case studies in abgs - seattle, · pdf filecase studies in abgs mountain to sound chapter of...
TRANSCRIPT
1
CASE STUDIES IN ABGS
Mountain to Sound Chapter of AACN
Objectives
Review normal and abnormal arterial blood gas values
Discuss common acid/base imbalances and treatments
Analyze case examples with treatment strategies
2
Blood gas acquisition
No need to ice the sample
Should be analyzed in < 30 minutes
Heparin syringe balanced to run electrolytes
Allen test prior to radial puncture
Arterial Blood Gases
Be methodical when assessing ABGs
Look at 3 main values to interpret:
pH PaCO2 HCO3
Lungs:Fast compensation
Kidney:Slow compensation
Homeostasis is achieved via the lungs, kidneys and blood buffers
3
Compensation
Blood buffers provide immediate protection
The lungs excrete 13,000 mEq/day of volatile acid Carbonic acid
The kidneys excrete 40 – 80 mEq/day of fixed acid Sulfuric & phosphoric acids
ABG Interpretation
pH: 7.35 ----- 7.40 ----- 7.45
Acid Alkaline
PaCO2: 35 ----- 40 ----- 45
Alkaline Acid
HCO3: 22 ----- 24 ----- 26
Acid Alkaline
4
ABG Interpretation
pH: 7.35 ----- 7.40 ----- 7.45
Acid Alkaline
PaCO2: 45 ----- 40 ----- 35
Acid Alkaline
HCO3: 22 ----- 24 ----- 26
Acid Alkaline
Normal Blood Gas values
Arterial Venous
pH 7.35 – 7.45 7.32 – 7.42
PaO2 80 - 100 28 - 48
PaCO2 35 - 45 38 - 52
HCO3 22 - 26 19 - 25
Base Excess/Deficit
- 2 to + 2
SaO2 95 – 100% 50 – 70%
5
ABG Analysis
1. Always assess the pH first!
2. Is it normal?
3. Is there acidosis or alkalosis?
4. Which other value (PaCO2 or HCO3) is trending with the pH?
pH: 7.28 PaCO2: 54 PaO2: 196 HCO3: 26
If PaCO2 is the cause, it’s RESPIRATORY!
If HCO3 is the cause, it’s METABOLIC
Another tip…
Look at the pH & CO2
If the pH & CO2 are both up or both down:
saME = Metabolic
Example: pH: 7.32(↓) CO2: 32 (↓) HCO3: 18
REverse = Respiratory
Example: pH: 7.28 (↓) CO2: 54 (↑) HCO3: 26
6
Compensation
If pH is normal & PaCO2 and HCO3
- are both abnormal, then the patient is compensated.
If pH is abnormal & PaCO2 and HCO3
- are both abnormal, then the patient is partially compensated.
If pH is abnormal, & either PaCO2 or HCO3
- are abnormal, then the patient is uncompensated.
Example:
pH 7.22 PaCO2 65 HCO3 24
Uncomp. Respiratory Acidosis
_______ _______ _______
7
Respiratory Acidosis Causes
Over-sedation Late respiratory failure Drug overdoses that cause
resp. depression COPD Brain stem dysfunction Extreme V/Q mismatch
Pulmonary embolus, PNA
Guillain Barre’ K+ / PO-4 imbalances Excessive CO2 production
(Sepsis, TPN, Burns)
Think hypoventilation!
Example:
pH 7.52 PaCO2 26 HCO3 22
Uncomp. Respiratory Alkalosis
_______ _______ _______
8
Respiratory Alkalosis Causes
Early respiratory failure
Anxiety or severe pain
Excessive tidal volume or rate on vent
ARDs
Heart failure
Neurologic disorders
Pulmonary embolus
Salicylate overdose (adults)
Decreased Cardiac Output/Shock
PaO2 < 60 (Cause & effect)
Think hyperventilation!
