Tor Frøysaker

Cerebral perfusion during nonpulsatile cardiopulmonary bypass

The recording of middle cerebral artery (MCA) flow velocity by the transcranial Doppler method offers a new, noninvasive, continuous technique for studies of cerebral circulation. Comparative studies of electromagnetic internal carotid artery (ICA) flowmetry and MCA flow velocity by the transcranial Doppler technique have demonstrated that observed changes in MCA flow velocities reflect concomitant changes in cerebral circulation. Eleven high-risk patients undergoing cardiopulmonary bypass (CPB) procedures were included in a pilot study. Arterial blood pressure (BP), central venous pressure, and epidural intracranial pressure (EDP) were recorded during CPB. Cerebral electrical activity was recorded by a cerebral function monitor. Flow velocity in the MCA was increased during nonpulsatile CPB in 10 of the 11 patients. This increase was related to the degree of hemodilution, and the flow velocity during steady-state CPB was 80 to 300% of the prebypass value. The MCA flow velocity changed, however, in a pressure-passive manner with the cerebral perfusion pressure (CPP = BP - EDP) in the individual patient, which indicates that cerebral autoregulation was not operative. During the first 15 minutes after termination of bypass, the MCA flow velocity was reduced, but remained higher than the prebypass level, 110 to 210% of the level during the last 5 minutes preceding CPB.

Dissociation between cerebral autoregulation and carbon dioxide reactivity during nonpulsatile cardiopulmonary bypass

Five patients undergoing cardiopulmonary bypass (CPB) procedures were extensively monitored because of anticipated high risk for neurological complications. Arterial blood pressure (BP), central venous pressure, and epidural intracranial pressure (EDP) were continuously recorded throughout CPB; thus, information on the cerebral perfusion pressure (CPP) was also continuously available (CPP = BP - EDP). Cerebral electrical activity was recorded by a cerebral function monitor. The flow velocity in the middle cerebral artery (MCA) was recorded using a transcranial Doppler technique. During steady-state CPB (constant hematocrit, constant temperature, and constant flow from the heart-lung machine) partial pressure of arterial carbon dioxide (PaCO2) was repeatedly changed to study the effect of changes in this variable on MCA flow velocity during nonpulsatile bypass. During CPB with constant temperature, hematocrit, and PaCO2, the effect of changes in CPP on MCA flow velocity was recorded and analyzed. During nonpulsatile, moderately hypothermic (28 degrees to 32 degrees C), low-flow (1.5 L/min/m2) CPB, there was no evidence of cerebral autoregulation, with CPP levels ranging from 20 to 60 mm Hg. The CO2 reactivity, however, was clearly present and in the range of 1.9 to 4.1%/mm Hg, indicating that there was a dissociation between cerebral autoregulation and CO2 reactivity under these circumstances.

Hemodynamic evaluation of the carbomedics prosthetic heart valve in the aortic position : comparison of noninvasive and invasive techniques

Seventy-three patients with a CarboMedics aortic bileaflet valve prosthesis were examined by Doppler ultrasonography, and 27 of them were also assessed by transseptal catheterization. The ultrasonic mean systolic gradient was 17.1 +/- 5.6 mm Hg for valve size 19 mm, falling gradually with increasing valve size to 6.8 +/- 2.5 mm Hg for size 27 mm. The catheter mean systolic gradient was consistently smaller than the ultrasonic gradient (4.3 +/- 4.8 mm Hg), but Tobit regression analysis showed a significant association between the two methods. In all patients both methods revealed negligible to small amounts of retrograde leakage, which is assumed to be a normal finding for this valve. The effective flow areas of the valves calculated from the ultrasonic data were similar to the in vitro calculated flow areas. The hemodynamic potential of this valve is therefore completely utilized in vivo. The effective orifice area corrected for body surface area increased with increasing valve size, which demonstrates a moderate valve-patient mismatch.

