Preparing the Patient for Polysomnography

Eileen B. Leary

The application of electrodes and sensors to the patient is one of the most important parts of a sleep study. If done poorly, the quality of the data will be compromised and a significant part of the night will be spent troubleshooting and problem-solving. Filters should not be used to compensate for poor-quality electrode application. Excessive use of filtration can significantly alter the integrity of the data and impact how the study is analyzed.

There are many different approaches to preparing a patient for a sleep study. This chapter will focus on the standard or classic method. In addition to the varied techniques utilized by different sleep centers, each sleep technologist will develop his or her own method of performing the application. Exchanging ideas with other technologists is an excellent way to continue to improve and refine one’s technique.

BEFORE THE PATIENT ARRIVES

It is critical to allow time at the beginning of the shift before the patient arrives to prepare for the night ahead. The technologist should use this time to review the practitioner’s orders, set up and calibrate the recording equipment, prepare the necessary supplies, and assess and respond to any special needs the patient may have.

Undergoing a sleep study can be stressful for a patient. An informed and knowledgeable technologist helps reduce that anxiety and creates a positive patient experience. Become familiar with the patient’s medical history by reviewing the chart before the patient arrives. Be sure to label any questionnaires or forms that require completion and check the physician’s order to determine which type of study has been prescribed (positive airway pressure [PAP] titration, diagnostic study, split-night study, or extended channel montage). If an order is unclear, contact the sleep center manager, on-call physician, or the practitioner who made the order for clarification.

The hookup procedure will be faster and more efficient if the supplies are prepared and organized in advance. For example, you can precut the tape and gauze, lay out gold cup electrodes, check for broken or damaged sensors, and stock the supply tray before the patient arrives. Ensure all items that will come into contact with a patient have been cleaned and disinfected according to infection control standards before use.

Table 36-1 Basic Supplies

General supplies
	Nonlatex gloves Scissors Towels Various types of medical tape (Transpore, Hypafix, or Medipore, and Scanpor) Impedance meter
For applying scalp and face electrodes (to record EEG, EOG, and chin EMG)
	Air compressor (if using collodion) Tape measure Grease pencil Hair pins/clips Hair comb Electrodes (gold cup with center hole) Alcohol swabs Abrasive skin preparation (NuPrep or Lemon Prep) Cotton-tip applicators EEG conductive paste Electrolyte gel or cream Collodion/EC2 paste Collodion remover/acetone Gauze (4 × 4 squares and/or roll of single-ply gauze) Medical tape (Micropore, Transpore, and fabric tape) Double-sided electrode collars
For applying ECG electrodes (to record the ECG)
	Disposable ECG snap pads ECG electrodes
For applying leg EMG electrodes (to record leg movements)
	Gold cup electrodes with extra long leads (72 in [182.9 cm]) Small ECG patches (optional)
For applying respiratory belts (to record respiratory effort)
	Thoracic/abdominal belts in various sizes Inductive plethysmography belts
For applying airflow sensor (to record respiratory airflow)
	Nasal cannula with pressure transducer and thermocouple, or thermistor
For applying snore sensor
	Snore sensor
For applying oximeter probe (to record SpO₂)
	Oximeter probe (disposable or reusable) Oximeter calibration tool (may have autocalibration)
ECG, electrocardiogram; EEG, electroencephalogram; EMG, electromyogram; EOG, electrooculogram.

APPLYING THE ELECTRODES AND SENSORS

Proper electrode and sensor placement is essential for recording a quality polysomnogram. Every technologist should be familiar with all electrodes and sensors, what they measure, where they are placed, and how they plug into the headbox (also called a jackbox). All electrodes and sensor leads should be easily identifiable to avoid confusion when connecting them to the headbox. Some technologists prefer to use labeled gold cup electrodes, whereas others plug each electrode into the headbox immediately after it is attached.

Suggested Routine for Electrode and Sensor Application

This chapter provides a suggested sequence for applying electrodes and sensors, but all technologists develop their own routine. Don’t be afraid to experiment and develop a system that suits your individual style.

Scalp and face electrodes
Snore sensor
Electrocardiogram (ECG) electrodes
Leg electrodes
Respiratory bands
Airflow sensor(s)
Oximeter probe

The airflow sensor and oximeter probe are typically applied shortly before bedtime as these sensors are more cumbersome to the patient. However, for some patients, it may be helpful to have a longer assessment of the individual’s waking oxygen levels. In those cases, the oximeter should be attached upon arrival to allow oxygen levels to be monitored throughout the hookup procedure.

