Surgery of the Lower Respiratory System: Lungs and Thoracic Wall

Chapter 30


Surgery of the Lower Respiratory System


Lungs and Thoracic Wall



General Principles and Techniques




Preoperative management


Animals with traumatic lesions that impair respiration (e.g., flail chest) or those with acute respiratory impairment (i.e., ruptured bulla or ruptured pulmonary abscess) often require emergency stabilization (e.g., stabilization of rib segments, thoracentesis, and oxygen therapy) before surgery. Equipment for thoracentesis and chest tube placement should be readily available, and clinicians should be familiar with these techniques (see pp. 996-997). The thorax is one of the most common regions injured following blunt trauma; thoracic injuries were identified in over 72% of patients in a recent study (Simpson et al, 2009). Concurrent abdominal and chest injuries were found in 50% of injured animals.



NOTE • Carefully auscultate the chest of all trauma patients. Most have pulmonary contusions, and finding abnormal sounds on chest auscultation typically correlates well with finding radiographic signs of thoracic trauma.


With large neoplastic lesions, positioning the animal in sternal recumbency or in lateral recumbency with the affected side down and providing oxygen (i.e., nasal insufflation or oxygen cage) often is beneficial. Blood gas analysis or evaluation with pulse oximetry is warranted preoperatively in patients undergoing thoracic surgery to detect and define the severity of respiratory impairment. Unexplained abnormalities should be investigated because ventilatory impairment caused by nonsurgically correctable disease (i.e., diffuse micrometastasis) occasionally is identified. If possible, significant anemia should be corrected before surgery (see p. 84).



Anesthesia


Respiratory patients should be managed with extreme care until intubation has been accomplished and ventilation can be assisted. Premedication with any drug that causes hypoventilation is contraindicated (see Table 31-3 on p. 994). Additionally, every attempt should be made to minimize stress to the patient prior to induction. Oxygen support, even while placing an intravenous catheter, may be necessary. Pulse oximetry with a sensor that can be secured to the tail can be especially helpful with perioperative monitoring of patients in respiratory distress. Prior to induction, the anesthesia provider should be prepared with airway devices, anesthesia machine, monitors, as well as induction and emergency drugs. Preoxygenating the patient for 3 to 5 minutes prior to induction (see p. 992) should be followed with a rapid induction and intubation. Intubation of a bronchus rather than the trachea may be disastrous in compromised animals; therefore, both sides of the chest cavity should be auscultated and the endotracheal tube palpated in the thoracic inlet to ensure proper placement. Confirmation should be made with the presence of end-tidal CO2 (EtCO2).


Animals with open chest cavities (including those with diaphragmatic hernias) require intermittent positive pressure ventilation. End-tidal CO2 is the measurement of CO2 in exhaled respiratory gases. EtCO2 is measured by capnography and serves as an estimate of arterial CO2. Thus, capnography is a noninvasive method of measuring systemic metabolism, cardiac output, pulmonary perfusion, and ventilation; its measurement may be helpful in identifying potentially life-threatening situations (e.g., hypoventilation, airway obstruction, hypotension, ventilator malfunctions, or esophageal intubation). The normal arterial CO2 in an awake and healthy animal is 35 to 45 mm Hg. If ventilation and perfusion are well matched, EtCO2 is generally 2 to 5 mm Hg less than that of the PaCO2.


If possible, positive pressure ventilation should be performed with lower tidal volumes, lower peak ventilation pressures, and higher respiratory rates. This will decrease leakage of air through damaged alveoli if pneumothorax is present. However, if the animal has a diaphragmatic hernia or pleural effusion, tidal volumes may be kept low but peak airway pressures may need to be higher to adequately ventilate the patient. If external pressures asserted on the lung tissue are completely compressing alveoli, bronchioles, and bronchi, it may take higher pressures to ventilate until the thorax is opened. When possible, however, smaller tidal volumes, higher respiratory rates, and lower peak airway pressures should be used. Dogs and cats with respiratory insufficiency should be maintained with inhalation anesthetics (i.e., isoflurane or sevoflurane) (Table 30-1). Inhalation anesthesia is advantageous because it allows rapid recovery and more precise control of anesthetic depth than does maintaining anesthesia with longer-acting intravenous anesthetics. Nitrous oxide should not be used in patients with pneumothorax or diaphragmatic hernias because it rapidly diffuses into air-filled spaces (i.e., pleural cavity or gas-filled organs) causing further lung compression or organ enlargement. Also, nitrous oxide is comparatively less soluble in plasma than are oxygen and other inhalation anesthetics; therefore, it rapidly diffuses into the alveoli when it is discontinued, resulting in diffusion hypoxia if the nitrous oxide is not turned off 5 to 10 minutes prior to extubation. Once surgery is completed, extubation should not be rushed. Make sure the patient is awake and not overly sedated, respirations are adequate, and the patient is comfortable prior to extubation.



