March 2002 / Volume 47 / Number 2 / Page 249
Indications for Mechanical Ventilation in Adults with Acute Respiratory Failure
IntroductionIncreased understanding of the mechanisms and effects of acute respiratory failure has not been accompanied by more precise criteria by which the clinician can determine when intubation should be carried out and invasive positive-pressure ventilation (IPPV) instituted in a given patient. The indications traditionally offered in reviews and textbooks have tended to be either so broad as not to be very helpful in an individual case, or of questionable clinical relevance and too cumbersome for practical use. This review updates the indications for IPPV in adult patients with acute respiratory failure by examining available evidence from clinical trials and by considering new management alternatives that have become available in the last 20 years. Indications for IPPV based on specific threshold values for PCO2 and pH or on various indices of arterial oxygenation have generally not been validated by clinical evidence, and it is unlikely that any cutoff value would be applicable to all patients or all categories of acute respiratory failure. Stated another way, there is probably no single value for arterial PCO2, pH, or PO2 that by itself constitutes an indication for IPPV. Compelling face validity justifies the use of IPPV in cases of apnea or when it appears certain that respiratory arrest is about to occur. However, dyspnea, tachypnea, or the subjective impression of respiratory distress are probably not in themselves justification for emergency intubation. It should be possible to avoid IPPV and its attendant complications in many cases of acute hypercapnic respiratory failure. In acute exacerbations of chronic obstructive pulmonary disease, noninvasive positive-pressure ventilation (NPPV) should be the initial ventilation approach unless the patient has one of several specific exclusion criteria such as cardiovascular instability or severely impaired mental status. It may also be possible to avoid intubation through the use of NPPV in certain immunocompromised patients with early acute hypoxemic respiratory failure. However, in other settings of acute hypoxemic respiratory failure, such as acute lung injury and acute respiratory distress syndrome, this has not been shown. The use of IPPV may improve outcomes in patients with severe cardiogenic shock. However, IPPV has not proven to be beneficial in traumatic brain injury and flail chest, in the absence of other indications.
Evolution of the Concept of Acute Respiratory Failure
Traditional Indications for Invasive Mechanical Ventilation
Why Revisiting the Traditional Indications Is Appropriate
Does Every Ventilated Patient Need to Be Intubated?
Does Every Intubated Patient Need to Be Ventilated?
Indications for Mechanical Ventilation in Different Clinical
Apnea and Impending Respiratory Arrest
Acute Exacerbation of COPD
Acute Severe Asthma
Acute Hypoxemic Respiratory Failure
Heart Failure and Cardiogenic Shock
Acute Brain Injury
Implications of Recent Research on Ventilator-Induced Lung Injury
Contraindications to Mechanical Ventilation
Conclusions and Recommendations
It seems logical that a state-of-the-art conference on the techniques and clinical applications of invasive mechanical ventilation should begin with a systematic review of the indications for using it. However, although there have been hundreds of studies on the technical aspects and clinical uses of ventilatory support, and on the process of discontinuing it once underway, surprisingly little work has been done on the reasons and circumstances for initiating this form of life support. In fact, although some textbooks dealing with mechanical ventilation include introductory chapters on indications, a substantial number do not, and in some books the indications for mechanical ventilation cannot even be found in the index. Reviews and chapters discussing indications usually either rehash the pathophysiology of respiratory failure or transpose guidelines developed for ventilator weaning to the “front end” of the mechanical ventilation sequence. Very few address head-on the question of whether and when a given patient should be intubated and placed on a ventilator.
This paucity of studies and explicit discussions of the indications for mechanical ventilation hints at the inherent difficulty of this topic. Because acute respiratory failure (ARF) is by definition a threat to a patient's life, clinicians have naturally regarded ventilatory support as a “given” in management. Specific indications have almost never been studied directly, something as true in 2002 as it was 2 decades ago when this subject was first addressed at a RESPIRATORY CARE state-of-the-art Journal conference.
But there have been important changes. Ventilators and ventilation techniques have evolved, and much more is known about the management of certain forms of ARF. In this article I review the development of the concept of ARF as it applies to the decision when to intubate and ventilate a given patient, and list the indications put forward in the past by different authors and expert groups. I then offer reasons why these traditional indications need to be revisited and review current understanding of the benefit of invasive mechanical ventilation in different categories of ARF. After a brief discussion of how recent data on ventilator-induced lung injury might impact the decision to initiate invasive mechanical ventilation, I conclude with a set of updated indications based on available experimental data in the context of our understanding of the benefits and hazards of this form of support.
This review is restricted to the ventilatory support of adult patients with ARF. Indications for mechanical ventilation in infants and children are not covered, nor is the subject of using long-term mechanical ventilation as an elective therapy (rather than as life support) to rest the ventilatory muscles in patients with chronic ventilatory insufficiency. Because there is no generally accepted abbreviation for invasive mechanical ventilation, and because the term “IMV” means something else, I use the acronym IPPV for invasive positive-pressure ventilation, in order to maintain a parallel with the standard term NPPV (noninvasive positive-pressure ventilation).