Association of the neutrophil-lymphocyte ratio with outcome in sick hospitalized neonatal foals

BACKGROUND

The neutrophil-lymphocyte ratio (NLR) in human medicine is an objective biomarker that reflects prognosis. The NLR as an independent biomarker to help predict nonsurvival in hospitalized neonatal foals has not been thoroughly interrogated.

OBJECTIVES/HYPOTHESIS

Retrospectively evaluate if the NLR at admission is associated with nonsurvival in sick hospitalized foals <4 days old. We hypothesized that a lower NLR will be associated with nonsurvival.

ANIMALS

One thousand one hundred ninety-six client-owned foals <4 days old of any breed and sex: 993 hospitalized foals and 203 healthy foals.

METHODS

Retrospective multicenter study. Medical records of foals presenting to 3 equine referral hospitals were reviewed. Foals were included if they had complete CBCs, sepsis scores, and outcome data. The NLR was calculated by dividing the absolute neutrophil count by the absolute lymphocyte count. Data were analyzed by nonparametric methods and univariate analysis.

RESULTS

Of the 993 sick hospitalized foals, 686 were sick nonseptic and 307 were septic. The median NLR was lower in sick hospitalized foals (median [95% confidence interval], 3.55 [0.5-13.9]) compared with healthy foals (6.61 [3.06-18.1]). Septic foals had the lowest NLR (2.00 [0.20-9.71]). The NLR was lower in nonsurviving (1.97 [1.67-2.45]) compared with surviving foals (4.10 [3.76-4.33]). Nonsurviving septic foals had the lowest NLR (1.47 [1.70-3.01]). Foals with a NLR of <3.06 or <1.6 at admission had odds ratio of 3.21 (2.24-4.29) and 4.03 (2.86-5.67) for nonsurvival, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

A NLR < 3.06 at admission in sick hospitalized foals is readily available and clinically useful variable to provide prognostic information.

The hypothalamic-pituitary-adrenal axis response to ovine corticotropin-releasing-hormone stimulation tests in healthy and hospitalized foals

BACKGROUND

The hypothalamic-pituitary-adrenocortical axis (HPAA) response to sepsis can be impaired in critical illness. Corticotropin-releasing hormone (CRH) stimulation test might assess HPAA function in foals.

OBJECTIVE

To evaluate plasma cortisol, ACTH, arginine vasopressin (AVP), and endogenous CRH (eCRH) response to different doses of ovine CRH (oCRH).

ANIMALS

Healthy (n = 14) and hospitalized (n = 15) foals <7 days of age.

METHODS

In this prospective randomized study, oCRH (0.1, 0.3, and 1 μg/kg) was administered intravenously and blood samples were collected before, 15, 30, 60, and 90 minutes after administration of oCRH to determine plasma hormone concentrations. The hormonal response was evaluated as the difference (Delta; μg/dL or pg/mL) or percent change between baseline hormone concentration and each time point after oCRH stimulation.

RESULTS

Cortisol concentrations increased from baseline at 15 minutes with 0.1 and 0.3 μg/kg and at 30 and 60 minutes from baseline with 1 μg/kg oCRH (P < .05) in healthy and hospitalized foals. ACTH concentrations increased from baseline at 15 minutes with 0.1 μg/kg and at 30 minutes with 1 μg/kg oCRH (P < .05) in hospitalized foals. Delta cortisol 0 - 30, ACTH 0 - 30, and eCRH 0 - 30 was higher for the 1 μg/kg compared with 0.1 μg/kg oCRH in healthy foals (P < .05). Delta ACTH 0 - 15 and eCRH 0 - 30 was higher for the 1 μg/kg compared with the lower doses of oCRH in hospitalized foals (P < .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

Cortisol, ACTH, and eCRH concentrations increased in response to administration of all doses of oCRH. One microgram per kilogram of oCRH appears to be optimal for the assessment of HPAA in healthy and hospitalized foals.

Effects of administration of ascorbic acid and low-dose hydrocortisone after infusion of sublethal doses of lipopolysaccharide to horses

Background

Sepsis is associated with ascorbic acid (AA) depletion and critical illness‐related corticosteroid insufficiency (CIRCI) in humans.

