A 72-year-old female is admitted to the ICU following a right upper lobectomy for squamous cell carcinoma that was found incidentally on workup of a thoracic vertebral compression fracture. Her past medical history is significant for 35 pack-year smoking history. She underwent preoperative PFTs that showed no evidence of significant pulmonary disease with a normal FEV1 and DLCO. Otherwise, she has an old compression fracture at T10, osteoarthritis, and mild peripheral vascular disease. She arrived to the ICU extubated, painfree with epidural analgesia, and on 10 L oxygen delivered via facemask with an oxygen saturation of 88%. An arterial blood gas is drawn, which reveals:
Given her age, smoking history, and right upper lobectomy, you are concerned about postoperative respiratory failure.
Which of the following is the best method during operative one lung ventilation to decrease the incidence of post-op acute lung injury?
Correct Answer: D
This topic remains somewhat controversial, as there is no clear evidence that ventilation with low tidal volumes in all patients undergoing one lung ventilation is universally beneficial. However, based on patients with acute lung injury, and on animal models where low tidal volume ventilation has been shown to improve survival, it has become accepted practice to reduce tidal volumes to 4 to 6 mL/Kg of IBW and apply moderate PEEP in the 5 to 10 cm H2O range to maintain adequate oxygenation in this patient population.
It is thought that lower tidal volumes during one lung ventilation may be protective against postoperative respiratory complications due to inflammation of the ventilated lung leading to postoperative injury such as pulmonary edema. This reduction in inflammation was demonstrated in a study of patients undergoing esophagectomy with single lung ventilation. In that study, ventilation with 5 mL/Kg of IBW and application of 5 cm H2O PEEP resulted in reduced levels of the inflammatory markers IL-1B, IL-6, and IL-8, compared to patients who were ventilated at 9 mL/Kg IBW without PEEP during one lung ventilation. Any maneuver that will increase tidal volume is likely to be harmful during single lung ventilation. Excessively high inspired oxygen levels are associated with oxygen free radical injury and should be avoided if at all possible.
A recent meta-analysis demonstrated higher postoperative PaO2 /FiO2 ratios in patients who were ventilated with low tidal volumes, versus conventional (8-10 mL/kg ventilation) during one lung ventilation. This same meta-analysis also demonstrated a decreased incidence of postsurgical pulmonary infiltrates and acute lung injury in patients ventilated with a low tidal volume strategy.
A 29-year-old male with a history of two spontaneous pneumothoraces in the past year, and mild exercise-induced asthma, is admitted to the ICU for monitoring after a video assisted thoracoscopic surgery for resection of a 6 × 10 cm bleb in the right lower lobe. The procedure was uncomplicated and the patient was extubated without difficulty in the operating room before transport to the ICU.
Per the anesthesiologist’s note, to facilitate surgical exposure on the operative lung, the patient was intubated with a left-sided DLT after induction of anesthesia. Single lung ventilation (of the nonoperative lung) was then initiated following conformation of proper position of the DLT using a flexible fiberoptic bronchoscope.
Which of the following is an advantage of a DLT over a bronchial blocker (BB)?
Correct Answer: C
There are a number of indications for lung isolation. In practice, the most common indications are for surgical exposure during thoracic, mediastinal, vascular, or esophageal procedures. Lung isolation is also used to prevent contamination to the contralateral lung from bleeding, pus, or saline lavage as in the case of hemoptysis, abscess, and whole lung lavage. In addition, lung isolation can be used for differential pattern of ventilation in cases of unilateral reperfusion injury (unilateral lung transplant or pulmonary thromboendarterectomy), trauma, and BPFs.
Lung isolation can be achieved by three different techniques: DLTs, BBs, or mainstem intubation using a single lumen endotracheal tube. The most common method is with a DLT, which is a bifurcated tube with both an endotracheal and an endobroncheal lumen and is used to isolate the right or the left lung. DLTs may be inserted by direct laryngoscopy or by guiding the endobronchial lumen to the mainstem bronchus using a flexible fiberoptic bronchoscope. Auscultation alone is not reliable to confirm proper positioning and bronchoscopic verification should be used, in addition to auscultation, to confirm placement every time a DLT is placed or when the patient is repositioned. DLT cannot be used for selective lobar isolation because both tracheal and endobronchial cuffs are positioned proximal to the lobar bronchi. Thus, ventilation through either lumen will result in inflation of all the lobes in that lung (B). DLTs are not ideal for placement in a tracheal stoma owing to their size. In a tracheostomized patient who cannot be intubated orally (eg post laryngectomy), BBs may be used to achieve one lung ventilation (D).
