An Unusual Cause of Refractory Hypoxemia Following Thoracentesis

Abstract

INTRODUCTION: Thoracentesis is a relatively safe procedure. Hypoxemia is a known complication that can occur post procedure. Hypoxemia that follows thoracentesis is most commonly caused by pneumothorax and rebound pulmonary edema. We report a case of refractory hypoxemia due to worsening ventilation(V)/perfusion(Q) mismatch post thoracentesis. CASE PRESENTATION: A 19 years old Caucasian female with past medical history of bipolar disorder was admitted for sertraline overdose. Patient after receiving charcoal aspirated and was intubated. She was started on midazolam for sedation. Patient few hours later had a temperature of 106 degrees Fahrenheit, hyperreflexia and clonus on examination. She was started on cooling and empirically on ampicillin/sulbactam for aspiration. BAL grew methicillin sensitive staphylococcus aureus and serratia. Patient clinically improved from serotonin syndrome but due to persistent right lung infiltrate vs. atelectasis and worsening right side pleural effusion patient had a thoracentesis. About 750 ml of yellow color pleural fluid removed. Within 10 minutes post thoracentesis patient developed hypoxia and fio2 was increased from 40% to 100%. PEEP was increased to 10 cm H20.Sao2 improved to 92%.On auscultation breath sound were bilaterally heard but decreased on the right base. Critical care ultrasound showed minimal B lines and no pneumothorax. No right to left intracardiac shunt with bubble study. Stat chest X-ray showed right side atelectasis, minimal effusion and pulmonary edema left greater than right side. However due to unexplained persistent hypoxemia a 14 French pigtail catheter was placed. No air leak noted. Patient also received one dose of 40 mg of Lasix. Patients Sao2 gradually improved over the next 12 hours and fio2 decreased to 40 %.Pig tail only drained 50 ml.Chest X-ray showed complete resolution of the atelectasis. Patient was soon extubated successfully. DISCUSSION: Our patient post thoracentesis only had a minimal right side pulmonary edema and no pneumothorax. However, the patient was having severe hypoxemia. Worsening V/Q mismatch due to increased blood flow through the previously atelectatic lobes and inadequate ventilation contributed to the worsening hypoxemia. With PEEP and continued positive pressure and oxygen the atelectasis improved and hypoxemia resolved. Previously it has been noted that it might take up to 20 minutes to 24 hours post thoracentesis to reach the baseline Pao2 pre thoracentesis(1). CONCLUSIONS: V/Q mismatch can contribute to significant hypoxemia following thoracentesis. Supplemental oxygen and time helps in resolution of the hypoxemia.