The immediate goal of resuscitation of serious trauma patients is to reverse the state of shock and tissue hypoxia by improving the delivery of oxygen (O₂) and nutrients to the tissues, and to arrest the cause of the shock. This involves the common sense, based on priority emergency medical care. Commonly referred to as the ABCs, these are briefly listed:

A - opening the airway; B - ensuring adequate ventilation; C - controlling hemorrhage, providing volume replacement as required, and support of the cardiovascular system; D - correcting anatomical defects caused by the injury that affect function (repairing the ruptured urinary bladder) before its consequences impart serious life-or limb (locomotion) threatening complications. The final goal is to have a comfortable and functional pet return to their owner.

Multiple factors affect oxygen delivery to the cells however, in general terms, O₂ delivery is dependent upon O₂ being delivered at the alveolar level, effective gas exchange, the presence of sufficient hemoglobin to carry the O₂, adequate cardiac output, and adequate blood flow to the tissues. Cardiac output is determined by circulating blood volume, cardiac muscle strength, vascular tone and heart rate. "High Priority Resuscitation Issues" are those that involve the trauma patient that cannot wait and are issues that MUST be addressed immediately upon arrival. These issues involve interventions that are aimed at maximizing oxygen delivery at all levels. Treatment must be appropriate and always be provided in a timely manner. If tissue oxygenation suffers below 20% of the baseline, mitochondrial and ATP manufacture dysfunction will begin. As a consequence plasma membrane integrity suffers as 90% of all ATP that is made will be used for membrane maintenance (Ozawa, K., et al 1976).

Research has shown that if cellular hypoxia to the gastrointestinal tract in dogs continues beyond an hour even though global resuscitation appears adequate, death from organ dysfunction and sepsis from gastrointestinal bacterial translocation and endotoxin absorption across the gut wall will likely occur from one day to several days afterwards (Baker, et al 1988). Irreversible cellular apoptosis (programmed cellular death) may also occur as an aftermath of the cellular stresses secondary to the global effects of the injury (Szabo, et al 1995).

Therefore, successful care requires timely and accurate patient examination, assessment and treatment that occurs in proper sequence according to physiologic priorities. Since all three of these components must occur simultaneously in the injured patient, all three are included in the decision making that must performed accurately and in as short of a time as possible. One thing that cannot be wasted is TIME. Therefore these decisions not only have to be accurate but also experienced. In this author's clinical experience, patients with significant airway or respiratory compromise are those most effected by the time-to-effective treatment lapse (Crowe 1986, Crowe 1989, Krantz 1996)

To provide the time needed to resuscitate the most severely traumatized dogs and cats a "state-of- readiness" is required. This is especially important with airway and ventilatory compromised cases. In cases of near or complete airway obstruction the seconds really do count. The most important key in these cases is the ability to perform a rapid induction and intubation with ventilation or the performance of an awake tracheotomy. With either of these methods, secretions, blood and/or vomit may require removal to allow for proper airway visualization, a patent airway, and prevention or treatment of aspiration.

A key piece of equipment required-and-ready upon arrival of the airway compromised trauma case is the suction unit. Although gravity can also be used for the evacuation of vomitus, blood clots, thick exudate, or saliva from the pharynx, larynx, and trachea, suction is also important and generally provides a more effective method for clearing the pharynx, larynx, and trachea of this material. This instrumentation includes the suction trap bottle, suction tubing, several types of aspirator tips (Yankauer Tip Suction for pharyngeal aspiration, dental tip for rima glottis and tracheal suctioning, and tracheal-whistle tip-catheters for tracheobronchial tree aspiration). A suction device capable of generating up to 300mmHg of vacuum that can be obtained within 4 seconds of clamping the tube is imperative (Stapleton et al 2001). The dental suction tip is used for the aspiration of large pieces of vomitus and clot from the while the whistle tip catheters are used for the aspiration of frothy secretions, vomit, exudate and blood. An endotracheal tube with suction applied to the connecting end can also be used to evacuate particulate debris from the pharynx and upper airway.

Interposition of a suction trap at the base of the dental suction tip or endotracheal tube "suction tip" device will prevent clogging of the latex connecting tubing resultant of large amounts of debris or blood clots that may be present. A trap has been described that attaches directly onto the endotracheal tube. This allows for effective suctioning to be performed during the act of intubation and can save valuable seconds. It is recommended that for the "state of readiness" that either a Yankauer Tip, medium sized dental suction tip, or endotracheal tube (with an inflatable cuff) be pre-attached to the suction unit via a 6' section of 5/8" tubing and that the other suction attachments be close at hand so exchange can be done quickly. The Yankauer Tip should be left inside of its plastic packaging after its connection to the tubing to allow for cleanliness. A section of suction tube with a side hole should be available as well. This tubing can be used to aspirate the pleural space that is continuously accumulating air or air-and-blood that is generally present in spontaneous pneumothorax or trauma cases.

Other key pieces or equipment and supplies for the respiratory compromised trauma patient that may not be as commonly found in some veterinary hospitals and clinics that will be needed and should be provided include the following (Crowe Sept 2003):

1. BVM (Bag Valve Mask with oxygen reservoir) - Cone shaped masks are preferred with rubber rings that allow for an effective face-seal that will provide for effective assisted ventilations by the rescuer.

