Continuous positive airway pressure (CPAP) therapy is the maintenance of a positive airway pressure greater than ambient pressure throughout inspiration and expiration. It can be delivered through a facemask, nasal mask or mouthpiece, or through an endotracheal or tracheostomy tube.
Related theory Continuous Positive Airway Pressure (CPAP)
The use of the CPAP circuit dates back to at least 1912 when Bunnell used a primitive circuit during thoracic surgery. The first recorded use in intensive care was by Poulton and Oxon in 1936. In the 1940s increased interest in CPAP was prompted by research into respiratory support in high-altitude flying. Further developments occurred in the 1950s and 1960s, and in 1976 Greenbaum et al. reported the use of CPAP with a facemask in adult respiratory distress syndrome. In 1972 Williamson and Modell successfully used CPAP for selected spontaneously breathing patients with acute respiratory failure. For treatment of acute pulmonary edema, CPAP alone is very effective.
Non-invasive ventilation
Non-invasive ventilation (NIV) refers to mechanical ventilatory support applied without an artificial airway (endotracheal tube or tracheostomy). It can be delivered to the patient via nasal cannulas, facemask or helmet. The patient must be conscious and cooperative for this type of ventilation to be effective. NIV has the advantage of avoiding the need for tracheal intubation, thus reducing rates of mortality and morbidity. It can be used for patients who do not require immediate intubation or for palliative patients where invasive ventilation may not be deemed appropriate and is particularly useful in patients with chronic respiratory disease.
• In restrictive pulmonary disease, for example, muscular dystrophy.
• In progressive neuromuscular disease, for example, motor neurone disease.
• In obstructive pulmonary disease, for example, COPD, bronchiectasis, cystic fibrosis.
• In nocturnal hypoventilation.
• In patients with acute exacerbation of the chronic respiratory disease.
• In patients in whom endotracheal intubation and ventilation may not be considered appropriate or where difficulties may be anticipated in weaning a patient from a ventilator.
Non-invasive ventilators generally fall into two categories:
• pressure preset machines
• volume preset machines.
Mechanical ventilation
A mechanical ventilator is a device used to replace or assist breathing in order for satisfactory gas exchange to take place. The decision to ventilate a patient will be made after careful clinical examination, including assessment of respiratory mechanics, oxygenation, and ventilation.
Ventilators are able to control tidal volume, respiratory rate, time of inspiration against the time of expiration, inspired flow rate and inspired oxygen concentration.
Negative pressure ventilators
These devices are now rarely used. They mimic normal breathing (negative pressure) and are known as iron lungs. The patient is enclosed in an airtight tank and negative pressure is created by a separate pump which causes the alveolar pressure to fall within the lungs so a pressure gradient results, with air flowing into the lungs along the pressure gradient in order for ventilation to take place. An adaptation from the tank ventilator is the cuirass shell, which surrounds the thorax and abdomen and works on the same principle. The rare use of these devices would be in patients with chronic respiratory failure (neuromuscular disease, skeletal deformity or sleep-related respiratory problems). Ventilators are divided into two main categories: negative pressure and positive pressure.
Positive pressure ventilators
These devices provide a satisfactory gas exchange when inflating the lungs with a positive pressure via an endotracheal tube or tracheostomy.
Positive pressure ventilators have four main functions to perform during each respiratory cycle.
• Inflate the lungs.
• Cycle from inspiration to expiration.
• Allow expiration to take place.
• Cycle from expiration to inspiration.
They have a driving mechanism and can cycle from one phase of the respiratory cycle to another by a preset pressure, preset time or preset volume.
Varying modes of ventilation can be used.
• Volume controlled, e.g. synchronized intermittent mandatory ventilation (SIMV).
• Pressure controlled, e.g. bilevel positive airway pressure (BiPAP), SIMV.
• Spontaneous/assisted ventilation, e.g. CPAP/bilevel NIV (CPAP ASB).
Hyperbaric respiratory therapy
Hyperbaric respiratory therapy is used mainly in the treatment of carbon monoxide poisoning, burns, gas gangrene, skin lesions, soft tissue injury, decompression sickness (the bends) and multiple sclerosis. The therapy is designed to give 100% oxygen at a range of pressures greater than atmospheric pressure. Oxygen is dissolved in the plasma, increasing the oxygen tension in the tissues.
Evidence-based approaches
The aim of CPAP therapy is to improve gas exchange (oxygen and carbon dioxide) within the lungs and improve the work of breathing. CPAP is able to do this by:
• increasing the functional residual capacity (FRC), which is the amount of gas left in the lungs at the end of normal expiration available for pulmonary gas exchange. In acute lung injury where the gaseous exchange is severely inhibited, CPAP increases the FRC by reopening collapsed alveoli and improving ventilation and oxygenation.