For specific anesthetic recommendations for animals with flail chest or pectus excavatum, see pages 974 and 985, respectively.



NOTE • Do not use mask or chamber induction in animals with respiratory dysfunction. Use anesthetics that allow for rapid intubation and control of the patient’s airway.


Thoracoscopy is best done without insufflation; simply establishing a pneumothorax is sufficient for almost all cases. Should intrathoracic insufflation be required for thoracoscopy, it may have profound effects on cardiopulmonary parameters. If insufflation pressures exceed central venous pressures, venous blood flow return to the heart decreases, causing a significant drop in cardiac output and systemic blood pressure. If the heart rate also decreases, this can be an ominous sign of cardiovascular collapse. Therefore, insufflation-assisted thoracoscopy should be done with care using the lowest inspiratory pressure (IP) possible. Use of 5 cm H2O of positive end-expiratory pressure (PEEP) increases the arterial partial pressure of oxygen (PaCO2) by decreasing shunt fraction and dead space in dogs with one lung ventilation, but it does not affect cardiac output (Kudnig et al, 2006). Therefore, PEEP is recommended with one lung ventilation.


Thoracotomy procedures often cause substantial pain, and multimodal postoperative analgesic therapy is indicated (see also Chapters 12 and 31). Performing intercostal nerve blocks prior to extubation can provide significant analgesia in the immediate postoperative period (see Box 31-2 on p. 992). Injectable analgesics may also be used (i.e., hydromorphone, butorphanol, or buprenorphine; see Table 12-3 on p. 141). Although opioids are respiratory depressants, the analgesic effects of these drugs often outweigh the negative respiratory effects. If hypoventilation occurs after administration of opioids, oxygen should be given by nasal insufflation (see Chapter 4). Epidural administration of morphine is an effective analgesic in patients undergoing thoracic procedures and should be considered in any patient undergoing a thoracotomy (see Table 12-4 on p. 142). There is a delay of the onset of thoracic analgesia of approximately 6 to 8 hours. This coincides with the wearing off of the intercostal nerve blocks. When used together, nerve blocks and epidural morphine can provide substantial pain relief for the first 12 to 24 hours postoperatively. Epidural administration of morphine alone does not usually cause significant changes in cardiorespiratory measurements, but these patients should be monitored carefully for 24 hours for a delayed respiratory depression, especially when intravenous (IV) opioids are also administered.



NOTE • If a morphine epidural has been administered perioperatively, butorphanol and buprenorphine should not be administered because of their antagonistic properties.


Reexpansion pulmonary edema (RPE) may develop in animals after chronically collapsed lung lobes are reexpanded and is not associated with cardiac disease. In sheep, goats, and rats, RPE can occur after lungs have been collapsed for 3 days or more. It is possible for RPE to occur in any type of chronically collapsed lung that can be reexpanded. Therefore, lung protective ventilator strategies are recommended for any lung reexpansion surgeries (e.g., diaphragmatic hernia, pectus excavatum, pleural effusion, pneumothorax, large pulmonary neoplasia). RPE is characterized by fluid within the alveoli, interstitial edema, and thickened basement membranes. It is believed that RPE is a permeability pulmonary edema associated with the injury of pulmonary microvessels.


