Anesthesia Curriculum Flashcards
Normal lung volumes (TLC, TV, VC, FRC)
Normal lung volumes (RV, ERV, IRV, FVC)
Effects of general anesthesia on the FRC
Hgb dissociation curve
Five etiologies of hypoxemia
Mallampati
Hyomental distance
- >3 cm is favorable for intubation
Thyromental distance
- > 6cm is favorable for intubation
Normal head extension
At least 35 degrees
Basics of the airway exam: The four M’s
- Mallampati
- Measurements (Hyomental, thyromental)
- Movement (Head extension)
- Malformation (anything obstructive or loose, BMI)
Airway emergency
Cannot intubate AND cannot ventilate
In other words, if you cannot intubate but you can bag and mask ventilate, it’s not an airway emergency.
Rapid sequence intubation
Induce the patient with an anesthetic and give a muscle relaxant (usually Succinylcholine or Rocuronium) that works fast in order to intubate the patient as soon as possible without mask ventilation
A rapid sequence induction is a good choice for patients that are at increased risk for aspiration (trauma, GERD, pregnant, diabetic gastroparesis, full stomach)
When a patient with 100% O2 sat is cyanotic, you always need to consider two things
- Carbon monoxide
- Methemoglobinemia
Cormack and Lehane classification
- Grade 1 view: all of vocal cords/laryngeal aperature
- Grade II view: arytenoids only
- Grade III view: epiglottis only
- Grade IV view: palate only
Levels of anesthesia
Minimal Sedation (Anxiolysis)
a drug-induced state during which patients respond normally to verbal commands.
Although cognitive function and physical coordination may be impaired,
airway reflexes, and ventilatory and cardiovascular functions are unaffected.
Monitored Anesthesia Care (“MAC”)
- Does not describe the continuum of depth of sedation
- Rather it describes “a specific anesthesia service performed by a qualified anesthesia provider, for a diagnostic or therapeutic procedure.”
- Indication: “the need for deeper levels of analgesia and sedation than can be provided by moderate sedation (including potential conversion to a general or regional anesthetic.”
Moderate Sedation/Analgesia (“Conscious Sedation”)
drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation.
No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate. Cardiovascular function is usually maintained.
Deep Sedation/Analgesia
a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully following repeated or painful stimulation.
The ability to independently maintain ventilatory function may be impaired. Patients may require assistance in maintaining a patent airway, and spontaneous ventilation may be inadequate. Cardiovascular function is usually maintained.
General Anesthesia
a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation.
The ability to independently maintain ventilatory function is often impaired. Patients often require assistance in maintaining a patent airway, and positive pressure ventilation may be required because of depressed spontaneous ventilation or drug-induced depression of neuromuscular function. Cardiovascular function may be impaired.
The laryngeal mask airway partially protects the larynx from ___, but not ___.
The laryngeal mask airway partially protects the larynx from pharyngeal secretions, but not gastric regurgitation.
The earliest evidence of bronchial intubation often is an increase in ___.
The earliest evidence of bronchial intubation often is an increase in peak inspiratory pressure.
Ensuring that when you intubate someone you haven’t gone into the esophagus
- direct visualization during intubation
- presence of bilateral breath sounds
- absence of gastric gurgling while ventilating
- analysis of exhaled gas for the presence of CO2
- chest radiography, airway ultrasonography, or use of fiberoptic bronchoscopy
Closing capacity
- The maximal lung volume at which airway closure can be detected in the dependent parts of the lungs
- Closing capacity is normally well below FRC, but it rises steadily with age. This increase is probably responsible for the normal age-related decline in arterial O2 tension.
FEF25-75 utility in obstruction
Whereas both forced expiratory volume in the first second of exhalation (FEV1) and forced vital capacity (FVC) are effort dependent,
forced midexpiratory flow (FEF25–75%) is more effort independent and may be a more reliable measure of obstruction.
Effects of the mechanics of anesthesia on the FRC
- Changes in lung mechanics due to general anesthesia occur shortly after induction.
- The supine position reduces the FRC by 0.8 to 1.0 L,
- and induction of general anesthesia further reduces the FRC by 0.4 to 0.5 L.
