I recently was assigned a research paper on the topic of mechanical ventilation and neurologic injury. I spent approximately 16 hours researching and writing this paper. It was written in APA format (re-formatted for the purpous of this blog post, the copy and paste was not quite as successful as the original formatting) and I've included a list of sources that I drew my information from. I'm a student and don't pretend to be a genius on this subject nor in the mechanics of writing a paper. I did recieve a 100% on this paper based on its meeting all of the assignment criteria. There was absolutely no plagerism intended, so if there's an issue please bring it to my attention so that I may rectify the situation. Happy reading!
The Roll of Mechanical Ventilation
Neurological injuries are commonly known as traumatic brain injuries, or TBI. In the United States alone TBI is reported in over 200 cases per 100,000. This means that with the US population being over 300 million that just about 600,000 cases of TBI are reported each year. This does not account for those cases not reported in an Emergency Department, or ED. As can be imagined, each person is very different, so each case of TBI can vary greatly from person to person.
There are three stages of brain injury. Included in these three stages are mild TBI, moderate TBI, and severe TBI. According to David W Crippen, MD “almost 100% of persons with severe head injuries and as many as two thirds of those with moderate head injury will be permanently disabled”. Economically this means that the cost of TBI is staggering on the public. A mild TBI is referred to as a concussion sometimes. Most patients diagnosed with TBI are mild. Losing consciousness briefly after a concussion is normal as is a general feeling of dizziness, confusion, and perhaps small losses in memory and physical abilities. The brains ability to send messages is temporarily blocked when the trauma occurs. Losing consciousness is the brains way of shutting down and restarting. Of course not every patient with a concussion will lose consciousness. Other conditions possibly associated with a mild TBI are post-traumatic amnesia that is short lasting and a slightly lower Glasgow Coma Score, or GCS. A moderate TBI has similar factors as a mild TBI but the symptoms last longer. Unconsciousness can last up to a full day as can memory loss and amnesia. A person with a moderate TBI would have a GCS ranging from 9-12. Finally a severe TBI will mean a patient is in a coma. All symptoms are elongated further and more severely. GCS score is lower than 8. A patient with a sever TBI will have trouble functioning normally after the incident. They may have trouble with attention span, memory and other cognitive problems. These patients could have loss of senses, like taste, touch, smell, etc and my develop seizures, pain, and lose some motor functions. The speed of which a body recovers from a TBI is also indicative of the type (Traumatic Brain Injury, 2011). A first sign of increasing ICP in a conscious TBI victim is a change in their level of consciousness. Careful observation of the pupils is important to see changes in pupillary mismatch and decreasing reaction to light.
There are many treatments for brain injuries with increased intracranial pressure. The most critical goal of managing neurological injury and adjacent intracranial pressure (ICP) is to reduce brain volume. The practitioner must decrease cerebrospinal fluid, or CSF, along with blood volume while maintaining cerebral perfusion in order to reduce ICP (Crippen, 2011). Normal ICP is 0-15 millimeters of mercury (mmHg). ICPs elevated to 35mmHg for prolonged amounts of time can be potentially harmful and once pressures increase above 40mmHg it is impossible not to have sustained some damage. There are three parts that make up the intracranial space. The brain, or parynchyma, consists of 1400ml of the space inside the skull while the CSF and blood both make up another 75ml each. The change in volume of the brain is interdependent on the change in the volume of either of the other two parts of the intracranial space (Sharma, 1999). Cerebral perfusion pressure is measured by taking the mean arterial pressure and subtracting the intracranial pressure, or CPP=MAP-ICP. According to Egan's MAP is normal at about 93mmHg if arterial blood pressure is in a normal range. ICP normally sits at 10mmHg or less. A good range for CPP is 83-93mmHg. If a bleed is present then MAP may be kept slightly higher in order to keep perfusion levels where they need to be. Ischemia, or insufficient blood flow to the brain, is caused by a decreased CPP in a vicious cycle that can possibly eternilize itself. If the CPP is reduced the body reacts by raising the blood pressure which in turn dilates the blood vessels in the brain. By dilating, or widening, the vessels the venous flow is increased and the blood volume increases in the brain. According to the CPP equation this process then increases ICP, which decreases CPP and the body starts all over with raising the blood pressure and so on (Tolias et al, 2003). So the higher the ICP the higher the practitioner has to increase the patient's MAP to prevent herniation, blockages of the ventricles, which leads to increasing CSF.
