Newer modes of mechanical ventilatory support

Automating the weaning process with advanced closed-loop systems

BACKGROUND

Limiting the duration of invasive ventilation is an important goal in caring for critically ill patients. Several clinical trials have shown that compared to traditional care, protocols can reduce the total duration of mechanical ventilation. Computerized or automated weaning has the potential to improve weaning, while decreasing associated workload, and to transfer best evidence into clinical practice by integrating closed-loop technology into protocols that can be operationalized continuously.

DISCUSSION

In this article, we review the principles of automated systems, discuss automated systems that can be used during weaning, and examine the best-current evidence from randomized trials and observational studies supporting their use. We highlight three commercially available systems (Mandatory Minute Ventilation, Adaptive Support Ventilation and SmartCare) that can be used to automate the weaning process. We note advantages and disadvantages associated with individual weaning systems and differences among them.

CONCLUSIONS

We discuss the potential role for automation in complimenting clinical acumen, reducing practice pattern variation and facilitating knowledge translation into clinical practice, and underscore the need for additional high quality investigations to evaluate automated weaning systems in different practice settings and diverse patient populations.

Mechanical ventilation in medical and neurological diseases: 11 years of experience

Mechanical ventilation (MV) is imperative in many forms of acute respiratory failure (ARF). The aim of this work was to review all episodes of MV in a Medical Intensive Care Unit (MICU) during the 11-year period 1976-1986. Four per cent (n = 1008) of 24,899 admissions to the MICU were treated with MV. The mean age of ventilator-treated patients was 53 +/- 18 years, and obviously it increased during the period of study. The average duration of MV was 4.7 d. MICU mortality, hospital mortality and 2-year mortality rates for patients subjected to MV were 33%, 38% and 46%, respectively. The mortality rate did not change during the study period. Cerebrovascular and malignant diseases carried the highest mortality rates, 75 and 79%, respectively, whereas mortality in patients ventilated because of drug overdose (n = 313) was only 2%. The results of this study confirm previously published findings concerning the outcome of MV, and we conclude that the effects of MV remain discouraging in medical and neurological patients. Improved quality of ventilator therapy and monitoring, as well as continued research directed at the causes of ARF, are equally important in reducing the mortality in ARF.

Mandatory minute volume weaning in patients with pulmonary pathology

This study evaluates mandatory minute volume (MMV) weaning in patients with pulmonary pathology. When weaning criteria were fulfilled, 22 patients were randomised to MMV and 18 to a control intermittent mandatory ventilation (IMV) group. With IMV weaning the ventilator rate was decreased by two breaths per minute at 3-4 hourly intervals during daylight hours. In the MMV group a target of 75% of the ventilator minute volume was set. All weans were considered complete four hours after the cessation of mechanical support, and were deemed successful if no further ventilation was required. The success rate was 86% in the IMV and 89% in the MMV group. MMV weaning was rapid (4.75 + 1.5 hrs) and proved less demanding on the ICU staff by providing a safe trial of spontaneous respiration, while retaining the facility for partial ventilation.

Ventilation and ventilators--an update

In the five years which have passed since the previous review, the literature has been concerned more with the ways in which ventilators may be applied to patients and the effects of differing patterns of ventilation than with the design philosophy of the ventilators themselves. This account should be read in conjunction with that of 1982 [1].