Thermistor Catheter Research Articles

A novel local impedance algorithm and contact force sensing to guide high power short duration radiofrequency ablation is efficient and safe for circumferential pulmonary vein isolation

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Local impedance (LI) drop can predict sufficient lesion formation during radiofrequency ablation (RF). Recently, a novel ablation catheter technology able to measure LI and contact force has been made available for clinical use. High power short duration (HPSD) RF ablation has been shown to be feasible for atrial fibrillation (AF) ablation with short procedure time. We used LI drop and plateau formation to guide duration of 50 Watt RF power applications for circumferential pulmonary vein isolation (PVI). Methods Consecutive patients with indication for de novo AF ablation (n = 32, age 65 ± 10 years) with paroxysmal (n = 16) or persistent (n = 16) AF underwent ultra high density 3D mapping of the left atrium and catheter ablation. Thereafter, ipsilateral PV encircling with 50 Watt RF-applications targeting an interlesion distance of ≤ 6mm and a contact force of 10-30g was performed. Duration of HPSD RF application between 7-15s was guided by impedance drop >20 Ohm and plateau formation of LI. Further ablation strategy was left to the investigator’s discretion. Esophageal temperature measurement was performed using a three thermistor catheter with temperature cut off 39.0°C. In case of temperature rise or very near esophageal contact to the circumferential line, RF application time was shortened to 7s. Patients underwent adenosine testing after PVI. Previously we performed all types of AF ablation using an LI guided HPSD ablation without contact force measurement capability in 80 patients. Results Complete PVI was achieved in all pts with only 13.5 ± 4.3 min cumulative RF application duration and an ablation procedure duration of 46.5 ± 10.4 min with the novel LI measuring catheter. First-pass isolation of ipsilateral veins was achieved in 75% of circles. Recurrence of PV conduction during waiting period (20min) and adenosine testing occured in 25% of circles, and was reablated in most patients with a single spot of HPSD application. Using 94 ± 36 RF application per patient, mean maximum LI drop was 23.6 ± 4.0 Ohm. Reconnected fibers were associated with low LI drop due to instability of contact in most cases due to breathing in case of difficult sedation of the patients. No serious complications occurred in all 32 pts using HPSD with the novel contact force catheter design. Conclusion Guiding of HPSD RF ablation by LI is highly efficient and safe. A novel local impedance algorithm in combination with contact force sensing enable short PVI times with low early recurrence of PV conduction. Prediction of permanent lesions seems possible and the only limitation seems to be unstable RF catheter contact due patients breathing. Follow up have to be waited.

Pulse index continuous cardiac output versus central venous pressure-based early goal-directed therapy for septic shock patients: a randomized trial

Background Central venous pressure-based early goal-directed therapy (EGDT) is considered the gold standard in the management of septic shock. We compared this approach with pulse index continuous cardiac output (PiCCO)-based EGDT in a randomized controlled study. Patients and methods Eighty septic shock patients were randomly divided into the conventional survival sepsis bundle group using central venous and arterial catheters (group C, n=40), and the modified survival sepsis bundle group using central venous and PiCCO arterial thermistor catheters (group P, n=40). Primary outcome included mortality at 28 days after diagnosis of shock. Secondary outcomes included ICU stay, days on mechanical ventilation, and renal replacement therapy (RRT). Results In comparison with group C, group P showed a lower mortality with no statistical differences at 28 days after diagnosis of shock [15 (37.5%) patients in the P group vs. 21 (52.5%) patients in the C group; P=0.11]. The population in the C group showed longer duration on ventilation, which was statistically significant [6 (5.0–7.0) in the C group vs. 3 (2.0–3.0) in the P group; P Conclusion PiCCO-based EGDT produced lower ICU stay, and shorter duration of ventilation and RRT; however, it did not reduce mortality in septic shock patients when compared with the conventional central venous pressure-based approach.

