Hypoxemia in Recovery Room after Thyroidectomy Case File

Hypoxemia in Recovery Room after Thyroidectomy Case File

Lydia Conlay, MD, PhD, MBA, Julia Pollock, MD, Mary Ann Vann, MD, Sheela Pai, MD, Eugene C. Toy, MD

Case 52

You are called to the recovery room because a patient reports difficulty in breathing, and the nurse notes that her O2 saturation is 89%. She is a 55-year-old woman who has just undergone a bilateral total thyroidectomy for cancer. Her past medical history is significant for hypertension and depression, for which she takes atenolol and fluoxetine (Prozac) respectively. She is a nonsmoker and denies other medical illnesses. She has undergone previous general anesthetics without complications.

The patient’s surgery was performed under general endotracheal anesthesia with inhalational sevoflurane, fentanyl 200 μg, and cisatracurium for muscle relaxation. Tracheal intubation was uneventful, with a grade I view of the larynx. On examination, the patient is sitting upright with labored breathing and breath sounds are bilateral with inspiratory stridor.

➤ What is the first therapeutic step even prior to your evaluation?

➤ How do you assess this patient in the recovery room?

➤ What is the differential diagnosis of decreased oxygen saturation (hypoxemia) in this patient?

ANSWERS TO CASE 52:

Hypoxemia in Recovery Room after Thyroidectomy

Summary: A 55-year-old woman status post thyroidectomy is reporting difficulty breathing in the recovery room with an O2 saturation of 89%.

➤ First therapeutic step: Increase the patient’s FIO2. This can be done by replacing nasal cannulae with a “green” mask, replacing a mask with a non-rebreathing mask, or replacing a non-rebreathing mask with a source of 100% oxygen such as an Ambu bag or a Briggs apparatus.

➤ Assessment: The immediate assessment of this patient in the recovery room should include a directed physical examination including auscultation of the lungs and heart, a check for obvious airway obstruction, and assessment of her vital signs. Initial assessment should also include ensuring that the patient is receiving supplemental oxygen via face mask or nasal cannula, and that the oxygen source is turned on and if an oxygen tank is being used, that the tank is not empty.

➤ Differential diagnosis of hypoxemia: This not only includes the usual causes of hypoventilation (Table 52–1) and hypoxemia (Table 52–2) after general anesthesia but also the potential causes unique to thyroidectomy including postoperative bleeding and hematoma causing airway compression, unilateral or bilateral recurrent laryngeal nerve injury, tracheomalacia following tracheal compression by a large mass, and hypocalcemia secondary to parathyroid gland removal.

Table 52–1 CAUSES OF POSTOPERATIVE HYPOVENTILATION IN THE PACU

Central nervous system depression—drug induced (inhalation anesthetics, opioids) or CNS event such as stroke

Residual neuromuscular blocking agents

Impairment of ventilatory muscles or obstructive sleep apnea

Increased production of carbon dioxide

Pre-existing pulmonary pathology such as COPD

Table 52–2 CAUSES OF ARTERIAL HYPOXEMIA IN THE PACU

Right-to-left intrapulmonary shunt (atelectasis)

Ventilation-to-perfusion mismatching (decreased functional residual capacity)

Obesity with obstructive apnea or decreased FRC and vent-perfusion mismatching

Increased oxygen consumption (shivering or sepsis)

Pulmonary embolism

Pulmonary edema (fluid overload,postobstructive or negative pressure pulmonary edema)

Congestive heart failure

Pneumothorax

Congestive heart failure

Adult respiratory distress syndrome

Aspiration of gastric contents

Posthyperventilation hypoxia

Diffusion hypoxia

Transfusion-related lung injury

ANALYSIS

Objectives

1. Develop a framework for evaluating a hypoxic patient in the recovery room.

2. Understand the differential diagnosis of decreased oxygen saturation in the recovery room.

3. Review causes and treatment of hypoxemia after thyroidectomy.

Considerations

In this particular patient, as with any patient presenting with decreased oxygen saturation

in the PACU, immediate assessment is required. The first considerations are

• Is the patient receiving oxygen?

• Is she getting better or worse?

• Are there any easily treatable causes of the hypoventilation or hypoxemia?

