The use of the iSTAT portable analyzer in patients undergoing cardiopulmonary bypass

Comprehensive Coagulation Profiling at the Point-of-Care Using a Novel Laser-Based Approach

Delays in identifying internal bleeding are life-threatening, thus underscoring the need for rapid and comprehensive coagulation profiling at the bedside. The authors review a novel optical coagulation profiler that measures several coagulation metrics including prothrombin time, activated clotting time, clot polymerization rate (α-angle), clot stiffness (maximum amplitude), fibrinolysis (LY), and platelet function, using a single multifunctional instrument. The optical profiler is based on the principles of Laser Speckle Rheology that quantifies tissue viscoelasticity from light scattering patterns called laser speckle. To operate the optical profiler, whole blood (40 μL) is loaded into a disposable cartridge, laser speckle patterns are recorded via a camera, and the viscoelasticity of clotting blood is estimated from speckle intensity fluctuations. By monitoring alterations in viscoelastic moduli over time during clot initiation, thrombin generation, fibrin crosslinking, clot stabilization, and LY, global coagulation parameters are obtained within 10 minutes using a drop of whole blood. Clinical testing in over 500 patients to date has confirmed the accuracy of the optical profiler for comprehensively assessing coagulation status against conventional coagulation tests and thromboelastography. Recent studies have further demonstrated the capability to quantify platelet aggregation induced by adenosine diphosphate in a drop of platelet-rich-plasma in the absence of applied shear stress. Together, these studies demonstrate that global coagulation profiling in addition to platelet function may be accomplished using a single multifunctional device. Thus, by enabling rapid and comprehensive coagulation and platelet function profiling at the bedside, the optical profiler will likely advance the capability to identify and manage patients with an elevated risk for hemorrhage.

Defining Dogma: Quantifying Crystalloid Hemodilution in a Prospective Randomized Control Trial with Blood Donation as a Model for Hemorrhage

BACKGROUND

The concept of hemodilution after blood loss and crystalloid infusion is a surgical maxim that remains unproven in humans. We sought to quantify the effect of hemodilution after crystalloid administration in voluntary blood donors as a model for acute hemorrhage.

STUDY DESIGN

A prospective, randomized control trial was conducted in conjunction with community blood drives. Donors were randomized to receive no IV fluid (noIVF), 2 liters of normal saline (NS), or 2 liters lactated Ringer's (LR) after blood donation. Blood samples were taken before donation of 500 mL of blood, immediately after donation, and after IV fluid administration. Hemoglobin (Hgb) was measured at each time point. Hemoglobin measurements between time points were compared between groups using standard statistical tests and the Bonferroni correction for multiple comparisons. Statistical significance was set at p ≤ 0.0167.

RESULTS

Of 165 patients consented, 157 patients completed the study. Average pre-donation Hgb was 14.3 g/dL. There was no difference in the mean Hgb levels after blood donation between the 3 groups (p > 0.05). Compared with the control group, there was a significant drop in Hgb in the crystalloid infused groups from the post-donation level to post-resuscitation (13.2 vs 12.1 vs 12.2 g/dL, p < 0.0001). A formula was created to predict hemoglobin levels from a given estimated blood loss (EBL) and volume replacement (VR): Hemodilution Hgb = (mean pre-donation Hgb - hemorrhage Hgb drop - equilibration hemoglobin drop - resuscitation Hgb drop) = Mean pre-donation Hgb - [(EBL/TBV)*l] - [(EBL/TBV)*h] - [(VR/TBV)*r], l = 5.111g/dL = blood loss coefficient, h = 6.722 g/dL = equilibration coefficient, r = 2.617g/dL = resuscitation coefficient.

CONCLUSIONS

This study proves the concept of hemodilution and derived a mathematical relationship between blood loss and resuscitation. These data may help to estimate response of hemoglobin levels to blood loss and fluid resuscitation in clinical practice.

Evaluation of point-of-care testing in critically unwell patients: comparison with clinical laboratory analysers and applicability to patients with Ebolavirus infection

Data on the performance of point-of-care (POC) or near-patient devices in the management of critically unwell patients are limited, meaning that there are demands for confirming POC test results in the routine clinical laboratory and so potentially leading to delay in treatment provision. We evaluated the performance of the i-STAT CHEM 8+ and CG4+, Hemochron Signature Elite, HemoCue Hb 201+ and WBC Diff Systems on whole blood collected from medical and surgical patients admitted to the intensive care unit at an Australian tertiary care hospital. Measurements obtained for haematology, coagulation, biochemistry and arterial blood gas parameters using POC devices were compared against clinical laboratory analysers (XE-5000, STA-R Evolution, Dimension Vista 1500 and ABL800 FLEX). Bland-Altman and Passing-Bablok regression plots were constructed to assess agreement. Good correlation was defined as a bias of <10% between the POC device and the reference method. Forty arterial blood samples were collected from 28 patients. There was good correlation demonstrated for sodium, potassium, chloride, ionised calcium, glucose, urea, haemoglobin and haematocrit values (i-STAT Chem 8+); pH, pCO(2), bicarbonate and oxygen saturation (i-STAT CG4+); haemoglobin, white cell, neutrophil count and lymphocyte counts (Hemocue); and internationalised normal ratio (INR; Hemochron Signature Elite), but not creatinine, anion gap, pO(2), base excess, lactate, eosinophil count, prothrombin and activated partial thromboplastin time. POC devices were comparable to clinical laboratory analysers in measuring the majority of haematology, biochemistry and coagulation parameters in critically unwell patients, including those with infections. These devices may be deployed at the bedside to allow 'real-time' testing to improve patient care.