Some Observations on Cerebral Perfusion during Cardiopulmonary Bypass

Blood flow was recorded with an electromagnetic flow probe on one internal carotid artery (ICA) during cardiopulmonary bypass (CPB) in 5 patients. The ICA flow was monitored continuously along with arterial blood pressure, epidural intracranial pressure, and cerebral electrical activity using a cerebral function monitor (3 patients). The ICA flow increased by 50 to 100% at the inception of extracorporeal circulation. This rapid enhancement of flow occurred within a thirty-second period and was due to rapid arterial hemodilution caused by introduction of the priming solution. A transitory fall in ICA flow was observed during subsequent minutes when the well-recognized drop in blood pressure took place and the cerebral perfusion pressure (CPP = blood pressure - epidural intracranial pressure) was reduced to less than 30 mm Hg. In only one instance, however, when CPP fell to 15 mm Hg, was the fall in flow lower than the prebypass level. Throughout the rest of CPB, with steady-state hemodilution and CPP levels in the range of 30 to 50 mm Hg, ICA flow was markedly enhanced (50 to 100% above the prebypass level). The flow pattern, however, disclosed a pressure-passive system, indicating that cerebral autoregulation was impaired or that the CPP levels were lower than the individual lower limit of cerebral autoregulation during the period of steady-state hemodilution on CPB. A transient depression of cerebral electrical activity was seen in 2 patients shortly after the introduction of CPB. This phenomenon is suggestive of qualitatively insufficient perfusion and was observed even when ICA bulk flow was increased (hematocrit values, 13 to 17%).

Use of Haemonetics cell saver for Autotransfusion in Cardiovascular Surgery

The Haemonetics Cell Saver was evaluated as a tool for the refining of blood shed during cardiovascular surgery. After blood filtration the red cells are concentrated, washed and re-infused as red cells suspended in normal saline (CS blood) with haematocrit around 60%. Platelets and plasma with desired and undesired components are removed. In 50 patients undergoing elective but complicated cardiovascular surgery an average of 4.4 units CS blood were produced. In 3 Jehovahs Witnesses the method was used in combination with immediate preoperative prebleeding and dextran infusion. No blood products were given. The haematocrit was maintained at a safe level subsequent to retransfusion. Platelet counts were never critically low and extremely low total protein did not lead to peripheral or pulmonary oedemas or coagulation problems. In an in vitro study it was shown that extreme dilution of coagulation factors is well tolerated before the clotting time (ACT) is affected. The Cell Saver proved to be an effective, reliable and safe device for autotransfusion of salvaged blood during cardiovascular surgery.

The CarboMedics valve: midterm follow-up with analysis of risk factors.

BACKGROUNDnThis study examined the midterm results with the CarboMedics prosthetic valve.nnnMETHODSnFrom 1987 through 1991 a total of 569 patients received the CarboMedics prosthesis.nnnRESULTSnEarly mortality was 4.9% and related to emergency operation, presence of diabetes mellitus, coronary artery disease, preoperative New York Heart Association class, duration of cardiopulmonary bypass, and aortic cross-clamp time. Midterm follow-up with respect to mortality was 100% complete. All patients were followed up in the hospital after 1 year. In addition 86% of the patients responded to a questionnaire. Mean follow-up was 3 years (range, 0 to 5.6 years). Cumulative survival at 1 and 4 years was 91.2% +/- 1.2% and 83.7% +/- 1.8%, respectively. Five patients experienced obstructive valve thrombosis (0.3%/patient-year), 16 patients had major thromboembolic events (0.9%/patient-year), and 10 patients had major warfarin-related bleeding (0.6%/patient-year) requiring hospitalization or blood transfusions. Eight patients were reoperated on for paraprosthetic leak (0.4%/patient-year). Prosthetic valve endocarditis developed in 4 patients (0.2%/patient-year). No structural valve failure was observed.nnnCONCLUSIONSnMidterm follow-up demonstrates that the CarboMedics mechanical prosthesis is reliable and has an acceptable rate of valve-related complications.

Normal Flow Pattern in the Superior Vena Cava in Man During Thoracotomy

In 17 patients with normal hearts undergoing thoracotomy for right-sided pulmonary diseases, a flow pattern in the superior vena cava was traced. Four parameters were recorded simultaneously: pressures in the right atrium and the right ventricle, ECG, and instantaneous volume flow in the superior caval vein. In 3 of the patients arrhythmias occurred, and in 1 patient the tracings were technically unsuccessful. In the remaining 13 patients a typical pulsatile, phasic flow pattern was obtained, similar to the pattern previously recorded in dogs. The theories about the active role of the heart on venous return to the right heart are briefly reviewed, and a more up-to-date view is presented.

