GI Case Management Flashcards
Oropharyngeal Diseases
Patients with pharyngeal dysphagia more prone to regurgitation, aspiration esp in cases where large space-occupying lesion compressing CN IX, X – responsible for series of involuntary movements that transport food bolus into stomach, protect airway during swallowing
Why Mandiblectomies Prone to Hemorrhage
inferior alveolar artery (br mandibular artery) runs through ramus of mandible, almost always transected during surgery
Coags before sx
Why Maxillectomies Prone to Hemorrhage
transection of either or both major palatine artery, infraorbital artery
o Transection depends on location of tumor
o Both = branches of maxillary artery
Rostral maxillectomy: diffuse bleeding from highly vascularized nasal turbinates
Oral Pharyngeal Dz and Intubation
Potential challenges for intubation- retrograde
eg TMJ ankylosis, MMM
o Puncture cricothyroid membrane with needle or IVC
o Insert guide wire through needle and advanced retrograde through mouth opening then feed ET over guide wire into larynx
o Remove guidewire so further advanced ET into trachea
Reflex Assoc with Maxillofascial Sx
trigeminovagal reflex (rarely reported in vet med)
Bezold-Jarish Reflex
stimulation of [ventricular] cardiac chemoR or stretch R (mechanoR) – induction of sinus bradycardia, hypotension, peripheral VD
Bainbridge Reflex
increase HR caused by rise in BP in great veins as enter RA
Fluid Bolus
Vasovagal Reflex
decrease in venous return to heart (hypovolemia, compression of caudal VC, regional analgesia) – sinus bradycardia, vasodilation
Esophageal Composition
o Dogs: striated m
o Cats, pigs, horses, primates: proximal 2/3 striated m, distal 1/3 SmM
Muscles that Compose UES
cricopharyngeus, thyropharyngeus m
What is the most common cause of benign esophageal stricture in dogs, cats?
GA-related GER –> esophagitis
Esophagitis Related to GER
esophageal mucosa exposed to caustic substances for prolonged periods +/- esophageal defense mechanisms (EDMs) impaired/overwhelmed
What are esophageal defense mechanisms?
superficial mucus/bicarb layer, tight junctions btw epithelial cells, intracellular/interstitial buffering capacity dependent on BF
Incidence, Consequence of GER/esophagitis?
Signs: days to three weeks to appear
Mortality: 21-30%, low incidence (~0.1%)
Greater risk with intraabdominal sx, esp OVH
CS perforation: pneumothorax, pleuritis, pyothorax, resp distress
MOA GER Esophagitis
Reduced LES pressure allows contents to enter esophagus more easily
Swallow reflex absent; acidic gastric acid contents (pH <4) cannot be neutralized by patient swallowing basic saliva
Reduced esophageal peristalsis
Factors that Increase GER/Decrease LES Pressure
Older or younger animals
Dogs >40kg
Large, deep chested dogs esp in sternal recumbency
Dorsal recumbency
Change in Position During GA
Prolonged fasting times (>10hr), shorter fasting times (3h)
Intraabdominal sx, including laparoscopy
Ax duration >105’
GA during second half of pregnancy
What percentage of animals that experience GER will actually regurgitate?
Only 0-15% in patients experiencing GER will actually regurg
Incidence of GER in dogs, cats without hx of GI or esophageal dz: 12-67% based on esophageal pH meters
Treatment of Esophagitis/GER
H2RA tachyphylaxis may occur in 3-13d – PPIs more effective at treating reflux esophagitis, maintaining effects on pH
Should you include an anticholinergic indiscriminately in your canine, feline premeds?
NO!
