Changes in intrathoracic blood volume associated with pneumoperitoneum and positioning

BACKGROUND: It is still controversial whether elevated cardiac filling pressures after the onset of pneumoperitoneum are the consequence of increased intrathoracic pressure or of increased venous return. The aim of this study was to assess the effects of pneumoperitoneum and body positioning on intrathoracic blood volume (ITBV). METHODS: Thirty anesthetized patients were randomly assigned to have CO2-pneumoperitoneum (13 mmHg) either in a supine, in a 15 degrees head-up tilt or in a 15 degrees head-down tilt position. Measurements of ITBV and hemodynamics by the double indicator method were recorded after induction of anesthesia and application of a fluid bolus (Lactated Ringer's solution 10 ml/kg), after positioning and after induction of pneumoperitoneum. RESULTS: Intrathoracic blood volume index (ITBVI) increased significantly after induction of pneumoperitoneum in all body positions (supine: from 18.5 +/- 3.3 -20.2 +/- 5.2 ml/kg (+6%) head-up from 16.7 +/- 3.8 - 17.4 +/- 3.7 ml/kg (+16%) and head-down: from 19.8 +/- 5.6 - 20.5 +/- 5.9 ml/kg (+14%)). Heart rate did not change significantly in any of the groups. Cardiac index showed a statistically significant change in the head-down position with pneumoperitoneum (-11%). A good correlation was found for stroke volume (SV) with ITBV (r = 0.79), but not with central venous pressure (r = 0.26). Systemic vascular resistance index increased significantly in all three groups (supine +6%, head-up +16%, head-down position +14%). CONCLUSION: The present study indicates that the onset of pneumoperitoneum, even with moderate intra-abdominal pressures, is associated with an increased intrathoracic blood volume in ASA I/II patients.     

Pneumoperitoneum versus abdominal wall lift: effects on central haemodynamics and intrathoracic pressure during laparoscopic cholecystectomy

BACKGROUND: It has been shown repeatedly that laparoscopic cholecystectomy using pneumoperitoneum (CO2 insufflation) may be associated with increased cardiac filling pressures and an increase in blood pressure and systemic vascular resistance. In the present study, the effects on the central circulation during abdominal wall lift (a gasless method of laparoscopic cholecystectomy) were compared with those during pneumoperitoneum. The study was also aimed at elucidating the relationships between the central filling pressures and the intrathoracic pressure. METHODS: Twenty patients (ASA I), scheduled for laparoscopic cholecystectomy, were randomised into two groups, pneumoperitoneum or abdominal wall lift. Measurements were made by arterial and pulmonary arterial catheterization before and during pneumoperitoneum or abdominal wall lift with the patient in the horizontal position. Measurements were repeated after head-up tilting the patients as well as after 30 min head-up tilt. The intrathoracic pressure was monitored in the horizontal position before and during intervention using an intraesophageal balloon. RESULTS: After pneumoperitoneum or abdominal wall lifting there were significant differences between the two groups regarding MAP, SVR, CVP, CI, and SV. Analogous to previous studies, in the pneumoperitoneum group CVP, PCWP, MPAP, and MAP as well as SVR were increased after CO2 insufflation (P < 0.01), while CI and SV were not affected. In contrast, in the abdominal wall lift group, CI and SV were significantly increased (P < 0.01), as was MAP (P < 0.01), while CVP, PCWP, MPAP, and SVR were not significantly affected. There was a significant difference in intraesophageal pressure between the two groups. In the pneumoperitoneum group, the intraesophageal pressure was increased by insufflation (P < 0.01) while, in the abdominal wall lift group, it was unaffected. In the pneumoperitoneum group the mean increases in cardiac filling pressures were of the same magnitude as the mean increase in the intraesophageal pressure. CONCLUSIONS: In healthy patients, abdominal wall lift increased cardiac index while pneumoperitoneum did not. Cardiac filling pressures and systemic vascular resistance were increased by pneumoperitoneum but unaffected by abdominal wall lift. The recorded elevated cardiac filling pressures during pneumoperitoneum may be only a reflection of the increased intra-abdominal pressure.     

