Stephen E. McNulty

Prevalence of Heparin-Associated Antibodies Without Thrombosis in Patients Undergoing Cardiopulmonary Bypass Surgery

BACKGROUND Patients with cardiovascular disease almost invariably receive heparin before cardiopulmonary bypass surgery, which places them at risk of developing heparin-associated antibodies with a risk of thromboembolic complications. This study was designed to determine the prevalence of heparin-induced antibodies in patients before and after cardiopulmonary bypass surgery. METHODS AND RESULTS Plasma from 111 patients was tested before surgery and 5 days after surgery for heparin-dependent platelet-reactive antibodies with a 14C-serotonin-release assay (SRA) and for antibodies to heparin/platelet factor 4 complexes with an ELISA. Heparin exposure after surgery was minimized. Heparin-dependent antibodies were detected before surgery in 5% of patients with SRA and 19% of patients with ELISA. By the fifth postoperative day, there was a marked increase in patients positive on the SRA or ELISA (13% and 51%, respectively; P < .01 for each). Patients who had received heparin therapy earlier in their hospitalization were more likely to have a positive ELISA before surgery (35%; P = .017) and a positive ELISA (68%; P = .054) or SRA (30%; P = .002) after surgery. However, there was no difference in the prevalence of thrombocytopenia or thromboembolic events between the antibody-positive and-negative groups. CONCLUSIONS Approximately one fifth of patients undergoing cardiopulmonary bypass surgery have heparin-induced platelet antibodies detectable before the procedure as a result of prior heparin exposure, and many more develop antibodies after surgery. The absence of an association between these antibodies and thromboembolic complications in this study may be, in part, attributable to careful avoidance of heparin after surgery. The high prevalence of heparin-induced antibodies in this setting suggests that these patients may be at risk of developing thrombotic complications with additional heparin exposure.

A comparison of four bedside methods of hemoglobin assessment during cardiac surgery

The purpose of this study was to compare the accuracy of conductivity, adjusted conductivity, photometric, and centrifugation methods of measuring or estimating hemoglobin (Hb) with Coulter measured HB as the reference.These bedside methods were studied in 25 cardiac surgery patients during euvolemia and hemodilution and after salvaged autologous red blood cell transfusion. In vivo patient blood samples were obtained before induction, at the start of cardiopulmonary bypass (CPB), after CPB, and after blood transfusion. In 10 patients, blood was sampled in vitro from units of processed blood. Hb values were determined using conductivity by Stat-Crit Registered Trademark, adjusted conductivity by Nova Stat Profile 9, bedside photometry by HemoCue Registered Trademark, and centrifugation methods. The calculated bias values of Coulter test method Hb (mean +/- SD) for in vivo patient blood samples (n = 90) were: Stat-Crit Registered Trademark = 0.6 +/- 0.8 g/dL; Nova Stat Profile 9 = -0.7 +/- 0.4 g/dL; HemoCue Registered Trademark = -0.1 +/- 0.2 g/dL; and centrifuge = 0.1 +/- 0.5 g/dL (P < 0.0001). Hb bias values (g/dL) for in vitro samples (n = 10) obtained from processed blood were Stat-Crit Registered Trademark = 5.1 +/- 0.6; Nova Stat Profile 9 = 3.0 +/- 0.6; HemoCue Registered Trademark = 0.4 +/- 0.4; and centrifuge = 0.6 +/- 0.3 (P < 0.0001). Hb assessment by different test methods may be significantly affected during hemodilution and after blood transfusion. In vitro conditions exaggerated the inaccuracy of conductivity and adjusted conductivity Hb estimates. The rank order of closest approximation to the Coulter measurement for all in vivo blood samples was provided by bedside photometry, followed by centrifugation, adjusted conductivity, and uncorrected conductivity methods. (Anesth Analg 1995;81:1197-202)