Closed brain traumas can be caused by many things. Tumors in the brain, falls, accidents, sporting activities, and blows to the head are the main cause of these types of injuries (Pillbeam, 1998). Other more specific causes can be shaken baby syndrome, stroke, intracranial bleeding,
hydrocephalus, Lyme Disease, etc.
In the news recently has been the discovery of high occurrences of concussions received by elite athletes, especially football players, over many years of playing. Statistically a professional athlete's life expectancy is about 1/3 that of the average human being and the average professional football player will live approximately 20 years shorter than average (Strength Planet, 2011). This statistic alone is evidence of how devastating closed head injuries and increased ICP can be. The focus of this topic is going to be mechanical ventilation and hyperventilation as a treatment for increased ICP but that will be discussed later.
There is quite a range of treatments for increased ICP. Starting with relatively non-invasive treatments for this disorder patients are put on fluid restriction and specialized diuretics prescribed by a neurologist. A patient with a closed brain injury would be on an ordered dietary NPO, or nothing by mouth, and would not be set up with IV liquids like most patients. A diuretic like Mannitol is delivered directly to the patient in a continual IV drip that removes water from the brain and expels it as waste. A patient with an edematous brain needs to be urinating as much of the fluid out as possible. Not only does Mannitol expel extra fluid as waste it also thins out the blood and increases cerebral blood flow which helps reverse the lowered CPP (Sharma, 1999). Corticosteroids can also be administered via an IV to decrease cerebral swelling. Steroids have many side affects and those should be considered when administering them to any patient.
Another non-invasive treatment for increased ICP is to raise the the head of the patient's bed 30 degrees to recruit gravity in helping improve venous drainage into the the spine. Also by lowering the mean arterial pressure, or MAP, using an anti-hypertensive, such as calcium channel blockers, the practitioner can decrease cerebral blood flow thus reducing CPP. Physiological circumstances that should be avoided or fixed are seizures, high temperatures, and restlessness. These increase the body's metabolic pursuit and oxygen consumption. High body temperatures will also increase vasodilation in the brain and rouse cerebral edema (Sharma, 1999). Keeping a patient sedated will decrease their agitation. However sedation on a patient with a head injury is done very very carefully because it is harder to assess cranial activity after sedation.
Normal laryngeal intubation can be very agitating on a patient. As stated the practitioner wants to keep the patient calm so as not to raise the ICPs any more so it is wise to pre-oxygenate a patient with a closed brain injury so as not to decrease the oxygenation in the bloodstream. Rapid sequence intubation, or RSI, is also indicated for this type of patient because it is quick and the patient is unconscious throughout the entire procedure thus not agitating and raising ICP levels. A quick sequence of drugs is given finishing with a paralyzing agent. RSI can be done within one minute (Lafferty, 2011).
There are much more invasive techniques which are used to treat increased ICP. A small lumbar puncture can be used to drain a small amount of CSF out of the spine. This procedure is helpful with the head of the patient elevated. The catheter inserted in the lumbar does not remove a lot of CSF but with the help of gravity any amount of fluid removal is imperative to severe patients. Both an epidural monitor and subarachnoidal bolts have their place in successfully draining CSF from the brain as well. Along with these there are intraventricular catheters which are one of the most popular devices used to drain CSF. A catheter is inserted directly into the the ventricle and both CSF draining and monitoring is possible (Sharma, 1999). Newer fiber optic technology has recently come out allowing monitoring and draining of CSF by a probe being surgically implanted in the brain, ventricles, and subdural space. A transducer is on the tip of the fiber optic to measure pressure and a catheter is put in place for drainage. The catheter can also be use to for introduction of medicine (Arbour, 2011).
A more serious increase in ICPs might require even more invasive procedures. Something called a burr hole can be drilled in the patients head in the OR or right at bedside. It creates a space just big enough to place and ICP catheter. If that small procedure isn't enough a decompressive
craniectomy can be done. This is where part of the skull is removed to allow the brain to swell without damaging the parynchyma or causing vessels to be crushed further increasing ICPs. The skull piece is surgically stored in the patient's abdomen until they are recovered and it can be put back into place (Egans, 2003).