Intrathoracic and pulmonary blood volume during CO2-pneumoperitoneum in humans

Background : Induction of CO₂-pneumoperitoneum may have significant effects on systemic and pulmonary haemodynamics. We hypothesized, that intrathoracic (ITBV) and pulmonary blood volume (PBV) are affected during intra-abdominal CO₂-insufflation, which may be pronounced by positional changes of the patient.
Methods : Sixteen anaesthetized patients were studied before, during and after CO₂-pneumoperitoneum for laparoscopic cholecystectomy. A dye indicator technique was used to assess ITBV and PBV. In addition, gas exchange and haemodynamics were recorded.
Results : In the supine position, induction of CO₂-pneumoperitoneum had no effects on ITBV, PBV and cardiac output. Mean systemic arterial pressure increased from 10.9±1.5 kPa (82±11 mmHg) to 12.7±1.5 kPa (95±11 mmHg, P<0.01). In the reverse Trendelenburg position ITBV decreased from 19.8±5.1 ml . kg^-1 to 16.7±3.7 ml . kg¹ ( P <0.05) during CO₂-insufflation, but increased to control values after 20 min. PBV decreased from 4.2±1.2 ml . kg^-1 to 3.4±1.1 ml . kg^-1 (P<0.05) and remained decreased during CO₂-pneumoperitoneum. Calculated venous admixture was unchanged throughout the study. Deflation of CO₂-pneumoperitoneum increased ITBV (22.4±5.2 ml . kg^-1, P<0.05) and cardiac output above control values.
Conclusions : In anaesthetized-paralyzed patients in the reverse Trendelenburg position intra-abdominal CO₂-insufflation is associated with significant alterations of ITBV and PBV. The release of CO₂-pneumoperitoneum is associated with a re-distribution of blood into the thorax.     

Stroke volume variation does not predict fluid responsiveness in patients with septic shock on pressure support ventilation

BACKGROUND: Stroke volume variation (SVV)--as measured by the pulse contour cardiac output (PiCCO) system--predicts the cardiac output response to a fluid challenge in patients on controlled ventilation. Whether this applies to patients on pressure support ventilation is unknown. METHODS: Thirty consecutive patients with septic shock were included. All were on pressure support ventilation, monitored using the PiCCO system and receiving 500 ml of colloid on clinical indications. Arterial pulse contour SVV and the transpulmonary thermodilution cardiac index were measured before and after fluid challenge. RESULTS: Forty-seven per cent of the patients were defined as fluid responders by an observed increase of > 10% in the cardiac index after fluid. Prior to fluid challenge, the cardiac index was lower in responders compared with non-responders (mean +/- SD, 3.0 +/- 0.6 vs. 4.0 +/- 1.2 l/min/m2, P < 0.01). In contrast, pre-infusion values of SVV were similar between subsequent responders and non-responders (13 +/- 5 vs. 16 +/- 6%, P =0.26). The mean areas under the ROC curves were 0.77 (95% confidence interval, 0.60-0.94) and 0.52 (0.30-0.73) for pre-fluid cardiac index and SVV, respectively, indicating a predictive power of only the cardiac index. CONCLUSIONS: SVV did not predict the response in cardiac output to fluid challenge in patients with septic shock on pressure support ventilation.     

Estimation of the parameters of cardiac function and of blood volume by arterial thermodilution in an infant animal model

BACKGROUND: Experimental studies in adults and in animals have reported that estimation of the intracardiac volumes by arterial thermodilution is a more reliable method of blood volume estimation than pressure measurement. The objective of this study has been to analyze the values of cardiac function and blood volume in an infant animal model using the arterial thermodilution technique. METHODS: A total of 202 measurements of cardiac output were performed by femoral arterial thermodilution in 38 Maryland piglets weighing between 8 and 16 kg, to determine the normal values of blood volume obtained by arterial thermodilution (PiCCO method) in an infant animal model. The following parameters were measured: blood volume [global end-diastolic volume index (GEDVI), total intrathoracic blood index (ITBI), extravascular lung water index (ELWI), systolic volume index (SVI)] and parameters of cardiac and vascular function [systolic volume index (SVI), cardiac function index (CFI), left ventricular contractility (Dp/dtmax), and systemic vascular resistance index) (SVRI)]. RESULTS: The cardiac index, 4.3 +/- 1.2 l x min(-1) x m(2), was within the normal range. The GEDVI, 198 +/- 48.6 ml x m(2), and ITBI, 574.1 +/- 113.4 ml x m(2), were lower than the normal values reported in adults, whereas the ELWI, 16.3 +/- 5.2 ml x kg(-1), was higher. CONCLUSIONS: Intrathoracic and intracardiac volume values obtained by arterial thermodilution are lower than those considered normal in the adult, whereas the extravascular lung water is higher. These values must be taken into account when the PiCCO method is used in small children.     

