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A Suzanne M. Burns, RN, MSN, RRT, ACNP, CCRN, replies:
IPF is an interstitial lung disease with a progressive and typically fatal outcome. Unfortunately, the median survival rate for this disease is often fewer than 3 years.1 The cause of IPF was previously thought to be inflammation but current information suggests that this disease is instead caused by epithelial injury that results in fibrosis, progressive decline of lung function, and death.2–4
Diagnosis
IPF is one of a group of interstitial diseases, as defined by the American Thoracic Society/European Respiratory Society international multidisciplinary consensus committee panel.5 The committee stated the importance of identifying or excluding IPF as early as possible because of its pattern of progressive decline and bad prognosis, and further suggested how IPF should be defined and diagnosed.
The consensus group recommended that IPF be defined as a condition characterized by dyspnea and chronic cough, restrictive lung disease, and the histopathologic pattern of usual interstitial pneumonia (UIP).5 The term UIP is used to describe the usual microscopic pattern seen with interstitial pneumonias and includes a number of features such as minimal areas of inflammation, the presence of fibroblasts, chronic fibroproliferation, and widespread scaring.4,6 Because the cause of UIP is unknown, this term is often used interchangeably with IPF.1,6,7
Surgical biopsy is the definitive method of diagnosing IPF; however, in practice this procedure is done in only 15% of patients.4,6 The American Thoracic Society/European Respiratory Society criteria for diagnosis of IPF in the absence of surgical lung biopsy are presented in Table 1
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In the past, steroids were commonly used to treat the cause of IPF, which was presumed to be an inflammatory process. Unfortunately, the response to steroids in IPF has been as low as 8% to 17%.6,8 Azathioprine and cyclophosphamide have also been used, alone or in combination with steroids, but again with limited response.9 Recent data suggest that interferon gamma-1b and the combination of steroids and azathioprine plus N-acetylcysteine may slow IPF progression in some patients. However, no large clinical trials have been done to definitively determine efficacy.10 Finally, single lung transplantation has demonstrated improved survival in patients with this disease, but few patients actually live to receive this treatment.11 Table 2 summarizes diagnostic features, treatment, and prognosis of IPF.
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The current management of IPF in the ICU setting is mainly supportive and includes the use of oxygen, mechanical ventilation, and often corticosteroids and cytotoxic drugs; although the drugs are rarely helpful. Therefore, the goals are to use mechanical ventilation to support the failing lung, ensure hemodynamic stability, prevent end-organ failure and iatrogenic conditions, and support the patient and family until transplantation can be accomplished. In the past, 30% of patients died while waiting for a transplant.6
Recently, the United Network for Organ Sharing introduced a lung allocation scoring system that awards IPF patients a higher score than previously. This change may result in more IPF patients receiving transplants in the future. Regardless, the patient and family are generally well aware of the prognosis and high potential for death associated with the need for mechanical ventilation and an ICU admission.
Although an extensive discussion of ICU management of the patient with IPF is beyond the scope of this article, the ventilatory management of these patients is briefly discussed below.
Mechanical Ventilation
Patients with IPF exhibit a rapid and shallow spontaneous breathing pattern; work of breathing is exceptionally high. Adequate oxygenation is hard to maintain because much of the lung parenchyma is fibrotic and stiff. There is widespread alveolar collapse and subsequent shunt. Respiratory failure ensues and intubation and ventilation are required. Ventilating patients with severe IPF is difficult because the lungs are extremely stiff and noncompliant. Furthermore, because of the decreased compliance, airway and plateau pressures are high, especially if ventilated with traditional lung volumes (ie, 8–12 mL/kg).
To protect the lungs, a low lung ventilation strategy similar to that used for patients with acute respiratory distress syndrome is employed, using volumes of 6 mL/kg (ideal body weight).12 Often, the patients require heavy sedation and sometimes paralytic agents to ensure patient/ventilator synchrony, a decreased respiratory workload, and adequate oxygenation. Positive end-expiratory pressure is applied to improve oxygenation and to promote the restoration of functional residual capacity by recruiting viable lung. However, this is not easily accomplished given the pathophysiology of the fibrotic lung.
Summary
Caring for critically ill patients with IPF is challenging. Although the outcome of the disease is poor without transplantation, the National Institutes of Health’s National Heart, Lung and Blood Institute has announced the establishment of an IPF Clinical Research Network, consisting of 11 medical centers across the country, that will focus on treatment options for IPF.13 Hopefully, more successful therapies will be discovered for this devastating disease.
References
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