Sedating the Cardiac Patient
Many veterinarians are apprehensive about sedating an animal with a potential heart problem, particularly one that is dyspneic. There is wisdom in this viewpoint and, let's face it, you may not know on the spot whether dyspnea is due to cardiac disease or a primary respiratory condition. A patient in severe respiratory distress is at risk of death as a consequence of minimal diagnostic or therapeutic interventions, but is also at risk if you do nothing; it would be well to advise your client of this at your initial contact!
I have a great deal of experience with this situation, and strong convictions as well. These patients die most commonly as a consequence of struggling and stress! I once actually witnessed the death of a cardiomyopathic Doberman who struggled and went into ventricular fibrillation while being restrained for an EKG; the owner watched the whole thing! While there is always an exception to the rule, appropriate sedation is my preference for handling these patients, hands down! Sedate first, i.e. before radiographs, IV catheter, thoracocentesis, echocardiogram, etc. Obviously I would prefer for the dyspneic patient to receive oxygen before, during, and after all interventions, but you've probably noted that some patients will struggle even if you are trying to blow some oxygen in their face; they may need sedation before you can even examine them.
My concoction of choice for sedating cardiac patients, both dogs and cats, is diazepam (Valium) and butorphanol, 0.2 mg/kg of each, mixed for an IV injection (stings if given out of the vein). This mixture will precipitate briefly, then clear after rocking the syringe back and forth a couple of times. Substitute midazolam for the diazepam (0.2 mg/kg again) and give it IM for the patient that can't even sit still for an IV. If your practice is narcotic friendly, you can substitute oxymorphone (0.05 – 0.10 mg/kg) or hydromorphone (0.10 – 0.20 mg.kg) in place of the butorphanol; use the lower end dosage of the narcotic for cats.
Note that this is not a potent sedative. If you give this to a fractious patient, you will likely still have a fractious patient after this medication. However it's usually just the ticket for the critically dyspneic pet or one with significant heart disease. It takes away enough stress so that you can accomplish critical procedures, such as those listed above, but the patient will still be able to stand, walk, or go home with the client (if appropriate) right after you're done. This is also my choice for pre-anesthesia in cardiac patients; more on this in another article.
One of the side effects of the above narcotics is respiratory depression. Nevertheless morphine has long been a staple therapy for people presented with congestive heart failure (although people are commonly intubated for assisted respiration as well). I don't know if the decreased respiratory drive may actually be an advantage, decreasing the stress associated with the patient's perceived need for oxygen. In any case, it's my strong belief that you will come out on the positive side of the risk/benefit ledger using this combination.
Another potential side effect of the narcotic is bradycardia. This can be enough of a problem that I would think twice about using the above if the patient is already bradycardiac. As an aside, a dog with bradycardia is probably not in congestive heart failure unless it has a significant bradyarrhythmia (e.g. second or third degree AV block) or it’s on other drugs that produce slowing of the heart rate (e.g. beta-blockers, sometimes pimobendan).
Other sedative choices I specifically recommend against for cardiology patients include acepromazine, atropine or glycopyrrolate, ketamine or tiletamine (in Telazol) for cats with cardiomyopathy, and particularly alpha agonists such as xylazine or medetomadine (in Domitor). Cardiologists have debated the use of various sedatives in their online specialty forums and the opinions expressed here are not universal. Acepromazine, for example, produces much greater sedative effect than the Valium/butorphanol mixture described. It's earned a reputation for treatment of acute respiratory distress caused by upper airway disease (e.g. laryngeal paralysis, brachiocephalic airway syndrome, collapsing trachea syndrome), particularly in conjunction with butorphanol. Acepromazine can be used at very low doses to help smooth an anesthetic recovery in some cardiac patients. However I don't recommend it at typical sedative dosages for dogs with severe heart disease (and neither do anesthesiologists) because of potential for hypotension and, in my experience, arrhythmogenesis.
As a past EKG interpreter for IDEXX/CardioPet, I would say one of the most common anesthetic misadventures veterinarians experience is to give an alpha agonist (xylazine or medetomadine) to any patient other than a young, healthy one. I also had the recent experience of reviewing an echocardiogram from a dog with serious heart disease where one of the technicians had given BAG (butorphanol, acepromazine, and glycopyrrolate) to sedate the patient before consulting with the veterinarian. The dog’s heart rate was over 300, the echocardiogram was uninterpretable, and while there were no lasting adverse effects, I think it's lucky that patient survived.
Rule #1: Never perform diagnostics or procedures on a critically dyspneic patient unnecessarily. You should have a clear idea in mind as to when risk exceeds benefit and be ready to abandon a procedure.
Rule #2: When you need to find out, sedate first. A common clinical problem, for example, is dyspnea secondary to pleural effusion in a cat. You need to first determine that the effusion is present, and then remove it (thoracocentesis). Radiographs often only tell you that pleural effusion is the cause of the dyspnea, not the cause of the effusion. I can usually tell with a few seconds of echocardiography whether heart failure is the cause of the effusion. However I believe that this patient needs a thoracocentesis before any diagnostics and would give the sedation even before the flash echo. Diuretic therapy is far too slow and inefficient a treatment in this setting, and Lasix might even be contraindicated if heart failure isn't the root problem. After determining that effusion is the cause of dyspnea (radiographs, ultrasound, or trial thoracic aspirate), drain the thorax under sedation before any further diagnostics! If you've determined that heart failure is the cause, you can consider giving some IV Lasix and oxygenate the patient for a little while prior to thoracocentesis. This is to treat the undetectable pulmonary edema that may be present concurrently, not the pleural effusion per se. I would definitely give the Lasix (4 mg/kg IV) if the sedated patient wasn’t comfortable for the chest tap. I prefer to drain the thorax as much as possible, then get the chest radiographs if I don't know the cause of the effusion.
I use the Valium and butorphanol combination for any dyspneic animal before placing an IV catheter, taking an x-ray, doing an echocardiogram, or performing a pericardiocentesis, thoracocentesis, or abdominocentesis. It's certainly true that you may have to treat presumptively (no sedation) if you are convinced of the diagnosis (e.g. dyspnea and pulmonary crackles in a 12 year old poodle with an intense murmur). In other cases, you may need to sedate first (IM) even to get a blood sample or cursory physical.
Other cardiologists tell me they don't necessarily sedate for a pericardial or chest tap. It will take some convincing to sway me from my approach (sedation) while aiming a sharp device at the heart and lungs. These procedures can take 20-30 minutes and this is not a time when you want the patient to be moving unexpectedly. I also use this sedation just to improve study quality, e.g. radiographs, echocardiograms, or electrocardiograms in the young, fidgety, or trembling pet. When diagnosing atrial fibrillation on an EKG, for example, you need to be certain that the baseline undulations are from atrial activity, not patient squirming. With the stated exception (bradycardia), I do not hesitate to give diazepam and butorphanol to patients with the most serious of cardiac conditions (except bradycardia).