Partial CO2 Rebreathing Technique Research Articles

Minimally invasive or noninvasive cardiac output measurement: an update.

Although cardiac output (CO) by pulmonary artery catheterization (PAC) has been an important guideline in clinical management for more than four decades, some studies have questioned the clinical efficacy of CO in certain patient populations. Further, the use of CO by PAC has been linked to numerous complications including dysrhythmia, infection, rupture of pulmonary artery, injury to adjacent arteries, embolization, pulmonary infarction, cardiac valvular damage, pericardial effusion, and intracardiac catheter knotting. The use of PAC has been steadily declining over the past two decades. Minimally invasive and noninvasive CO monitoring have been studied in the past two decades with some evidence of efficacy. Several different devices based on pulse contour analysis are available currently, including the uncalibrated FloTrac/Vigileo system and the calibrated PiCCO and LiDCO systems. The pressure-recording analytical method (PRAM) system requires only an arterial line and is commercially available as the MostCare system. Transesophageal echocardiography (TEE) can measure CO by non-Doppler- or Doppler-based methods. The partial CO2 rebreathing technique, another method to measure CO, is marketed by Novametrix Medical Systems as the NICO system. Thoracic electrical bioimpedance (TEB) and electric bioreactance (EB) are totally noninvasive CO monitoring. Nexfin HD and the newer ClearSight systems are examples of noninvasive CO monitoring devices currently being marketed by Edwards Lifesciences. The developing focus in CO monitoring devices appears to be shifting to tissue perfusion and microcirculatory flow and aimed more at markers that indicate the effectiveness of circulatory and microcirculatory resuscitations.

Monitoring during mechanical ventilation

SUMMARY Monitoring is the continuous, or nearly continuous, evaluation of the physiologic function of a patient in real time to guide diagnosis and management decisions - including when to make therapeutic interventions and assessment of those interventions. Many physiologic parameters can be monitored during mechanical ventilation, including pulse oximetry, capnography, and ventilator graphics. Although its impact on patient outcomes has not been well studied, monitoring has become an integral part of the care of mechanically ventilated patients. Continuous pulse oximetry has become a standard of care for critically ill mechanically ventilated patients. Two wavelengths of light (660 nm and 940 nm) are passed through a pulsating vascular bed using two light-emitting diodes and a photodetector. This is translated into a plethysmographic waveform and the ratio of the amplitudes of these two plethysmographic waveforms is translated into a display of oxygen saturation. A number of limitations of pulse oximetry should be recognized, appreciated, and understood by everyone who uses pulse oximetry data. Most pulse oximeter errors can be explained as too little signal (e.g., low perfusion, improper probe placement) or too much noise (e.g., motion, ambient light). The newest generation of pulse oximeters is affected less by these potential errors. At saturations >80%, the accuracy of pulse oximetry is about 4–5%. Below 80%, the accuracy is worse, but the clinical importance of this is questionable. New pulse oximeters also measure carboxyhemoglobin and methemoglobin in addition to oxygen saturation. Capnometry is the measurement of CO2 at the airway opening during the ventilatory cycle. The relationship between the PaCO2 and end-tidal PCO2 will vary depending upon the relative contributions of various V/Q units of the lungs. Thus, caution should be exercised when extrapolating end-tidal PCO2 to PaCO2. End-tidal PCO2 is a standard of care to determine proper endotracheal tube position (no exhaled CO2 with esophageal placement). The slope of the capnogram is increased in patients with airway obstruction. Volume-based capnography can be used to assess carbon dioxide production (metabolic rate) and dead space ventilation. Using volume-based capnography, it is also possible to nonnvasively measure cardiac output with the partial CO2 rebreathing technique. Pulmonary mechanics is the expression of lung func

A comparison of noninvasive cardiac output measurement by partial carbon dioxide rebreathing with the lithium dilution technique in anesthetized foals

