Arterial Blood gas interpretation

# Arterial Blood gas interpretation

## Arterial Blood gas interpretation

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1. Arterial Blood gas interpretation • pH PaCO2 PO2 on FIO2 =…. • pH then PCO2 for acid-base balance • for an acute change in PCO2 of 10, the pH goes 0.08 units in the other direction. • PCO2 and PO2 and FIO2 for gas exchange

2. Examples of Acid-Base Imbalance: Bicarbonate is never measured, it is calculated from the Henderson-Hesselbach equation using measured pH and paCO2

3. Describe the Acid-Base Imbalance (1): • pH=7.42, PCO2=48 • PaCO2 is slightly high • pH is on the alkaline side of normal • This is most probably a compensated metabolic alkalosis

4. Describe the Acid-Base Imbalance (2): • pH=7.36, PCO2=52 • PaCO2 is high • pH is normal, but on the acid side of 7.40 • This is most probably a compensated respiratory acidosis

5. Describe the Acid-Base Imbalance (3): • pH=7.20, PCO2=52 • pH is quite acid • PaCO2 is less high than you expect for a pure respiratory acidosis, (PCO2 up by 12, pH should go down by ~ .10 units) • this is a mixed acidosis

6. Assessment of Gas Exchange: • Question: While breathing room air, a comatose hyperpneic youth arrives in the ER. He is pink. An ABG shows: • pH=7.15; PCO2=20, PO2=95 • Acid-base status?Acute Metabolic Acidosis • Are his lungs normal?NO as A-a DO2 is

7. The Flow-Volume loop 1 2 • A. Normal • Identify • 1 Peak flow rate • 2 RV • 3 TLC • What is B? 3

8. The Flow-Volume loop • A. Normal • B. Restrictive • C. Large airway fixed obstruction • D. Small airways variable obstruction • E. Extra-thoracic variable obstruction

9. Exercise Testing: Stage I Screening • Quantitate exercise capacity c.f. predicted • Assess oxygen saturation on exertion • Factors limiting Exercise • Pulmonary Mechanics • Pulmonary Vascular • Cardiac or peripheral (including unfitness) • Anxiety

10. Inhaler Devices: Dry powder inhalers (DPI) - (Diskus or Turbuhaler or Handihaler) • Pressurized Metered Dose Inhalers-(Freon-free)(HFA MDIs) eg Advair 250, Qvar,Salbutamol, Mometasone • pulmonary deposition may be improved • side-effects decreased • Patients still need careful instruction in the use of any inhaler device

11. Inhaled Steroids: (IS) • Fluticasone (Flovent) , Budisonide (Pulmicort), Ciclesonide (Alvesco) • all have similar local side effects - sore throat, thrush, dysphonia ( try a spacer and do a swish, gargle and spit) (Ciclesonide may be exception) • Enough absorption to cause bruising

12. Inhaled Steroids (IS): Potential side-effects if long-term, high dose therapy: • Cataracts, • Osteoporosis • osteoporosis prevention may be important with children on high dose IS, but not adults. • Inactivity due to uncontrolled asthma promotes osteoporosis also • Delayed growth • Adrenal insufficiency

13. Long-lasting B2 Agonists (LABAs): • Examples: • Salmeterol (Serevent) 25 ugpii bid • Formoterol (Oxeze) 12 ugpi bid • Second-line drug for ongoing acute bronchospasm despite optimal inhaled steroids • Decreases nocturnal exacerbations • Does not eliminate the need for short-acting B2-agonists • Not a rescue medication

14. Combination IS/LABA: • Examples: • Advair discus(fluticasone + salmeterol • Symbicort turbuhaler (budisonide + formoterol • Indication in Asthma: • When IS in doses of 500-1000 ug/day are insufficient to eliminate frequent rescue with SABAs • Indication in COPD: • May increase interval between AECB .

15. Leukotriene Antagonists • Montelukast (Singulair) 10 mgm qhs • Block leukotriene-derived mediators (SRS-ALTC4 and LTD4, but not prostaglandins • Montelukast is accepted for children down to age 6 years (5 mgm strength) • It is helpful in a minority of asthmatics

16. Leukotriene Antagonists • Role: • a second line drug • If inhaled steroids are insufficient to control symptoms or are contra-indicated • May help: • ASA-sensitive individuals • restore sense of smell (Systemic distribution) • may be useful to prevent progressive asthma • Side effects - None

17. IgE Antagonists: Omalizumab (Xolair) • Monoclonal antibodies block action of IgE on mast cell • Effective if IgE levels are only slightly elevated (500-1200) • Monthly injection • Extremely expensive ?\$45,000/year • Use if frequent need for oral steroids despite optimum conventional Rx and patient has drug plan or \$\$\$

18. Acute asthma, ER management • Mild: B2 agonist; start IS • Moderate: add O2, oral steroids • Severe: add continuous B2 aersols, Ipatropium, 100% O2 • Near death: add intubation, ventilation, kitchen sink (Theophylline, MgSO4, Halogenated anesthetic) • Discharge criteria: track record, response to B2 agonists, prior steroids, compliance