Noninvasively Measured Hemoglobin Concentration Reflects Arterial Hemoglobin Concentration Before but Not After Cardiopulmonary Bypass in Patients Undergoing Coronary Artery or Valve Surgery

OBJECTIVE

This study compared noninvasively measured hemoglobin and arterial hemoglobin before and after cardiopulmonary bypass in patients undergoing coronary artery or valve surgery.

DESIGN

Observational study with retrospective data analysis.

SETTING

Veterans Affairs hospital.

PARTICIPANTS

Thirty-five men.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Hemoglobin values were measured noninvasively by co-oximetry to corresponding arterial hemoglobin concentrations taken at clinically relevant time points chosen at the discretion of the cardiac anesthesiologist. Thirty-five and 27 pooled pairs of data were obtained before and after cardiopulmonary bypass, respectively. Arterial hemoglobin concentration was analyzed using i-STAT CG8+test cartridges routinely used in the authors' operating rooms and those of other institutions. Linear regression and Bland-Altman analysis revealed a significant positive bias, wide limits of agreement, and low correlation coefficients between the noninvasive and arterial hemoglobin measurements. These findings were especially notable after compared with before cardiopulmonary bypass.

CONCLUSIONS

The results suggested that noninvasive measurement of hemoglobin overestimates arterial hemoglobin by almost 1 g/dL when compared to iSTAT. A lack of precision also was observed with noninvasive measurement of hemoglobin, especially after cardiopulmonary bypass. These findings supported the contention that sole reliance on noninvasive measurement of hemoglobin for transfusion decisions in cardiac surgery patients may be inappropriate.

Accuracy of noninvasive hemoglobin monitoring in patients at risk for hemorrhage

BACKGROUND

Monitoring for acute blood loss is critical in surgical patients, and delays in identifying hemorrhage can result in poor outcomes. The current standard of care for monitoring patients at risk for bleeding is serial measurement of hemoglobin (Hgb) by standard laboratory complete blood count (CBC). Point-of-care testing (i.e., iSTAT) can be a rapid method of evaluating Hgb, and spectrophotometry-based devices (i.e., Radical-7) offer the advantages of being continuous and noninvasive. We sought to evaluate the accuracy of Radical-7 and iSTAT in measuring Hgb and assessing for blood loss when compared with the criterion standard CBC.

METHODS

Adult patients at risk for hemorrhage admitted to the surgical intensive care unit of a tertiary referral, Level I trauma center were eligible for this study. Serial CBC Hgb measurements were drawn as clinically indicated. The Radical-7 device was placed on the patient for noninvasive Hgb measurements (SpHb), and at each CBC measurement, concurrent iSTAT Hgb measurements were obtained. Bland-Altman analysis was used to compare the three methods of measuring Hgb with accuracy defined as measurements within 1.0-g/dL CBC Hgb. Concordance measurements were also performed to compare trends between values.

RESULTS

Eighty-eight patients were enrolled and underwent 572 CBC measurements. Bland-Altman analysis of SpHb versus CBC resulted in an estimated bias of 1.49 g/dL, with 95% limits of agreement of -2.2 g/dL to 5.0 g/dL. iSTAT versus CBC resulted in an estimated bias of -0.63 g/dL, with 95% limits of agreement of -3.4 g/dL to 2.2 g/dL. Changes in SpHb had concordance with CBC Hgb 60% of the time, compared with 76% for iSTAT versus CBC CONCLUSION: Radical-7 SpHb was inaccurate when compared with CBC Hgb levels, and serial SpHb achieved concordance with CBC Hgb 60% of the time. As such, the clinical utility of Radical-7 as a rapid, noninvasive predictor of acute hemorrhage may be limited.

LEVEL OF EVIDENCE

Diagnostic study, level II; care management, level III.

