regurgitation and aspiration during anesthesia
TRANSCRIPT
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Regurgitation and aspiration Sileshi A.
8/24/2014
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Introduction
First recognized as a cause of an anesthetic-related death in
1848
In 1946, Mendelson described the relationship between
aspiration of solid and liquid matter
Rare but potentially devastating complication of general
anaesthesia
1 in 3000 and 1 in 6000 anesthetics.
Increases to 1 in 600 for emergency anaesthesia in adults.
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Definition
Inhalation of material into the airway below the level of
the true vocal cords.
Linked with a range of clinical outcomes
Asymptomatic in some instances and resulting in severe
pneumonitis and ARDS.
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Pathophysiology
LOS acts as a valve preventing the reflux of gastric contents.
Barrier pressure is the difference between LOS pressure (normally
20-30mmhg) and intra-gastric pressure (normally 5-10mmhg)
Both are influenced by different factors.
Can you list conditions associated with changes in LOS tone?
What is the difference between regurgitation and vomiting?
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Cont.
LOS pressure is reduced by
Peristalsis, vomiting, during pregnancy (a progesterone effect)
as well as pathological conditions such as achalasia, and various
drugs (anticholinergics, propofol, thiopentone, opioids).
Intragastric pressure is
Increased if the gastric volume exceeds 1000ml, and with raised
intra-abdominal pressure such as that occurring with
pneumoperitoneum during laparoscopy.8/24/2014
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Vomiting Vs Regurgitation
Regurgitation is a passive process that may occur at any time & often
silent.
The common cause of regurgitation is a decreasing in closing pressure of
the sphincter.
In contrast, vomiting is an active process which involves contraction of
abdominal muscles that occur in lighter stages of anesthesia.
Factors determining the extent of gastric regurgitation include:-
Function of the LOS8/24/2014
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Cont.
Gastric volume is influenced by:-
Rate of gastric secretions (0.6ml/kg/hr)
Swallowing of saliva (1ml/kg/hr)
Ingestion of solids/liquids, and
The rate of gastric emptying
The rate of gastric emptying for non-caloric clear fluids is rapid – the half-time being about 12 minutes.
Solids however, require six hours or more to be cleared from the stomach, displaying zero-order kinetics. 8/24/2014
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Factors affecting gastric emptying Cause Increase Decrease
Physiologic Gastric distentionNeurosis
FoodAcidPregnancy
Pathologic Thyrotoxicosis AnxietyPyloric stenosisPain e.g. AnginaShock, DM
Pharmacologic MetoclopromidePropronalolNeostigmineNicotine (smoking)
OpiodsAlcoholTCAAnticholonergics 8/24/2014
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Severity and effects of aspiration
Effects of aspiration
1. Airway obstruction
2. Chemical pneumonia
3. Bacterial contaminations
Death
Factors w/c increase severity
1. Volume of aspirate, >25ml
severe
2. PH of aspirated matter, < 2.5
fatal
3. Extent of lung involved, one
or both
4. Type of aspiration,
solid/blood/fluid
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Who are at risk?
1. Patient factors
Increased gastric content
Intestinal obstruction
Non-fasted
Drugs
Delayed gastric
emptying
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LOS incompetence
Hiatus hernia
Gastro-oesophageal
reflux
Pregnancy
Morbid obesity
Neuromuscular
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Cont.
Decreased laryngeal reflexes
Head injury
Bulbar palsy
Gender
Male
Age
Elderly8/24/2014
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Cont.
2. Operation factors
Procedure
Emergency
Laparoscopic
Position
Lithotomy 8/24/2014
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3. Anesthetic factors
Airway
Difficult intubation
Gas insufflation
Maintenance
Inadequate depth
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Classification
1. Aspiration pneumonitis
2. Aspiration pneumonia
3. Particulate-associated aspiration
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1. Aspiration pneumonitis
AKA mendelson’s syndrome
Involves lung tissue damage as a result of aspiration of non-infective
but very acidic gastric fluid.
Two phases
1. Desquamation of the bronchial epithelium causing increased alveolar
permeability. Results in:-
Interstitial oedema,
Reduced compliance and
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Cont.
