Resistance of vascular access catheters for continuous renal replacement therapy: An ex vivo evaluation.

AIM: To assess the resistance posed by double-lumen vascular access dialysis catheters at low and high blood flow. DESIGN: Controlled ex vivo study Setting: ICU Laboratory of tertiary hospital. SUBJECTS: Eleven proprietary vascular access catheters for continuous renal replacement therapy. METHODS: Heparinized spent red cells diluted in polygeline solution were pumped using the Aquarius hemofiltration machine (Edwards Life Sciences, Sydney, NSW, Australia) and its standard circuit through several vascular access catheters. Blood flow was increased and then decreased in steps of 50 ml/min (50, 150, 200, 250 and 300 ml/min) while catheter outflow and inflow pressures were recorded. The pressure-flow relationship (hydraulic resistance) of each catheter was then calculated. Study catheters were divided into two groups according to their internal diameter (large gauge vs. smaller gauge) or length (long or short). Hydraulic resistances were compared between the groups. RESULTS: Different double lumen catheters posed clearly different resistances to flow. For all groups of catheters, there was a linear relationship between pressure and flow. No statistically significant difference between short and long catheters could be demonstrated (p=0.715). On the other hand, larger gauge catheters (13 Fr or greater) had significantly lower resistances than smaller gauge (<13 Fr) catheters (p=0.0062). Furthermore, all larger gauge catheters had resistances lower than 0.430 mmHg/ml/min, while all smaller gauge catheters had resistances greater than 0.490 mmHg/ml/min. CONCLUSIONS: Commercial double-lumen dialysis catheters have variable resistance to blood flow under standard ex vivo conditions. Although both length and internal diameter varied, internal diameter had a dominant effect on resistance. This information might be useful to clinicians in guiding their choice of catheters for clinical use.

The acid-base effect of changing citrate solution for regional anticoagulation during continuous veno-venous hemofiltration.

PURPOSE: To compare the acid-base balance effects of two different citrate doses for regional citrate anticoagulant (RCA) for continuous veno-venous hemofiltration (CVVH). METHODS: We used a commercial citrate fluid (citrate concentration: 11 mmol/L) from July 2003 to July 2004 (period A) in 22 patients; then changed to a new citrate fluid (citrate concentration: 14 mmol/L) from July 2004 to Feb 2005 (Period B) in 21 patients. Replacement fluid rate was fixed at 2,000 ml/h. We measured all relevant variables for acid-base analysis according to the Stewart-Figge methodology. RESULTS: After commencement of RCA-CVVH, there was a change in bicarbonate and base excess (BE) toward acidosis for both fluids. This change was significantly different between period A and B at 6 and 12 hours (pH: p<0.01, BE: p<0.05) with greater decreases with the 11 mmol/L citrate fluid. These changes were mostly secondary to an increase in the strong ion difference (SID) and occurred despite an increased strong ion gap (SIG) (+0.5 mEq/L vs. +1.5 mEq/L; p<0.01) in the higher citrate concentration fluid. Cessation of RCA-CVVH was associated with short-lived differences in bicarbonate and SIG which were similar to those seen on initiation of RCA-CVVH but in the opposite direction. CONCLUSIONS: A small increase This was partly offset by an increase in SIG, consistent with increased citratemia. Cessation of treatment showed a differential improvement in SIG also consistent with disposal of therapy-associated citrate. These observations might assist clinicians in interpreting acidbase changes during RCA-CVVH.in citrate infusion rate caused an alkalinizing increase in SID.

Beta2-microglobulin removal and plasma albumin levels with high cut-off hemodialysis.

