For the purposes of epidemiological studies, the definition of severe CAP as "CAP needing ICU admission" is adequate. In practical management terms, however, a more detailed method of assessment is needed. Severe CAP is almost always a multiorgan disease and patients with severe CAP at presentation will either already have, or will be rapidly developing, multiple organ failure. It is important that respiratory and other "front line" physicians appreciate this aspect of the disease. Apparent stability on high flow oxygen can rapidly change to respiratory, circulatory, and renal failure. Progressive loss of tissue oxygenation needs to be anticipated, recognised quickly, and rapid action taken to prevent its progression to established organ failure.
The BTS guidelines define severe pneumonia ("rule 1") as the presence of two or more of the following features on hospital admission4:
• Respiratory rate > 30/minute
• Diastolic blood pressure <60 mm Hg
The guidelines include three additional assessment recommendations. The presence of any one of these approximately doubles the rate of death:
• Altered mental status, confusion or an Abbreviated Mental Test score of <8/10
• Hypoxaemia (Po2 <8 kPa or O2 saturation <90%), with or without a raised Fio2
• Bilateral or multilobar (more than two lobes) shadowing on the chest radiograph
Using the need for ICU admission as the end point, various combinations of minor and major criteria give different combinations of specificity and sensitivity.1 In the presence of at least one of the ATS criteria sensitivity was 98% but specificity only 32%. Positive predictive power was much improved using a combination of two of three major criteria and multilobar involvement. Sensitivity was 78% and specificity 94%.
More than a decade ago the BTS performed a ground breaking study on severe CAP.8 In their series 60 patients from 25 hospitals required ICU care in a 12 month period. One of the more striking findings was that eight patients were admitted to the ICU only after suffering cardiorespiratory arrest on general medical wards. In retrospect, six of these eight could have been identified using the BTS "rule 1" severity guide. In a related study CAP related deaths over 3 years in patients aged <65 years in the Nottingham area of the UK were retrospectively audited.9 They found evidence of suboptimum care in a number of cases, including a lack of appreciation of disease severity, lack of input from senior doctors, and lack of suitable investigations including arterial blood gas measurements. These and other studies provided evidence of suboptimal management of patients with severe CAP in the late 1980s and early 1990s. They also produced clear and simple assessment tools and guidelines to improve practice. Unfortunately, recent reports suggest that these important lessons have not been learnt. McQuillan and coworkers recently performed a confidential inquiry into the quality of care before admission to the ICU10 which covered a wide range of both medical and surgical admissions including patients with severe CAP. The study found that suboptimal care had been given to 54% and, importantly, that hospital mortality in this group was significantly higher than in those managed well (56% v 35%). Errors in the management of the airway, breathing, circulation, monitoring, and oxygen therapy were common.
Correct management of severe CAP before admission to the ICU is therefore essential. Recognition of the severity of illness is the first vital step, in which application of the BTS severity rules and screening pulse oximetry are useful tools. Repeated regular assessment by the same observer in the initial stages of the illness is necessary and rapid review by a critical care practitioner should be arranged for any patient who meets the BTS or similar severity criteria or who is deteriorating. The need for increasing Fio2, altered mental state (confusion, aggression), and the onset of either respiratory or metabolic acidosis are all signs of disease progression and the need for further intervention.
In the UK the recent publication of the Department of Health document "Comprehensive Critical Care'11 suggests expanding high dependency or—in the new terminology— level 2 care. This would provide a suitable environment for the initial treatment of patients with severe CAP who do not need immediate mechanical ventilation. These patients are likely to benefit from more intensive monitoring (arterial line, central venous line, urinary catheter) and treatment (rapid correction of hypovolaemia, inotropic support, continuous positive airway pressure (CPAP), non-invasive ventilation (NIV)). Level 2 care also allows the rapid initiation of invasive mechanical ventilation when needed.
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