals, and the acceleration/ejection time ratios were measured or calculated from the Doppler recordings. The relations between the Doppler parameters and heart rate, age, and body surface area were analyzed separately for the children below and above 6 months of age. The normal values for the two groups are given as the median and range and as the mean and standard deviations, respectively. For the older age group, strong negative correlations with heart rate were found for stroke distance and ejection time, suggesting that these parameters should be evaluated in relation to heart rate. Intraobserver and interobserver reproducibility were studied in 10 children. Good reproducibility was found for stroke and minute distance, peak velocity, and left ventricular ejection time. For measurements related to acceleration, the reproducibility was less good.     

Transcranial Doppler scanning and the assessment of stroke risk in children with HbSC [corrected] disease.

OBJECTIVE: To assess the role of transcranial Doppler (TCD) scanning in assessing the risk of stroke in children with haemoglobin SC (HbSC) disease. TCD scanning has an established role in primary stroke prevention in sickle cell anaemia but its value in HbSC is unknown. DESIGN: A retrospective audit of routinely performed TCD scans and routinely collected clinical data. SETTING: A paediatric sickle cell clinic in a teaching hospital in south London, UK. PATIENTS: 46 children with HbSC disease who have undergone routinely performed TCD scans and steady-state blood tests. MAIN OUTCOME MEASURES: The time-averaged mean of the maximum velocity (TAMMV) in the middle cerebral artery circulation correlated with clinical and laboratory data. RESULTS: The mean TAMMV was 94 cm/s, with a 98(th) centile of 128 cm/s. This is significantly less than the published ranges for HbSS, with a mean reading of 129 cm/s. One child had a stroke at the age of 5 years, when her TAMMV was measured at 146 cm/s. CONCLUSIONS: Further studies are needed to assess stroke risk in HbSC disease, but we suggest that TCD measurements are potentially useful in this condition, and that readings greater than 128 cm/s are abnormally high and warrant further investigation.     

Assessment of portable continuous wave Doppler ultrasound (ultrasonic cardiac output monitor) for cardiac output measurements in neonates

Background and study purpose:   The ultrasonic cardiac output monitoring (USCOM, USCOM Pty Ltd, Coffs Harbour, NSW, Australia) device provides a new method of non-invasively assessing cardiac output (CO). It has been successfully used in adults, but there have been few studies in neonates.
Aims:   To study the inter-operator reliability, and to compare the aortic (systemic) CO and pulmonary CO in a neonatal population.
Patient and methods:   In a study using the USCOM device, we have determined: (i) the inter-operator (rater) agreement for aortic (left ventricular output) and pulmonary (right ventricular output) CO; and (ii) by combining the measurements of aortic and pulmonary CO from each operator to obtain average aortic and pulmonary CO in neonates admitted to the neonatal unit during the first 8 days of life. Neonates with congenital heart disease were excluded from the study.
Results:   Twelve neonates were enrolled in the study, and their mean gestational age was 34.1 ± 3.7 weeks, mean birth weight 2.268 ± 0.872 kg with eight boys and four girls. There was no significant difference in CO measurements between the two operators (inter-rater correlation = 0.93 (0.86–0.97 (95% CI), P < 0.0001). However, the mean aortic CO was significantly lower than the mean pulmonary CO (228 mL/kg/min (202–254 (95% CI)) versus 282 mL/kg/min (256–309 (95% CI), P = 0.006).
Conclusions:   Although there was a good correlation between operators, further investigations are required to study the discrepancy between aortic (systemic)/pulmonary CO in this population. Other than this discrepancy, the validity of this technique in neonates requires further detailed studies as it uses continuous wave Doppler for the measurements.     

