Continuous positive airway pressure

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Continuous positive airway pressure (CPAP) is the use of continuous positive pressure to maintain a continuous level of positive airway pressure in a spontaneously breathing patient. It is functionally similar to positive end-expiratory pressure (PEEP), except that PEEP is an applied pressure against exhalation and CPAP is a pressure applied by a constant flow.[clarification needed] The ventilator does not cycle during CPAP, no additional pressure above the level of CPAP is provided, and patients must initiate all of their breaths. Nasal CPAP is frequently used in infants[citation needed], though its use is controversial[citation needed]. Studies have shown nasal CPAP reduces ventilator time but an increased occurrence of pneumothorax was also prevalent.[1]

As a treatment or therapy, CPAP uses mild air pressure to keep an airway open. CPAP typically is used for people who have breathing problems, such as sleep apnea.

CPAP also may be used to treat preterm infants whose lungs have not yet fully developed. For example, physicians may use CPAP in infants with respiratory distress syndrome. It is associated with a decrease in the incidence of bronchopulmonary dysplasia. In some preterm infants whose lungs haven't fully developed, CPAP improves survival and decreases the need for steroid treatment for their lungs.

CPAP at home utilizes machines specifically designed to deliver a constant flow or pressure. Some CPAP machines have other features as well, such as heated humidifiers. CPAP is the most effective treatment for obstructive sleep apnea, in which the mild pressure from CPAP prevents the airway from collapsing or becoming blocked.[2]

Settings and measurements[edit]

  • CPAP
This is the pressure applied without pause or end to the airway. Generally utilizing flow to generate the pressure.
  • PEEP
Positive end-expiratory pressure (PEEP) is the pressure in the lungs (alveolar pressure) above atmospheric pressure (the pressure outside of the body) that exists at the end of expiration.
The fractional O2 percentage that is being added to the delivered air.


High flow therapy[edit]

A High Flow Therapy (HFT) device mounted on an IV stand

Humidified high flow nasal airway respiratory support is a method of delivering a high minute volume of respiratory gas via nasal cannula. The respiratory gas is heated to near body temperature and humidified, usually to saturation vapor pressure. This form of respiratory support is generally referred to as High Flow Therapy (HFT). HFT is also referred to as Transnasal Insufflation (TNI),[3] especially when used for treatment of sleep apnea.

Nasal cannula usually used for oxygen delivery usually deliver 1–6 liters of oxygen per minute. The FiO2; the percent oxygen inhaled by the patient, usually ranges roughly from 24% to 35% as 100% O2 delivered from the cannula is diluted with air at about 21% oxygen. Flow rates for delivery of oxygen using typical nasal cannula are limited because medical oxygen is anhydrous, and when delivered from a pressurized source the gas cools as it expands with the drop to atmospheric pressure. Delivery of cold dry gas is irritating to the respiratory mucosa, can cause drying and bleeding of the nasal mucosa, trigger bronchospasm in asthmatics, and can increase metabolic demand by cooling the body. Thus oxygen delivery by nasal cannula is limited to less than 6 liters per minute.[4]

Even with quiet breathing, the inspiratory flow rate at the nares of an adult usually exceeds 12 liters a minute, and can exceed 30 liters a minute for someone with mild respiratory distress. The typical upper limit of oxygen delivery via nasal cannula of six liters a minute does not meet the inspiratory flow rates of the average adult and therefore the oxygen is then diluted with room air during inspiration. Prior to the advent of HFT, when high FiO2 was required for respiratory support special face masks or intubation was required. With HFT, respiratory gas flow volume is delivered which meets or exceeds the patient's inspiratory flow rate, and is heated and humidified, allowing for comfortable delivery of respiratory support.

For HFT, a source of oxygen is usually blended with compressed air. Hospitals usually have 350 kPa (50 psi) compressed O2 and air available for therapeutic use. This allows the delivery of air, blends of air and O2 from 22% to 99%, or delivery of 100% oxygen with the use of an oxygen blender. The gas is then heated, generally to about 37 °C, and humidified to near 100% RH using a humidifier. The gas is transported to the patient through a heated delivery tube to prevent cooling and condensation of the water vapor which has been added to the respiratory gas(es).

HFT requires the use of special nasal cannula and tubing large enough to deliver flow rates of respiratory gas, up to 50 liters per minute in adults. At the same time the nasal cannula must be small enough that they do not seal inside the nares, as this allows flow during exhalation and excess gas flow during inhalation to escape. If the cannula did seal, the high flow volume could produce excessive pressure in the airway and might provoke barotrauma.

