9.1

Anesthesia

Chapter 9

Anesthesia

Introduction

Battlefield anesthesia primarily describes a state of balanced

anesthesia using adequate amounts of anesthetic agents to

minimize cardiovascular instability, amnesia, analgesia, and a

quiescent surgical field in a technologically austere environment.

Adapting anesthetic techniques to battlefield conditions requires

flexibility and a reliance on fundamental clinical skills. While

modern monitors provide a wealth of data, the stethoscope may

be the only tool available in an austere environment. Thus, the

value of crisp heart sounds and clear breath sounds when caring

for an injured service member should not be underestimated.

In addition, close collaboration and communication with the

surgeon is essential.

Airway

Many methods for securing a compromised airway exist,

depending on the condition of the airway, the comorbid state of

the patient, and the environment in which care is being rendered.

When a definitive airway is required, it is generally best secured

with direct laryngoscopy and an endotracheal tube (ETT), firmly

secured in the trachea.

Indications for a Definitive Airway

 Apnea/airway obstruction/hypercarbia.

 Impending airway obstruction: facial fractures, retropharyngeal hematoma, and inhalation injury.

 Excessive work of breathing.

 Shock (bp < 80 mm Hg systolic).

 Glasgow Coma Scale (GCS) < 8. (See Appendix 2.)

 Persistent hypoxia (SaO2 < 90%).
9.2

Emergency War Surgery

Secondary Airway Compromise Can Result From

 Failure to recognize the need for an airway.

 Inability to establish an airway.

 Failure to recognize an incorrectly placed airway.

 Displacement of a previously established airway.

 Failure to recognize the need for ventilation.

Induction of General Anesthesia

The Anesthesia Provider Must Evaluate the Patient for

 Concurrent illness and current state of resuscitation.

 Airway — facial trauma, dentition, hyoid-to-mandibular

symphysis length, extent of mouth opening.

 Cervical spine mobility (preexistent and trauma related).

 Additional difficult airway indicators.

ο Immobilization.

ο Children.

ο Short neck/receding mandible.

ο Prominent upper incisors.

Rapid Sequence Intubation Checklist

 Equipment.

ο Laryngoscope, blades, and batteries (tested daily).

ο Suction, O2

 setup.

ο Endotracheal tubes and stylet.

ο Alternative tubes (oro, nasopharyngeal, LMA [laryngeal

mask airway]).

ο IV access items.

ο Monitors — pulse ox, ECG, BP, end-tidal CO2.

ο Positive pressure ventilation (Ambu bag or anesthesia

machine).

 Drugs.

ο Narcotics.

ο Muscle relaxants.

ο Anxiolytics and amnestics.

ο Induction agents and sedatives.

ο Inhalation agents.

 Narcotics.

ο Fentanyl, 2.0–2.5 μg/kg IV bolus, then titrate to effect.
9.3

Anesthesia

ο Morphine, 5–10 mg IV bolus to load, then 2 mg q5min to

effect.

o Dilaudid (Hydromorhone), 1–2 mg IV to load, then 0.5

mg q5min to effect.

 Muscle relaxants.

ο Depolarizing.

♦ Succinylcholine.

◊ 1.0–1.5 mg/kg.

◊ Onset 30–60 sec.

◊ Duration 5–10 min.

◊ Can cause bradycardia, fasciculations, elevated

intragastric pressure, elevated ICP, elevated intracranial pressure, potassium release (especially in

“chronic” burn or immobile patients).

◊ Potent trigger of malignant hyperthermia (MH).

Succinylcholine should be NOT be used in patients

with burns or crush injuries > 24 hours old or chronic

neuromuscular disorders due to risk for hyperkalemia

— rocuronium is the next best choice.

ο Nondepolarizing.

♦ Vecuronium: induction dose of 0.1 mg/kg with an onset

of 2–3 minutes and duration of action of 30–40 minutes.

♦ Rocuronium: induction dose of 0.6 mg/kg with an onset

of 1.5–2.5 minutes and duration of action of 35–50

minutes. At 1.2 mg/kg onset similar to succinyl-choline,

but, unfortunately, a duration of action that can exceed

60–90 minutes.

♦ Pancuronium: induction dose of 0.15 mg/kg with an

onset of 3.5–6 minutes and duration of action of 70–120

minutes.

 Anxiolytics and amnestics.

ο Versed (midazolam), 1–2 mg IV slowly (over 2 min).

ο Scopolamine, 0.4 mg IV.