PURPOSE: beta2-microglobulin (beta2MG) is pivotal to the pathogenesis of dialysis-related amyloidosis. We compared the effects of high cut-off hemodialysis (HCO-HD) with those of standard high-flux hemodialysis (HF-HD) regarding the concentration and clearance of beta2MG and albumin. DESIGN: We enrolled ten patients with acute renal failure in a double-blind, cross-over, randomized controlled trial. PROCEDURES: Each patient received four hours of HCO-HD (estimated in vivo cutoff 50-60 kDa) and four hours of HF-HD (estimated in vivo cutoff 15-20 kDa) in random order. Statistical methods and outcome measures: As data lacked normal distribution, we used nonparametric statistical analysis. Plasma and dialysate concentrations of beta2MG and albumin were measured at baseline and after four hours of each study treatment. MAIN FINDINGS: We found significantly greater diffusive beta2MG clearances for HCO-HD compared to HF-HD (at the start: 71.8 ml/min vs. 5.1 ml/min; P=0.008 and at the end: 68.8 ml/min vs. 5.7 ml/min; P=0.008). We found a reduction in plasma beta2MG concentrations of -31.6% during HCO-HD compared to an increase by 25.7% during HF-HD; P=0.008. At baseline (HCO-HD: 26.0 g/L vs. HF-HD: 26.5 g/L), and at the end of both treatments, plasma albumin concentrations were comparable (HCO-HD: 25.5 g/L vs. HF-HD: 26.5 g/L; P=0.25). During HCO-HD, albumin clearance was 1.9 ml/min at the start and decreased significantly to 0.8 ml/min at the end; P=0.008. HF-HD had an albumin clearance of 0.01 ml/min. CONCLUSIONS: HCO-HD was more effective in decreasing plasma beta2MG concentrations than standard HF-HD and did not reduce plasma albumin levels. Further studies of HCO-HD in the treatment of dialysis-related beta2MG accumulation appear warranted.

Fluid balance error in continuous renal replacement therapy: a technical note.

BACKGROUND: The reliability and safety of continuous renal replacement therapy (CRRT) machines have improved, yet there still remains the potential for fluid balance errors to occur during treatment. METHODS: In vitro testing of two Kimal Hygieia CRRT machines (Plus and Ultima) was performed. Normal saline to simulate the blood circuit and standard bicarbonate-based fluid for replacement were used. All tests were performed in CVVH mode at four ultrafiltration (UF) rates. The testing was based on creation of a voluntary fluid balance error by clamping the line that fills the replacement fluid chamber to stop flow to the (simulated) patient. The time to alarms and fluid balance errors were recorded. The alarms were overridden and the accumulated fluid balance error allowed by the machine was determined. RESULTS: The alarm occurred approximately 1 minute after the replacement fluid line was clamped at all UF rates. There was no limit to the number of times the alarm could be overridden and the accumulated negative fluid balance was proportional to the prescribed UF rate. After the replacement fluid chamber was allowed to re-fill, the machine attempted to correct the fluid deficit and consistently delivered excess fluid to generate a positive fluid balance error. CONCLUSIONS: The Hygieia machines appear designed with appropriate alarm and safety features. However, simulated fluid balance errors raise caution for operators. Clinicians and nurses need to understand the clinical implications of alarm overrides. Fluid balance errors caused by failure to acknowledge and correct replacement fluid failure alarms may cause harm to patients.

A pilot randomized controlled crossover study comparing regional heparinization to regional citrate anticoagulation for continuous venovenous hemofiltration.

OBJECTIVE: To evaluate the efficacy and safety of a regional heparinization and a regional citrate method of anticoagulation in CVVH. DESIGN: Randomized controlled cross-over study. SUBJECTS: Ten critically ill patients with acute renal failure. SETTING: ICU of tertiary hospital. INTERVENTION: CVVH was performed with pre-filter fluid replacement at 2000 ml/h and a blood flow rate of 150 ml/min. Regional heparinization was by the administration of heparin pre-filter at 1500 IU/h and protamine post-filter at 15 mg/h. Regional citrate anticoagulation was by means of a citrate-based replacement fluid (14 mmol/L) administered pre-dilution. RESULTS: We studied nine males and one female. The mean age and APACHE II score were 70.5 and 17 respectively. Median circuit life was 13 hours (IQR 9.28) for the regional heparinization method compared to 17 hours (IQR 12,19.5) for the regional citrate method (p=0.77). There were no episodes of bleeding in either group. CONCLUSION: Regional heparinization and regional citrate anticoagulation achieve similar circuit life in critically ill patients receiving CVVH.

A pilot randomized controlled comparison of extended daily dialysis with filtration and continuous veno-venous hemofiltration: fluid removal and hemodynamics.

