Thermal safety of a filamented pulmonary artery catheter

Cardiac arrhythmias related to continuous thermodilution cardiac output measurement in an anaesthetized sheep

A case of cardiac arrhythmias related to continuous thermodilution cardiac output (CCO) is reported. A sheep anaesthetized for experimental purpose was instrumented with a special Swan-Ganz catheter-type to be used for CCO measurements. One hour after starting the CCO monitoring, isolated ventricular extrasystoles were noticed on the electrocardiogram with an increasing frequency. Subsequently bursts of extrasystoles occurred. Atrioventricular dissociation was also observed. The peaks of temperature of the thermal filament were within the normal range and their presence was noticed when arrhythmias appeared. Mean blood pressure and cardiac output did not change during this episode. When the CCO was switched off, no more arrhythmias were observed. The CCO Swan-Ganz by itself did not generate any arrhythmia. The sheep recovered uneventfully. When arrhythmias occur during anaesthesia where CCO is used, a thermal filament induced origin of the arrhythmia must be considered.

Uncalibrated Arterial Pulse Contour Analysis Versus Continuous Thermodilution Technique: Effects of Alterations in Arterial Waveform

OBJECTIVE

To compare an arterial pressure-derived cardiac output (APCO) (Vigileo software version 1.07; Edwards Lifesciences, Irvine, CA) and a thermodilution cardiac output (CCO) as methods for measuring cardiac output under different pathologic and experimental conditions that induce changes in arterial waveform morphology.

DESIGN

A prospective study.

SETTING

A university hospital, single institutional.

PARTICIPANTS

Fifty-two patients undergoing elective cardiac surgery.

INTERVENTIONS

Simultaneous APCO and CCO were compared in low-risk patients undergoing elective coronary artery surgery (without valvular disease) (control, n = 20), patients with aortic stenosis (AS, n = 10), aortic insufficiency (AI, n = 10), and intra-aortic balloon pump (IABP, n = 12). In the control group, additional data were registered before and after median sternotomy and phenylephrine administration.

MEASUREMENTS AND MAIN RESULTS

In the control group, Bland-Altman showed a bias of -3% (95% limits of agreement: -59% to +53%) before cardiopulmonary bypass (CPB) and of -1% (95% limits of agreement: -51% to +50%) after CPB. In the AS group, the bias was -5% (95% limits of agreement: -34% to +24%) before CPB and 1% (95% limits of agreement: -28 to +30%) after CPB. In the AI group bias was +32% (95% limits of agreement: -4% to +68%) before CPB and -2% (95% limits of agreement: -35% to +32%) after CPB. Median sternotomy decreased CCO by 10% +/- 10%, whereas it increased APCO by 56% +/- 28%. Phenylephrine administration decreased CCO by 11% +/- 16%, whereas it increased APCO by 55% +/- 34%.

CONCLUSIONS

Cardiac output measurement based on uncalibrated pulse contour analysis is able to reflect cardiac output measured with the continuous thermodilution method in patients undergoing uncomplicated coronary artery surgery. However, in situations in which the arterial pressure waveform is changed, agreement between techniques may be altered and data obtained with uncalibrated pulse contour analysis may become less reliable.

Continuous cardiac output measurement: arterial pressure analysis versus thermodilution technique during cardiac surgery with cardiopulmonary bypass

This study compared cardiac output measured with an arterial pressure-based cardiac output measurement system and a thermodilution cardiac output measurement system. We studied 36 patients undergoing cardiac surgery with cardiopulmonary bypass. Simultaneous arterial pressure-based and thermodilution cardiac output measurements were compared before and after cardiopulmonary bypass, and after phenylephrine administration. Bland-Altman analysis showed good overall agreement between the two methods. Bias (limits of agreement) before and after cardiopulmonary bypass were - 0.21 (- 2.97-2.55) lxmin(-1) and 0.01 (- 3.79-3.81) lxmin(-1), respectively. Phenylephrine administration decreased thermodilution cardiac output by a mean (SD) of 11 (16)% and increased arterial pressure-based cardiac output by 55 (34)%. We conclude that arterial pressure-based cardiac output and thermodilution cardiac output measurement systems yield comparable results during cardiac surgery with cardiopulmonary bypass. However, after phenylephrine administration, the two measurement systems provided opposing results.

