Pulmonary Artery Catheter Waveforms and Normal Values

As the PAC is inserted, the following waveforms can be observed.

1. When the catheters enters the RA, a CVP tracing is seen – characterized by a and v waves.img_1652

 

 

 

 

 

 

 

 

 

2. As the catheter enters the RV, a sharp increase in systolic pressure is noted.img_1653

3. As the catheter is advanced to the pulmonary artery, an increment in diastolic pressure is seen as well as the presence of a dichromatic notch. img_1654

4. When the catheter is advanced further into the pulmonary artery, and wedged – a sine wave that oscillates with respiration is seen. img_1655

THE RA WAVEFORM:

The RA waveform is characterized by presence of 2 waves: a wave (contraction of the RA) and the v wave (passive filling of the RA).

The x descent represents RA relaxation, which is interrupted by the c wave which represents closure of the tricuspid valve.

The y descent follows the v wave, which signals the opening of the tricuspid valve and exit of blood from the RA to the RV.

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OVERDAMPING:

The wave below illustrates flushing of the catheter – which results in high pressures in the transducer (1). Flushing stops, and results in fall in pressures and an overshoot (2), and a return to normal waveform.

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The wave below – overshooting is absent, and the waveform is flattened, which is found in an overdamped waveform. Overdamping can be caused by a kinked catheter, air bubbles, fibrin clot.

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CATHETER WHIP.

The graph below illustrate catheter whip – where ventrcicular contractions are transmitted to the PAC.

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OVERWEDGING:

The arrow indicates when the balloon is inflated. There is a sustained increment in pressure reading.

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ACUTE MITRAL INSUFFICIENCY

Prominent v waves represent blood that enters the LA during ventricular systole due to an incompetent mitral valve.

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TRICUSPID REGURGITATION

Broad c-v waves can be seen.

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RV INFARCTION

Marked acute dilatation of the RV occurs. Acute dilatation is limited by the pericardium. Deep x and y descents, resembling the letter W is seen.

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MEASURED HEMODYNAMICS VARIABLES:

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DERIVED HEMODYNAMICS VARIABLES

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OXYGEN TRANSPORT VARIABLES

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Reference:

Criner, G., Barnette, R. and D’Alonzo, G. (2010). Critical Care Study Guide. Dordrecht: Springer.

Decompressive Hemicraniectomy,

Evidence for DHC:

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Mortality Reduction in Percentages:

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Mortality at 12months after malignant MCA infarction. Forest plot presenting risk difference and 95% confidence interval (CI) for a pooled analysis of mortality at 12months from RCTs comparing DC and best medical care:

Surgical Technique:

  • Place head in rigid 3-pin fixation
  • A large reverse question mark flap is turned to allow access to a large part of the hemicranium.
  • Large craniectomy of frontotemporoparietal region
  • Avoid frontal air sinus
  • Take the inferior bone cut as low as possible to the floor of the middle fossa and ronguer/drill additional bone to accomplish this
  • typical craniectomy flap measures at least 15 cm anteroposteriorly and 10 to 12 cm craniocaudal
  • dura is opened in a C-shaped or stellate manner
  • When the anterior temporal lobe is infarcted and tentorial herniation is present or impending, perform an anterior temporal lobectomy with resection of the uncus and visualization of the tentorial edge, third nerve, and midbrain
  • lax duraplasty with autologous pericranial graft, closure must be capacious; be able to pick up and freely slide the lax dural sac
  • Muscle reapproximated loosely or not at all
  • Scalp is closed in layers (drains optional but preferred)
  • parenchymal or subdural ICP monitor optional
  • bone flap typically discarded (prefer delayed cranioplasty with a custom implant) or store bone flap in abdominal wall or cryopreserve
  • transfer to NSICU without extubation.
Post-op Management:
  • standard ICU ICP management
  • attempt early extubation without gagging
  • early enteral nutrition by POD1
  • SQH after 24 hours unless with C/I
  • early trach / PEG if needed
  • if stable post-op CT, ASA after 24 h
  • aggressive PT, speech, rehab

 

While technical details certainly vary between individual surgeons or centers, this brief outline describes a typical operation: the procedure is performed in a supine position with the head rotated to the contralateral side. A wide curved incision is performed either beginning behind or in front of the ear. The scalp flap and temporalis muscle are then deflected to expose the skull. Burr holes are created and subsequently connected to achieve an anterior to posterior diameter of the craniectomy area of at least 12 cm, with the recommended diameter in adult TBI

patients being 15 cm. The DC is finally extended to expose the floor of the middle cranial fossa. An adequately sized craniectomy is essential in achieving the desired decompressive effect. Moreover, a suboptimal DC will lead to exacerbated external brain her niation and shear forces at the bone edges, which can cause intraparenchymal hemorrhage and kinking of the cerebral

veins. After sufficient bony decompression has been achieved, the dura is incised to create a large dural opening. For coverage of the exposed brain, allogenic or autologous dural grafts can be used.

