Sunday, April 11, 2021

Airway Management/Respiratory Failure Case File

Posted By: Medical Group - 4/11/2021 Post Author : Medical Group Post Date : Sunday, April 11, 2021 Post Time : 4/11/2021
Airway Management/Respiratory Failure Case File
Eugene C. Toy, MD, Manuel Suarez, MD, FACCP, Terrence H. Liu, MD, MPH

Case 8
You are called to manage the airway of a 22-year-old male boxer who is admitted to the ICU for inspiratory stridor after suffering from head and neck trauma during a professional boxing match earlier that evening. He is suffering from rhabdomy­olysis and a concussion. He is confused about the timeline of events that night. ACT scan of his brain reveals mild cerebral edema and no evidence of intracranial bleeding. He is responsive to deep voice stimuli. He is 72 in tall and 80 kg in weight . 

What is the most important initial step in the management of this patient?
What are other management considerations?

ANSWER TO CASE

Airway Management/Respiratory Failure

Summary: This 22-year-old boxer has inspiratory stridor, which indicates impending respiratory failure due to upper airway obstruction or collapse. 
  • Most important initial management: ( 1 ) Rapid-sequence intubation (RSI ) to protect the airway; ( 2 ) avoid the use of a nasal gastric tube (NGT) since this patient has facial trauma, and there is risk of perforation of the cribriform plate by the NGT. Insertion via the mouth is the preferred option. 
  • Other steps: Chest x-ray to evaluate the trachea and correct placement of the endotracheal tube (ETT) as well as pneumothorax. If cerebral edema is present, high minute ventilation should be used to produce a respiratory alkalosis to decrease intracranial pressure ( ICP) . Positive end expiratory pressure ( PEEP) should not be excessive to avoid increasing ICP. Propofol is indicated for induction and sedation since it lowers ICP, has anti-seizure activity, and has a rapid elimination profile allowing for accurate assessment of the CNS status.
ANALYSIS

Objectives
  1. To understand the indications and contraindications for endotracheal intubation (ETI ) .
  2. To understand alternative methods for airway control.
  3. To understand the most common complications of endotracheal intubation.
  4. To understand the required steps and tools for endotracheal intubation.
Considerations
This 22 -year-old boxer presents with head and neck trauma and shows inspiratory stridor, which portends possible airway collapse. This requires RSI for the protection and control of the airway. A "wait and see" attitude in this patient would likely lead to devastating consequences. A nasogastric tube may be required to reduce the likelihood of aspiration of blood. Aspiration precautions were begun with elevation of the head of the bed to 45 degrees upright. Mechanical ventilation is begun on assist control (AC) mode of 22 breaths/minute with a tidal volume of 500 mL with a 100% Fro2 , and a PEEP of 5 . A higher minute ventilation is prudent to decrease intracerebral pressure.

Approach To:
Airway Management/Ventilator Support

INTUBATION IN CRITICAL CARE SETTINGS
The most common indication for endotracheal intubation (ETI ) is to treat hypoxic respiratory failure and hypercarbic ventilatory failure. The initial treatment for hypoxia begins with the insertion of a low-flow nasal cannula and the delivery of about 3 % per liter of Fro2 then escalating to 1 00% with the use of a non-rebreather mask or high-flow 02 therapy. Patients with impaired consciousness and an inability to protect their airway have secondary indications for ETI. One should assure that the patient does not have any documentation where endotracheal intubation and mechanical ventilation have been refused or where a do-not-intubate ( DN I ) or do not resuscitate ( DNR) order exists. The patient's wishes or those of the family or the legal guardian should be considered prior to further invasive measures. Other secondary indications for ETI include the significant aspiration of particulate matter.

ETI may be indicated for patients requiring bronchoscopy and pulmonary lavage, those with neurological or traumatic injuries who need deep sedation and intubation to perform necessary imaging tests or diagnostic and therapeutic procedures, and for individuals with status epileptics who require deep sedation or paralysis for treatment of seizures.