OBJECTIVES: Extended intermittent dialytic techniques are increasingly being reported in the treatment of ARF in the ICU but few randomized controlled trials exist. We compared one such technique to a technique of continuous renal replacement therapy with regard to fluid removal and hemodynamics. METHODS: Sixteen critically ill patients with ARF were enrolled in a randomized controlled trial at the ICU of a tertiary hospital. We randomized eight patients to three consecutive days of treatment with either Extended Daily Dialysis with filtration (EDDf) or Continuous Veno-Venous Hemofiltration (CVVH) and compared fluid removal and hemodynamics during treatment. RESULTS: A total of 16.6 liters of fluid were removed during EDDf (830 mL/day over 20 treatment days) compared with 15.4 liters (700 ml/day over 22 treatment days) during CVVH. Median fluid removal per day was 1837 mL in the EDDf group compared with 1410 mL per day in the CVVH group, p=0.674. Median hourly fluid removal rate was 252 mL for EDDf and 128 mL for CVVH (p<0.01). Mean arterial pressure in the EDDf group was lower at two hours after starting treatment (76 mmHg vs. 94 mmHg) in the CVVH group; p= 0.031. There was no significant difference between groups for heart rate, CVP and noradrenaline dose at all time intervals measured. CONCLUSIONS: Adequate prescribed fluid removal was achieved with both techniques. However, as expected, fluid was removed at a faster rate during EDDf. This was initially associated with a lower blood pressure than during CVVH where blood pressure increased.

Commercial low-citrate anticoagulation haemofiltration in high risk patients with frequent filter clotting.

This study assessed the safety and efficacy of a commercial low-citrate concentration-based pre-filter replacement fluid during continuous veno-venous haemofiltration (CVVH) in patients with frequent filter clotting and high risk of bleeding. We used a commercial low-citrate fluid as pre-dilution replacement fluid during CVVH (citrate: 11 mmol/l (33 meq/l), sodium: 140 mmol/l, chloride: 108 mmol/l and potassium: 1 mmol/l). A calcium and magnesium infusion was delivered separately by central line for the maintenance of serum ionized calcium (Cai) and total magnesium (Mg). In this prospective observational study, 30 patients, 124 filters and 1,515 treatment-hours were observed. Median filter life of citrate CVVH was 9.5 hours. Filter life in the 48 hours prior to citrate CVVH was also observed. In the patients on prior non-anticoagulant CVVH (n=14) filter life increased significantly with citrate (9.5 hours vs 5 hours; P<0.0001). In patients on prior heparin CVVH (n = 15), filter life was similar with citrate (10 hours vs 8 hours; P = 0.68). However, in patients with prior early/frequent filter clotting despite heparin (n = 11) filter life increased significantly (10 hours vs 7 hours; P=0.038). Of 411 serum Cai measurements, none showed a Cai < 0.85 mmol/l and, of 84 observations, none showed a serum Mg<0. 6 mmol/l. One patient with sepsis and shock needed to cease citrate CVVH because of progressive ionized hypocalcaemia and increasing anion gap. No other adverse effects were observed. In selected patients, CVVH with a commercial low-citrate concentration solution as pre-filter replacement fluid and a simultaneous calcium and magnesium infusion protocol appears generally safe. Filter life was acceptable and superior to that achieved with previous treatment.

[Long-term intermittent renal replacement therapy at an intensive care unit].

Standard intermittent hemodialysis (IHD) used for the treatment of acute renal failure (ARF) at an intensive care unit has significant biochemical and physiological drawbacks. In the past 20 years, these drawbacks have stimulated the development of continuous renal replacement therapy (CRRT) and its ever-increasing use. However, CRRT is technically complicated and requires 24-hour monitoring. In some clinics, the use of CRRT leads to that each patient is under his/her nurse's surveillance, instead 1 nurse per 2 patients as before; this change has economic consequences and may limit nursing accessibility to other patients. The procedures prolonging intermittent therapy do not require 24-hour monitoring may benefit the treatment of ARF at the intensive care therapy. In this paper the authors call such procedures for continuous intermittent renal replacement therapy. They are characterized by a number of basic principles: (1) the use of modified or standard dialysis apparatuses; (2) the application of diffuse, convection, or both; (3) a certain reduction in the rate of elimination of dissolved substances as compared with IHD; (4) more prolonged treatment: above usual 3 or 4 hours of IHD, but not more than 8-12 hours (hence the term "intermittent"); (5) the use of on-line generation dialysate or substituting fluid. Information on the effectiveness and safety of this procedure is being now compiled.

Low-dose citrate continuous veno-venous hemofiltration (CVVH) and acid-base balance.

