Research

Does Respiratory Muscle Function Change in Patients Being Weaned from Long-Term Mechanical Ventilation?

To determine factors contributing to inability to wean from long-term mechanical ventilation, we studied the change in respiratory function in patients admitted to a specialized unit for weaning. With a maximum follow-up of 45 days, 15 patients were successfully weaned (WS) and 13 patients failed to wean (WF). Measurement of respiratory system mechanics, maximal inspiratory pressure (P_I max), breathing frequency and tidal volume (V_T )were done on admission and then at least weekly. The change in each variable from the first half to the second half of follow-up in WS and WF patients were analyzed by two-way ANOVA. Compared with WS patients, WF patients had a lower V_T throughout both periods (p=0.002).

From the beginning to the end of the weaning process, P_I max increased in WS patients but did not change in WF patients (p=0.006). No significant differences were found in respiratory system mechanics or breathing frequency in WS and WF patients. In conclusion, patients who are successfully weaned from long-term mechanical ventilation improve their capacity to generate tidal volume and maximal inspiratory pressures.

Can We Predict Weaning in Patients Receiving Prolonged Mechanical Ventilation?

The care of patients requiring prolonged mechanical ventilation is costly and time consuming. To customize management for patients transferred to a unit that specializes in weaning patients from long-term mechanical ventilation, it would help to be able to predict the outcome for a patient on admission.

To identify such indexes, we allowed the patients on admission to breathe spontaneously through a tracheostomy after measuring several physiologic variables. With a maximum follow-up of 45 days, 22 patients were able to breathe spontaneously through a tracheostomy for five consecutive days and were considered weaning successes (WS), and 19 patients who did not meet this criterion were considered weaning failures (WF).

Compared to WS patients, WF patients had smaller tidal volume (0.22 ± 0.03 vs. 0.3 ± 0.02 L, p=0.03), a shorter spontaneous breathing trial on the first day (128 ± 50 vs. 378 ± 86 minutes, p=0.02), and a higher frequency-to-tidal volume ratio (223 ± 25 vs. 142 ± 23 breath/minute/L, p=0.02). The area under the receiver-operating-characteristic (ROC) curve for these indexes ranged between 0.72 and 0.77 and did not differ from each other. Respiratory frequency, minute ventilation, maximal inspiratory pressure, and respiratory system mechanics were similar in two groups.

In conclusion, aspects of a patient's breathing pattern and a patient's ability to sustain spontaneous breathing on admission to a facility for long-term mechanical ventilation help in predicting eventual weaning outcome.

Does the Method of Weaning Influence Time Spent by Respiratory Therapists at a Patient's Bedside?

To determine whether the time a respiratory therapist spends at a patients' bedside varies with the method of weaning, we measured the time taken by respiratory therapists in caring for 10 patients being weaned by a daily trial of spontaneous breathing (SB) and eight patients being weaned by pressure support ventilation (PSV). Between 6 a.m. and 7 p.m., therapists were instructed to record the time of entering and leaving patients' rooms, and the purpose for entries (e.g., tracheal suctioning or response to an alarm).

Therapists were later asked to rate their compliance in recording the room entries. The total time spent by a therapist was greater for PSV (66.1 ± 6.7 min) than for SB (51.2 ± 2.8 min, p=0.03). Room entries tended to be more frequent for PSV (5.8 ± 0.7 vs. 4.6 ± 0.2 times/day, p=0.07), although the number of room entries in response to an alarm was similar in the two groups (SB 1.6 ± 0.4 vs. PSV 2.4 ± 0.5, times/day p=0.18). The duration of each room entry was similar in the two groups. The number of suctionings per day tended to be higher with PSV than with SB (6.8 ± 1.6 vs. 4.8 ± 0.3 suctioning/day, respectively, p=0.12) Therapists rated their recording of room entries as 83% complete.

In conclusion, respiratory therapists spend more time administering care at the bedside of patients being weaned by PSV than with SB, and this difference arose largely because of the method of weaning itself rather than to the patients' need for suctioning or urgent care.

Mortality in Patients Admitted To a Specialized Facility for Weaning From Mechanical Ventilation

A prospective study was done to determine the outcome in 41 patients transferred to a specialized facility for weaning from mechanical ventilation. On admission, patients were 72 ± 2 (SE) years old and 72% were women. Patients had received mechanical ventilation for 30 ± 2 days. The indications for prolonged mechanical ventilation were post-operative respiratory failure (n=20), exacerbation of COPD (n=11), and acute hypoxic respiratory failure (n=10). The length of stay at the facility was 59 ± 6 days, and hospital mortality was 54%.

Patients who failed to wean after 14 days of follow-up (n = 31) had a trend towards higher mortality (OR=3.7, 95% interval 0.6-22.9, p=0.18) than patients successfully weaned. Causes of death were withdrawal of support (n=4), cardiopulmonary arrest (n=5), and medical complication leading to death or withdrawal of support (n=13).

Patients who died during the hospitalization were older than patients discharged alive (76 ± 2 vs. 68 ± 3 yr, p=0.03). Patients who developed sepsis had higher mortality than patients who did not (75% vs. 40% p=0.06). Patients' gender, indication, and duration of mechanical ventilation, left ventricular ejection fraction, and respiratory system mechanics were similar in patients discharged alive and those who died during hospitalization.

In conclusion, mortality in patients admitted to a special facility for long-term mechanical ventilation was related to age and the development of sepsis and not to the indication for mechanical ventilation nor baseline cardiopulmonary function.