Ventilators and the Treatment of ARDS

 

The primary treatment of ARDS involves supportive care in an intensive care unit (ICU), including use of a mechanical ventilator and supplemental oxygen to help patients breathe. The goal of mechanical ventilation is to support the patient's breathing during the time needed for the patient's lungs to heal. ARDS patients can be deeply sedated into a drug-induced coma and sometimes intentionally paralyzed (although the use of paralytic drugs is currently used less frequently) to prevent them from fighting the ventilator and to ensure all available oxygen is made available for the functioning of critical organs. Patients may be placed on a special bed, such as an "air bed" or a rotating bed to position them properly to help prevent complications such a bed sores and pneumonia. There are no currently established standard medication treatments for combating ARDS itself. Most medication treatments are oriented toward the underlying medical problems which the patient is battling, such as sepsis and trauma. In addition, other common medications which may be employed during the battle with ARDS include sedating drugs, paralyzing drugs, anti-anxiety medication, and antibiotics to combat or stave off infections. These medications do not directly battle ARDS in a medical sense, rather they are supportive in the battle against ARDS to allow the lungs to heal in hopefully the best medical and physical situation possible considering the underlying medical problems and the severity of the ARDS. Mechanical ventilators deliver breaths of oxygen enriched air to the body and remove breaths of carbon dioxide produced by the body, to maintain enough oxygen in the bloodstream while patients recover from ARDS and their other injuries or illness. A ventilator can breathe completely for a patient or assist a patient's own breathing. Ventilators deliver their oxygen enriched breaths through an artificial airway or endotracheal tube. The tube is connected to the ventilator. While in place, the tube temporarily interferes with the patient's ability to speak since it passes between the vocal cords. Positive end-expiratory pressure (PEEP), is a special setting on the ventilator that keeps the lungs expanded to help get oxygen from the lungs into the bloodstream. Most often and common, the tube is inserted through the mouth or nose. Sometimes, however, depending on the severity of the ARDS and the patient's ability to tolerate ventilation through the mouth (that is, fighting the ventilator), a tracheostomy is performed where an opening is cut through the neck into the trachea and the ventilation tube is inserted through this opening for a safe airway. "Fighting the vent" does not necessarily mean a conscious fighting in the sense most people would understand that phrase. The body and lungs themselves may exhibit a "fighting of the vent" which is not readily visible to family and friends visiting the patient. A medical decision to proceed with a tracheostomy IS NOT an indication of a worsening of the patient's condition. Instead, it is usually an indication that the mechanical ventilation is not being optimized through the tube inserted through the mouth. A tracheostomy might afford the patient a better pattern of breathing and hence a better possibility of surviving ARDS. A tracheostomy might also make for an easier, somewhat more comfortable course of treatment, in patients who are prone to "fighting the vent". There are a number of controls or settings on the ventilator that are ordered by the doctor. The amount of oxygen that the patient receives can be adjusted. The air we normally breathe contains 21% oxygen. It is possible to give a patient as much as 100% oxygen through a ventilator but this, too, can cause damage to the lung so an effort is made to give the lowest amount of oxygen necessary. The use of Positive End Expiratory Pressure (PEEP) controls is one way to avoid giving the patient high levels of oxygen. While early data did not establish whether high or low pressure was the better course of treatment in assisting patients to recover from ARDS, on March 15, 1999, the National Institutes of Health issued a press release concerning the early termination of the ventilator study being done by the ARDS Clinical Network (ARDSNet) in the United States because the results showed that lower pressure is the overwhelming favored treatment course, not entirely surprisingly because high pressure ventilation itself may cause lung damage sometimes irreversible which may significantly effect a patient's ability to recover from ARDS or have life long medical implications. PEEP is adjusted through the ventilator. It keeps some pressure in the lungs at the end alveoli, the tiny air sacs where oxygen passes into the bloodstream, from collapsing. The pressure is measured and carefully adjusted because there can be complications with high levels of PEEP. The amount of PEEP is often increased and decreased gradually but occasionally it is important to change the level of PEEP more quickly. Other adjustments on the ventilator include the size of each breath (Tidal Volume) the patient receives and the number of breaths (respiratory rate) the patient receives each minute. The ventilator can be adjusted so that it does all of the breathing or so that the patient breathes partially on his or her own. These settings are adjusted depending on the amount of oxygen and carbon dioxide in the blood as well as other tests of lung function. Study data has shown that the use of lower Tidal Volume is associated with less lung damage and improved chance of survival (lower mortality rate). The ventilator can sense when the patient takes a breath of his or her own, timing the set number of breaths to the patient's own rhythm. Often the amount of breathing needed by the body is much more than the patient is able to do on his or her own. The patient may require sedatives or relaxing drugs to help them breathe with the ventilator. PEEP is an odd sensation because it feels like the lungs do not empty at the end of each breath. However, the patient may also feel better because it can make breathing easier and gets more oxygen into the bloodstream. The ventilator and these settings, which sometimes may be adjusted numerous times and quite often by the doctors, are designed to assist the patient's body in performing the critical pulmonary function of getting oxygen (O2) into the blood and carbon dioxide (CO2) removed from the body. The primary measure of this is the O2 saturation (Sat) level. With normal pulmonary functioning the O2 Sat level should be in the high nineties in percentage (96-99% range). If pulmonary function is compromised as it is with ARDS (and many lung disorders and diseases), the O2 Sat level can drop often precipitously, rapidly, and dangerously. The lower the O2 Sat level, the more damage to vital organs and body processes may begin to be manifested. If the O2 Sat level is not brought up and maintained at adequate levels, this will lead to significant damage, often irreversible, including severe brain damage and death. This is why it is important to know what is going on within the entire body, the vital organs and body processes. While ARDS is a pulmonary condition involving the lungs the effects of ARDS may be manifested throughout the body.