In our study, rates of PTX after insertion of CVCs did not vary by the month of the year, but did vary by the week of the month. Specifically, PTX after CVC insertion was more common in the last week of the month than in the first week of the month. This effect persisted after controlling for a variety of potential confounders.
These findings were surprising. We hypothesised that rates of PTX would be greatest at the beginning of the month (ie, start of the ICU rotation for most housestaff), and believed that rates would decrease as the rotation progressed, as housestaff would presumably became more comfortable and competent at performing procedures.
The explanation for the increased rate of PTX at the end of the rotation is open to speculation. One possibility is that there may be greater supervision of housestaff at the beginning of the rotation by fellows and staff than at the end of the rotation. Also, residents may become more aggressive or overconfident in the insertion of CVCs as they gain general experience, leading to multiple passes with the needle and a consequently greater rate of PTX. Third, ICU rotations tend to have frequent overnight shifts, leading to chronic sleep deprivation.4,5
Given that fatigue adversely affects motor coordination,6
increased fatigue by the end of the rotation may be associated with increased rates of procedural complications. Fourth, it is possible that senior residents may have performed more procedures at the beginning of the month, rather than at the end of the month, whereas the opposite was true for junior residents.
Because we did not collect information regarding these variables (eg, subjective or objective measures of fatigue, number of CVCs placed by each resident, extent of supervision during the procedure, level of experience of operator/supervisor), we do not know which (if any) of these might account for our findings. Future prospective studies that collect this information may provide us with greater insight into how to reduce these complications in the future.
A recent comprehensive study of serious medical errors in the ICU has shown that 75% of incidents occur during treatments or procedures.7
Our findings suggest that resident scheduling affects rates of these complications. Although we have potentially demonstrated this for only one safety outcome, rates of other procedure‐related complications may be similarly affected. If this is the case, interventions designed to provide closer supervision of residents at the end of their rotation may substantially improve patient safety.
The lack of a relationship between the month of the year and rates of PTX was also surprising. One potential possibility for the lack of relationship may be increased supervision of residents by staff and fellows at the beginning of the academic year, thus counterbalancing the inexperience of residents at this time. This would be consistent with other studies that have demonstrated no reduction in the quality of care in patients admitted to teaching hospitals in July,8
and no increase in mortality in patients admitted to the ICU in July.9
Our study has several strengths. First, it was based on >3500 patients admitted to mixed medical–surgical ICUs in two hospitals over 7 years. The lack of selection bias and the similarity of our patient population to that of other ICUs probably improves the generalisability of our findings to other similar ICUs. Second, we used multivariate analyses to determine the independent effects of the month of the year, and the week of the month. Specifically, we adjusted for potential confounders, including age, gender, severity of illness, hospital site and numbers of CVCs placed.
We acknowledge that there are a number of limitations to our study. First, it is a study based on only two tertiary ICUs in a single geographical area; these findings may not apply to non‐tertiary care ICUs or to specialty ICUs that cater to a specific group of patients. Second, approximately 20% of residents did not start their ICU rotations during the first week of the month. As such, the effect we observed may be an underestimate of the true effect of the week of rotation. Also, data regarding duration and start date were based on data from 2002 to 2005, rather than from 1999 to 2005. However, there have been no substantial changes in these logistics for many years, and we are thus confident that these descriptors are accurate for the period of this study as well. Third, we may not have captured all PTX. We doubt that this would be the case as our rate of PTX was slightly greater than that reported by others.10
In addition, even if some PTX were missed, it is unlikely that the probability that a PTX was missed would vary by the month or by the week of the month. Fourth, ultrasound guidance was not used consistently in our ICUs for insertion of catheters during this time period. This technology reduces the risk of PTX,11
and regular use of this technology might have modified our results. In these two ICUs, ultrasound was used more often during the last few years of the study, and was not used consistently before this time. Indeed, consistent with this concept, rates of PTX were greater during the first 4 years (1999–2002) of the study (2.55%) than during the last 3 years (1.46%). Fifth, on the basis of the language used to describe catheters in our database, we cannot be certain that all of the catheter insertions were in one of the internal jugular or subclavian veins. Specifically, it is possible that some of the pulmonary arterial catheters, or pacemakers, or “CVCs” were inserted in the femoral vein. However, on the basis of our own observations of practice in these ICUs, we believe that most of these catheters would have been placed in one of the neck veins. Sixth, the fourth week included events that occurred from the 22nd day to the end of the month. Although we acknowledge that this would include a larger number of days than the other weeks, this should not affect the rate of PTX per CVC placement. Finally, because our analysis was based on a retrospective post hoc analysis of an audit database, we lacked information about some potentially important confounders. For instance, we did not have information about the person attempting insertion (ie, the experience and level of training of the resident), the degree of supervision, time of procedure, the difficulty, number of passes with the needle and whether ultrasound was used for a particular CVC placement.
Because of these limitations, we acknowledge that our results should be considered more “hypothesis‐generating” as opposed to definitive. Nevertheless, we believe that our study is useful because it highlights the need to examine and audit the performance of residents when they are performing procedures with potentially significant complications.