AN IMPROVED NASAL PRONG APPARATUS FOR END-TIDAL CARBON DIOXIDE MONITORING IN AWAKE, SEDATED PATIENTS

We describe and evaluate a new apparatus that monitors end-tidal carbon dioxide (PetCO2) and augments the inspired oxygen concentration in awake, sedated patients. The unit was evaluated for its effectiveness as an oxygenation device and its accuracy as a predictor of PaCO2 through the correlation of PaCO2 withPetCO2. Twenty cardiac surgical patients, physical status ASA 2–4, participated in this study. ThePetCO2 monitoring device consisted of a dual-prong nasal oxygen cannula and a 14-gauge intravenous catheter that was inserted into one limb of the oxygen supply tubing and connected to a Datex gas analyzer (Datex Instrumentation Corp, Helsinki, Finland) to measurePetCO2. The cross-over passage between the prongs was intentionally blocked with the end of a wooden-core cotton swab. The oxygen flow rates were randomly varied (2, 4, and 6 L/min) every 5 minutes, and values forPetCO2 as well as arterial blood samples for analysis of PaCO2 and PaO2 were obtained at the end of each 5-minute period. The accuracy of the system was assessed by comparing the PaCO2-PetCO2 differences (bias) at each oxygen flow rate. The ratios ofPetCO2 compared with PaCO2 were 0.98, 0.94, and 0.85, with correlation coefficients ofr=0.81, 0.85, and 0.63, respectively. The PaO2 values were 114, 154, and 183 mm Hg for the corresponding nasal oxygen flow rates of 2, 4, and 6 L/min, respectively. This study indicates that this modified nasal cannula provides supplemental oxygen adequately and yields a satisfactory reflection of the PaCO2 depending on the oxygen flow rate delivered.We describe and evaluate a new apparatus that monitors end-tidal carbon dioxide (PetCO2) and augments the inspired oxygen concentration in awake, sedated patients. The unit was evaluated for its effectiveness as an oxygenation device and its accuracy as a predictor of PaCO2 through the correlation of PaCO2 withPetCO2. Twenty cardiac surgical patients, physical status ASA 2–4, participated in this study. ThePetCO2 monitoring device consisted of a dual-prong nasal oxygen cannula and a 14-gauge intravenous catheter that was inserted into one limb of the oxygen supply tubing and connected to a Datex gas analyzer (Datex Instrumentation Corp, Helsinki, Finland) to measurePetCO2. The cross-over passage between the prongs was intentionally blocked with the end of a wooden-core cotton swab. The oxygen flow rates were randomly varied (2, 4, and 6 L/min) every 5 minutes, and values forPetCO2 as well as arterial blood samples for analysis of PaCO2 and PaO2 were obtained at the end of each 5-minute period. The accuracy of the system was assessed by comparing the PaCO2-PetCO2 differences (bias) at each oxygen flow rate. The ratios ofPetCO2 compared with PaCO2 were 0.98, 0.94, and 0.85, with correlation coefficients ofr=0.81, 0.85, and 0.63, respectively. The PaO2 values were 114, 154, and 183 mm Hg for the corresponding nasal oxygen flow rates of 2, 4, and 6 L/min, respectively. This study indicates that this modified nasal cannula provides supplemental oxygen adequately and yields a satisfactory reflection of the PaCO2 depending on the oxygen flow rate delivered.

Relationship between arterial carbon dioxide and end-tidal carbon dioxide when a nasal sampling port is used

End-tidal carbon dioxide (ETCO2) values obtained from awake nonintubated patients may prove to be useful in estimating a patient’s ventilatory status. This study examined the relationship between arterial carbon dioxide tension (PaCO2) and ETCO2 during the preoperative period in 20 premedicated patients undergoing various surgical procedures. ETCO2 was sampled from a 16-gauge intravenous catheter pierced through one of the two nasal oxygen prongs and measured at various oxygen flow rates (2, 4, and 6 L/min) by an on-line ETCO2 monitor with analog display. Both peak and time-averaged values for ETCO2 were recorded. The results showed that the peak ETCO2 values (mean = 38.8 mm Hg) correlated more closely with the PaCO2 values (mean = 38.8 mm Hg; correlation coefficient r = 0.76) than did the average ETCO2 values irrespective of the oxygen flow rates. The time-averaged PaCO2-ETCO2 difference was significantly greater than the PaCO2-peak ETCO2 difference (P < 0.001). Values for subgroups within the patient population were also analyzed, and it was shown that patients with minute respiratory rates greater than 20 but less than 30 and patients age 65 years or older did not differ from the overall studied patient population with regard to PaCO2-ETCO2 difference. A small subset of patients with respiratory rates of 30/ min or greater (n = 30) did show a significant increase in the PaCO2-ETCO2 difference (P < 0.001). It was concluded that under the conditions of this study, peak ETCO2 values did correlate with PaCO2 values and were not significantly affected by oxygen flow rate. However, obtaining peak ETCO2 values is clinically more difficult, especially when partial air-way obstruction is present.

