Safety Monitors in Hemodialysis

Hemodialysis monitors include machines, devices, protocols, and personnel. The major goal is to ensure patient safety during the hemodialysis procedure. All tasks that check, observe, keep track of, and control the hemodialysis treatment is monitoring procedures. These important tasks are too often lightly dismissed.

This chapter focuses on the fluid delivery system and extracorporeal circuit, their respective monitoring devices, functions, locations, performance standards, and management. Monitoring of the patient and hemodialysis prescription pre, during, and post dialysis are covered in other sections of this book. Incorporated are parts of the Conditions of Coverage (CfCs) dictated by the Department of Health and Human Services Center for Medicaid and Medicare Services (CMS), effective October 3, 2008, for end-stage renal disease (ESRD) facilities. The revised regulations update standards for delivering safe, high-quality care to dialysis patients. Specific regulations regarding dialysate (§494.40 Condition: Water and Dialysate Quality) remain unchanged. First-time regulations specific for dialysate include mixing, distribution, labeling, and use.

Definitions and Overview

The fluid delivery system is commonly called “the machine.” The fluid delivery system prepares dialysate, a body temperature electrolyte solution. The dialysate flows through the dialysate compartment of the dialyzer, where dialysis occurs. A blood pump circulates the patient's blood through the extracorporeal circulation to the blood compartment of the dialyzer and back to the patient. The two major categories to monitor are the dialysate circuit and blood circuit.

The blood circuit consists of a blood tubing set (arterial and venous), blood side of the dialyzer, intravenous (IV) normal saline and administration line, and heparin syringe and infusion line.

The blood and dialysate are separate circuits that interface at the dialyzer membrane. The machine design must involve extensive monitoring of both circuits. Specific warning alarms must be initiated when the machine's preset limits are exceeded and/or an unsafe condition exists.

Dialysate Solution

Dialysate solution or dialyzing fluid is a nonsterile aqueous electrolyte solution that is similar to the normal levels of electrolytes ( Table 9.1 ) found in extracellular fluid, with the exception of the buffer bicarbonate and potassium. Dialysate solution is almost an isotonic solution, with the usual osmolality of approximately 300 ± 20 milliosmoles per liter (mOsm/L). To ensure patient safety and prevent red blood cell (RBC) destruction by hemolysis or crenation, the osmolality of dialysate must be close to the osmolality of plasma. The osmolality of plasma is 280 ± 20 mOsm/L. Dialysate solution commonly contains six electrolytes: sodium (Na ⁺ ), potassium (K ⁺ ), calcium (Ca ^{2 +} ), magnesium (Mg ^{2 +} ), chloride (Cl ^– ), and bicarbonate (HCO ₃ ^– ). A s). A seventh component, the nonelectrolyte glucose or dextrose, is invariably present in the dialysate. The dialysate concentration of glucose is commonly between 100 and 200 mg/dL. Freshly prepared dialysate solution circulates continuously to the dialyzer in the extracorporeal circuit. After making a single pass through the dialyzer, the effluent dialysate goes to the drain.

Table 9.1

Comparison of Normal Blood Values and Dialysate Composition

From Pittard J, De Palma J. Dialysate Monograph . 1st ed. Glendale, CA: Hemodialysis, Inc.; 2013.

Electrolyte	Dialysate Level Range	Normal Blood Value Range
Sodium	135–145 mEq/L	135–145 mEq/L
Potassium	0–4 mEq/L	3.5–5.5 mEq/L
Calcium	2.25–3.0 mEq/L	4.5–5.5 mEq/L
Magnesium	0.5–1.0 mEq/L	1.5–2.5 mEq/L
Chloride	100–115 mEq/L	95–105 mEq/L
Bicarbonate	30–40 mEq/L	22–28 mEq/L
Nonelectrolyte
Dextrose	0–200 mg/dL	80–120 mg/dL

Fluid Delivery System

The vast majority of dialysis facilities in the United States use single-patient fluid delivery systems. This type of equipment is self-contained, preparing the dialysate only for the individual machine. Some dialysis facilities use central delivery systems with central manufacture of dialysate. Although that system is more economical, it is less safe than the individual machines. The discussion will focus on single-patient machinery. A few safety issues unique to a central delivery system are explored as well.