There are two major causes of RPE. One is the abnormality of the pulmonary microvessels caused by the chronic collapse. The microvasculature becomes thickened, less flexible, and more susceptible to injury. The second is mechanical stress caused by the abrupt reexpansion. For years, barotrauma had been discussed as the primary cause of this mechanical stress. However, more recent research into ventilation induced lung injury (VILI) and acute respiratory distress syndrome (ARDS) has revealed that there are multiple aspects to lung injury with barotrauma playing less of a role than initially believed. The mechanical stress of volutrauma (the overdistension of alveoli) may occur whenever chronically collapsed lungs are reexpanded. When a given tidal volume is delivered, it goes to the areas of the lung that are most compliant, which generally is not the area that is diseased or collapsed. If normal tidal volumes are used, these healthy and compliant regions become overly distended with subsequent shearing of alveolar walls and destruction of pulmonary microvasculature. This overdistention and initiation of an inflammatory cascade may have severe systemic consequences. Another mechanical stress, atelectrauma, occurs with repeated opening and closing of the collapsed alveoli. These unstable alveoli may undergo opening and closing with each respiratory cycle. This rapid and repetitive wall stress can also destroy pulmonary microvessels, contributing to the pulmonary edema seen with reexpansion of collapsed lungs.


To avoid RPE, there are two general concepts to consider. The first is slow recruitment of collapsed lung by using positive end expiratory pressure (PEEP). A PEEP of 5 to 10 helps to prevent recollapsing of alveoli and the associated atelectrauma. The second strategy is to be very careful not to over distend healthy lungs. This may be challenging because most veterinary anesthesia machines do not have measured tidal volume displays. Therefore, careful observation of the lungs within the surgical field is imperative. Use estimated tidal volumes of < 6 ml/kg, being careful not to over inflate normal lung tissue. Do not attempt to rapidly recruit collapsed lung because this will only damage healthy, compliant lung. To achieve adequate oxygenation, lung volumes will need to be small and respiratory rates more frequent. Do not administer “sighs,” as they will almost certainly cause overdistention. Once the chest tube is in place and the thoracic closure is being completed, do not distend the lungs to remove the air from the pleural space. Slowly correct the pneumothorax by incrementally removing small portions over several hours. The goal is not to rapidly correct the pneumothorax but to gradually do so to avoid further lung trauma. Although not easy to do, avoiding RPE is much easier than treating it. Glucocorticoids are of little value in treating RPE once it has occurred. In severe RPE cases, prolonged ventilation using low tidal volumes, higher respiratory rates, and PEEP is usually necessary. Other therapies targeting oxygen-derived free radicals may be on the horizon, but currently the best treatment of RPE is careful avoidance.


Obstruction of blood flow in the pulmonary vasculature by a thrombus or an embolus formed in the systemic venous system or right side of the heart is pulmonary thromboembolism (PTE). It may occur as a complication of a number of diseases (e.g., neoplasia, cardiac disease, sepsis, immune-mediated hemolytic anemia, hyperadrenocorticism, heparin-induced thrombocytopenia, and protein-losing nephropathy or enteropathy). It is difficult to diagnose antemortem because of the lack of specific signs. If it happens while the animal is under anesthesia, a rapid drop in EtCO2 may occur. This is followed by a significant drop in blood pressure, a rise in heart rate, and a decline in SpO2. Clinical signs associated with feline PTE include lethargy, anorexia, weight loss, and difficulty breathing. In dogs, vomiting, melena, fever, labored breathing, and lethargy have been reported. Risk factors for PTE include administration of corticosteroids, chemotherapeutic agents, or blood; indwelling catheters; and recent surgery. PTE should be suspected in animals with thoracic radiographic changes suggestive of uneven distribution of blood flow between lung lobes or patchy interstitial densities; pulmonary perfusion scintigraphy or computed tomography (CT) angiography may help confirm the diagnosis. Treatment of PTE includes anticoagulant and thrombolytic therapies plus standard hemodynamic and respiratory support (Box 30-1). Heparin acts primarily to limit the conversion of fibrinogen to fibrin by accelerating the action of antithrombin III in inhibiting activated coagulation factors (II, IX, X, XI, and XII). Unfractionated heparin (UFH) has been most commonly used because of its widespread availability and low cost. It should be dosed to prolong the activated partial thromboplastin time (aPTT) 1.5 to 2 times that of baseline. Fractionated or low-molecular-weight heparin (LMWH; enoxaparin, dalteparin) differs from UFH in that it more specifically acts on factor X and is likely more effective. It also requires different monitoring than UFH and is more expensive. Prolongation of the aPTT does not occur at therapeutic doses of LMWH, but patients may be monitored by following clinical signs and assessing for anti-Xa activity. Warfarin prevents the formation of vitamin K–dependent coagulation factors (II, VII, IX, and X). It also inhibits production of protein C. Warfarin therapy is monitored using prothrombin time (PT) and the calculated international normalization ratio (INR). The traditional end point of warfarin therapy is a PT of 1.5 to 2 times that of baseline; however, due to variations in the PT assay, PT standardization is best achieved using INR (Box 30-2). The therapeutic range of warfarin is an INR of 2.0 to 3.0. Low-dose aspirin administration to inhibit platelet activity may be considered, but care must be taken to ensure that the aspirin does not cause renal or gastrointestinal complications, especially in patients receiving steroids or other nephrotoxic drugs.



image Box 30-1   Drugs Used in Medical Management of Pulmonary Thromboembolism









*Dose to be adjusted, based on aPTT results (goal is to prolong it to 1.5 to 2 times baseline).


