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Paramedic of emergency medical service helping man after cardiopulmonary resuscitation. Themes help, hope a health care.
By Colby Costa, BS, NRP, FP-C, CCP-C
Patients with physiologically difficult airways are those requiring airway management who have underlying physiologic derangements putting them at higher risk for peri-intubation and post-intubation decompensation, including hypoxia, cardiovascular collapse, cardiac arrest, etc. Indicators of a physiologically difficult airway include physiologic derangements, including, but not limited to any of the following [1,2]:
- Hypoxemia
- Hypermetabolic state
- Hemorrhage
- Hypotension
- Right heart failure
- Severe metabolic acidosis
The presence of hypoxia before intubation provides evidence that the patient has a decreased oxygen reserve and an SpO2 near 90% increases risk of precipitous desaturation [3]. In hemorrhage, there is a decrease in total hemoglobin. Although high SpO2 levels can be easily reached in hemorrhagic shock, there is a decrease in peripheral oxygen delivery accompanied by a hypermetabolic state [4]. Critically ill patients are often in a hypermetabolic state in which cellular oxygen consumption is elevated. This can be the result of toxins, fever, inflammatory response, etc. In any of these physiologic derangements, the safe apnea time is shortened and there is a high risk for precipitous desaturation.
The effects of induction medication and initiation of positive pressure ventilation (PPV) can cause decreased cardiac output (CO) and vasodilation, negatively impacting hemodynamics. The transition to PPV increases intrathoracic pressure, which strains the right ventricle and decreases CO. Hypotension before intubation creates a lesser threshold of hemodynamic impact to proceed into hemodynamic collapse. Similarly, underlying right heart failure causes a greater hemodynamic impact on the initiation of positive pressure ventilation, which can lead to a drastic reduction in cardiac output and hemodynamic collapse [5].
In acidosis, oxygen has a decreased affinity and increased unloading to hemoglobin, complicating preoxygenation. Severe metabolic acidosis is normally accompanied by compensatory respiratory alkalosis. This compensatory mechanism involves rapid deep breaths resulting in a high minute volume which is difficult to replicate with mechanical ventilation. The increase in CO2 resulting from the apnea period and decreased minute volume causes worsening acidosis that can lead to hemodynamic collapse [6].
| More: On-Demand Webinar: Plan C: Navigating the difficult airway
Nearly all pre-hospital intubations are performed in critically ill patients with at least one, often multiple, of these physiologic derangements present. Although some of these factors can be identified in the field, often they cannot, and other physiologic derangements can result in difficult airway management. Knowing this, why arrent all pre-hospital intubations performed as if they are a physiologically difficult airway?
RSI
Rapid-sequence intubation (RSI) is the simultaneous or near simultaneous process of induction and administration of paralytic medications to facilitate intubation. RSI has been the standard for emergent airway management and has been considered one of the most advanced skills performed by a few advanced pre-hospital programs. Sedation-only intubation is still present in many services, but it has become well-supported that RSI has higher success with fewer complications [7,8].
Many pre-hospital services have begun adapting RSI protocols and although this shows an advancement in care, more techniques are available that could further enhance abilities.
DSI
One technique is delayed-sequence intubation (DSI). DSI is the separation of induction and paralytic administration to allow for procedures or interventions to be performed.
During DSI, ketamine is the induction agent of choice as it does not blunt spontaneous ventilation or airway reflexes. Many critically ill patients experience altered mental status or agitation secondary to hypoxia, hypercapnia, encephalopathy, etc. This can create difficulty in performing critical interventions such as vascular access, medication administration and preoxygenation, as these patients are often uncooperative and unable to tolerate non-rebreather or NIV masks.
After induction, patients are sedated, and these interventions can be performed without interference from the patient. Many patients with severe tachypnea and shallow respirations even tend to improve their ventilation status with slower, deeper and more effective respirations [9-11]. This allows for better preoxygenation and the effects of some physiologic derangements can be minimized. The only randomized trial comparing RSI and DSI showed DSI to have higher first-attempt success and SpO2 level before intubation with a decrease in hypoxic events when compared to RSI with no difference in hemodynamic effects of airway-related adverse events [12].
Preoxygenation
Previously, preoxygenation was emphasized by providing 100% FiO2 to increase oxygen content and denitrogenation to prolong the safe apnea time. Noninvasive positive pressure ventilation (NIPPV) has been a long-standing treatment in the management of hypoxic and hypercapnic respiratory failure; however, it has not been a standard method of preoxygenation.
A recent pragmatic randomized control trial compared standard preoxygenation (NRB and NC) to NIPPV preoxygenation, excluding crash airways. The study showed NIPPV to be superior in nearly all applications. Major takeaways from the study include occurrences of hypoxemia, cardiac arrest, SpO2