Monitoring

Besides the American Society of Anesthesiologists standard monitoring, invasive monitoring is necessary for abdominal major vascular injury cases: arterial line, central venous pressure, and potentially transesophageal echocardiography. Arterial line is important for hemodynamic management on induction and during maintenance of anesthesia and should be placed prior to induction of anesthesia.

Induction of Anesthesia

These patients are considered “full stomach” with high risk of aspiration. An adequate preoxygenation, rapid sequence induction and intubation with cricoid pressure, and in-line stabilization of cervical spine are recommended approaches for the endotracheal tube placement. Airway management may take place in the emergency department or the operating room (if not already performed in the prehospital setting). Capnography is the most reliable method for confirmation of endotracheal tube placement.

Etomidate and ketamine are the preferred induction agents in hypotensive patients with major abdominal vascular injury. Etomidate (0.1–0.2 mg/kg) has the advantage of inducing less hemodynamic changes in comparison to other induction agents. Ketamine (0.25–1.0 mg/kg) may cause hypertension and tachycardia from endogenous catecholamine release, which may be advantageous in patients with hemorrhagic shock. It is important to recognize that both induction agents can cause hypotension and decrease in cardiac output in trauma patients; thus, conventional dosages should be reduced. Succinylcholine (1.0–1.5 mg/kg) is a neuromuscular blocker of choice for rapid sequence induction, due to its rapid onset (less than 1 min) and short duration (5–10 min). If succinylcholine is contraindicated, rocuronium (1.0–1.2 mg/kg) is recommended neuromuscular-blocking agent for rapid sequence induction. Cricoid pressure should be applied throughout induction and attempts at intubation. However, cricoid pressure can be released to ease intubation or insertion of laryngeal mask airway if necessary. Waking up the patient is not the choice in patient with abdominal vascular injury, and trauma team should be ready to rapidly proceed with invasive airway in the case of unsuccessful intubation and “cannot intubate, cannot ventilate” scenario.

The patients with major abdominal vascular injury have high abdominal pressure from hemoperitoneum. Thus, patient’s abdomen and thorax should be “prepped and draped” before the induction of anesthesia because the latter is often associated with rapid hemodynamic decompensation in this patient group. After rapid sequence induction and intubation, a rapid midline incision is made to enter the abdomen. Intraperitoneal blood is evacuated and abdomen is rapidly packed in all four quadrants with laparotomy pads. The surgery is then temporarily suspended to allow anesthesia team to catch up with the patient’s resuscitation as needed. Once the patient is sufficiently hemodynamically stable, a systemic exploration of the entire abdomen is accomplished. Proximal and distal control should be obtained for any vascular injury.

Maintenance of Anesthesia

It is often very challenging to meet all objectives of anesthetic maintenance and to provide adequate depth of general anesthesia in a hemodynamically unstable patient such as a patient with major abdominal vascular injury. General anesthesia is usually maintained with a combination of volatile agent, benzodiazepines, and narcotics. Isoflurane, sevoflurane, and desflurane all decrease arterial blood pressure through reduction in systemic vascular resistance. Thus, in hypotensive bleeding patient, minimum alveolar concentration (MAC) of volatile agent must be decreased, and the anesthetic agent titrated to maintain minimum necessary blood pressure and adequate tissue perfusion. MAC of 0.3–0.5 is often used in addition to midazolam to prevent recall of intraoperative events. Small boluses of midazolam may be administered repeatedly throughout the surgery to assure amnesia. Fentanyl is another adjuvant anesthetic and is usually administered in increments throughout the procedure. However, fentanyl alone does not guarantee amnesia.

Aortic Cross-Clamping and Unclamping

Temporary clamping of the abdominal aorta may be required during the surgery for abdominal major vascular injuries, and adequate preparation is essential to prevent severe hemodynamic changes and decompensation. Application of aortic cross-clamp results in a sudden increase in afterload and systemic blood pressure. Increased afterload results in increased left ventricular end-systolic wall stress. These changes are accompanied with decrease in cardiac output. A sudden increase in afterload can lead to left ventricular failure, especially in patients with noncompliant left ventricle. All these changes are more profound in the case of a supraceliac cross-clamp placement. The addition of inotrope may be necessary in the case of left ventricular failure. After the removal of aortic cross-clamp, systemic vascular resistance and arterial blood pressure decrease dramatically, as a result of peripheral vasodilation. Vasodilation can become systemic as the lactic acid is washed out of the extremities into central circulation. In order to minimize hypotensive response, volume loading prior to cross-clamp release is necessary to raise filling pressures to slightly above normal. Acidosis should be corrected and calcium replaced immediately after the removal of aortic cross-clamp (Gelman 1995). The patient may require temporary pharmacologic support to achieve an acceptable blood pressure. Ephedrine, an indirect alpha- and beta-receptor-stimulating agent can be used. Other options include appropriate dosing of direct alpha- and beta-receptor agonists such as epinephrine, norepinephrine, and dopamine. Phenylephrine, a pure alpha₁ receptor agonist, can be also used to increase patient’s blood pressure. However, phenylephrine has not been shown to improve end-organ perfusion and may result in end-organ ischemia, especially bowel ischemia, in hypovolemic patients (Thiele et al. 2011). Transesophageal echocardiography can be useful in differentiating between myocardial ischemia and cardiac failure versus continuous hemorrhage and consequent hypovolemia. Myocardial ischemia or cardiac failure results in elevated filling pressures, while hemorrhage results in low filling pressures.

Damage Control Surgery (DCS)

DCS refers to a limited surgical procedure or set of procedures with very discrete, life-saving goals and the intent to defer more definitive repair until resuscitation has occurred (Sagraves et al. 2006). The basic principles of DCS include rapid surgical control of bleeding, control of sources of contamination, and deferral of definitive procedure until patient is more stable. Patients with major abdominal vascular injuries may benefit from early damage control and definitive reconstruction at a later stage after resuscitation and stabilization in the ICU. Damage control approach should be considered before the patient becomes severely hypotensive and coagulopathic. With the damage control approach, any large vessel bleeding should be surgically controlled and repaired in an expeditious fashion. Any source of contamination, such as injury of gastrointestinal tract, should be controlled as well. If possible, vascular continuity should be restored by either expeditious definitive repair or temporizing measure such as vascular shunt. The abdomen is closed temporarily with vacuum dressing techniques in order to prevent abdominal compartment syndrome. The damage control strategy has been shown to lead to better than expected survival rates for abdominal trauma.

Abdominal Compartment Syndrome (ACS)

All patients with severe abdominal trauma, especially vascular trauma, are at risk of developing ACS. Major risk factors include massive blood transfusion, prolonged hypotension, hypothermia, aortic cross-clamping, damage control procedures, and tight closure of abdominal wall. ACS is characterized by a tense abdomen, tachycardia with or without hypotension, respiratory dysfunction with high peak inspiratory pressure in mechanically ventilated patients, and oliguria. After damage control procedures, the abdominal wall should never be closed under tension because postoperative bowel edema results in ACS in most patients. When the bowel edema improves, usually within 2–3 days, the patient is returned to the operating room for definitive vascular repair and abdominal wall closure. Knowledge of ACS is important, and necessary measures for prevention of this complication should be undertaken whenever possible.