19. Chronic asthma management • Minimal: B2 agonist prn. • Mild: add inhaled steroids • Moderate : • Leucotriene antagonist • long lasting B2 agonist • Short course oral prednisone • Severe: • add oral steroids dose large enough, duration long enough to return patient to “personal best” • “Bronchial barbecue”- bronchial thermoplasty

20. Asthma Consensus Guidelines Treatment Continuum Next edition ?2009 Inhaled Corticosteroid PREDNISONE ** LABAs, LTRAs ?Pred. Additional Therapy * µg 0 250 500 1000- 1500 Dose Lower Short-acting ß2-agonist on demand Environmental Control and Education Very Mild Mild Moderate Moderately Severe Severe Preclinical Intermittent Persistent * ß2 agonist need < 3 times/week (excluding 1 dose/day before exercise) ** ICS dose required > 400-500 mcg/day (as beclomethasone equivalent)

21. COPD • 4% of Canadians • 4th leading cause of death • Over 40 years of age • Mortality rate rising, especially for females • Occasionally occupation causes COPD

22. COPD Guidelines • Do not screen asymptomatic smokers • Assess with spirometry if symptomatic • Cough • SOBOE • wheeze • persisting colds • FEV1/ FVC< .7 • Do ABG if FEV1 <40% predicted

23. Mild- SOBOE if hurrying Moderate Stops after walk of few minutes Severe SOB on ADL Resp failure R CHF Very Severe SOB at rest FEV1% predicted >80% 50%<80% 30%<50% <30% COPD-Assesment: (FEV1/ FVC< .7)

24. Continuum of COPD Management CTS guidelines, Canadian Respiratory J 2008;SuppA 15:1-8

25. COPD- Management • Education • Smoking cessation • Pharmacotherapy • Regular exercise is part of therapy- Education! • Inhaled steroids only for repeated AECB responding to prednisone

26. Smoking Cessation • Counseling • If patient is motivated to quit : +/-Nicotine replacement (patch, gum, etc) -(doubles success) +/-Bupropion (Zyban) start 1week prior to quit day (doubles success) +/-Combination =4x as successful- (40%non smokers after 1 year, c.f. 10%) Champix (varenicline tartrate) –a pseudonicotine new kid on the block

27. Champix (varenicline tartrate) • Pseudonicotine • ..more effective than Bupropion initially • Side efect nausea 15-30% • Dose: (half in renal disease) • .5 mgm qd x 3d • .5mgm bid x 4 d then D/C cigarettes • 1 mgm bid x 12 weeks • Cost: \$3.37/day (~ to “patch”; c.f. \$1.84/day for Zyban)

28. Inhaled Anti-Cholinergics: Tiotropium (Spireva) • Useful in COPD • significant increase in Vital Capacity • may help FEV1 • Supplants Ipatropium (Atrovent) as DPI • No side effects (?glaucoma exacerbation) • Dose: 18 ug tablet DPI inhaled qAM via Handihaler • Not a limited use drug

29. COPD long-term management - continued • Bronchodilators • B2 (SABA-> LABA) • and/or Ipatropium/Tiotropium • Steroids: only 10% respond - document response! • Combination IS/LABA may increase time between exacerbations • Theophyllines: popularity fluctuates • Annual Influenza vaccination • ? Pneumovax q 5-10 years

30. COPD long-term management - continued • Long-term O2 prolongs life: • if PaO2= or<55 mmHg • if SpO2= or<88% • if pulmonary hypertension, polycythemia, nocturnal desaturation PaO2<60, SpO2<90 • Palliative grounds allowed • Antibiotics for purulent bronchitis –Trimethoprim, Tetracycline, Clavulin, Cefuroxime, Clarithromycin, respiratory quinolone

31. COPD long-term management - continued • Rehabilitation- exercise! (GOYA to complex) • Breathing exercises (? unproven) • Surgery: • Lung Volume reduction • extra 2 years survival • Lung transplantation • No longer smokes • Even if alpha 1 pt. • Patient not on a ventilator • Median survival 2-4years

32. AECB= Acute exacerbation of Chronic Bronchitis • Over 50% associated with infections • Average of 2 AECBs/year • Diagnose if patient has 2 or 3 of the following symptoms: • Increase in Dyspnea • Increase in sputum volume • Purulent sputum

33. Management of AECB • Usual bronchodilator Rx • Prednisone 25-50 mgm x 7-14 days • Antibiotics will attenuate the AECB • Faster resolution of clinical criteria and Peak Flow Rates, reduced LOS* • Choice based on antibiotic hx and local factors *Anthonisen NR, et al.: Ann Intern Med 1987; 106(2):196-204.

