Cardiopulmonary bypass and forearm blood flow

STUDY OBJECTIVE

To assess the effect of cardiopulmonary bypass (CPB) on muscle blood flow (MBF) when measured in the forearm by venous occlusion plethysmography.

DESIGN

This was a prospective study.

SETTING

Operating room area of a tertiary care university medical center.

PARTICIPANTS

Twenty-seven patients (25 men and 2 women), aged 62 +/- 1.5 years, undergoing elective coronary bypass grafting.

INTERVENTIONS

Measurements were made during the surgical procedure: before, during cold and warm, and after discontinuation of CPB.

MEASUREMENTS AND RESULTS

Changes in forearm blood flow (FBF), derived forearm vascular resistance (FVR), mean arterial pressure (MAP), and cardiac output (CO) were evaluated by repeated measures analysis of variance. The control FBF (measured before CPB) was found to be approximately 50 percent lower than that previously reported for awake volunteers and patients. The FVR was similarly higher. From these low values, the FBF increased significantly (p < 0.001) during normothermic bypass and after CPB. Forearm vascular resistance decreased significantly (p < 0.001) throughout the cold, warm, and postbypass periods. Only during the warm and the postbypass periods did FBF and FVR reach normal values. Mean arterial pressure decreased significantly (p < 0.01) throughout. There was no statistically significant association between any of the variables and FBF or FVR. After correcting for patient and surgical phase variability, only MAP had a statistically significant effect (p = 0.042) on FVR; blood temperature, skin temperature, hematocrit level, PaCO2, serum potassium, and systemic vascular resistance (SVR) had no effect on either FBF or FVR when tested singly or in combination. When correction for multiple comparisons was applied, the lowest probability value became greater than 0.25. There was no correlation between combinations of covariates and FBF or FVR after adjustments for the surgical phase of the study either.

CONCLUSION

These findings indicate that the increase in MBF seen during warm and the post-CPB periods is only a recovery toward normal blood flow. The role of this change in the low SVR that usually accompanies CPB is equivocal.

Utility of intraoperative fine needle aspiration biopsy in the surgical management of patients with pulmonary masses

Sporadic reports have postulated that intraoperative fine needle aspiration biopsy (FNAB) is a useful adjunct in the surgical management of patients with pulmonary masses. We reviewed 38 consecutive intraoperative pulmonary FNABs performed at our institution in order to assess the efficacy of this technique, as measured by (1) its sensitivity, specificity, predictive values and concordance rates, and (2) the appropriateness of the resultant surgical therapy. Six cases were benign (16%) and 32 malignant (84%); none were small cell carcinomas. Aspirates from the six benign lesions were designated either benign or nondiagnostic; there were no false-positive diagnoses (specificity = 100%). Aspirates from 30 of the 32 malignant neoplasms were diagnosed as malignant, one was considered suspicious for carcinoma, and one was interpreted as benign (sensitivity = 97%). The positive and negative predictive values were 100% and 86%, respectively. The concordance rate for benignancy/malignancy between the intraoperative FNAB interpretation and final diagnosis was 97%. The intraoperative FNAB diagnosis contributed to less-than-optimal surgical therapy in only one case. Thus, we conclude that intraoperative pulmonary FNAB has utility in the proper surgical management of pulmonary masses.

Reliability of the radial arterial pressure during anesthesia. Is wrist compression a possible diagnostic test?

STUDY OBJECTIVE

To evaluate wrist compression as a test to identify low radial from low systemic pressure and to see if the gradient found after cardiopulmonary bypass is also present whenever hand vascular resistance may decrease.

DESIGN

This was a prospective study.

SETTING

Operating room area of a university medical center.

PARTICIPANTS

(1) Forty patients undergoing coronary bypass grafting studied at discontinuation of cardiopulmonary bypass. (2) Twenty-six patients received isoflurane anesthesia before major noncardiac operations. (3) Hydraulic model: a fluid container with a tube 66-cm long, 6- to 1.8-mm internal diameter, connected at its base.

