Tissue oxygen tension measurement for monitoring musculocutaneous and cutaneous flaps

In pigs, latissimus dorsi musculocutaneous island flaps and buttock skin island flaps were raised. Subcutaneous (PscO2) and intramuscular oxygen tension (PimO2) were measured using a non-heated needle electrode before, during and after repeated occlusion of the supplying artery or the draining vein. During arterial and venous occlusion, the tissue oxygen tension in the musculocutaneous flap dropped rapidly. A plateau was reached after 15 min. After arterial occlusion the mean value was 20 mmHg (SEM = +/- 5 mmHg, N = 6) in the subcutis and 16 mmHg in the muscle (SEM = +/- 4 mmHg, N = 10). After venous occlusion the mean value was 11 mmHg (SEM = +/- 3 mmHg, N = 6) in the subcutis. In the skin flap the drop of PscO2 was slower, and after 30 min of arterial occlusion the mean value was 29 mmHg (SEM = +/- 9 mmHg, N = 6). This study has shown that tissue oxygen tension measurement can be used as a sensitive indicator of acute impairment of the supplying vessels in island flaps. The method seems to have potential for monitoring free tissue transfers. A comparable decrease in PscO2 was found for arterial and venous impairment.     

Acute normovolemic hemodilution improves oxygenation in ischemic flap tissue

BACKGROUND: The flaps used in reconstructive surgery are prone to ischemia and hypoxia, which imply a considerable risk of wound-healing complications. During normovolemic hemodilution, the oxygenation may further deteriorate because of the lack of erythrocytes or improve because of increased microcirculatory blood flow. The aim of this study was to investigate the net effect of normovolemic hemodilution of various degrees on the microcirculation and oxygenation in ischemic flap tissue in adult minipigs. METHODS: A rectangular flap was raised in the middle of the epigastrium, consisting of an adequately perfused portion and a partly ischemic portion. The animals were randomly assigned to either the control group (n = 10) or the experimental group (n = 10) receiving graded normovolemic hemodilution with 6% hydroxyethyl starch 200-0.5. RESULTS: Normovolemic hemodilution caused a significant linear increase in total blood flow to the flap (measured by transit time flowmetry). In the ischemic flap tissue, both oxygen tension (measured by polarographic cells) and venous base excess were transiently improved during hemodilution (F = 4.79 and P = 0.019 for the regression of tissue oxygen tension on hemoglobin and hemoglobin squared, and F = 4.18 and P = 0.029 for base excess). The expected values reached a peak at hemoglobin concentrations of 9.1 and 8.5 g/dl, respectively. The measured values at this level of hemodilution were 17 +/- 10.7 mmHg (mean +/- SD) versus 7.6 +/- 1.9 mmHg (baseline) for oxygen tension and -1.7 +/- 3.4 versus -5.6 +/- 4.1 mM for venous base excess. CONCLUSIONS: Our results suggest that the oxygenation in ischemic and hypoxic flap tissue may be improved by normovolemic hemodilution. The maximal benefit may be expected at a hemoglobin concentration at or slightly less than 9 g/dl.     

Effects of acute isovolemic hemodilution and anesthesia on regional function in left ventricular myocardium with compromised coronary blood flow

The effects of progressive, isovolemic hemodilution using Dextran 70 and the effect of halothane (0.7, 0.9, 1.1, and 1.3% end-tidal, administered randomly at each level of hemodilution) on global cardiovascular and regional LV contractile functions were investigated in 24 dogs with induced critical constriction of the left anterior descending coronary artery (LAD). Two additional groups of six dogs each (with and without LAD stenosis) not undergoing hemodilution served as time controls. Regional LV contractile function was assessed by sonomicrometry in the flow-compromised apical LAD territory, as well as in three non-compromised LV areas supplied by the left circumflex coronary artery. Regional myocardial function was found to be stable throughout the study period of 4-5 h in both time control groups. Mean arterial and coronary perfusion pressures as well as LV dP/dtmin decreased (P < 0.01) during hemodilution. LV dP/dtmax remained unchanged, and heart rate and LVEDP increased slightly (P < 0.05). Systolic shortening (SS) in the LAD territory was unchanged at a hematocrit (HCT) of 33.5 +/- 0.3% (mean +/- s.e. mean), and decreased marginally at an HCT of 24.2 +/- 0.1% (SS of 17.4 +/- 1.0% as compared to 20.2 +/- 1.6% at critical constriction (CC), P < 0.05). No increase in post-systolic shortening (PSS) occurred in the compromised area. Severe LAD dysfunction was observed in the LAD territory at an HCT of 14.9 +/- 0.1%, as systolic shortening decreased (11.8 +/- 1.1%, P < 0.01 vs CC) and PSS increased (31.2 +/- 3.4%, P < 0.01 vs CC). The effects of hemodilution on global cardiovascular and regional myocardial functions were unaffected by halothane.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute Normovolemic Hemodilution Improves Oxygenation in Ischemic Flap Tissue