Newer techniques for cardiac output (Q) determinations that are minimally invasive remain to be validated in neonatal foals against other accepted techniques such as the lithium technique (LiDCO). This study compares Q determinations using the partial CO2 rebreathing technique (NICO) with LiDCO in anesthetized neonatal foals. Ten foals were instrumented for NICO and LiDCO determinations. For each foal low, intermediate and high levels of cardiac output were achieved in that order using an end-tidal isoflurane (ETI) concentration of 1.3 – 2.1% for the lowest rate; an ETI of 0.85–1.4% and a constant-rate infusion of dobutamine (1–3 ?g/kg/min) for the intermediate rate; and an ETI of 0.83–1% and dobutamine (2–6 ?g/kg/min) for the highest rate.

Cardiac Output Measurement

Maintaining tissue perfusion, thus, obtaining optimal oxygen delivery to the tissue is the final goal of hemodynamic monitoring. Cardiac output is the most valuable parameter among the hemodynamic variables. Although there is no true reference for the cardiac output monitoring, thermodilution cardiac output remains the current clinical standard for measuring cardiac output. New cardiac output techniques are compared with thermodilution method in accuracy and relevance, although thermodilution cardiac output monitoring has been shown to increase the morbidity and mortality, and mortality, and be inaccurate in several clinical settings. New techniques of cardiac output monitoring have been introduced to increase the safety, convenience, accuracy and reproducibility. Especially, to decrease the time-delay of therapeutic intervention, continuous monitoring is preferred. Among these, partial CO₂rebreathing technique based on Fick principle and esophageal Doppler technique are optimal for intraoperative and intensive care settings during mechanical ventilation. They are non- or minimally invasive methods and don`t need that much extra training to operate the machines. Esophageal Doppler monitoring provides further data on preload and contractility, but partial CO₂rebreathing technique does not. In case of cardiac or pulmonary dysfunction, cardiac output monitoring technique which could give more information about preload is beneficial. In cardiac surgery, transesophageal echocardiogram is getting to substitute for pulmonary artery catheter for cardiac output monitoring. For cardiac output monitoring, less invasive, more accurate, and continuous technique is preferred, but it should be chosen according to the clinical setting such as type of operation and cardiac and/or pulmonary function of the patient. (Korean J Anesthesiol 2004; 46: 1∼9)

Comparison of continuous cardiac output measurements in patients after cardiac surgery

Objective: To investigate in a direct comparison accuracy and precision of continuous cardiac output measurements assessed by continuous pulmonary artery thermodilution technique (TDCCO), continuous pulse contour analysis (PCCO), and noninvasive partial CO2-rebreathing technique (NICO) in patients after coronary artery bypass grafting (CABG) during the postoperative period. Design: Prospective, controlled clinical study. Setting: University hospital. Participants: Twenty-two patients undergoing elective CABG surgery. Interventions: Hemodynamic measurements were performed after admission to the ICU and in sequence every 2 hours during the subsequent 6-hour period. Simultaneously, cardiac output (CO) was measured using a TDCCO, PCCO, and NICO. After the continuous cardiac output measurements were read, bolus thermodilution-derived cardiac output was obtained from thermodilution curves detected in the pulmonary artery (TDBCOpa). Four intermittent consecutive boli consisting of 10 mL of ice-cold saline were randomly injected over the ventilatory cycle. Measurements and Main Results: The comparison between the continuous cardiac output measurement methods TDCCO versus PCCO showed a bias of −0.12 L/min, between TDCCO versus NICO −0.17 L/min, and between PCCO versus NICO −0.44 L/min. The comparison to the reference technique between TDBCOpa versus TDCCO revealed a bias of −0.28 L/min, between TDBCOpa versus PCCO −0.40 L/min, and between TDBCOpa versus NICO −0.64 L/min. Conclusions: The results of this clinical investigation show agreement between TDCCO and PCCO to satisfy clinical requirements in a setting of postoperative patients after cardiac surgery. In contrast, the NICO monitor is of very limited use in these patients. © 2003 Elsevier Inc. All rights reserved.

