Mass spectrometry (Perldn-Elmer MGA 1100, Marquette Gas Monitoring Corp, St. Louis) was used to monitor end-tidal nitrous oxide so that hypoxemia from the second gas effect would not have occurred. All patients who had received regional anesthesia had been breathing 2 to 4 L/min of oxygen by nasal cannulas intraoperatively. All SaOs values were 97 percent prior to transport to PAR. During the less than 2-min transport to PAR, all patients spontaneously breathed room air. canadian pharmacy
On PAR admission, all patients were awake and responsive with no artificial airways in place. The SaOs monitoring began within 30 s of admission utilizing pulse oximeters (Nellcor-N 200, Nellcor Corp, Hayward, Calif) with a disposable probe attached to the distal phalanx of a finger. After an initial SaO, measurement, each patient received oxygen by aerosol face tent (Hudson Oxygen Therapy Sales Co, Temecula, Calif). The aerosol face tent is a variable performance device that is comfortable, nonocclusive, and allows the nursing staff access to the patients mouth for suctioning and allows the patient to easily verbalize. The wall oxygen flow was 12 L/min with a minimum oxygen concentration of 0.40. Air entrainment increased the total gas flow through the face tent to at least 36 L/min. The wall outlets for oxygen were checked for accuracy of delivered oxygen concentration by mass spectrometry. Each patient was also monitored by automatic, oscillometric blood pressure measurements, electrocardiography, and for temperature and respiratory rate. Any invasive monitors used intraoperatively, such as arterial pressure catheters or pulmonary artery catheters, were also monitored during the recovery period.
Patient data (Table 1) were gathered from the chart and anesthesia record. The SaOt, pulse rate, and the oximeter signal intensity were stored in each monitors memory and printed onto a strip chart recorder at the termination of each patient study. If the signal intensity tracing was abnormal, indicating poor tracking of the arterial pulse (potentially secondary to such factors as poor peripheral perfusion, vasoconstriction, or shivering), the corresponding recorded SaO, values were considered potentially inaccurate and were excluded from the study results. For the purposes of this study, a decrease of SaOt to less than 92 percent for greater than 30 s was considered a clinically relevant desaturation. A saturation value of 92 percent was chosen because of its location on the oxyhemoglobin dissociation curve. Values below this level have a minimal margin of safety, with small decreases in oxygen partial pressure resulting in large decrements of SaOs.
Recovery room nurses and attending physicians were not blinded to the SaOa display so that routine care of the patients was not influenced by the investigation. The duration of recovery room stay was based on each patients clinical condition as determined by the recovery room physician, who was not a member of the investigating team.
The influence of individual patient, surgical and anesthesia factors on the incidence and duration of desaturations was analyzed for statistical significance by multiple regression analysis. Student’s t tests were utilized where applicable. A p value <0.05 was considered significant.