2. Clear endotracheal tubes with low-pressure high volume cuffs - These tubes can be split down the center and made into "tracheotomy" tubes. This type of tracheotomy tube is preferred over that commercially available tubes for humans as the tips are less likely to protrude into the wall of the trachea (Crowe, 1992).

3. PEEP Valve - These will allow continuous positive pressure breathing as this valve fits onto the end of the exhalation port of the BVM or anesthetic machine. As the patient exhales the breath flow is inhibited by a section of rubber that is affected by a spring. The spring can be tightened by the user as needed to assert more resistance to the patient's passive exhalation. This device contributes to complete exhalation and reduces the build up of air that has a tendency to accumulate within the patient's alveolar space. The valve can be adjusted to provide approximately 5 mmHg of positive airway pressure at the conclusion of the exhalation phase of breathing. This valve is frequently utilized with the BVM to provide an increase in functional residual capacity and prevents and "treats" edema formation.

4. Oxygen - A source that can be portable and be given to the patient at any location as the patient travels throughout the hospital is paramount. This should include an E or D cylinder and a regulator-reducing valve with oxygen flow meter that allows the patient to continually to receive oxygen supplementation during transport to other hospitals for care or anywhere within the hospital regardless of location. Research has shown that the very common ventilation - perfusion mismatching observed in trauma patients is most effectively treated with supplemental oxygen (Roca and Roisin, 2000).

5. Laryngoscope and blades with malleable stylettes that can be used to guide the endotracheal tube.

6. Atricurium (or other nondepolarizing muscle blocker) - This will be utilized to stop movement and allow BVM ventilation and tracheal intubation without providing significant cardiovascular compromise. DOSE: atricurium 0.25 mg/kg IV with subsequent doses of 50% of the initial dose.

7. Mechanical ventilators (anesthetic and ICU such as a Hallowell and NewPort Breeze respectively) - Older model (used) ventilators such as a Bear or Bennet MA1 are also effective, especially if they can be fitted with am IMV (Intermittent Mechanical Ventilation valve).

Care of the "incoming patient" with the initial act of assessment and management beginning at the scene of the accident by owners or bystanders is often life-saving with the multiple injury patient. Assessment and care often starts with the answering of the phone by veterinary hospital personnel. If an owner with an injured pet telephones, the call should be immediately forwarded to a doctor or experienced VMT (veterinary medical technician), unless the receptionist has the training to be able to give suggestions for at-the-scene care and transport. Basic life-support instructions can be given over the phone. A flow chart or checklist should be available within easy reach of the phone to allow for the technician to deliver complete instructions to the owner. In this author’s experience, a triage sheet that allows the technician answering the telephone to scribe crucial information regarding the case not only provides an invaluable legal record, but also functions as a checklist. Remember if you didn’t write it down, you didn’t do it!

Experience has proven that owners can provide effective rescue breathing and stop major external hemorrhage. They can be instructed to on how to transport the injured pet on a flat object, which globally splints and immobilizes the abdomen, spine pelvis, and limbs. Experience and research has proven this treatment to be important in the management of internal hemorrhage, fractures, luxations, and spinal injuries. Regarding the respiratory compromised trauma patient my clinical experience has documented the life-saving procedure of rescuer mouth to patient nose "rescue breathing". Ideally this technique is taught prior to its need at a Pet Owner First Aid Course. However, the technique can be explained and recommended over the phone in selected circumstances. In one case with a traumatically induced cervical disc rupture, the unconscious dog stopped breathing and the owner provided effective mouth to nose rescue breathing for over 20- minutes. Upon arrival the dog was temporarily ventilated with a BVM and supplemental O₂ and while anesthesia was induced with ketamine, diazepam, and butorphenol. The dog was then immediately placed on an anesthetic ventilator. Radiographs and myelogram identified a ruptured disc. Surgery was accomplished and the ventral disc was removed via a slot technique. The dog remained on a ventilator for 5 more days and with subsequent resumption of spontaneous and effective ventilation he was weaned. Eventually, a full neurologic recovery was enjoyed.

Triage Assessment and Resuscitation on Arrival

Basic trauma care at the hospital begins with rapid assessment and if required resuscitation for the detected life-threatening problem upon arrival of the patient. It should be assumed that every trauma patient has a life-threatening injury until secondary assessment proves otherwise. A capsule history is obtained as the patient enters the facility. A veterinary technician (nurse) or veterinarian should begin by looking at the animal from a distance. Any blood on the patient should be followed with the examiners immediately donning gloves and using universal health precautions with body - substance - isolation (BSI) precautionary procedures. This is done to protect the health care team from zoonotic diseases such as leptospirosis and others. It is also possible that the blood seen on the patient is that of a human such as the owner, and because of this, BSI becomes paramount. Hepatitis and HIV are the most serious communicable diseases that could be encountered by this human blood contamination. If there is any doubt it is best to don gloves and automatically use BSI precautions in every case assuming that every patient is infected.

