Do we need an esophagram to evaluate a spontaneous pneumomediastinum in kids?

The paper was published in JPS a few days after the subject was brought up amongst our group.  Basically, what do we do with a kiddo who presents with a pneumomediastinum with no antecedent history of trauma or retching, and who is otherwise doing well with no fever or signs of mediastinitis.

In this paper, the authors retrospectively reviewed 27 patient with a spontaneous pneumomediastinum(SPM) who underwent an esophagram as part of their evaluation. The authors noted that none of the patient had a demonstrable injury to the esophagus. They concluded that an esophagram is not necessary for the evaluation of SPM. They felt the source of the air in this group of patients was alveolar disruption and not an esophageal injury.

Needles to say, a series of 27 patients is not sufficient to make a final conclusion on the subject. That being said, the series helps us support any decision we make regarding clinical follow up on a patient with a SPM, who is otherwise well with no other signs of esophageal injury such as dysphagia or pleural effusion on a CXR. 

Metal allergies and the Nuss bar

At least it was not a wound infection, but now what?

Patients who have a previously unrecognized allergy to metal and undergo a Nuss repair with a stainless steel bar can present with a picture of wound infection after bar placement.  Although not as detrimental as a wound infection, metal allergies are not to be taken lightly.

Contact dermatitis from the Nuss bar is a type IV delayed hypersensitivity reaction that occurs in response to one of the components of stainless steel, usually Zinc or Chromium.  The reaction can range from mild with localized dermatitis, to a more systemic inflammatory response.  Patients occasionally simply present with chronic fatigue.

Preoperative screening for metal allergies should include inquiry about personal or family history of metal allergies (specifically ask for problems with metal touches the skin, not just "does anyone in the family have metal allergies").  Even in the absence of a history of atopy, some recommend screening all patients with a patch test that identifies such allergies (T.R.U.E test or AllergEAZE).

In a recent study by Shah et al, the authors recommended testing all patients preoperatively, regardless of family or personal history of allergy, as they recognized a higher incidence of metal allergy (6.4%) than previously reported (2.2%).

Once metal allergy is identified, patients can be treated with a course of steroids, and removal of the bar can be avoided in most cases.

Suction device for correction of pectus excavatum

Some information to file under the "good to know" category.

The suction bell  is a device that uses negative pressure (15% below atmospheric) to pull the sternum out and into a more natural position.  The principle involves repetitive intermittent use until the deformity is corrected.

In a paper by F. Haecker, the author describes a wide range of applications times, but recommends twice daily application for 30 minutes at a minimum. After the device is positioned over the deformity, the patient uses a hand pump to apply negative pressure, which instantaneously pulls the sternum up. The duration of use is limited by pain and the development of a transient subcutaneous hematoma in most of the patients.

Long term results are not available, but over a short period of use, patients experience "dramatic" results.  In the aforementioned paper, the author reports a sternal elevation of 1.5 cm in 70% of patients within a 3 month period. Again, patient dedication and level of commitment being a major determinant of outcome.  Additionally, the author suggest that the best results tend to occur in patients with milder forms of symmetric pectus excavatum.

Needless to say, this sounds like a very promising non-operative option, though the jury is still out on what is the optimal application protocol is as well as long term results and durability of the correction

The "correction index" as a measure of severity of pectus excavatum.

Pectus excavatum is a condition where the sternum and adjacent ribs develop in an abnormal way, resulting in a depression in the middle of the chest.  The consequences of the depression are mainly esthetic, but may affect lung and cardiac function (controversial evidence)

Figure 1

The Haller index (Figure 1) has been classically used as a measure of the severity of the pectus deformity, where a HI >3.25 is considered an indication for consideration for surgical correction.

An innate fault of this measurement, as St Peter et al pointed out in their paper, is the fact that this number relies heavily on the cross sectional diameter of the chest (Figure 1; measurement a), which varies between patients.  They noted that when they measured the HI in patients with a pectus deformity, there was a 45% cross-over with normal patients. Essentially, the authors suggest that the HI is not a reliable measure of severity of a pectus deformity.

Figure 2

As an alternative, the authors recommend using a measurement they referred to as the correction index (Figure 2).  Simply put, CI is the ratio of the anticipated rise in the sternal defect after bar placement (Figure 2; measurement a-b), to the maximal anterior to posterior dimension of the inner chest, multiplied by 100.

