Anesthesia and Supplemental Oxygen

Anesthesia results in depression of breathing. Thoracic respiratory excursion is reduced. The tone and pattern of contraction of the respiratory muscles, particularly the diaphragm and the intercostal muscles, change, which contributes to many secondary cardiovascular and pulmonary effects observed after surgery. The loss of end-expiratory diaphragmatic tone causes the diaphragm to ascend into the chest by 2 cm during anesthesia with or without paralysis.¹¹ Reductions in functional residual capacity (FRC) are correlated with this change and with altered chest wall configuration and increased thoracic blood volume.^12,13 One of the most pervasive and predictable clinical effects observed in the postoperative period is alveolar collapse. Total lung capacity, FRC, and residual volume are decreased. The FRC is reduced in the supine position compared with the erect sitting position^14,15 and is further reduced with the induction of anesthesia. Anesthesia, however, fails to reduce FRC in the sitting position.

The consequences of reduced FRC with anesthesia and surgery have major implications for postoperative complications and the course of recovery. Airway closure occurs with anesthesia, and this likely contributes to intrapulmonary shunting. Compression atelectasis of the dependent (lowermost) lung fields occurs during surgery.¹⁶ In addition, compression atelectasis occurs when lung tissue and surrounding structures are being physically manipulated by the surgeon. Although reduced airway caliber in areas of low lung volume can be offset by the airway-dilating effect of many inhaled anesthetics, airway resistance is increased by obstruction of the breathing circuits, valves, and tracheal tubes. The airways may also be obstructed with foreign matter such as blood and secretions, or from bronchospasm caused by irritation. Because of the decrease in FRC, lung compliance is decreased and the work of breathing is increased. Hypoxemia secondary to transpulmonary shunting is usually maximal within 72 hours after surgery and may not be completely resolved for several days. Persistent reduction in FRC after surgery delays the restoration of the normal alveolar-arterial oxygen gradient.

Anesthesia and tissue dissection contribute to major changes in lung volume, mechanics, and gas exchange. The extent and duration of these changes increase with the magnitude of the operative procedure and degree of anesthesia required. Tissue oxygenation can be threatened during the intraoperative period, and the relationship between oxygen consumption (VO₂) and delivery (DO₂) compromised.¹⁷ Mismatch between VO₂ and DO₂ is associated with a complicated clinical course and prolonged intensive care unit stay in the absence of conventional indicators such as low ejection fraction and longer cardiovascular and pulmonary bypass time.¹⁸ Oxygen extraction increases to compensate for reduced DO₂. Early optimization of the ratio of VO₂ and DO₂ is indicated to reduce perioperative morbidity and mortality.

The fraction of inspired oxygen (FiO₂) depends on the mode of oxygen administration. Low-flow nasal oxygen reduces hypoxemia in the absence of hypercapnia and marked transpulmonary shunting in the postoperative patient. Low oxygen flows and low FiO₂ tend to be delivered via nasal cannula whereas higher flows can deliver higher FiO₂ via oxygen masks and masks with reservoir bags. FiO₂ and the body position of the patient at the time a blood sample is taken must always be considered when arterial blood gas values are interpreted. The FiO₂ is selected to provide adequate oxygenation with the lowest oxygen concentration possible.

After surgery the normal pattern of breathing is disrupted. Shallow, monotonous tidal ventilation without normal occasional, spontaneous deep breaths causes alveolar collapse within an hour.¹⁵ Unless resolved within a few hours, atelectasis becomes increasingly resistant to reinflation. This complication is exacerbated in patients receiving narcotics.

Tachypnea and tachycardia are commonly observed, with gross atelectasis secondary to hypoventilation. Breath sounds are decreased at the bases, and the coarse wheezes associated with mucus obstructing airflow can be heard on auscultation. Left lower lobe atelectasis is common after cardiac surgery.

Immediate Postoperative Period

After surgery the patient is detained in the recovery room until vital signs have stabilized, there is no apparent internal or external bleeding, and the patient is responding to his or her name. Patients recovering from minor surgery are usually transferred to a ward once discharged from the recovery room. A patient is transferred to the intensive care unit after surgery if complications arose during surgery, if the patient cannot be readily stabilized and requires close monitoring, or if the patient had more serious surgery such as cranial, cardiovascular thoracic, or emergency surgery such as that resulting from multiple trauma (see Chapter 35).

Rest during the postoperative period needs to be prescribed as carefully as treatment because rest is the time for healing, repair, and restoration. Sleep deprivation impairs recovery and healing. Sleep at night is biologically more restorative than daytime sleep. Thus daytime and nighttime cues are given to restore the patient’s circadian rhythms. Although injudicious and excessive recumbency, bed rest, and prolonged periods in any given body position are deleterious, special attention is given to maximizing the periods of high-quality rest and sleep and minimizing disruption of nighttime sleep. Appropriate rests are interspersed within each treatment according to the patient’s needs to avoid reaching suboptimal, suprathreshold physiological states. Suprathreshold states are associated with an inappropriate balance between DO₂ and VO₂ such that the patient’s condition becomes compromised (e.g., hemodynamically unstable, cardiovascular and pulmonary distress is precipitated, or both).

