ICU Fellowship Vivas – TENS, Aortic Dissection and Proning

Dr Swapnil Pawar March 5, 2022 373

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    ICU Fellowship Vivas – TENS, Aortic Dissection and Proning
    Dr Swapnil Pawar

Written by – Dr Madhuri Anupindi

  1. 56M: BG of gout, RA admitted with 24hours of fever, joint pains, fatigue, cough, SOB and erythematous rash. Over the next 24 hours the rash worsened to involve his entire body. His CXR showed widespread interstitial opacities and he rapidly progressed to type 1 respiratory failure needing ICU. What is your differential diagnosis for this patient’s presentation?


  • Drug related
    • TENS (toxic epidermal necrolysis syndrome)
    • DRESS (drug reaction with eosinophilia and systemic symptoms)
    • Acute generalised exanthematous pustulosis
    • Bullous fixed drug eruptions
  • Autoimmune disease + malignancy
    • Pemphigus vulgaris: lesions on mucus membranes, blistering,
    • Severe acute graft vs host disease (unlikely in this patient unless he’s had recent stem cell transplant)
    • Paraneoplastic pemphigus
    • Sweet syndrome
  • Infection
    • Erythema multiforme: usually triggered by infections especially HSV
    • Staphylococcal scalded skin syndrome
    • DIC

What features on history and examination would be important to evaluate the cause of this patient’s deterioration?


  • Presenting complaint and trajectory:
    • Medications: allopurinol, antibiotics (penicillin, cephalosporin, quinolones, tetracyclines, vancomycin), anticonvulsants (carbamazepine, phenytoin, lamotrigine), NSAIDs
      • Time course between commencement of medication and clinical manifestations (longer in DRESS 2-8 weeks, TENS 1 – 4 weeks, AGEP hours to days)
    • Systemic symptoms: prodrome – fever, flu like symptoms, localising signs of infection, lymphadenopathy
    • Co-morbidities: HIV (increased risk of TENS), malignancy, autoimmune conditions
    • Allergies


  • Rash:
    • Characteristics of the rash
      • Erythema multiforme: target lesions, symmetrical distribution on extensor surfaces of acral extremities
      • TENS: Ill defined erythematous macules with purpuric centres, form bullae and slough, macular erythema, flaccid blisters, symmetrical distribution, scalp often spared, painful
      • DRESS: maculopapular eruption may progress to erythema, infiltrated plaques, pustules, purpura, facial oedema
      • Staph scalded skin syndrome: erythema in skin folds, flaccid bullae then appear, crusting around mouth nose and eyes
      • Sweet syndrome: tender, inflamed papules and nodules, asymmetrical distribution most often affecting upper extremities
    • Nikolsky sign: elicitation of skin blistering as a result of gentle pressure on skin
      • Present in TENS, staph scalded skin syndrome, bullous pemphigoid
    • Mucosal involvement:
      • Involved with erythema multiforme, TENS, DRESS (but milder than TENS), pemphigus vulgaris
      • Uncommon in Sweet syndrome, staph scalded skin syndrome
    • Organ involvement:
      • Respiratory, cardiac, renal, hepatic, neuro
        • More common in DRESS, TENS, sweet syndrome

You are concerned that this patient may have toxic epidermal necrolysis. What investigations would help in your diagnosis?

  • Skin biopsy
    • Early stage: apoptotic keratinocytes in basal layer of epidermis, perivascular, mononuclear infiltrate in the papillary dermis composed mainly of T lymphocytes
    • Later: subepidermal bullae with full thickness epidermal necrosis
    • Direct immunofluorescence negative
  • Organ function
    • ABG: gas exchange, metabolic parameters, glucose (may have decreased oral intake)
    • FBC: anaemia and lymphopenia is common
    • LFTS: hypoalbuminemia, transaminitis
    • UEC/CMP: electrolyte imbalance
    • ECG
    • Consider troponin/lipase/CK (may be involved in DRESS)
  • Septic screen
    • Evaluate for sepsis, bacterial superinfections of wounds – culture of blood, urine, swabs of wound
    • Serology for mycoplasma, HIV, coxsackie
    • Swabs of lesions for HSV, PCR
  • Imaging
    • CXR given hypoxic respiratory failure
    • Consider further imaging such as CT to evaluate for malignancy/infections

The patient is diagnosed with toxic epidermal necrolysis. What are the management principles?


