Why Are My CPAP Events Per Hour Increasing?

Rising events per hour on your CPAP usually means something has changed with your body, your equipment, or the conditions under which you sleep. The machine’s event count (often called AHI, or apnea-hypopnea index) is a running tally of breathing interruptions that slip past the therapy. A number that was once low and stable can creep upward for a dozen different reasons, some as simple as a stretched-out mask cushion and others as complex as a shift in how your brain controls breathing. The good news is that most causes are identifiable and fixable once you know where to look.

Mask Leak Is the Most Common Culprit

Air escaping around or through your mask is the single most frequent reason CPAP events tick upward. When the seal breaks, the machine can no longer maintain stable pressure in your airway. Your device tries to compensate by ramping up airflow, but if the leak outpaces the compensation, your airway gets less pressure than it needs and partial or full obstructions sneak through. Research on CPAP titration patients found that those with higher leak rates were significantly more likely to develop central apneas during the study, with median maximum leak roughly 75 liters per minute in the group with elevated central apnea indexes compared to about 60 liters per minute in the group without.

1PubMed Central. Air leak during CPAP titration as a risk factor for central apnea

Leak does not just let obstructive events through. It can confuse the machine’s sensors. Auto-adjusting devices rely on flow signals to detect breathing irregularities, and large unintentional leaks distort those signals, sometimes making the machine misidentify events or respond with the wrong pressure adjustment. This means your reported AHI can spike partly because the leak is causing real breathing problems and partly because the machine’s readings become less accurate during heavy leak.

2PubMed Central. Auto-adjusting positive airway pressure: the fine line between engineering and medicine

Common leak causes include a mask that has shifted during sleep, facial hair growth, a pillow pushing the mask out of position, or simply opening your mouth while using a nasal mask. If your machine’s leak data shows high or erratic numbers on the same nights your events climb, that connection is worth addressing first.

Worn-Out Equipment

Mask cushions degrade over time. Silicone and gel lose their flexibility, develop micro-cracks, and stop conforming to your face as well as they once did. A large observational study tracking CPAP masks across three years of real-world use found that mean mask leak and mean on-therapy AHI were both higher in certain mask types and brands, with full-face (oronasal) masks averaging about 5.1 events per hour compared to roughly 3.6 for nasal masks and 3.7 for nasal pillows.

3BMJ Open Respiratory Research. Evaluation of CPAP mask performance during 3 years of mask usage: time for reconsideration of renewal policies?

Headgear elasticity also matters. Stretched straps mean you tighten them to compensate, which pushes the cushion out of shape and creates new leak channels. Most manufacturers recommend replacing cushions every one to three months and the full mask assembly every six to twelve months, though real replacement schedules vary widely by insurance rules and personal wear patterns. If your numbers were good six months ago with the same mask and nothing else has changed, replacing your cushion is a low-cost first step.

Tubing deserves a mention too. Small holes, loose connections at the machine or mask end, and condensation buildup inside the hose can all reduce effective pressure delivery. Running your fingers along the tubing while the machine blows air can reveal tiny holes you would not notice otherwise.

Weight Changes

Gaining weight is one of the strongest predictors of worsening sleep apnea over time. Fat deposits around the neck and throat narrow the airway, and even a modest gain can push events upward. A study following sleep apnea patients across five years found that those who gained weight saw increases in AHI and oxygen desaturation, with the severity of respiratory events climbing alongside the amount of weight gained.

4Comprehensive Physiology. Obstructive Sleep Apnea

The reverse also holds. Weight loss tends to bring events back down, sometimes substantially. If your CPAP numbers have been creeping upward over months and your weight has also been trending upward, the two are very likely connected. A higher AHI often means your current pressure setting is no longer enough to splint the airway open against the increased tissue load, especially if you are on a fixed-pressure device rather than an auto-adjusting one.

Sleeping Position

The position you sleep in can double your event count. A study using head and trunk position sensors found that over half of sleep apnea patients had significantly worse breathing when lying on their back compared to their side. In about half of that position-dependent group, head position added another layer: having both trunk and head in the supine position raised the AHI substantially compared to turning the head to one side.

