cost-benefit analysis of nitrous oxide in major surgery presenter: dr alison graham 2 nd year...

Cost-benefit analysis of nitrous oxide in major surgery

Presenter: Dr Alison Graham

2nd year Anaesthesia Advanced Trainee

Co-Authors: Prof Paul S. Myles, Prof. Kate Leslie,

Prof. Matthew T.V. Chan, Prof. Michael J. Paech,

Dr Philip Peyton and Prof. Abdelazeem A. El. Dawlatly

Topics:

• Review ENIGMA trial• Cost-benefit analysis

– Methods– Results– Limitations– Conclusion

ENIGMA Trial

• The Avoidance of Nitrous Oxide in Major Surgery• What are the consequences of using nitrous oxide?

80% O2 & 20% N2 30% O2 & 70% N2O

VS

ENIGMA Results

Variable Nitrous-oxide free group

Nitrous-oxide group

p-value

Hospital LOS,

days (IQR)7.0 (4.0 – 10.9) 7.1 (4.0 – 11.8) 0.06

Time to eligibility to discharge from PACU,

minutes median (IQR)

84 (64 – 120) 92 (65 – 125) 0.02

ICU admissions,

No. (%)122 (12%) 140 (14%) 0.3

ENIGMA Trial Results

Kaplan-Meier estimates of discharge from the intensive care unit

ENIGMA ResultsVariable Nitrous oxide-

free Group No. (%)

Nitrous oxide GroupNo. (%)

AdjustedOdds Ratio

(95% CI)

p-value

Severe nausea or vomiting

104 (10) 229 (23) 0.40 (0.31-0.51) <0.001

Wound infection 77 (7.7) 106 (10) 0.72 (0.52-0.98) 0.036

Fever 275 (28) 345 (34) 0.73 (0.60-0.90) 0.003

Pneumonia 15 (1.5) 30 (3.0) 0.51 (0.27-0.97) 0.040

Atelectasis 75 (7.5) 127 (13) 0.55 (0.40-0.75) <0.001

Pneumothorax 1 (0.1) 3 (0.3) - -

Myocardial infarction

7 (0.7) 13 (1.3) 0.58 (0.22-1.50) 0.26

Thromboembolism 16 (1.6) 10 (1.0) 1.60 (0.72-3.55) 0.25

Blood transfusion 188 (19) 202 (20) 0.96 (0.75-1.21) 0.71

Stroke 1 (0.1) 1 (0.1) - -

Awareness 0 (0.0) 2 (0.2) - -

Death within 30 days

3 (0.3) 9 (0.9) 0.33 (0.09-1.22) 0.096

Criticism of the ENIGMA Trial

•“Despite the concerns regarding its adverse effects, nitrous oxide has actually had a central position in anesthetic practice primarily becauseit is inexpensive, widely available, and has a long-standing safety profile. The most obvious advantage of using nitrous oxide is that it allows a dose reduction of other anesthetic agents and opioids, which translates into less cardiovascular depression and significant cost reduction”

Anesthesiology 2008; 108:541-2

Cost-Benefit Analysis of the ENIGMA Trial

• What is the financial cost of using nitrous oxide?

Health economics

Health economics

Cost Minimisation

Cost benefit - $ only

Cost effectiveness – natural units

Cost utility - QALY

Health economics

Cost-Benefit Analysis of the ENIGMA Trial

• What is the financial cost of using nitrous oxide?• From the hospital administration’s point of view

Cost-benefit N2O: variable costs

• Costs saved– Maintenance anaesthetic– Analgesia– Vasopressors

• Expenses

– PONV prophylaxis

– PONV

– Infection/fever

– Pneumonia

– Atelectasis

– PACU

– ICU

– HLOS

Contributing Cost Estimates

Contributing cost description Estimated cost per unit

(2010 US dollars)

Gas supplies:

nitrous oxide $0.0123/L

oxygen and medical air $0.003/L

Induction agents:

Propofol $1.40 per 200 mg ampoule

Thiopentone $12.60 per 500 mg ampoule

Inhalational agents:

Sevoflurane $11.40 MAC hour

Isoflurane $1.50 MAC hour

Desflurane $12.60 MAC hour

Prophylactic antiemetic therapy: $4.95 per treatment

Contributing Cost Estimates

Contributing cost description

Estimated cost per unit

(2010 US dollars)Number of studies

PACU stay $0.81/minute 3

PONV$22.56 for 1 or more

episodes7

Wound infection $10,514/infection 30

Pneumonia $13,439/infection 9

ICU stay $2,110/day 11

ENIGMA Cost-Benefit Analysis: Results

Nitrous oxide-free

Group

(n = 997)

Nitrous oxide

Group

(n = 1,015)

p-value

Anaesthetic drugs

27 ± 22 26 ± 22 0.16

Bed days 12,793 ± 11,547 14,685 ± 18,718 0.005

Complications 1,017 ± 3,496 1,500 ± 4,210 0.006

Total costs 13,837 ± 13,256 16,203 ± 20,842 0.002

Estimated costs per patient (US dollars), Mean ± SD

ENIGMA Cost-Benefit Analysis: Sensitivity Analysis

Nitrous oxide-free group

(n = 997)

Nitrous oxide group

(n = 1,015)p-value

Total estimated costs (base line) 13,837 ± 13,256 16,203 ± 20,842 0.002

¼ of component costs

(i) Wound infection 13,228 ± 12,421 15,379 ± 19,902 0.004

(ii) Pneumonia 13,686 ± 12,734 15,915 ± 20,136 0.003

(iii) Bed days 4,242 ± 5,301 5,187 ± 7,487 0.001

4x component costs

(i) Wound infection 16,273 ± 18,712 19,500 ± 26,536 0.002

(ii) Pneumonia 14,444 ± 16,127 17,356 ± 24,631 0.002

(iii) Bed days 52,218 ± 47,604 60,269 ± 76,765 0.005

Estimated costs per patient (US dollars), Mean ± SD

Cost-Benefit Analysis Limitations

• Estimated costs (but the statistics are real)• Hospital perspective only• Use of published estimates of costs

– Precedent studies mostly from developed countries– No discrimination on methods

• Variable costs only included• PACU costs controversial

Conclusions

• There are significant additional costs with N2O use

• No compelling argument to use N2O on the basis that it is an inexpensive drug

Questions

Sensitivity AnalysisNitrous oxide-

free Group

(n = 997)

Nitrous oxide Group

(n = 1,015)P value

Total estimated costs

(US dollars), Mean ± SD13,837 ± 13,256 16,203 ± 20,842 0.002

¼ of costs from main analysis:

i. Wound infection 13,228 ± 12,421 15,379 ± 19,902 0.004

ii. Pneumonia 13,686 ± 12,734 15,915 ± 20,136 0.003

iii. Bed days 4,242 ± 5,301 5,187 ± 7,487 0.001

4x costs from main analysis:

i. Wound infection 16,273 ± 18,712 19,500 ± 26,536 0.002

ii. Pneumonia 14,444 ± 16,127 17,356 ± 24,631 0.002

iii. Bed days 52,218 ± 47,604 60,269 ± 76,765 0.005

Cost estimates if including non-statistically significant complications

13,890 ± 13,595 16,303 ± 21,038 0.002

cost-benefit analysis of nitrous oxide in major surgery presenter: dr alison graham 2 nd year...

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