INTRODUCTION — Interest in the role of glucocorticoids in the pathophysiology of critical illness has existed since the early part of the 20th century, when investigators observed that the adrenal glands are crucial to survival under conditions of physiologic stress [1,2]. The subsequent development of cortisone for clinical use was followed by clinical studies exploring the potential therapeutic role of corticosteroids in the treatment of severe infections [3-7].
The following issues are discussed in this topic review:
Other aspects of the management of severe sepsis and septic shock are reviewed separately. (See "Management of severe sepsis and septic shock in adults".)
EFFECTS OF CRITICAL ILLNESS — The hypothalamus continuously integrates stimuli and secretes corticotropin releasing hormone (CRH) whenever homeostasis is threatened. CRH stimulates the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary, which induces cortisol secretion from the adrenal glands. Cortisol is the effector molecule of the hypothalamic-pituitary-adrenal (HPA) axis.
Activation of the HPA axis — Normal serum cortisol levels range between 5 and 24 mcg/dL, with significant variability depending upon the time of day [8]. The HPA axis is activated and diurnal variation is lost during physiological stress (eg, major surgery, hypotension, severe infection) [9,10]. Serum cortisol increases as a result, reaching levels as high as 40 to 50 mcg/dL (figure 1) [9,11-14].
In addition to activation of the HPA axis by physiological stress, cortisol metabolism and function may be considerably altered by other aspects of critical illness:
Impairment of the HPA axis — There are circumstances in which cortisol availability cannot be increased sufficiently to meet demand. As an example, drugs like ketoconazole, phenytoin, and etomidate may impair cortisol synthesis [11,19,20]. An observational study of 62 patients found that the use of etomidate for intubation was associated with increased likelihood of having a poor response (≤9 mcg/dL) to ACTH stimulation 24 hours later (odds ratio 12, 95% CI 3-50) [21].
The clinical importance of this observation is uncertain. While some evidence suggests that a single dose of etomidate is associated with worse outcomes in patients with septic shock [22], a randomized trial that compared etomidate with ketamine for rapid sequence induction found that etomidate was NOT associated with worse clinical outcomes despite an increased incidence of adrenocortical hyporesponsiveness to synthetic adrenocorticotropic hormone (ACTH) [23]. The clinical implications of these findings are uncertain because both studies measured plasma cortisol using an immunoassay, which correlates poorly with the reference standard (liquid chromatography with mass spectroscopy) [24].
Head injury, central nervous system depressants, pituitary infarction, adrenal hemorrhage, infections, malignancy, and previous corticosteroid therapy can also impair the HPA axis [11]. Sometimes an etiology cannot be identified.
ASSESSING ADRENAL RESERVE
Random serum cortisol — Serum cortisol levels vary widely in patients with septic shock [14,25-30]. This observation led multiple investigators to try to determine whether serum cortisol is predictive of mortality in patients with septic shock. Numerous studies found increased mortality associated with both low serum cortisol levels and high serum cortisol levels [31-36]. Other studies were unable to find a relationship between cortisol levels and mortality [26,28,37].
ACTH stimulation tests — An adrenocorticotropic hormone (ACTH) stimulation test requires that a baseline serum cortisol be drawn and then synthetic ACTH (cosyntropin) administered intravenously. Serum cortisol levels are drawn 30 and 60 minutes later.
There are two types of ACTH stimulation tests. A high-dose ACTH stimulation test involves the administration of 250 mcg of synthetic ACTH. In contrast, a low-dose ACTH stimulation test involves the administration of only 1 mcg of synthetic ACTH.
High-dose ACTH test — Studies using a high-dose ACTH stimulation test have yielded variable results in septic shock [26,29,37-39]. A prospective cohort study performed high-dose ACTH stimulation tests on 189 patients with septic shock [39]. The results correlated with 28-day mortality: a baseline serum cortisol level >34 mcg/dL and a maximum increase in cortisol of ≤9 mcg/dL were identified as risk factors for death. Three prognostic groups were proposed:
The results from this study are supported by a more recent and larger retrospective cohort study, in which 477 patients with severe sepsis or septic shock underwent high-dose ACTH testing [40]. Nonsurvivors had a higher baseline cortisol level (30 versus 24 mcg/dL) and a smaller cortisol increase (6 versus 11 mcg/dL) than survivors. Patients with either a baseline cortisol level <15 mcg/dL or a cortisol increase ≤9 mcg/dL had a higher mortality, longer duration of shock, or shorter survival time.
Low-dose ACTH test — Some investigators believe that 250 mcg of cosyntropin is supraphysiologic and stimulates adrenal secretion of cortisol even when adrenal dysfunction exists, noting that even patients with impaired adrenal reserve can mount an apparently normal adrenal response to such a high dose of cosyntropin. Use of low-dose (1 mcg) cosyntropin has been proposed as an alternative [41]. (See "Evaluation of the response to ACTH in adrenal insufficiency", section on 'Low-dose ACTH stimulation test'.)
