Cattle frequently develop pathological changes in the thoracic cavity, and presumptive diagnosis of these abnormalities is often made on the basis of clinical signs. Treatment of affected cattle generally resolves the clinical signs, and the animals return to production (ie, milk production or growth), albeit that production may be less efficient than it was before those animals became sick. For cattle with refractory disease, especially those of high genetic value, ancillary diagnostic tools are necessary to obtain a definitive diagnosis.
For cattle with signs of respiratory tract disease that are examined at veterinary referral centers, thoracic radiography is routinely used to evaluate the type (eg, interstitial vs alveolar) and extent of pneumonia and aids in the localization of pulmonary abscesses or emphysematous bulla and identification of other pathological changes such as pleural effusion and pneumothorax. Ultrasonography is also used to evaluate the thoracic cavity of cattle and is useful for the diagnosis of superficial pulmonary abscesses, pulmonary consolidation, pleural effusion, and pneumothorax and evaluation of the heart and pericardium.1,2 In adult cattle, thoracic ultrasonography is being conducted with increasing frequency because it can be performed in a field situation, whereas thoracic radiography typically can only be performed at referral centers that have the capability to effectively radiograph the thorax of such a large animal. A disadvantage of thoracic ultrasonography is that only the most superficial aspects of the thoracic cavity can be evaluated.
Definitive diagnosis of thoracic abnormalities in cattle will generally be made on the basis of radiographic or ultrasonographic imaging. However, abnormalities of the mediastinum and other lesions can be difficult to identify with 2-D radiography or ultrasonography, and visual examination of the pleural cavity by means of thoracoscopy could be beneficial. Thoracoscopy is a minimally invasive surgical technique that has been described in horses.3 It can be safely performed on standing horses, and numerous cardiovascular and pulmonary structures are readily visible through a dorsal approach.4 In horses, thoracoscopy is used as a diagnostic tool3 and to obtain biopsy specimens5 and treat several abnormalities of the pleural cavity.5,6 To our knowledge, descriptions of thoracoscopy in cattle are lacking except for a case report7 of a cow with pericardial lymphoma in which pericardiotomy was performed by thoracoscopy.
The objectives of the study reported here were to determine and describe the optimal thoracoscopic approach to the pleural cavity of adult cattle, describe the structures readily visible by thoracoscopy, and evaluate the short-term (ie, ≤ 24 hours) effects of the procedure on the cardiovascular and pulmonary function of healthy cattle. Our hypothesis was that thoracoscopy could be safely performed with minimal effects on cardiovascular and pulmonary function of healthy cows restrained in a standing position.
Materials and Methods
Animals—Six healthy adult (≥ 5 years old) Holstein cows that weighed between 500 and 700 kg were used for the study. Each cow was determined to be healthy on the basis of results of a physical examination performed the day before the initial thoracoscopic examination was performed. Cows with clinical signs associated with primary or secondary cardiovascular or pulmonary disease were excluded from the study. All cows were owned by the University of Montreal, and study procedures were approved by the Committee for the Ethical Use of Animals (Comité d'éthique de l'utilisation des animaux) of the University of Montreal.
Study design—For each cow, thoracoscopy was performed twice: once in the left hemithorax and once in the right hemithorax, with a 24-hour interval between thorascopic examinations. The order in which the hemithoraxes were examined was determined in a random manner.
Preparation of cows for thoracoscopy—Food but not water was withheld from each cow for 24 hours immediately prior to the initial thoracoscopic examination. In preparation for the procedure, each cow was restrained in standing position in a chute. A 14-gauge, 5.5-inch catheter was aseptically placed in a jugular vein, and an 18-gauge, 1.5-inch catheter was aseptically placed in an auricular artery. Hair was clipped from the thorax extending caudally from the caudal border of the scapula to the 13th rib and ventrally from the dorsal midline to the level of the elbow joint. Each cow was administered ceftiofur sodiuma (1 mg/kg, IV), flunixin meglumineb (1 mg/kg, IV), and acepromazinec (0.05 mg/kg, IM) and left undisturbed for 30 minutes for the sedative to take effect.
Ultrasonographyd was performed to outline the thoracic cavity and determine the location for thoracoscopic portal placement. A 7.5-MHz linear probe was used to scan ICSs 6 through 12. The junction between the visceral pleura sliding on the parietal pleura and the abdominal cavity was identified as the most ventral location considered safe for placement of a portal.
Once the location for the dorsal-most thoracoscopic portal was determined, that area of the thoracic wall was cleaned for locoregional anesthesia. In the ICS for the proposed portal and in the ICSs just cranial and caudal to that space, an 18-gauge, 3.5-inch spinal needle was used to infuse 15 mL of a 2% lidocaine solution around the area of the neurovascular bundle in the manner described.8 At the area proposed for the portal, an 18-gauge, 1.5-inch needle was used to infuse 8 mL of a 2% lidocaine solution in the SC tissue and intercostal muscle layers.