Upon arrival immediate assessment - resuscitation is completed. Assessment is done by noting the following:

LOC (level of consciousness) and AVPU scoring is made:

A = alert

V = only verbally or visually responsive on touching but not alert

P = only responsive when pain is inflicted such as squeezing a toe-nail bed hard

U = unresponsive to all stimuli (comatose). If this is observed the patient should be suspected of having received a severe traumatic brain injury (TBI) and BVM ventilation with 100% supplemental oxygen should be immediately initiated, as most TBI cases on arrival are not ventilating adequately by themselves. Research on TBI has revealed that effective ventilation and supplemental oxygen are the most important clinical treatments that can be performed for the TBI patient (Manley 2002).

Airway patency is assessed by listening for increased or absence of airway sounds. If severe airway compromise is detected by noting its absence, the patient's head and neck are extended and preparations made to either perform an emergent induction and intubation, or to perform an awake tracheotomy or cricothyroidotomy. If there is significant upper airway sounds and increased inspiratory effort noted, blow-by oxygen is started and IV access is begun in preparation for an IV induction dose of ketamine/ diazepam. Placement of an endotracheal tube using lidocaine as a local aneshtetic is achieved on the cervical midline of the patient as an awake tracheotomy is completed. Common causes of severe partial airway obstructions post injury are, severe swelling, cervical or sublingual hematoma, or disruptive laryngeal or tracheal injury.

Breathing rate and effort is determined by watching for chest movement. Effectiveness of breathing is also assessed by observing membranes and listening to breath sounds, preferably with a stethoscope. Any compromise detected is immediately treated with blow-by oxygen to start in the conscious patient. If the patient is unconscious, it is assumed that spontaneous breathing will be ineffective and therefore, immediate "rescue breathing" must be initiated. Initially, this is best accomplished using a BVM connected via a reservoir to an oxygen source with flow rates from 5 (cat) to n15 L/minute (large dog). This is best described as a "preoxygenation-preventilation" process. After preoxygenating - preventilating the patient approximately 20-30 seconds the trachea should be intubated. Most commonly by use of a laryngoscope and a small dose of ketamine - diazepam - butorphenol (1-3 mg/kg, 0.1 mg/kg) is indicated. Tracheotomy is optioned if the upper airway is compromised significantly and endotracheal intubation is contraindicated.

Cardiovascular assessment is completed by palpating the strength and rate of central pulses, auscultation of heart tones, and determining the color of mucus membranes and capillary refill time. In most cases of respiratory compromise, fluid support with standard crystalloid solutions is contraindicated as airway and lung edema will be worsened. Hypertonic saline and colloid combinations are recommended at the onset. As IV catheter placement is performed, it is highly recommended to place as large a bore peripheral catheter as plausible and facilitate this placement by using an 18-20 g needle and making a small incision over the vein with the bevel. The incision should pass completely through the skin. If severe hypotension is present the vein will not fill well and catheter placement will be more difficult. In these cases a small curved hemostat is used to sculpture the sides of the vein. The curved hemostat is then passed underneath the vein and tensed distally thus facilitating much more effective venous access. As a guideline, any hypotensive patient should receive supplemental oxygen begun before the fluid support is initiated. Research has shown that increased reperfusion injury occurs in animals not receiving supplemental oxygen prior to beginning fluid resuscitation

Volume resuscitation is provided as required to gain Doppler blood flow and "some" jugular vein distension, at least to the point of recognition of its presence in cases where hemorrhage could still be ongoing. This is the situation in most trauma cases that are not of recent incidence. This will be addressed further in the next paper text to come.

Primary surveys are completed by examining for any disruptions of the skin, muscle, ligaments, bone and any neurologic disabilities. Examination should include looking for any outward abnormalities such as active hemorrhage, sucking wounds in the neck or chest or an expanding abdomen. The head, neck, chest and abdomen should be observed and palpated and then the limbs are examined briefly.

Taking over the patients breathing whenever it remains difficult is a key to survival in the emergency trauma patient. The patient that does not respond to oxygen supplementation may tire quite rapidly and die from simple muscle exhaustion. They must be aggressively managed with either sedation or awake laryngoscopically assisted intubation, or awake tracheotomy assisted with a local block. Despite which intervention is chosen, positive pressure ventilation (PPV) remains the primary goal. A second alternative is to use a muscle blocker such as atricurium after administration of a neuroleptic analgesic to gain control of the patients breathing with a bag-valve-mask AMBU system. The author has both laboratory and clinical proof that one of the most damaging things that can be done is simply place the tiring respiratory exhausted animal in an oxygen cage as they are shown to simply go there and die. All patients must be given supplemental oxygen by "blow-by" as they are receiving sedation (ketamine, acepromazine, butorphenol mixture given in the epaxial muscle) prior to placing the appropriate airway adjunctive device. These patients may also be placed within or under a clear plastic bag containing nearly100% oxygen. The leg of the patient may then brought out of the clear oxygen canopy as an IV is achieved and secured. With the aid of further medication, the patient can either receive bag-valve-mask assisted ventilation because now he accepts the mask without a struggle.

