Aortic Dissection

How to select optimal PEEP ?

Optimal PEEP can be estimated from various techniques -

1)Pressure Volume Loop

• PV Loops represent the dynamic interaction of changes in pressure and volume during the inspiratory and expiratory portions of a breath. It helps us to monitor lung compliance and airway resistance.
• When lung compliance decreases PV loop rotates closer to the X-axis, lying more horizontally whereas when compliance increases, the PV loop rotates towards the Y- axis, lying more vertically. 

• There two important inflection point on the static PV loop.
• The lower inflection point (LIP) is located on the inspiratory limb of PV loop. This represents the point at which compliance increases significantly, likely due to recruitment and opening of alveoli.
• The upper inflection point (UIP) on the inspiratory limb is suggested to be a point at which compliance increases significantly, likely due to the recruitment and opening of alveoli. The decrease in compliance and overdistension of alveoli creates a classic beaking apperance to the PV loop. 

• PV loop can be used to set PEEP by using LIP. Matamis et al suggested setting PEEP above LIP on the inspiratory limb of the PV loop to prevent distal airway collapse and to maximise alveolar recuritment.PEEP is set at 2cm H20 above LIP. 

2) Driving Pressure (DP)

• DP is calculated as the difference between inspiratory plateau pressure and PEEP or ratio of TV to compliance. 

• DP = Pplat - PEEP or DP = TV/Compliance

• In the absence of respiratory effort by the patient, DP represent the pressure above PEEP which is applied to achieve ventilation.It reflects the size of TV relative to aerated lung volume and therefore correlates with overall lung strain and pulmonary compliance.

• ARDS patients with Driving pressure (DP) > 7 have been shown increased risk for  mortality, recently studies have shown DP>  14cmH20 on day 1 is associated with worse outcome. 
• Decrease in DP have been shown to be more strongly associated with lower mortality compared to increase in the Pa02/FiO2 ratio.

3) Stress Index (SI)

• SI is measured by determining the slope of the airway pressure time curve during inspiration, based on two timepoints on a dynamic airway pressure scaler.
• Measurement of SI requires volume control ventilation and constant flow pattern, which keeps alveolar volume and pressure constant. Under these condition, the slope of the airway pressure rise will represent changes in compliance. 

• SI >1:  indicates decreasing compliance
• SI < 1: indicates increasing compliance

• Using SI to determine optimal PEEP involves setting PEEP to a pressure at which SI =1, when it is thought that hyperinflation or recruitment is occuring.
• Clinical utility of SI is limited because of the need for quantitative analysis of the shape of the pressure time curve with dedicated instruments or specific ventilators.            

• Stress Index may also be visually analysed from Pressure Time Scalar.

4) Transpulmonary Pressure

• Transpulmonary pressure (Ptp) is defined as the difference between the airway pressure and pleural space pressure and it represents the pressure required to move air through airways and to overcome elastic recoil. 

• Pleural pressure is most commonly estimated by measuring esophgeal pressure using esophgeal manometry. 
• Transpulmonary pressure guided PEEP approaches have shown to improve oxygenation, increase compliance and decrease DP. 

5) Electric Impedance

• Electrical Impedance Tomography is a non invasive bedside technique which allows real time visualisation of changes in the distribution of ventilation and perfusion. 

• It involves placing several electrodes around the patients chest, which measures thoracic impedance to small alternating electrical currents that are applied through electrodes. Software analyses this data and creates a image of the lung depicting ventilation and perfusion. 

• Following a recruitment manuver, lung compliance is estimated for decremental PEEP. The PEEP should then be set at the point of intersection between collapse and over distension percentage curve assessed by EIT. 

Reference

• Zersen KM. Setting the optimal positive end-expiratory pressure: a narrative review. Front Vet Sci. 2023 Jul 19;10:1083290. doi: 10.3389/fvets.2023.1083290. PMID: 37538169; PMCID: PMC10395088.

Kigalli Modification of Berlin Criteria

• Kigali Modification of the berlin criteria was designed to estimate the incidence of ARDS in a resource limited setting.
• They modified berlin criteria without requirement for positive end-expiratory pressure, hypoxia cutoff of SpO2/FiO2 less than or equal to 315, and bilateral opacities on lung ultrasound or chest radiograph.

