A man is brought into the emergency department by police. The patient was found somnolent in the park and did not respond to questioning. The patient's past medical history is unknown, and he is poorly kempt. The patient's personal belongings include prescription medications and illicit substances such as alprazolam, diazepam, marijuana, cocaine, alcohol, acetaminophen, and a baggie containing an unknown powder. His temperature is 97.0°F (36.1°C), blood pressure is 117/58 mmHg, pulse is 80/min, respirations are 9/min, and oxygen saturation is 91% on room air. Physical exam reveals pupils that do not respond to light bilaterally, and a somnolent patient who only withdraws his limbs to pain. Which of the following is the best next step in management?

Supportive therapy, thiamine, and dextrose

Two hours after undergoing elective cholecystectomy with general anesthesia, a 41-year-old woman is evaluated for decreased mental status. BMI is 36.6 kg/m2. Respirations are 18/min and blood pressure is 126/73 mm Hg. Physical examination shows the endotracheal tube in normal position. She does not respond to sternal rub and gag reflex is absent. Arterial blood gas analysis on room air shows normal PO2 and PCO2 levels. Which of the following anesthetic properties is the most likely cause of these findings?

Low brain-blood partition coefficient

High minimal alveolar concentration

A 63-year-old man undergoes workup for nocturnal dyspnea and what he describes as a "choking" sensation while sleeping. He also endorses fatigue and dyspnea on exertion. Physical exam reveals a normal S1, loud P2, and a neck circumference of 17 inches (43 cm) (normal < 14 inches (< 35 cm)). His temperature is 98.8°F (37°C), blood pressure is 128/82 mmHg, pulse is 86/min, and respirations are 19/min. He undergoes spirometry, which is unrevealing, and polysomnography, which shows 16 hypopneic and apneic events per hour. Mean pulmonary arterial pressure is 30 mmHg. Which of the following complications is this patient most at risk for?

Chronic obstructive pulmonary disease

A 67-year-old woman is brought by ambulance from home to the emergency department after she developed weakness of her left arm and left face droop. According to her husband, she has a history of COPD, hypertension, and hyperlipidemia. She takes hydrochlorothiazide, albuterol, and atorvastatin. She is not on oxygen at home. She is an active smoker and has smoked a pack a day for 20 years. Her mother died of a heart attack at age 60 and her father died of prostate cancer at age 55. By the time the ambulance arrived, she was having difficulty speaking. Once in the emergency department, she is no longer responsive. Her blood pressure is 125/85 mm Hg, the temperature is 37.2°C (99°F), the heart rate is 77/min, and her breathing is irregular, and she is taking progressively deeper inspirations interrupted with periods of apnea. Of the following, what is the next best step?

Start tissue plasminogen activator (tPA)

Obtain non-contrast enhanced CT of brain

A 19-year-old man is brought to the emergency department 35 minutes after being involved in a high-speed motor vehicle collision. On arrival, he is alert, has mild chest pain, and minimal shortness of breath. He has one episode of vomiting in the hospital. His temperature is 37.3°C (99.1°F), pulse is 108/min, respirations are 23/min, and blood pressure is 90/70 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 92%. Examination shows multiple abrasions over his trunk and right upper extremity. There are coarse breath sounds over the right lung base. Cardiac examination shows no murmurs, rubs, or gallop. Infusion of 0.9% saline is begun. He subsequently develops increasing shortness of breath. Arterial blood gas analysis on 60% oxygen shows: pH 7.36 pCO2 39 mm Hg pO2 68 mm Hg HCO3- 18 mEq/L O2 saturation 81% An x-ray of the chest shows patchy, irregular infiltrates over the right lung fields. Which of the following is the most likely diagnosis?

Acute respiratory distress syndrome

A 60-year-old man is brought to the emergency department 25 minutes after falling and hitting his left flank on a concrete block. He has severe left-sided chest pain and mild shortness of breath. He underwent a right knee replacement surgery 2 years ago. He has type 2 diabetes mellitus. He has smoked one pack of cigarettes daily for 42 years. Current medications include metformin, sitagliptin, and a multivitamin. He appears uncomfortable. His temperature is 37.5°C (99.5°F), pulse is 102/min, respirations are 17/min, and blood pressure is 132/90 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 96%. Examination shows multiple abrasions on his left flank and trunk. The upper left chest wall is tender to palpation and bony crepitus is present. There are decreased breath sounds over both lung bases. Cardiac examination shows no murmurs, rubs, or gallops. The abdomen is soft and nontender. Focused assessment with sonography for trauma is negative. An x-ray of the chest shows nondisplaced fractures of the left 4th and 5th ribs, with clear lung fields bilaterally. Which of the following is the most appropriate next step in management?

