Interrupter mechanics of patients admitted to a chronic ventilator dependency unit

Expiratory Flow Limitation During Mechanical Ventilation

Expiratory flow limitation (EFL) is present when the flow cannot rise despite an increase in the expiratory driving pressure. The mechanisms of EFL are debated but are believed to be related to the collapsibility of small airways. In patients who are mechanically ventilated, EFL can exist during tidal ventilation, representing an extreme situation in which lung volume cannot decrease, regardless of the expiratory driving forces. It is a key factor for the generation of auto- or intrinsic positive end-expiratory pressure (PEEP) and requires specific management such as positioning and adjustment of external PEEP. EFL can be responsible for causing dyspnea and patient-ventilator dyssynchrony, and it is influenced by the fluid status of the patient. EFL frequently affects patients with COPD, obesity, and heart failure, as well as patients with ARDS, especially at low PEEP. EFL is, however, most often unrecognized in the clinical setting despite being associated with complications of mechanical ventilation and poor outcomes such as postoperative pulmonary complications, extubation failure, and possibly airway injury in ARDS. Therefore, prompt recognition might help the management of patients being mechanically ventilated who have EFL and could potentially influence outcome. EFL can be suspected by using different means, and this review summarizes the methods to specifically detect EFL during mechanical ventilation.

Effect of series of resistance levels on flow limitation in mechanically ventilated COPD patients

In severe chronic obstructive pulmonary disease (COPD) lung emptying is disturbed by airways compression and expiratory flow limitation. Application of an external resistance has been suggested to counteract airways compression and improve lung emptying. We studied the effect of various resistance levels on lung emptying in mechanically ventilated COPD patients. In 18 patients an adjustable resistor was applied. The effect on airways compression was assessed by iso-volume pressure--flow curves (IVPF) and by interrupter measurements. Respiratory mechanics during unimpeded expirations were correlated to the results obtained with the resistances. The resistances caused an increase in iso-volume flow at the IVPF-curves in six patients, indicating that airways compression was counteracted. Interrupter measurements showed that overshoots in flow (as measure of flow limitation) were significantly reduced by the resistor. These effects could be predicted on basis of respiratory mechanics during unimpeded expiration. In conclusion, mechanically ventilated COPD patients can be identified in whom application of external resistances counteracts airways compression and reduces flow limitation.

Weaning from prolonged mechanical ventilation

The development of weaning failure and need for PMV is multifactorial in origin, involving disorders of pulmonary mechanics and complications associated with critical illness. The underlying disease process is clearly important when discussing mechanisms of ventilator dependence; interventions therefore must be tailored to individual patients. Unfortunately, the main conclusion that can be drawn from the sum of the studies investigating patients on PMV to date is that an evidence-based approach to weaning is not possible and more research needs to be done. New studies need to incorporate severity-of-illness scores and an assessment of principal and comorbid conditions to allow for comparison of the findings from different centers. The best approach to a patient requiring PMV after exclusion of easily treatable conditions is not known. The literature regarding both acute and chronic cases suggests that a systematic approach to weaning involving the participation of multiple caregivers, including nurses, physicians, and respiratory, physical, and speech therapists facilitates liberation from MV. Although a gradual decrement in ventilator support would seem prudent, Scheinhorn et al have begun to identify a subpopulation of patients who can tolerate an acceleration of the weaning process. Given the known complications associated with MV, it is crucial that further research be performed to identify patients as soon as they are capable of breathing spontaneously. The literature demonstrates through multiple studies that satisfactory patient outcomes are attainable and can be achieved at LTAC facilities in a more cost-effective manner than in an ICU setting. The trend toward the concentration of patients into specialized regional weaning centers should facilitate the research process and continue to improve outcomes in this population.

The Mayo Ventilator-Dependent Rehabilitation Unit: a 5-year experience

OBJECTIVE

To describe the outcomes of 206 patients admitted to the Mayo Ventilator-Dependent Rehabilitation Unit (VDRU) during a 5-year study period.

DESIGN

We analyze the patient data for 1990 through 1994, which had been prospectively entered into a computer database for a cohort of 206 patients who had become ventilator dependent during their current hospitalization.

MATERIAL AND METHODS

Patients in the VDRU were classified into one of six categories that reflected the reasons for ventilator dependence. Ability to be weaned from mechanical ventilation, duration of hospital stay and ventilator dependence, outcome, disposition, demographics, and long-term survival were analyzed. The VDRU patient group was compared for hospital and follow-up outcomes with a group of historical control patients previously described by us.

RESULTS

The Mayo VDRU was established in January 1990. During the first 5 years of its operation, 206 newly ventilator-dependent patients were admitted to the VDRU, 190 (92%) of whom survived to be dismissed; 16 patients (8%) died in the hospital. Of the 190 patients dismissed, 77% were able to return to their homes. Overall, 153 patients were liberated from mechanical ventilation, whereas 37 remained either completely or partially ventilator dependent. Of these 37 patients, 27 (73%) were receiving nocturnal mechanical ventilation only. The 4-year survival was 53%.

CONCLUSION

The Mayo VDRU has been highly successful in liberating newly ventilator-dependent patients from mechanical ventilation. The long-term survival after management in the VDRU has been excellent. In addition, the medical charges for care in the VDRU are less than intensive-care unit charges.

Outcome of patients cared for in a ventilator-dependent unit in a general hospital

We describe our initial experience with the admission of 129 patients for 132 episodes of ventilator-dependence to a self-contained ventilator-dependent unit (VDU) in a general hospital and present a survival comparison between VDU patients and a historic control population from the same institution. Forty-three patients were screened and denied admission to the VDU because long-term ventilator dependence was not felt to be a probable outcome (56%); they were medically unstable, often requiring electrocardiographic monitoring (19%), they had poor rehabilitation potential because of markedly depressed mental status (13%), or they preferred to be treated closer to their homes (12%). Thirteen (9.8%) of the VDU patients died in the hospital compared to 44 (42%) in the historic control group. After exclusion of patients with multiorgan failure (who made up 26% of the control group) and using a proportional hazard model to adjust for group differences in age and disease class, the difference in hospital mortality remained highly significant (p < or = 0.01). Ninety-one of the 119 VDU patients (77%) were ultimately able to return home; 16 (13%) continued to use a ventilator intermittently at night; 26 patients (22%) were permanently placed in nursing homes, all off of the ventilator. Overall, 88% of the 119 patients discharged had been liberated from mechanical ventilation. Ninety-seven (82%) and 86 (72%) remain alive 1 and 2 years after discharge, respectively. Some of the survival benefits may be directly attributed to the VDU. Others reflect a change in treatment philosophy, which was nevertheless reinforced by our VDU experience.