†These are doses currently thought to be appropriate; however, as of this writing, there has been minimal research published on the use of this product in diseased animals.


‡There is minimal experience with this drug in veterinary medicine, and serious side effects are possible. Its use is not recommended except by internists with experience and training with this drug.


§Dose to be adjusted, based on PT results (goal is to prolong it to 1.5 times baseline; OR, attain international normalized ratio [INR] of 2.5 to 3.5; see Box 30-3).



image Box 30-2   Calculation of International Normalized Ratio (INR) for Warfarin Therapy*


image




PT, Prothrombin time.


*See www.easycalculation.com/medical/inr.php.


†In humans, the normal range for INR is 0.8 to 1.2. The therapeutic range for anticoagulation is 2 to 3. Values less than 0.5 indicate high risk for clot formation; values greater than 3.5 indicate a high risk for bleeding.



Antibiotics


Animals with underlying pulmonary disease or trauma (i.e., pulmonary contusions) are at increased risk of developing pulmonary infections. These patients should be monitored carefully, and prophylactic antibiotics (e.g., cefazolin; 22 mg/kg IV at induction; repeat once or twice at 2- to 4-hour intervals) should be provided, or therapeutic antibiotics should be initiated at the earliest sign of infection (i.e., leukocytosis and/or fever). Until culture and antimicrobial susceptibility test results return, ampicillin and enrofloxacin are other rational choices for treatment of suspected infectious lower respiratory tract diseases of dogs.


Appropriate use of prophylactic antibiotics depends on the length of surgery, the type of surgery being performed, the animal’s immune status, and the underlying disease process. Debilitated animals undergoing thoracotomy for removal of large neoplastic lesions (which may contain focal areas of necrosis) are likely to benefit from prophylactic antibiotic therapy. Prophylactic antibiotics should be given intravenously at induction of anesthesia and generally discontinued within 12 to 24 hours (see Chapter 9).



Surgical Anatomy


The thoracic cavities of dogs and cats are compressed laterally; therefore, the greatest dimension is dorsoventral. The ribs, sternum, and vertebral column form the thoracic skeleton. The sternum is composed of eight unpaired bones and forms the floor of the thorax (Fig. 30-1). The first and last sternebrae are known as the manubrium and xiphoid, respectively. There are usually 13 pairs of ribs. The tenth, eleventh, and twelfth ribs do not articulate with the sternum but instead form the costal arch bilaterally. The cartilaginous portion of the thirteenth rib terminates free in the musculature. The space between the ribs, known as the intercostal space, generally is two to three times as wide as the adjacent ribs. Blood supply to the thoracic wall is provided by the intercostal arteries, which lie caudal to the adjacent rib in conjunction with a satellite vein and nerve. A typical intercostal nerve begins where the dorsal branch of the thoracic nerve divides and runs distally among the fibers of the internal intercostal muscle. In most intercostal spaces, intercostal vessels and nerves are covered medially only by the pleura.



The muscles of the thorax not only serve a structural function but also are important in respiration. The deepest muscles of the thoracic wall are the intercostal muscles. The fibers of the external intercostal muscle arise on the caudal border of each rib and run caudoventrally to the cranial border of the next rib. This muscle is important primarily in inspiration. The internal intercostal muscles, on the other hand, run from the cranial border of one rib to the caudal border of the preceding rib, primarily functioning to aid expiration. Other inspiratory muscles are the scalenus, serratus dorsalis cranialis, levatores costarum, and diaphragm. Additional expiratory muscles include the rectus abdominis, external abdominal oblique, internal abdominal oblique, transversus abdominis, serratus dorsalis caudalis, transversus costarum, and iliocostalis.