OBJECTIVE: To evaluate the acid-base effect of low-dose regional citrate anticoagulation (RCA) during continuous veno-venous hemofiltration (CVVH). DESIGN: Prospective observational study. SETTING: ICUs of tertiary public and private hospitals. SUBJECTS: Thirty critically ill patients with acute renal failure at risk of bleeding or with a major contraindication to heparin-CVVH and/or short filter life. METHODS: We used a commercial citrate-based fluid (11 mmol/L, sodium: 140 mmol/L, chloride: 108 mmol/L and 1 mol/L of potassium) as pre-dilution replacement fluid during CVVH. Further potassium was added according to serum potassium levels. We measured all relevant variables for acid-base analysis according to the Stewart-Figge methodology. RESULTS: Before treatment, study patients had a slight metabolic acidosis, which worsened over 6 hours of RCA-CVVH (pH from 7.39 to 7.38, p < 0.005; bicarbonate from 23.2 to 21.6 mmol/L, p < 0.0001 and base excess from -2.0 to -3.0 mEq/L, p < 0.0001) due to a significant increase in SIG (from 5.8 to 6.6 mEq/L, p < 0.05) and a decrease in SIDa (from 37.5 to 36.6 mEq/L, p < 0.05). These acidifying effects were attenuated by hypoalbuminemia and a decrease in lactate (from 1.48 to 1.34 mmol/L, p < 0.005) and did not lead to progressive acidosis. On cessation of treatment, this acidifying effect rapidly self-corrected within six hours. CONCLUSIONS: Low dose RCA-CVVH induces a mild acidosis secondary to an increased strong ion gap and decreased SIDa which fully self-corrects at cessation of therapy. Clinicians need to be aware of these effects to correctly interpret changes in acid-base status in such patients.

A comparison of two citrate anticoagulation regimens for continuous veno-venous hemofiltration.

AIMS: To assess the safety and efficacy of two different commercial citrate containing pre-filter replacement fluids during continuous veno-venous hemofiltration (CVVH) in patients with frequent filter clotting. SETTING: Four intensive care units. PATIENTS: Sixty-three critically ill patients with acute renal failure (ARF). DESIGN: Prospective observational study. METHODS: We used a commercial citrate fluid (citrate: 11 mmol/L -fluid A) as predilution replacement for CVVH. We then changed to a new commercial citrate fluid (citrate: 14 mmol/L-fluid B) as replacement fluid and performed statistical comparisons. Replacement fluid rate was fixed at 2,000 ml/hour. RESULTS: Filter life was 12.2 hour with fluid A compared with 17.1 hour with fluid B on average (p=0.0001). Mean post filter ionized calcium concentration was 0.52 mmol/L with fluid A compared with 0.40 mmol/L with fluid B (p<0.0001). Citrate intolerance led to cessation of treatment in one patient with fluid A and one patient with fluid B. Overall ionized calcium levels were higher (A: 1.18 vs B: 1.13 mmol/L; p<0.0001) and bicarbonate was lower (A: 22.4 vs B: 24.5 mmol/L; p<0.0001) during treatment with fluid A. Alkalemia was seen in 10 patients treated with fluid A and 16 patients treated with fluid B (NS). CONCLUSIONS: We have developed a simple approach to regional citrate anticoagulation for CVVH using a commercial citrate-containing fluid as replacement fluid. Increasing citrate concentration from 11 to 14 mmol/L increased filter life while maintaining relative safety and simplicity.

Prolonged daily intermittent renal replacement therapy in ICU patients by ICU nurses and ICU physicians.