The Level of Cardiac Output Affects the Relationship and Agreement Between Pulmonary Artery and Transpulmonary Aortic Thermodilution Measurements in an Animal Model

The authors investigated the relationship between pulmonary artery and transpulmonary aortic thermodilution cardiac output measurements under conditions of increasing cardiac output (CO). Animal study with repeated simultaneous measurements comparing 2 cardiac output measurement techniques. Experimental animal facility of a university hospital. Ten female pigs. In anesthetized pigs, an aortic thermistor catheter and a pulmonary artery catheter (PAC) were inserted. Then dobutamine was infused under continuous cardiac output (CCO) monitoring to target different levels of CO. After each L/min increase of CCO simultaneous aortic and PAC thermodilution, CO measurements were performed by using a bolus injection of cooled normal saline and the amount of thermal indicator loss (TL) was calculated. Pooled analysis of CO data with the method of Bland and Altman showed that aortic thermodilution CO was higher than PAC thermodilution CO with a bias of 3.8% +/- 11.1%. The range of TL was 30.4% to -10.1%. Differential analysis according to the range of CO revealed that, in each animal under conditions of low CO, aortic thermodilution CO was higher than PAC thermodilution CO, whereas results were inverse under conditions of high CO. The authors concluded that the amount of CO differentially affects the relationship between aortic and PAC thermodilution CO. TL and recirculation may be the explanation for this finding.

Comparison of a Saline Irrigated Cooled-Tip Catheter to Large Electrode Catheters with Single and Multiple Temperature Sensors for Creation of Large Radiofrequency Lesions

Several catheter technologies for creating large radiofrequency (RF) lesions are used in clinical practice, but direct comparisons of the pathological lesions created by these technologies are unavailable. The purpose of this study was to compare the safety and efficacy of lesions created by three different large lesion RF ablation technologies. RF lesions were created in all four chambers of 15 mongrel dogs using 10 mm-tip multiple temperature sensor catheters, 10 mm tip single temperature sensor catheters, and 4 mm cooled-tip catheters. Pathological lesions were bisected, and measured after viability staining. A total of 242 (79 large-tip single sensor, 82 large-tip multiple sensor, and 81 cooled-tip) lesions were created. All atrial lesions were transmural but tended to have larger surface areas with the single thermistor large-tip catheter (73.4 +/- 24.8 mm2) compared to either the multithermistor large-tip (60.9 +/- 28.3 mm2) or the cooled-tip (61.9 +/- 28.5 mm2) catheters (p = 0.07), especially those in the IVC-TA isthmus. Depths and volumes of ventricular lesions created by the multiple-thermistor catheter (5.0 +/- 1.5 mm; 260 +/- 168 mm3) were smaller than either the single thermistor (5.7 +/- 1.5 mm; 428 +/- 290 mm3) or cooled-tip (6.1 +/- 1.8 mm; 403 +/- 217 mm3) catheters (p < 0.05). The difference in the depth and volume of lesions made by large-tip single thermistor and cooled-tip catheters was not significant. Char formation occurred during 11% of ablation with the single thermistor catheter, 6% with multithermistor and 8% of cooled-tip catheter (p = NS). There were no complications of ablation. All three catheters reliably created full thickness atrial lesions. For ventricular lesions, depths and volumes were similar for 10 mm-tip single thermistor and cooled-tip catheters. The multithermistor catheter lesions were smaller due to more precise temperature regulated power control. Safety was similar in all 3 groups.

Measuring cardiac output in one-lung ventilation: a comparison of pulmonary artery and transpulmonary aortic measurements in pigs

Objective: The agreement between cardiac output measurements via pulmonary artery thermodilution (CO[PA]) and transpulmonary aortic thermodilution (CO[AT]) during one-lung ventilation was studied. Design: Animal study with repeated simultaneous measurements comparing 2 cardiac output measurement techniques. Setting: Experimental animal facility of a university department. Participants: Forty-eight female pigs (26–42 kg). Interventions: The pigs were anesthetized, tracheally intubated, and mechanically ventilated. After placement of an aortic thermistor catheter via the femoral artery and a pulmonary artery catheter, a double-lumen tube was placed via tracheotomy. During one-lung ventilation in each animal, 3 measurements with pulmonary artery thermodilution and transpulmonary aortic thermodilution were performed in different hemodynamic states. Both thermistors were connected to 1 computer system, and 144 simultaneous cardiac output measurements were analyzed. Measurements and Main Results: Linear regression analyses revealed a close relationship between the 2 methods: CO(AT) = 0.81 CO(PA) + 1.04 (L/min) ( r = 0.96, p < 0.0001). Bland-Altman analysis showed that CO(AT) was slightly higher than the CO(PA) with a bias of 0.2 ± 0.5 L/min. However, in higher CO states, an inversion of this relationship was found, possibly because of indicator loss and recirculation. Conclusions: The pulmonary artery thermodilution and the transpulmonary aortic thermodilution techniques both accurately measure cardiac output during one-lung ventilation.

