The ER calls with a 45 year old female requiring admission for respiratory failure. She has been previously healthy but recently caught a cold which progressed into pneumonia. The only new issues in her clinical history include a 50 pound weight loss, with her current weight noted at 130 pounds and stands 5 ft 5 inches tall. Her ABG reveals 7.25/40/50 on 100% Fi02. CXR revealed bilateral infiltrates.
What is her A-a gradient? (show your calculations for all question :)
What ventilator settings would you choose and why?
The team placed the patient on ACV with a peep of 5 and Fi02 of 80%. On this setting her ABG revealed a 7.30/35/70/18. What is her P/F ratio?
What will be your treatment stategy for this patient?
A-a O2 Gradient = [ (FiO2) × (Atmospheric Pressure - H2O Pressure) - (PaCO2/0.8) ] – PaO2 = 613 mm Hg
ReplyDeleteVent settings: TV would be 8mL/kg of ideal body weight since the pt is non- ARDS. So 456 for this patient. Rate of 15. PEEP of 5. Flow of 75 .FiO2 of 100%. Mode ACV. The pt has acute resp acidosis so the goal of these vent settings is to assist the body to get rid of the CO2.
P/F ratio is 70/.8 =87.5
This pt has acute respiratory acidosis due to her PNA which can be life threatening. Treatment strategy for this patient is to start treating the infection with abx to help lungs get rid of the CO2. Wean off the vent eventually. And to extubate eventually once the PNA is treated.
Daily CXR and ABGs to monitor improvement.
Her calculated A-a gradient is 623 mm Hg while her expected A-a gradient based on her age is 12. This is calculated by: ExpectedAaG = 2.5 + (0.21 * Age)
ReplyDeleteMeasuredAaG = (FiO2 * (pAtm - pH2O)) - (pCO2 / Respiratoryquotient) + (pCO2 * FiO2 * (1 - Respiratoryquotient) / Respiratoryquotient) - PaO2
As for ventilator settings, I would chose ACVC TV 350 Rate 16 FiO2 80 and PEEP 14 initially and titrate to maintain adequate oxygenation. This is based on 6mL/kg ideal body weight for TV.
On those vent settings her P/F ratio is 88 suggesting severe ARDS.
My treatment for this patient will be to utilize low tidal volume ventilation with a goal to maintain a peak pressure <30cm H2O. I will also provide supportive care including sedation, dvt ppx, nutrition, glucose control and measures to decrease rate of infections.
A-a gradient = (FiO2 x (Patm –PH2O) – (PaCO2/0.8)] –PaO2
ReplyDeleteA-a gradient = [1.0 (760- 47) – (40/0.8)] – 40
A-a gradient = [713- 50] – 40
A-a gradient = 623 mm Hg
Expected A-a gradient is Age/4 + 4 = 45/4 + 4 = 15
Reasons for elevated A-a gradient includes V/Q Mismatch which may be for patient due to Pneumonia or Right to Left intrapulmonary shunt which can be due to pneumonia or ARDS
P/F ratio is the PaO2/FiO2 ratio which for this patient is 70/0.8 = 87.5
Patient has a low P/F ratio. There are bilateral infiltrates. Order CT chest, Echo, Blood cultures, possibly bronchoscopy. If not other explained cause for volume overload then consider ARDS. Clinical picture with low P/F indicate Severe ARDS.
Vent Settings: ACV, TV: 354 (6mL/kg), PEEP >12, RR: 20-30
IF ARDS than additional management of conservative fluid management, cisatracurium use for NM blockade, prone positioning. If continued refractory case (PaO2 <80 for 6hrs), consider ECMO.
