If closed-chest BLS is unsuccessful (as determined by lack of spontaneous respiration or inability to generate detectable forward blood flow) after 5–10 minutes, open-chest CPR (see below) is indicated.
Instances when open-chest CPR is indicated during initial BLS include:
recent abdominal or thoracic surgery
suspected pleural or pericardial disease
trauma or pathology of the chest or abdominal wall with blood loss
larger dogs in which external compressions are unlikely to generate an adequate forward blood flow
If possible, a quick clip of the hair along the intended incision site is helpful. There is no time for an aseptic preparation of the area. A scalpel blade or Mayo scissors are used to incise the skin, subcutaneous tissues, and muscle layers along the cranial border of the fourth or fifth rib from the spine to sternum. Guarded by the thumb and forefinger to prevent injury to the heart and lungs, closed Mayo scissors or Carmalt forceps are used to bluntly enter the pleural space while ventilations are temporarily discontinued. After the pleura is entered, Mayo scissors are used to incise the intercostal muscles along the entire length of the intercostal space on the cranial aspect of the rib. Care should be taken to avoid incising the internal thoracic vessels running parallel and lateral to the sternum. To improve visualization, Finochietto retractors may be used; suction or temporarily placing the patient in sternal recumbency may be necessary to rapidly remove blood.
After the thoracic cavity is opened, manual ventilations should resume. The pericardiodiaphragmatic ligament should be elevated with a finger or instrument and incised with scissors, extending the incision dorsally, taking care to avoid causing injury to the phrenic nerve. The heart is then lifted out of the pericardial sac and observed for any coordinated spontaneous contractions. If no cardiac contractions are noted, the heart is grasped with one or both hands and compressed progressively from the apex to the base. The compression is then released to allow the cardiac chambers to fill with blood. If fine or coarse fibrillation of the heart muscle is noted, internal defibrillation should be performed. Any active bleeding can be clamped at this time.
The descending aorta is located on the dorsal midline and can be isolated and temporarily cross-clamped to direct blood flow to the brain. Aortic cross-clamping can be performed with atraumatic vascular clamps or by using a modified Rommel tourniquet, passing a rubber tube, latex tube, or umbilical tape around the aorta with the assistance of curved hemostats and then clamping on the tube to occlude aortic flow. Aortic cross-clamping can be performed for 10 minutes without serious complications (from lack of blood flow to the spinal cord) and then should be released for 2 minutes.
The ECG is evaluated and drugs given as indicated during ALS procedures. Return of spontaneous circulation allows lavage of the thorax with large quantities of sterile, warm, isotonic saline; placement of a thoracostomy tube; and surgical closure of the thorax. Cardiovascular support is frequently required to maintain circulation while the underlying cause of the arrest is treated.