Background: The flaps used in reconstructive surgery are prone to ischemia and hypoxia, which imply a considerable risk of wound-healing complications. During normovolemic hemodilution, the oxygenation may further deteriorate because of the lack of erythrocytes or improve because of increased microcirculatory blood flow. The aim of this study was to investigate the net effect of normovolemic hemodilution of various degrees on the microcirculation and oxygenation in ischemic flap tissue in adult minipigs.

Methods: A rectangular flap was raised in the middle of the epigastrium, consisting of an adequately perfused portion and a partly ischemic portion. The animals were randomly assigned to either the control group (n = 10) or the experimental group (n = 10) receiving graded normovolemic hemodilution with 6% hydroxyethyl starch 200-0.5.

Results: Normovolemic hemodilution caused a significant linear increase in total blood flow to the flap (measured by transit time flowmetry). In the ischemic flap tissue, both oxygen tension (measured by polarographic cells) and venous base excess were transiently improved during hemodilution (F = 4.79 and P = 0.019 for the regression of tissue oxygen tension on hemoglobin and hemoglobin squared, and F = 4.18 and P = 0.029 for base excess). The expected values reached a peak at hemoglobin concentrations of 9.1 and 8.5 g/dl, respectively. The measured values at this level of hemodilution were 17 +/- 10.7 mmHg (mean +/- SD) versus 7.6 +/- 1.9 mmHg (baseline) for oxygen tension and -1.7 +/- 3.4 versus -5.6 +/- 4.1 mm for venous base excess.     

急性等容血液稀释对犬单肺通气期间肺分流与氧合的影响

目的 观察犬单肺通气期间，不同程度急性等容血液稀释对肺分流和氧供、氧耗等的影响。方法 12只健康杂种犬，基础麻醉后插入双腔气管导管，股动、静脉置管。稳定30分钟（HD0）后，以血定安等速置换全血，分别达到轻度（HD1）、中度（HD2）、重度（HD3）和极重度（HD4）血液稀释四个阶段。每阶段均分为双肺通气（TLV）和单肺通气（ OLV），分别于各阶段TLV、OLV15分钟后测量分流（Qs/Qt)及氧供（DO2）、氧耗（VO2）等各指标变化。结果 随着HD程度的加深，平均动脉压、心输出量、肺血管阻力（PVR）、平均肺动脉压（MPAP）、氧分压、DO2等趋于降低，氧摄取率（EPO2）、血乳酸、Qs/Qt趋于增加，到HD3、HD4时已出现DO2－VO2依赖性降低及无氧酵解征象。与TLV时相比，OLV期间HD0、HD1及HD2组PVR、MPAP增高明显（P＜0．01）。而HD3、H4D4组变化不大（P＞0．05） ；OLV时QS／Qt增加更为明显，HD2、HD3及HD4组分别较基值增加74％、164％及177％（P＜0．01） 。结论 缺氧、ANHD均为影响Qs/Qt与氧合的重要因素，OLV时ANHD应以不低于中度为准。     

Continuous assessment of oxygen saturation and subcutaneous oxygen tension after abdominal operations