Performance of the partial CO2 rebreathing technique under different hemodynamic and ventilation/perfusion matching conditions

The partial CO2 rebreathing technique has been demonstrated to accurately measure the effective pulmonary capillary blood flow (PCBF) in different clinical situations. Usually, PCBF is calculated from changes in CO2 elimination (VCO2) and end-tidal partial pressure of CO2 (PetCO2 ), which can be obtained noninvasively. In this study, we investigated the performance of the partial CO2 rebreathing technique under different conditions of ventilation/perfusion matching and hemodynamic states. In addition, we investigated whether the determination of arterial blood gases combined with mathematical modeling of gas exchange can improve the performance of this method. Prospective, controlled animal laboratory study. Experimental research facility of a university hospital. Sixteen female sheep weighing 45-55 kg. Cardiac output and ventilation/perfusion matching were manipulated during three phases: phase I, variation in cardiac output to achieve normal, hyperdynamic and hypodynamic states; phase II, increase of alveolar deadspace and variation in cardiac output; phase III, lung injury and increased alveolar deadspace. Partial CO2 rebreathing maneuvers were performed to obtain variations in VCO2 and PetCO2 between a nonrebreathing (NR) and a rebreathing (R) period. PCBF was measured by the rebreathing method as PCBF = -DeltaVCO2/f(Pc'CO2 (R), Pc'CO2(NR), Hb), where f is the CO2 dissociation curve in blood, Pc'CO2 is the end-capillary partial pressure of CO2, Delta is the variation between NR and R periods, and Hb is hemoglobin concentration. Pc'CO2 was estimated from PetCO2 according to two algorithms. In the so-called "noninvasive algorithm," Pc'CO2 = PetCO2, with PetCO2(NR) and PetCO2(R) being determined as the mean PetCO2 value of the last 60 secs preceding rebreathing and within 15-30 secs of rebreathing, respectively. In the "semi-invasive algorithm," Pc'CO2(NR) was estimated as the PaCO2, and Pc'CO2(R) was estimated as follows: First, a monoexponential function was fitted to PetCO2 values during rebreathing and the asymptote represented PetCO2(R). Second, the Pc'CO2(R) to PetCO2(R) difference was calculated by means of a bicompartmental, tidal model of gas exchange, which showed that such differences decrease with the degree of rebreathing. PCBF values obtained with both algorithms were compared with thermodilution cardiac output minus intrapulmonary shunt flow. Bias and precision calculations with the noninvasive algorithm in phases I, II, and III were, respectively, -1.0 +/- 1.9, -2.1 +/- 2.6, and -2.4 +/- 1.2 L/min. The semi-invasive algorithm had an overall better performance in the phases investigated: -1.2 +/- 1.9, -0.6 +/- 2.0, and -0.2 +/- 3.0 L/min, respectively. The noninvasive algorithm showed a slight tendency to overestimate lower reference PCBF values and, importantly, to underestimate higher PCBF values in all three phases (r = -.66, p<.0001; r = -.75, p<.001; r = -.60, p<.0001, respectively). A similar figure was observed with the semi-invasive algorithm in phase I (r = -.47, p<.01) but not in phases II and III (r = -.1, p=.54; r =.62, p<.001, respectively). Although PCBF is systematically underestimated during hyperdynamic cardiac output states and high alveolar deadspaces, the performance of the partial CO2 rebreathing technique can be improved by means of arterial blood gas sampling and an algorithm that takes in account the effects of nonequilibration of PetCO2 during rebreathing and the variation of Pc'CO2 to PetCO2 differences from the nonrebreathing to the rebreathing period. Such an algorithm may prove useful under moderately increased alveolar deadspace and normal to hypodynamic cardiac output states.