Reference

• Riviello ED, Kiviri W, Twagirumugabe T, Mueller A, Banner-Goodspeed VM, Officer L, Novack V, Mutumwinka M, Talmor DS, Fowler RA. Hospital Incidence and Outcomes of the Acute Respiratory Distress Syndrome Using the Kigali Modification of the Berlin Definition. Am J Respir Crit Care Med. 2016 Jan 1;193(1):52-9. doi: 10.1164/rccm.201503-0584OC. PMID: 26352116.

What is ROX Index ?

ROX Index

• ROX index was first described by Roca et al to predict HFNC failure in ICU patients suffering from pneumonia.It is defined as a combination of ratio of oxygen saturation to the fraction of inspired oxygen (SpO2/FiO2) and respiratory rate.

• Roca et al study was done on 157 patients were included, of whom 44 (28.0%) eventually required MV (HFNC failure). After 12 hours of HFNC treatment, the ROX index demonstrated the best prediction accuracy (area under the receiver operating characteristic curve 0.74 [95% confidence interval, 0.64-0.84]; P < .002). The best cutoff point for the ROX index was estimated to be 4.88. In the Cox proportional hazards model, a ROX index greater than or equal to 4.88 measured after 12 hours of HFNC was significantly associated with a lower risk for MV (hazard ratio, 0.273 [95% confidence interval, 0.121-0.618]; P = .002), even after adjusting for potential confounding.

• Similarly meta analysis by Prakash et al has demonstrated that ROX index has good discriminating power for prediction of HFNC failure in COVID-19 patients with AHRF. 

Reference

• Prakash J, Bhattacharya PK, Yadav AK et al (2021) ROX index as a good predictor of high fow nasal cannula failure in COVID-19 patients with acute hypoxemic respiratory failure: A systematic review and metaanalysis. J Crit Care 66:102–108.https://doi.org/10.1016/j.jcrc.2021.08.012
• O. Roca, J. Messika, B. Caralt, et al.Predicting success of high-flow nasal cannula in pneumonia patients with hypoxemic respiratory failure: the utility of the ROX index J Crit Care, 35 (2016), pp. 200-205, 10.1016/j.jcrc.2016.05.022
  

`What is SF Ratio ?

SF Ratio 

SpO2/FiO2 (S/F) ratio can be used instead of PaO2/FiO2 (P/F) ratio as a measure of the degree of hypoxemia. SF ratio is less invasive and more readily available.

Study done by Rice et al (2007) on derivative data set of 2613 measurements found that S/F ration threshold values of 235 and 315 resulted in 85% sensitivity with 85% specificity and 91% sensitivity with 56% specificity, respectively for P/F ratios of 200 & 300. 

There are concerns about accuracy in dark skin and those in shock with or without poor distal perfusion. Patients may also be treated to keep SpO2 in excess of 97% resulting in uninformative SF Ratio.

Reference

• Rice TW, Wheeler AP, Bernard GR et al (2007) Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS. Chest 132:410417.https://doi.org/10.1378/chest.07-​0617
•  Brown SM, Grissom CK, Moss M et al (2016) Nonlinear imputation of Pao2/Fio2 from Spo2/Fio2 among patients with acute respiratory distress syndrome. Chest 150:307–313. https://doi.org/10.1016/j.chest.2016.01.003

IV Fluids in Sepsis present concept ..

RL or NS which is better in sepsis? 

SSG 2021 recommends crystalloids as first line fluid for resuscitation (Strong Recommendation).

Crystalloids are used for resuscitation in sepsis and septic shock as it inexpensive and widely available. Commonly available IV fluids are NS & RL. Optimal fluid of choice has been point of debate and NS has used for decades as fluid of choice. Recent studies and evidences have raised concern of using NS due to hyperchloremic metabolic acidosis, renal vasoconstriction, AKI, increased cytokine secretion. 

SALT-ED (2018) Trial is a single center, pragmatic, multiple crossover trial comparing balanced crystalloid (Lactated Ringers solution or Plasma-Lyte A) with saline among adullts who were treated with IV crystalloids in the ED and hospitalised outside ICU. A total of 13347 patients enrolled. Study found that hospital free days didn't differ between the balanced crystalloids and saline group (median, 25 days in each group). But study also showed that balanced cyrstalloid group has lower incidence of adverse kidney events within 30 days than saline (4.7% v/s 5.6%, p=0.01).