Accuracy and reliability of the i-STAT point-of-care device for the determination of haemoglobin concentration before and after major blood loss

We investigated the accuracy of i-STAT(®) (Abbott Point of Care Inc., Princeton, NJ, USA) haemoglobin (Hb) measurement in surgical patients with an estimated blood loss of ≥25% of total blood volume. Blood tests for i-STAT(®) Hb, laboratory Hb (Sysmex XE-2100(™), Sysmex Corporation, Kobe, Japan) and total plasma proteins were obtained at the start of surgery (T=0) and when an estimated 25% total blood volume loss had occurred (T=1). Thirty-one patients were recruited. The coefficient of variation of the paired i-STAT(®) Hb estimates was 2.8% and 2.9% at T=0 and T=1, respectively. The mean difference between i-STAT(®) and laboratory Hb was -7.6 g/l (standard deviation 6.5) at T=0 and -5.1 g/l (standard deviation 12) at T=1. The mean total plasma protein difference (total plasma protein T=0 minus T=1) was 13.6 g/l (95% confidence interval 10.2 to 17.0). There was poor correlation between total plasma protein and bias in i-STAT(®) measurements. The i-STAT(®) Hb had an acceptable coefficient of variation, but the Hb levels were lower than those estimated by the laboratory. The standard deviation of i-STAT(®) Hb was greater after ≥25% estimated total blood volume loss. Clinicians should not use the i-STAT(®) Hb in isolation for clinical decision-making when considering blood transfusion in a situation of 25% or greater blood loss.

Present technology and future trends in point-of-care microfluidic diagnostics

This work reviews present technologies and developing trends in Point-of-Care (POC) microfluidic diagnostics platforms. First, various fluidics technologies such as pressure-driven flows, capillary flows, electromagnetically driven flows, centrifugal fluidics, acoustically driven flows, and droplet fluidics are categorized. Then three broad categories of POC microfluidic testing devices are considered: lateral flow devices, desktop and handheld POC diagnostic platforms, and emergent molecular diagnostic POC systems. Such evolving trends as miniaturization, multiplexing, networking, new more sensitive detection schemes, and the importance of sample processing are discussed. It is concluded that POC microfluidic diagnostics has a potential to improve patient treatment outcome and bring substantial savings in overall healthcare costs.

Evaluation of two devices for point-of-care testing of haemoglobin in neonatal pigs

In veterinary medicine, point-of-care testing (POCT) techniques have become popular, since they provide immediate results and only small amounts of blood are needed. However, their accuracy is controversial. Pigs are often used for research purposes and accurate measurement of haemoglobin (Hb) is important during invasive procedures. The aim of this study was to evaluate two different Hb POCT devices in neonatal pigs. A prospective study with 57 pigs of 3-6 weeks of age, weighing 4.1-6.2 kg (median 5.1 kg) was performed. Fifty-seven blood samples were analysed for Hb using a conductivity-based and a photometrical POCT device and compared with a photometrical reference method. Statistical analysis was performed with Bland-Altman analysis, Spearman correlation and Passing-Bablok regression analysis. Hb values ranged from 32 to 108 g/L (median 80 g/L) using the reference method. The bias of the photometrical method (HemoCue(®)) to the reference method was -1 g/L, with limits of agreement (LOA) of -7 to 6 g/L. The conductivity-based method (i-STAT(®)) had a bias of -15 g/L with LOA from -24 to -6 g/L. There was a significant association between protein values and the bias of i-STAT versus CellDyn (r(2) = 0.27, P < 0.05) but not with the bias of HemoCue versus CellDyn (r(2) = 0.001, P = 0.79). The lower the protein values were, the lower the Hb values were measured by the i-STAT. The conductivity-based measurement of Hb constantly underestimated Hb values, whereas the photometrical method demonstrated a better accuracy and is therefore more reliable for on-site measurement of Hb in pigs.

Conductivity-Based Hematocrit Measurement During Cardiopulmonary Bypass

OBJECTIVE

In a recent clinical study on the reliability of a point-of-care (POC) analyzer, we described a downward bias in hematocrit measurement during cardiopulmonary bypass leading potentially to overtreatment with packed red cells. We hypothesized that the detected deviation is caused by variations in electrolyte concentration rather than by colloids used.

METHODS

Blood was sampled from patients before cardiac surgery to obtain undiluted anticoagulated whole blood samples (n = 53). From each sample, four dilution series covering a hematocrit range of 15-30% were made using NaCl (0.9%), modified gelatine (4%), hydroxyethylstarch (6%), or a potassium-based (16 mEq/l) solution, respectively. In each dilution series, hematocrit was measured by POC and via the "golden standard" microcentrifugal method to determine whether the deviation of the POC-analyzer to the microcentrifuge was dependent on the type and dilution level of the solution used.

RESULTS

In contrast to the colloid-based dilution series, the crystalloids revealed a significant downward bias of the POC-analyzer with respect to the microcentrifuge (p < 0.05). Due to the correction algorithm for sodium in the POC-analyzer, this deviation was nearly constant for NaCl (mean of difference: -1.8 +/- 0.1%), but increased significantly in case of the potassium-based solution (up to -8.2 +/- 0.4% after 1.5-times dilution). The starch- and gelatine-based solutions led to a significant upward bias (p < 0.05) that increased with progressing dilution (up to 1.2 +/- 0.1% for hydroxyethylstarch and up to 1.3 +/- 0.1% for modified gelatine after 1.5-times dilution).

CONCLUSIONS

Conductivity-based POC hematocrit measurement suffers from biases due to changes of the plasma constituents. The downward bias in hematocrit as often seen during cardiopulmonary bypass is driven by changes of different electrolyte concentration rather than by colloids used per se.