  • Identify and stop culprit medication
  • Use of IVIG, steroids and plasmapheresis have conflicting evidence and there is no clear consensus on their role
  • There is some growing evidence that cyclosporine use may be beneficial early in the course of TENS

Specific organ support

  • Mucosal:
    • Ocular: early opthal involvement, saline rinses, topical steroids, lubricants, topical antibiotics
    • Urogenital: females – early gynae involvement, intravaginal corticosteroids, regular use of soft vaginal molds to prevent vulvovaginal sequelae
    • Oral: mouthwashes
    • Wound management: dressings, avoid hypothermia, fastidious care and monitoring for superimposed infection
      • Sterile handling, repeated cultures
    • Respiratory
      • Supplemental oxygen if required, physio, humidification
      • May require further respiratory support and intubation depending on degree of respiratory failure


  • Multidisciplinary management in ICU/burns unit
  • Nutrition  early NGT to facilitate nutrition if required, IV fluids and electrolyte replacement and monitoring (generally 1/3 less replacement volume compared to patients with equivalent BSA burns)
  • Line site access: consider early PICC
  • Multimodal analgesia
  • VTE and ulcer prophylaxis
  • IDC


  1. A 76M presented 4 hours after onset of acute, severe chest and back pain and hypotensive 80/50. BG: HTN and 40 pack year smoking. What are the life threatening causes and what findings on clinical examination would you seek to differentiate between these causes:
  • Aortic dissection
    • Radial radial delay, differential BP, neurological signs (Horner syndrome, stroke), loss of pulses upper extremity, paraplegia abdominal pain ?mesenteric ischaemia, new AR (early diastolic decrescendo murmur best heart left lower sternal edge, louder on expiration), soft heart sounds (tamponade), lower extremity pain/weakness
  • Oesophageal perforation
    • SOB, tachycardia,
    • Subcutaneous emphysema, decreased AE one side (pleural effusion), nausea/vomiting
  • AMI
    • Diaphoresis, nausea, SOB
    • Signs of heart failure
    • Valvular failure  new murmur
  • Spontaneous tension pneumothorax
    • SOB, desaturation, unequal chest movement
    • Nil AE one side, hyperresonant percussion, subcutaneous emphysema
    • Tracheal deviation away from affected side
  • PE
    • Calf pain/swelling
    • Tachypnoea, tachycardia, desaturation
    • Chest clear on auscultation
  • Intra-abdominal: perforated viscus
    • Tender abdomen with guarding/rigidity

You are concerned about a thoracic aortic dissection. What investigations could be performed to aid in the diagnosis and what are their advantages and disadvantages? 


  • ECG:
    • Findings: may be normal or have non specific ECG changes, may have signs of LVH,
    • Advantages: cheap, easy to perform, may point to other diagnosis (STEMI, signs of right heart strain in PE), non-invasive, not resource or labour intensive
    • Disadvantage: non specific, poor sensitivity
  • CXR:
    • Findings: widened mediastinum, double aortic contour, irregular aortic contour, unexplained unilateral pleural effusion
      • If mediastinal haematoma present: obscuration of aortic knob, apical capping especially on the left, deviation of oesophagus and trachea to the right and left main bronchus inferiorly
    • Advantages: rapidly available, can point to other pathologies, cheap
    • Disadvantages: some radiation, poor sensitivity
  • Echocardiogram
    • Findings: dissection flap, dilated aortic root
    • Advantages: if TTE minimally invasive
      For both TTE and TOE: can assess valves, moderate sensitivity and specificity, no contrast, allows detection of tamponade, allows assessment of proximal coronary arteries and LV function, able to detect intramural haematoma, intimal flap, true and false lumen, rapid results
    • Disadvantages: TOE – invasive, requires sedation +/- airway protection, may cause hypertension, less availability, can cause oesophageal trauma

For both: accuracy is operator dependent, specialised expertise require, blind spot due to interposition of trachea and left main bronchus between the oesophagus and the aorta, doesn’t evaluate distal extent – can’t visualise abdominal aorta


  • CT
    • Advantages: readily available, rapid results, high sensitivity and specificity, provides information about end organ ischaemia, can help for planning of surgical/endovascular treatment of dissection, can exclude other conditions
    • Disadvantages: requires contrast, risks of transfer to CT, requires expert interpretation, does not provide information about valves, coronaries or LV function
  • Aortogram
    • Advantages: highly sensitive and specific, allows for assessment of valves, LV function, tamponade and coronaries, may allow for endoluminal repair during same procedure, provides better anatomical details
    • Disadvantages: high contrast load, not readily available, time consuming, risks of transfer, ineffective in detecting intramural haematoma, risks of arterial access, requires specialised skills, invasive
  • MRI
    • Advantage: high sensitivity and specificity, has less nephrotoxic contrast, gives information about end organ ischaemia, allows planning for potential surgical/endovascular intervention
    • Disadvantages: risk of transfer, less available, requires expertise to interpret, monitoring is difficult, certain patient populations unable to have an MRI e.g. certain pacemakers, difficult to evaluate coronary arteries

What are the management principles? 

