Hyperventilation

Hyperventilation is excessive ventilation of the lungs, beyond what is required to achieve normal arterial blood gases.

Hyperventilation has little effect on arterial pO₂ and almost no effect on oxygen saturation which is nearly 100% under normal circumstances. Its main effect is to lower pCO₂ and produce a respiratory alkalosis. A secondary hypocalcaemia also occurs as calcium dissociation is shifted towards the unionised, bound form.

There are many factors that influence the respiratory drive including the elasticity of the lungs and the resistance in the airways but the most important factors are:

1. Arterial pH
2. pCO₂
3. pO₂

Of these, pCO₂ is most important although some people with COPD can be dependent upon the hypoxic drive.

Hyperventilation can result from:

• Disordered blood chemistry with normal homeostatic response to stimulate the brain's respiratory centre, increasing rate and depth of breathing.
• Voluntary and conscious act.
• Psychological response to anxiety or stress, with little awareness.

Hyperventilation syndrome (HVS) is where hyperventilation occurs chronically or in recurrent episodes and is associated with somatic (respiratory, neurological, intestinal) or psychological (anxiety) symptoms.¹ Some prefer to describe it as 'psychogenic dyspnoea' or 'behavioural breathlessness', emphasising hyperventilation as the consequence rather than cause of the perceived breathlessness.² There is a strong overlap with panic disorder - most patients showing characteristics of both disorders - but generally lack the positive finding of any underlying organic disease. About 5-10% of general medical outpatients are thought to suffer from this syndrome and because of the range of somatic symptoms, the risk of misdiagnosis is high.

• It is quite common but precise prevalence is unknown. A postal survey indicated that 8% adults without asthma suffer from functional breathing problems (of which symptomatic hyperventilation is the most common).³
• It can occur at any age after infancy but the onset is usually between the ages of 15-55 years with a female preponderance of around 7:1.
• It is more common in asthmatic patients, occurring in 29% in one survey.⁴

The commonest reason for increasing respiratory rate and depth is exercise, the extent depending upon the level of exercise. However, as this is a normal physiological response, it is inappropriate to call it hyperventilation. Other causes include:

• Metabolic acidosis will cause compensatory hyperventilation. This may occur with diabetic ketoacidosis or with renal failure. Carbon dioxide is a very weak acid but the volume exchanged in a day makes it the most important contributor to acid base balance.
• There may be problems of respiratory exchange including V/Q imbalance due to, for example, pulmonary embolism or poor gas exchange with pulmonary oedema.
• Hypoxia can be the result of altitude, especially when ascent has been too rapid and acclimatisation has not occurred. Hyperventilation can cause mountain sickness with cerebral oedema. Rapid descent is imperative as the condition can be fatal.
• Fever, toxins and drugs can all increase the respiratory rate, possibly by a central action on the brain.
• Aspirin overdose leads first to a primary hyperventilation and respiratory alkalosis by central stimulation and then a secondary hyperventilation for the metabolic acidosis caused by the acidic nature of the drug.
• Iatrogenic hyperventilation by over-ventilating patients with head injuries was once a common technique but it has fallen from favour as it has been shown to produce a worse outcome.⁵
• Hyperventilation in response to anxiety is common. It is more likely in women and may be associated with panic attacks.
• Hyperventilation may also occur as part of dysfunctional breathing in asthma sufferers.⁴

The remainder of this article will concentrate on HVS as it may present in Primary Care.

Symptoms

• The complaint is usually of a paroxysmal rather than a continuous nature although chronic hyperventilation can occur.
• The patient may complain of shortness of breath when an attack occurs.
• Pain or discomfort in the chest is common.
• Paraesthesiae usually affects both arms. The complaint is often of numbness or tingling in the fingers and sometimes toes.
• Other symptoms include:
  • Dizziness
  • Perioral tingling
  • Weakness
  • Tinnitus
  • Palpitations
  • Feeling of choking or suffocation
  • Wheezing
  • Sweating
  • Loss of consciousness (uncommon)⁶

Ask about precipitating or relieving factors and what does the patient does when she gets an attack.