• improving the ventilation/perfusion ratio: decreased intrapulmonary shunting with hypoxia could cause ventilation to the lungs to be reduced or blood flow to them impaired. Intrapulmonary shunting can then occur with underventilation of the lungs. CPAP helps to decrease intrapulmonary shunting by improving the ventilation/perfusion mismatch.
• improved lung compliance (elasticity) of the lungs: in respiratory failure, the lungs become much stiff er and less compliant and breathing can become more difficult. Reduction in lung volume below a certain level results in airway collapse and underventilation. The increase in transpulmonary pressure required to overcome this can be achieved by CPAP.
• increasing lung volume (alveolar volume) for gaseous exchange to take place. The factors above enable an increase in the surface area of alveoli available for gas exchange. As a result, the work of breathing and the percentage of oxygen required may be reduced.
Rationale
Continuous positive airway pressure is the maintenance of a positive pressure throughout the whole respiratory cycle when breathing spontaneously. CPAP provides an additional therapy between conventional oxygen therapy and controlled ventilation. It helps prevent atelectasis, reduce the work of breathing and eliminate or reduce hypoxia whilst allowing the normalization of the FRC. Other benefits include the preservation of the ability to speak, cough, clear secretions and swallow whilst warming and humidifying inspired air via natural upper aiway mechanics.
Indications of Continuous Positive Airway Pressure (CPAP)
Continuous positive airway pressure is usually commenced to improve lung expansion. CPAP is also indicated in the presence of clinically significant pulmonary atelectasis when other forms of therapy, such as HFOT, incentive spirometry, chest physiotherapy and deep breathing exercises, have been unsuccessful.
• Acute respiratory failure
• Hypercapnic acute respiratory failure.
• Acute exacerbation of COPD.
• Post-extubation difficulty.
• Weaning difficulties.
• Post-surgical respiratory failure.
• Thoracic wall deformities.
• Cystic fibrosis.
• Status asthmaticus.
• Acute respiratory failure in obesity hypoventilation syndrome and obstructive sleep apnoea.
• Chronic respiratory failure.
• Chronic heart failure.
• Immunocompromised patients.
• Neuromuscular disease.
• Patients ‘not for intubation.
• Hypoxaemic acute respiratory failure.
Contraindications of Continuous Positive Airway Pressure (CPAP)
• Recurrent pneumothoraces/untreated pneumothorax – may contribute to barotraumas.
• An inability to protect their own airway.
• Vomiting or excessive secretions and a high risk of aspirating.
• Severe postoperative pulmonary air leak.
• Central apnoea.
• Epistaxis.
• Any condition where an elevated intracranial pressure is undesirable or where reduction in cerebral blood flow is inappropriate.
• Any situation where there is already significant lung overdistension.
• Unstable facial fractures, extensive facial surgery or lacerations and facial burns.
• Laryngeal trauma, recent tracheal anastomosis.
• Recent ear, nose and throat surgery.
• Basilar skull fracture – at risk of pneumocephalus.
Methods of delivering CPAP
Continuous positive airway pressure can be delivered by nasal mask, facemask or helmet.
Anticipated patient outcomes
• Ability to wean patient off CPAP mask and improvement of respiratory status with lower oxygen requirements.
• For lung expansion therapy, a minimum delivered tidal volume of at least one-third of the predicted inspiratory capacity (IC) (1/3 × 50 mL/kg) has been suggested. This corresponds to approximately 1200 mL in a 70 kg adult patient.
• An increase in peak flow.
• Cough more effective with treatment and secretion clearance enhanced as a consequence of deep breathing and coughing.
• Chest radiograph improved.
• Breath sounds improved.
Legal and professional issues
Competencies Close and thorough clinical assessment is of paramount importance when caring for a patient receiving CPAP or NIV. Physiological monitoring is not a substitute for clinical assessment and observation of the patient on the ventilator should be carried out regularly. Nursing staff caring for patients requiring CPAP ventilation would therefore need to be trained in advanced respiratory care or work in areas such as the high-dependency unit (HDU) or critical care unit (CCU) setting.
Pre-procedural considerations
Care of patients with CPAP should be provided in HDU or CCU settings with cardiac and respiratory monitoring equipment. CPAP should be considered only with a co-operative patient who can control their airway and secretions with an adequate cough reflex. The patient should be able to coordinate breathing with the ventilator and breathe unaided for several minutes if CPAP is delivered via a ventilator.
Equipment
• Flow generator with variable flow such as WhisperFlo. A means of generating a flow of pressurized breathable gas at variable rates and oxygen concentrations.
• CPAP mask (two-port type) or CPAP helmet with securing straps.
