The clinical applications of ventilation and the use of specific modes during the acute stage of illness focus on protecting the lung and improving the patient outcomes.
Acute respiratory distress syndrome (ARDS), the most severe presentation of acute lung injury, results from an acute insult to the body that may be direct or indirect (pneumonia vs sepsis). The release of mediators and a host of other toxic substances affect the alveolar- capillary permeability adversely and result in a noncardiac pulmonary edema. Pathology includes decreased compliance, shunting, and refractory hypoxemia. No definitive treatment, but the therapy focus on managing the underlying condition and on supportive mechanical ventilation.
The two most common types of ventilations:
- Pressure support ventilation (PSV)
- a form of ventilation for the stable, spontaneously breathing patient during weaning
- designed for the spontaneously breathing patient but requires that a pressure level be selected by the clinician – when the patient initiates a breath, the ventilator senses the negative pressure, which triggers and delivers a high flow of gas to the patient until the selected pressure level is reached early in inspiration.
- a “comfortable” mode for spontaneously breathing patient as it enables the patient to determine inspiratory time, volume, and respiratory rate.
- In less stable patients, close monitoring of tidal volume and respiratory rate is necessary.
- Nursing assessment:
- comfort as the patient controls inspiratory and expiratory time, rate, and volume, the patient should be comfortable and without dyspnea
- secretions can increase resistance and decrease tidal volume. Ensure airway patency with adequate humidification and suctioning as needed. If secretions are copious, pressure support may be contraindicated.
- compliance changes: decreased lung compliance results in decreased tidal volume and often an increase in respiratory rate
- conditioning: PSV is good for promoting endurance of the respiratory muscles by gradually increasing workload overtime.
- Use caution when chest tube leaks and cuff leaks are present. Patients with large air leaks from chest tubes and /or endotracheal tube cuffs should not be placed on PSV. When a leak is present, the patient may not be able to control the parameters of inspiratory time, rate, or volume.
- PSV should be used very cautiously in patients with asthma or in patients with rapidly changing physical status (for example, with acute bronchospasm, airway resistance increases, tidal volume will decrease and respiratory rate will increase.)
- Bilevel positive airway pressure (BiPAP)
- a noninvasive mode of ventilation that combines two levels of positive pressure (PSV and PEEP positive end-expiratory pressure) by means of a full face mask, nasal mask, or nasal pillows.
- designed to compensate for leaks in the setup
- can be very labor intensive, especially when used to prevent reintubation following extubation.
- full face mask ventilation is cautiously used because the potential for aspiration is high. If full face mask ventilation is chosen, the patient should be able to remove the mask quickly if nausea or vomiting is imminent.
- Obtunded patients and those with excessive secretions are not good choices for bilevel ventilation.
- Nursing assessment:
- rate and pattern of breathing: the patient should look comfortable with no evidence of accessory muscle use and a reasonable respiratory rate
- although ABGs are often obtained, SaO2 in conjunction with assessment of rate and pattern of breathing, mental status and vital signs, tells us much about how the patient is tolerating the mode.
- the method of ventilation is labor intensive and requires that the nurse and respiratory therapist work together to determine the best settings for the patient
- a chin strap may be used if the patient cannot maintain a good seal by keeping his or her mouth closed.
- decreased mental status is a relative contraindication for bilevel because the patient may not be able to protect the airway. Any acute change in mental status should be promptly reported and continued use of bilevel carefully evaluateI. intubation may be necessary
- if the patient becomes nauseated, aspiration risk is increased. Make sure the patient can quickly remove the face or nasal mask if necessary.
Other Ventilation modes are pressure control and pressure controlled/inverse ratio ventilation (PC/IRV), volume-guaranteed pressure modes of ventilation (pressure augmentation), airway pressure release ventilation and biphasic ventilation (APRV), adaptive support ventilation (ASV), proportional assist ventilation and neurally adjusted ventilatory assist (PAV), automatic tube compensation (ATC), and high-frequency oscillation (HFO).