To the Editor:—
Preoxygenation before induction of general anesthesia is problematic in claustrophobic patients. Anesthesia masks often cause patients to feel as though they are being smothered, and when a mask is applied by someone other than the patient, claustrophobia may be compounded by the patient’s perceived loss of control in a threatening environment. Alternative approaches to traditional preoxygenation, such as using a “blow-by” of supplemental oxygen from the anesthesia circuit or the application of a face shield containing supplemental oxygen, can increase inspired and arterial oxygenation but do not permit the maximum increases in oxygen or the displacement of nitrogen that is attained with a closed system.1,2
These challenges with preoxygenation can be overcome in the majority of claustrophobic patients with use of standard anesthesia equipment. With the anesthesia circuit fresh oxygen flow set to a large value (e.g. , 10 l/min) and the pop-off valve opened, the patient is instructed to hold the anesthesia circuit tubing with the preferred hand. Next, the patient is instructed to place the L-connector between the lips and to seal the lips around the connector and breathe exclusively through the mouth. If continued nasal breathing is of concern, he may elect to use the contralateral hand to pinch the nose and facilitate mouth-only breathing; however, this addition may not be tolerated in some. The technique is demonstrated in figure 1.
The efficacy of this mouth-to-circuit (MTC) method is determined by three factors: (1) the patient’s ability to sustain MTC breathing for sufficient time to wash oxygen into, and nitrogen from, the lungs; (2) the ability of the patient to breath exclusively from the mouth and circuit, not around the circuit or through the nose; and (3) the diminished dead space of the circuit compared with a traditional mask approach.
During a 3-yr period and in more than 50 patients reporting intense claustrophobia, we have collectively observed that every single one asked to use the MTC technique was able to make a good seal around the L-connector, without evidence of leak or nasal breathing. Before this experience, we had determined that patients seemed to tolerate normal tidal volume breathing through the circuit (which in turn required longer periods of nitrogen wash-out), compared with fewer, larger, “cleansing” breaths.3Normal breathing was reported to result in less of a sensation of “breathing through a straw” when compared with supranormal tidal volume breaths. There seemed little need to have the patient manually pinch the nose to prevent nasal breathing, although this may certainly be an option in some patients.
To determine the efficiency of the MTC technique, we conducted an institutional review board–approved, minimal risk protocol in 10 healthy, nonclaustrophobic volunteers. End-expired oxygen, nitrogen, and carbon dioxide concentrations were measured with a Rascal II gas monitor (Ohmeda, Louisville, CO) via a sampling catheter attached to the L-piece of the circuit. Each volunteer pinched his own nose closed. Measurements were recorded before initiation of preoxygenation and at 30, 60, 90,120, 150, and 180 s thereafter. The study divided the volunteers into two groups and used a crossover design. Mean concentrations of circuit oxygen, nitrogen, or carbon dioxide were similar between the two arms of the study. For example, mean carbon dioxide concentrations never differed by more than 1 mmHg, denoting constant respiratory effort. Circuit nitrogen concentration (mean ± SD) for MTC versus facemask breathing were 25 ± 5 and 30 ± 7%, respectively, at 30 s; 11 ± 5 and 15 ± 6% at 60 s; 3 ± 2 and 6 ± 5% at 120 s; and 2 ± 1 and 4 ± 6% at 180 s.
After preoxygenation with this technique and anesthesia induction with an intravenous drug, ventilation of the lungs can be rapidly converted to a standard mask technique immediately after the patient loses consciousness.
The advantages of the MTC technique for claustrophobic patients are that it requires no special equipment, the patient’s face is not covered by a mask, and the patient is in total control of the airway (hence reducing the sense of helplessness). When a complete seal is formed around the L-connector and mouth breathing is used exclusively, the oxygen wash-in, nitrogen wash-out properties of the patient–circuit unit should be nearly identical to that attained with the more traditional mask-facilitated preoxygenation used in nonclaustrophobic patients.
*Mayo Clinic, Rochester, Minnesota. email@example.com