Goals: Plat Pressure <30 cmH2O, PaCO2 < 65mmH2O, pH >7.2
1) A-a gradient:
ReplyDeleteA-a gradient = PAO2 - PaO2
PAO2 = (Patm-Pwater)FiO2 - PaCO2/.8
=(760mmHg - 47mmHg)x1 - 40/.8 = 663
PAO2 - PaO2 = 663 - 50 = 613 mmHg
Expected A-a gradient = 2.5 + (0.21 x AGE)
= 2.5 + (o.21 x 45) = 11.95
613 mmHg > 11.95 mmHg
Measured A-a gradient is greater than expected A-a gradient here indicating hypoxemia. Causes of hypoxemia with increased A-a gradient can be due to Diffusion limitation such as pulmonary fibrosis, pulmonary edema, V/Q mismatch or right-to-left shunt. Common causes of shunt include pulmonary edema and pneumonia.
2) Ventilator settings:
ACVC
Initial Tidal volume = 6ml/kg predicted body weight
Predicted body weight for females= 45.5 + 0.91 x (centimeters of height - 152.4)= 45.5 + 0.91x(165.1cm-152.4) = 57.057
6 x 57.057 = 342.342
Therefore, Tidal volume = 342 based on 6ml/kg predicted body weight.
PEEP = 8
FiO2 = 80%
Respiratory rate =20
Since lung size depend mostly on sex and height, predicted body weight should be used as an initial tidal volume setting. A low tidal volume should be used to avoid ventilator-induced lung injury. In ARDS patient, aerated lung volume is reduced due to atelectasis and edema. A high tidal volume use therefore may cause hyperinflation of aerated lung and disrupt alveolar and capillary epithelium and induce inflammatory response.
Reference:
Atul Malhotra. Low-Tidal-Volume Ventilation in the Acute Respiratory Distress syndrome. N Engl J Med. 2007 Sep 13; 357(11): 1113–1120.
3) P/F ratio = 70/.8 = 87.5 .
According to Berlin definition, PaO2/FiO2 <100 mmHg with PEEP equal to or greater than 5 cmH2O is defined as severe ARDS.
4) Treatment strategy:
-Adjust RR and VT to achieve pH goal :7.30-7.45 and plateau pressure goals <30 cm H2O
-Adjust PEEP to reach goal of PaO2 55-80 mmHg
-Place a central line to measure the central venous pressure (goal : maintain the CVP <4cm H2O)
-Give antimicrobials for pneumonia to treat infectious cause for ARDS
-CT scan to further support diagnosis of ARDS.
-Order Echo, ECG to rule out any cardiogenic cause of problems
-Blood culture, sputum culture, CBC to check for any other signs of infection.
-DVT prophylaxis, blood glucose control, and maintain mean arterial pressure >60 mmHg
-Prone position for 18 to 20 hours- to improve oxygenation and reduce mortality.
-Repeat Chest x-ray once the patient becomes stable.
-Check procalcitonin.
1
ReplyDeleteA-a gradient = PAO2 - PaO2
PAO2 = (Patm-Pwater)FiO2 - PaCO2/.8
=(760mmHg - 47mmHg)x1 - 40/.8 = 663
PAO2 - PaO2 = 663 - 50 = 613 mmHg
Expected A-a gradient = 2.5 + (0.21 x AGE)
= 2.5 + (o.21 x 45) = 11.95
613 mmHg > 11.95 mmHg
Measured A-a gradient greater than expected meaning there is hypoxemia.
2 Vent setting
Based on ARDSNET
TV= 6ml/kg (ideal body weight)
Calculated to be around 350
Peep needs to be around 8-10
FiO2 80%
RR 20
Goal plateau 25-33cm H2O
Decreases mortality and more vent free days
Cochrane meta-analysis recent trail has confirmed this
3
P/F ratio = 70/.8 = 87.5
Berlin definition
200-300 mild ards
200-100 moderate ards
<100 severe ards
4
Optimize RR and TV to maintain PH 7.30-7.45 and plateu press 20-30
Increase PEEP 8-10
Check procal lactic cultures and start antibiotics
Dry lungs=Happy lungs
obtain ECHO/EKG