Noninvasive Cardiac Output Measurements: Comparison of Partial CO2 Rebreathing Technique and Pulse Dye Densitometry Technique

Noninvasive Cardiac Output Measurements: Comparison of Partial CO2 Rebreathing Technique and Pulse Dye Densitometry Technique

Clinical evaluation of a partial CO2 rebreathing technique for cardiac output monitoring in critically ill patients

Monitoring central hemodynamics is essential in critically ill patients and less invasive techniques are needed. In this study, the clinical and technical performance of a new non-invasive cardiac output monitor (NICO) based on partial CO2 rebreathing technique and a modified Fick equation were evaluated. The various sources of possible errors in measurement of cardiac output (CO), carbon dioxide production (VCO2) and pulmonary shunt were also assessed. Simultaneous measurements of CO with partial CO2 rebreathing technique (CO(nico)) and thermodilution (CO(td)) were performed in 15 patients during major surgery or in the ICU. Pulmonary shunt was estimated from this device and compared to values obtained by standard shunt formula. The accuracy of VCO2 measurements was assessed in a mechanical lung model. A good correlation was found between CO(nico) and CO(td) (r = 0.96, within-subject correlation r = 0.88) with a small underestimation of cardiac output by the NICO of 0.04 L/min, limits of agreement (+/- 2 SD) being - 1.68 and 1.76 L/min. In hemodynamic unstable patients the method closely tracked changes in CO. Pulmonary shunt was underestimated by approximately 11%-units compared to standard shunt calculations using arterial and mixed venous blood gases. We also observed an underestimation in VCO2 measurements. Clinical evaluation shows that partial CO2 rebreathing technique provides a useful and accurate non-invasive estimate of cardiac output. Although this technique cannot fully replace the pulmonary artery catheter, it may be used to monitor central hemodynamics in a large number of critically ill patients.

Clinical evaluation of a partial CO2 rebreathing technique for cardiac output monitoring in critically ill patients

Clinical evaluation of a partial CO2 rebreathing technique for cardiac output monitoring in critically ill patients

Initial experience of cardiac output estimation by partial CO2 rebreathing technique

Initial experience of cardiac output estimation by partial CO2 rebreathing technique

Partial CO2 rebreathing indirect Fick technique for non-invasive measurement of cardiac output.

Evaluation in animals of a non-invasive and continuous cardiac output monitoring system based on partial carbon-dioxide (CO2) rebreathing indirect Fick technique. We have developed a non-invasive cardiac output (NICO) monitoring system, based on the partial rebreathing method. The partial rebreathing technique employs a differential form of the Fick equation for calculating cardiac output (QT) using non-invasive measurements. Changes in CO2 elimination (deltaVCO2) and partial pressure of end-tidal CO2 (deltaPETCO2) in response to a brief period of partial rebreathing are used to measure pulmonary capillary blood flow (Q(PCBF)). A non-invasive estimate of anatomic and intrapulmonary shunt fraction (Q(S)/Q(T)), based on oxygen saturation from pulse oximetry (SpO2) and inspired oxygen concentration (FIO2), is added to compute total cardiac output [Q(T) = Q(PCBF)/(1 - Q(S)/Q(T))]. The performance of the NICO was compared with iced 5% dextrose bolus thermodilution cardiac output (TDco) measurements in 6 dogs. Cardiac output was varied using dobutamine, and halothane, and by clamping of the inferior vena cava. Two hundred and forty-six (n = 246) paired measurements of TDco and NICO over a range of cardiac outputs (TDco range = 0.60-8.87 l/min) were compared using Bland-Altman analysis and weighted correlation coefficient. The Bland-Altman technique yielded a NICO precision of +/- 0.70 l/min (13.8%) with a mean bias of -0.07 l/min (-1.4%) compared to TDco. The weighted correlation coefficient between TDco and NICO values was: r = 0.93 (n = 246). The partial CO2 rebreathing technique for measurement of cardiac output is non-invasive, automated, and based on the well accepted Fick principle. The limits of agreement between NICO and TDco is within the recommended value for NICO to be a clinically acceptable method for cardiac output measurement. The results of this canine study show that NICO performed as well, and in some cases better, than other currently available non-invasive cardiac output techniques over a wide range of cardiac outputs.