Hypotheses

Intravenous infusion of lipopolysaccharide (LPS) would (a) decrease endogneous AA concentrations, (b) induce CIRCI and (c) administration of a combination of AA and hydrocortisone (HC) would have decreased indices of inflammation compared to either drug alone.

Animals

Thirty‐two healthy horses.

Methods

Randomized placebo‐controlled experimental trial. Horses were assigned to 1 of 4 groups (saline, AA and HC, AA only, or HC only). Treatments were administered 1 hour after completion of LPS infusion. Clinical signs, clinicopathological variables, pro‐inflammatory cytokine gene expression and production, and plasma AA concentrations were assessed at various time points. Serum cortisol concentrations and ACTH stimulation tests were used to detect CIRCI.

Results

There was no effect of drug on clinical signs or pro‐inflammatory cytokine gene expression or production compared to controls at any time point. Administration of AA was associated with higher blood neutrophil counts 6 hours after LPS infusion (11.01 ± 1.02 K/μl) compared to other groups (8.99 ± 0.94 K/μL; P < .009). Adminstration of HC was associated with higher blood neutrophil counts 12 hours after LPS infusion (10.40 ± 0.75 K/μl) compared to other groups (6.88 ± 0.68 K/μl; P < .001). Serum cortisol increased from 5.11 ± 1.48 μg/dL before LPS administration to 9.59 ± 1.83 μg/dL 1 h after completion of LPS infusion (T1) without an effect of treatment (P = 0.59).

Conclusions and Clinical Importance

Ascorbic acid and HC appeared to protect against LPS‐induced neutrophil depletion and could be considered as adjunctive therapy in horses with endotoxemia.

Clinical Pathology in the Foal

The dynamic physiologic changes and unique diet during the neonatal period contribute to key differences in clinicopathologic test results of healthy foals relative to healthy adult horses. When reporting results, most diagnostic laboratories only provide reference intervals for mature horses. Thus, failure to recognize the unique differences that occur in foals relative to adult horses can lead to erroneous interpretation of neonatal clinical pathologic values. Thus, the main objective of this article was to review distinct features of common clinicopathologic tests in foals, relative to mature horses.

Modelling of oscillatory cortisol response in horses using a Bayesian population approach for evaluation of dexamethasone suppression test protocols

Cortisol is a steroid hormone relevant to immune function in horses and other species and shows a circadian rhythm. The glucocorticoid dexamethasone suppresses cortisol in horses. Pituitary pars intermedia dysfunction (PPID) is a disease in which the cortisol suppression mechanism through dexamethasone is challenged. Overnight dexamethasone suppression test (DST) protocols are used to test the functioning of this mechanism and to establish a diagnosis for PPID. However, existing DST protocols have been recognized to perform poorly in previous experimental studies, often indicating presence of PPID in healthy horses. This study uses a pharmacokinetic/pharmacodynamic (PK/PD) modelling approach to analyse the oscillatory cortisol response and its interaction with dexamethasone. Two existing DST protocols were then scrutinized using model simulations with particular focus on their ability to avoid false positive outcomes. Using a Bayesian population approach allowed for quantification of uncertainty and enabled predictions for a broader population of horses than the underlying sample. Dose selection and sampling time point were both determined to have large influence on the number of false positives. Advice on pitfalls in test protocols and directions for possible improvement of DST protocols were given. The presented methodology is also easily extended to other clinical test protocols.

A quantitative approach to analysing cortisol response in the horse

The cortisol response to glucocorticoid intervention has, in spite of several studies in horses, not been fully characterized with regard to the determinants of onset, intensity and duration of response. Therefore, dexamethasone and cortisol response data were collected in a study applying a constant rate infusion regimen of dexamethasone (0.17, 1.7 and 17 μg/kg) to six Standardbreds. Plasma was analysed for dexamethasone and cortisol concentrations using UHPLC-MS/MS. Dexamethasone displayed linear kinetics within the concentration range studied. A turnover model of oscillatory behaviour accurately mimicked cortisol data. The mean baseline concentration range was 34-57 μg/L, the fractional turnover rate 0.47-1.5 1/h, the amplitude parameter 6.8-24 μg/L, the maximum inhibitory capacity 0.77-0.97, the drug potency 6-65 ng/L and the sigmoidicity factor 0.7-30. This analysis provided a better understanding of the time course of the cortisol response in horses. This includes baseline variability within and between horses and determinants of the equilibrium concentration-response relationship. The analysis also challenged a protocol for a dexamethasone suppression test design and indicated future improvement to increase the predictability of the test.

