Advaced-Opthalamic Flashcards
Which of the following will have the greatest effect on increasing intraocular pressure:
A. Hyperventilation
B. Decreased diastolic pressure
C. Increased venous pressure
D. Hypoxia
What’s normal IOP?
Therefore, factors that increase blood flow to the eye (same factors as the head) such as increased PaCO2 (answer A), increased mean arterial pressure (answer B), or hypoxia (answer D) will increase blood volume. Factors that decrease venous drainage (and in this case aqueous humor drainage as well) also increase the pressure, such as increased central venous pressure or venous obstruction directly from the eye. Coughing, bucking, and straining can increase venous pressures significantly and transmit directly back to the eye. In fact, venous pressures likely have more effect on intraocular pressures than arterial pressure in most circumstances (which is why in the answer choices hypoxia has less of an effect than increased venous pressure)
Normal IOP: 12-20
Which of the following is most likely to lead to a decrease in intraocular pressure:
A. 1 mg/ kg Rocuronium B. 1 mg/ kg Succinylcholine C. 2 mg/kg Ketamine D. 1 MAC Desfulurane E. 0.2 mg atropine
D: 1 MAC Desfulurane
Of the above choices, only volatile agents would be expected to lead to a decrease in intraocular pressure. This is likely due to decreased arterial and venous pressures (maybe especially venous?) as well as muscle relaxation (of extraocular muscles), decreased CNS outflow, and possibly decreased aqueous humor production
Eye injury in a 6 yo with a full stomach-what are you going to do?
In the setting where a rapid sequence induction is indicated with an open eye injury, succinylcholine should not be avoided for this reason.
Many authors suggest (and a FDA black box warning once existed for this purpose) to avoid succinylcholine in all pediatric patients due to:
undiagnosed myopathies that may lead to hyperkalaemia-not MH!
The oculocardiac reflex occurs in response to ____ and involves which ganglia?
pressure on the globe or traction on an extraocular muscle. The signal is carried through ciliary nerves to the ciliary ganglion just behind the orbit. From the ciliary ganglion it travels along the 1st division of the trigeminal nerve (V1) to the trigeminal ganglion, also known as the gasserian ganglion. The signal reaches the trigeminal nucleus and communicates with the vasomotor center, leading to the efferent vagal pathway (producing bradycardia
Treatment for oculocardiac reflex:
In most circumstances, simply ceasing the stimulus can interrupt the reflex and other options can be considered. If the patient remains bradycardic, atropine is typically administered because it has a quicker onset then glycopyrolate (answers A & B). Afterwards, the surgery can commence. If the reflex still leads to extreme bradycardia, the muscle can be infiltrated with local anesthetic (answer D). The reflex tends to self extinguish with repeated stimulation and rarely requires further intervention. Furthermore, the reflex is normal (although more pronounced in certain individuals) and is not indicative of underlying cardiac disease (answer E).
What pretreatment is needed for oculocardiac reflex?
Atropine, given either IM or IV have been used to prevent the occulocardiac reflex with mixed results. Retrobulbar block has also been shown to prevent the reflex, but can also cause the reflex (during the actual procedure) and has associated significant risks as well (see question10). Epinephrine and morphine are distractors. Since the oculocardiac reflex is nearly always benign, no pretreatment for prevention is needed. Short story-none
Long story:
Nitrous and SF6-rules?
Therefore, N2O should be discontinued at least 15 minutes prior to injection of SF6 and should be avoided for the next 10 days.
Why should ecthiophate and succinylcholine not be used together?
Ecothiophate is an irreversible cholinesterase inhibitor which causes miosis when applied the eyes. Treatment with this drug can, supposedly, have clinically significant blood levels to inhibit plasma cholinesterase, including pseudocholinesterase (remember all anticholinesterases we use can do this, just not as avidly as ecothiophate). Because this can lead to unpredictable durations of action of drugs metabolized by this pathway (succinylcholine), they should be avoided
Five minutes following a retrobulbar block, a patient desaturates. What is the most likely reason for this:
A. Oculoapneic reflex B. Seizure C. Pulmonary oedema D. Local anesthetic in the cerebrospinal fluid (CSF) E. Globe rupture
D: Local anesthetic in the cerebrospinal fluid (CSF)
It’s a very easy question, even when worded confusingly, so do not miss this on your exam…it’s a freebee. Accidental blind injection of local anesthetic in the optic nerve sheath can spread back towards the CSF, essentially producing a high spinal. The patient should be assessed for respiratory efforts, and if none are available, positive pressure ventilation is needed. Injection of local anesthetic into the artery, if forceful enough, can make its way back to the brain and cause seizures. Globe rupture, optic nerve damage, and neurogenic pulmonary odema have also occurred. There is no such thing as the oculoapneic reflex.
Normal PSI of jet ventilator, and what is the Venturi effect?
A small side port is attached to the surgeon’s laryngoscope and high pressure (~50 psi) oxygen is directed towards the trachea in short bursts. The oxygen hose typically delivers about 40-50 psi, but looses pressure as it flows through the jet ventilator side port, but gains velocity. This principle is known as the venturi effect-losing pressure, but gaining velocity
Why is the FiO2 lower with jet ventilation, and why does the Difference between ETCO2 and PACO2 increase with jet ventilation?
The high velocity stream of oxygen actually entrains room air, therefore lowering the overall FiO2 (answer A). In this setting, oxygenation is active, but ventilation is passive. Without patient effort, CO2 slowly diffuses out of the lung and consequently, CO2 is retained. Because ventilation (CO2 removal from the lungs) is passive (and ineffective), capnography underestimates the CO2 concentration in the alveoli (~ETCO2). Therefore the difference between the capnography value and PaCO2 value increases.
Is oxygenation preserved with jet ventilation? And is jet ventilation necessary in a spontaneously breathing patient?
Oxygenation, on the other hand, is well preserved, well over a half hour (assuming the jet ventilator is being used appropriately) (answer D). Jet ventilation is unnecessary if spontaneous ventilation is present
When would one use a microlaryngeal tube? How’s the volume and pressure?
The microlaryngeal tube can be used for situations where structures on or near the glottis need to be operated on, but a regular endotracheal tube would be too large and obstructive. The ETT is long and thin, with a (very) high volume, low pressure cuff.
In what way is the microlaryngeal tube similar to others?
Like regular ETT cuffs, it is assumed to protect against aspiration (answer B). Positive pressure ventilation can be delivered (answer C) with regular oxygen or air (answer D, see Resp 8). If the MITT still obstructs the view of the surgeon, either jet ventilation on the laryngoscope or transtracheal route can be used, as well as intermittent ventilation, with or without an ETT.
