I am currently in the process of updating a class in Studio called "Little Obese Adults." The concept behind this class is to parallel the desaturation, chest-wall/lung interactions, and pre-oxygenation techniques with a patient who is morbidly obese. After all, they desaturate at a similar rate.
The reason desaturation occurs rapidly after apnea is due to a reduced functional residual capacity (FRC). This is the amount of air left in your lungs at the end of exhalation. Once a patient becomes apneic, the FRC becomes the sole source for the alveoli to pull oxygen from. I think of this volume as the size of the self-contained breathing apparatus (SCBA) that divers and firefighters use.
In the morbidly obese population, the chest wall has excessive adipose tissue that weighs down on the chest wall. The larger abdomen also displaces into the diaphragm when laid in the supine position. The combination of these results in decreased lung inflation and, if left unresolved, atelectasis. The reason this occurs in pediatric patients is a little bit different, but the mechanism is similar. Kids have very compliant ribs, and those pliable ribs decrease how much the chest wall can hold up the lungs when a child is apneic and supine.
The goal of pre-oxygenation is to set yourself up with a safety net of lung recruitment and oxygen reserves to avoid rapid desaturation during the intubation attempt. How this is best done depends on whether or not the child will tolerate the pre-oxygenation process. Because children often resist the pre-oxygenation period, sedative agents are administered to facilitate nasal cannula or non-rebreather. Sometimes, the provider may try to justify just using blow-by oxygen as a pre-oxygenation strategy. Unfortunately, the agent used to help facilitate these techniques tend to cause shallower ventilations that get closer and closer to their functional residual capacity. Here is a mental model of how specific medications cause a reduction in tidal volume over time. This graph is based purely on my anecdotal experience.
Ideally, the provider will utilize BVM ventilations during pre-ox to recruit the most amount of lung and not dip into the functional residual capacity before apnea. Since assisted ventilations are preferred, induction agents with a longer half-life that reduce anxiety and facilitate pre-ox are preferred. This is why ketamine tends to be popular in this scenario.
Avoiding excessive pressures ( >20 cmH2O) when providing BVM ventilations during pre-ox is important to prevent gastric insufflation. For this reason, a manometer is an essential piece of equipment on the BVM. I did a review on a few different pediatric variations to the BVM. You can check it out below:
It is important to pull the face to the mask as opposed to pushing the mask down into the face. Knowing the tongue is attached to the mandible, displacing the mandible into the hypopharynx can cause an airway obstruction that increases manometer pressure without or with inadequate chest rise.
Apneic Oxygenation (ApOx) in Kids
ApOx has become the standard of care when intubating adult patients. This is typically done by placing a standard nasal cannula on the patient and turning the oxygen to a flush rate. The idea behind this concept is that by having a steady flush rate of oxygen flowing into the hypopharynx, the CO2 within that dead space will be washed out and replaced with oxygen. The alveoli can hopefully absorb that oxygen when the provider attempts intubation and the patient is apneic.
Safe Flow Rates
While there is not enough data to recommend a specific flow rate, multiple studies have evaluated this technique's safety profile at low and high flow rates with no recorded adverse events except a small study by Vukovic that stated: "four patients demonstrated the inability of providers to obtain an effective seal during BVM ventilation." As you can see from the table below, the flow rates were all over the place in terms of LPM. The Humphreys study utilized an actual high-flow nasal cannula (HFNC) with humidified oxygen. While this technique is ideal, it is likely not pragmatic for standard ALS crews because of equipment. It does appear that higher flow rates show a higher statistical significance in apnea times without desaturation.
I think the flow rate protocol that makes the most sense to me is the one proposed by Napolitano et al. They used 5 LPM for < 1 year, 10 LPM from 1-7 years old, and 15 LPM for anyone 8 years or older.
Utilizing the current evidence, I came up with the following mock guideline. This is NOT a recommendation but rather a mental model.
Properly pre-oxygenating your patient prevents precipitous drops in oxygen saturations and associated complications. A solid pre-ox plan will make it much easier when trying to pre-oxygenate a combative child who keeps ripping out their IV and nasal cannula.
A Note on Ketamine for DSI
It is important to remember the complications that can arise from ketamine (especially if you push it too fast). In some circumstances, the provider may decide to administer ketamine IM because an IV has not been able to be established or to prevent a combative child from causing the provider to naturally push the ketamine too fast into an established IV.
Some may also prefer an agent such as midazolam to facilitate pre-oxygenation.
If your agency has a specific guideline for pediatric pre-oxygenation, I would love to hear from you! You can email me at firstname.lastname@example.org.
Dancy, Mark A. MSN, RN, CPNP-AC, CFRN, CEN, CPEN. Efficacy of Apneic Oxygenation During Pediatric Endotracheal Intubation. Pediatric Emergency Care: October 2021 - Volume 37 - Issue 10 - p 528-532 doi: 10.1097/PEC.0000000000002539
Noce, J., Olvera, D., & Davis, D. (2022). The optimal preoxygenation target to avoid desaturation during pediatric rapid sequence intubation. Air Medical Journal, 41(1), 26. https://doi.org/10.1016/j.amj.2021.08.021
Scott, A., Chua, O., Mitchell, W., Vlok, R., Melhuish, T., & White, L. (2019). Apneic Oxygenation for Pediatric Endotracheal Intubation: A Narrative Review. Journal of pediatric intensive care, 8(3), 117–121. https://doi.org/10.1055/s-0039-1678552