Lung isolation with a BB is achieved by occluding a mainstem bronchus and allowing lung collapse distal to the occlusion. These devices are most commonly placed within a single lumen tube, and a fiberoptic bronchoscope is required to position the blocker in the appropriate bronchus. They can also be placed in a lobar bronchus to selectively isolate a lobe (B). Suctioning of the nonventilated lung (or lobe) is not possible when using a BB because the bronchus is completely occluded by the device (C).
Another advantage of the BB is when postoperative mechanical ventilation is being considered after prolonged thoracic or esophageal surgery. These patients often have significant airway edema at the end of the procedure. If a BB is used, there is no need to change the endotracheal tube and there is no compromise of the airway if mechanical ventilation is needed in the postoperative period (A). Prolonged use of DLT without an indication for OLV is not recommended.
A 46-year-old previously healthy male who was recently diagnosed with lymphoma is transferred to your ICU from an outside hospital in septic shock due to presumed pneumonia. On arrival he is developing worsening hypoxemic, hypercarbic respiratory failure, and will need to be intubated. A CXR is significant for bilateral, patchy opacities, and a widened superior mediastinum.
Which of the following tests would be most helpful in determining the patient’s risk for airway compromise during induction of general anesthesia (GA) and intubation?
Correct Answer: B
Given this patient’s recent diagnosis of lymphoma and widened superior mediastinum on CXR, there is concern for an anterior mediastinal mass, which may lead to airway compromise during induction of GA. During spontaneous ventilation, extrinsic intrathoracic airway compression is mitigated by bronchial smooth muscle tone and airway distension as a result of the normal transpleural pressure gradient during inspiration. These protective mechanisms are blunted or eliminated during GA, and tracheobronchial diameters are further reduced as a result of decreased lung volumes and through possible compression from the anterior mediastinal mass. In light of this, a methodical induction and intubation plan must be formulated for these patients. Ideally, in a patient such as this, available chest CT images should be reviewed before proceeding with intubation. This is done to better characterize the size and location of the mass and any airway displacement or narrowing to determine the difficulty of passing an endotracheal tube distal to the obstruction. As this patient is heading toward emergent intubation because of his concomitant respiratory failure, the decision to intubate will have to proceed without this information.
In the presence of an anterior mediastinal mass, a patient’s ability to lie flat without orthopnea or coughing has been found to be the best predictor of airway compromise during induction of anesthesia. These symptoms can be classified as mild, moderate, or severe. Patients with severe symptoms will be unwilling to lie flat, even for short periods of time, and carry the highest risk of airway compromise.
Though abnormalities in air flow patterns on pulmonary function tests do accompany severe tracheal obstruction in patients with mediastinal masses, the classical blunting of the expiratory limb does not appear to be pathognomonic for variable intrathoracic airway obstruction in the setting of anterior mediastinal mass and has not been shown to predict airway complications during induction and intubation. However, the presence of a mixed restrictive/obstructive pattern may predict postoperative pulmonary complications including atelectasis and pneumonia as it implies the compression of lung parenchyma.
If chest imaging, physical examination and or vital sign changes indicate pericardial effusion or compression of cardiac chambers or major vessels, an echocardiogram is indicated to further evaluate for the risk of hemodynamic compromise on induction of GA but will not predict the risk of airway compromise.
Lung auscultation should always be performed before intubation however; it will not provide a reliable prediction of airway compromise in this patient.
A 46-year-old female with a history of atrial fibrillation presents with a left atrial appendage clot, despite being on oral anticoagulation therapy. She was admitted to the ICU from the electrophysiology laboratory following left atrial appendage isolation with the LARIAT procedure. She received 5000 units of heparin before trans-septal puncture. Following successful left atrial appendage exclusion, she received protamine and all procedural catheters were removed. Over the course of her first hour in the ICU she has become progressively more hypotensive and tachycardic, and she remains in atrial fibrillation. On physical examination she is tachypneic with jugular venous distension and muffled heart sounds.