Effect of acute intravenous cocaine administration on endothelium-dependent vasodepressor responses to acetylcholine.

Cardiovascular events commonly associated with acute and chronic cocaine abuse include coronary vasospasm, arrhythmias, myocardial infarction, and sudden death. It has been suggested that cocaine causes endothelial dysfunction and vasoconstriction by inhibiting local production of nitric oxide and that endothelial dysfunction may be involved in the cardiovascular events associated with cocaine use. The present study investigated the effect of acute intravenous cocaine administration on endothelium-dependent vasodepressor responses to acetylcholine in the anesthetized rat. Rats were anesthetized with intraperitoneally Inactin (140 mg/kg) and catheters were inserted into the jugular vein and iliac artery for the injection of drugs and measurement of systemic arterial pressure. A thermistor catheter was advanced to the aortic arch for the measurement of cardiac output via the thermal dilution technique. A 5 mg/kg intravenous dose of cocaine, which enhances the vasopressor response to norepinephrine and blocks the vasopressor response to tyramine, had no effect on the vasodepressor response to the endothelium-dependent vasodilator acetylcholine. In addition, responses to the nitric oxide-donor sodium nitroprusside and the vasoconstrictor peptide angiotensin II were not altered by administration of cocaine. Acute administration of cocaine in a dose that blocks norepinephrine uptake into adrenergic terminals had no effect on endothelial function as measured by the absence of an effect on the vasodepressor response to intravenous injections of acetylcholine. Although chronic cocaine exposure has been shown to cause vascular dysfunction, eventually leading to impairment of the nitric oxide pathway, it appears that acute cocaine administration does not inhibit this pathway in the anesthetized rat.

Reliability of cerebral blood flow measurements by transcerebral double-indicator dilution technique.

The recently developed transcerebral double-indicator dilution technique has proven to be a feasible monitoring alternative to measure global cerebral blood flow at the bedside. However, the short-term repeatability of transcerebral double-indicator dilution measurements has not yet been investigated. The present study was designed to investigate the accuracy in terms of reliability for repeated transcerebral double-indicator dilution measurements to assess global cerebral blood flow during a definite carbon dioxide challenge in a clinical trial. The investigation was performed in 10 patients scheduled for elective coronary artery bypass grafting. After induction of anaesthesia, repeated cerebral blood flow measurements using transcerebral double-indicator dilution were performed during target normocapnia, hypocapnia and hypercapnia. For transcerebral double-indicator dilution measurements, a bolus injection of ice-cold indocyanine green was administered into a central vein. The resulting thermal dye dilution curves were recorded simultaneously in the aorta and the jugular bulb using combined fibreoptic thermistor catheters. Cerebral blood flow was calculated from the mean transit times of the indicators through the brain. Additionally, transcranial Doppler sonography was simultaneously performed to measure transient changes in the cerebral blood flow velocity. Transcerebral double-indicator dilution measurements revealed a reasonable coefficient of repeatability with 9.1, 9.7 and 20.2 mL min-1 100 g-1 during normo-, hypo- and hypercapnic conditions, respectively. However, a total of 20% of the administered measurements had to be rejected for methodological reasons. Repeated measurements with the transcerebral double-indicator dilution method show a reasonable repeatability. With consideration to the limitations of the transcerebral double-indicator dilution technique, this new method proves to be a reliable monitoring tool to measure global cerebral blood flow at the bedside.

Das Monitoring des Verbrennungsschocks mittels transpulmonaler Indikatorverfahren

proach for Hemodynamic Monitoring of Burn Shock. The pathophysiologic changes following thermal injury exceed those of any other trauma we know. Myocardial depression, capillary leakage and extravascular edema lead to hemodynamic collapse and organ failure, if not adequately treated. Being able to objectively measure these extreme fluid shifts would allow an individually based fluid treatment instead of the traditional, formula based shock therapy. The transpulmonary thermodilution (TPID) allows an individually based burn resuscitation, which uses measurements of intravascular volume deficits as guide for fluid therapy. This technique utilizes a computerized analysis of double-indicator (temperature and dye) dilution, and has been successfully used to manage the therapy of critically ill patients, especially following cardiac surgery. The technique requires only a central venous catheter and an arterial fiber optic thermistor catheter inserted into the femoral artery. TPID determines the intrathoracic blood volume that has been shown to reflect circulatory filling and volume status more precisely than CVP and PCWP. Additionally extravascular lung water can be determined, which may offer a precise estimation of the interstitial water in the lung. This allows a rational substitution of fluid during burn shock; restoring intravascular volumes while being able to monitor the interstitial fluid of the lung to avoid pulmonary edema. The aim of this article is to provide an introduction to the basic principles of TPID and an evaluation of our experience with this technique for guidance of shock therapy of severely burned patients.