Specific management:

Prevent further propagation of the dissection flap by reducing aortic wall stress

  • Reduce heart rate and contractility: generally aiming HR < 60  intravenous beta blockers
    • Labetalol: 10 – 20mg IV max dose 300mg, IV infusion 0.5-2mg/min
    • Esmolol 0.05-0.3mg/kg/min IV infusion or 0.25-0.5mg/kg IV over 1 min
  • Reduce blood pressure: generally aiming SBP 100 – 110mmHg
    • GTN 5-10microg/min titrated
    • SNP: 0.3microg/kg/min – 10microg/kg/min
    • Ensure that patient is effectively beta blocked first to avoid reflex tachycardia


Surgical/interventional plan

  • Liaise with cardiothoracics/vascular surgery regarding plan for treatment
  • Some uncomplicated Type B dissections are conservatively managed


Supportive management:

  • Adequate IV access and monitoring: admission to ICU, large bore IVCs, arterial line +/- Central line, IDC, full cardiac monitoring, ensure valid G+H and crossmatch, monitor for propagation of dissection and for end organ impairment
  • Adequate IV fluids, correct coagulopathy
  • Bedrest initially
  • Limit pain and distress: adequate analgesia, reassurance
  1. 25F day 4 in ICU after diving into a river and hitting a submerged object, leading to near drowning and aspiration of a large volume of river water. She has progressive bilateral infiltrates on CXR and is requiring an fio2 of 0.6 and high levels of PEEP to achieve sats of 88% and pao2 of 60mmHg. How would you decide if prone positing was an appropriate option for this patient at this time?

This would depend on; disease related factors, patient related factors and logistic issues, and would involve assessment of her history especially her trajectory in ICU, examination and investigative findings.

Disease related factors

  • Trajectory in ICU: is hypoxia worsening or improving, amount of PEEP, any complications from ventilator settings (barotrauma)
  • Reversible pathology that we can optimise  evaluate vitals, lungs on auscultation, ventilator settings, gas exchange, recent imaging, recent micro
    • ETT: obstruction, secretion, positioning
    • Infection: antimicrobials, cultures
    • Fluid balance: diuresis, chest drains for effusions
    • Sputum: bronchoscopy
    • Pneumothoraces: drainage
    • Cardiac failure: inotropy, diuresis
    • Dysynchrony: sedation/paralysis

Patient related

  • Body habitus
  • Other injuries from diving ?spinal injury/precautions
    • Abdominal injuries, pelvic instability, abdominal distension, traumatic brain injury or refractory raised ICP, unstable fractures, significant chest wall trauma
  • Significant haemodynamic instability
  • Pregnancy
  • Other background
  • Grade of intubation


  • Familiarity in centre
  • Staffing

What is the rationale for prone positioning?


  • Improved VQ matching:
    • ARDS lung there is a significant VQ mismatch in the supine position as blood flow is greatest in the dependent area but so is alveolar collapse so that alveolar ventilation is greater in the non dependent areas of lung
    • Prone positioning improves VQ matching as ventilation and perfusion becomes more uniformly distributed and previously collapsed alveoli are recruited.
  • Homogenous alveolar ventilation
    • Reduces the difference between the dorsal and ventral transpulmonary pressure (which estimates the distending pressure across the lung)
    • In ARDS lung the dorsal pleural pressure is greater than the ventral pleural pressure resulting in more overinflation of the ventral alveoli and collapse of the dorsal alveoli
    • Prone positioning reduces this difference, thereby reducing the risk of overdistension and cyclic atelectasis.
  • Reduced lung deformation
    • While supine the heart and the diaphragm compress part of the lung
    • In prone position the heart is dependent and the diaphragm is displaced caudally which decreases lung compression
  • Increases functional residual capacity
  • Theoretically enhances drainage of respiratory secretions
  • May increase cardiac output due to reduction in hypoxic pulmonary vasoconstriction resulting in increased right ventricular preload and decreased right ventricular afterload
  • Improved chest wall mechanics in obese patients

What are the risks of prone positioning?

  • Logistical issues:
    • Poor control of airway, drains, lines  risk of accidental extubation, dislodgement
    • Difficult CVC insertion
    • Difficult to perform CPR/defib if required
    • Difficult positioning and increased workload on staff
    • Difficult monitoring
  • Increased risk of pressure areas: especially of pressure prone areas such as the ASIS, knees, scrotum, lips, bridge of nose
  • Retinal damage
  • Nerve injury: especially brachial plexus, ulnar nerves
  • Poor NG feed tolerance and risk of aspiration
  • Facial oedema
  • Increased ICP and intra-abdominal pressure
  • Haemodynamic instability: arrhythmias, hypotension
  • May delay initiation of other therapy such as ECMO

Briefly outline the evidence for prone positioning

The major trial is the PROSEVA trial in 2013 which studied 466 patients with severe ARDS and randomised them to prone positioning for at least 16 consecutive hours a day or semi-recumbent position. This study found that 28 day mortality was significantly lower in the prone group with no difference in ICU length of stay or complications.

A 2015 Cochrane review of 9 RCTs found no significant difference in mortality with prone positioning except in three sub-groups; those who were proned within 48 hours of meeting entry criteria, those proned for 16 or more hours a day and those with more severe hypoxemia.


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