The question then becomes, what CI should be used as an indication for surgery?  The authors suggested that a 10% or higher CI reflects a pectus deformity severe enough to warrant correction.

Thoracostomy and fibrinolysis for the management of empyema

A little throw back to 2009 prompted by a discussion on management of parapneumonic effusion/empyema.

In the frequently quoted study out of The Center for Prospective Clinical Trials in Kansas City, the authors compared the effectiveness of VATS vs thoracostomy/fibrinolysis in 36 patients.  Empyema was defined based on imaging characteristics or WBC content and then managed with either VATS or thoracostomy (chest catheter drainage with a12 F tube) with fibrinolysis using 3 doses of 4 mg of Altase given over a 48 hour period.

No significant difference was found in the outcomes assessed, which were days of hospitalization (6.9 vs. 6.8 days), days of oxygen requirement (2.3 days), days until afebrile (3.1 vs. 3.8), or analgesic requirements. The difference in cost was $11.7K vs $7.6K between VATS and thoracostomy /fibrinolysis, respectively.

Although fibrinolysis was sufficient for most patients, 16.6% still needed VATS; an important point to mention to parents when discussing the procedure.

Another important point to stress here is that in many institutions, the most common chest catheters available are 8.5 Fr (and not 12 Fr), and one should make sure the appropriate catheter is used to optimize the chance for success.

What is the most common type of vascular rings in children?

The basic back bones of the development of the vascular system are the dorsal aortae and ventral roots, and 6 aortic arches that join the two, on the right and left.

Regression of some of the arches in central to the normal development of the vascular system.
Only the 3rd, 4th, and part of the 6th arches should persist to contribute to the carotid arteries, right subclavian/aortic arch, and the pulmonary arteries, respectively (figure).

The most common vascular ring (1% of population) results from a right subclavian artery that takes off from the arch of the aorta on the left, due to abnormal regression of the right 4th arch. The subclavian artery passes behind the esophagus.  This type of incomplete vascular ring rarely causes symptoms in children, and surgical therapy, if needed, consists of division of the vessel through a left thoracotomy.

Reference:
Pediatric Surgery.  Coran A. 7th edition

Sketchnotes: Differential diagnosis of mediastinal masses

Lung metastectomy in osteosarcoma: thoracotomy or VATS?

Osteosarcoma, which presents with metastatic lung disease in 15-20% of cases, is one of the few malignancies (along with non-rhabdo soft tissue sarcoma and hepatoblastoma) where resection of metastatic disease to the lung can improve survival.

Although lung metastectomy has been shown to be beneficial in this group, the optimal modality of resection, whether by open thoracotomy or VATS, is not clear. The argument for the use of an open thoracotomy in the management of lung mets has to do with the ability to palpate lesions, whereas VATS relies on imaging for detection of lung nodules. Studies have shown that a CT scan that detects a nodule(s) in the lung can miss additional palpable ones in 50% of patients, approximately half of which contain viable malignant tissue. So, in essence, VATS would likely miss additional malignant nodules, and thus leave behind otherwise palpable malignant lesions, in 25% of patients.

So it seems obvious that an open thoracotomy is the way to go, except that we don’t really know if a VATS followed by close monitoring to detect the 25% of patients with missed nodules that can be salvaged by a second VATS (and thus spare a number of kids a thoracotomy) changes the outcome in terms of long term survival when compared to primary resection of all the palpable nodules with an open thoracotomy.

Reference:
1. St Jude Oncology Review Course
2. Kayton ML et al. Computed tomographic scan of the chest underestimates
the number of metastatic lesions in osteosarcoma (2006);41:200

Which babies "sink" after PDA ligation?

30% of preemies who are over 32 weeks GA, and 60% who are under 28 weeks GA have a PDA.

Ligating a symptomatic PDA in a fragile premature infant can have substantial (but usually transient) unwanted hemodynamic consequences. The sudden ligation of the PDA causes an instantaneous rise in afterload, resulting from the obliteration of the the pop-off circuit into the low resistance pulmonary circulation, and an associated drop in preload. This sudden change may not be tolerated well by preemies, most likely due to underlying cardiac dysfunction. So how can we predict which infant is going to fare worse after ligation?

