A sleep study is a non-invasive, overnight test conducted in a specialized lab to record various physical activities while a person sleeps. This comprehensive monitoring process provides medical professionals with the detailed data needed to diagnose sleep disorders, such as obstructive sleep apnea. The split-night study is a modified version of this traditional test, designed to maximize efficiency by combining both the diagnostic phase and the initial treatment phase into a single night. This approach allows patients with severe breathing issues to begin their treatment plan more quickly than the standard two-night procedure.
How a Split Night Differs from Standard Sleep Studies
A standard, full-night polysomnography is purely diagnostic, meaning the patient spends the entire night being monitored solely to determine if a sleep disorder exists. If obstructive sleep apnea is diagnosed, a second, separate night is often scheduled later to find the appropriate therapeutic pressure. The split-night protocol streamlines this process, removing the need for two separate visits to the sleep facility. This combined approach is typically recommended when a healthcare provider strongly suspects moderate to severe sleep apnea based on a patient’s initial symptoms. The primary advantage of the split-night study is its efficiency and convenience, reducing the overall cost and time required to establish a diagnosis and secure a treatment device.
The Diagnostic Phase and Switch Criteria
The split-night begins exactly like a standard sleep study, with the first half of the night dedicated entirely to diagnosis. During this phase, a technologist attaches various sensors to the patient’s scalp, face, chest, and limbs to monitor specific physiological parameters. These sensors track:
- Brain waves
- Eye movements
- Muscle activity
- Heart rate
- Leg movements
- Nasal/oral airflow and blood oxygen levels
This initial diagnostic period must last a minimum of two hours of recorded sleep time. The technologist monitors the patient’s breathing for events like apneas (complete pauses in breathing) and hypopneas (partial reductions in airflow). If the accumulated data reveals a sufficiently high number of respiratory events, the night is then “split” to begin treatment. The crucial threshold used to trigger the switch is the Apnea-Hypopnea Index (AHI), which represents the average number of apneas and hypopneas per hour of sleep. Clinical guidelines stipulate that a night can be split if the AHI reaches 20 or more events per hour during the diagnostic period. Meeting this threshold indicates a severity level that warrants immediate intervention.
The Treatment Titration Phase
Once the switch criteria are met, the technologist introduces the Continuous Positive Airway Pressure (CPAP) device. This device delivers pressurized air through a mask to keep the patient’s upper airway open and prevent respiratory events. The second half of the night is called the titration phase, where the technologist’s goal is to find the optimal air pressure setting for the patient. The process involves the technologist remotely and incrementally adjusting the air pressure while continuing to monitor the patient’s sleep data. They observe how the patient’s breathing responds to each pressure change, looking for the level that eliminates or significantly reduces apneas, hypopneas, and snoring.
The technologist must confirm that respiratory events are suppressed during the patient’s Rapid Eye Movement (REM) sleep, which is often when breathing issues are most pronounced. For the titration to be successful, this treatment phase must last for at least three hours. If a patient cannot tolerate the high pressures of a standard CPAP, a Bi-level Positive Airway Pressure (BiPAP) device, which uses separate pressures for inhalation and exhalation, may be introduced. The final pressure setting determined during this phase will form the basis of the patient’s long-term CPAP prescription.
Study Preparation and Next Steps
Preparing for a split-night study involves a few logistical steps to ensure accurate data collection. Patients are advised to maintain their regular sleep schedule in the days leading up to the study. It is important to avoid consuming caffeinated beverages, alcohol, or taking daytime naps on the day of the study, as these can interfere with normal sleep architecture. Patients should pack comfortable sleeping attire and bring any medications they routinely take.
Upon arrival, the technologist will place the sensors and fit the patient with a mask. After the study concludes in the morning, the sensors are removed, and the patient is free to resume normal daily activities. The collected data is then scored and analyzed by a technologist and reviewed by a board-certified sleep physician. The physician interprets the AHI, the CPAP pressure requirements, and other details to formulate a final diagnosis and treatment plan. Patients typically receive a follow-up appointment within one to two weeks to discuss the results and receive their personalized CPAP prescription.