Man versus Machine

aka  012

A 25 year-old male was intubated for airway protection following a 90 mg/kg carbamazepine overdose — he was GCS 7 prior to intubation. He is sedated with morphine and midazolam infusions and mechanically ventilated in the emergency department while awaiting an ICU bed.

Forty-five minutes after intubation, the patient’s nurse calls for help because the patient has become hypoxic. Intubation was uneventful, there was no suspicion of aspiration and he had an SpO2 of 100% both prior to and immediately after intubation.

You arrive at the beside and note an SpO2 of 87%.


Q1. What are the causes of hypoxia occurring soon after intubation?

Think DOPES:

  • Displacement of the endotracheal tube (ETT)
  • Obstruction of the ETT
  • Patient — especially pneumothorax; also: pulmonary embolism, pulmonary edema, collapse, bronchospasm
  • Equipment — ventilator problems
  • Stacked breaths’ — a reminder about bronchospasm and ventilator settings.

This extended mnemonic is courtesy of Scott Weingart‘s fantastic EMCrit Podcast 16 – Coding Asthmatic, DOPES, & Finger Thoracostomy.

Q2. What is your first step in managing an intubated and ventilated patient who is hypoxic?

Disconnect the ventilator and administer high-flow 100% oxygen (FiO2 1.0) using a bag-valve-mask.

Disconnection allows the release of trapped gas in the patient with severe bronchospasm — these patients usually have evidence of bronchospasm and/ or hypotension in addition to hypoxia. Also, if the patient is easy to ventilate and re-oxygenate, then the problem probably lies with the ventilator or the circuit.

In a ventilated patient that has a problem always think: (wo)man versus machine.

man versus machine

(source unknown)

Q3. What are the most important things to check when there is a problem with a mechanically ventilated patient?

First determine the severity of the problem — do you need to start immediate resuscitation?

Then assess MASH:

  • Movement of the chest during ventilation —
    is it absent or is movement only on one side? Is the chest hyper-expanded?
  • Arterial saturation (SaO2) and PaO2 —
    obtain an ABG sample
  • Skin colour of the patient (is he turning blue or pinking up?) —
    the SO2 monitor lags behind the true oxygen saturation of the patient.
  • Hemodynamic stability.

Now you can attempt to diagnose the problem.

Q4. The patient is difficult to manually ventilate. What should you do next?

Determine if the problem lies with the endotracheal tube or with the patient.

If there is little chest movement, a patient problem is still possible, but a problem with the ETT needs to be be ruled out urgently:

  • check ETCO2 to ensure the ETT is not in the esophagus and is patent.
  • pass a suction catheter and/ or a bougie to ensure the ETT is not obstructed.
  • check the placement of the tube visually — preferably by bronchoscopy, or alternative by by laryngoscopy from the top end (although this is far from 100% reliable).
  • consider a CXR to check ETT position if hypoxemia is not critical, especially if endobronchial intubation is suspected.

If in doubt, and the hypoxia has not been rapidly resolved, take the tube out… and replace it.

If there is reasonable chest movement, a patient problem is most likely. Perform a focused exam and urgently seek and treat the following life-threats:

  • pneumothorax
    (look for asymmetrical chest movement)
  • lung collapse
    (look for asymmetrical chest movement)
  • pulmonary edema
  • bronchospasm
    (chest wall movement may be minimal — look for hyperexpansion)
  • pulmonary embolus

Q5. What may have occurred if the bag is easy to compress during manual ventilation, but there is little or no chest movement?

Suspect either:

  • a circuit leak (e.g. cuff leak, disconnection, or a hole in the circuit)
  • dislodgement of the endotracheal tube — you may be ventilating the oropharynx or the stomach.

Q6. What if the patient is easy to ventilate with the bag and the hypoxemia rapidly resolves?

Find out what happened just before the desaturation:

  • had there been a disconnection of the ventilator/circuit?
  • had suctioning been performed?
    (in some settings the loss of PEEP during disconnection of the circuit may lead to derecruitment and atelectasis, result in desaturation).

Otherwise, there may be a problem with the ventilator settings or there was an equipment failure.