The addition of continuous positive pressure ventilation (CPAP) by way of a small PEEP valve added to the exhalation arm of the bag-valve system using a tee, can be life-saving for the patient with pulmonary edema, pulmonary contusion and hemorrhage, and severe pneumonia. Other emergency methods including thoracentesis, chest-tube placement, and tracheotomy maybe indicated as well as continuous "bagging" of the patient with an AMBU bag after tracheal intubation. A mechanical ventilator is ideal to have on hand and something we can all strive for. However in this author’s clinical experience, many patients that have survived when all that was available was a $20.00 disposable AMBU bag connected to an oxygen source. A $20.00 disposable variable level PEEP valve attached to the AMBU bags exhalation arm with a tee, and a small group of people, often the owners, are taught how to squeeze the bag. They continued to provide PPV through many hours as needed. Of course oxygen saturation or other monitors are nice for the assessment of adequate oxygen and carbon dioxide gas exchange and are indicative of sufficient oxygen delivery to the tissues.

With that introduction let us now begin the discussion of management of the respiratory crisis patient.

Pulmonary ventilation-perfusion mismatches (VQ mismatch) can be caused by many conditions (Table 1) and are common in emergency patients including the trauma patient. Because of poor oxygen uptake in these conditions, oxygen tension is often low or marginal at best in these animals. The results are marginal to precarious oxygen saturation (SaO₂) levels that ensues together with suppressed tissue delivery from volume loss or simple vasoconstriction from pain, and or hypoxia. Stressing these animals further by performing even simple manipulations can cause marked oxygen desaturation in some cases and result in severe tissue hypoxia. Therefore, if there is any doubt about the patient’s ability to oxygenate, which should be thought of a potential in all trauma emergency patients, supplemental oxygen should be provided. Research and clinical studies have revealed this to be one of the most important procedures that can be instituted for those critical patients that are assessed to have adequate airway and breathing capabilities (Sassoon 2000).

General indications governing the use of supplemental oxygen are provided in Table 2 (Bistner 2000). The main indication for supplemental oxygen is hypoxemia due to impaired gas exchange (diffusion impairment, ventilation-perfusion mismatch, or both). Hypoventilation alone, although not a specific indication for oxygen supplementation as a primary treatment, is indicative of such treatment by emergency personnel while time is being taken to prepare to provide for adequate ventilation and treat its cause. Supplemental oxygen, through increasing the partial pressure of oxygen (PaO₂) in the alveoli where gas exchange takes place, will effectively treat the secondary ventilation-perfusion mismatch. Therefore, supplementing oxygen is always still indicated in cases of hypoventilation (Sassoon 2000, Stapleton 2001).

To simplify the decision of whether or not to supplement oxygen, one can attempt to determine if adequate oxygen levels are reaching the tissues. The simplest method of making this determination is examination of the patient. If the patient is exhibiting signs of systemic hypoxemia (restlessness, tachycardia, tachypnea, or pale-gray-cyanotic mucus membrane color in severe cases), oxygen is definitely indicated should be supplemented. Pulse oximetry can also be used as this provides a more sensitive means of determining superficial oxygen desaturation. SaO2 levels below 92% indicate the need for supplemental oxygen (Sassoon 2000, Hendricks 1993). However, because of the time it takes to get reliable oximetry readings in emergency situations and with the unreliability seen also with some instruments, it is best to assume marginal oxygenation and provide supplemental oxygen if there is any possibility. A danger with the use of pulse oximetry is the false assurance of a "normal" SaO2 reading for a patient who is receiving supplemental O2. Yet, the patient may be experiencing life-threatening hypercapnia from ineffective ventilation (Sassoon 2000). This is due to the lack of knowledge of the basic principles and interpretation of pulse oximetry readings verses capnography (Hendricks 1993, Matthews 1995) and subjectively, a tendency for clinicians to rely on technology rather than patient assessment. Habits should always be honed to treat the patient and not the monitor.

The only means of effectively knowing whether effective ventilation is occurring is either by measuring the tidal (TV) and minute volumes (MV) of the patient directly using a respirometer or with capnography not oximetry (Kruse-Elliott et al 2003). Both unfortunately require a patient tolerant to a tight-fitting facemask. Therefore when performed, these tests generally require sedation. Capnography can also be performed with a nasopharyngeal catheter and a capnograph that is capable of aspirating air samples. This technioque measures the amount of carbon dioxide in the patients exhaled breath. However, placement of the nasopharyngeal catheter also requires sedation in most cases. It is recommended to seek the following good reference for the interpretation of capnography; Capnography: A Reference Handbook: Novametrix Medical Systems, Wallingford, CT 06492 and study it. Arterial blood gas (ABG) determination also is an accurate indicator of the presence or absence of effective ventilation.

Sedation may be required in the emergency patient to decrease anxiety and help the animal accept necessary treatment but generally this sedation is NOT performed immediately to help ensure that a physical exam is not confused or impaired by drugs on board. However if the animal cannot be handled without undue stress, or a lifesaving intervention is not possible without it, always keep the animals in an enriched oxygen environment from the very start. Owners, if they call complaining that their pet is having difficulty with breathing, should be told to place the animal in a cardboard box that can be closed and to transport the animal in the box. As a result, when they arrive at your facility the animal will be started on high flow (15 LPM) supplemental oxygen even before they are handled. The animal can be observed while they are receiving the oxygen in the box by lifting up one of the flaps slightly. This simple maneuver has been shown to deliver up to 80% oxygen (FiO₂) within a few minutes, thus raising the partial pressure (PaO₂) of the gas from approximately 150 mm Hg to 600 mm Hg (Engelhardt, Crowe 2004). The animal is left (attended) in the box for a few minutes thus allowing him or her to become hopefully more calm while receiving the best oxygen deliver possible for the situation. This will be followed by laying the box on its side and shaking the box slightly in order to facilitate sliding the animal into a large CLEAR plastic bag with preconnected high flow oxygen being delivered into it. The animal is then entirely surrounded by the plastic that is expanded by the oxygen gas. Although this might appear a little funny, the animal and doctor especially if the patient is a cat are much better off.

