Discussion
Intraoperative pneumothorax is a rare, albeit known, complication of posterior spinal surgery possibly that can result from a difficult dissection, aberrant probe or screw placement, or barotrauma. Initial management typically consists of evacuating the pneumothorax by needle aspiration, percutaneous placement of a drainage catheter, or tube thoracostomy. Prone positioning during scoliosis surgical procedures may affect access to those intervention sites.
Although certainly on the differential for any intraoperative respiratory problem, the development of a pneumothorax is primarily a clinical diagnosis that relies on a high index of suspicion. Some clinical findings suggestive of a pneumothorax include sudden increased airway pressures, unexplained hypoxia, rising end tidal carbon dioxide, and unilateral absence of breath sounds to auscultation. Under positive pressure mechanical ventilation, intrapleural pressures can rapidly increase from an unrecognized pleural defect to become a tension pneumothorax. This can be life threatening, resulting in quick deterioration including tachycardia, tachypnea, hypotension, and tracheal and cardiac deviation leading to severe hemodynamic compromise and cardiopulmonary collapse.4
Interestingly, we observed none of these clinical signs throughout the procedure until the end of the case when turning from prone back to supine position. There were no airway or pulmonary issues that occurred prior to that incident that would suggest a pneumothorax. One possible explanation is that a pleural tear occurred during hardware placement and the increased intrathoracic pressure was relieved during the open/prone portion of the case. Thus air trapping only manifested once the wound was closed and the patient returned to supine position. Additionally, the development of the pneumothorax may have progressed slowly due to the patient spontaneously breathing during wound closure with pressure support ventilation. Outside of known pleural tears, there have also been reports of spontaneous pneumothorax (without evidence of intraoperative pleural injury) in the perioperative period following posterior spinal fusion surgery, with a reported incidence 0.2 to 1.6%.5-7 Potential risk factors for the development of an intraoperative pneumothorax include blebs or bullae, or longer amounts of time in the chest with multiple passes and probing. In the absence of a known pleural injury or these risk factors, potential causes of a pneumothorax in the perioperative period are few. Re-expansion of an occult pneumothorax or damage from elevated peak inspiratory pressures are possibilities. Of note, underlying pulmonary dysfunction has not been associated with an increase in the overall risk of pulmonary complications during spinal deformity surgery.8
Our differential diagnosis for the hypoxia consisted of atelectasis, inadequate minute ventilation, pain, endotracheal tube migration, fluid overload, mucous plug, neuromuscular weakness, and pneumothorax. Although pneumothorax is not usually high on the differential for hypoxia in most circumstances in the operating room, the hypoxia that occurred in our patient was acute and severe. Fortunately, the timing of our patient’s respiratory distress opened several diagnostic and therapeutic options that would have been difficult in the prone position. We ruled out other potential causes and then quickly obtained a portable chest radiograph confirming a pneumothorax. Transthoracic ultrasound is another valuable tool used to pare down the list of diagnoses in a hypoxic patient, potentially leading to a timelier intervention.9 Unfortunately, we are unable to discern the etiology of the pneumothorax in our patient but it most likely resulted from a difficult dissection. Our surgical team never had any indication that a pleural injury occurred.
The delayed hypoxia in this patient is an unusual event related to an intraoperative pneumothorax. Having had no indication of any respiratory problems throughout the case and then to have severe and acute hypoxia on emergence is a rare complication. It is therefore imperative to recognize the clinical signs that may warrant an intervention to maintain the patient’s safety.