Adequate analgesia and conservative management

Admission and surveillance in the intensive care unit

Prophylactic antibiotic therapy

Continuous positive airway pressure

A 75-year-old man is brought to the emergency department because of a 5-hour history of worsening chest pain and dyspnea. Six days ago, he fell in the shower and since then has had mild pain in his left chest. He appears pale and anxious. His temperature is 36.5°C (97.7°F), pulse is 108/min, respirations are 30/min, and blood pressure is 115/58 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 88%. Examination shows decreased breath sounds and dullness to percussion over the left lung base. There is a 3-cm (1.2-in) hematoma over the left lower chest. An x-ray of the chest shows fractures of the left 8th and 9th rib, increased opacity of the left lung, and mild tracheal deviation to the right. Which of the following is the most appropriate next step in management?

Chest tube insertion in the fifth intercostal space at the midaxillary line

Admission to the ICU and observation

Needle thoracentesis in the eighth intercostal space at the posterior axillary line

Monitored anesthesia care — USMLE Lesson

👀 The Vigilant Watch

A specific anesthesia service for procedures performed with local/regional anesthesia.
Goals: Provide sedation, anxiolysis, and analgesia while maintaining cardiorespiratory function.
Patient typically maintains spontaneous ventilation and airway reflexes, responding to stimuli.
The anesthesia provider is always prepared to convert to general anesthesia (GA).

⭐ MAC is distinct from moderate sedation because an anesthesia professional is required, prepared to convert to general anesthesia or rescue the airway at any moment.

🎯 Clinical Uses - Who Gets MAC?

MAC is ideal for procedures where deep sedation isn't needed but patient comfort and safety are paramount. It bridges the gap between local/regional anesthesia and general anesthesia (GA).

Common Procedures:
- Endoscopy (e.g., colonoscopy, EGD)
- Ophthalmology (e.g., cataract surgery)
- Minor orthopedic or plastic surgery
- Interventional radiology/cardiology procedures
Patient Selection:
- Cooperative patients undergoing uncomfortable procedures.
- Patients too frail or with significant comorbidities (e.g., severe COPD, low EF) for GA.
- Procedures performed under local or regional anesthesia that may require supplemental sedation/analgesia.

⭐ A key distinction: MAC is always administered by an anesthesia professional prepared to convert to general anesthesia if the patient's condition deteriorates.

💊 Drug Class/MOA - The MAC Cocktail

A synergistic combination tailored for sedation, anxiolysis, and analgesia while maintaining spontaneous respiration.

Drug Class	Example(s)	MOA & Key Features
Benzodiazepine	Midazolam	Anxiolysis/Amnesia. ↑ frequency of GABA-A $Cl^-$ channel opening. Reversible with Flumazenil.
Opioid	Fentanyl, Remifentanil	Analgesia. Potent μ-opioid receptor agonist. Reversible with Naloxone. Risk of chest wall rigidity.
Hypnotic	Propofol, Ketamine, Dexmedetomidine	Sedation/Hypnosis. Propofol: Potentiates GABA-A; rapid on/off, hypotension. Ketamine: NMDA antagonist; dissociative, preserves respiratory drive. Dexmedetomidine: α2-agonist.

⚙️ Management - The MAC Workflow

Goal: Provide sedation, anxiolysis, and analgesia while preserving spontaneous ventilation and airway reflexes.
Titration is key: Adjust drug infusions (e.g., propofol) based on patient response and surgical stimulus.
Constant vigilance: Anesthesiologist must be prepared to convert to general anesthesia (GA) if needed.

⭐ MAC is not "light" anesthesia. It requires an anesthesia professional prepared to manage complications, including apnea, airway obstruction, and hemodynamic instability, and convert to general anesthesia if necessary.

⚠️ Complications - When Sedation Slips

Primary Risk: Unintended progression to general anesthesia.
Respiratory Cascade: Oversedation → airway obstruction (tongue prolapse), hypoventilation, apnea → hypoxia ($SpO_2$ < 90%), hypercarbia.
Hemodynamic: Hypotension, bradycardia (common with propofol, opioids).
Other Risks: Aspiration (loss of protective reflexes), patient awareness/recall (undersedation).

⭐ The most frequent serious complication of MAC is respiratory depression leading to hypoxia, requiring immediate airway intervention.

High-Yield Points - ⚡ Biggest Takeaways

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