Day-to-day energy expenditure variability in low birth weight neonates

We estimated the metabolic rate of 13 low birth weight infants over a 9-day period, using indirect calorimetry in conjunction with serial measurements of oxygen consumption, carbon dioxide production, and total urinary nitrogen excretion. The mean percent error for oxygen consumption and carbon dioxide production measurements (determined by alcohol combustion experiments) assignable to the open-circuit system was 0.4 and 3.8%, respectively. Error in the total urinary nitrogen excretion measurement was less than 1% by the Kjeldahl technique. In the clinical setting, however, the range of deviation of measured oxygen consumption, carbon dioxide production and total urinary nitrogen excretion was +/- 12, 12, and 15% of the mean value respectively for an individual patient under standardized controlled conditions. The variability of metabolic rate between infants may be as much as 76%. Factors that had a small effect on metabolic rate were difficult to detect because of the variability inherent in the short-term measurement of metabolic rate. It was virtually impossible to control the sources of variation in the resting metabolism of low birth weight neonates over extended experimental periods. Day-to-day variations in resting energy expenditure may explain, in part, the widely different growth rates of premature infants receiving similar caloric intakes.     

Intra-individual variation in blood flow velocities in cerebral arteries of children with sickle cell disease

BACKGROUND: Children with sickle cell disease (SCD) are at elevated risk of stroke. Risk increases with blood flow velocity in selected cerebral arteries, as measured by transcranial Doppler (TCD) ultrasound, and use of TCD to screen these patients is widely recommended. Interpretation of TCD results should be based on knowledge of intra-individual variation in blood flow velocity, information not currently available for sickle cell patients. PROCEDURES: Between 1995 and 2002, 4,141 subjects, 2-16 years old, with homozygous SCD or Sbeta0-thalasemmia and no history of stroke were screened with TCD, including 2,018 subjects screened in one clinical trial (STOP), 1,816 screened in another (STOP 2), and 307 screened in an interim ancillary prospective study. The 812 subjects with >or=2 examinations<6 months apart were selected for analysis, including 242 (29.8%) subjects with normal average velocities (i.e., <170 cm/sec), 350 (43.1%) subjects with conditional velocities (i.e., 170-199 cm/sec), and 220 (27.1%) subjects with abnormal velocities (i.e., >or=200 cm/sec). The intra-subject standard deviation of TCD velocity was estimated from the difference between velocities at the first two interpretable examinations on each subject. RESULTS: An intra-subject standard deviation of 14.9 cm/sec was obtained. Seven (0.9%) subjects had unusually large and unexplained differences between velocities at the two examinations (range of absolute differences: 69-112 cm/sec). CONCLUSIONS: While stroke risk is well demonstrated to increase with increasingly abnormal TCD velocity, given the relatively large intra-subject variability, one TCD examination is generally not sufficient to characterize stroke risk in this patient population.     

The effect of asphyxia on gut blood flow in term neonates

Transcutaneous Doppler ultrasound measurements were made of the superior mesenteric artery of 25 term infants to correlate the intestinal blood flow with neonatal acid-base status as measured in umbilical artery blood and newborn condition as reflected by Apgar score. Compared with the babies whose umbilical artery pH was higher than 7.20 (peak systolic velocity: 84.1 cn/sn, mean velocity 48.6 cm/sn), the blood flow of superior mesenteric artery was significantly decreased in the newborn babies whose umbilical artery pH was less than 7.20 (peak systolic velocity 48.8 cm/sn, mean velocity=32.6 cm/sn). Although no such relationship existed between Apgar scores and superior mesenteric artery blood flow indices, a significant linear correlation between superior mesenteric artery blood flow and umbilical artery pH was noted. A reduction of intestinal circulation was observed during umbilical cord blood acidemia and hypoxemia.     

Diastolic forward blood flow in the pulmonary arteries of normal children: a Doppler echocardiographic study