Ten patients undergoing abdominal operations had oxygen saturation (SpO2) and transcutaneous (PtcO2) and subcutaneous (PscO2) oxygen tensions monitored continuously during the second and third postoperative nights from 11 pm to 7 am. At the end of the second postoperative night an oxygen stimulation test (10 l/min by face mask) was carried out in eight of the 10. Median SpO2 was 91% (range 82-95) on the second, and 91% (86-95) on the third, postoperative nights, respectively. Six patients had intermittent episodes of desaturation to less than 80%, each of less than one minute's duration. PtcO2, but not PscO2, followed the episodic variations in SpO2. PscO2 was 58 mmHg (46-69) on the second postoperative night and 61 mmHg (48-71) on the third postoperative night. PscO2 correlated with SpO2 in all but one patient who had lower PscO2 than expected from the measured SpO2 and estimated PaO2. Oxygen treatment increased individual PscO2 by 14 mmHg (9-49), PtcO2 by 38 mmHg (10-104), and SpO2 to 99% (95-100), but stable PscO2 was not achieved within the 20 minute period of treatment. These results obtained during continuous measurements show pronounced intersubject differences in oxygen tensions near the surgical wound in the late postoperative period. The results suggest that pulmonary oxygenation is the most important determinant of mean subcutaneous oxygen tension after uncomplicated elective abdominal operations.     

血液稀释联合硝酸甘油对腹腔镜亲属捐肾者全身氧合的影响

目的:观察血液稀释联合硝酸甘油对腹腔镜亲属捐肾者全身氧合的影响。方法:选择行气腹腹腔镜肾脏切除术的健康亲属捐肾者30例,随机分为实验组(S组,n=15)与对照组(C组,n=15)。麻醉诱导前15 min至肾动脉阻断时两组连续输注4%琥珀酰明胶(MFG)及乳酸林格氏液(LR)(MFG∶LR=1∶1),目标血液稀释值红细胞压积(HCT)为35%。S组同时应用微量泵输注硝酸甘油,初始量为1.5～2μg.kg-.1min-1,维持平均动脉压(MAP)在基础值±25%之内。两组呼气末二氧化碳分压(PETCO2)维持在35～40 mmHg;CO2气腹压力维持在10～13 mmHg。于诱导前(T0)、麻醉平稳后10 min(T1)、气腹时(T2)、气腹后30 min(T3)、肾动脉阻断时(T4)及手术结束时(T5)测定两组患者SaO2、HCT、CO、Lac、胃黏膜PgCO2及血气分析、血流动力学参数等,计算DO2、VO2、Pg-aCO2的变化,并记录术毕液体出入量、麻醉时间、手术时间、液体灌注时间及术中麻醉药物、硝酸甘油用量等。结果:两组液体出入量、麻醉时间、手术时间、液体灌注时间、术中麻醉药物及不同时间点HCT、VO2等指标差异无统计学意义(P>0.05)。与T0相比,两组供肾者T2～T4时MAP、HR显著升高(P<0.05);T2时两组DO2、CO均降低,T4时均升高(P<0.05);C组供肾者T2、T3时Lac、Pg-aCO2有升高趋势(P<0.05)。与C组相比,S组T2～T4时MAP、HR、CVP显著降低,T2、T4时DO2、CO升高明显,T2、T3时Lac、Pg-aCO2降低(P<0.05)。结论:气腹腹腔镜肾脏切除术中行轻度血液稀释联合硝酸甘油,对亲属捐肾者安全性较高,而且其全身氧代谢稳定,内脏氧合良好,未见启动无氧代谢状态。     

Application of hemodilution in microsurgical free flap transplantation

The intra-operative hemodilution and blood auto-transfusion is a blood-saving technique that can be performed when major blood loss is expected. The effects of this technique were studied in 30 microsurgical free flap transplantation patients. Between 400–600 ml blood was collected from the patients before surgery. The patients received dextran, a balanced salt solution, and glucose with the ratio of 3:1 to the collected blood volume, bleeding, and urine before the blood autotransfusion. There were no significant changes in RBC, HCT, MCV, blood pressure, or heart rate. Of the 30 free flaps, 28 were successful with a 93.3% survival rate. The safety of intra-operative hemodilution and autologous blood transfusion in microsurgery as well as the effect of hemodilution on transplanted flap survival are discussed in this study © 1997 Wiley-Liss, Inc MICROSURGERY 17:487–490 1996     

Moderate and extreme hemodilution in open-heart surgery: fluid balance and acid-base studies.