Endotracheal Intubation
Endotracheal intubation (ETI ) is the definitive method for control of the airway, and a common procedure for patients undergoing general anesthesia. The laryngeal mask airway (LMA ) , device that does not require a tube through the trachea or a laryngoscope for placement, and is an alternative for patients scheduled for shorter surgeries. The LMA is a short ETT-type tube that is surrounded and held in place by a laryngeal mask. The apex of the mask, with its open end pointing downward toward the tongue, is pushed backward toward the uvula. The LMA is effective as a short-term option and does not require as much expertise for placement as ETI. Those patients who may need airway control range from those scheduled to receive anesthesia to critically ill patients with multi-system disease or injuries. Emergency situations such as cardiac or respiratory arrest also require the need for ETI . It is effective in situations to protect the airway from aspiration, address inadequate oxygenation or ventilation, and for patients with existing or anticipated airway obstruction. These indications are increasingly more complicated in an era of advanced technology in oxygen delivery systems and noninvasive forms of ventilation. These forms can be divided in 3 basic categories: ( 1 ) hypoxic respiratory failure (decreased Po2), (2) hypercarbic ventilator failure ( including cardiac arrest) , drug overdose ( elevated Pco2 ) , and (3 ) impaired level of consciousness, requiring airway protection to prevent aspiration.

The excessive presence and inability of the patient to clear secretions are more important indicators for airway protection and ETI than is absence of the gag reflex. The lack of a gag reflex is not a sensitive predictor for ETI for airway control.

Checking o f the gag reflex should b e performed with suctioning equipment i s at hand, since it may induce vomiting and cause aspiration. The accumulation of large amounts of secretions in the oral cavity, without ability to clear, is an indication for ETI. If the patient can speak, is cooperative, and responds to verbal questioning, then one should consider a trial of NIY (noninvasive ventilation) , provided it does not delay an eventual ETI. The assisted ventilation provided from NIY therapy can provide additional time for the treatment of underlying medical conditions with steroids, bronchodilators, diuretics, nitrates, or other medications.

Hypoxic Respiratory Failure
Hypoxic respiratory failure or Type 1 hypoxic respiratory failure is defined as hypoxemia without hypercarbia. An impairment of oxygen exchange via the pulmonary alveolar capillary membrane ( >A-a gradient) results in hypoxemia, leading to a diminished delivery of oxygen to the cells and tissues. A quick and easy way to calculate the A-a gradient is shown later. You should not have a negative A-a gradient as determined by the equation:

A-a gradient = (F102 X 7 ) - PA02 - (PAC02 X 1.2 ) normal is <20 mm Hg


The initial treatment of all causes of hypoxemia includes: (a) ensure a patent airway, (b) provide adequate ventilation, and (c) provide supplemental oxygen. A PAO2 value of 60 mm Hg or an arterial oxygen saturation of 90% to 92% is often suggested as a minimal accepted value. Patients with hypoxemia will improve upon delivery of increasingly higher F102 , indicating VQ mismatch as the underlying pathophysiologic cause. If the hypoxemia is resistant to high F102 concentration, the most likely cause is shunting (eg, ARDS ) .

The treatment of hypoxia begins by ensuring a patent airway for adequate ventilation and oxygenation of the patient. Trials of noninvasive ventilation (NIV) may be indicated, but this should not delay intubation and MV if needed. If the O2 saturation fails to improve on 100% F102, then ETI and MV should be undertaken so PEEP can be administered.

Hypercarbic Ventilatory Failure (PACO2)
Hypercarbic ventilatory failure occurs when there is an inability to remove carbon dioxide (CO2) from the alveoli. This condition may be the result of a primary lung disorder or secondarily associated with cardiac, neurologic, or metabolic causes.

