Chronic Critical Illness in Patients With Sepsis is Associated With Persistent Anemia, Inflammation, and Impaired Functional Outcomes

Abstract

Introduction:

Survivors of sepsis will progress towards rapid recovery (RAP) or enter a state of persistent organ dysfunction and chronic critical illness (CCI). Independently, anemia is known to be a significant factor in functional recovery of hospitalized patients. This study aims to analyze long-term hemoglobin levels and functional outcomes following RAP and CCI.

Methods:

A prospective, cohort study was performed in septic patients who were stratified into RAP (N = 54) with ICU length of stay < 14 days or CCI (N = 63) with ICU length of stay > 14 days. CBC and plasma inflammatory markers were measured on the day of enrollment, weekly until day 42, then at 3 and 6 months. Functional outcomes using Zubrod scale, gait speed test, and total short physical performance battery (SPPB) were assessed at 3, 6, and 12 months.

Results:

Mean age was 59 years (range: 20-83) and 62% were male. Hemoglobin was significantly decreased at 3 and 6 months in CCI compared to RAP (8.9* and 9.2* vs 10.4 and 11.1 g/dL), despite receiving significantly more red blood cell transfusions. CCI patients had persistent elevation of CRP, IL-6 and TNF-α. CCI patients had worse functional outcome with a significantly higher Zubrod score, and lower SPPB, and gait speed score at 3, 6, and 12 months.

Conclusion:

Despite receiving more pRBC transfusions, CCI patients had a persistent anemia that was associated with chronic systemic inflammation and poor functional outcomes six months following sepsis. Alleviating prolonged inflammation could improve persistent anemia and functional outcomes in CCI patients.

Introduction

Over the past few decades, inpatient mortality due to sepsis events have dramatically declined. Factors affecting sepsis recovery following discharge from the hospital include the presence or absence of physical, mental, and cognitive deficits, long-term medications, and complications such as infection, heart failure, renal failure, and aspiration.¹ Furthermore, sepsis survivors will either undergo rapid recovery (RAP) or go on to develop chronic critical illness (CCI), a condition characterized by the pathophysiology of persistent inflammation, immunosuppression, and protein catabolism leading to poor long-term functional recovery, cachexia, and discharge to long-term acute care and skilled nursing facilities. CCI following sepsis has also been shown to be associated with increased mortality.^2-5

Independently, anemia has been demonstrated to be a significant factor in the functional recovery and clinical outcomes of hospitalized patients.^6-8 Anemia is a common complication in critically ill surgical patients in the intensive care unit (ICU) and it is known to persist months after discharge.^9-11 Decreased hemoglobin levels have been shown to be associated with persistent inflammation in these patients.¹² Etiologies of anemia in the critically ill ICU patient include blood loss from surgery, phlebotomy, or trauma, iron and nutritional deficiencies, hemolysis, myelosuppression, renal insufficiency, and impaired erythropoiesis, inflammation, and infection.⁹ Critically ill patients with significant anemia often receive more packed red blood cell (pRBC) transfusions, which places them at higher risk for infectious complications, increased mortality, and other transfusion-related complications.^13-15

This study sought to analyze the associations between hemoglobin concentrations, inflammatory markers, and functional outcomes between those with RAP and CCI in ICU survivors following sepsis. We hypothesized that CCI patients have persistent anemia and prolonged systemic inflammation that is associated with poor functional outcomes.

Methods

Patient Enrollment

This was a retrospective analysis of prospectively obtained cohort data of surgical intensive care unit (ICU) patients who developed sepsis. This study was approved by the institutional review board and was performed between January 2015 and June 2019 at an academic quaternary-care referral center. The study was registered with clinicaltrials.gov (NCT02276417) and conducted by the Sepsis and Critical Illness Research Center, whose study design and protocols have been previously published.¹⁶ Critically ill septic patients from two surgical/trauma intensive care units (SICU) at an academic medical center were evaluated for enrollment. Differences in long-term outcomes of sepsis survivors were compared between patients that developed CCI (≥14 ICU days with persistent organ dysfunction) as compared to those who exhibited rapid recovery (RAP; <14 ICU days with organ recovery). We defined “persistent organ dysfunction” as the presence of abnormal organ function in one or more systems as measured by Sequential Organ Failure Assessment (SOFA) score on day 14 (cardiovascular SOFA ≥ 1, or score in any other organ system ≥ 2).