Continuously assessed right ventricular end-diastolic volume as a marker of cardiac preload and fluid responsiveness in mechanically ventilated cardiac surgical patients

Introduction

Assessing cardiac preload and fluid responsiveness accurately is important when attempting to avoid unnecessary volume replacement in the critically ill patient, which is associated with increased morbidity and mortality. The present clinical trial was designed to compare the reliability of continuous right ventricular end-diastolic volume (CEDV) index assessment based on rapid response thermistor technique, cardiac filling pressures (central venous pressure [CVP] and pulmonary capillary wedge pressure [PCWP]), and transesophageal echocardiographically derived evaluation of left ventricular end-diastolic area (LVEDA) index in predicting the hemodynamic response to volume replacement.

Methods

We studied 21 patients undergoing elective coronary artery bypass grafting. After induction of anesthesia, hemodynamic parameters were measured simultaneously before (T1) and 12 min after volume replacement (T2) by infusion of 6% hydroxyethyl starch 200/0.5 (7 ml/kg) at a rate of 1 ml/kg per min.

Results

The volume-induced increase in thermodilution-derived stroke volume index (SVI_TD) was 10% or greater in 19 patients and under 10% in two. There was a significant correlation between changes in CEDV index and changes in SVI_TD (r² = 0.55; P < 0.01), but there were no significant correlations between changes in CVP, PCWP and LVEDA index, and changes in SVI_TD. The only variable apparently indicating fluid responsiveness was LVEDA index, the baseline value of which was weakly correlated with percentage change in SVI_TD (r² = 0.38; P < 0.01).

Conclusion

An increased cardiac preload is more reliably reflected by CEDV index than by CVP, PCWP, or LVEDA index in this setting of preoperative cardiac surgery, but CEDV index did not reflect fluid responsiveness. The response of SVI_TD following fluid administration was better predicted by LVEDA index than by CEDV index, CVP, or PCWP.

Pulse contour analysis versus thermodilution in cardiac surgery patients

BACKGROUND

Previous studies have demonstrated that there is a lack of agreement between intermittent cold bolus thermodilution (ICO) and a semicontinuous method with dilution of heat (CCO) in cardiac surgical patients following hypothermic extracorporeal circulation (HCPB). Therefore, the aim of the present study was to compare both ICO and CCO with continuous pulse contour analysis (PCCO): a method based on a fundamentally different principle of determining cardiac output (CO).

METHODS

A prospective criterion standard study of 25 cardiac surgery patients undergoing HCPB. Cardiac output was determined using the three methods (ICO, CCO, and PCCO) before and after HCPB up to 12 h after arrival on the ICU. Bias and precision were evaluated.

RESULTS

A total of 380 triple determinations of CO could be analyzed. During the entire study period bias PCCO-ICO was -0.14 l*/min (precision 1.16 l*/min) and bias CCO-ICO was -0.40 l*/min (precision 1.25 l*/min). Up to 45 min after bypass PCCO agreed with ICO (bias -0.21 l*/min, precision 1.37 l*/min), while bias CCO-ICO was -1.30 l*/min (precision 1.45 l*/min).

CONCLUSION

The agreement between PCCO and ICO in contrast to CCO in the first 45 min after HCPB indicates that CCO underestimates CO during this period.