Attempts at handling the anxious cat with difficulty breathing generally leads to the rescuer getting injured and the cat either falling to the floor or being placed in an oxygen cage environment where he or she will only receive a maximum of 50% oxygen. Furthermore, it should be noted that it takes approximately 20-minutes (minimum) to reach the 50% level in an oxygen cage! The animal will not be able to receive a physical examination except by visualization when the cage method is used as well. With the plastic bag system, oxygen saturation levels reach 90% plus within a few minutes and animals can be manipulated from outside of the clear plastic. As previously discussed, animals that are semiconscious can just have a section of plastic sheet cover them and the oxygen can flow underneath the cover and provide them with at least 40-60% oxygen.

If an animal collapses suddenly, oxygenation should be provided by the blow-by method until more team members arrive and equipment becomes available. Auscultation of lung sounds should take place at this point as well. If the animal is very anxious, sedation in the form of an IM injection of a mixture of acepromazine (0.1 mg /kg), butorphenol (0.1-0.2 mg/kg) and ketamine

(1-5 mg/kg) may be used. These medications can be placed in the same syringe. If the injection is given slowly IM there will be less perceived discomfort.

Ketamine is shown to be a very good bronchodilator and at the dosage mentioned above, will produce minimal cardiovascular suppression. Some authors have suggested its use as a cerebral protective drug in brain injury at low doses because it blocks the adverse effects of excitatory amino acids from the injured brain (Prough 1994). The best place for the IM injection is in the epaxial muscle to either side of the thoraco-lumbar region. It is the author’s experience that IM injections given in this region generally have a more rapid uptake than IM injections given in the legs and are safer. After the animal gets quieter a leg can be pulled out from the plastic and an IV catheterization can be achieved.

Further assessment of the patient may require changing the method of providing the supplemental oxygen, however the supplemental oxygen should be continued until after other assessments including radiographs are completed. Other methods of providing oxygen are summarized in this article and most work well enough to be able to provide at least 40-50% oxygen at flow rates that vary from 1-6 LPM. Placing the animal in a standard oxygen cage provides 25-30 % in most cases (Engelhardt, Crowe 2004).

You can also check an arterial blood gas for evidence of hypoxemia (p_aO₂ < 60 mm Hg), despite adequate ventilation or for hypercarbia (p_aCO₂ >55mm Hg) indicating the need for assisted ventilation. This however requires an arterial blood gas sample, which would demand some patient cooperation and is often stressful for the patient and the staff. This author unfortunately has observed good intentioned doctors and nurses – technicians trying to obtain an arterial sample for assessment of ventilatory and oxygenation status causing subsequent rapid deterioration of the patient.

All maneuvers that cause stress to the animal should be avoided if at all possible. This includes separating the animal with obvious difficult breathing from the owner’s arms in the reception area. This will cause additional stress on the animal and should be avoided. Rather the owner should continue holding the dog and both taken together to where oxygen can be easily delivered. Another alternative is to use a portable oxygen caddy that has an E-cylinder with a regulator/flow meter and small diameter oxygen tubing attached (Crowe 2001, Crowe 2003). These devices are very portable and can be taken anywhere in the hospital where NO SMOKING takes place (which should be the entire hospital). An anesthetic machine can also be instituted with a Y-connector attached to the oxygen tubing prior to the vaporizer. In this fashion, the flow can either be diverted to a small oxygen supply line or to the vaporizer itself. This author recommends if many things are occurring in the treatment area of the hospital, it may become more appropriate to bring a portable oxygen caddy to the owner/patient’s side in the waiting area and the supplemental oxygen therapy be instituted there. Assist the owner either holding the animal in their arms or on the exam table or sitting in a chair. In some instances they can hold the section of administration set tubing connected to the oxygen tank and delivering a 2-6 LPM flow near the animal’s mouth and nose. This simple Blow By maneuver has been found to deliver 40% oxygen, thus raising the PaO₂ of the gas from approximately 150mm Hg to 300mm Hg. This may be the first immediate action taken on any animal that suddenly appears unstable in the hospital. An assistant can provide the flow of oxygen while other emergency team members are arriving. At the alveolus, this increased gas pressure (PaO₂) provides for more effective O₂ uptake by the red cell in the pulmonary capillary. Thus a simple technique of providing oxygen by blow-by can be easily performed and may be one of the best "first treatments" that can be performed when faced with a critical patient.

