[New technical developments for inhaled sedation]

[Treatment of extreme anemia with polymerized bovine hemoglobin : Case report and review of the literature]

This article reports the case of a 29-year-old female Jehovah's Witness with severe anemia after intrauterine fetal death in the 25th week of gestation, complicated by vaginal bleeding, acute renal failure and hemolysis. Due to her religious beliefs the patient categorically refused blood transfusions. Despite adhering to the recommendations for patient blood management, the hemoglobin (Hb) level gradually decreased to 1.9 g/dl on day 10, when she fainted and had to be sedated and invasively ventilated. Inhalative isoflurane was chosen for sedation because of its potential organ-protective effects and because it provides deep sedation with reduced oxygen requirements, while enabling rapid neurological examination during the sedation windows as well as regular and calm spontaneous breathing. Posthypoxic encephalopathy was demonstrated clinically and electroencephalographically by seizure activity during the sedation windows. Anticonvulsive treatment was started. At a hemoglobin of 1.8 g/dl, she received 2 units of polymerized bovine hemoglobin (Hemopure®, Hemoglogin Oxygen Therapeutics LLC, Souderton, PA, USA), repeated several times on subsequent days because of its short half-life. Considerable methemoglobinemia was noted. After subtracting methemoglobin, the hemoglobin rose by 0.4-0.8 g/dl after each 2 units, initially increasing the oxygen binding capacity of the blood by 33%. After a full neurological recovery and weaning from the ventilator but still on hemodialysis, the patient was transferred to another hospital after 38 days.If allogeneic blood transfusion is not an option, administration of polymerized bovine hemoglobin can temporarily increase the oxygen transport capacity as a last resort treatment. Reduction of oxygen requirements by deep inhaled sedation with isoflurane also seems beneficial and provides advantages.

Halving the Volume of AnaConDa: Evaluation of a New Small-Volume Anesthetic Reflector in a Test Lung Model

BACKGROUND

Volatile anesthetics are increasingly used for sedation in intensive care units. The most common administration system is AnaConDa-100 mL (ACD-100; Sedana Medical, Uppsala, Sweden), which reflects volatile anesthetics in open ventilation circuits. AnaConDa-50 mL (ACD-50) is a new device with half the volumetric dead space. Carbon dioxide (CO2) can be retained with both devices. We therefore compared the CO2 elimination and isoflurane reflection efficiency of both devices.

METHODS

A test lung constantly insufflated with CO2 was ventilated with a tidal volume of 500 mL at 10 breaths/min. End-tidal CO2 (EtCO2) partial pressure was measured using 3 different devices: a heat-and-moisture exchanger (HME, 35 mL), ACD-100, and ACD-50 under 4 different experimental conditions: ambient temperature pressure (ATP), body temperature pressure saturated (BTPS) conditions, BTPS with 0.4 Vol% isoflurane (ISO-0.4), and BTPS with 1.2 Vol% isoflurane. Fifty breaths were recorded at 3 time points (n = 150) for each device and each condition. To determine device dead space, we adjusted the tidal volume to maintain normocapnia (n = 3), for each device. Thereafter, we determined reflection efficiency by measuring isoflurane concentrations at infusion rates varying from 0.5 to 20 mL/h (n = 3), for each device.

RESULTS

EtCO2 was consistently greater with ACD-100 than with ACD-50 and HME (ISO-0.4, mean ± standard deviations: ACD-100, 52.4 ± 0.8; ACD-50, 44.4 ± 0.8; HME, 40.1 ± 0.4 mm Hg; differences of means of EtCO2 [respective 95% confidence intervals]: ACD-100 - ACD-50, 8.0 [7.9-8.1] mm Hg, P < .001; ACD-100 - HME, 12.3 [12.2-12.4] mm Hg, P < .001; ACD-50 - HME, 4.3 [4.2-4.3] mm Hg, P < .001). It was greatest under ATP, less under BTPS, and least with ISO-0.4 and BTPS with 1.2 Vol% isoflurane. In addition to the 100 or 50 mL "volumetric dead space" of each AnaConDa, "reflective dead space" was 40 mL with ACD-100 and 25 mL with ACD-50 when using isoflurane. Isoflurane reflection was highest under ATP. Under BTPS with CO2 insufflation and isoflurane concentrations around 0.4 Vol%, reflection efficiency was 93% with ACD-100 and 80% with ACD-50.

CONCLUSIONS

Isoflurane reflection remained sufficient with the ACD-50 at clinical anesthetic concentrations, while CO2 elimination was improved. The ACD-50 should be practical for tidal volumes as low as 200 mL, allowing lung-protective ventilation even in small patients.