Example:
pH 7.16 PaCO2 35 HCO3 14
Uncomp. Metabolic Acidosis
_______ _______ _______
9
Metabolic Acidosis Causes
Acute kidney injury
Drug overdoses
Diabetic Ketoacidosis
Sepsis
Lactic Acidosis
Toxins
Aspirin overdose
Liver failure
Calculate an anion gap!!!
May lead to hyperkalemia
Suppresses myocardial contractility (↓ CO, ↓ BP)
Example:
pH 7.49 PaCO2 36 HCO3 29
Uncomp. Metabolic Alkalosis
_______ _______ _______
10
Metabolic Alkalosis Causes
NG tube to suction Emesis Hypokalemia Antacid abuse Excessive sodium bicarb infusion Inadequate renal perfusion Diuretics Excessive albuterol use Hyperaldosteronism (d/t RAAS activation)
Practice:
pH 7.50 PaCO2 28 HCO3 24
Uncomp. Respiratory Alkalosis
_______ _______ _______
Causes: Hyperventilation, early respiratory failure, Anxiety, excessive tidal volume on vent
11
Practice:
pH 7.24 PaCO2 87 HCO3 26
Uncomp. Respiratory Acidosis
_______ _______ _______
Causes: Hypoventilation, Late respiratory failure, over-sedation, brain stem dysfunction
Practice: Patient with bacterial infection
pH 7.49 PaCO2 28 HCO3 24
Uncomp. Respiratory Alkalosis
_______ _______ _______
Causes: Sepsis – Pneumonia with RR 30s
12
Practice: PaO2: 44 COPD patient admitted with SOB
pH 7.36 PaCO2 49 HCO3 23
Compensated Resp. Acidosis
_______ _______ _______
Causes: COPD, CO2 retainer hypoxemic
Practice: Same COPD patient -12 hours later, more somnolent
pH 7.32 PaCO2 54 HCO3 30.6
Uncomp. Respiratory Acidosis
_______ _______ _______
Causes: COPD patient who is getting tired
13
Practice: Aspirin overdose
pH 7.31 PaCO2 22 HCO3 18
Uncomp. Respiratory Acidosis
_______ _______ _______
Cause: Seen in aspirin OD
Practice: Post operative patient just admitted from the PACU
pH 7.28 PaCO2 62 HCO3 30
Uncomp. Respiratory Acidosis
_______ _______ _______
Causes: Hypoventilation, over-sedated
14
Practice: Septic patient with lactate 4.8
pH 7.32 PaCO2 28 HCO3 17
Partially Metabolic Acidosis
compensated _______ _______
Causes: Hypo-perfused in the state of sepsis
Practice: Type 1 Diabetic presenting with sepsis
pH 7.26 PaCO2 28 HCO3 14
Uncomp. Metabolic Acidosis
_______ _______ _______
Causes: ketoacidosis, check a lactate for hypoperfusion
15
Case
62 year old has the following ABG:pH: 7.36 PaCO2 58, PaO2 62, HCO3 28
The patient likely has:
Uncompensated respiratory acidosis Compensated respiratory alkalosis Acute kidney injury COPD Acute myocardial infarction
Case
You are assessing venous & arterial labs in your patient. You note the venous bicarb (CO2) = 29 mEq/L, while the arterial is only 25 mEq/L.
Why the difference?
It must be a lab error
This is actually expected
The labs were drawn at different times
16
Case
58 year old admitted with pneumonia
HR 126, BP 84/52, RR 32, SaO2 85% on 4 L NC
Given fluids, antibiotics
Initial lactate 2.8
ABG: pH 7.48/ PaCO2 30/ PaO2 62/ HCO3 24
Your interpretation?
Uncompensated Respiratory Alkalosis
3 hours later…
The patient is tiring and getting more lethargic & sleepy
Repeat lactate 5.2 after a total of 5 L of fluid
ABG: pH 7.26/ PaCO2 58/ PaO2 52/ HCO3 20
Your interpretation?
Uncompensated Respiratory/Metabolic Acidosis
Moderate hypoxemia
17
What should we do now?
