Summary

Background and objectives: This study was undertaken to compare the effect of alpha-stat vs. pH-stat strategies for acid–base management on regional cerebral oxygen saturation (RsO2) in patients undergoing moderate hypothermic haemodilution cardiopulmonary bypass (CPB). Methods: In 14 adult patients undergoing elective coronary artery bypass grafting, an awake RsO2 baseline value was monitored using a cerebral oximeter (INVOS 5100). Cerebral oximetry was then monitored continuously following anaesthesia and during the whole period of CPB. Mean ± SD of RsO2, CO2, mean arterial pressure and haematocrit were determined before bypass and during the moderate hypothermic phase of the CPB using the alpha-stat followed by pH-stat strategies of acid–base management. Alpha-stat was then maintained throughout the whole period of CPB. Results: The mean baseline RsO2 in the awake patient breathing room air was 59.6 ± 5.3%. Following anaesthesia and ventilation with 100% oxygen, RsO2 increased up to 75.9 ± 6.7%. Going on bypass, RsO2 significantly decreased from a pre-bypass value of 75.9 ± 6.7% to 62.9 ± 6.3% during the initial phase of alpha-stat strategy. Shifting to pH-stat strategy resulted in a significant increase of RsO2 from 62.9 ± 6.3% to 72.1 ± 6.6%. Resuming the alpha-stat strategy resulted in a significant decrease of RsO2 to 62.9 ± 7.8% which was similar to the RsO2 value during the initial phase of alpha-stat. Conclusion: During moderate hypothermic haemodilutional CPB, the RsO2 was significantly higher during the pH-stat than during the alpha-stat strategy. However, the RsO2 during pH-stat management was significantly higher than the baseline RsO2 value in the awake patient breathing room air, denoting luxury cerebral perfusion. In contrast, the RsO2 during alpha-stat was only slightly higher than the baseline RsO2, suggesting that the alpha-stat strategy avoids luxury perfusion, but can maintain adequate cerebral oxygen supply-demand balance during moderate hypothermic haemodilutional CPB.

Summary

Background and objective: Acute isovolaemic haemodilution increases local and mean cerebral blood flow. It is not known whether a single haemodilution has a short-term effect only or whether it affects cerebral perfusion over a longer time period. In the present study, local and mean cerebral blood flow were determined in conscious rats after a 4, 24 and 48 h period following one-time haemodilution.

Methods: Thirty-six rats were randomized to three untreated sham groups and three groups of haemodilution (4, 24 or 48 h, n = 6 for each group). Isovolaemic haemodilution with albumin 5% aimed to a target haematocrit of 0.2. Local cerebral blood flow was measured in 38 brain regions by the iodo-[14C]antipyrine method in conscious normothermic rats.

Results: Isovolaemic haemodilution reduced haematocrit from 0.44 to 0.20. During the following 24 and 48 h periods, haematocrit remained low (0.22 and 0.21). Mean cerebral blood flow was similar in untreated sham groups (88 ± 12 after 4 h, 92 ± 11 after 24 h, 96 ± 10 mL 100 g−1 min−1 after 48 h). Haemodilution increased mean cerebral blood flow after 4 h (184 ± 11 mL 100 g−1 min−1), after 24 h (153 ± 13 mL 100 g−1 min−1) and 48 h (149 ± 15 mL 100 g−1 min−1) (P ≤ 0.05). Local cerebral blood flow increased in all 38 structures after 4 h haemodilution but decreased with time in six of 38 brain structures after 24 h and in 15 regions after 48 h (P ≤ 0.05).

Conclusions: A single one-time haemodilution increased mean cerebral blood flow for 2 days. However, local adaptation of cerebral blood flow to a chronic low haematocrit occurred but was heterogeneous within the brain.

Background and objective: The study investigated the effect of acute normovolaemic haemodilution on haemodynamics, blood flow and oxygen transport variables with regard to skeletal muscle tissue oxygenation in a canine model.