Bedside monitoring of cerebral blood flow in patients with acute hemispheric stroke.

To test the practicability of a new double indicator dilution method for bedside monitoring of cerebral blood flow (CBF) and to assess the clinical value of CBF monitoring as a prognostic tool for outcome and in therapy of elevated intracranial pressure (ICP) in patients with acute hemispheric stroke. Prospective study. Clinical evaluation of a new method. Neurological intensive care unit of a university hospital. Ten patients with acute complete middle cerebral artery territory- or hemispheric infarctions. Two combined fiberoptic thermistor catheters were placed in the right jugular bulb and in the thoracic aorta. Central venous injections of ice-cold indocyanine green dye were performed. CBF was estimated by calculating the mean transit times of the cold bolus and dye. A total of 104 reproducible CBF measurements were obtained. No complications associated with the method were observed. Twelve pairs of measurements were performed within 30 mins with unchanged clinical conditions. The standard deviation of repeated measurements was 2.7 mL/100 g/min; the interrater reliability was between 0.95 and 0.99. The median CBF in patients who died (n = 4) was lower (27 mL/100g/min) than in those who survived (n = 6) (45 mL/100g/ min). Patients who died more frequently had low CBF values of <30 mL/100g/min (22 of 38; 58%) than patients who survived (10 of 54; 19%). A total of 37 CBF measurements were done during ICP elevation of >20 mm Hg. In patients who survived, ICP elevations were only associated with low CBF values in 5 of 26 events; whereas in patients who died, ICP elevations were associated with low CBF values in 8 of 11 events. The new double indicator dilution technique may be suitable for serial bedside CBF measurement. It is easy to perform and can be rapidly repeated in the ICU environment. Validation of the method by comparison with standard methods is needed. The preliminary data indicate that bedside monitoring of CBF may give prognostic information for outcome and may guide therapy of elevated ICP in patients with malignant hemispheric infarction.

Improved accuracy and precision of thermodilution cardiac output measurement using a dual thermistor catheter system

OBJECTIVESTo assess whether thermodilution cardiac output determination based on measurement of injectate temperature in vivo leads to more accurate and precise estimates and to study the influence of chilled injectate on test performance.BACKGROUNDCardiac output measurement via right heart catheterization is used extensively for hemodynamic evaluation in a variety of diagnostic, perioperative and critical care settings. Maximizing accuracy is essential for optimal patient care.METHODSThis prospective study of 960 thermodilution cardiac output measurements was conducted using conventional and dual thermistor techniques. Specialized dual thermistor right heart catheters were constructed using a second thermistor positioned to measure injectate temperature in vivo just prior to entry into the right atrium. To eliminate interinjection variability, a custom set-up was developed that permitted output measurement using both techniques simultaneously. Both ambient temperature injections and cooled injections were investigated.RESULTSThe dual thermistor technique demonstrated significantly less measurement variability than the conventional technique for both ambient temperature (precision = 0.41 vs. 0.55 L/min, p < 0.001) and cooled (precision = 0.35 vs. 0.43 L/min, p = 0.01) injections. Similarly, the average range of cardiac output values obtained during five sequential injections in each patient was less using the dual thermistor approach (1.05 vs. 1.55 L/min, p < 0.001). The use of cooled injectate reduced the mean error of the dual thermistor technique but actually increased the mean error of the conventional technique. Even with ambient temperature injections, injectate warming during catheter transit varied considerably and unpredictably from injection to injection (2 SD range = −0.22 to 5.74°C). Conventional ambient temperature and cooled measurements significantly overestimated Fick cardiac output measurements by 0.32 and 0.50 L/min, respectively (p < 0.001). In contrast, dual thermistor measurements were statistically similar (−0.08 and −0.08 L/min, p = 0.34) to Fick measurements.CONCLUSIONSThis new dual thermistor approach results in a significant improvement in both precision and accuracy of thermodilution cardiac output measurement.

