Table of Contents
Historical Background…………………………………………………………………………….3
Basic Principles……………………………………………………………………………………3
Various Sides of the Issue…………………………………………………………………………6
Present Status and Future Prognostication………………………………………………………...7
Conclusion………………………………………………………………………………………...9
References………………………………………………………………………………………..11
Mechanical Ventilation
Mechanical ventilator support is a basic function to support the respiratory status of the critically ill patient. You have probably heard of mechanical ventilation being referred to as life support or a breathing tube. It has been a trending process since biblical times. The first form of negative-pressure support was founded in the 1800’s. The first form of positive-pressure ventilation appeared in the 1900’s and the kind we use today was discovered around the 1940’s. So far, there have been 4 different generations of ventilators since the 1940’s. Each generation builds on the last. The future of mechanical ventilation is bright and the key term to identify these future ventilators will be smart! The ventilators used today have many different functions and principles (Kacmarek, 2011).
Basic Principles There are many basic principles of mechanical ventilation systems. The most commonly used ventilators in today’s Intensive Care Unit (ICU) are positive pressure mechanical ventilation systems. They have many different controls and modes and support functions. The basic principles included in positive pressure mechanical ventilation are airway pressures, volumes, and oxygen.
Airway pressures in positive pressure ventilation supplies a tidal volume to the patient’s lungs under pressure. Air flowing into the lungs acts like fluid and follows the path of least resistance. Due to the fact that most patients being put on a ventilator have some kind of lung abnormality, we have to continuously monitor certain parameters of ventilator. One of these parameters is the peak inspiratory pressure (PIP). This is the maximal airway pressure during the respiratory cycle. Peak pressures typically measures the pressure of the major airways. If there is any sudden or acute change in pressure then we must find the cause since prolonged elevated peaked pressures can cause more trauma to the patient. There is also what is known as plateau pressures which provides the pressure at the end of inspiration and displays the pressure within the alveoli. This parameter is a major determining factor for volutrauma and other major complications. Volumes are another basic function of the ventilator.
The tidal volume (Vt) is described as the amount of air breathed in and out during a respiratory cycle. The normal respiratory tract has several non-perfused areas also known as dead space (V DS). Together the trachea, bronchus, and alveolar components make up dead space because they are not involved in gas exchange. This is important because certain lung injuries, such as a pulmonary embolism, can cause a larger amount of dead space where lung tissue is not performing oxygenation and blood perfusion appropriately. When this happens, it leads to an increased V DS/Vt ratio, resulting in ineffective air ventilation as well as oxygenation. Oxygenation is another very important component to the ventilator.
The percentage of oxygen that exists in the air that is being inhaled by the patient is called the fraction of inspired oxygen (FiO2). Regular air that we all breathe is about 0.21 or 21% FiO2. Patients who require a higher amount of FiO2 (>60%) have the potential of developing oxygen toxicity. Sometimes those patients with acute respiratory problems may require 60% or higher FiO2 to maintain appropriate blood level oxygenation. This should not be prevented at the expense of tissue oxygenation which takes precedence in order to keep that tissue viable. There are many functions that can work directly with these 3 parameters that were discussed. Some of