Negative effect of insufflation on cardiac output and pulmonary blood volume

In 14 anaesthetized young pigs the changes in pulmonary blood flow and pulmonary blood volume (Qp) during mechanical ventilation were quantified. Ventilation was performed at 10 cycles per min and tidal volume (VT) was adjusted to an arterial PCO2 of about 40 mmHg (5.3 kPa). In 4 animals, 7 ventilatory cycles with an inspiratory pause (IP) of 7.2 s but different tidal volumes were inserted at intervals of 5 min to determine the decrease in Qp (delta Qp) from the differences between right ventricular (Qs,rv) and left ventricular (Qs,lv) stroke volume, and to relate delta Qp to VT. We measured pressure in the aorta (Pao), central veins (Pcv), right and left ventricles (Prv, Plv) pericardium (Pit), and trachea (PT). Blood flow was measured electromagnetically (EM) in the pulmonary artery (Q'pa) and aorta (Q'ao). Stroke volumes were derived from the EM-flow curves. In the other 10 experiments, Qs,lv was derived from the aortic pulse contour. Beat-to-beat analyses of Qs,rv and Qs,lv and blood pressures during the normal ventilatory cycles and those with an IP revealed the following: 1) The end-expiratory RV output and LV output were constant and were defined as baseline values. 2) The accumulated decrease in Qs,rv during insufflation caused a mean deficit in cardiac output of 10.3 +/- 3.2% (s.d.), n = 135; the same was found for Qs,lv, indicating the pulse contour as a useful method to estimate the variations in cardiac output during a ventilatory cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

脉搏指示连续心排血量技术在心脏前负荷测量的应用近况

监测心脏负荷变化对了解心脏功能具有十分重要的临床意义。中心静脉压(CVP)与右心前负荷虽存在一定关系,但不能完全反映左心前负荷。经动脉插管入左心房及肺动脉漂浮导管(Swan-Ganz导管)测量肺小动脉嵌顿压(PCWP)评估左心前负荷的方法,虽能为判断心脏前负荷提供较为可靠的依据,     

Hemodynamic changes associated with thermodilution cardiac output determination in canine acute blood loss or endotoxemia

Since the technique of thermodilution (TD) cardiac output measurement, per se, causes hemodynamic alterations, the author examined whether the alterations elicited by iced injectate are augmented in the presence of acute blood loss or endotoxemia, compromized conditions frequently associated with critically ill patients. Acute blood loss (N = 8) and endotoxemia (N = 8) were induced by withdrawing arterial blood approximately 20–30 ml kg^-1 over 30 min and by a slow intravenous infusion of E. coli endotoxin 2.5-3.0 mg kg^-l over 10 min, respectively, in anesthetized dogs. The magnitudes of decreases in mean arterial and pulmonary artery pressures during slowing of heart rate (HR) following injection of iced injectate 3 ml were slightly less in acute blood loss than in normovolemia, whereas in endotoxemia the degree of mean arterial pressure decrease during slowing of HR following iced injectate 3 ml was slightly less as compared with that before endotoxemia. However, the alterations in other hemodynamic variables following injection of iced injectate 3 ml were similar between dogs with and without acute blood loss or endotoxemia. No profound hemodynamic changes were observed during any TD cardiac output measurements under both conditions. Cardiac output estimated by TD correlated closely with pulmonary blood flow measured by electromagnetic flowmeter in endotoxemia (r > 0.9) but not during acute blood loss. These results indicate that TD cardiac output determination does not cause serious hemodynamic alterations in endotoxemia or acute blood loss, and can estimate right ventricular output accurately in endotoxemia but not in acute blood loss.     