Role of nitric oxide in sepsis-associated pulmonary edema.

Transient pulmonary hypertension after inhibition of nitric oxide synthase (NOS) does not alter pulmonary reflection coefficients or lymph flows in endotoxemic sheep. To test the effects of persistent pulmonary hypertension induced by N omega-nitro-L-arginine methylester (L-NAME) and of inhaled NO on pulmonary edema, 18 sheep (three groups) were chronically instrumented with pulmonary artery catheters, femoral arterial fiberoptic thermistor catheters, and tracheostomy. The awake, spontaneously breathing animals received Salmonella typhi endotoxin (lipopolysaccharide; LPS) (10 ng/kg/ min) for 28 h. After 24 h, an airflow of 6 L/min was delivered through the tracheostomy. One group of animals (L-NAME/air) received L-NAME intravenously (25 mg/kg + 5 mg/kg/h) and breathed air. The second group (L-NAME/NO) was given L-NAME and NO (40 ppm) was added to the airflow. The third group was given NaCl 0.9% and breathed air (NaCl/air). Extravascular lung water was measured through the double-indicator dilution technique. Endotoxemia caused pulmonary edema, which was aggravated by L-NAME. Breathing of NO normalized pulmonary artery pressure (Ppa) and ameliorated pulmonary edema. Inhalation of NO may therefore be a therapeutic option for pulmonary edema associated with pulmonary hypertension.

Cardiorespiratory and anesthetic effects of propofol and thiopental in dogs

Abstract Objective To compare cardiorespiratory and anesthesia effects of IV administered propofol and thiopental in dogs. Animals 6 healthy mixed-breed dogs. Procedure Each dog was anesthetized with isoflurane, then a thermistor catheter was inserted in the pulmonary artery. After a minimum of 2.5 hours of recovery, a catheter was placed in a cephalic vein for administration of lactated Ringer's solution and drugs. Propofol (8 mg/kg of body weight) or thiopental (19.4 mg/kg) was administered to each dog in a randomized crossover design study. All dogs were intubated and allowed to breathe 100% oxygen spontaneously. Heart rate and rhythm; systolic, diastolic, and mean arterial blood pressures; respiratory rate; end-tidal carbon dioxide concentration; tidal volume; and reflexes (toe web pinch, palpebral response, and jaw tone) were measured before and every 2 minutes for the first 10 minutes, then at 15, 30, and 60 minutes after drug administration. Cardiac output was determined at 0, 2, 6, 10, 15, 30, and 60 minutes, and blood samples were collected at 0, 2, 10, and 30 minutes. Time to endotracheal extubation, head lift, and ability to sit sternally and walk unaided were recorded. Results 3 of 6 dogs in each group were apneic after drug administration. Reflexes were decreased similarly for both anesthetic agents, but were not completely lost. Time to sternal position and walking unaided were significantly shorter in response to propofol. Conclusion Anesthesia was rapid; however, respiratory depression and apnea were major adverse effects associated with propofol and thiopental. Propofol has the advantage of inducing rapid, coordinated anesthesia recovery. (Am J Vet Res 1998;59:1137-1143)

Accuracy and reproducibility of the measurement of actively circulating blood volume with an integrated fiberoptic monitoring system