As previously published, screening for sepsis was carried out using the Modified Early Warning Signs-Sepsis Recognition System (MEWS-SRS), which quantifies derangements in vital signs, white blood cell count, and mental status.^3,4 All patients eligible for inclusion in the study were enrolled within 12 hours of sepsis protocol onset. If written informed consent could not be obtained from the patient or their legally assigned representative within 96 hours of study enrollment, the patient was removed from the study. All patients with sepsis were managed using a standardized, evidence-based protocol that emphasizes early goal-directed fluid resuscitation as well as other time-appropriate interventions such as administration of broad-spectrum antibiotics.¹⁷ Patients eligible for participation in the study met the following inclusion criteria: (1) admission to the surgical or trauma ICU; (2) age ≥18 years; (3) clinical diagnosis of sepsis, severe sepsis or septic shock with this being the patient’s first septic episode; and (4) entrance into our sepsis clinical management protocol. Patients were excluded if any of the following were present: (1) refractory shock (ie, patients expected to die within the first 24 hours); (2) an inability to achieve source control (ie, irreversible disease states such as unresectable dead bowel); (3) pre-sepsis expected lifespan <3 months; (4) patient/family not committed to aggressive management; (5) severe congestive heart failure (NYHA Class IV); (6) Child-Pugh Class C liver disease or pre-liver transplant; (7) known HIV with CD4⁺ count <200 cells/mm³; (8) organ transplant recipient or use of chronic corticosteroids or immunosuppressive agents; (9) pregnancy; (10) institutionalized patients; (11) chemotherapy or radiotherapy within 30 days; (12) severe traumatic brain injury (ie, evidence of neurological injury on CT scan and a Glasgow Come Scale <8); (13) spinal cord injury resulting in permanent sensory and/or motor deficits; or (14) inability to obtain informed consent.

Patient Classification

Patients were diagnosed with sepsis, severe sepsis, or septic shock using the definitions established by the Society of Critical Care Medicine, the European Society of Intensive Care Medicine, the American College of Chest Physicians, the American Thoracic Society, and the Surgical Infection Society (SCCM/ESICM/ACCP/ATS/SIS) 2001 International Sepsis Definitions Conference.¹⁸ Demographic information was collected in addition to the number of packed red blood cell (pRBC), fresh frozen plasma (FFP), and platelet transfusions.

Clinical Outcomes

The short physical performance battery (SPPB) is based on a timed short-distance (4 m) walk, repeated chair stands, and balance test. Gait speed was measured during the 4 m walk. These outcomes were measures at 3, 6, and 12 months.

In terms of functional outcomes, the Zubrod score was determined. The Zubrod score ranges from 0 to 5, with increasing score reflecting worse performance status: 0, asymptomatic (fully active); 1, symptomatic but completely ambulatory (restricted in physically strenuous activity); 2, symptomatic, <50% in bed during the day (ambulatory and capable of all self-care but unable to perform any work activities); 3, symptomatic, >50% in bed, but not bedbound (capable of only limited self-care); 4, bedbound (completely disabled, incapable of any self-care); and 5, death. Baseline or pre-hospitalization performance status was determined as soon as possible after study enrollment based upon patient or proxy reported 4-week recall assessment. Functional outcomes were subsequently measured at 3 months, 6 months, and 12 months.

