![]() ![]() During the inspiratory phase, the ventilator’s driving pressure actively compresses the bellows to deliver a breath, and the ventilator’s exhaust valve is closed. Similarly, if the oxygen flush valve is used during the inspiratory phase of mechanical ventilation, the patient’s lungs may be exposed to excessive pressure and overdistension. Therefore, use of the flush valve while a patient is connected to a nonrebreathing system transmits excess volume and pressure directly to the patient’s airway and lungs. 3,4 A nonrebreathing system (eg, Bain breathing system) has a relatively small inner volume and little compliance. The oxygen flush valve allows oxygen at high pressure and volume into the breathing system (35-70 L/min with a pressure of 45-60 pounds per square inch gauge, which becomes approximately 1 L/s into the breathing system). If machine malfunction is suspected, it may be prudent to quickly replace the machine with a different machine.Excessive inflow can occur from improper use of the oxygen flush valve, aggressive ventilator settings (high airway pressures and tidal volumes), and/or inappropriate connection of oxygen tubing (meant for oxygen insufflation via open mask) to a cuffed endotracheal tube, laryngeal mask airway, or other airway device without the ability to allow excess gas to vent. If hypercapnia persists, investigate causes of increased inspired CO 2 including excessive dead space, exhausted CO 2 absorbent or one-way valves not functioning properly in an RC, or inadequate oxygen flow in an NRC. ![]() PPV can also cause barotrauma, so ventilator settings should start conservatively and be adjusted based on ETCO 2. If BP declines, decrease peak airway pressure and consider a fluid bolus (5–20 mL/kg) if there is the potential that the patient is hypovolemic. Prior to instituting PPV, the hemodynamic status of the patient should be stable, if possible, as PPV can negatively affect cardiac output through impaired venous return. Courtesy of Heidi Shafford, published in the Journal of Feline Medicine and Surgery, 2018 20:602-34Ī mechanical ventilator can be used if the anesthetist is knowledgeable and comfortable with ventilator use. Bain non-rebreathing circuit (NRC) adapter with in-circuit manometer (white arrow) and safety pop-off valve (black arrow). A safety pop-off relief valve will prevent this complication. The anesthetist can deliver breaths by manually squeezing the reservoir bag while occluding the adjustable pressure limiting valve, taking great care to not leave the valve closed except when delivering a breath. ![]() Initiate PPV if ETCO 2 is >60 mm Hg (hypercapnia). To correct increasing CO 2, first ensure that the cause is not excessive anesthetic depth by checking the vaporizer setting and evaluating indicators of the patient’s anesthetic plane. Thus, hypoventilation should be corrected.ĮTCO 2 is ~35–45 mm Hg in awake patients and ~40– 50 (up to 55) mm Hg in patients in an appropriate surgical plane of anesthesia. Hypoventilation can cause hypercarbia, with subsequent respiratory acidosis, and hypoxemia. Hypoventilation can be estimated by observing respiratory rate and depth (very subjective) and can be quantified using capnometry.
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