The symptoms and signs of hypercarbia are explained by the fact that increasing PACO2 results in vasoconstriction, confusion, sedation, and acidosis. Diagnosis of hypercarbia is confirmed with an ABG with a PACO2 >45 mm Hg and significant acidemia secondary to the elevated PACO2- The rate of change in PACO2 will affect the signs and symptoms. If the change in PAco2 is gradual, then the onset of symptoms such as lethargy, headache, and confusion will be more gradual. However, if the PACO2 rapidly changes, then the onset of symptoms will be more pronounced. Treatment of hypercarbic ventilator failure includes supplemental oxygenation and ensuring that the patient has a patent airway. The treatment should be specifically directed toward the underlying etiology. If the patient's condition does not improve with the initial treatment, then increasing the minute ventilation is necessary.

Noninvasive positive pressure ventilation should be attempted first unless there is an obvious need for an ETI. The indications for progressing to ETI are ventilatory failure despite CPAP, signs of impending respiratory failure such as increasing dyspnea, tachypnea, the use of accessory breathing muscles, and low tidal volume ventilation.

Impaired Consciousness and Airway Protection
Patients with Glasgow coma scale (GCS ) values of 8 or less should be intubated because of diminished levels of consciousness, continued hypoventilation, and a need for airway protection. Comatose patients have decreased respiratory drive, hypoventilation, airway obstruction and the decreased ability to clear secretions. Thirty percent of the patients with subarachnoid hemorrhage and traumatic brain injury are likely to develop pulmonary edema, severe acute adult lung injury, or ARDS. When there is concern of increased ICP and uncal herniation, hyperventilation with alkalosis has been shown to be helpful by inducing cerebral vasoconstriction. Propofol for sedation has also been shown to reduce intracranial pressure. Prolonged hyperventilation for prophylaxis of ICP should be avoided because of the risk for ischemic brain injury. Other indications for ETI include traumatic injury or swelling to the face or neck, or other obstructive airway processes.

Contraindications to Endotracheal Intubation
Because of the urgency for ventilatory support or airway control, relatively few contraindications exist for ETI . Direct laryngoscopy is contraindicated in patients with partial transection of the trachea because this can cause a complete loss of the airway. In this situation, one should consider establishing a surgical airway. If the cervical spine is unstable to bending as in RA, then strict, inline stabilization of the cervical spine is needed and must be maintained during ETI to avoid cord injury and paralysis. Of note, video-assisted ETT placement has reduced the need to hyperextend the neck during intubation.

Special Considerations
Before intubation, all the necessary equipment must be at hand. The recommended equipment includes: gloves, protective face shield, suction system, bag-valve mask attached to an oxygen source, ETT with a stylet, 10 mL syringe, ETT holder, end tidal carbon dioxide detector, stethoscope, and laryngoscope with blade or new fiberoptic technology. The fiberoptic laryngoscope allows visual guidance of the blade and observing the insertion of the ETT past the vocal cords. The two common types of blades currently in use are the Miller straight blade and the curved Macintosh blade. ETTs are available in different internal diameters: 7.0, 7.5, and 8 mm. In adults, the 8-mm diameter tube should be used when possible. The tracheal size is best estimated by the patient's predicted BMI and not actual BMI. The ETT are available cuffed and uncuffed varieties. The uncuffed tubes are usually for children whereas the cuffed tubes are for older children and adults. Cuffs should not be overinflated, since they are designed as large-volume, low-pressure systems to prevent mucosal ischemia of the trachea. Pre-oxygenation, with 1 00% oxygen by a nonrebreather mask or a bag-valve mask is necessary to increase oxygenation in the blood; this is achieved b y replacing the higher proportion of N2 in the room air with oxygen. This is accomplished by using 100% O2, which also increases the patient's functional reserve capacity with oxygen and increases the interval before the next desaturation. Increasing the amount of oxygenation reduces the amount of positive-pressure ventilation, which reduces the risk of aspiration of gastric contents.

