BROCHURE CPAP in ambulance service Introductory course This brochure was written in connection with the introduction of CPAP into the ambulance service at University Hospital Northern Norway. The authors of the brochure are Lars-Jøran Andersson, Morten Lyngås Føyen and Johannes Strand. As authors we wish to give special thanks to Ole Magnus Filseth, who made his compendium on respiratory physiology available to us. Portions of this brochure quote directly from it. In addition to this, we have used Knut Dybwik’s book on respiratory treatment as a source for the brochure. Johannes Strand did the layout and design. 2 It has been decided to introduce CPAP into CPAP is an advanced form of care. Knowledge the ambulances at the University Hospital of the indications and contraindications of Northern Norway. is therefore important. Successful CPAP This brochure has been written as part of treatment demands good cooperation this introduction. The brochure will be an between the provider and the patient, introduction about what CPAP is and will and alertness by the provider. Serious provide the necessary basics for using the complications with CPAP are rare and the tool in an ambulance. treatment can, when necessary, be quickly stopped. We believe that CPAP treatment In addition to this, all personnel will receive will be used relatively seldom, but for the a day of training in the CPAP before it is put individual patient the treatment can offer a into service. significant health advantage. It is important Within emergency medicine, CPAP has that one knows the equipment well so that traditionally been a procedure that was the threshold for using it will be low. only available inside the hospital. In the ambulance service, CPAP treatment I n t r o d u c t i o n The reason we wish to start using CPAP will be prescribed by the doctor in the same in the ambulance service is that early way as medicinal treatment. treatment contributes to shorter hospital stays and better care for the patient. What is CPAP and how does it work? CPAP treatment requires that the 2. By displacing pulmonary fluid in lung patient breathes in a closed tubal system congestion. Positive airway pressure that registers a continuous positive airway reduces venous return to the heart pressure. In our case, this will be a CPAP (lowers “preload”). In left ventricle mask that is driven by the oxygen we have failure, the heart’s per minute volume in the vehicles. will increase as a consequence of reduced “preload”. In the ambulance service, CPAP is used for 3. By better lung compliance (respiration patients with serious respiratory failure. The becomes easier and the quantity of CO2 indications will be: Pulmonary edema, in the blood is thereby reduced). It is asthma and COPD. easier for the patient to breathe with CPAP improves oxygenation for a lung that is inflated than when the these patients in three ways: resting volume of the lung is reduced. 1. By causing the patient to breathe with In other words, CPAP works in several ways a higher lung volume, which to improve the patient’s oxygenation. In will increase the diffusion order to have a good understanding surface (reducing of how this works, we must delve shunting). The resting a little deeper into respiratory lung volume (functional physiology... residual capacity - FRC) increases and atelectatic tissue (collapsed lung tissue) is inflated and atelectasis is prevented from reforming. Don’t worry, Some unfamiliarthe words explanation and expressions? is coming ;-) 3 Anatomy and physiology Airways the alveoli are covered with a lipoprotein The upper and lower airways have the task (surfactant), which reduces the surface tension of conducting air to and from the lungs. and thereby prevents the alveoli from closing at In addition, they take care of filtering, the same time that it ensures that they don’t also warming and humidifying the air. over-distend. The lungs are very elastic and can be compared Lungs to a rubber band. A network of elastic fibers is The inner surface of the lungs of an adult found all over the lungs. From the person has an area the size of a tennis court. resting position of the lungs, this The primary tasks of the lungs can be can be stretched out and filled divided into three main functions; with air. For this to happen, the oxygen uptake, carbon dioxide force that will expand the lung elimination and pH regulation. must overcome the elastic The alveoli are covered with a single forces of the lung tissue. layer of flat epithelial cells which form a In addition, there is the thin membrane between the air in the alveoli elastic resistance found in and the blood in the capillaries. In addition, the chest wall. Inspiratory reserve volume Vital capacity approx. 5000 ml approx. 