Bedside monitoring of circulating blood volume has become possible with the introduction of an integrated fiberoptic monitoring system that calculates blood volume from the changes in blood concentration of indocyanine green dye 4 mins after injection. The aim of this investigation was to compare the blood volume estimate of the integrated fiberoptic monitoring system (group 1) with the standard methods of blood volume measurement using Evans blue (group 2), and indocyanine green measured photometrically (group 3). Prospective laboratory study. Animal laboratory of a University's institute for experimental surgery. Eleven anesthetized, paralyzed, and mechanically ventilated piglets. A central venous catheter was used for the injection of the indicator dyes (Evans blue and indocyanine green). A fiberoptic thermistor catheter was advanced into the thoracic aorta. The fiberoptic catheter detects indocyanine green by reflection densitometry for the estimation of blood volume of the integrated fiberoptic monitoring system. Samples for the determination of Evans blue and indocyanine green concentrations were drawn from an arterial catheter in the femoral artery over a period of 17 mins after injection. Measurements were performed during normovolemia, hypovolemia (blood withdrawal of < or = 30 mL/kg), and hypervolemia (retransfusion of the withdrawn blood plus an infusion of 10% hydroxyethyl starch [45 mL/kg]). Linear regression, correlation, and bias were calculated for the comparison of the blood volume estimates by the fiberoptic monitoring system (group 1) vs. the total blood volume estimates using Evans blue (group 2) and indocyanine green (group 3): group 1 = 0.82.group 2-26 mL; r2 = 82.71%; r = .91; n = 40; group 1-group 2 +/- 1 SD = -435 +/- 368 mL; group 1 = 0.79.group 3 + 50 mL; r2 = 74.81%; r = .87; n = 28; group 1-group 3 +/- 1 SD = -506 +/- 374 mL. The results demonstrate that the blood volume estimate of the fiberoptic monitoring system (group 1) correlates closely with the total blood volume measurement using Evans blue (group 2) and indocyanine green (group 3). Trapped indicator in the packed red cell column after centrifugation of the blood samples may account for an overestimation of group 2 and group 3 of approximately 10% to 14%, but there still remains a proportional difference of 10% between group 1 vs. group 2 and vs. group 3. This difference is due to the longer mixing times of group 3 (16 mins) and group 2 (17 mins), during which they are distributed in slowly exchanging blood pools. It seems that the blood volume estimate of the fiberoptic monitoring system (group 1) represents the actively circulating blood volume and may be useful for bedside monitoring.

Application of a transpulmonary double indicator dilution method for postoperative assessment of cardiac index, pulmonary vascular resistance index, and extravascular lung water in children undergoing total cavo-pulmonary anastomosis: preliminary results in six patients

Total cavo-pulmonary anastomosis (TCPA) is used for the functional correction of an increasing spectrum of congenital heart diseases. The passive pulmonary perfusion after surgical exclusion of the right ventricle has significant implications for the postoperative hemodynamic management of these patients. Because conventional pulmonary artery thermodilution catheters present methodologic problems in patients after TCPA, important cardiovascular variables such as cardiac index (CI) and pulmonary and systemic vascular resistance indices (PVRI, SVRI) usually cannot be assessed directly. In a preliminary series of six patients undergoing TCPA (age 6–22 years), the applicability of a transpulmonary double indicator dilution technique for postoperative determinations of CI, PVRI, SVRI, and extravascular lung water (EVLW) was investigated. After central venous injection of ice-cold indocyanine green (5 mg), thermal and dye dilution curves were recorded in the abdominal aorta using a combined 4F fiberoptic thermistor catheter. Qualitative assessment of the tracer curves did not show major differences in measurements in patients with pulsatile perfusion of the lungs. CI, SVRI, and EVLW could be determined by use of standard algorithms. Pulmonary perfusion pressure for the calculation of PVRI was based on the gradient between central venous and left atrial pressure. The quality of indicator dilution curves allowed determination of flow-related variables in 33 of a total of 34 sets of measurements. No catheter-related problems occurred during or after the period of investigation. Postoperative EVLW was within the range that is commonly accepted as normal for adults. Mean PVRI initially decreased during the postoperative course but showed a significant increase after extubation. It was concluded that a transpulmonary double indicator dilution method using combined thermal/fiberoptic detection in the abdominal aorta can be usefully applied for extended hemodynamic monitoring in children and young adults undergoing TCPA.

A new approach for bedside measurement of left-to-right shunts in patients using fiberoptic thermistor catheters and double indicator dilution technique

A new approach for bedside measurement of left-to-right shunts in patients using fiberoptic thermistor catheters and double indicator dilution technique

Influence of intracardiac left-to-right shunts on thermodilution measurements of cardiac output