Two groups of patients underwent aortic valve replacement. Fifteen patients received moderate hemodilution (mean hematocrit, 27%) with 40% donor blood in the priming solution. Extreme hemodilution was used in 14 patients (mean hematocrit, 18%) with a nonhemic prime and withdrawal of blood at the start of operation. Both groups were given more than 7 liters of fluid during operation; donor blood was primarily used in the moderately diluted patients, and Ringer's acetate was primarily given to the other group. The diuretic response to this fluid load was much more pronounced in the extreme than in the moderate hemodilution group. Eighteen hours postoperatively, patients in the moderate and extreme hemodilution groups had an excess of about 2 and 1.5 liters of water, respectively. In the patients who had moderate dilution an average of 1,000 ml of erythrocytes disappeared from circulation; no such disappearance could be found in the other group. The moderate group showed significantly lower arterial PO2 postoperatively than the extreme group. There were, however, no differences between the two groups in mixed venous PO2 during perfusion or in acid-base and osmolality values.     

急性等容血液稀释对组织氧供氧耗的影响

目的：通过观察急性等容血液稀释（ＡＮＨＤ）时组织ＤＯ２、ＶＯ２的变化，寻找ＡＮＨＤ的生理极限。方法：１０只健康成年杂种犬，用戊巴比妥钠、维库溴铵静脉麻醉后行气管内插管，控制呼吸。每只犬进行三个水平即中度（ＨＤ１）、深度（ＨＤ２）、极深度（ＨＤ３）ＡＮＨＤ，然后回输自家血，测定血流动力学指标，动脉及混合静脉血气，动脉血乳酸等，以观察ＡＮＨＤ时ＤＯ２、ＶＯ２的变化。结果：ＨＤ１（ＨＣＴ＝１９．４３％±１．９７％），ＨＤ２（ＨＣＴ＝１４．７３％±０．９９％）时，ＤＯ２分别降低４２％和５２％，ＥＲＯ２分别升高４０％和８８％，ＣＩ升高４１％和４８％，而ＶＯ２只降低４．８％和５．２％，动脉血乳酸末升高。ＨＤ３（ＨＣＴ＝９．５０％±０．８８％）时，ＤＯ２降低７３％，ＥＲＯ２升高２００％，ＣＩ降低，ＶＯ２降低３５％，动脉血乳酸显著增加。回输自家血后，ＤＯ２、ＶＯ２及血乳酸均恢复。结论：中、深度ＨＤ时，ＤＯ２减少，ＶＯ２可通过增加ＥＲＯ２和ＣＩ代偿；极深度ＨＤ时ＶＯ２降低显著，出现无氧代谢，ＨＤ达极限。     

Evaluation of tissue oximetry in perioperative monitoring of colorectal surgery.

Twenty patients undergoing elective colorectal surgery were studied during and after operation by means of tissue oximetry measuring the subcutaneous partial pressure of oxygen (PscO2) and by gastric intramural pH measurement. Mean(s.d.) PscO2 recorded 24 h after surgery was significantly lower than the peroperative value: 14(10) versus 24(14) mmHg, P less than 0.02. The postoperative PscO2 was also significantly lower than that measured in a control group of ten healthy volunteers: 14(10) versus 34(18) mmHg, P less than 0.001. The peroperative PscO2 of the patients who developed a postoperative complication was significantly lower than that of those who had an uneventful postoperative clinical outcome: 16(9) versus 32(14) mmHg, P less than 0.02. The peroperative PscO2 of the patient group with complications was also significantly lower than that of the control group: 16(9) versus 34(18) mmHg, P less than 0.02. The peroperative PscO2 of the group of patients without complications was almost identical to that of the control group. During operation only one patient developed gastric intramural acidosis. Perioperative oxygen debt and the response of subcutaneous tissue oxygen tension to oxygen breathing seemed to correlate better with clinical outcome than gastric wall pH values and the conventional parameters of tissue perfusion.     

Human middle cerebral artery flow velocity during controlled hypotension combined with hemodilution-transcranial Doppler study