INTERVENTIONS

Before induction of anesthesia, the radial artery was cannulated and, in the first group, the aorta or femoral arteries as well. The radial pressure was compared consecutively with and without wrist compression. In the model, the pressure was recorded simultaneously at three sites along the tube while different flows ran through its distal end.

MEASUREMENTS AND RESULTS

Overall, wrist compression increased radial (p < 0.001) systolic, diastolic, and mean arterial pressures. In the first group, compression reduced the femoral/aortic-radial mean pressure difference by 50 percent and never produced higher radial than central mean pressure. Plot of the pressure difference produced by wrist compression against the average of the (compared) radial pressures and considering increases > or = 4 mm Hg as real, showed that, in the first group, systolic arterial pressure (SAP) increased 13 +/- 1.4 mm Hg in 22 of 40 patients; diastolic arterial pressure (DAP) increased 7.8 +/- 1.1 mm Hg in 4; and mean arterial pressure (MAP) increased 7.7 +/- 1.6 mm Hg in 9 patients. In the second group, SAP increased 16.0 +/- 1.7 mm Hg in 24 of 26 patients, DAP increased 6.0 +/- 1.4 mm Hg in 5, and MAP increased 7.0 +/- 0.7 mm Hg in 18 of 26 patients. In the model, base pressure at 94 mm Hg, the pressures were 1.2 to 28.1 mm Hg lower for flows ranging from 10 to 122 ml/min at the 54-cm distance (wrist equivalent).

CONCLUSION

The systemic-radial artery pressure gradient seen at the end of cardiopulmonary bypass seems to be a phenomenon common to patients with decreased hand vascular resistance. Wrist compression decreases or abolishes the gradient in most cases. It does not produce false positives, so an increase indicates a greater aortic than radial pressure. The difference is likely to be only temporary.

Amrinone in cardiac surgical patients with left-ventricular dysfunction. A prospective, randomized placebo-controlled trial

STUDY OBJECTIVE

To evaluate the efficacy of amrinone for facilitating weaning from cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized, double-blind, placebo-controlled trial with epinephrine as "rescue" therapy.

SETTING

Operating room of a large, metropolitan tertiary-care center.

PATIENTS

Thirty-nine patients with preoperative left ventricular dysfunction undergoing cardiac surgery. Thirty-three patients underwent aortocoronary bypass grafting; six patients underwent valve replacement for severe mitral or aortic regurgitation.

INTERVENTIONS

Patients received either amrinone (1.5 mg/kg loading dose plus 10 micrograms/kg/min maintenance infusion; n = 20) or placebo (n = 19) in a randomized double-blind fashion shortly (median, 10.5 min; range, 2 to 24 min) before separation from CPB. Inotropic drugs (other than the study drug) were withheld prior to separation from CPB unless safety considerations demanded that the protocol be broken. Patients who could not be weaned from CPB, as well as those with a cardiac index of 2.2 L/min/m2 or less after weaning from CPB, received epinephrine (60 to 120 ng/kg/min) by infusion.

MEASUREMENTS AND RESULTS

Fourteen of 19 patients receiving placebo but only 1 of the 20 patients receiving amrinone (p = 0.00001) required epinephrine infusion to separate from bypass. The cardiac index of 4 patients receiving placebo (but no patients with amrinone) failed to exceed 2.2 L/min/m2 despite epinephrine infusion, requiring the protocol to be broken (p < 0.08). Blood concentrations of amrinone determined (only in the amrinone group) after separation from CPB confirmed that the dosage of amrinone produced an effective blood concentration. Fourteen of 19 patients receiving placebo and 17 of 20 patients receiving amrinone required an infusion of phenylephrine titrated to maintain systolic blood pressure less than 90 mm Hg. Seven patients (four with amrinone and three with placebo) required antiarrhythmic drug therapy. The outcome at 3 months was similar in the 2 groups.

