Respiratory failure is caused by a disturbance in gas exchange on the alveolar level or a disturance of pulmonary ventilation, or - in most cases - by both. The former leads to hypoxemia, the latter to hypercapnia.
The condition derives from a disturbance in the function of the respiratory centre or in the function of the nerves, respiratory muscles, chest, lungs or pulmonary circulation that play a role in breathing. The condition may be acute or chronic.
Acute symptoms include subjective breathing difficulty, increased work of breathing, restlessness/anxiety, confusion and disturbances of consciousness. Symptoms of chronic respiratory failure include dyspnoea, restless sleep, daytime fatigue, cyanosis, polycythaemia and signs of increased workload of the right heart.
A pulse oximeter reveals a disturbance in the gas exchange (hypoxemia), but not impaired ventilation (hypercapnia), the detection of which requires determination of carbon dioxide concentration by arterial blood gas analysis, capillary sample or skin carbon dioxide measurement.
In an acute situation, it is most important to ensure an open airway and adequate oxygen supply to the tissues, and to rapidly begin the symptomatic treatment of the underlying cause.
In chronic respiratory failure, the primary treatment is assisting ventilation with a bilevel positive airway pressure (BiPAP) ventilator, combined, as necessary, with oxygen therapy.
Definitions
Respiratory failure usually means disturbance in gas exchange between ambient air and arterial blood (arterial blood pO2< 8 kPa, arterial blood pCO2> 6.0 kPa; see Blood Gas Analysis and Acid-Base BalancePulse Oximetry.
It is usually divided into two main types:
disturbance of gas exchange at the alveolar level (hypoxaemia as the primary problem)
impaired pulmonary ventilation, i.e. hypoventilation (hypercapnia as the primary problem)
In acute hypoventilation, the increase in carbon dioxide concentration is associated with respiratory acidosis (aB-pH < 7.35).
In chronic hypoventilation the pH is normal.
Acute respiratory failure
In acute respiratory failure, either a disorder in oxygenation, accumulation of carbon dioxide, and/or an increased breathing workload cause a disturbance in body equilibrium that requires immediate care.
In practice, most patients have at the same time features of disturbance in gas exchange and of hypoventilation, and the breathing workload is increased as regards to the patient's reserves.
Treatment aims at ensuring sufficient gas exchange, i.e. tissue oxygenation and elimination of carbon dioxide, and tolerable breathing workload.
Aetiology
Respiratory centre depression
Overdose of drugs (opioids!), intoxications
A disease in the central nervous system
Unconsciousness from various causes
Incautious oxygen therapy for a patient with chronic hypoventilation
Nerve impulse is not transmitted to respiratory muscles
Spinal cord injury
Myelitis
Infections (tetanus, poliomyelitis, botulism)
Neurolomuscular diseases (myasthenia gravis, motoneuron diseases, muscular dystrophies): usually chronic hypoventilation with an acute exacerbation, e.g. during a respiratory infection
Polyradiculitis
Impaired ventilation mechanics
Crush injury of the thorax, tears of the diaphragm
Severe kyphoscoliosis ( usually chronic hypoventilation with an acute exacerbation, e.g. during a respiratory infection)
Severe obesity (obesity hypoventilation syndrome, also known as Pickwickian syndrome; usually chronic respiratory failure which is acutely worsened e.g. during a respiratory tract infection)
Restlessness, confusion, and disturbances of consciousness
Increased breathing workload, use of accessory respiratory muscles, increased respiration rate
Investigations
Peripheral oxygen saturation with a pulse oximeter (SpO2) Pulse Oximetry
Good in detecting hypoxaemia but does not detect hypercapnia caused by hypoventilation
The treatment goal must be adjusted according to the patient and to the situation.
Usually values > 90% are sufficient. In acute situations, the goal is in the range of 94-98% if the patient is not prone to carbon dioxide retention (NB patients with COPD).
Note: a patient receiving supplemental oxygen may have severe hypoventilation and high concentration of arterial carbon dioxide (aB-pCO2) even though peripheral oxygen saturation is > 90%.
Arterial blood gas analysis
Provides a more accurate estimate of oxygenation (pO2> 8 kPa is usually sufficient).
Essential in recognition of hypoventilation (pCO2 level)
In acute hypoventilation, pCO2 rises to > 6 kPa and the patient has concomitant respiratory acidosis.
Acidosis with pH < 7.35 calls for treatment measures.
Investigations required to identify the cause of the respiratory failure
Basic principles of treatment
The primary therapeutic aim is to maintain adequate tissue oxygenation. Keep in mind all the following aspects: oxygenation of arterial blood, cardiac output and the oxygen carrying capacity of the blood (haemoglobin concentration).
Always ensure unobstructed airways.
At the same time, start without delay causal treatment for the condition underlying the respiratory failure (e.g., medication for pneumonia, heart failure, airway obstruction).
Supplemental oxygen therapy (oxygen concentration of the air inhaled = FiO2 is raised to above 0.21)
Carried out in a controlled manner (monitoring with pulse oximeter) aiming at sufficient correction of oxygen deficit but avoiding over-correction especially if the patient has chronic hypoventilation.
Use e.g. a Venturi mask (28-40%), nasal cannulas or high-flow oxygen device (21-100%) for patient interface.
The goal for arterial oxygen partial pressure increase is 8-10 kPa and for oxygen saturation over 90%.
In case of COPD exacerbation the goal for oxygen saturation is 88-92% or the patient's known normal level.
Treatment with continuous positive airways pressure (CPAP)
Increases lung volume, keeps upper airways patent, opens collapsed airways, improves gas exchange and decreases breathing workload but does not assist respiration mechanically.
The patient must have sufficient own breathing capacity left.