  • check ventilator settings
  • trouble-shoot equipment failure


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  1. [...] High Peak Inspiratory Pressures in a ventilated patientvar _gaq=_gaq||[];_gaq.push(['_setAccount','UA-10404823-1']);_gaq.push(['_setCustomVar',1,'author','chris-nickson',3],['_setCustomVar',2,'tags','airway alveolar asthma mechanical-ventilation peak-inspirato',3],['_setCustomVar',3,'year','2010',3],['_setCustomVar',4,'categories','clinical-interpretation elearning emergency-medicine h',3],['_trackPageview'],['_trackPageLoadTime']);(function(){var ga=document.createElement('script');ga.type='text/javascript';ga.async=true;ga.src=('https:'==document.location.protocol?'https://ssl&#039;:'http://www&#039;)+'';var s=document.getElementsByTagName('script')[0];s.parentNode.insertBefore(ga,s);})();var _sf_startpt=(new Date()).getTime()function expand(param){"none")?"":"none";}.printfriendly{margin:0px 0px 0px 0px}.printfriendly a{text-decoration:none}.printfriendly a:hover{cursor:pointer}.printfriendly .printfriendly-text{margin-left:3px;color:#55750C}.printfriendly a img{border:none;padding:0}.alignleft{float:left;margin:5px 20px 20px 0}.alignright{float:right;margin:5px 0 20px 20px}.aligncenter{text-align:center;margin:5px auto 5px auto}.printfriendly{display:none}#header{background:url( scroll no-repeat 0 0}.wp-table-reloaded{background-color:#CDCDCD;margin:10px 0px 15px 0px;font-size:11pt;width:98%;text-align:left}.wp-table-reloaded th{background-color:#E6EEEE;border:1px solid #FFF;padding:4px}.wp-table-reloaded td{color:#3D3D3D;padding:4px;background-color:#FFF;vertical-align:top}.wp-table-reloaded .even td{background-color:#FFF}.wp-table-reloaded .odd td{background-color:#F0F0F6}.wp-table-reloaded .header{background-image:url(;background-repeat:no-repeat;background-position:center right;cursor:pointer}.wp-table-reloaded .headerSortUp{background-color:#8DBDD8;background-image:url(}.wp-table-reloaded .headerSortDown{background-color:#8DBDD8;background-image:url(}Life in the Fast Lane Medical BlogEmergency medicine clinical education blogAboutAuthorsAffiliatesAwardsArchivesAnalyticsLegal DisclaimerBlogExamsACEM PrimaryACEM FellowshipCICM FellowshipUtopian CollegeACTM FellowshipConferenceEducationClinical CasesR&R in the FASTLANEToxicologyHistoryClinical ExaminationInvestigations [tests]ProceduresLecture NotesMedicine 2.0OslerismsResourcesStuff We ReadImage DATABASEEmergency Medicine BlogsPodcastsANZ MedBloggersInternational Emergency MedicineEponymous FracturesGlossary of termsPaediatricsMedical HumourECG LibraryECG BasicsECG Clinical CasesCardiology EponymsA-Z by DiagnosisECG ReferencesECG Exam TemplateBooksOn Call PrinciplesEmergency MedicineToxicology HandbookCritical Care Drug ManualEMA JournalReviewsDecember 14, 2011LITFL » Education » Clinical Interpretation » Alarmingly high pressures…Alarmingly high pressures…July 29, 2010 By Chris Nickson 1 Comment Print PDF aka Pulmonary Puzzle 014 Having overcome his worrying episode of post-intubation hypotension in the emergency department, the man who was intubated for severe asthma in Pulmonary Puzzle 013 is now in the intensive care department. He remains mechanically ventilated.You are asked to review him because the high airway pressure alarm is going off.QuestionsQ1. Why is the airway pressure alarm important?Answer and interpretationexpand(document.getElementById('ddet830757610'));expand(document.getElementById('ddetlink830757610'))For at least three reasons:Excessive airway pressure may have adverse effects on the patient.High airway pressures may indicate a deterioration of the patient’s condition.It may indicate an equipment problem that needs to be addressed.Q2. What are the potential adverse effects of excessive airway pressure?Answer and interpretationexpand(document.getElementById('ddet1440917094'));expand(document.getElementById('ddetlink1440917094'))High airway pressures do not correlate with lung barotrauma.Airway pressure itself is not particularly deleterious unless it reflects excessive alveloar pressure. Excessive alveolar pressure can have a number of adverse effects:barotrauma may result in acute lung injury (leading to ARDS) or air leaks (e.g. pneumothorax, pneumomediastinum).Excessive intrathoracic pressure may also result, with potential hemodynamic consequences (particularly decreased venous return, leading to hypotension and potentially cardiac arrest).High airway pressures may result in inadequate ventilation.Inadequate ventilation can occur because many ventilators are set to terminate the inspiratory flow if the upper pressure limit setting is reached. When this occurs inspiratory volumes are markedly reduced, resulting in low tidal volumes and minute ventilation. Other ventilators do not do this but will simply hold the airway pressure at the pressure limit, resulting in a smaller reduction in tidal volume.Q3. How is airway pressure related to alveolar pressure?Answer and interpretationexpand(document.getElementById('ddet1810786251'));expand(document.getElementById('ddetlink1810786251'))airway pressure = flow x resistance + alveolar pressureThus if flow or resistance is markedly altered, a change in airway pressure will not be indicative of a change in the alveolar pressure.Airway pressure is more conveniently measured than alveolar pressure. Peak inspiratory pressure (PIP) is displayed on most ventilators.A maximum acceptable PIP of <35 cmH20 is widely used.Q4. How can alveolar pressure be estimated?Answer and interpretationexpand(document.getElementById('ddet2025893033'));expand(document.getElementById('ddetlink2025893033'))Alveolar pressure is estimated by