The NVA® is a convenient, non-invasive, pressure-sealing and self-retaining nasal cannula used with an anesthesia circuit to deliver a precise concentration of oxygen under a pressure sufficient to stent open the upper airway of the anesthetized patient.


NVA® / SNOR-TAL®
THOUGHTS
on
APPLICATION

  • Anatomically, SNOR is comparable to OSA. Pharmacology makes the difference: The airway obstruction of SNOR is drug-induced, so is the depression of the rescuing reflexes that are fully active in OSA.
  • The NVA® is used with conventional anesthesia circuits to control oxygen concentration, to preserve airway patency with positive pressure and to promote spontaneous respiration.
  • The NVA® in SNOR-TAL® configuration is not the usual CPAP interface. It is not vented. It requires that CO2 be eliminated through a conventional anesthesia circuit.
  • In the treatment of SNOR, a fluctuating positive airway pressure (FPAP) fluctuates up and down passively with respiration under the influence of a continuous gas flow from an anesthesia circuit. Passively, inspiration becomes relatively more negative than expiration.
  • In the treatment of OSA, a continuous positive pressure (CPAP) continues throughout respiration under the influence of a variable gas flow produced by an airflow generator that keeps pressure continuous. In Bi-PAP, the generator senses inspiration and actively increases flow to achieve a higher pressure and deliver more volume.
  • The relatively lower pressure on inspiration with FPAP as compared to the more continuous pressure of CPAP is, arguably, more conducive to venous return to the heart.
  • After proper sizing, the NVA® can be inserted into the nasal vestibules of the awake patient with a reasonable degree of comfort. The vestibule is lined by skin.
  • The long poles of the flanges of the NVA® are fully inserted into the nares and then together rotated up into the domes of the nasal vestibules.
  • As the NVA® is rotated, a finger retracts one corner of the nose at a time to allow the wedge-shaped short poles to slide over the inferior cartilaginous rims of the lobules of the nose.
  • The NVA® locks into the vestibules behind the cartilaginous rim surrounding the nares. Further stabilization may be achieved by hooking the SNOR-TAL® around the chin before connecting to the circuit.
  • The flanges of the NVA® are 32/32" long and marked at 30, 28, 26 and 24/32". 26 is a common size for women and 28 for men. However, every nose is different and experience will soon determine size.
  • The user should first practice locking the NVA® into his /her own nasal vestibules before placing it in a patient.
  • The awake patient will release the pressure from building in the nose by opening the soft-palate and breathing through the mouth. The pressure gauge will read, "0".
  • As sedation deepens, the soft palate relaxes and is pushed by the nasal gas flow to seal behind the tongue to create a positive pressure sufficient to stent open the oropharynx.
  • There is a "functional pop-off" of excess gas from the oropharynx around the tongue and soft palate that is consistently less than 20 cm of H2O even for the highest flow rates produced in an anesthesia circuit.
  • The mechanical pop-off valve of the anesthesia circuit is usually completely closed and the gas flow is adjusted to achieve a pressure sufficient to eliminate upper airway obstruction and to create a FPAP.
  • Peak airway pressures less than 20cm of H2O ( the opening pressure of the esophageal sphincter ) are unlikely to pressurize the stomach.
  • Positive airway pressure generates positive intra-pleural pressure which generates positive intra-esophageal pressure which increases the barrier pressure that opposes esophageal reflux. Elevation of the back, if possible, adds the effect of gravity to oppose reflux.
  • Likewise, the gradient of positive pressure ( oropharynx > oral cavity ) and gas flow tends toward clearing the oropharynx and preventing the backflow from the mouth of secretions, blood and irrigation.
  • Upper airway obstruction, as signaled by inspiratory stridor, is conveniently detected by a SNOR-SCOPE®. A fluctuating needle of the pressure gauge confirms unobstructed spontaneous respiration.
  • Since gas flow rates high enough to relieve obstruction may prevent back breathing to the level of the circuit sampling port, CO2 may have to be sampled at the mouth.
  • A sampling device may be fashioned from a nasal trumpet inserted flange first behind the teeth and connected to the sampling line.
  • A spontaneously breathing patient is unlikely to have completely depressed protective laryngeal reflexes and, therefore, is not likely to aspirate silently. However, reflexes cannot be relied upon to protect the airway and, at the first sign of a problem ( laryngospasm, cough, breath hold, swallow, etc. ), the phaynx should be suctioned immediately to check for reflux.
  • Patients, who breath spontaneously and without obstruction at a normal respiratory rate under FPAP will eliminate CO2 adequately (mild hypercapnia) for many hours of general anesthesia.
  • After thorough pre-oxygenation with an NVA®/SNOR-TAL® apneic oxygenation can maintain oxygen saturation for a prolonged period of apnea.
  • In normal lungs, an oxygen concentration of 30% will normalize arterial pO2 for a severe degree of hypoventilation.
  • In addition to preventing upper airway obstruction, positive airway pressure tends to augment FRC to prevent shunt and atelectasis.
  • Basically, FPAP and CPAP prevent upper airway obstruction but, in a patient who needs active ventilatory support, Bi-PAP or a full-function ventilator may be required.

2008 ©Copyright Noble Anesthesia-Air, Inc. All rights reserved.