Intraoperative PNS

One of the more frequently used tools in the OR is the peripheral nerve stimulator (PNS). The battery powered device delivers depolarizing current via two electrodes. When properly placed, it can be used to evaluate the level of neuromuscular blockade in a patient and tell us when it is appropriate to use neuromuscular blockade reversal agents. One of the more commonly used devices is pictured below. The device is pretty intuitive to use, so I won't go into too many details. This tutorial is more focused on proper lead placement to optimize your results. Just know that the black represents the negative lead and the red represents the positive lead.

Early on in my education, I felt like it was one tool I was not using properly. In particular, my lead placement was kind of all over the place. There were often times when I would be getting no PNS response only to have the surgeon yelling about the patient moving moments later. Briefly, I am going to go over how to properly place the leads using the more common nerves. These are not the only nerves you can use, but they are utilized often because they exhibit a visible motor reaction when stimulated, are close to the surface of the skin, and are often easy to access during a variety of surgeries.

Ulnar Nerve: In general, this is your best option for evaluating a patient for extubation and reversal of neuromuscular blockade. When giving muscle relaxants, this nerve response will be the first to go and last to return. That means it is not a great indicator for intubation but gives a larger margin of safety when determining status for reversal and extubation.

For proper PNS, extend the arm in a relaxed state with the palm up. The two electrodes will be placed over the path of the ulnar nerve. The more distal and negative electrode is placed at the level of the wrist on the ulnar surface at the flexor crease. The positive lead is then place a few cm proximal to the first. See the image below.

Facial Nerve: When giving muscle relaxants, this nerve is one of the last responses to disappear and one of the first to reappear. For this reason, it can be reliably used for intubation (not something you will often see) but isn't the standard of care for extubation and reversal, even though the onset, duration, and sensitivity of the muscles stimulated are the same as most of the respiratory muscles.

The positive electrode is placed on face at the outer canthus of the eye. The negative lead is then attached a few cm beloe, at the same level of the tragus of the ear. See picture below.

Posterior Tibial Nerve: This nerve is often used in surgeries when the head of the bed is turned 180 degrees (craniotomy, ENT, etc). Sensitivity should be very similar to that of the ulnar nerve.

The negative electrode is placed more distally, just posterior to the medial malleolus. The positive electrode should be placed a few cm above the first, more proximal. See image below.

Nasal Intubation Guide

Introduction 

As a student, I found it very difficult to find a good guide online or in text books on how to setup and perform nasal intubations. This seemed very strange to me, as it is one commonly performed airway management techniques, especially in dental procedures and surgeries involving the mandible. Without knowing what to set up or how to prepare, nasal intubations always seemed like a very daunting task. This tutorial is here to bring it down to size. It really isn't much more difficult than a standard laryngoscopy, as long as you know what to do and how to prepare. This tutorial is here to show you a common setup and describe the procedure itself. Follow these simple steps and you'll be able to safely secure your patient's airway while providing adequate surgical exposure for the surgeon.

Setup

There are a few items from a standard ETT setup that you will want to make sure you have ready to go.

• Appropriately sized blade with working handle - Mac 3, Mac 4, Mil. 2, Mil 3. 
• Appropriately sized oral airway - It is vital that we are able to mask ventilate our patient.

Here's where things start to change up. There are a number of different items. Sometimes you can find them in the OR, other times you may need to go to pharmacy or the anesthesia techs for help.

• Pharmacy Nasal Pack - At some hospitals you can go to pharmacy and ask for a pack by name. They may have all the components compiled already, however, in some hospitals you may just have to ask for the individual components. 

1. Afrin nasal spray - This spray is an alpha adrenergic agonist. It causes vasoconstriction of the vessels in the nasal cavity to reduce the risk of bleeding. As you will see shortly, it can also be used to help us identify which nasal cavity in which to place the ETT.  

 

1. Lidocaine Jelly - Many practicioners will use this as lubricant for nasal trumpets and ETT. If not available, you can use a standard water based lubricant. 