Methods: Twenty foxhounds were anaesthetized, mechanically ventilated with 30% oxygen in air and underwent first-step normovolaemic haemodilution with Ringer's lactate solution to haematocrit (Hct) 30 and 25% and second-step acute normovolaemic haemodilution with 6% Hetastarch 70 000/0.5 to Hcts of 20, 15 and 10%. Catheters were inserted into femoral arteries and veins and into the pulmonary artery for measurements of haemodynamics, temperature, and sampling of arterial and mixed-venous blood. A flow probe was placed around the left femoral artery. Skeletal muscle tissue oxygen tension (tPO2) was measured in the gastrocnemius muscle using a stepwise driven polarographic needle probe creating histograms from 200 single tPO2 measurements.

Results: Until a Hct of 25% was reached, the heart rate, mean arterial pressure, global and muscular oxygen delivery and consumption remained constant, while the cardiac index and oxygen extraction ratio were significantly increased when compared with baseline. The median tPO2 was significantly decreased at Hcts 15 and 10%, despite increased cardiac index and regional blood flow. The ratio of tPO2 and cardiac index as a marker for efficiency of acute normovolaemic haemodilution started to decline beyond Hcts of 25% (change of slope).

Conclusions: In acute normovolaemic haemodilution to the level of Hct of 25%, the ratio between tPO2 and cardiac index decreases in the healthy dog, indicating an uneconomic relation at the threshold of Hct of 25%.

Background and objective: Assessment of the effects of normovolaemic haemodilution on middle cerebral artery blood flow velocity with transcranial Doppler ultrasonography, intracranial pressure, cerebral perfusion pressure, arterial oxygen content and cerebral oxygen delivery.

Methods: Normovolaemic haemodilution was induced in rabbits under general anaesthesia, and the haematocrit was allowed to decrease to 30% in Group 1 (n = 6) and to 20% in Group 2 (n = 6). Peak systolic and diastolic velocities, mean blood flow velocity, and pulsatility and resistance indices of the middle cerebral artery were measured by transcranial Doppler ultrasonography. Changes in intracranial pressure, cerebral perfusion pressure, arterial oxygen content and cerebral oxygen delivery were also assessed.

Results: In Group 2, middle cerebral artery blood flow velocity increased from 0.4 ± 0.01 to 0.51 ± 0.02 m s−1 after the induction of normovolaemic haemodilution (P = 0.04), while arterial oxygen content decreased from 16.2 ± 0.1 to 8.5 ± 0.1 mL dL−1 (P = 0.002). The decrease in cerebral oxygen delivery from 6.5 ± 0.2 to 4.3 ± 0.2 was also significant (P = 0.02). However, no associated changes in intracranial pressure and cerebral perfusion pressure could be demonstrated.

Conclusions: Normovolaemic haemodilution resulted in an increase in the mean blood flow velocity of the middle cerebral artery. However, this increase did not compensate for the consequences of the altered oxygen delivery to the brain when the haematocrit was reduced to 20%

Background and objective The efficiency of intraoperative autotransfusion in scoliosis surgery is poorly known but needs to be evaluated, not least because of the large blood losses in these patients. This is a retrospective analysis of transfusion requirements of 43 such patients.

Methods Records from 43 patients were studied. During surgery, the shed blood was salvaged and washed in an autotransfusion device (AT1000 Autotransfusion Unit®) and a suspension of red cells was reinfused.

Results Fifty-eight per cent of the intraoperative blood loss was salvaged. The total blood loss during the patients' hospital stay was calculated from the haemoglobin balance; 24% of this loss was salvaged by the device. Moreover, 36 of the patients needed allogeneic blood transfusion.

Conclusion The efficiency of the autotransfusion device was relatively low in relation to the total extravasation, mainly because the postoperative blood loss is substantial.