Control Panel and Monitor Display

All modern fluid delivery systems have a frontal control panel ( Fig. 9.1 ) by which pressure and other limits may be set and system parameters may be viewed. The control panel and monitor display on the face of the machine will have audible and visual warning alarms as a mandatory part of safe dialysis monitoring.

Monitor Failure

Machine monitors are either mechanically or electrically operated, or a combination of both. All monitors can fail. Murphy's Law (if anything can go wrong, it will) should be remembered and accepted as fact. Murphy's Law is attributed to an engineer working at the Los Alamos laboratories in the 1950s. The truth of this statement can be reworded to, “If you can think of a possible disaster with the present equipment, take the necessary precautionary steps immediately, or it will happen.” If one can access misadventure and incident reporting, virtually every possible projected failure of a monitor has occurred and has resulted in patient/staff injury or death.

Fail-Safe, a Misnomer

Machine monitors are frequently thought to be fail-safe devices, but they are not. A truly fail-safe device cannot be overridden to cause harm either by electronic or human intervention. By this narrow definition, there are no fail-safe dialysis machine monitors. Because all dialysis machine monitors can fail, they ought to be simple to operate and accurate—and should signal a warning when they are out of limits or not working properly. Any important factor requires dual monitoring: the machine monitor device and dialysis personnel. No machine, computer, or device can replace the continuous surveillance of the hemodialysis personnel.

Dialysate Circuit

Fig. 9.2 displays components of the dialysate fluid path. Dialysate monitoring includes prescription, composition (conductivity and pH), temperature, flow, pressure, effluent, absence of impurities (cleaning and disinfecting agents), potential pyrogenic agents, and microbiologic testing. Each monitor or control is discussed in order of the usual flow of fluid, from the water inlet solenoid valve to the effluent dialysate drain line.

Why Discuss the Details of Dialysis Machinery?

Each dialysis treatment exposes the ESRD patient's blood to hundreds of liters of dialysate. The dialysate should be of pharmaceutical grade, as dialysate is the equivalent of an IV solution. The machinery that manufactures dialysate can silently and quickly cause a patient serious injury or death because of contaminants or incorrect solute concentration. Even more distressing, if the machinery manufactures a substantially hypotonic fluid, but at a concentration that does not cause hemolysis, the patient may rapidly develop water intoxication, cerebral edema, seizures, and noncardiogenic pulmonary edema—signs and symptoms that the dialysis staff can easily misinterpret as requiring more ultrafiltration and more dialysis!

With current therapy using blood flow rates of 300 to 450 mL/min, the entire patient's circulating blood may be exposed to toxic chemicals or a hemolytic state in less than 15 minutes. Death can be both swift and the cause undiagnosed, even with postmortem examination. Each component of the dialysate circuit discussed, if it malfunctions, may induce hemolysis.

Water Inlet Solenoid

The water inlet solenoid permits the flow of treated water into the dialysis machine when the main power switch is activated and stops the flow when the main power is turned off. Treated water enters the machine via a water inlet valve with water pressure usually between 20 and 105 pounds per square inch (psi). The treated water for hemodialysis must meet the Association for the Advancement of Medical Instrumentation (AAMI) standards. Not all machines have a water inlet solenoid. Allowing water to flow into the machine without activating the machine's main power switch can cause problems with bacterial buildup in that portion of the fluid pathway.

Solenoid Monitoring

The inlet water pressure can be measured using a dial-type manometer. This mechanism may malfunction or leak in the on or off position. There are neither published performance standards nor standard alarms for this device. Many machines have a continuous audible warning alarm to alert the staff of problems. If an alarm condition exists that indicates inadequate water flow or pressure, its role may be to prevent water from being overheated by the water heater. Overheated dialysate causes gross hemolysis.