Decreases LES tone
Minimal effect on gastric pH at clinical doses – higher doses, will inhibit H plus secretion by gastric parietal cells via M1
Congenital or Idiopathic ME
defect of vagal sensory innervation where esophageal peristalsis does not occur, no detection of dilation caused by food bolus
Acquired Megaesophagus
mechanical obstruction –> Vascular ring anomaly, esophageal stricture, hiatal hernia, tumor, granuloma, FBs
* Over time, dilation of esophagus proximal to lesion becomes irreversible
Idiopathic acquired: most common form in adults – loss of normal esophageal motility eventually results in dilation
Secondary to/assoc with other diseases:
* Peripheral neuropathy, laryngeal paralysis, MG, severe esophagitis, lead poisoning, lupus myositis, chronic/recurrent GD or GDV
Main Anesthetic Concerns Assoc with ME
GER, regurg, aspiration
Prolonged fasting not necessary: dysmotility, dilation prevent complete emptying of esophageal contents
Potential for repeated episodes of asp pneumonia, greater risk for postop hypoxemia
Stricture Ballooning/Upper GI Endoscopy
o Pyloric sphincter tone may increase with pure MOR agonists, ketamine
o Gastric distention: hypoventilation, decreased venous return; vagal nerve stimulation from distended viscous
o Overdistention of GIT = activation of stretch R within walls, sudden/profound vagally-mediated bradycardia, tx: immediate deflation, atropine
o Inflation of hollow viscus with air = dull cramping pain of poorly localized discomfort ; Intraop analgesia +/- TAP block: more stable plane of ax
Laparoscopy - Effects of CO2 Insufflation
Decrease venous return, impair ventilation
Increase in SVR, decreased preload, potential for hypotension
Decreases FRC, reduced compliance – predisposed to VQ mismatch
Cranial displacement of diaphragm – more difficult for SpV to maintain adequate minute ventilation, IPPV may be required
PPV: decreases HBF
CO2 freely diffuses into splanchnic circulation
Levels of Abdominal Pressure Assoc with Laparoscopy
Intraabdominal pressure 10-16 mmHg, HBF increased >12mm Hg (humans)
o Ideally want intraabdominal pressure as low as possible
o Decrease in blood flow to GIT
o Decreased GFR = AKI
Transient increases in hepatic transaminases up to 48hr after desufflation
o Increases in ALT, AST directly proportional to intra-abdominal pressure, duration of insufflation
Other Effects of Laparoscopy
VQ mismatch: potential for large differences btw ETCO2, PaO2, worse with Trendelenburg
Increased ICP
Hypercapnia
Air Embolism
Air Embolism with Laparoscopy
Absorption of CO2 via ruptured blood vessel, etc: rapid absorption of CO2 into tissues (as opposed to nitrogen) means that it seldom causes clinical problems
Microemboli don’t cause as severe issues as pass through right side of heart»_space; Wedge in pulmonary vessels where they create V/Q mismatching/ pulmonary hypertension/ atelectasis, can be eliminated through lungs
Large gas emboli can become lodged in RA or RV or PA where they stop passage of blood through the heart»_space; Rapidly fatal
If reach systemic circulation, obstruct BF - cause hypoxia in critical organs (eg cerebral, coronary arteries most vulnerable)
Tolerable Levels of Air in Circulation
0.35mL/kg/min in dogs, pigs 2mL/kg
How Reduce Risk of Embolism with Laparoscopy
by slowing rate of abdominal insufflation to <1 L/min more time for pulmonary clearance of air bubbles
Diagnosis of Air Embolism
Behavior changes (agitation, change in demeanor)
changes in ETCO2 readings (V/Q mismatch with rapid drop in CO2 when ventilation held constant)
development of mill-wheel heart murmur (harsh, churning, splashing, metallic)
Hypotension, tachypnea
TEE = definitive diagnosis
Treatment of Air Embolism
Remove insufflated gas from abdomen
Address any non-ligated vasculature
increase CVP (to encourage bleeding rather than air entrainment)
discontinue N2O admin, administer 100% O2
Nitrous and Air Emboli
Admin of N2O: exacerbates gas emboli as diffuses into air pockets, expands them
Induction and Maintenance of Patients with GDV, Splenic Masses
TP, propofol sensitize myocardium to catecholamine-assoc arrhythmias
o Also why des, iso, sevo preferred for maintenance vs halothane
* DO NOT INDUCE VIA INHALANT TECHNIQUE
Pathogenesis of SI Intraluminal Obstruction
Intestine rostral to FB extends with gas, fluid (fluid DT increased secretion from intestinal glands, retention of fluid)
Fluid shifts from serosa into peritoneal cavity
Circulation in mucosa becomes ischemic, wall necrosis possible
Bacterial overgrowth, may translocate if normal mucosal barrier impaired by distention, ischemia
Consequences of Manipulation, Derotation of Ischemic Bowel
release of numerous inflammatory mediators that cause VD, cardiac dysfunction
Ischemic reperfusion injury, endotoxemic shower/shock
Lidocaine CRI, dexmedetomidine CRI
Analgesia in Abdominal Sx
Innervation: sympathetic chain T1-L3/4, abdominal wall innervation T11-13/L1-3
Innervated primarily by C fibers: poorly localized, may be assoc with autonomic responses DT adjacent travel with ANS fibers
Stimulus from distention, contraction, inflammatory mediators, ischemia
Referred pain: distant from source, DT convergence of afferent nerve pathwas onto same DH neurons
Pathophysiology of GDV
Gastric distention, torsion – compromised BF to stomach, surrounding organs
CV compromise DT obstruction of (low pressure) caudal VC, portal vein, splenic veins
Obstruction of vessels = decreases venous return, increased venous pressure –> severe hypovolemic shock, decreased oxygen delivery
DO CO, hypotension + splanchnic pooling/portal hypertension = interstitial edema, loss of IV volume
o Distention of stomach, increased abdominal pressure restricted ventilation via interference with diaphragmatic excursion
Respiratory compromise, possible partial lung collapse
Decreased VT, VQ mismatch – hypercapnia, hypoxemia despite increased RR, effort
Consequences of GDVs
- Arrhythmias
- Hemoabdomen - rupture of short, large bore gastric arteries
- Mixed Acid, base Disturbances
- Splenic Compromise/Vascular avulsion