A 27-year-old man is brought to the emergency department with an anterior abdominal stab injury sustained in a street fight. He has a history of alcohol and polysubstance abuse. Imaging reveals free air under the diaphragm. The patient undergoes urgent exploratory laparotomy. General anesthesia is achieved with an inhalation anesthetic agent, muscle relaxant, and opioid, and ventilation is mechanically controlled. Intraoperatively, he also receives intravenous fluids and packed red blood cell transfusion. Anesthesia is terminated after successful repair of the liver and small intestinal lacerations. Prior to the transfer to the recovery unit, the patient is breathing spontaneously. Blood pressure is 160/90 mm Hg, pulse is 130/min, and respirations are 9/min. An hour later, blood pressure is 110/60 mm Hg, pulse is 70/min, and respirations are 7/min. Arterial blood gas analysis shows pH 7.30, pCO2 50 mm Hg, and pO2 70 mm Hg. Which of the following best explains this patient's postoperative findings?
Return to consciousness after anesthesia (emergence) typically occurs within 15 minutes of extubation; at a minimum, patients should be responsive with intact protective (eg, gag) reflexes within 30-60 minutes of the last administration of an anesthetic or adjuvant agent (eg, opiate, muscle relaxant). Delayed emergence occurs when a patient fails to regain consciousness within the expected window. The etiology is typically multifactorial but generally occurs due to 1 of 3 major causes:
Drug effect: Preoperative drug ingestion (eg, opiates, benzodiazepines, illicit drugs, anticholinergic drugs, antihistamines) may potentiate anesthetic effects. Prolonged anesthesia duration or higher medication doses may also delay emergence.
Metabolic disorder: Common etiologies include hyper- or hypoglycemia, hyper- or hypothermia, hyponatremia, and liver disease.
Neurologic disorder: Intraoperative stroke, seizure (or postictal state), or elevation of intracranial pressure can cause prolonged alterations in mental status.
This patient's arterial blood gas demonstrates acute hypercarbic and hypoxic respiratory failure (low pH, elevated pCO2, low pO2) due to hypoventilation. In association with the worsening bradypnea and drop in pulse (which were likely initially elevated due to agitation postextubation), this suggests that the patient's delayed emergence is due to a prolonged medication effect, possibly potentiated by preoperative drug or alcohol ingestion in this patient with a history of polysubstance abuse. Management of acute respiratory failure includes ventilatory support (eg, bag and mask, reintubation); reversal agents (eg, naloxone) may also be indicated.
(Choice A) Acute cardiogenic pulmonary edema can occur in cardiogenic shock, which may be precipitated by surgery. However, patients with cardiogenic shock are typically elderly, have multiple cardiac risk factors, and exhibit elevated jugular venous pressure, hypotension, tachycardia, and tachypnea.
(Choice B) Malignant hyperthermia is a hypermetabolic state that occurs in response to volatile anesthetics (eg, isoflurane, halothane) or succinylcholine. Due to increased CO2 production, patients have a respiratory and metabolic acidosis; however, malignant hyperthermia causes hyperventilation rather than hypoventilation. In addition, patients typically have muscle rigidity, hyperthermia, and tachycardia.
(Choice D) Intraabdominal hemorrhage would be expected to cause hypotension, tachycardia, and abdominal distension. Hypercarbic respiratory failure would be unexpected.
(Choice E) Postextubation laryngeal edema could cause hypercarbic and hypoxic respiratory failure; however, patients would be expected to be stridorous, with tachypnea (rather than bradypnea) and tachycardia.
Educational objective:
Delayed emergence from anesthesia is defined as the failure to return to consciousness within the expected window of the last administration of an anesthetic or adjuvant agent (typically 30-60 minutes). The etiology is often multifactorial, however; the presence of respiratory failure (eg, low pH, elevated pCO2, low pO2), bradypnea, and bradycardia suggests prolonged medication effect resulting in hypoventilation.