Monitoring unfractionated heparin in pediatric patients with congenital heart disease having cardiac catheterization or cardiac surgery.

Determine the effect of age and congenital heart disease (CHD) on whole blood tests for monitoring unfractionated heparin (UFH) in children. Determine correlation with anti-Xa levels in children undergoing cardiac catheterization or cardiac surgery. A prospective cross-sectional study of 211 healthy children about to have minor surgery (median age 3.5 years) and 110 CHD patients (median age 2.1 years) undergoing cardiac catheterization or cardiac surgery. Commonly used whole blood tests (two activated clotting times and an activated partial thromboplastin time; ACT+, ACT-LR, and APTT, respectively) were obtained before procedures and after UFH in CHD patients. Data were analyzed for effect of age and CHD and correlation with anti-Xa levels. In healthy subjects the ACT+ was lower in younger (<3 years) patients while the ACT-LR and APTT were unaffected. CHD patients exhibited an opposite trend with higher values in the younger patients. After bolus heparin the ACT+ exhibited the strongest correlation (r = 0.89) with anti-Xa levels in both locations (the APTT was too sensitive at post-bolus levels). When anti-Xa levels were below 1.0 IU/ml (range of thromboembolism therapy 0.35-0.7 IU/ml), the APTT correlation coefficient was 0.72. Some whole blood coagulation tests are affected by age in healthy children similar to laboratory tests and are variably influenced by the presence of CHD. ACT+ is the most reliable predictor of anti-Xa levels in both catheterization and surgery for pediatric patients. The APTT exhibited stronger correlation with anti-Xa than previous reports of laboratory APTT and warrants further evaluation for monitoring heparin thromboembolism therapy.

Increased accuracy and precision of heparin and protamine dosing reduces blood loss and transfusion in patients undergoing primary cardiac operations.

Individual aspects of heparin or protamine dosing have been better controlled than previously as useful tests have become available. Although many variables including drug potency, drug source, and individual patient response have been separately identified, there has not been an attempt to integrate them into a single management strategy. This study was undertaken to learn whether more precise control of drug variables and patient response would affect blood loss and transfusion requirements. Adult patients having primary cardiac operations were prospectively randomized into two groups. A control group received heparin and protamine by conventional methods. The test group received heparin and protamine according to in vitro predictive tests integrating drugs, tests, and patient response. Supplemental protamine was given in this group only if heparin was specifically found by testing. Anticoagulation in all patients was maintained at an activated coagulation time greater than 400 seconds, and any other treatment for bleeding was at the discretion of the clinical team caring for the patients. Testing and treatment for both groups followed routine practice after patient arrival in the intensive care unit. Test patients received slightly more heparin and a markedly lower dose of protamine than the control patients. Testing identified patients with decreased heparin sensitivity (preoperative heparin therapy) and correctly predicted the effective heparin dose. Supplemental protamine was given twice as often to control patients and frequently when no heparin was detectable (retrospectively). Test patients exhibited less 24-hour chest tube drainage (671 ml versus 1298 ml) and fewer patients received transfusion (9/22 versus 18/24) with fewer donor exposures (22/22 versus 101/24). The management strategy used for heparin and protamine added accuracy and precision, which was associated with improved hemostasis. Although the observation is valid, the mechanism or mechanisms are not completely clear. Nevertheless, it is reasonable to apply basic pharmacologic principles and establishment of consistent, predictable protocols that are beneficial. It is against this background that the efficacy of additional drugs or equipment should be assessed. It is quite possible that only marginal if any improvement in hemostasis may be found in patients having primary, uncomplicated cardiac operation with the addition of more costly drugs or equipment.

Desmopressin does not decrease bleeding after cardiac operation in young children.

Young children undergoing complex cardiac operation lose more blood after cardiopulmonary bypass than do older patients. This study was designed to investigate the effect of desmopressin on blood loss during the first 24 hours after cardiac operation in children undergoing principally complex surgical procedures. The study consisted of a randomized, blinded comparison of 112 pediatric patients who received either desmopressin 0.3 microgram/kg or saline solution placebo after cardiopulmonary bypass. A coagulation profile including bleeding time, quantitation of von Willebrand factor, and qualitative analysis of the factor VII:von Willebrand factor complex was performed before, 30 minutes after, and 3 hours after the operation. Blood loss and blood replacement were recorded for the first 24 hours after the operation. The surgeon classified the technical difficulty of each procedure as simple or complex. Statistical analysis was performed with Student's unpaired t test and chi 2 analysis. Significance was defined as p < 0.05. Results are listed as mean +/- standard deviation. Data collection was completed for 95 patients. The mean age of all patients was 26 +/- 40 months, and the mean weight was 10 +/- 11 kg, with 84% undergoing complex procedures. There were no differences between the desmopressin and placebo groups with respect to age, weight, or surgical complexity. Twenty-four-hour blood loss and replacement between the desmopressin and placebo groups were not different (blood loss: desmopressin 30 +/- 33 ml/kg, placebo 35 +/- 36; blood replacement: desmopressin 65 +/- 43 ml/kg, placebo 64 +/- 46 ml/kg). Coagulation profiles between the desmopressin and placebo groups were not different at any time. We conclude that desmopressin does not reduce blood loss or blood replacement in young children after cardiopulmonary bypass for either simple or complex cardiac surgical procedures.

