Table 1

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study weaknesses
Stapakis JC et al, 1992, USA	13 patients with known pneumoperitoneum after diagnostic peritoneal lavage	Diagnostic study of upright PA chest radiograph against CT of abdomen	Sensitivity of chest radiograph and CT for detection of pneumoperitonem	CT demonstrated free gas in all cases	Iatrogenic pneumoperitoneum
					Small numbers of cases
					What size collection is clinically relevant?
Woodring JH et al, 1995, USA	100 consecutive patients with pneumoperitoeum from a variety of causes	Diagnostic study	Sensitivity of upright PA chest radiograph	80%	Pneumoperitoneum form a variety of causes
			Sensitivity of lateral upright chest radiograph	98%	Only 7 patients presenting as emergencies with acute perforated abdominal viscus
			Difference between upright and lateral	18% p<0.01	Gold standard for pneumoperitoneum variable
			Sensitivity of both radiographs	100%