Kinetics of acid-base parameters in conventional hemodialysis

Details about the acid-base changes in hemodialysis are scarce in the literature but are potentially relevant to adequate management of patients. We addressed the acid-base kinetics during hemodialysis and throughout the interdialytic period in a cross-sectional study of adults undergoing conventional hemodialysis. Samples for blood gas analysis were obtained from the arterial limb of the arteriovenous fistula before the first session of the week (HD1), immediately at the end of HD1, and on sequential collections at 15, 30, 45, 60, and 120 min post-HD1. Additional blood samples were collected after ∼20 h following the end of the first dialysis and immediately prior to the initiation of the second dialysis of the week. Thirty adult patients were analyzed (55±15 years, 50% men, 23% diabetic; dialysis vintage 69±53 months). Mean serum bicarbonate levels increased at the end of HD1 (22.3±2.7 mEq/L vs 17.5±2.3 mEq/L, P<0.001) and remained stable until 20 h after the end of the session. The mean values of pCO2 before HD1 were below reference and at 60 and 120 min post-HD1 were significantly lower than at the start (31.3±2.7 mmHg and 30.9±3.7 mmHg vs 34.3±4.1 mmHg, P=0.041 and P=0.010, respectively). The only point of collection in which mean values of pCO2 were above 35 mmHg was 20 h post-dialysis. Serum bicarbonate levels remained stable for at least 20 h after the dialysis sessions, a finding that may have therapeutic implications. During dialysis, the respiratory response for correction of metabolic acidosis (i.e., pCO2 elevation) was impaired.

Kinetics of acid-base parameters in conventional hemodialysis.

Details about the acid-base changes in hemodialysis are scarce in the literature but are potentially relevant to adequate management of patients. We addressed the acid-base kinetics during hemodialysis and throughout the interdialytic period in a cross-sectional study of adults undergoing conventional hemodialysis. Samples for blood gas analysis were obtained from the arterial limb of the arteriovenous fistula before the first session of the week (HD1), immediately at the end of HD1, and on sequential collections at 15, 30, 45, 60, and 120 min post-HD1. Additional blood samples were collected after ∼20 h following the end of the first dialysis and immediately prior to the initiation of the second dialysis of the week. Thirty adult patients were analyzed (55±15 years, 50% men, 23% diabetic; dialysis vintage 69±53 months). Mean serum bicarbonate levels increased at the end of HD1 (22.3±2.7 mEq/L vs 17.5±2.3 mEq/L, P<0.001) and remained stable until 20 h after the end of the session. The mean values of pCO2 before HD1 were below reference and at 60 and 120 min post-HD1 were significantly lower than at the start (31.3±2.7 mmHg and 30.9±3.7 mmHg vs 34.3±4.1 mmHg, P=0.041 and P=0.010, respectively). The only point of collection in which mean values of pCO2 were above 35 mmHg was 20 h post-dialysis. Serum bicarbonate levels remained stable for at least 20 h after the dialysis sessions, a finding that may have therapeutic implications. During dialysis, the respiratory response for correction of metabolic acidosis (i.e., pCO2 elevation) was impaired.

Renal artery revascularization in patients with atherosclerotic renal artery stenosis and impaired renal function: conservative management versus renal artery stenting.

BACKGROUND: The impact of percutaneous renal artery angioplasty and stenting (PTRAS) for treatment of atherosclerotic renal artery stenosis (ARAS) is not fully understood, especially in patients with chronic kidney disease (CKD). The goal of this study was to compare renal outcomes in patients treated with PTRAS with those managed conservatively. METHODS: Retrospective cohort study of 118 prevalent patients with significant ARAS and moderate-to-severe CKD who were treated medically (n = 71) or with PTRAS (n = 47). The primary endpoint was change in renal function over the first year after diagnosis/treatment. RESULTS: Average age was 73 +/- 8 years, baseline glomerular filtration rate was 37 +/- 15 ml/min/1.73 m2, and average follow-up was 34 months. Baseline characteristics were similar between the two groups, with the exception of higher diastolic blood pressure in the PTRAS group (75 versus 70 mmHg, p = 0.028). There were no significant differences between the two groups during follow-up. The decline in glomerular filtration rate was similar in both groups (-1.6 ml/min/1.73 m2 in the medical group versus -1.4 ml/min/1.73 m2 in the PTRAS group, p = 0.938). Multivariate models did not indicate an association between treatment modality and changes in renal function or rates of ESRD or death. CONCLUSION: In patients with advanced kidney disease, medical therapy and renal artery stenting appear comparable in stabilizing renal function for ARAS.