CONCLUSIONS

Amrinone by itself is an effective agent to facilitate weaning from CPB, and therapy with amrinone reduced the need for individualized titration of epinephrine. Amrinone is as effective as individualized titration of epinephrine (after CPB) to improve cardiac function. Patients in the group receiving amrinone had no greater need for vasoconstricting agents than did patients in the group receiving placebo; however, proactive administration of amrinone before separation from CPB appears to offer no greater benefit to high-risk patients than selective administration of drugs (epinephrine) only to those patients who demonstrate the need for drug support at the time of weaning.

Combined inotropic effects of amrinone and epinephrine after cardiopulmonary bypass in humans

Amrinone, a phosphodiesterase inhibitor, and epinephrine, an alpha- and beta-adrenergic receptor agonist, are inotropic drugs used during cardiac surgery to reverse myocardial depression after cardiopulmonary bypass. However, these drugs have not been compared separately, or in combination, in this patient population. We hypothesized that the combination might have complementary actions in improving myocardial function. We, therefore, compared amrinone, epinephrine, and the combination of amrinone and epinephrine in a randomized, blinded, placebo-controlled study in patients undergoing coronary artery bypass grafting. Forty patients with ejection fractions > 0.45 were studied. Right ventricular ejection fraction pulmonary artery catheters and radial arterial catheters were inserted before fentanyl-midazolam anesthesia. After separation from bypass, patients received either a placebo (n = 20) or amrinone bolus (1.5 mg/kg, n = 20) at time 0 and a placebo (n = 20) or epinephrine (30 ng.kg-1.min-1, n = 20) infusion at time 5 min. This resulted in four study groups, n = 10 in each group. Data were collected every 2.5 min for 10 min. Epinephrine, amrinone, and the combination of both drugs significantly increased cardiac output, stroke volume, O2 delivery, and left ventricular stroke work. The increase in stroke volume (P < 0.05) was 12 +/- 6, 16 +/- 4, and 30 +/- 4 mL/beat with epinephrine, amrinone, and the combination of amrinone and epinephrine, respectively. The amrinone-epinephrine combination increased stroke volume as much as the sum of amrinone and epinephrine given separately. Systemic vascular resistance and pulmonary vascular resistance decreased with amrinone and amrinone-epinephrine, but not with epinephrine. Epinephrine increased mean arterial and mean pulmonary arterial pressures. Right ventricular ejection fraction did not significantly increase (P = 0.09) with epinephrine, but increased significantly with amrinone (0.45 to 0.53, P = 0.01), and with the combination (0.43 to 0.55, P = 0.006). These data indicate that amrinone and epinephrine effectively increase myocardial performance during cardiac surgery. Right ventricular function especially was improved with amrinone and the combination of amrinone and epinephrine. The combined effects of amrinone and epinephrine may be useful in patients recovering from the ischemia and reperfusion injury resulting from coronary artery bypass grafting.

Does radial artery pressure accurately reflect aortic pressure?

STUDY OBJECTIVE

Our objective was to determine whether the systolic, diastolic, and mean arterial pressures measured in the radial artery accurately reflect corresponding pressures in the ascending aorta in narcotic-anesthetized patients with known obstructive coronary artery disease, before being subjected to cardiopulmonary bypass (CPB).

DESIGN

This was a prospective study.

SETTING

The cardiac operating room of a large, tertiary-care university medical center.

PARTICIPANTS

Fifty-one patients (45 men and six women; age range, 48 to 77 years) with documented atherosclerotic coronary artery disease were studied. All patients underwent elective coronary artery bypass grafting after the study.

INTERVENTIONS

Patients were premedicated with lorazepam and morphine 60 min before administration of Fentanyl-pancuronium anesthesia. The radial artery was cannulated before induction of anesthesia and the aorta approximately 45 min later. Comparisons of radial and aortic pressures were then performed.

