OBJECTIVE: To examine the effect of abnormal cardiac index on the accuracy of measurement of oxygen saturation by pulse oximetry. METHODS: Forty-six patients (mean age, 49 years) in a 9-bed medical ICU were studied. Measurements of oxygen saturation obtained with pulse oximeters and with a functional cooximeter were collected at baseline and 4, 8, 16, 24, 32, 40, and 48 hours later. Hemodynamic and cardiopulmonary parameters were recorded. RESULTS: The Bland-Altman technique yielded upper and lower limits of agreement of 2.53% and -7.11%. Most (95.7%) of the differences between the measurements of oxygen saturation obtained with the 2 methods were within these limits, although some of these differences may be clinically unacceptable. The bias was -2.29%, and the precision was 2.41%. The clinical conditions associated with inaccurate tracking of saturation by pulse oximetry across the range of actual arterial oxygen saturation values were abnormal cardiac index, partial pressure of carbon dioxide, heart rate, and pulmonary capillary wedge pressure. CONCLUSIONS: In patients with abnormal cardiac index, the pulse oximeter measurements exceeded the actual oxygen saturation by up to 7%. Pending prospective studies, clinicians should be aware that when certain cardiopulmonary parameters are abnormal, the margin of error in measurements of oxygen saturation obtained with a pulse oximeter may be greater than when those parameters are normal.
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.
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.
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.
OBJECTIVE: To describe the etiologies and indicators of weaning failure and to provide a framework for planning interventions to facilitate weaning of long-term ventilation patients. DATA SOURCE: A Medline search of human studies in English on weaning from mechanical ventilation. ARTICLE SELECTION: Articles were selected if they pertained to the assessment and management of weaning failure. Both research and review articles were included. DATA EXTRACTION: All pertinent articles were described, along with their limitations. DATA SYNTHESIS: Weaning from mechanical ventilation is an emerging science. Caring for patients who are difficult to wean requires expert clinical decision making so patients do not feel defeated and have the best chances for success. Combining the limited research on weaning intervention with clinical expertise helps to build a scientific basis for care and can assist clinicians in tailoring interventions to specific problems that precipitate weaning failure. CONCLUSION: A scientific approach to care may promote weaning in difficult cases and provide directions for future research into the etiologies of weaning failure.