A review of equine sepsis

Sepsis is defined as an exaggerated, systemic inflammatory response to infection and is a common condition in horses. Systemic inflammatory response syndrome (SIRS) associated with bacterial infection is a hallmark of sepsis. Sepsis in neonatal foals is a common sequela of failure of passive transfer and, in addition to development of SIRS, may be characterised by bacteraemia, pneumonia, enterocolitis, omphalophlebitis, meningoencephalitis or arthritis. Sepsis in mature horses is most commonly observed secondary to gastrointestinal lesions that result in disrupted mucosa and bacterial translocation into circulation (endotoxaemia). Pleuropneumonia and metritis may also cause sepsis in mature horses. Diagnosis of sepsis is based on SIRS criteria as well as suspected or confirmed infection. Due to the relatively low sensitivity of microbial culture and the subjectivity of sepsis scoring, many sepsis biomarkers are being studied for their usefulness in diagnosis and prognostication of sepsis in horses. Treatment of sepsis requires an intensive care approach that includes antimicrobial drug administration, fluid resuscitation and pressure support, and treatment for inflammation, endotoxaemia and coagulopathy. Early recognition of sepsis and prompt antimicrobial drug treatment are critical for a successful outcome. Multiple organ dysfunction syndrome may occur in severe cases of sepsis, with common manifestations including laminitis and coagulopathies. Although prognosis for septic mature horses depends highly on the primary disease process, the overall survival rate in septic neonatal foals ranges from 26 to 86%, with most studies indicating a survival rate of 45-60%.

Effects of low-dose hydrocortisone therapy on immune function in neonatal horses

Low-dose hydrocortisone (LDHC) therapy modulates inflammatory responses in adults and improves outcomes in some septic adults and neonates, but its immunologic effects have not been evaluated in neonates. The objective of this study was to evaluate effects of LDHC therapy on ex vivo immune function in neonatal horses (foals). We hypothesized that LDHC treatment would dampen proinflammatory responses without impairing neutrophil function. Hydrocortisone (1.3 mg/kg/d i.v.) was administered to foals in a tapering 3.5 d course. Peripheral blood leukocytes were collected from foals before, during, and after hydrocortisone treatment. A separate group of age-matched untreated foals served as controls. Endotoxin-induced peripheral blood mononuclear cell gene expression of inflammatory cytokines was measured by real-time quantitative RT-PCR. Neutrophils were incubated with labeled, killed Staphylococcus aureus or Escherichia coli for assessment of phagocytosis, and with phorbol myristate acetate, zymosan, or endotoxin for measurement of reactive oxygen species (ROS) production. Neutrophil phagocytosis and ROS production were similar in both groups. Foals receiving hydrocortisone had significantly decreased endotoxin-induced expression of TNF-α, IL-6, IL-8, and IL-1β. These data suggest that this LDHC treatment regimen ameliorates endotoxin-induced proinflammatory cytokine expression in neonatal foals without impairing innate immune responses needed to combat bacterial infection.

Adrenocortical insufficiency in horses and foals

The adrenal cortices produce various steroid hormones that play vital roles in several physiologic processes. Although permanent adrenocortical insufficiency is rare in all species, emerging evidence in both human and equine medicine suggests that transient reversible adrenocortical dysfunction resulting in cortisol insufficiency frequently develops during critical illness. This syndrome is termed relative adrenal insufficiency (RAI) or critical illness-related corticosteroid insufficiency (CIRCI) and can contribute substantially to morbidity and mortality associated with the primary disease. This review discusses the mechanisms, diagnosis, and clinical consequences of adrenocortical insufficiency, with particular focus on the current understanding of RAI/CIRCI in horses and foals.