Practical management of severe lung disease and injury (Proceedings)
The principles of management of patients with severe lung disease and injury are summarized and the cases depicting the use if these management techniques are presented
Provide oxygen early and calm the patient with drugs so that they do not become more stressed.Cats and small dogs that arrive should be immediately placed in a small box and this box flooded with high flow – 20-Liter per minute – of oxygen. It is preferred if the "struggling to breath pet be actually place in a cardboard box at the scene, before travel. If travel is being done by a pet ambulance carrier they should be instructed to provide this "high flow oxygen" into the box. Obviously those that are NOT CONSCIOUS require at least mouth to nose ventilation, or bag-valve-mask ventilation with near 100% oxygen.
Large dogs, that are too large for small boxes should receive a sedating drug on admission..prefer ketamine and butorphenol and acepromazine in doses of 1-2 mg/kg, 0.1 mg/kg and 0.01 mg/kg respectively given in the epaxial muscles and then as they settle oxygen is switched from giving by jet-flow and canopy techniques to bag-valve-mask with a tight fitting mask.
Animals that were initially placed in the small confined box should now be given the same cocktail of ketamine, butorphenol and acepromazine. This can be done by use of the IM epaxial route OR it may be that an IV rout can be provided by using an "oxygen bag-over-the cat technique" where the patient's small box is covered with a large enough clear-plastic bag and oxygen continued to be given at high levels enough to inflate the bag covering the box. The cat is "shaken" out of the box and into the clear-plastic flexible bag filled with oxygen. This technique is recommended to be able to give the cat its epaxial ket-but-ace cocktail – injecting right through the bag. It is very important not to try and handle the cat before it is sedated adequately enough. Ketamine is a very good bronchial-dilator and is good for the asthmatic case; the butorphenol is a redistributor of lung blood volume and a lowerer of vascular resistance and blood pressure which decreases intrapulmonary hemorrhage and edema in heart failure patients, the acepromazine cancels out the systemic hypertension caused by the ketamine. Together they work very well in most cases in my experience. This combination is also a good pre-anesthesia or pre-muscle blocker in those cases that will require rapid-sequence-induction and intubation to gain tracheal – airway control to allow for positive pressure ventilation, which many severe lung disease or injury cases will require.
If the animal is not responsive to supplemental oxygen is a very positive way with a very visible decrease in the patient's "work of breathing" then bag-valve-mask ventilation should be started and a PEEP valve on the end of the AMBU exhalation arm should be added and set for 5 cm H2O to start.
During that time an iv access should be gotten and other added medications considered to be given. These include further medication to calm the patient if needed, furosemide for cardiac and centroneurogenic induced pulmonary edema at 4-8 mg/kg body weight, mannitol for oxygen radical scavenging at a dose of 200 mg/kg body weight given very slowly, consider the use of methylprednisolone sodium succinate for the inflammatory component of pulmonary injury, at a dose of 2-4 mg/kg body weight. Note this is a very small dose compared to those used in the past which caused significant immune system compromise; and controversial but in my experience helpful in cases of aspiration pneumonia, severe lung hemorrhage and contusion and in suspected pneumonia, the delivery of a broad-spectrum bactericidal antibiotic such as a first generation cephalosporin, giving the first dose at double the regular dose to gain a tissue level rapidly. However, in these cases I recommend getting a culture of deep bronchus secretions and Gram's stain just before giving and tailoring subsequent iv doses with the finding on the Gram's stain and cytology. The sample collection is generally gotten before the iv antibiotics are given but the antibiotics not delayed past that time.
If the bag-valve mask ventilation does not decrease the patient's work of breathing within minutes and the WOB is still very severe, make sure that the following have been ruled out: 1. Pneumo or hemo or hydrothorax either by auscultation, ultrasound or horizontal beam preferred radiology. 2. Diaphragmatic hernia by same methods. If able to decompress the pleural space conditions with chest aspiration this should be accomplished immediately. In some cases, rapid sequence induction (RSI), will still need to be completed to gain control of the patient to allow decompression to be able to completed with as little stress as possible. In cases of pneumothorax, please keep in mind that by using IPPV we may be making the pneumothorax considerably worse rapidly. In these cases it is imperative to move quickly to decompress the pleural space. If RSI was deemed necessary in this case a simple but very effective means of decompression is to ias is to perform immediate small opening thoracotomy. This can be later converted to chest tube entrance sight or at least a facilitator of the placement of a chest – tube (preferred). This mini-thoracotomy can also be used to collect blood should evidence of a hemothorax is also noted with the chest is entered. Again usually in blunt or penetrating trauma causes of hemothorax the immediate placement of a chest tube and the continued aspiration of the blood from the chest will cause the leaks in the lungs to stop or at least greatly slow down. If after a few minutes it is noted that this is not occurring either a parasternotomy or formal mid-thoracotomy should be performed.
Rapid Sequence Intubation carries some risks to it is imperative that the following be completed in the following steps to avoid complications:
1. The patient must be first receiving oxygen by non-invasive ventilation (bag-valve mask assisted or anesthetic circuit assisted). If intubation is attempted in the very acidemic or hypoxic patient this can cause vaso-vagal induced profound hypotension, bradycardia, or ventricular asystole or fibrillation.
2. Even though the term RSI has the word "rapid" in it the drugs that are given are titrated in to provide the effect needed and it is OK to wait for the drug to take effect and this may be slightly longer than anticipated, especially in cardiovascularly compromised patients.
3. Begin by giving a pain reliever as intubation is painful and also give a parasympatholylitic such as glucopyrolate (preferred) or atropine. I like hydromorphone at 0.05 – 0.1 mg/kg slowly given and then give a hypnotic that will allow intubation. In my experience I like ketamine WITH diazepam because the combination can be fairly safe in the cardiovascularly compromised patient. A one-one volume mixture of these are given, generally slowly at a rate of 0.1 ml/kg (one ml per20 lb body weight). This generally allows gentile and safe intubation and does not drop blood flow as much as Propofol in my experience. Some animals may only require the hydromorphone while others will be so amped up that they will require a bit more ketamine. If they continue to "buck the IPPV provided by the person doing the hand bagging or the anesthetic or ICU ventilator then a muscle blocker is recommended. I prefer atricurium at 0.25 mg/kg body weight and then half doses are repeated as needed. Of course isoflurane can also help but care is given to watch for hypotension or decreased blood flow.
Use a lung protective strategy (LPS) and ventilate for at least several hours to several days depending on arterial blood gases, end tidal CO2 levels, spO2 and radiographic changes. The LPS involves keeping barotraumas and lung shear stresses minimized. This involves aiming for peak inspiratory pressures to be limited to 17-18 cm H2O, using PEEP at 5-12 cm H2O, delivering oxygen concentrations below 60 mmHg if at all possible.