Page 132 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

98 PART 1: An Overview of the Approach to and Organization of Critical Care

12 TABLE 14-2 Risk Factors for Chronic Critical Illness
Advanced age
10 8 Severe sepsis
Total annual days in millions 6 4 Multiple trauma
Multilobar pneumonia or ARDS
Severe cerebrovascular accident or traumatic brain injury
Comorbidities
COPD
Renal insufficiency
CHF
Postoperative complications
2
Preoperative instability
Prolonged operation
0 Ventilator-associated pneumonia or central line–associated bloodstream infection
2000 2010 2020
Year ICU-acquired weakness
ICU Days Hospital Days
polyneuropathy (CIP), critical illness myopathy, and immobility. CIP
FIGURE 14-1. Projected increases in ICU and hospital bed days for patients requiring at is evident in up to 47% of patients who are ventilated for greater than 7
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least 96 hours of mechanical ventilation (prolonged acute mechanical ventilation [PAMV]). days and in 95% of patients who are ventilated for more than 28 days.
(Adapted with permission from Zilberberg MD, Shorr AF. Prolonged acute mechanical ventila- The presence of the systemic inflammatory response syndrome (SIRS)
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tion and hospital bed utilization in 2020 in the United States: implications for budgets, plant and hyperglycemia are the greatest risk factors. The use of aminogly-
and personnel planning. BMC Health Serv Res. November 25, 2008;8:242.) cosides, neuromuscular blockers, and steroids may also contribute to the
development of CIP although studies are conflicting. Abnormalities on
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neurophysiologic testing persist for up to 5 years. There is no specific
These CCI patients represent 0.25% of the 35 million annual hospital therapy for this condition other than aggressive rehabilitation. In most
discharges in the United States. Although this is a small fraction of all cases, recovery is very slow. Diaphragm paralysis from phrenic nerve
hospital admissions, CCI patients have a substantial impact on hospital injury is another neuromuscular condition that contributes to PMV. It is
resources owing to prolonged stays and high-intensity care. Importantly, difficult to diagnose, but it should be suspected in any patient who has
52% of CCI patients are over age 65. This reflects an overall higher inci- had cardiothoracic or neck surgery and has difficulty with spontaneous
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dence of acute respiratory failure in elderly patients. As the baby boom breathing, especially while in the supine position. An elevated hemi-
generation approaches this age group in the next 10 years, the number diaphragm on chest radiograph is suggestive, but it is often not present.
of patients at risk for CCI is expected to more than double, demanding a Real-time ultrasound during spontaneous breathing is a simple and
significant increase in ICU and hospital bed days (Fig. 14-1). 14 accurate means to establish the diagnosis. 21b
RISK FACTORS
PATHOPHYSIOLOGY OF CHRONIC CRITICAL
Patients who are susceptible to chronic critical illness are as heteroge- ILLNESS: THE NEUROENDOCRINE MODEL
neous as the general ICU population. The most significant risk factor
for CCI is multiorgan failure including shock or ARDS at admission Despite the varied definitions and nonspecific clinical findings that have
(Table 14-2). Severe sepsis and multiple trauma are common etiolo- been used to describe CCI patients, they appear to be a physiologically
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gies as are severe neurologic injuries such as stroke or traumatic brain distinct subset of the overall ICU population. This has been best dem-
injury. While PMV is a hallmark of CCI, and patients with end-stage onstrated by the work of Grete Van den Berghe and others who have
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lung disease or neuromuscular disorders are certainly susceptible, such examined neuroendocrine responses to critical illness. During the acute
patients with single organ failure represent a small proportion of the phase of critical illness, adrenocorticotropic hormone (ACTH), cortisol,
CCI population. Patients with postoperative complications from cardiac and prolactin levels are elevated, whereas thyrotropic and gonadotropic
or abdominal surgery are at risk, and trauma patients are common as hormone levels are reduced. During the chronic phase of critical
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well. Critically ill patients admitted to the ICU with significant comor- illness, hormonal responses are significantly different (Table 14-3).
bidities are at higher risk, especially those with underlying heart disease, ACTH and other anterior pituitary hormone levels decrease, but
chronic obstructive pulmonary disease (COPD), and kidney disease. For hypercortisolism persists, suggesting an alternative pathway for cortisol
surgical patients, preoperative instability, COPD, prolonged operation, release. CCI patients lose thyroid-stimulating hormone (TSH) pulse
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and in the case of cardiac surgery patients, increased bypass time are amplitude, which results in typically low or low-normal TSH levels and
important risk factors for PMV. Development of nosocomial pneumo- low thyroxine (T ) and triiodothyronine (T ) concentrations compared
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4
3
nia, aspiration events, and failed extubations are additional proven risk to acutely stressed patients. This may be related to reduced expression
factors for PMV. A predictive model quantifies the risk of prolonged of the thyrotropin-releasing hormone (TRH) gene in the hypothalamic
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(greater than 7 days) mechanical ventilation by including the primary paraventricular nuclei. 25
disease, acute physiology by APACHE III score, age, presence of COPD, The somatotropic axis also demonstrates important differences
prior functional limitations, and length-of-hospital stay prior to ICU between acute and chronic critical illness. For patients who are in the
admission. The acute physiology score and primary reason for ICU acute phase of critical illness, the pituitary gland actively secretes growth
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admission accounted for 0.66 of the explanatory power for the model. hormone (GH) into the circulation in a pulsatile fashion that is regulated
ratio, by hypothalamic growth hormone–releasing hormone (GHRH). GH
Of the variables in the acute physiology score, pH, Pa CO 2 , Pa O 2 /Fi O 2
albumin level, and respiratory rate were significant predictors. Further levels and GH pulse frequency are increased compared with normal
development of clinically useful prediction models for PMV would be of function. In contrast, for patients who have received mechanical ventila-
great benefit for resource planning in the ICU. tion for greater than 21 days, the pattern of GH secretion is less regular,
Perhaps one of the most important risk factors for chronic criti- and the amount that is released in pulses is greatly reduced. Nocturnal
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cal illness is ICU-acquired weakness associated with critical illness secretion of GH is reduced relative to the acute stressed condition.

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