determining the inspiratory pause pressure, which corresponds to the plateau pressure.The inspiratory pause pressure is determined by observing the plateau pressure in an apneic ventilated patient when when the ‘inspiratory pause hold‘ control is activated. Because flow is reduced to zero, airway pressure and alveolar pressures will equalise and the airway pressure will correspond to the alveolar pressure at full inspiration.airway pressure = 0 x resistance + alveolar pressure = alveolar pressure Normal curve -- demonstrates normal PIP , Pplat , PTA (transairway pressure), and Ti (inspiratory time). High Raw curve -- A significant increase in the PTA is associated with increased airway resistance. High Flow curve -- the inspiratory time is shorter than normal, indicating a higher inspiratory gas flow rate. Decreased Lung Compliance curve -- An increase in the plateau pressure and a corresponding increase in the PIP is consistent with decreased lung compliance.Q5. What is an excessive alveolar pressure?Answer and interpretationexpand(document.getElementById('ddet208740141'));expand(document.getElementById('ddetlink208740141'))To prevent lung injury, alveolar pressure (aka the plateau pressure) should be kept <30 cmH2O.High alveolar pressures can be due to excessive tidal volume, gas trapping, PEEP or low compliance as shown by this relationship:alveolar pressure = (volume/ compliance) + PEEPQ6. What are the two main categories of causes of high airway pressure?Answer and interpretationexpand(document.getElementById('ddet2034993494'));expand(document.getElementById('ddetlink2034993494'))As always, when it comes to ventilated patients you need to think:Man versus Machine(source unknown)Q7. What is the most useful first step in isolating the cause of high airway pressures?Answer and interpretationexpand(document.getElementById('ddet193630577'));expand(document.getElementById('ddetlink193630577'))Disconnect the patient from the ventilator and manually bag the patient using high-flow oxygen. If the patient is difficult to ventilate the problem is not with the ventilator or the circuit, but the patient or endotracheal tube.That’s right — deja vu all over again!Q8. What are the possible causes of high airway pressures in the intubated and ventilated patient?Answer and interpretationexpand(document.getElementById('ddet1780296665'));expand(document.getElementById('ddetlink1780296665'))First, let’s consider the machine:Ventilatorinappropriate settingsventilator malfunctionCircuitkinkingpooling of condensed water vapourwet filters causing increased resistanceEndotracheal tubedisplacement, e.g. endobronchial intubationkinkingobstruction with foreign materialAnd now the man:bronchospasm (e.g. asthma)decreased compliancelung  (e.g. collapse, consolidation, pulmonary edema)pleural  (e.g. pneumothorax, pleural effusion)chest wall (e.g. abdominal distention, kyhposcoliosis, obesity)patient-ventilator dysynchrony, coughingQ9. How will you go about identifying the cause of the high airway pressure?Answer and interpretationexpand(document.getElementById('ddet1359578980'));expand(document.getElementById('ddetlink1359578980'))The key steps are:While the patient is disconnected from the ventilator assess the “feel” of the lungs while bagging:If the patient is not difficult to ventilate then the problem is with the ventilator or the circuit.If the patient is difficult to ventilate it is a problem with the endotracheal tube or the respiratory system.For ventilator and circuit problems:check the ventilator settings that it is functioning correctly (e.g. on a test lung)check the circuit for obstruction or kinking.For patient or ETT problems:examine the patient looking for:wheezeasymmetrical chest expansionevidence of collapseevidence of dyssynchronyPass a suction catheter through the ETT to check its patency.perform a CXR to check ETT position and look for potential causes of decreased compliance.If the cause is still not clear measure inspiratory pause pressure to estimate alveolar pressure, in addition to the peak inspiratory pressure that reflects airway pressure.If both airway and alveolar pressure are high the problem is due to poor compliance (e.g. pulmonary edema).If only the airway pressure is high the problem is one of high resistance (e.g. bronchospasm).Upon assessing the patient you decide that the high airway pressure alarms are due to patient-ventilator dyssynchrony, in addition to ongoing bronchoconstriction.Look out for an upcoming post on patient-ventilator dyssynchrony….ReferencesBersten AD, Soni N. Oh’s Intensive Care Manual (6th edition). Butterworth-Heinemann, 2008.Gomersall C. ICU Web — Trouble-shooting mechanical ventilation; Asthma.Life in the Fast Lane — ICU Mind Maps: Abnormal ventilator waveforms; Acute Severe AsthmaWeingart S. EMCrit Podcast 16 – Coding Asthmatic, DOPES, & Finger Thoracostomy.Related posts:Quiz Radiology 002Quiz Trauma 010EBM Upper GI HaemorrhageShare:Filed Under: Clinical Interpretation, eLearning, Emergency Medicine, Health, Intensive Care, Respiratory Tagged With: airway, alveolar, asthma, mechanical ventilation, peak inspiratory pressure, PEEP, plateau pressure About Chris NicksonAn oslerphile suffering from a bad case of knowledge dipsosis. Key areas of interest include: emergency medicine, critical care, toxicology, tropical medicine, clinical epidemiology, history, literature and the internet-learning revolution. @precordialthumpComments Dr harsha MAKWANA says: August 21, 2010 at 4:13 pmexcellent knowledge delievered in puzzle form ReplySpeak Your Mind Cancel replyName *Email *Website [...]

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