Criteria abstracted from The Users' Guide to Medical Literature, from the Health Information Research Unit and Clinical Epidemiology and Biostatistics, McMaster University

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The questions for diagnostic technology articles are based upon: Keenan SP, Guyatt GH, Sibbald WJ, Cook DJ, Heyland DK, Jaeschke RZ. How to use articles about diagnostic technology: gastric tonometry. Crit Care Med. 1999;27(9):1726-31 [abstract]

Article Reviewed:

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Accuracy and utility of a continuous intra-arterial blood gas monitoring system in pediatric patients

Coule LW, Truemper EJ, Steinhart CM, Lutin WA.

Crit Care Med. 2001;29(2):420-6. [abstract]

Reviewed by Janani Tuladhar, MD LeBonheur Children's Medical Center, Memphis, TN

Review posted July 26, 2001

I. What is being studied?

Study objective:

1. To determine the accuracy of the Paratrend 7 continuous intra-arterial blood gas monitor (CI-ABGM) in radial and femoral artery catheters placed in children compared with simultaneous measurements of intermittent blood gas analysis
2. To determine sensor longevity in pediatric patients at different arterial sites
3. To determine the utility of CI-ABGM for tracking unanticipated events related to blood gas determination

Study design:

A prospective clinical investigation was done. Patients with indwelling 18 or 20 gauge radial or femoral artery catheters had the device inserted. Paired measurements from the Paratrend and arterial blood gases (ABG's) were obtained, representing 1445 blood gas pairs. The sensors were used for 0.75 to 403.7 hours (mean = 108).

The patients investigated:

50 critically ill pediatric patients (1wk to 18yrs of age), admitted to the PICU at the Medical College of Georgia Hospital and Clinics, who required either radial or femoral artery catheters for intermittent ABG monitoring, were enrolled in the study.

Measurements and Outcomes:

1. When an ABG was drawn for any reason by the clinical team, the PO2, PCO2, pH from Paratrend 7 was recorded.
2. Sensor adjustments were made if Paratrend 7 values showed pH > 0.05, PCO2 > 5 or PO2 > 15% from the arterial sample values.
3. Descriptive account of values during unanticipated events: 49 unanticipated events and 52 individual deleterious changes in gas exchange in 17 patients were identified. A majority (46) of the events were complicated by a change in one blood gas or pH value and three were complicated by either hypoxemia or hypercapnia or hypoxemia and metabolic acidosis.

• A tracing of continuous ABG values recorded from a patient with tracheal stenosis who was sedated and paralyzed initially showed a period of stability followed by hypercapnia secondary to a displaced endotracheal tube. The hypercapnia was noted by the Paratrend 7 before any decrease in O2 saturation (pulse oximetry).
• Abnormalities of gas exchange caused by pneumothoraces were first noticed by the Paratrend 7.
• Cardiovascular compromise occurred in a few instances resulting in metabolic acidosis and/or hypoxemia
• Iatrogenic changes caused by turning the patient, endotracheal tube suctioning and from inhalational therapy demonstrating hypoxemia were determined by the Paratrend 7.

II. Does the technology work as it should?

1. Does the Technology Perform to Specifications in a Laboratory Setting?

The authors refer to previous papers for the design, mechanics and operation of the technology. The continuous intra-arterial blood gas monitor has been shown to measure and trend arterial blood gases with an acceptable level of clinical accuracy in adults (1-5).

The Paratrend 7 CI-ABGM sensor is comprised of two optodes for the measurement of pH and pCO2, a miniaturized Clark electrode for measurement of pO2 and a thermocouple for the measurement of temperature. Sensing elements are housed in a single unit with a 0.5 mm diameter and located in distal 4 cm of the sensor. The surface is covered with a covalent heparin bonded coating. Before insertion, the sensor requires computer-controlled calibration performed by diffusing precision gases of fixed concentration into a tonometer solution for 30 minutes. Insertion of the sensor for a minimum distance of 4-7 cm beyond arterial catheter tip is required to avoid flush contamination of the blood gas sensing elements.

2. Does the Technology Provide Important Diagnostic Information in a Number of Clinical Situations?

The monitor was used in different disease categories, including infectious, postoperative cardiac, respiratory, trauma, metabolic, neurology/neurosurgery and oncology patients. There is no mention of any hemodynamic instability or use of vasoactive agents in these patients. Particularly interesting would be an evaluation of the monitor in low flow states or when vasoactive agents are being used when pulse oximetry may be unreliable. They had only three patients with sepsis.

3. Does the Technology Provide Information That Allows a More Accurate Assessment of the Presence or Severity of Disease in Patients?

There is a mention of several life threatening gas exchange abnormalities, e.g. pneumothoraces, mucous plugging and displacement of the endotracheal tube, being detected by acute changes recorded by the Paratrend 7 monitor 2 minutes to several hours before detection of any changes in clinical conditions or noted by other noninvasive monitors,.

The calculated bias and precision values obtained from the Paratrend 7 demonstrated the accuracy of pH, pCO2 and pO2 values, which were consistent across a broad range and were comparable with other methods of intra-arterial blood gas monitoring (fiber optic monitor or CDI 2000 monitor in adults). The number of comparisons made for pH, pCO2 and pO2 were 1411, 1408 and 1326 respectively. The bias and precision for pH, pCO2 and pO2 were 0.00 ± 0.04 units, -0.4 ± 4.8 mmHg and 1 ± 25 mmHg respectively.