Effects of body temperature on accuracy of continuous cardiac output measurements

Intermittent measurement of cardiac output is routine in the critically ill surgical patient. A new catheter allows real-time continuous measurement of cardiac output. This study evaluated the impact of body temperature variation on the accuracy of these measurements compared to standard intermittent bolus thermodilution technique. This prospective study in a university hospital surgical intensive care unit included 20 consecutive trauma patients. Data were collected with pulmonary artery catheters, which allowed both continuous (COC) and bolus (COB) thermodilution measurements. The catheter was placed through either the subclavian or internal jugular vein. Measurements for COB were performed using a bolus (10 cm3) of ice-cold saline with a closed-injectate delivery system at end-expiration. Computer-generated curves were created on a bedside monitor, and the average of three measurements within 10% of one another was used as COB. COC was determined as the average of the displayed CO before and after thermodilution CO measurements. Body temperature was measured from the pulmonary artery catheter and was grouped as < or =36.5 degrees C, 36.6-38.4 degrees C, and > or =38.5 degrees C. COB and COC were compared for agreement by plotting the mean of the differences (COB - COC) between the methods. The differences were plotted against the average of each pair and analyzed with linear regression. One hundred seventy-eight paired measurements were made over a period of 1 to 3 days. CO ranged from 3.7 to 15.5 L/min. Eighty-one percent of measurements were at a temperature of 36.5-38.4 degrees C. Approximately 7% of measurements were at a temperature below 36.5 degrees C and 11.2% were in patients with a core temperature above 38.5 degrees C. Correlation between the two techniques was 0.96, 0.91, and 0.82 for temperatures of < or =36.5 degrees C, 36.6-38.4 degrees C, and > or = 38.5 degrees C, respectively. In conclusion, the COC measurements correlate well with COB in trauma patients with a core temperature < or =38.5 degrees C. The accuracy degraded at higher temperatures, which may be related to the smaller signal-to-noise ratio at elevated body temperatures.

Evaluation of a new continuous thermodilution cardiac output monitor in cardiac surgical patients: a prospective criterion standard study

OBJECTIVE

To evaluate the accuracy of a new continuous cardiac output monitor in critically ill patients.

DESIGN

Criterion standard study.

SETTING

Cardiac surgery intensive care unit in a university hospital.

PATIENTS

Twenty cardiac surgical patients requiring intensive care treatment with pulmonary artery catheters after surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Cardiac output was monitored continuously with a modified pulmonary artery catheter that has a heating filament on the outside of the catheter. Four modes of data processing with different response times ("Normal," "Fast," "FastFilter," and "Urgent" modes) used by the monitoring system. A total of 240 determinations of cardiac output were performed using conventional bolus thermodilution technique; these results were compared with those obtained using three of the four continuous measuring modes available ("Normal," "FastFilter," and "Urgent"). Cardiac output ranged from 3.47 to 15.77 L/min (bolus thermodilution). The mean (bias) +/- SD of differences (precision) for all measurements was 0.40+/-1.26 L/min in the Normal mode (cardiac output <10 L/min: 0.34+/-0.66 L/min), 0.53+/-1.27 L/min in the FastFilter-mode (cardiac output <10 L/min: 0.60+/-0.75 L/min), and 0.63+/-1.34 L/min in the Urgent mode (cardiac output <10 L/min: 0.57+/-0.82 L/min).

CONCLUSIONS

Continuous cardiac output measurement using the thermodilution technique is reasonably accurate, reliable, and applicable in routine clinical practice. The values obtained using the Normal mode of the monitor agreed significantly better with the conventional thermodilution method than the results of the two other modes studied (FastFilter and Urgent). In addition, measurements in two patients with cardiac output values of >10 L/min did not agree with the results of the bolus thermodilution method.

Evaluation of the accuracy and response time of STAT-mode continuous cardiac output

OBJECTIVES

This study was conducted to compare continuous cardiac output (CCO) with bolus thermodilution cardiac output (BTD) at steady state, and to compare the response time of STAT CCO with that of trend CCO, mean arterial pressure, and mixed venous oxygen saturation [SvO2] during an acute hemodynamic change.

DESIGN

Prospective study.

SETTING

University hospital.

PARTICIPANTS

Twenty-nine patients undergoing cardiac surgery or liver transplantation.