SMART Trial (2018) is  pragmatic, cluster randomized, multiple crossover trial conducted in 5 ICU in a single academic centre, open label. Total of 15802 patients were randomised to receive either NS or balanced cyrstalloid. Study found among 7942 patients in the balanced group, 1139 (14.3%) had a major adverse kidney event compared to 1211 of 7860 patients (15.4%) saline group(p-0.04) . Hospital mortality at 30 days was 10.3% in the balanced-crystalloids group and 11.1% in the saline group (P=0.06). The incidence of new renal-replacement therapy was 2.5% and 2.9%, respectively (P=0.08), and the incidence of persistent renal dysfunction was 6.4% and 6.6%, respectively (P=0.60). Study concluded that among critically ill adults, the use of balanced crystalloids for intravenous fluid administration resulted in a lower rate of the composite outcome of death from any cause, new renal-replacement therapy, or persistent renal dysfunction than the use of saline.

SPLIT study (2015)  is a double blind, cluster randomised, double crossover trial done on all patients admitted to ICU requiring crystalloid fluid therapy. 1152 patients recieved buffered crystalloid and 1110 patients recieved saline.Study found that in cyrstalloid group 9.6% developed AKI compared to 9.2% in saline group within 90 days of enrollement. Among the patients receiving crystalloid fluid therapy in the ICU, use of buffered crystalloid compared with saline didnot reduce the risk of AKI.

From these evidences SSG 2021suggest using balanced crystalloid instead of normal saline for resucitation.

BaSCIS Trial (2021) is a double blind,RCT conducted at 75 ICU in brazil. Study was done to determine the effect of a balanced solution v/s saline solution on 90 day survival in critically ill patients. Study concluded that among critically ill patients requiring fluid challenges, use of a balanced solution compared to 0.9% saline did not significantly reduce 90 day mortlaity.  

Reference

1) Semler MW, Self WH, Wanderer JP, Ehrenfeld JM, Wang L, Byrne DW, Stollings JL, Kumar AB, Hughes CG, Hernandez A, Guillamondegui OD, May AK, Weavind L, Casey JD, Siew ED, Shaw AD, Bernard GR, Rice TW; SMART Investigators and the Pragmatic Critical Care Research Group. Balanced Crystalloids versus Saline in Critically Ill Adults. N Engl J Med. 2018 Mar 1;378(9):829-839. doi: 10.1056/NEJMoa1711584. Epub 2018 Feb 27. PMID: 29485925; PMCID: PMC5846085.

2) Self WH, Semler MW, Wanderer JP, Wang L, Byrne DW, Collins SP, Slovis CM, Lindsell CJ, Ehrenfeld JM, Siew ED, Shaw AD, Bernard GR, Rice TW; SALT-ED Investigators. Balanced Crystalloids versus Saline in Noncritically Ill Adults. N Engl J Med. 2018 Mar 1;378(9):819-828. doi: 10.1056/NEJMoa1711586. Epub 2018 Feb 27. PMID: 29485926; PMCID: PMC5846618.

3) Young P, Bailey M, Beasley R, Henderson S, Mackle D, McArthur C, McGuinness S, Mehrtens J, Myburgh J, Psirides A, Reddy S, Bellomo R; SPLIT Investigators; ANZICS CTG. Effect of a Buffered Crystalloid Solution vs Saline on Acute Kidney Injury Among Patients in the Intensive Care Unit: The SPLIT Randomized Clinical Trial. JAMA. 2015 Oct 27;314(16):1701-10. doi: 10.1001/jama.2015.12334. Erratum in: JAMA. 2015 Dec 15;314(23):2570. PMID: 26444692.

3) Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021

How much fluid is too much ?

How fluid is too much ?

Rivers et al in 2001 had shown that Early Goal Directed Therapy (EGDT) provided significant benefits with respect to outcome in patients with severe sepsis and septic shock.  Use EGDT resulted use of large volume of fluids and PRBC for resuscitation. Since then multiple studies has tested the validity of EGDT against usual care notably ARISE, ProcESS and ProMISE Trial. All the study  failed to show any mortality benefits of EGDT compared to usual or standard care. Surviving Sepsis Guidelines (SSG 2021) suggest using 30ml/kg based on the fact that average amount of fluid received in all these trials pre randomisation was in the range of 30ml/kg.

To further analyse the use of restrictive and liberal fluids two other recent trials were done. CLOVERS Trial (2023) was done to asses early restrictive or liberal fluid management for sepsis induced hypotension which is better. Patients where randomly assigned to restrictive (782)and liberal fluid(781) strategy for 24 hours. They randomised the patients who met criteria for sepsis induced hypotension refractor to initial treatment with 1 to 3L of IV fluid. Study found that patients in restrictive fluid strategy had to use early, prevalent and longer duration of vasopressors. Study concluded that in patients with sepsis induced hypotension, the restrictive fluid strategy (14%) didnot lower the mortality at 90 days compared to liberal fluid strategy (14.9%) p=0.61.

