My patient with COPD exacerbation has an elevated venous blood PCO2. How accurate is the peripheral venous blood gas PC02 in patients with hypercarbia?

Short answer: Not as accurate as we might like! An elevated venous pC02 is a good indicator of the presence of arterial hypercarbia but beyond that if you really want to know what the arterial pC02 is in your patient with hypercarbia, you should get an arterial blood gas (ABG).

 
A meta-analysis of studies involving patients with COPD presenting to the emergency department (ED) found a good agreement for pH and bicarbonate values between arterial and venous blood gases but not for pC02 or p02 (1). More specifically, the 95% limit of agreement varied widely from -17 to +26 mmHg between venous and arterial pC02 (average difference ~6.0 mm). In the same study, a venous pC02 of ~45 mmHg or less correctly identified patients who were hypercarbic based on ABG. Similar results have been reported by other studies involving patients with COPD exacerbation (2,3).

 
Another meta-analysis involving all comers (COPD and non-COPD patients) concluded that venous pC02 should not be used as a substitute for arterial pC02 when accurate pC02 is required (4). In fact, they emphasized that venous pC02 was not always greater than arterial pC02!

 
Bonus pearl: Did you know that an unexpectedly low bicarbonate level in a patient with COPD and CO2 retention should alert us to the possibility of concurrent metabolic acidosis (eg, due to lactic acidosis, uremia)?

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References
1. Lim BL, Kelly AM. A meta-analysis on the utility of peripheral venous blood gas analyses in exacerbations of chronic obstructive pulmonary disease in the emergency department. Eur J Emerg Med 2010;17:246-48. https://journals.lww.com/euro-emergencymed/Abstract/2010/10000/A_meta_analysis_on_the_utility_of_peripheral.2.aspx
2. McCanny P, Bennett K, Staunton P, et a. Venous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease. Am J Emerg Med 2012;30:896-900. https://www.sciencedirect.com/science/article/abs/pii/S0735675711002865
3. McKeevere TM, Hearson G, Housely G, et al. Using venous blood gas analysis in the assessment of COPD exacerbations: a prospective cohort study. Thorax 2016;71:210-15. https://www.researchgate.net/publication/285545995_Using_venous_blood_gas_analysis_in_the_assessment_of_COPD_exacerbations_A_prospective_cohort_study
4. Byrne AL, Bennett M, Chatterji R, et al. Peripheral venous and arterial blood gas analysis in adults:are they comparable? A systematic review and meta-analysis. Respirology 2014;19:168-75. https://onlinelibrary.wiley.com/doi/full/10.1111/resp.12225

My patient with COPD exacerbation has an elevated venous blood PCO2. How accurate is the peripheral venous blood gas PC02 in patients with hypercarbia?

My 70 year old male patient is admitted with 1 day of fever, dysuria, and urinary frequency and urgency, but has a negative urine dipstick test for nitrites and leukocyte esterase. Could he still have acute bacterial prostatitis?

Short answer: Yes! In fact, no routine clinical imaging test can adequately rule out prostatic involvement in men with urinary tract infection (UTI) symptoms (1)! 

Although the presence of nitrites and leukocyte esterase (LE) may have a high positive predictive value for acute bacterial prostatitis (ABP) (~95%), their combined absence has a negative predictive value of only ~70%; ie, we may miss about one-third of patients with UTI symptoms if we relied solely on the results of nitrite and LE urine dipstick (2,3). Negative nitrites alone has a negative predictive value of only ~ 45%, while a negative LE has a negative predictive value of ~60% (3).

To evaluate for ABP, our patient should undergo rectal exam for prostatic tenderness, as should all men with UTI symptoms. The finding of a tender prostate in this setting is supportive of ABP, although its absence will still not rule out this diagnosis because the reported sensitivity of rectal exam may vary from 9% to 100% in ABP (1). 
Although there may not be a general agreement on the definition of ABP, 2 studies utilizing indium-labeled leukocyte scintigraphy or a combination of PSA levels and transrectal ultrasound have provided evidence for frequent prostatic involvement in men with UTI symptoms (4,5).  In these studies, an inflammatory reaction within the prostate was seen in the majority of cases, even when the digital rectal examination was not painful or when clinicians diagnosed pyelonephritis without prostatitis.
Bonus pearl: Did you know that the lifetime probability of a man receiving a diagnosis of prostatitis is >25% (1)? 

