Weaning from mechanical ventilatory support: refinement of a model.

The American Association of Critical-Care Nurses sponsored the third National Study Group to advance the science of weaning from mechanical ventilatory support and to guide clinical practice. The study group proposed a model of weaning in 1994 to provide an organizing framework for scientific inquiry. Since the model was first proposed, the ongoing work of the study group has led to refinement of the model. The purpose of this brief communication is to inform critical care clinicians and researchers about the refinements.

A volunteers in participatory sampling survey of weaning practices. The Third National Study Group on Weaning from Mechanical Ventilation.

The survey results of the VIPs membership described in this article add qualitative information to the growing body of scientific knowledge on weaning patients off ventilators. Clearly, quantitative studies exploring the efficacy of different weaning practices across the continuum must be done if we are to accurately compare practices and prescribe the "when" and "how" of weaning. To this end, the Third National Study Group is revising the proposed weaning model and model in order to further elucidate the state of the art and science of weaning.

Effect of formulation and processing factors on the characteristics of biodegradable microcapsules of zidovudine.

Biodegradable microcapsules of zidovudine (AZT) were prepared using poly-(lactide/glycolide) by the solvent evaporation technique. The objective of this project was to focus on the effect of several formulation and processing factors on the efficiency of encapsulation, surface morphology, and drug release profiles. When the drug was incorporated as powder or as aqueous suspension containing a high amount of insoluble particles, to the organic phase the surface of the microcapsules was appeared to be wrinkled. The efficiency of encapsulation decreased when AZT powder was dispersed directly into the organic solvent instead of adding as an aqueous solution. When the relative volume of the aqueous phase containing 1% PVA was changed from 25 up to 125% of the volume of the organic phase, the efficiency of encapsulation, surface morphology, and release profiles did not change significantly. The efficiency of encapsulation decreased from 9 to 3.8% when the drug loading was increased from 10 to 50% of the weight of the polymer.

Preparation of biodegradable microcapsules containing zidovudine (AZT) using solvent evaporation technique.

Sustained release biodegradable microcapsules of AZT were prepared using different concentrations of copolymer of poly(lactic/glycolic) acid (PLGA 50:50 and PLGA 90:10). Solid microcapsules were collected following the complete evaporation of the solvent. The yield of microcapsules was increased two fold with a two-fold increase of the polymer concentration. The efficiency of encapsulation of AZT was also increased with the increase of the polymer concentration. These microcapsules were characterized using scanning electron microscopy. The dissolution of AZT from the microcapsules of PLGA (50: 50) was higher than the microcapsules of PLGA (90:10); the PLGA (50:50) microcapsules containing 1:10 drug/polymer ratio showed higher dissolution than the microcapsules containing 1:20 drug/polymer ratio. The PLGA (90:10) microcapsules containing 1:6 drug/polymer ratio showed higher dissolution than the microcapsules containing 1:10 drug/polymer ratio. In conclusion, the dissolution of AZT was dependent on the type of the copolymer used and the relative concentrations of the drug and the copolymer.

Weaning from long-term mechanical ventilation.

Although many investigators have attempted to identify weaning predictors and weaning modes for use in long-term mechanically ventilated patients, none has emerged as superior. Furthermore, few investigators have viewed the process of weaning as a dynamic continuum; thus, guidelines for care of these patients have yet to be developed. Facilitative methods and therapies to enhance weaning potential, although attractive, have little scientific basis for application. Care delivery systems, which focus on systematic, comprehensive and coordinated care, are promising because outcomes demonstrate that they are economical, safe, and effective. This article reviews the research on weaning adult, long-term mechanically ventilated patients, suggests future research directions, and highlights the scientific basis for practice guidelines.

Terminal weaning from mechanical ventilation: a review.

Terminal weaning is a clinical intervention for withdrawing mechanical ventilatory support when such support is an unacceptable outcome for a patient. Withdrawal of life support must be done in a humane manner for the patient, the family, and the patient's care providers. Research-based directions for clinical practice are limited because of the paucity of research in this area. Recommendations for future study are related to methods, facilitative therapy, patient, family, and caregiver responses, and care delivery models.

Weaning from mechanical ventilation: concept development.

This article, the first in a series, is written to clarify the process of weaning from mechanical ventilation and to promote the development of a common language for understanding the complex weaning process. The Third National Study Group on Weaning From Mechanical Ventilation proposes a conceptual model and definitions that will provide a framework for future research on this important topic. This conceptual framework describes the preweaning phase, the weaning process, and the outcome phase of mechanical ventilation. Potential outcomes are completion of weaning, lack of completion, and terminal weaning. The weaning decision continuum incorporates: (1) when and how to begin the weaning process, (2) how to select therapies to assist with difficult weaning and chart progress during weaning, and (3) when to stop weaning if progress is no longer being made. An inherent assumption of this model is that each patient will display unique responses to the weaning process. The proposed conceptual framework and definitions provide a foundation for developing clinical practice guidelines and for guiding future ventilator weaning research.