• Magill forceps - They make a smaller version for pediatric patients. This will later be used to help advance the tube through the vocal cords.  

• Nasal trumpets of varying size - Some attendings like to use these to dilate out the nasal cavity before passing the ETT. If you look at the back of the packaging, usually the outside diameter will be labeled in mm. In the picture below, the size is shown as 9.3mm. The outside diameter of the ETT is usually listed on it's package as well. I like to compare the two and have one nasal trumpet with an OD just smaller than the ETT and then one about the same size OD or slightly larger. Before going to get the patient, you can cover the trumpets in the lidocaine jelly and leave wrapped in the package. 

• Nasal RAE endotracheal tubes - The ETT's are designed to pass through the nasal cavity, through the vocal cords, and can be secured out of the surgical field. A tube is pictured below. The sizing of nasal rae tubes generally follows the same guidelines as regular ETT's. It is a good idea, however, to have a size above and below what you anticipate using, just in case. 

• Warm bottle of NS - Before going to get the patient grab a warm bottle of NS from the core. If you don't know where to find it, ask one of the nurses, they should be able to tell you. Place the nasal rae tubes in the warm bottle of NS. It will make the tube more compliant ad easier to pass through the nasal cavity. 

In the pre-op area

In adults, you can take the Afrin nasal spray and ask them to spray it in each nostril themselves. Pediatric patients wont likely tolerate this and you will likely have to use the spray during bag mask ventilation. If the patient is able to use the spray in the preop area, take a look at their nostrils afterwards. In general, the nostril with the smaller diameter after using the spray will have the larger nasal cavity and will be ideal for placing the tube.

This is also a good time to look for any CT scans or images that may be useful. For one, it will be able to accurately give you an idea of the size of the nasal cavities and if there are any obstructions. Secondly, if the surgery is fixing a mandibular fracture, it is likely the patient will have a limited mouth opening. A CT scan can give you an idea if this limited opening is due to pain (in which case general anesthesia will relax the patient and it shouldn't be an issue) or if it is a physical obstruction related to the injury (this is more a cause for concern and should be discussed with your attending. If it really an issue, nasal fiberoptic intubation may be your next option).

In the operating room

Initially, you will do things as you normally would in the OR. Get the patient situated on the OR table and connect the standard asa monitors and begin to pre-oxygenate. While preoxygenating, it is a good idea to make sure that all of your supplies are ready to go. Open your Magill forceps, remove the ETT from the warm saline and put some of the lidocaine jelly/lube on the end of it, and lube nasal trumpets if you have not done so already.

Push your induction drugs when you are ready and asses if the patient is asleep. Once asleep, bag mask ventilate as you normally would. Feel free to turn on some volatile agent. While masking, tape the eyes and spray some afrin in the nostrils if you did not do so in the preop area. After you have done this, pass the smaller nasal trumpet into the chosen nasal cavity. Give a few breathes with thi sin place. Remove this trumpet and place the larger one and give a few more breathes. The nasal cavity should now be properly dilated and you are ready for intubation.

Take the nasal rae ETT and introduce into the nasal cavity. The tube should enter at a 90 degree andle to the OR table. It should pass easily. If you meet resistance, try to reposition or consider using the other nostril. Don't advance the tube too far just yet. At this point, take you laryngoscope and DL as you normally would to gain a view of the vocal cords. Once you have your view, ask for someone to advance the tube until it is in your field of view, if it is not already. Now take the magill forceps and place them in the oral cavity. You will use them to grab and direct the ETT in the direction of the cords. Just be careful not to grab the cuff, as you can rupture it. ALWAYS grab distal or proximal to the cuff. Once in line with the vocal cords, again ask someone to advance the tube and visualize it as it passes through the cords. Remove the blade and forceps, inflate the cuff, and connect your circuit. Once proper placement is confirmed, you can secure the tube. Sometimes the surgeon will stitch it in place, so ask them if this something that they are going to do.