The lungs of dogs and cats have deep fissures that create distinct lobes, which allow the lungs to alter their shape in response to alterations in the shape of the thoracic cavity (i.e., that caused by diaphragmatic movement or flexion or extension of the spine). These fissures also allow individual lobes to be isolated and removed without compromising the integrity of the surrounding lobes. The left lung is divided into a cranial lobe, with a cranial and caudal part, and a caudal lobe (Fig. 30-2). The right lung is larger than the left and is divided into cranial, middle, caudal, and accessory lobes (see Fig. 30-2). The cardiac notch is a small area overlying the heart where lung tissue is not interposed between the heart and body wall. It usually is located at the ventral aspect of the fourth intercostal space and is larger on the right side.



The pulmonary arteries carry nonaerated blood from the right ventricle of the heart to the lungs, and the pulmonary veins return aerated blood from the lungs to the left atrium. The left pulmonary artery lies cranial to the left bronchus, whereas the left pulmonary veins are ventral to it. On the right side, the pulmonary artery lies dorsal and slightly caudal to the right bronchus, and the pulmonary veins lie craniodorsal and ventral to it.



Surgical Technique



Thoracotomy


Thoracotomy may be performed by incising between the ribs or by splitting the sternum. The approach used depends on the exposure needed and underlying disease process. Regardless of the type of thoracotomy performed, a large area should be prepared for aseptic surgery to allow extension of the incision if needed. Depending on which left lobe is affected, a left lateral thoracotomy at the fourth, fifth, or sixth intercostal space provides adequate exposure for lobectomy (Table 30-2). A left fourth intercostal space thoracotomy allows exposure of the right ventricular outflow tract, main pulmonary artery, and ductus arteriosus. Bilateral removal of the pericardial sac can be difficult from this approach. A right intercostal thoracotomy provides exposure of the right side of the heart (auricle, atrium, and ventricle), cranial and caudal vena cava, right lung lobes, and azygous vein. Median sternotomy affords exposure to both sides of the thoracic cavity. Bilateral, partial lobectomy is easily performed from a median sternotomy; however, complete lobectomy often is difficult. The caudal vena cava, main pulmonary artery, and both sides of the pericardial sac can be isolated and manipulated through this approach.



image TABLE 30-2


Recommended Intercostal Spaces for Thoracotomy*



























































  Left Right
Heart 4,5 4,5
PDA 4(5)  
PRAA 4  
Pulmonic valve 4  
Lungs 4-6 4-6
Cranial lobe 4,5 4,5
Middle lobe   5
Caudal lobe 5(6) 5(6)
Esophagus    
Cranial 3,4  
Caudal 7-9 7-9
Cranial vena cava (4) 4
Caudal vena cava (6-7) 6-7

PDA, Patent ductus arteriosus; PRAA, persistent right aortic arch.


*Numbers in parentheses indicate alternative surgical sites.


Modified from Orton EC: Thoracic wall. In Slatter D, editor: Textbook of small animal surgery, ed 2, Philadelphia, 1993, WB Saunders.



NOTE • Be sure to count surgical sponges at the start of the surgical procedure and before closure of the thorax. This helps to ensure that you do not leave a sponge in the thoracic cavity.



Intercostal thoracotomy


With the dog in lateral recumbency, select the site for incision. Locate the approximate intercostal space, and sharply incise the skin, subcutaneous tissue, and cutaneous trunci muscle. The incision should extend from just below the vertebral bodies to near the sternum. Deepen the incision through the latissimus dorsi muscle with scissors (Fig. 30-3, A), then palpate the first rib by placing a hand cranially under the latissimus dorsi muscle. Count back from the first rib to verify the correct intercostal space.



The ribs cranial to an intercostal incision are more easily retracted than the caudal ribs; therefore, choose the more caudal space if you must choose between two adjacent intercostal spaces. Transect the scalenus and pectoral muscles with scissors perpendicular to their fibers, then separate the muscle fibers of the serratus ventralis muscle at the selected intercostal space (Fig. 30-3, B). Near the costochondral junction, place one scissor blade under the external intercostal muscle fibers, and push the scissors dorsally in the center of the intercostal space to incise the muscle (Fig. 30-3, C). Incise the internal intercostal muscle similarly. Notify the anesthetist that you are about to enter the thoracic cavity and, after identifying the lungs and pleura, use closed scissors or a blunt object to penetrate the pleura. This allows air to enter the thorax, causing the lungs to collapse away from the body wall. Extend the incision dorsally and ventrally to achieve the desired exposure. Identify and avoid incising the internal thoracic vessels, as they course subpleurally near the sternum. Moisten laparotomy sponges and place them on the exposed edges of the chest incision. Use a Finochietto retractor to spread the ribs (Figs. 30-3, D, and 30-4). If further exposure is necessary, a rib adjacent to the incision can be removed; however, this is seldom required.