Dialysate Temperature

A heater raises the temperature of the incoming water to approximately body temperature. Heating partially degasses the cold water, which improves the mixing of water and dialysate concentrate. A thermistor feedback circuit usually controls the electrical heating elements. The heater may have a coarse adjustment control inside the machine and a fine adjustment control on the front panel. There may be a simple bimetallic dial thermometer within some machines that, though not alarmed, provides visual observation of its function.

The dialysate temperature is usually maintained between 37°C and 38°C (98.6°F and 100.4°F) throughout the dialysis treatment although recent research has suggested that somewhat lower dialysate temperature, as tolerated, may be beneficial and better maintain intradialytic cardiovascular stability. An internal temperature sensor ( Fig. 9.3 ) monitors the dialysate temperature continuously. In some cases, the actual temperature reading is displayed on the front panel of the machine. Other machines have lights on the front panel that indicates an alarm condition. Most fluid-delivery machines have high- and low-temperature monitor alarms. Some older-model machines have only high-temperature alarms. If the high or low internal temperatures exceed the preset internal limits, three actions result: an audible alarm, a visual alarm, and activation of the bypass mode.

Heater and Temperature Monitoring

Internal, factory-set, controls should limit dialysate temperature to between 33°C (92°F) and 39°C (102°F). The fine adjustment control knob on the front panel of the machine should not be capable of overriding this setting.

Temperatures Greater Than 106°F

The usual causes of high dialysate temperature are either a malfunctioning water heater with a temperature controller or a water flow restriction. The high internal limit should be set no higher than 41°C (105.8°F). Normal RBCs begin to hemolyze at 42°C. Overheated dialysate has been known to precipitate cardiac arrhythmias.

Although it is true that the efficiency of diffusion during dialysis is increased with increased dialysate temperature, without excellent electronic temperature monitoring, this is a dangerous way to increase dialysis efficiency. Under no circumstances should the high limit be adjusted above 41°C. Several articles in the literature suggest that the upper limits be set at 42°C (107.6°F), which is probably too high and may cause hemolysis. It should be remembered that uremic RBCs are more osmotically fragile and have a shorter half-life than normal RBCs. It is reasonable to assume that these uremic RBCs are more sensitive to all mechanical and thermal causes of trauma than normal RBCs.

Temperatures Less Than 98.6°F

Some nephrologists use lower-temperature dialysate in the belief that this promotes a more stable blood pressure response to high ultrafiltration. If low-temperature dialysate is used, the total dialysis time needs to be increased by about 8% for every 3°C below 98.6°F, as that is the theoretical loss in diffusivity with temperature decrease. Low dialysate temperatures may induce venous vessel spasms and make it impossible to obtain maximum blood flows through the artificial kidney.

With dialysate temperatures below 98.6°F, patients may complain of being cold, ask for a blanket, and some will actually shiver in an attempt to increase their core body temperature. An increase in cardiac irritability in patients with coronary vessel disease may be observed if temperatures are too low.

Deaeration System

The deaeration system removes dissolved gases by exposing water to subatmospheric pressures generated by a vacuum pump. The gases coalesce, form bubbles, and are vented to the atmosphere by a bubble trap. Improper or inadequate removal of dissolved gases in dialysate can be a hidden cause of several serious dialysis problems, including false blood-leak alarms, false conductivity alarms, interference with volumetric control function, and decreased dialysis efficiency by air bubbles trapped on the dialyzer membrane that reduces functional dialyzer surface area. Microbubbles streaming from dialysate into blood have been reported to collect in the right atrium of the heart and cause air embolism without triggering an air-foam detector alarm. Exaggerated frothing and blood clotting in the drip bulb chamber with minute blood clots being carried to the right atrium may also be seen. A substantial number of all adults have a potentially patent foramen ovale. If the pulmonary artery pressure increases, the foramen ovale can shunt blood from the right to the left atrium. This can result in a transfer of these small clots into the left heart and result in cerebral embolism. This set of conditions has occurred and is known as paradoxical embolism, which can be misdiagnosed as a transient ischemic attack (TIA) or other vascular insult and not embolic phenomenon.

