Measurement of the activated clotting time during cardiopulmonary bypass: differences between Hemotec ACT and Hemochron Jr apparatus

BACKGROUND

Measurement of the activated clotting time (ACT) represents a standard method for coagulatory assessments. The test employs specific agents to trigger the coagulation process. The present study aimed to compare kaolin (Hemotec) versus a combination of silica, kaolin and phospholipid (Hemochron Jr) ACTs.

METHODS

Hemotec and Hemochron Jr ACT monitors were compared by simultaneous measurement of paired arterial blood samples (n = 114) with respect to precision and bias during clinical conditions of cardiopulmonary bypass (CPB). The influence of haemodilution on the ACT was tested in an ex-vivo model.

RESULTS

The precision of Hemotec and Hemochron Jr ACT measurements attained 21 +/- 2.6 s versus 27.0 +/- 2.6 s (p = 0.126) during CPB and 2.5 +/- 2.2 s versus 9.4 +/- 6.9 s (p = 0.000) after protamine administration, respectively. The Hemochron Jr monitor was associated with a bias of -102 +/- 13.7 s compared to the Hemotec ACT monitor (p = 0.000) during CPB and -6.9 +/- 2.9 s after protamine (p = 0.025). Linear regression analysis of ACT readings between monitors reached r = 0.526 (p = 0.000). Hemochron Jr ACT values correlated with the erythrocyte volume fraction r = 0.379 (p = 0.000). Ex-vivo data indicated that the Hemotec ACT monitor was associated with relatively higher ACT readings after haemodilution.

CONCLUSION

The ACT is not a standardized measure. Test results are strongly associated with the specific compounds used to initiate the coagulation process.

Use of heparin-bonded circuits in cardiopulmonary bypass improves clinical outcome

OBJECTIVE

The use of heparin-coated surfaces in cardiopulmonary bypass has been shown to decrease the inflammatory response imposed by the contact between blood and artificial surfaces. One would expect this reaction to improve clinical outcome. However, this has been difficult to verify. This investigation is based on an aggregation of two randomized studies from our institution and highlights possible effects of heparin coating on a number of clinically oriented parameters.

DESIGN

Departmental analysis of patients subjected to coronary artery bypass surgery using heparin-coated circuits. Cardiopulmonary bypass was employed using either the Carmeda or Duraflo heparin coatings compared with a control. The systemic heparin dose was reduced in the heparin-coated groups (ACT > 250 s) vs control group patients (ACT > 480 s). The effects of heparin coating related to clinical outcome were studied.

RESULTS

The use of heparin-coated circuits reduced the mean length of stay in hospital from 7.8 +/- 2.5 to 7.3 +/- 1.8 days (p = 0.040) and postoperative ventilation time from 9.7 +/- 9.2 to 8.2 +/- 8.5 h (p = 0.018), blood loss 8 h post surgery from 676 +/- 385 to 540 +/- 245 ml (p = 0.001), individual perioperative change of haemoglobin loss (p = 0.001), leukocyte count (p = 0.000) and creatinine elevation (p = 0.000), proportion of patients exposed to allogenous blood transfusions 39.2 vs 23.9% (p = 0.001), postoperative coagulation disturbances 4.4 vs 0.4% (p = 0.006), postoperative deviations from the normal postoperative course 47.2 vs 36.7% (p = 0.035), neurological deviations 9.4 vs 3.9% (p = 0.021) and atrial fibrillation 26.4 vs 18.0% (p = 0.041). No effects were found with respect to perioperative platelet count, postoperative fever reaction and 5-year survival.

CONCLUSION

Based on several indicators, the use of heparin coating in cardiopulmonary bypass is associated with improved clinical results.

Neurological and general outcome in low-risk coronary artery bypass patients using heparin coated circuits

OBJECTIVE

The clinical significance of heparin coating in cardiopulmonary bypass has previously been investigated. However, few studies have addressed the possible influence on brain function and memory disturbances.

METHODS

Three hundred low-risk patients exposed to coronary bypass surgery were randomised into three groups according to type of heparin coating: Carmeda Bioactive Surface, Baxter Duraflo II and a control group. Outcome was determined from a number of clinically oriented parameters, including a detailed registry of postoperative deviations from the normal postoperative course. Brain damage was assessed through S100 release and memory tests, including a questionnaire follow-up.

RESULTS

Clinical outcome was similar for all groups. Blood loss (Duraflo only), transfusion requirements and postoperative creatinine elevation were reduced in the heparin-coated groups. A lower incidence of atrial fibrillation was noted in the Duraflo group. Heparin coating did not uniformly attenuate the release of S100 or the degree of memory impairment.

CONCLUSIONS

Cardiopulmonary bypass (CPB) with heparin coating and a reduced dose of heparin seems to be safe. Clinical outcome and neurological injury seem not to be associated with type of heparin coating used for CPB. However, blood loss and transfusion requirements may be reduced.