Before any procedure is initiated, one should confirm that consent forms have been signed, unless it is an emergency. If it is an emergency, one should ensure that there is no order for do-not-resuscitate ( DNR) or a do-not-intubate ( DN I ) . The stylet, is normally flexible and can be reshaped, is usually placed into the ETT to maintain the natural curvature of the airway. IV access should be established and the patient's vital signs should be continuously monitored. Proper positioning the patient before intubation is important. The patient's head should be level with the lower portion of the sternum. The "sniffing" position can be accomplished by placing a pillow or folded towel beneath the patient's occiput. Alignment of the 3 axis of the oral cavity, pharynx, and larynx, which is ideal for vocal cord visualization, can be arranged by flexing the neck and extending the head. Any dentures should be removed. An assistant should perform the Sellick maneuver ( applying firm pressure to the cricoid cartilage ) , which compresses the esophagus between the cricoid cartilage and the cervical vertebrae avoiding aspiration of the gastric content. This maneuver reduces the risk of passive aspiration of gastric contents and improves visualization of the glottis.

INTRAVENOUS ACCESS AND DRUGS FOR SEDATION AND PARALYSIS
Neuromuscular blocking agents and strong sedatives are used to improve visualization of the vocal cords and to reduce the likelihood of vomiting and aspiration. Midazolam and fenyanyl are the hypnotic agents typically used for induction. Other combinations include thiopental and ketamine. A commonly used neuromuscular blocking agent is succinylcholine. Rocuronium is a substitute when there is a contraindication for succinylcholine especially in the presence of hyperkalemia. Succinylcholine should be avoided in hyperkalemia because of the depolarization at the neuromuscular junction. Edema, obstruction, tumors, trauma, and infections can all increase the difficulty of intubation. Other situations that can make intubation more difficult are small mandible, limited neck mobility, and edematous tongue (angioedema, amyloidosis). Neuromuscular blockers used to paralyze the patient for MY are associated with neurological deficits and sequelae and should be avoided.

Confirmation
After the placement, the ETT should be in the mid trachea, with the ETT tip 3 to 4 cm above the carina. Bilateral breath sounds and equal expansion of the lungs should be noted. An end-tidal carbon dioxide detector ( capnography) needs to be connected to the ETT, and this monitor should change color within the first 6 breaths. Lack of color change suggests that the ETT is not in the trachea. The ETT should be repositioned until the CO2 monitor confirms correct endotracheal placement by changing colors. A chest x-ray is needed to verify ETT placement and ensure that the ETT is not in the right or left main stem bronchus. After successful ETI , the tube should be secured via an ETT holder or adhesive tape. If facial hair interferes with securing the ETT, simply shave the patient.

Maj or complications of ETT placement include: bronchospasm, hypoxemia, hypercapnia, and death. Vomiting, bradycardia, laryngospasm, pneumonitis, and pneumonia are also seen. Some authorities recommend IV lidocaine prior to ETI to reduce ETI-induced bronchospasm. ETI and MV also are associated with increased cases of ICU delirium.

SUMMARY
The main goal of ETI and MV is to provide a patent airway for the delivery of oxygen and proper ventilation that are primary to a patient's survival. This also allows suctioning of secretions, application of PEEP, and delivery of aerosolized medications. The decision to proceed with this invasive ETI requires an understanding of the pathologic and physiologic disorders that necessitate its use. A qualitative colorimetric EtCO2 monitor is commonly used to determine placement and is nearly 100% sensitive and specific for ETT placement in the trachea.

CLINICAL CASE CORRELATION
  • See also Case 3 (Scoring Systems and Patient Prognosis), Case 9 (Ventilator Management) , Case 11 ( Asthmatic Management) , and Case 12 (Noninvasive Methods of Ventilatory Support).

COMPREHENSION QUESTIONS

8.1 A 34-year-old man arrives in the emergency department (ED) 45 minutes after being shot in the abdomen with a .38-caliber handgun. On arrival the patient is alert, oriented to person, place, and time with blood pressure 76/50 mm Hg, pulse 1 40 beats/minute, respiratory rate 3 2 breaths/minute, and pulse oximetry of 72 % initially on room air. Chest x-rays showed bilateral pneumothoraces with partial lung collapse. RSI is begun with an 8-mm ETT. Bilateral chest tubes are inserted. The patient is started on a pressure support of +10 mm Hg with 0 PEEP and FIO2 of 1 00%. Additional chest x-rays and blood gas determinations are pending. Which of the following is the most reliable confirmation of the proper tracheal placement of the ETI ?
A. Ease of bagging with ventilation
B. Positive color changes on a CO2 monitor attached to the endotracheal tube
C. Auscultation by stethoscope for good breath sounds bilaterally
D. Pulse oximetry reading above 95%
E. Chest expansion with every breath