INTERVENTIONS

STAT and trend CCO were compared with BTD cardiac output during steady state intraoperatively and postoperatively in the intensive care unit. Ten patients, who required epicardial pacing after cardiac surgery, were studied to compare the response time of STAT CCO with that of trend CCO, mean arterial pressure, and BvO2 after a 10% to 20% increase in pacing rate.

MEASUREMENTS AND MAIN RESULTS

A total of 108 cardiac output data sets were analyzed at steady state. Steady state was defined as stable heart rate and mean arterial pressure (+/- 5%) and stable central venous pressure (+/- 2 mmHg) measured immediately before and after each data set. Cardiac output ranged from 2.3 to 8.5 L/min. The correlation between STAT CCO and BTD was r = 0.94, and for trend CCO and BTD was r = 0.94. The bies and precision for STAT CCO versus BTD were 0.06 L/min (Cl 95%: -0.08 to 0.18) and 0.61 L/min. The bias and precision for trend CCO versus BTD were 0.06 L/min (Cl 95%: -0.04 to 0.16) and 0.49 L/min. Eleven data sets were analyzed to study response time of STAT CCO, which was defined as the first time the percent change of the mean of each variable was significantly increased from baseline. Significant increases in mean arterial pressure and SvO2 were detected after 30 seconds (2.5%, p = 0.01) and 90 seconds (2.0%, p = 0.04), respectively. A significant increase in STAT CCO was reached at 270 seconds (4.4%, p = 0.005). Trend CCO tended to increase but did not reach statistical significance within 6 minutes.

CONCLUSIONS

STAT and trend CCO are accurate and precise and show close agreement with BTD cardiac output at steady state. The faster algorithm of STAT CCO offers some advantage over trend CCO during an acute hemodynamic change. However, because of the averaging process for determining CCO, the response time of STAT CCO is slower than that of mean arterial pressure and SvO2.

Reproducibility of thermodilution cardiac output determination in critically ill patients: comparison between bolus and continuous method

OBJECTIVE

A semi-continuous thermodilution method (CCO) was recently developed to measure cardiac output with less risk of bacterial contamination, fluid overload, and user-induced errors than the classical bolus technique (BCO). Previous comparison between these two methods showed negligible bias. However, large limits of agreement suggest that the two methods are not interchangeable. We hypothesized that this poor agreement may be due to differences in reproducibility.

METHODS

In 23 critically ill patients, 369 paired measurements of CCO and BCO were compared (range of cardiac outputs: 2.8 to 16 L/min). The reproducibility of BCO and CCO methods was evaluated on a sample of 205 and 209 determinations, respectively.

RESULTS

The comparison between the CCO and the BCO methods confirmed previous results: i.e., small bias (-0.39 L/min) and large limits of agreement (-2.06 to +1.28 L/min). Reproducibility showed no bias for either the CCO or the BCO method. Limits of reproducibility agreement between repeated determinations were approximately 50% less for CCO than for BCO method: respectively -0.87 to +0.82 L/min for the CCO method and -1.56 to +1.37 L/min for the BCO method. Consequently, the threshold necessary to ascertain that the difference between two measurements was not due to the internal variability of the method (3 x SEM) was 0.39 for the CCO method and 0.75 L/min for the BCO method.

CONCLUSION

Differences in reproducibility may explain the poor agreement between the CCO and BCO methods. The better reproducibility of the CCO method allows the detection of smaller variations in cardiac output and suggests the superiority of this new method.

Semi-continuous versus injectate cardiac output measurement in intensive care patients after cardiac surgery

OBJECTIVE

Commercially available semi-continuous cardiac output (SCCO) monitoring systems are based on the pulsed warm thermodilution technique. There is evidence that SCCO fails to correlate with standard intermittent bolus cardiac output (ICO) in clinical situations with thermal instability in the pulmonary artery. Furthermore, ventilation may potentially influence thermodilution measurements by enhanced respiratory variations in pulmonary artery blood temperature and by cyclic changes in venous return. Therefore, we evaluated the correlation, accuracy and precision of SCCO versus ICO measurements before and after extubation.

DESIGN

Prospective cohort study.

