What are the recommended monitoring procedures and parameters during a hemodialysis session?

Monitoring During Hemodialysis

During every hemodialysis session, measure venous dialysis pressure at blood flow 200 mL/min within the first 2-5 minutes, blood pressure at least twice (pre- and post-dialysis, both seated and standing), and continuously track ultrafiltration rate to ensure it does not exceed 13 mL/kg/hour. 1, 2, 3

Vascular Access Pressure Monitoring

Venous pressure surveillance is critical for detecting access stenosis before thrombosis occurs:

• Establish a baseline venous dialysis pressure when the access is first used 1
• Measure venous pressure from the hemodialysis machine at blood flow 200 mL/min during the first 2-5 minutes of every session 1
• Use standardized needle size (15-gauge recommended) and maintain consistent measurement technique 1
• Ensure the venous needle is properly positioned in the vessel lumen, not against the vessel wall 1
• Document pressures at the same level relative to the hemodialysis machine for all measurements 1

Threshold values for intervention:

• For Cobe Centry 3 machines with 15-gauge needles: venous pressure >125 mmHg indicates likely venous outlet stenosis 1
• For Gambro AK 10 machines with 15-gauge needles: threshold is 150 mmHg 1
• Three consecutive measurements exceeding the threshold warrant referral for venography 1
• Trend analysis is more important than single measurements - progressive upward trends predict stenosis even if absolute values remain below threshold 1

Blood Pressure Monitoring

Minimum required measurements:

• Measure blood pressure at least twice per session: once before dialysis (at least 5 minutes before needle insertion) and once at the end 2
• Obtain both seated and standing measurements at each timepoint 2
• Patient must be seated quietly for at least 5 minutes with feet flat on floor and arm supported at heart level before measurement 2
• Standing blood pressure should be obtained after at least 2 minutes upright with arm supported at heart level 2

Technical requirements:

• Use auscultatory method with Korotkoff sounds for diastolic pressure 2
• Appropriate cuff size with bladder encircling at least 80% of arm circumference 2
• Avoid caffeine, exercise, and smoking for at least 30 minutes before measurement 2
• Do not measure immediately after needle insertion, as this causes stress-induced elevation 2

Increased monitoring frequency:

• For patients experiencing hypotensive episodes or requiring vasopressor support to maintain mean arterial pressure ≥65 mmHg, increase blood pressure measurements to every 30 minutes during the session 2
• For sessions with ultrafiltration rates approaching 13 mL/kg/hour, monitor blood pressure every 30 minutes 3

Orthostatic hypotension detection:

• Standing measurements are essential to detect orthostatic hypotension (fall ≥15 mmHg systolic and ≥10 mmHg diastolic after standing) 2
• Autonomic dysfunction is common in ESRD patients, making standing measurements particularly important in elderly patients and those with diabetes 2

Ultrafiltration Rate Monitoring

Calculate and monitor ultrafiltration rate continuously to prevent cardiovascular complications:

• Maximum safe ultrafiltration rate is 13 mL/kg/hour 3
• Calculate minimum treatment time using: Treatment Time (hours) = Ultrafiltration Volume (mL) ÷ [13 × Body Weight (kg)] 3
• Never write orders as "ultrafiltration as tolerated" without calculating the maximum safe rate 3

When ultrafiltration requirements exceed safe rates:

• Extend treatment time rather than attempting to achieve dry weight in a single session 3
• Consider adding additional dialysis sessions 3
• Address sodium restriction (target 85-100 mmol/day) to reduce interdialytic weight gain 3

Treatment Time and Session Duration

Minimum treatment time requirements:

• Patients with residual kidney function <2 mL/min undergoing thrice-weekly hemodialysis require a bare minimum of 3 hours per session 1
• Consider longer treatment times or additional sessions for patients with: 1
  • Large interdialytic weight gains
  • High ultrafiltration rates
  • Poorly controlled blood pressure
  • Difficulty achieving dry weight
  • Poor metabolic control (hyperphosphatemia, metabolic acidosis, hyperkalemia)

Physical Examination of Vascular Access

Perform physical examination at each session:

• Palpate for thrill at arterial, mid, and venous segments of grafts - palpable thrill predicts flows ≥450 mL/min 1
• A pulse instead of thrill suggests lower flows and potential stenosis 1
• Intensification of bruit suggests stricture or stenosis 1
• Persistent abnormalities in pulse, thrill, or bruit should prompt referral for venography 1

Common Pitfalls to Avoid

• Do not rely solely on pre- or post-dialysis blood pressure readings, as they correlate poorly with interdialytic ambulatory blood pressure 2
• Do not skip standing blood pressure measurements, especially in high-risk populations 2
• Do not ignore progressive trends in venous pressure even if absolute values remain below threshold 1
• Do not use automated blood pressure devices without validation, as they systematically overestimate blood pressure by 14/7 mmHg in dialysis patients 2
• Do not measure blood pressure immediately after needle insertion 2