Trendelenburg positioning does not prevent a decrease in cardiac output after induction of anaesthesia with propofol in children

BACKGROUND AND OBJECTIVE: Induction of anaesthesia may cause decreased cardiac output and blood pressure. Head-down tilt is often the first clinical step to treat hypotension. The objective of this randomized single centre study was to determine, with the use of impedance cardiography (ICG), whether Trendelenburg positioning modifies the haemodynamic response to propofol/fentanyl induction of anaesthesia in ASA I children. METHODS: Thirty ASA I children aged between 7 and 16 years scheduled for elective minor orthopaedic surgery were included. After intravenous induction with propofol and fentanyl in the head-down group (HDG, n = 15), 5 min of 20 degrees head-down tilt was applied. In the supine group (SG, n = 15), no change in the supine position was made. Heart rate (HR), mean arterial blood pressure (MABP), end-tidal carbon dioxide (ETCO(2)), stroke volume index (SVI), cardiac index (CI), systemic vascular resistance index (SVRI) and Heather index (HI) were recorded before (B), at 3 (A(3)), 5 (A(5)) and 8 (A(8)) minutes after induction in each group. RESULTS: After induction, a significant decrease in CI, MABP, HR and HI was recorded in both groups. In the study group, significantly lower values of HR (66 vs. 78 beat/min) and higher values of SVI (42.9 vs. 40.6 ml/min/m(2)) were measured at A(3) compared with the control group. After induction, no difference in CI and SVRI was found between the two groups. CONCLUSION: The present study shows that cardiac performance is not improved by Trendelenburg positioning after propofol/fentanyl induction of anaesthesia in children.     

Haemodynamic, acid-base and blood volume changes during prolonged low pressure pneumoperitoneum in rabbits

Background. The anaesthetic management of small infants duringadvanced laparoscopic surgery can be complicated by the majorpathophysiological effects of increased intra-abdominal pressure.In this study haemodynamic, acid–base and blood volumechanges were investigated during pneumoperitoneum in a smallanimal model. Methods. Ten fasted, anaesthetized, mechanically ventilatedand multi-catheterized New Zealand rabbits were randomized tocarbon dioxide pneumoperitoneum (PP, duration 210 min, pressure8 mm Hg) or control group. Cardiac index was determined usingtrans-cardiopulmonary thermodilution and total blood volumewas measured by thermal-dye dilution with indocyanine greenusing a fibreoptic monitor system. Results. In PP cardiac index (CI), central venous oxygen saturation(SCV_O2), total blood volume (TBV) and base excess (BE) decreasedsignificantly during the study whereas all variables remainedconstant in the control group. After release of PP the measuredvariables did not return to baseline within 30 min [PP, baselinevs study end: CI 108 (22) vs 85 (14) ml kg^–1 min^–1,SCV_O2 81.4 (8.9) vs 56.7 (9.8)%, TBV 318 (69) vs 181 (54) ml,BE –1.9 (2.7) vs –8.7 (1.8) mmol litre^–1;P<0.01]. Conclusion. Our animal model suggests that a decrease in CI,metabolic acidosis and hypovolaemia could occur after prolongedlow pressure pneumoperitoneum in small infants, which is possiblynot detectable by the standard monitor setting. Therefore, theroutine use of an extended monitoring including measurementof central venous oxygen saturation and acid–base parametersshould be considered during and soon after operation, when pneumoperitoneumwill last longer than 2 h.     

Lack of agreement between thermodilution and carbon dioxide-rebreathing cardiac output