SETTING

Intensive care unit (ICU) of a university hospital.

PATIENTS AND PARTICIPANTS

22 cardiac surgical ICU patients.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

SCCO and ICO data were obtained at nine postoperative time points while the patients were on controlled mechanical ventilation. Further sets of measurements were taken during the weaning phase 20 min before extubation, and 5 min, 20 min and 1 h after extubation. SCCO and ICO measurements yielded 286 data pairs with a range of 1.8-9.9 l/min for SCCO and 1.9-9.8 l/min for ICO. The correlation between SCCO and ICO was highly significant (r = 0.92; p < 0.01), accompanied by a bias of -0.052 l/min and a precision of 0.56 l/min. Correlation, accuracy and precision were not influenced by the mode of respiration.

CONCLUSIONS

Our results demonstrate excellent correlation, accuracy and precision between SCCO and ICO measurements in postoperative cardiac surgical ICU patients. We conclude that SCCO monitoring offers a reliable clinical method of cardiac output monitoring in ICU patients following cardiac surgery.

Continuous versus intermittent cardiac output measurement in cardiac surgical patients undergoing hypothermic cardiopulmonary bypass

OBJECTIVE

Continuous thermodilution cardiac output (CCO) measurement was clinically evaluated in patients who underwent coronary revascularization using hypothermic low-flow, low-pressure cardiopulmonary bypass (CPB).

DESIGN

Prospective study.

SETTING

University hospital setting.

PARTICIPANTS

30 cardiac surgical patients.

INTERVENTIONS

CCO was correlated to standard bolus thermodilution cardiac output (ICO) obtained at end-expiration.

MEASUREMENTS AND MAIN RESULTS

Measurements were taken at selected time points (n = 18) before anesthesia induction, before CPB, and 5 minutes to 12 hours after CPB. A total of 540 data pairs were thus obtained. ICO ranged from 1.9 to 9.9 L/min, CCO from 1.5 to 9.9 L/min. Correlation between ICO and CCO was highly significant (r = 0.872; p < 0.01), accompanied by an excellent accuracy (bias -0.0213 L) and precision (0.59 L) before CPB and more than 45 minutes after CPB. However, during the first 45 minutes after CPB, there was no correlation (r = 0.273) between ICO and CCO, and ICO tended to be relatively high, whereas CCO measurements showed relatively low values. During the first 45 minutes after hypothermic CPB, but not during the ensuing time period, central blood temperature decreased, which may be interpreted as a lack of thermal equilibration between central and peripheral compartments. It is hypothesized that thermal instability in combination with increased respiratory variations in pulmonary artery blood temperature caused inhomogenous rewarming of different body sites and might be the main reason for the lack of correlation between ICO and CCO.

CONCLUSIONS

Despite an excellent correlation, accuracy, and precision between CCO and ICO before CPB and more than 45 minutes after hypothermic CPB, a lack of correlation in the early phase after CPB has been found. Further investigation is needed to elucidate the underlying cause of these findings and to clarify whether ICO or CCO or both fail to represent the real cardiac output up to 45 minutes after weaning from hypothermic CPB.

Continuous cardiac output measurements in the perioperative period

Management of critically ill patients is based on knowledge of fundamental physiologic variables. Automatized and continuous measurement of these variables is preferable. A new system based upon the thermodilution method has been developed to measure cardiac output automatically and continuously. We evaluated the system in the potentially unstable perioperative period with possible great and rapid changes in cardiac output. Twenty patients, scheduled for open heart or abdominal aortic aneurysm surgery, were included in the study, which was approved by the local ethical committee. The patients were monitored up to 30 hours. At random intervals five, iced, bolus thermodilution cardiac output (BCO) determinations were made and compared to the continuous cardiac output measurements (CCO). Two hundred and thirty-one pairs of data were obtained. The cardiac outputs ranged from 2.5-14.9 l.min-1. The absolute bias was 0.31 l.min-1 (95% limits of agreement -14 l.min-1 to 2.0 l.min-1). The mean relative error was 4.7% with a standard deviation of the relative error of 15.4%. The linear regression was represented by: CCO = 1,1352.BCO-0.36. The correlation coefficient R was 0.90 (P < 0.001). In conclusion, the CCO measurement technique is a promising clinical method. The method is straightforward, requires no calibration, is independent of vascular geometry and measures with its limitations volumetric flow. Finally automatic and continuous patient monitoring provides more information and has potential to reveal previously undetected haemodynamic events.

