Thoracocentesis

This procedure is an important skill with which we must all be familiar. Patients presenting with diminished lung sounds, increased respiratory effort and/or respiratory distress may benefit from the removal of air, blood or fluid from the pleural space. Presence of fluid or air in the pleural space prevents the lungs from expanding to their full capacity. This results in diminished oxygenation and respiratory compromise. Removal of the offending substance allows the lungs to fully inflate and provides the animal with immediate, though potentially temporary, relief. In the distressed patient, thoracocentesis must be performed prior to radiography or any other clinical procedure. Flow-by oxygen should be provided immediately and continued until the animal is stable enough to tolerate placement of a nasal cannula. If possible, intravenous access can be established and used for mild sedation before attempting thoracocentesis; however, in many cases, this is not feasible.

Procedure

1.  Clip the fur over the area of the seventh intercostal space and surgically prepare the area.

2.  Attach an extension set with a three-way stopcock to a large syringe.

3.  Pass a catheter or butterfly needle through the seventh intercostal space, into the pleural space slightly above (air) or slightly below (fluid) the costochondral junction.

4.  The bevel of the needle should be facing away from the body wall, directed dorsally to collect air and ventrally to collect fluid.

5.  Advance the catheter into the pleural space and remove the stylet.

6.  The extension set can be pre-fastened to the butterfly needle, or quickly fastened to the catheter; be cautious not to leave the system open to the environment at any time.

7.  Gently pull back on the plunger of the syringe to evacuate the contents of the pleural space.

8.  If negative pressure is encountered, do not apply more force as this is painful!

Nasal Cannula Placement

In many cases patients require oxygen supplementation for an extended period of time. Placement of an indwelling nasal cannula is the most effective way in which this may be achieved. A variety of different tubes may be used as cannulas; selection should be made based on patient size and clinic preferences.

Procedure

1.  Provide sedation if necessary or if patient condition permits.

2.  Place 2–3 drops of local anaesthetic in one or both nostrils (ophthalmic anaesthetic agent).

3.  Premeasure nasal cannula from tip of rostrum to medial canthus; mark measurement on catheter with permanent marker.

4.  Lubricate cannula with 2% lidocaine lubricant.

5.  Gentle, dorsally directed pressure may be applied to the tip of the nose to facilitate passage of the cannula.

6.  Slide cannula into nostril directing ventromedially. If resistance or a 'crunchy' sensation is encountered, stop and make another attempt.

7.  The cannula should be able to pass beyond the marked measurement without a significant amount of resistance.

8.  With the marker at the tip of the rostrum, loop cannula around nostril and fasten with a tiny drop of glue. Cannula should be fastened at a few sites and positioned mid-forehead, directed caudally, between the ears. Sutures can also be used to fasten cannula in place.

Nasal cannulas are not typically suitable for patients with coagulopathies.

Tracheostomy

Fortunately, it is not common to have a patient present with a complete upper airway obstruction. However, in the event that this should occur, it is prudent to be familiar with the procedure and equipment involved in placing an emergency tracheostomy tube. Tracheostomies are indicated in patients that are in respiratory distress due to an obstruction of their upper airway. Clinics should endeavour to have several sizes of tracheostomy tubes available, but in the event that this is cost prohibitive, an endotracheal tube can be used as a substitute. To render the endotracheal tube useful as a tracheostomy tube, the distal end of the tube is cut lengthwise, leaving the cut ends attached and peeled outwards like a banana. These flaps can be used to secure the tube in place by attaching some umbilical tape to each end and tying the tape ends together behind the patient's head. Ideally, whichever tube is used, it should be sterile.

Procedure

1.  If the patient is still conscious, injectable anaesthetics can be used.

2.  Some patients can be intubated and ventilated for the procedure once sedated/anaesthetised.

3.  Position the patient in dorsal recumbency, forelimbs parallel to thorax.

4.  Shave and surgically prepare a large area on the ventral neck.

5.  Incise the skin between the larynx and the seventh tracheal ring.

6.  Carefully separate the musculature covering the trachea.

7.  Incise the trachea horizontally between the fourth and fifth rings. Incision should not extend farther than 50% of circumference.

8.  Stay sutures are placed around the rings caudal and cranial to the incision. These will facilitate tube placement and replacement if needed.

9.  A vertical incision through the third to fifth rings is an alternative approach. This is more suitable in extremely small patients.

10.  Tube is placed through incised area into trachea. Tube should not occupy more than 75% of tracheal lumen. Tube should be the length of approximately six tracheal rings.

11.  The incision is closed cranial and caudal to the tube.

Tracheostomy tube care is of utmost importance as the animal's airway can still become obstructed with the tube in place. The focus of these notes is temporary or emergency care and as such only a brief outline of tracheostomy tube care will follow.

The tube must be suctioned at regular intervals in order to maintain its patency. If the tube remains in place for 24 hours, a schedule of tracheostomy tube care should be in place. Suctioning the tube every 4 hours, more frequently if needed, is appropriate. It is important that the suction catheter is introduced into the trachea before negative pressure/suction is applied. A small amount (~1 ml) of sterile saline can be introduced to the tracheostomy tube prior to suctioning. This can help loosen debris or dried blood and facilitate its removal. Each introduction of the suction catheter should last no longer than 10 seconds as its presence can cause hypoxia. Administration of small amounts of saline also accomplishes the task of moisturising the airway. Airways should be humidified regularly, either by administration of 1–5 ml of sterile saline or by using a nebuliser.