BACKGROUND: A continuous, accurate, non-invasive monitor of cardiac output would represent a major step forward in patient management. A cardiac output computer, NICO2, based on the Fick principle and an automatic partial carbon dioxide (CO2)-rebreathing technique has just become available. We compared the performance of this monitor with the standard thermodilution method. METHODS: Thirty patients were investigated after cardiac surgery. Replicate measurements were performed simultaneously with the thermodilution and NICO2 techniques. An Altman-Bland analysis was used to assess repeatability of each of the two methods and to determine the agreement between the two techniques. RESULTS: The repeatabilities of thermodilution and CO2-rebreathing cardiac output were excellent, with coefficients of repeatability of 0.35 l/min and 0.60 l/min. Mean thermodilution and NICO2 cardiac output were 4.4 l/min (SD 0.9, range 2.7-6.1) and 4.6 l/min (SD 1.3, range 1.6-6.9). A comparison of the methods, however, revealed excessive limits of agreement (+/-1.80 l/min). CONCLUSION: The agreement between the NICO2 derived cardiac output and the de facto standard - thermodilution cardiac output - is poor. The methods are not interchangeable with the present version of the NICO2. The repeatability of the partial CO2-rebreathing technique holds promise that a sufficient accuracy may be obtained by suitable modifications of the monitor's algorithms.     

Metabolic regulation of cardiac output during inhalation anaesthesia in dogs

BACKGROUND: The metabolic regulation of tissue blood flow manifests itself in a linear relation between blood flow and oxygen consumption, the latter being the independent variable. It is unknown, however, if this fundamental physiological principle operates also during inhalation anaesthesia known to be associated with decreases in both cardiac output (Q) and oxygen consumption (VO2). METHODS: Seven dogs (23-32 kg) with chronically implanted flow probes around the pulmonary artery were repeatedly anaesthetized with halothane, enflurane, isoflurane, sevoflurane, and desflurane at increasing minimum alveolar concentrations (1-3 MAC). Cardiac output (ultrasound transit-time flowmeter) and VO2 (indirect calorimetry) were measured continuously. We also imposed selective changes in Q, and thus of O2 supply, to see if and to what extent this would alter VO2 during anaesthesia (1.5 MAC). RESULTS: In awake dogs under basal metabolic conditions, VO2 was 4.6 +/- 0.1 ml.kg-1.min-1 and Q 105 +/- 3 ml.kg-1.min-1 (mean +/- SEM). During inhalation anaesthesia, VO2 and Q decreased by approximately 30% and 60%, respectively. The concentration-effect relations of both variables did not differ between anaesthetics, yielding a uniform Q/VO2 relation, which was nearly linear in the range (0-2 MAC) with an average slope of 39 +/- 1 (range 30-55). Above 2 MAC, Q decreased more for a given change in VO2, and O2 extraction increased by 50%, indicating compromised oxygen delivery (DO2). Imposed changes in Q, both in awake and anaesthetized dogs, yielded Q/VO2 relations which were notably steeper (slopes 114 to 187) than those observed during inhalation anaesthesia. More important, imposed increases in Q and thus DO2 during anaesthesia (1.5 MAC) to rates comparable to that in the awake state produced a much less than proportional increase in VO2 without restoring it to baseline. CONCLUSIONS: Inhalation anaesthesia is characterized by a uniform Q/VO2 relation with an almost linear course at an anaesthetic concentration up to 2 MAC, regardless of the anaesthetic. Metabolic regulation of blood flow apparently operates also during inhalation anaesthesia up to 2 MAC so that the decrease in VO2 determines Q. This implies that cardiac output alone provides little information on the function of the circulation during inhalation anaesthesia unless related to metabolic demands, i.e. to VO2.     

Intra- and inter-observer reliability using a noninvasive ultrasound cardiac output monitor in healthy anesthetized children

Background: Accurate and reliable evaluation of cardiac index (CI) in critically ill pediatric patients can optimize their management. Although validated, noninvasive ultrasound measurement techniques have been previously shown to be unreliable because of observer variability. Objective: To confirm intra‐ and inter‐observer reliability when using the noninvasive USCOM^® in healthy anesthetized children. Methods: Prospective observational study at the Children’s Hospital of Eastern Ontario, Ottawa, included newborns to 12 years of age undergoing elective surgery or magnetic resonance imaging. The USCOM^® was used to assess CI via aortic flow with a trans‐sternal approach. Two trained observers were responsible for taking two measurements of CI each at steady state in randomized succession after stable depth of anesthesia was achieved. Results: Fifty‐nine patients were included. Forty‐seven (80%) were between 3 and 7 years old, with 57% male. The mean difference ± sd for repeat CI measurements by each of two observers was 0.11 ± 0.47 and 0.05 ± 0.65 l·min^?1·m^?2, respectively. Intra‐observer reliability for these repeat measurements by each observer determined by Lin’s concordance correlation coefficient was 0.92 and 0.85, respectively. The mean difference ± sd between observers was 0.16 ± 0.59 l·min^?1·m^?2, and Lin’s concordance correlation coefficient was 0.87. The two observers subjectively rated measurements as ‘Difficult’ or ‘Very difficult’ only 14% (16/118) and 3% (4/118) of the time, respectively. No adverse events were reported. Conclusion: This study confirms that the USCOM^® is relatively easy to use and reliable in healthy children when operated by trained users.     