STUDY OBJECTIVE: To evaluate the effects of controlled hypotension combined with hemodilution on human middle cerebral artery flow velocity (Vmca) by transcranial Doppler ultrasonography. DESIGN: Randomized prospective study. SETTING: Inpatient surgery at Nagasaki Rosai Hospital. PATIENTS: Thirty American Society of Anesthesiologists physical status I and II patients scheduled for total hip arthroplasty. INTERVENTIONS: Anesthesia was maintained with nitrous oxide-oxygen (N(2)O-O(2)) and sevoflurane during normocapnia. Hemodilution was carried out after induction of anesthesia, in which blood was withdrawn then replaced with the same amount of hydroxyethyl starch to achieve a final hematocrit level of 32% (group A = mild hemodilution group, N = 15) or 24% (group B = moderate hemodilution group, N = 15). In both groups, controlled hypotension was induced with prostaglandin E(1) to maintain mean arterial pressure at approximately 55 mm Hg for 80 minutes. MEASUREMENTS AND MAIN RESULTS: Vmca and blood gas were measured before hemodilution, after hemodilution, 80 minutes after starting hypotension, and 60 minutes after recovery from hypotension. Vmca significantly increased in group A (+122%) and group B (+156%) after each hemodilution. In group B, Vmca was significantly greater than baseline values at 80 minutes after starting hypotension (+135%) and 60 minutes after recovery from hypotension (+140%). CONCLUSION: The combination of moderate hemodilution, such as hematocrit value of 24%, and prostaglandin E(1)-induced hypotension would not impair middle cerebral artery flow during sevoflurane-N(2)O-O(2) anesthesia during normocapnia.     

Influence of positive end-expiratory pressure ventilation on peripheral tissue perfusion evaluated by measurements of tissue gases and pH. An experimental study in pigs with oleic acid lung injury.

Measurements of subcutaneous oxygen tension (PscO(2)), subcutaneous carbon dioxide tension (PscCO(2)) and subcutaneous pH (pHsc) were used for evaluation of peripheral oxygenation in pigs subjected to oleic acid-induced lung injury during ventilation with increasing levels of positive end-expiratory pressure (PEEP). Lung injury resulted in a decrease of arterial oxygen tension (PaO(2)) from 93 to 37 mm Hg (p<0.01) with maintained cardiac output. PscO(2) decreased from 45 to 17 mm Hg (p<0.01) and pHsc from 7.47 to 7.39 (p<0.05), and PscCO(2) increased from 46 to 59 mm Hg (p<0.05). Increase of PEEP level between 5 and 20 cm H(2)O resulted in a continuous increase of PaO(2) from 45 to 145 mm Hg and a decrease of cardiac output from 4.1 to 2.0 liters/min (p<0.01). PscO(2) increased up to a PEEP level of 15 cm H(2)O, reaching 26 mm Hg. Further increase of PEEP level up to 20 cm H(2)O resulted in an increase of PscCO(2) from 65 to 71 mm Hg (p<0.05) and a decrease of pHsc from 7.31 to 7.29 (p<0.05). In conclusion: measurements of tissue gases and pH can be used to evaluate optimum peripheral tissue oxygenation during titration of PEEP level. Whether these measurements can be used as the only indicator to guide therapy in an individual case remains to be studied.     

Effects of hypothermia and hemodilution on oxygen metabolism and hemodynamics in patients recovering from coronary artery bypass operations

The coexistence of hypothermia and hemodilution in patients in the intensive care unit immediately postoperatively after coronary artery bypass graft operations presents concerns regarding the adequacy of hemodynamics and oxygen metabolism. We evaluated the hemodynamic status and oxygen metabolism during the postoperative recovery period in six patients with moderate hemodilution (hematocrit value 34% +/- 3%) and in eight patients with marked hemodilution (hematocrit value 23% +/- 2%). All patients were well sedated and paralyzed with pancuronium bromide during the study period, during which their body temperature was slowly returning toward normal. In both groups, cardiac index at 34 degrees C was about 40% lower than at 37 degrees C. This was associated with 50% higher systemic vascular resistance and 30% lower oxygen availability to tissue. Oxygen consumption, however, was proportionally lower (45%) and coronary perfusion pressure was higher (28%) at 34 degrees C than at 37 degrees C; thus neither mixed venous nor coronary sinus blood oxygen saturation was compromised under hypothermic conditions. Although the trends in hemodynamic changes were similar in both groups, cardiac indices in patients with marked hemodilution were higher than cardiac indices in those with moderate hemodilution at all temperatures. This observation indicates that the hemodilution-induced rise in cardiac index remains intact even under hypothermic conditions. Under the conditions we studied, hypothermia with or without hemodilution had no significant adverse effects on hemodynamics and oxygen metabolisms of the whole body or of the heart.     