Sample Collection and Laboratory Analysis

Serial blood samples were collected from hospitalized septic patients at 12 hours and on days 1, 4, 7, 21, 28, 35, and 42. Complete blood counts were performed by a hematology analyzer. Blood samples were then spun down for plasma by centrifuging the blood in a lavender top (EDTA) blood collection tube at room temperature (22°C) for 10 minutes at 1800 × g, with the brake on low. Interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α) and C-reactive protein (CRP) were measured using multiplex. Luminex® multiplex assays utilize specialized magnetic microsphere beads coated with analyte specific antibodies. Multiple analyte specific beads of choice are combined with a test sample allowing for the detection and quantification of multiple targets in a single sample. Once the sample and beads have been combined, biotinylated detection antibodies and a streptavidin-phycoerythrin conjugate are added creating a capture sandwich immunoassay on each individual bead. These complexes are then analyzed with the Luminex® MAGPIX® instrument using Luminex’s xMAP® technology. The results are exported to the VigeneTech’s MILLIPLEX™ Analyst software and a complete detailed report of the data is produced.

Statistical Analysis

Data are presented as frequency and percentage, mean and standard deviation, or median and interquartile range. Statistical analysis was performed in GraphPad Prism version 7.05 (GraphPad Software, La Jolla, CA). Fisher’s exact test was used to compare categorical variables. Figures are illustrated as line graphs over several time points and bar graphs. Data were compared by two-way analysis of variance using Tukey’s multiple comparisons test at each time point based on clinical trajectory (CCI vs RAP). Significance was set at P = .05 between groups.

Results

Study Population

Figure 1 depicts overall subject enrollment, withdrawal, mortality, and follow-up. A total of 205 patients were enrolled and consented into the study, of which 6 were early deaths (expired prior to day 14), 12 withdrew from the study. The septic patients included at discharge had a mean age of 59 (range: 20-83) and 62% were male. The reason for hospital admission was active infection (62%), elective surgery (19%), trauma (10%), and other non-infectious complications (9%). Characteristics of RAP and CCI patients are provided in Table 1. There was no difference in severe sepsis between RAP and CCI patients (44% vs 44%, P = .788), however, there were significantly more patients with septic shock in the CCI group as compared to RAP (44%* vs 15%, P < .001). Majority of causes of sepsis in both groups was intra-abdominal (RAP: 42% vs CCI: 46%, P = .678) and there was no difference in operative intervention in both groups (RAP: 49% vs CCI: 48%, P = .889). Patients with CCI had a significantly longer hospital length of stay (28* vs 15 days, P < .001).

Figure 1.

Flowchart of patient enrollment and subsequent study population.

Table 1.

Characteristics of Patient Population.

	Rapid recovery patients (n = 126)	Chronic critical illness (n = 79)	P-value
Demographics
Male, n (%)	63 (49)	48 (61)	.2401
Age in years, mean (SD)	57 (17)	62 (13)	.101
Age ≥ 65, n (%)	49 (39)	34 (43)	.6941
Race, n (%)
Caucasian	107 (85)	71 (90)	.3041
African American	13 (10)	7 (9)
Asian	4 (3)	0 (0)
Other	4 (3)	1 (1)
BMI, median (IQR)	29 (24-37)	30 (25-39)	.6288
Inter-facility hospital transfer, n (%)	45 (36)	41 (52)	.119
Sepsis severity by sepsis 2 criteria, n (%)
Sepsis	52 (41)	9 (12)	<.001
Severe sepsis	55 (44)	35 (44)	.788
Septic shock	19 (15)	35 (44)	<.001
Primary sepsis diagnosis, n (%)
Bacteremia	4 (3)	2 (2)	.36
Intra-abdominal infection	53 (42)	36 (46)	.678
Necrotizing soft tissue infection	4 (3)	4 (5)	.2611
Pneumonia	21 (17)	13 (17)	.1501
Surgical site infection	32 (25)	14 (18)	.6911
Urosepsis	6 (5)	4 (5)	.267
Other	6 (5)	6 (7)	.6781
Creatinine at sepsis onset, median (IQR)	1.1 (.6-1.2)	1.1 (.8-2)	.1773
Lactate at sepsis onset, median (IQR)	1.5 (1.1-2.7)	1.8 (1.2-2.8)	.6106
Inpatient outcomes
In-hospital mortality, n (%)	0 (0)	6 (8)	<.0001
Intensive care unit Length of stay (LOS), median (IQR)	9 (5-12)	24 (18-39)	<.0001
Hospital LOS, median (IQR)	15 (12-30)	28 (24-48)	<.0001
Multiple organ failure incidence, n (%)	14 (36)	60 (76)	<.0001
30-day mortality, n (%)	1 (3)	7 (9)	.2679