Generalized Anesthetic Plan at TMC

Early in my education, I often had a difficult time looking at the bigger picture while taking care of patients in the operating room. It is easy to focus attention on skills and exciting surgeries when you are seeing many things for the first time and initially getting involved in airway and line management. One thing that really helped me was to write out anesthetic plans the night before and refine the details as you find out more information the next day when you arrive and have a chance to see the patient. To help you with this further, I have constructed a guide below describing how your setup and plan changes before a case as you learn more details about the specific case and patient. This post is very broad fairly basic. It is designed so that you should be able to understand it very early on in your education. You will learn that things are not always so straight forward and patient co-morbidities are more complex than they are portrayed to be here. However, this is a good starting place. Just be sure to ask yourself as you evaluate your patients in the preoperative area how each detail will impact your management, if at all. Take it step by step and it will being to come more naturally over time. As with many tutorials in this blog, most of the details are in reference to Memorial Hermann-TMC.

When arriving in the OR in the morning, the first thing I do before heading to my assigned room is grab a schedule. There are four main things I look at on the schedule that impact how I set up my room: The procedure being done, the age of the patient, the gender of the patient, and the weight of the patient (if listed).

M – Machine 

Machine check doesn’t change based on these factors.

S – Suction. 

Suction setup doesn’t change based on these factors.

M – Monitors 

For each case, I will automatically make sure we have standard ASA monitors BP cuff, pulse oximeter, and a 5-lead EKG. The other factors may change what else I have set up.
If the patient is much older, with possible underlying cardiovascular issues and/or the procedure listed is known to be invasive with the potential for lots of blood loss, I will make sure to have an arterial line set up and ready to go.

If it is a cardiac procedure or the procedure requires monitoring such as SSEP’s that would impact how much volatile agent we can use, I would consider getting a BIS in the room to help insure that the patient is not aware during the procedure.

A – Airway

At TMC I will usually have a general airway setup assembled on the anesthesia machine, but the factors on the schedule will impact what components I add and what I plan to use.

Is the patient male of female?: This will generally dictate whether I plan to use a 7.0 or 8.0 ETT. It will also impact what size oral airway I will plan to use.

What is the patient’s weight?: This will tell me if the patient is possibly obese and if I should get a video-scope in the room for intubation. If this is the case, I like to set up blankets on the bed to get the patient in a proper sniffing position, as well. Any advantage helps. Also, if it is a large male, I will consider using a MAC 4, as opposed to the Mac 3.

Does the procedure relate to a possible neck injury?: If it is imperative that we keep the patient’s neck stable, I can call for a glidescope or fiber-optic bronchoscope.

Is the indicated procedure working in the area of head and neck?: I can determine if I need to get any oral or nasal RAE tubes for intubation.

Is the procedure to be completed in the prone position?: If this is the case, I like to use benzo to help secure the ETT to prevent any dislodgment.

Is it a short, relatively non-invasive procedure?: I can consider just setting up and LMA of the appropriate size and plan to let the patient breathe on his or her own for the duration of the surgery.

Will the bed be turned 180 degrees for the procedure?: I can determine if I need to get an accordion for the ETT.

I – IV

I will always have a standard IV kit set up with a varying sizes of IV’s ranging from 16-20 gauge. In addition, I will prepare a few other things.

Is the patient coming from DSU?: If yes, I will not need to spike a bag of LR, since they will get one in the pre-op area.

Is the patient coming from ICU and/or is this an invasive procedure with potential for blood loss?: If this is the case, I will have a hotline spiked and ready to go to help with fluid resuscitation and to have the potential to give blood.

D – Drugs

Generally, I will set up syringes for Propofol, Lidocaine, Rocuronium, and Versed, and Fentanyl. It can be difficult to tell from the schedule if you will need a different set up from this other than if the patient is old enough that you might not want to give versed.

S- Special
Is it listed on the schedule that X-ray will be used? If so I’ll grab some lead from the tech room.
If it is an invasive procedure or if I know my attending likes it, I will consider getting some colloid in the room.