Moin et al, in a study that evaluated 100 premature infants who underwent PDA ligation, noted that 32% of preemies required vasopressor support (either starting pressors or increasing the dose of preexisting pressor support) within 72 hours of PDA ligation. Risk factors associated with need for vasopressor support were a lower gestational age (25 vs 26 weeks), lower birth weight (714 vs 870 grams), and relatively high ventilatory support (RIS>6).

Additionally, those infants who required pressor support after ligation had an increased risk of death before 36 week adjusted gestational age.

The authors cautioned that the study had several limitations by virtue of it's design and that further studies are needed to confirm their observations.

References:

Moin F et al. Risk factors predicting vasopressor use after patent ductus arteriosus ligation. American Journal of Perinatology;20(6)2003:313-320

PDA ligation controversies

Well, that was another excellent joint neonatal-Pediatric surgery conference at WCHOB. The subject was PDA and the discussion included basic PDA physiology, morbidity, treatment strategies, post ligation syndrome, and most importantly looked at the evidence (or lack of) supporting the need for PDA ligation.

The discussion began with the general principles of PDA physiology, including the normal role of prostaglandins produced by the placenta and the high intraluminal blood pressure in the ductus (secondary to high pulmonary vascular resistance) in keeping the ductus patent in utero. Normal term delivery reverses these factors and results in closure of the ductus initially by smooth muscle constriction then then anatomic remodeling.

The clinical consequences of a PDA are a result of the left to right shunt, and subsequent change in blood flow to vital organs with subsequent metabolic acidosis, increased risk of IVH and NEC secondary to diastolic steal, and pulmonary vascular disease due to continuous dilation of pulmonary vessels during diastole.

The main strategy for prophylaxis and treatment is the administration of Indomethacin, and when that fails, surgical ligation.

The first issue that comes up is the evidence for the need for the prophylaxis and treatment of PDA.

The literature supports the benefit of the prophylactic use of indomethacin for it's effectiveness of PDA closure, decrease the need for surgical ligation, decrease in the incidence and severity of pulmonary hemorrhage, and decrease in incidence of grade 3 and 4 IVH.

Indomethacin, however, is not innocuous. It can cause a transient change in renal function, increases the risk of GI perforation when administered simultaneously with steroids. It was not found to have any neurodevelopemental effects.

So why should a PDA be treated? A study looking at infants <1500 g showed an 8 fold increase in mortality in the presence of a PDA.

When it came to the subject of surgical ligation of PDA, the data was much less convincing and somewhat troubling. Studies not only shed doubt on the proposed rapid improvement of cardiovascular parameters (Raval et al. J Ped Surg 2007.42(1):69), some actually showed that surgical ligation may be associated with an increased risk of BPD, severe ROP, and neurosensory impairment in ELBW infants (Kabra et al. J Peds 2007;150:229).

Finally, the subject of post ligation cardiac dysfunction was addressed. This results from ligation of the PDA, which results in a sudden switch from volume to pressure overload on the heart which was, as a baseline, subjected to impaired coronary perfusion (form diastolic steal with a PDA), and preexisting pulmonary edema and cardiac failure. Post ligation cardiac dysfunction presents with severe hypotension, failure of oxygenation, and myocardial dysfunction. The hemodynamic profile shifts from pre ligation state of a high preload/low after load and myocardial ischemia from decreased diastolic perfusion, to post ligation state of a sudden increase in after load, decreased LV end diastolic volume, and decreased LV output.

Importantly, the extent of post ligation dysfunction depends on pre ligation hemodynamic, with some authors supporting the prophylactic use of milrinone when the pre ligation LV output is < 200 ml/kg/minute.

As to the management of post ligation cardiac dysfunction, the strategy is to use inotropes that do not increase after load (Milrinone/dobutamine), optimize oxygen carrying capacity, and fluid management.

The upshot on PDA interventions was that prophylactic ligation does not improve outcome, indomethacin prophylaxis decreases IVH and need for PDA ligation, indomethacin prophylaxis does not improve neurodevelopemental outcome in survivors, earlier Indomethacin treatment is associated with higher rates of DA closure. As to the ideal timing of medical or operative closure, that remains to be clarified.

With the current available data, many questions remain unanswered:

can we identify infants whose ductus will close spontaneously?
can we reduce the number of doses of indomethacin without compromising outcome?