Signs

There are unlikely to be any signs unless the patient is seen during an acute attack when:

• The patient will look very anxious and be struggling to breath.
• Speech is difficult and the accessory muscles of ventilation are used.
• Note the ratio of the inspiratory duration to the expiratory duration:
  • In quiet breathing this is about 1:2.
  • In asthma the expiratory phase is prolonged, especially if severe and the patient may expire through pursed lips.
  • In hyperventilation, the inspiratory phase may be more energetic and the expiratory phase is not prolonged.
• Trousseau's sign (also called "main d'acoucher" or carpo-pedal spasm) is muscle spasm in the hands, with the tips of the fingers and thumb apposed and the fingers straight. It results from hypocalcaemia.
• Chvostek's sign is also due to hypocalcaemia. Flick behind the ear, just in front of the mastoid bone where the facial nerve emerges. The hypersensitive facial nerve makes the muscles of the face twitch.

Chronic hyperventilation

Chronic hyperventilation may be rather more difficult to diagnose. The patient rarely hyperventilates in a clinically apparent manner and may have already been through multiple investigations already.

• There may be a persistently low arterial pCO₂ with a high renal excretion of bicarbonate so that pH is normal.
• Occasional deep, sighing breathes may be noted. These keep the pCO₂ depressed.
• They may hyperventilate more obviously when stressed and readily produce symptoms under these conditions.

The diagnosis may be obvious from the history.

• Panic attack or agoraphobia
• Asthma (mild asymptomatic asthma is not associated with clinically significant hyperventilation but is associated with a significant reduction in both arterial and end tidal pCO₂ relating to airway hyperresponsiveness)⁷
• Other causes of respiratory distress e.g. recurrent pulmonary emboli or pneumothorax
• Chest pain (hyperventilation can precipitate angina)
• Cervical spondylosis and nerve compression (where sensory symptoms are unilateral)
• Migrainous vertigo (especially in adolescents with dizziness and headache)⁸

Chronic hyperventilation may mimic many serious organic disorders, but features are often atypical. Patients with exercise-induced hyperventilation are more likely to have a psychiatric than a cardiac disorder. Early detection and treatment of these patients may reduce the potential morbidity associated with unnecessary invasive investigations.⁹

The diagnosis is essentially clinical one but it may be necessary to perform various tests to exclude other conditions:

• Arterial blood gases in an attack may be helpful but pCO₂ can also be measured in end expiratory air. The latter test is more often used as it is less invasive, less painful and so less likely to induce hyperventilation.
• ECG may exclude ischaemic heart disease or arrhythmia and D-dimers and chest x-ray may be required in case of pulmonary embolism or pneumothorax. It may also reveal a prolonged QT interval due to hypocalcaemia during an acute attack.
• Toxicology screen.
• Hyperventilation provocation tests have poor specificity and are of dubious value.¹⁰

• Anxiety can cause hyperventilation, producing symptoms that are interpreted as indicating serious physical illness. This causes more hyperventilation, worse symptoms and a vicious circle.
• Careful explanation of the nature of the condition is needed. Patients may find it difficult to accept the aetiology. Reproducing symptoms with voluntary hyperventilation may be useful.
• Rebreathing into a paper bag can be used to help build up the pCO₂ but this should only be used where the diagnosis is certain as it may be dangerous if there is physical disease.¹²
• Relaxation techniques and breathing exercises may be helpful.¹³ Patients who hyperventilate are often thoracic rather than diaphragmatic breathers and teaching diaphragmatic breathing can help to overcome chronic hyperventilation.
• Treating asthmatics with dysfunctional breathing using a brief physiotherapy intervention (teaching breathing retraining exercises) improves quality of life but this is only maintained in a quarter of patients six months on.¹⁴

Drugs

The basis of treatment should be CBT rather than medication but there may be a place for drugs.

• Benzodiazepines can be used in the acute situation if severe. Use only occasionally as there is the potential for sedation and dependence.
• Propranolol may be of value if asthma has been excluded.
• Tricyclic antidepressants and SSRIs may also be of value.

Treat any associated contributory conditions:

• Approximately 50% of patients with panic disorder and 60% of patients with agoraphobia hyperventilate as part of their disorder but only 25% of patients with hyperventilation syndrome also have panic disorder.
• Other psychiatric disorders e.g. obsessive-compulsive disorders but not all patients have demonstrable psychological pathology.¹⁵

• Mortality attributable to hyperventilation syndrome is vanishingly rare.
• There is significant psychiatric morbidity associated with the syndrome.
• Individuals are at risk of iatrogenic complications from investigation or treatment of wrong diagnosis.

• It tends to be a long term and recurrent condition, especially if it started at an early age.
• Management of associated disorders such as agoraphobia will alter the course of the hyperventilation.
• Treatment with breathing retraining, stress reduction interventions and certain drug treatment (e.g. SSRIs) appear to experience significant reductions in the frequency and the severity of exacerbations.