Two investigations have compared a low-dose (1 mcg) ACTH stimulation test to a high-dose (250 mcg) ACTH stimulation test [42,43].
The first study was a prospective cohort study of 59 patients with septic shock who were sequentially administered 1 mcg and 250 mcg of cosyntropin intravenously [42]. All of the patients then received hydrocortisone 100 mg intravenously every eight hours. Patients were designated as steroid responsive if they were able to maintain a mean arterial blood pressure >65 mmHg without norepinephrine infusion within 24 hours after starting hydrocortisone:
The second study was similar, administering low-dose (1 mcg) and high-dose (250 mcg) cosyntropin consecutively to 46 patients with septic shock [43]. Serum cortisol levels were measured at baseline and after each stimulation test. A positive response to ACTH stimulation was defined as a serum cortisol increase >9 mcg/dL. Patients who responded to low-dose and high-dose ACTH were more likely to survive than those who did not respond to either dose. In addition, a response only to high-dose ACTH stimulation was associated with lower survival than a response to both low-dose and high-dose ACTH stimulation, suggesting that low-dose ACTH stimulation identified a subgroup of patients with inadequate adrenal reserve that would have been missed by high-dose ACTH stimulation alone.
Larger studies are needed before the significance of the findings from these two investigations can be fully understood.
Limitations — ACTH stimulation tests may be unreliable in critically ill patients for several reasons:
Free cortisol — In critically ill patients, loss of cortisol binding globulin (CBG) results in decreased protein-bound cortisol and increased free cortisol. Therefore, for any given amount of serum total cortisol, there is a shift from inactive protein-bound cortisol to physiologically active free cortisol. This suggests that standard assays for plasma cortisol (which measure total plasma cortisol) underestimate HPA axis activity. It has been proposed that free cortisol more accurately reflects HPA axis activation [48].
This was illustrated by a study comparing total serum cortisol and free serum cortisol levels in 33 healthy volunteers to those in 60 critically ill patients (18 had sepsis) [48]. The critically ill patients had total serum cortisol concentrations that were two to three times higher and free cortisol levels that were 7 to 10 times higher than healthy volunteers. Although the total serum cortisol appeared lower in critically ill patients with hypoalbuminemia (albumin ≤2.5 g/dL) than in critically ill patients with preserved albumin concentrations, the free cortisol levels were similar.
The study has two major limitations. First, the critically ill patients did not include any patients with septic shock [49]. Second, the degree of hemodynamic instability at the time of plasma cortisol sampling was not reported. Thus, it is impossible to correlate the cortisol level with severity of illness or physiologic status [50]. The applicability of the study to routine clinical practice is uncertain because the free cortisol assay is not available at most clinical centers [51].
In another investigation, 74 patients had their total and free cortisol levels measured before and after the administration of 250 mcg of cosyntropin [52]:
Whether the free cortisol level provides useful prognostic information in critically ill patients has not been formally investigated.
RELATIVE ADRENAL INSUFFICIENCY — Cortisol is necessary to survive critical illness [1,2]. But, how much is enough?
Absolute adrenal insufficiency is rare among critically ill patients, with an incidence estimated to be ≤3 percent [53]. However, the following observations argue that suboptimal cortisol production may be common and associated with worse outcomes:
Suboptimal cortisol production during septic shock has been termed "functional" or "relative" adrenal insufficiency [11]. This condition has also been called “critical illness-related corticosteroid insufficiency (CIRCI)” [54]. There is no consensus about the diagnostic criteria or indications for treatment of this entity. In addition, there exists considerable disagreement over what cortisol level is "normal" or "appropriate" in septic shock, what constitutes an adequate response to ACTH, and what dose of synthetic ACTH should be used for stimulation testing.
The question of how much cortisol is enough for a critically ill patient is confounded by the possibility that glucocorticoid resistance exists at the target-tissue level. Few data support the notion that genetic or acquired glucocorticoid receptor abnormalities affect critically ill patients. Assays of the cellular activity of cortisol, cortisol-glucocorticoid-receptor binding, and glucocorticoid-receptor transcription activity are limited to experimental investigations and their clinical relevance is unknown [55]. The mechanisms of glucocorticoid resistance are discussed separately. (See "Glucocorticoid-resistant asthma", section on 'Mechanisms of glucocorticoid resistance'.)
Using an overnight metyrapone stimulation test as the reference standard, a prospective cohort study found that patients with septic shock who had a baseline total cortisol level <10 mcg/dL or a change in total cortisol <9 mcg/dL after high-dose ACTH stimulation, were likely to have adrenal insufficiency [56]. Conversely, patients with septic shock who had a baseline total cortisol level ≥44 mcg/dL or a change in total cortisol ≥16.8 mcg/dL, were unlikely to have adrenal insufficiency. The generalizability of these results has been questioned because the frequency of absolute adrenal insufficiency in this study was nearly four times that previously reported [57]. In addition, the values were not used to guide therapeutic decision making and, therefore, their impact on clinical outcome is unknown.
