Glycated Haemoglobin (HbA1C) as a predictor of outcome in trauma patients in the Surgical Intensive Care Unit

INTRODUCTION: The prevalence of diabetes in adult population in India has now reached alarming proportions with about 15 percent of those aged above 20 years in urban settings being diabetic. Using similar diagnostic criteria (known diabetes and/or fasting and post-glucose load hyperglycaemia) the age-adjusted diabetes prevalence among adults in urban Chennai increased from 8.3% in 1988-89, to 11.6% (1994-95), 13.5% (2000) and 14.3% in 2003-04. Increase in diabetes prevalence has also been reported from rural Tamil Nadu. Most diabetics remain unrecognized as a result of inadequate access to healthcare and screening programs and because they are not symptomatic until they have advanced stages of disease. A substantial proportion of those without overt diabetes has one or both of the prediabetic states: Impaired fasting glucose and impaired glucose tolerance with risk of progression to diabetes. With the emerging epidemic of diabetes in India, it is imperative to know if the preadmission diabetic status influences ICU outcomes, and if so further research would be warranted into management paradigms that will optimize outcomes. HbA1C expressed as a percentage of adult hemoglobin that is glycated, is the most widely used measure of chronic glycaemia. HbA1C assay that was introduced in the late 1970’s has become the benchmark in assessing chronic glycaemia in research and the management of diabetes. Maintaining HbA1C within normal limits has been shown to reduce long term complications. HBA1C reflects the average plasma glucose levels over the previous 120 days which corresponds with the lifespan of an RBC. Standardized methods for estimating HBA1C is now readily available in most tertiary care facilities. Large studies have validated the correlation between mean plasma glucose levels in diabetics with HBA1C and have shown that HBA1C can be used to prognosticate outcomes in diabetics. Patients in intensive care units frequently develop elevated blood sugars as a response to stress. Stressed Induced Hyperglycaemia (SIH) refers to a complex metabolic response to stress through raised catecholamines and stress hormones resulting in elevated blood sugar levels. Intensive care experts recognize that this hyperglycaemia is associated with higher mortality. Patients requiring prolonged intensive care are at high risk for multiple organ failure and death. Differentiating SIH from diabetic hyperglycaemia is challenging in the ICU setting in view of the universally elevated blood sugars. HBA1C provides intensive care physicians a means to detect those with diabetes and those at risk of developing diabetes in ICU settings and also helps to differentiate SIH from diabetics. Aim: To evaluate if initial glycated hemoglobin (HbA1C) level in trauma patients predicts the outcome of patients admitted to Surgical Intensive Care Unit (SICU). OBJECTIVES: 1. Estimate the prevalence of abnormal HbA1C levels in trauma patients irrespective of their admission glycaemic status. 2. To explore the relationship between the initial HbA1C and the outcome of SICU admission among trauma patients. 3. Estimate the correlation between the initial HbA1C level and the a) duration of SICU stay, b) length of ventilated days, c) and incidence of hospital acquired infections (HAI) among trauma patients admitted to SICU. HYPOTHESIS: Trauma patients with HbA1C levels above 6.0% will have a greater incidence of HAI, increased number of ventilated days, increased duration of stay in SICU and poorer outcomes in terms of mortality. PATIENTS & METHODS: Settings: The study was done in the Surgical Intensive Care Unit (SICU) of Christian Medical College Hospital, Vellore which is a 2000 bedded tertiary care hospital serving about 90,000 inpatients and 1.5 million outpatients annually. Tight glycaemic control in SICU patients is done to maintain the blood sugar level between 80 to 120 mg/ dl. Control of sugars in the SICU is done following a sliding scale. When sugars are abnormal the following algorithm is used. The algorithm is explained in appendix 2. Insulin is given as an infusion with the help of a syringe pump which contains 20 units of short acting insulin in 20 ml of normal saline. Insulin infusion is started when there are more than two blood sugars values of greater than 120mg/dl. Blood sugars are checked every four hours on a routine basis and in some cases every one hour till appropriate control of sugars is achieved. Inclusion criteria: 1. Age more than 16 years. 2. All trauma patients who came to the operation theatre and required. post-operative SICU care or those who required pre – operative stabilization in the SICU Exclusion criteria: 1. Age less than 16 years. 2. If consent was not given by the patients’ relatives/guardians the study recruited consecutive patients who met the inclusion criteria from January to October 2010 after informed consent was obtained from their legally acceptable guardian. The protocol received approval from the Institutional Review Board of Christian Medical College, Vellore and was funded by the fluid research fund of the Christian Medical College. Statistical Methods: The primary analysis used a binary logistic regression to estimate risk for poor outcomes between those with high and low HBA1C groups (>=6 or <6) adjusted for APACHE II score, injury severity score, admission blood sugars and age. Risk estimates were provided with exact p values and a 95% CI of the odds ratio. Univariate analysis used appropriate tests of significance (independent samples T test for normally distributed continuous variables and Pearson’s χ2 or Fishers exact test for categorical variables). Secondary analysis included estimates of association between diabetic status, APACHE II scores, comorbidities and the incidence of HAI, number of ventilated days and number of SICU days. Exploratory analysis of these relationships at different levels of admission blood sugars were also carried out in a hypothesis generation exercise. Statistical analysis was done with STATA 11 (StataCorp, Texas USA). RESULTS: One hundred and twenty trauma patients requiring admission to SICU between January and October 2010 were recruited. Male patients 108/120 (90%) dominated SICU admissions for trauma. The age at admission ranged from 16 to 75 with a mean of 36 years (SD 15yrs). The mean APACHE II was 9.8 (SD 6.9) and the mean Injury Severity scores was 17.2 (SD 7.1). The mean HbA1C was 5.8% (SD 1.0). The mean admission blood sugar was 180.3 mg/dl (SD 102.1). Admission RBS was not available in seven of the patients. CONCLUSIONS: This cohort study of trauma patients admitted to Surgical ICU examined the relationship between HBA1C and the outcomes of ICU stay. 1. The prevalence of HBA1C ≥ 6% in this study was 24.2% and these individuals would be either diabetic or at risk of developing diabetes. 2. Six out of 17 diabetic patients (35%) did not know that they were diabetic at admission. 5.5% (6/109) of this cohort has occult diabetes mellitus. 3. There was a 3.14 times greater risk of poor outcomes in those with HBA1C ≥ 6% or above as compared to those with HBA1C < 6%. This association strengthened on adjusting for admission blood sugars, APACHE II, ISS to an odds ratio of 4.6. 4. Those with elevated HBA1C (>=6%) had, on average, 2.1 days more of ventilation and 1.5 days longer ICU admission. 5. Sixty five (54%) of the participants developed Hospital Acquired Infections with similar proportions in those with normal and elevated HBA1C. 6. That 14.2% of the adults were diabetic and that 35% of these diabetic individuals were undiagnosed before admission combined with the increased risk of poor outcomes among those with higher HBA1C suggests screening for diabetes may be useful in managing patients in ICU settings.