Superpulsed CO2 Laser Treatment of Basal Cell Carcinoma With Intraoperatory Histopathologic and Cytologic Examination

background. CO₂ laser is currently one of the most versatile and useful laser devices in dermatologic practice in the fields of both cosmetology and oncology. The CO₂ laser in a superpulsed mode enables the operator to effect precise and adequate vaporization of the affected area, with the possibility to appreciate visually the depth achieved, and, when necessary, to perform histologic and cytologic examination of the surrounding skin.
objective. To show superpulsed CO₂ laser treatment of basal cell carcinoma.
methods. One hundred forty patients presenting single, multiple, superficial, or nodular basal cell carcinoma (BCC) have been treated with the superpulsed CO₂ laser. Before the laser treatment the lesion was subjected to cytologic examination by scraping; this examination was then repeated when the papillary dermis was clinically detectable, and again when the operator considered the BCC completely vaporized. In selected subjects, histopathologic examination was done three times (biopsies were obtained at the same time as the samples for the cytologic examination).
results. Recovery time was fast, with good healing outcomes. After 3 years follow-up no recurrences were seen. The cytologic and histopathologic examinations showed BCC in the specimens obtained prior to and during laser therapy, but not in those obtained after laser therapy.
conclusion. This technique causes minimal thermal cellular damage and no severe morphologic cellular alterations. Thus it permits an intraoperatory cytologic and histopathologic examination. Finally, this technique enables the operator to recognize the different skin levels removed by vaporization and to stop the vaporization as soon as unaffected dermis has been reached, as shown by intraoperatory cytologic and histopathologic examination.     

The Use of the 1.0 mm Handpiece in High Energy, Pulsed CO2 Laser Destruction of Facial Adnexal Tumors

Background. The treatment of syringoma and trichoepithelioma has included punch and shave biopsy, excision, electrodessication, as well as continuous wave and superpulsed carbon dioxide laser ablation. More recently, high-energy pulsed CO₂ lasers have been reported to be effective with standard available handpieces that deliver collimated beams.
Objective. To report our experience using a focusing handpiece (1.0mm spot at focus) with a high energy pulsed CO₂ laser.
Methods. Four patients with syringoma and two with multiple trichoepithelioma were treated with a high energy pulsed CO₂ laser using a 1mm spot size focusing handpiece. Pulse energies ranged from 125 to 250 mJ. All patients were followed 2 weeks after treatment and then for variable periods ranging from 8 to 18 months (mean = 13.3 months).
Results. The 1mm spot focusing handpiece permitted rapid tumor ablation with optimal matching of lesion size and laser spot diameter. Recurrence of tumor was associated with superficial ablation while complications such as hypopigmentation and atrophy were associated with deeper ablation.
Conclusion. Facial adnexal tumors such as syringoma and trichoepithelioma can be successfully treated with the 1.0mm handpiece in tandem with high energy pulsed CO₂ lasers.     

Improvement of Dermatochalasis and Periorbital Rhytides With a High-Energy Pulsed CO2 Laser: A Retrospective Study

Background. Upper eyelid dermatochalasis is typically treated with excisional blepharoplasty. The role of the CO₂ laser previously had been confined to that of a vaporizing, incisional, or hemostatic tool. Over the past several years, however, ablative CO₂ laser skin resurfacing has been popularized as an adjunctive treatment to blepharoplasty to minimize periorbital rhytides through its vaporizing as well as skin-tightening action.
Objective. To evaluate the safety and efficacy of a high-energy pulsed CO₂ laser as a stand-alone treatment for dermatochalasis and periorbital rhytides.
Methods. Sixty-seven patients (skin phototypes I–IV) with mild-to-severe upper eyelid dermatochalasis and periorbital rhytides received periocular CO₂ laser skin treatment. Global assessment scores of dermatochalasis and rhytides were determined by a side-by-side comparison of periocular photographs preoperatively and 1, 3, and 6 months postoperatively. In addition, caliper measurements of upper eyelids before and 1, 3, and 6 months after treatment were obtained.
Results. Both dermatochalasis and periorbital rhytides were significantly improved after periocular CO₂ laser skin resurfacing. Patients with more severe dermatochalasis and rhytides showed greater improvement after CO₂ laser treatment than did those with mild or moderate involvement. Side effects were limited to erythema and transient hyperpigmentation. No scarring, hypopigmentation, or ectropion were observed.
Conclusions. Periocular skin resurfacing with a CO₂ laser can safely and effectively improve upper eyelid dermatochalasis and periorbital rhytides.     