Patients in all types of shock present with various causes of hypoxia (Shoemaker 2000). The types of shock hypoxia include stagnant hypoxia (low blood flow caused by many etiologies the common being hypovolemic or traumatic-hemorrhagic shock), anemic hypoxia (low hematocrit or hemoglobin), hypoxic hypoxia (low arterial oxygen), and tissue hypoxia (intracellular metabolic derangements such as those caused by carbon monoxide inhalation). All have been found to ameliorated with increased oxygen levels inhaled (>40-60%). During the early stages of resuscitation from shock and trauma with crystalloid or colloid fluid infusion, oxygen demand and uptake of the reperfused tissues increases 30% over baseline. Providing supplemental oxygen should thus be performed prior to fluid resuscitation. Shock patients will also commonly present to some degree with ventilation – perfusion mismatch (VQ) due to the maldistribution of microcirculatory blood flow and interstitial and endothelial edema in the lung. Diffusion impairment due to the swelling of pulmonary alveolar and extra-alveolar interstitium and the endothelial cells themselves results (Riede). However, providing high levels of oxygen after a delivery of fluids and episodes of severe hypotension and hypoxia for over an hour may bring about more cell injury and death (reperfusion damage) than if only room air is provided (Feet).

Therefore it is very important provide high oxygen levels early, prior to much cellular injury and stress. A rule of thumb provides that supplemental oxygen should be initiated immediately whenever any of the following clinical signs are observed (Table A).

Once the decision is made to begin supplemental oxygen therapy, choose a method of delivery that fits the needs of the patient. One way already mentioned is to place the animal in a humidity and temperature-controlled oxygen cage, but this isolates the patient and makes close physical evaluation impossible. One alternative is to place a piece of clear plastic over the patient's head and neck or body. Another method is to use an oxygen cannula, either infant, pediatric or adult size depending on the size of the animal. The cannula is introduced into the nose after instilling a small amount of proparacaine or lidocaine (the former preferred in cats). The cannula is generally sutured into place after a small amount of tape is used to make a nose-bridge that helps hold the cannula in place, but staples may be used as a temporary security method. The E-collar method helps hold the oxygen given through the cannula in the local area for possible inhalation when the oxygen tube is secured into the collar with tape and a clear plastic sheet is tape to partially obstruct the opening creating an oxygen door. The oxygen door is awkward to use and inefficient for maintaining normal environmental temperatures and humidity. A small amount of sedation may be required as well with the use the E-collar method.

Prevalent in all of the cage methods, oxygen levels fall to 20% within 20-seconds in most cases when you open the cage door, which can stress an animal that has been relying on a 40% or more oxygen environment. These methods are also expensive, because of the initial cost of the equipment and the relatively high oxygen flow rates needed to reestablish the enriched oxygen environment after the door has been opened (10 to 15 LPM for several minutes minimum and continuous).

In 1982 to circumvent these problems, this author discovered that indwelling nasal oxygen catheters were a successful intervention and have become popular since. Results of their effectiveness was published in1986 when dogs with nasal oxygen being administered also had transtracheal catheters placed. The transtracheal catheters were used to aspirate samples of tracheal gas (Fitzpatric, Crowe 1986)). Levels observed varied from 40%-90% on flows that varied from 5 to 20 ml/kg. Catheters are practical, reliable, tolerated by most patients, and easy to use. Usually the catheter is a 5-8 French, flexible rubber tube with two or three added side ventilation holes placed in the distal 2cm of its length. When inserted into a nostril, the tip of the catheter should lie within the ventral meatus in the middle of the nasal cavity. This author has encountered few difficulties with this type of catheter with the well over 1000 patients it has been used on. Approximately 10-years ago, we began placing these catheters deeper so that the tip was in the proximal nasal pharynx (hence the term nasopharyngeal catheter) or in the thoracic portion of the trachea (hence the name nasotracheal catheter). Experience with the nasotracheal oxygen catheter was first reported by Crowe and Whitfield in 1996.

To insert a nasal, nasopharyngeal or nasotracheal catheter:

1. Sedate the apprehensive or anxious patient first. Commonly use acepromazine 0.1 mg to 0.5 mg with butorphenol 0.1 – 0.2 mg / kg IV.

2. Place a few drops of 2% lidocaine (dogs) or preparacaine (cats) into one nostril. Wait a few minutes and then place a few more drops in the same nostril. Carefully consider the total dose in small patients because these anesthetic agents are readily absorbed. Local anesthesia can be omitted in depressed patients.

3. Select a catheter of the appropriate size (3.5 Fr small cat, very small dog, 5 Fr large cat or small dog, 8 Fr large dog) and cut the side (ventilation) holes into the tube. Then determine the depth of insertion you desire as per anatomical reference points and mark this distance on the catheter. Use the tip of the nose as a reference point.

Nasal O2 Catheters are placed with the tip at the midnasal region, at the level of the second premolar.

Nasopharyngeal O2 Catheters are placed with the tip in the nasopharynx region, at the angle of the jaw .

Nasotracheal O2 Catheters are placed with the tip passing into the trachea and resting at the proximal thoracic tracheal segment.

4. Place a skin suture in the ventral rim of the nostril using 3-0 or 2-0 silk on a swaged-on cutting needle. No local anesthesia is required, but pass the needle quickly so it causes little discomfort. Tie the suture in place and leave the ends long. (The ends will later be wrapped and tied around the catheter where it exits the nostril)

5. Lubricate the catheter with water-soluble jelly and insert it into the nose. Direct the tube dorsally for the first 1 to 2cm to avoid the nasal vestibule and then advance it ventrally and medially to guide it into the ventral meatus. The animal will object to the advancing catheter until it is in place and motionless. If the animal objects strenuously then provide sedation as outlined or titrate further sedation to effect. The animal should not struggle. Mild sedation is preferred to a stressed agitated animal. In cats a small amount of ketamine (1-3 mg/kg) added to the acepromazine and butorphenol works very well. The nose in dogs can also be pushed upward (sniffing) to assist with catheter placement into the ventral nasal meatus.