Complications:

  • Hygroma / subdural fluid collection most common (50-58%), most clinically insignificant
  • delayed HCP in 7-12%
  • infection 2-7%
  • sinking flap syndrome (syndrome of trephined)

 

Operative technique of supratentorial DC. Artist’s rendition of a human head with a typical incision line for DC (gray line).

3D reconstruction of a human skull demonstrating burr holes (gray circles), craniectomy (gray area), and additional osteoclastic decompression of the middle cranial fossa floor (hatched area) as well as typical dural incision (red lines).

3D reconstruction of a human skull with a typical hemicraniectomy skull defect:

Intraoperative photography of a human brain after DC:

stepwise reduction in ICP after decompressive hemicraniectomy:

Suboccipital or Infratentorial Decompressive Craniectomy

In comparison with supratentorial DC, the technical details of suboccipital or infratentorial DC are less clearly established. Important aspects such as overall craniectomy size, laterality of the decompression, and necessity of resection of the posterior arch of the atlas all vary in the published literature. However, the basic surgical aim is decompression above the swollen cerebellum. In general, this procedure is performed with the patient in a prone or semi-prone/lateral position. A linear midline incision is made from the inion to the upper cervical spine, and the muscular layers are subsequently separated in the midline avascular plane, exposing the suboccipital skull, atlanto-occipital membrane, and posterior arch of the atlas. A wide craniectomy is performed extending into the foramen magnum. As the next step, to avoid tonsillar herniation, we routinely remove the posterior arch of the atlas. The dura is then usually opened in a Y-shaped fashion, and an expansion duroplasty is performed.

2018 AHA ASA Guidelines:

The guideline recommends early transfer of patients at risk of malignant cerebral edema to a center with neurosurgical expertise. Patient-centered preferences in shared decision-making regarding the interventions and limitations of care should be ascertained at an early stage. With regard to neurosurgical management, the guideline states that in patients ≤ 60 years of age, who deteriorate neurologically (defined as a decrease in the level of consciousness attributed to brain swelling despite medical therapy) within 48 h after MCA infarction, DC with expansion duroplasty is reasonable. In patients > 60 years of age, the same approach may be considered. For patients with cerebellar malignant stroke, the guideline recommends sub-occipital DC with expansion duroplasty upon neurological deterioration despite medical therapy, with concurrent EVD insertion to treat obstructive hydrocephalus.

Reference:

Gupta, Aman et al. “Hemicraniectomy For Ischemic And Hemorrhagic Stroke”. Neurosurgery Clinics of North America 28.3 (2017): 349-360.

Beez, T., Munoz-Bendix, C., Steiger, H. and Beseoglu, K. (2019). Decompressive craniectomy for acute ischemic stroke. Critical Care, 23(1).

Salt Equivalents

As an exercise, I tried to figure out the equivalent amount of salt for 1 bullet of 23.4% (30mL) compared with the other hypertonic saline solutions.

 

23.4%:  30mL = 120 mEq Na Cl;

3%, 5%, 14.6% contain 0.51, 0.86, 2.5 mEq/mL of NaCl

3% 235 mL,

5% 140mL

14.6% 48mL

 

And came up with this table.

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XLS FILE (Old Table)

 

REVISED TABLE 05/03/2018

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PDF FILE (New Table)

DOC FILE (New Table)

XLS FILE (New Table)

References

Zakaria, Asma. Neurocritical Care Board Review. New York, NY: Demos Medical, 2014.

Treatment of Native Vertebral Osteomyelitis (IDSA, 2015)

Parenteral Antimicrobial Treatment of Common Microorganisms Causing Native Vertebral Osteomyelitis

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Reference:

Berbari, Elie F. et al. “2015 Infectious Diseases Society Of America (IDSA) Clinical Practice Guidelines For The Diagnosis And Treatment Of Native Vertebral Osteomyelitis In Adults”. Clinical Infectious Diseases 61.6 (2015): e26-e46. <PDF link>