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Tachypnea or hypopnea after surgery is common.
Postoperative tachypnea may be secondary to hypoxia or non-hypoxic causes.
Most hypopnea is secondary to pharmacological causes.
Opioids, benzodiazepines, and neuromuscular blockers contribute to hypopnea.
Bedside capnography or arterial blood gas sampling is needed to rule out serious hypoventilation which may occur in patients receiving supplemental oxygen without overt hypoxia.
Respiratory issues are some of the most common and challenging problems encountered in a Post-Anesthesia Care Unit (PACU). Anesthesia and surgical manipulation disrupt normal pulmonary physiology and can also exacerbate underlying pulmonary pathophysiology. Changes in respiratory rate, such as tachypnea or hypopnea, can herald the onset of major physiological derangement. In the PACU, respiratory compromise may also present as cardiac or neurological dysfunction, making expeditious recognition and treatment paramount.
Respiratory function is largely controlled by subcortical structures on the unconscious level. The brainstem is responsible for basic respiratory function, with the medulla oblongata acting as the “pacemaker” for respiration and the pons housing the pneumotaxic and apneustic centers which control the depth of inspiration.[1] Higher cortical centers may adjust respiration in response to information received from peripheral chemoreceptors, peripheral stretch receptors, and central nervous system receptors. Chemoreceptors, found in the carotid and aortic bodies, trigger changes in respiration due to fluctuations in PaO2 and PaCO2. In general, derangements in respiratory rate are due to conscious effort by the patient, physiological disturbance, or pharmacologic effect.[1] This chapter will review the commonly encountered causes of tachypnea and hypopnea in the PACU.
Tachypnea
Tachypnea means “rapid breathing.” In an adult this can be defined as a respiratory rate above 20 breaths/min.[1] Young children have a much higher resting respiratory rate, especially during the first three years of life.[2] The initial evaluation of the tachypneic postoperative patient should always include an immediate assessment of all vital signs and a focused history and physical exam, with attention to surgical procedure, type of anesthetic, and anesthetic course. Causes of tachypnea can be divided into two main categories, hypoxic and non-hypoxic (see Tables 11.1 and 11.2). When evaluating a postoperative patient, it is important to make this distinction rapidly. A decreased pulse oximetry reading (less than 90%) is probably the most efficient method of determining whether or not hypoxia is the cause.
| Cause | Additional signs and symptoms | Diagnostic tests | Initial treatment |
|---|---|---|---|
| Pain | Tachycardia, hypertension, agitation, delirium, diaphoresis | Pain score assessment | Analgesics |
| Anxiety | Tachycardia, hypertension, agitation, delirium, diaphoresis | Pain score assessment | Anxiolytics (e.g. benzodiazepines) |
| Dehydration | Tachycardia, hypotension, pulse pressure variation on pulse oximeter/arterial line, decreased urinary output | Hemoglobin and hematocrit | Fluid bolus, reassess for improved hemodynamics and urine output, search for underlying cause |
| Acidosis | Confusion, lethargy, hyperventilation (compensatory in metabolic acidosis) in response to hypercarbia or hypoventilation (respiratory acidosis) | Arterial blood gas | Determine underlying cause as respiratory or metabolic in nature and treat accordingly |
| Malignant hyperthermia | Increased temperature, tachycardia, muscle rigidity | Arterial blood gas, assess for hyperkalemia and acidemia | Dantrolene |
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