G. Hanekop

Comparison of cardiac output assessed by pulse-contour analysis and thermodilution in patients undergoing minimally invasive direct coronary artery bypass grafting

OBJECTIVE To investigate the precision and accuracy of continuous pulse contour cardiac output (PCCO) compared with intermittent transcardiopulmonary (TCPCO) and pulmonary artery thermodilution (TDCO) measurements in patients undergoing minimally invasive coronary bypass surgery (MIDCAB). DESIGN Prospective, controlled, clinical study. SETTING University hospital. PARTICIPANTS Twelve patients undergoing MIDCAB. INTERVENTIONS Thirty-six measurements of PCCO and thermodilution cardiac output (CO) were simultaneously performed after the start of surgery, during bypass grafting, and at the end of surgery. TCPCO and TDCO were simultaneously assessed by three injections of ice-cold saline randomly spread over the respiratory cycle. The pulse contour device was initially calibrated with an additional set of aortic thermodilution measurements. MEASUREMENTS AND MAIN RESULTS Absolute values of CO ranged between 1.6 and 9.2 L/min. A close agreement among the three techniques was observed at all measurements. Mean bias between PCCO and TDCO and TCPCO was 0.003 L/min (2 SD of differences between methods = 1.26 L/min) and 0.27 L/min (2 SD of differences between methods = 1.16 L/min), respectively. The correlation coefficients were r2 = 0.90 for TCPCO versus PCCO and r2 = 0.88 for TDCO versus PCCO. CONCLUSION The results of the present study show that compared with thermodilution CO, pulse contour analysis enables accurate measurement of continuous CO in patients undergoing MIDCAB.

Cerebral inflammatory response during and after cardiac surgery.

Background and objective: Neurological dysfunction is a common problem after cardiac surgery with cardiopulmonary bypass (CPB). Cerebral ischaemia associated with the use of CPB may result in a release of neuronal‐ischaemic markers and a subsequent cerebral inflammatory response which may additionally release inflammatory cytokines. In order to locate the origin and to quantify the release of neuronal‐ischaemic markers and cytokines we investigated arterial‐cerebral venous concentration gradients during and after CPB in a clinical setting. Methods: In twenty‐five patients scheduled for coronary artery bypass grafting surgery we measured the plasma concentration of neuron‐specific enolase, S‐100&bgr; protein as well as interleukins (IL) IL‐6, IL‐8 and IL‐10 from arterial and cerebral venous blood samples prior to surgery (baseline), during hypothermic CPB at 32°C, after termination of bypass, as well as 2, 4 and 6 h after admission to the intensive care unit. Results: Arterial‐cerebral venous concentration gradients of neuron‐specific enolase, S‐100&bgr;, IL‐6, IL‐8 and IL‐10 were neither detectable during nor after CPB. Compared to the baseline period, S‐100&bgr; and neuron‐specific enolase significantly increased during hypothermic CPB. After termination of CPB, neuronal‐ischaemic markers as well as cytokines were increased and remained elevated during the investigated time course without reaching baseline values. Conclusions: Although we found an overall increase in plasma concentrations of neuronal‐ischaemic markers, IL‐6, IL‐8 and IL‐10 during and after CPB, arterial‐cerebral venous gradients were not detectable for any of these parameters. Our results suggest that the increase of investigated parameters associated with the use of CPB are not primarily caused by a cerebral inflammatory response but rather reflect a release from other sources in the systemic circulation.

Intrathoracic fire during preparation of the left internal thoracic artery for coronary artery bypass grafting

A surgical fire is a serious complication not previously described in the literature with regard to the thoracic cavity. We report a case in which an intrathoracic fire developed following an air leak combined with high pressure oxygen ventilation in a patient with severe chronic obstructive pulmonary disease. The patient presented to our institution with diffuse coronary artery disease and angina pectoris. He was treated with coronary artery bypass graft surgery, including left internal thoracic artery harvesting. Additionally to this rare presentation of an intrathoracic fire, a brief review of surgical fires is included to this paper.

Instantaneous diastolic pressure-flow relationship in arterial coronary bypass grafts.

Objective: The objective of this study was to describe the diastolic pressure–flow relationship and to assess critical occlusion pressure in arterial coronary bypass grafts in human beings. Methods and results: Fifteen patients were studied following elective surgical coronary artery bypass grafting. Flow in the left internal mammary artery bypass to the left anterior descending artery was measured and simultaneously, aortic pressure, coronary sinus pressure and left ventricular end‐diastolic pressure were recorded. The zero‐flow pressure intercept as a measure of critical occlusion pressure was extrapolated from the linear regression analysis of the instantaneous diastolic pressure–flow relationship. Mean diastolic flow was 46 ± 17 mL min−1, mean diastolic aortic pressure was 60.5 ± 10.0 mmHg. Diastolic blood flow was linearly related to the respective aortic pressure in all patients (R‐values 0.7–0.99). The regression lines had a mean slope of 2.1 ± 1.2 mL min−1 mmHg−1. Mean critical occlusion pressure was 32.3 ± 9.9 mmHg and exceeded mean coronary sinus pressure and mean left ventricular end‐diastolic pressure by factors of 3.1 and 2.6, respectively. Conclusions: Our data demonstrate the presence of a vascular waterfall phenomenon in the coronary circulation after internal mammary artery bypass grafting. Critical occlusion pressure in arterial grafts considerably exceeds coronary sinus pressure as well as left ventricular end‐diastolic pressure and should thus be used as the effective downstream pressure when calculating coronary perfusion pressure. Our data further suggest that the slope of diastolic pressure–flow relationships provides a more rational approach to assess regional coronary vascular resistance than conventional calculations of coronary vascular resistance.