Thoracoscopy—The anesthetized area was aseptically prepared and thoracoscopy was performed as described.9,10 Briefly, a No. 21 scalpel blade was used to make a 10-mm skin incision in the designated ICS at the proposed portal location. The SC tissue and a portion of the underlying muscle layers were incised. A 3-inch-long stainless steel teat cannula with a blunt end was inserted into the incision at the cranial aspect of the caudal rib to avoid trauma to the neurovascular bundle. The cannula was inserted until it entered the pleural cavity as determined by the whistling sound of air passing through the cannula into the pleural cavity. An infusion line was immediately attached to the cannula to measure the pleural cavity pressure, and then a pneumothorax was created by the infusion of CO2 at a rate of 5 L/min. When the pleural pressure reached 0 mm Hg, CO2 infusion was discontinued and the teat cannula was replaced with a 150-mm-long, 10-mm-diameter pyramidal trocar-cannula unit.e Through this trocar-cannula unit, a 30° rigid laparoscopef (diameter, 10 mm; length, 57 cm) was introduced into the pleural cavity. The laparoscope was connected to a video camera,g 300-W xenon light source,h and recording unit.i The location of the laparoscope was evaluated, and CO2 insufflation was resumed at a rate of 1 L/min to achieve a maximum pleural pressure of 3 mm Hg.
Thoracoscopic examination began dorsally until the lung fully collapsed. All visible structures were identified and recorded. Fifteen minutes after initiation of the examination, a second thoracoscopic portal was created cranial and ventral to the first portal for further evaluation of 9 of 12 hemithoraxes. The location of the second portal was determined by thoracoscopic guidance. The area was aseptically prepared and anesthetized, and a 150-mm-long, 10-mm-diameter pyramidal trocar-cannula unite was used to create the second portal in the same manner as described for the first portal. The laparoscope was removed from the first portal and passed through the second portal, and the evaluation continued for another 15 minutes. Just prior to the end of several examinations, a laparoscopic grabber forcepsj (diameter, 10 mm; length, 30 cm) was introduced through each portal (dorsal and ventral) to evaluate the potential for moving or accessing various structures.
At the end of the procedure, the laparoscope was removed from the ventral portal, which was closed with a cruciate skin suture of polyamide (USP 2). The laparoscope was replaced through the dorsal portal, and suction was applied at a rate of 80 to 120 mm Hg to resolve the pneumothorax. The laparoscope was removed from the portal just before the lung came into contact with the scope, and the dorsal portal was closed in the same manner as the ventral portal. Each cow was returned to a separate stall and fed within 15 minutes after the procedure. Cows were allowed access to feed for 12 hours before it was again withdrawn for the 12 hours preceding examination of the contralateral hemithorax. Thoracoscopic examination of the contralateral hemithorax was performed in the same manner as the initial examination.
Monitoring of cardiovascular and pulmonary function—Heart rate, RR, capillary refill time, and mucous membrane color were recorded every 15 minutes after sedation until 15 minutes after the end of the thoracoscopy. During thoracoscopy, the level of discomfort for each cow was monitored objectively by HR and subjectively by assessment of behavior. For each cow following each thoracoscopic examination, a physical examination was performed every 6 hours for 24 hours and then once daily until the cow was returned to the university farm 2 days after the second thoracoscopic examination.
For each cow, a 1-mL arterial blood sample was obtained through the catheter in the auricular artery just prior to and 30 minutes after sedation, 15 minutes after initiation of thoracoscopy, and 15 minutes and 24 hours after the completion of thoracoscopy. Each blood sample was immediately analyzedk for pH, bicarbonate concentration, total CO2 concentration, Paco2, Pao2, and Sao2. If Sao2 was < 95% at any time, oxygen was supplemented through an intranasal cannula at a rate of 10 L/min.
Thoracic ultrasonography was performed immediately and at 24 hours and 1 week after each thoracoscopic examination to evaluate the extent of residual pneumothorax. Pneumothorax was diagnosed when the visceral pleura could not be observed sliding on the parietal pleura.
Statistical analysis—Outcomes of interest were HR, RR, Paco2, Pao2, and Sao2. For each respective outcome, a nonparametric Friedman test was used to compare measurements obtained prior to sedation, after sedation, and during and after the 2 thoracoscopic examinations. When results of the Friedman test suggested that measures differed significantly (ie, P < 0.05) among the times assessed, comparisons between the various times were performed by means of a Wilcoxon test with a Bonferroni correction for multiple comparisons (ie, significance level set at P < 0.008). All analyses were performed with a computer software program.l
Results
Cows—Thoracoscopy was well tolerated by healthy adult cows. All of the cows remained standing throughout the procedure, and none developed respiratory distress.
Thoracoscopic technique—The left hemithorax was examined first in 3 cows, and the right hemithorax was examined first in the 3 remaining cows. For all cows, placement of the teat cannula into the pleural cavity was easily determined by the whistling sound of air passing through the cannula into the pleural cavity immediately upon the cannula breaching the parietal pleura and the loss of negative pressure within the cavity. During each of 3 thoracoscopic examinations, a small blood clot was found within the pleural cavity, which was believed to be a consequence of hemorrhage from the parietal pleura rather than from the lungs.
The dorsal portal for thoracoscopic examination of the left hemithorax was located in the 9th ICS for 4 cows and the 10th ICS for 2 cows. This portal was located approximately 15 cm ventral to the transverse processes of the thoracic vertebrae. The structures visible through the dorsal portal did not vary regardless of whether it was located in the 9th or 10th ICS. However, placement of a portal in the 10th ICS made manipulation of the laparoscope in the ventral and caudal directions more difficult, compared with that for a portal located in the 9th ICS, owing to its closer proximity to the diaphragm. For the first 2 cows examined, only a dorsal portal was created for thoracoscopic examination of the left hemithorax, whereas for the remaining 4 cows, a ventral portal was created for additional examination. This ventral portal was located in the seventh ICS for 2 cows and in the eigth ICS in 2 cows and was 15 to 20 cm ventral to the dorsal portal (ie, approx 30 cm ventral to the transverse processes of the thoracic vertebrae). Manipulation of the laparoscope through the ventral portal was more difficult than it was through the dorsal portal. Signs of pain were elicited in all 4 cows when the laparoscope was moved cranially and caudally via the ventral portal as evidenced by the cows becoming agitated and shifting their weight. The ventral portal allowed observation of structures in the cranioventral aspect of the left hemithorax, and those structures could be better observed when the portal was located in the seventh ICS than when it was located in the eigth ICS.