 Induction agents and sedatives (Table 9-1).
9.4

Emergency War Surgery

Table 9-1. Induction Agents and Sedatives.

Agent Routine Dose* Characteristics Concerns

Ketamine 1.0–2.0 mg/kg IV Dissociative anesthetic Varying degrees

and amnestic. of purposeful

Sympathomimetic skeletal moveeffects (useful in ment despite

hypovolemia). intense

Potent bronchodilator. analgesia

and amnesia.

4.0–8.0 mg/kg Onset within 30–60 sec. Increased

IM Emergence delirium salivation,

avoided with con- consider an

comitant benzodia- antisialagogue.

zepine use.

Barbiturates 3–5 mg/kg Onset within 30–60 May cause

(eg, thiopental) seconds. profound

hypotension in

hypovolemic

shock patients.

Propofol 1.5–2.5 mg/kg Mixed in lipid, strict Contraindicated

sterility must be in acute

ensured. hypovolemic

Rapid onset and rapidly shock patients.

metabolized.

Onset within 30–60

seconds.

Etomidate 0.2–0.4 mg/kg Onset within 30–60 May cause

seconds. clonus.

Duration 3–10 min.

Minimal cardiac effects.

Minimal effects on

peripheral and

pulmonary circulation.

Maintains cerebral

perfusion.

* All induction agents can be used for induction of severely injured patients

if reduced dosages are used (eg, 1/2 of the lower recommended dose).

However, the recommended choice for hypovolemic patients would be

Ketamine > etomidate >> thiopental > propofol.
9.5

Anesthesia

Rapid Sequence Intubation (RSI) 7 steps*

1. Preoxygenate with 100% oxygen by mask.

2. Consider fentanyl—titrate to maintain adequate blood

pressure and effect (2.0–2.5 μg/kg).

3. Cricoid pressure—Sellick maneuver until endotracheal

tube (ETT) placement is confirmed and balloon is

inflated.

4. Induction agent: etomidate 0.1–0.4 mg/kg IV push.

5. Muscle relaxant: succinylcholine 1.0–1.5 mg/kg IV push.

6. Laryngoscopy and orotracheal intubation.

7. Verify tube placement.

*For children, see page 33.6.

 Endotracheal intubation.

ο Orotracheal.

♦ Direct laryngoscopy 60–90 seconds after administration

of induction agents and neuromuscular blockade.

♦ First attempt is the best chance for success, but have a

backup plan:

◊ Optimize positioning of patient and anesthesia

provider.

◊ Have adjuncts readily available (stylet, smaller

diameter tubes, alternative laryngoscope blades,

suction, laryngeal mask airway, lighted stylet).

ο Nasotracheal should generally not be performed.

ο Other considerations.

♦ Maintain cricoid pressure until balloon inflated and tube

position is confirmed.

♦ Hypertension can be managed with short-acting

medications such as beta blockers (labetalol, esmolol)

or sodium nitroprusside.

♦ May treat induction-related (transient) hypotension

initially with small dose of ephedrine (5–10mg) or

Neosynephrine (50 μg), but if hypotension persists after

induction agents are metabolized, use fluids to treat the

persistent hypovolemia. The anesthesiologist must

convey this situation to the surgeon, as the need to

control bleeding becomes urgent.
9.6

Emergency War Surgery

♦ A sensitive airway can be topically anesthetized with

lidocaine 1.5 mg/kg 1–2 minutes before laryngoscopy.

 Verify ETT placement.

ο Auscultate the lungs.

ο Measure the end-tidal CO2.

ο Ensure that the SaO2 remains high.

ο Palpate cuff of ETT in sternal notch.

ο Place the chemical CO2 sensors in the airway circuit.

Verification of tube placement is VITAL. Any difficulty

with oxygenation/ventilation following RSI should

prompt evaluation for immediate reintubation.

The Difficult Airway (see Chapter 5, Airway and Breathing)

Initially provide airway management with jaw-thrust, facemask

oxygenation, and assess the situation. Failed RSI may be due to

inadequate time for induction agents to work; inadequate time

for muscle relaxation to occur; anatomically difficult airway; or

obstruction due to secretions, blood, trauma, or foreign material.

 Resume oxygenation; consider placing a temporary oral airway.

 Reposition patient and anesthesia provider.

 Call for help.

 Consider alternatives to RSI.

ο Awake intubation.

ο Laryngeal mask airway.

ο Regional anesthesia or local anesthesia.

ο Surgical airway.