A New Device for Intraoperative Renal Blood Flow Measurement During Open-Heart Surgery: An Experimental Study and the Clinical Pilot Study

Renal blood flow (RBF) may vary during cardiopulmonary bypass and low flow may cause insufficient blood supply of the kidney triggering renal failure postoperatively. Still, a valid intraoperative method of continuous RBF measurement is not available. A new catheter combining thermodilution and intravascular Doppler was developed, first calibrated in an in vitro model, and the catheter specific constant was determined. Then, application of the device was evaluated in a pilot study in an adult cardiovascular population. The data of the clinical pilot study revealed high correlation between the flow velocities detected by intravascular Doppler and the RBF measured by thermodilution (Pearsons correlation range: 0.78 to 0.97). In conclusion, the RBF can be measured excellently in real time using the new catheter, even under cardiopulmonary bypass.

Changes of jugular venous blood temperature associated with measurements of cerebral blood flow using the transcerebral double-indicator dilution technique.

Background and objective: The transcerebral double-indicator dilution technique is a recently developed method to measure global cerebral blood flow at bedside. It is based on bolus injection of ice-cold indocyanine green dye and simultaneous recording of resulting thermo- and dye-dilution curves in the aorta and the jugular bulb. However, with this method 40 mL of ice-cold solution is administered as a bolus. Therefore, this prospective clinical study was performed to elucidate the effects of repeated administration of indicator on absolute blood temperature and on cerebral blood flow and metabolism. Methods: The investigation was performed in nine male patients scheduled for elective coronary artery bypass grafting. Absolute blood temperature was measured in the jugular bulb and in the aorta before and after repeated measurements using the transcerebral double-indicator dilution technique. Results: During the investigated time course, the blood temperature in the jugular bulb, compared to the aorta, was significantly higher with a mean difference of 0.21°C. The administration of an ice-cold bolus reduced the mean blood temperature by 0.06°C in the jugular bulb as well as in the aorta. After the transcerebral double-indicator dilution measurements a temperature recovery to baseline conditions was not observed during the investigated time period. Cerebral blood flow and cerebral metabolism did not change during the investigated time period. Conclusions: Repeated measurements with the transcerebral double-indicator dilution technique do not affect absolute jugular bulb blood temperatures negatively. Global cerebral blood flow and metabolism measurements remain unaltered. However, accuracy and resolution of this technique is not high enough to detect the effect of minor changes of physiological variables.

Description of the instantaneous pressure-flow relationship and critical occlusion pressure in arterial coronary bypass grafts: 119

Duration of CPB were 107 6 min and 106 5 min respectively. Haemodynamic parameters and left atrial pressure were the same in both groups during all observed time. At the end of the second training day inspiratory capacity increased to 162% (P 0.05). After operation inspiratory capacity was significantly lower and returned to baseline at the 6th postoperative day. No patients had severe myocardial failure after CPB (CI 2.7 l min 1m 2). Arterial hypoxaemia with PaO2/FiO2 200 were observed in 13.9% group S and in 32% group C patients at stage 3 (P 0.05). Duration of MV in group S was 7.3 h, in C 10.4 h (P 0.05). 32.5% of S and 13.3% of C group patients met the conventional criteria and were extubated in the OR (P 0.05). Discussion: Incentive spirometry significantly improved lung inspiratory capacity, arterial oxygenation and lung shunt after CPB. Spirometry training before and after operation is effective in decreasing the duration of MV. Reference: 1 Crowe JM, Bradley CA. The effectiveness of incentive spirometry with physical therapy for high-risk patients after coronary artery bypass surgery. Phys Ther 1997; 77(3): 260–268.

Possibilities of neuromonitoring in cardiac surgery with cardiopulmonary bypass

Zusammenfassung Patienten nach kardiochirurgischen Eingriffen mit extrakorporaler Zirkulation weisen eine hohe Inzidenz neurologischer bzw. neuropsychologischer Symptome auf. Die Ursachen für derartige Störungen sind als multifaktoriell einzuordnen und lassen sich Risikofaktoren zuweisen, die durch den Einsatz einer extrakorporalen Zirkulation und durch patientenspezifische Charakteristika bedingt sind. In dieser Übersicht werden nicht-invasive (Transkranielle Doppler-Sonographie, Elektroenzephalographie, Infrarotspektroskopie) und invasive (Messung der jugularvenösen Sauerstoffsättigung, Kety-Schmidt-Technik, Xenon-Clearancetechnik, Transzerebrale Doppelindikatorverdünnungstechnik) Überwachungs- und Untersuchungsverfahren auf ihre Einsetzbarkeit und Aussagekraft zur Detektion von Störungen der zerebralen Hämodynamik und des Hirnmetabolismus bei kardiochirurgischen Eingriffen betrachtet.Summary In patients receiving surgical interventions with the use of cardiopulmonary bypass, the incidence of postoperative neurological and neuropsychological dysfunction still remains high. The reasons for these disorders may be seen as multifactorial and can be divided into patient and cardiopulmonary bypass related risk factors. In this review non-invasive (transcranial Doppler sonography, electroencephalography, infrared spectroscopy) and invasive (measurement of jugular venous oxygen saturation, Kety-Schmidt technique, 133Xenon-clearance technique, transcerebral double indicator dilution technique) monitoring methods were evaluated for clinical applicability and evidence to detect cerebral hemodynamic and metabolic impairment during and after the cardiopulmonary bypass period.