Intubate/mechanically ventilate This patient is high risk for: ARDS!!!
Vent settings: AMV rate 14, ~8 cc/kg TV, +5 PEEP, 60% FiO2
Post intubation: ABG: pH 7.30/ PaCO2 52/ PaO2 68/ HCO3 24 Your interpretation? Uncompensated (or partially compensated)
respiratory acidosis
Next steps?
Vent settings: AMV rate 14, ~8 cc/kg TV, +5 PEEP, 60% FiO2
Post intubation: ABG: pH 7.30/ PaCO2 52/ PaO2 68/ HCO3 24
Increase the vent rate Increase the PEEP/FiO2
Calculate the P/F Ratio PaO2 68/FiO2 .60 = 113
18
What therapy will improve the FiO2?
PEEP!
19
Diagnosis:
Pulmonary infiltrates on CXR **P/F Ratio:
< 300 – Mild ARDS < 200 – Moderate ARDS < 100 – Severe ARDS
Predisposing conditions Absence of left heart failure or left
atrial HTN PAOP abandoned to assist diagnosis
Mimics pneumonia & cardiogenic pulmonary edema
Berlin Criteria - 2012
ARDS Severity PaO2/FiO2* Mortality**
Mild 200 – 300 27%
Moderate 100 – 200 32%
Severe < 100 45%
*on PEEP 5+; **observed in cohort
JAMA 2012
20
Acute Respiratory Distress Syndrome (ARDS)
Inflammatory lung disease
It is not a primary disease, but a result of:
Sepsis
Trauma
Multiple blood transfusions
Pancreatitis
Cardiopulmonary bypass
Pulmonary contusion
Pneumonia/aspiration
Broncho-alveolar Lavage (BAL)
Diagnostic that is highly underutilized!
Small bronchoscope Lavage with Normal Saline Sample examined for
neutrophils & protein Neutrophils:
NL: 5% ARDS: Up to 80%!
Protein: < 0.5 – pulmonary edema > 0.7 - inflammation
21
ARDS Treatment:
Mechanical ventilation
Lung Protective Ventilation (LPV):
Low tidal volumes (6 ml/kg)
Large tidal volumes over distend & rupture distal air space (volutrauma)
Pressure related (barotrauma)
ARDS Net trial – 9% reduction in mortality
Compared 6 ml/kg vs. 12 ml/kg
Use predicted body weight
End inspiratory plateau pressure < 30
ARDS Management Con’t
Low tidal volume (6 ml/kg) Permissive Hypercapnia
PEEP: Like a stent to keep the
alveoli open When increasing PEEP,
monitor for signs of decreased cardiac output!!!
Neuromuscular blockade if dysynchrony with the ventilator
PEEP Ladder from ARDSNet
22
Other therapies:
Diuretics: FACTT Trial – Conservative
fluid management Some benefit Did not reduce inflammation
Improving O2 delivery: -Cardiac Output:
Dobutamine -PaO2: PEEP -Hemoglobin: Transfuse only
if necessary!
Steroids: No benefit from early steroids Some benefit days 7 – 14 Methylprednisolone 2 – 3
mg/kg/day Inhibits fibrinolysis Prone Therapy: New evidence of benefit Must be done early, not rescue
strategy
**Mortality increases with advanced age & multi-organ failure
Next steps?
ABG: pH 7.30/ PaCO2 52/ PaO2 68/ HCO3 24Vent settings: AMV rate 14, ~8 cc/kg TV, +5 PEEP, 60% FiO2
Changes: AMV rate 18, ~6 cc/kg TV, +10 PEEP, 70% FiO2
ABG after changes: ABG: pH 7.34/ PaCO2 48/ PaO2 72/ HCO3 26
Uncompensated Respiratory Acidosis Increase the vent rate or possibly hold
23
Case study
Michelle is a 49 year old Type 1 Diabetic who is admitted with LOC changes.
Labs:
Na 152, K+ 6.5, glucose 483, + ketones blood & urine
ABG: pH 7.12/ PaCO2 24/ PaO2 85/ HCO3 14
Your interpretation?