Visceral and peripheral tissue perfusion after cardiac surgery

Visceral and peripheral tissue perfusion and oxygenation were studied in ten patients in the early phase after coronary artery bypass grafting. Visceral perfusion was assessed indirectly, by determining gastric intramucosal pH. As parameters of peripheral tissue perfusion and oxygenation, subcutaneous tissue PO2 (PscO2), transcutaneous PO2 (PtcO2). PtcO2 index (PtcO2/PaO2), laser-Doppler skin red-cell flux (RCF) and fingertip temperature (Tft) were recorded in the upper extremity. Central haemodynamics, rectal temperature and blood gases were also measured. The inspired oxygen concentration was maintained at 30 v/v%. Gastric intramucosal pH declined progressively during the first 3 hours in the intensive care unit, reached its minimum at 5 hours and thereafter slowly increased. The peripheral vascular bed was shut down on admission to the ICU, as indicated by low values of PscO2, PtcO2, PtCO2 index, RCF and Tft. These parameters began to rise after the next 2-4 hours and peaked by the end of the 8-hour study period, indicating complete opening of the peripheral vascular bed.     

'Alveolar recruitment strategy' improves arterial oxygenation during general anaesthesia

Abnormalities in gas exchange during general anaesthesia are caused partly by atelectasis. Inspiratory pressures of approximately 40 cm H2O are required to fully re-expand healthy but collapsed alveoli. However, without PEEP these re-expanded alveoli tend to collapse again. We hypothesized that an initial increase in pressure would open collapsed alveoli; if this inspiratory recruitment is combined with sufficient end-expiratory pressure, alveoli will remain open during general anaesthesia. We tested the effect of an 'alveolar recruitment strategy' on arterial oxygenation and lung mechanics in a prospective, controlled study of 30 ASA II or III patients aged more than 60 yr allocated to one of three groups. Group ZEEP received no PEEP. The second group received an initial control period without PEEP, and then PEEP 5 cm H2O was applied. The third group received an increase in PEEP and tidal volumes until a PEEP of 15 cm H2O and a tidal volume of 18 ml kg-1 or a peak inspiratory pressure of 40 cm H2O was reached. PEEP 5 cm H2O was then maintained. There was a significant increase in median PaO2 values obtained at baseline (20.4 kPa) and those obtained after the recruitment manoeuvre (24.4 kPa) at 40 min. This latter value was also significantly higher than PaO2 measured in the PEEP (16.2 kPa) and ZEEP (18.7 kPa) groups. Application of PEEP also had a significant effect on oxygenation; no such intra-group difference was observed in the ZEEP group. No complications occurred. We conclude that during general anaesthesia, the alveolar recruitment strategy was an efficient way to improve arterial oxygenation.      

Retinal artery air embolism in dogs: fluorescein angiographic evaluation of effects of hypotension and hemodilution.

Cerebral air embolism can cause cerebral complications after open heart surgery. The duration of cerebral artery occlusion by air embolism is thought to vary depending on the conditions. However, no study has evaluated factors affecting the duration of occlusion. In this study, we examined the effects of blood pressure and hemodilution on the duration of retinal artery occlusion caused by air embolism in dogs. The duration of retinal artery occlusion caused by the injection of 0.6 mL of air into the common carotid artery was measured by fluorescein angiography and compared among the following three periods: a control period, during which the mean blood pressure (MBP) was maintained at 80 mm Hg; a hypotension period, during which MBP was decreased to 60 mm Hg by exsanguination; and a hypotension plus hemodilution period, during which an additional exchange of blood with hydroxyethyl starch solution was performed and MBP was maintained at 60 mm Hg. When MBP was lowered from 80 to 60 mm Hg, the duration of retinal artery occlusion was prolonged from 34+/-39 to 166+/-90 s (P < 0.01). In dogs with MBP of 60 mm Hg, hemodilution (12.0+/-0.9 to 7.3+/-0.5 g/dL hemoglobin concentration) shortened the duration from 166+/-90 to 75+/-50 s (P < 0.05). Our results demonstrate that hypotension prolongs and hemodilution shortens the duration of retinal artery occlusion caused by air embolism. IMPLICATIONS: We evaluated the effects of blood pressure and hemodilution on the duration of retinal artery occlusion caused by air embolism by retinal fluorescein angiography. Hypotension prolonged and hemodilution shortened the duration of retinal artery occlusion caused by air embolism.     

Twelve year clinical study of patients with hypoxic cor pulmonale given long term domiciliary oxygen therapy.