Weaning from short-term mechanical ventilation: a review.

The purposes of this article are to: identify gaps in the research literature on weaning adult patients from short-term mechanical ventilation, highlight the scientific base for practice guidelines, and suggest future research directions. Data bases from 1989 through June 1993 were reviewed, and relevant research articles were extracted, analyzed, and synthesized within the AACN Third National Study Group framework. Seminal work and other supportive literature also were used in this review. Despite considerable research on predictors and patient responses to weaning from short-term mechanical ventilation, few of the findings can be applied to clinical practice at this time. Less research is available on weaning modes and therapies that facilitate weaning from short-term mechanical ventilation; fruitful research in these areas depends in part on a better understanding of patient responses and accurate weaning predictors.

Caring for individuals using home ventilators: an appraisal by family caregivers.

This article describes a study of the effects of caregiving on family members who assumed primary responsibility for managing the care of ventilator-assisted individuals in the home. Thirteen caregivers were interviewed and five variables associated with their role were assessed: caregiving tasks, burden of caregiving, impact of caregiving, mastery of the caregiving role, and satisfaction with caregiving. Data were collected using the Caregiving Appraisal Scale (CAS), a list of caregiving tasks, and a semistructured interview. Caregivers assumed multiple responsibilities for individuals who were completely ventilator-dependent (n = 5), partially ventilator-dependent (n = 3), or nocturnally ventilated (n = 5). Caregivers reported feeling moderate levels of both the burden and the negative impact of caregiving but a positive sense of mastery and satisfaction. They described problems with home healthcare nurses, insurance coverage, and equipment suppliers. Lack of preparation, in terms of education provided by healthcare professionals, limited their ability to manage these problems quickly and effectively. Caregivers suggested that healthcare providers expand discharge planning to include provision of problem-solving strategies.

Respiratory muscle conditioning and the work of breathing: a critical balance in the weaning patient.

Normal ventilatory function depends on a balance between ventilatory demand and ventilatory capacity. The respiratory muscles play a critical role in achieving this balance. For patients experiencing ventilatory dysfunction, interventions that improve respiratory muscle function and therefore increase ventilatory capacity may be one way of restoring the balance and promoting ventilatory function. Respiratory muscle conditioning, or training the muscles to improve their strength and endurance, may be a useful clinical intervention in the weaning patient. Results of research show that muscle training may increase the ability of some patients to resume spontaneous ventilation. Continued research is needed to identify the appropriate training protocols for patients experiencing an acute imbalance between ventilatory demand and capacity.

Communicating with ventilator dependent patients.

One major psychosocial problem of mechanically ventilated patients is their inability to speak because of the cuffed endotracheal or tracheostomy tube obstructing the larynx and airflow. The authors analyze the research findings to suggest research-based strategies for communicating with ventilator patients.

Coping with chronic respiratory difficulty.

The major point of this article is that the pathologic process of chronic respiratory disease interacts with psychologic and psychosocial factors as determinants of the respiratory patient's quality of life. The assessment, support, and reinforcement of a patient's psychosocial assets and ability to cope with chronic respiratory difficulty can help enhance that quality. This outcome should be a primary consideration of the nurse caring for a respiratory patient despite the fact that, in this era of cost containment, improved life quality may be an outcome that is overlooked, ignored, or undervalued.

Ineffective airway clearance related to artificial airway.

Ineffective airway clearance occurs when an artificial airway is used because normal mucociliary transport mechanisms are bypassed and impaired. Nursing assessment and intervention are the keys to maintaining airway patency in the patient with an artificial airway in place. The assessment of breath sounds is critical to making a valid clinical judgment about airway patency. Nursing interventions such as tracheobronchial suctioning, postural drainage, and providing exogenous humidity to the inspired air are indicated to maintain airway patency, which is the goal of treatment. Suggested areas for future research related to this diagnosis include validation of the signs and symptoms which are proposed as being specific to the causes of ineffective airway clearance and the continuation of experimental studies to demonstrate the efficacy of various interventions for this nursing diagnosis.

Ammonia, octanoate and a mercaptan depress regeneration of normal rat liver after partial hepatectomy.

Four injections of subcoma doses of ammonium acetate, octanoic acid or dimethyl disulfide during the first 24 hr after two-lobe hepatectomy in normal rats markedly depressed DNA synthesis as reflected by liver thymidine kinase activity or the incorporation of tritiated thymidine into hepatic DNA. Recovery from the depressant effects of the three toxins took 16 to 28 hr. Similar doses of the same toxins injected hourly for 3 or 5 hr after the two-lobe hepatectomy had similar depressant effects on the early peak of ornithine decarboxylase activity measured at 4 or 6 hr. Recovery occurred within 3 hr perhaps because of the very short half-life of ornithine decarboxylase and its rapid regeneration time. These observations may have implications for the lack of regeneration observed in many patients with fulminant hepatic failure who have accumulated sufficient ammonia, methanethiol and fatty acids over periods of days or weeks to become encephalopathic.