The surgical site should be kept clean at all times. Small amounts of discharge from the wound can be expected and should be gently removed using sterile gauze. Occasionally it is necessary to apply a small amount of barrier cream to the surrounding area.

Thoracostomy Tube Placement

Thoracostomy tubes are not typically placed by technicians. However, the technician's familiarity with this practice will smooth the progress of the veterinarian performing the procedure.

Procedure

1.  Patient is clipped from caudal aspect of scapula to last rib.

2.  Aseptic preparation of entire area.

3.  Select appropriate tube size. Tube should be size of diameter of mainstem bronchus; largest size that will comfortably fit between the patient's ribs:

a.  < 7 kg: 14 Fr

b.  7–15 kg: 18 Fr

c.  16–30 kg: 22 Fr

d.  > 30 kg: 28 Fr

4.  Skin caudal to scapula is grasped and pulled cranially.

5.  Local analgesics can be administered via injection at approximately seventh intercostal space.

6.  Tube is measured from point of insertion to roughly the second rib.

7.  Small incision is made in skin, and muscle is dissected.

8.  Tube is inserted through pleura with caution - do not allow stylet to advance into thorax.

9.  Tube is passed in direction of clinician's choice. N.B. cranioventral is typical for removal of fluid, caudodorsal for removal of air.

10.  Tube should be clamped while stylet is removed.

11.  As skin is released tube is tunneled under skin which provides added security against leaks.

12.  Tube is secured using purse-string suture and Chinese finger trap.

13.  Adapter is placed on end of tube, often with three-way stopcock, to facilitate removal of air/fluid by syringe.

14.  Chest bandage or stockinet should be used to protect tube. Bandage should be evaluated several times/day. Bandage changes as needed or every 24–48 hours.

15.  Radiographs will confirm appropriate placement of tube.

16.  N.B. never apply more than 5 ml negative pressure to syringe as this is painful for patient. Plunger should be moved gently and slowly during evacuation of chest.

17.  Chest should be evacuated as needed, typically every 1–4 hours.

18.  Continuous suction (10–15 cm constant negative pressure) is indicated in cases that cannot be evacuated as quickly as fluid/air accumulates.

19.  Tube can be removed once fluid/air production has ceased for at least 12 hours. Acceptable fluid accumulation with thoracostomy tube in place can be up to 2 ml/kg/day.

20.  Gauze square with antibiotic ointment can be placed over stoma during and after removal of tube. Bandage thorax for 24–48 hours post removal.

Monitoring the Respiratory Patient

Initially, our focus is on re-establishing a suitable concentration of oxygen in the arterial blood, removing excess amounts of carbon dioxide and decreasing the work of breathing. Once these priorities have been addressed, the focus shifts towards continuous re-evaluation of the patient's status and need for oxygen supplementation.

Pulse Oximeter

 Portable unit that measures the percentage of hemoglobin that is saturated with oxygen

 Normal is > 95%

 Difficult to use in some veterinary patients

 Questionable reliability

Capnograph

 Monitors the concentration of carbon dioxide in exhaled gases. Measurement is called end-tidal CO₂ (ETCO₂).

 Is an indirect way of monitoring the partial pressure of carbon dioxide in the arterial blood. Normally see approximately 5 mmHg difference between ETCO₂ and arterial blood. Difference between concentration in expired gas and concentration in arterial blood increases with respiratory disease.

Arterial Blood Gases

 Identifies oxygen and CO₂ in arterial blood

 Excellent means of identifying how effectively lungs are functioning

Measurement of Vital Signs

 Body temperature increases with the work of breathing - monitor frequently

 Continuous measurement recommended for ventilator patients

 Increase can be early warning that CO2 is increasing

 Heart rate and rhythm

 Tachycardia can suggest hypoxia

 Arrhythmias can be present due to tissue hypoxia

 Respiratory rate and quality

 Tachypnoeic - abnormally fast RR

 Bradypnoeic - abnormally slow RR

 Dyspnoeic - abnormal effort

 Apnoeic - not breathing

 Hyperpnoeic - exaggerated depth of breathing to meet metabolic demands such as hypercarbia or anaemia

 Cheyne-Stokes respiration - gradually increasing and decreasing depth of respirations with intermittent episodes of apnoea

 Mucous membranes

 Dusky to dark or purple - cyanosis. Blue colour due to haemoglobin that is without oxygen. Concentration of arterial oxygen is below 85% when membranes appear cyanotic.

 Bright red. Can be due to hyperthermia (work of breathing), carbon monoxide poisoning or is seen in other conditions that may not be related to primary respiratory disease.

 Mentation/disposition

 Anxious - due to confined environment of oxygen cage/hood

 Air hunger - may be gasping or may be displaying more subtle signs such as restlessness

 Orthopnoea - increased difficulty of breathing while lying down; patients choose either to rest in sternal recumbency or to stand up

 Sleep - animals in respiratory distress usually cannot sleep