Partial CO2 rebreathing cardiac output--operating principles of the NICO system.

The partial rebreathing method of cardiac output estimation is reviewed with a particular focus on its application for continuous monitoring, rebreathing and implementations and from both a historical and technical perspective. The assumptions of the method are discussed as well as the various implementations. The NICO monitor and rebreathing valve are described from a functional view. The clinical data including (a) comparisons between bolus thermodilution and continuous thermodilution in patients in the OR setting, (b) comparisons to continuous thermodilution with both the Baxter and Abbott continuous cardiac output devices and (c) comparison between different means of shunt correction are presented. Compared to conventional cardiac output methods, the partial CO2 rebreathing technique is non-invasive, can easily be automated and can provide real-time and continuous cardiac output monitoring. Taking advantage of modern sophisticated sensor and signal processing technology and integrating multiple monitored physiological variables the NICO monitor is the first commercially available cardiac output system making use of the partial rebreathing of CO2.

PARTIAL CO2 REBREATHING FICK TECHNIQUE FOR NONINVASIVE MEASUREMENT OF CARDIAC OUTPUT

Introduction: The noninvasive partial CO2 rebreathing technique uses a differential form of the Fick Equation tocalculate cardiac output (CO). The ratio of the change in end-tidal CO2 and CO2 excretion, in response to a brief period of rebreathing, gives a non-invasive estimate of the CO. [1,2] The method assumes that the difference between end-tidal and arterial CO2 content does not change during rebreathing. We have developed a partial CO2 rebreathing algorithm based on a two-compartment lung model, which minimizes error in estimation of CO when this assumption is not true. This model compensates for the changing end-tidal to arterial CO2 gradient during partial rebreathing. Methods: After IRB approval and patient consent the system was tested in seven patients (6 Male, 1 Female, Age 47-78 Years) undergoing cardiac surgery. End-tidal CO2 was measured using a mainstream CO2 analyzer and a disposable pneumotachograph (COSMO[registered sign], Novametrix Medical Systems, Wallingford, CT). CO2 production was calculated as the integral of the flow and CO2 signals over the entire breath. Actuation of a pneumatic valve under computer control resulted in breathing circuit changes, which increased airway dead space by 120 ml thereby causing partial rebreathing of exhaled gas. The valve was actuated for 50 seconds once every 3 minutes. Changes in CO2 excretion and etCO2 were used to calculate the partial CO2 rebreathing CO using the differential Fick equation. An average of three consecutive thermodilution cardiac output (TDco) measurements made during end expiration were compared with corresponding partial CO2 rebreathing cardiac output measurements. Measurements made during the first 45 minutes after bypass were discarded since thermal noise can make the TDco measurement unreliable [3]. Results: A total of 44 comparisons were made with CO ranging from 2.5 to 9.4 L/min. Regression analysis gives an r = 0.90 with a slope of 0.71 and an offset of 1.49 L/min. Bland-Altman analysis resulted in a bias of 0.07 L/min with a precision (1SD) of +/- 0.85 L/min. Discussion: The results suggest that partial CO2 rebreathing technique may be a clinically acceptable method for measurement of CO. Observed differences between the two techniques may have resulted from intrapulmonary shunts. The partial CO2 rebreathing system is completely automatic and can provide frequent, nearly continuous measurements of CO. (Figure 1)Figure 1