5PubMed. Quantitative Effects of Trunk and Head Position on the Apnea Hypopnea Index in Obstructive Sleep Apnea

If you recently changed your pillow, switched to a different bed, or notice from your mask marks that you are ending up on your back more often, that postural shift alone could explain rising numbers. Some people find that wearing a positional therapy device or using a wedge pillow reduces supine time enough to bring events down. Others simply notice that a bad night on their data log matches a night they slept on their back.

Nasal Congestion and Allergies

A stuffy nose forces you to breathe harder through a narrower passage or switch to mouth breathing, either of which undermines CPAP therapy. Research from a large population study found that people reporting nasal congestion from allergies were 1.8 times more likely to have moderate-to-severe sleep-disordered breathing than those without.

6Journal of Allergy and Clinical Immunology. Nasal obstruction as a risk factor for sleep-disordered breathing

Seasonal patterns are a clue. If your events rise every spring or fall, allergies are a likely driver. Chronic sinus problems, a deviated septum, or even dry air from running the CPAP without adequate humidification can all increase nasal resistance enough to raise your numbers. Using your machine’s heated humidifier, adding a saline rinse before bed, or treating underlying allergies can make a measurable difference. If you use a nasal mask or pillows and find yourself waking up with a dry mouth, you are likely mouth-breathing around the therapy, and that leads directly to both leak and higher events.

Treatment-Emergent Central Apnea

Some people develop a new kind of breathing disruption after starting CPAP that was not present before. Treatment-emergent central sleep apnea occurs when the machine eliminates the obstructive events but the brain temporarily “forgets” to send the signal to breathe. The mechanism involves carbon dioxide levels: CPAP can sometimes drop COâ‚‚ below the threshold that triggers breathing, and during those brief pauses the brain does not initiate a breath.

7PubMed Central. Treatment-emergent central sleep apnea: a unique sleep-disordered breathing

This can appear weeks or months into therapy, or even after a pressure change. If your machine’s detailed data shows that the events are predominantly central rather than obstructive, that distinction matters. Central events do not respond to more pressure; in fact, increasing pressure can make them worse. A ventilatory control instability or a low arousal threshold makes some people more susceptible. For most, these central events resolve on their own within a few months of CPAP use, but persistent cases may require a different device mode.

How Auto-CPAP Machines Score Events

If you use an auto-adjusting machine, it is worth understanding that different brands count events differently. Each manufacturer uses a proprietary algorithm to detect apneas, hypopneas, and flow limitation, and these algorithms do not always agree with each other or with what a sleep technologist would score manually. Bench testing of multiple auto-CPAP devices showed that their responses to identical simulated breathing patterns varied considerably: some machines eliminated the events while others failed to address prolonged flow limitation at all.

8PubMed Central. Comparative assessment of several automatic CPAP devices’ responses: a bench test study

This means a jump in your reported AHI might partly reflect how the machine interprets ambiguous signals rather than a true worsening of your airway. Leak, as mentioned earlier, makes this problem worse because the distorted flow signal feeds noisy data into the algorithm. A review of auto-CPAP technology noted that these algorithms are poorly understood even by clinicians, and that variability in event detection and pressure adjustment among devices adds genuine complexity to reading your nightly data.

2PubMed Central. Auto-adjusting positive airway pressure: the fine line between engineering and medicine

None of this means your machine’s numbers are useless. Trends over weeks matter more than any single night. But if your AHI spiked on one or two nights and then returned to normal, the spike may have been an artifact of leak, sleeping position, or algorithm sensitivity rather than a real change in your sleep apnea severity.

REM Sleep and Aging

Your event count is not evenly distributed across the night. During REM sleep, the body naturally suppresses muscle tone, and the muscles surrounding the upper airway become especially relaxed. This makes obstruction more likely during REM periods than during other sleep stages.

9PubMed Central. REM Obstructive Sleep Apnea: Risk for Adverse Health Outcomes and Novel Treatments

If you are sleeping more deeply than usual, catching up on missed sleep, or taking a medication that increases REM time, you may be spending more of the night in REM and therefore experiencing more events. The practical implication is that a rising AHI can sometimes reflect better sleep quality rather than worse apnea control: you are finally getting the deep sleep stages your body needs, and those stages happen to be harder on your airway.