34. Microbiology of AECB:Most Common Pathogens by Class • Mild COPD • H. influenzae, other Haemophilus species,S. pneumoniae, M. catarrhalis • Moderate COPD with risk factors • Class I pathogens • Klebsiella sp. • Increased likelihood of beta-lactam-resistance • Severe COPD, • needs hospitalization • Class I and II pathogens • Increased risk of P. aeruginosa

35. AECB: Antibiotic Therapy • Simple • COPD mild-moderate; FEV1 >50% pred • RX: Tetra, Amoxi, Cephalosporin GI or GII, Macrolide GII or GIII (clarithromycin or telithromycin) • Complicated • COPD severe; FEV1 <50% pred • Any of • <4 AECB/year, Chronic O2 rx, Recent antibiotics, CAD, other chronic illness • RX: Respiratory quinolone, (Gemflox, Levoflox, Moxiflox)

36. Acute on chronic respiratory failure • Determine cause • ?Pneumonia • ?AECB • ?CHF • ?Sedatives • Assess with spirometry and ABG • Oxygenate temperately: avoid greed • Drugs: as per asthma, plus Ipatropium (Atrovent)

37. Pathogens in CAP Outpatients Inpatients Nursing Home S. Pneumoniae S. pneumoniae S. pneumoniae H. Influenzae H. Influenzae H. Influenzae Atypicals (2)*Atypicals (3)** Atypicals (3) ** GNR GNR** * Atypicals (2) = M. pneumoniae, C. pneumoniae ** Atypicals (3) = M. pneumoniae, C. pneumoniae, Legionella spp. GNR = Gram negative rods ** Negated in EU guidelines

38. Type of pneumonia Modifying factors and/or pathogens First-choice therapy Second-choice therapy Outpatient w/out modifying factors — Macrolide Doxycycline Outpatient w/ modifying factors – COPD (no recent anti-biotics or oral steroids within past 3 months) – COPD (recent antibiotics or oral steroids within past 3 months)—H. influenzae & enteric Gram-negative rods – Suspected macroaspiration—oral anaerobes Macrolides Respiratory fluoroquinolone Amox/clav +/- macro-lide, or 4th-gen. cephalosporin Doxycycline Amox/clav + macrolide or 2nd-gen. cephalo-sporin + macrolide 3rd-gen cephalosporin + clindamycin or metronidazole Nursing-home residents in nursing home S. pneumoniae, enteric Gram-negative rods (?), H. influenzae Respiratory fluoroquinolone alone or amox/clav + macrolide 2nd-gen. cephalosporin + macrolide CAP: Selecting Treatment Mandell LA, et al.: Can J Inf Dis 2000; 11(5):237-47. Adopted by the CIDS and the CTS

39. Type of pneumonia Modifying factors and/or pathogens First-choice therapy Alternative Inpatient ward — Resp quinolone ICU – Pseudomonas negative Pseudomoonas positive Resp. quinolone plus B-lactam/B-l inhibitor or cefotaxime Cipro plus antipseudomonal B-lactam CAP: Selecting Treatment (cont’d) • Cephalosporin • + Macrolide • Macrolide plus • ceftriaxone or B-lactam/B-l inhibitor • Antipseudomonal • B-lactam plus • aminoglycoside plus • macrolide Mandell LA, et al.: Can J Inf Dis 2000; 11(5):237-47.

40. Pulmonary Arterial Hypertension - Classification • Ideopathic -includes Collagen vascular disease, portal hypertension, HIV, anorexogens • Secondary to Pulmonary venous hypertension - esp CHF • Hypoxemic related PAH • Thrombo-embolic PAH

41. Pulmonary Arterial Hypertension:Diagnosis • Unexplained exertional dyspnea • Isolated impairment of DCO • Exercise test • Echocardiogram • Specialized tests (one or more of): • Spiral CT • V/Q scan • Pulmonary angiogram

42. Pulmonary Arterial Hypertension:Therapy of Primary PHtn • Refer to specialty clinic • Oxygen if indicated • Medications • …Calcium channel blockers • Epoprostenol (prostacycline analog) • Bosentan (endothelin antagonist) • Sildenofil (PDE5 inhibitor) • Lung transplantation

43. Dyspnea management in palliation: • Reverse what can be reversed • Oxygen for hypoxemia or pre-emptive • Opiates - • Morphine oral • 15-120 mgm q12h • s/c route 5-10 mgm q1-6h. • Dilaudid s/c .5-1.0 mgm q1-6h

44. Obstructive Sleep Apnea Syndrome • Heavy snoring • Daytime hypersomnolence • Obesity • Other manifestations: • Hypertension • Unexplained Cor Pulmonale • Nightmares • Impotence • Depression

45. Obstructive Sleep Apnea Syndrome Diagnosis: • Sleep study or Polysomnography • EEG to stage sleep • Electro-oculography • EKG • Oronasal airflow • Respiratory effort • SpO2

46. Obstructive Sleep Apnea Syndrome • RDI= Respiratory disturbance index = # of apneas or hypopneas/hr Mild OSA- RDI 5-15 Moderate OSA RDI16-30 SevereOSA RDI >30 • Therapy: • Weight reduction • CPAP / BiPAP • Mandibular Prosthesis, Tracheostomy

47. LMCC topics understressed • Hemoptysis: • Refer if major (>200 ml / 24 hours) • Treat the cause • Antibiotics • Pleural effusion • Treat the cause • Drain if pus • Pleurex indwelling catheter if chronic • Pleurodesis if cancer prognosis>3 months and pleurex support not available