The dorsal portal for thoracoscopic examination of the right hemithorax was located in the 9th ICS for 4 cows and in the 10th ICS for 2 cows. Similar to examination of the left hemithorax, the dorsal portal was located approximately 15 cm ventral to the transverse processes of the thoracic vertebrae, and portals located in the 10th ICS did not provide any detectable advantages over those located in the 9th ICS. A ventral portal was created in only 5 of the 6 cows and was located in the seventh ICS for 3 cows and in the eighth ICS for 2 cows, 15 to 20 cm ventral to the dorsal portal. Manipulation of the laparoscope through the ventral portal was more difficult and elicited signs of pain in all cows, and ventral portals located in the seventh ICS allowed for better observation of structures in the cranioventral aspect of the right hemithorax than did ventral portals located in the eighth ICS.
Anatomic structures visible during thoracoscopy—All structures observed during the examination of the left and right hemithoraxes were summarized (Table 1). With the laparoscope in the dorsal portal of the left hemithorax, the aorta was located by directing the laparoscope medially and was the first structure identified for navigation purposes. Dorsal to the aorta, the sympathetic trunk was viewed as a white filamentous band coursing cranially to caudally, and several lymph nodes appeared as dark red structures between the sympathetic trunk and the aorta (Figure 1). As the left lung lobes collapsed, the aortic arch, left azygos vein crossing over the aorta, and esophagus were observed. The esophagus was a flaccid purple structure ventral to the aorta, and the act of the cow swallowing helped verify its location. With the laparoscope directed medially and cranially, the dorsal branch of the vagus nerve (flat white band) was observed dorsal to the esophagus, and in 1 cow, the bifurcation of the vagus nerve into its dorsal and ventral branches was identified. When the laparoscope was moved cranially, the aortic groove was located on the collapsed lung. By directing the laparoscope toward the parietal pleura, the costocervical vein could be observed cranial to the aortic arch. Only when the dorsal portal was located in the ninth ICS could the laparoscope be moved even further cranially past the aortic arch, which allowed observation of the brachiocephalic trunk, thoracic duct, and cranial portion of the esophagus. When the laparoscope was directed caudally, the contralateral lung was observed through the mediastinum between the aorta and esophagus, the aortic hiatus and the esophageal hiatus were identified passing through the diaphragm, the tendinous and muscular portions of the diaphragm were evaluated, and the pulmonary ligament was observed coursing from the left caudal lung lobe to the mediastinum. Rotation of the laparoscope laterally allowed observation of the ribs, intercostal muscles, and neurovascular bundles. The left caudal lung lobe and the caudal portion of the left cranial lung lobe were observed with the laparoscope directed ventrally.
Representative thoracoscopic images of the left hemithorax of a healthy adult Holstein cow obtained through a portal in the ninth ICS, approximately 15 cm ventral to the transverse processes of the thoracic vertebrae (ie, dorsal portal). In panel A, the laparoscope is directed cranially to observe the aorta (Ao), lymph nodes of the thoracic aorta (LNA), and sympathetic trunk (ST). In panel B, the laparoscope is directed cranially and dorsally to observe the aorta (Ao), left caudal lung lobe (CLL), dorsal branch of the vagus nerve (DBVN), esophagus (E), left azygos vein (LAV), and pulmonary ligament (PL). In panel C, the laparoscope is directed cranially and dorsally to observe the aortic arch (AA), brachiocephalic trunk (BCT), costocervical vein (CCV), left caudal lung lobe (CLL), esophagus (E), left azygos vein (LAV), and thoracic duct (TD).
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Representative thoracoscopic images of the left hemithorax of a healthy adult Holstein cow obtained through a portal in the ninth ICS, approximately 15 cm ventral to the transverse processes of the thoracic vertebrae (ie, dorsal portal). In panel A, the laparoscope is directed cranially to observe the aorta (Ao), lymph nodes of the thoracic aorta (LNA), and sympathetic trunk (ST). In panel B, the laparoscope is directed cranially and dorsally to observe the aorta (Ao), left caudal lung lobe (CLL), dorsal branch of the vagus nerve (DBVN), esophagus (E), left azygos vein (LAV), and pulmonary ligament (PL). In panel C, the laparoscope is directed cranially and dorsally to observe the aortic arch (AA), brachiocephalic trunk (BCT), costocervical vein (CCV), left caudal lung lobe (CLL), esophagus (E), left azygos vein (LAV), and thoracic duct (TD).
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Representative thoracoscopic images of the left hemithorax of a healthy adult Holstein cow obtained through a portal in the ninth ICS, approximately 15 cm ventral to the transverse processes of the thoracic vertebrae (ie, dorsal portal). In panel A, the laparoscope is directed cranially to observe the aorta (Ao), lymph nodes of the thoracic aorta (LNA), and sympathetic trunk (ST). In panel B, the laparoscope is directed cranially and dorsally to observe the aorta (Ao), left caudal lung lobe (CLL), dorsal branch of the vagus nerve (DBVN), esophagus (E), left azygos vein (LAV), and pulmonary ligament (PL). In panel C, the laparoscope is directed cranially and dorsally to observe the aortic arch (AA), brachiocephalic trunk (BCT), costocervical vein (CCV), left caudal lung lobe (CLL), esophagus (E), left azygos vein (LAV), and thoracic duct (TD).
