Respiratory Complications Flashcards
when can respiratory complications occur
at any stage in the anesthesia process:
- sedation
- induction/intubation
- maintenance
- recovery
- post-anesthetic period
what is the best thing do to to prevent respiratory complications
be prepared! know common species/breeds, procedures, conditions, medications and positioning that leads to respiratory complications
what is the most common cause of respiratory complications in anesthesia and why
hypoventilation - because of the drugs we use
what are the 6 common respiratory complications during anesthesia
- airway obstruction
- tension pneumothorax
- hypoxemia
- hypoventilation
- hyperventilation
- apnea
what does an oxygen saturation curve look at (x axis and y axis)
x: PaO2 (mmHg O2 in blood)
y: SpO2/SaO2 (% of Hb with O2)
what is relative (mild), absolute (moderate) and absolute (severe) hypoxemia (give both SpO2 and PaO2)
Relative: <80 mmHg / SpO2 <95%
Absolute:
Moderate <60 mmHg / SpO2 <90%
Severe <40-45 mmHg / SpO2 <80%
what delineates cyanosis
5.0 g/dL of deoxyhemoglobin or more (lower if anemic)
what SpO2 does cyanosis correspond to if the Hb is normal
<85%
what is the FiO2 of room air vs the FiO2 of inspired air during anesthesia? what are the implications?
FiO2 room air: 21%
FiO2 during anesthesia: 100%
During anesthesia, the PaO2 is 663 mmHg (HUGE O2 reserve)
T/F SpO2 is a limited value when FiO2 = 0.21
F; SpO2 a limited value when FiO2 = 1 (i.e during anesthesia)
what animal is the exception to the rule that most animals will not get hypoxemic during anesthesia
horses (due to their weight)
what are 5 causes of hypoxemia during anesthesia
- V/Q mismatch: atelectasis, pulmonary edema, thromboembolism, asthma…
- R-L shunt: intracardiac or intrapulmonary
- diffusion impairment (pneumonia, interstitial lung disease)
- severe hypoventilation
- decreased FiO2
how do we treat hypoxemia (6)
Treat the underlying problem
- increase FiO2, check O2 source
- lung re-expansion, reposition
- bronchodilators
- support and optimize ventilation
- diuretics
- surgical correction if needed
when do we want to pay special attention for hypoxemia
1) induction (pre-oxygenate)
2) recovery (switching back to room air)
what is the definition of apnea
> 1 min without spontaneous breathing
what are some causes of apnea (6)
- after induction (rapid high doses of propofol, alfaxalone, thiopental)
- excessive depth (1.5-3x MAC) or additional drug administration (opioids)
- hypocarbia
- airway obstruction
- inability to ventilate
- cardiopulmonary arrest
what is the best prevention for apnea
pre-oxygenate the animal: increases the O2 reserve and therefore gives more time for you to correct the apnea without the patient becoming hypoxemic
what MUST you have to diagnose hypoventilation
a CO2 monitor
by definition, what is hypoventilation
insufficient ventilation leading to hypercapnia (PaCO2 > 50-55 mmHg)
what is normal ETCO2 relative to PaCO2
ETCO2 usually 3-5 mmHg less than PaCO2
what causes hypoventilation
- decrease in tidal volume
- decrease in respiratory rate
- increase in dead space
- combination of the above
what are the physiological effects of hypoventilation (hypercapnia) (6)
- stimulates respiratory drive
- respiratory acidosis
- increase cerebral blood flow
- CNS depression
- sympathetic stimulation (increase HR and BP)
- hypoxemia
why does severe hypercapnia lead to hypoxemia
space-occupying (displacement of O2)
what are some causes of hypoventilation/hypercapnia during anesthesia
- anesthetic drugs
- pre-existing conditions
- positioning
- equipment
what are some pre-existing conditions that can cause hypoventilation/hypercapnia during anesthesia
- age
- hyperthermia
- obesity
- neurologic disorders
- pathologies of thoracic wall or lungs
what are equipment related causes of hypoventilation/hypercapnia
- increased dead space
- increased work of breathing (tube too small)
- CO2 rebreathing (low FGF, exhausted soda lime, unidirectional valves faulty)
why might laparoscopy be a risk for hypercapnia
absorption of the CO2 used to distend the abdomen for the procedure
how do we treat hypoventilation/hypercapnia
Treat the underlying cause!
- be aware of conditions
- monitor ETCO2 or PaCO2
- check the patient for depth
- correct body temperature
- check equipment
- support ventilation as needed
what is hyperventilation and the consequences
increased respiratory rate leading to hypocapnia and respiratory alkalosis
what are some causes of hyperventilation
- light plane of anesthesia/nocicipetion
- hypercapnia
- hypoxemia
- metabolic acidosis (respiratory compensation)
when does airway obstruction most commonly occur
premedication and recovery
what is the difference between partial and total airway obstruction
partial: increased work of breathing
total: inability to move air
what are some causes of airway obstruction
- anatomy (brachycephalics)
- underlying upper/lower airway disease
- airway swelling
- aspiration of foreign material
- external pressure
- equipment problems or errors
what are the ways to diagnose airway obstruction
- paradoxic breathing
- generating high pressure when trying to ventilate
- rebreathing bag not moving
- capnograph wave abnormal or gone
- prolonged inspiratory time
- hypoxemia and/or cyanosis
what is paradoxic breathing characterized by
- thoracic wall sucks inward
- abdominal wall expands
- neck flexed
- stridor
- open mouth breathing
- nostril flare
why are brachycephalic breeds predisposed to airway obstruction (what are the anatomical features)
- stenotic nares
- elongated soft palate
- everted saccules
- hypoplastic trachea
what indicates lower airway obstruction on a capnograph
shark fin: tells you increased effort at start of expiration
how should you treat bronchospasm to prevent airway obstruction
bronchodilators, epinephrine, antihistamines
how should you treat upper airway obstruction (prevention)
- topical anesthetic
- small tube size
- be ready to intubate
- pre-oxygenate
how do you prevent airway collapse from airway inflammation
- corticosteroids
- vasoconstrictors
- dextrose 50% locally
how do you treat airway obstruction:
- at induction
- intra-op
- recovery
At induction:
- suction
- tracheostomy
- get airway
Intra-op:
- check patient and equipment quickly
- manually ventilate to assess
- suction tube, change if needed
Recovery:
- extend head, pull out tongue
- re-intubate if necessary
what is a tension pneumothorax
life-threatening emergency in which air accumulates under pressure, compressing the lungs and venous return
how do we diagnose tension pneumothorax
- increased respiratory effort
- lack of lung sounds
- resistance to ventilation
- capnograph dissapears
- cardiac arrest
how do we treat tension pneumothorax
- tap chest
- chest tube
- suction