6. Continue to pass the catheter until the predetermined level is reached. With nasotracheal catheters, the head of the animal is hyperextended when the catheter is believed to be in the mid- nasopharynx. The tip is then to be passed rapidly and with the curve pointing ventrally as the animal takes a breath. The animal may or may not experience coughing.

7. Pass the tip to the predetermined level. Attach a syringe to the end of the catheter and aspirate. If air aspirates very easily, and on the injection of air you can hear the swish of air at the thoracic inlet, the tip is generally considered to be in the trachea. If upon aspiration the air does not aspirate easily you are generally not in the trachea. To be sure of placement, a radiograph will be needed and is recommended. In my experience passage of the catheter occurs on the first attempt in excess of 50% of all cases. The catheter can also be placed by direct visualization with the patient under extreme sedation or general anesthesia after an endotracheal tube has been removed.

8. Secure the catheter with the replaced suture, wrapping the ends around the catheter several times to form a friction knot.

9. Secure the catheter to the side of the face or midnasally using either; A) Sutures: First placing loose sutures through the skin and then securing them around the catheter with friction knots. Or, B) Skin staples to trap the catheter onto the patient. Or, C) Use a dab of cyanoacrylate adhesive to secure the catheter to the animal’s face. (Caution: Excessive amounts of glue applied to the site may make it difficult to remove the catheter later and may cause necrosis of the superficial layers of the skin.)

10. Incorporate the catheter in adhesive tape that encircles the neck. Attach the catheter to the oxygen tubing from the flow meter of the oxygen source (either an oxygen tank or an anesthesia machine).

11. Administer oxygen as required. In general, a flow rate of 100-200 ml/kg/min will provide an inspired oxygen concentration of at least 40% with nasal catheters (Fitzpatrick & Crowe 1986). Doubling this flow rate generally provides at least 70 to 80% FiO₂. Larger dogs tend to have more dead space in their noses than smaller dogs and typically require higher flow rates to attain the desired inspiratory oxygen concentration (e.g. 200 ml/kg/min for an FiO₂ of 40% oxygen). Nasopharyngeal catheters at that these flow rates will generally increase oxygen levels to an FiO₂ of 60% while nasotracheal catheters will provide up to 80% FiO₂. It is very important to provide humidification to the oxygen being administered directly into the trachea. Only a soft occasional cough is generally observed with nasotracheal catheter use.

If oxygen supplementation will be required for several days, or if the patient is very small, warm and humidify the oxygen. A bubble or jet humidifier with a heating coil is best and can generally be purchased for around $80. A homemade humidifier can be made by bubbling oxygen through the "air vent tubing" of a bottle of intravenous fluids and then out the port where a fluid administration set is usually attached. Occasionally a patient needs to wear an Elizabethan collar to keep it from pawing at the catheter.

Once the nasal, nasopharyngeal or nasotracheal oxygen catheter is in place and oxygen is being administered, monitor the patient to see if oxygen supplementation is beneficial. If the response is favorable, you will see a decrease in anxiety and restlessness, an improvement in the color of the mucous membranes, and a decreases heart rate as well as rate and depth of respiration.

However, the results of arterial blood gas analysis are more sensitive indicators of the success of nasal oxygen supplementation. A strong indication that further techniques are necessary to help oxygenate the animal is when the p_aO₂ concentration remains lower than 60mmHg (with normal or low levels of P_aCO₂), despite oxygen administration at a rate above 100-200 ml/kg minute. If P_aO₂ levels remain low despite adequate ventilation (P_aCO² < 40 to 45 mm Hg), then other methods of supplementation should be explored.

Both nasopharyngeal and nasotracheal catheterization may provide mild continuous positive airway pressure (cpap). As the animal exhales, the air exhaled flows against a stream of positive pressure oxygen. Nasopharyngeal catheters, in which the tip of the catheter is placed in the nasopharynx, increase the oxygen concentration and effective oxygen flow delivered to the animal. These increases occur because the supplemental oxygen flow is directed at the laryngopharynx and larynx, providing an even more concentrated flow at that level.

If the level of Oxygen flow seems insufficient based upon the patient’s clinical signs or lab test results (p_aO₂ < 60 mm Hg), then placement of a second catheter through the opposing nostril is indicated. This catheter is placed into the pharynx as well and an oxygen flow rate of 200 ml/kg/minute is utilized (Dunphy, et al 2002). In prospective reseach studies conducted with normal dogs, bilateral nasal catheters were able to provide supplemental oxygen levels as high as 66% FiO₂ with flow rates at 100 ml/kg/minute and up to 90% FiO₂ with flow rates of 200 ml/kg/minute without visible discomfort. Levels of 70 - 80% FiO₂ have been able to be achieved with singe nasal catheters used in normal dogs (Fiztpatrick Crowe 1986, Mann, et al 1992). However, with bilateral catheters it is more probable that all flow rates provide the upper airway with a small amount of continuous positive pressure, which may improve the degree of oxygenation by keeping the alveoli open and expanded throughout the respiratory cycle. This has been the author’s experience on clinical patients. Nasopharyngeal catheters inherently may produce more CPAP because gas flow is directly in-line with the prelaryngeal region. Difficulties with nasopharyngeal oxygen supplementation are more common than with nasal catheters, and may include patient intolerance, aerophagia, gastric dilatation, and ineffectiveness as a result of mouth breathing. Nasopharyngeal oxygen supplementation and CPAP, however, can successfully raise p_aO₂ in some situations when nasal oxygen administration does not.