After the room is set up, I can finally head to the pre-op area to see the patient or to look up patient information if they are coming directly from their room or the ICU. This is the point when I can really gather some information and start to tailor a more specific anesthetic plan to the patient. Each section of the pre-op sheet will greatly impact our plan. This is usually the order that I actually go through the pre-op with the patient.

If not in DSU or pre-op holding and the patient is coming down from ICU, there is a chance that we will have to go and get the patient. If this is the case, I would go get a transport monitor from the tech room. I would also grab airway supplies and some emergency drugs in a large suction bucket to take with me incase anything happens during transport.

Verify surgery site- Once confirmed, you want to ensure that you don’t plan to have any IV’s or monitors that will interfere with the surgery or prep site.

Allergies- If the patient is allergic to latex or any medications you need to make sure that it is a true allergy and avoid these things. For medications, this means finding an alternative to what the patient is allergic to. For example, if the patient has a PCN allergy, I would consult with the surgeon and plan to avoid cephalosporins.

NPO Status – If the patient is deemed to have a full stomach (ate within a 8 hour period, is diabetic, is pregnant, or has a small bowel obstruction) and we are using a general anesthetic, the plan will automatically go to a GETA with a rapid sequence induction to prevent aspiration. This will include cricoid pressure, suction on hand, and succinylcholine (or rocuronium succ. Is contraindicated – ie. Elevated potassium levels, muscular dystrophy, recent burns, recent CNS trauma. It could also be advantageous to give pre-medications such as Pepcid, Reglan, and Bicitra.

Respiratory-

Recent cough or cold – May be better to postpone the surgery if it is an elective procedure. If not, be prepared that the patient may have a reactive airway more prone to laryngospasm and bronchospasm.

Asthma – If patient has asthma, and hasn’t used their inhaler that day, it may be wise to get an albuterol inhaler for them to use before heading back to surgery or giving a small dose of steroids. Keep a close eye on the capnograph waveform to see if patient has had an attack during airway management.

OSA – If patient has OSA and is non-compliant with a CPAP machine, they may live at a higher 

PaCO2 than the average person and it may take more to get them to breathe at the end of surgery. Also, prepare for a potentially difficult bag mask at the start and end of case, preparing oral and nasal airways as needed.

COPD - People with COPD are often smokers. Be prepared with suction for lots of secretions. These patients also live at a higher PaCO2 than the average person so it may be more difficult to get to breathe on their own at the end of the case. I would consider trying to limit my narcotics until the patient is breathing on their own, as to not further depress their respiratory drive. 

Cardiovascular –  

HTN – “Keep them where they live.” If a person normally has an elevated blood pressure, we want to keep them within 20% of that normal range, not 20% the average person’s value. This can be particularly important in people with chronic hypertension as they may have associated cardiovascular co-morbidities.

MI – It is important to ask what kind of treatments these patients have undergone, if they are symptomatic, and how recently they had a cardiac workup. If they have been doing well after their procedure, you may not have to be too concerned. Still may be advantageous to put in an A-line and induce with Etomidate to keep a tight control on BP and maintain perfusion to the coronary arteries. 

Pacemaker/defibrillator- Find out what type of implanted device they have and when it was last interrogated to ensure optimal function. Talk with the surgeon concerning electro-cautery to ensure patient safety. Make sure to have a magnet in the room to put the pacer in asynchronous mode or deactivate the defibrillator in the case of an emergency.

Murmurs/arrhythmias - Find out if they are on any medications for their arrhythmias and if they are currently in that arrhythmia. Know how to manage specific arrhythmias –ie keep a lower heart rate with people in A. fib to allow for adequate filling time of the atria.

Neurological –

TIA/CVA – In patients with TIA or CVA, find out when they have occurred and what precipitated it. They can be on anti-coagulant drugs that you need to be aware of and you will need to ensure adequate blood flow to the brain through maintaining adequate volume status and keep blood pressures from dropping to low.

