Vol. 13 •Issue 9 • Page 20
Ventilation Today
When Conventional Ventilation Fails, Call Upon These Unique Therapies
Studies and years of experience have given clinicians the expertise and skill to optimize ventilator settings to achieve the best possible outcomes. But sometimes our efforts are futile when faced with the sickest patients, forcing us to venture into infrequently used, experimental or unproven modalities in an attempt to save lives.
If you find yourself trying one of these methods or other new approaches that may come down the road, it’s important to understand the theory behind them and the associated side effects so that the patient can be properly monitored to prevent more harm than good.
HIGH FREQUENCY VENTILATION
High frequency ventilation such as the oscillator and the jet is a class of ventilators that sway from conventional thought in that they deliver tidal volumes at a volume less than the dead space of the patient. They deliver respiratory rates as high as 900 breaths per minute and rely on the mixing of gases to achieve gas exchange.
Neither the oscillator nor the jet is new, and both have proven themselves in the neonatal population, making them a therapy well worth the money. In the adult arena, however, it’s a different story with multiple conflicting studies on the efficacy of high frequency ventilation, making it a therapy of “last-ditch” efforts.
It’s questionable if high frequency oscillators in the adult population have any affect on mortality. High frequency ventilation has all the side affects of conventional ventilation with the additional risk of tracheal injury caused by the vibrating endotracheal tube.
An institution that doesn’t often use high frequency ventilation will need to keep staff trained and familiar with the equipment so that they’ll be able to cope with its emergent setup. Also, strategies used for high frequency ventilation are much different from those in conventional ventilation, so the physician and therapist must be properly trained to safely reach the desired effects.
ECMO
Another therapy that has been available for some time is extracorporeal membrane oxygenation (ECMO), which supports a patient with lung or heart failure until the disease process is reversed or repaired. ECMO involves the cannulation of the major vessels of the neck from which blood is removed and then returned by a circulatory machine. While pumping blood, the machine also replenishes the oxygen supply and removes carbon dioxide.
This therapy is expensive and invasive. In addition to the nursing staff and respiratory therapist, there’s the added cost of a specially trained technologist who continuously monitors the machine.
The side effects of ECMO result from the removing of blood, risking clots or stroke. Uncontrollable bleeding also may be experienced due to the blood thinners used to prevent clots. While ECMO usually is considered a last-ditch therapy, it has had good success in some of the sickest patients experiencing acute lung/heart failure or as a bridge to surgery, especially in the neonatal population.
PRONE VENTILATION
Historically, prone ventilation has been controversial. When a patient is lying in bed, the blood of their pulmonary vascular pools to the dorsal regions. The pressure of the bed or poor posture may close off ventilation to these highly perfused areas causing a ventilation/perfusion mismatch. The theory is if we were to flip the patient prone, blood would relocate or pool to the anterior ventilated alveoli while removing the pressure from the dorsal areas and allowing them to re-expand.
Despite the mixed results from studies, prone ventilation may be a beneficial therapy for some patients at a relatively low cost. It only requires manpower and pillows or folded blankets for propping. Be sure to get enough people to easily flip the patient while monitoring the endotracheal tube and lines to prevent their unplanned removal.
While prone positioning may work on some patients, the overstimulation could be more detrimental than helpful to other patients. Dangerous changes in vitals upon the actual event of turning may occur. Also, having the patient prone makes assessment difficult, and access is nearly impossible should an emergency arise. The patient needs to be propped to keep tubes and lines from kinking, and it’s important to be sure the pillows don’t impede movement of the patient’s diaphragm.
NITRIC OXIDE
A newer therapy that also has been proven to improve vitals when used properly is nitric oxide. Nitric oxide is a pulmonary vasodilator that has a very short half-life, reducing the number of side effects seen in systemically given drugs.
Because it’s bled into a ventilator circuit in a dose measured by parts per million, it must be delivered via a system that can compensate for changes in the patient’s minute volume to keep the dose constant. Sudden changes in its dose could cause severe rebounds.
Nitric oxide’s claim to fame is for pulmonary hypertension, causing instantaneous gratification with a SpO2 going from the gutter to 100 percent in seconds. It also has been used for refractory hypoxemia, but it hasn’t been convincing in those patients.
The cost is high to use this drug. It’s charged by a meter (like your electric bill), and insurance reimbursement can be difficult to get and is only available in some cases. While not expensive to keep this therapy available in your facility, caution must be taken to quickly withdraw the therapy if there’s no improvement to prevent the busting of the budget or risk side effects such as changes to blood cells that hinder their ability to carry oxygen. If this therapy doesn’t work in the first few minutes, it won’t work later.
It’s also questionable that, despite drastic changes in oxygenation in a flash, whether this therapy has any effect on mortality.
PROSTACYCLIN
Prostacyclin via IV previously was used for pulmonary hypertension but failed due to severe systemic side effects. Now it has returned in the nebulized form.
This continuous nebulizer is an economic option to nitric oxide at about one-tenth the cost. While the cost is lower, it’s more labor intensive, requiring calculations, dumping and refilling for each dose change. Also, care must be used in the repositioning of a patient receiving nebulized prostacyclin to prevent lavaging the patient’s airway with the drug or causing an overdose if the nebulizer were to tip over. Two IV pumps may be used to set the ratio of drug to saline being infused into the nebulizer.
TRACHEAL GAS INSUFFLATION
Tracheal gas insufflation is the administration of a flow of gas via a catheter placed near the distal end of the endotracheal tube. The theory is that the gas flow will “wash out” the volume of gas in the larger airways causing a reduction in effective dead space. This may allow for better ventilation or reduced settings for lung protection. It works best for anatomic dead space, so you won’t see improvement in patients with a tracheostomy or with alveolar dead space.
Because of the lack of availability of systems to do tracheal gas insufflation, facilities build their own by using a jet adapter and a central venous pressure catheter adapted to fit oxygen tubing. The cost to do tracheal gas insufflation this way is minimal but not without some risks.
The dry gas delivered into the airway must be humidified properly to prevent mucosal injury. Also, a catheter partially blocking the airway with an added flow of gas could cause severe air trapping that may not only reduce the patient’s ability to trigger the ventilator, but possibly cause a pneumothorax. Monitor patients closely.
Some companies are in the process of developing systems for tracheal gas insufflation that would ensure proper humidification and allow the tracheal gas flow to only be applied during designated parts of the respiratory cycle.
LIQUID VENTILATION
Liquid ventilation may be the future therapy of choice for our sickest patients. It uses perfluorocarbons to fill the lungs, and then the patient is connected to a ventilator. Perfluorocarbons are a clear, odorless fluid with a low surface tension that can easily carry oxygen and carbon dioxide. The low surface tension helps hold collapsed alveoli open while giving the added benefit of washing debris from the lung, which may aid in the resolution of inflammation.
Perfluorocarbons are thought to have no side effects while delivering superior ventilation with little risk of lung injury. While sounding promising, this is still experimental and unavailable. You’ll have to wait with the rest of us.
McCormick is supervisor of respiratory services, Hahnemann University Hospital, Philadelphia.