Benefits[edit]

Since the delivered flow rate of HFT can meet the inspiration flow rate, the delivered gases are not diluted by room air. The FiO2 is controlled by the clinician, and can be set from 21% to 100% oxygen. Nasal high flow therapy reduces respiratory dead space and generates some positive airway pressure resulting from the expiratory resistance generated by continuous high flow gas delivery. Flow rates exceeding inspiratory demand may also provide positive pressure during inspiration. Heated humidification of the respiratory gas facilitates secretion clearance and decreases the development of bronchial hyper-response symptoms.[5] Some patients requiring respiratory support for bronchospasm benefit using air delivered by HFT without additional oxygen.[6] HFT is useful in the treatment of sleep apnea.[7] During use of HFT the patient can drink, and speak. Most patients find HFT more comfortable than using oxygen masks. As this is a non-invasive therapy, it avoids the risk of ventilator-associated pneumonia in situations where it can supplant the use of a ventilator.

Use in neonates[edit]

Nasal HFT has shown to be useful in neonatal intensive care settings for premature infants with Infant respiratory distress syndrome,[8] as it prevents many infants from intubation, and allows safe respiratory management at lower FiO2 levels, and thus reduces the risk of retinopathy of prematurity or other forms of oxygen toxicity.

Dr. Henrik Verder invented of the INSURE (Intubation Surfactant Extubation) method combined with nasal CPAP (Continuous Positive Airway Pressure).In 1989 he used this pioneering method to successfully treat the first infant with severe RDS.[9]

Criticism[edit]

Critics of HFT point out that while there are many reports of the positive outcomes, little is known about the mechanisms of action of HFT and what levels may be unsafe. There has been concern that HFT delivery settings prescribed are largely empiric, with large variation of pressure produced by HFT between individuals.[10]

Development[edit]

HFT was originally developed for use in race horses.[11]

References[edit]

  1. ^ Morley, C. J.; Davis, P. G.; Doyle, L. W.; Brion, L. P.; Hascoet, J. M.; Carlin, J. B.; Coin Trial, I. (2008). "Nasal CPAP or Intubation at Birth for Very Preterm Infants". New England Journal of Medicine 358 (7): 700–708. doi:10.1056/NEJMoa072788. PMID 18272893.  edit
  2. ^ General Information about Sleep Apnea Machines
  3. ^ McGinley, B.; Halbower, A.; Schwartz, A. R.; Smith, P. L.; Patil, S. P.; Schneider, H. (2009). "Effect of a High-Flow Open Nasal Cannula System on Obstructive Sleep Apnea in Children". Pediatrics 124 (1): 179–188. doi:10.1542/peds.2008-2824. PMC 2885875. PMID 19564298.  edit
  4. ^ Waugh, J. B.; Granger, W. M. (2004). "An evaluation of 2 new devices for nasal high-flow gas therapy". Respiratory care 49 (8): 902–906. PMID 15271229.  edit
  5. ^ Roca, O.; Riera, J.; Torres, F.; Masclans, J. R. (2010). "High-flow oxygen therapy in acute respiratory failure". Respiratory care 55 (4): 408–413. PMID 20406507.  edit
  6. ^ Waugh, J. B.; Granger, W. M. (2004). "An evaluation of 2 new devices for nasal high-flow gas therapy". Respiratory care 49 (8): 902–906. PMID 15271229.  edit
  7. ^ McGinley, B. M.; Patil, S. P.; Kirkness, J. P.; Smith, P. L.; Schwartz, A. R.; Schneider, H. (2007). "A Nasal Cannula Can Be Used to Treat Obstructive Sleep Apnea". American Journal of Respiratory and Critical Care Medicine 176 (2): 194–200. doi:10.1164/rccm.200609-1336OC. PMC 1994212. PMID 17363769.  edit
  8. ^ Shoemaker, M. T.; Pierce, M. R.; Yoder, B. A.; Digeronimo, R. J. (2007). "High flow nasal cannula versus nasal CPAP for neonatal respiratory disease: A retrospective study". Journal of Perinatology 27 (2): 85–91. doi:10.1038/sj.jp.7211647. PMID 17262040.  edit
  9. ^ Verder, H; Agertoft, L; Albertsen, P; Christensen, NC; Curstedt, T; Ebbesen, F; Greisen, G; Hobolth, N; Holm, V; Jacobsen, T (Jul 27, 1992). "[Surfactant treatment of newborn infants with respiratory distress syndrome primarily treated with nasal continuous positive air pressure. A pilot study].". Ugeskrift for laeger 154 (31): 2136–9. PMID 1509593. Retrieved 15 July 2014. 
  10. ^ Kubicka, Z. J.; Limauro, J.; Darnall, R. A. (2008). "Heated, Humidified High-Flow Nasal Cannula Therapy: Yet Another Way to Deliver Continuous Positive Airway Pressure?". Pediatrics 121 (1): 82–88. doi:10.1542/peds.2007-0957. PMID 18166560.  edit
  11. ^ Waugh, Jonathan. "Trends in Noninvasive Respiratory Support: Continuum of Care" (PDF). Clinical Foundations. Retrieved 2014-04-24.