Gases
Ali Rezaie, MD, MSc, FRCPC
Assistant Professor
Division of Gastroenterology and Hepatology
Cedars-Sinai
Objectives
• Basics of gas production by microbiome
• Clinical implications of breath gas measurement
• How does breath gas measurement help us
advance our knowledge on microbiome?
Gases
• Hippocrates: Aroma of human breath can provide clues to diagnosis
• Avicenna of Persia described the change in breath smell and sweet taste of urine as prognosticating factor
Canon of Medicine.1025 AD
Gases
• Antoine Lavosier
discovered O2 and H2 in
1772
– Found CO2 in exhaled
breath: “Respiration is
combustion”
Opuscules physiques et chimiques. 1774
Intestinal Gas-The Basics
• On average healthy subjects have ~100 cc of
intestinal gas (range 30-200 cc)
• 99% of intestinal gas is composed of odorless
O2, H2
, N2, CO2
and CH4
• <1% include other gases such as H2S, indole,
skatole and NH3
Levitt M. NEJM. 1971
Intestinal Gas-The Basics
• Intestinal gas is eliminated via four mechanisms
– Belching
– Diffusion
– Bacterial consumption
– Flatus
Levitt M. NEJM. 1971
Intestinal Gas-The Basics
• Intestinal gas derives from four sources
– Swallowed air and air mixed with food
– Chemical reactions (e.g. H+ + HCO3- H2O+CO2)
– Diffusion of gases from blood stream
– Bacterial metabolism (CO2+4H2O CH4+2H2O)
Levitt M. NEJM. 1971
CH4 and H2 Exclusive Biomarkers of
Gut Microbiome
• Source of CH4 and H2 in the breath in the
intestinal gas is from the bacterial metabolism
– Germ free rats
– Infants in the first day of life
Levitt M. Gastroenterology.1970
Bacterial
fermentation of
carbohydrates
H2
CO2
Methanogens: CH4
Sulfate reducers: H2S
Nitrate reducers: NH4
Acetogens: CH3COO-
Simplified Pathways of Gas Production
by Microbiome
Yang et al.Front Microbiol. 2016
Diagnosis of SIBO
• Gold standard:
Concentration of bacteria
in the jejunum is more
than 103 CFU/ml using
small bowel aspiration
Rezaie A et al. North American consensus. DDW 2016
Greiner AK et al. Am J of Physiology 2014
What Are the Symptoms of SIBO?
• Abdominal distention
• Bloating
• Early satiety
• Dyspepsia
• Nausea
• Abdominal discomfort
• Fatigue
• Post-prandial “Brain fog”
Rezaie A, Pimentel M, Rao SS. Curr Gastro Report. 2016
Greiner AK et al. Am J of Physiology 2014
What Are the Symptoms of SIBO?
• Diarrhea (Hydrogen-predominant SIBO)
• Constipation (Methane-predominant SIBO)
• Weight loss
• Rarely: Vitamin B12 and iron deficiency
Rezaie A et al. Curr Gastroenterol Report 2016
Causes of SIBO
SIBO is not a primary disease
Small bowel dysmotility: Connective tissue diseases, anti-vinculin/anti-CdtB
antibodies, diabetes
Post-surgical: Gastric bypass, ileocecal resection
Medication: Narcotics, anticholinergics and anti-diarrheals
Lack gastric acid secretion: PPIs, autoimmune gastritis and gastrectomy
Rezaie A et al. Curr Gastroenterol Report 2016
Diagnosis of SIBO
• Current gold standard: Small bowel aspiration
– Invasive
– Costly
– Time-consuming
• Breath testing:
– Non-invasive
– Inexpensive
Rezaie A et al. Curr Gastroenterol Report 2016
Jacobs et al. APT 2013
Basic Principles of
Breath Test
• Lactulose and
glucose are the most
common substrates
for diagnosis of SIBO
CH4
H2
CH4
H2
Blood stream
Food
Depending on the type of
excessive bacteria, H2
and/or CH4 gases are
produced
Glucose
Lactulose
Rezaie A et al. North American Consensus statement on Breath testing. 2016
0 15 30 45 60 75 90 105 120 135 150 165 180
H2 8 12 9 11 16 14 12 16 17 12 18 25 29
CH4 1 1 2 0 1 2 1 1 1 1 2 1 1
0
20
40
60
80
BR
EA
TH
HY
DR
OG
EN
AN
D M
ET
HA
NE
C
ON
CE
NT
RA
TIO
N (
PP
M)
Normal Breath Test
Rezaie A et al. Curr
Gastroenterol Report 2016
Positive test: Rise of hydrogen by
20 ppm within 90 minutes
Rezaie A et al. Curr
Gastroenterol Report 2016
Small intestinal bacterial overgrowth
(Hydrogen producing bacteria)