Aging compounds this. Over years, the muscles and nerves that keep the airway open gradually weaken, and the tissues become more collapsible. Sleep apnea severity tends to progress naturally with time, and a pressure setting that worked well five years ago may no longer be sufficient. Periodic reassessment with your sleep provider, rather than assuming your original settings are permanent, is a reasonable approach.

4Comprehensive Physiology. Obstructive Sleep Apnea

Altitude and Travel

If your events spiked during a trip, altitude could be the reason. At higher elevations, lower oxygen levels alter your breathing pattern and can trigger central apneas that your machine was never designed to handle. A study comparing three locations at different altitudes found that central apneas during PAP therapy averaged about 5 per hour at the lowest site, roughly 10 per hour at the mid-altitude site, and over 19 per hour at the highest site. The proportion of patients meeting the threshold for clinically significant central apnea climbed from about 11% at low altitude to nearly 39% at the highest location.

10PubMed Central. The Effects of Altitude Associated Central Apnea on the Diagnosis and Treatment of Obstructive Sleep Apnea: Comparative Data from Three Different Altitude Locations in the Mountain West

A case report from a rally driver using auto-CPAP at progressively higher altitudes showed residual AHI jumping from 5 events per hour at baseline to 45 events per hour at the highest altitudes reached.

11PubMed Central. Effectiveness of a lightweight portable auto-CPAP device for the treatment of sleep apnea during high altitude stages of the Dakar Rally: a case report

These altitude-related events are predominantly central apneas driven by the body’s hypoxic ventilatory response, not the obstructive type. They resolve once you return to lower elevations. If you live at moderate altitude and your baseline numbers have always been slightly elevated, this could be a contributing factor your original titration did not account for, especially if your sleep study was performed at a different elevation.

Alcohol and Sedatives

Conventional wisdom holds that alcohol before bed worsens sleep apnea, and there is a reasonable physiological basis for that: alcohol relaxes upper airway muscles, potentially making obstruction easier. Interestingly, one controlled study of moderate alcohol intake (vodka, in this case) in people with mild-to-severe sleep apnea found little effect on breathing events or oxygen levels during sleep, and no change in the pressure required by CPAP to prevent apneas.

12PubMed. Influence of moderate alcohol consumption on obstructive sleep apnoea with and without AutoSet nasal CPAP therapy

That finding, though, was specifically about moderate amounts in a controlled setting. Heavier drinking, benzodiazepines, opioids, and other sedating medications are a different story. These substances can significantly depress respiratory drive and relax airway musculature beyond what your current pressure can overcome. If your events started climbing around the time you began a new medication or changed your drinking habits, it is worth flagging for your prescriber. Opioids in particular are well known to produce central apneas that standard CPAP does not address well.

Fluid Shifts and Heart Conditions

For people with heart failure or other conditions that cause fluid retention, lying down at night triggers a gradual shift of fluid from the legs upward into the neck and chest. This fluid accumulates in the soft tissues around the airway, narrowing it and making both obstructive and central events more likely. Research in men with heart failure identified this nocturnal fluid shift as a unifying mechanism behind both types of apnea in that population.

13PubMed. Nocturnal rostral fluid shift: a unifying concept for the pathogenesis of obstructive and central sleep apnea in men with heart failure

You do not need to have diagnosed heart failure for this to matter. Any condition that causes lower-limb edema, including chronic kidney disease, venous insufficiency, or even prolonged sitting during the day, can produce enough fluid redistribution to raise events. Wearing compression stockings during the day, elevating your legs before bed, and managing the underlying condition with your doctor can all help. If your events are worse on days when your ankles are more swollen, the connection is worth investigating.

When to Talk to Your Sleep Provider

A handful of high-event nights mixed into otherwise good data is usually nothing to worry about. A sustained upward trend over weeks, especially one you cannot link to an obvious cause like a bad mask seal or a head cold, deserves professional attention. Your provider can download detailed data from your machine that breaks events into obstructive, central, and hypopnea subtypes, which helps narrow the cause. They can also determine whether your pressure settings need adjustment, whether a different mask type would serve you better, or whether a repeat sleep study is warranted. Many of the factors covered here, from weight changes to aging to altitude, quietly shift the goalposts over time, and the therapy that was dialed in perfectly at your original titration may simply need updating.