while any patient undergoing renal hemodialysis may encounter complications because of the frequency and duration of treatment , certain patient subgroups appear to be especially prone to complications such as hypotension occurring early in the procedure or in the later stages . these recurrent hypotensive episodes can be generally of two types , ( 1 ) in which blood pressure fluctuates , sometimes erratically , or ( 2 ) the patient experiences a sudden drop in pressure resulting in dizziness and actual fainting . these episodes may be accompanied by cardiac arrhythmia , which actually contributes to the condition . such sudden drops in pressure may occur more than once in a single dialysis procedure . in general , a hypotensive event is said to occur when blood pressure falls either suddenly or transiently about 10 minutes after procedure initiation , by greater than about 20 mm hg , or when systolic blood pressure falls below 100 mm hg although these criteria will vary and are often interpreted very subjectively . patients who experience hypotension or blood pressure fluctuation can be identified from their file histories , and may be considered for the hemoglobin therapy of the present invention if routine adjustments in the dialysis procedure ( lowering rate of ultrafiltration , salt concentration of the dialysate , etc .) do not produce a remission of the episodes . it will largely be a matter for the attending physician or nephrologist to ascertain those who qualify for hemoglobin therapy , taking into account factors such as the age and condition of the patient , secondary pathologies , drug regimens , the frequency and severity of hypotensive episodes , etc . administration of hemoglobin suppresses blood pressure fluctuation , and largely prevents intradialytic hypotension . one unexpected benefit is to minimize and virtually obviate conventional therapeutic intervention , even for causes of hypotension classically associated with fluid imbalances . infusions of albumin , iso - and hypertonic saline , are avoided , which enhances patient comfort and well - being during the dialysis procedure . the hemoglobin therapy of the present invention involves administration of hemoglobin in a pharmacologically effective amount , generally , at low doses . in the clinical studies set forth in the example , three dose levels of 25 , 50 and 100 mg hemoglobin / kg body weight were infused . in other studies , and from animal models , pharmacologic efficacy is achieved in dose ranges from 10 mg / kg to about 1200 mg / kg . any dose in this range is &# 34 ; low &# 34 ; when defined as an amount of hemoglobin too low to serve as a one - for - one oxygen carrying replacement for whole blood in which blood loss results in hypotension at least as pronounced as is observed in susceptible patients undergoing hemodialysis . response of individual patients to particular doses of hemoglobin will vary , as with any drug , and the physician will adjust the dose to achieve the optimal effect . in some patients a dose of 15 mg / kg may be adequate , but in others a dose towards the high end of the recommended dose range ( 1200 mg / kg ) may be required . in the occasional patient a dose in excess of 1200 mg / kg may be needed to be pharmacologically effective , and is still considered by applicants to be within the scope of the invention so long as the low dose definition set forth herein is met . while it is known that the pharmacologic effects of hemoglobin are dose dependent up to a certain threshold , the duration of the effects is affected by dose , with the effects obtained at a larger dose continuing longer . in patients having a history of primarily late stage hypotension , larger doses may be indicated so that an adequate level is present at later times in the dialysis treatment , when hypotensive episodes are anticipated . in some patients , it may be most beneficial to administer the hemoglobin in more than one dose , or even in a continuous dose , over the course of dialysis . such variations are within the scope of the present invention , so long as administration occurs peridialytically in relation to the treatment . timing of hemoglobin administration is preferably coincident with the commencement of dialysis , and continues by intravenous infusion over a 10 to 45 minute period . although hemoglobin administration may be efficacious as a palliative during acute episodes of hypotension , the principal embodiment of the invention is to administer the hemoglobin prophylactically in advance of such episodes so as to prevent hypotensive episodes from occurring . the hemoglobin utilized in the treatment of this invention is stroma - free , substantially free of endotoxin , and sterile . while unmodified stroma - free hemoglobin is pharmacologically effective , it tends to dissociate readily into its subunits giving it a much reduced half - life in the bloodstream . renal toxicity has also been reported . it is therefore preferable to utilize a cross - linked , or cross - linked polymerized hemoglobin manufactured according to a number of methods in the art , for example , as described in u . s . pat . nos . 4 , 826 , 811 , 4 , 001 , 401 , 4 , 412 , 989 , and 5 , 084 , 558 . most preferred is diaspirin cross - linked hemoglobin made as disclosed in u . s . pat . nos . 4 , 600 , 531 and re34 , 271 hereby incorporated by reference . the hemoglobin is further purified and sterilized as disclosed in u . s . pat . nos . 4 , 831 , 012 , 4 , 861 , 867 , and 5 , 128 , 452 . further advantages of the present invention will be apparent from the example which follows : diaspirin cross - linked hemoglobin ( dclhb ) in a 10 percent solution was infused into patients undergoing hemodialysis according to the randomized , single - blinded , cross - over protocol illustrated in fig1 . approximately equal numbers of patients ( n = 3 ) for a test group and a control group receiving normal saline , for each of 3 treatment groups ( 25 , 50 , and 100 mg hemoglobin / kg of body weight ) were infused on day 1 with either saline or dclhb . at day 7 the groups were reversed and then infused with the opposite of either saline or dclhb than they received on day 1 . since one patient received only the control solution and did not cross - over , an extra patient was added to the control group , bringing the total to 19 . patients were unaware of which treatment was received . various physiologic parameters were monitored , including blood pressure and the incidence of conventional intervention for hypotension . fig2 a and 2b depict the data for systolic and diastolic pressures . it is evident that the test and control groups at each dosage level do not differ at the commencement of dialysis , but thereafter out to about 210 minutes there is a significant elevation in both systolic and diastolic pressures . thereafter , the groups once again become indistinguishable . table 1 summarizes the combined systolic blood pressure data . blood pressure increases are dose dependent averaging 2 mm hg for 25 mg / kg dose and 29 mm hg for the 100 mg / kg group . table 1______________________________________blood pressure change 25 50 100 mg / kg mg / kg mg / kg______________________________________change in bps dclhb 2 ± 12 * 15 ± 29 * 29 ± 8 * change in bps placebo - 1 ± 9 4 ± 10 - 4 ± 12______________________________________ * p & lt ; 0 . 05 vs . placebo ; manova correspondingly , the control groups generally demonstrated a reduction in systolic blood pressure . the results in table 2 indicate an increase in hypotensive events as indicated by increased administration of hypertonic saline . the frequency of hypertonic saline interventions were significantly less in the dclhb groups . the stabilization of blood pressure as indicated by the number of hypertonic saline interventions ( table 2 ) indicates 1 hypotensive episode in one of 18 patients receiving dclhb compared to 20 episodes in 9 of 19 patients while receiving the control solution . thus , low dose hemoglobin administration incident to hemodialysis stabilizes blood pressure and significantly reduces the need for conventional hypotensive interventions . table 2______________________________________frequency of 23 . 4 % nacl ivp for treatment or prevention ofhypotension dclhb normal saline # interventions # interventions (# patients ) (# patients ) ______________________________________25 mg / kg 1 ( 1 ) 3 ( 2 ) 50 mg / kg 0 ( 0 ) 9 ( 5 ) 100 mg / kg 0 ( 0 ) 8 ( 2 ) total interventions 1 ( 1 ) 20 ( 9 )( total patients ) ______________________________________
low doses of stroma - free diaspirin cross - linked hemoglobin are administered to patients undergoing hemodialysis , to achieve hemostabilization and avoid hypotensive episodes in susceptible patients . hemoglobin therapy when implemented prophylactically in hemodialysis also partially obviates the need for further interventions to control circulatory system instability .