Carbon dioxide rebreathing with the anaesthetic conserving device, AnaConDa

The anaesthetic conserving device (ACD) AnaConDa was developed to allow the reduced use of inhaled agents by conserving exhaled agent and allowing rebreathing. Elevated has been observed in patients when using this ACD, despite tidal volume compensation for the larger apparatus dead space. The aim of the present study was to determine whether CO2, like inhaled anaesthetics, adsorbs to the ACD during expiration and returns to a test lung during the following inspiration. The ACD was attached to an experimental test lung. Apparent dead space by the single-breath test for CO2 and the amount of CO2 adsorbed to the carbon filter of the ACD was measured with infrared spectrometry. Apparent dead space was 230 ml larger using the ACD compared with a conventional heat and moisture exchanger (internal volumes 100 and 50 ml, respectively). Varying CO2 flux to the test lung (85375 ml min(1)) did not change the measured dead space nor did varying respiratory rate (1224 bpm). The ACD contained 3.3 times more CO2 than the predicted amount present in its internal volume of 100 ml. Our measurements show a CO2 reservoir effect of 180 ml in excess of the ACD internal volume. This is due to adsorption of CO2 in the ACD during expiration and return of CO2 during the following inspiration

Wash-in kinetics for sevoflurane using a disposable delivery system (AnaConDa (R)) in cardiac surgery patients

The use of volatile anaesthetics has increased in situations where conventional anaesthetic machines are inadequate or unavailable, for example, cardiac surgery and intensive care. The disposable anaesthetic conserving device, AnaConDa (R), allows vaporization of liquid volatile anaesthetics from a syringe pump and rebreathing of exhaled anaesthetic. Clinical use requires understanding of device-specific anaesthetic agent kinetics, which are not fully known. We compared the wash-in kinetics for sevoflurane administered by a conventional vaporizer in a non-rebreathing system and the AnaConDa (R) and evaluated if a standard anaesthesia gas monitor gave accurate readings while using the AnaConDa (R). Cardiac surgery patients were randomized to maintenance of anaesthesia with sevoflurane either via a vaporizer or via the AnaConDa (R) (n=8 in each group). Sevoflurane in arterial blood and airway gas was measured with gas chromatography and standard gas monitoring. The initial increase in arterial sevoflurane tension was greater with the vaporizer than with the AnaConDa (R), but the time to reach 80% of maximum sevoflurane tension was close to 8 min in both groups. End-tidal sevoflurane tension mirrored arterial tension in both groups, whereas measured inspired tension was lower than expired and arterial tensions with the use of the AnaConDa (R). The wash-in kinetics for sevoflurane delivered by the AnaConDa (R) are similar to a vaporizer. End-tidal sevoflurane tension accurately reflects arterial tension whereas inspired tension may be underestimated using an AnaConDa (R)

Anaesthetic conserving device AnaConDa®: dead space effect and significance for lung protective ventilation.

The anaesthetic conserving device AnaConDa(®) (ACD) reflects exhaled anaesthetic agents thereby facilitating the use of inhaled anaesthetic agents outside operating theatres. Expired CO2 is, however, also reflected causing a dead space effect in excess of the ACD internal volume. CO2 reflection from the ACD is attenuated by humidity. This study tests the hypothesis that sevoflurane further attenuates reflection of CO2. An analysis of clinical implications of our findings was performed

Wash-in kinetics for sevoflurane using a disposable delivery sytem (AnaConDa) in cardiac surgery patients

Background. The use of volatile anaesthetics has increased in situations where conventional anaesthetic machines are inadequate or unavailable, for example, cardiac surgery and intensive care. The disposable anaesthetic conserving device, AnaConDaw, allows vaporization of liquid volatile anaesthetics from a syringe pump and rebreathing of exhaled anaesthetic. Clinical use requires understanding of device-specific anaesthetic agent kinetics, which are not fully known. We compared the wash-in kinetics for sevoflurane administered by a conventional vaporizer in a non-rebreathing system and the AnaConDaw and evaluated if a standard anaesthesia gas monitor gave accurate readings while using the AnaConDaw. Methods. Cardiac surgery patients were randomized to maintenance of anaesthesia with sevoflurane either via a vaporizer or via the AnaConDaw (n¼8 in each group). Sevoflurane in arterial blood and airway gas was measured with gas chromatography and standard gas monitoring. Results. The initial increase in arterial sevoflurane tension was greater with the vaporizer than with the AnaConDaw, but the time to reach 80% of maximum sevoflurane tension was close to 8 min in both groups. End-tidal sevoflurane tension mirrored arterial tension in both groups, whereas measured inspired tension was lower than expired and arterial tensions with the use of the AnaConDaw. Conclusions. The wash-in kinetics for sevoflurane delivered by the AnaConDaw are similar to a vaporizer. End-tidal sevoflurane tension accurately reflects arterial tension whereas inspired tension may be underestimated using an AnaConDaw