CLASSIC Trial (2022) was done to study long term outcomes of restrictive versus standard intravenous IV fluid therapy in adult critically ill patients with septic shock. A total of 1549 patients where enrolled in the study 767 to restrictive group and 782 to standard fluid group. Study found that one year mortality was  (51.3%) among restrictive group compared to standard fluid group (49.9%) p =0.55. Study concluded that restrictive v/s standard therapy resulted in similar survival, health related quality of life and cognitive function at 1 year. 

SSG 2021 suggests use of crystalloid fluid at 30ml/kg IV within first 3 hours of resuscitation. Further resuscitation of the patients should be decided based on the intravascular status and organ perfusion. Dynamic measures including passive leg raising combined with cardiac output measurement (CO), fluid challenge against stroke volume, systolic pressure or pulse pressure. 

In a resource limited setting a increase of pulse pressure by 15% following passive leg raising test for 60-90 seconds could indicate fluid responsiveness. 

Reference

• Meyhoff TS, Hjortrup PB, Wetterslev J, Sivapalan P, Laake JH, Cronhjort M, Jakob SM, Cecconi M, Nalos M, Ostermann M, Malbrain M, Pettilä V, Møller MH, Kjær MN, Lange T, Overgaard-Steensen C, Brand BA, Winther-Olesen M, White JO, Quist L, Westergaard B, Jonsson AB, Hjortsø CJS, Meier N, Jensen TS, Engstrøm J, Nebrich L, Andersen-Ranberg NC, Jensen JV, Joseph NA, Poulsen LM, Herløv LS, Sølling CG, Pedersen SK, Knudsen KK, Straarup TS, Vang ML, Bundgaard H, Rasmussen BS, Aagaard SR, Hildebrandt T, Russell L, Bestle MH, Schønemann-Lund M, Brøchner AC, Elvander CF, Hoffmann SKL, Rasmussen ML, Martin YK, Friberg FF, Seter H, Aslam TN, Ådnøy S, Seidel P, Strand K, Johnstad B, Joelsson-Alm E, Christensen J, Ahlstedt C, Pfortmueller CA, Siegemund M, Greco M, Raděj J, Kříž M, Gould DW, Rowan KM, Mouncey PR, Perner A; CLASSIC Trial Group. Restriction of Intravenous Fluid in ICU Patients with Septic Shock. N Engl J Med. 2022 Jun 30;386(26):2459-2470. doi: 10.1056/NEJMoa2202707. Epub 2022 Jun 17. PMID: 35709019.
• National Heart, Lung, and Blood Institute Prevention and Early Treatment of Acute Lung Injury Clinical Trials Network; Shapiro NI, Douglas IS, Brower RG, Brown SM, Exline MC, Ginde AA, Gong MN, Grissom CK, Hayden D, Hough CL, Huang W, Iwashyna TJ, Jones AE, Khan A, Lai P, Liu KD, Miller CD, Oldmixon K, Park PK, Rice TW, Ringwood N, Semler MW, Steingrub JS, Talmor D, Thompson BT, Yealy DM, Self WH. Early Restrictive or Liberal Fluid Management for Sepsis-Induced Hypotension. N Engl J Med. 2023 Feb 9;388(6):499-510. doi: 10.1056/NEJMoa2212663. Epub 2023 Jan 21. PMID: 36688507; PMCID: PMC10685906.
• Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021

OMI

Outside ECG

ECG at ED

A 50 year old known hypertensive presented with central chest pain since 4 am referred from a local hospital with a report of negative Trop I. On arrival  @8:00am HR 40, BP 140/70 on arrival. ECG Shows subtle J point elevation over II,III, aVF, ST Depression over aVL. A clinical diagnosis of OMI was done though ECG doesn't satisfy diagnostic criteria of STEMI. PCI pathway was activated immediately. Patient went to cardiac arrest during Cath, had VT defibrillated and stabilized. PCI revealed RCA Occlusion. Isolated T wave inversion with a subtle J point elevation should rise  a strong suspicion of IWMI. One should not wait for a full ST Elevation in ECG to develop. These patients should be taken up for PCI at the earliest.

Any primary STD in aVL (i.e not secondary to LBBB, LVH or WPW) makes any inferior STE an inferior MI until proven otherwise, and excludes pericarditis.