Heparin-induced thrombocytopenia: bovine versus porcine heparin in cardiopulmonary bypass surgery.

BACKGROUND Studies have demonstrated a high incidence of antibodies to heparin/platelet factor 4 complexes, the antigen in heparin-induced thrombocytopenia, in patients after cardiopulmonary bypass surgery. In many hospitals, beef lung heparin has been used historically for cardiopulmonary bypass, and there has been reluctance to change to porcine heparin despite concerns of an increased incidence of heparin-induced thrombocytopenia in patients receiving bovine heparin. METHODS A prospective randomized trial comparing bovine and porcine heparin in cardiopulmonary bypass surgery was conducted. Presurgery and postsurgery heparin antibody formation was studied using the serotonin release assay and a heparin/platelet factor 4 enzyme-linked immunosorbent assay. RESULTS Data available on 98 patients, randomized to receive either bovine or porcine heparin, revealed no significant difference in patient positivity by serotonin release assay (12% in both groups) or by the heparin/platelet factor 4 enzyme-linked immunosorbent assay (29% with porcine and 35% with bovine heparin) postoperatively. There were no significant differences between preoperative and postoperative platelet counts or thromboembolic complications. CONCLUSIONS Our study does not support the belief that bovine heparin is more likely than porcine heparin to induce the development of antibodies to heparin/platelet factor 4.

Induced hypotension with labetalol for orthognathic surgery

Induced hypotension is an accepted technique for reducing blood loss in various surgical procedures. This study evaluates the effectiveness of labetalol in producing controlled reduction in mean arterial pressure during orthognathic surgery. The potential advantages of this technique are ease of administration, decreased pulmonary shunting, and absence of tachycardia or rebound hypertension compared to other commonly used agents.

The effect of the prone position on venous pressure and blood loss during lumbar laminectomy

STUDY OBJECTIVE To determine the effects of three different prone support systems (Andrews spinal surgery frame, Cloward surgical saddle, and longitudinal bolsters) on inferior vena cava (IVC) and superior vena cava (SVC) pressures; the validity of measuring central venous pressure (CVP) for the determination of ideal positioning of the patient; and the relationship among frame type, blood loss, and hemodynamic measurements. DESIGN Prospective, randomized study of the hemodynamic effects of the prone position. SETTING Inpatient surgery at a university hospital (regional spinal cord injury treatment center). PATIENTS Eighteen patients free of significant coexisting disease (ASA physical status I and II) undergoing elective lumbar laminectomy. INTERVENTIONS Patients were assigned to one of three support frames and measurement of SVC pressure, IVC pressure, and mean arterial pressures (MAP) were obtained supine, prone, and after repositioning. These pressures and measured blood loss were obtained every 15 minutes during the surgical laminectomy portion of the procedure. MEASUREMENTS AND MAIN RESULTS Patients positioned on the Andrews frame had decreased mean SVC and IVC pressures from 8.7 mmHg and 8.4 mmHg in the supine position to 3.3 mmHg and 1.8 mmHg in the prone position, respectively (p less than 0.001). Prone position CVP also was significantly lower in the Andrews group compared with that in the other two groups (p less than 0.001). Repositioning efforts did not significantly decrease CVP. Blood loss was higher in the Cloward group (1,150 +/- 989 ml) than in the Andrews (245 +/- 283 ml) and bolsters (262 +/- 188 ml) groups (p less than 0.02). CONCLUSIONS Increased blood loss was not associated with increased SVC or IVC pressure, nor was there any significant correlation between any demographic or hemodynamic variable and blood loss. There was no evidence that CVP is useful in determining the ideal prone position in patients undergoing lumbar laminectomy.