IQR=INTERQUARTILE RANGE AND BMI=BODY MASS INDEX

Persistent Anemia Following CCI

Anemia was present in both the RAP and CCI groups at the beginning of the study with hemoglobin measurements on the day of enrollment (RAP: 9.5±1.9 and CCI: 8.6±1.8* g/dL; *P < .0009)(Figure 2A). Hemoglobin levels remained < 9 g/dL in CCI patients until 3 months. The CCI patients had significantly lower hemoglobin levels on day 4 and 7 when compared to RAP patients (CCI 8.6* and 8.5* vs RAP: 9.2 and 9.1 g/dL, P = .001 and P =.002). Improving anemia for both groups was observed from day 42 to 3 months and again from 3 months to 6 months as indicated by increasing hemoglobin levels, with the most significant improvement occurring between day 42 and 3 months for both RAP and CCI. However, persistent anemia remained in the CCI group at 3 and 6 months with significantly decreased hemoglobin levels (8.9 ± 1.4 and 9.2 ± 1.5 g/dL, respectively). There was significant improvement in the RAP group at 3 and 6 months (10.4 ± .6 and 11.1 ± 2.0 g/dL, respectively). This difference in hemoglobin levels between the 2 groups occurred despite the CCI group receiving more pRBC transfusions as compared to the RAP group (7.1 ± 6.8* vs 4.0 ± 3.9u pRBC, P = .009)(Figure 2B). When examining the time of pRBC transfusions, there was no significant difference in early pRBC transfusions, the significant difference occurred after 14 days. The RAP group received more FFP (7.4 ± 8.5 units) than the CCI group (4.7 ± 3.1 units, P = .29). Platelet transfusions were also similar between the 2 groups (RAP: 2.7 ± 1.8 units and CCI: 2.6 ± 2.1 units, P = .97).

Figure 2.

(A-B). Long-term anemia despite increased transfusions. (A). Hemoglobin trends from the day of enrollment until 6 months for rapid recovery patients and CCI patients. (B). Increased number of pRBC transfusions for CCI patients. RAP=rapid recovery patients; CCI = chronic critical illness; pRBC=packed red blood cell transfusions; *P < .05.

Prolonged Systemic Inflammation Following CCI

Persistent elevations in serum pro-inflammatory cytokines IL-6, TNF-α, and CRP were observed in the CCI group at day 35 and day 42(Figure 2A-C). In contrast, means for all 3 pro-inflammatory cytokines for the RAP group were within normal intervals by day 35 and 42. Mean IL-6 levels at 12 hours were 3 times higher in the CCI group than the RAP group (1340±2487* vs 401±618 pg/mL, P = .01)(Figure 3A). IL-6 levels in the CCI group decreased between 12 hours and day 4. IL-6 levels continued to decline from day 4 to day 28 in the CCI group. However, an increase in IL-6 was observed at day 35 (119 ± 161 pg/mL) with a slight improvement at day 42 (90 ± 48 pg/mL). RAP patients had a decline in IL-6 from day 14 until reaching normal on day 35 that persisted on day 42.

Figure 3.

(A-C). Persistent inflammatory cytokine profiles following CCI. (A). Plasma Il-6 is significantly elevated at the time of sepsis onset and on day 4 in CCI patients. (B). Plasma TNF-α is significantly elevated 4 weeks in CCI patients. (C). Plasma CRP is significantly elevated at 2 and 4 weeks in CCI patients. RAP = rapid recovery patients; CCI = chronic critical illness; IL-6=interleukin-6; TNF-α=tumor necrosis factor alpha; CRP= c-reactive protein; *P < .05.

