Obesity Hypoventilation Syndrome

We oftentimes hear of patients who are morbidly obese coming in for issues with respiratory distress or failure. Why exactly is this? Many of these patients have an actual syndrome called obesity hypoventilation syndrome (OHS) or Pickwickian Syndrome. Let's look at what a patient suffering from this might look like.

Signs and Symptoms

Many patients with OHS come into the hospital showing signs of respiratory distress. What does this look like? Increased respiratory rate (normal is 12-20) in the 30-40 range, use of accessory muscles, increased oxygen demand. OHS causes people to have poor breathing habits which causes increased carbon dioxide in the blood and decreased oxygen in the blood. 

Controversy surrounds the pathophysiology. Only a small proportion of morbidly obese patients suffer from the condition, so factors other than obesity must be at work. Some authors believe that the basic problem relates to the way the ventilatory drive reacts to hypoxia and hypercapnia.[3] Others consider that fat distribution, hormones and upper airway size are involved.
— Patient.info

What will the labs look like? Most likely the doctor will have you do a venous or arterial blood gas to look at how effectively the patient is breathing. In my hospital usually they perform venous blood gases (VBGs) because they are less invasive but still provide us with adequate information for determining respiratory status. A patient's VBG may look like this upon admit: 

pH: 7.11 (normal: 7.32-7.32)

pCO2: 91 (normal: 40-60)

Bicarbonate: 25 (normal: 22-27)

Why is the pH so low? Carbon dioxide (CO2) is an acid which lowers your overall pH. If a person isn't breathing efficiently and the CO2 builds up in their system, the pH is lowered. How do you combat this? You breathe quickly! Each time that you breathe you exhale CO2, so your patient will be tachypneic (breathing quickly) to try and compensate for their acidic pH. This can exhaust your patient to the point of needing mechanical assistance for their breathing.

Causes of OHS

Patients with OHS fail to breathe either quickly enough or deeply enough to exhale adequate amounts of carbon dioxide. This main cause of this syndrome is obesity. Many patients also have periods of time where they stop breathing altogether called sleep apnea. Patients usually have issues with daytime sleepiness due to their lack of quality sleep at night and their increased CO2 levels.

Treatments for OHS

If a patient has moderate OHS, the best treatment is losing weight. This will decrease the amount of strain they have with each breath allowing them to take deeper and fuller breaths. Better respiratory status = normal carbon dioxide levels!

In the hospital, the main treatment for respiratory failure from OHS is either continuous positive airway pressure (C-PAP) or bilevel positive airway pressure (Bi-PAP). Patients can receive more support and tidal volume (the amount of air inhaled with each breath) using these treatments. If you breathe faster or larger breaths, you will breathe out more CO2 which both decreases your serum CO2 and increases your pH. Patients with severe enough respiratory distress may require mechanical ventilation with either an endotracheal tube or tracheostomy.

AuthorCourtney Tracy