2. Due to acute inflammatory response
Occur within 2 to 3 hrs
Mediated by proinflammatory cytokines, i.e.
Tumour necrosis factor alpha
Interleukin 8 and
Reactive oxygen products
Clinically may be
Asymptomatic, or
Present as tachypnoea, bronchospasm, wheeze, cyanosis and respiratory insufficiency. 8/24/2014
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2. Aspiration pneumonia
Due to inhaling infected material or
Secondary to bacterial infection following chemical
pneumonitis.
Typical symptoms
Tachycardia, tachypnea, cough and fever
CXR- segmental or lobar consolidation
Unlike CAP, cavitation and lung abscess occur more
commonly.
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3. Particulate-associated
aspiration
If particulate matter is aspirated
acute obstruction of small airways will lead to
distal atelectasis.
If large airways are obstructed, immediate
arterial hypoxemia may be rapidly fatal. 8/24/2014
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PREVENTION
A. Preoperative fasting
Current guidelines are:-
2 hours for clear fluids,
4 hours for breast milk, and
6 hours for a light meal, sweets, milk (including formula) and
clear fluids.
B. Reducing gastric acidity
Histamine (H-2) antagonists and proton pump inhibitors (PPIs)
commonly used to increase gastric Ph.
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Cont.
They do not affect the Ph of fluid already in the stomach
Oral sodium citrate solution reliably elevates gastric Ph above 2.5, but it
increases gastric volume, and is associated with nausea and vomiting.
(30ml 10’ before opx)
An oral H2 antagonist (ranitidine 150-300mg PO) must be given night
before and 1-2 hours before anaesthesia and a PPI, (omeprazole 40mg
before the night and 2hr preop.)
Ranitidine superior to PPIs in both reducing gastric fluid volume and
acidity. (Clark et al )
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Cont.
Metoclopramide has a prokinetic effect promoting gastric
emptying
Usual pre-medication for caesarean section under general
anesthetic.
There is little evidence to support its use
10mg/PO 15min before surgery, slowly to avoid abdominal cramp8/24/2014
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Cont.
C. Rapid Sequence Induction (RSI)
high risk of aspiration? Do a RSI, unless difficult airway to warrant
an awake fibreoptic intubation.
Adequate depth of anaesthesia is important to avoid coughing,
laryngospasm and vomiting.
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Cricoid pressure
Described by sellick in 1961
Remains an essential maneuver
performed as part of RSI
Aim is to compress the
oesophagus between the cricoid
ring cartilage and the sixth
cervical vertebral body thus
preventing reflux of gastric
contents.
Force recommended is 30N
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BA Sellick, 1918-1996
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Cont.
D. Nasogastric tube placement
E. Airway device
A cuffed ETT is considered the gold standard device used
for airway protection
Alternative supraglottic devices include the classic laryngeal
airway (LMA) and
The proseal LMA, providing a higher seal pressure (up to
and a drainage channel for gastric contents is an other
LMAs during difficult airways
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Management
A. Initial management
Recognition of aspiration visible gastric
contents in the oropharynx, or
More subtle indications such as hypoxia,
increased inspiratory pressure, cyanosis,
tachycardia or abnormal auscultation8/24/2014
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Differentials must be thought
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Once Dx is suspected
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Cont.
Clinical decision b/n surgeon and anesthetist to proceed or not!!
Depends on
Underlying health of the patient,
The extent of the aspiration, and
Urgency of the surgical procedure.
A chest x-ray (CXR) can be useful in the case of suspected pulmonary
aspiration, although in about 25% of cases there are no radiographic
changes initially.
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If stable extubate and send to RR
If patient develop a new cough/wheeze, tachycardia or tachypnea,
drop their spo2 on room air (by >10% of pre-operative value), or
Have new pathological changes on CXR should be further
managed in an ICU
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Further management
Empirical ABCs if patient has developed a subsequent
pneumonia.
Treatment should then ideally only be prescribed once the
organism has been identified, commonly gram negative
bacilli.
Corticosteroids should not be given prophylactically in the
acute phase following aspiration.
No evidence to support a reduction in the inflammatory
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