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Anatomic structures observed during thoracoscopy of the left and right hemithoraxes of 6 healthy adult Holstein cows.
| Structure | Left hemithorax | Right hemithorax |
|---|---|---|
| Aorta and aortic arch | 6 | 6 |
| Sympathetic trunk | 6 | 6 |
| Intercostal vasculature | 6 | 6 |
| Aortic hiatus | 6 | 4 |
| Azygos vein | 6 | 6 |
| Costocervical vein | 6 | 6 |
| Cranial mediastinum | 6* | 0 |
| Thoracic esophagus | 6 | 6* |
| Dorsal branch of vagus nerve | 6* | 4* |
| Ventral branch of vagus nerve | 1* | 0 |
| Pulmonary ligament | 6 | 6 |
| Contralateral lung | 6 | 6 |
| Hiatal and costal diaphragm | 6 | 6 |
| Brachiocephalic trunk | 6 | — |
| Caudal lung lobe | 6 | 6 |
| Cranial lung lobe, dorsal and costal surfaces | 6 | 0 |
| Middle lung lobe, dorsal and costal surfaces | — | 6 |
| Pericardium | 3 | 3* |
| Intercostal muscles | 6 | 6 |
| Ribs | 6 | 6 |
| Intercostal nerves | 6 | 6 |
| Thoracic duct | 2* | — |
| Mediastinal lymph nodes | 4 | 5 |
| Costocervical trunk | — | 2* |
Numbers represent the number of cows in which the structure was observed. During each thorascopic evaluation, a dorsal thoracoscopic portal was created in the 9th (n = 4 cows) or 10th (2 cows) ICS approximately 15 cm ventral to the transverse processes of the thoracic vertebrae. Additionally, during thorascopic examination of the left hemithorax of 4 cows and of the right hemithorax of 5 cows, a ventral portal was created in the seventh (left side, 2 cows; right side, 3 cows) or eighth (left side, 2 cows; right side, 2 cows) ICS approximately 30 cm ventral to the transverse processes of the thoracic vertebrae.
Structure most easily observed via a ventral portal in the seventh ICS.
— = Structure not expected to be observed.
The only advantage of thoracoscopic examination of the left hemithorax through the ventral portal, compared with that through the dorsal portal, was that it allowed closer evaluation of some structures such as the cranial portion of the esophagus, thoracic duct, and brachiocephalic trunk. In 2 cows, pericardial fat was observed between the left caudal lung lobe and the caudal portion of the left cranial lung lobe (Figure 2).
Representative thoracoscopic image of the left hemithorax of a healthy adult Holstein cow obtained through a portal in the seventh ICS approximately 30 cm ventral to the transverse processes of the thoracic vertebrae (ie, ventral portal). The laparoscope is directed cranially and ventrally to observe the caudal portion of the left cranial lung lobe (CaCLL), left caudal lung lobe (CLL), pericardial fat (PF), and thoracic wall (TW).
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Representative thoracoscopic image of the left hemithorax of a healthy adult Holstein cow obtained through a portal in the seventh ICS approximately 30 cm ventral to the transverse processes of the thoracic vertebrae (ie, ventral portal). The laparoscope is directed cranially and ventrally to observe the caudal portion of the left cranial lung lobe (CaCLL), left caudal lung lobe (CLL), pericardial fat (PF), and thoracic wall (TW).
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Representative thoracoscopic image of the left hemithorax of a healthy adult Holstein cow obtained through a portal in the seventh ICS approximately 30 cm ventral to the transverse processes of the thoracic vertebrae (ie, ventral portal). The laparoscope is directed cranially and ventrally to observe the caudal portion of the left cranial lung lobe (CaCLL), left caudal lung lobe (CLL), pericardial fat (PF), and thoracic wall (TW).
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Thoracoscopic examination of the right hemithorax was performed in a manner similar to that of the left hemithorax, and the structures observed were likewise similar. Compared with thoracoscopic examination of the left hemithorax, the pulmonary ligament was more prominent (Figure 3) in the right hemithorax, whereas the aortic arch was less prominent because of its right-to-left orientation toward to the left aortic vasa vasorum. The right azygos vein had more ramifications observed in the right hemithorax than did the left azygos vein in the left hemithorax, and 1 branch of the right azygos vein was observed anastomosing with the intercostal veins. The costocervical truck, which appeared as a pulsating, white tubular structure coursing in a craniocaudal direction, was observed in only 2 cows. The esophagus was difficult to locate in the right hemithorax but was observed in all 6 cows. With the laparoscope directed ventrally, the right caudal lung lobe, middle lung lobe, and caudal portion of the right cranial lung lobe were observed; however, the cranial portion of the right cranial lung lobe and the accessory lung lobe could not be identified. Just caudal and ventral to the middle lung lobe, pericardial fat was observed in 4 cows and the pericardium was observed in 2 cows. In general, structures within the mediastinum were easier to identify and observe during thoracoscopy of the left hemithorax than they were during thoracoscopy of the right hemithorax, with the exception of the pericardium, which was easier to identify in the right hemithorax.