Evaluation of a new continuous thermodilution cardiac output monitor in critically ill patients: a prospective criterion standard study

OBJECTIVE

To evaluate the accuracy of a new continuous cardiac output monitor (one based on the thermodilution principle) in critically ill patients.

DESIGN

Criterion standard study.

SETTING

Multidisciplinary intensive care unit in a university hospital.

PATIENTS

Fourteen critically ill patients, with different diseases, requiring pulmonary artery catheterization.

INTERVENTIONS

In two patients with a left ventricular assist system, a defined, sudden 1 L/min change in cardiac output was carried through to evaluate the in vivo response time of the continuous cardiac output monitoring system. In the remaining 12 patients, cardiac output was altered by varying the dose of catecholamines, by volume loading, or by varying the level of sedation. In four patients, a rapid infusion of cold saline was given through a central venous catheter to test the performance of the system under these conditions.

MEASUREMENTS AND MAIN RESULTS

Cardiac output was monitored continuously. A total of 163 (13 to 18 per patient) bolus determinations of cardiac output were performed, using the conventional thermodilution technique and simultaneously using the indocyanine green dye dilution technique. The range of cardiac output was 3.8 to 15.6 L/min. The results of the continuous thermodilution method were compared with the results of the bolus thermodilution and the dye dilution methods, respectively. The mean difference (bias) +/- SD of differences (precision) was 0.35 +/- 1.01 L/min for continuous vs. bolus thermodilution and 0.34 +/- 1.01 L/min for continuous thermodilution vs. indocyanine green dye dilution. Linear regression (correlation) analyses were y = 0.95x + 0.76 (r2 = .91) for continuous and bolus thermodilution and y = 0.93x + 0.87 (r2 = .91) for continuous thermodilution and dye dilution. The 75% in vivo response time was 10.5 mins. The infusion of cold isotonic saline led to erroneous continuous cardiac output values. When the conventional bolus thermodilution and dye dilution techniques were compared, mean difference was -0.01 +/- 0.54 L/min and the results of linear regression analyses were y = 0.97x + 0.22 (r2 = .97).

CONCLUSIONS

Continuous cardiac output measurement using the thermodilution technique is reasonably accurate and is reliable and applicable in routine clinical practice, and therefore may add to patient safety. However, the response time is too slow for the immediate detection of acute changes in cardiac output. Some clinical conditions such as the rapid infusion of cold solutions can interfere with the continuous cardiac output measurement. Conventional bolus thermodilution and indocyanine green dye dilution methods showed good agreement and can be used interchangeably.

Continuous thermodilution cardiac output measurement in intensive care unit patients

A new continuous thermodilution cardiac output measurement technique and companion flow-directed pulmonary artery catheter were evaluated in intensive care unit (ICU) patients. Continuous cardiac output was monitored for 6 hours in each patient, and, at selected intervals, a series of bolus thermodilution cardiac output determinations was made and averaged for comparison. A total of 222 data pairs was obtained in 54 patients. The cardiac outputs ranged from 2.8 to 10.8 L/min. The linear regression is represented by the following equation: continuous thermodilution = 0.99 bolus thermodilution + 0.02. The correlation coefficient r was 0.94, the Syx was 0.54. The mean relative error was 0.3%, and the standard deviation of the relative error was 11.5%. The absolute measurement bias was 0.02 L, and the 95% confidence limits were 1.07 and -1.03 L. The results demonstrated that the new continuous thermodilution cardiac output measurement technique provided acceptable accuracy and was considerably easier to use in the clinical situations studied in the ICU.