Also see a related P4P pearl: https://pearls4peers.com/2017/07/27/should-male-patients-with-suspected-urinary-tract-infection-routinely-undergo-a-prostate-exam/

 

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References
1. Etienne M, Chavanet P, Sibert L, et al. Acute bacterial prostatitis: heterogeneity in diagnostic criteria and management. Retrospective multicentric analysis of 371 patients diagnosed with acute prostatitis. BMC Infect Dis 2008, 8:12 doi:10.1186/1471-2334-8-12. https://bmcinfectdis.biomedcentral.com/articles/10.1186/1471-2334-8-12
2. Lipsky BA, Byren I, Hoey CT. Treatment of bacterial prostatitis. Clin Infect Dis 2010;50:1641-1652. https://academic.oup.com/cid/article/50/12/1641/305217
3. Etienne M, Pestel-Caron M, Chavanet P, et al. Performance of the urine leukocyte esterase and nitrite dipstick test for the diagnosis of acute prostatitis. Clin Infect Dis 2008; 46:951-53. https://academic.oup.com/cid/article/46/6/951/351423
4. Velasco M, Mateos JJ, Martinez JA, et al. Accurate topographical diagnosis of urinary tract infection in male patients with (111)indium-labelled leukocyte scintigraphy. Eur J Intern Med 2004;15:157-61. https://www.ncbi.nlm.nih.gov/pubmed/15245717
5. Ulleryd P, Zackrisson B, Aus G, et al. Prostatic involvement in men with febrie urinary tract infection as measured by serum prostate-specific antigen and transrectal ultrasonography. BJU Int 1999;84:470-74. https://onlinelibrary.wiley.com/doi/full/10.1046/j.1464-410x.1999.00164.x

 

My 70 year old male patient is admitted with 1 day of fever, dysuria, and urinary frequency and urgency, but has a negative urine dipstick test for nitrites and leukocyte esterase. Could he still have acute bacterial prostatitis?

My patient has developed isolated eosinophilia without symptoms while receiving an antibiotic. Should I consider discontinuing the antibiotic or can I just continue it as long as she has no symptoms?

Short answer: We don’t really know what’s the best way to manage patients with  isolated (asymptomatic) eosinophilia (IE) that develops during antibiotic therapy. We do know that the majority of patients with IE may never develop hypersensitivity reaction such as rash, renal or liver injuries, but predicting who will or will not get HSRs is a challenge.1-3 Couple of studies may help us in our decision making, however.

In a 2015 study1 involving patients receiving outpatient parenteral antibiotics, eosinophilia was present in 25% of patients during their course of treatment, of whom 30% subsequently developed HSR and 5% developed more than 1 sign of HSR. Patients with IE and subsequent HSR developed eosinophilia earlier in their course of treatment (median 11 vs 17 days) and had a higher peak absolute eosinophil count (~ 850 vs ~700/ ml).  The authors suggested that close monitoring for rash and renal injury in patient with IE during antibiotic therapy be considered, and that medication changes may be necessary when IE is associated with earlier onset of eosinophilia or higher absolute eosinophil count.

In a 2017 prospective study2 of patients with eosinophilic drug reactions (~20% related to antibiotics), the majority (56%) were asymptomatic. Earlier onset of eosinophilia and higher eosinophil count were associated with symptomatic eosinophilia, similar to the aforementioned study. The frequency of patients with IE who went on to have symptomatic eosinophilia when the suspect drug was continued vs those in whom it was not continued remains unclear from these studies.

Ultimately, the decision to continue or discontinue a suspect antibiotic when your patient has new-onset IE should be made on a case-by-case basis, taking into account the severity of the patient’s infection, availability of equally effective and tolerated alternative drugs and the ability to closely monitor for symptomatic disease. The timing of onset of eosinophilia and its peak absolute count may also play a role.

Bonus pearl: Did you know that only 18% of inpatients with cutaneous drug eruptions may have peripheral eosinophilia?4

The author acknowledges the invaluable input of Kimberly Blumenthal, MD in composing this pearl.