Changes in stroke volume cause change in cardiac output in neonates and infants when mean airway pressure is altered

Background: Based on early studies in the lamb, and in spite of more recent studies in humans, it has been the received opinion that neonates and infants can not change their stroke volume significantly, but are mainly dependent on changes in heart rate, to change cardiac output. To further evaluate the relationship between cardiac output and stroke volume during mechanical ventilation of neonates and infants, we have studied the effects on cardiac output and stroke volume by two different ways of changing mean airway pressure.
Methods: In one group, mean airway pressure was decreased by using a patient triggered mode: pressure support ventilation; in the other, mean airway pressure was increased by increasing positive end-expiratory pressure (PEEP). Changes in cardiac output, heart rate and stroke volume were assessed with the Doppler technique, measuring blood flow velocity in the ascending aorta.
Results: Without a significant change in heart rate, we found a significant increase in cardiac output of +16±2% ( P <0.01) with a decrease in mean airway pressure and a decrease in cardiac output of −13±4%, ( P <0.02) with an increase in mean airway pressure, depicting a change in stroke volume of +17±2% ( P <0.02) and −14±5%, ( P <0.01) respectively.
Conclusions: We conclude that neonates and infants are able to regulate cardiac output by changing the stroke volume to a greater extent than presumed, at least when cardiac output is influenced by changes in the mean airway pressure.     

A new method of using gas exchange measurements for the noninvasive determination of cardiac output: clinical experiences in adults following cardiac surgery

New mathematical algorithms have been applied to a computer controlled closed breathing circuit system for non-invasive measurement of cardiac output (COniv). This system has been described in an animal study. Forty patients were studied 5 and 18 hours after cardiac surgery using the thermodilution technique as the reference (COtd). The variables entered into the algorithms for COniv were oxygen uptake, carbon dioxide elimination, end-tidal carbon dioxide partial pressure, tidal volume and arterial oxygen saturation. Mixed venous carbon dioxide partial pressure was obtained from an automatically implemented short rebreathing manoeuvre. Pulmonary perfusion was calculated by a modified Fick equation for carbon dioxide and the shunt flow added to obtain COniv. During mechanical ventilation, there was a good agreement between COtd and COniv (r=0.8). The bias was -0.14 1/min and the precision was 0.77 1/min. The reproducibility of COniv was 0.03 1/min and for COtd -0.03 1/min with a standard deviation of the difference being 0.35 1/min for COniv and 0.31 1/min for COtd. In awake, but sedated extubated patients, the method proved unsatisfactory on account of uneven tidal volumes and difficulties with leakage around the mouth piece. We conclude that this new technique provides reliable and reproducible measures of cardiac output in sedated, ventilated patients.     

Precision of bolus thermodilution cardiac output measurements in patients with atrial fibrillation

