From SKYbrary Wiki
In layman’s terms, Hyperventilation can be described as excessive over-breathing. Over-breathing can occur from an increased rate or depth of breathing (or both together).
This is how a person may describe another who is hyperventilating, or starting to hyperventilate: panting – rapid shallow breathing – gulping – choking – constant deep breathing – hiccupping. It can be distressing to see someone gasping for air, so an observer may not be able to use such precise adjectives! Some of the other symptoms described below (Signs and Symptoms) may also be visible to an observer but, without a visible or audible connection to excessive breathing, an observer may not connect them as anything to do with hyperventilation.
To be more precise Hyperventilation is breathing in excess of the metabolic needs of the body.
Our “breathing-in” response is triggered by the amount of CO2 in our system rather than the lack of Oxygen. Compare staying under water with a lung full of air to doing the same with completely empty lungs. In the first example we gasp for air on surfacing and our heart is pounding in the chest; in the second example we have no breathlessness on surfacing, we just take a normal breath. When in a physically relaxed state, the amount of CO2 in the blood stimulates the respiratory centre and our breathing rate is stabilised around 12 to 20 breaths per minute. When we undertake physical activity our body cells use more Oxygen and this in turn produces more CO2. This excess CO2 enters the blood and consequently our breathing increases in depth and rate to remove it.
If we hyperventilate when not physically exercising, i.e. when sat in the cruise monitoring the aircraft systems, we are not burning-off Oxygen and converting it into CO2. The CO2 that is already in the system gets “washed out” by the increased respiration. The lowering of blood CO2 (hypocapnia) gives rise to an increased blood pH (respiratory alkalosis). This is quite a profound chemical change in the body and alkalosis will give rise to a broad-range of symptoms. Affecting both the cardiovascular system and the central nervous system, the immediate effects are increased heart rate, reduced blood pressure, reduced blood flow to the brain due to vasoconstriction and muscle spasms.
If the actions described later in this Article are followed, then the breathing and the body quickly return to normal and there should be no long-term damage.
Signs and Symptoms
Hyperventilation can lead to a wide-range of symptoms that will degrade physical and mental performance; in extreme cases it can result in unconsciousness. It is therefore important for pilots to be familiar with the signs and symptoms of Hyperventilation in others and in themselves.
It is worth noting that as well as “overt” onset of Hyperventilation, like you might witness when someone becomes extremely nervous before an exam or test, it can also be induced “covertly”. If respiration is only increased slightly (e.g. 20%) for a prolonged period, then this can also cause Hyperventilation.
Initially you may notice a feeling of dizziness, a coldness and tingling around the lips and a feeling as though there was a band around the head. You may feel nauseous. Peripherally there is vasodilatation and stimulation of sensory nerves causing a sensation of pins and needles in the hands and in the feet.
The symptoms associated with Hyperventilation include:
- Paraesthesia (“pins and needles” - tickling, tingling, burning, pricking, or numbness) especially in the extremities.
- Increased heart rate
- Blurred vision
- Impaired judgment
- Memory impairment
- Muscle spasms and tics
- Muscle weakness
In prolonged cases of Hyperventilation, the muscle spasms can develop into severe and painful contractions of the hands, fingers, feet and toes (carpopedal spasms). If unconsciousness occurs then these spasms may turn into fixed contractions, including the limbs (tetany).
Most of these symptoms will be visible, or detectable, in others.
Triggers and Aggravating Factors
Basically, anything physical, mental, emotional or environmental that causes the breathing rate and/or depth to increase without an equivalent increase in physical activity can cause Hyperventilation.
More common reasons for pilots Hyperventilating include:
- encountering unexpected and/or unfamiliar situations
- excessive concentration on a flight procedure
- experiencing a significant emergency
- having difficulty accomplishing procedures
- being examined or audited
Each of these can cause (unconsciously as well as consciously) anxiety or fear, activating the sympathetic nervous system (fight or flight) leading to Hyperventilation. Furthermore, a pilot experiencing any of these events may be too distracted to notice any symptoms, or may dismiss the symptoms as something “to be expected under the circumstances” and therefore nothing to worry about.
The cockpit and cabin environment can also trigger Hyperventilation. Increased levels of Carbon Monoxide and exposure to toxic substances are both triggers. Also, when the level of Oxygen is reduced significantly, this can lead to Hyperventilation. Hypoxia definitely will lead to Hyperventilation. The signs and symptoms of Hypoxia and Hyperventilation overlap significantly and are easily confused.
It is essential that if a pilot suspects he has symptoms of Hyperventilation he instead takes action as though he is Hypoxic!
- Underlying health conditions, such as: pregnancy, pneumonia, lung disease, asthma, cancer, fever, infections, liver disease and brain tumours, can also give rise to Hyperventilation.
- A condition called Metabolic Acidosis may also cause Hyperventilation; this condition can arise due to: type 1 diabetes, severe diarrhoea, excessive exercise, drug and alcohol abuse and hypoglycaemia.
- Stress, worry, difficulties, pressures and emotional problems at home can reduce a pilot’s resilience to stress in the cockpit and therefore makes them more susceptible to an early onset of Hyperventilation.
Response in Flight
In flight it can be difficult to distinguish between the symptoms of Hyperventilation from those of Hypoxia. Therefore, the worst case must be assumed and the response must be the same as for Hypoxia: follow your approved procedures for Hypoxia in line with your training. Such drills may cover the following points:
- immediate donning of oxygen mask on suspicion of any symptoms
- ensuring oxygen is 100% and flow is appropriate
- slowing and deepening the breathing
- check oxygen system for connection, leaks and proper functioning
- check for potential sources of Hypoxia – e.g. pressurisation, smoke and fumes etc…
- Warn others
- Help others don their Oxygen masks and check proper functioning
- Consider informing Air Traffic Control (important for solo pilots)
Above 10,000ft altitude, if one crewmember is Hyperventilating, the other crewmembers should also assume it could be due to Hypoxia and also complete the Hypoxia response. It is usual to don your own mask and establish oxygen flow before helping others.
Response on the Ground
On the ground or below 10,000ft altitude without the presence of smoke and fumes, the treatment for Hyperventilation involves restoring the proper CO2 level in the body. Breathing normally is both the best prevention and the best cure for Hyperventilation. In addition to slowing the breathing rate, breathing into a paper bag or talking aloud helps to overcome Hyperventilation. Recovery is usually rapid once the breathing rate is returned to normal.
It is possible to become familiar with some of the early onset symptoms of Hyperventilation by voluntarily breathing several deeps breaths at an accelerated rate. It is important to consult a Doctor/Medic before attempting this. If you are permitted to conduct this exercise, then certain precautions should be taken for your own safety.
- Never conduct this exercise by yourself – have someone monitor you.
- Never conduct this whilst working, driving, operating any machinery or when flying!
- Sit down before you start and ensure that you won’t fall.
- As soon as you have experience several mild symptoms, return to your normal rate of breathing.
- Only stand up when you are certain that all symptoms of dizziness and muscle weakness have dissipated.
Becoming familiar with the early warnings that your own body experiences can reduce the chance of you missing the symptoms should they occur in-flight.