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References

  1. Blumenthal KG, Youngster I, Rabideau DJ, et al. Peripheral blood eosinophilia and hypersensitivity reactions among patients receiving outpatient parenteral antibiotics. J Allergy Clin Immunol 2015;136:1288.1294. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4640981/
  2. Ramirez E, Mdrano-Casique N, Tong HY, et al. Eosinophilic drug reactions detected by a prospective pharmacovigilance programme in a tertiary hospital. Br J Pharmacol 2017;83:400-15. https://bpspubs.onlinelibrary.wiley.com/doi/pdf/10.1111/bcp.13096
  3. Rauscher C, Freeman A. Drug-induced eosinophilia. Allergy Asthma Proc 2018;39:252-56. https://www.ncbi.nlm.nih.gov/pubmed/29669671
  4. Romagosa R, Kapoor S, Sanders J, et al. inpatient adverse cutaneous drug erutpions and eosinophilia. Arch Dermatol 2001; 137:511-12. https://www.ncbi.nlm.nih.gov/pubmed/11295947   

 

 

My patient has developed isolated eosinophilia without symptoms while receiving an antibiotic. Should I consider discontinuing the antibiotic or can I just continue it as long as she has no symptoms?

My elderly patient with abdominal pain has a negative Murphy’s sign on physical exam. How accurate is Murphy’s sign in diagnosing cholecystitis?

Not as accurate as we might like! In fact, no single clinical finding has been found to carry sufficient weight in ruling in or excluding cholecystitis and Murphy’s sign (inability to take a deep breath due to pain upon palpation of the right upper quadrant) is no exception. 1

A meta-analysis of patients with Murphy’s sign reported a sensitivity of 65% and a specificity of 87% (positive LR 2.8, negative LR 0.4, with 95% C.I. including 1.0 in both). 1,2  However, among the elderly (mean age 79 y), the sensitivity may be a slow as 48% 2 and in patients with gangrenous cholecystitis as low as 33%.3  

In contrast, Murphy’ s sign elicited at the time of ultrasound of the gallbladder (ie,“sonographic Murphy’s) is generally thought to very sensitive  (>90%) for acute cholecystitis;3,4 1 study reported a sensitivity of 63%, however (specificity 94%).5  Remember that altered mental status may also mask sonographic Murphy’s sign. 

Indirect fist percussion of the liver has been suggested by some authors as a more sensitive alternative to Murphy’s sign (100% vs 80%) in a small series of patients with cholecystitis.2

Bonus pearl: Did you know that another technique originally described by the famed American surgeon, John Murphy, to diagnose acute cholecystitis consisted of the “hammer stroke maneuver” in which percussion of the right midsubcostal region with the bent middle finger of the left hand was performed using the right hand to strike the dorsum of the left hand with hammer-like blows? 6

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References

  1. Trowbridge RL, Rutkowski NK, Shojania KG. Does this patient have acute cholecystitis. JAMA 2003;289:80-86. https://jamanetwork.com/journals/jama/article-abstract/195707
  2. Ueda T, Ishida E. Indirect fist percussion of the liver is a more sensitive technique for detecting hepatobiliary infections than Murphy’s sign. Current Gerontol Geriat Res, Volume 2015, Article ID 431638. https://www.hindawi.com/journals/cggr/2015/431638/
  3. Simeone JF, Brink JA, Mueller PR, et al. The sonographic diagnosis of acute gangrenous cholecystitis. The importance of the Murphy sign. AJR 1989;152:289-90. https://www.ncbi.nlm.nih.gov/pubmed/2643262
  4. O’Connor OJ, Maher MM. Imaging of cholecystitis. AJR 2011;196:W36774. https://www.ajronline.org/doi/full/10.2214/AJR.10.4340
  5. Rallis PW, Lapin SA, Quinn MF, et al. Prospective evaluation of the sonographic Murphy sign in suspected acute cholecystitis. J Clin Ultrasound 1982;10:113-5. https://www.ncbi.nlm.nih.gov/pubmed/6804512
  6. Salati SA, al Kadi A. Murphy’s sign of cholecystitis-a brief revisit. Journal of Signs and Symptoms 2012;1:53-6. https://www.researchgate.net/publication/230820198_Murphy’s_sign_of_cholecystitis-_a_brief_revisit

 

 

My elderly patient with abdominal pain has a negative Murphy’s sign on physical exam. How accurate is Murphy’s sign in diagnosing cholecystitis?