Treatment of Upper Lip Wrinkles: A Comparison of the 950 μsec Dwell Time Carbon Dioxide Laser to Manual Tumescent Dermabrasion

Background. High-energy pulsed or computer-scanned continuous-wave carbon dioxide (CO₂) laser resurfacing has gained popularity as a wrinkle treatment because of its minimal thermal injury and precise control of tissue vaporization depth. Manual tumescent dermabrasion has also been effective for treating facial wrinkles. This is, to our knowledge, the first study comparing the use of CO₂ laser to manual tumescent dermabrasion for the treatment of wrinkles on the upper lip.
Objective. To compare prospectively the clinical efficacy of the 950 μsec dwell time CO₂ laser to that of manual tumescent dermabrasion in the treatment of upper lip wrinkles.
Methods. Twenty female subjects with moderate to severe upper lip wrinkles were randomly treated with the 950 μsec dwell time CO₂ laser on one side of the upper lip and manual tumescent dermabrasion on the other.
Results . The average upper lip laser-treated wrinkle score (0 = none to 5 = severe) decreased from 4.3 ± 0.2 before treatment to 1.8 ± 0.3 at 6 months after treatment. The average upper lip dermabrasion-treated wrinkle score decreased from 4.4 ± 0.2 to 1.5 ± 0.3. The degree to which the wrinkle score improved after laser treatment compared with that after dermabrasion was not statistically significant ( P = .216).
Conclusion. Manual tumescent dermabrasion and 950 μsec dwell time CO₂ laser resurfacing are equally effective for the treatment of upper lip wrinkles.     

Effect of Pretreatment on the Incidence of Hyperpigmentation Following Cutaneous CO2 Laser Resurfacing

Background. Transient hyperpigmentation is the most common complication seen following cutaneous carbon dioxide (CO₂) laser resurfacing.
Objective. The purpose of this study was to determine whether the use of a topical skin lightening regimen prior to cutaneous laser resurfacing reduces the incidence of post-laser resurfacing hyperpigmentation.
Methods. One hundred consecutive CO₂ laser resurfacing patients (skin types I–III) were randomized to receive preoperative treatment with 10% glycolic acid cream twice daily (n = 25), hydroquinone 4% cream qHS and tretinoin 0.025% cream twice daily (n = 25) or no pretreatment (n = 50, control) for at least 2 weeks. Clinical and photographic assessments were performed prior to laser resurfacing and at 4 and 12 weeks following treatment.
Results. There was no significant difference in the incidence of post-CO₂ laser resurfacing hyperpigmentation between subjects who received pretreatment with either topical glycolic acid cream or combination tretinoin/hydroquinone creams and those who received no pretreatment regimen.
Conclusion. It is postulated that reepithelialization after cutaneous laser resurfacing includes follicular melanocytes that have not been affected by topical pretreatment. When instituted as a component of the skin care regimen postoperatively, topical hydroquinone, tretinoin and/or glycolic acid preparations may be helpful in reducing post-laser resurfacing hyperpigmentation.     