Background: The precision of bolus thermodilution cardiac output measurements in patients with atrial fibrillation (AF) has not previously been determined. A priori we suspected that the precision would be lower in patients with AF than in patients with sinus rhythm (SR). Consequently, we also determined if the precision could be improved by injecting the thermal indicator into the right ventricle instead of the right atrium. Methods: Cardiac output was determined as the average result of four injections of 10 ml of iced saline. Replicate measurements were performed with thermal indicator injections into the right atrium and ventricle. The coefficients of variation and the precisions were calculated. Results: In the 25 patients with AF, mean cardiac output was 3.96 l min^?1 (range 2.4–7.4), the coefficient of variation 0.073 (95% CI ± 0.011), and the precision 0.38 l min^?1 (95% CI ± 0.14) with injection into the right atrium. In the 25 patients with SR, mean cardiac output was 4.73 l min^?1 (range 2.4–7.3), the coefficient of variation 0.047(95% CI ± 0.006), and the precision 0.38 l min^?1 (95% CI ± 0.14). In both groups, an agreement analysis demonstrated that the injection of indicator into the right ventricle resulted in a significantly higher cardiac output [AF+0.25 (95% CI ± 0.15) l min^?1, SR+0.29 ( ± 0.20) l min^?1]. Conclusion: The coefficient of variation for cardiac output determinations is 55% higher in patients with AF. Two measurements, separated by time or intervention, must differ by 15% in AF patients and 9% in SR patients before one can be 95% confident that a real change has taken place.     

Clinical validation of bioreactance for the measurement of cardiac output in pregnancy

Maternal cardiac dysfunction is associated with pre-eclampsia, fetal growth restriction and haemodynamic instability during obstetric anaesthesia. There is growing interest in the use of non-invasive cardiac output monitoring to guide antihypertensive and fluid therapies in obstetrics. The aim of this study was to validate thoracic bioreactance using the NICOM® instrument against transthoracic echocardiography in pregnant women, and to assess the effects of maternal characteristics on the absolute difference of stroke volume, cardiac output and heart rate. We performed a prospective study involving women with singleton pregnancies in each trimester. We recruited 56 women who were between 11 and 14 weeks gestation, 57 between 20 and 23 weeks, and 53 between 35 and 37 weeks. Cardiac output was assessed repeatedly and simultaneously over 5 min in the left lateral position with NICOM and echocardiography. The performance of NICOM was assessed by calculating bias, 95% limits of agreement and mean percentage difference relative to echocardiography. Multivariate regression analysis evaluated the effect of maternal characteristics on the absolute difference between echocardiography and NICOM. The mean percentage difference of cardiac output measurements between the two methods was ±17%, with mean bias of −0.13 l.min⁻¹ and limits of agreement of −1.1 to 0.84; stroke volume measurements had a mean percentage difference of ±15%, with a mean bias of −0.8 ml (−10.9 to 12.6); and heart rate measurements had a mean percentage difference of ±6%, with a mean bias of −2.4 beats.min⁻¹ (−6.9 to 2.0). Similar results were found when the analyses were confined to each individual trimester. The absolute difference between NICOM and echocardiography was not affected by maternal age, weight, height, race, systolic or diastolic blood pressure. In conclusion, NICOM demonstrated good agreement with echocardiography, and can be used in pregnancy for the measurement of cardiac function.     

Changes in circulating blood volume following isoflurane or sevoflurane anesthesia

Changes of circulating blood volume (CB volume) measured by the dual indicator dilution method were observed in 33 chronically instrumented mongrel dogs following either alpha-chloralose-urethane (C group), additive isoflurane (I group) or sevoflurane anesthesia (S group). These anesthetic groups were each divided into two subgroups with regard to respiratory care, namely Cp, Ip and Sp for those with intermittent positive pressure ventilation (six animals per subgroups), and Cs, Is and Ss for those with spontaneous breathing (five animals per subgroups).The CB volume under positive pressure ventilation remained unchanged in the Ip and Sp groups at both 0.5 and 1.0 MAC, and in the Cp group. The CB volume remained essentially unchanged in the Cs and Is groups at both 0.5 or 1.0 MAC, but the plasma volume tended to increase slightly in the Is group at 1.0 MAC.In the Ss group under spontaneous breathing, however, the CB volume increased from 84.4 ± 7.0 to 91.4 ± 7.7 at 0.5 MAC, and to 91.4 ± 10.2ml·kg^–1 at 1.0 MAC (0.01 P 0.05). These increases were caused by an increase in the plasma volume.The above data suggests that a concomitant increase in the venous pressure associated with an increase in the intrathoracic pressure produced by positive pressure ventilation would attenuate changes in the CB volume during sevoflurane anesthesia.(Hamada H, Takaori M, Kimura K, et al.: Changes in circulating Blood volume following isoflurane or sevoflurane anesthesia. J Anesth 7: 316–324, 1993)