Place a chest tube through an intercostal space caudal to the incision prior to closing the thorax. Alternatively, remove residual air from the thoracic cavity using an over-the-needle catheter following rib apposition and muscular closure.


Close the thoracotomy by preplacing four to eight sutures of heavy monofilament absorbable or nonabsorbable suture (3-0 to No. 2, depending on the animal’s size) around the ribs adjacent to the incision (Fig. 30-5, A). Approximate the ribs with a rib approximator or have an assistant cross two sutures to appose the ribs (Fig. 30-5, B), then tie the remaining sutures. Tie all the sutures before you remove the rib approximator. Suture the serratus ventralis, scalenus, and pectoralis muscles in a continuous pattern with absorbable suture material. Appose the edges of the latissimus dorsi muscle similarly. Remove residual air from the thoracic cavity using the preplaced chest tube or an over-the-needle catheter (see p. 997). Close the subcutaneous tissue and skin in a routine fashion.



A muscle-sparing technique may also be performed in cats and small dogs. Here, rather than incising the latissimus dorsi muscle, the muscle is sharply separated along its ventral fascial attachments and elevated. Puppies may be more willing to ambulate shortly after thoracotomy if the latissimus dorsi muscle has not been cut; however, studies have not been done to compare lameness or other outcomes after various types of intercostal thoracotomy in dogs. Transcostal sutures have also been reported for closure of intercostal thoracotomies; small holes are drilled in the caudal rib through which the suture is passed to avoid entrapment of the intercostals nerve against the rib. This closure method appears to result in markedly less postoperative pain; however, it is time consuming and may be associated with rib fracture in smaller animals.



Median sternotomy


When performing median sternotomy, two or three sternebrae should be left intact cranially or caudally (depending on where the lesion is located) to reduce postoperative pain and prevent delayed healing caused by sternebral shifting. If exposure of the lungs or heart is necessary (i.e., in dogs with spontaneous pneumothorax or for pericardiectomy), the sternotomy should extend from the xiphoid cartilage cranially to the second or third sternebra. If exposure of the cranial mediastinum is desired, the sternotomy should extend from the manubrium caudally to the sixth or seventh sternebra.


In large dogs, sternotomies closed with wire are more stable, and healing is associated with chondral or osteochondral bridging. Single or double-twist figure-8 patterns centered between two sternebrae are associated with least displacement during biomechanical loading (Davis et al, 2006).


With the dog in dorsal recumbency, incise the skin on the midline over the sternum. Expose the sternum by a combination of sharp incision and blunt dissection of the overlying musculature. Transect the sternebrae longitudinally on the midline with a sternal saw (Fig. 30-6), bone saw (Fig. 30-7), or chisel and osteotome. A sternal saw has a guide that sits under the sternum, making it much easier to cut the sternum without damaging the heart or lungs underneath. In young animals, heavy straight scissors may be adequate; however, avoid crushing the bone. Splitting the sternebrae on the midline facilitates closure. If using a bone saw or chisel, take extra precaution to ensure that the underlying lung and heart are not damaged while completing the sternotomy. Place moistened laparotomy sponges on the incised edges of the sternebrae and retract the edges with a Finochietto rib retractor. If a chest tube is to be placed, do so before closing the sternotomy. Do not exit the tube from between the sternebrae; exit it from between the ribs or through the diaphragm. Close the sternotomy with wires (dogs larger than approximately 15 kg) or heavy suture (cats and dogs smaller than approximately 15 kg) placed around the sternebrae in a figure-8 pattern (Fig. 30-8). Suture the subcutaneous tissue in a simple continuous pattern with absorbable suture. Remove residual air from the thoracic cavity and close the skin routinely.