We investigated the effects of controlled hypotension with haemodilution under isoflurane anaesthesia on splanchnic perfusion in elderly patients. We determined the intramucosal pH using gastric tonometry in 28 patients scheduled for hip surgery. Patients without cardiac disease were assigned to two groups according to age. Group A (adult patients, n=14) included patients aged less than 60 years (range 29–58 years, 47±11 years, mean±SD) and group B(elderly patients, n=14) more than 65 years (68–78 years, 72±5 years). Anaesthesia was maintained with N2O-O2-isoflurane. After induction of anaesthesia, haemodilution was produced by drawing 800–1000 mL of blood and replacing it with the same amount of hydroxyethyl starch. Final haematocrit values were 23–24% in all groups. Controlled hypotension was induced with prostaglandin E1 (PGE1) and mean blood pressure was maintained at approximately 60 mmHg for approximately 80 min. Measurements, including gastric intramucosal pH (pHi), arterial blood pH (pHa) and serum lactate were measured before haemodilution (T0), after haemodilution (T1), 80 min after starting hypotension (T2), 60 min after recovery from hypotension (T3) and on the 1st post-operative day (T4). The values of pHa and lactate showed no change in the groups throughout the time course. The gastric pHi values showed significant decreases from 7.418±0.035 to 7.334±0.024 (P < 0.05) in group A and from 7.428±0.029 to 7.320±0.039 (P < 0.05) in group B after haemodilution, while no further decreases were found at 80 min after starting the hypotension (7.329±0.038 in group A and 7.322±0.031 in group B) and 60 min after recovery from hypotension (7.331±0.029 in group A and 7.328±0.034 in group B). It can be concluded that moderate haemodilution under isoflurane anaesthesia might impair splanchnic perfusion in adult and elderly patients. The addition of controlled hypotension with PGE1 or an increase in age did not further impair splanchnic perfusion nor the splanchnic oxygen supply.

Ringer's solution expands blood volume by between 20% and 25% in awake volunteers, but little is known about its volume effect during general anaesthesia. In 35 men with a mean age of 70 years, the power of various intra-operative factors to change blood volume as estimated by the haemoglobin dilution method were analysed by multiple linear regression every 10 min during transurethral resection of the prostate performed under enflurane anaesthesia. The results show that blood volume increased by 60% of the infused Ringer's solution and by 35% of the irrigating fluid absorbed directly into the blood, while it decreased by slightly more than 100% of the bled volume. There was no correlation between systolic pressure and blood volume changes. This suggests that the volume effect of Ringer's solution in the blood is greater than generally believed during general anaesthesia.

The influence of acute moderate haemodilution on the relation between dose and response for rocuronium was evaluated in 60 adult patients, ASA grade I, undergoing elective plastic surgery. The patients were randomly allocated to either the control or the haemodilution group. Following the induction of general anaesthesia, the status of acute moderate haemodilution in the haemodilution group was achieved by draining venous blood, and intravenous infusion of lactated Ringer's solution, 6% dextran or gelofusine, during which the levels of haemoatocrit and haemoglobin dropped from 44% to 27.5% and from 148.3 to 91.3 g L−1, respectively. Neuromuscular function was assessed mechanomyographically with train-of-four stimulation at the wrist every 12 s and the percentage depression of T1 response was used as the study parameter. The relation between dose and response for rocuronium in the two groups was determined by the cumulative dose–response technique. The results showed that the dose–response curve for rocuronium during acute moderate haemodilution was shifted in a parallel fashion to the left and the potency of rocuronium was increased. There were significant differences in ED50, ED90 and ED95 between the two groups. The ED50, ED90 and ED95 of rocuronium in the haemodilution group was decreased by 28.2%, 35.4% and 38.8%, respectively, compared with the control group.

