Point-of-care testing (POCT) is defined as tests designed to be used at or near the site where the patient is located; they do not require permanent dedicated space, and they are performed outside the physical facilities of the clinical laboratories. POCT has grown in popularity as advancements in computer chip technology made POC devices more affordable, portable, and easy to use. Examples include circulating blood glucose monitors (glucometer), blood gas analyzers, activated clotting time (ACT) monitors, and heparin concentration monitors (Hepcon). There are a myriad of other POCTs that are used outside of the operating room but are not discussed in this chapter. Some examples of these POCT devices include those for testing hemoglobin A_1c (Hb A_1c), mircoalbumin, cardiac enzyme markers, cholesterol, infectious disease, etc. POCT can be found almost anywhere patients need quick and cost-effective testing such as a physician’s office, ICU, emergency rooms, hospital wards, and even in a patient’s home. However, this chapter gives a brief overview on POCT equipment that is commonly found in or around the operating room. The main emphasis of this chapter is on the organization of POCT from initial start-up to daily operations.

The operating room is a unique environment in which a life-threatening situation needs to be identified and treated immediately. For example, hypoglycemia can lead to poor neurologic outcomes, cardiovascular collapse, and death if not identified and treated promptly. The clinician cannot wait for the long turnaround time required for tests sent to a central laboratory. Even STAT labs have a much longer turnaround time than POCT. A handheld glucometer allows the clinician to quickly detect the patient’s circulating blood glucose and perform the appropriate intervention. The most efficient use of POCT occurs when an abnormality is quickly detected and an intervention is performed before any harm or escalation of patient care has occurred.

POCT is composed of five essentials: equipment, personnel (not trained as certified laboratory personnel), procedure, quality control, and records and reports. It is governed by the College of American Pathologist (CAP) and Clinical Laboratory Improvement Amendments (CLIA). CLIA issues the certificate that allows the laboratory to function, and CAP is the regulatory body that governs daily operations. The POCT laboratory allows no disruption of patient care, samples never leave the immediate patient care area, and the results are immediate; however, clinicians must guard against interpreting POCT as the same accuracy as the main laboratory. When there is a question of the results, the best rule of thumb is to draw another sample and perform a test on the POCT machine and send a sample to the central laboratory for comparison.

A blood gas machine is a portable system that analyzes whole blood for pH, partial pressure of CO₂ and O₂, bicarbonate levels (HCO₃^–), electrolytes, lactate, and hematocrit. There are a multitude of clinical scenarios in which an anesthesiologist may need to interpret the blood gas. A blood gas sample may be obtained from an artery or a vein depending on the clinical situation as the blood gas values will differ and will yield different information for the clinician. Arterial blood gases are more common and most often obtained from the radial artery as it is easily accessible.

The blood sample is drawn into a heparinized syringe to prevent the blood from clotting. The blood sample is then taken to the blood gas analyzer where the sample is drawn into the machine for analysis. Blood gas analyzers today are fast and accurate. Most instruments are fully self-contained, consisting of the machine and disposable cartridges containing reagents, sensors, waste containers, and quality control (QC) pack. Usual systems are fully automated with self-calibration and self-quality control.

Although today’s blood gas analyzers are accurate, there are many preanalytic errors that can occur, which can give erroneous results:

Malfunctions such as calibration errors, failed quality control, and bad sensors are usually identified during machine-initiated calibrations or quality controls. These problems are corrected by most current blood gas machines with a “lock-out” feature that will not allow further sampling. In some cases, the machine will allow a sample, but without the faulty “locked-out” analyte. High and low settings are set internally during the machine setup prior to initial use. The high/low settings are agreed upon with the main laboratory, and in the case of hematocrit and glucose, a reading outside those settings will require a sample to be drawn and double checked with the main laboratory.

Note: High and low settings are set by the main laboratory and reflect the range of normal values. While the patient is in the operating room, it is not unusual for PCO₂, PO₂, hematocrit, and other values to be out of the “normal” range due to a variety of circumstances encountered during surgery.

The ACT detects clot formation. Patients who are having certain invasive procedures, such as cardiac bypass, require anticoagulation with heparin to prevent catastrophic thrombosis formation while on bypass. The heparin required to achieve a specific target level varies with individual patients and must be closely monitored.

Clot formation is detected with an optical electromechanism located in an actuator block of the instrument. Single-use disposable cartridges contain the activator kaolin. The actuator mixes the kaolin with the blood sample and starts the timer. When blood is exposed to a foreign surface, the clotting process is triggered and fibrin forms. The optical system detects this change and displays the clotting time in seconds.