Representative thoracoscopic images of the right hemithorax of a healthy adult Holstein cow obtained through a dorsal portal. In panel A, the laparoscope is directed cranially and dorsally to observe the right caudal lung lobe (CRL), intercostal vein (ICV), pulmonary ligament (PL), and right azygos vein (RAV). In panel B, the laparoscope is directed cranially and ventrally to observe the caudal portion of the middle lung lobe (CaML), cranial portion of the middle lung lobe (CrML), pericardium (P), and thoracic wall (TW). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Representative thoracoscopic images of the right hemithorax of a healthy adult Holstein cow obtained through a dorsal portal. In panel A, the laparoscope is directed cranially and dorsally to observe the right caudal lung lobe (CRL), intercostal vein (ICV), pulmonary ligament (PL), and right azygos vein (RAV). In panel B, the laparoscope is directed cranially and ventrally to observe the caudal portion of the middle lung lobe (CaML), cranial portion of the middle lung lobe (CrML), pericardium (P), and thoracic wall (TW). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Representative thoracoscopic images of the right hemithorax of a healthy adult Holstein cow obtained through a dorsal portal. In panel A, the laparoscope is directed cranially and dorsally to observe the right caudal lung lobe (CRL), intercostal vein (ICV), pulmonary ligament (PL), and right azygos vein (RAV). In panel B, the laparoscope is directed cranially and ventrally to observe the caudal portion of the middle lung lobe (CaML), cranial portion of the middle lung lobe (CrML), pericardium (P), and thoracic wall (TW). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Similar to thoracoscopy of the left hemithorax, thoracoscopic examination of the right hemithorax through a ventral portal had few advantages. The pericardium and esophagus were easier to observe through the right ventral portal than they were through the right dorsal portal.
Thoracoscopic manipulation of the pleural structures—Laparoscopic forceps inserted through the dorsal or ventral portal was used to carefully move the caudal lung lobe so that its diaphragmatic surface could be evaluated along with a greater proportion of the diaphragm (Figure 4). The cranial and middle lung lobes could not be similarly manipulated by the forceps so that the pericardium could be better observed.
Representative thoracoscopic image of the left hemithorax of a healthy adult Holstein cow obtained through a ventral portal. The laparoscope is directed caudally and laparoscopic forceps (F) have been inserted through a dorsal portal to displace the left caudal lung lobe (CLL) cranially so that the lumbar portion (LD) and tendinous center (TD) of the diaphragm can be evaluated. See Figures 1 and 2 for remainder of key.
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Representative thoracoscopic image of the left hemithorax of a healthy adult Holstein cow obtained through a ventral portal. The laparoscope is directed caudally and laparoscopic forceps (F) have been inserted through a dorsal portal to displace the left caudal lung lobe (CLL) cranially so that the lumbar portion (LD) and tendinous center (TD) of the diaphragm can be evaluated. See Figures 1 and 2 for remainder of key.
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Representative thoracoscopic image of the left hemithorax of a healthy adult Holstein cow obtained through a ventral portal. The laparoscope is directed caudally and laparoscopic forceps (F) have been inserted through a dorsal portal to displace the left caudal lung lobe (CLL) cranially so that the lumbar portion (LD) and tendinous center (TD) of the diaphragm can be evaluated. See Figures 1 and 2 for remainder of key.
Citation: American Journal of Veterinary Research 75, 5; 10.2460/ajvr.75.5.468
Effect of thoracoscopy on cardiovascular and pulmonary function—Cardiovascular and pulmonary variables before, during, and after thoracoscopy were summarized (Table 2). Sedation did not significantly affect HR, RR, or any arterial blood gas variables. For all cows, initiation of thoracoscopy and induction of pneumothorax resulted in significant increases in HR and RR and significant decreases in Sao2 an and an Pao2, regardless of the hemithorax examined. Respiratory rate during the second procedure was significantly (P = 0.042) increased from that during the first procedure; however, significant changes between the first and second thoracoscopic examinations were not observed for any of the other variables. At 15 minutes after completion of thoracoscopy, HR, RR, Sao2, and Pao2 values did not differ significantly from those prior to induction of pneumothorax. During thoracoscopy, Sao2 fell to < 95% for all cows; thus, all cows received supplemental oxygen through a nasal cannula. Sedation and thoracoscopy had no significant effect on Paco2.
Mean ± SD cardiovascular and pulmonary variables for 6 healthy adult Holstein cows as determined immediately before and 30 minutes after sedation with acepromazine (0.05 mg/kg, IM), 15 minutes after induction of pneumothorax during thoracoscopy, and 15 minutes after completion of thoracoscopy.
| Variable | Hemithorax examined | Immediately before sedation | 30 minutes after sedation | 15 minutes after induction of pneumothorax | 15 minutes after completion of thoracoscopy |
|---|---|---|---|---|---|
| HR (beats/min) | Left | 55.00 ± 15.00 | 55.00 ± 11.30 | 64.67 ± 9.64* | 57.00 ± 13.65 |
| Right | 55.00 ± 8.62 | 54.17 ± 3.85 | 66.33 ± 12.24* | 56.00 ± 7.30 | |
| RR (breaths/min) | Left | 17.00 ± 3.96 | 17.33 ± 1.88 | 25.00 ± 5.38* | 18.67 ± 8.22 |
| Right | 19.67 ± 4.68 | 17.33 ± 2.75 | 24.00 ± 6.11* | 18.67 ± 4.71 | |
| Sao2 (%) | Left | 98.00 ± 0.58 | 98.17 ± 0.69 | 92.83 ± 1.95* | 97.83 ± 0.90 |
| Right | 98.67 ± 0.75 | 97.50 ± 0.76 | 91.50 ± 3.04* | 97.50 ± 0.96 | |
| Pao2 (mmHg) | Left | 95.33 ± 7.89 | 102.50 ± 10.14 | 63.00 ± 5.54* | 96.33 ± 11.05 |
| Right | 115.17 ± 19.7 | 94.67 ± 6.4 | 60.33 ± 12.64* | 92.83 ± 9.49 | |
| Paco2 (mmHg) | Left | 39.65 ± 3.21 | 40.48 ± 3.45 | 40.87 ± 2.68 | 38.60 ± 2.64 |
| Right | 36.55 ± 5.86 | 39.53 ± 5.86 | 40.50 ± 1.42 | 40.77 ± 1.86 |
For each cow, thoracoscopy was performed on both the right and left hemithoraxes with a 24-hour interval between procedures.
