To the Editor:

McIsaac et al.1  recently published their population-based cohort study on outcomes after total knee arthroplasty in relation to the use of peripheral nerve blocks. The primary outcome was length of stay (LOS), and they concluded that nerve blocks reduced LOS (risk ratio = 0.98!).

Although such large cohort studies may be valuable, we find the discussion insufficient in relation to the primary outcome, where we get no information on why the patients were hospitalized or whether a type of fast-track care was implemented.2  Furthermore, there is no information about discharge destination, which we know from several studies may hinder sufficient interpretation of LOS, because transfer of patients to rehabilitation or other institutions may depend on potential economic benefit3  or on local traditions4  and may misleadingly reduce the registered LOS after surgery.3  Finally, their mean LOS was approximately 4.7 days, which is beyond what has been published before (but not referred to) from prospective multicenter studies with a mean LOS of 3.0 days5  from well-defined fast-track programs without the use of peripheral blockades. Also, median values of LOS of approximately two days in subsequent large cohorts are available.6 

In summary, when discussing LOS as a primary outcome, interventional studies in perioperative medicine need to include data on why the patient was hospitalized, as well as discharge destination.4 

Competing Interests

The authors declare no competing interests.

References

References
1.
McIsaac
DI
,
McCartney
CJL
,
van Walraven
C
:
Peripheral nerve blockade for primary total knee arthroplasty: A population-based cohort study of outcomes and resource utilization.
Anesthesiology
2017
;
126
:
312
20
2.
Kehlet
H
:
Fast-track hip and knee arthroplasty.
Lancet
2013
;
381
:
1600
2
3.
Cram
P
,
Lu
X
,
Kates
SL
,
Singh
JA
,
Li
Y
,
Wolf
BR
:
Total knee arthroplasty volume, utilization, and outcomes among Medicare beneficiaries, 1991–2010.
JAMA
2012
;
308
:
1227
36
4.
Pitter
FT
,
Jørgensen
CC
,
Lindberg-Larsen
M
,
Kehlet
H
;
Lundbeck Foundation Center for Fast-track Hip and Knee Replacement Collaborative Group
:
Postoperative morbidity and discharge destinations after fast-track hip and knee arthroplasty in patients older than 85 years.
Anesth Analg
2016
;
122
:
1807
15
5.
Jørgensen
CC
,
Kehlet
H
;
Lundbeck Foundation Centre for Fast-track Hip and Knee Replacement Collaborative Group
:
Role of patient characteristics for fast-track hip and knee arthroplasty.
Br J Anaesth
2013
;
110
:
972
80
6.
Jørgensen
CC
,
Knop
J
,
Nordentoft
M
,
Kehlet
H
;
Lundbeck Foundation Centre for Fast-track Hip and Knee Replacement Collaborative Group
:
Psychiatric disorders and psychopharmacologic treatment as risk factors in elective fast-track total hip and knee arthroplasty.
Anesthesiology
2015
;
123
:
1281
91