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

Highlighted lines and questions below provide links to the pertinent description of criteria in The EBM User's Guide, now available at the Canadian Centres for Health Evidence

Article Reviewed:

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Pulmonary Risk Factors Compromising Postoperative Recovery After Surgical Repair for Congenital Heart Disease.

Bandla HPR, Hopkins RL, Beckerman RC, Gozal D.

Chest 1999;116:740-747. [abstract]

Reviewed by J Geracht MD, J Barron MD, D Epstein MD, Mattel Children's Hospital at UCLA Medical Center

Review posted December 7, 2004

I. What is being studied?:

The study objective:

The objective of the study is to identify the non-infectious pulmonary risk factors that are associated with ICU stay greater than 7 days in children less than two years of age undergoing surgery for congenital heart disease (CHD).

The study design:

This is a retrospective case series analysis.

The outcomes assessed:

Pulmonary complications, e.g., central airway compression, phrenic nerve dysfunction, pleural effusions and pulmonary hypertension are risk factors that are associated with prolonged mechanical ventilation and ICU stay.

II. Are the results in the study valid?

Primary questions:

1. Was there a representative and well-defined sample of patients at a similar point in the course of the disease?

Yes, there was a well-defined and representative sample of patients studied. The authors defined the study sample as all patients undergoing surgical repair for CHD under 2 yrs of age. There were 134 consecutive patients with diverse cardiac lesions representative of common cardiac lesions found in the pediatric population. Premature infants and infants with pre-existing lung disease or with other major congenital anomalies (n = 13) and patients who died within 48 hours of surgery were excluded.

The resulting sample of 97 infants studied appeared to be low risk based on the exclusion criteria but was nevertheless heterogeneous, ranging from those receiving simple ASD repairs to Stage I Norwood. Patients were assigned to two groups based on the duration of ICU stay: < 7 days (group 1) and > 7 days (group 2).

It is difficult to assess similarity of course of the disease, as authors do not mention pre-operative morbidity. Authors do not comment if patients were hospitalized pre-operatively, if they required pre-operative mechanical ventilation, if they required inotropic support prior to surgery, if surgical intervention was emergent, or if patients underwent elective repair, which would influence post operative course. Some of these factors, however, may be inferred based on cardiac lesion and age of the patient.

2. Was follow-up sufficiently long and complete?

Yes, this was a retrospective study with well defined points of outcome: wean from mechanical ventilation, discharge from ICU, and discharge from hospital.

Secondary questions:

3. Were objective and unbiased outcome criteria used?

Many outcomes involved subjective decisions, for example, when to extubate or to discharge from the ICU or from hospital. These factors can not be controlled for given a retrospective chart review.

In addition, was a prolonged stay due exclusively to pulmonary factors, or did other factors (e.g., cardiac, neurologic, feeding, social) also contribute to increased length of stay as well? These patients with multiple complications were stratified into groups based on a "consensus" as to what was the major complicating post operative factor. The authors did not specify the guidelines that were used to stratify patients.

4. Was there adjustment for important prognostic factors?

Evaluating the differences between group 1 and group 2, we can see that group 2 patients were significantly younger. Surgical cardiopulmonary bypass time (CPB) time and aortic cross clamp time were both longer in group 2. The authors did simple, univariate linear regression to evaluate CPB time and aortic cross clamp time, and determined that these factors did not correlate with length of ICU stay. However, no other prognostic factors were mentioned, and readers do not know if these factors were adjusted for in analyzing data, as co-morbid factors could influence time on ventilator, as well as ICU and hospital stay. The authors did not comment on different prognosis for each child, or pre-operative morbidities of patients prior to the surgical repair.

III. What are the results?

1. How large is the likelihood of the outcome event(s) in a specified period of time?

	< 7 day stay in ICU Group 1	>7 day stay in ICU Group 2
With pulmonary complications	4	18
Without pulmonary complications	53	22

What is the likelihood of being discharged later than 7 days given the presence of a pulmonary complication (e.g., extrinsic airway compression, tracheobronchomalacia, pulmonary hypertension, phrenic nerve palsy, and pleural effusion)?

Sensitivity: The likelihood that a patient with pulmonary disease will have prolonged ICU stay: = (18 / (18 + 22) = 45%

Specificity: The likelihood that patient without pulmonary disease will have ICU stay less than 7 days: = (53 / (53 + 4) = 93%

Hence, the risk factor of pulmonary complications is more specific than sensitive. We can infer that without pulmonary complications, patients are more likely to have shorter ICU stay.

Positive Predictive Value: The likelihood that a patient with pulmonary complications will have prolonged ICU stay = 18 + (18 + 4) = 82%.

Negative Predictive Value : The likelihood that a patient without pulmonary complications will have a shorter ICU stay = 53 / (53 + 22) = 71%

Odds Ratio: Odds ratio is the equivalent of relative risk used in retrospective case-control studies such as these; describes the odds of prolonged ICU stay in patients with pulmonary complications compared to those without =(18 x 53)/(22 x 4) = 10.8. This association appears to be significant.

The other most significant finding was that the group of subjects with prolonged ICU stay had 41 extubation failures vs. three extubation failures in the shorter ICU stay group (p < 0.0001).

2. How precise are the estimates of likelihood?

In order to determine the precision of the risk (of prolonged ICU stay associated with pulmonary complications), we need to calculate the 95% confidence interval for the odds ratio of 10.8. The confidence interval for this study was wide at 3.3 to 35.8. Although the lower limit does not cross one (indicating statistical significance), the width of the interval indicates a lack of precision.

IV. Will the results help me in caring for my patients?

1. Were the study patients and their management similar to my own?

The group of study patients were similar to the patient population cared for at our institution. Cardiac lesions described are similar, and post operative and pulmonary complications are similar as well.

2. Will the results lead directly to selecting or avoiding therapy?

The results of this study might encourage intensivists to search in a timely manner for a pulmonary complication in patients with prolonged ICU stays that fail extubation.

However, this paper discusses what is already well established: patients with postoperative complications - particularly pulmonary complications - have longer times spent receiving mechanical ventilation and longer lengths of stay. It would have been more helpful to further identify underlying risk factors that might assist in the preoperative or immediate perioperative identification of these patients.

3. Are the results useful for reassuring or counseling patients?

Although all surgeries have different complication rates, dependent on lesion, pre-operative morbidity, post-operative morbidity, the results from this study may help in counseling parents that pulmonary complications lead to increased risk for prolonged mechanical ventilation, ICU stay and total hospital stay.

 

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