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Signs and Symptoms of Chest Diseases |

What's the Gap

Sameep Sehgal, MBBS; Sritika Thapa, MBBS; Abhishek Sharma, MBBS; David Weisman, DO
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Good Samaritan Hospital, Towson, MD


Chest. 2013;144(4_MeetingAbstracts):963A. doi:10.1378/chest.1704057
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Abstract

SESSION TITLE: Miscellaneous Student/Resident Case Report Posters I

SESSION TYPE: Medical Student/Resident Case Report

PRESENTED ON: Tuesday, October 29, 2013 at 01:30 PM - 02:30 PM

INTRODUCTION: Saturation gap is the difference between SpO2 calculated by ABG and the Spo2 measured by pulse oximetry. Difference of more than 5% is a positive saturation gap. The causes are carboxyhemoglobin, methemoglobin( Met Hb) and infrequently sulfhemoglobin( Sulf Hb).

CASE PRESENTATION: 45 year old male with bipolar disorder, COPD, and illicit drug use presented with progressive dyspnea on exertion, and mild chest discomfort for a week. He had similar episodes in the past. He admits to use of marijuana & “Rush poppers” [amyl nitrate]. On exam he was awake, lethargic, verbalizing in complete sentences without accessory muscle use. HR 108, BP 102/55, RR 36/min, Spo2 68% on room air, and 89% on 100% oxygen via a non-rebreathing mask. Chest was clear to auscultation. Labs showed Hgb of 8mg/dl , lactic acid of 3.7mg.dl, U.Tox + BZDs ,Cannabis. CT-A of the chest was negative for PE. EKG and 2D ECHO were normal. He was diagnosed with hypoxic respiratory failure requiring urgent intubation. Post intubation ABG was 7.32/43/328/24/90. In the ICU, he continued to have high PO2 (300-400 ) with low SpO2 ( 80%-85%) on ventilator. Spectroscopic examination showed a CarboxyHb of 1.5(nml), MetHb 1.1 (nml), SulfHb 0.8(0.0-0.4). He received 3 units blood and was eventually extubated. SulfHb secondary to drug use was diagnosed, though the exact offending agent was elusive. On discharge, he continued to use drugs and presented several times subsequently with a similar clinical picture.

DISCUSSION: SulfHb and methHb are rare causes of cyanosis, both causing dyspnea, cyanosis and a saturation gap. SulfHb usually does not cause significant respiratory distress, since it increases oxygen delivery by shifting the dissociation curve to the right. Literature shows, similar drugs often cause both sulfHb and MetHb. Although, Rush Poppers( Amyl nitrates) can cause MetHb, no cases of SulfHb are reported. It is important to distinguish between the two, as the treatment varies. This can can be done using isoelectric focusing, addition of isocyanate, gas chromatography and new generation co-oximeters. Automated spectrophotometers often group the two together. Methylene blue reverses MetHb , butcan lead to hemolysis and thus should be given judiciously. SulgHb is a self limiting condition, treatment is supportive and blood transfusion is generally helpful.

CONCLUSIONS: It is important to look for a saturation gap in any patient presenting with hypoxia. If the gap is greater than 5%, metHb or sulfHb should be considered, as early diagnosis can be lifesaving.

Reference #1: Akhtar J, et al. Mind the gap. J Emerg Med. 2007 Aug;33(2):131-2. Epub 2007 Jun 5

Reference #2: Park CM, et al Sulfhemoglobinemia. Clinical and molecular aspects. N Engl J Med. 1984 Jun 14;310(24):1579-84

Reference #3: Gharahbaghian L et al Methemoglobinemia and sulfhemoglobinemia in two pediatric patients after ingestion of hydroxylamine sulfate. West J Emerg Med. 2009 Aug;10(3):197-201

DISCLOSURE: The following authors have nothing to disclose: Sameep Sehgal, Sritika Thapa, Abhishek Sharma, David Weisman

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