Value differs significantly (P < 0.05) from that obtained at 30 minutes after sedation (ie, prior to induction of pneumothorax).
Complications associated with thoracoscopy—All cows tolerated the induction of pneumothorax well. One cow began coughing and appeared anxious during aspiration of the pneumothorax. The aspiration rate was decreased, and the coughing stopped.
Thoracic ultrasonography performed immediately after thoracoscopy revealed moderate pneumothorax near the dorsal portal in 2 cows (1 in the left hemithorax and 1 in the right hemithorax). Ultrasonography performed at 24 hours after thoracoscopy revealed moderate pneumothorax near the dorsal portal in all 6 cows (3 in the left hemithorax and 3 in the right hemithorax) at least once; however, the mean HR, RR, and arterial blood gas values at 24 hours after thoracoscopy were all within reference limits and did not differ significantly between cows that did and did not have pneumothorax at that particular point. For all affected cows, ultrasonography performed 1 week after thoracoscopy indicated that the pneumothorax diagnosed at 24 hours after the procedure was still present, albeit to a lesser extent, which suggested it was resolving.
Subcutaneous emphysema developed around 7 of 21 (33%; 4 right and 3 left) portal sites. In 2 cows, the SC emphysema was generalized and involved the entire thoracic area. At 1 week after thoracoscopy, the extent of SC emphysema was decreased in all affected cows.
Discussion
Results of the present study indicated that thoracoscopy could be safely performed in healthy cattle restrained in a standing position. For both the left and right hemithoraxes of cattle, thoracoscopic examination was easiest through a portal in the ninth ICS approximately 15 cm ventral to the transverse processes of the thoracic vertebrae (ie, dorsal portal). Most thoracic structures could be observed through this dorsal portal. Thoracoscopic examination through a ventral portal located 15 to 20 cm ventral to the dorsal portal (generally in the seventh or eigth ICS) allowed for closer examination of structures in the cranioventral portion of the hemithorax, but was frequently accompanied by signs of pain in the patient. Thus, thoracoscopic examination should be first performed through a dorsal portal and a ventral portal created only when necessary. The anatomic structures identified by thoracoscopy in cattle were similar to those identified by thoracoscopy in horses,3,4 with the exception of structures located in the mediastinum. In the cattle of the present study, the dorsal aspect of the mediastinum was thin and the contralateral lung lobes could be easily seen through it; however, the ventral aspect of the mediastinum frequently contained a substantial amount of fat, which made observation of structures such as the esophageal artery and vein, ventral branch of the vagus nerve, pulmonary vein, and mainstem bronchi difficult or impossible. In horses, thoracoscopic identification of the heart and pericardium is difficult and the heart is generally best observed with thoracoscopy of the left hemithorax,3,4 whereas in the cattle of the present study, the heart was more easily observed with thoracoscopy of the right hemithorax.
In the present study, placement of the dorsal portal in the 9th ICS allowed for easy manipulation of the laparoscope in all directions, whereas placement of the dorsal portal in the 10th ICS resulted in limited movement of the laparoscope in the caudal and ventral directions owing to its closer proximity to the diaphragm. During the first 3 thoracoscopic examinations, a ventral portal was not created because most of the anatomic structures of interest were observed through the dorsal portal and we did not believe that a ventral portal would be beneficial to the examination. However, after 3 thoracoscopic examinations (2 of the left hemithorax and 1 of the right hemithorax), we decided to create a second portal cranial and ventral to the dorsal portal to evaluate whether such a portal would have any advantages or disadvantages, compared with the dorsal portal, and to determine whether insertion of an instrument through a ventral portal could be used to manipulate the lung lobes and improve observation of some structures. Compared with thoracoscopy through the dorsal portal, thoracoscopy through the ventral portal allowed for improved visual inspection of structures in the cranioventral aspect of the hemithorax such as the heart and pericardium, and laparoscopic forceps inserted through this portal could be used to displace the caudal lung lobes so that the diaphragm could be better evaluated. Results of the present study suggested that the best location for a ventral portal in both the left and right hemithoraxes of cattle was in the seventh ICS approximately 30 cm ventral to the transverse processes of the thoracic vertebrae. At this location, the laparoscope could be easily directed dorsally and ventrally, but manipulation of the laparoscope cranially and caudally was difficult and caused patient discomfort, findings that were similar to those of studies3,4 involving thoracoscopy in horses.
The thoracoscopic technique used in the present study was relatively simple; however, it can be complicated by some intrinsic cow factors such as intercostal muscle mass and body condition score. For example, in very obese cattle, it may be difficult to identify the ICSs and abundant SC fat increases the thickness of the body wall, which can complicate manipulation of the laparoscope in a cranial-to-caudal direction. Additionally, obese cows generally have more mediastinal fat than do thinner cows, which makes observation of structures within the mediastinum difficult.
