The 7 steps of a case analysis in anesthesia

Anesthesia Equipment Problems that Masquerade as Patient Problems

Much of my consulting time is spent responding to inquiries about adverse anesthesia events. My colleagues reach out because they want to understand what has gone wrong in the hopes of preventing a recurrence. This review process really helps clinicians enhance their understanding of anesthesia.

Here is an example of an adverse event that demonstrates how sometimes what appears to be a medical problem is actually an equipment problem (You’d be surprised how often this happens).

My patient won’t stay asleep!

Even healthy patients can throw us curve balls during anesthesia. This particular scenario cropped up during a recent hands-on anesthesia workshop. I was instructing a group of vets and technicians. We were exploring the components of anesthesia safety while delivering anesthesia to healthy dogs and cats undergoing elective procedures.

A nicely premedicated 4 kg lean, young adult female cat (healthy on physical exam and history) is uneventfully induced with IV propofol while receiving oxygen supplementation by face mask, is then intubated (using a laryngoscope) and placed on 1 liter/minute oxygen flow rate through a Bain circuit for maintenance inhalant anesthesia with isoflurane in preparation for spay surgery.

Surgical prep and local anesthetic placement take about 15 minutes (we were teaching 😊) and are conducted outside the surgical suite. During this time, anesthesia is uneventful and stable. The patient is then moved to the operating room. That’s when all the fun starts.

About 2-3 minutes after relocating to surgery, the patient develops a brisk palpebral reflex, rapid breathing and tachycardia indicating that anesthetic depth is insufficient. We attribute the change in depth to stimulation during the move to surgery. Additional IV propofol is administered and the delivered concentration of isoflurane is increased. Everything settles down until 2-3 minutes later, the patient again begins to move. So we give additional IV propofol to regain control. This scene repeats itself over 10 minutes. By the fourth IV propofol top-up and vaporizer setting adjustment, the anesthetist notices that the patient’s mucous membranes are no longer as pink as they were at induction (the beginning of hypoxemia). At this point, the astute anesthetist also notices that the anesthesia machine is set up incorrectly – the oxygen/isoflurane mixture is being delivered to the pediatric circle system but the patient is connected to the Bain circuit.

The anesthetist quickly switches out the Bain circuit and connects the patient to the pediatric circle. Mucous membrane colour returns to normal (PHEW!). Surgery and recovery then proceed uneventfully.

In our group discussion after the patient was extubated and awake, we reviewed 7 potential rule-outs that needed to be considered in a situation where a patient won’t stay asleep.

Let’s explore each of these possibilities:

1. Had the patient been agitated before the beginning of induction?

Nope, she’d had a smooth loss of consciousness and transition from injectable to inhalant anesthesia. Sometimes, induction can be stormy. The patient becomes agitated and combative during handling because of insufficient chemical restraint. I find that when the patient has this kind of induction experience, the surge of adrenalin (think fight or flight response) acts as an “upper” and interferes with the patient achieving a proper and stable plane of anesthesia. It can take me up to 30 minutes to calm things down. As long as I have verified that nothing is wrong with the equipment and that my patient’s vital signs don’t suggest cardiovascular depression (usually its the opposite), I forge ahead and remind myself yet again why it is so important to use effective premedication.

2. Was the anesthesia machine set up properly?

In this instance, the anesthesia machine was the source of the problem. We had performed a proper function test on the anesthesia machine in the surgical prep area but no one had thought to check the machine in surgery and verify which circuit this cat was supposed to be connected to – she would do well on either a Bain or a pediatric circle so it was just failure to communicate that got us into trouble.

At this point, you might wonder why it took a whole 10 minutes for hypoxemia to develop since the patient was not receiving any supplemental oxygen in the operating room. Two reasons: First, she had been receiving 100% oxygen in the prep area which meant that she had a reserve of oxygen in her lungs to rely on after disconnection from the prep room machine. Second, there was enough oxygen in the room air of the Bain circuit hose to provide oxygen delivery for a little while.

3. Had the ETT shifted during transport?

This was a distinct possibility given that hypoxemia did eventually develop: If the endotracheal tube is accidentally pushed further down the trachea because of jostling during transport, it may enter a bronchus whereby the patient receives oxygen only to one lung rather than two. This is an important rule out when your healthy patient is successfully intubated and is receiving oxygen through the anesthetic machine and yet starts to turn blue. Two other observations by the anesthetist can increase their suspicion that this has happened: a) the partially full reservoir bag is barely moving with each breath and b) when the reservoir bag is squeezed to provide ventilation support, it feels “tight” as if it is hard to deliver the breath. When the endotracheal tube is gently retracted, there is a rapid return to normal.