General Suggestions to Optimize Electrode Application

During the application procedure, the technologist should explain the procedure to the patient. This is an ideal time to provide education on sleep hygiene, obstructive sleep apnea, and/or whatever sleep topic seems appropriate for the patient.
The patient’s skin and hair should be clean and dry. Electrodes applied to oily skin or hair will likely have high impedance levels, resulting in poor signal quality, and are more susceptible to becoming detached during the night. Patients should be instructed by the daytime staff to shower or bathe before arriving. If necessary and if shower facilities are available, ask the patient to shower at the sleep center before beginning the hookup. If the patient has very dirty or oily hair and a shower is not
possible, use alcohol or acetone wipes to remove the excess oil. Alcohol dries quickly, so the site can be prepped and the electrode attached almost immediately.
When using tape or gauze to adhere an electrode, scrub only the small area where the electrode will be placed. If excess prep material remains in the vicinity of the electrode, gently cleanse the area with rubbing alcohol because tape will not stick to the gritty prep.
Facilitate tape removal in the morning by using small pieces of tape and making tabs by folding down one end. The tape should be just large enough to secure the sensor and wire throughout the study (Fig. 36-1).
Point the wires toward the crown of the head or nape of the neck to make them more manageable. Consider where the headbox will be placed during the night when selecting how to bundle the wires.
Provide extra slack in the wires to avoid putting stress on the electrodes.

Attaching Gold Cup Electrodes

Before starting the application process, all electroen-cephalogram (EEG) electrode sites should be measured and marked using the International 10/20 System (1) described later in the chapter. Scalp electrodes can be attached using paste or collodion. When deciding which method to use, signal quality, stability of sensor, convenience of application, and removal as well as cleanup should be considered. Collodion requires an air compressor to dry the glue, has a strong odor, is highly combustible, and requires storage in fireproof safe and a solvent to remove in the morning. Paste is removed with water, but electrodes may move slightly or loosen during the night, particularly if the patient sweats. Although collodion is more secure, most labs use paste because it is more convenient and less caustic.

Figure 36-1 Suggested approach to tabbing tape. Note the small crease at the bottom center of the tape.

Preparing the Electrode Sites

Preparing the skin before attaching the electrode is essential for reducing impedance levels and ensuring signal quality. Be sure to discuss the procedure with the patient so that he or she is not surprised by the process. First, clean the area with an alcohol swab to remove any makeup or oil on the skin. Then, using a small cotton-tipped applicator, gently scrub the area where the sensor will be placed with an abrasive skin preparation, such as NuPrep or Lemon Prep, for 5 to 10 seconds, applying moderate pressure. The skin may redden slightly from the procedure.

To prevent signal contamination and possible bridging with other electrode sites, be sure to only scrub the area covered by the electrode cup. Likewise, avoid using excessive amounts of prep material because it has conductive properties and electrodes attached with tape will not stick to the prep. If there is excess prep material, the area can be cleaned again with rubbing alcohol. Be sure to wipe away from the electrode site to avoid transferring skin oils from the surrounding area.

Attaching Gold Cup Electrodes with Electrode Paste

Fill the electrode disk with conductive paste, so the surface is slightly rounded, making sure that there are no air pockets. Using the wooden side of the cotton-tipped applicator or a comb, part the hair in the same direction in which the lead wire will be positioned. Hair clips can be used to keep the site clear. Spread a small amount of electrode paste evenly on one side of a 3-cm square of gauze. Position the electrode in the center of the prepped site so the paste is against the skin. Cover the electrode with the gauze square, paste side down. Distribute the electrode paste around the head of the electrode, keeping it firmly in place until the paste begins to set. Check for a secure application by gently tugging on the electrode wire.

Attaching Gold Cup Electrodes with Collodion

When using collodion, the hookup process should be performed in a well-ventilated area as the glue is very pungent and flammable. If there is limited space available, an air filtration or exhaust system can be used to reduce the fumes. For safety purposes, collodion and acetone should always be handled carefully and stored in a fireproof safe. Collodion and acetone spills pose a safety risk; consequently, all sleep centers should have a protocol for handling and properly disposing of these materials.

