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Admission Ionized Calcium Levels in Level One Trauma Patients as Prognostic Indicators of Shock Severity and Mortality

Medical Student

Nathan Rhodes
Class of 2005
Student Box 210
Email: npr104@psu.edu

Faculty Sponsor

Dr. Robert Cherry, Trauma/Critical Care

Research Period

April 2004 – January 2005

Objectives

  1. Examine the relationship between Ionized Calcium (iCa) levels in level one trauma patients and injury severity, shock severity, resource utilization, age and incidence of mortality.
  2. Determine if iCa levels drawn from level one trauma patients can be used as prognostic indicators of severity of shock and risk of mortality.

Background

Calcium is a divalent cation involved in several critical cellular processes.  Studies have shown the importance of calcium in regulating vascular and myocardial contraction; in activating membrane receptors during cellular signal transduction; in releasing hormones by exocytosis; in controlling several transport processes; and, in promoting thrombus formation as co-factor IV.3-7  Total serum calcium exists in three forms: 1) ionized; 2) bound to plasma proteins such as albumin; and 3) complexed to anions such as lactate and phosphate. Ionized calcium is the physiologically active form of calcium found in the blood, and direct measurement of ionized calcium levels is critical in the evaluation of concentrations of ionized calcium.2,  The measurement of total serum calcium is an unreliable measure of ionized calcium levels.9

Hypocalcemia has been reported in critically ill patients, most commonly in association with sepsis syndrome.1 It has been known for some time that all pathophysiologic changes in shock and trauma have their basis at the cellular and molecular levels. Ionized hypocalcemia develops when calcium cannot be mobilized from the skeleton quickly enough to meet ongoing losses. One study observed hypocalcemia in 88% of critically ill patients, and decreased calcium levels were correlated with increased mortality.1 However, the relationship between hypocalcemia and shock severity and mortality risk in trauma patients has not been well defined.

General observation in the trauma bay has been that patients presenting with more severe trauma also tend to have lower initial iCa levels. Previously serum calcium levels were considered or assumed normal in trauma patients prior to the injury.10There have been studies focusing on the role of ionized hypocalcemia among critically ill patients1,10, but to date there has been little research studying the relationship between low presenting iCa levels and injury and shock severity, resource utilization and incidence of mortality. In this study we intend to explore these relationships and determine if presenting/admission iCa levels can be used as prognostic indicators. This study may also further discussion on the role of endpoints in resuscitation efforts, including iCa, base deficit and lactate levels, as well as discussion on the economic feasibility and necessity of serial lab work.

Methods

Level-one trauma activations from January 2000 to December 2002 with iCa levels drawn in the trauma bay were identified from the trauma registry. 433 activations met this criterion, and these activations were stratified by iCa levels, with a low iCa level defined as less than or equal to 1 mmol/L and all other iCa levels defined as greater than 1 mmol/L. The relationship between iCa levels drawn from level-one trauma patients in the trauma bay and injury severity (defined by TRISS, ISS, RTS, GCS), shock severity (systolic blood pressure <90), resource utilization (hospital length of stay, ICU length of stay and ventilator days), and mortality were examined using statistical analysis (chi-square, p<0.05).

IRB approval was granted Nov 03.  Protocol #03282EP.

Student’s Responsibilities

  1. Literature review.
  2. Data gathering and statistical interpretation.
  3. Prepare manuscript and/or presentations.

Sponsor’s Responsibilities

  1. To provide guidance in all phases of the study.
  2. To ensure that all data gathering and evaluation are complete and accurate.
  3. To evaluate and critique any presentations and/or manuscripts from this study.

References

  1. Zivin, JR, Gooley, T, Zager, RA, Ryan, MJ.  Hypocalcemia: A pervasive metabolic abnormality in the critically ill. Am. J. Kidney Dis. 2001 Apr; 37(4): 689-98.
  2. Ivatury, RR, Simon, RJ, Rohman, M. Cardiac complications, in Mattox, KL. (ed): Complications of Trauma. New York, NY, Churchill Livingstone, 1994. Pages 409-428.
  3. Drop L. Ionized calcium, the heart, and hemodynamic function. Anesth Anal. 1985; 64: 432-451.
  4. Power, ML, Hearney RP, Kalkwarf HJ, et al. The role of calcium in health and disease. Am J Obstet Gynecol. 1999; 181: 1560-1569.
  5. Rassmussen H. The calcium messenger system. N Engl J Med. 1985; 314: 1094-1101, 1164-1170.
  6. Zaloga GP. Hypocalcemia in critically ill patients. Crit Care Med. 1992; 20: 251-262.
  7. Zaloga, GP, Roberts, OR. Calcium, magnesium, and phosphorus disorders, in Grenvik A, Ayres, S, Holbrook, P, et al (eds): Textbook of Critical Care. Philadelphia, PA, Saunders, 2000. pages 862-875.
  8. Koch, SM, Warters, RD, Mehlhorn, U. The simultaneous measurement of ionized and total calcium and total magnesium in intensive care unit patients. J Crit Care. 2002; 17(3): 203-205.
  9. Dickerson, RN, Alexander, KH, Minard, G, et al. Accuracy of Methods to estimate ionized and “corrected” serum calcium concentrations in critically ill multiple trauma patients receiving specialized nutrition support. JPEN J Parenter Enteral Nutr. 2004; 28(3): 133-141.
  10. Ward, RT, Colton, DM, Meade, PC, et al. Serum levels of calcium and albumin in survivors versus nonsurvivors after critical injury. J Crit Care. 2004; 19(1): 54-64.

Signatures

I do give permission for my proposal to possibly be published on the College of Medicine website.

Nathan Rhodes – Date

Robert Cherry, MD – Date