Pharmacological Considerations

Common pharmacological agents prescribed for patients perioperatively are described in Chapter 45. Physical therapists need a thorough knowledge of these when managing the surgical patient so management can be optimized.

Several factors are particularly important in managing surgical patients because these factors can affect the patients’ sensitivity to narcotic analgesics such as morphine.19,20 There is considerable intersubject response variability to these agents. Older patients, for example, can be expected to be more sensitive to narcotics. Diverse multisystem pathology has a marked effect on the degradation, absorption, biotransformation, and excretion of morphine. Exaggerated effects of morphine have been reported when administered in conjunction with other agents such as other narcotic analgesics, phenothiazines, tranquilizers, or sedative-hypnotics; in addition, such exaggerated effects have been reported in patients with respiratory depression, hypotension, and sedation and in patients who are unconscious. Situations in which exaggerated drug effects have been reported are commonly encountered in the intensive care setting and can result in unpredictable responses. Finally, the physical dependence and abuse potential of these agents cannot be ignored.

The physical therapist must be familiar with the patient’s medications and the indications, side effects, and contraindications of each. The physical therapist can determine to what extent oxygen transport may be compromised by medication effects and whether some recommendation must be made to minimize untoward drug effects on arousal or some other factor that negatively affects oxygen transport and gas exchange. For example, although narcotics are excellent analgesics, they have widespread systemic effects including reduced arousal, cardiovascular and pulmonary depression, gastrointestinal depression, and muscle relaxation, all of which can compromise oxygen transport. Thus, consideration must be given regarding whether other forms of analgesia including non pharmacological interventions can be used. In managing the needs of a patient experiencing postoperative pain, the following questions should be considered:

The administration of narcotics has important implications for physical therapy. These powerful analgesics are often the medications of choice for major pain relief and comfort. Their secondary effects, however, which include reduced arousal and monotonous tidal ventilation, are primary physical therapy concerns. Narcotics interfere with a patient’s ability to cooperate with treatment. If narcotics impair the patient’s ability to participate in treatment, analgesia with a less systemic effect is indicated. Patient-controlled analgesia (PCA) is an effective means of having the patient regulate the amount of analgesia he or she is receiving.²¹ Patients have been reported to administer less medication to themselves than nurses assessing their analgesia needs. Intravenous administration prolongs the peak-effect time of analgesics and therefore helps the patient tolerate longer, more intense treatments. Oversedation must be avoided if the patient is to derive maximal benefit from cardiovascular and pulmonary physical therapy treatments.

Physical therapists have available to them a range of noninvasive pain control interventions that should be considered in the acute surgical ward as well as in postsurgical follow-up in the outpatient clinic. These include relaxation strategies, deep breathing, body positioning, physical support, coordination of treatments, and electrotherapy. Transcutaneous electrical nerve stimulation (TENS), for example, can be a useful adjunct in the management of postoperative pain in some patients. Pain control with TENS may enable the patient to participate more fully in mobilization, deep breathing, and coughing. Research is needed, however, to evaluate this technique in the management of acute pain and define the prescription parameters necessary to produce an optimal therapeutic effect for a given patient. The role of nonpharmacological means of managing acute pain in place of or in conjunction with pharmacological means warrants greater exploitation clinically to produce the best analgesia with the least side effects and risks. Nonpharmacological analgesia enables patients to participate more fully in physical therapy treatments in the absence of the untoward side effects often associated with drug administration.

Prevention of Complications

Special attention in the postoperative period is given to the prevention or management of cardiovascular and pulmonary complications associated with reduced arousal, surgical pain, and restriction of lung capacity and secondary to dressings, binders, and diminished ability to cooperate, move spontaneously, and hyperventilate the lungs periodically. Patients are prone to aspiration in the immediate postoperative period, particularly while the sedation and anesthetic agents are wearing off. This risk is further increased if an artificial airway is required, or if an artificial airway is needed and mechanical ventilation is instituted. Postextubation atelectasis must be anticipated and avoided. To minimize this risk, patients are asked not to eat or drink fluids the day before surgery.

Endotracheal intubation and mechanical ventilation are indicated if blood gas values fail to improve with conservative management. See Chapter 33 for treatment priorities for a patient during mechanical ventilation and the course of weaning.

A complication of thoracic and upper abdominal surgery is irritation or compression trauma of the phrenic nerve. This complication may be more common than expected. Inhibition of the phrenic nerve impairs the contraction of the affected hemidiaphragm, causing it to ascend into the thorax and contribute to atelectasis on that side. This inhibition may last for several days.

The patient’s body position is changed frequently in the initial postoperative period. The patient is usually encouraged to change his or her body position frequently, transfer, sit in a chair, and ambulate as soon as possible after surgery. The importance of frequent postural changes and early ambulation in the initial postoperative period are stressed. Early ambulation is a priority in the management of all surgical patients unless contraindicated.

Factors Determining Surgical Response and Outcomes

A patient’s response to and outcome after surgery as well as potential complications depend on multiple factors (see Box 30-2