As with many POCTs, there are some instances that can cause false values:

It should also be noted that there are two major manufacturers of ACT monitors. The ACT is not a standardized measurement, so an ACT of 300 seconds from one manufacturer does not correlate with an ACT of 300 seconds from another manufacturer.

The heparin concentration (Hepcon) monitor is a device that measures the actual concentration of heparin in the patient’s blood. Hepcon is another POCT equipment that is used to gauge the adequacy of anticoagulation for certain procedures such as cardiopulmonary bypass. Hepcon is an integrated system consisting of a component for tracking clot detection and computing results, a component for sample delivery, and the single-use test cartridges for actual performance of the tests. The cartridge instructs the system, through an optical code, as to the type of test being performed, the calculations and the format
required for results, and the volume of sample needed for each channel. The detection process uses the plunger assembly within the cartridge. This assembly is lifted and dropped through the sample/reagent mixture by a lifting mechanism actuator. As the sample clots, a fibrin web forms around the daisy located on the bottom of the plunger assembly and impedes the rate of descent of the assembly. This change in fall rate is detected by a photooptical system located in the actuator assembly of the instrument. The end point of the test is the time at which clot formation is detected; from these clotting times, derived results are calculated for all tests.

The causes of faulty Hepcon readings are basically the same as those that occur with the ACT machine.

Thromboelastography (TEG) is a device that allows the clinician to evaluate the patient’s ability to maintain hemostasis. In order for a patient to form a fibrin clot that is sufficient in strength to maintain hemostasis, the body depends on the interaction of enzymatic proteins (clotting factors) and platelets. Laboratory tests such as international normalized ratio (INR), partial thromboplastin time (PTT), ACT, and Hepcon measure the integrity of the clotting factors, whereas the TEG evaluates the entire coagulation process including platelet function. The TEG is generally used to monitor defects in the coagulation process and help guide the clinician to the appropriate treatment for those defects. Less commonly, the TEG can be used to monitor the adequacy of anticoagulation for patients undergoing procedures such as cardiac bypass.

The TEG evaluates the ability to form clots by measuring the tensile strength of the fibrinplatelet complex. A sample of blood is placed into a cuvette with a metal pin in the center. The cuvette is slowly rotated at approximately 6 cycles/min. An activator is added to the sample and clot begins to adhere to the side of the cuvette and the metal pin. This creates resistance to rotation, which is then measured and plotted on a graph. The shape of the graph and time to when clot is formed gives the clinician information on the integrity of hemostasis and the presence of specific deficiencies.

There are several preanalytical errors that can cause erroneous values for the TEG:

Appropriate blood samples for the TEG include whole blood, citrated blood, or heparinized blood. Each sample type is used in different clinical situations. Care should be taken to ensure the proper anticoagulant is used in the sample.

The INR is a test that measures the adequacy of anticoagulation for patients taking warfarin. Many patients presenting for surgery are taking warfarin for the treatment or prevention of thrombosis. Patients having invasive procedures or surgery normally stop taking warfarin 5-7 days prior to surgery. These patients need to have their INR checked the day of surgery as the effect of warfarin is highly variable from patient to patient. The INR is often sent to a central lab that may take hours to run the sample; POCT can give an accurate measurement of INR within minutes. This can decrease the time and complexity for patients who need to coordinate the timing of lab draws and the time of surgery.

The INR is analyzed on a portable coagulometer much the same way that a patient’s circulating blood glucose is analyzed. A sample of blood is placed on a test strip after a finger stick is obtained. The test strip is then placed in the coagulometer at which time the sample is mixed with a thromboplastin reagent, causing a clot to form. There are several coagulometers available, and each has its own operating principles. However, all devices are accurate and can give results in under 3 minutes.

Glucometer is a medical device for determining the approximate concentration of glucose in the blood. It is a key element of hospital and home blood glucose monitoring by people with
diabetes mellitus or hypoglycemia. Glucometers are very accurate; however, a glucose reading from the main laboratory is always considered the gold standard.

Clean the skin with an alcohol swab and allow the site to completely dry. Skin with alcohol may cause a faulty reading. A small drop of blood, obtained by pricking the skin with a lancet, is placed on a disposable test strip that is read by the meter and used to calculate the blood glucose level. The meter then displays the level in milligrams per deciliter or millimol per liter.

With a hospital glucometer, daily quality controls are required prior to use and most meters have a lock-out system until the quality controls are complete. Quality control fluids are good for 90 days after opening unless the expiration date is before.