A 58 year old man is admitted to the Intensive Care Unit, intubated and ventilated. Haemodynamic monitors have been inserted and the following haemodynamic measurements have been recorded:
Mean arterial pressure 53 mmHg
Central venous pressure 15 mmHg
Cardiac output 6.8 L/min
Cardiac index 3.8 L/min/m2
21.1. Describe this circulatory disturbance.
21.2. Give five possible clinical scenarios consistent with the above circulatory dusturbance.
21.3. A review of the notes reveals that this man has a positive blood culture with Staph. aureus. Outline three mechanisms that lead to vasodilation in sepsis?
21.4. Briefly outline what initial agent you will use to treat the circulatory disturbance and how would you initially titrate the dose of the agent
21.1. Describe this circulatory disturbance.
Hyperdynamic circulation with moderate hypotension (Increased cardiac output and hypotension suggests low SVR). More information needed before labelling this as ‘shock’. If they mention vasodilated state that is also acceptable.
If they mention the word shock, that is incorrect .
21.2. Give five possible clinical scenarios consistent with the above circulatory dusturbance.
° Septic shock
° Non-septic inflammatory states
° Pancreatitis
° Burns
° Post cardio-pulmonary bypass
° Vasculitis
° Thyrotoxicosis
° Induced hypotension – nitroprusside, GTN
° A-V fistula – trauma, Pagets etc
° B1 deficiency
° Severe liver disease
° Severe anaemia
° Spinal shock
° Other
° Anaphylaxis – data inconclusive
° Poisonings – CO, CN
21.3. A review of the notes reveals that this man has a positive blood culture with Staph. aureus. Outline three mechanisms that lead to vasodilation in sepsis?
° Reduced Ca2+ entry into vascular SM myocyte due to membrane hyperpolarisation following K+ efflux via activated ATP-sensitive K+ channels.
° Activation of inducible NO synthase, increasing NO production (cyclic GMP)
° Relative deficiency of endogenous vasopressin
° Relative adrenocortical insufficiency
21.4. Briefly outline what initial agent you will use to treat the circulatory disturbance and how would you initially titrate the dose of the agent
Lots of ways of doing this and any sensible answer is acceptable. Some units titrate mcg/kg/min, others will for example put 6 mg in 100 ml such that 1 ml/hr = 1 mcg/min
Candidate must comment on the need to confirm adequate volume before winding up the noradrenaline (or at least simultaneous Norad and volume replacement). Lots of ways to assess volume.
One reasonable titration scheme is:
° Starting dose 0.1 mcg/kg/min
° Usual dose range 0.05 to 0.5 mcg/kg.min
° Titrated to MAP > 65 mm Hg
° Higher MAP if pre-existing hypertension
Noradrenaline in resuscitation of septic shock and the calculation of SVR are all discussed in a related chapter in the Required Reading section.
21.1 - This looks like a hyperdynamic circulation with decreased peripheral resistance. You can even calculate SVRI using the usual equation:
SVRI = ([MAP-RAP] × 79.9) / CI
Thus, the SVRI is ([59-15] × 79.9 )/ 3.8
= 925 dynes×sec/cm5/M2
That is pretty low - the normal range is 1800-2400.
21.2 Why would the peripheral resistance be so low?
21.3 Mechanisms of vasodilation in sepsis:
21.4 is asking about noradrenaline. A good specific answer would provide doses. In order to sound professional, one should talk in terms of μg/kg/min. Thus, the patient could be started at 0.1μg/kg/min, which for a 100kg person ends up being about 10ml/hr of a standard dilution (6mg in 100ml). One would then titrate this dose up or down, depending on the individial response.
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