Uncompensated (Partially compensated) Metabolic Acidosis
Anion gap: Normal < 11 - 12
Na++ Cl-
K+ (don’t count) HCO3-
>12 – Metabolic acidosis
M: Methanol P: Propylene glycolU: Uremia I: IsoniazidD: DKA L: Lactic acidosis
E: Ethylene glycolS: Salicylates
24
Lack of insulin leaves too much
circulating glucose +
Ketone body production
Osmotic diuresis
profound water loss
Leads to glucosuria,
dehydration & electrolyte imbalance
Stress, infection, medications,
diet
In DKA & HHNS, always ask…
Is there something else going on?
Non-compliance?
Infection?
Sepsis?
Pancreatitis?
Myocardial infarction?
New medication? (steroids)
25
DKA: Treatment Insulin + Fluids
Decreased Insulin
Serum & urine ketonesIncreased glucoseKetone body production
Osmotic diuresis & dehydrationAcidosis
Anion gap acidosis – Excess serum K+,
Total body depletion of K+/PO4
↑ K+ ↑ Crea nine
Renal Failure
INSULIN FLUIDS
Hyperglycemic crisis (BG 300 - 800)
Metabolic acidosis↓ pH: > 7.0 self correct, < 7.0 consider bicarb
Serum bicarb < 20 mEq/L
Anion gap >12*
Elevated serum ketones
Elevated urine ketones
Electrolyte imbalance: Increased K+ (acidosis causes K+ to shift out of cell)
decreased Na+/Ca++
26
3 P’s: Polyuria (early), oliguria – (late) Polydipsia Polyphagia
Neuro:Headache↓ Deep Tendon Reflexes (DTRs)
Visual disturbances
Hypo/hyperthermiaDecreased LOC – advancing to coma
CV:Tachycardia
Decreased CVP & PAOP
Pulmonary:Kussmaul’s breathing
Acetone/fruity odor to breath
GI:Nausea, vomiting
Abdominal painWeight loss
Fluid Replacement 0.9% Saline or Lactated Ringers (isotonic)
Add dextrose to IVF when BG reaches 250 mg/dL
Then, 0.45% saline @ 250-500 mL/hr
Correct total fluid deficit (~ 50 – 100 mL/kg deficit)
Depending on fluid deficit:
Administer 1-3 L during the first hour
Administer 1 L during the second hour
Administer 1 L during the following 2 hours
Administer 1 L every 4 hours, depending on the degree of dehydration
27
Insulin Management - DKA
Insulin (Regular)Assess BG every 1 - 2 hours until goal is reached
Run infusion at 0.1 units/kg/hour
Then, insulin infusion goal: decrease glucose SLOWLY!!!
Do not drop BG by more than 50-100 mg/dL per hour
Transition to subcutaneous
2 hour overlap period – you don’t want the patient going without insulin
DKA – Insulin infusion
Transition to SQ insulin – Overlap by 2 hours
Goal is to shut down ketone production!!!
Electrolyte replacementPotassium Total body potassium depletion Serum is often normal or elevated Transcellular shifts of K+ with insulin therapy Begin K+ replacement at high normal ranges Monitor closely
PhosphateDepletion is common Routine replacement is not recommended (little impact on outcome
in DKA) If level < 1 mg/dL, replacement should be given
Bicarbonate Replacement not recommended unless pH < 7
28
Acidosis in Hyperglycemia
For every 0.1 ↓ in pH
If pH is: 7.4
pH 7.3pH 7.2pH 7.1pH 7.0pH 6.9
0.6 ↑ in serum K+
And, K+ is 4.0
K+ 4.6K+ 5.2K+ 5.8K+ 6.4K+ 7.0
Lab values associated with DKA:
Lab Value
Blood glucose > 250 mg/dL
pH (arterial) ≤ 7.3
Anion gap > 10
Bicarb ≤ 18
Ketones Present in serum & urine
Creatinine Can be elevated
Sodium Normal or elevated
Potassium Normal or elevated
Phosphate Normal or elevated
WBC Often elevated
29
Top 5 priorities in managing DKA:
Correction of fluid loss with intravenous fluids
Correction of hyperglycemia with insulin
Correction of electrolyte disturbances, particularly potassium loss
Correction of acid-base balance
Treatment of concurrent infection, if present
Discharge when they are stabilized on their home insulin regimen
Case Scenario
Marvin is a 68 year old patient with COPD who presents with SOB. He is given a nebulizer treatment, but remains SOB.