A towel should be placed around the patient’s shoulders to protect his or her clothing from the glue. Separate the hair using a comb or the wooden side of the cotton-tipped applicator so that the skin is visible. Hair clips can be used to help hold the hair in place
and keep the electrode site in view. Once the site is prepped, position a clean gold-cupped electrode on the scalp and place a small square of single-ply gauze on top (˜2 to 3 cm). Insert the air compressor stylus through the gauze into the hole at the top of the electrode to hold it in place against the scalp. Using a syringe or another disposable applicator, apply just enough glue to saturate the gauze. If the electrode is moved after the glue is applied, the collodion may seep between the scalp and the electrode, which will raise the impedance level and compromise signal quality. Smooth the gauze tightly over the scalp while the glue is dried with the air compressor, taking care not to adhere your gloves to the electrode. If long enough, the patient’s hair can be used to help anchor the electrode to the scalp. Before removing the stylus, twist the end to break any seal that may have formed from the glue. The collodion bottle should be kept tightly closed when not in use to avoid spills and maintain the liquid nature of the glue. When collodion is exposed to air for an extended time, it becomes viscous and difficult to apply in moderation.

When all electrodes are glued in place, use a blunt-tipped needle syringe to fill the electrodes with electrolyte gel or cream. Be careful not to overfill the electrode cup, or the gel may leak out the side and break the collodion seal, causing electrode popping artifact during the recording.

Attaching Gold Cup Electrodes with Tape

Fill the electrode cup with conductive paste or electrolyte gel so it is slightly rounded, making sure there are no air pockets. To help ensure a solid connection with the skin, center a double-sided electrode collar over the cup and remove the paper backing. Place the electrode onto the prepped site, paste side down, with the wire pointed toward the crown of the head, and cover with a piece of tape. Press firmly around the rim of the cup to obtain a good seal. To facilitate removal in the morning, fold one end of the tape, creating a small tab; this makes it easier to pull the tape off at the end of the study (Fig. 36-1).

Managing the Electrode Leads

Organizing and securing the wires during the electrode application procedure will reduce the likelihood of electrodes being inadvertently pulled off during the night. After attaching the electrodes to the face and scalp, gather all the wires together into a ponytail at the crown of the head or nape of neck, making sure no wire is pulled taut. Bundle the wires together with pieces of tape or Velcro strips. If tape is used, both ends should be folded over for easy removal. The wires should be secured every 4 to 6 in (10.2 to 15.2 cm) to reduce tangling. The leads from the other sensors can also be grouped separately and taped together to make the wires more manageable.

If using tape to bundle the electrodes becomes problematic because of the sticky tape residue, try using Coban tape. This tape sticks to itself, comes in many colors, and is disposable. Posey straps, or even the ends of old PAP headgears, can also be used, although they have a tendency to slide and the added weight may put extra strain on the sensors.

Experienced sleep technologists usually develop their own approach for arranging and managing the wires, which helps facilitate easy removal in the morning. A neatly organized application also makes it easier to troubleshoot recording problems and replace sensors when necessary.

EEG Scalp Electrodes

According to the standard practice, EEG electrodes are applied using the International 10/20 System of Electrode Placement (1). When applying the electrodes, there are three key elements that are vital to collecting quality data:

Electrodes must be placed in the correct location.
Electrode sites must be properly prepared.
Electrodes must be securely attached.

The current AASM Scoring Manual (2) recommends six EEG scalp electrodes for polysomnography (PSG): two frontal electrodes (F3 and F4), two central electrodes (C3 and C4), and two occipital electrodes (O1 and O2). In addition, two mastoid electrodes M1 and M2 are placed on the mastoid processes, the bony protrusion located behind each ear.

The primary recording derivations are F4-M1, C4-M1, and O2-M1. Backup electrodes should be placed in order to record the backup derivations F3-M2, C3-M2, and O1-M2 in the event an electrode signal becomes compromised during the study. Most sleep centers include both the recommended and the backup electrode derivations in a standard PSG recording montage to ensure all EEG channels are visible during data collection and allow for troubleshooting.

Determining the EEG Electrode Placements: The International 10/20 System

The International 10/20 System of Electrode Placement (1) is a standardized method for identifying equally spaced electrode positions on the scalp on the basis of four identifiable skull landmarks. This method was developed in 1958 to provide a consistent procedure for collecting EEG data and to develop common terminology. The system is termed 10/20 because the measurements are spaced either 10% or 20% of the distance
between a given pair of skull landmarks. Percentages are used rather than absolute distances to allow for normal variations in head shape and size.

