Supplemental oxygen is commonly administered to patients to prevent or resolve hypoxemia in clinical veterinary practice. There are various methods to provide supplemental oxygen, including delivery via a nasal insufflation catheter, flow-by, face mask, use of an oxygen chamber, and transtracheal administration.1–9
Delivery of oxygen with flow-by and face mask techniques can be simple, but these are not always well tolerated and usually require technical support to hold the oxygen line or face mask close to the nose of the patient and create an increased oxygen concentration in that area.5 Commercially available oxygen chambers are sealed compartments with mechanisms to provide oxygen supplementation, eliminate exhaled CO2, and regulate humidity and ambient temperature.8 These chambers are helpful for long-term oxygen supplementation but are not always available and can make patient evaluation more difficult, especially when continuous oxygen administration is required. Transtracheal or nasotracheal oxygen supplementation requires invasive measures under sedation or general anesthesia for catheter placement. However, supplemental oxygen administration via catheters extending to the mid trachea may be beneficial when considerable oropharyngeal swelling is present (eg, following surgical manipulation or trauma).6
Insufflation via nasal catheter is an effective, economical, and minimally invasive method of providing supplemental oxygen to dogs.5 Nasal catheter placement is a simple procedure that can be easily implemented in most patients without sedation. The catheter, once secured in place, allows for easy transportation, examination, and treatment of dogs during supplemental oxygen delivery. These catheters are well tolerated at flow rates between 50 and 150 mL/kg/min in most patients.1–4
Monitoring of patients receiving supplemental oxygen includes the use of pulse oximetry and blood gas analysis. In particular, arterial blood gas analysis is sometimes necessary to accurately evaluate and monitor a patient's response to oxygen treatment.5 Knowing the Fio2 is necessary to critically evaluate arterial blood gas data, particularly when managing hypoxemic patients. The alveolar-to-arterial oxygen difference is commonly calculated to help evaluate gas exchange. This calculation also requires knowledge of the Fio2. During oxygen insufflation with a nasal catheter, accurate measurements of Fio2 require gas collection from the mid trachea. The inspired oxygen concentration changes continuously during nasal oxygen delivery; therefore, gas samples must be taken throughout the entire inspiratory phase to accurately determine mean Fio2. This makes the measurement of the Fio2 difficult in awake clinical patients receiving oxygen via this route.
Several factors may affect the Fio2 during oxygen insufflation via a nasal catheter, including tidal volume, respiratory rate, and oxygen flow rate.1–4 Increasing the flow rate during nasal oxygen delivery has been shown to increase the Fio2 in various species, including dogs.1–4,9 Because control of tidal volume and respiratory rate is not possible in awake clinical patients, previous studies have not determined how these factors may affect Fio2. Additionally, air-containing space in a dog's head may act as a reservoir for insufflated oxygen during the expiratory pause between breaths. These spaces include the nasal cavity, pharyngeal region, and oral cavity.
The objective of the study reported here was to measure the effects of tidal volume, respiratory rate, and oxygen insufflation rate on the Fio2 in cadaveric canine heads attached to a lung model consisting of corrugated tubing, a sample port, and a variable-volume piston ventilator. We hypothesized that higher insufflation rates, lower respiratory rates, and smaller tidal volumes would result in increased Fio2, compared with values achieved with lower insufflation rates, higher respiratory rates, and larger tidal volumes. Because, to our knowledge, no techniques to measure the air-containing spaces in the heads of canine patients have been previously published, a secondary aim was to estimate the volume of air-containing spaces in canine cadaver heads by use of a water displacement method.
End-tidal carbon dioxide
Fraction of inspired oxygen
Least squares mean
Digital micrometer Absolute Digmatic, Mitutoyo Co, Kawasake, Kanagawa, Japan.
Modified air pump, Respiration pump model No. 607, Harvard Apparatus, Holliston, Mass.
Kendall feeding tube, Tyco Healthcare, Mansfield, Mass.
Oxygen flowmeter B250-2-B3123, Parker Hannifin Co, Hartfield, Penn.
Flowmeter F150-AHR-4/B125-40B1557, Parker Hannifin Co, Hartfield, Penn.
Carbon dioxide flowmeter F65-AHR-1/A 125-B3670, Parker Hannifin Co, Hartfield, Penn.
Teledyne AX 300 oxygen analyzer, Teledyne Technologies Inc, City of Industry, Calif.
Nelcor N-85 microstream capnograph, Tyco Healthcare, Pleasanton, Calif.
Datex Ohmeda Cardiocap/5 Anesthesia Monitor, Datex-Ohmeda Inc, Madison, Wis.
Ohmeda ventilometer, Datex-Ohmeda Inc, Madison, Wis.
Hans Rudolf calibration syringe Model 5530, Hans Rudolph Inc, Shawnee, Kan.
GLIMMIX, SAS, version 9.2, SAS Institute Inc, Cary, NC.
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2. Mann FA, Wagner-Mann C, Allert JA, et al. Comparison of intranasal and intratracheal oxygen administration in healthy awake dogs. Am J Vet Res 1992; 53:856–860.
3. Loukopoulos P, Reynolds W. Comparative evaluation of oxygen therapy techniques in anaesthetized dogs: intranasal catheter and Elizabethan collar canopy. Aust Vet Pract 1996; 26:199–205.
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6. Senn D, Sigrist N, Forterre F, et al. Retrospective evaluation of postoperative nasotracheal tubes for oxygen supplementation in dogs following surgery for brachycephalic syndrome: 36 cases (2003–2007). J Vet Emerg Crit Care 2011; 21:261–267.
7. Sullivan LA, Campbell VL, Radecki SV, et al. Comparison of tissue oxygen saturation in ovariohysterectomized dogs recovering on room air versus nasal oxygen insufflation. J Vet Emerg Crit Care 2011; 21:633–638.
8. Drobatz KJ, Hackner S, Powell S. Oxygen supplementation. In: Bonagura JD, Kirk RW, eds. Kirk's current veterinary therapy small animal practice. 12th ed. Philadelphia: WB Saunders Co, 1995;175–179.
9. Crumley MN, Hodgson DS, Kreider SE. Effects of tidal volume, ventilatory frequency, and oxygen insufflation flow on the fraction of inspired oxygen in cadaveric horse heads attached to a lung model. Am J Vet Res 2012; 73:134–139.