Too much PEEP or continuous positive airway pressure (CPAP) can interfere with pulmonary-venous return and can be a deadly complication. The nurse needs to monitor the patient closely for any signs of this if PEEP or CPAP is increased.
Cardiovascular impairment is a known consequence of, or a combination of, ventricular dysfunction or chronic heart failure; angina pectoris due to myocardial ischemia or infarction; syncope, or near syncope, due to inadequate cerebral perfusion; and cyanotic heart disease.5
Positive pressure, which is applied within the chest cavity, increases intrathoracic pressures. This increased pressure compresses blood vessels, increases the pressures against which the heart must pump and impedes venous return to the heart. Decreased cardiac output affects venous return and renal blood flow, and tissue oxygenation declines. Hypotension, diminished amplitude of peripheral pulses, decreased urine output, tachycardia, mental confusion and heart failure can occur if the patient is receiving too much PEEP or CPAP.
Cardiac depression is greatest with healthy, compliant lungs and less with diseased, non-compliant lungs. The diseased lungs act to buffer the pressure changes and actually protect the chest cavity from some of the negative effects of positive pressure.
With inspirations, the amount of the inspiratory time should be less than or equal to the expiratory time. If this cycle is reversed, such as with an incorrect ventilator setting, the air will become trapped in the alveoli because the alveoli isn't given enough time to expel all the air in it, resulting in air trapping. As a life-threatening event to the patient, the LP10 ventilator has a setting-error alarm should this occur. This alarm sounds if the inspiratory/expiratory ratio is not correct and can only be silenced if the problem is corrected. The laptop ventilator doesn't allow this cycle to be reversed; therefore it does not have a setting-error alarm.
There are several ways in which patients can be weaned off a ventilator. To begin the process, a patient might go from the assist-control setting to a synchronized intermittent mandatory- ventilation setting.6 The breathing effort can be more negative to exercise the respiratory muscles and the diaphragm to generate negative pressure in the chest and lungs to draw fresh air into the lungs.6 The breath rate can also be gradually decreased and PEEP can be gradually reduced to zero. A trial of CPAP might also be given.6 Some physicians will also order increasing times off the ventilator once the settings are low, such as 5 minutes off the ventilator, 5 minutes on, and gradually increase the time off as tolerated by the patient.
One way of weaning a patient from a ventilator is to set it at a higher negativity on the LP10 or a higher sensitivity on the LTV so the patient works those chest muscles and diaphragm to help them get stronger.
The goal in caring for patients at home is to assist them in participating in the most normal life as possible and fulfilling their goals for the best quality of life they can attain.
Part two of this article, which posts on Feb. 17, addresses the basics of ventilator settings and alarms.
1. Agency for Healthcare Research and Quality. (2007). Project XTREME: Model for health professionals' cross-training for mass casualty respiratory needs (Publication No. 07-0017), Author: Washington, DC.
2. Wilgis, J. (2008, April), How to be prepared for a pandemic. AARC Times, pp. 28-30.
3. From around the Network: Equipment and interfaces. (2007). Ventilator-Assisted Living, 21(1), 5
4. Pruitt, W., & Jacobs, M. (2004, July/August). Take a deep breath . and conquer your fear of mechanical ventilation. Nursing Made Incredibly Easy, pp.10-20
5. Astle, S., & Smith, D. (2007). Taking your patient off a ventilator. RN, 70(5), 34-39
6. Capuano, A., Sepe, V., Cianfrone, et al. (1990). Cardiovascular impairment, dialysis strategy and tolerance in elderly and young patients on maintenance haemodialysis. Nephrology, Dialysis, Transplantation, 5(12), 1023-30.
Rosalyn Scherf is clinical educator for South Florida Pediatric Homecare, Pembroke Pines, FL. Christine Carr is a certified respiratory therapist for Hollywood Medical Supply Co., Hollywood, FL.