Primary treatment in cardiogenic pulmonary oedema Positive Pressure Airway Support for Cardiogenic Pulmonary Oedema, pneumonia and other disturbances in gas exchange when supplemental oxygen is not sufficient but hypoventilation has not developed (pCO2> 6 kPa)
Treatment with mechanical ventilation
Mechanically assists and maintains respiratory activity, diminishes respiratory workload, increases lung volume, helps in opening collapsed airways, intensifies ventilation and enhances gas exchange.
If only possible, carry out without an artificial airway.
Bilevel positive airway pressure ventilation (BiPAP, also BPAP) is the primary method in exacerbations of COPD and in other hypercapnic respiratory failures when the situation does not require immediate intubation.
When BiPAP therapy is started in good time it will reduce the need for an artificial airway and complications related to such.
In an exacerbation of COPD, BiPAP is started when arterial blood pH is < 7.35 and arterial carbon dioxide (aB-pCO2) > 6-6.5 kPa (or higher than the patient's normal level).
BiPAP is the primary treatment option in acute respiratory failure in immunosuppressed patients.
The patient must have sufficient spontaneous respiration.
Use a face mask of the pressure supported ventilation type (BiPAP).
Intubation and invasive respirator treatment is usually necessary in
severe disturbance in gas exchange (e.g. ARDS)
severe hypoventilation (pH < 7.20) and the patient is in active treatment
need of an artificial airway to ensure airway patency (unconscious patient)
patients with insufficient spontaneous respiration.
Invasive respirator treatment is carried out in a monitoring / intensive care unit. BiPAP treatment can also be carried out on a ward with appropriately trained staff.
It is beneficial for patients with COPD to use BiPAP ventilation directly after extubation when weaning from invasive respirator treatment.
Initiation of invasive ventilator treatment does not belong to the treatment options in the terminal life phase of a patient with a severe primary disease.
Chronic respiratory failure
Chronic respiratory failure may be divided into two main types in the same manner as acute respiratory failure (see definitions); both types may co-exist.
Arterial pCO2 is > 6 kPa and/or pO2< 8 kPa; pH is normal.
In chronic hypoventilation, hypercapnia appears first and is accentuated during sleep.
Disturbance of gas exchange is manifested as chronic hypoxaemia and is usually associated with chronic pulmonary diseases (COPD, pulmonary fibrosis).
Chronic hypoxaemia is treated with continuous oxygen therapy (oxygen therapy at home).
The background of chronic hypoventilation is usually in a long-term disturbance in alveolar ventilation.
Aetiology
Long-term or permanent disturbance in the functions of the respiratory centre, the nerves controlling respiration, respiratory muscles, thorax, or the lungs.
Chronic hypoventilation often gets acutely worse during respiratory infections.
The most common diseases leading to chronic hypoventilation include
COPD
neuromuscular diseases (e.g., ALS, muscular dystrophies, dysfunction of the diaphragm)
diseases that restrict the mobility of the thorax (kyphoscoliosis and other deformities of the thorax, sequela of polio, severe ankylosing spondylitis, morbid obesity)
severe sleep apnoea and hypoventilation associated with obesity (obesity hypoventilation syndrome, or Pickwickian syndrome).
Diagnostics
Symptoms and signs
Dyspnoea, cyanosis, polycythaemia, symptoms and signs of right cardiac load
Symptoms that point to night-time hypoventilation
Restless sleep, morning headache and drowsiness
Day-time tiredness and fatigue
Deterioration of memory and concentration
Recurrent acute episodes of respiratory failure
Investigations
Arterial blood gas analysis
In awake state: oxygen (pO2) < 8 kPa and/or carbon dioxide (pCO2) > 6 kPa, pH normal, BE and HCO3 increased
Night-time oxygen saturation (SpO2) recording with pulse oximeter, and recording of skin carbon dioxide concentration (PtcCO2). The following values suggest night-time hypoventilation:
night-time oxygen saturation at least 20% of the time < 90%, and the lowest values < 85%
night-time PtcCO2 increased (> 7-8 kPa).
Spirometry (in sitting and recumbent position)
Maximal inspiratory and expiratory pressures
Respiratory rate at rest
General treatment principles
Oxygen therapy used alone may make the hypoventilation worse.
The primary treatment is assisted ventilation using a ventilator (BiPAP ventilation).
Assisted ventilation is required primarily during sleep/night-time, and night-time only ventilator support with mask often is sufficient therapy.
The aim of BiPAP treatment is to prevent respiratory depression during sleep, to relieve symptoms associated with night-time hypoventilation, to improve the quality of sleep, to positively affect day-time performance and to reduce acute episodes of respiratory failure.
Supplemental oxygen may be combined with BiPAP treatment, as necessary.
BiPAP ventilation, when assisted ventilation during night-time/sleep is sufficient.
Invasive ventilator treatment through tracheostomy, when assisted ventilation is required for at least 15 h/24 hours (for example, sequela of a high-level spinal cord injury) or the mask ventilation is not suitable or is no more sufficient.
The arrangement of a long-term invasive ventilator treatment at home may require some kind of formal health authority decision of respiratory paralysis.
Other treatment options
Phrenic nerve pacing
In central hypoventilation when the functions of diaphragm and phrenic nerve are intact and the mobility of the thorax is good.
Respiratory stimulators
An option when home ventilator treatment is not suitable
Most experience and evidence has been gathered about medroxyprogesterone (respiratory failure in postmenopausal women), acetazolamide and almitrine.
References
Masa JF, Pépin JL, Borel JC, et al. Obesity hypoventilation syndrome. Eur Respir Rev 2019;28(151). [PubMed]
Rochwerg B, Brochard L, Elliott MW, et al. Official ERS/ATS clinical practice guidelines: noninvasive ventilation for acute respiratory failure. Eur Respir J 2017;50(2). [PubMed]