The role of ultrasound as an adjunct to arterial catheterization in critically ill surgical and intensive care unit patients

INTRODUCTION

Arterial catheterization is frequently performed on critically ill and surgical patients and is the second most common intervention performed in the ICU (1). Indications for arterial line insertion include the need for invasive hemodynamic monitoring (arterial blood pressure and cardiac output monitoring), guidance of fluid, vasopressor and inotropic therapy and frequent blood sampling (arterial blood gas analysis and general laboratory evaluation) (2). Contraindications to arterial catheterization include severe coagulopathy, thrombocytopenia (platelets <50,000), infection or burns at the proposed insertion site, traumatic injury proximal to the proposed insertion site and the presence of synthetic vascular grafts (3, 4). Potential complications associated with arterial catheterization are presented in Table I. Major complications such as pseudoaneurysm or vessel occlusion leading to acute limb ischemia are rare (2).

TABLE I -

PERCENTAGE OF ARTERIAL LINE-ASSOCIATED COMPLICATIONS BY SITE (3)

	% Incidence
Complication	Radial site	Femoral site
Temporary ischemia	19.7	1.5
Permanent ischemia	0.1	0.2
Hematoma	14.4	6.1
Bleeding	0.5	1.6
Pseudoaneurysm	0.09	0.3

The standard method of placing an arterial cannula is by direct palpation of the artery and puncture with a needle/catheter unit, followed by threading of the cannula into the vessel. Alternatively, a catheter with a separate or integral guidewire may be used (catheter over guidewire or Seldinger technique) (5). ICU and critically ill surgical patients can be particularly challenging for even the most experienced intensivists and perioperative physicians. Many of these patients have associated cardiovascular instability, peripheral edema, instituted vasoactive drug therapy and previous multiple arterial cannulation attempts. All of these factors, often in combination, augment straightforward blind insertion (6). Table II summarizes these factors, further demonstrating the usefulness of ultrasound (US) in such situations (6).

TABLE II -

INDICATIONS FOR US-GUIDED ARTERIAL CATHETERIZATION IN CRITICAL ILLNESS (7)

Patient factor	Resultant difficulty with palpation method of insertion
1. Shock	Often results in weak peripheral pulse; nothing to palpate
2. Vasopressor therapy	Resultant peripheral vasospasm as blood flow is directed toward central vessels
3. Significant pitting edema at the desired site	Produces difficulty palpating pulse
4. Previous multiple cannulation attempts at the desired site	Resultant vasospasm or thrombus blockage of vessel
5. Previous multiple arterial blood gas sampling attempts at the desired site	Resultant vasospasm or thrombus blockage of vessel
6. Severe coagulopathy/thrombocytopenia	Immediate hematoma; particularly on multiple attempts and failure to first pass access the vessel

Invasive hemodynamic monitoring has become the gold standard of intensive care medicine. There have been many advances in the complexity of data derived from the arterial wave form over the last 5 years. Continuous analysis of such data permits rapid, targeted restoration of intravascular volume, assessment of volume responsiveness and, ultimately, preservation of organ perfusion (7). Therefore, in the critically ill patient, it is of paramount importance to obtain arterial cannulation expeditiously. US is becoming an essential tool for the physician to minimize cannulation time and maximize successful first attempts.

The National Institute for Health and Care Excellence (NICE) and the Agency for Healthcare Research and Quality (AHRQ) recommend the routine use of US for central venous catheter (CVC) insertion. As a result, US machines have become ubiquitous in most ICUs (8, 9). Yet, US-guided arterial cannulation is not subject to any published guidance and as a result, fewer ICU and perioperative physicians are familiar with its use for this purpose.

The purpose of this paper is to review the evidence behind US-guided arterial access and its influence on clinical outcomes in perioperative critical care.