Proper placement of the endotracheal tube requires that the cuffed end of the tube be outside the thoracic inlet – cranial/forward of the point of the shoulder. You can use the point of the shoulder as an external landmark when assessing tube length in advance. It is easy to advance the endotracheal too far, especially in cats and cat-sized dogs unless you shorten the ETT length beforehand. Practice tip: after securing the ETT, take a moment to observe the alignment of one of the ETT’s external markings with one of the teeth such as an upper canine. Over the course of the procedure, you can then easily and quickly verify that your tube has not moved – especially useful during long dental procedures when the patient’s head may be repeatedly repositioned.

Esophageal intubation is another possibility here. It can happen surprisingly easily, especially if a laryngoscope is not being used (or used properly – you should be able to clearly see the arytenoid cartilages). It seriously interferes with oxygen delivery for obvious mechanical reasons. However, if the patient is able to get room air into its lungs by inhaling around the tube, then hypoxemia may take a surprising amount of time to develop (10+ minutes if oxygen is delivered by mask before and during induction) or may not develop at all. The patient will just keep waking up because no isoflurane is reaching the brain.

If esophageal intubation occurs at induction, the anesthetist will be unable to obtain a proper seal around the tube cuff despite filling the cuff to excess. The patient will likely keep waking up in the prep area. However, I had one situation where someone other than me intubated the patient, and because we were so fast with prep and we had a heavy premed on board, the patient didn’t start to wake up until we were in the process of placing the drapes in the OR. Whenever I need to verify proper ETT placement (immediately after intubation and any time it looks like to tube has shifted, I simply palpate the throat: if I can identify only one rigid structure, then the ETT is in the trachea. If I identify two rigid structures then the ETT is in the esophagus. Quick, easy and fail-safe.

Esophageal intubation may happen in transit if the ETT starts to fall out of the mouth and someone quickly pushes it forward to reposition it. It is very easy to advance the ETT into the esophagus.

4. Was the vaporizer empty?

Easy enough to rule out and part of the pre-surgical function testing process for the anesthesia machine. The vaporizer does not need to be completely full. If you detect any amount of liquid in the vaporizer window, there is sufficient inhalant to get you through the procedure. So, the vaporizer is not the issue. If you don’t see any fluid at all then you may have a problem. Remember to check both the machine in prep and the machine in the OR.

5. Was the flowmeter on and delivering oxygen?

Always a good idea to verify that there is sufficient pressure in your oxygen tanks. When you turn the oxygen on, you should see the flow indicator rise in the flowmeter tube and you should also be able to detect an increase in the size of the reservoir bag.

6. Could the patient have an unknown subclinical medical condition?

This needs to be considered but I would not put it high up on my list of possibilities since the patient was asymptomatic at presentation and did well under anesthesia for at least 10 minutes. For a pre-existing condition to be bad enough that it can cause hypoxemia during delivery of 100% oxygen, it would have to also cause detectable symptoms in the awake patient as long as someone takes the time to perform a physical assessment. Having said that, remember that the chest does not give up its secrets easily and no one has ever said “I knew I shouldn’t have taken that x-ray!” When in doubt, take chest x-rays, preferably before anesthesia.

7. Had the patient experienced an adverse reaction to the repeated propofol injections?

Again, the timing was wrong – the patient had received propofol at induction without any ill effects. Had there been an issue with the propofol, symptoms would have manifested shortly after injection. Repeated propofol injections are not an issue since propofol is quickly cleared for circulation and does not build up. When I witness anaphylaxis from induction drugs, the symptoms show up in the prep area and include sudden hypotension and tachycardia along with (sometimes) edema or a rash on various parts of the body and evidence of bronchospasm on the capnograph display. There may or may not be hypoxemia depending on how bad the bronchospasm is.

Key to understanding the gravity of this particular situation was focusing on the development of hypoxemia in an otherwise healthy cat. Hypoxemia is a life-threatening emergency. Once it is detected, there is little time to correct the problem before the patient is put at risk of permanent harm. Hypoxemia quickly made me think about equipment problems, especially since we had just moved to a different anesthesia machine and up until then, anesthesia had been pleasantly boring.

We don’t need any extra drama during anesthesia and surgery. There is enough excitement even when things go well. So, be sure to verify that all your equipment is in proper working order and do this before every case, not just at the beginning of the day. Since there are so many aspects of our work and our patients’ conditions, we owe it to ourselves to control what we can. This approach to anesthesia delivery will help us troubleshoot effectively when the unavoidable curve balls get thrown at us.