PARTIAL CO2 REBREATHING FICK TECHNIQUE FOR NONINVASIVE MEASUREMENT OF CARDIAC OUTPUT

Introduction: The noninvasive partial CO2 rebreathing technique uses a differential form of the Fick Equation tocalculate cardiac output (CO). The ratio of the change in end-tidal CO2 and CO2 excretion, in response to a brief period of rebreathing, gives a non-invasive estimate of the CO. [1,2] The method assumes that the difference between end-tidal and arterial CO2 content does not change during rebreathing. We have developed a partial CO2 rebreathing algorithm based on a two-compartment lung model, which minimizes error in estimation of CO when this assumption is not true. This model compensates for the changing end-tidal to arterial CO2 gradient during partial rebreathing. Methods: After IRB approval and patient consent the system was tested in seven patients (6 Male, 1 Female, Age 47-78 Years) undergoing cardiac surgery. End-tidal CO2 was measured using a mainstream CO2 analyzer and a disposable pneumotachograph (COSMO[registered sign], Novametrix Medical Systems, Wallingford, CT). CO2 production was calculated as the integral of the flow and CO2 signals over the entire breath. Actuation of a pneumatic valve under computer control resulted in breathing circuit changes, which increased airway dead space by 120 ml thereby causing partial rebreathing of exhaled gas. The valve was actuated for 50 seconds once every 3 minutes. Changes in CO2 excretion and etCO2 were used to calculate the partial CO2 rebreathing CO using the differential Fick equation. An average of three consecutive thermodilution cardiac output (TDco) measurements made during end expiration were compared with corresponding partial CO2 rebreathing cardiac output measurements. Measurements made during the first 45 minutes after bypass were discarded since thermal noise can make the TDco measurement unreliable [3]. Results: A total of 44 comparisons were made with CO ranging from 2.5 to 9.4 L/min. Regression analysis gives an r = 0.90 with a slope of 0.71 and an offset of 1.49 L/min. Bland-Altman analysis resulted in a bias of 0.07 L/min with a precision (1SD) of +/- 0.85 L/min. Discussion: The results suggest that partial CO2 rebreathing technique may be a clinically acceptable method for measurement of CO. Observed differences between the two techniques may have resulted from intrapulmonary shunts. The partial CO2 rebreathing system is completely automatic and can provide frequent, nearly continuous measurements of CO. (Figure 1)Figure 1

Partial carbon dioxide rebreathing

To determine the validity and clinical utility of the partial CO2 rebreathing technique for measurement of nonshunted pulmonary capillary blood flow and cardiac output. Prospective, controlled animal laboratory investigation and clinical trial. Animal research facility and intensive care unit of a university hospital. Fifteen adult sheep, weighting 58 to 78 kg. Mechanically ventilated patients with different underlying diseases (n = 12) and with adult respiratory distress syndrome (ARDS) (n = 8). CO2 elimination rate (VCO2) was measured breath-by-breath with a system developed for the study and also by gas collection (validation procedure in patients with different underlying diseases). Partial CO2 rebreathing maneuvers, cardiac output by thermodilution, and blood gas analysis were performed in sheep with lung atelectasis and in patients with ARDS. The degree of correlation between VCO2 measured with the system developed and gas collection was very good (r2 = .95, p < .0001), and bias and precision calculations (1 +/- 9 mL/min) showed close agreement between methods. The overall degree of correlation between partial CO2 rebreathing measurements and cardiac output was moderate (r2 = .54, p < .0001), the noninvasive method tending to underestimate cardiac output, as shown by bias and precision calculations (-1.69 +/- 1.90 L/min). In contrast, the overall degree of correlation between partial CO2 rebreathing measurements and nonshunted pulmonary capillary blood flow was good (r2 = .73, p < .0001). Bias and precision calculations (0.25 +/- 0.83 L/min) showed a tendency for the partial CO2 rebreathing technique to slightly overestimate pulmonary capillary blood flow. Variance differences between partial CO2 rebreathing measurements and cardiac output could be mostly explained by intrapulmonary right-to-left shunt fraction (r2 = .51, p < .0001). Our results support the use of the system developed for breath-by-breath VCO2 measurements. The lack of agreement between partial CO2 rebreathing measurements and cardiac output was mostly explained by intrapulmonary right-to-left shunt, suggesting that this technique may not be appropriate for monitoring cardiac output in patients with increased venous admixture. In contrast, our results demonstrate that the partial CO2 rebreathing technique is reliable for measurement of the effective nonshunted pulmonary capillary blood flow. This technique may prove useful to guide ventilatory therapy adjustments in an attempt to optimize nonshunted pulmonary capillary blood flow.