Thermodilution measurements of cardiac output (CO) by means of Swan-Ganz catheters, in a strict sense, represent pulmonary arterial blood flow (PBF). In principle, this is also true in the presence of intracardiac left-to-right shunts due to atrial or ventricular septal defects. However, early recirculation of indicator may give rise to serious methodological problems in these cases. We sought to determine the influence of intracardiac left-to-right shunts on different devices for thermodilution measurements of CO using an extracorporeal flow model. Methods. Blood flow was regulated by means of a centrifugal pump that at the same time enabled complete mixing of the indicator after injection (Fig. 1). Pulmonary and systemic parts of the circulation were simulated using two membrane oxygenators and a systemic-venous reservoir to delay systemic recirculation of indicator. Control measurements of PBF (Qp) and systemic (Qs) blood flow were performed by calibrated electromagnetic flow-meters (EMF). Blood temperature was kept constant using a heat exchanger without altering the indicator mass balance in the pulmonary circulation. Left-to-right shunt was varied at different systemic flow levels applying a Qp:Qs ratio ranging from 1:1 to 2.5:1. Thermodilution measurements of PBF were performed using two different thermodilution catheters that were connected to commercially available CO computers. Additionally, thermodilution curves were recorded on a microcomputer and analysed with custom-made software that enabled iterative regression analyses of the initial decay to determine that part of the downslope that best fits a monoexponentially declining function. Extrapolation of the thermodilution curve was then based on the respective curve segment in order to eliminate indicator recirculation due to shunt flow. Results. At moderate left-to-right shunts (Qp:Qs<2:1) all thermodilution measurements showed close agreement with control measurements. At higher shunt flows (Qp:Qs≥2:1), however, conventional extrapolation procedures of CO computers considerably underestimated PBF (Fig. 2). This was particularly true when a slow-response thermistor catheter was used (Fig. 3). The reason for this underestimation of Qp was an overestimation of the area under curve because of inadequate mathematical elimination of indicator recirculation by standard truncation methods (Fig. 4). However, curve-alert messages of the commercially implemented software did not occur. A high level of agreement could be consistently obtained using a fast-response thermistor together with individual definition of extrapolation limits according to logarithmic regression analyses. Discussion and conclusion. Under varying levels of left-to-right shunt, both the reponse time of thermodilution catheters and the algorithms for calculation of flow considerably influenced the validity of thermodilution measurements of PBF in an extracorporeal flow model. The use of computer-based regression analyses to define the optimal segment for monoexponential extrapolation could effectively eliminate indicator recirculation from the initial portion of the declining thermodilution curve and showed the closest agreement with EMF measurements of Qp. The quality of thermodilution curves with respect to recirculation peaks in the flow model was slightly better than in clinical routine. Nevertheless, the clinical applicability of the modified extrapolation algorithm could be illustrated during pulmonary thermodilution measurements in an exemplary patient with a ventricular septal defect (Fig. 5). PBF at extremely high shunt ratios, however, cannot be assessed by monoexponential extrapolation in principle (Fig. 6). Insufficient elimination of indicator recirculation resulted in flow values that closely resembled systemic rather than PBF. This finding is in accordance with a mathematical analysis of the underlying Steward-Hamilton equation if an infinite number of recirculations would be included in the area under curve.

Epidural cooling for regional spinal cord hypothermia during thoracoabdominal aneurysm repair

Purpose: We investigated the feasibility of achieving regional hypothermia of the spinal cord with an infusion of iced (4° C) saline solution administered into an epidural catheter while monitoring cerebral spinal fluid (CSF) temperature in eight patients undergoing thoracic or thoracoabdominal aneurysm resection.Methods: As part of the anesthetic management, an epidural catheter was placed at T11–12, and a subarachnoid thermistor catheter was placed at L3–4. Approximately 30 minutes before aortic cross-clamping, iced (4° C) saline solution was infused into the epidural catheter until CSF temperature decreased to approximately 25° C. The infusion was then adjusted to maintain this temperature until the aorta was unclamped. The subarachnoid catheter was also used to measure CSF pressure and provide for CSF drainage. Surgery was performed in all patients with a clamp-and-sew technique with selective intercostal vessel reattachment.Results: Infusion of a mean volume of 489 ml (range 80 to 1700 ml) of iced saline solution into the epidural space before aortic cross-clamping led to a decrease in mean CSF temperature to 26.9° C (range 25° to 28.8° C) in 15 to 90 minutes. During cross-clamping and aortic replacement the mean CSF temperature was maintained between 25.2° to 27.6° C and, with discontinuation of the infusion, returned to within 1° C of body core temperature by the end of the procedure. Body core temperature was not significantly affected by the epidural infusion. Mean CSF pressure increased during the epidural infusion but could be reduced by removing saline solution from the epidural space. No postoperative neurologic deficits were observed.Conclusion: Epidural cooling appears to be a satisfactory method of achieving regional spinal cord hypothermia in patients requiring resection of thoracic or thoracoabdominal aortic aneurysms.

