A previously healthy 34-year old 68 kg man fractured his cervical spine upon diving into a swimming pool four hours ago. He is scheduled for emergency cervical laminectomy in the prone position. He has paresthesias in both upper extremities, with progressive partial motor and sensory loss in both lower extremities. He is apprehensive and dyspenic. Blood pressure is 95/55 mmHg, pulse is 112 bpm, respirations are 32, temperature is 35.8 degrees centigrade, and hematocrit is 44.
I. Dyspnea and tachypnea
1. Why is he dyspenic?
2. Why is he tachypneic? Explain the mechanism.
3. Room air arterial blood gas shows a pH of 7.24, paCO2 of 32 mmHg, and paO2 of 56 mmHg. What is your interpretation?
The patient is acidotic, with a mild respiratory alkalosis. The paO2 is abnormally low, and the alveolar-arterial gradient should be calculated. Alveolar oxygen is barometric pressure minus water pressure, minus the alveolar CO2 times 1.25. This gives a gradient of about 100, which indicates intrinsic pulmonary parenchymal disease.
4. What is your treatment?
5. Would this explain the tachycardia? Explain.
6. How do you diagnose and treat aspiration?
1. Discuss indications for premedication.
Premedication is indicated for anxiolysis, sedation, amnesia, analgesia, to decrease gastric volume or pH, to decrease airway secretions or bronchospasm, to decrease nausea and/or vomiting, to decrease sympathetic or parasympathetic responses, as prophylaxis against allergic reactions, as continued therapy for current medical conditions, or to prevent infection.
1. Is premedication indicated? Explain.
This patient is a head trauma, unstable cervical spine, "full stomach" scheduled for emergent surgery. He has focal neurologic dysfunction and dyspnea probably secondary to aspiration. Other considerations for premedication include his ASA status of IVE, age, his "full stomach", level of responsiveness and pain, allergies, and the planned procedure.
Since this patient is of advanced age, has sustained a head injury, and is a full stomach, he is not a candidate for premedication for analgesia, amnesia, or sedation. Other factors that would negate premedication include hypovolemia, or decreased cardiopulmonary reserve. He may be a candidate for premedication to decrease and alkalinize intragastric contents. In this case, he may be given nonparticulate antacid such as sodium bicitrate, and metoclopramide.
2. Why is gastric pH and volume a concern?
Gastric volume over 25 ml and gastric pH less than 2.5 is associated with increased risk for aspiration pneumonitis, or Mendelson's syndrome. Pretreatment to decrease volume and increase pH decreases the incidence and severity of aspiration.
3. Name factors that place patients at risk for aspiration pneumonitis.
Patients with obesity, pregnancy, trauma, pain, increased intraabdominal pressure, ileus or obstruction, opiate use, diabetes mellitus, difficult airway, "full stomach", alcohol ingestion, and gastroesophageal reflux, are at increased risk of aspiration pneumonitis.
2. What are the advantages and hazards of diazepam 10 mg intramuscular?
3. Is a drying agent useful?
4. Which one will you use, and explain why.
1. Do you want an arterial catheter? Explain.
2. Describe the risks of arterial catheter placement.
3. How can you prevent complications?
4. Do you want a pulmonary artery catheter? Explain.
5. Do you want a central line catheter? Explain.
6. What is the comparative value of each of the above?
II. Establishment of an airway
1. How do you plan to secure the airway?
2. Should you anesthetize the airway? Explain.
3. You decide to anesthetize the airway. How will you do it?
4. How would you avoid coughing?
5. How will you stabilize the patient's neck during intubation?
III. Choice of anesthesia
1. What is your drug choice for maintenance of anesthesia? Explain.
2. Is nitrous oxide indicated?
3. Explain the benefits and risks of nitrous oxide.
4. Spinal cord function will be monitored using cortical somatosensory evoked potentials. Will this influence your choice of anesthetic? Explain.
IV. Air embolism
1. The end-tidal CO2 suddenly decreases from 30 to 10 mmHg, and the blood pressure drops from 100/60 to 60/30 mmHg. What is your differential diagnosis?
2. What is the mechanism for low CO2 for each of your diagnoses?
3. What is the treatment for air embolism?
I. Respiratory care
1. When would you remove the endotracheal tube?
2. How will you determine if the patient will breathe adequately?
3. What will you recommend in order to minimize postoperative atelectasis?
II. Neurological deficit
1. The patient awakens with a sensory deficit below T4. The surgeon asks if this is related to intraoperative hypotension. Your answer?
2. Would edema be a cause?
3. Are any diagnostic tests indicated?
4. Is any treatment indicated?