Peripheral vascular response to potassium administration during cardiopulmonary bypass.

Potassium (K+) is often administered to patients during cardiopulmonary bypass (CPB). The effects of rapid K+ administration during CPB were studied in 30 adult patients. Each patient received one bolus dose (2, 4, 8, 12, or 16 mEq) of potassium chloride (KCl) (2 mEq/ml) during CPB. Serum K+ was significantly increased from baseline values at KCl doses of 8 mEq and larger (p less than 0.05). All increases in serum K+ returned to clinically acceptable levels within 5 minutes after the bolus. Mean arterial pressure (MAP) (torr) and total peripheral resistance (TPR) (dynes sec cm-5) changes were biphasic; after an initial transient decrease, maximal with the 16 mEq K+ bolus (MAP -21 +/- 6, TPR - 315 +/- 135), these parameters increased (8 mEq K+ bolus, MAP + 15 +/- 16, TPR + 301 +/- 90; 12 mEq K+ bolus, MAP + 43 +/- 9, TPR + 998 +/- 250; 16 mEq bolus, MAP + 51 +/- 9, TPR + 1,216 +/- 120) with a peak at 3 minutes after the bolus. Hypertension, in nine of 18 patients receiving a KCl bolus of 8 mEq or larger, was of such magnitude (range 132 to 196 torr) as to require rapid therapeutic intervention to lower blood pressure. When KCl supplementation is required on CPB and slow infusion rates seem unreasonable, bolus doses of less than 8 mEq may be administered without vascular effect.

An enclosed system for continuous postoperative mediastinal aspiration.

Blockage of mediastinal drainage tubes in the postoperative cardiac surgical patient can result in tamponade, and the small child, with a necessarily small drainage tube, is particularly susceptible to instability arising from accumulating blood in the mediastinum. A system for continuous evacuation of blood in drainage tubes is described that decreases the likelihood of blocked tubes and resultant tamponade.

Monitoring heparin anticoagulation and its neutralization.

Heparin anticoagulation and its neutralization were monitored by three different techniques: a manual protamine titration, an automated activated coagulation time, and an automated protamine titration. All three techniques provided satisfactory information. The decision of which to use must be based on other considerations such as available manpower and cost of equipment. The effect of using the automated protamine titration test on heparin and protamine requirements, and on blood loss measured intraoperatively after bypass and in overnight chest bottle drainage in two groups of comparable patients undergoing coronary artery bypass operation was studied. The heparin requirements were similar (24,420 +/- 584 units, control group; 23,550 +/- 849 units, treatment group), but the protamine requirements were markedly different (429 +/- 14.7 mg, control; 258 +/- 10.4 mg, treatment; p < 0.05). There was no statistical difference in intraoperative blood loss or overnight chest bottle drainage.

Carbon dioxide prevents pulmonary overcirculation in hypoplastic left heart syndrome.

Circulatory and metabolic homeostasis in patients with hypoplastic left heart syndrome is dependent on a delicate balance between systemic and pulmonary blood flow. Hypocarbia can result in a marked decrease in pulmonary vascular resistance accompanied by pulmonary overcirculation, systemic hypotension, metabolic acidosis, and death. This report illustrates that early and precise control of the arterial carbon dioxide tension using inspired carbon dioxide can be effective in preventing or treating instability arising during management of a patient with hypoplastic left heart syndrome.

Management of bleeding and coagulopathy after heart surgery.

Mechanisms of bleeding common to virtually all patients after heart surgery are platelet dysfunction, enhanced fibrinolysis, dilution of all components of the coagulation system, and the presence of heparin and protamine. The use of warfarin is increasing in patients with heart disease requiring surgery. The replenishment of vitamin K-dependent factors beyond a normal prothrombin time is not assessable, and the dilution associated with cardiopulmonary bypass can reach coagulopathic levels. Optimal preoperative preparation is required and intraoperative therapy initiated when indicated. Individualized heparin and protamine dosing, antifibrinolytic drug administration, minimization of blood loss and dilution, and minimal time on cardiopulmonary bypass are basic adjuncts to meticulous surgical hemostasis. When bleeding is observed in the postoperative period, a sequential assessment of the probable cause leads to initial therapy while laboratory test results are obtained. Ongoing assessment for hemodynamic instability caused by accumulated mediastinal blood is needed while managing the bleeding patient. A chest radiograph and transesophageal echocardiogram can be useful in diagnosing cardiac tamponade.