Maintenance of General Anesthesia

General Anesthesia Is Maintained After Intubation With

 Oxygen. Titrate to maintain SaO2 > 92%.

 Ventilation.

ο Tidal volume (TV) 10–15 cc/kg.

ο Respiratory rate (RR) 6–10/min.

ο PEEP (positive end-expiratory pressure) if desired at 5 cm

H2O, titrate as necessary.

 Minimal alveolar concentration (MAC).

ο 0.3–0.5 MAC: awareness abolished although 50% of

patients respond to verbal commands.
9.7

Anesthesia

ο 1 MAC: 50% of patients do not move to surgical stimulus.

ο 1.2 MAC: 95% of patients do not move to surgical stimulus.

ο Common inhalation agent MACs:

♦ Halothane: 0.75%.

♦ Sevoflurane: 1.8%.

♦ Isoflurane: 1.17%.

♦ Enflurane: 1.63%.

♦ Nitrous Oxide (N2

O) = 104%.

♦ Additive effects (eg, 60% N2O mixed with 0.8%

sevoflurane yields 1 MAC).

 Total intravenous anesthesia (TIVA).

ο Mix midazolam 5 mg, vecuronium 10 mg, ketamine 200

mg in 50 cc normal saline (NS) and infuse at 0.5 cc/kg/h

(stop 10–15 minutes before end of surgery).

ο Mix 50–100 μg of ketamine with 500 mg of propofol (50 cc

of 10% propofol) and administer at 50–100 μg/kg/min (21–

42 mL/h for a 70 kg patient).

 Balanced anesthesia (titration of drugs and gases) combine:

ο 0.4 MAC.

ο Versed 1–2 mg/h.

ο Ketamine 2–4 mg/kg/h.

Conclusion of General Anesthesia

 If the patient is to remain intubated, anesthetics may be terminated but sedatives and muscle relaxants are maintained.

 If the patient is to be extubated, ventilation is decreased to

allow the patient to spontaneously breathe.

ο Anesthetic agents are stopped 5 minutes before conclusion

of surgery.

ο Glycopyrrolate (Robinul) (0.01–0.02 mg/kg IV over 3–5

minutes) to decrease parasympathetic stimulation and

secretions. This can be administered at the same time or

before neostigmine.

ο Muscle relaxation reversal with neostigmine (0.04–0.08

mg/kg IV over 3–5 minutes, can be mixed in same syringe

as glycopyrrolate).

 Extubation criteria include reversal of muscle relaxation,

spontaneous ventilation, response to commands, eye
9.8

Emergency War Surgery

opening, and head lifting for 5 seconds. When in doubt, keep

the patient intubated.

 Amnestic therapy with midazolam and analgesic therapy

with a narcotic is appropriate in small amounts so as not to

eliminate the spontaneous respiratory drive.

Regional Anesthesia

Regional anesthesia (RA) is a “field friendly” anesthetic requiring

minimal logistical support while providing quality anesthesia

and analgesia on the battlefield. Advantages of RA on the

modern battlefield are listed below.

 Excellent operating conditions.

 Profound perioperative analgesia.

 Stable hemodynamics.

 Limb specific anesthesia.

 Reduced need for other anesthetics.

 Improved postoperative alertness.

 Minimal side effects.

 Rapid recovery from anesthesia.

 Simple, easily transported equipment needed.

Recent conflicts have revealed that the majority of casualties will

have superficial wounds or wounds of the extremities. RA is well

suited for the management of these injuries either as an adjunct to

general anesthesia or as the primary anesthetic. The use of basic

RA blocks is encouraged when time and resources are available.

 Superficial cervical plexus block.

 Axillary brachial plexus block.

 IV regional anesthesia.

 Wrist block.

 Digital nerve block.

 Intercostobrachial nerve block.

 Saphenous nerve block.

 Ankle block.

 Spinal anesthesia.

 Lumbar epidural anesthesia.

 Combined spinal-epidural anesthesia.

 Femoral nerve block.
9.9

Anesthesia

Prior training in basic block techniques is implied, and use of a

nerve stimulator, when appropriate, is encouraged to enhance

block success. More advanced blocks and continuous peripheral

nerve blocks are typically not available until the patient arrives

at a combat support hospital (CSH) or higher level health care

facility where personnel trained in these techniques are

available. A long-acting local anesthetic such as 0.5% ropivacaine

is used for most single-injection peripheral nerve blocks.

Peripheral nerve blocks can often be used to treat pain (without

the respiratory depression of narcotics) while patients are

waiting for surgery.

 Neuraxial anesthesia.