MEASUREMENTS AND RESULTS

Radial and aortic pressures were recorded through standard, fluid-filled, high-pressure, 91-cm (36-in) long tubing and disposable transducers, meticulously cleared of air bubbles. Additional measurements included cardiac output, central venous pressure, core temperature, blood gas levels, and hematocrit reading. Radial-aortic pressure differences were as follows: systolic arterial pressure (SAP), 12 +/- 1 mm Hg; mean arterial pressure (MAP), -0.8 +/- 0.3 mm Hg; and diastolic arterial pressure (DAP), -1.0 +/- 0.3 mm Hg. All were significant (p < 0.001), but the SAP difference was more than ten times that of either the MAP or the DAP values. The coefficients of determination (r2) indicated that the radial-aortic dependence was 0.44 for the SAP, 0.90 for the DAP, and 0.98 for the MAP relationship. Plotting the respective differences against the arithmetic mean of simultaneously measured pressures indicated that the radial SAP was 4 to 35 mm Hg higher than the aortic in 42 patients (82 percent) and was 10 to 35 mm Hg higher in 26 patients (51 percent); radial-aortic MAP differences clustered within 3 mm Hg in 47 patients (92 percent); radial DAP was +/- 3 mm Hg different from the aortic in 46 patients (90 percent). The largest MAP difference was -6 mm Hg in one patient. The largest DAP difference was +/- 5 mm Hg in three patients.

CONCLUSIONS

In this group of patients, who were studied before undergoing CPB, the radial SAP gave a poor estimate of that present in the ascending aorta, since in more than 50 percent of the cases, the radial SAP was 10 to 35 mm Hg higher than that in the aorta. The radial MAP and DAP are reliable, since in 90 percent and 92 percent of the patients, respectively, the pressure differences were within +/- 3 mm Hg of those in the aorta.

Dobutamine increases heart rate more than epinephrine in patients recovering from aortocoronary bypass surgery

To determine whether epinephrine might prove to be a cost-effective substitute for dobutamine, two 8-minute infusions of either epinephrine (10 and 30 ng/kg/min, n = 28) or dobutamine (2.5 and 5 micrograms/kg/min, n = 24) were administered to 52 patients recovering in the intensive care unit (ICU) after aortocoronary bypass (CABG) surgery. At the higher dose, both drugs significantly (P < .05) increased cardiac index (CI), epinephrine from 2.8 +/- 0.1 at baseline to 3.3 +/- 0.1 L/min/m2, and dobutamine from 3.2 +/- 0.1 at baseline to 4.1 +/- 0.2 L/min/m2. Epinephrine increased CI significantly less than dobutamine. Both drugs significantly increased stroke volume index (SVI), epinephrine from 32 +/- 1 at baseline to 36 +/- 1 mL/beat/m2, and dobutamine from 36 +/- 1 at baseline to 40 +/- 2 mL/beat/m2. At the higher dose, the effects of the two drugs on SVI were indistinguishable. On the other hand, while the higher dose of both drugs significantly increased heart rate (HR), epinephrine from 88 +/- 2 at baseline to 90 +/- 2 beats/min and dobutamine from 89 +/- 2 at baseline to 105 +/- 3 beats/min, the increase following the higher dose of dobutamine was significantly greater than that seen after epinephrine. Effects of the two drugs on mean arterial pressure, central venous pressure, pulmonary artery occlusion pressure, systemic vascular resistance, pulmonary vascular resistance, and left-ventricular stroke work did not significantly differ. Similar results were obtained in the subset of patients with baseline CI less than 3 L/min/m2 who more closely resembled patients who might acutely require inotropic drug administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Surgical management of thoracic empyema

Thoracic empyema usually results from pulmonary infection or thoracic surgery. Antibiotic therapy is an essential part of the treatment, but surgical techniques to drain the pleural fluid and obliterate the empyema space often are required. A wide range of closed and open surgical techniques are available. This article reviews the various surgical options for the treatment of nontuberculous bacterial empyema secondary to pulmonary infection in the patient with a normal immune response. Emphasis is placed on a thorough understanding of the pathophysiology and natural history of empyema for selection and timing of appropriate treatment. Thoracic imaging techniques play a substantial role in the evaluation and treatment of empyema and in assessing the outcome of surgical therapy.

