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Wednesday, June 19, 2013

By Michelle Gerhard Jasny V.M.D.
Published: June 4, 2009

As the nurses prepped my husband for surgery, I grilled the anesthesiologist. Did he know about Max's hypertension? His glaucoma? What kind of anesthesia was planned? "I'm a veterinarian," I explained, apologetically, "which means I know just enough about what you do to be scared."

The doctor patiently answered my questions, then remarked kindly, "I'm amazed by veterinarians. You have to do all the jobs - diagnostician, anesthesiologist, surgeon."

"Well, your job is the one I like the least," I admitted. Anesthesiology has been described as hours of utter boredom punctuated by moments of sheer terror. It's the terror part I don't like so much.

My very first clinical rotation as a senior at the University of Pennsylvania School of Veterinary Medicine was anesthesiology, and because UPenn cared for the animals of the Philadelphia Zoo, one of my first cases was a kangaroo undergoing cataract surgery. After assisting induction and intubation of the big marsupial, I was relegated to the role of charting heart rate, respiration, and temperature, and trying not to nod off. When one eye was completed, the surgeons informed the anesthesiology team it was time to reposition. Adjusting our tubes and wires, we rolled the kangaroo from one side to the other. As her legs flopped over, I watched and waited for her chest to rise as she inhaled so I could resume my chart-keeping. "Hey," I called out after a minute, "she's not breathing." The real anesthesiologists immediately sprang into frenetic activity all around me. Hours of boredom. Moments of sheer terror.

Anesthesiology is the art of creating a reversible and controlled loss of bodily sensation with or without loss of consciousness. It is something your veterinarian does routinely for spays, neuters, dental cleanings, and miscellaneous surgery, ranging from cut feet to emergency splenectomies.

Let's talk about your dog. Let's call him Max (because, as my husband says, we know more dogs named Max than people.) Say Max arrives at my office with a big gash on his leg that clearly needs stitches. I will often suggest a local anesthetic for such minor mishaps. After cleaning the wound, a numbing agent is injected directly into the area. The first poke is uncomfortable, but after that the numbness spreads quickly and usually makes it easy to complete the job. Local anesthetics are great for cooperative patients with superficial wounds.

Nerve blocks are another form of local anesthesia in which the numbing agent is injected at the nerve that supplies the affected area, like when the dentist gives you a shot of Novocaine. Local anesthesia is quick and easy. Side effects are very rare, and patients generally walk out of the office under their own steam in short order.

But what if Max won't hold still or needs a complicated procedure requiring him to be completely immobilized? Now we're talking general anesthesia, i.e., drugs that will cause loss of consciousness. In veterinary medicine such drugs are often administered by intramuscular or intravenous injection. Intravenous drugs may be given as a single bolus, or carefully titrated "to effect." An intramuscular shot is a good choice for easy administration to agitated or aggressive patients. Several drugs may be used in combination to achieve the desired balance of pain control, immobility, and unconsciousness. Some drugs can be chemically reversed, allowing a veterinarian to anesthetize Max briefly then wake him with a second injection. In a healthy, stable animal, injectable anesthetics are great choices for minimally invasive, routine procedures.

But what if Max is seriously ill, or old as the hills? What if, God forbid, he has heart problems, or failing kidneys? What if the surgical procedure is extremely invasive, or of unknown duration, such as an exploratory laparotomy where the surgeon doesn't know what she may find until she begins? In such cases, inhalation anesthesia is necessary. The first inhalants used in modern Western medicine were drugs like ether, chloroform, and nitrous oxide. Today we use inhalants like isoflurane and sevoflurane, but the principle is the same.

Max may first be given injectable preoperative medications designed to calm him, then a short-acting induction agent to render him sufficiently unconscious for intubation, i.e., the placing of a flexible tube into the windpipe. Because animals under general anesthesia may have a reduced or absent gag reflex, the tube has an inflatable cuff that seals it in place, preventing Max from aspirating any secretions, saliva, or stomach contents should he vomit. (Obviously, fasting prior to anesthesia is ideal, but not always possible in emergency situations.) The endotracheal tube is attached to an anesthesia machine, where oxygen passed through a vaporizer creates a controllable concentration of anesthetic gas.

The gas is delivered to the patient's respiratory system via the endotracheal tube, or in some cases a simple face mask, where it is rapidly absorbed into the bloodstream. Depth of anesthesia can be raised or lowered fairly rapidly by adjusting the concentration of gas.

This is all pretty straightforward. The vast majority of anesthetic procedures go off without a hitch...but kangaroos happen. Our exotic patient had gone into cardiac arrest and could not be revived, despite the best efforts of a team of experts.

The reality is that there is no such thing as 100-percent "safe" or "routine" anesthesia. The challenge is to find the balance. It doesn't make sense to be so worried about anesthesia that Max doesn't get necessary surgical care. For your average patients, trust your veterinarian's advice and try to relax. If you have an extremely high-risk pet, and are willing to spend extra time and money, specialty practices can offer expertise and state-of-the-art options to which your regular veterinarian may not have access. In any case, remember that anesthetic complications and deaths are rare and that the art of modern anesthesia is a blessing that allows us to humanely perform a multitude of beneficial and life-saving procedures.