Sample of convenience: A non-random selection of easily available patients (or things). Statistically, this is generally considered lower-level research and not representative of larger groups.
Retrospective review: A method of performing research looking backward in time, usually with a chart review. This method is not as desirable as “prospective” (looking forward in time) studies.
Field experience with needle thoracostomy during a presumed tension pneumothorax is rare, and in the prehospital setting, it’s difficult to determine whether one exists. “Typical” signs may be masked, lung sounds are difficult to hear in noisy environments and jugular venous distention may be absent due to hypotension (or hidden by C-collars). To complicate matters, once we perform the procedure, we might not hear the “classic” rush of air or see signs of clinical of improvement.
Does it work?
Blaivas M. Inadequate needle thoracostomy rate in the prehospital setting for the presumed pneumothorax: An ultrasound study. J Ultrasound Med. 2010;29:1285–1289.
Traditional teachings tell us needle thoracostomy will either relieve a tension pneumothorax or create a small pneumothorax. This first study is a three-year sample of convenience in a Level I trauma center. Emergency physicians evaluated 57 adult patients who received needle thoracostomy in the prehospital setting. They used ultrasound and CT scans, seeking to confirm the presence of a pneumothorax. Fifteen patients in their sample (26%) had no pneumothorax, which means these patients received unnecessary needle thoracostomy and did not get a pneumothorax after needle thoracostomy.
The study suggests reconsidering the in-hospital standard of inserting a chest tube in all patients with pneumothorax. Prehospital providers should take notice; EMS providers misdiagnosed tension pneumothorax 26% of the time, and needle thoracostomy may have failed 26% of the time. I’m not sure which is worse—the misdiagnosis or the fact that a real tension pneumothorax needle thoracostomy may have been too shallow.
Limitations: In addition to the weak methodology of the study, the author also didn’t report the length of the catheter used or the location of insertion in these needle thoracostomy cases. This leads me to the second study.
Is a longer needle better?
Ball CG, Wyrzykowski AD, Kirkpatrick AW, et al. Thoracic needle decompression for tension pneumothorax: Clinical correlation with catheter length. Can J Surg. 2010:53;184–188.
In this two-year retrospective chart review, researchers studied the effectiveness of helicopter EMS (HEMS) crews using a 4.5 cm (1.77") sheath (5 cm or 2" needle size) for a needle thoracostomy compared with ground EMS (GEMS) crews using a shorter 3.2 cm (1.25") sheath.
Only 1.5% of patients (n=142) received needle thoracostomy. Failure to decompress occurred in 65% of GEMS (n=17) and 4% (n=3) in HEMS. The authors concluded that the longer 4.5 cm (1.77") needle was more reliable. Granted, this is a low sample size, but a 65% failure rate to decompress still isn’t good. The authors do point out that needles longer than 5 cm may increase the risk of cardiac damage, and that lateral (mid-axillary) decompression may work better in obese patients.
Chest wall thickness
McLean AR., Richards ME, Crandall CS, et al. Ultrasound determination of chest wall thickness: Implications for needle thoracotomy. Am J Emerg Med. DOI: 10.1016/j.ajem.2010.06.030; 14 October 2010; PMID 20947279.
This study used ultrasound to look at chest wall thickness of 51 adults lying supine. They measured chest wall thickness to be 2.1–2.3 cm deep. Using body mass index tables, they estimated less than 1% of the population would have a chest wall thickness greater than 4.5 cm. More importantly, they concluded that chest wall thickness may not always be the source of failed needle decompression in presumed tension pneumothorax.
These studies remind us to be careful of non-randomized studies with low sample sizes. The three featured studies confirm previous research showing that needle thoracostomy needs to be evaluated in a more formal manner, but concluding much more than this may be premature. Previous studies with larger sample sizes found chest wall thickness to be higher—as much as 35% of the population greater than 4.5 cm, and still another found prehospital needle thoracostomy to be lifesaving.
What we know: As many as 30% of cases with presumed tension pneumothorax are missed in the prehospital setting.
What these studies add: Ultrasound helps identify tension pneumothorax in emergency settings, and catheter length for needle thoracostomy should be at least a 14 gauge, that is 4.5 cm (1.77"). JEMS
Pierog JE, Zaia BE, Bhat SR, et al. Out-of-hospital evaluation of effusion, pneumothorax and standstill: EMS and point-of-care ultrasonography. Ann Emerg Med. 56; P-S115; Abstract 355:2010.
The authors presented an abstract in September evaluating the use of ultrasound in prehospital assessment of tension pneumothorax. They trained 57 EMT and paramedic students in a one-hour class. A pretest and two post-tests showed these providers were able to improve their ability to recognize pneumothorax from 55%–93% accuracy.
This article originally appeared in February 2011 JEMS as “Size Matters: Treating presumed tension pneumothorax.”