Page 359 - Clinical Small Animal Internal Medicine

33 Surgical Approaches to Thoracic Disease 327

pyothorax, or pneumothorax. In such cases, thoracos- measurement, pulse oximetry, and arterial blood gas
VetBooks.ir tomy tubes remain in place for several days following analysis, as well as end‐tidal CO 2 and tidal volume in
patients requiring continued mechanical ventilation.
surgery for continual thoracic evacuation and fluid sam-
pling. Occasionally, continual effusion or pneumothorax
occurs postoperatively, exceeding expected volumes. Electrocardiography
Predictable pleural effusion secondary to an indwell-
ing thoracostomy tube should approximate 2.0 mL/kg/ Electrocardiographic monitoring provides early detection
day. Fluid production above this may represent continual and continuous monitoring of cardiac arrhythmias.
disease. Fluid analysis, including cell counts and cytol- Postoperative arrhythmias may be observed primarily as a
ogy, can help the clinician assess if the fluid is reflective result of surgical trauma, prior manual cardiac manipula-
of ongoing disease. If cell counts and cytology do not tion, or direct pericardial or epicardial irritation from the
support ongoing inflammation, infection or neoplasia, indwelling thoracostomy tube. Arrhythmias may also
then it is possible that the ongoing fluid production is occur secondary to pain, hypoxemia, hypovolemia, or
related to a systemic vasculitis, low oncotic pressure or electrolyte imbalances. Observation of hemodynamically
elevated hydrostatic pressure. The pleural space volume significant postoperative atrial or ventricular arrhythmias
is approximately 100–140 mL/kg in small animals. As necessitates therapeutic intervention including supple-
such, when volumes of air or fluid exceed this value, it mental oxygen therapy, aggressive analgesia, correction of
can be classified as a continuous process (e.g., continu- hypovolemia and electrolyte imbalance, and possibly anti-
ous pneumothorax). arrhythmic medications. Diagnostic evaluation of postop-
erative arrhythmias may include electrolyte measurement,
arterial blood gas analysis, and echocardiography.
Thoracostomy Tubes

Thoracostomy tubes are a mainstay in the management Arterial Blood Pressure
of postthoracotomy patients. Depending on patient sta-
bility, a thoracostomy tube may be placed preoperatively As mentioned, changes in transpulmonary and pleural
or intraoperatively. Patients with viscous thoracic effu- pressures can have significant hemodynamic effects.
sions or large‐volume pneumothoraces may require Direct arterial blood pressure measurement is the gold
bilateral thoracostomy tube placement. standard for monitoring patient stability and diagnosing
Conventional thoracostomy tubes consist of large‐bore changes in intrathoracic pressure. A sudden reduction in
plastic tubing made from silicone or polyvinyl chloride. blood pressure may indicate an acute increase in pleural
Soft, small‐bore thoracostomy tubes (e.g., Mila®, Mila pressure, such as pneumothorax, warranting immediate
International) that can be placed using a percutaneous investigation. Central venous pressure (CVP) monitor-
catheter and guidewire are preferred by many emergency ing can guide fluid therapy for postthoracotomy patients,
and critical care clinicians. The small bore tubes can be but CVP is known to be affected by changes in intratho-
placed with ease and minimal risk to the patient either pre racic pressure due to respiration, PEEP, and abdominal
or intra-operatively. The smaller diameter low profile hypertension as each of these is known to decrease right
thoracostomy tubes are effective for all disease processes, ventricular compliance and thus artificially augment
including viscous effusions such as pyothorax. A cadaver CVP. For these reasons, routine measurement of CVP in
study evaluating traditional large bore chest tubes to small the postoperative patient with significant pleural space
bore tubes in efficiency to remove air, low viscosity fluid disease is not recommended.
and high viscosity fluid found that small bore tubes were
as effective as large bore tubes. It is the authors’ opinion
that the more traditional larger diameter tubes should be Pulse Oximetry and End‐Tidal CO 2
very rarely utilized, and that these tubes contribute to Pulse oximetry can provide valuable information regard-
patient discomfort without providing any significant ing arterial hemoglobin saturation but it can also be
advantage with regards to evacuating the pleural space. affected by multiple patient factors. End‐tidal CO 2
(ETCO 2 ) and tidal volume are helpful monitoring tools
in the postthoracotomy patient requiring extended intu-
Postoperative Monitoring bation and mechanical ventilation. Changes in ETCO 2
may be the first indicator of acute deterioration such as a
Intensive postoperative monitoring is imperative fol- large pulmonary thromboembolism or cardiopulmonary
lowing thoracotomy. Ideal monitoring would include arrest in these critical patients, emphasizing the impor-
electrocardiography, direct arterial blood pressure tance of capnography.