Page 133 - JSOM Fall 2018

agent reservoirs of draw­over vaporizers and the lack of inter­ 1. Anesthetic induction—choice of IV versus volatile induc­
nal low agent alarms. tion or volatile and IV co­induction. An unfasted unstable
patient will require an IV rapid sequence intubation (RSI);
However as draw­over anesthesia is most likely to be used in however, with a pediatric fasted patient, the anesthetist
the austere environment, it is still feasible that agent and CO may decide on a volatile gaseous induction.
2
monitoring might not be present due to either lack of resources 2. Ventilation—a choice of either controlled ventilation versus
or power failure. When not available the anesthetist requires spontaneous. The surgical technique may demand muscle
a higher level of vigilance to reduce the risk of the above com­ relaxation in order to optimize surgical access, as is the case
plications. This can be achieved by monitoring the patient’s in abdominal surgery. In this situation, it will be necessary
respiration using a precordial or esophageal stethoscope to to ventilate the patient using either an SIB or a mechanical
auscultate heart and lung sounds, or through observing the ventilator.
movement of the patient chest or nonrebreather valve. 35 3. Percentage of oxygen in the carrier gas—If oxygen is
available, it should be used. However, if supplies are lim­
ited and resupply is not guaranteed, then the anesthetist
Delivering a Draw-over Anesthetic—
The Practicalities may elect to use only air for the anesthetic. In this situation,
a patient who could have been anesthetized maintaining
Equipment Check their own respirations may require assisted ventilation to
As with all anesthetic equipment, prior to use the Operator maintain adequate oxygenation.
should do a full equipment check including drugs, suction, 4. Depth of anesthesia required—this decision will be based
monitoring, oxygen supply, and the draw­over itself. To check on patient factors such as how hemodynamically stable
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a draw­over system, I start with a quick visual inspection of the the patient is, as a shocked patient will require less volatile
vaporizer, check the type of volatile anesthetic contained within, anesthetic to achieve the same depth of anesthesia. Added
and check that the correct scale is attached. I then rotate the to this, excessive anesthesia will further reduce an already
vaporizer mechanism on and off through its full range of move­ compromised patient’s cardiac output. Logistical constrains
ment to check that the output adjustment works smoothly. I may come into this decision; for example, if the stores of
finally check the circuit to ensure that I am able to ventilate the volatile are low, a decision might be made to reduce the level
patient. This is similar to the checks performed on an SIB. of volatile anesthetic given while supplementing it with IV
agents such as ketamine, opiates, benzodiazepines, or other
Draw-over Circuit Check sedatives.
1. Connect test lung to patient nonrebreather valve. 5. Ability to monitor end­tidal CO and volatile agent.
2
2. Operate the SIB and observe for flow of air through the
patient valve to the test lung. Draw-over Technique Examples
3. Empty test lung to ensure expired air exits through expira­
tory portion of patient valve out to the environment. 1. Unstable patient requiring trauma laparotomy
4. Place hand at the inlet port of the vaporizer and operate The draw­over anesthetic technique would involve intubation
the SIB ensuring, no back­flow of air passes through the via an RSI, and maintenance of anesthesia with volatile anes­
vaporizer. thetic and positive pressure ventilation. This could be achieved
5. Remove test lung and block the patient valve’s 15mm con­ using the following steps.
nector with a finger.
6. Operate SIB to ensure no leaks in any of the connectors 1. Optimize monitoring.
or tubing and the SIB’s one­way valve is working with no 2. Obtain adequate IV access and initiate blood products for
back­flow of air through the vaporizer (pressure in the SIB resuscitation if required.
should be maintained for 10 seconds while squeezing it). 3. Preoxygenate using a mask and SIB connected to bottled
7. Test for leaks in the vaporizer by blocking the vaporizer oxygen or an oxygen concentrator.
inlet, turning on the vaporizer, and squeezing the SIB. The 4. Perform an RSI using IV ketamine and rocuronium.
SIB will remain collapsed if there are no leaks. 5. Confirm endotracheal tube placement by ventilating with
the SIB.
Testing of the content of the vaporizer can be difficult. If you 6. Connect the patient expiratory valve from the SIB to the
have agent monitoring, it can identify the agent; otherwise, the outlet port of the draw­over vaporizer using corrugated
Operator is only able to check the labels on the anesthetic bot­ tubing and set the desired volatile concentration.
tles and perform a sniff test to see if they can identify the scent 7. Connect a transport ventilator to the inlet port of the va­
of the volatile. If in doubt, drain the contents of the vaporizer porizer in push­over mode.
and refill the chamber with new volatile from a labeled bottle. 8. Adjust the ventilator settings to achieve normocarbia.
9. Volatile anesthetic concentration required will depend on
the hemodynamic stability of the patient.
Anesthetic Plan
Before anesthetizing a patient, an anesthetic plan needs to be 2. Stable, fasted patient requiring elective or semielective
made depending on the patient’s condition, type of surgery, surgery
length of surgery, and medical logistics. Logistical constraints If the surgical technique does not require muscle relaxation or
may include equipment availability including vaporizer, venti­ a definitive airway (i.e., an endotracheal tube), the anesthetist
lator, oxygen, and monitoring. Consumable stores including can elect to use a supraglottic airway such as a laryngeal mask
the current holding of drugs, availability of resupply, and op­ airway (LMA) and allow the patient to breath spontaneously.
tions of locally sourced medications should also be considered. A spontaneous ventilation technique when agent monitoring is
Decisions should be made with specific consideration to: unavailable will reduce the risk of patient awareness, because

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