Deaeration System Monitoring

Frequent false blood-leak alarms or rapid fluctuations in conductivity can indicate a malfunction of the vacuum pump. The machine should be removed from service and undergo maintenance. If the dialysate inflow and/or outflow lines are not correctly attached to the dialyzer, air can be pulled into the system. Proper technique by the dialysis staff who set up the dialysis machinery prior to dialysis and who secure the quick disconnects of the dialysate lines on the dialyzer dialysate ports will prevent this problem.

Mixing Device

The mixing device, also known as the proportioning system, proportions treated water and dialysate concentrate to create dialysate of the correct ionic concentration. The proportioning system ratio depends on the type of dialysate concentrate used and the type of fluid delivery system. Typical mixing ratios of water to dialysate concentrate are

34:1 or 44:1 for acid concentrate
20:1 or 25:1 for bicarbonate concentrate

The supply of treated water and dialysate concentrate generates dialysate flow rates between 500 and 1000 mL/min. The two basic types of proportioning systems are fixed-ratio mixing and servo-controlled mixing.

Fixed-ratio mixing uses diaphragms or piston pumps to deliver a set volume of water and concentrate to the mixing chamber. Servo-controlled mechanisms continuously monitor the dialysate composition with conductivity sensors that adjust the amount of concentrate mixed with water to maintain a variable or set composition.

In machines that add concentrate by a servo-controlled mechanism until the dialysate reaches a desired conductivity, a second independent conductivity and pH monitor must cause an alarm if the conductivity is incorrect. If acid and bicarbonate inputs are reversed, or if the wrong concentrates are used for a bicarbonate machine, the servo loops may make a solution of acceptable ionic strength (correct conductivity) but of lethal ionic composition. In this case, the pH monitor or concentrate pump speed monitor becomes critical. However, not all machines are equipped with pH monitors, and this deadly event will not be diagnosed.

Mixing Device Monitoring

The conductivity and pH monitor will verify proper mixing with a fixed-ratio proportioning system. Equipment using servo-controlled mechanisms requires a diligent and trained staff to ensure that the proper dialysate concentrate is attached to the proper concentrate lines on the machine.

Composition and Conductivity of Dialysate

Analysis of the dialysate for the proper composition is necessary after it has been mixed, and prior to exposing it to the dialyzer and patient. All modern fluid delivery systems have conductivity cells and meters. Total conductivity of dialysate is measured as a simple assessment and surrogate for dialysate ionic content. A conductivity cell is connected to a meter that displays the total ionic concentration of dialysate. Conductivity cells should be made of high-quality, corrosion-resistant materials. The conductivity of an electrolyte solution increases as the temperature increases. Conductivity cells used to monitor dialysate must be temperature compensated.

Measuring Conductivity

In dialysis, conductivity is usually measured using a two-electrode system. The electrodes are connected to a constant current and an ammeter ( Fig. 9.4 ). An electric current is passed through the solution between the electrodes. The ammeter measures the flow of current (the inverse of electrical resistance) that passes through the solution between the electrodes. The conductivity measurement is an estimate of the total ionic content of the dialysate and does not measure or reflect specific ions or electrolytes.

The conductivity meters read the conductivity in millimhos per centimeter (mmhos/cm) or milliSiemens per centimeter (mS/cm). A range of 12.5–16.0 mS/cm is acceptable for a standard dialysate solution. Some facilities prefer a tighter range, 13.0–15.5 mS/cm. The range varies slightly from facility to facility, depending on the dialysate formula in use.

Monitoring Conductivity

Conductivity meters on dialysis machines have external and internal limits set. Some machines may have three internal conductivity sensors set at different intervals of control. The conductivity, or dialysate ionic composition, is so important that this monitoring redundancy is a commonsense safeguard against single-monitor failure. The closest tolerance internal high-low limits are set at ± 5%; the last set of conductivity monitoring may be set at 50% of normal conductivity. If the first two monitors fail, the patient, without any alarms being triggered, will receive a massive infusion of hypotonic dialysate. Because different mixtures of ions have different conductivities, it is mandatory that the dialysate formulas determine the established conductivity setting.