OBJECTIVES: Prolonged daily intermittent renal replacement therapy (PDIRRT) has been proposed as a new form of treatment for severe acute renal failure (ARF). However, this treatment has so far implied a) full dependence on nephrological input, b) lack of any convective clearance and c) limited purification of dialysate water. The aim of this study was to establish the feasibility and safety of performing PDIRRT in the ICU with a) no nephrological input, b) the addition of some convective clearance with on-line fluid replacement and c) a new advanced water purification system. DESIGN: Prospective observational study. PATIENTS: Fourteen patients treated with PDIRRT. SETTING: ICU of tertiary institution. INTERVENTIONS: Treatment of patients with severe ARF and critical illness with PDIRRT. Prescription of treatment by ICU physicians. Conduct of treatment by ICU nurses. Use of combined convective and diffusive therapy with on-line generation of fluid replacement, application of a double-filtration water purification system. MEASUREMENTS AND MAIN RESULTS: We prospectively collected demographic, biochemical, hemodynamic and clinical data in 14 patients, who received 30 PDIRRT treatments for a cumulative treatment time of 205.4 hours. The mean age was 57.9 +/- 16.0. Eight patients were male and 6 female. Their mean APACHE II score was 24.6 +/- 5.9 and their SAPS II score was 41.7 +/- 18.8. PDIRRT was used after at least 24 hours of initial stabilization with continuous veno-venous hemofiltration (CVVH). Blood flow was kept at 100 ml/min dialysate flow at 200 ml/min and convective clearance varied from 21 ml/min to 33 ml/min. All patients were either anuric or oliguric (UO < 400 ml/day). Ten patients were on mechanical ventilation and 11 patients on vasopressor support. Mean treatment session time was 6.9 +/- 1.8 hours. The mean pre-PDIRRT urea was 19.2 +/- 6.9 mmol/L and the creatinine was 274 +/- 116 micromol/L. The mean pre-PDIRRT lactate was 2.95 +/- 2.24 mmol/L. Following treatment, all had significantly decreased to 13.2 +/- 6.3 mmol/L, 215 +/- 95 micromol/L and 2.25 +/- 1.61 mmol/L, respectively (p=<0.0001, <0.0001, <0.05). Bicarbonate levels remained stable during treatment (23.0 +/- 3.8 mmol/L to 23.1 +/- 2.5 mmol/L). Mean norepinephrine dose changed from 8.8 +/- 11.9 microg/min to 12.9 +/- 27.0 microg/min after treatment (NS). There were no complications of therapy. Patient ICU survival was 71.4%. CONCLUSIONS: PDIRRT with combined diffusive and convective clearance is an efficacious form of renal replacement, which can be safely and effectively conducted by ICU nurses following prescription by ICU physicians without any nephrological involvement and with adequate double filtration water purification.

Super high flux hemodialysis at high dialysate flows: an ex vivo assessment.

BACKGROUND AND OBJECTIVES: The removal of cytokines by standard hemofiltration is limited. Super high flux membranes may significantly improve removal even when used in dialysis mode. We sought to measure cytokine clearance using a large surface super high-flux membrane and a standard hemodialysis setting. SETTING: ICU laboratory of a tertiary institution. SUBJECTS: Six healthy volunteers. METHODS: Blood form healthy volunteers was incubated for 4 hours with E. coli endotoxin to stimulate cytokine production. Cytokine containing blood was then circulated through a dialysis circuit at 3 different dialysate flow rates. Blood and dialysate were sampled for cytokine and albumin measurements and calculation of clearances. RESULTS: Super high-flux dialysis achieved high median cytokine clearances (IL-1 clearance of 106 ml/min, IL-6 clearance of 66.8 ml/min, IL-8 clearance of 61.7 ml/min and TNF clearance of 36.1 ml/min). Increasing dialysate flow rate from 300 to 500 ml/min did not significantly increase cytokine clearances. Albumin clearances however were between 2.7 and 5.4 ml/min. CONCLUSIONS: Cytokine dialysis is feasible at high dialysate flow rates yielding high cytokine clearances. Albumin loss, however, is appreciable and may require separate supplementation in the clinical setting.

Beta2-microglobulin clearance with super high flux hemodialysis: an ex vivo study.

BACKGROUND: Beta2m accumulation induces disease in patients with end-stage renal failure (ESRF). Thus, its removal from patients with ESRF appears desirable. Current dialysis technology, however, has limited effectiveness. AIMS: To measure beta2m clearance with a novel super high flux membrane. DESIGN: Ex vivo experimental study. SETTING: Intensive Care Laboratory of Tertiary institution. SUBJECTS: Six volunteers. MEASUREMENTS AND RESULTS: At a blood flow of 300 ml/min, the clearance of beta2-MG increased from 113.5 +/- 38.5 ml/min with a dialysate flow rate of 200 ml/min to 184.8 +/- 61.1 ml/min with a flow rate of 300 ml/min and 195.0 +/- 60.0 ml/min with a 500 ml/min flow rate. The clearance of albumin was 4.5 ml/min with a dialysate flow rate of 200 ml/min, 5.2 ml/min for a flow rate of 300 ml/min and 5.8 ml/min for a flow rate of 500 ml/min. CONCLUSIONS: High levels of beta2m clearance can be achieved with a super high flux membrane while albumin losses remain limited.