- Net: reduction by 1.2 to 1.5 L
- FRC reduction is a consequence of alveolar collapse and compression atelectasis due to loss of inspiratory muscle tone, change in chest wall rigidity, and upward shift of the diaphragm.
Anesthesia and shunt
General anesthesia commonly increases venous admixture to 5% to 10%, probably as a result of atelectasis and airway collapse in dependent areas of the lung.
Direct effects of alveolar CO2 on O2
Large increases in PaCO2 (>75 mm Hg) readily produce hypoxia (PaO2 <60 mm Hg) at room air,
but, not at high FiO2.
Central chemoreceptors
Central chemoreceptors are thought to lie on the anterolateral surface of the medulla and respond primarily to changes in cerebrospinal fluid [H+].
This mechanism is effective in regulating PaCO2, because the blood–brain barrier is permeable to dissolved CO2 but not to bicarbonate ions.
Chemoreceptor summary image
Effects of anesthesia on CO2 ventilation curve and apneic threshold
With increasing depth of anesthesia, the slope of the PaCO2/min ventilation curve decreases, and the apneic threshold increases.
The mechanism is probably dual: central depression of the chemoreceptor and depression of external intercostal muscle activity.
PaCO2 ventilation curve
PaO2 ventilation curve
Class and Grade of airway
Stable angina as a surgical risk factor
Really not a very significant risk factor. Stable angina is not an indication to reschedule a procedure and consult cardiology.
Unstable angina, on the other hand, would be an indication for this.
Pros and Cons of patient controlled analgesia
-
Pros
- Peaks and troughs are less severe
- Analgesic level better matched to analgesic need
- Patient has autonomy
-
Cons
- May lead to pruritis, ileus, sedation, respiratory depression
- may not cover all major surgical pain, but may provide additive effect
Precedex
- Centrally acting alpha 2 agonist analgesic
- Much higher affinity for alpha 2 receptors than clonidine, the other centrally acting alpha 2 agonist
- Clonidine also has weak analgesic properties
Para-aminophenol
- COX-3 inhibitor analgesic
- Same mechanism as acetominophen
- Controversy exists over the exact mechanism, as for tylenol
Where different analgesics act
Trauma patients are generally not going to be ___
Trauma patients are generally not going to be NPO
Good anesthetic choices for asthmatic patients
-
Induction agents
- Propofol
- Ketamine
-
Analgesics
- Fentanyl
-
Gas anesthetics
- Isoflurane
- Sevoflurane
-
Muscle relaxants
- Succinylcholine
- Rocuronium
What anesthetics do you want to avoid in asthmatic patients?
- Morphine (causes histamine release, bronchoconstriction)
- Atracurium (causes histamine release, bronchoconstriction)
- Desflurane (causes airway irritation, especially in smokers)
Normal ETCO2 curve
ETCO2 curve in obstruction
Management of asthma attack during anesthesia
- Increase bronchodilatory gas anesthetic (if using)
- Add albuterol inhaler via endotracheal tube
- If no improvement, administer lidocaine
- If no improvement, administer epinephrine
Things that may mimic bronchoconstriction during anesthesia
- Inadequate anesthetic depth
- Mechanical obstruction (patient biting on tube, tube kinks)
- Secretions (may be seen in tube, can suction to remove)
- Pneumothorax from barotrauma (unlikely, but do not miss)
Assist-controlled ventilation vs SIMV
-
Assist-controlled:
- If ventilator senses a patient-initiated breath, it delivers a full tidal volume. Thus, patient controls the ventilatory rate, with a built-in minimum baseline rate
- May worsen air-trapping/breath-stacking/dynamic hyperinflation in those with obstruction, but allows for minimal work of breathing. PEEP may increase intrathoracic pressure and decrease venous return.
-
SIMV:
- Combination of spontaneous, unsupported breathing with a built-in minimum baseline rate. Leaves a “window” of breathing opportunity for the patient. Does not deliver a set tidal volume upon patient breaths.
- Improves V/Q matching, but may produce an excessive work of breathing and more likely to be dyssynchronous than AC
Pressure support ventilation
- Similar to pressure-controlled assist-controlled, but different mechanism terminates inspiration:
- In AC, inspiration is determined by time. In PS, inspiration is determined by decreasing gas flow (~25%)
- Patient triggers each breath, but provides decreased work of breathing. WOB can be gradually increased by playing with settings.