Gas exchange and haemodynamics during thoracotomy

Cardiac index, systemic and pulmonary arterial pressures, carbon dioxide elimination and ventilation of each lung were studied during thoracotomy. Seventeen patients, placed in the full lateral position, were ventilated mechanically through a Carlens' tube to moderate hypocapnia. Mean cardiac index increased by 12% as the pleura was opened (P less than 0.05), with no further change during surgery on the still ventilated upper lung. Mean arterial pressure was unchanged after opening the pleura, but decreased from 114 +/- 15 mm Hg (mean +/- 1 SD) to 104 +/- 18 mm Hg during surgery on the lung (P less than 0.01). Mean pulmonary artery pressure was unchanged. There was a significant (P less than 0.01) increase in carbon dioxide elimination from the upper lung when the pleura was opened. In addition, the ventilation of this lung increased significantly (P less than 0.05). Mean end-tidal PCO2 of the lower lung increased from 4.1 to 4.2 kPa after opening the pleura, while that of the upper lung increased from 3.0 to 3.6 kPa (P less than 0.01). VD/VT decreased from 43 to 38% as the pleura was opened (P less than 0.01). During surgical handling of the lung, marked decreases in ventilation, compliance, carbon dioxide elimination and end-tidal PCO2 were observed in the upper lung. We conclude that ventilation-perfusion mismatch decreased on opening the pleura, and that neither opening the pleura nor the subsequent lung surgery (both lungs being ventilated) caused any clinically important derangements in haemodynamics or oxygenation

Carbon dioxide elimination from each lung during endobronchial anaesthesia. Effects of posture and pulmonary arterial pressure

The ventilation and carbon dioxide elimination of each lung, and pulmonary arterial pressure, were studied in 17 patients during the early phases of anaesthesia for pulmonary surgery. The patients were ventilated mechanically to moderate hypocapnia. Expired tidal volume and carbon dioxide elimination rate of the lung to be operated on, and of the other lung, were similar in the supine position. There was a significant (P less than 0.01) increase in ventilation and a decrease in end-tidal PCO2 of the upper lung after turning the patient on to the side. Simultaneously, the physiological deadspace fraction of tidal volume (VD/VT) increased from 42 to 45% (P less than 0.05). Mean pulmonary arterial pressure (MPAP) increased slightly as surgery on the chest wall commenced. A concomitant increase of carbon dioxide elimination from the upper lung occurred also, although the distribution of ventilation, between the lungs, was unchanged in comparison with the conditions during undisturbed anaesthesia. Individual changes in MPAP (delta MPAP) and corresponding changes in VD/VT (delta (VD/VT)) were negatively correlated (r = -0.68, P less than 0.01). The regression equation was delta (VD/VT) (%) = 0.7 - 0.83 X delta MPAP (mmHg). It was concluded that variations in pulmonary arterial pressure during surgical stimulation may significantly affect the pattern of carbon dioxide elimination in the lungs. However, there was no evidence that these effects were important clinically

Apparent Dead Space with the Anesthetic Conserving Device, AnaConDa®: A Clinical and Laboratory Investigation.

The anesthetic conserving device (ACD) reduces consumption of volatile anesthetic drug by a conserving medium adsorbing exhaled drug during expiration and releasing it during inspiration. Elevated arterial CO2 tension (PaCO2) has been observed in patients using the ACD, despite tidal volume increase to compensate for larger apparatus dead space. In a test lung using room temperature dry gas, this was shown to be due to adsorption of CO2 in the ACD during expiration and release of CO2 during the following inspiration. The effect in the test lung was higher than in patients. We tested the hypothesis that a lesser dead space effect in patients is due to higher temperature and/or moisture attenuating rebreathing of CO2

A randomized study of coronary artery bypass surgery performed with the Resting Heart™ System utilizing a low vs a standard dosage of heparin.

OBJECTIVES: Allogeneic blood transfusion and reoperation for postoperative bleeding after the coronary artery bypass grafting have a negative impact on the patient outcome. This study aimed at evaluating the effects of reduced doses of heparin and protamine on the patient outcome, using a heparin-coated mini-cardiopulmonary bypass (CPB) system. METHODS: Sixty patients undergoing elective first-time CPB were prospectively randomized either to have a reduced systemic heparinization [activated clotting time (ACT) = 250 s] or to a control group perfused with a full heparin dose (ACT = 420 s). Blood transfusions, ventilation time, early postoperative bleeding, ICU stay, reoperations for bleeding, postoperative cognitive status and the level of mobilization were registered. RESULTS: Twenty-nine patients were randomized to the control group, 27 patients to the low-dose group and 4 patients were excluded because of protocol violations. Four patients in the control group received a total of 10 units of packed red blood cells, and in the low-dose group, no transfusions were given, P = 0.046. No patient was reoperated because of bleeding. The ICU stay was significantly shorter in the low-dose group (8.4 vs 13.7 h, P = 0.020), less dependent on oxygen on the first postoperative day (78 vs 97%, P = 0.034), better mobilized (89 vs 59%, P = 0.006) and had less pain (visual analogue scale 2.0 vs 3.5, P = 0.019) compared with the control group. CONCLUSIONS: The use of a mini-CPB system combined with a low dose of heparin reduced the need for blood transfusions and may facilitate the faster mobilization of the patients