Safety issues in heparin and protamine administration for extracorporeal circulation.

This article reviews past approaches to heparin and protamine dosing and summarizes current practice. The author elucidates his experience with the Celite activated coagulation time (ACT), with attention to his adoption of a value of 400 seconds for this time; the adoption of an ACT of 480 seconds by Bull et al (J Thorac Cardiovasc Surg 69:674-684, 1975) and Young et al (Ann Thorac Surg 26:231-240, 1978); the proposed use of heparin response curves by Bull et al; the author's experience with a unitized dosing system to individualize dosing of heparin; and the use for this purpose by Despotis et al (J Thorac Cardiovasc Surg 110:46-54, 1995) of a system based on protamine titration. In more than 270 adult cardiac surgery patients, the unitized dosing system identified patients with high sensitivity or resistance to heparin and facilitated exact individualized doses to be given to produce the desired effect. Thus, less heparin was used in short bypass runs. Patients received less protamine than they would have with any other formula, and there was less blood loss and fewer transfusions required. Currently, no claims for efficacy or safety can be made for maintaining heparin concentrations greater than 3 U/mL. Pending further clarification, heparin dosage cannot be safely reduced when using heparin-bonded circuits. Aprotinin is not a procoagulant during cardiopulmonary bypass. Emerging studies suggest that graft patency is not affected by aprotinin use. The Celite ACT should not be used to monitor heparin effect and safety when using aprotinin; the kaolin ACT should be used instead.

Continuous in-vivo blood-gas determination in man: reliability and safety of a new device.

The Sentorr is a gas chromatograph that monitors Pa2 and PaCO2 every 4 min from a probe placed through an intraarterial cannula. The accuracy of this device and complications resulting from its use were studied in 46 patients undergoing cardiac surgical procedures with oxygen to nitrous oxide-halothane anesthesia. Sentorr blood-gas values were compared with simultaneous samples analyzed with standard electrodes. During relatively steady states of respiration and circulation, and in the lower (50-125 torr) range of oxygen tensions, the measurements correlated closely (r = 0.92). The device also functioned well during low-flow states, but during hypothermic cardiopulmonary bypass, the correlation was only fair (r = 0.62). When nitrous oxide was present in the inspired gas, Sentorr PaO2 readings were a third lower than actual PO2 measurements, an effect corroborated by an in-vitro experiment. Directional changes of oxygen and carbon dioxide tensions were always correct in all situations. Placement of the probe in a radial artery was unsatisfactory because it significantly interfered with blood pressure measurement and resulted in inaccurate results for this patient population. The brachial artery was a satisfactory site for insertion, although attenuation of the arterial pressure tracing by the presence of a Sentorr probe resulted in systolic pressure readings that averaged 12 torr lower with mean arterial pressure readings 5 torr lower. No increase in morbidity due to use of a Sentorr probe for brachial arterial pressure monitoring could be identified. The most potentially serious complication encountered was transient loss of a palpable pulse without interruption of blood flow in one or more distal arteries after decannulation. This was observed in seven patients (four of whom had diminished distal pulses whith normal flow before cannulation).

A hazard of the Intraflo continuous flush system.

Patency of pressure sensing systems can be provided by the Intraflow Continuous Flush System (Sorenson Research Company, Salt Lake City, UT 84115). This device allows continuous flow of flush solution through a regulatory valve while preventing transmission of the high pressure of the flush solution. The case presented describes the recognition of a false elevation of a monitored pressure secondary to the malfunction of the Intraflo regulatory valve. Elimination of the flush solution high pressure during monitoring prevents inappropriate data collection.

Comparison of internal and external jugular cannulation of the central circulation in the pediatric patient.

Percutaneous catheterization of the central circulation via the internal jugular vein was compared to cannulation via the external jugular vein, in a retrospective review of 200 pediatric patients. The internal approach resulted in an 86% rate of successful cannulations with 99.9% of the catheters positioned in the thorax; this technique was accompanied by an 8% incidence of carotid artery puncture. The external jugular route eliminated the risk of carotid artery puncture; however, it was successful in only 65% of the attempts, and 14% of the successful cannulations had catheter tips incorrectly positioned outside the thorax.