3000 ml Tidal volume at rest is approx. 500 ml Expiratory reserve volume approx. 1500 ml Residual volume approx. 1000 ml A healthy adult male has a total lung If you add ERV and RV you get capacity (TLC) of approx. 6 liters, functional residual capacity (FRC), that is, the quantity of air found in the which is the normal resting volume lungs after maximal inspiration. of the lungs. (During CPAP The tidal volume (TV) is the volume treatment, FRC is increased.) If that is inspired in normal respiration after normal inspiration you and is approx. 0.5 liter. continue to breathe in as much as you can, you obtain an inspiratory After normal expiration, a healthy reserve volume (IRV), that is adult male could expire approx. 1.5 approx. 3 liters. liter. This is called expiratory reserve volume (ERV). Lung capacity and volume What is left in the lungs is called residual volume (RV). 4 The elastic forces in the lungs and chest wall during expiration The organism’s oxygen supply depends (breathing out) contract the lung upon its ability to take up oxygen and back into the resting position. the ability to transport it out of the body. Under normal circumstances, the oxygen Expiration is therefore normally a supply depends upon the following factors. passive act. In technical literature, 1. Hemoglobin level the term compliance is used for 2. Oxygen saturation the lungs’ elasticity. 3. Cardiac minute volume In order to obtain an adequate supply of oxygen, it is often possible to influence these three factors even by simple means The body’s oxygen supply The oxygen body’s outside of the hospital. Words and Expressions... Hypoxia: Hemoglobin (Hb): Reduction of the oxygen supply in the Oxygen-bearing molecules in tissues, despite adequate blood supply, erythrocytes. Every hemoglobin molecule is usually due to hypoxemia. can bind to four O2 molecules. Each gram Hypoxemia: of hemoglobin can bind to 1.34 ml of oxygen. If we want to indicate whether Reduced oxygenation of the blood causes hemoglobin is bound to oxygen or not, we Respiratory physiology hypoxia. In practice, hypoxemia and can distinguish between oxyhemoglobin hypoxia are often used interchangeably. (oxygen is bound) and deoxyhemoglobin. Ischemia: The quantity of hemoglobin in the body is Lack of oxygen in tissue, which is due normally 11.5 - 17 g/dl. to reduced blood supply in the tissue, SaO2: as for example in angina pectoris. Oxygen saturation in arterial blood. Asphyxia: When all hemoglobin in the blood is Lack of oxygen in the inspired air, or saturated with oxygen, SaO2 is 100%. If absence of air to breath, synonymous SaO2 is, for example, 60%, this means with asphyxiation. that 60% of the binding sites for oxygen Hypercapnia: are bound to oxygen. Increased quantity of CO2 in the SpO2: blood, synonymous with hypercapnia. The designation for arterial oxygen Hypercapnia is a strong stimulus to saturation when it is measured in increase respiration. Attempt to hold the peripheral arterial blood using a your breath while you measure oxygen pulse oximeter. The pulse oximeter saturation and you will experience a distinguishes between oxygenated and strong need to inhale before oxygen deoxygenated hemoglobin using light saturation falls. with different wave lengths. Hypocapnia: With correct use and interpretation, Reduced quantity of CO2in the blood, SpO2 will correspond to SaO2. for example, a hyperventilating episode. 5 Functional residual capacity (FRC) is the FRC is reduced also by general anesthesia quantity of air that is left in the lungs after (narcosis) because of the loss of muscle tone in normal expiration. When you breathe out and the diaphragm. reach FRC, you are doing fine. You can then In a normal healthy young adult all of the lung’s begin to breathe in, which will be both easy segments will be open at the end of a normal and natural. You can also choose to continue expiration. But when we breathe out to the to breathe out until you reach residual volume, maximum, the small airways that exist farthest which is the amount of air which is left in the down in the lungs are closed. This is called static lungs after maximum expiration; it will feel airway collapse. The lung volume at which this heavier. Ordinarily we do not think about when occurs is called closing capacity. We do not need we should stop breathing out and begin to to worry about this as long as it occurs after we breathe in, this is controlled by the respiratory have reached the functional residual capacity in center in the brainstem. expiration. Thus we choose unconsciously when we should Closing capacity is determined by the lung tissue’s begin to inhale. Even though the choice is elastic properties. Closing capacity can be highly unconscious, it is sensible and oriented toward elevated in COPD.