There are many possible causes of hypoxemia in the recovery room (Tables 52–1 to 52–3). It is essential that the anesthesia provider has an 

Table 52–3 CAUSES OF DECREASED OXYGEN SATURATION IN PACU AFTER THRYOIDECTOMY

Unilateral recurrent laryngeal nerve injury

Bilateral recurrently laryngeal nerve injury

Tracheal compression from hematoma or tracheomalacia

Hypocalcemia secondary to removal or parathyroid glands

intimate, working knowledge of this differential, and not just those causes of hypoxia specific to the patients post thyroid surgery.

The first step in evaluating this patient is a directed physical examination and determination of whether the patient’s status is improving or deteriorating. If the patient is improving, then she may be observed at the bedside and a differential diagnosis can be established. If the patient’s condition is deteriorating, then her airway may need to be secured first and a differential diagnosis established later. Once the need for immediate airway intervention is determined, the provider can look for easily treatable causes of decreased oxygen saturation such as equipment failure, airway obstruction, hypoventilation from inadequately reversed opioids, residual anesthetic agents, or neuromuscular blocking drugs.

This patient appears to be clinically stable in the PACU. However, on physical examination an expanding hematoma is discovered near the site of the surgical dressing. It is determined that this hematoma is most likely causing tracheal compression and airway compromise. While the surgical team is called, the anesthesiologists must decide if the hematoma is expanding rapidly enough that the patient must be reintubated immediately. Ideally, she would be intubated in the operating room using either a fiberoptic (a popular choice for many anesthetics) or direct laryngoscopy with the surgeon in attendance. This situation is ideal because in the event that the trachea cannot be intubated, the surgeon could open the wound under direct vision thus reducing the compression on the tracheal and theoretically improving intubation conditions.

APPROACH TO

The Hypoxemic Patient in the PACU

DEFINITIONS

HYPOXEMIA: Decreased oxygen saturation following anesthesia has two primary causes, hypoventilation (inadequate ventilation) and hypoxemia (decreased delivery of oxygen in the presence of adequate respiratory ventilation). Atelectasis along with hypoventilation is the most common cause of arterial hypoxemia in the recovery room.

RECURRENT LARYNGEAL NERVE PARALYSIS: The most common nerve injury after thyroid surgery is unilateral damage to the recurrent laryngeal nerve, resulting in hoarseness and a vocal cord paralyzed in the intermediate position. If the tecurrent laryngeal nerve paralysis is bilateral, the vocal cords flap together during inspiration, resulting in airway obstruction.

SUPERIOR LARYNGEAL NERVE PARALYSIS: This results in hoarseness and decreased sensation above the vocal cords, making patients vulnerable to aspiration.

TRACHEOMALACIA: It is a softening of the tracheal rings that occurs from prolonged compression and pressure on the trachea from a large mass or goiter. This softening may cause the trachea to collapse, leading to airway obstruction.

NIMS TUBE—A NIMS tube is a specialized endotracheal tube that when positioned properly can monitor the EMG or electromyographic function of the recurrent laryngeal nerves. Studies are in progress to determine if this monitoring will decrease the incidence of recurrent laryngeal nerve injury during thyroid surgery.

CLINICAL APPROACH

When called to assess a patient in the postoperative care unit for decreased oxygen saturation, there is a long differential diagnosis. The most common causes are hypoventilation (Table 52–1), arterial hypoxemia (Table 52–2), or problems specific to the patient’s particular surgery (Table 52–3). On initial assessment, it is usually fairly easy to determine if the patient’s ventilatory effort is adequate. If the patient is not making good ventilatory effort, then the differential diagnosis includes central nervous system depression from narcotics, volatile agents or central neurologic event, the residual effects of neuromuscular blocking agents, and an increased production of carbon dioxide or pre-existing pulmonary disease—specifically COPD.

If the patient is making adequate ventilatory effort, then the differential diagnosis shifts to causes of arterial hypoxemia. The most common cause of arterial hypoxemia in the recovery period is right-to-left intrapulmonary shunt secondary to atelectasis. Additional causes include ventilation-perfusion mismatching secondary to decreased functional residual capacity or obesity, congestive heart failure, pulmonary edema from fluid overload or negative pressure, pulmonary embolus, aspiration pneumonitis, increased oxygen consumption due to shivering or sepsis, adult respiratory distress syndrome, or transfusion-related lung injury.