Cerebral carbon dioxide reactivity during nonpulsatile cardiopulmonary bypass.

Five patients undergoing extensive cerebral monitoring during cardiopulmonary bypass (CPB) procedures were subjected to studies on cerebral CO2 reactivity during nonpulsatile CPB. The cerebral monitoring included recording of arterial blood pressure (BP), central venous pressure (CVP), epidural intracranial pressure (EDP), cerebral electrical activity by a cerebral function monitor (CFM), and middle cerebral artery (MCA) flow velocity by transcranial Doppler technique. The cerebral perfusion pressure (CPP) was thus continuously recorded (CPP = BP - EDP). During steady-state CPB with constant hematocrit, temperature, and arterial carbon dioxide tension (PaCO2), MCA flow velocity varied with changing CPP in a pressure-passive manner, indicating that the cerebral autoregulation was not operative. During moderately hypothermic (28 to 32 degrees C), nonpulsatile CPB, with steady-state hematocrit, temperature, and pump flow, we deliberately and rapidly changed PaCO2 for periods of 1 or 2 minutes by increasing gas flow to the membrane oxygenator, thereby testing the cerebral CO2 reactivity. Nineteen CO2 reactivity tests, performed at CPP levels ranging from 17 to 75 mm Hg, disclosed that the cerebral CO2 reactivity decreased with CPP, especially with CPP levels below 35 mm Hg. In these patients, concomitant changes in CPP during the CO2 reactivity test could be compensated for by adjusting the observed change in MCA flow velocity. The corrected CO2 reactivity values obtained in this way ranged from below 1.0 (observed at CPP levels below 20 mm Hg) to a 3.0 to 4.5% X mm Hg-1 change in PaCO2 (observed at CPP levels above 35 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of pressure gradient in the Hancock mitral valve from noninvasive ultrasound Doppler data.

The accuracy with which the pressure gradient in the Hancock mitral valve can be determined from noninvasive ultrasound Doppler data was explored in a study of eight adult patients. The mean manometric pressure gradient (delta PM) was determined by performing simultaneous left atrial and left ventricular catheterization. The mean diastolic pressure gradient was also determined from noninvasive ultrasound data (delta PU). Identical cardiac cycles were used to compare delta PM and delta PU. In the eight patients delta PM ranged from 3.0 to 9.0 mmHg and cardiac output from 3.7 to 5.5 l/min. The difference delta PM-delta PU was 0.3 +/- 0.9 mmHg (mean +/- SD). The results thus indicated that noninvasive ultrasound can determine the mean diastolic gradient in the Hancock mitral valve with an accuracy which approaches that attained with conventional manometric methods.

Cerebral Damage Following Open-Heart Surgery in Deep Hypothermia and Circulatory Arrest

Six patients undergoing aortic arch replacement during deep hypothermia and circulatory arrest were subjected to studies including serial determinations of total creatine kinase (CK) activity in the cerebrospinal fluid (CSF), monitoring of the intracranial epidural pressure and the cerebral perfusion pressure and clinical neurological evaluation. In two of four patients with postoperative pressure monitoring, a marked increase in pressure was seen. In one case this pressure rise terminated in brain tamponade six days postoperatively, despite aggressive treatment with steroids, mannitol and barbiturate. In comparison with patients undergoing surgery for valve replacement or aorto-coronary by-pass, some of the patients with aortic arch replacement clearly sustained more severe cerebral damage, as judged by clinical examination and autopsy findings as well as by assessment of the degree or extent of the neuronal damage from CK activity in CSF. Patients of this type are obvious candidates for postoperative neuro-intensive monitoring and care. Repeated pulsed Doppler flow velocity determinations in precerebral arteries, performed bedside, combined with monitoring of the cerebral perfusion pressure, provide a useful indication of the cerebral circulatory state in such situations.