Comparison of ear-based, bladder, oral, and axillary methods for core temperature measurement

To determine the accuracy and repeatability of ear-based, bladder, oral, and axillary temperature methods. Prospective, descriptive comparison of the accuracy of four temperature methods in relation to pulmonary artery temperature and the repeatability of each method. Critical care units of a university teaching hospital. Convenience sample of 38 adult patients with indwelling pulmonary artery thermistor catheters. None. Ear-based estimates of core temperature with an infrared thermometer and pulmonary artery, bladder, oral, and axillary temperatures with thermistor-based instruments were made every 20 mins for 4 hrs. Mean offsets (+/- SD) from pulmonary artery temperature for each method were as follows: ear-based 0.07 +/- 0.41 degrees C; bladder 0.03 +/- 0.23 degrees C; oral 0.05 +/- 0.26 degrees C; and axillary -0.68 +/- 0.57 degrees C. The accuracy of each method varied with the level of pulmonary artery temperature. Repeated measurements with all four methods had mean SD values within +/- 0.2 degrees C. Infrared ear thermometry provided a relatively close estimate of pulmonary artery core temperature, although with more variability than bladder or oral methods, while axillary readings were substantially lower than the pulmonary artery temperature and highly variable.

Retrograde versus antegrade cardioplegia: Impact on right ventricular function

Retrograde cardioplegia administered through the coronary sinus has several documented advantages over antegrade cardioplegia but has been thought to provide inadequate right ventricular myocardial protection. We prospectively compared the effects of retrograde and antegrade cardioplegia on right ventricular performance in patients undergoing myocardial revascularization. Two groups of similar age, extent of disease, and preoperative left ventricular ejection fraction received retrograde (n = 16) or antegrade (n = 14) crystalloid cardioplegia. A right ventricular rapid-response thermistor catheter, previously developed and validated in our institution, was used to measure right atrial pressure, pulmonary artery pressure, right ventricular ejection fraction, end-diastolic volume index, and stroke volume index before bypass (baseline) and at several intervals after bypass. There were no differences in cross-clamp time, heart rate, cardiac enzymes, inotrope requirements, or arrhythmias between the two groups. Right ventricular parameters were equivalent in both groups at all time intervals except 30 minutes after bypass, at which time right ventricular end-diastolic volume index was lower (80 ± 6 versus 93 ± 6 mL/m 2; p < 0.05) and right ventricular stroke volume index was higher (35 ± 3 versus 29 ± 2 mL/m 2, p < 0.05) in the retrograde group compared with the antegrade group, indicating better right ventricular function with retrograde cardioplegia early after bypass. In both groups, right ventricular end-diastolic volume index was higher than baseline ( p < 0.05) during the first 4 hours after bypass. No other important differences were found. At 24 hours after bypass, right ventricular end-diastolic volume index remained higher than baseline with both antegrade and retrograde cardioplegia, suggesting continued impaired right ventricular performance in both groups. Except for a minor advantage of retrograde cardioplegia early after bypass, these results suggest that right ventricular protection during myocardial revascularization is similar with retrograde and antegrade cardioplegia.

Heat leakage across the abdominal wall and meal-induced thermogenesis in normal-weight and obese subjects

The mechanism behind the meal-induced increase in energy expenditure in humans and its reduction in obesity was examined in 15 normal-weight and seven obese subjects. The subjects were studied by indirect calorimetry in the basal state and during 2 hours after a mixed meal corresponding to 40% of the 24-hour basal energy requirement. Artificial thermal insulation was applied over the abdominal area before the study in seven of the normal-weight subjects. Thermistor catheters were inserted into a hepatic vein, the pulmonary artery, and a systemic artery for blood sampling and recording of blood temperatures. Basal hepatic venous drainage of heat in relation to the splanchnic oxygen uptake in the normal-weight subjects was low (12 ± 1 J/mL O 2) and became even lower after the meal (5 ± 3 J/mL). In the obese individuals and the insulated subjects, blood-drained splanchnic heat amounted to 19 to 21 J/mL oxygen both before and after the meal. The postprandial increase in whole body energy expenditure was diminished both in the obese (12% ± 1% above basal) and in the insulated subjects (15% ± 1%) compared with the noninsulated controls (22% ± 2%). In normal-weight subjects, there is a leakage of heat across the abdominal wall. Reduction or prevention of this leakage by artificial thermal insulation or by obesity is accompanied by a reduction of the postprandial increase in energy expenditure.