The IVD or Intraventricular Drain has several names. External Ventricular Drain and ventriculostomy are similar devices. The IVD is a piece of medical equipment that is used in closed neurological injuries. It was designed to decrease elevated ICPs and hydrocephalus when there is something obstructing the normal flow of CFS around the brain. It is a small, plastic tube that is surgically inserted in the side of the brain that is blocked to drain fluids from the ventricles thus reducing ICPs. A ventricular drainage device is designed to shunt cranial fluid from the brain. The small plastic tubing is surgically placed in the ventricle where pressure buildup is taking place using a one-way valve into another portion of the brain that is not blocked and/or down into the stomach where the extra fluid would be excreted as waste (Dempsey, 2012). This type of drain would be internal. The external drains would drain into a bag at bedside. These types of devices are used quite commonly in neonates. Babies have the probability of having the shunt device in their cranium their entire lives, although some may be able to have them removed eventually. Complications can arise such as shunt blockage and infection. Like any surgical procedure infection is highly likely if not cared for properly. Watching for signs of infection such as swelling, fever, and lack of healing is important in these patients. Vomiting and seizures are signs to watch for that indicate the catheter has a blockage. Permanent brain damage can occur if these things occur (Kakarla et al, 2008).
Now is where the respiratory department can aid in decreasing a patient's ICPs. The patient will need to be monitored for clear, patent airways, breathing and oxygenation. A direct cause of vasodilation is low tissue oxygenation, hypoxia, and high levels of carbon dioxide, hypercapnia, in the blood. If the vessels dilate it allows increasing amounts of blood flow to the brain increasing the
vicious cycle of raising the patient’s ICPs. Hyperventilating a patient can temporarily reduce cranial swelling. The brain swells immediately in a patients with TBI. If hyperventilation is applied quickly for less than 48 hours ICP may be able to be reduced. Because the body is always trying to balance itself, or keep itself in homeostasis after 48 hours or more the body adjusts against the settings and normalizes it's blood gas values. Reducing cerebral blood flow is important to reduce ICP. Alkalosis in combination with hypocapnia can help reduce blood flow in the brain therefore keeping the pressure of arterial carbon dioxide levels, or PaCO2, between 25-30mm Hg is important.
Of course as all science and technologies the medical field is constantly advancing and changing. New therapies and procedures are discovered all the time to improve patient care. So as new information is received old information is often shelved or put on a back burner. Such is the case with hyperventilating a patient in order to decrease ICP. All the advance drains, monitors, and drugs combined have much less harmful side affects than keep a person's blood gas levels in a state of alkalosis. Hyperventilation would be a last ditch effort if none of the other procedures or therapies worked. This does not mean that the role of the respiratory therapist is obsolete during this particular trauma. The respiratory staff will always work side by side with the nursing staff in care of a patient with a TBI. Monitoring of the oxygen in the blood would be a main concern for respiratory. Not to mention if a TBI patient is on a ventilator they would need a respiratory therapist monitoring that patient.
- Kakarla UK, Kim LJ, Chand SW, Theodore N, Spetzler RF (2008). “Safety and accuracy of bedside external ventricular drain placement”. Neurosurgery 63 (1 Suppl 1)
- Crippen DW. 2011. “Head Trauma”.Emedicine.com
- Davis DP, Kimbro TA, Vilke GM. The use of midazolan for prehospital rapid sequence intubation may be associated with dose-related increase in hypotension. Prehospital Emergency Care 2001; 5:163-168.
- Lafferty KA. 2011 “Rapid Sequence Intubation” Emedicine.com
- Tolias C, Sgouros S. 2003 “Initial Evaluation and Management of CNS Injury” Emedicine.com
- Sharma A, (1999). Raised Intracranial Pressure and its Management. Vol 1 No 1
- 15 Facts About World Class Athletes. (2001) Retrieved from: http://strengthplanet.com
- Arbour, R. 2011. “Intracranial Hyptertension Monitoring and Nursing Assessment” ccn.aacnjournals.org
- Traumatic Brain Injuy (2011) The Journey Home. Retrieved from http://www.traumaticbraininjuryatoz.org/
- Pilbeam SP, Cairo JM, (1998). Mechanical Ventilation Physiological and Clinical Applications. St Louis, MO: Mosby, Inc.
- Wilkins RL, Stoller JK, Kacmarek R. (2003). Fundamentals of Respiratory Care. St. Louis, MO: Mosby, Inc.