It is now mandatory to perform and document an independent conductivity test prior to preparing the dialyzer for patient use and before the dialysis treatment is initiated. There are several methods available to perform an independent analysis of the machine's conductivity. The most common method is to use a portable conductivity meter that measures the total conductivity. Laboratory analysis that measures each electrolyte level can also be done.

When using independent analysis, be sure the reference conductivity meter is calibrated accurately prior to use. All standard solutions should be fresh and render acceptable readings.

If independent verification of the dialysate conductivity does not validate the conductivity meter, do not dialyze the patient with that machinery. A complete resolution of the problem is necessary before dialysis. Failure to resolve a problem prior to dialysis will only invite a potential disaster. It is best to bring in another dialysis machine and start over.

All facilities must have an established acceptable conductivity range, and this range must be publicly posted. Any deviation in the conductivity limits set should cause a conductivity alarm. A conductivity alarm causes three actions on the dialysis machine: an audible alarm, a visual alarm, and activation of the bypass system.

The bypass system diverts the dialysate to the drain before it can enter the dialysate inflow line leading to the dialyzer. Thus, exposure of the patient's blood in the dialyzer to an incorrect or unsafe dialysate composition is avoided.

No Intradialytic Conductivity Adjustments

Only a qualified and trained machine technician should adjust the external or internal conductivity limits. Under no circumstances should they be adjusted during the dialysis treatment. They must be properly adjusted and preset before the dialysis treatment. Serious and fatal accidents have occurred as a result of improper adjustments of the conductivity limits.

Low Conductivity

A low-conductivity alarm is the most common type of conductivity alarm ( Fig. 9.5 ). The usual cause is a lack of concentrate in one or both acid and bicarbonate concentrate containers. Rarely, a low-conductivity alarm is due to incorrect dialysate concentrate.

If the internal or external low-conductivity limits are not adjusted properly and/or the machine does not go into the bypass mode, the patient's blood is exposed to hypotonic dialysate. Exposure to hypotonic dialysate can be fatal within a few minutes. Hypotonic dialysate causes a hypoosmolar state, and even without acute hemolysis, water intoxication can occur, which can also be lethal.

Low-Conductivity Monitoring

There must be an adequate amount of dialysate concentrate in the container(s) before starting dialysis. Dialysis staff should not rely on the conductivity meter to monitor dialysate concentrate supplies.

True, if the dialysis machine goes into bypass mode, there is no harm to the patient. But, when the dialysis machine is in the bypass mode, no dialysis is taking place and the time lost on dialysis is rarely, if ever, made up with a longer dialysis time the next dialysis session. If one accepts that the average dialysis in the United States comprises not the maximal amount of dialysis time, but probably the minimal amount of dialysis time, placing the dialysis machinery in bypass routinely will shorten the patient's life span.

Most new model fluid-delivery machines have timers that stop with a dialysate circuit alarm. This ensures that the patient receives their allocated time on dialysis.

High Conductivity

High-conductivity alarms ( Fig. 9.6 ) can result from inadequate water flow to the proportioning system, untreated incoming water with an excess of calcium, or incorrect hook-up of dialysate concentrate to the dialysis machine (if using servo-controlled mechanisms) and sodium modeling. Newer-model fluid delivery systems will not go into conductivity with incorrect hook-ups.

With older machines, a common, serious cause of high conductivity occurs when two acid concentrate containers are connected to the dialysis machine instead of one acid container to the acid port and one bicarbonate container to the bicarbonate port. If the dialysis machine goes into bypass mode, there is no harm to the patient. However, if the internal or external high-conductivity limits have not been set correctly, the patient's blood is exposed to hypertonic dialysate and possibly hyperosmolar coma.

New model fluid-delivery systems have anautomatic built-in adjustment of conductivity limits for sodium variation, which causes an increase in conductivity. If sodium variation is done incorrectly, the patient will leave the dialysis thirsty, in a hyperosmolar state, and attempt to relieve that thirst with free water. This will result in a marked expansion of their extracellular volume (ECV), and possibly malignant hypertension.

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