Thoracoscopy


Video-assisted thoracic surgery (VATS) or thoracoscopy is a minimally invasive technique for diagnostic and therapeutic procedures of the thoracic cavity. Thoracoscopy is performed in either dorsal recumbency with the camera portal placed in a paraxiphoid position or lateral recumbency with camera and instrument portals placed through intercostals spaces. To improve visualization and operative working space, one-lung ventilation or mainstem bronchial blockade can be performed. Procedures that can be performed by thoracoscopy include, but are not limited to, exploratory thoracotomy (e.g., pyothorax); biopsies of lung, mediastinum, or pleura; pericardiectomy; lung lobectomy; correction of vascular ring anomalies; thymoma removal; and thoracic duct ligation. Thoracoscopy is associated with less postoperative pain, fewer wound complications, decreased recovery time, shorter hospitalization periods, and more rapid return to function. See also Chapter 13.



Lung Biopsy



Fine-needle aspiration


This technique is best suited for nodular lesions that are close to the thoracic wall or diffuse pulmonary infiltrates. Fine-needle aspiration may be performed blindly or be guided by ultrasound or fluoroscopy. Using ultrasound or fluoroscopy to direct the aspiration substantially increases the chances of accurate needle placement in focal lesions; it can be easy to miss such lesions when determining needle placement from radiographs. Sometimes air in the lungs makes pulmonary lesions difficult to detect on ultrasound. In the case of nodules deep in the pulmonary parenchyma, one may anesthetize the patient and place it under a fluoroscopic unit so that respirations can be controlled and the needle accurately placed. Radiographs may help determine the optimal site for needle placement if ultrasound or fluoroscopy is not available. In addition, CT-guided aspirates can be performed if this modality is available. In the case of diffuse lesions, it is usually best to aspirate the larger caudal lobes to stay away from the heart and major vessels. There is always the risk of pneumothorax after such a procedure. Despite the risk being small, patients have died from complications of aspirates, and clinicians must be prepared to place a chest tube and/or do a thoracotomy to stop air leakage. After identifying the appropriate spot to puncture the thoracic wall, clip and prep the area. If the patient will remain still, no sedation or anesthetic is required; however, anesthesia is generally recommended to ensure that the animal does not move during the procedure. For superficial lesions, typically use a 25-gauge hypodermic needle; for deep lesions, a 25-gauge spinal needle with a stylet is preferred. Once the needle is believed to be in the correct spot, apply several bursts of 5 to 8 ml of negative pressure, and then withdraw the needle without maintaining the negative pressure. If blood is seen entering the hub, stop the procedure and withdraw the needle. Blood is undesirable because it dilutes the sample and can make cytologic analysis more difficult. Perform the procedure quickly so that respiratory movement does not cause pulmonary laceration. After performing the procedure, watch the patient carefully for the next 30 to 60 minutes to ensure that pneumothorax does not cause clinical compromise.



Keyhole biopsy


Identify the appropriate intercostal space, and make a 3- to 7-cm keyhole intercostal thoracotomy approach (see the previous discussion) to expose the lung. Place a small Finochietto rib retractor into the space to gain exposure to the thoracic cavity. Exteriorize the lung lobe and obtain a lung biopsy using an encircling ligature or thoracoabdominal (TA) stapler (see p. 969). Inspect the stump that remains after biopsy for evidence of hemorrhage and evaluate it for air leakage by filling the thoracic cavity with warm sterile saline solution and examining for air bubbles. Evacuate the fluid using suction. Place a chest tube if necessary, or close the chest routinely (see previous discussion) and aspirate air from the thoracic cavity with a needle or catheter (see p. 997).







Partial Lobectomy


Partial lobectomy may be performed to remove a focal lesion involving the peripheral one half to two thirds of the lung lobe or for biopsy. Partial lobectomy may be performed through a lateral fourth or fifth space intercostal thoracotomy or median sternotomy.


Identify the lung tissue to be removed, and place a pair of crushing forceps across the lobe proximal to the lesion (Fig. 30-9, A). Place a continuous, overlapping pattern of absorbable suture (2-0 to 4-0) 4 to 6 mm proximal to the forceps (Fig. 30-9, B). If necessary, place a second row of sutures in a similar manner. Excise the lung between the suture lines and clamps, leaving a 2- to 3-mm margin of tissue distal to the sutures (Fig. 30-9, C). Oversew the lung in a simple continuous pattern with absorbable suture (3-0 to 5-0; Fig. 30-9, D). Replace the lung in the thoracic cavity and fill the chest cavity with warmed sterile saline solution. Inflate the lungs and check the bronchus for air leaks. Remove the fluid before closing the thorax.


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