In a diagnosis list, the OHS medical abbreviation most often means obesity hypoventilation syndrome, a breathing disorder in which a person with obesity does not breathe deeply enough, so carbon dioxide builds up in the blood during the day as well as at night. It is closely tied to sleep apnea, and the two often appear together.
In cardiac surgery notes, OHS can instead mean open heart surgery. A third, related search is OHSS, which is a different condition seen in fertility care. This page walks through each one, explains the blood test numbers you may see beside OHS, and points out the nearby words that separate one meaning from another.
At a glance
Stands for
Obesity hypoventilation syndrome (in diagnosis lists)Other meanings
Open heart surgery (cardiac context); occupational health and safety (workplace)Do not confuse with
OHSS, ovarian hyperstimulation syndrome; OSA, obstructive sleep apneaSpecialty
Pulmonology, sleep medicine, critical careKey lab
Arterial blood gas showing high carbon dioxide while awakeOlder name
Pickwickian syndrome
Obesity hypoventilation syndrome explained
Hypo means under, and ventilation is the movement of air through the lungs. In obesity hypoventilation syndrome, extra weight around the chest and belly makes breathing harder, and the brain's drive to breathe may also be weaker. The lungs do not clear enough carbon dioxide, and oxygen levels can fall.
The diagnosis usually needs three things together: obesity, generally a body mass index of 30 or higher; a high carbon dioxide level on a blood gas while awake, usually above 45 mm Hg; and no other condition, such as a lung or nerve disease, that better explains it. Most people with OHS also have obstructive sleep apnea.
Reading OHS in a hospital chart
Pulmonary consult line: "OHS/OSA, chronic hypercapnic resp failure, on BiPAP qHS, bicarb 36." This says the patient has obesity hypoventilation and sleep apnea, a long standing high carbon dioxide level, uses a bilevel breathing machine at bedtime, and has a high bicarbonate, which the kidneys raise to balance the extra carbon dioxide.
| Shorthand | Plain meaning |
|---|---|
| ABG | Arterial blood gas, the test that measures carbon dioxide |
| pCO2 or PaCO2 | The carbon dioxide level in arterial blood |
| Hypercapnia | Too much carbon dioxide in the blood |
| BiPAP or CPAP | Machines that push air through a mask during sleep |
| AHRF | Acute hypoxemic respiratory failure, a low oxygen emergency |
Lab ranges differ a little between hospitals, so the report itself lists its reference values.
OHS medical abbreviation in cardiac notes
On a cardiac surgery or cardiology chart, OHS can mean open heart surgery, a broad term for operations where the chest is opened to work on the heart. Examples include bypass surgery, written CABG, and valve repair or replacement. A history line might read s/p OHS for AVR, meaning status post open heart surgery for aortic valve replacement.
The clue is the neighborhood. Sternotomy, bypass pump, valve or graft words point to surgery. Blood gas, sleep study, weight or BiPAP words point to the breathing disorder.
OHSS: one extra letter, a different condition
Anyone looking up the OHSS medical abbreviation is usually reading fertility clinic notes. OHSS stands for ovarian hyperstimulation syndrome. It can occur during fertility treatment, when medicines used to stimulate the ovaries cause them to swell and fluid to shift into the belly. Mild cases are common and settle on their own; severe cases are less common and are managed by the fertility or gynecology team.
OHSS has nothing to do with breathing or heart surgery. If you see OHSS in a fertility clinic record, it refers only to this ovarian condition.
How OHS is usually managed
Treatment notes for obesity hypoventilation syndrome often mention positive airway pressure at night, either CPAP or BiPAP, to support breathing during sleep. Weight loss through diet, activity, medicine or surgery is also a common long term goal, since it can improve breathing. During a hospital stay, teams watch blood gas results and oxygen levels closely and may adjust machine settings.
Every plan is set by the treating pulmonary or sleep team. A related condition often listed beside it is COPD, which can also raise carbon dioxide levels.
Questions to ask when OHS appears in your records
- Does OHS here mean the breathing disorder or a past heart operation?
- What were my carbon dioxide and bicarbonate results, and how do they compare with before?
- What machine settings should I use at home, and how is the mask fitted?
- Who should I call if I feel unusually sleepy or have morning headaches?
Abbreviations with more than one meaning are best clarified by the clinician who wrote the note. Your pulmonary, sleep or heart team can explain how OHS applies to your care.
Breathing and sleep terms like OSA are part of our diagnosis abbreviations list.
Frequently asked questions
What does OHS mean in a cardiac chart?
In a cardiac chart, OHS usually means open heart surgery, such as bypass surgery or a valve operation. A line like s/p OHS means the person has had open heart surgery in the past.
Is OHS the same as sleep apnea?
No, but they are closely linked. Obstructive sleep apnea involves blocked breathing during sleep, while obesity hypoventilation syndrome means carbon dioxide stays high even while awake. Most people with OHS also have sleep apnea.
What does OHSS stand for?
OHSS stands for ovarian hyperstimulation syndrome, a condition that can occur with fertility treatment. It is unrelated to OHS, the breathing disorder, or to open heart surgery.
Which test confirms obesity hypoventilation syndrome?
An arterial blood gas taken while awake shows a high carbon dioxide level, usually above 45 mm Hg. Doctors also check that no other lung, nerve or chest wall condition better explains it, and many order a sleep study.
What is the older name for OHS?
It was once called Pickwickian syndrome, a name borrowed from a character in an old novel. Modern charts use obesity hypoventilation syndrome or OHS instead.