If the Paratrend 7 monitor values from the ABG analyzer values were outside of the specified ranges, they adjusted the Paratrend values to match the analyzer value. From 5679 hours of monitoring, the pH, pCO2 and pO2 were adjusted 110, 286 and 396 times respectively. For the pH, pCO2 and pO2, there were average 51 hours, 20 hours and 14 hours between the changes. This means this technology cannot be relied upon independently from ABG's, since the latter are used periodically to recalibrate the former. Also, a number of data points were excluded for different reasons: 70 pO2 data sets were excluded for optode or electrode failure; altogether 57, 31, 26, 9 and 6 data sets were excluded for dampened waveform, unstable value for comparison, adjustment error by staff, sensor being pulled back < 4cm past the end the catheter, patient core versus sensor temperature gradient > 2 C and wrong in vitro calibration respectively.

Interesting to note were the pO2 values of > 200 torr not being as accurate or precise as the pH and pCO2 ranges, according to Bland-Altman plot (6) showing the difference in Paratrend 7 value and ABG analyzer value versus the means of both values (Figure 4, Page 424). Bias was also affected at that range. Bias and precision calculated for 141 comparisons of pO2 > 150 were -1.8 ± 44.3.

Though Paratrend 7 seems to detect changes in patient's condition quickly and is comparable with other methods, it does not necessarily allow a more accurate assessment or severity of disease in patients. Its primary potential benefit entails its use as continuous monitor of parameters that are currently usually monitored intermittently.

III. What Is The Impact Of The Diagnostic Technology?

1. Does the Technology Increase Healthcare Worker Confidence?

The drawback of the monitor is the need for adjusting the values periodically. This obviously does not increase confidence of the healthcare worker using the device. Though pH values did not need adjustments frequently, pO2 and pCO2 values needed adjustments every 14 and 20 hours respectively.

2. Are Therapeutic Decisions Altered as a Result of the Technology?

There are examples in the study to show that necessary interventions were done in timely manner and the Paratrend 7 continuous ABG values seemed to reflect the change in respiratory status of the patient before any decrease in oxygen saturation. However, no comparative study was done. It is hard to determine from the study, whether the therapeutic interventions would have differed if only intermittent blood gases were obtained, instead of the continuous arterial blood gases. Also, no comparison was done with the less invasive end-tidal or transcutaneous CO2 monitors and pulse oximetry. Also, the authors do not recommend the device for smaller arteries, so it could influence arterial line site decisions.

3. Does Application of the Technology Result in a Benefit to the Patients?

There are benefits to the patients in terms of continuous assessment of blood gases without blood loss. The device seems to be capable of tracking fluctuations in gas exchange with a response rate suitable for making real-time therapeutic decisions, thereby benefiting the patients. However, there have been no studies to show that continuous blood gas monitoring improves patient outcomes compared with intermittent blood gas analyses. Nine out of fifteen radial artery Paratrend 7 devices had to be pulled and resulted in the need for another a-line site. The potential risk of femoral arterial thrombosis is worrisome from using more femoral arterial lines.

IV. Can I Apply The Diagnostic Technology In My Practice?

1. Can I Expect a Similar Benefit in My Setting?

There is potential benefit in my setting from the use of Paratrend 7 monitor since the study population is similar to most PICUs. The authors indicate that the femoral arterial catheters were more reliable than the radial ones and this might be a limiting factor in many PICUs, since femoral arterial lines might only be used as a last resort.

2. Are the Expected Benefits Worth the Associated Costs?

There is no mention of the actual cost of Paratrend 7 sensor device. According to Diametrics Medical, the manufacturer of the device, each individual unit costs $ 22,180.00 plus tax. It is an expensive invasive device. Staff need to be specially trained in its use and proper calibration. The insertion of the sensor has to be at minimum 4 cm distance beyond the arterial catheter tip and it has 3 ml dead space requiring judicious use of arterial flush when blood gases are drawn. There is a mention of several sensors being removed from radial artery due to persistent dampening of the waveform and inability to draw blood. The pO2 electrochemical portion of the sensor was demonstrated to fail after protracted monitoring in a few sensors.

Potential benefits are the early detection of the change in status of the patient and a lower amount of blood loss, assuming fewer ABG's need to be drawn. It might have a role in management of a limited number of critically ill children. More studies are needed before utilizing this technique of continuous intra-arterial blood gas monitoring in pediatric patients.

References

1. Zimmerman JL, Dellinger RP: Initial evaluation of a new intra-arterial blood gas system in humans. Crit Care Med 1993; 21:495-500. [abstract]
2. Mahutte CK, Holody M, Maxwell TP, et al: Development of a patient-dedicated, on-demand blood gas monitor in medical ICU patients. Am J Respir Crit Care Med 1994; 149:862-859. [abstract]
3. Mahutte CK, Sasse SA, Chen PA, et al: Performance of a patient-dedicated, on-demand blood gas monitor in medical ICU patients. Am J Respir Crit Care Med 1994; 150:865-869. [abstract]
4. Venkatesh B, Clutton-Brock TH, Hendry SP: A multiparameter sensor for continuous intra-arterial blood gas monitoring: A prospective evaluation. Crit Care Med 1994; 22:588-594. [abstract]
5. Haller M, Kilger E, Briegel J, et al: Continuous intra-arterial blood gas and pH monitoring in critically ill patients with severe respiratory failure: A prospective, criterion standard study. Crit Care med 1994; 22:580-587. [abstract]
6. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1:307-310. [abstract]

 

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