0 15 30 45 60 75 90 105 120 135 150 165 180
H2 8 3 9 11 9 4 12 12 8 6 9 2 10
CH4 42 45 49 52 41 47 43 44 46 44 43 47 39
0
20
40
60
80
BR
EA
TH
HY
DR
OG
EN
AN
D M
ET
HA
NE
C
ON
CE
NT
RA
TIO
N (
PP
M)
Small intestinal bacterial overgrowth (Methane producing bacteria)
Positive test: Methane level ≥10 ppm
0 15 30 45 60 75 90 105 120 135 150 165 180
H2 2 2 2 1 2 1 2 2 2 2 2 2 2
CH4 0 0 0 0 0 0 0 0 0 0 0 0 0
0
20
40
60
80B
RE
AT
H H
YD
RO
GE
N A
ND
ME
TH
AN
E
CO
NC
EN
TR
AT
ION
(P
PM
)
Small intestinal bacterial overgrowth
(H2S producing bacteria)
Rezaie A et al. Curr
Gastroenterol Report
2016
SIBO
Excessive methane production
or flat-line
Hydrogen-predominant SIBO
without excessive methane production
Combine broad spectrum
antibiotic with neomycin 500 mg PO
BID for 14 days
Broad spectrum antibiotic
(amoxicillin, ciprofloxacin, trimethoprim-
sulfamethoxazole or rifaximin)
for 14 days
Consider alternative
antibiotics or elemental diet Clinical Response
No
Yes
Recurrence - Educate patient about the risk of recurrence
- Adopt a strategy for maintenance of remission
Maintenance of
remission
Consid
er
elim
inatio
n o
r m
odific
ation o
f th
e u
nd
erl
yin
g c
ause o
f S
IBO
Induction of Remission
Re
za
ie A
, P
ime
nte
l M
, R
ao
SS
. C
urr
Ga
str
oente
rol R
ep
ort
20
16
Ø
*
• Rifaximin 400mg TID vs. tetracycline 333mg TID in SIBO patients
• Significant improving in Rifaximin arm for diarrhea, fatigue and borborygmi
Di Stefano et al. APT 2000
Rifaximin-SIBO
Ø
*
P<0.01 • TARGET 1 & 2 RCTs (n= 1,258)
• Rifaximin 550 mg PO TID for 14 days vs placebo
Pimentel M et al. NEJM. 2011
Rifaximin-Single course for IBS-D
P<0.01
Ø
*
P<0.01
Lembo A, Pimentel M et al. Gastroenterology. 2016
Rifaximin-Repeat therapy for IBS-D (TARGET 3)
P<0.01 • N = 2,579
• No statistically significant AEs between placebo and Rifaximin
• One case of C diff in the observation phase while patient being treated for UTI
• No change in MICs
n=1,891
Rezaie A et al. ACG 2015
Fasting
methane
level
(ppm)
Sensitivity
(95% CI)
Specificity
(95% CI)
PPV
(95% CI)
NPV
(95% CI) +LR -LR
≥5 96.1
(95.1-96.9)
99.7
(99.6-99.8)
98.5
(97.8-99.0)
99.3
(99.1-99.4) 353 0.04
Accuracy of a single fasting measurement of methane as
compared to 2–hour lactulose breath testing (gold standard)
Rezaie A et al. ACG 2015
n=12,183
Prevalence of Excessive Methane
Producers Increases by Age
Chang B, Pimentel M, Rezaie A. Gastroenterology. 2015. S-729
21 yo female with refractory clostridium difficile colitis
Fecal microbiota transplantation in July 2014
Eradication of Cdiff but severe distention, fatigue
and constipation
W/U Neg
No response to Antidepressants, low
FODMAPs, peppermint, OTC laxatives, linaclotide,
lubiprostone and prucalopride
Found to have methane-predominant bacterial
overgrowth in Oct 2015
Perfect response to Rifaximin and neomycin
FMT donor was found to be an excessive methane producer!
Chang B and Rezaie A. AJG 2016 (in press)
Ø
* P <0.01 Ø P <0.001
* *
Rezaie A, Pimentel M, McGovern D. DDW 2016
• Methanogenesis is significantly suppressed in
IBD patients; however, if present it is associated
with severe constipation
• A flatline breath test is more prevalent in CD
which may suggest excessive H2S production
Rezaie A, Pimentel M, McGovern D. DDW 2016
Conclusion
• Exhaled breath gases are non-invasive, inexpensive
and accessible alternatives to assess gut
microbiome in research and clinical practice
– Diagnosis of SIBO and carbohydrate malabsorption
– Tailored microbiome-directed therapy and diet
– Dynamism of microbiome
– Variability in metabolic behavior of gut microbiome
– Differences in microbiome in various diseases
Acknowledgments
• Dr. Mark Pimentel
• Dr. Ruchi Mathur
• Dr. Niki Pichetshote
• Dr. Gillian Barlow, Shari Chua,
Walter Morales, Stacey Weissman,
Emily Marsh