Each location is named with a letter indicating the corresponding lobe of the brain and a number or letter identifying the exact site. The locations on the left side of the head are odd numbered, the right side are even numbered, and the midline is represented by the letter ‘z’. From front to back, the lobes are: pre-frontal (Fp), frontal (F), temporal (T), central (C), parietal (P) and occipital (O).

Before starting the measuring process, have the patient sit in a chair that is low enough to allow you to see the top of the head. Ensure that all reusable equipment (grease pencil, hair clips, measuring tape) has been cleaned and disinfected according to facility protocols for infection control. When using a paper measuring tape, be sure to fold the end down at the zero line to avoid computation errors.

Identifying the Landmarks

The four standard landmarks used in the 10/20 system are the nasion, inion, and left and right preauricular points (Fig. 36-2). If the landmarks are not correctly identified, electrode placement will not be accurate. Each site should be marked to facilitate the measuring process keeping in mind that these sites are used as landmarks only and are not electrode positions.

Figure 36-2 Identifying the landmarks. (From Harner, P. F., & Sannit, T. (1974). A review of the International Ten-Twenty System of Electrode Placement. Quincy, MA: Grass Instrument Co. Courtesy of Natus Medical Incorporated, Middleton, WI.)

Preauricular Points

The opening of the ear canal is protected by a small piece of cartilage called the “tragus.” The preauricular points are the indentations just above this cartilage. If you are unsure of the location, place a finger on the patient’s cheek, touching the tragus, and ask the patient to open and close his or her jaw. The indentation will become more pronounced with this movement.

Nasion

The nasion is the indentation between the forehead and the nose formed by the intersection of the frontal bone and two nasal bones of the skull. While facing the patient, find the small dip at the bridge of the nose between the eyes and lightly mark the point with a grease pencil.

Inion

The inion is the ridge or knob at the back of the head. When running your finger up the back of the neck to the skull, you should feel a depression with the ridge of the protruding inion just above it. This landmark may
be difficult to find on some individuals, so ask the patient to tilt his or her head all the way back, or forward, while you try to feel the ridge. If you are unable to locate the inion, mark it at the same level as the preauricular points. A common mistake is to use the underside of the protrusion instead of the tip, which will impact the accuracy of electrode placement.

Measuring the Scalp Electrode Sites

Each electrode site is determined by the intersection of two lines created by calculating distances, measured in centimeters, stemming from the four main landmarks (Fig. 36-3). Start the measuring process by marking each of these landmarks with the grease pencil.

Step 1 in Determining Cz

Many PSG software systems use Cz for the system reference electrode, which is not the same as the patient ground. Even if an electrode is not attached at Cz, it should be marked as a reference point for identifying other electrode sites.

While standing to one side of the patient, place the zero line of the measuring tape on the marked inion. Stretch the tape measure upward, over the crown of the head, until it reaches the marked nasion. Determine the total distance between the inion and the nasion in centimeters. Using your grease pencil, mark the values for 10%, 50%, and 90% of that total distance. The marks at 10% and 90% will be used for identifying other electrode sites. Next, measure the distance between the marks made at 10% (will become Fpz) and 50% (will become Cz) and draw a line halfway between the two for Fz. Be sure to mark these sites with straight horizontal lines that are prominent enough to be easily located later.

Figure 36-3 Measuring the scalp between the two preauricular points. The measured distances in centimeters are provided as an example; actual distances will vary depending on the size and shape of the scalp. (From Harner, P. F., & Sannit, T. (1974). A review of the International Ten-Twenty System of Electrode Placement. Quincy, MA: Grass Instrument Co. Courtesy of Natus Medical Incorporated, Middleton, WI.)

Step 2 in Determining Cz

Standing behind the subject, reposition the zero end of the tape measure on one of the preauricular marks. Stretch the measuring tape over the top of the head through the 50% mark that was made during step 1, until it reaches the opposite preauricular mark. Determine the total distance from preauricular to preauricular point. Calculate 10%, 50%, and 90% of the total distance and mark each location. The point where the 50% mark intersects with the line drawn indicating 50% of the distance between nasion and inion is the site for Cz.

Step 1 in Determining C3 and C4

Standing to one side of the patient, place the zero line of the measuring tape on Cz and measure the distance to the mark made at 10% above one of the preauricular points (T3 or T4). Calculate 50% of this distance and mark the location. Repeat the process standing on the other side of the patient. These are the first set of marks necessary in determining C3 and C4. The second set of marks will be established after O1 and O2 have been identified.

Step 1 in Determining O1, O2, Fp1, and Fp2

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