The cows of the present study were of typical size for adult Holstein cows examined at our hospital. The optimal location for thoracoscopic portals may vary among cows of different sizes and breeds. Therefore, we recommend that thoracic ultrasonography to outline the caudal and ventral limits of the pleural cavity be performed prior to thoracoscopy to reduce the risk of inserting the laparoscope into the abdominal cavity and through the diaphragm.
At the end of each thoracoscopic examination in the present study, as much air as possible within the hemithorax was aspirated; however, aspiration was discontinued when the lung was observed at the level of the dorsal portal so that the lung would not be damaged by the cannula. The extent of residual pneumothorax was evaluated only by ultrasonography. Thoracic radiography was not performed because of additional costs and the fact that, in human patients, ultrasonography is a more sensitive method for detection of pneumothorax than is radiography.11
In 2 cows, the extent of pneumothorax at 24 hours after thoracoscopy was more severe than it was immediately after the procedure. This was most likely caused by the redistribution of air that was sequestered in the cranial portion of the hemithorax after the end of the procedure. Air could have also entered the hemithorax through the thoracoscopic portals.
Only the skin was sutured at the portal sites, although in hindsight, given the size of the laparoscope (10 mm) and the straight angle of the portals, it might have been better to suture the intercostal muscle aponeuroses to decrease the potential for aspiration of air into the hemithorax. Finally, the increase in the extent of pneumothorax in those cows could have been from a tear in the lung. For the dorsal portal, the first cannula introduced into the pleural cavity and through which the pneumothorax was induced had a blunt end; however, the trocar introduced into the pleural cavity after the pneumothorax was induced had a sharp edge. For each thoracoscopic examination, this trocar was inserted only after the pneumothorax had been induced and the lungs had collapsed beyond its reach, and it was quickly replaced by the laparoscope. For the thoracoscopic examinations that involved creation of a ventral portal, this portal was created by thoracoscopic guidance through the dorsal portal, and similar to creation of the dorsal portal, a blunt-ended teat cannula was initially introduced into the pleural cavity. The only cannula that could have traumatized the lung was the blunt-ended teat cannula, and bubbles on the surface of the dorsal lung surface that would be indicative of a lacerated lung lobe were not observed during any thoracoscopic examination. Therefore, we do not believe that a lacerated lung was the cause of the increase in the extent of pneumothorax in those 2 cows.
In the present study, HR, RR, and arterial blood gas variables were monitored every 15 minutes throughout each thoracoscopic examination. Although the Pao2 and Sao2 decreased significantly after pneumothorax was induced, the effect of thoracoscopy on the other variables was minimal. Moreover, even though the study cows were healthy, the Sao2 of all cows decreased to < 95% during the procedure, which necessitated the administration of supplemental oxygen. Thus, thoracoscopy of cows with compromised respiratory function could be accompanied by substantial risk for anoxia, and we recommend that all cattle be administered oxygen by means of nasal insufflation to decrease the impact of pneumothorax during the procedure.
Acepromazine was chosen to sedate the cows of this study instead of xylazine, which is a more commonly used sedative for cattle because it causes less cardio-respiratory and gastrointestinal (ie, less rumen tympany) depression than does xylazine.12 Additionally, cows sedated with acepromazine are less likely to become recumbent than are cows sedated with xylazine,13 which is very important when a procedure must be performed with cows in a standing position. Diazepam, which has even less effect on the cardiorespiratory system of cattle than does acepromazine, also could have been used to sedate the study cows; however, we chose to use acepromazine because of the relatively high cost and limited availability of diazepam. For the cows of this study, sedation with acepromazine had no significant effect on the HR, RR, and arterial blood gas variables, and the only disadvantage of acepromazine administration was the time required after injection (30 minutes) for the cows to achieve the desired level of sedation.
In the present study, feed was withheld from cows for 12 hours prior to each thoracoscopic examination to decrease ruminal atony and distension associated with sedation and to minimize the pressure that the rumen would exert on the diaphragm during the procedure. Because thoracoscopy was not performed on any cows that had unrestricted access to feed, it is unknown what effect feed restriction had on the thoracoscopic procedure. We suspect that the 12-hour feed restriction period allowed insufflation of a sufficient amount of air into the hemithorax to view ventrally located structures. It is unknown whether a similar amount of air could be insufflated into the hemithorax of cows from which feed was not withheld, and the effect of feed restriction on the thoracoscopic technique in cattle warrants further investigation.
Cows in the present study were administered ceftiofur sodium (1 mg/kg, IV) 30 minutes before initiation of thoracoscopy for prophylactic purposes. This represents extralabel use of ceftiofur sodium because it is not approved for this purpose or route of administration, and although such use is legal in Canada, it is illegal in the United States. The FDA prohibits the use of approved cephalosporins in cattle except at doses, routes, frequency, and duration of administration approved for that species and production class.14 Ceftiofur sodium is approved for IM and SC injection in cattle.15 Thus, US practitioners should not administer ceftiofur sodium to cattle by the IV route.
Thoracoscopy is complementary to other diagnostic methods for evaluation of the thorax of cattle. Thoracoscopy allows direct observation of many structures such as the mediastinal lymph nodes, thoracic portion of the esophagus, and dorsal branch of the vagus nerve, which could aid in the diagnoses of megaesophagus and vagal indigestion. It also allows visual examination of the dorsal portion of various lung lobes and could aid in the identification of lung abscesses and the optimal location for thoracic drainage. In cattle with atypical pneumonia, thoracoscopy could be used to safely obtain lung biopsy specimens in a manner similar to that in horses.4 In research settings, thoracoscopy might be useful for monitoring the effects of various disease processes or treatments on the lungs.