An ABG reveals the following: pH 7.22/PaCO2 92/ PaO2 103/ HCO3 28. This ABG confirms:
A. Uncompensated metabolic acidosis
B. Compensated metabolic alkalosis
C. Uncompensated respiratory acidosis
D. Compensated respiratory alkalosis
30
Case Scenario:
A patient with ESKD presents with mental status changes after he skipped dialysis for 3 days. His ABG reveals the following: pH 7.12/ PaCO2 32/ PaO2 180/ HCO3
18. After analyzing the results, you know the patient has:
A. Uncompensated respiratory alkalosis
B. Uncompensated respiratory acidosis
C. Uncompensated metabolic alkalosis
D. Uncompensated metabolic acidosis
Case Scenario:
You are caring for a 46 year old patient with pneumonia and sepsis. He was treated with 4 days of antibiotics and IV fluids. He is increasingly short of breath and is now on 100% FiO2 via non-re-breather mask.
You obtain an ABG with the following results: pH 7.20 / PaCO2 68/ PaO2 102/ HCO3 28. A chest x-ray reveals bilateral pulmonary infiltrates.
The patient is likely developing: A. Worsening pneumonia
B. Acute Respiratory Distress Syndrome
C. Pulmonary embolus
D. Atelectasis
31
Case Scenario:
The next course of anticipated action is to:
A. Intubate & place on low PEEP with high tidal volume (12 cc/kg)
B. Initiate non-invasive CPAP
C. Administer additional nebulizer treatments
D. Intubate & place on PEEP with low tidal volume (6 cc/kg)
Case Scenario:
When increasing the level of PEEP, you should monitor for which of the following adverse effects?
A. Hypotension
B. Hypercapnia
C. Worsening acidosis
D. Increased lactate level
32
Case Scenario:
You are caring for a patient who developed ARDS after bacterial pneumonia. The CXR shows diffuse patchy infiltrates with progressive worsening hypoxemia. Vent settings: TV 6 cc/kg (540 cc), Rate 24, FiO2 100%, PEEP 10.
An ABG reveals the following: pH 7.22, PaCO2 56, PaO2 42, HCO3 28.
Which of the following interventions would be appropriate at this time?
A. Decrease the set ventilation rateB. Increase the tidal volumeC. Decrease the inspiratory hold timeD. Increase the PEEP
Review question:
pH PaCO2 PaO2 HCO3
7.35/ 54 / 72/ 26
7.49 / 28 / 58 / 24
7.38 / 56 / 44 / 23
Compensated Resp. Acidosis
Pre-Bariatric Surgery –Hypoventilation Syndrome
Uncompensated Resp. Alkalosis
Sepsis – Pneumonia with RR 30s
Compensated Resp. Acidosis
COPD with hypoxia – give O2
33
Review question:
pH PaCO2 PaO2 HCO3
7.32 / 62 / 40 / 30.6(same patient)
7.31 / 22 / 98 / 18
Respiratory Acidosis with partial compensation
Same COPD patient, now failing, using accessory muscles
Uncompensated metabolic acidosis
(ASA OD)
Review question:
pH PaCO2 PaO2 HCO3
7.28 / 62 / 52 / 30
7.32 / 28 / 98 / 18
Respiratory Acidosis with partial compensation
Post-op patient, very sleepy, over-sedated
Metabolic acidosis with partial compensation
Septic patient Lactate 6.2