Changes in delivered tidal volume with the addition of carbon dioxide to mechanical ventilation

Objective:  To determine discrepancies in delivered tidal volumes induced by the addition of carbon dioxide (CO₂) during mechanical ventilation.
Design:  Prospective, experimental, lung model study.
Setting:  Research laboratory at a University hospital.
Subjects:  Ventilator set-up using a mechanical lung model.
Interventions:  Tidal volumes were measured during pressure and volume limited ventilation at various pressures and volumes with the addition of inspired CO₂ concentrations of 0, 1, 2, and 4%. Three ventilator set-ups were used including the addition of CO₂ to the inspiratory limb (M1), the use of two external blenders to mix air, oxygen and CO₂ prior to entry to the ventilator (M2), and the use of one external blender to mix air and CO₂ prior to addition to the ventilator.
Measurements and main results:  Statistically significant increases in delivered tidal volume were noted with the addition of CO₂ with all three of the ventilator set-ups (M1, M2 and M3). However, the maximum increase was 2.4% above that of baseline (no CO₂ added). With the M2 set-up, there was also a significant discrepancy noted between the set and the delivered tidal volumes (16–17%) when using the volume limited mode even without the addition of CO₂.
Conclusions:  Either the M1 or the M3 set-up functioned efficiently without clinically significant alterations in ventilator performance. We prefer the M1 set-up as it is the one that is used most commonly in clinical practice and does not require significant alterations in the working configuration of the ventilator.     

Vasopressin decreases intestinal mucosal perfusion: a clinical study on cardiac surgery patients in vasodilatory shock

Background: Low to moderate doses of vasopressin have been used in the treatment of cathecholamine-dependent vasodilatory shock in sepsis or after cardiac surgery. We evaluated the effects of vasopressin on jejunal mucosal perfusion, gastric-arterial p CO₂ gradient and the global splanchnic oxygen demand/supply relationship in patients with vasodilatory shock after cardiac surgery.
Methods: Eight mechanically ventilated patients, dependent on norepinephrine to maintain mean arterial pressure (MAP) ≥60 mmHg because of septic/post-cardiotomy vasodilatory shock and multiple organ failure after cardiac surgery, were included. Vasopressin was sequentially infused at 1.2, 2.4 and 4.8 U/h for 30-min periods. Norepinephrine was simultaneously decreased to maintain MAP at 75 mmHg. At each infusion rate of vasopressin, data on systemic hemodynamics, jejunal mucosal perfusion, jejunal mucosal hematocrit and red blood cell velocity (laser Doppler flowmetry) as well as gastric-arterial p CO₂ gradient (gastric tonometry) and splanchnic oxygen and lactate extraction (hepatic vein catheter) were obtained.
Results: The cardiac index, stroke volume index and systemic oxygen delivery decreased and systemic vascular resistance and systemic oxygen extraction increased significantly, while the heart rate or global oxygen consumption did not change with increasing vasopressin dose. Jejunal mucosal perfusion decreased and the arterial-gastric-mucosal p CO₂ gradient increased, while splanchnic oxygen or lactate extraction or mixed venous–hepatic venous oxygen saturation gradient were not affected by increasing infusion rates of vasopressin.
Conclusions: Infusion of low to moderate doses of vasopressin in patients with norepinephrine-dependent vasodilatory shock after cardiac surgery induces an intestinal and gastric mucosal vasoconstriction.     

The detection of carbon dioxide embolism during laparoscopy in pigs: a comparison of transesophageal Doppler and end-tidal carbon dioxide monitoring

Background: The aim of the study was to compare the value of transesophageal Doppler and end-tidal carbon dioxide monitoring to detect venous carbon dioxide embolism in pigs during laparoscopic cholecystectomy.
Method: Ten pigs were anesthetized under constant ventilation, and instrumented for laparoscopic cholecystectomy. CO₂ pneumoperitoneum was performed at 15 mmHg and then, successive increased intravenous gas boluses of 0.1 to 4 ml/ kg injectedthrough the femoral vein using a 55-mm long catheter. The responses indicative of embolism were defined as: 1) a change in Doppler tone placed facing the junction of the right atrium and inferior vena cava; 2)
Results: Doppler was more sensitive in detecting 0.1, 0.2 and 0.4 ml/mg of CO₂ embolism than end-tidal CO₂ ( P <0.05). Over 0.4 ml/mg no differences in sensitivity were found but the Doppler signal modifications occurred earlier than the changes in end-tidal CO₂. Moreover, these changes always consisted of a reduction of the value.
Conclusions: During laparoscopic cholecystectomy in pigs, transesophageal Doppler was a highly sensitive monitor which provided an earlier detection of CO₂ embolism and at lower doses than end-tidal CO₂ monitoring.     