Systolic pressure measurement in the ascending aorta: augmentation at the aortic cannula sideport

To assess whether arterial blood pressure measured at the sideport of the aortic cannula mirrors that measured within the ascending aorta, the two pressures were compared in 10 consecutive patients undergoing cardiopulmonary bypass. The mean arterial pressures (MAP) were equal both before and after bypass, but the sideport systolic arterial pressure (SAP) was 6.0 +/- 0.8 mm Hg higher than the aortic SAP before bypass and 9.1 +/- 0.5 mm Hg higher than the aortic SAP after bypass (P less than 0.001). Hematocrit, blood temperature, cardiac output, and heart rate did not correlate with the differences in SAP, suggesting that the higher SAP seen at the sideport was generated within the tube connecting the oxygenator to the aorta. This theory was investigated by decreasing the tube length distal to the sideport in three patients in this group who had sideport SAPs higher than their aortic SAPs, a measure that decreased the SAP difference between the two sites. At the end of cardiopulmonary bypass in 20 other consecutive patients, the effect of shortening the aorta-oxygenator tube from 1.8 to 0.25 m was tested. The SAP in the sideport decreased by 4 to 12 mm Hg in 12 of the 20 patients, while the MAP was unaffected by this maneuver. It is concluded that the MAP measured at the sideport of the aortic cannula closely reflects the MAP in the ascending aorta, whereas the SAP measured at the sideport does not reflect the aortic SAP. Thus, when aortic pressure is measured at the sideport to confirm an artificially low radial arterial pressure, systolic amplification at the sideport might simulate or exaggerate radial artery hypotension.

Intraoperative use of dual-chamber demand pacemakers for open heart operations

The availability of external atrioventricular sequential pacemakers has improved the management of patients with sinus bradycardia, junctional rhythm, and atrioventricular block. However, these pacemakers are of less value in patients with postoperative heart block and accelerated atrial rhythms. The temporary use of a modified explanted dual-chamber demand pacemaker may counteract that problem by providing atrially triggered, P-wave-synchronous ventricular pacing. We report 2 patients in whom the temporary use of the dual-chamber demand pacemaker greatly facilitated weaning from cardiopulmonary bypass after coronary artery bypass grafting.

Radial artery-to-aorta pressure difference after discontinuation of cardiopulmonary bypass

To test whether the radial artery-to-aorta pressure gradient seen in some patients after cardiopulmonary bypass (CPB) is due to reduction in hand vascular resistance, the authors compared pressures in the ascending aorta with pressures in the radial artery before and after CPB in 12 patients. They increased hand vascular resistance by briefly occluding the radial and ulnar arteries at the wrist and recorded that effect on the radial artery-to-aorta pressure relationship. They also recorded the effect of wrist compression on radial artery pressures before and after CPB in 38 patients not having aortic pressure measurements. Before CPB in the first 12 patients, the radial systolic arterial pressure (SAP) was significantly higher (P less than 0.05) than the ascending aortic SAP, and wrist compression did not significantly affect that difference (P greater than 0.05). After CPB, the radial artery and aortic SAPs were not statistically different (P greater than 0.05), but wrist compression restored the higher radial artery SAP. The mean arterial pressure (MAP) was equal in four patients and 1-3 mmHg higher or lower in eight patients before CPB, and wrist compression did not alter those relationships. After CPB, MAP was equal in four patients; radial MAP was 1-3 mmHg higher or lower in six patients, and 7 and 10 mmHg lower in the last two patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Current treatment of traumatic aortic disruptions