The effects of acute haemodilution, during prostaglandin E1 (PGE1)-induced hypotension, on the blood coagulation-fibrinolysis system were studied in 40 patients undergoing hip surgery. The patients were randomly divided into four groups of 10 patients each; Group A (control) received no induced hypotension or haemodilution, group B received hypotension alone, group C received haemodilution alone and group D received the combination of induced hypotension and haemodilution. Haemodilution in groups C and D was produced by drawing ≈ 1000 mL of blood and replacing it with the same amount of 6% hydroxyethyl starch. Induced hypotension in groups B and D was conducted with PGE1 and mean blood pressure was maintained at 55 mmHg. The mean dosage of PGE1 was 648 mug in group B and 661 mug in group D. In the control and PGE1-induced hypotension groups there was no significant change in platelet count (PLT), prothrombin time (PT), activated partial thromoplastin time (aPTT), fibrinogen (FIB), antithrombin-III (AT-III) or plasminogen (PLG). Haemodilution alone caused significant decreases in PLT (−43%), PT (+21%), FIB (−33%), AT-III (−21%) and PLG (−27%), and a significant increase in aPTT (+26%), whereas the combination of PGE1-induced hypotension did not cause any further change in these parameters. Serum-fibrin degradation products (FDP) significantly increased (+300%) and PLG significantly decreased (−30%) after surgery in all groups. It can be concluded that acute haemodilution to a haematocrit value of 22 ± 2% causes a slight coagulopathy, which is not enhanced when combined with PGE1-induced hypotension.

Combined effects of prolonged prostaglandin E1 (PGE1)-induced hypotension and haemodilution on hepatic function were studied in 30 patients undergoing hip surgery. The patients were randomly allocated to one of three groups; those in group A (n = 10) were subjected to controlled hypotension alone, those in group B (n = 10) to haemodilution alone and those in group C (n = 10) to both controlled hypotension and haemodilution. Haemodilution in groups B and C was produced by withdrawing approximately 1000 mL of blood and replacing it with the same amount of dextran solution, and final haematocrit values were 21 or 22%. Controlled hypotension in groups A and C was induced with PGE1 to maintain mean arterial blood pressure at 55mmHg for 180 min. Measurements included arterial ketone body ratio (AKBR, aceto-acetate/3-hydroxybutyrate) and clinical hepatic function parameters. AKBR and biological hepatic function tests showed no change throughout the time course in groups A and B. In group C, AKBR showed a significant decrease at 120 min (−40%) and at 180 min (−49%) after the start of hypotension and at 60 min (−32%) after recovery of normotension, and SGOT, SGPT, LDH and total bilirubin showed significant increases after operation. The results suggest that a prolonged combination of more than 120 min of PGE1-induced hypotension and moderate haemodilution would cause impairment of hepatic function.

The influence of haemodilution with colloids on somatosensory evoked potentials in non-premedicated volunteers is reported. In seven volunteers (randomized crossover design), blood (20 mL kg−1 within 30 min) was removed and simultaneously replaced by gelatin 3% or hydroxyethylstarch 6%. After 30 min, blood was retransfused within 30 min. Median and posterior tibial nerve somatosensory evoked potentials were recorded from the cortex, second cervical vertebra, Erb's point and 1st lumbar vertebra, respectively. One volunteer experienced a severe allergic reaction to gelatin, therefore only six gelatin trials were evaluated. Haemodilution decreased the haematocrit from 39.8 ± 1.6% (mean ± SD) to 31.1 ± 2.0% (gelatin) and from 40.7 ± 1.7% to 29.8 ± 1.5% (hydroxyethylstarch), respectively. Retransfusion increased haematocrit to 34.4 ± 0.9% (gelatin) and to 34.2 ± 1.3% (hydroxyethylstarch). Neither haemodilution with gelatin nor haemodilution with hydroxyethylstarch or retransfusion influenced evoked potentials. In conclusion, the treatment of blood loss up to 30% of estimated blood volume with gelatin or hydroxyethylstarch will not affect somatosensory evoked potential monitoring provided normovolaemic conditions are maintained.