Dr Ho Ka Yee; Supervisor: Dr. Tang Kam Shing; Tuen Mun Hospital
Abstract
Background: Mycobacterium tuberculosis (MTB) infection is endemic in Hong Kong. The annual incidence is ten times higher than that of western countries (1). The reported hospital mortality of MTB admitted to intensive care unit (ICU) was 67-81% (2). Poor prognostic factors in this subgroup have been identified in oversea studies. Hong Kong, as a developed city with high MTB endemicity, has no published data focusing on these patients yet.
Objectives: To describe clinical characteristics and outcomes, identify poor prognostic factors and formulate an equation to predict the 60-day mortality.
Design and setting: Retrospective study in a mixed surgical and medical ICU in a tertiary hospital in Hong Kong.
Patients: Critically ill patients diagnosed to have active MTB from January 2004 to December 2009.
Results: Ninety one patients were identified as potential subjects. Nine patients had nontuberculous mycobacterial (NTM) infection and 13 patients admitted with MTB as co-morbidity were excluded. Sixty-nine patients (aged 56.30± 16.50 years) admitted for MTB were included. Thirty percent of patients were above 65 year-old. Forty percent had underlying cardio-respiratory co-morbidities. Seventy percent presented with respiratory and constitutional symptoms. Sixty-eight percent admitted to ICU for respiratory failure. Thirty-six percent had both pulmonary and extrapulmonary MTB. Fifty percent had smear-positive MTB. Thirteen percent developed cavitations on CXR and 21.74% showed miliary CXR patterns. Seventy-five percent had upper zones involvement and 5.80% had no consolidation. Eight-four percent were put on invasive mechanical ventilator, 17.39% on renal replacement therapy and 75.36% required vasopressors. Fifteen percent developed MTB drugs related hepatotoxicity. The hospital mortality for all subjects is 60.87% and 70.69% for patients put on mechanical ventilations. The total Acute Physiological and Chronic Health Evaluation (APACHE) Score II, Sequential Organ Failure Assessment (SOFA) and Murray Lung Injury Score (Murray score) were higher in non-survivors.
By multivariate Cox proportional hazards model, anti-tuberculosis (anti-TB) regimen containing ≦ 3 drugs (HR 2.28, 95% CI: 1.19-4.39, p= 0.01), ≧ 3 quadrants of Chest X Ray (CXR) involvement (HR 2.26, 95% CI: 1.20-4.25, p= 0.01), Alkaline phosphatase (ALP) ≧ 3 times of upper normal limit (UNL) (HR 2.35, 95% CI: 1.11-4.98, p= 0.03), pH ≦ 7.2 on ICU admission or during the first week of anti-TB regimen (HR 2.32, 95% CI: 1.18-4.55, p=0.02), acute kidney failure (AKF) (HR 2.28, 95% CI: 1.13-4.59, p= 0.02) and mean arterial pressure (MAP) ≦ 60 mmHg (HR 3.43, 95% CI: 1.61-7.29, p=0.00) were identified as poor prognostic factors contributing to mortality.
We derived a simple scoring formula to facilitate the prediction of mortality of patients. Giving one point to each of the factor, the sum of the points is the mortality predicting score. Mortality rate is 14% if score 0-1 point; 65% if score 2-3 points and 100% if score 4-6 points.
Conclusion: Diagnosis of MTB remains a challenge as clinical symptoms and CXR findings do not always present classically. A high index of suspicion is always necessary. The above mortality predicting formula can be utilized to identify the prognosis of patients who received one week of intensive care support.
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