Evaluating the evidence

Evidence supporting US-assisted arterial catheterization

Several randomized controlled trials (RCTs) have assessed the value of US in arterial catheter insertion. Shiver et al randomized 60 patients admitted to a tertiary center emergency department to either palpation or US-guided arterial cannulation. They demonstrated a first-pass success rate of 87% in the US group compared with 50% in the landmark technique group (10). In the same study, the use of US was also associated with reduced time needed to establish arterial access and a 43% reduction in the development of hematoma at the insertion site (10). Levin et al demonstrated a first-pass success rate of 62% using US versus 34% by palpation alone in 69 patients requiring intraoperative invasive hemodynamic monitoring (11).

Randomized trials in the pediatric population showed a success rate of 14%-67% using the US-guided technique, compared with 14%-20% for palpation alone (12, 13). Ishii et al performed a trial looking at infants and small children undergoing cardiac surgery (requiring radial artery cannulation). The success rates after a single attempt and after three consecutive attempts were significantly higher in the US group (76.3% and 91.5%, respectively) than those in the palpation group (35.6% and 50.8%, respectively; p<0.001 for both comparisons) (14).

One meta-analysis focused upon pooled data obtained from 4 RCTs (total of 311 adult and pediatric patients). US guidance increased the likelihood of first-pass success rate by 71% (first-pass success rate of 27% using palpation technique vs 43% using US guidance). The use of US also significantly reduced the time to successful cannulation, the number of punctures and the number of arterial lines required per procedure (15).

In a multicenter RCT, routine US guidance improved the success rate of common femoral artery (CFA) cannulation in a subgroup of patients with high CFA bifurcations. It also reduced the number of attempts, time to access, risk of venipuncture and overall vascular complications associated with femoral arterial access (16).

Dudeck et al randomized 112 patients undergoing femoral artery cannulation to US-guided versus the traditional palpation technique. They found that the use of US significantly decreased the number of attempts needed, as well as the time to successful arterial puncture. The cohort of patients studied were considered to be ‘difficult,’ as they had weak femoral arterial pulses and leg circumferences of 60 cm or greater (17).

Gratrix et al provided preliminary observations on US-assisted cannulation of the impalpable sections of the radial artery (higher in the forearm) as a rescue procedure when the landmark technique was not possible or had failed (18). This route of access could potentially be useful in those ICU patients with hypotension and peripheral edema.

Evidence opposing US-assisted arterial catheterization

Tada et al randomized 166 surgical patients to either palpation or US-assisted arterial line insertion and found that US guidance offered no additional benefit in cases where the radial arterial pulse was palpable (19). Multivariate analysis also demonstrated that systolic blood pressure or body mass index was not significantly related to the outcome of arterial cannulation (19).

Ganesh et al performed a prospective randomized study in children requiring radial artery catheterization. They found no statistically significant differences between the US-guided cannulation and palpation technique groups with respect to the time to successful cannulation, total number of attempts, number of successful cannulations during the first attempt or number of cannulae used for catheterization (20).

CONCLUSIONS

Of note, none of the above RCTs had been conducted in the ICU setting. Most were of small sample size and were performed in patients undergoing major elective surgery. Another confounding variable within all of the trials is that the level of operator experience is unclear. If those partaking in the trials are experienced US users from the outset, then the technique can be promoted with more vigor and opinion may be biased toward US usage.

The evidence does demonstrate a clear role for US-assisted arterial cannulation within perioperative critical care and the ICU, particularly in situations where difficulty is anticipated due to associated patient factors. Published literature references reduction in the number of attempts, time to successful catheterization and reduced overall complication rate. However, the evidence is less supportive for its routine usage in situations where difficulty is not anticipated.

Given the fact that the technique and requirements mirror those for CVC placement, it is unlikely that any additional cost or time for training will be required to adopt it for arterial line placement in the ICU setting (15).

Well-designed and adequately powered RCTs are warranted to define the role of US as an adjunct to arterial cannulation in critically ill patients. US operator experience level should be standardized where possible in order to exclude experience bias in the results. It would also be useful and insightful if more studies focused on the effect peripheral arterial catheters may have on patient outcome. Perhaps we will see NICE and AHRQ beginning to insist upon US guidance for arterial cannula insertion as they have done for central venous catheterization.

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