• Bacterial-viral filter ( not an HME). Provides protection against various types of particles including bacteria, viruses and water droplets. The filter helps protect the patient, the equipment and the breathing circuit from contamination.
• Aerosol tubing.
• Oxygen analyzer and T-piece.
• CPAP positive end-expiratory pressure (PEEP) valve of prescribed level.
• Higher rated CPAP valve (+20 cmH 2O) and T-piece (if using WhisperFlo device).
• Water humidification chamber (heated wire).
Warms and humidifies inspired gas to core temperature and 100% relative humidity, which maximizes mucociliary clearance and prevents inflammatory reactions while sustaining airway patency and lung compliance. (If the humidifier is used a patient section and 1 litre bag of water for inhalation will be required.) In some departments, a complete circuit is available with all of the disposable items provided in one kit.
Assessment and recording tools
While on CPAP, it is essential to monitor the patient’s cardiovascular status, respiratory rate, capnography (EtCO 2), pulse oximetry and fluid balance at least hourly as well as regular ABG sampling.
Clinical features that should be assessed are
• chest wall movement
• co-ordination of respiratory effort with the ventilator
• accessory muscle recruitment
• general assessment – patient sweating/clammy/dyspnoeic
• auscultation of the chest
• patient comfort
• neurological status – signs of confusion/tiredness.
The patient receiving NIV or CPAP should be fully monitored:
• heart rate and rhythm
• respiratory rate
• blood pressure
• oxygen saturation measured by pulse oximetry.
It has been reported that oxygen levels improve rapidly on NIV so it is important to measure SpO 2 continuously in the first 24 hours, aiming to keep it >95% with supplemental O 2. All the above observations need to be documented on the observation chart or HDU observation chart as applicable.
Essential equipment
• Drager bellows or similar high-flow oxygen delivery system.
• Compressed air supply.
• CPAP helmet or mask.
• CPAP circuit.
• Humidification system (mask only) with temperature control.
• Flowmeter.
• Oxygen analyzer.
• Pulse oximetry.
• Nasogastric tube.
• Urinary catheter.
Procedure Guideline of Continuous Positive Airway Pressure (CPAP)
| Assess patient’s conscious level. | To obtain a baseline and to be able to assess for change in condition. |
| Explain the principles of CPAP to the patient and family and demonstrate the system to them. Observe and record the following. (a) Patient’s respiratory function (b) Respiratory rate (c) Work of breathing (d) Colour, skin and mental status (e) Tissue oxygen saturation (SaO 2 ). | To gain consent, minimize anxiety, increase knowledge and aid in patient compliance. To obtain a baseline of respiratory function. To observe for any change in respiratory function. A reduction in the level of consciousness or altered mental status may indicate hypoxemia. |
| Decide whether it is appropriate to insert an arterial cannula. | In order to monitor the acid/base balance. |
| Observe and record the patient’s cardiovascular function, including: (a) heart rate (b) blood pressure (c) temperature (d) central venous pressure (if patient has a central venous access device). | To obtain a baseline in order to assess any change in conditions. |
| Assess fluid balance. (a) Input (b) Output (c) Accumulative balance (d) Overall fl uid balance (e) Daily weight | To obtain a baseline of fluid balance. To enable assessment of dehydration or fluid overload. |
| Assess the patient’s level of anxiety and compliance with treatment (the patient’s ability to cope with the treatment). | To enable an assessment to be made and an evaluation of the suitability of CPAP therapy. |
| Set up CPAP circuit. | To prepare equipment for use |
| Ensure the patient is in a comfortable position, sitting up in bed at a 45° angle or more or in a chair well supported by a pillow. | To promote comfort and aid lung expansion and breathing |
| Explain to the patient how the helmet or mask is to be applied. | To relieve anxiety and to reassure patients. To aid patient’s compliance with CPAP. |
| Apply helmet/mask gently, applying pressure as the patient adapts to the tight-fitting mask. Hold mask until the patient is comfortable and settled. | To relieve anxiety and to reassure patients. To aid patient’s compliance with CPAP. |
| Once the patient is settled with mask/helmet, apply the head strap or shoulder straps. Ensure mask/helmet and head strap are comfortable for the patient; alter position as required. | To retain mask in place and aid patient comfort (Keilty and Bott. |
| Ensure a good seal and that no leaks are present. | To ensure a tight seal in order that the system functions optimally |
| Apply tissue-protective dressing around vulnerable pressure points: nose, ears, back of head and neck. | To alleviate pressure and prevent tissue breakdown. |
| Give a further explanation to family/next of kin of how CPAP works and the importance of their presence and participation in communication. | To relieve anxiety and support and reassure family and patient. |
| Reassure the patient constantly. | To relieve patient anxiety and promote co-operation. |