We believe that it is uncertain whether "relative adrenal insufficiency" or a synonymous condition is a true diagnostic entity, since a clear definition is lacking and the cortisol assays that are available at most clinical laboratories are unreliable in the critically ill patient.
CORTICOSTEROID THERAPY — Interest in the possible therapeutic role of corticosteroids in severe infections has existed for at least 50 years [4-7,58,59].
Clinical evidence — In the 1980s, three randomized, double-blind, placebo-controlled studies were published [60-62]. None of the trials found a mortality benefit and only one trial noted decreased duration to shock resolution associated with the administration of corticosteroids. All of the trials administered high-dose corticosteroids for a short duration and used early endpoints.
In the 1990s, interest in corticosteroids as a therapy in septic shock was renewed, this time using smaller, more physiological doses for longer duration. Three small trials (approximately 40 patients each) compared corticosteroid administration to placebo in patients with septic shock and found decreased duration of shock associated with corticosteroid therapy [63-65]. These trials prompted larger randomized trials.
French trial — In a multicenter, double-blind trial conducted in France, 300 patients were randomly assigned to receive placebo or hydrocortisone (50 mg intravenously every six hours) plus fludrocortisone (50 mcg enterally once a day) within eight hours of the onset of septic shock [66]. Treatment continued for seven days. Based upon a high-dose (250 mcg) ACTH stimulation test, the patients were classified as having adequate adrenal reserve (maximum increase in serum cortisol of >9 mcg/dL) or inadequate adrenal reserve (maximum cortisol increase of ≤9 mcg/dL):
The trial was criticized for its high placebo-group mortality and the statistical methods used to describe outcomes [67-69].
The association between corticosteroid therapy and improved mortality was supported by two subsequent meta-analyses [70,71]. However, no significant benefit was noted in a large randomized trial (CORTICUS) published after the meta-analyses.
CORTICUS — The Corticosteroid Therapy of Septic Shock (CORTICUS) trial was a multicenter, double-blind trial that randomly assigned 499 patients with septic shock to receive hydrocortisone (50 mg) or placebo intravenously every six hours for five days, followed by a tapering regimen [72]. Based upon a high-dose (250 mcg) ACTH stimulation test, the patients were classified as having inadequate adrenal reserve (maximum cortisol increase of ≤9 mcg/dL) or adequate adrenal reserve (maximum increase in serum cortisol of >9 mcg/dL).
Hydrocortisone administration did not improve 28-day mortality (35 versus 32 percent in the placebo group). This was also true in the two pre-defined subgroups – patients with inadequate adrenal reserve and patients with adequate adrenal reserve. The hydrocortisone group had faster reversal of shock among all patients (3.3 versus 5.8 days in the placebo group) and increased incidence of new infection that did not reach statistical significance (odds ratio 1.27, 95% CI 0.96-1.68). The trial was criticized for the lower than expected placebo-group mortality (32 percent versus the anticipated 50 percent).
Comparison — These randomized trials have important differences that may, at least in part, explain their conflicting results.
These differences imply that corticosteroid therapy is most likely to benefit patients with severe septic shock. This was supported by two meta-analyses that looked at the effects of long courses of low-dose steroids (≤300 mg per day of hydrocortisone or an equivalent for ≥5 days) in patients with septic shock:
Both meta-analyses detected possible publication bias and the latter meta-analyses had a moderate amount of heterogeneity, limiting our confidence in the estimate of the effect.
Conclusions — Several conclusions can be based upon the available evidence:
Administration — Hydrocortisone is a pharmacologic form of cortisol. Compared to hydrocortisone, other pharmacologic corticosteroids bind cortisol-binding globulin (CBG) poorly, resulting in more free, physiologically active corticosteroid and greater potency at any given dose. The different preparations vary widely in anti-inflammatory and mineralocorticoid potency.
Most studies evaluating the effect of corticosteroids in septic shock used hydrocortisone, although administration protocols and treatment durations varied. It is unknown whether the findings can be generalized to other synthetic corticosteroids. We typically administer 50 mg of hydrocortisone every six hours or 100 mg of hydrocortisone every eight hours.
There is no consensus regarding the optimal administration protocol or treatment duration, because no study has compared fixed-duration regimens to clinically-guided regimens, or tapering to abrupt cessation [77]. However, in one clinical study, abrupt cessation was associated with rebound of hemodynamic abnormalities and increased inflammatory markers [78].
Although one of the large randomized trials added fludrocortisone at a dose of 50 mcg per day for seven days, we do not typically add fludrocortisone because we believe that hydrocortisone alone has sufficient mineralocorticoid effect and absorption of the enterally administered drug is questionable in situations of compromised splanchnic perfusion [66]. Our decision to forego fludrocortisone is supported by a trial (the Corticosteroids and Intensive Insulin Therapy for Septic Shock [COIITSS] trial) that randomly assigned 509 patients with septic shock to receive either hydrocortisone plus fludrocortisone or hydrocortisone alone [79]. There was no difference in any of the clinical outcomes.
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