Detection of carbon dioxide in expired air after oesophageal intubation; the role of bystander mouth-to-mouth ventilation

Background: The identification of a correctly placed tube during anaesthesia routinely depends on the detection of carbon dioxide (CO₂) in the expired air.
Results: We describe a previously unreported cause of false-positive prediction in two patients with high initial values of CO₂ in expired air after oesophageal intubation. Both patients had received bystander cardiopulmonary resuscitation with mouth-to-mouth ventilation, and the CO₂ from the rescuers' expired air was trapped and subsequently detected after oesophageal intubation.     

Periorbital Rejuvenation: A Review of Dermatologic Treatments

Background. The periorbital region serves as a barometer of chronologic and environmental age and, as such, patients often seek its cosmetic rejuvenation.
Objective. The purpose of this article was to review the dermatologic treatments available for periorbital skin rejuvenation.
Methods. Topical retinoic and glycolic acid preparations, chemical peels, botulinum and collagen injections, dermabrasion, and laser resurfacing procedures for periorbital skin rejuvenation were reviewed. The relative benefits and risks of each treatment were detailed.
Results. Minimal photodamage with mild rhytides should be responsibe to topical acid therapy and superficial peels, whereas moderate wrinkling and photodamage generally require medium-depth peels, collagen injections, or erbium:YAG laser resurfacing. Deeper rhytides and more extensive cutaneous photodamage usually necessitate CO₂ laser resurfacing and botulinum injections.
Conclusions. Proper patient selection and assessment of aging severity are critical to determine the best therapeutic option.     

Comparison of body temperature changes during laparoscopic and open cholecystectomy

Background: Prevention of hypothermia during abdominal surgery by insulating or heat-transferring methods has been the subject of numerous investigations. This study approaches the problem from a less discussed point of view, i.e. the effect of different surgical techniques on body temperature changes.
Methods: Body temperature was measured at 3 core and 6 skin points in 40 patients scheduled for cholecystectomy through open laparotomy or laparoscopy with pneumoperitoneum created and maintained with unwarmed carbon dioxide (CO₂) insufflation. End-tidal CO₂ was kept constant by adjustments of respiratory frequency. Anaesthesia, intravenous infusions, and draping of the patients were standardized.
Results: During the first 1 h of anaesthesia core temperatures decreased approximately by 0.7˚C and distal skin temperatures increased by 7˚C in both groups. At the end of surgery heat balance was similar in both groups. An increase of 2.5 1 min^-1 in respiratory minute volume was needed to control end-tidal CO₂ levels in the laparoscopy group during pneumoperitoneum, which was maintained with a CO₂ flow of 1.2 l-min^-1 through the abdominal cavity.
Conclusion: Laparoscopic technique with unwarmed carbon dioxide insufflation does not offer any advantage in terms of body temperature changes when compared to open surgery.     

Effects of sevoflurane on intracranial pressure, cerebral blood flow and cerebral metabolism: A dose-response study in patients subjected to craniotomy for cerebral tumours