Mean serum TNF-α levels at 12 hours were higher in the CCI group versus the RAP group (70.0 ± 100 vs 53 ± 45 pg/mL, P = .27)(Figure 3B). Serum TNF-α levels for the RAP group steadily declined continuously until falling into the normal interval range at days 35 and 42. In contrast, TNF-α levels for the CCI group declined steadily until an increase was observed at day 7. Maximum TNF-α levels for the CCI group occurred at day 28 (72±50 pg/mL) before steadily declining until day 35 and from day 35 to day 42 (38±29 pg/mL).

Both RAP and CCI had high CRP levels at the time of enrollment (Figure 3C). Both groups reached their maximum mean serum CRP levels at day 1. Mean serum CRP levels for the RAP group steadily declined until falling into the normal interval range by day 35 and day 42. Serum CRP levels declined for the CCI group but remained elevated on day 35 and day 42 (108006±84442 and 94052±73730 ng/mL).

Poor Functional Outcomes Following CCI

Functional outcomes, including gait speed, SPPB, and Zubrod tests, were worse in the CCI group versus the RAP group at 3, 6 and 12 months (Figure 4A-C). Mean gait speed was significantly lower at 3 months for CCI (RAP: 2.7 ± 1.7 vs CCI: 1.4 ± 1.7*, P = .018). Gait speed improved slightly for both RAP and CCI groups from 3 to 12 months. Gait speeds at 12 months for RAP and CCI were 3.1 ± 1.5 and 2.1 ± 1.7*, P = .038, respectively. This corresponded to a 4 m gait speed average of 4.8-6.2 seconds for RAP and 6.2-8.7 seconds for CCI.

Figure 4.

(A-C). CCI patients have worse functional outcomes. (A). Improved gait speed in RAP patients. (B). Improved SPPB in RAP patients at 3, 6 and 12 months. (C). Significantly elevated Zubrod scores at 3, 6, and 12 months in CCI patients. RAP = rapid recovery patients; CCI = chronic critical illness; SPPB = short physical performance battery; *P < .05.

Mean SBBP scores were significantly lower for CCI patients at 3, 6, and 12 months when compared to RAP patients (Figure 4B). While both groups saw improvement in SPPB scores from 3 to 12 months, the RAP group had greater increases in SPPB scores. This led to a greater difference between the RAP and CCI SPPB scores at 12 months (RAP: 9.3 ± 4 vs CCI:5.3 ± 5*, P = .003).

Baseline mean Zubrod scores were similar for RAP and CCI patients (Figure 4C). While both groups saw an increase in Zubrod scores from baseline to 3 months, there was a substantially higher increase in the CCI group (CCI: 3.6 ± 1.3* vs RAP: 2.2 ± 1.3, P < .0001). There was a significantly worse Zubrod score at 12 months in the CCI group (CCI: 3.4 ± 1.8* vs RAP: 1.7 ± 1.6, * P < .001). At 12 months, Zubrod scores remained >3 for CCI patients which meant that 50% of the time CCI were confined to a bed as compared to RAP patients that had a functional outcome of restricted strenuous activity.

Discussion

Despite discharge from the hospital, our study shows that survivors of sepsis that progress to chronic critical illness have significantly poorer long-term functional outcomes, prolonged systemic inflammation, and persistent anemia in comparison to patients who exhibit rapid recovery. Although baseline anemia was observed in both CCI and RAP groups, hemoglobin levels were markedly lower in the CCI group at 3 and 6 months. The difference in hemoglobin levels between the 2 groups was observed despite the CCI group receiving more pRBC transfusions compared to the RAP group. Furthermore, the lower hemoglobin levels are associated with a persistent inflammatory response in the CCI group as indicated by elevated CRP, TNF-a, and IL-6 at 3 and 6 months. Even more significant, marked elevations in inflammatory markers occur much earlier in the disease process for CCI patients in contrast to RAP patients. Specifically, IL-6 levels were over 3 times higher at 12 hours and 1 day in the CCI group and more than double at day 4 in comparison to the RAP group. TNF-a levels fluctuated before ultimately increasing by Day 28 for CCI patients while a steady decline was observed in the RAP group. CRP levels increased 2-fold and 6-fold by Day 21 and 28 for CCI patients. The findings of this study are significant in that they suggest that early identification of sepsis survivors at high risk to progression to chronic critical illness via elevated inflammatory markers and subsequent alleviation of prolonged inflammation may improve both anemia and long-term functional outcomes.