Circadian blood pressure: clinical implications based on the pathophysiology of its variability.

The circadian blood pressure (BP) rhythm is associated with worsened cardiovascular outcomes in patients who have an excessive morning BP surge and in those who lack the normal nocturnal BP fall (non-dippers). There are multiple pathophysiologic mechanisms underlying abnormalities in circadian BP, most importantly abnormalities in sympathetic nervous system activity, salt and volume balance, and activation of the renin-angiotensin system. Several of these factors can be modified by clinical interventions, either related to lifestyle changes and/or antihypertensive drug therapy. The timing of drug administration or specific drug delivery systems that lead to a greater effect at night and/or mitigate the early morning BP surge can correct abnormal circadian rhythms. Although these strategies have not yet been shown to alter clinical outcomes, it is reasonable to understand their biologic basis and take them into consideration when designing antihypertensive therapy.

Ondansetron or droperidol for prophylaxis of nausea and vomiting after intrathecal morphine.

BACKGROUND AND OBJECTIVE: There is a controversy regarding the best drug for prevention of nausea and vomiting in patients receiving intrathecal morphine. The aim of this study was to examine efficacy and tolerability of droperidol compared with ondansetron for the prevention of morphine-induced nausea and vomiting. METHODS: In a randomized, placebo-controlled trial, 120 women undergoing Caesarean section under spinal anaesthesia with intrathecal morphine 0.1 mg received intravenous ondansetron 4 mg (n = 40), droperidol 1.25 mg (n = 40) or saline (n = 40) immediately after umbilical-cord clamping. Nausea and vomiting were graded according to intensity at 1, 2, 4, 6, 12 and 24 h. RESULTS: Nausea or vomiting occurred in 14 patients (35%) in the placebo group, 4 (10%) in the ondansetron group and 10 (25%) in the droperidol group; the difference between ondansetron and placebo was statistically significant (P = 0.007). Eleven of the 14 placebo patients (27.5%) vomited, compared with none of the 4 ondansetron patients (vs. placebo, P = 0.0004) and 5 of the droperidol patients (vs. placebo, P = 0.18). Three of the 14 placebo patients (7.5%) were nauseous, compared with 4 (10%) receiving ondansetron and 5 (12.5%) receiving droperidol. CONCLUSIONS: Ondansetron was effective in reducing the incidence of nausea and vomiting in patients receiving intrathecal morphine for Caesarean section.

Birth, death, and resurrection of the physical examination: clinical and academic perspectives on bedside diagnosis.

The physical examination has a historically prominent role in medical practice, being an important tool in diagnosis and in developing rapport with patients. Yet, physicians have lost bedside skills in recent years, with increasing use of technology at the expense of time spent with the patient. This is concerning, especially in the present era of cost-containment in health care. Approaches to improve bedside diagnosis skills include increased emphasis on instruction in physical examination during medical school and postgraduate training, and careful scrutiny of physical examination techniques, with formal evaluation of their accuracy and reproducibility. Only through education and research will the physical examination recover its central role in the clinical encounter.

Efficacy of prophylactic droperidol, ondansetron or both in the prevention of postoperative nausea and vomiting in major gynaecological surgery. A prospective, randomized, double-blind clinical trial.

We conducted a prospective, randomized, double-blind clinical trial comparing droperidol 1.25 mg intravenously (i.v.) (group 1, n = 30), ondansetron 4 mg i.v. (group 2, n = 30), or both (group 3, n = 30) in the prevention of postoperative nausea and vomiting (PONV) in the first 24 h following major gynaecological procedures under combined general and epidural anaesthesia. PONV was analysed by a linear nausea/vomiting score, incidence of nausea and vomiting, and the need for antiemetic rescue. Our results showed a similar incidence of nausea and vomiting in all groups (G1 33%, G2 40%, G3 43%). However, when comparisons were made according to the time of assessment, combination therapy resulted in significantly lower PONV than droperidol in the first hour (0% vs. 13%, P < 0.05) and second hour (0% vs. 13%, P < 0.05), and than ondansetron on the first hour (0% vs. 13%, P < 0.05). A trend persisted up to the fourth hour but was not statistically significant in either group. In conclusion, droperidol and ondansetron are effective agents in the prevention of PONV, and their combination seems to provide slightly better results than either drug alone.

Reproducibility of ambulatory blood pressure monitoring in hemodialysis patients.