Patients presenting with chronic obstructive airways disease and hypoxic cor pulmonale were assessed during a period of clinical stability. Seventy two patients (53 male) with a mean age of 60 years were selected for long term oxygen therapy. Mean FEV1 was 0.78 l and forced vital capacity 1.9 l. The mean arterial oxygen tension (PaO2) was 6.1 kPa (46 mm Hg) and the mean arterial carbon dioxide tension (PCO2) 6.9 kPa (52 mm Hg). All patients had a PaO2 of less than 8.0 kPa (60 mm Hg) and 57 patients had a PCO2 of more than 6.0 kPa (45 mm Hg). Pulmonary haemodynamics were measured in 45 patients yielding the following mean values: pulmonary artery pressure 28.3 mm Hg; cardiac output 5.9 l min-1; total pulmonary vascular resistance 59.2 kPa l-1 S. Oxygen delivery systems, including 23 oxygen concentrators, were installed in the patients' homes. Flow rates were adjusted to raise PaO2 to more than 8.0 kPa (60 mm Hg) for at least 15 hours each day and close supervision was maintained. Overall five year survival was 62%, which is better than previously reported for this type of patient; but the 10 year survival was only 26% owing to an observed acceleration in death rate at about this time. Progressive disturbances of the pulmonary circulation were arrested. Mortality was associated with the severity of airflow obstruction, reflecting a continuing pathological process affecting the airways.     

Oxygen Transport to Tissue under Normovolemic Moderate and Extreme Hemodilution during Coronary Bypass Operation

Oxygen transport to tissue was studied in 12 patients undergoing coronary bypass operation under normovolemic moderate and extreme hemodilution. Normovolemic moderate hemodilution (15 ml per kilogram of body weight), carried out immediately after induction of anesthesia, decreased the mean hematocrit from 0.43 to 0.33. Simultaneously, the cardiac index and the left ventricular filling pressure increased slightly but the systemic oxygen transport was reduced by 20%. The subcutaneous tissue oxygen tension (Po₂) was approximately 40 mm Hg after induction of anesthesia and underwent a transient increase during moderate hemodilution. During cardiopulmonary bypass and extreme hemodilution, the mean hematocrit declined to 0.16. Concurrently, the mean tissue Po₂ fell sharply and reached a minimum of 14 mm Hg at deepest hypothermia. After decannulation and reinfusion of autologous blood, the Po₂ rose to 30 mm Hg. In general, total-body oxygen consumption changed along with tissue Po₂. Blood lactate concentration underwent a clear increase in the early phase of extracorporeal circulation and remained rather stationary thereafter. No perioperative myocardial infarctions were encountered, and each patient made an uneventful recovery.     

Dynamics of re-expansion of atelectasis during general anaesthesia

A major cause of impaired gas exchange during general anaesthesia is atelectasis, causing pulmonary shunt. A 'vital capacity' (VC) manoeuvre (i.e. inflation of the lungs up to 40 cm H2O, maintained for 15 s) may re-expand atelectasis and improve oxygenation. However, such a manoeuvre may cause adverse cardiovascular effects. Reducing the time of maximal inflation may improve the margin of safety. The aim of this study was to analyse the change over time in the amount of atelectasis during a VC manoeuvre in 12 anaesthetized adults with healthy lungs. I.v. anaesthesia with controlled mechanical ventilation (VT 9 (SD 1) ml kg-1) was used. For the VC manoeuvre, the lungs were inflated up to an airway pressure (Paw) of 40 cm H2O. This pressure was maintained for 26 s. Atelectasis was assessed by analysis of computed x-ray tomography. The amount of atelectasis, measured at the base of the lungs, was 4.0 (SD 2.7) cm2 after induction of anaesthesia. The decrease in the amount of atelectasis over time during the VC manoeuvre was described by a negative exponential function with a time constant of 2.6 s. At an inspired oxygen concentration of 40%, PaO2 increased from 17.2 (4.0) kPa before to 22.2 (6.0) kPa (P = 0.013) after the VC manoeuvre. Thus in anaesthetized adults undergoing mechanical ventilation with healthy lungs, inflation of the lungs to a Paw of 40 cm H2O, maintained for 7-8 s only, may re-expand all previously collapsed lung tissue, as detected by lung computed tomography, and improve oxygenation. We conclude that the previously proposed time for a VC manoeuvre may be halved in such subjects.