Background: Studies concerning the cerebrovascular effects of sevoflurane in patients with space-occupying lesions are few. This study was carried out as a dose-response study comparing the effects of increasing sevoflurane concentration (1.5% (0.7 MAC) to 2.5% (1.3 MAC)) on cerebral blood flow (CBF), intracranial pressure (ICP), cerebrovascular resistance (CVR), metabolic rate of oxygen (CMRO₂) and CO₂-reactivity in patients subjected to craniotomy for supratentorial brain tumours.
Methods: Anaesthesia was induced with propofol/fentanyl/atracurium and maintained with 1.5% sevoflurane in air/oxygen at normocapnia. Blood pressure was maintained constant by ephedrine. In group 1 (n=10), the patients received continuously 1.5% sevoflurane. Subdural ICP, CBF and CMRO₂ were measured twice at 30-min intervals. In group 2 (n=10), sevoflurane concentration was increased from 1.5% to 2.5% after CBF₁. CBF₂ was measured after 20 min during 2.5% sevoflurane. Finally, CO₂-reactivity was studied in both groups.
Results: In group 1, no time-dependent alterations in CBF, CVR, ICP and CMRO₂ were found. In group 2, an increase in sevoflurane from 1.5% to 2.5% resulted in an increase in CBF from 29 ± 10 to 34±12 ml 100g⁻¹ min⁻¹ and a decrease in CVR from 2.7±0.9 to 2.3±1.2 mmHg ml⁻¹ min 100g ( P <0.05), while ICP and CMRO₂ were unchanged. CO₂-reactivity was maintained at 1.5% and 2.5% sevoflurane.
Conclusion: Sevoflurane is a cerebral vasodilator in patients with cerebral tumours. Sevoflurane increases CBF and decreases CVR in a dose-dependent manner. CO₂-reactivity is preserved during 1.5% and 2.5% sevoflurane.     

The influence of arterial carbon dioxide on cerebral oxygenation and haemodynamics during ECMO in normoxaemic and hypoxaemic piglets

Objective. To investigate the cerebrovascular response to changes in arterial CO₂ tension during extracorporeal membrane oxygenation (ECMO) in normoxaemic and hypoxaemic piglets.
Methods. Four groups of six anaesthetized, paralysed and mechanically ventilated piglets: group 1 - normoxaemia without ECMO, group 2 - ECMO after normoxaemia, group 3 - hypoxaemia without ECMO, and group 4 -ECMO after hypoxaemia, were exposed successively to hypercapnia and hypocapnia. Changes in cerebral concentrations of oxyhaemoglob in (cO₂Hb), deoxyhaemoglobin (cHHb), (oxidized - reduced) cytochrome aa₃ (cCyt. aa₃) and blood volume (CBV) were continuously measured using near infrared spectrophotometry. Heart rate, arterial O₂ saturation, arterial blood pressure, central venous pressure, intracranial pressure (ICP) and left common carotid artery blood flow (LCaBF) were measured simultaneously.
Results. Hypercapnia resulted in increased CBV, cO₂Hb and ICP in all groups, while cHHb was decreased. No changes in LCaBF were found. Hypocapnia resulted in decreased cO₂Hb and increased cHHb except in group 3. LCaBF decreased in all groups except group 2. CBV decreased only in groups 2 and 4. No effect on ICP was observed in any of the groups. The other variables showed no important changes either during hypercapnia or hypocapnia. ECMO after hypoxaemia resulted in a greater response of cO₂Hb and cHHb during hypocapnia. The effect of hypercapnia on CBV while on ECMO was greater than without ECMO.
Conclusion. Since cerebrovascular reactivity to CO₂ remains intact during ECMO in piglets, it is important to keep arterial CO₂ tension stable and in normal range during clinical ECMO.     

Nitric oxide administration after the ventilator: evaluation of mixing conditions