Pulmonary arterial flow was examined in 60 normal children with a mean age of 8.5 +/- 3.7 years (range 3.3 to 17.9 years) and mean body surface area of 0.95 +/- 0.3 m2 (range 0.6 m2 to 1.7 m2) by pulsed Doppler echocardiography. Two distinct antegrade waveforms during diastole were detected. The peak velocities of early diastolic forward flow ranged from 20 to 30 cm/s (mean 26 +/- 4) and the late diastolic forward flow ranged from 16 to 29 cm/s (mean 23 +/- 3). The integrals of early diastolic forward flow ranged from 2.1 to 4.7 cm (mean 3.1 +/- 0.7) and late diastolic forward flow ranged from 1 to 3.6 cm (mean 2.1 +/- 0.7). Duration of early diastolic forward flow ranged from 161 to 256 ms (mean 187 +/- 29) and late diastolic forward flow ranged from 82 to 188 ms (mean 133 +/- 29). Data analysis for age indicated no significant difference in these measurements between children three to nine years old (n = 33) and children 9.1 to 18 years old (n = 27). The effect of respiration was observed in 10 randomly chosen subjects (mean age 8.6 +/- 4.1 years). Although early and late diastolic peak forward flow velocities, flow velocity integrals and flow duration during inspiration tended to be larger than during expiration, only late diastolic peak forward flow velocities during inspiration were significantly larger than during expiration (24.2 +/- 3.2 versus 18.2 +/- 3 cm/s, p = 0.001). This study defines normal Doppler ultrasound pulmonary arterial flow velocities, flow velocity integrals and flow duration during diastole in normal children. These results can be used for comparison with patterns found in disease states.     

Can peak systolic velocities be used for prediction of stroke in sickle cell anemia?

Background and purpose Ischemic stroke occurs in at least 11% of patients with homozygous sickle cell anemia (SCD) by the time they turn 20 years old. High risk associated with distal intracranial internal carotid (ICA) and proximal middle cerebral artery (MCA) stenosis can be detected by transcranial Doppler (TCD). TCD screening offers the possibility of reducing the risk of first stroke significantly based on a paradigm tested and proven to be effective in a stroke prevention trial in sickle cell anemia (STOP). Children with high flow velocity in the ICA and MCA of 200 cm/s time average mean of the maximum (TAMM) or higher had a 10% per year risk of first stroke that was reduced to <1% with regular red cell transfusion (reduction of hemoglobin S <30%). The clinical application of the STOP results could be enhanced if criteria for treatment could be found that are based on peak systolic velocity (PSV), the measure more commonly used in vascular ultrasound practice.Objective To compare PSV and end diastolic velocity (EDV) with TAMM for prediction of stroke and to derive PSV cutpoints for STOP protocol definitions of conditional and abnormal TCD. Using the STOP TCD and stroke outcome data to compare PSV and TAMM in terms of stroke prediction, PSV cutpoints comparable to those based on TAMM and used in STOP were derived. Because of their familiarity to the vascular ultrasound community, PSV cutpoints should be an important alternative to TAMM and may increase availability of screening and risk stratification for children with this disease.Materials and methods Data from 1,937 baseline TCD studies from STOP were correlated with stroke outcome in those not treated with transfusion. Stroke prediction was assessed with survival analysis using TAMM, PSV and EDV as continuous variables individually and then pair-wise in the same model, which contained 53 stroke events.Results PSV and EDV were highly correlated to the TAMM velocity (r=0.94). The multivariate model for prediction indicated that TAMM velocity was a better predictor than EDV, and PSV and TAMM were approximately equivalent. PSV cutpoints defining the two relevant STOP risk categories—conditional, which should lead to increased TCD surveillance, and abnormal, which should lead to strong consideration for treatment according to STOP—were derived taking into consideration known differences in measurements between the dedicated Doppler systems (TCD) used in STOP and the transcranial Doppler imaging (TCDI) systems commonly used in clinical practice. The recommended PSV cutpoint for conditional TCD is 200 cm/s, and for abnormal TCD triggering consideration for treatment is 250 cm/s.Conclusion Assuming TCDI equipment is used and the STOP protocol is applied, a PSV cutpoint of 200 cm/s is recommended as the threshold for increased TCD surveillance (comparable to a TCD TAMM of 170 cm/s in STOP); a PSV of 250 cm/s is recommended as the cutpoint at which, if confirmed in a second examination, chronic transfusion should be considered. Assuming the STOP scanning protocol is used, PSV is at least as good as TAMM and can be used to select children with SCD for treatment or increased surveillance to prevent first stroke.     

