Читать книгу Ottawa Anesthesia Primer - Patrick Sullivan - Страница 104

A previously healthy 40-yr-old male was involved in a high-speed motor vehicle accident. The paramedics have transported him urgently to the emergency department. Initial assessment reveals a pale middle-aged male in moderate distress and moaning incoherently. His BP is 90/30, HR 140 beats∙min^-1, and he has a Glasgow Coma Scale (GCS) of 12. A non-rebreathing facemask with oxygen is applied, respiration is 30 breaths∙min^-1, and pulse oximetry records 90% saturation. The trauma surgeon requests intubation and transport to the operating room (OR) for an urgent exploratory laparotomy. The patient has a clinically reassuring airway examination for direct laryngoscopy, a distended abdomen, and no evidence of head or spinal trauma. Heart sounds are normal, his trachea is midline, and air entry is present in both lung fields. Two large bore intravenous catheters are secured, a bolus of warmed crystalloid is administered, and blood is sent for laboratory investigations with a stat crossmatch for four units of packed red blood cells (PRBCs).

The specific goals for intubation include:

1 Amnesia for intubation

2 Avoiding further exacerbation of the shock state (i.e., further depression of the blood pressure or elevation of the heart rate)

3 Hemodynamic support and fluid resuscitation

4 Prevention of gastric aspiration

5 Rapid paralysis to optimize conditions for direct laryngoscopy and tracheal intubation

6 Tracheal intubation

7 Preparation of rescue airway equipment and medications prior to induction of anesthesia.

The immediate considerations for this patient include:

1 Trauma patient with both identified and unidentified injuries

2 Limited information regarding the patient’s medical history, medications, allergies, and anesthetic history

3 Limited time to assess and optimize the patient

4 Full stomach and heightened risk of aspiration

5 A shock state presumed to be secondary to hypovolemic shock

6 Urgent need for tracheal intubation

7 Urgent need for medical (fluid and blood product resuscitation) and surgical control of the bleeding

8 Limited oxygen reserve and potential for rapid desaturation with induction of anesthesia

9 Remote location with limitations in available equipment and personnel.

The identified conflicts between our goals for intubation and immediate considerations include:

1 The need for rapid sequence induction (RSI) with cricoid pressure (CP) using a fixed dose of drugs to decrease the risk of aspiration (see Chapter 9)

2 An increased risk of hemodynamic collapse if a standard RSI dose of medication is administered

3 A heightened risk of aspiration if drugs are titrated slowly

4 A heightened risk of hemodynamic collapse if drugs are not titrated slowly

5 Recognition that drugs used to provide amnesia and decrease awareness may also further depress blood pressure.

Identifying the goals, considerations, and conflicts for tracheal intubation in this patient highlights the importance of developing a patient-specific goal-oriented modification to the induction plan.

Having identified the goals, considerations, and conflicts, an anesthetic plan is developed to proceed with a RSI using CP. The mnemonic “A Basic Mad Poster” (Chapter 6) was used as a memory aid to prepare the equipment and medications for intubation. The patient is administered 100% oxygen using an AMBU® bag and mask unit; a no. 7.5 endotracheal tube with a stylet is prepared, and suction with a rigid Yankauer suction tip is checked and confirmed to be functional. The patient’s weight is estimated to be 80 kg. Medications for anesthesia induction as well as rescue medications (i.e., atropine, phenylephrine, ephedrine, midazolam, and fentanyl) are prepared. A rescue video laryngoscope is checked, functional, and available for use if difficulty with direct laryngoscopy and tracheal intubation is encountered. A pillow is placed behind the patient’s head to create mild flexion of the cervical spine. The height of the patient’s bed is adjusted such that the patient’s head is at the level of the clinician’s waist. The audible tone on the saturation monitor is enabled and continuous echocardiography (ECG) and noninvasive blood pressure (NIBP) monitoring is confirmed. The laryngoscope is checked, and an assistant instructed in the proper application of cricoid pressure is positioned to the right of the patient’s head.

A decision to avoid propofol is made due to its potential to depress blood pressure and perfusion further in the setting of hypovolemic shock. As the assistant applies cricoid pressure, intravenous ketamine 1 mg∙kg^-1 is administered and immediately followed by succinylcholine 1 mg∙kg^-1. The patient’s trachea is intubated with direct laryngoscopy, and the position of the endotracheal tube is confirmed by auscultation and end-tidal carbon dioxide (ETCO₂). The endotracheal tube position is secured and mechanical ventilation is initiated. The patient’s heat rate and blood pressure continue to be monitored, and small doses of midazolam (20 µg∙kg^-1) and fentanyl (1 µg∙kg^-1) are titrated to effect while attention is directed to further fluid resuscitation and transport the patient to the OR.

Intravenous anesthetic drugs, such as ketamine and etomidate, cause minimal cardiac depression with administration. In hypovolemic shock, these agents may be preferred over thiopentothal and propofol, both of which will accentuate myocardial depression in this setting. In this case, ketamine was chosen as the intravenous induction agent due to its tendency to cause less cardiac depression compared with an induction dose of propofol. Etomidate in a 0.3 mg∙kg^-1 dose could also have been used for anesthetic induction in this patient. If propofol is used for induction, consider reducing the dose and adding a vasoactive agent, such as phenylephrine or ephedrine, to avoid hypotension with its administration.

In the setting of more severe degrees of shock, a small dose of benzodiazepine to provide amnesia (e.g., midazolam 20-40 µg∙kg^-1) and a muscle relaxant administered in a RSI fashion with cricoid pressure may be all that is required to ensure preservation of sympathetic tone, hemodynamic stability, and optimum muscle relaxation for laryngoscopy and tracheal intubation. In the setting of circulatory collapse or a full cardiac arrest, anesthesia is a luxury that simply cannot be afforded. In this setting, direct laryngoscopy and tracheal intubation are performed without the aid of a muscle relaxant.

Following successful intubation of this patient’s trachea, the focus is changed to optimize tissue perfusion and oxygenation (see Chapter 23). The patient’s vital signs are consistent with class IV hemorrhagic shock and a blood loss equivalent to > 40% of his blood volume (see Chapter 22 hypovolemic shock). Immediate goals include blood loss replacement and surgical control of the bleeding. Immediate transfusion should be initiated using a fluid warmer for transfusion of both PRBCs and fresh frozen plasma (FFP). In additional to crystalloid and colloid administration, calcium chloride and other blood products, including cryoprecipitate and platelets, may also be required (see Chapter 21)