Quality assurance in clinical perfusion

OBJECTIVE

To investigate the properties and usefulness of prospective routine registration of incidents related to cardiopulmonary bypass and its clinical significance as a quality assurance instrument.

METHODS

Incidents or deviations from the normal course observed during cardiopulmonary bypass procedures were registered in a computer database. Each incident was classified according to 14 pre-defined categories. The cause of each incident was evaluated, as well as patient outcome. Incidents leading to permanent or temporary injury were denoted accidents. The general- and category-related incidence rate was calculated for the observation period 1989-1997 encompassing 6918 cardiopulmonary bypass procedures.

RESULTS

The general incidence rate varied between 4.5-7.6% per year during the registration period. Most incidents (57%) occurred during established, or start of, cardiopulmonary bypass, whereas the remaining proportion of incidents were detected either before (27%) or when terminating (16%). The most common category of incidents was oxygenator failure (1.6%), followed by mechanical (1.4%) and surgical (1.2%) incidents. Accidents and fatal outcomes occurred in 0.03% of the cases.

CONCLUSIONS

Routine registration of incidents yields a clinically attractive instrument of controlling safety aspects and quality measures in cardiopulmonary bypass. The observed incidence rates are somewhat higher than previously reported, probably primarily related to the methodology implemented in this study.

The relative safety of an oxygenator

Analysis of prospectively registered incidents related to cardiopulmonary bypass (CPB) was initiated to establish the incident rate for 10 different oxygenator brands employed over a seven-year period in 5000 clinical perfusions. A general safety index (SI) was defined as the number of recorded incidents in a given series of oxygenators divided by its total number and multiplied by 100. Specific SI was calculated for each of the following categories: high-pressure drop, debris, gas exchange, leakage, material failure and oxygenator change-out. An SI of 0.2 was arbitrarily set as a reference and an acceptable safety level. An estimate of the relative risk for a particular oxygenator brand was compared with the reference by calculating the odd's ratio with a 95% confidence interval. The mean SI was determined to be 1.6, ranging from 0 for the Maxima CBAS and the Cobe CML to 2.92 for the Safe oxygenator. The dominating specific type of incident was HPD with an SI of 0.81 followed by debris, SI = 0.71. A systematic analysis of adverse events in CPB may be used to evaluate and to set standards, a method already employed in the pharmaceutical industry. Our results indicate that oxygenator safety margins may vary between different brands.

Clinical effects of the heparin coated surface in cardiopulmonary bypass

OBJECTIVE

In a randomised study of 120 patients, undergoing primary operation for coronary heart decease, two groups were investigated as regards to the effects of heparin coated cardiopulmonary bypass on brain function parameters and general clinical outcome. The study group (n = 56) was perfused using an extra-corporeal circuit treated with covalent bonded heparin; the control group (n = 59) used an identical set-up without heparin treatment. Systemic heparin doses were calculated to achieve ACT levels of 250 and 500 s, respectively. Postoperative course was evaluated by examining a set of clinically relevant parameters including a detailed registry of postoperative deviations. Brain function was assessed by the biochemical marker S-100 and tests of memory performance.

RESULTS

There were several signs of reduced operative trauma in the study group. Hospital stay was reduced by nearly 1 day (P < 0.05). Time on postoperative ventilatory support was approximately 4 h shorter (P = 0.009). Chest drain blood loss was decreased both at 8 (P = 0.01) and 24 h (P = 0.007) postoperatively. Body temperature was lower after surgery and especially on days 2 (P = 0.03) and 3 (P = 0.01). Perioperative creatinine elevation was significantly reduced (P = 0.03). Neurological deviations were fewer (P = 0.01). Brain function assessment revealed reduced plasma levels of S-100 both at termination of cardiopulmonary bypass (P = 0.008) and 7 h later (P = 0.04). However, no remediation of memory impairment could be demonstrated.

CONCLUSIONS

Cardiopulmonary bypass with covalent bonded heparin attached to the extra-corporeal circuit in combination with a reduced systemic heparin dose seems to reduce safely and effectively the operative stress to the patient. There were also signs of improved cerebral protection.

Continuous venous oximetry: a comparative study between the CDI 100 and the Bentley OxySat II

Two in-line oxygen saturation monitors, the CDI 100 and OxySat II, were evaluated in the clinical setting. Eighty-seven venous blood samples were drawn during 20 elective cardiopulmonary bypass procedures. Monitor readings were compared to OSM III co-oximeter values. The results revealed that saturation (%) determination was biased, -3.16 +/- 2.21 SD for the CDI 100 and -0.34 +/- 2.17 SD for the OxySat II. Hemoglobin (g/dl) and hematocrit (%) measurement, available only for the CDI 100, resulted in a bias of +5.54 +/- 5.68 SD and +1.94 +/- 1.78 SD, respectively. It was concluded that both monitors operated within clinically acceptable limits, with a more favorable outcome for the OxySat II.