Continuous haemodynamic monitoring in children: use of transoesophageal Doppler

A wide range of invasive and non-invasive techniques for monitoring the haemodynamic condition of critically ill patients is now available. A general reluctance on the part of paediatric intensive care specialists to use pulmonary artery thermodilution catheters and the need for constant realignment of hand-held Doppler probes has necessitated the search for a technique which is relatively non-invasive and provides continuous information on the haemodynamic condition of critically ill paediatric patients. We sought to establish if transoesophageal Doppler fulfilled these criteria. Eleven children who had recently undergone cardiac surgery were studied. Median age was 39 months and weight 14.9 kg. Five simultaneous pairs of measurements of cardiac index (CI: thermodilution) and minute distance (MD: transoesophageal Doppler) were made, as a baseline, when each child was haemo-dynamically stable. Following a fluid challenge, five repeat pairs of measurements were made. The mean percentage changes for CI and MD were 16.4% (range 5.3-44%) and 16.6% (3.4-47.7%), respectively. The average coefficients of variation for measurements of CI and MD were 3.5% and 2.9%, respectively. The mean difference in percentage change between CI and MD was -0.5% (95% confidence interval for the bias –4% to 3%; limits of agreement –10.7 to +9.7%). Our study indicates that transoesophageal Doppler is reproducible, easy to use and provides clinically acceptable information when following changes in CI in haemodynamically stable paediatric patients. ? Cardiac index, minute distance, pulmonary artery catheter, thermodilution, transoesophageal Doppler     

Measurement of functional residual capacity in rabbits and children using an ultrasonic flow meter

A sulfur hexafluoride (SF(6)) washin/washout technique was developed using an ultrasonic flowmeter to measure functional residual capacity (FRC) during mechanical ventilation. The ultrasonic flowmeter measures simultaneously flow and molar mass of the mainstream gas. Ventilation distribution was studied using moment ratios analysis (alveolar-based mean dilution number). Accuracy and precision of the measurement technique were tested in a mechanical lung model, and the method's sensitivity to changes of FRC was assessed in seven ventilated rabbits and six children. In the mechanical lung model with a volume range from 10 to 60 mL, the mean error of FRC measurement was 0.096 +/- 0.9 mL (range, 0-2 mL). In seven rabbits (mean body weight, 3.6 kg), measurements of FRC and alveolar-based mean dilution number were made at positive end-expiratory pressures (PEEP) of 0, 3, and 6 cm H(2)O. The mean coefficient of variation of 66 FRC-measurements was 5.5% (range, 0-15.3%). As the applied PEEP increased, mean FRC per kilogram body weight increased from 13.3 +/- 3.4 mL/kg (PEEP of 0 cm H(2)O) to 16.7 +/- 3.6 mL/kg (PEEP of 3 cm H(2)O) and to 20.8 +/- 4.3 mL/kg (PEEP of 6 cm H(2)O). Alveolar-based mean dilution number decreased accordingly from 1.94 +/- 0.42 (PEEP = 0; mean +/- SD), to 1.91 +/- 0.45 (PEEP = 3) and to 1.59 +/- 0.35 (PEEP = 6). In the six children, as applied PEEP increased, mean FRC per kilogram increased from 21.1 +/- 4.51 mL/kg (PEEP = 0), to 22.4 +/- 1.8 mL/kg (PEEP = 5) and 27.2 +/- 3.4 mL/kg (PEEP = 10). FRC measurement using the ultrasonic flowmeter is accurate and simple to use in ventilated and spontaneously breathing children.     

Intraobserver variation in Doppler ultrasound assessment of pulmonary artery pressure.

Intraobserver variation associated with the non-invasive assessment of pulmonary artery pressure (PAP), using measurement of pulmonary artery Doppler derived systolic time intervals, was investigated. Forty pairs of independent ultrasound examinations of the pulmonary artery were performed by a single observer in 20 preterm infants, median gestation 27 weeks (range 24-31 weeks). Median age at study was 17 days (range 1-47 days). paired measurements of acceleration time (AT), ratio between acceleration time and right ventricular ejection time (AT:RVET), corrected AT, and corrected AT:RVET were compared to assess intraobserver agreement. For the corrected AT:RVET ratio, the mean percentage difference between observations was -0.9% (95% confidence intervals -5.0 to 3.1%). The limits of agreement for the two measurements were -26.3 to 24.5%. The coefficient of repeatability was 25.4%. Variation for other indices was similar. Non-invasive assessment of PAP using Doppler derived systolic time intervals is associated with considerable intraobserver variation.