7: Mechanical Ventilation

Introduction

Ventilator management for most thoracic surgery patients involves two distinct phases: (1) support in the operating room while the patient is undergoing surgery and receiving general anesthesia, and (2) support in the postoperative recovery room or intensive care unit (ICU) as the patient is recovering from surgery. Issues relating to the intraoperative ventilator management of thoracic surgery patients are largely the responsibility of the anesthesiologist and are discussed in Chapter 5. Issues relating to the postoperative management of mechanical ventilation are the responsibilities of the thoracic surgeon and intensivist.

Effects of Anesthesia and Thoracic Surgery on Respiratory System Physiology

In the transition from the operating room to the recovery room or ICU it is important to appreciate that general anesthesia and thoracic surgery adversely affect nearly all aspects of respiratory physiology. These include anesthetic-related alterations in respiratory drive, reductions in lung volume due to loss of chest wall tone, changes in the ventilation perfusion relationship, and increased airway resistance in the setting of diminished lung volumes. Given the postoperative structural changes in the lung as well as its native state of disease, these alterations may have variable effect on overall function and be unpredictable in duration. They certainly must be taken into account during initial ventilatory management.

Postoperative Ventilator Strategies

The overall approach to mechanical ventilation in the postoperative thoracic surgery patient is similar to that used in the critically ill medical patient. Preexisting lung disease, intraoperative complications, and known physiologic alterations associated with a planned surgery require more innovative approaches.

There are two basic approaches to mechanical ventilation in patients who have undergone thoracic surgery. These are (1) methods used to support postoperative patients who are kept intubated after surgery for a specific indication that is expected to resolve within hours, allowing for rapid discontinuation of ventilator support; and (2) methods used to support patients who develop hypoxic or hypercarbic respiratory failure as a consequence of a primary process that will resolve over a period of days to weeks and may require more gradual weaning.

Extubation of the Stable Patient

In most patients, the physiologic alterations caused by anesthesia and thoracic surgery are well tolerated. These patients generally have minimal to mild preexisting pulmonary disease and are either extubated in the operating room or arrive in the postoperative recovery area or ICU ready for extubation with normal Pao₂ and Paco₂ blood gas values on minimal ventilator support. Successful extubation in this group is associated with: (1) intact mental status; (2) reasonable assurance that the patient will have the ability to cough and protect his or her airway; and (3) initiation of an analgesic protocol that optimizes respiratory mechanics without causing undue respiratory depression.

Although mental status is usually simple to assess, often it is not possible to ...