Neuropathy – It is important to find out about preexisting neuropathies and make note of them in the pre-op chart. In these patients you need to be conscious of positioning as to not worsen any neuropathy, create new neuropathy, or cause ischemia. Many neuropathies can originate from the head or neck. If this is the case, plan accordingly as to get video airway equipment and stabilize the head and neck during intubation if necessary.

Seizures – If a patient has a history of seizures, be sure to find out how often they have them and what medications they are taking. Be prepared with midazolam or propofol on hand if you need to, at any point, acutely treat a seizure. Also, many of the medications that people take for epilepsy can increase the metabolism of paralytics that we give. If needed for the procedure, you may have to give more than you would to many of your other patients.

Head injury – Does the patient have an increased ICP from an injury to the head? How is their mental status at the start of the case? If the patient has an already increased ICP or is at risk for an aneurism rupture, you need to take proper measures to ensure that you don’t further increase ICP – keep stimulation minimal during intubation, limit volatile gases, use positioning to your advantage, use diuretics in needed, mildly hyperventilate the patient, etc.

Gastrointestinal –

GERD – If your patient normally has reflux, you need to find out if it is controlled and what kind of conditions normally trigger it. It is possible that they are at an increased risk for aspiration and your anesthetic plan needs to account for this. This can include things such as pre-medicating with Bicitra, Pepcid, and Reglan. Also consider doing a rapid sequence induction with cricoid pressure and starting with the patient in a reverse trendelenburg position.

Hiatal Hernia – Patients with hiatal hernias are increased risk for reflux and aspiration. Similar precautions as listed above need to be taken.

Metabolic –

DM – Patients with DM often have lots of other comorbidities, so be conscious of this. It is important to check glucose levels and make sure they are in a normal range before heading back to the OR to improve pot-operative outcomes. Be conscious of neuropathies and unstable mandibular and alanto-occipital joints when positioning and do not give drugs that will raise the blood sugar, before you consider all of the outcomes.

Sickle Cell – Patients with sickle cell disease have a number of perioperative issues. Generally, they are poor temperature regulators, poor oxygen carriers, and tend to be hypercarbic and acidodic. Things we can do you help with this as anesthesia providers is give plenty of fluid and blood (sometimes preoperatively), keep a warm temperature in the room, utilize Bair Huggers, and use higher percent Fi02 if needed.  

Thyroid issues – Whether it be hyper or hypothyroidism, find out if the patient takes a medication regularly to keep it in control. If they are symptomatic be conscious of issues such as myxedema coma for hypothyroidism and thyrotoxicosis for hyperthyroidism and how to treat these (for example giving propranolol as the first line of defense for thyroid storm). Thyroid goiters can also potentially lead to difficult airway management. May be beneficial to use video scopes or fiberoptic bronchoscopes.

Steroid use – It is important to find out what kind of PO steroids patients are taking, why they are taking them, and what dose they take it at. If they take them on a daily basis, it may be wise to give a stress dose of steroids at the start of the procedure to ensure that their vascular smooth muscle has an adequate response to endogenous and exogenous vasopressors.

Kidneys –

ESRD – There are a number of issues that are associated with ESRD patients that we need to be concerned with. One issue is access. It may be difficult to get IV access, so we need to make sure that we have as many working IV’s as we need. In addition we need to find out the patient’s dialysis schedule, when they were last dialyzed, and what their current volume status is. The amount of fluid that we can give them greatly depends on this. It is a delicate balance and we want adequate perfusion, but we don’t want to volume overload them. We will also need to check their electrolytes and use fluids – NS, Albumin, and PRBCs, as to not increase the levels of any electrolytes that we don’t want to. Patients may also be anemic due to lack of erythropoietin production. Finally, many drugs are partially metabolized and excreted by the kidneys and we want to avoid them due to adverse or prolonged effects (examples include merperidine and rocuronium). We need to find alternates to some of these drugs.

Liver –

A number of drugs are metabolized in the liver and may have a prolonged effect in people with liver issues. People with liver issues may also have problems with coagulation and you may anticipate more bleeding during surgical procedures. People with liver disease may have perfusion issues, various organ comorbidities, and issues with their lungs. It is important to be aware of all of these.

