Page 431 - Clinical Small Animal Internal Medicine

40 Mechanical Ventilation 399

Humidification two or three times as long as the patient’s oxygenation
VetBooks.ir Anesthetized patients are not able to cough or clear remains adequate and the patient does not seem dis-
tressed. If suctioning is productive, it can be performed
airway secretions effectively and this can contribute
to development of ventilator‐associated pneumonia as frequently as every 2–4 hours.
The risks of suction include hypoxemia, patient dis-
(VAP) and tube occlusion. Airway management is essen- comfort, damage to the tracheal mucosa, collapse of
tial in an effort to try to reduce these complications. small airways and alveoli, and contamination of the
Gas flow bypasses the nasal passages during mechanical lower airways.
ventilation and is therefore not humidified or filtered. If the secretions are too dry to suction well or ade-
This can lead to a loss of heat and moisture, which can quate humidification is not being provided, small
damage the respiratory epithelium. Humidification is aliquots of sterile saline (0.2 mL/kg) may be instilled
also critical in making secretions less viscous and easier into the airway prior to suctioning. This practice has
to remove. been challenged because of the lack of evidence of
The breathing circuit should be humidified appropri-
ately without excessive accumulation of liquid in the cir- beneficial effects coupled with the risk of introducing
infection.
cuit. There are two basic options for airway humidification:
active heated water humidifiers or passive heat moisture
exchangers. The heated water humidifiers are very effec- Tracheal Tube Management
tive, are ideal in patients with substantial airway secre- Ventilator patients require an artificial airway, which is
tions, and help prevent hypothermia, which can be an most commonly accomplished via endotracheal (ET)
issue in small patients. They are expensive and unless intubation and general anesthesia. It is important that
they are used in conjunction with heated wire circuits, ET tubes are sterile and ideally have high‐volume/low‐
they are associated with substantial “rain out” in the pressure cuffs. Tracheal mucosal blood flow can be
circuit. This refers to water accumulating in the limbs occluded by pressures over 25–35 mmHg. Ideally, cuff
of the breathing circuit, which in large volumes can pressure should be maintained between 20 and 25 mmHg
interfere with ventilator function. More concerning, and measured regularly with a pressure gauge system.
it greatly increases the risk of VAP. Heat moisture Higher pressures impede mucosal blood flow and may
exchangers (HME) are inexpensive devices that fit on lead to tracheal necrosis. Lower cuff pressures are asso-
the end of the endotracheal tube and passively take heat ciated with an increased risk of aspiration. Although fre-
and moisture from the exhaled gas and return it to the quently used, the pilot balloons do not correlate well
inhaled gas. They have been found to be equally effec- with cuff pressure and should not be used as an indicator
tive at humidifying the airways as the active humidifiers of appropriate inflation.
and may reduce the incidence of VAP by reducing Tracheal injury can also be minimized by deflating
moisture in the circuit. They can occlude and this has the cuff and repositioning the ET tube slightly to
the potential to be a life‐threatening event. For this change the pressure point and then reinflating the cuff
reason, the authors advise that they be avoided in every four hours. The mouth and pharynx should be
patients with excessive airway secretions.
flushed and suctioned prior to deflating the cuff.
Endotracheal tubes should be securely tied with IV
Suctioning tubing or another nonporous material, which is less
likely than gauze to become saturated with oral secre-
Airway suctioning is another critical aspect of airway tions and bacteria. The ties should be moved and
management. There are risks associated with this proce- secured in a different position every four hours to min-
dure, and proper technique must be followed. The imize lip trauma.
inhaled oxygen concentration should be increased to The endotracheal tube may need to be changed every
100% prior to and during suctioning. The suction cathe- 24–48 hours, depending on the amount and character of
ters should be sterile, soft, and flexible with more than the secretions. It is important to preoxygenate with 100%
one distal opening and a proximal thumbhole to control oxygen prior to changing the tube and to be prepared for
the level of suction. Sterile gloves should be worn and a difficult intubation. Tracheostomy tubes should ideally
sterile technique observed throughout the procedure. have an inner cannula, which should be cleaned every
Closed suction systems are also available which are help- four hours. If there is no cannula, the tube should be suc-
ful in maintaining sterility and preventing issues with tioned regularly and changed every 24 hours. The tra-
disconnection. Suction should be applied while with- cheostomy tube should also have a cuff to protect the
drawing the catheter from the airway for no more than airway from the migration of oral secretions and to allow
five seconds at a time. This procedure can be repeated PEEP to be used.