The effect of circuit "down-time" on uraemic control during continuous veno-venous haemofiltration.

OBJECTIVE: The term continuous veno-venous haemofiltration (CVVH) suggests a treatment without interruption. However, interruptions do occur and the duration of the haemofiltration circuit "down-time" may influence uraemic control. We conducted a prospective study to ascertain the percentage of operative "down-time" for CVVH in our intensive care unit and to test the hypothesis that it significantly affected uraemic control. PATIENTS AND METHODS: Prospective data measuring the time spent off the filter in ten patients receiving CVVH were collected. Continuous veno-venous haemofiltration was performed at 2 litres per hour of ultrafiltration. Anticoagulation was maintained using unfractionated heparin administered pre-filter and infused at a rate to achieve a systemic APTT varying between 30-45 seconds. The circuit functional life was documented for each CVVH circuit as progressive cumulative hours of operation. The time off treatment was calculated for each 24-hour period. These data were then correlated with the change in plasma urea and creatinine concentrations for each 24-hour cycle. The APTT, INR, haemoglobin and platelet count were measured and levels were correlated with the filter duration. RESULTS: Ninety three days of CVVH treatment were assessed in 4 female and 6 male patients. The mean circuit "down-time" in these patients for this period was 22% or 5.27 hours per day. The most common cause of circuit "down-time" was circuit clotting, followed by a need for radiological procedures, time spent in the operating theatre and catheter malfunction requiring replacement. There was a strong correlation between circuit "down-time" and increase in plasma urea (p = 0.0017) and creatinine (p = 0.0451) concentrations. Circuit "down-time" was also inversely correlated with the platelet count (p = 0.0048) but not significantly correlated with the APTT, INR or haemoglobin values. CONCLUSIONS: In our study the average daily duration of an interruption in CVVH (i.e. circuit "down-time") represented > 20% of the potential operative time. There was a strong correlation between time without treatment and solute control during CVVH. The percentage of "down-time" may be a useful marker of operative quality during CVVH.

Prolonged intermittent renal replacement therapy in the intensive care unit.

OBJECTIVE: To present a review on the use of prolonged intermittent renal replacement therapy in the intensive care patient. DATA SOURCES: Articles and abstracts reporting the use of renal replacement therapy. SUMMARY OF REVIEW: Standard intermittent haemodialysis (IHD) has significant shortcomings in the treatment of the acute renal failure (ARF) of critical illness. These shortcomings include haemodynamic instability, the need to remove excess fluid over a short period of time, the episodic nature of small solute control, the limited ability to achieve middle molecular weight solute control and the episodic nature of acid-base control. Over the last 20 years, these limitations have stimulated the evolution and increased application of continuous renal replacement therapy (CRRT) which provides major biochemical, biological and physiological advantages compared with IHD, although it remains unclear as to whether such advantages translate into a survival advantage. However, CRRT is technically demanding, requires supervision 24 hr per day and is often associated with the need for continuous anticoagulation, which, in some patients, might be undesirable. In some institutions, CRRT changes the nurse to patient ratio from 1:2 to 1:1, an alteration which has cost implications and might affect resource availability for other patients. Accordingly, techniques which prolong the duration of intermittent therapy and avoid the need for 24 hr treatment may offer "best value" in the management of ARF in the intensive care unit (ICU). These techniques will be referred to as prolonged intermittent renal replacement therapies (PIRRT) in this article. They are characterised by several fundamental principles: 1. Use of a modified or standard dialysis machines, 2. Use of diffusion, convection or any combination of the two, 3. Application of a decreased intensity of solute removal compared with IHD, 4. Extended duration of treatment beyond the typical 3 or 4 hr of standard IHD (hence the term prolonged) but not beyond an 8-12 hr period (hence the term intermittent) and 5. Use of "on-line" generation of dialysate or replacement fluid from tap water. CONCLUSIONS: Information is now being obtained on the efficacy and safety of PIRRT in the ICU. Several units in Australia have started applying this technology to patient care. It is now important that critical care physicians and nurses become familiar with its principles and practice.