Original article: cardiovascularHeparin-induced thrombocytopenia: bovine versus porcine heparin in cardiopulmonary bypass surgery

BACKGROUND Studies have demonstrated a high incidence of antibodies to heparin/platelet factor 4 complexes, the antigen in heparin-induced thrombocytopenia, in patients after cardiopulmonary bypass surgery. In many hospitals, beef lung heparin has been used historically for cardiopulmonary bypass, and there has been reluctance to change to porcine heparin despite concerns of an increased incidence of heparin-induced thrombocytopenia in patients receiving bovine heparin. METHODS A prospective randomized trial comparing bovine and porcine heparin in cardiopulmonary bypass surgery was conducted. Presurgery and postsurgery heparin antibody formation was studied using the serotonin release assay and a heparin/platelet factor 4 enzyme-linked immunosorbent assay. RESULTS Data available on 98 patients, randomized to receive either bovine or porcine heparin, revealed no significant difference in patient positivity by serotonin release assay (12% in both groups) or by the heparin/platelet factor 4 enzyme-linked immunosorbent assay (29% with porcine and 35% with bovine heparin) postoperatively. There were no significant differences between preoperative and postoperative platelet counts or thromboembolic complications. CONCLUSIONS Our study does not support the belief that bovine heparin is more likely than porcine heparin to induce the development of antibodies to heparin/platelet factor 4.

The Design and Implementation of an Automated System for Logging Clinical Experiences Using an Anesthesia Information Management System

BACKGROUND:Residents in anesthesia training programs throughout the world are required to document their clinical cases to help ensure that they receive adequate training. Current systems involve self-reporting, are subject to delayed updates and misreported data, and do not provide a practicable method of validation. Anesthesia information management systems (AIMS) are being used increasingly in training programs and are a logical source for verifiable documentation. We hypothesized that case logs generated automatically from an AIMS would be sufficiently accurate to replace the current manual process. We based our analysis on the data reporting requirements of the American College of Graduate Medical Education (ACGME). METHODS:We conducted a systematic review of ACGME requirements and our AIMS record, and made modifications after identifying data element and attribution issues. We studied 2 methods (parsing of free text procedure descriptions and CPT4 procedure code mapping) to automatically determine ACGME case categories and generated AIMS-based case logs and compared these to assignments made by manual inspection of the anesthesia records. We also assessed under- and overreporting of cases entered manually by our residents into the ACGME website. RESULTS:The parsing and mapping methods assigned cases to a majority of the ACGME categories with accuracies of 95% and 97%, respectively, as compared with determinations made by 2 residents and 1 attending who manually reviewed all procedure descriptions. Comparison of AIMS-based case logs with reports from the ACGME Resident Case Log System website showed that >50% of residents either underreported or overreported their total case counts by at least 5%. CONCLUSION:The AIMS database is a source of contemporaneous documentation of resident experience that can be queried to generate valid, verifiable case logs. The extent of AIMS adoption by academic anesthesia departments should encourage accreditation organizations to support uploading of AIMS-based case log files to improve accuracy and to decrease the clerical burden on anesthesia residents.

A comparison of labetalol and nitroprusside for inducing hypotension during major surgery.

The hemodynamic and intrapulmonary shunt effects of intravenous labetalol and nitroprusside were compared during induced hypotension for major spinal surgery. A randomized, double-blind protocol was used in which 20 patients, ASA physical status I or II, received either nitroprusside infusion (n = 10) or labetalol bolus injections of 10 mg every 10 min (n = 10) until mean arterial blood pressure was reduced to 55--60 mm Hg. Pulmonary artery pressures were measured and mixed venous samples obtained via a pulmonary artery catheter. Nitroprusside increased heart rate significantly more than labetalol during the period of hypotension. When compared with prehypotension baseline values, nitroprusside increased heart rate significantly with a concomitant significant decrease in systemic vascular resistance. Cardiac output increased significantly 60 min after hypotension was achieved in patients treated with nitroprusside. Systemic vascular resistance decreased significantly below baseline levels in patients treated with labetalol but without changes in cardiac output, heart rate, or mean pulmonary artery pressure. There was a 122% increase in intrapulmonary shunt with nitroprusside administration, compared with an 11% increase with labetalol. Labetalol was effective for inducing hypotension and was not associated with an increase in heart rate, intrapulmonary shunt, or cardiac output as seen with nitroprusside.