Background: Because of the potential toxicity of nitric oxide (NO) and its oxidising product nitrogen dioxide (NO₂), any system for the delivery of inhaled NO must aim at stable and predictable levels of NO and as low concentrations as possible of NO₂.
Methods: In a laboratory set-up, we have evaluated mixing conditions in a system where NO is added after the ventilator with continuous flow. Mixing was studied by using carbon dioxide (CO₂) as a tracer gas since capnography has a short response time (360 ms) in comparison with measurements of NO with electrochemical fuel cells (response time of 18s). CO₂ (in volumes corresponding to an ideal mixture of 1,3 and 6%) was fed, after the ventilator, either into plain breathing tubing, into one or two soda lime absorbers, or into an empty and a soda lime-filled canister, at different ventilatory rates and different I: E ratios. Samples were drawn from the inspiratory limb close to the Y-piece. NO was added in the same way and in the same volume as the highest concentration of CO₂.
Results: CO₂ added to plain tubing resulted in peak levels up to five times the set levels, while addition to a mixing box with an empty and a soda lime-filled canister resulted in even mixing with gas concentrations close to the ideal. When NO was fed into plain tubing, low levels were measured at the Y-piece, indicating poor mixing. Gas supply to a mixing chamber resulted in even concentrations.
Conclusions: Even and predictable levels of NO can be obtained with continuous flow of NO to the inspiratory limb, after the ventilator, if a mixing chamber is used. To obtain adequate mixing, the volume of the mixing box should be greater than the tidal volume.     

Halothane Anaesthesia with Spontaneous Respiration for Tonsillectomy in Children

Bain's anaesthetic circuit was used in 22 children undergoing tonsillectomy under halothane anaesthesia with spontaneous respiration. End-tidal CO₂ was monitored by capnography. The median maximum end-tidal CO₂ was 7%, and during surgery nine patients had an end-tidal CO₂ higher than 7%, corresponding to a Paco₂ close to 8 kPa when the arterial to end-tidal CO₂ difference is taken into consideration. Increase in fresh gas flow or change to a non-rebreathing system had virtually no effect on end-tidal CO₂. However, following discontinuation of halothane or during controlled respiration, acceptable values of end-tidal CO₂ were reached, leading to the conclusion that respiratory depression was responsible for the high values of end-tidal CO₂ rather than properties of Bain's circuit or too low gas flow rates.     

The oxygen status of fetal blood

Objective: To estimate the acid-base and oxygen status of fetal blood and compare with maternal placental venous blood.
Data sources and calculations: We selected pH and blood gas data from the literature pertaining to umbilical vein and artery blood obtained by cordocentesis and estimated values for the 30th and 40th gestational week.
Average values for maternal venous blood leaving the placenta were estimated on the assumption of equal maternal arterio-venous and umbilical veno-arterial total oxygen concentration differences.
Results: pH and p CO₂ of maternal blood leaving the placenta and umbilical vein blood are almost identical at week 30. A small p CO₂ and pH difference may exist at week 40. The p O₂ of the maternal placental venous blood and umbilical vein blood are almost identical at week 30, but at week 40 a p O₂ difference indicates an umbilical arterio-venous shunting of as much as 30%. The fetal mixed venous p O₂ falls from 2. 6 kPa to 2. 2 kPa from the 30th to the 40th gestational week.
Conclusion: More accurate measurements are needed to confirm our results. Future measurements should be performed with a combined pH-blood gas analyser and haemoximeter to allow determination of the complete oxygen status of the blood.     

Novel Use of Erbium:YAG (2,940-nm) Laser for Fractional Ablative Photothermolysis in the Treatment of Photodamaged Facial Skin: A Pilot Study

BACKGROUND The use of CO₂ or conventional erbium laser ablation or more recent nonablative laser photothermolysis for skin rejuvenation is associated with significant disadvantages.
OBJECTIVE The objective was to assess the efficacy of the erbium:YAG laser (2,940 nm) using the "ablative" fractional resurfacing mode to improve photodamaged skin.
METHODS A total of 28 patients, 27 women and 1 man, aged 28 to 72 years (mean age, 54.2 years), with Fitzpatrick Skin Types II to IV, were treated for mild to moderate actinic damage using fractional erbium:YAG laser (2,940 nm) combined with Pixel technology. Sessions were scheduled at 4-week intervals. Response to treatment was evaluated by two physicians on a five-tiered scale.
RESULTS Patients underwent one to four treatment sessions (mean, 3.2). The initial reaction consisted of erythema and minimal swelling. On clinical assessment 2 months after the final treatment, the results were rated excellent by 21 patients (75%) and good by 7 (25%). Nineteen of the 21 were also evaluated 6 to 9 months after final treatment without any significant change in the results.
CONCLUSIONS Fractional ablative photothermolysis using erbium:YAG laser (2,940 nm) is a promising option for skin resurfacing with reduced risk and downtime compared to existing laser methods.     