ο Subarachnoid block (SAB).

ο Epidural block.

When the patient’s physical condition allows the use of spinal

or epidural anesthesia those techniques are encouraged. The

sympathectomy that results is often poorly tolerated in a trauma

patient and this must be factored into any decision to use those

techniques. Peripheral nerve blocks do not have this limitation.

 Local anesthesia.

When local anesthesia would suffice, such as in certain wound

debridements and wound closures, it should be the technique

of choice.

Field Anesthesia Equipment

There are two anesthesia apparatuses currently fielded in the

forward surgical environment: (1) the draw-over vaporizer and

(2) a conventional portable ventilator machine. A schematic of

the draw-over system is shown in Figure 9-1.

 Draw-over vaporizer.

ο Currently fielded model: Ohmeda Portable Anesthesia

Complete (PAC).

ο Demand type system (unlike the plenum systems in

hospital-based ORs).

♦ When the patient does not initiate a breath or the selfinflating bag is not squeezed, there is no flow of gas.

No demand equals no flow.

ο Temperature-compensated flow-over in-line vaporizer.
9.10

Emergency War Surgery

ο Optimal oxygen conservation requires a larger reservoir

(oxygen economizer tube [OET]) than is described in the

operator’s manual — a 3.5 ft OET optimizes FIO2.

ο May be used with spontaneous or controlled ventilations.

ο Bolted-on performance chart outlines dial positions for

some commonly used anesthetics (eg, halothane, isoflurane, enflurane, and ether). Ether is highly flammable;

use extreme care.

Ohmeda UPAC Draw-Over Apparatus in Combination With

the Impact Uni-Vent Eagle 754Portable Ventilator:

 Currently, there is no mechanical ventilator specifically

designed for use with the UPAC draw-over apparatus, but

use with various portable ventilators has been studied in both

the draw-over and push-over configuration.

ο Adding the ventilator frees the anesthesia provider’s hands

while providing more uniform ventilation and more

consistent concentrations of the inhalational anesthetic

agent.

Fig. 9-1. Draw-over apparatus in combination with the ventilator.

150
9.11

Anesthesia

ο The draw-over configuration places the ventilator distal

to the vaporizer, entraining ambient air and vapor across

the vaporizer in the same manner as the spontaneously

breathing patient. Do not attach a compressed source of

air to the Impact Uni-Vent Eagle 754 in this configuration

because the Uni-Vent Eagle 754 will preferentially deliver

the compressed gases and will not entrain air/anesthetic

gases from the UPAC draw-over.

ο The push-over configuration places the ventilator proximal

to the vaporizer, effectively pushing entrained ambient air

across the vaporizer and then to the patient.

 The Impact Uni-Vent Eagle 754 portable ventilator (Figure 9-1)

is not part of the UPAC apparatus but is standard equipment

for the US military. It has been used in combination with the

Ohmeda UPAC Draw-Over Apparatus.

ο The air-entrainment (side intake) port is used to create the

draw-over/ventilator combination.

♦ The side intake port of the ventilator contains a

nonreturn valve preventing back pressure on the

vaporizer which could result in erratic and inconsistent

anesthetic agent concentrations.

ο The patient air-outlet port on the ventilator also contains

a nonreturn valve, preventing back flow into the ventilator

from the patient side.

ο Scavenging of waste gases can be accomplished by

attaching corrugated anesthesia tubing to either the outlet

port of the Ambu-E valve (induction circuit) or the

exhalation port of the ventilator tubing (ventilator circuit)

venting to the outside atmosphere.

ο The following items are added to the circuit to improve this

UPAC/Impact Uni-Vent Eagle 754 ventilator combination:

♦ Small and large circuit adapters to aid in attachment of

various pieces.

♦ PALL Heat and Moisture Exchange Filter to conserve

heat and limit patient contact with the circuit.

♦ Accordion circuit extender to move the weight of the

circuit away from the patient connection.

♦ O2

 extension tubing to attach supplemental O2.
9.12

Emergency War Surgery

ο Two separate circuits should be constructed for use with

the UPACTM/Uni-Vent Eagle 754 combination: one for

induction and spontaneous ventilation and the second for

controlled ventilation using the portable ventilator.

♦ This process can be complicated because switching

circuit components requires several disconnections and

reconnections, creating the potential for error. (Practice.)

 Conventional plenum anesthesia machine.

ο Currently fielded models: Drager Narkomed and Magellan

2000.

ο Compact version of standard OR machines, with comparable capabilities.