| Discuss with doctor use of medication that might aid patient compliance with CPAP therapy and administer as necessary. | Prophylactic administration of small doses of anxiolytic can aid compliance with CPAP therapy. |
| Continue observation of vital signs and work of breathing. If patient is tiring, notify doctor. | To prevent acute respiratory deterioration or to inform the doctor in a timely manner in order to intubate the patient to avoid a respiratory arrest situation. |
| Continue documenting NEWS score in order to flag up deterioration quickly. | To prevent acute respiratory deterioration or to inform the doctor in a timely manner in order to intubate the patient to avoid a respiratory arrest situation. |
Problem-solving Prevention and Solutions of Continuous Positive Airway Pressure (CPAP)
| Problem | Cause | Prevention | Suggested action |
| Maintenance of airway. | Deteriorating respiratory function. Physical tiring. | Use of NEWS scoring to identify deterioration. | Regular monitoring of respiratory function including skin colour,1 breathing pattern, respiratory rate, oxygen saturation, blood gases. Discuss changes with medical or anesthetic staff. |
| Inability to eat. | Gastric distension due to CPAP. Loss of appetite. Difficulty in eating; distress caused by respiratory status and CPAP. Nausea and vomiting. | Provide small but regular easily managed (soft) oral diet or supplement drinks. | Encourage diet and oral supplementary fluids. If unable to take orally, refer to a dietician as an alternative method of feeding may be considered, for example, enteral feeding via a nasogastric or jejunal tube or intravenous feeding (PN). Administer antiemetic. Encourage and reassure the patient. |
| Aspiration, if unable to maintain own airway. | Inability to maintain own airway. Continuous pressure from CPAP system. Insufflation of air. | Seek SLT assessment. Keep NBM and insert nasogastric tube. Insert nasopharyngeal tube | Observe and assess patient closely. After discussion with medical staff , a a nasogastric tube may be inserted to reduce gastric distension. |
| Dry mouth. | CPAP system utilizes a very high oxygen fl ow which has a drying effect. | Provide adequate oral hydration. | Carry out regular mouthcare. Give patient regular sips of water, ice to suck or drinks as patient is able to take. Humidify, as in CPAP circuit. |
| Eyes (only applies to facemask CPAP): Dry Sore Conjunctival edema | Mask: air leak. High-flow oxygen. Facial pressure from mask causing edema. | Protect eyes from drying out. Use the correct size of mask/helmet for patient. | Ensure mask/helmet is well sealed with no leaks. Apply pressure-relieving padding around the mask. Apply regular eyecare (see Chapter 8 : Patient comfort and end-of-life care). Adjust mask to facial contour. Alter and position mask as comfortably as possible. Position padding around the head strap to relieve pressure. |
| Mask/helmet incorrectly sealed. | Incorrect size of mask or helmet. | Use appropriate size mask/ helmet. | Alter mask/helmet position to correct and ensure comfort. Ensure mask/helmet is the correct size. Alter position to ensure a correct seal. |
| Non-compliance with CPAP equipment. | Anxiety. | Calm, informative communication. | Inform the patient of any changes taking place. Communicate with the patient’s family, keep them informed and involve them in care and communication with patient. Inform doctor of patient’s anxiety level. Administer prescribed anxiolytic agent if required. |
| Helmet not inflating or patient finding it difficult to breathe with mask. | Disconnection of tubing. Not connected to piped oxygen. | Switch on all audible alarms on equipment. Clarify alarm parameters with medical/senior nursing staff. Keep bed space tidy and free from clutter. If possible, ensure bed space is close to/visible from nurse station. | Ensure nurse present with patient at all times. Observe patient and CPAP system closely to ensure equipment is working optimally and there is no failure of the system. |
| Inability to communicate effectively. | Mask/helmet restriction. | Provide means of non-verbal communication. | Reassure patient and ensure they are comfortable. |
| Feelings of isolation. | Ask relative/carer/HCA to stay with patient. | Encourage patient to communicate and explain how they can use letterboard to do so. Reassure patient. |
Complications of Continuous Positive Airway Pressure (CPAP)
With any circuit that includes the use of PEEP, there is the possibility of a reduction in cardiac output. However, spontaneous ventilation decreases both the incidence and severity of this complication. There is also a risk of vomiting and aspiration of gastric insufflation (blowing of air causing gastric distension), although this is minimized when used in awake patients or by the insertion of an oro/nasogastric tube. Patients requiring CPAP should ideally be in an HDU setting so a higher level of observations can be maintained. Preventive pressure dressings should be considered in underweight patients or those with bony facial prominences, in addition to regular skin checks to ensure that the tight-fitting facemask required for CPAP is not compromising the skin integrity of vulnerable areas on the bridge of the nose and over the ears.
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