Medications – It is essential to find out what medications they are normally on and if their medical issues are normally pretty well controlled. It is also crucial to find out what medications they have recently taken (that morning, the night before, earlier that week). The following can impact our anesthetic plan.

Chronic pain medications – Pain management can be potentially difficult in these patients and require increased amounts of pain medication. It helps to find out the frequency and amount of what they take to determine if this might be needed.

Diuretics – Used to control BP, they can sometimes have an effect on electrolytes. Be sure to check labs and get anything in order that might be necessary.

ACE inhibitors and ARBs – These BP meds can mess with a patient’s electrolyte levels and also make keeping up blood pressures increasingly difficult in the OR. We may need to give more fluids and use stronger, direct acting vasopressors.

Anti-epileptics – In these patients, we may need to give increased amounts of muscle relaxant in order to keep them paralyzed throughout the procedure. It is also important to find out when they last took the medication. On occasion, you will need to give a dose in the OR.  

ASA- If the patient has kept taking ASA within a 7 day period, they may have issues with coagulation. It is possible that you can cancel the surgery but if not, keep an eye on blood loss and be sure to communicate with your surgeon throughout the procedure.

Inulin/DM meds – It is important to check glucose levels regardless of when they took their medication but this should give you a better idea of where it will be and if you need to take measures to control it (ie giving insulin)

Steroids – Patients that take steroids on a regular basis may need a stress dose of steroids in order to keep management on their BP.

Social History-

Alcohol – If the patient has a history of chronic alcohol use, be conscious of associated liver issues. Also, they may have a higher tolerance and require larger doses of anesthetics. If they are acutely intoxicated, they will need less.

Smoking – Smoking can lead to a number of respiratory issues, as discussed above in the COPD section.

Illicit drugs – Certain illicit drugs can impact the effect of agents that we give as anesthesia providers. Be conscious of this and find alternatives. For example, in cocaine users, ephedrine will not be as effective because of depleted NE stores.

Surgical History –  If during past surgeries, does the patient have history of:

PONV – Consider scopolamine patch, numerous IV anti-emetics (Zofran, Decadron, phenergen, etc). Also consider limiting opioids and running a TIVA instead of using a full MAC of volatile agents.

MH – If patient or family has history of MH, we need to avoid volatiles and Succinylcholine. This means flushing the anesthesia machine and planning to run a TIVA. If paralytic is needed, stick to Rocuronium or others. 

Surgeries that impact the airway – Has the patient been trached before or had surgery that might impact the airway and make for a difficult mask or intubation. Be prepared for the difficult airway algorithm.

Severe issues with pain control- Explore options with long acting narcotics or talking with the block to team to see if there is a possibility for them to work on post-op pain control.

Labs – Part of the anesthetic plan can be deciding what labs to get and then deciding what to do once you have a chance to view those values.

CHEM 7 – These values will let you know how the patient’s electrolyte levels and balances are, as well as giving an idea of kidney function. These values will let you if it is safe to go into surgery, if you can anticipate cardiac arrhythmias, if you should use specific drugs, and if you should use specific types of fluids (ie NS over LR).

Coags. – These values can give you insight to liver function, how much the patient might bleed during surgery, and if you should run further tests, such as a TEG, in order to know which blood products would be appropriate to give during surgery.

H and H – Low H and H values can let you know if your patient is optimized for surgery or if you may need to type and screen, type and cross, or even have some blood available in the room.

Tests  - Similarly to labs, part of the anesthetic plan is deciding what type of tests to run on a patient and then making decisions based on the results you find.

CXR – Can let you know the current state of respiratory issues of patients and follow the plan as listed above in the respiratory section. Can also let you know of any masses that might hinder your management of airway and patient ventilation.

EKG & echo – Good to check these in older patients, patients undergoing stressful surgeries, and patients with previous cardiac issues. Will let you know the current state of their heart and how to proceed according to the cardiac section listed above. 

All of these components are combined to create an anesthetic plan that is specific to each patient and each surgery.