Validity and feasibility of nasopharyngeal end-tidal carbon dioxide tension monitorings: a novel approach in spontaneous breathing patients.

Conventional end-tidal CO2 (Pe'CO2) monitoring is difficult and impractical in nonintubated patients who are either sedated or anesthetized while spontaneous respiration is maintained. An alternative technique using nasopharyngeal end-tidal carbon dioxide tension (PNe,CO2) has been developed. The present study evaluates the feasibility and validity of PNe,CO2 as a reliable respiratory monitoring method. Sixty patients in ASA class status I or II and scheduled for elective surgery were divided into two groups. In group 1 (n = 30), conventional Pe'CO2 was used in intubated patients under general anesthesia. In group 2 (n = 30), PNe,CO2 monitoring was used in patients under regional anesthesia with spontaneous respiration maintained. A 12 FG suction catheter, connected to the sampling tube of a CO2 analyzer, was inserted via the nasal airway to within 1 cm of the nasopharyngeal orifice. Arterial blood gas (PaCO2) was sampled 25 minutes after the operation began, Pe'CO2 (group 1) and PNe,CO2 (group 2) were recorded simultaneously. In both groups, PaCO2 was highly correlated with Pe'CO2 (r = 0.6938) and PNe,CO2 (r = 0.8613). The difference between the two values, (a-e')PCO2 = 0.35 +/- 0.33kPa and (a-Ne')PCO2 = -0.1 +/- 0.51kPa, indicates that PNe,CO2 is more closely correlated to PaCO2 than conventional Pe'CO2. The reduced (a-Ne')PCO2 in group 2 may be explained by CO2 rebreathing and a reduced respiratory deadspace during anesthesia and spontaneous breathing. Interestingly, 60% of the (a-Ne')PCO2 measurements were negative values, suggesting that PNe,CO2 and a spatial V/Q mismatch is caused by sedation; higher CO2 production and CO2 rebreathing may explain the results.(ABSTRACT TRUNCATED AT 250 WORDS)

[The effects of ketamine, propofol and nitrous oxide on visual evoked potential during fentanyl anesthesia].

To evaluate the effects of ketamine, N2O, propofol on visual evoked potential (VEP) during fentanyl anesthesia, 14 patients undergoing transphenoid pituitary dissections were studied. Visual stimulation was done by using the goggles with red light diodes through closed eyelids and responses were recorded in one channel montage, Cz against Oz. The stimulus frequency was 1.9 flashes/sec. The VEPs were recorded from skin incision until the opening of the dura. For comparison, the preanesthesia to anesthesia values were determined. The ratio for N2 (N75) latency were 100.5 +/- 13.9% in ketamine group, 104 +/- 3.5% in N2O group, 100.5 +/- 4.2% in propofol group. The ratios for P2 (P100) latency were 97.45 +/- 5.7% in ketamine group, 101.9 +/- 3.5% in N2O group, 96.8 +/- 5.5% in propofol group. For N2P2 amplitude, the ratios were 36.3% +/- 31.4% in ketamine group, 138.5 +/- 58.0% in N2O group, 80.8 +/- 42.2% in propofol group. The percentage of inadequate recordings were 2.5 +/- 4.3% in ketamine group, 19.2 +/- 2.2% in N2O group and 20.6 +/- 16.0% in propofol group. The percentage of false positive results were 0 +/- 0% in ketamine group, 9.8 +/- 19.9% in N2O group, 12.7 +/- 13.2% in propofol group. Satisfactory anesthesia was achieved in all groups except for ketamine group which required additional medications for elevated blood pressure and intracranial pressure, and postoperative nausea and vomiting. It is concluded that there was great variability of VEP during anesthesia and surgery. Amplitude rather than latency changes were observed during anesthesia combined with fentanyl.(ABSTRACT TRUNCATED AT 250 WORDS)