Several specific complications from thyroid surgery can lead to postoperative respiratory insufficiency. These include damage (either unilateral or bilateral) to the laryngeal nerves, tracheal compression from hematoma or from tracheomalacia, or accidental removal of the parathyroid glands. The laryngeal innervations are supplied by the two superior and two recurrent laryngeal nerves. The superior laryngeal nerves provide the motor supply to the cricothyroid muscles, and sensation above the vocal cords. The recurrent laryngeal nerves supply motor innervation to all the other muscles of the larynx, and sensation below the vocal cords. The most common nerve injury after thyroid surgery is unilateral damage to the recurrent laryngeal nerve, which can be either temporary or permanent. Unilateral damage to the recurrent laryngeal nerve results in hoarseness and a vocal cord paralyzed in the intermediate position (not completely opened or closed). Bilateral recurrent laryngeal nerve paralysis results in cords that can flap together during inspiration and cause airway obstruction. Superior laryngeal nerve paralysis results in hoarseness and a decreased sensation above the vocal cords, which renders patients vulnerable to aspiration. In addition to complications resulting from nerve damage, compression of the trachea may be caused by hematoma formation or by tracheomalacia.

Finally, an accidental or unrecognized removal of the parathyroid glands is an uncommon but recognized complication which follows thyroid surgery. Patients post removal of the parathyroid glands may develop hyperparathyroidism and hypocalcemia. Signs and symptoms can occur as early as 1 to 3 hours after surgery, but do not typically present until 24 to 72 hours postoperatively. The first symptoms of hypocalcemia may be inspiratory stridor progressing to laryngospasm. Other symptoms include circumoral paraesthesia, carpopedal spasm, tetany, a prolonged QT interval, and/or mental status changes.

Comprehension Questions

52.1. A 47-year-old woman is in the recovery room following general anesthesia for arthroscopic surgery of the knee. You are called because her oxygen saturation is 88% and her respiratory rate is 4 breaths/minute. The most likely cause of her decreased oxygen saturation is which of the following?

A. Residual inhalational anesthetics

B. Inadequate reversal of neuromuscular blocking agents

C. Narcotic overdose

D. Oxygen tank equipment malfunction

E. Equipment malfunction of the pulse oximeter

52.2. A healthy 20-year-old is in the PACU 3 hours after tonsillectomy. Immediately after extubation in the operating room, the patient developed severe laryngospasm with good respiratory effort. Now he has developed hypoxemia, fluffy infiltrates on chest x-ray, and productive cough with watery sputum. Which of the following is the most likely diagnosis?

A. Congestive heart failure

B. Atelectasis

C. Pulmonary embolism

D. Negative pressure pulmonary edema

E. Iatrogenic fluid overload

52.3. A 60-year-old patient appears weak and is struggling to breathe following emergent open cholecystectomy in the PACU. The patient’s oxygen saturation is 85%. You suspect inadequate reversal or neuromuscular blocking agents. Your first step should be which of the following?

A. Sit the head of the bed up higher.

B. Assist the patient’s ventilation with bag mask.

C. Go to get a neuromuscular stimulator to check for adequate return of neuromuscular function.

D. Administer neostigmine.

E. Administer midazolam for amnesia.

ANSWERS

52.1. C. Narcotic overdose. This patient’s extremely slow respiratory rate is indicative of narcotic overdose. Her airway can be assisted with an Ambu bag and mask or naloxone can be administered in small titrated doses up to a maximum of 1 to 4 μg/kg.

52.2. D. The most likely diagnosis in this otherwise healthy patient is negative pressure pulmonary edema. This occurs when a large negative pressure inspiratory breath is attempted against an obstructed or closed airway. Since this patient is symptomatic and hypoxemic, he will require hospital admission and at a minimum overnight observation. Patients are most symptomatic 8 to 12 hours after the negative pressure episode.

52.3. B. The most appropriate first step is to assist the patient with ventilation. Once oxygenation is assured, neuromuscular function can be assessed and reversal agents can be given if appropriate.

Clinical Pearls

➤ Hypoxemia in the post-anesthesia care unit from any cause requires immediate assessment and treatment.

➤ Extubation of the trachea following thyroid surgery should be performed under ideal conditions.

➤ Bilateral recurrent laryngeal nerve injury is a potentially devastating complication; though it is extremely rare.

➤ Laryngeal stridor progressing to spasm may be one of the first indications of hypocalcemic tetany.

References

Horn D. Intraoperative EMG Monitoring of the Recurrent Laryngeal Nerve in Langenbeck’s Archives of Surgery. Berlin: Springer; 1999. 

Stoelting RK, Miller RD. Basics of Anesthesia. 5th ed. Philadelphia, PA: Churchill Livingstone; 2007.

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