8.2 You are called t o evaluate a 45-year-old white man who developed a pneumothorax after abdominal surgery. He had been intubated with an 8-mm ETI for anesthesia. He is 5 '2" and weighs 60 kg. His front teeth are at the 32 cm mark on the ETI. Examination reveals good breath sounds and definite expansion of the left chest, but no breath sounds and no expansion of the right chest. What is the most likely etiology for these findings ?
A. Carbon monoxide poisoning.
B. Low Fro2 on ventilator settings.
C. Adult respiratory distress syndrome.
D. Esophageal placement.
E. Endotracheal tube is in the right main stem bronchi.

ANSWERS TO QUESTIONS

8.1 B. The most reliable methods of confirming that the ETT is in the trachea are seeing the ETT go through the vocal cords or noting the change in color of a CO2 monitor connected to the ETT while the patient is being ventilated. Regardless, a chest x-ray is performed for confirmation of tube placement. Sometimes, bronchoscopy may be needed to confirm proper placement or to
assist in placement of the ETT. The tip of the ETT should be 3 to 4 cm above the carina. Head flexion makes the "ETT tip go away from carina" and can cause extubation. Head extension makes the "ETT tip come closer to carina" and can selectively intubate the right main stem bronchus. Other maneuvers that are usually performed include pulse oximetry and auscultation of the lung fields; however, these measures are not as good predictors of accurate ETT placement.

8.2 E. The patient's ETT is placed too low, causing the right main stem to be selectively intubated because of its more direct angle versus the left main stem bronchus. The left main stem bronchus diverges at a 45-degree angle, making it less likely to be selectively intubated. A common error in intubation is esophageal placement of the ETT. Proper placement of the ETT requires confirmation visually or via a CO2 monitor connected to the ETT. A chest x-ray to assure correct positioning of the ETT tip 3 to 4 cm above the carina should be performed.

CLINICAL PEARLS
 Clinical  assessment,  combined  with medical experience, is  the most important tool for identifying patients requiring intubation. 
 Indications for  ETI and MV are commonly divided  into hypoxic respira­tory failure, hypercarbic ventilatory  failure, impaired consciousness, and a need for airway protection. 
 Planned ETI in a controlled  setting is always preferable to emergent air­way management. 
 Ventilation can  be monitored by capnography, which  noninvasively measures the partial pressure of carbon dioxide in the exhaled breath. 
 ABG and PACO2 measurements are  necessary  to evaluate  hypercarbic ventilatory  failure because pulse oximetry values can remain near normal until ventilatory collapse occurs. 
 Unlike pulse oximetry for detecting hypoxemia, bedside monitors for detecting hypercarbia are not routinely available. 
 Neurologic indications for ETI for impaired consciousness and presumed airway protection may account for 20% of patients intubated in the intensive care unit (ICU). 
 Auscultation is not  reliable for determining the placement of the endo­tracheal tube. 
 Patients requiring RSI usually present with increasing dyspnea, tachypnea, use of accessory breathing muscles, and low tidal volume ventilation with paradoxical breathing.

References

Grekin P, Chin MM. Syncope, In: Toy EC, Simon BC, Takenaka KY, Baker B, Rosh AJ . Syncope. Case Files , Emergency Medicine, Second Edition. New York, NY: McGraw-Hill, 2009. 

Loscalzo J. Harrison's Pulmonary and Critical Care Medicine. New York, NY: McGraw-Hill; 2010. 

Orebaugh S, Snyder JV. Direct Laryngoscopy and Tracheal Intubation in Adults. Waltham, MA: Up To Date; 2 0 1 1 .

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