What is the next best step in confirming her diagnosis?
This patient has risk factors for and signs of cardiac tamponade. Noninvasive procedures involving trans-septal puncture carry the risk of bleeding into the pericardium should the proceduralist mistakenly exit and reenter the heart when traveling from the right to left atrium rather than directing their catheter through the fossa ovalis. The gold standard for identifying pericardial effusions causing tamponade is echocardiography, which allows assessment of the size and location of the effusion and also the pathognomonic signs of late diastolic right atrial collapse and early diastolic right ventricular collapse. Although pulsus paradoxus is often present in cardiac tamponade it may be absent in many instances leading to a false negative test. These conditions include: the presence of a large ASD, severe aortic regurgitation, loculated effusions, left-ventricular hypertrophy, hypovolemic shock, severe LV dysfunction, low-pressure tamponade, right ventricular hypertrophy, positive pressure ventilation, and arrhythmias such as atrial fibrillation. A cardiac MRI will also provide information regarding the size and location of effusion but could lead to an inappropriate delay in diagnosis or management in an unstable patient. Although this patient may ultimately go to the cardiac catheterization laboratory where hemodynamic parameters can be confirmed and the effusion can be drained via pericardiocentesis, an echo should first be performed to confirm the diagnosis.
A 68-year-old male with a thoracic aortic aneurysm underwent thoracic endovascular aortic stent graft repair (TEVAR). A lumbar spinal drain was placed at the start of the case for spinal cord protection and cerebral spinal fluid (CSF) pressure was maintained at less than 15 mm Hg by intermittent CSF drainage as needed throughout the case. The procedure went well and lasted approximately 6 hours. At the end of the case, the patient was extubated and was admitted to the ICU for post-op management.
The spinal drain was kept in place, and the CSF pressure was maintained in the 10 to 12 mm Hg range for the first 24 hours with intermittent CSF drainage as needed. On postoperative day #2, the patient remained neurologically intact and the drain was clamped. The following day, he was noted to have bilateral lower extremity weakness. The ICU team was called urgently to evaluate him. He was hemodynamically stable with a heart rate of 65, blood pressure of 110/55 with a MAP of 73, respiratory rate of 12 on room air with an oxygen saturation of 98%. Laboratory test results revealed a white blood cell count of 10, hemoglobin of 8, and platelets of 220. Physical examination was remarkable only for symmetric bilateral lower extremity weakness of 2/5.
Which of the following interventions would be the least helpful to restore neurologic function in the patient?
Spinal cord injury following TEVAR has been reported to occur in up to 12% of cases. This is comparable to open surgical repair; however, with endovascular procedures, there is a greater percentage of patients who present with delayed onset paraplegia. In a few randomized clinical trials and multiple retrospective studies, CSF drainage has been shown to reduce the risk of postoperative spinal cord injury.
In TEVAR procedures, spinal cord injury is believed to occur via occlusion of spinal cord perfusing intercostal arteries by the covered stent graft. Essentially the treatment goal to prevent postoperative paraplegia is to increase oxygen delivery to the partially ischemic spinal cord. Oxygen delivery is maximized by increasing the hemoglobin level in the blood as well as by improving blood flow to the cord through optimization of the spinal cord perfusion pressure (SPP). This pressure is the difference between MAP and spinal fluid pressure (SFP) and is demonstrated by the following formula:
SPP = MAP - SFP
Therefore, by both raising MAP and reducing SFP, SPP is optimized. Current consensus guidelines recommend a MAP of at least 80 mm Hg, and a CSF pressure between 10 to 12 mm Hg for at least 48 hours in the perioperative period to improve cord perfusion pressure. Over drainage of the CSF with pressures below 10 mm Hg, or removing more than 10 to 15 mL per hour may cause intracranial hypotension resulting in intracranial hemorrhage. In addition to optimizing SPP, consensus guidelines also recommend keeping hemoglobin levels at 10 or greater to increase the oxygen carrying capacity of the blood that is reaching the spinal cord, thereby improving oxygen delivery.
Excessive drainage of CSF (such as draining 30 mL/h to drive CSF pressure to less than 10 mm Hg) risks intracranial hemorrhage.
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