Whole-blood aggregometry: are there any limits with regard to platelet counts?

BACKGROUND: Whole-blood aggregometry (WBA) is a promising tool to assess platelet function in its physiological environment. Dilution of whole blood in WBA disregards platelet concentrations that may impact the results, especially in the case of low platelet counts. In a blinded, prospective in vitro study, the influence of platelet concentrations on WBA was assessed. METHODS: Aggregation studies were carried out using whole blood from 10 healthy volunteers adjusted to platelet concentrations of 150, 100, 75, 50 and 25/nl using a plasma-balanced crystalloid solution. Platelet aggregation was measured by a new near-side whole blood aggregometer, activated by adenosin-diphosphate, collagen and thrombin-receptor activating protein. Three different approaches were applied: P1: whole blood diluted by an isotonic saline solution before activation, P2: undiluted whole blood with the single and P3: with the twofold concentration of the stimulating agent. RESULTS: Aggregometry in diluted whole blood (P1) decreased significantly from a platelet concentration of 100/nl (P<0.01). In undiluted whole blood, aggregation declined significantly from concentrations of 75 and 50/nl for P2 and P3 (P<0.01). No correlation to platelet count occurred in the undiluted approaches until a platelet concentration of 75/nl, whereas correlation in the diluted test run was detected starting from 100/nl. CONCLUSIONS: This study demonstrates that WBA depends on the platelet count and sensitivity towards low platelet concentrations may be improved by abdication of further dilution and the use of undiluted whole blood.

Individual titration of propofol plasma target improves anaesthetic stability in patients undergoing major abdominal surgery: a comparison with manually controlled infusion.

BACKGROUND AND OBJECTIVE: The impact of anaesthesia using target-controlled infusion with propofol on intraoperative stability, recovery and cost compared to manually controlled infusion has been evaluated with inconsistent results. We studied a new device that allows more individual titration of propofol target-controlled infusion by using the effect-site concentration at the loss of eyelash reflex to predict the maintenance infusion rate (FM-TCI). METHODS: Fifty-six patients undergoing major abdominal surgery lasting >2 h were randomly assigned to receive either FM-TCI (n = 28) or MCI-controlled (n = 28) anaesthesia. Both groups were Bispectral Index-monitored and thoracic epidural analgesia was established. Anaesthetic stability, incidence of haemodynamic abnormalities, time to extubation, propofol consumption and patient satisfaction were assessed. RESULTS: In the FM-TCI group, a significantly improved anaesthetic stability was achieved (0.43 +/- 0.44 vs. 1.31 +/- 0.78 adjustments of propofol infusion per patient per hour, P = 0.003) and time to extubation was significantly shorter (9.6 +/- 2.1 vs. 15.7 +/- 9.6 min P = 0.011). With FM-TCI, propofol consumption was significantly lower. Haemodynamic stability and patient satisfaction did not differ between the groups. CONCLUSION: FM-TCI helps to provide more stable anaesthesia conditions requiring less-frequent adjustments of the propofol infusion compared to manually controlled infusion in patients undergoing major abdominal surgery.

Influence of controlled hypotension using esmolol and sodium nitroprusside on natriuretic peptides in patients undergoing endonasal sinus surgery.

BACKGROUND AND OBJECTIVE: Atrial and brain natriuretic peptide, synthesized by cardiac myocytes, are mediators secreted secondary to cardiac volume expansion and increased filling pressure. The study was designed to assess serum concentration of atrial and brain natriuretic peptide in patients undergoing endonasal sinus surgery receiving controlled hypotension. METHODS: We studied 45 patients without cardiovascular history, scheduled for elective endonasal sinus surgery. Patients were allocated to one of three groups: controlled hypotension was induced either by using esmolol (n = 15) or sodium nitroprusside (n = 15) with a mean arterial pressure of 50-55 mmHg. In the control group (n = 15), mean arterial pressure was adjusted to 70-80 mmHg. Atrial and brain natriuretic peptides were measured preoperatively (T1), at the end of surgery (T2), 2 h (T3), 24 h (T4) and 48 h (T5) postoperatively. RESULTS: Preoperative atrial and brain natriuretic peptide plasma levels were within normal ranges and similar between all groups. Patients treated with esmolol (atrial natriuretic peptide: 2.46 +/- 0.75 microg mL(-1) brain natriuretic peptide: 4.34 +/- 3.06 microg mL(-1)) and sodium nitropusside (atrial natriuretic peptide: 2.48 +/- 0.92 microg mL(-1); brain natriuretic peptide: 4.49 +/- 3.21 microg mL(-1)) showed significantly lower concentrations of atrial and brain natriuretic peptide at T2 and T3 compared with controls (atrial natriuretic peptide: 5.31 +/- 2.32 microg mL(-1); brain natriuretic peptide: 13.26 +/- 8.98 microg mL(-1)) , P < 0.01) as well as a reduction in blood loss and duration of surgery. CONCLUSIONS: Controlled hypotension decreases the release of natriuretic peptides in cardiovascular healthy patients. This effect may be contributed to by changes in cardiac filling pressure due to lower systemic resistance and diminished perfusion pressure.

Semi-invasive monitoring of cardiac output by a new device using arterial pressure waveform analysis: a comparison with intermittent pulmonary artery thermodilution in patients undergoing cardiac surgery.

BACKGROUND: Thermodilution technique using a pulmonary artery catheter (PAC) is a widely used method to determine cardiac output (CO). It is increasingly criticized because of its invasiveness and its unclear risk-benefit ratio. Thus, less invasive techniques for measuring CO are highly desirable. We compared a new, semi-invasive device (FloTrac/Vigileo) using arterial pressure waveform analysis for CO measurement in patients undergoing cardiac surgery with bolus thermodilution measurements. METHODS: Forty patients undergoing coronary artery bypass grafting or valve repair were enrolled. A PAC was inserted and routine radial arterial access was used for semi-invasive determination of CO with the Vigileo. CO was measured simultaneously by bolus thermodilution and the Vigileo technique after induction of anaesthesia (T1), before cardiopulmonary bypass (CPB) (T2), after CPB (T3), after sternal closure (T4), on arrival in the intensive care unit (ICU) (T5), and 4 h (T6), 8 h (T7), and 24 h after surgery (T8). CO was indexed to the body surface area (cardiac index, CI). RESULTS: A total of 244 pairs of CI measurements were analysed. Bias and precision (1.96 sd of the bias) were 0.46 litre min(-1) m(-2) and +/- 1.15 litre min(-1) m(-2) (r = 0.53) resulting in an overall percentage error of 46%. Subgroup analysis revealed a percentage error of 51% for data pairs obtained intraoperatively (T1-T4), 42% in ICU (T5-T8), and 56% for values obtained during low CI (T1-T8). CONCLUSIONS: In cardiac surgery patients, CO measured by a new semi-invasive arterial pressure waveform analysis device showed only moderate agreement with intermittent pulmonary artery thermodilution measurement.