- No true back-up rate
- Ideal mode for ventilator weaning
Indications for spontaneous breathing trial
- Improvement in factors that led to ventilator dependence in the first place
- Assessment of oxygenation:
- PaO2/FiO2 ≥ 150 mmHg
- PEEP ≤ 8 cm H2O
- FiO2 ≤ 0.5
- pH ≥ 7.25
- Hemodynamic stability (low dose vasopressors ok)
- Spontaneous respirations
Criteria for a successful SBT
- 30-120 minute duration
-
None of the following met/exceeded:
- RR > 35 breaths/minute
- HR > 140 or a sustained ↑ of 20% from baseline
- SBP > 180 mmHg or DBP > 90 mmHg
- ↑ anxiety
- ↑ diaphoresis
WHEANS NOT mnemonic for difficult to wean patients
- Wheezing
- Heart disease
- Electrolyte problem
- Anxiety, aspiration, alkalosis
- Neuromuscular weakness
- Sepsis
- Nutritional deficit
- Obesity
- Thyroid disease
CPAP vs BIPAP
-
CPAP
- continuous stream of pressure throughout respiratory cycle, stents the airway open, portable
-
BIPAP
- increased pressure on inspiration, less on expiration, better tolerated than CPAP but requires constant supervision of pressures
Why is aortic stenosis such a big deal in anesthesia?
Three reasons:
- The coronaries are on the other side of the aortic valve, so their arterial pressure is already reduced by the addition of a large resistor
- Anesthetics will lower the arterial blood pressure, resulting in an even lower arterial pressure
- PEEP from ventilation increases venous pressure
- The net effect of all of the above is significantly reduced coronary perfusion pressure
Effects of benzodiazepines on hemodynamics
Really no significant effects. They are decent at facilitating induction in patients with cardiovascular issues
Effects of opioids on hemodynamics
- Decrease SNS activity, decreasing SVR and HR
Effects of paralytics on hemodynamics
- Pancuronium: increases HR, BP and CO due to a possible vagoly:c and sympathomime:c effect
- Atracurium: causes histamine release, resulting in vasodilation and drop in SVR and BP
- Vecuronium: May cause tachycardia
- Rocuronium and succinylcholine have negligible effects.
Effects of induction agents on hemodynamics
- Generally all decrease SVR and preload, with the exception of Etomidate
Effects of inhaled anesthetic gases on hemodynamics
- Most decrease SVR and increase HR
- The exception is halothane, which decreases CO via direct myocardial effects
We don’t cancel surgery for stable angina, but we do for symptomatic ___
We don’t cancel surgery for stable angina, but we do for symptomatic aortic stenosis
Management of aortic stenosis intraoperatively (if you have to do surgery on someone with significant aortic stenosis)
Effects of left ventricular hypertrophy on the atrial kick
Makes the atrial kick more imporant:
It’s relative contribution to preload increases from 10% to 30-40%.
So, atrial fibrillation in someone with LVH really drops the blood pressure, since it is both uncoordinated and you lose the preload contribution.
LV and RV perfusion
The LV is only performed during diastole, while the RV is performed continuously (due to relative pressures)
Components of an ABP tracing
____ have the added benefit of protec:ng the myocardium from ischemia and reperfusion injury and decreasing MI size.
Volatile anesthetics have the added benefit of protec:ng the myocardium from ischemia and reperfusion injury and decreasing MI size.
Clonidine for opioid withdrawal
Methadone for OUD
Buprenorphine for OUD
Long term antagonism with naloxone . . .
. . . increases sensitivity to opioids
Since it is blocking endogenous receptors – it makes neurons upregulate them. So, you really want to avoid opioids in patients taking chronic naloxone.
In someone with a poor gag reflex who has poor ventilation, why can’t you bag and mask to ventilate?
To prevent aspiration
Severe sinus bradycardia and AV block after insufflation for laporoscopy
Sometimes observed due to activation of the peritoneal stretch receptors
Anesthesia must monitor the patient very carefully for this vagal response during insufflation
Respiratory Alkalosis of Pain
Untreated pain alone can produce a substantial respiratory alkalosis
If you see a respiratory alkalosis and hyperventilation without a good etiology (such as in the context of a reasonable pO2 greater than 80)
