9. Anesthesia for Patients w/ Resp Dz Flashcards
How do we prepare for anesthesia in a patient w/ resp dz
id problems pre-op
stabalize patient’s condition b4 anes** and improve pulmon func
understand pathophysiology and choose anes protocol for patient
prei-and intraop monitoring (spo02 and capnography)
supportive care(preop o2, pos pressure ventilation during anes, anti-anxiety meds)
How does saturation of 100, 95, 90, 75 and 50% relate to arterial PaO2, what is the normal Spo2 and paO2
- Saturation of 100% PaO 2 100mmHg or more
- Saturation of 95% PaO 2 80mmHg
- Saturation of 90% PaO 2 60mmHg HYOXEMIA !!
- Saturation of 75% PaO 2 40mmHg
- Saturation of 50% PaO 2 27mmHg
Normal SpO 2: 95-100%
Normal paO 2: 80-100mmHg
At what spo2 lvl is cyanosis visible?
<85%
What is preoxygenation?
admin of O b4 induction of anes
replaced alveolar N (79%) w/ O2
creates an intrapulmonary O2 reserve (FRC)
Hb fully saturated, dissolved O2 increases
What does FRC mean?
functional residual capacity
Volume of air left over once you expire
Why might we preoxygenate in dogs?
delays onset of hypoxemia during apnea/hypoventilation
preox for 3m
w/o pre-ox: hypoxemia occurs in <70s
W pre-ox: apnea tolerance <298s
Avoid stress to prevent an inc o2 consumption
Does flowby pre-oxygenation make a difference to breathing room air?
The delay of onset of hypoxemia
Flowby: hypoxemia occurs in <66s
Mask pre-ox: apnea tolerance <187s
What are some good tips of preox?
- Size of mask – Avoid superfluous dead space
- Oxygen flow rate – Avoid rebreathing
- How long?
- 3 minutes
- FEO 2 > 90% (fraction of expired oxygen)
- Don’t stop during induction
Who benefits from preoxygenation?
- Important when difficult airway is anticipated - Brachycephalics
- Pregnant patients
- Patients with increased intra-abdominal pressure
- Patients with cardiovascular disease
- Patients with respiratory disease
- Critical ill patients
- Obese patients
Why is use of atropine and glycopyrrolate controversial?
May have some laryngeal manipulation and cause profound vagally mediated bradycardia
in brachcephalics will cause elevated vagal tone
If using as antisialogoues or to dec resp tract secretions - generally not recommended, change secretory composition: from watery fluid to thick mucus
The tachycardia inc myocardial work and O2 demand
will have some bronchodilator (use bronchodilator drugs instead compared to these drugs)
Should we sedate patients with compromised respiratory system?
sedation rarely affects it BUT;
clin signs: aggravated by hyperventilation
Avoid: anxiety, excitement, physical exertion, hyperthermia
Inc in patient’s work of breathing will exacerbate neg pressure in upper airway
pronounced neg pressure promotes inward collapse of airway
WHat is the bernoulli effect?
Physical principle to explain airway collapse during hyperventilation
“ Increase in gas velocity, which occurs when gases traverse a constriction, lowers
pressure at that point and promotes collapse
What might we use for sedation in dyspneic patients?
Low doses of sedatives/analgesics to take edge off, breath slowly and deeply
-reduction in airblow turbulence and work of breathing, continuous monitoring during sedation, avoid drugs
Avoid drugs that induce vomiting and panting
Anxiolysis (pre or in hospital, slow onset time)
* Trazadone: 2-10 mg/kg (administered ideally prior to leaving home, continued during hospitalization)
* Gabapentin 10-20mg/kg
Sedation (inhospital)
1. Butorphanol: 0.2-0.4 mg/kg
2. Acepromazine: 0.005-0.02 mg/kg
3. Dexmedetomidine: : 1-2 μg/kg
What is brachycephalic obstructive airway syndrome?
upper airway gas flow is restricted by stenotic nares, hyperplastic soft tissue,
enlarged, thick soft palate
hypoplastic trachea
everted laryngeal saccules
oversides, elongated tongue
Prolonged obstruction - excessive oropharyngeal soft tissue weakness > laryngeal collapse, pulmonary hypertension (due chronic hypoxia)
What can make clinical signs of BOAS worse?
heat, exercise, stress/anxiety, panting
What other abnormalities might happen when an animal has BOAS?
esophageal and GI abnormalities
inc risk of GER and regurg > aspiration, esophagitis and stricture formations
Prevalence for regug: fresh bulldogs 93%, English bulldogs 58%, pugs 16%
How can we reduce GER and aspiration?
appropriate fasting
preanes tx of omeprazole (1mg/kg) 4-24h b4 induction, maropitant b4 premed (1hr SQ, 2hr PO), prokinetics like cisapride, metoclopramide
If GER is observed: gently suction and lavage esophagus w/ water, instil diluted bicarb, recheck esophagus and oral cavity b4 recovery
What are some anticipated anestetic complications w/ BOAS?
upper airway obstruction in periop period - time btw premed and tracheal intubation, tracheal extubation and full recover
prone to hyperthermia - panting is difficult and ineffective
occular care: higher incidence of corneal ulceration
What are the goals of premed and sedation in an animal with BOAS?
sedate > reduce anxiety > facilitate IV cath placement > reduce dose of induction agent > anesthetic sparing > analgesia
No “perfect” premed/sedation protocol exists
drug selection depends on temp, severity of concurrent dz and procedure
With the effects of sedation in animals with BOAS, what do we want?
want to improve ventilation by slowing inspiratory flows
avoid relaxation of oropharyngeal muscles > aggravation of obstruction
Panting, vomiting, excitement
avoid drugs that induce profound sedation, vomiting panting and marked resp depression
Continuous monitoring during sedation
Why do we need to be vigilent when recovering brachycephalics?
high risk period, position in sternal recumbency, continue O provision
leave IV cath in place until full recovered
Late extubation
in patients w/ laryngeal collapse - anticipate upper airway obstruction and have a plan ready before extubation
have equipment/drugs available for re-intubation
What are some problems in recovery with brachycephalic?
minor post-extubation obstruction - extend head and neck to open airway, pull tongue rostrally, open mouth: use gag if necessary, open jaw with bandage strips
major obstruction - re-anesthetise and intubate if necessary, place temporary tracheostomy
What do we do in recovery when its a cat with upper airway obstruction?
place in sternal, extend head/neck, pull tongue forward
admin O2, try to inspect oral cavity
What can cause upper airway obstruction in cats?
A mucus plug: causes suction
Some lube is water soluble, so don’t go too crazy with it
laryngeal edema: use corticosteroids (dexamethason 0.2mg/kg)
What is laryngeal spasm?
larynx must not be stimulated further
avoid multiple attempts of intubation
Keep patient oxygenationed: facemask, supraglottic airway device
optimize head neck position
tx options: lidocaine spray, depend anes, muscle relaxant: rocuronium (0.5-1mg/kg) need to ventilate, consider tracheostomy
no guarantee that spams will not reoccur when anesthesia lightens
What is the goal of anesthetic induction?
adequate anesthetic depth to allow
jaw relaxation to position laryngoscope and maintain intact laryngeal reflexes
How do we perform anesthesia for diagnosis for laryngeal function?
premed improves quality of laryngeal examination
alfaxalone or propofol alone not reliable
either alfax or propofol can be used after ace/but or dexmex/but
doxapram (0.5-2mg/kg, IV) - resp stimulant, inc laryngeal motion in healthy dogs, prods passive paradoxical arytenoid motion in dogs w/ laryngeal paralysis