Complications due to nasal and nasopharyngeal catheters are rare. They include mild epistaxis, serous discharge, and rhinitis resolving after catheter removal; kinking and dislodgment of the catheter, persistent sneezing, and pawing at the face requiring the use of an Elizabethan collar or small doses of sedatives in some cases. During one study, an immunosuppressed patient developed sinusitis after receiving nasal oxygen supplementation for more than 10 days. The condition resolved after removal of the catheter.

Nasal and nasopharyngeal catheters are contraindicated in animals with significant nasal masses, nasal or naso-oral secretions, and nasal hemorrhage or fracture. Administering oxygen into a nasal passage already containing proteinaceous material may cause bubbling and frothing that interferes with ventilation. Conscious animals with nasal or facial fractures also do not tolerate catheterization. In these patients, there is a risk of advancing the catheter through the ethmoid area and into the calvarium.

When continuous oxygen supplementation is indicated but nasal catheters are contraindicated (such as nasal hemorrhage on-going following a blunt trauma to the skull) consider transtracheal catheterization (Mann et al 1992). These catheters can be placed easily and are similar to the diagnostic transtracheal catheters used for aspiration. Placement involves using a local anesthetic placed in the skin mid-tracheal region or at the cricothyroid membrane on the midline and usage of either a commercially available within-the-needle 14-17 gauge jugular vein catheter, a 5-8 French urinary of feeding tube placed through a 12-14 gauge hypodermic needle, or a catheter inserted between he tracheal rings (Crowe 2003). Suture the catheter to the skin and cervical fascia with friction sutures, securing it with a light neck bandage (gauze and tape). Attach an oxygen source to the catheter that heats and humidifies the gas. In this author’s experience, a visit to the respiratory department of the local human hospital has often lead to the ability to borrow a humidification unit that can be heated via an electrical plug collar surrounding the humidifier. A flow rate of 50ml/kg/min provides an FiO₂ of 40% minimum.

Adjust the flow rate based on the patient’s response and p_aO₂ values. If the p_aO₂ levels remain low despite adequate ventilation and flow rates that provide mild continuous positive airway pressure (CPAP) (200 ml/kg/min), then high-frequency jet ventilation or mechanical ventilation with positive-end expiratory pressure (PEEP) is indicated (Haskins 1984, Douglas 1984).

In this author’s experience, mild CPAP increases Functional Residual Capacity (FRC) of the lungs and decreases the work of breathing of patients with pulmonary disease. Furthermore, transtracheal catheters also have been shown to be beneficial in dogs with laryngeal dysfunction or collapse that is not quite severe enough to warrant tracheotomy.

The last methods of oxygen supplementation that are useful and recommended for use with the trauma patient are those that the author terms "hood devices". Some hood devices are available commercially (Bubble, Complete Collar), others can be home-made. In1993-94 a Personal Oxygen Device (POD) was developed by the author wherein an animal could wear an "oxygen collar" and receive continuous oxygen while in his cage, in radiology, in transport down the hall, etc., (Crowe 1994). It was demonstrated that owners could also use these devices to transport their animal to another facility, etc. The simple to make oxygen collar is made of a plastic Elizabethan collar and clear plastic wrap that covers the ventral ½ to ¾ of the front of the collar. Oxygen is administered via an IV administration set taped to the ventral inside portion of the collar. The collar should be large enough that there is adequate reservoir space for the oxygen to rest and also enough opening at the top of the collar that heat, humidity and carbon dioxide do not build up inside of the device. In cats and small dogs this may require only a few inches however in the large dog only the ventral 1/3 of the collar need be covered. The author terms this as an "oxygen boat," wherein an area is provided where the animal can place its head and receive an FiO₂ of approximately 40% oxygen but also remains cool enough to stay comfortable. This same concept is utilized in human medicine in the recovery room with an oxygen chin boat device.

The author has found that the home made POD collar works extremely well if the patient is provided with some sedation. Particularly, this has been observed to be beneficial in cats with cardiomyopathy where stress must be avoided. Pre-sedation BEFORE the collar is applied is important and before the animal becomes agitated. With 5 LPM flow rates, oxygen concentrations have been observed to be as high as 85%^6. The amount of oxygen within the collar ideally should be tested with appropriate oxygen sensors (Minox–Puritan Bennet). As a guide however, rely on what the animal tells you from his or her respiratory rate, effort, and mood. As a guide, begin with 5 LPM and if a positive repose is seen gradually decrease the rate. A rate of 2 LPM is commonly used in cats with CHF. The POD can also be used as an adjunct to the already placed nasal, nasopharyngeal or nasotracheal catheters.

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