Table 14.2.

Clinical variables used to assess intravascular volume status during anesthesia.

Variable	Skin turgora	Neck veins	Systolic Blood Pressureb	Variability of blood pressure with respirationj	Central venous pressure (CVP)c	Urine output (UO)d	Heart rate (HR)e	Hypotension with anesthesia esp. volatilef	Orthostasisg	Base excess (BE)h, i Or (HCO3-) meq/l
Hypovolemic	Loose	Flat	Low	High	Less than 8	Low	High	Likely	High	Less than -2 (or less than 22)
Euvolemic	Normal	Pulsatile	Normal	Normal	8-12	Normal (0.5-1 ml/kg/h)	Normal	Normal	Normal	[−2 to +2] (22-30)
Hypervolemic	Puffy	Bulging, distended	Normal to High	Low	Greater than 12	High	Low	Unlikely	Low	[−2 to +2] (22-30)

^aPatients with low oncotic pressure (from low serum albumin, etc.) or patients who have been given considerable crystalloid, will be puffy yet may still be hypovolemic in the intravascular space and thus prone to hypotension.

^bMany patients do not show higher blood pressures if hypervolemic. Also, hypertensive patients may still be hypovolemic.

^cRequires central venous line access. Values noted are approximate; follow trends in CVP rather than absolute values.

^dThis is affected by many other factors besides volume: ADH secretion, diuretics, intrinsic renal function, etc.

^eHR variability with volume status is best seen in young healthy awake patients. It is not well seen in elderly, deeply anesthetized or beta-blocked or calcium-channel blocked patients. Nor is it seen in patients with intrinsic nodal or conduction system disease.

^fHypovolemic patients become hypotensive with even small amounts or concentrations of anesthetics.

^gTilting the patient’s body or trunk “head up” when initially supine will result in hypotension if hypovolemic; less so if hypervolemic.

^hBase excess or bicarbonate (HCO₃−) measurements if acidotic (less than −2 (BE) or less than 22 (HCO₃−) suggest hypovolemia and hypoperfusion leading to lactate accumulation in the blood. This rule presupposes no other cause of acidosis besides hypovolemia.

ⁱRequires an arterial line for instantaneous pressure (variability with respiration) or sampling of arterial blood (base excess or HCO₃−).

How to use Table 14.2 : Each clinical variable in the top row is easy to assess. The table describes signs of hypo-, euvolemia, and hypervolemia. Exceptions exist for each of the above rules; they are for approximate assessment of volume status. More than one variable typically follows during anesthesia, and they usually confirm each other.