Eighteen patients with traumatic disruptions of the descending thoracic aorta were treated at the Wake Forest University Medical Center from 1979 through 1986. Their preoperative evaluation and operative management are presented, with emphasis being placed on methods for preventing complications related specifically to aortic cross-clamping. Two patients died, for an operative mortality of 11 per cent. One of the two patients had exsanguinating hemorrhage with profound shock on the way to the operating room; in the second patient, the aorta was occluded just beyond the disruption, and there had been no distal perfusion for several hours before operation. Four patients (22%), three of whom had not had a shunting procedure, had major neurologic complications relating to the spinal cord. Thus, shunting procedures during repair of descending aortic disruption appear to offer some protection from neurologic deficits.

Response of cerebral blood flow to phenylephrine infusion during hypothermic cardiopulmonary bypass: influence of PaCO2 management

Twenty-eight adult patients anesthetized with fentanyl, then subjected to hypothermic cardiopulmonary bypass (CPB), were studied to determine the effect of phenylephrine-induced changes in mean arterial pressure (MAP) on cerebral blood flow (CBF). During CPB patients managed at 28 degrees C with either alpha-stat (temperature-uncorrected PaCO2 = 41 +/- 4 mmHg) or pH-stat (temperature-uncorrected PaCO2 = 54 +/- 8 mmHg) PaCO2 for blood gas maintenance received phenylephrine to increase MAP greater than or equal to 25% (group A, n = 10; group B, n = 6). To correct for a spontaneous, time-related decline in CBF observed during CPB, two additional groups of patients undergoing CPB were either managed with the alpha-stat or pH-stat approach, but neither group received phenylephrine and MAP remained unchanged in both groups (group C, n = 6; group D, n = 6). For all patients controlled variables (nasopharyngeal temperature, PaCO2, pump flow, and hematocrit) remained unchanged between measurements. Phenylephrine data were corrected based on the data from groups C and D for the effect of diminishing CBF over time during CPB. In patients in group A CBF was unchanged as MAP rose from 56 +/- 7 to 84 +/- 8 mmHg. In patients in group B CBF increased 41% as MAP rose from 53 +/- 8 to 77 +/- 9 mmHg (P less than 0.001). During hypothermic CPB normocarbia maintained via the alpha-stat approach at a temperature-uncorrected PaCO2 of approximately equal to 40 mmHg preserves cerebral autoregulation; pH-stat management (PaCO2 approximately equal to 57 mmHg uncorrected for temperature, or 40 mmHg when corrected to 28 degrees C) causes cerebrovascular changes (i.e., impaired autoregulation) similar to those changes produced by hypercarbia in awake, normothermic patients.

Combined radiological and surgical management of arteriovenous malformation of the lung

Multiple, bilateral arteriovenous malformations (AVMs) of the lung are diagnostically and therapeutically challenging. In staged procedures over seven days, a 19-year-old woman underwent blocking of the feeding artery to six moderate-sized AVMs in the left lower lobe, embolization of three more AVMs in the left lower lobe, and resection of a large AVM in the right lower lobe through a right-sided thoracotomy. These procedures preserved maximal lung tissue, and one year later the patient is essentially symptom free.

Massive rectal bleeding from colonic fistula in pancreatitis

Two cases of massive hematochezia from pancreatitis-associated colonic fistulae occurred. Diagnosis was made by arteriography; prompt surgical intervention ensued and both patients recovered. This rare complication of pancreatitis should be considered in every patient with rectal bleeding and a history consistent with pancreatitis, especially when an abdominal mass is present. Contrast enema examinations may help to make the diagnosis, but visceral arteriography is preferred because it defines the source of bleeding and guides the operative plan. The minimal surgical treatment consists of ligating bleeding vessels, debriding necrotic tissue, widely draining the peripancreatic space, and creating a totally diverting colostomy. All involved organs should be resected when technically feasible, since this eliminates abnormal tissue and minimizes the chances that hemorrhage will occur.