Page 2400 - Cote clinical veterinary advisor dogs and cats 4th

1186 Ventilation, Positive Pressure

○ Alfaxalone 0.5 mg/kg boluses IV titrated ○ Can be used for long-term care (days to ventilated animals that suddenly develop
to effect up to 3 mg/kg total dose in dogs ○ Relatively expensive • Oral and ocular ulcers: usually avoided with
weeks)
shock.
VetBooks.ir to effect. In cats, it is not recommended as Anticipated Time good nursing care
and cats, followed by CRI (6-10 mg/kg/h)
a single agent IV due to the potential for
○ Use sterile eye lubricant, and cleanse
rough recoveries, which may exacerbate
dyspnea. Can be combined with other • Can take several minutes to set up mechanical mouth with 0.1% chlorhexidine solution–
soaked gauze sponges every 4 hours.
ventilators.
drugs for balanced total IV anesthesia • Initiate manual PPV (takes seconds to initi-
○ Close cardiovascular monitoring is ate) while mechanical ventilators are being Procedure
required in animals under heavy sedation. set up. NOTE: Step-by-step guidelines to initi-
• Minimum recommended monitoring • Duration of ventilation time varies with the ate PPV are beyond the scope of this text.
○ Vital signs underlying disease and animal’s response. Clinicians should consult more extensive
○ Level of consciousness reviews to become familiar with different
○ ABGs or pulse oximetry and end-tidal Preparation: Important ventilator modes and their indications. The
Checkpoints
CO 2 following are suggested guidelines for start-
○ Arterial blood pressure (BP) (p. 1065) • Ensure oxygen source, monitoring equip- ing PPV. Adjust settings based on patient
○ Continuous ECG (p. 1096) ment, and suction devices are available. response. Most cases do better in sternal
○ Volume of fluids in and out (urinary • Nutritional support should be available for recumbency.
catheter) long-term cases. • Ambu bag
○ Hematocrit, total protein, glucose, and • Pleural space disease (pneumothorax, pleural ○ Bag size (in milliliters) should be at least
urine specific gravity effusion) should be identified and treated 15 × body weight (kilograms) to deliver
○ Ventilator settings should be recorded before ventilation. adequate tidal volumes.
every hour. ○ Thoracocentesis (p. 1164) in suspected ○ Set oxygen flow rates at 10-15 L/min
Manual: cases; untreated pleural space disease (delivers 50%-90% oxygen levels).
• Ambu bag and attached oxygen is associated with higher incidence of ○ Attach adjustable PEEP valve to exhaust
○ Inexpensive ventilatory complications (p. 1102). limb if PEEP desired (requires compatible
○ Readily available • Check that Ambu bag valves are functioning attachment site). Adjust PEEP by turning
○ Pediatric-sized bag most common (typi- properly (not sticking) between uses. valve to the desired level (start with 5 cm
cally 450-950 mL volume) • Check anesthetic machine and anesthesia H 2 O).
○ Can be used without supplemental oxygen ventilator, and check that mechanical ventila- ○ Higher (90%-100%) inspired oxygen
(not ideal) tor tubing is correctly connected, valves are levels can be achieved with an oxygen
○ Excellent for short-term use (i.e., functioning, humidifiers are full, and there reservoir bag.
during cardiopulmonary resuscitation are no leaks in the system. ○ Animals can breathe spontaneously while
[CPR]) connected to Ambu bags, although airway
○ Can add positive end-expiratory valves, Possible Complications and resistance is higher.
which create positive end-expiratory Common Errors to Avoid • Anesthetic machine with manual ventilation
pressure (PEEP) to recruit collapsed • Barotrauma: avoid airway pressure > 30 cm ○ Insert adjustable PEEP valve in the expira-
alveoli and improve oxygen exchange H 2 O. tory limb of tubing (bidirectional valves
(typically in 0-10 cm or 0-20 cm H 2 O • Cardiovascular effects: PPV increases eliminate the risk of occlusion associated
sizes) intrathoracic pressures, which may impede with backward insertion of unidirectional
○ Some Ambu bags have a removable safety venous return and subsequently decrease valves) if PEEP is desired.
valve that opens when a specific airway cardiac output; at a minimum, monitor Suggested initial PPV setting guidelines
pressure is exceeded (typically 40 cm H 2 O). heart rate and BP closely. • Inspired oxygen concentration (FIO 2 ): start
○ Difficult to determine tidal volume and • Oxygen toxicosis: substantial risk after 12 with 100% FIO 2 .
airway pressures delivered (vary with size hours if FIO 2 remains > 60% ○ For long-term (many hours) use, decrease
and degree of manual pressure applied to • Ventilator-associated pneumonia: monitor to the lowest FIO 2 that maintains desired
the bag) for deterioration of respiratory function or PaO 2 /SaO 2 to reduce the risk of oxygen
• Anesthesia machine with manual ventilation unexplained fever. toxicosis.
○ Readily available ○ Confirm diagnosis with radiographs, • Respiratory rate (RR): 8-20 breaths/min
○ Estimate tidal volume delivered with the lung ultrasound, and endotracheal wash ○ Increase the RR to decrease the PaCO 2
size of the reservoir bag (p. 1073). if > 50 mm Hg.
○ Can monitor airway pressure with attached • Pneumothorax: more common with high ○ New RR = RR × PaCO 2/desired PaCO 2
pressure gauge airway pressures (>30 cm H 2O) ○ RR often > 20 breaths/min if underlying
○ Can apply adjustable PEEP valves (typical ○ Can cause acute deterioration in ventila- pulmonary disease is present
range, 0-40 cm H 2O) tory parameters • Oxygen flow rates: start with 0.5-1 L/kg/
Mechanical: ○ Auscultation usually reveals dull breath min.
• Anesthesia ventilators sounds in upper parts of thorax (e.g., ○ Often need to increase if underlying
○ Limited choice of ventilator modes dorsally when animal is in sternal pulmonary disease is present
○ Typically deliver only 100% inspired recumbency). • Tidal volume (amount of air delivered with
oxygen concentrations (FIO 2) ○ The absence of a glide sign with thoracic each breath). Normal values: 10-15 mL/kg.
○ Increased risk of oxygen toxicosis if focused assessment of sonography for ○ Values of 4-6 mL/kg are associated with
ventilating > 12 hours trauma (TFAST) strongly suggests fewer lung injuries in people.
• Mechanical ventilators pneumothorax (p. 1102). ○ Volumes in excess of 20 mL/kg are likely
○ Allow greatest control over type of breath ○ Perform thoracocentesis in suspected cases to cause lung injury (barotrauma and
delivered (pressure, volume, flow rate, (p. 1164). volutrauma).
FIO 2 , respiratory rate, sensitivity to trigger ○ Tension pneumothorax causes a severe ○ May need to increase tidal volume if
a breath, and PEEP) decrease in cardiac output and hypoten- PaCO 2 does not respond to increased
○ Supply humidified oxygen sion; check for tension pneumothorax in RR

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