Ambulatory blood pressure monitoring (ABPM) has been increasingly used in hemodialysis (HD) practice and research; however, no study has evaluated the reproducibility of ABPM in this population. To address this question, we performed 48-hour interdialytic ABPM on 21 HD patients (mean age, 53 +/- 16 years; 7 women) on two different occasions 68 +/- 34 days (range, 30 to 154 days) apart. To qualify for the protocol, patients had to be at the same dry weight and on the same vasoactive drug regimen at both monitoring periods. BP was analyzed according to three different methods: isolated pre-HD and post-HD values, average pre-HD and post-HD values for the five HD sessions surrounding each monitoring period, and 48-hour interdialytic ABPM. Reproducibility was determined by analysis of the SD of the differences (SDD) between the two monitoring periods and the coefficient of variation of each method of BP determination. Our results show better reproducibility of ABPM (SDD, 10.6/6.6 mm Hg; coefficient of variation, 7.5%/8.1%) compared with isolated pre-HD BP (SDD, 24.4/11.3 mm Hg; coefficient of variation, 16.7%/14.1%) or post-HD BP (SDD, 16.8/14.5 mm Hg; coefficient of variation, 11.7%/17.8%), and averaged pre-HD BP (SDD, 14.7/7.2 mm Hg; coefficient of variation, 10.1%/9.1%) or post-HD BP (SDD, 12.4/8.7 mm Hg; coefficient of variation, 8.9%/11.1%). The reproducibility of the decrease in BP during sleep was poor, with up to 43% of the subjects changing dipping category within or between interdialytic periods. We conclude that ABPM is the most accurate method to study BP in HD patients over time. However, variability is significant, and there is poor reproducibility of the nocturnal decline in BP.

Validation of the SpaceLabs 90207 ambulatory blood pressure device for hemodialysis patients.

BACKGROUND: Background Ambulatory blood pressure monitoring (ABPM) has been used increasingly in assessing dialysis patients. However, devices have not been validated formally for this population. Formal device validation is important in order to guarantee adequate performance for populations with special characteristics, such as patients undergoing hemodialysis. OBJECTIVE: To achieve formal validation of the SpaceLabs 90207 ambulatory blood pressure device (SLD) using a modified British Hypertension Society protocol. METHODS: Eighty-five hemodialysis patients were studied, generating 255 readings. Readings were obtained with patients supine (in a dialysis chair) over 5-10 min during hemodialysis. Simultaneous, same-arm readings were obtained through the use of a T connector to a calibrated mercury manometer. The mean differences between readings obtained by observers and those obtained by the device were calculated. Limits of agreement between observers and SLD were determined and plotted according to the method of Bland and Altman. For grading of performance, we determined the number of readings for which the readings obtained by the device were within 5, 10, and 15mmHg of manometer readings. Final gradings were ascribed according to British Hypertension Society criteria. RESULTS: The mean blood pressure (+/-SD) was 141/76+/-31/15mmHg (observers) and 141/77+/-27/15mmHg (SLD), and the mean (+/-SD) difference between observers and device (observer-device) was -0.5+/-7.5mmHg for systolic blood pressure (SBP) and -0.2+/-5.2mmHg for diastolic blood pressure (DBP). The device was less accurate in extreme ranges of SBP. In fact, there was a positive correlation between average [(observer+device)/2] and difference (observer-device) for SBP (r =0. 54, P <0.0001), showing that underestimation in higher ranges, and overestimation in lower ranges of blood pressure occurred for SBP. For SBP, 53% of readings were within 5mmHg of those obtained by the observers, 85% were within 10mmHg, and 97% within 15mmHg. For DBP, 78% were within 5mmHg, 96% within 10mmHg, and 98% within 15mmHg. These observations conferred on the device grade C for SBP and grade B for DBP. The type of vascular access and the presence of non-functioning arteriovenous grafts and fistulas in the ipsilateral arm did not alter these results significantly. CONCLUSIONS: These data validate the use of this device for hemodialysis patients. However, caution should be exercised in the evaluation of upper and lower ranges of SBP.

Delayed gallium-67 uptake in renal atheroembolic disease.

The differentiation between atheroembolic disease (AED) and allergic interstitial nephritis (AIN) may pose a clinical challenge. Gallium scans have been proposed to identify AIN with good discriminating ability. We report herein a case of atheroembolic disease presenting as acute renal failure with persistent delayed uptake of gallium-67 by nuclear imaging. The distinction between AED and AIN could be made only with a renal biopsy, which confirmed the correct diagnosis. This case report and the presented review of the literature suggest that gallium scans are nonspecific and should not supplant renal biopsy for definitive histological diagnosis.