Prior studies have independently demonstrated that anemia is a significant factor in recovery, complications, and mortality of hospitalized patients, particularly in patients undergoing vascular, cardiac, and major non-cardiac surgery.^6,19-27 A retrospective analysis of 34, 397 patients who underwent either endovascular aneurysm repair (EVAR) or open aortic repair for intact abdominal aortic aneurysm showed that decreased preoperative hemoglobin levels were significantly associated with 30-day mortality and in-hospital adverse events in the EVAR group but not the open aortic repair group.¹⁹ These outcomes were observed even when controlling for other prognostic factors such as heart disease and renal dysfunction.¹⁹ Severe anemia in patients undergoing EVAR has also been correlated with elevated inflammatory markers and long-term adverse cardiovascular outcomes.²⁰ Other studies have demonstrated that significantly decreased hemoglobin levels in major non-cardiac surgery are associated with increased risk of cardiac, respiratory, and urinary tract complications, as well as venous thromboembolism, wound events, and sepsis.²⁶ However, none of these studies assessed functional outcomes after hospital discharge. A study examining functional outcomes in stroke patients using the Functional Independence Measure (FIM), which assesses function in self-care, continence, mobility, transfers, communication, and cognition, found that patients with ischemic stroke and anemia had lower FIM score improvement (FIM at discharge-FIM at admission) and FIM efficiency (FIM change/length of stay).²⁸ Improvement in hemoglobin levels are also positively associated with improvement in FIM-motor efficacy and decreased length of stay.²⁹ Another study showed that lower postoperative hemoglobin concentration in patients undergoing surgery for hip fracture are associated with longer length of stay and more readmissions, but anemia did not affect rates of FIM or death.³⁰

Previously, we have shown that patients who develop CCI after a sepsis event have significantly decreased self-reported health-related quality of life and objective physical function in comparison to patients who exhibit rapid recovery.⁵ These functional deficits occur despite similar baseline levels of physical function between the 2 groups.⁵ Patients with CCI develop an underlying pathophysiology of persistent inflammation, immunosuppression, ongoing organ injury, protein catabolism, and poor nutrition leading to muscle wasting, cachexia, poor wound healing, and continual decline leading to an indolent death.² Thus, these patients exhibit poor long-term functional recovery, decreased quality of life, increased healthcare costs, likely discharge to a long term acute care facility, and increased long-term mortality.^2,5 This study demonstrates that patients with CCI have persistently elevated inflammatory markers which are accompanied by lower hemoglobin concentrations and impaired functional outcomes. Preventing the development of CCI, or potentially even the treatment of ongoing inflammation in these high-risk patients, may have a positive impact on anemia recovery and functional outcomes, however, dedicated investigations will be necessary to substantiate this finding.

One limitation of this study was that data was limited to a single institution. Therefore, the results from a single institution may not be generalizable. In addition, the difference in the number of transfusions received between groups may impact cytokine profiles and anemia recovery. In addition, this study did not account for the number of blood draws/patient as well as the timing of nutritional support which both could influence the degree of anemia as well as the number of cofactors available for red blood cell production. While lower extremity fractures could contribute to functional outcome differences, there was no significant difference in trauma patient enrollment between the RAP and CCI groups. Therefore, this potential confounder should be similar for both groups. Compliance with in-person assessments at 3 and 6 months is a challenge and there may a selection bias because those too sick to participate may not have had assessments. This may underestimate the outcomes in the CCI group.

Conclusion

Patients with CCI also have elevated inflammatory markers and worse functional outcomes than those with shorter recoveries from critical illness. Prevention of CCI or treatment of persistent inflammation may improve hemoglobin and functional recovery, and future studies are necessary to further assess these relationships.