In adult cattle, thoracic radiographs of diagnostic quality are difficult to obtain and generally require powerful stationary radiographic units that are typically found only at referral hospitals. Thus, most practitioners rely on auscultation and occasionally ultrasonography to evaluate the thoracic cavity of adult cattle. Cattle with signs of respiratory tract disease that fail to respond to routine treatment might be candidates for thoracoscopy. It is not uncommon for cattle practitioners to use a portable laparoscope in the repair of a displaced abomasum, and this laparoscope could be also be used for thoracoscopy. The laparoscope provided in the kit for repair of a displaced abomasum generally has a 0° viewing angle. In the present study, we used a laparoscope with a 30° viewing angle, which allowed observation of a larger portion of the hemithorax than could be achieved with a laparoscope with a 0° viewing angle. However, a laparoscope with a 0° viewing angle should be adequate to evaluate the dorsal aspect of the lung lobes and the structures within the mediastinum. The only additional equipment needed for thoracoscopy that is not included in laparoscopic displaced abomasum repair kits is a small portable vacuum pump to aspirate the pneumothorax at the end of the procedure.
Thoracoscopy can be safely performed in healthy cows that are sedated and restrained in a standing position. Further investigation of the safety of thoracoscopy in cattle with cardiac or pulmonary disorders is necessary.
ABBREVIATIONS
| ICS | Intercostal space |
| HR | Heart rate |
| RR | Respiratory rate |
| Sao2 | Arterial oxygen saturation |
Naxcel, Zoetis, Kirkland, QC, Canada.
Banamine, Schering Plough Animal Health, Pointe Claire, QC, Canada.
Atravet, Boerhinger Ingelheim Ltd, Burlington, ON, Canada.
Metal sleeve standard straight distal tip and trocar pyramidal tip, Richard Wolf GmbH, Knittlingen, Germany.
High-performance German optic lens, 3.5 × 26 × 3.5, Surgical Direct, Deland, Fla.
Endocam 5512, Richard Wolf GmbH, Knittlingen, Germany.
5131 Auto LP, Richard Wolf GmbH, Knittlingen, Germany.
DMR EH55, Panasonic Canada Inc, Mississauga, ON, Canada.
Richard Wolf GmbH, Knittlingen, Germany.
i-STAT System, Abbott Point of Care Inc, Mississauga, ON, Canada.
IBM SPSS Statistics, version 20 for Windows, IBM Canada Ltd, Markham, ON, Canada.
References
1. Flöck M. Diagnostic ultrasonography in cattle with thoracic disease. Vet J 2004; 167: 272–280.
2. Braun U, Sicher D, Pusterla N. Ultrasonography of the lungs, pleura, and mediastinum in healthy cows. Am J Vet Res 1996; 57: 432–438.
3. Peroni JF, Horner NT, Robinson NE, et al. Equine thoracoscopy: normal anatomy and surgical technique. Equine Vet J 2001; 33: 231–237.
4. Peroni JF, Robinson NE, Stick JA, et al. Pleuropulmonary and cardiovascular consequences of thoracoscopy performed in healthy standing horses. Equine Vet J 2000; 32: 280–286.
5. Relave F, David F, Leclère M, et al. Thoracoscopic lung biopsies in heaves-affected horses using a bipolar tissue sealing system. Vet Surg 2010; 39: 839–846.
6. Malone ED, Farnsworth K, Lennox T, et al. Thoracoscopic-assisted diaphragmatic hernia repair using a thoracic rib resection. Vet Surg 2001; 30: 175–178.
7. Van Biervelt J, Kraus M, Woodie B, et al. Thoracoscopic pericardiotomy as a palliative treatment in a cow with pericardial lymphoma. J Vet Cardiol 2006; 8: 69–73.
8. Piccioni F, Langer M, Fumagalli L, et al. Thoracoscopic para-vertebral anaesthesia for awake video assisted thoracoscopic surgery daily. Anaesthesia 2010; 65: 1221–1224.
9. Loddenkemper R. Thoracoscopy—state of the art. Eur Respir J 1998; 11: 213–221.
10. Molnar TF. (Video assisted) thoracoscopic surgery: getting started. J Minim Access Surg 2007; 3: 173–177.
11. Alrajab S, Youssef AM, Akkus NI, et al. Pleural ultrasonography versus chest radiography for the diagnosis of pneumothorax: review of the literature and meta-analysis. Crit Care 2013; 17: R208.
12. Ruckebusch Y, Allal C. Depression of reticulo-ruminal motor functions through the stimulation of alpha 2–adrenoceptors. J Vet Pharmacol Ther 1987; 10: 1–10.
13. Greene SA. Protocols for anesthesia of cattle. Vet Clin North Am Food Anim Pract 2003; 19: 679–693.
14. Department of Health and Human Services, FDA. 21 CFR Part 530 (Docket No. FDA-2008-N-0326). New animal drugs; cephalosporin drugs; extralabel animal drug use; order of prohibition. Federal Register 2012;Jan 6:77. Available at: www.gpo.gov/fdsys/pkg/FR-2012-01-06/pdf/2012-35.pdf. Accessed Dec 27, 2013.
15. Zoetis. Naxcel product insert. Available at: https://online.zoetis.com/US/EN/Products/PublishingImages/NAXCEL_Compliance_Rev_2006.pdf. Accessed Dec 27, 2013.