Atypical Mycobacterial Infection Following Blepharoplasty and Full-Face Skin Resurfacing With CO2 Laser

background. With the popularity of laser skin resurfacing for the correction of photoaging and the improvement of acne scarring, it is important to note complications that may result from this procedure. Infections must be recognized and treated early, as some can result in permanent local destruction and systemic spread to other body sites.
objective. To increase the awareness of an unusual infection that may result from laser resurfacing.
methods. We report the case of a 52-year-old woman who presented with two symmetrical nodules 1 month after full-face skin resurfacing with CO₂ laser. These were found to be abscesses caused by Mycobacterium fortuitum infection.
results. The diagnosis was established following surgical debridement and subsequent culture grown from the exudate. Oral antibiotic treatment guided by organism sensitivity resulted in complete clearance of the infection with no recurrence or sequelae after 3 years of follow-up.
conclusion. This case demonstrates that atypical mycobacterial infections may arise after laser resurfacing procedures, despite proper technique, sterile instrumentation, and appropriate perioperative medications and postoperative wound care. If diagnosed and treated early, this potentially disastrous complication can be cured with no permanent sequelae.     

Control of Carbon Dioxide in Modified Mapleson A and D (Hafnia) Anaesthetic Systems. An Experimental Model

The effects of varying ventilations (V_e) and fresh gas flows (FGF) on end-expiratory CO₂ (F eco ₂) levels were investigated in an experimental model lung, employing the Hafnia modification of the Mapleson A and D anaesthetic systems during CO₂-absorption and CO₂-wash-out (rebreathing). Identical results were found in both systems: F eco ₂ was constant and independent of FGF with CO₂-absorption and constant V_e, whereas rebreathing resulted in increasing F eco ₂ levels as FGF was decreased. As control of F eco ₂ in the rebreathing systems by regulating FGF could only take place within F eco ₂ levels higher than that determined by V_e at complete CO₂-absorption, e. g. for the Hafnia A and D rebreathing systems, control of FGF necessitates relative hyperventilation. F eco ₂ with constant FGF decreased with increasing V_e during CO₂-absorption, as well as during rebreathing, although this decrease was less in the rebreathing systems. Thus a decrease in F eco ₂ with rising V_e can be avoided and hypocapnia prevented. The results agree with those obtained in clinical studies.     

Uptake of inhaled nitric oxide in acute lung injury

Background: Despite the widespread use of inhaled nitric oxide (NO), little is known of its pulmonary uptake in patients with acute respiratory failure.
Methods: Fourteen patients with acute lung injury (ALI) and ongoing NO therapy were studied. Three doses of NO (5, 10 and 40 ppm) were given for 20 min and at each dose level the following parameters were recorded: minute ventilation, inspiratory NO cone, mixed expired NO cone, end-tidal NO cone, mixed expired CO₂ cone, end-tidal CO₂ cone and arterial CO₂ tension. Total uptake was calculated and correlated to the total amount of NO inhaled, the amount of NO administered to the alveolar space, and the amount of NO administered to the perfused alveolar space.
Results: About 35% of the total amount of NO delivered is taken up by the lungs, 70% of NO administered to the alveolar space is taken up, and 95–100% of the NO administered to perfused alveolar space is taken up. The size of the alveolar dead space varied between 10 and60% of the alveolar space. At 40 ppm of inhaled NO there was no difference between inspired and mixed expired NO₂ concentration, indicating that there is no significant NO₂ formation taking place in the lungs during NO inhalation at the concentrations studied.
Conclusions: Practically all NO administered to the perfused alveolar space is taken up. The total uptake differs from that of healthy persons probably because of differences in the alveolar dead space.