Respiratory Failure
In this section we will take a look at reparatory failure, covering
To watch the YouTube video click here
Regulating the respiratory system
Respiratory failure occurs when regulation of the respiratory system fails. It can be helpful to first understand how healthy regulation is conducted. Below is a (brief) overview of the components involved in maintaining blood oxygen and carbon dioxide levels within a normal range.
brain
lungs
chemoreceptors
Chemoreceptors: Situated in major blood vessels and around the brain. They are sensitive to the blood pH, blood-oxygen levels, and blood carbon dioxide levels. Elevated pH & carbon dioxide levels stimulate them, as do low oxygen levels. These nerve impulses are then transmitted to the brain.
The brain: The respiratory centres are located in the brainstem, which collects information from the chemoreceptors (plus other sources such as stretch receptors in the the lungs). Stimulation from the chemo receptors in turn stimulates the respiratory centres, which will then dictate the rate and the rhythm of the respiratory muscles.
The lungs: are responsible for taking in oxygen and removing carbon dioxide. Oxygen is absorbed into the lungs on inspiration from where is passes into the blood. Carbon dioxide is removed from the body on expiration. Increased respiratory effort (faster/bigger breaths), will remove more CO2 from the body than slower, more shallow breathing.
Defining Hypercapnia
Carbon dioxide is produced in the body essentially by accident, or more accuratly, as a by-product. Our cells need a lot of energy to function, energy which is produced by our cells mitochondria. These little power station break down the food we eat and use it to create ATP, our bodies main fuel source. A consequence of this process is the production of carbon dioxide.
This is potentially a problem as CO2 has a tendency to combine with water to form an acid (carbonic acid). If two much CO2 is allowed to build up then the body may be pushed into a respiratory acidosis . Luckily the lungs are normally quite adept at removing carbon dioxide from our blood.
Arterial blood CO2 levels are normally kept somewhere between 4.5-6kpa. The body maintains this by monitoring blood co2 levels via the chemoreceptors, and then increasing or decreasing respiratory effort as carbon dioxide levels fluctuate. If CO2 levels increase above the normal range, the respiratory muscles start to work harder, leading to bigger breaths and a faster respiratory rate, clearing more co2 from the body until levels return back to normal range. Problems arise when the amount of co2 being produced by the body begins to surpass the amount being cleared through the lungs.
Learn more about identifying hypercapnia from an ABG
Hypercapnia arising from Neurological issues
The brain plays a crucial role in respiration. It is stimulus from the brainstem that drives the respiratory muscles, dictating the work of respiration. It is therefore not surprising that a neurological issue often leads to a respiratory issue. Below are some examples.
Drugs and the brain
Some medications can have a suppressive effect on the respiratory centres of the brainstem. For example, an opioid, such as morphine, administered to enthusiastically after a surgical procedure can significantly reduced respiratory effort. If the patient is becoming drowsy and starting to loose their respiratory drive then it is possible to reverse the effects of an opioid with Naloxone, but be warned! Any pain that the morphine was masking will also come back with a bang! Many medications used in anaesthetics will also supress respiratory effort. For example, benzodiazepine's such as midazolam.
Traumatic injury and stroke
A brain injury severe enough to suppress consciousness will likely have an effect on respiratory function. Following a major trauma it may be necessary to intubate and ventilate the patient in order to take over the work of breathing and protect their airway. 'Less than 8, intubate' is a common mantra post brain trauma. For more information on the use of mechanical ventilators see my video.
Not surprisingly, many causes of hypercapnia result from issues with the muscles that drive respiration (principally the diaphragm and intercostal muscles). Below are some examples you may come across in your clinical area.
Hypercapnia arising from pulmonary issues
Neuro muscular disease
Acquired weakness
Reading list
The two principle texts I used when putting together the video's and webpage were
-West's Respiratory Physiology, the essentials (amazon.co.uk link),
-West's Pulmonary Pathophysiology, the essentials (amazon.co.uk link)